<table><thead><tr><th>HGTD components per end-cap</th><th>Thickness (mm)</th><th>z<sub>in</sub>/z<sub>out</sub> (mm)</th><th>R<sub>in</sub>/R<sub>out</sub> (mm)</th><th>Weight (kg)</th></tr></thead><tbody><tr><td>Vessel Front cover</td><td>13.0</td><td>3420/3433</td><td>110/1000</td><td>25</td></tr><tr><td>Front double side layer (2 half disks)</td><td>26.0</td><td>3433/3459</td><td>120/920</td><td>60</td></tr><tr><td>Rear double side layer (2 half disks)</td><td>26.0</td><td>3459/3485</td><td>120/920</td><td>60</td></tr><tr><td>Internal Moderator</td><td>30.0</td><td>3485/3515</td><td>120/900</td><td>75</td></tr><tr><td>Vessel Back cover</td><td>7.0</td><td>3515/3522</td><td>110/1100</td><td>15</td></tr><tr><td>Vessel inner ring</td><td>10.0 (*)</td><td>3433/3542</td><td>110/120</td><td>5.0</td></tr><tr><td>Vessel outer ring</td><td>20.0 (*)</td><td>3433/3515</td><td>980/1000</td><td>35</td></tr><tr><td>External Moderator</td><td>20.0</td><td>3522/3542</td><td>110/1100</td><td>75</td></tr><tr><td>Air gap with LAr cryostat</td><td>3.0</td><td>3542/3545</td><td>110/1100</td><td>0</td></tr><tr><td><strong>HGTD with moderators</strong></td><td><strong>125.0</strong></td><td></td><td></td><td><strong>350</strong></td></tr></tbody></table>

<table><thead><tr><th>Double side layer breakdown</th><th>Thickness (mm)</th><th></th><th></th></tr></thead><tbody><tr><td>Air gap with vessel or with moderator</td><td>2</td><td></td><td></td></tr><tr><td>Flex tail packing (0.22 mm per unit)</td><td>4.2</td><td></td><td></td></tr><tr><td>Module package</td><td>4.2</td><td></td><td></td></tr><tr><td>Cooling + support plate</td><td>6</td><td></td><td></td></tr><tr><td>Module package</td><td>4.2</td><td></td><td></td></tr><tr><td>Flex tail packing (0.22 mm per unit)</td><td>4.2</td><td></td><td></td></tr><tr><td>Inter-layer gap</td><td>1.2</td><td></td><td></td></tr><tr><td><strong>Total per double sided layer</strong></td><td><strong>26.0</strong></td><td></td><td></td></tr></tbody></table>

Table 11.1: HGTD components per end-cap. The top part of the table shows the components with their dimensions in *z*, *r* and their weights. Each double sided layer is divided in two half circular disks of 30 kg each. Double side layer weight also includes PEB weight. The total weight of the detector, including the moderator is 350 kg (275 kg without the external moderator). The bottom part of the table shows a breakdown of the front double sided layer. The breakdown of the back layer is identical. (*) Numbers are the thickness of the rim of the vessel of the inner and outer rings.

needed to extract a certain amount of heat but also that the temperature of the liquid phase remains constant, while that of the vapour increases only slightly. The cooling power is then determined by how much CO₂ is left in a liquid state. Because it is used in mixed states (liquid and vapour), a significant mass reduction is introduced when comparing with other liquid mono-phase refrigerants.

### 11.3.1 Requirements

An operation temperature of -35 °C must be maintained inside the HGTD vessel, in the vicinity of the cooling channels close to the modules, with a stability of a few degrees Celsius. As discussed in Chapter 5, the operating temperature must be kept as low as possible as, after irradiation, the leakage current of the sensors increases with temperature. The operating
temperature of the peripheral on-detector electronics is flexible. It can be in the range of -35 °C up to 20 °C, making the cooling and stability requirements of these components less stringent. Taking into account that these electronics are located within the cold vessel, they will need to be maintained at a temperature close to the sensor operation point to avoid excess heat flowing towards the sensors. The electronics will be used as pre-heaters to stabilise the cooling parameters before the coolant reaches the modules.

Table 11.2 summarises the power consumption estimated for the various components of the detector. This defines a need for maximum cooling power of 40 kW in total (20 kW per end-cap) at the end of life time of the HL-LHC. However, most of the components listed in the table are not yet fully designed, therefore the estimate of the total maximal power consumption has about a 10 % uncertainty. A careful re-evaluation of the power consumption of each component will be done with the first prototypes.

<table><caption>Table 11.2: Total maximum power consumption estimates for the HGTD at the start and end of the HL-LHC. A breakdown for the various components is also given. (*) The sensors power consumption range from 30 to 100 mW cm⁻² expected respectively for sensors non irradiated (at the start of the HL-LHC) and irradiated at the max expected irradiation of 2.5x10¹⁵neq/cm². (**) The 19.2 kW corresponds to 1.2 W (or 300 mW cm⁻²) consumed by each ASIC when calibration is taking place and is equivalent to 10% occupancy of all channels of an ASIC. During normal data taking, the total power consumed by the ASIC is 17.6 kW, smaller than during calibrations.</caption><thead><tr><th>HGTD Component</th><th>Power consumption</th><th>Total [kW]</th></tr></thead><tbody><tr><td>Sensor</td><td>30 to 100 mW cm<sup>-2</sup></td><td>2.0–6.4 (*)</td></tr><tr><td>ASIC</td><td>&lt; 300 mW cm<sup>-2</sup></td><td>17.6–19.2(**)</td></tr><tr><td>Flex cable</td><td>6.8 mW cm<sup>-1</sup></td><td>2.0</td></tr><tr><td><strong>Total in active region</strong></td><td></td><td><strong>21.6–27.6</strong></td></tr><tr><td>HGTD vessel heaters</td><td>100 W m<sup>-2</sup></td><td>1.3</td></tr><tr><td>Pre-heaters (Perip. electr.)</td><td></td><td>8.8</td></tr><tr><td>Ambient pick-up</td><td></td><td>2.5</td></tr><tr><td><strong>Total power dissipation</strong></td><td></td><td><strong>34.2–40.2</strong></td></tr></tbody></table>

The ASICs, followed by the sensors, consume the most power, with up to 300 mW cm⁻² by the ASIC and up to 100 mW cm⁻² by the sensors at the innermost radius. The power dissipation of the ASICs decreases slightly as a function of their radial position because the hit rate decreases at larger radius, as shown in Figure 11.4. Taking this radial dependence into account, the total power consumed by the ASIC amounts to 17.6 kW during data taking. The total power consumed by the ASIC increases to 19.8 kW when calibrations are taking place and is equivalent to 10% occupancy across all channels in the ASIC, for all ASICs.

The power dissipated in the flex cables is expected to be 6.8 mW cm⁻¹, leading a total power dissipation for the flex cables about 2.0 kW

The peripheral electronics boards will act as pre-heaters for the cooling system. On these
<figure><img src="image_159.png" /><figcaption>Figure 11.4: Average power consumption per ASIC (in mW) as a function of the ASIC radial position relative to the beam pipe axis. Each ASIC is 4 cm².</figcaption></figure>

boards, the DC-DC converters will be the component with the highest power dissipation. Assuming a 72% efficiency for the DC/DC converters, the peripheral electronics will dissipate an estimated power of 8.8 kW.

Given the uncertainties on current estimates of the power dissipation of some components, a cooling unit dedicated to HGTD of 50 kW will be constructed (25 kW per end-cap). A spare cooling station of 50 kW, shared with ITk, is also foreseen.

### 11.3.2 Cooling design

The cooling design is based on the technology implemented for the ATLAS Insertable B-Layer detector and on industrial standards. Tri-axial vacuum-insulated transfer lines will be used to connect the CO₂ cooling station located in USA15 to a junction & distribution box to be located on the outer radius of the end-cap tiles calorimeter on the HO side, close to the HGTD patch panel area, detailed in Section 12.3. One such box per end-cap will be used to distribute the CO₂ flow from one big transfer line to four smaller proximity lines. A second function of these boxes, which is being studied, should maintain the detector under cooling
conditions during ATLAS Short opening (winters' YETS). Additional lines, which are also under study, should provide detector cooling during ATLAS large opening.

When the cooling is turned off, due to transfer lines disconnection or any other unexpected operating failures, the temperature inside the vessel could increase up to room temperature. The main remaining heat source is the anti-condensation heaters which should also be switched on full time to prevent any temperature decreasing on the hermetic vessel outer skin. A second heat source is the N₂, blowing at 20 °C, with a flow rate up to 750 l h⁻¹, improving the warm up of the on detector parts. The estimated warm up time to reach 20 °C from -35 °C of the HGTD cold mass (200 kg, corresponding to the on-detector system and moderator inner part (see Table 11.1)), is determined by the equivalent specific heat capacity (c in J kg⁻¹ K⁻¹) of the cold mass. Considering the thermal power input as 650 W, mainly from the heaters, and the equivalent specific heat in the range of c = 750 J kg⁻¹ K⁻¹, the increasing gradient is about 4 min per degree centigrade, and a total of 3–4 hours to reach room temperature.

Rigid proximity transfer lines are under development for Phase-II upgrade applications for ATLAS and CMS targeting a transfer capacity of about 5 kW per unit. The HGTD design places an inner hose, with an inner diameter of 5 mm for the CO₂ liquid, inside a 16 mm mid-hose for the vapour return. This hose, made out of a multi-layer insulated (MLI) pipe, is enclosed within a vacuum hose of outer diameter less than 50 mm. The vacuum level inside the transfer lines must be less than $1 \times 10^{-4}$ mbar in order to avoid convection and condensation on the outer wall. The relatively small outer diameter of such lines, less than 50 mm, will facilitate their routing in the gap between the barrel and end-cap calorimeters, through a dedicated slot in $\phi$ allocated inside the original ITk envelope, as agreed with the ITk and Technical Coordination groups.

In order to prevent connection and disconnection of CO₂ transfer lines during long shut-downs, alternative flexible lines are under study which could be implemented in a dedicated flexible chain along ATLAS translation rails.

The four tri-axial rigid lines, one for each half-disk cooling plate, enter the HGTD vessel at the top position (11.25° from the vertical line). They are holding capillary lines with 0.75 mm inner diameter and length up to 5 m, ending inside the hermetic vessel at the manifold R-$\phi$ location. They supply CO₂ liquid to the 8 cooling loops that are embedded in each half-disk cooling plate on a semi-circular concentric pattern, as shown in Figure 11.5. The radial distance between the concentric pipes in the loops at 120 mm < r < 640 mm is 16 mm. This is the region covered by active modules placed on both faces of the cooling disk with overlap from 20% up to 70%. In the peripheral electronics area, at r > 680 mm, where the dissipated power is used as pre-heaters, the distance between pipes is increased to 30 mm to take into account the lower heat dissipation, thus keeping a uniform temperature distribution on the total area of the cooling disk.
<figure><img src="image_160.png" /><figcaption>Figure 11.5: Detailed layout of the 8 cooling loops on a half disk support. The central cooling loops (below 640mm radius) with a pitch of 16mm are dedicated to the silicon sensors & their ASICs. The outer loops with a pitch of 30mm are cooling the Peripheral Electronic Boards (PEB).</figcaption></figure>

<figure><img src="image_161.png" /><figcaption>Figure 11.6: Cooling loop prototype corresponding to the inner part of the half-disk support.</figcaption></figure>

The choice of the pipe material should take into account several parameters such as the mechanical properties, the thermal deformation, the thermal runaway (see section 7.5), the induced radioactivity and the material radiation length. Two options for the material to be used are being studied: titanium and aluminum, while the stainless steel is only used for bending and assembly feasibility.

A first prototype has been made of stainless steel (4.0 mm outside diameter and 5.0 mm thickness widely available and easy to machine). It is shown in Figure 11.6. This prototype
corresponds to the inner region of the cooling half-disk with a radial spacing of 16 mm as foreseen for the HGTD. It has been successfully tested up to 165 bar at the CERN proof pressure facility. Thermal tests will be undertaken with the CERN CO₂ cooling setup before integration into the sandwich structure of the cooling support. These measurements will be applied to validate parameters used in the thermal runaway studies. However, stainless steel is not considered as candidate for the cooling pipe material due to its short radiation length and induced activity (stainless steel Xo 13.84, equivalent to 1.757 cm).

The current baseline is to make the cooling pipes of titanium T40 grade 2 or equivalent, as used in to the IBL and ITK projects (titanium Xo 16.16 g cm⁻², equivalent to 3.56cm, almost double of the stainless steel value). A prototype of the inner region is going to be manufactured with T40-G2 pipes, 4.0 mm outside diameter and 3.0 mm thickness.

Cooling pipes made of Aluminum may still be considered for the final detector to reduce the radiation length between the active layers and thereby improve the ability to associate ITk tracks with HGTD hits (aluminum Xo 24.01 g cm⁻², equivalent to 8.897 cm, almost 2.5x the titanium value). In addition, Aluminum is less activated by radiation and therefore may allow faster access to the detector components. This is important for replacing the over-irradiated inner rings and for maintenance during long shutdowns. The thickness of the Al cooling pipes would have to be larger than with Titanium to sustain the pressure, but would have the advantage of the same thermal and mechanical properties as the sandwich structure of the support plates. The welding of the Al pipes to the stainless steel fittings, at the manifolds level, is more challenging than with Titanium. Bimetal transitions (aluminum-stainless steel) can be used to fulfil these specific piping connections.

The cooling plant is protected against over-pressure with safety valves set to 130 bar. This value is used as the maximum design pressure on the cooling loops. To ensure that the pipes can sustain such levels of CO₂ pressure, the wall thickness of the pipes must be at least 0.3 mm. The outer diameter of the pipes is 4.0 mm. Their length varies from 4 to 6 m for different loops. The maximal transfer capacity of the cooling loops corresponds to 100 W m⁻¹. The characteristics of the loops are defined in close collaboration with the CERN Cooling group.

The half disks with embedded cooling loops are the main support structure for the instrumented active layers, as described in Section 11.6. In addition to their high thermal conductivity, their own stiffness should guarantee a surface disk flatness within one millimetre. Given the challenging performance requirements of the on-detector cooling system, one full scale prototype of cooling half-disk support will be produced, including aluminum panels and embedded cooling loops, equipped with appropriate heaters to simulate the silicon modules power dissipation. This prototype will be subjected to several thermal cycles to study the thermo-mechanical behaviour, temperature distribution, CO₂ cooling parameters, and the performance of conductive media needed in between the modules, the support plates and the cooling channels.
### 11.3.3 Cooling plant demonstrator

One important milestone for the cooling development is the proof that the CO₂ evaporation temperature of -35 °C can be achieved at the local HGTD support disks with realistic transfer lines and coolant distribution. Because of the critical importance of this technology in the ITk and HGTD systems, a CO₂ cooling test facility called "Baby demonstrator" was set up by the CERN cooling team in collaboration with ATLAS and CMS. This facility, which is being tested, is installed in Building 180, next to the mock-up of the ATLAS calorimeter (see Figure 11.7). It will be used for tests of prototypes of ITk and HGTD cooling components with a real-scale geometry. This chiller demonstrator will operate at low temperature with a

<figure><img src="image_162.png" /><figcaption>Figure 11.7: CO₂ cooling plant demonstrator located in Building 180 at CERN.</figcaption></figure>

limited cooling power of 5 kW. The fluid transfer is subject to losses, which, in a two phase system, appears as a drop of saturation temperature on the return line due to the frictional pressure drop of the flowing media and static height differences. The main results were already presented in [86], in the context of ITk. As an example, Figure 11.8 shows a typical temperature distribution in the cooling system from the CO₂ plant to ITk on-detector loops and back, reaching the temperature of -40 °C, the target temperature for the ITk modules. To provide this temperature in the detector units, the cooling plant temperature needs to deliver -45 °C to account for the estimated 5 °C lost in the distribution and transfer lines.

In order to optimise the performance of HGTD local supports at -35 °C, specific prototypes as well as the half disk cooling supports will be submitted to real scale CO₂ tests on the Baby-Demo facility at CERN.
<figure><img src="image_163.png" /><figcaption>Figure 11.8: Typical temperature distribution between the CO₂ cooling plant and ITk loop [86].</figcaption></figure>

## 11.4 Moderator

The moderator, to be placed between the end-cap calorimeters and the active layers of the detector, will protect both the ITk and HGTD against the back-scattered neutrons that are produced by the end-cap calorimeters. The moderator disks will be made of borated polyethylene with a density of 0.95 kg L⁻¹, similar to the one used in the present ATLAS detector. As seen in Figure 2.4, the new moderator will be divided into two disks per end-cap, one inside and one outside the HGTD hermetic vessel.

The moderator on the outside is mechanically separated from the HGTD hermetic volume. It will be screwed to the LAr cryostat wall with an air gap using spacers of a few millimetres and will provide the necessary flat surface on which the HGTD will be installed with accessible bolting brackets. In order to minimize the mechanical impact on the LAr end-cap cryostat, the vessel interface with the cryostat wall will be made using the same threaded holes that are at present used to mount the MBTS. To allow the integration of anti-condensation heaters on the back cover, specific thin pockets, matching the heaters footprint, will be machined on the moderator surface with associated radial grooves to route power and monitoring cables. This moderator has a thickness that varies along the radius, 10 mm only in the region 180 mm < r < 342 mm (to absorb the over thickness with respect to the cryostat wall due to the LAr central flange and its bolts head) and 20 mm elsewhere (140 mm < r < 180 mm and 342 mm < r < 1100 mm) (see technical drawing in Figure D.4). The weight of this external moderator is in the range of 75 kg.

Potential conflicts with the water cooling pipe, currently installed on the cryostat front wall and used for cooling of the beam pipe during the bake-out procedure, require verification at the LS2 time-slot. The goal is to optimize the water cooling pipe shape, elbows and fittings in order to minimize the grooves size to be machined on the external moderator.

The part of the moderator to be placed inside the vessel has a thickness of 30 mm, a radial coverage of 120 mm < r < 900 mm, and a weight of about 75 kg (see technical drawing in Figure D.5). It provides appropriate R-φ sliding support for the instrumented layers and, because it does not extend to radii higher than r = 900 mm, it leaves enough free space for
the cooling services as shown in Figure 11.13 left and right details. In each end-cap, the total moderator thickness in z, summing the two disks, will then be 50 mm, except at the inner and outermost radii. There it will be 40 mm in the region between 110 mm–342 mm and 20 mm for $r > 900$ mm. During maintenance, and when the replacement of the radiation damaged modules takes place at the surface, the outer moderator disk may stay bolted on the LAr cryostat, while the back cover is moved up with the HGTD vessel.

## 11.5 Hermetic vessel

The hermetic vessel is the primary integration structure of the HGTD detector. It consists of four main components made of composite structures in carbon fiber, as seen in Figure 2.4: the front and back covers, the inner ring and the outer ring which will hold all the service connectors and the cooling line flanges. The vessel measures 1100 mm at the outer radius and 110 mm at the inner radius (see technical drawing in Figure D.6 for a view of HGTD vessel with components). The thicknesses of front and rear covers are 13 mm and 7 mm, with an estimated weight of 25 kg and 15 kg, respectively. The Faraday cage will be performed by using aluminum mesh tightly integrated to the hermetic vessel outer skin, similar to what is currently used in the other LHC experiments.

### 11.5.1 Requirements

The hermetic vessel provides a robust support structure to the detector instrumented disks in a cold and dry over pressure volume (+10 mbar maximum relative to atmospheric pressure). All materials chosen must satisfy safety requirements related to the expected radiation levels, described in Section 2.4, and the operational temperature range (OTR). They shall also comply the CERN safety instruction IS41 (Fire safety rules), in particular flammable resin epoxy composites are not allowed. Assuming no replacement of components during the HL-LHC, the materials used have to withstand $8.3 \times 10^{15} \text{ n}_{\text{eq}} \text{ cm}^{-2}$ and 7.5 MGy, including safety factors. Components that will be replaced midway through the HL-LHC will see these criteria divided by two.

The safe temperature range is defined by the acceptable minimum coolant temperature, -35 °C, and the expected module interlock temperature, 30 °C, with a margin of 20 °C on both sides. This results in a safe OTR from -45 to 40 °C and a 100 thermal cycles life time, which is similar to recent ITK engineering specifications.

The vessel tightness should ensure the detector volume permanently dry, keeping the dew point at -60 °C or below, to avoid condensation on the detector components. Considering 5 mbar nominal over pressure of the 125 liters dry nitrogen volume, and an acceptable pressure drop of 10%, which is equivalent to 0.05 mbar, the leak rate has to be better than
1.75x10⁻³ mbar.l/sec. This requirement can be achieved by permanent flushing with dry N₂ at 0.5% over pressure above atmospheric reference. The N₂ flow will renew gas in the vessel volume up to 10 times per hour, which is equivalent to 750 l·h⁻¹ per end-cap. For this purpose, the HGTD vessel was designed to be hermetic as possible, in particular the electrical connectors and cooling flanges at the outer ring.

Another requirement is to keep the temperature of the outer surface of the HGTD vessel safely above the cavern dew point (~12°C). This will be achieved by placing flat Kapton heaters on the external skin of HGTD hermetic vessel and as close as possible to the outer ring, due to the high thermal conductivity of the electrical services, in particular when the detector power is turned off while the cooling is maintained.

### 11.5.2 Front cover

The front cover is designed as a sandwich structure, consisting of a Nomex honeycomb core placed between two thin Carbon Fibre Reinforced Plastics (CFRP), as shown in Figure 11.9 (see the technical drawing in Figure D.6 for a detailed view of the front cover). As a means to reduce the front cover deflection from over pressure and CTE mismatch, radial stiffeners are integrated into the structure during the curing process of the epoxy composite. Considering the possible opening of the hermetic vessel with the beam pipe in place, during YETS maintenance for example, the front cover is designed to be two half-moon parts with vertical junction edges. These edges are manufactured out of PEEK reinforced 30% carbon fiber as baseline design to provide stiffness and low thermal conductivity of the front cover. Other similar material, free of epoxy resin, like Torlon polyamide-imide technology are also an alternative solution.

The tightness is the result of a trapezoidal gasket shape (EPDM or NBR radiation resistance elastomer) compressed in between the two screwed half moon parts (see Figure 11.10). This gasket is also compressed against the inner and outer ring elastomer gasket to provide tightness continuity between the front cover and the inner and outer ring. The stiffness of the vessel assembly when mounted on the cryostat wall has been studied using FEA 3D model. In this computed assembly, 5 mbar over-pressure has been applied, corresponding to dry nitrogen blowing inside the vessel to prevent any ambient humidity leak from outside. The results are presented in Figure 11.11, showing a maximum deflection of 1.5 mm on the front cover. This is equivalent to a maximum stress (Von Mises) of 70 MPa, located on the carbon fiber panels. The composite rods along the two half disks of the front cover will change the global stiffness of the honeycomb panels and will absorb the induced stress. A safety factor of 1.5 is considered to take into account the dry nitrogen network differential pressure relief valves setting up to 1010 mbar.

The HGTD inner volume will be operating at a temperature of -35°C, therefore heaters will be required on the external faces of the hermetic vessel to prevent condensation on
<figure><img src="image_164.png" /></figure>

Figure 11.9: General view of the closed hermetic vessel. The front cover (Kapton heaters partially shown) is made of two parts which are bolted together with composite bracket and tight gasket. The outer ring is holding all electric connectors and coaxial cooling flanges.

<figure><img src="image_165.png" /></figure>

Figure 11.10: Detailed 3D view of the front cover junction connecting the two half moon parts. The central rod, on the right, is bolted on the two parts with trapezoidal elastomer gasket in place

the outer surfaces. In a way similar to what is done on the LAr end-cap cryostat front face, heaters will be placed on the external face of the front and back covers, the inner and outer rings. Their purpose is to ensure a minimal temperature of 14 °C outside the HGTD vessel, safely above the cavern dew point of 12 °C. The expected power density of the heaters on the vessel outer skins is 100 W m⁻² This leads to a total contribution of approximately 650 W per end-cap expected from the heaters, which is included in the CO₂ cooling plant budget summarized in Table 11.2. The standard Kapton heaters technology is delivering
<figure><img src="image_166.png" /><figcaption>Figure 11.11: Finite Element Analysis (FEA) of the hermetic vessel with an over-pressure of 5 mbar. The red area of the front cover, which is represented as a single disk, corresponds to a maximum deflection of 0.7 mm. Due to the fact of manufacturing two half-disk parts with bolted junction edges, the maximal deflection is expected to be 1.5 mm.</figcaption></figure>

usual power amount of 500 W m⁻², as confirmed with liquid argon cryostats units. This selected technology is giving a comfortable safety factor of five compared to our expected needs. The temperature distribution expected on the hermetic vessel parts is shown in Figure 11.12. In these temperature calculations, which were performed using Finite Element Analysis (FEA) method, the ambient temperature of 20 °C and heat exchange coefficient of 5 W m⁻² K⁻¹ were taken as input parameters. Inside the hermetic vessel, the instrumented layers have been represented as a uniform material conductivity of 35 W/m·K with cooling channels at -35°C. The moderator conductivity has been set to 0.23 W/m·K, and the CFRP honeycombs 0.04W/m·K. Due to its tiny thickness, similar to double pane glass windows, the dry nitrogen has been represented as a conductive media with 0.04 W/m·K. In fact, the convective model was much less conservative as heat transfer phenomena. A temperature distribution in the range of 14 to 17 °C has been confirmed by this FEA output plot.

### 11.5.3 Back cover

Similar to the front cover, the back cover is also designed as a sandwich structure, consisting of a Nomex honeycomb core placed between two thin Carbon Fibre Reinforced Plastics (CFRP). Due to its tiny thickness and to procure additional stiffness, the back cover is used to hold the internal moderator using several tight bolting spots. This assembly technique increases the thickness from 7mm up to 37mm. The bolting connection between the CFRP back cover and the moderator is only blocked in Z and sliding in R-φ using large spring washers. In order to prevent any condensation in the thin air gap with the liquid argon cryostat wall, kapton heaters will be installed on the back cover with their temperature gauges and cables. Simultaneously, the existing cryostat heaters will continue to operate in their normal mode. The temperature distribution results of Figure 11.12 are taking into account the back cover heaters while the cryostat wall is not included in the FEA model.
<figure><img src="image_167.png" /><figcaption>Figure 11.12: Temperature distribution within the FEA axisymmetric model of the detector assembly in the ATLAS experiment, with anti-condensation heaters powered on (front cover 80 W m⁻², back cover 85 W m⁻², outer ring 230 W m⁻², inner ring 60 W m⁻², total per end-cap 650 W). The dew point is set to 14°C and the temperature distribution is plotted with detector units turned on at 0.35 W cm⁻² (a) and turned off (b).</figcaption></figure>

The alignment of the hermetic vessel on the calorimeter end-cap will be based with respect to the axis of the cryostat warm tube, in the ATLAS coordinates system as illustrated in Figure 11.13. This survey reference should take into account the existing cylindrical moderator which is not represented in Figure 11.13. To optimise cavern access during the hermetic vessel installation/removal, the proposed design is to have the bolting/unbolting of the back cover to the cryostat wall throughout the external moderator. This procedure makes the installation and removal of the hermetic vessel easier, in particular without any required opening of the front cover.

### 11.5.4 Inner ring design

The inner ring of the hermetic vessel borders the beam pipe, resulting in a high level of radiation and heat exposure. Design efforts are ongoing to select the best material with high radiation resistance and low thermal conductivity to provide a shielding barrier during the beam pipe bake-out. Earlier projects with a similar environment, such as the ATLAS IBL and the LHC beam-pipe, have demonstrated good performance for carbon fibre structures and the aerogel insulating layers.

The inner ring of the current design, represented in the technical drawing of Figure 11.14, is composed of a sandwich structure consisting of eight millimetres of honeycombs and
<figure><img src="image_168.png" /><figcaption>Figure 11.13: 3D cut view of the two instrumented layers inside the closed hermetic vessel. The main assembly parts are shown in their operating run configuration. The 2D sections on the bottom right and left are detailing the cooling manifolds area and the peripheral electronics boards respectively.</figcaption></figure>

aerogel core enclosed between two thin sleeves made of CFRP high module panels. Further studies on high performance materials, such as Kevlar panels and honeycombs, are being undertaken to address the required stiffness, thermal protection, and radiation resistance, challenged by the low space allocated close to the beam pipe vacuum components.

To provide tightness as well as the alignment of the vessel with respect to ATLAS coordinate system, precisely-machined collars made of low thermal conductivity material, such as high performance PEEK polymer or Torlon polyamide-imide technology, will be installed on both extremities of the inner ring. Appropriate threaded inserts will be incorporated into the two assembly collars to allow tightening of the bolts of the front cover. The machined slots will hold the sealing O-ring made out of PUR or EPDM material. The back collar will be bolted to the central flange of the external moderator, providing the hermetic vessel alignment with respect to the central tube of the LAr cryostat.

### 11.5.5 Outer ring design

All available routes for off detector services between the detector volume (dry and cold environment) and the outside world, are implemented on the outer ring. These passages are routing conductor cables, optical fibres, CO₂ cooling lines, and nitrogen tubes. The outer
<figure><img src="image_169.png" /><figcaption>Figure 11.14: Central inner ring with its front and back collars. It is the central structure of the hermetic vessel, which ensures stiffness and tightness, thermal shielding, and HGTD positioning on the LAr cryostat.</figcaption></figure>

ring structure, which is an assembly of several parts, must be made of a stiff material with low thermal conductivity. As for the inner ring collars, the main candidate materials are the high performance PEEK polymer and Torlon polyamide-imide technology. Taking into account the large diameter of this part (up to 2000 mm), the manufacturing process is still under study to meet the specifications within a reasonable cost.

The interfaces to all HGTD services are implemented on the outer ring. It includes the cable and optical fibre connectors and the fittings for the CO₂ transfer lines and N₂ gas pipes. Such a design, shown in Figure 11.15, will allow a complete assembly and test of the detector at the surface integration area. The detector can then be transported to the pit for installation inside the closed vessel. All services connections will be done after fixing the HGTD on the calorimeter end-cap front wall.

To optimise the half-disks assembly and their integration into the vessel, the outer ring is composed of several sections, associated with each half-disk, as illustrated in Figure 11.15. Each of these sections contains only connectors belonging to the corresponding half-disk. This allows to complete the assembly of the half-disk with the pigtails connected to electronics boards and outer ring, before integrating it into the vessel. The advantages of such an approach are more complete tests of the assembly and its faster integration in the vessel, which is particularly important in the scenario of incomplete detector in LS3 and the need to install the missing half-disk during the next YETS in the cavern.

In the long shut-downs the closed HGTD vessel will be transported onto the surface for maintenance and replacement of the middle or inner rings, as described in Section 13.2.2. The final design and selection of materials is ongoing, it must satisfy the requirements regarding the tightness of the vessel, thermal isolation, radiation hardness, grounding and Faraday cage completeness. The CO₂ transfer lines will pass through the cold-warm interface of the
<figure><img src="image_170.png" /><figcaption>Figure 11.15: The outer ring assembly. The largest part of the hermetic vessel, with 2 m in diameter, it contains the service feedthroughs for cables, CO₂ transfer lines, and dry N₂ pipes. The outer ring is divided into sections, associated with each half-disc. The sections belonging to different half-discs are shown with different colors, as well as a small section with connections of the CO₂ transfer lines.</figcaption></figure>

outer ring using standard conical sealing made of PUR or EPDM (Ethylene-Propylene-Diene Monomer), currently used in vacuum technology. The design of these cooling lines will be developed in a common program with CMS Phase-II HGCAL, which will transport a similar amount of power dissipation (4.7 kW for CMS and 5.0 kW for HGTD per line) under similar cooling specifications. In general, it is planned to work closely with the present program for both ATLAS and CMS trackers to develop and implement common solutions, such as appropriate improvements which can be made to the feed-through design and potting techniques.

## 11.6 Support and cooling disks

The design of the support and cooling disks features four half disks per end-cap to provide the cooling and support on both sides for the detector units and peripheral electronics boards. Cooling piping with a semi-circular concentric pattern is embedded into sandwich structure of rigid supports to extract heat dissipation produced in the modules and peripheral electronics, as described in Section 11.3.1 and Section 11.3.2. The $\phi$ position of the two fully instrumented layers inside the hermetic vessel is defined according to the technical drawing Figure D.8 and their tilt in relation to each-other is in the range of 15° to 20° (the exact tilt angle is still being optimised). This angle optimizes the overlap of modules while taking into account the needed space for the Peripheral Electronic Boards (PEB), connectors and flex stack up as well as cooling manifolds access space. Specific piping components are under investigation to reduce the dimensions of the cooling manifolds, fittings and capillary lines.
### 11.6.1 Requirements

As described in the hermetic vessel requirements, all selected materials shall withstand radiation hardness, fire instructions and OTR lifetime cycles (100 cycles from -45°C up to +40°C), in addition to specific mechanical and thermal behaviours. In order to prevent predicted thermal runaway, the heat transfer impedance from the ASICs to the coolant should be as high as possible to satisfy Section 7.5 thermal runaway criteria.

The final assembly of support and cooling disks, including adhesives and bolting design, should comply the Coefficient of Thermal Expansion mismatches (CTE) over the temperature range specified above. The bending over the two meters diameter half disks is a critical parameter and should not be amplified due to the bimetal switch effects. Taking into account the detector tight space, available in the z direction, the maximum acceptable deformation of the on-detector support and cooling half disk should not exceed ±0.5 mm. In the R-φ directions, the instrumented half disks are less constrained due to the assembly isostatic boundary conditions (bolted on the inner ring and sliding at the large radius locked brackets). However, the expected thermal expansion vs shrinkage during OTR lifetime cycles should not produce additional bending or buckling effects. They are estimated to be in the range of +0.5 mm vs -1.5 mm in R and +0.75 mm vs -2.25 mm in φ with aluminum machined plates.

The instrumented half disks integration inside the hermetic vessel requires full access to manifolds area in order to achieve high pressure tight fittings (165 bar of pressure test). These connections to peripheral transfer lines should not induce additional thermo-mechanical constraints and deformation to the instrumented half disks, in particular during cooling down and warm up cycles. On the other hand, the frequency modes of the instrumented half disks should be safely shifted from vibrations generated by the cooling system. All manifold fittings should also be safely locked to prevent any release due to vibrations and OTR detector lifetime cycles.

### 11.6.2 Geometry and design

The baseline design is a half disk composed of two aluminum plates screwed face to face with the titanium cooling loop inserted in between, using thermal grease and an appropriate pressure torque to provide the required heat conductivity from the coolant to the heat source (optimisation of the Thermal Figure of Merit TFM). The feasibility of such a large assembly frame is challenging if the serpentine geometrical accuracy is not matching the machining grooves in the aluminum plates.

In addition, the different thermal expansion properties of the titanium and aluminum (CTE mismatch) need to be considered. Preliminary FEA studies of a full assembly of one cooling half disk are ongoing to evaluate the thermo-mechanical deformation and stress range, in particular the bi-metal switch effects. If the maximal deformation, in z direction, is over the
expected values of ±0.5 mm, the half disk Aluminum structure might not be manufactured
in a single massive piece.

Sandwich structures with two high stiffness carbon fibre panels (CFRP), and a thermally conductive foam core including embedded cooling loops are considered as good alternative solution to the Aluminum single plates, even if they are less optimal for the thermal runaway study (see Section 7.5). A high performance candidate for the foam is a composite pyrolytic graphite foam similar to the selected material planned for ITk. It has high thermal conductive characteristics and absorbs the mismatched thermal expansion of the embedded cooling pipes and carbon-fibre panels. A thermally conductive reinforced elastomer is also under study as material core, due to its bonding characteristics, thermal performance, and reasonable cost.

The X-Y high thermal conductivity of carbon fibre panels is giving uniform temperature distribution over the large cooling disks. The CFRP drawback is driven by the Z low thermal conductivity that is increasing the thermal runaway hazards. The surface finishing of all borders of this alternative solution will be sealed by pultruded carbon fibre U-shaped crowns, which will be the direct interface with the HGTD hermetic vessel. High performance PEEK polymer and Torlon polyamide-imide technology are considered as good candidates to seal these boarders.

11.6.3 Assembly criteria

In order to perform the long term stability and accurate alignment in the ATLAS coordinate
system, the instrumented disks will be directly connected to the inner ring at one extremity
and peripheral edges of inner moderator at the other extremity. Integration tooling is under
study to allow possible half disk insertion into the hermetic vessel both on vertical and
horizontal positions. Taking into account the tight access to manifolds connections and
the possible half disk maintenance disassembly, high performance fitting are proposed as
baseline design. Due to these access and maintenance reasons, the welding solution pointed
out several integration difficulties and was not considered.

In order to accommodate the thermo-mechanical expansion vs shrinkage during OTR
lifetime cycles (see Section 11.6.1), 2 mm free gap is foreseen in between the assembled half
disks to absorb the expected 1.5 mm expansion and prevent any buckling effect. Each half
disk is designed to have a locked $\phi$ slot in the middle of its large radius circumference to
equally balance thermo-mechanical deformation in its peripheral directions. The inner and
outer mechanical connections of each half disk should also carry grounding continuity of
the instrumented layers up to the hermetic vessel ground.
# 12 Detector Infrastructure

## 12.1 Specifications

The HGTD services (cables, fibres, pipes) can be grouped in several categories depending on their role: optical fibres for data transmission; bias voltage for the sensors (high voltage-HV); power for the electronics (low voltage-LV); DCS control, temperature sensors, heaters; dry gas flushing; and CO₂ cooling. The milestones and review process are listed in Table 15.8. The HGTD services summary schedule can be seen in Figure 15.7.

<table><caption>Table 12.1: Summary of HGTD services required for each end-cap, including spares. In the upper part of the table are listed the cables, fibre bundles and pipes, which start on HGTD vessel. Some of them are routed directly to racks located in USA15 or UX15. Others go to PP-EC area on calorimeter end-caps. From the PP-EC the other group of cables are routed to service caverns, they are shown in bottom part of the table. The local to service caverns cables routed between racks are not included in the table.</caption><thead><tr><th>HGTD Services</th><th>Number</th><th>Diameter (mm)</th><th>Routing</th></tr></thead><tbody><tr><td>Optical bundles</td><td>40</td><td>9.5</td><td>HGTD - USA15</td></tr><tr><td>HV proximity cables</td><td>160</td><td>16</td><td>HGTD - (PP-EC)</td></tr><tr><td>DC-DC power control</td><td>40</td><td>14</td><td>HGTD - USA15</td></tr><tr><td>Interlock temp. sensors cables</td><td>32</td><td>16</td><td>HGTD - USA15</td></tr><tr><td>Sensors cables</td><td>10</td><td>12</td><td>HGTD - UX15</td></tr><tr><td>10 V power cables</td><td>72</td><td>15</td><td>HGTD - (PP-EC)</td></tr><tr><td>N₂ gas pipes</td><td>2</td><td>15 and 18</td><td>HGTD - USA15</td></tr><tr><td>CO₂ cooling lines</td><td>4</td><td>&lt;50</td><td>HGTD - (PP-EC)</td></tr><tr><td><strong>Total in barrel-end-cap gap</strong></td><td><strong>356</strong></td><td></td><td></td></tr><tr><td>HV cables</td><td>170</td><td>15.3</td><td>(PP-EC) - USA15</td></tr><tr><td>300 V LV</td><td>10</td><td>14.4</td><td>(PP-EC) - USA15</td></tr><tr><td>300 V LV control</td><td>10</td><td>12</td><td>(PP-EC) - USA15</td></tr><tr><td>DCS cables</td><td>16</td><td>14</td><td>UX15 - USA15</td></tr></tbody></table>

The services will include patch panels (PP-EC), which will be located on the calorimeter end-cap in several accessible places, close to the New Small Wheel ($z \approx 6$ m). The main purpose of the PP-EC is to provide a disconnection point for those services, which cannot be accommodated in flexible chains due to lack of space and must be disconnected before
ATLAS opening. The PP-EC will also allow to realise mapping between connectors on back end electronics and on the detector. More details on PP-EC are given below in Section 12.2 and in Section 12.3.

An estimate of the required services per end-cap is summarised in Table 12.1 and is discussed in detail below. The table does not include the pigtails, which serve for interconnection between cables and peripheral electronics boards inside the vessel.

* The number of optical links per end-cap is 1464, including 520 up-links for data readout, 520 down-links for electronics configuration and fast commands (clocks, trigger, etc), and 424 up-links for luminosity readout. Multi-mode optical fibres will be used for data transmission. They will be grouped in bundles containing 48 fibres connected to 2 MTP connectors, 24 fibres per connector. The fibres will be encapsulated in a common sheath with reinforcement filler in order to be safely routed on cable trays and in the flexible chains. The number of fibres per bundle and per connector is optimised taking into account the routing of the fibres inside the HGTD vessel and the space available in flexible chains. Including spare fibres, a total of 40 bundles per end-cap are needed. Optical patch panels will be implemented in USA15 to organise the correct mapping for DAQ and luminosity readout.

* The baseline for the HV distribution is to provide individually adjustable voltage for each HGTD module. Consequently, 4016 HV lines are needed per end-cap. They will be grouped into 168 cables with an outer diameter of about 16 mm. Adding 2 spare cables, it gives a total of 170 HV cables per end-cap, to be installed between the HV power supplies located in USA15 and the HGTD PP-EC. On PP-EC the HV lines will be re-mapped into 160 cables, containing a different number of wires, to match the connectors on the peripheral electronic boards.

* Powering is organised in three stages. The bulk power supplies located in service caverns provide 300 V DC current to the DC-DC converters that will be placed in the PP-EC area. These second-stage multi-channel DC-DC units convert 300 V to 10 V to supply the radiation hard DC-DC converters that will be located on the peripheral electronics boards inside the vessel. The last converters power the on-detector chips and peripheral electronics, providing 1.2 V DC power and also 2.5 V for the optical links. The 10 V voltage can be adjusted to take into account the voltage drop on the cables. With such a layout the following cables are needed per end-cap: 4 cables to deliver 300 V DC power, 4 cables for control and monitoring, 4 cables for interlock and 4 cables for monitoring the DC-DC converters on PP-EC, all of them to be routed between service caverns and the PP-EC area. In addition, 72 proximity cables are needed to connect the DC-DC (300 V to 10 V) units located on the PP-EC area to the peripheral electronics boards, inside the vessel.
* The DCS requirements and related components are described in Chapter 8 and Chapter 9. The DCS services include the following cables per end-cap:

- Control and monitoring for peripheral electronics, 40 cables.

- Readout of temperature sensors on cooling loops, pressure sensors, mechanical interlocks etc., 10 cables.

- Interlock temperature sensors on detectors, 32 cables.

* The heaters, similarly to the ones currently installed on the LAr cryostat flange, will be installed on the HGTD vessel front cover, between the external moderator and the LAr cryostat and in the proximity of the connectors on outer ring. Several power and temperature sensor cables will be needed for the HGTD heaters.

* The HGTD hermetic vessel will be flushed with dry nitrogen to prevent condensation on the detector components. For gas circulation one inlet pipe and one outlet pipe, with an inside diameter of 16 mm and 13 mm respectively, will be installed to each vessel.

* Four CO₂ cooling pipes <50 mm in diameter will be routed from the vessel feed-throughs to the cooling box located in the PP-EC area. The routing of the transfer lines between cooling box and CO₂ cooling plant located in USA15 is discussed in the next section.

## 12.2 Services layout

The overall HGTD service layout is illustrated in Figure 12.1.

As described above, the detector vessel will be fixed on the calorimeter end-caps, which move when ATLAS is opened. In the present ATLAS detector all end-cap services are installed in flexible chains to avoid their disconnection before movement. Currently all the chains are fully occupied, but it is expected that they will be partly rearranged for the ATLAS Phase-II upgrade and some space will be made available for a fraction of the HGTD services. Also two new small flexible chains are considered to be installed for HGTD. The priority for installation in flexible chains will be given to those cables and pipes, which are most critical concerning disconnection. The other services should be disconnected before the calorimeter end-caps are moved. For that purpose the patch panels (PP-EC) will be organised on the calorimeter surface in accessible places. The 300 V to 10 V DC-DC converters will also be installed in the PP-EC area in order to make LV cables as short as possible, which is necessary to minimise the power losses (and voltage drops) on cables.

The baseline layout of the CO₂ transfer lines provides for the rigid lines installed between the CO₂ cooling plant located in USA15 and the manifold box placed on the calorimeter
end-cap in the PP-EC area. Four smaller transfer lines, one for each instrumented half-disk, are routed on the calorimeter end-cap surface from the manifold box towards the HGTD vessel. With such a layout, the transfer lines must be disconnected from the manifold box before moving the calorimeter end-cap. A more attractive approach consists in avoiding the disconnection of the transfer lines at least at standard openings in YETS. To realise this, the CO₂ transfer lines must include rigid and flexible parts. The rigid lines are installed between the CO₂ cooling plant and the manifold box, located on the voussoir platforms in the ATLAS toroid area above the calorimeter end-caps. From the manifold box, two flexible lines, one inlet and one outlet, are routed to the splitter box on the top of the calorimeter end-cap on the IP side, close to HGTD. From the splitter box four smaller rigid lines are installed on the calorimeter front wall and connected to the HGTD vessel. The use of flexible lines avoids the disconnection of CO₂ cooling lines during standard openings. However, on the platforms, there is not enough room to accommodate flexible lines, long enough for full openings in LS periods, when calorimeter end-caps are moved by about 12 meters. For such an openings, the flexible lines must be disconnected from the splitter box on the calorimeter. A more in-depth study is necessary to confirm the feasibility of implementing the layout with flexible lines.

<figure><img src="image_171.png" /><figcaption>Figure 12.1: Overall HGTD services layout from the detector to USA15 or UX15. The optical fibre bundles, N₂ gas pipes, interlock and cooling temperature sensor cables, part of DCS cables and, still to be confirmed, the 300 V power supply cables are planned to be installed in flexible chains. The HV cables and rest of DCS cables will be routed through the patch panels, where they will have a disconnection point.</figcaption></figure>
To allow commissioning of the detector after installation in the experimental cavern, and for maintenance during shutdown periods, it should be possible to operate the HGTD when ATLAS is in the open configuration, which requires reconnecting the services in the open position. For that purpose, it is envisaged to install extenders of cables and CO₂ cooling lines between respective positions of the patch panels in closed and open configurations. Most of these extensions should be permanently held in place, which will help minimise the time required to put the HGTD in working order after each opening.

## 12.3 Patch panels in PP-EC area

The positions of the PP-EC boxes and DC-DC units on the calorimeter end-caps will be chosen in discussion with Technical Coordination, and placed in several sectors in accessible areas to allow disconnection of services. It will also be possible to replace any faulty DC-DC converter with a short access during the run. The preliminary study of the patch panel locations by ATLAS Technical Coordination is shown in Figure 12.2.

<figure><img src="image_172.png" /><figcaption>Figure 12.2: The preliminary layout of the HGTD patch panels (PP-EC) on the surface of the end-cap calorimeters. The 300 V to 10 V DC-DC converters and the cooling splitter box will also be located in this region. The PP-EC components are distributed in several places around the calorimeter end-cap surface (some of them are indicated by arrows in the image).</figcaption></figure>

The strength of the magnetic field, along with radiation levels, are critical parameters for the design of the DC-DC power converters. The magnetic field in the patch panel region is
shown in Figure 12.3, varying from 0.05 T up to 0.5 T. The power supplies should be placed
in areas where the field is the weakest, midway between two barrel toroids and as close as
possible to the surface of the calorimeter. Radiation levels in these areas have been estimated
using FLUKA calculations, giving a maximum of 15 Gy and less than $1 \times 10^{12} \text{ n}_{\text{eq}} \text{ cm}^{-2}$ (no
safety factors applied) at the outer radius of the calorimeter end-cap, where the patch panel
boxes will be located.

<figure><img src="image_173.png" /><figcaption>Figure 12.3: Magnetic field in the region of the HGTD PP-EC patch panels.</figcaption></figure>

The DC-DC power converters located in the PP-EC area will require water cooling. Assuming 80% power efficiency, about 4 kW of cooling power is needed in all PP-EC locations, combined for each end-cap. The existing ATLAS leak-less water cooling systems have a sufficient capacity to supply the HGTD detectors on both end-caps. Dedicated connecting pipes and manifolds on the calorimeter will be required.

12.4 Services routing on the calorimeter front wall

The space available to route the HGTD services in the gap between the calorimeter barrel
and end-cap is very limited, making the design and installation of the services a challenging
task. This space is shared between ITk and HGTD services. In addition, scintillator counters,
belonging to the Tile calorimeter system, are installed there. In the present configuration,
the counters are fixed on the Tilecal and LAr front face, where the HGTD cables will be
routed. In LS3 the scintillators must be replaced by new ones. It was agreed with the Tilecal
system and Technical Coordination that the scintillator counters will be installed on top of
the HGTD services, which will be fixed on the wall of the calorimeter. Such a layout will
guarantee access to the counters and their replacement during HL-LHC lifetime. In order to
provide more robust support and fixations for HGTD cables and for scintillator counters
and, at the same time, to protect the Tile calorimeter, whose scintillator tiles and fibres are
visible on its front side, thin aluminium support plates will be fixed on the Tile calorimeter
modules.

<figure><img src="image_174.png" /><figcaption>Figure 12.4: The envelope for HGTD services. On the left: front view of the calorimeter end-cap on side A. The space available for HGTD services is shown with yellow color. With red rectangles is shown the area, where the space for the HGTD services is very limited. On the right: the HGTD services envelope in the gap between calorimeter barrel and end-cap. The envelopes for ITk services and the Tilecal scintillator counters are also shown.</figcaption></figure>

The envelop for HGTD services is shown in Figure 12.4. All space in $\phi$ on the front wall of the LAr end-cap cryostat is available for HGTD services, while at bigger radius they have to be grouped to fit in the space between LAr barrel crates and further between Tilecal barrel fingers, sharing the space with ITk services installed on the calorimeter barrel. The space in two gaps between LAr barrel crates on top cannot be used to route the HGTD cables. One constraint comes from the requirement to keep free access to the end plates of three Tilecal modules, located at the top of the calorimeter, to give access to the electronics of these modules. Space in another gap is occupied by a LAr HV filter box. The space in $z$ available for HGTD services on the LAr end-cap cryostat wall at radius >1.4 m is only 17 mm. Exceptionally, there will be a dedicated slot for four CO$_2$ cooling pipes, as described in Section 11.3.2.

The HGTD services routing on the calorimeter end-cap front wall is shown in Figure 12.5. The cables, connected to the outer ring of the HGTD vessel in four layers, will be rearranged to one layer at $r > 1.4$ m to fit within the envelope of 17 mm. Below the Tilecal barrel fingers, the cables will be regrouped to a few layers to come out on the calorimeter surface through the gaps between the fingers. As discussed above, the HGTD cables cannot be routed in two top gaps between the LAr barrel crates. Due to that the cables from the top section of the HGTD deviate towards neighbouring gaps. From the gaps, the cables will be routed
## 12 Detector Infrastructure

over the surface of the calorimeter end-cap, to PP-EC located in several places around the calorimeter.

<figure><img src="image_175.png" /><figcaption>Figure 12.5: HGTD services routing on the calorimeter end-cap wall. The LAr crates and Tilecal fingers, both belonging to the calorimeter barrel, are also shown in the picture.</figcaption></figure>

## 12.5 Services connection to outer ring and inside the vessel

The outer ring of the HGTD vessel provides the interface for all the services. With such an approach, the HGTD detector can be completely assembled and tested at the surface and brought down to the experimental cavern for installation as a closed vessel. Once the vessel is fixed to the front wall of the LAr cryostat, the pipes, cables and optical bundles will be connected to the detector. To realise such a scenario, the cooling and gas pipe fittings, electrical and optical connectors will be embedded in the outer ring, as shown in Figure 12.6. The layout of the outer ring is shown in Figure 11.15.

The organisation of services inside the HGTD vessel is schematically shown in Figure 12.7.
<figure><img src="image_176.png" /><figcaption>Figure 12.6: Fragment of the outer ring of the HGTD vessel. The electrical and optical connectors embedded into the ring are shown.</figcaption></figure>

The short pigtails, one per cable, will interconnect the cables and the peripheral electronics boards (PEB). The optical bundles, connected to the outer ring, will be terminated with 24-fibre MPO connectors. The optical pigtails will be used to distribute these 24 fibres from each bundle to several VTRx+ optical link modules installed on the PEB. One bundle is required per PEB, including spare fibres. The optical pigtails will also contain spare fibres terminated by connectors.

## 12.6 Services installation

The installation of services and patch panels will be done in close collaboration with Technical Coordination. The delivery of CO₂, under-pressure water cooling stations and the N₂ gas plant is the responsibility of Technical Coordination and the CERN support cooling and gas teams.

The various components should be available at different times depending on the delivery and final location in the ATLAS cavern. To decouple the installation of cables, patch panels and the detector, the mock-ups of patch panels and outer ring indicating the positions of the connectors will be installed in their final place with the aim to precisely indicate the cable connection points.

In an environment as complex as ATLAS, cable routing requires numerous turns and transitions between cable trays, which makes it impossible to estimate the lengths of cables with an accuracy of several centimetres at connection points. As a consequence, some extra length
<figure><img src="image_177.png" /><figcaption>Figure 12.7: Illustration of the services layout inside the HGTD vessel. On the right part of the picture the cross section of the services area is shown.</figcaption></figure>

has to be allowed for each cable, which could then be accommodated on cable trays, however this is not always possible due to the lack of space.

Therefore, the common approach for installing long cables is to pull cables with the connect-
ors attached only on the detector side, to allow adjustments to the cable length on the other
side. The connector at the second end of the cable should be attached in situ, though that is
not always feasible due to connector complexity or lack of space or time for this work. Given
all this, different installation scenarios are foreseen for different HGTD services, as described
below. The detailed plans and schedule for the installation of each type of HGTD services
will be developed in collaboration with Technical Coordination as part of the preparation of
activities for LS3. All cables, except optical bundles, must be tested before installation in the
cavern.

The **Optical bundles** will be delivered with connectors attached and protected at both ends. They will be tested at the factory. Some space should be reserved to accommodate an extra length on the cable trays below the racks in USA15. The optical bundles will be routed through small plastic flexible chains available in sector 11, to avoid disconnecting them at ATLAS openings. An optical patch panel will be used in USA15 to remap the fibres between luminosity and data readout.

For the **HV cables** two installation scenarios are considered. If space on the cable trays below the racks in USA15 is available to accommodate an extra length, the HV cables will be delivered with connectors fixed at both ends. Otherwise, the cables will be made in
double length, folded in the middle, with connectors attached at both ends, to be routed
to the PP-EC patch panel. Such a configuration makes it possible to test the cables and
connectors before installation. After pulling such cable pairs into the service cavern, the
loop will be cut out to the precise length and the missing connectors attached in-situ. One of
these scenarios will be chosen when the layout of the racks and the services in the service
caverns are available from Technical Coordination.

The LV and DCS cables to be routed between the experimental and service caverns will be installed with one connector (detector side), the second connector will be attached in-situ near racks. The same scenario will be applied for DCS cables between the HGTD or patch panels and racks in UX15.

The **Proximity cables** listed in Table 12.1 must be delivered with connectors attached at both ends, because it would be extremely difficult to install them in-situ, near the calorimeter. Before installing the connectors, the length of these cables must be precisely measured in-situ, by pulling pilot cables between the mock-up of outer ring and the patch panel box, placed in their final positions.

All the described above installation scenarios were successfully applied in ATLAS during its
original installation.

The installation of the patch panels and services, and the respective connectivity will be done
when access is allowed by Technical Coordination. These activities will start well before the
HGTD installation and will be spread over time. In the current schedule, these activities are
planned over approximately 16 months, from January 2025, the beginning of LS3, to April
2026.

Technical Coordination will have responsibility for the planning and installation of the
transfer lines for the CO₂ cooling system and pipes for the N₂ gas system.
<figure><img src="image_178.png" /></figure>
# 13 Detector Assembly, Installation, and Commissioning

## 13.1 Assembly and commissioning on surface

The detector assembly and QA will be done at CERN in a clean room, using dedicated tools and testbenches. These activities will include the assembly of the instrumented half disks by installing the detector components (detector units, PEB, flex tails) on the cooling plates, and the integration of the assembled half disks, sensors and services inside the vessels. Each assembly step will include all the procedures necessary for QA. Several Institutes will participate in the assembly activities, which are planned for the periods between September 2024 and October 2025 for HGTD-A and between October 2025 and October 2026 for HGTD-C. A schedule of the assembly can be seen in Figure 15.8 and a schedule for the installation can be seen in Figure 15.9.

### 13.1.1 Half disks instrumentation

In order to prevent any contamination of the active sensors (dust, metallic chips), all detector assemblies and testing must take place in a clean environment, equipped with temperature and humidity control gauges. The floor should be ESD protected (ElectroStatic Discharge) for personnel and components at all work-stations and setups. Specifications for this environment are under development considering that all critical assembly steps shall take place in a clean room class ISO-8 or better.

The detector units (see Section 7.4.2), corresponding to 32 quarter disks, 96 pieces for the middle disks and 96 pieces for the outer disks, will be assembled and qualified in different Institutes and shipped to CERN to be mounted on the cooling plates. Separately, the peripheral electronics boards and the flex tails will be qualified at collaborating Institutes and shipped as well to CERN. The QA procedure on the detector units, peripheral electronic boards and flex tails will be repeated at CERN, at least on a sample of elements, to confirm that no damage has occurred during shipping.

The half disks will be instrumented by mounting first the peripheral electronic boards, followed by the outer ring and the detector units. After mounting the outer ring and before
## 13 Detector Assembly, Installation, and Commissioning

adding the detector units, the pigtails will be connected. The last step is to connect the flex tails between the modules and the peripheral electronic boards.

At this stage the full on-detector readout chain is connected for the first time and the first full calibration will be performed, as described in Section 13.1.3. After having completed all the tests and replaced the defective components if necessary, the instrumented half-disks are ready to be installed in the hermetic vessel.

Each instrumented half disk will be a single item weighing 30 kg with 12 cm inner radius and 92 cm outer radius. A breakdown of the contribution of each component to the thickness can be found in Table 11.1. Dedicated tools will be developed to allow the disks assembly in the optimal position (horizontal vs vertical) with appropriate rotation to fully instrument the two faces of the half disk.

### 13.1.2 Detector assembly on hermetic vessel

Before being delivered to CERN, the hermetic vessels will be mechanically tested at the Institutes responsible for their production. The mechanical tests will be repeated at CERN to exclude damage due to shipping and the air tightness of the vessel will be checked. After this step and the installation of the CO₂ cooling pipes, the instrumented half disks will be installed in the vessel and the CO₂ services will be connected. The next step will be to attach the temperature sensors to the manifolds and cooling pipes, install the interlock temperature sensors, the pressure sensors and connect the relevant services. After that, the hermetic vessel will be closed with a front cover. Prior to any integration step the mechanical envelopes of previously installed components must be validated and the spacing between each component must be controlled. Once the vessel is assembled, it can be connected to the baby demo CO₂ cooling system (see Section 14.2) to perform pressure and cooling tests, in addition to further performance tests, as described below.

### 13.1.3 Quality Assurance after assembly

The first set of tests after instrumentation of the half disks will probe the electrical connectivity, followed by a first full calibration of all the on-detector elements and a full-chain test, using the particle signals from a radioactive source. The test bench will include a cold box with a radioactive source movement system, an interlock system, a portable system for powering, read-out and control to be used on surface for the tests described in this section and in the cavern before the detector is connected to the ATLAS DCS and DAQ systems. The test bench will facilitate the testing of all the detector elements connected to one peripheral electronics boards (PEB) at once.

To test electrical connectivity, commands will be sent from the DAQ and DCS modules to each stage of the electronics, reading back the response of the commands. First the
communication with the PEB will be tested, then the communication with ASICs and some of their functionalities will be tested, which also probes the flex tails and module flexes. Finally, the whole chain will be tested sending a calibration signal to the sensors. To speed up the calibration procedure, the already known optimal settings for the modules and for the PEBs, obtained in previous steps of the production process, will be applied in tests with and without particles. Only readout channels, which show a change in characterization compared to the earlier calibration, will be re-calibrated.

A database will be used to record the status of each component at all assembly steps, in particular the electronic and the thermal parameters of the instrumented half disks. The aim is to have a full history from the production process up to the final assembly and testing. Existing ATLAS databases will be adapted to avoid duplication of the software development efforts. The database identification protocol of all mechanical components will be based on a serial number and/or QR code (bar-code if any). In addition, detailed technical parameters (row material, chemical composition, manufacturing process, testing) will be included in the database to allow monitoring of the construction progress. After completion of the detector installation in the experimental cavern, the database will evolve towards a collection of system configuration data, necessary to analyze the detector operation conditions and performance.

# 13.2 Installation in the cavern and commissioning

## 13.2.1 Access and maintenance scenarios

The access for installation and maintenance of the detector and the off-detector electronics located in UX15 can only occur in breaks of LHC operation, and the intervention actions depend on the duration, induced radiation levels and ATLAS opening scenarios. The back-end electronics situated in USA15 will be accessible at any time, but interventions will be limited during data taking. The access scenarios and possible interventions on the detector during the various types of breaks in the operation of the HL-LHC are described below.

**Short access** for a few hours only, primarily for LHC machine interventions and usually announced on short notice. In these periods, the electronic components located in the HGTD PP-EC areas can be accessed for simple interventions, for example to replace the 300 V-10 V DC-DC converter modules. Access to the DCS equipment in the racks in UX15 will also be possible.

**Technical Stop**, typically of one week duration, for maintenance of the LHC and of the experiments. The same areas as for the short access periods will be accessible, but it will be possible to perform more complex and long operations.
**Year-End Technical Stop (YETS)**, the yearly maintenance for about 12 weeks. In this period the ATLAS detector is partly opened, keeping the beam pipe in place as illustrated in Figure 13.1. The distance between the calorimeter barrel and end-cap is typically 3.1 m. The access to the HGTD components inside the vessel would be very difficult due to the high radiation level and the complexity of the detector construction, so the opening of the vessel in situ during YETS is not planned. However, the construction of the vessel and instrumented discs allow to open the detector and remove or install instrumented half-disks. The maintenance or upgrade of all off-detector components, including patch panels, electronics and services is possible, depending on the duration of the foreseen operations and the radiation level in the accessed areas.

**Long shutdown (LS)**, which typically lasts 2 years, is foreseen for large upgrade and consolidation programs for the experiments and the LHC. The ATLAS detector will be in the large opening position, with the beam pipe removed, as shown in Figure 13.2. The distance between the barrel calorimeter face and the HGTD face is at most 12 m. After the LS3, when the HGTD should be installed, the next long shutdowns should be used for extensive maintenance and upgrade of the detector. After each $1000 \text{ fb}^{-1}$ of collected data, which approximately corresponds to the run period between two long shutdowns, the detector modules located in the innermost ring must be replaced. Every $2000 \text{ fb}^{-1}$ the modules in the middle ring will be replaced. These operations, along with reparations and consolidations of the detector, will be performed on the surface integration area. Once the area has reached an acceptable radiation level, the services will be disconnected from the HGTD vessel, then the closed vessel will be removed from the calorimeter end-cap and brought to the surface. For the replacement of the detector modules and the tests and commissioning after consolidation, the same tooling and procedures as for the detector assembly will be used. In addition, due to the exposure of the HGTD to radiation during data taking, safety guidelines will be strictly enforced to protect the personnel when accessing and manipulating the HGTD components, following the radioprotection measures and procedures prescribed by the CERN Radio Protection experts.

### 13.2.2 Transport and installation the HGTD in the cavern

The installation of HGTD and the connection of all services will take one month for each end-cap and is planned, in accordance with the ATLAS TC schedule available in mid-January 2020, for April 2026 and January 2027 for the A side and C side, respectively. More details on the schedule are given in Section 15.2. The development and optimisation of the schedule of ATLAS upgrade activities in LS3 will continue for several years and could lead to advancing the installation of HGTD by a few months. In this case, the HGTD schedule will be adapted to the overall LS3 schedule. If necessary, the design of the HGTD allows the installation of instrumented disks in the next YETS, even in the presence of the beam pipe.
<figure><img src="image_179.png" /><figcaption>Figure 13.1: ATLAS in standard opening configuration.</figcaption></figure>

The installation of the detector will be done in the large detector opening configuration as shown in Figure 13.2. This operation can start only after the external part of the moderator has been installed on the LAr front wall.

As it is described above, both HGTD end-caps will be fully assembled and tested on surface. The closed vessels will be transported to the pit for installation on the calorimeter end-caps, using dedicated installation tooling. This is the baseline assembly and installation scenario, however the staggered installation of different half disks in situ is also possible.

The total weight is 275 kg per end-cap, assuming that the external moderator part will be transported separately. The overall dimensions are 1100 mm radius and 105 mm thickness. These parameters should be taken into account for the transport truck and lowering, but they are well below the lifting capacity limit of the crane in ATLAS SX1 surface building and the dimensions of both shafts. Each end-cap, HGTD-A and HGTD-C, will be lowered on side A and side C, respectively, directly from the surface to the minivans, which are shown in Figure 13.3. A local lifting tool is needed to lift the fully assembled end-cap detector and accurately align it with respect to the LAr end-cap inner warm tube, to avoid any conflict with the beam pipe ionic pump and its services.

Specific tools will be constructed to perform the transport, lowering and installation of the HGTD on the calorimeter end-cap. All these tools are still at a conceptual stage and will need to be carefully designed, and, where possible, use synergies with tools already developed for other sub-detectors.
13 Detector Assembly, Installation, and Commissioning

<figure><img src="image_180.png" /><figcaption>Figure 13.2: ATLAS in large opening configuration. The HGTD is superimposed to the MBTS scintillators that are presently installed on the calorimeter end-cap cryostat.</figcaption></figure>

13.2.3 Services connection and commissioning

As described in Section 12.6, all HGTD services will be already in place before the installation of the detector. After fixing the HGTD vessels on the LAr end-caps, the cables and the pipes will be connected, and the connectivity will be tested as part of the initial commissioning. The extensive tests and validation of interlock, detector safety system and DCS must be completed prior to the next commissioning steps.

Access to the detector components during the commissioning should be possible until approximately April 2027, close to the expected end-cap calorimeter closure. This will leave at least 3 months of intense commissioning while access is still possible. Both the installation and the commissioning of the HGTD will be carried on with the participation of several collaborating Institutes.
## 13.2 Installation in the cavern and commissioning

<figure><img src="image_181.png" /><figcaption>Figure 13.3: ATLAS in large opening configuration. HGTD detector superimposed on the MBTS scintillators, that are currently installed on the LAr end-cap cryostat.</figcaption></figure>

### 13.2.4 Radiation environment, and radio protection

During all ATLAS upgrade and maintenance activities, as on the CERN site in general, the ALARA (As Low As Reasonably Achievable) radio-protection principles will be strictly followed. It will be implemented during the installation and maintenance activities of the HGTD, in accordance to the rules and recommendations of the CERN Radiation Protection service and in close collaboration with Technical Coordination.

In order to plan the HGTD installation and further consolidation activities and to optimise the work procedures accordingly to this concept, estimates of the radiation environment are needed. Estimates of the ambient dose equivalent rates in LS3, when the HGTD is installed, and in the following LS periods, when part of HGTD detector modules are replaced, were provided by the RP group, using FLUKA calculations, and can be found in Ref. [98] and [99]. The uncertainty on these calculations, evaluated by comparing them with ambient dose equivalent rate measurements during YETS 2016-2017, includes a systematic underestimate up to a factor of 2 in the region between the ID and LAr end-cap. This uncertainty comes most likely from the imprecise material description in the simulation.

The dose equivalent rate map for LS3, after 28 days of cool-down time, is shown in Figure 13.4, for the geometry corresponding to the completed large opening, with all beam pipes and inner detector removed.
## 13 Detector Assembly, Installation, and Commissioning

<figure><img src="image_182.png" /><figcaption>Figure 13.4: FLUKA simulations of the ambient dose equivalent rate in LS3, after 297 fb⁻¹ of accumulated data and 28 days of cool-down period. ATLAS is in the large opening configuration, all beam pipes and inner detector are removed. The boundaries of various radiation areas are shown with coloured lines [98].</figcaption></figure>

The HGTD installation will take place after about 1.5 years of cool-down time. In that period the radiation level will drop by a large factor compared to the one shown in Figure 13.4. On the other hand, the extension of Run 3 by one year might cause an increase of the equivalent dose rate. Calculations dedicated to each LS must be performed to estimate the radiation environment during the replacement of the inner and middle rings with reasonable accuracy. FLUKA simulations exist for the dose equivalent rate in the LS5 period, assuming 2177 fb⁻¹ of accumulated data, a cool-down period of 181 days and the standard opening configuration. The results are shown in Figure 13.5. In this configuration the radiation levels expected in the HGTD region are expected to be in the range of 30 to 50 µSv h⁻¹ (from the outer to the inner radius). When replacing the inner part of the detector, the expected dose rates should be lower due to the longer cool-down time and the absence of the beam pipes. Nevertheless, it will be well above the threshold defining the simple controlled area (10 µSv h⁻¹). Therefore the work duration will be severely limited.

Before accessing the components of the detector to be moved to the surface for replacement of the inner and middle ring, additional cool-down time will be necessary. In order to minimise the radioactivity of the detector, material less prone to activation must be used in the construction, in particular by avoiding the use of stainless steel components and giving preference to aluminium or plastic. First of all, the possibility of manufacturing the
aluminium or titanium pipes integrated in the cooling supports is considered.

<figure><img src="image_183.png" /><figcaption>Figure 13.5: FLUKA simulations of ambient dose equivalent rate in LS5, after 2177 fb⁻¹ of accumulated data and 181 days cool-down period. ATLAS is in the standard opening configuration [98].</figcaption></figure>

<table><caption>Table 13.1: ALARA classification criteria.</caption><thead><tr><th>Classification criteria</th><th>Level 1</th><th>level 2</th><th>level 3</th></tr></thead><tbody><tr><td>Individual dose equivalent</td><td>&lt;100 µSv</td><td>100 µSv - 1 mSv</td><td>&gt;1 mSv</td></tr><tr><td>Collective dose equivalent</td><td>&lt;500 µSv</td><td>500 µSv - 5 mSv</td><td>&gt;5 mSv</td></tr><tr><td>Ambient dose equivalent rate</td><td>&lt;50 µSv h<sup>-1</sup></td><td>50 µSv h<sup>-1</sup> - 2 mSv h<sup>-1</sup></td><td>&gt;2 mSv h<sup>-1</sup></td></tr><tr><td>Airborne activity</td><td>&lt;5 CA</td><td>5 CA - 200 CA</td><td>&gt;200 CA</td></tr><tr><td>Surface contamination</td><td>&lt;10 CS</td><td>10 CS - 100 CS</td><td>&gt;100 CS</td></tr></tbody></table>

It is expected that the HGTD installation zone will be classified at least as a "simple controlled radiation area", which is defined as the area whose ambient dose equivalent rate H*(10) does not exceed 10 µSv h⁻¹ at workplaces or 50 µSv h⁻¹ in low occupancy areas. All work in controlled radiation areas will be planned and optimised including an estimate of the collective dose and the individual effective doses to the personnel participating in the activity. This will be described in the DIMR file (Dossier D'Intervention en Milieu Radioactif), which must be prepared for each intervention. The Radiation Protection service will assign an ALARA level to each type of activity, accordingly to the CERN classification criteria, which are shown in Table 13.1. Since the airborne radioactivity and contamination can be ruled out,
the ALARA level classification will be primarily determined by individual and collective
effective dose. As can be seen from the table, the HGTD installation activities will be situated
between ALARA Level 1 and Level 2, considering the ambient equivalent dose. However,
the collective dose during replacement of the inner part of the HGTD at half-life time of
HL-LHC on both end-caps might approach the limit of 5 mSv, which corresponds to the
Level 3 threshold. In this case the Level 3 scenario is applied, which involves additional
optimisation efforts and implies that dose planning and work organisation are reviewed by
the ALARA committee. DIMR level I and level II will be prepared and discussed between
the intervening personnel and the ATLAS radiation safety officer (RSO) and LEXGLIMOS
prior to intervention, which can only start when the DIMR is approved. All the activities will
be followed by the RSO and LEXGLIMOS on a day-by-day basis, involving CERN Radio
Protection experts when necessary.

Beside the careful work optimisation, additional measures to help minimise the exposure
of personnel to radiation will be considered. Such measures include shielding, which will
reduce the dose rate to the human body; use of tools for remote handling; organising the
working place in such a way, that people are placed in the outer radius of HGTD avoiding
exposure to the area near the beam line, where the dose rate is much higher.
# 14 Demonstrator

## 14.1 Introduction

The R&D period will extend up to early 2022 to validate the choice of many components before the Final Design Reviews. In addition, it is essential to validate some key aspects of the integration during this period by building a realistic demonstrator. The plan is to have a two step plan decoupling the mechanics/cooling aspects from the full electronics/DAQ demonstrator activities. The heater demonstrator will be based on a silicon-based heater substrate to study the thermal performance of the system, instead of a real sensor and ASIC module which will only be ready at the earliest by 2021 (further information may be found in Section 6.9). The full demonstrator will be similar to the heater demonstrator but equipped with some HGTD modules and read-out through a prototype of the peripheral electronics and back-end. A dedicated organisation is being set up to ensure coherence of the numerous parallel activities and monitor the schedule.

## 14.2 Heater demonstrator

The goals of this demonstrator are:

* Use the simple cooling plate system to validate the CO₂ thermal calculation which will be used for the final design of the HGTD cooling loops.

* Choose and validate the module loading procedure (intermediate plate, gluing, flex cable stacking...) by equipping the demonstrator with heaters in a geometry similar to the HGTD modules.

The demonstrator will consist of a rectangular cooling plate covering about 7 cm × 80 cm as displayed in Figure 14.1, corresponding roughly to the longest detector unit in the HGTD. The cooling system will be made of a single loop (technical details given in Annex) embedded in a carbon fibre structure and will be used first to validate the thermal calculation of the CO₂ cooling on a simple design: CO₂ cooling parameters such as pressure and flow will be varied and the temperature on the plate will be measured with Resistance Temperature Detectors (RTDs) embedded into heaters. Heaters are used as a replacement of the full size module (sensor + ASIC). They will be placed on top of the cooling plate in a similar manner
<figure><img src="image_184.png" /><figcaption>Figure 14.1: Schematic view of the cooling structure equipped with heater modules in blue. The green area corresponds to the peripheral electronics board.</figcaption></figure>

as the modules in a given readout row. A dedicated vessel should be also built, allowing dry nitrogen flushing and a feed-through for electrical connections. The convection conditions should be as close as possible to the final ones. The mechanical prototype can be found in Figure D.9.

After this first set of measurements, the detector unit should be mounted on the top and bottom faces of the cooling plates. Figure 14.2 shows preliminary calculations of the temperature uniformity for both options that will be compared to the measurements. As expected, the calculation predicts a uniform temperature with the pattern intermediate plate, 0.4 K between inner and outer module, while up to 1.8 K is observed with the full intermediate plate.

Real HGTD modules will not be available before 2021. Consequently to mimic the radial heat dissipation expected in the HGTD, silicon heater devices similar to the ones used by the pixel ITk demonstrator will be used for the module loading. Thus the silicon heater demonstrator program will address two important aspects of the HGTD system: module loading and thermal performance. A schematic drawing of the silicon heater is shown in Figure 14.3.

The heaters consist of a silicon substrate with a similar geometry (area) as the modules and a thickness of 300 µm. A geometry slightly smaller than the final HGTD module was chosen due to ease of production by the manufacturer. The heaters will have a size of 20.2 mm × 38.4 mm. They will be made of a TiW continuous layer produced on a 300 µm
## 14.2 Heater demonstrator

<figure><img src="image_185.png" /><figcaption>Figure 14.2: Expected temperature uniformity on the demonstrator equipped with the full intermediate plate (left) or the pattern intermediate plate (right)</figcaption></figure>

<figure><img src="image_186.png" /><figcaption>Figure 14.3: Silicon heater transverse view</figcaption></figure>

thick wafer. The heaters dissipate power by applying a current through a thin metal layer embedded in the silicon substrate. The amount of generated heat can be controlled through the provided current. In order to monitor the temperature of the heater RTDs are implanted on top of the thin metal separated by an oxide layer. The RTDs will then be placed on top of a second oxide layer separating the heater from the RTDs, which will also be made from TiW. They are operated by applying a current and reading the voltage drop across the RTD which is previously calibrated to provide temperature information. The RTDs are controlled through a flexible cable that also provides the current to the heater element. The flex is glued to the top of the heater and its pads are wire-bonded to the heater. The heater flex PCB design can be found in Figure 14.4. The design has been optimized to be as close as possible to the final design choice for the HGTD.

The heater flex will be designed to mimic the HGTD module flex cable in terms of geometry, material and rigidity. It will contain a connector similar to the one being considered for
<figure><img src="image_187.png" /><figcaption>Figure 14.4: Heater flex PCB layout.</figcaption></figure>

the final flex design, which can provide power to the heaters and individual readout lines for the RTDs on each heater. The flex cables will be layered one on top of each other out to the peripheral readout boards. Though the final specifications of the peripheral readout boards will not be available, a compact connector scheme is foreseen. The system will be controlled by external power supplies that will provide the desired operational thermal range to fully study the system performance. The nominal power dissipation foreseen for the innermost part of the heater detector unit is 400 mW cm⁻², but deviations from this value will be explored. The entire heater demonstrator will be placed within an isolated container box to maintain temperatures close to -30°C and allow for nitrogen or dry air to be flushed into the apparatus to maintain a dry atmosphere. The CO₂ cooling will be provided by the CO₂ baby demo cooling plant, sitting nearby, as shown in Figure 11.7. The design of the heater demonstrator apparatus can be found in Figure 14.5.

The Institutes that plan to participate in the HGTD module assembly and loading effort will also participate in the heater (and/or full) demonstrator effort and will thus gain expertise on the module assembly process. The calibrations of the RTDs will also be carried out by the Institutes, before and after module loading. The assembly of the intermediate plates around the cooling plane will be carried out at CERN, where the full cooling tests will be conducted.

In summary, the heater demonstrator will allow to validate the thermal performance of the HGTD, by using heaters loaded into a long detector unit and combined with a CO₂ cooling system. Furthermore, the exercise of assembling the heater modules, populating
<figure><img src="image_188.png" /><figcaption>Figure 14.5: Silicon heater demonstrator apparatus including additional components located outside the apparatus. Heaters are shown in red, placed on top of the cooling place. The peripheral boards are shown in green. The flex cables which will connect the heaters to the peripheral boards are not explicitly shown in the figure. A multiplexer is foreseen to switch the active readout between the 96 RTD signals.</figcaption></figure>

the intermediate plates and mounting the full heater demonstrator is expected to provide valuable experience towards the final HGTD detector unit assembly and loading effort. The silicon heater schedule and timeline is detailed in the full demonstrator planning at the end of the chapter in Figure 14.8.

**14.3 Peripheral and back-end electronics, data acquisition**

The readout demonstrator will exercise the final HGTD read-out path and will be used to validate the PEB, the clock distribution and the FELIX board used for the data acquisition.

**14.3.1 Peripheral electronics demonstrator**

The peripheral electronics demonstrator will evaluate the different paths from the module flex to the PEB via flex cables like the data transmission, high voltages and the power
distribution. In addition, it will allow to exercise the assembling, connection and integration
of the peripheral electronics. It consists of a PEB connected up to 56 HGTD modules via
a stack of flex cables. In a first stage, an Spartan-7 FPGA will be used to emulate the
ALTIROC2 ASIC and a Kintex-7 FPGA to emulate the lpGBT chipset, while the VTRx+ and
the bPOL12V will be replaced by similar commercial components (SPF+ and TPS56428RHLR
respectively), given the unavailability of the different items. A scheme of the peripheral
electronics demonstrator is shown in Figure 14.6. The design of the different items has
already started and a peripheral electronics demonstrator will be ready by Summer 2020.
On a second stage, the different components will be replaced by the ones of the final design
and will be integrated in the full demonstrator set-up.

<figure><img src="image_189.png" /><figcaption>Figure 14.6: Block diagram of the peripheral electronics board demonstrator. A Kintex-7 FPGA will be used to emulate the lpGBT chipset, a SPF+ will replace the VTRx+ and a TPS56428RHLR will be used instead of the bPOL12V DC-DC converter.</figcaption></figure>

14.3.2 DAQ demonstrator

The DAQ demonstrator will exercise the entire read-out path up to the off-detector back-end.
Activities at CERN have already started and a Phase-I FELIX board and its DAQ PC have
been purchased. On a first stage, the HGTD e-link data will be emulated inside FELIX
in order to test the read-out chain. Afterwards, the FELIX board will be connected to an
FPGA emulator that will send HGTD data in FULL mode in order to validate the readout
chain. The ALTIROC2 FPGA emulator described in the previous section can be used for this purpose. When available, the ALTIROC2 will be connected to the readout chain. A GBT chip can serve as the interface between the FELIX board and the ASIC. On a second stage, a Phase-II FELIX board will be purchased for the integration and validation of lpGBT. The DAQ demonstrator roadmap is shown in Figure 14.7.

<figure><img src="image_190.png" /><figcaption>Figure 14.7: DAQ demonstrator roadmap. In 2020, an ALTIROC2 FPGA will be used to interface with FELIX. In 2021 an ALTIROC2 ASIC will be connected to FELIX using a GBT chip as interface. In 2021 a Phase-II FELIX board will interface the ALTIROC2 via lpGBT close to the final design.</figcaption></figure>

Furthermore, the DAQ demonstrator will be used to measure the different contributions to the clock jitter at different stages (FELIX, lpGBT, FLEX, ALTIROC2). It will be used to develop a calibration procedure close to the final design. Finally, the DAQ demonstrator will be integrated in the full demonstrator set-up.

### 14.3.3 HGTD module

The production of the HGTD modules will be used to validate the module assembly, loading process (gluing, wire bonding and mounting), and quality control measurements procedures used during the production.

To gain experience for this process, smaller bare modules have been assembled in house during 2019 using the ALTIROC1 ASICs and the existing 5 × 5 pads sensor. For test beam purposes, dedicated printed circuit boards have been developed and already used to test the ASIC. It is also foreseen to develop a flex compatible with the ALTIROC1 read-out to exercise the gluing and wire bonding of the bare module, as a first step of the validation of the module assembly. Dedicated custom made readout boards will be used to validate these modules, using calibration signals and a beta source. These read-out boards could be used on the demonstrator until the FELIX setup is operational.
The bump bonding of the sensor to the ASIC will be outsourced to a company and require a
complete wafer for the under-bump-metalization process before the flip-chip. A specification
document has been prepared and is currently in discussion with two companies in Germany
and China. Complete wafers will be available only after the production of ALTIROC2 and a
dedicated sensor production. The validation of the industrial bump bonding process will
be completed early Q3/2021. The possibility to produce the hybrids for the demonstrator
program in the HGTD Institutes that have this capability in-house is also an option. Between
5 to 10 bare HGTD modules are expected to be delivered by end of Q3 2021.

Prototypes of the flex cable should also be produced, but the connector to the peripheral
board might still be not the final one.

## 14.4 Full demonstrator

The assembly of the demonstrator will start in Q4 2021. It will be made of:

* The mechanical structure as used in the heater demonstrator, available by mid 2020.

* Five to ten HGTD modules available by end of Q3 2021 and heater modules. A test of these modules after integration on the detector units should be done using the custom made read-out board to qualify the modules.

* At least one peripheral board able to read up to five HGTD modules connected through flex cables.

* A FELIX I/O card with its DAQ PC.

* Prototypes of Low Voltage and High Voltage modules, with DCS, might be used but are not mandatory for this test.

## 14.5 Full demonstrator tests

A period of about three months will be available before the first FDR. While intense elec-
tronics calibration sequence tests will be performed, two options are investigated for the
calibration sources : cosmic test bench with a precise trigger time measurement (although
the rate might be insufficient) or a portable x-ray source (8 keV or 40 keV source) with a
motorised stage to scan the detector unit.
## 14.6 Schedule and organisation

A tentative plan for the demonstrator program is shown in Figure 14.8. While the schedule for the heater demonstrator contains some contingency, the main risks for the full demonstrator rely on the availability of the modules in Q3 2021. This is strongly linked to the ASIC and sensor productions. Beginning in Q3 2020, weekly follow-up meetings will be mandatory to fulfil this aggressive schedule. A dedicated working group has been set up in Q2 2019, focussing on both mechanics/module oriented demonstrator activities for the heater demonstrator as well as the electronics/DAQ oriented activities. Beyond January 2022, the demonstrator is expected to stay operational until the end of the production for additional tests.

<figure><img src="image_191.png" /><figcaption>Figure 14.8: Planning of the heater and full demonstrator from January 2020 to January 2022. Red items show the timeline of the overall demonstrator projects; blue items show the expected progress of the individual items.</figcaption></figure>
<figure><img src="image_192.png" /></figure>
# 15 Project Organization, Costs, and Schedule

This chapter describes the overall organization of the HGTD project. Section 15.1 presents the way the project is organized and the management of the different activities, including a detailed breakdown for each component of the project. Section 15.2 discusses the schedule towards the detector completion. The foreseen available resources are discussed in Section 15.3. Finally, in Section 15.4 the risks involved with the project and the strategies to mitigate them are discussed.

## 15.1 Organization and management

### 15.1.1 Upgrade organisation in ATLAS

The highest-level executive body in ATLAS is the Executive Board (EB), chaired by the Spokesperson with the Technical Coordinator (TC) as deputy chair. The overall steering and monitoring of the upgrade activities is delegated to the Upgrade Steering Committee (USC), which is a sub-committee of the EB, with an extended membership. The USC is chaired by the Upgrade Coordinator (UC). The review and approval of Upgrade Projects (UPRs) is steered by the UC and the USC, with approval of such projects by the EB, subject to endorsement by the Collaboration Board (CB). The UC also oversees and monitors the overall upgrade planning and schedules. The management of approved Upgrade Projects rests with the Upgrade Project Leader (UPL) of that UPR, acting together with the parent system's Project Leader (PL) and Institute Board chair. The UC should be well informed of the activities in the UPRs, and interacts regularly with the UPLs to anticipate technical, schedule, resource, or other problems. The TC, supported by the Technical Coordination organization (TCn), is responsible for ensuring that all the upgrades can be successfully integrated in the ATLAS detector, that their installation schedules are compatible with shutdown schedules, and that there are adequate resources allocated for the installation and commissioning of the upgrade detectors. To this end the TC has organized an Upgrade Project Office (UPO) that provides technical support to the UPRs and the UC. Moreover the TC is responsible for the upgrade of all the common infrastructure needed for the upgrade program.
The Review Office is an independent body embedded in TCn. In close collaboration with the UC, the TC, and the UPLs, the Review Office develops and organizes technical reviews for the components of the upgrades following the ATLAS review strategy, see Section 15.1.3.

### 15.1.2 HGTD project organisation

The HGTD started as an organized activity in summer 2015 and the corresponding new sub-detector proposal was part of the ATLAS Upgrade Scoping Document [43]. The Initial Design Report and Expression of Interest were approved by ATLAS and LHCC in 2017. The Technical Proposal was approved by the LHCC in June 2018 [100], with the recommendation to proceed to the Technical Design Report. The HGTD Interim Upgrade Project Leader(s) represent the project in the ATLAS USC and chair the HGTD Steering Group.

The current HGTD project management organization is shown in Figure 15.1. The Resources and Risk Coordinator assists the Project Leader(s) in the Resources and Risk management. He/she coordinates the preparation of the material to be reviewed by the Upgrade Costing Group (UCG), Memorandum of Understanding (MoU) and works closely with the other members of the management team. The HGTD Institute Board (IB) has one representative per Institution.

The project is organized in eight working groups (WG). Each WG, coordinated in general by two co-coordinators (LV2 coordinators), carries out several activities, as detailed in the organization chart shown in Figure 15.1:

* **Sensors:** Currently in charge of the sensor R&D including irradiation tests with the aim of delivering the specifications of the final sensors. It works closely with the electronics WG as the expected performance relies strongly on the combined performance sensor+ASIC and with the testbeam WG. After the R&D Phase, it will have the charge to perform the market survey and manage the production and QA tests.

* **Electronics:** In charge of all electronics activities from the ASIC (design, specifications, production and QA) to the Peripheral Electronics Boards (design, specifications, production and QA). It interacts with the sensors WG (for the ASIC specifications, High Voltage), the DAQ WG (for the data format, bandwidth) and the Module assembly (for the flex) and the Mechanics/assembly WG (for the CO₂ cooling power, services).

* **Luminosity DAQ and control:** Responsible for the simulation studies and the specific hardware for the luminosity measurement and the DAQ aspects (including the FELIX, and control). It makes the interface with the ATLAS luminosity group and the ATLAS upgrade DAQ and DCS projects. A specific sub-group is in charge of studying and implementing the clock calibration (online and offline).
* **Modules and Detector Units:** In charge of defining the module assembly (bump bonding, gluing, flex) specifications, procedure and QA, and the modules loading in Detector Units specification and QA.

* **Test Beam:** In charge of developing the needed tools for the testbeam (DAQ and hardware) and of the data analysis. It works closely with the sensors and electronics WG.

* **Demonstrator:** Cross-cutting WG to all the others at the exception of the Simulation/Performance WG. It will start its activity after the TDR delivery with the aim of building the demonstrator and validate the performance for the PDR of most of the components as described in chapter 12. This WG on long-term might evolve to take the charge of the commissioning of the final detector.

* **Mechanics, assembly and installation:** In charge of providing the specifications and building the vessels and cooling plates, the service definition and routing (with TC), and the water/CO₂ cooling plants (with CERN support groups). It is also in charge of the tools design needed for the assembly at surface and installation in the pit. The Detector assembly and final installation procedures are also discussed here. In a later stage this WG will be split into more WGs, when the assembly and Installation will represent a sizeable effort.

* **Simulation performance and physics:** Responsible for providing the most realistic simulation package and reconstruction tools (in interaction with the ATLAS Upgrade ITk simulation and performance and the Upgrade Physics group) to evaluate the performance on the object reconstruction and the impact on some physics channels.

In a few cases, the level 3 activity coordinators are already identified, and will all be appointed after the TDR approval. All LV2 coordinators are members of the HGTD Steering Group. Topical meetings in each WG area are organized by the WG coordinators on a bi-weekly basis. HGTD general meetings are organized by the UPLs and take place bi-monthly during 3-day Mini-Weeks. During these HGTD weeks joint Steering Group and IB meetings are organized to discuss and endorse any strategic decision on detector layout, resource needs, etc.

In the Summer 2020, a formal IB including only the institutions that will participate in the HGTD construction will be created. After the expected approval of the TDR by the CERN Research Board in September 2020, the new elected IB chair will start the process of the new UPL(s) election. One interim PL and its deputy will stay in charge until beginning of 2021, when the new UPL(s) will be elected. The need of a technical coordinator after the TDR approval, or for the construction phase, will be carefully evaluated.

The ongoing R&D is carried out by roughly 150 physicists, engineers and technicians from 30 ATLAS Institutes, and 13 countries/Funding Agencies, see Table 15.1, who are committed to carry out the R&D needed to mature the proposed detector. Table 15.2 summarizes the
15 Project Organization, Costs, and Schedule

<figure><img src="image_193.png" /><figcaption>Figure 15.1: HGTD organisation chart.</figcaption></figure>

present involvement of the Institutes in the various R&D activities, planned until 2021. A sizeable fraction of these Institutes are already committed to the next steps of construction, installation and commissioning of the HGTD, and are able to cover the necessary labour effort, discussed in Section 15.3.2.
<table><caption>Table 15.1: List of countries/Funding Agencies and corresponding Institutes contributing to HGTD R&D. OMEGA and SINANO are ATLAS Technical Associate Institutes. *Goettingen and USA Institutes will only be involved in the R&D phase.</caption><thead><tr><td>Country/FA</td><td>Institutes involved in HGTD R&D</td></tr></thead><tbody><tr><td>Brazil</td><td>USP</td></tr><tr><td>CERN</td><td>CERN</td></tr><tr><td>China</td><td>IHEP, NJU, USTC, SINANO, SJTU</td></tr><tr><td>France</td><td>IJCLab, LPC, LPNHE, OMEGA</td></tr><tr><td>Germany</td><td>Mainz, Giessen, Goettingen*</td></tr><tr><td>JINR</td><td>JINR</td></tr><tr><td>Morocco</td><td>UIT, UH2C, UM5R, UMP</td></tr><tr><td>Russia</td><td>MEPhI</td></tr><tr><td>Slovenia</td><td>JSI</td></tr><tr><td>Spain</td><td>IFAE</td></tr><tr><td>Sweden</td><td>KTH</td></tr><tr><td>Taiwan</td><td>AS, NTHU</td></tr><tr><td>USA*</td><td>BNL, SLAC, SMU, UCSC, SUNYSB</td></tr></tbody></table>

<table><caption>Table 15.2: List of R&D activites and participating Institutes. OMEGA and SINANO are ATLAS Technical Associate Institutes. US groups will only be involved in the R&D phase. Goettingen is only involved in the Sensors R&D phase.</caption><thead><tr><td>R&D Activities/WG</td><td>Institutes</td></tr></thead><tbody><tr><td>Sensors</td><td>BNL, CERN, Goettingen, IFAE, IHEP, JINR, JSI, USTC, USP, UCSC</td></tr><tr><td>Electronics</td><td>AS, Giessen, IFAE, IHEP, IJCLab, JINR, KTH, LPC, NJU, NTHU, Omega, SLAC, SMU, SUNYSB, UIT, UH2C, UM5R, UMP, USTC</td></tr><tr><td>Luminosity, DAQ and Control</td><td>IHEP, KTH, Giessen, UCSC, UIT, UH2C, UM5R, UMP</td></tr><tr><td>Test beams and demonstrator</td><td>All Institutes</td></tr><tr><td>Module assembly and loading</td><td>BNL, IFAE, IHEP, IJCLab, JINR, LPNHE, Mainz, UIT, UH2C, UM5R, UMP, USTC, SINANO</td></tr><tr><td>Mechanics, assembly and installation</td><td>CERN, IHEP, IJCLab, JINR, LPNHE, MEPhI</td></tr><tr><td>Simulation/Performance/Physics</td><td>All Institutes</td></tr></tbody></table>

### 15.1.3 Technical milestones

All of the custom components used for the HGTD have to pass through a series of reviews before purchase orders can be placed for procurement of parts and production of the deliverables. These reviews are used to ascertain the quality and reliability of the components at various steps in the development and production process. They can also help to shorten
the design phase, by enforcing in-depth presentations of the status at various stages. Reviews
are usually conducted as a half-day or full-day meeting between a review panel and the
group of people in charge of the component design and construction. The review panel is
designated by the UC or by the Upgrade Review Office, and includes experts in the relevant
technology, and, if applicable, users of the object to be reviewed or those interfacing other
objects to it. This procedure is the ATLAS standard. There are four main reviews for each
custom component:

**Specifications Review (SPR)** This review verifies that complete written requirements exist, that they are sufficient to develop the designs, and specifications include sufficient opportunities for QC/QA. Specifications are compiled in a **Specifications Document**, which is internally reviewed in the project prior to the SPR, and formally released after a successful SPR.

**Preliminary Design Review (PDR)** The PDR verifies that prototype designs meet all as-
pects of the specifications documents. Technical feasibility of the design must be
demonstrated, so simulations or partial prototypes demonstrating feasibility for crit-
ical functions are important. Furthermore, test plans shall show how the prototype
devices will be tested to demonstrate functionality that meets the specification. Safety
aspects of the design will be reviewed. Integration of the system into its environment
will be verified and its installation feasibility will be assessed.

**Final Design Review (FDR)** The FDR reviews all the available data from prototypes to determine how well the design meets specifications. For components of a larger system, analysis and measurements demonstrating compatibility with external interfaces, consistent with specifications, are essential. Specifications documents should have been approved after SPR, and if applicable, modified and again approved after the PDR. A successful FDR gives the green light for the pre-production fabrication or build to proceed, and for the first CORE expenditures. The number of prototype devices produced after the review is usually small and is up to the discretion of the project leader, however must be of a large enough number to provide at least the minimum of meaningful statistics (typically 5% of the total production).

**Production Readiness Review (PRR)** The purpose of the production readiness review (PRR) is to demonstrate overall production readiness and assure that the items to be produced will meet the defined requirements. The results from pre-production are used to verify that larger scale production can be done with the acceptable yields, and that the quality control process is sufficiently thorough to filter out devices that will not meet the performance specification over the lifetime of ATLAS. All necessary production plans, travelers, tools, facilities and other resources shall be in place. Closure of Actions from the previous Reviews is a requirement as well. After successful PRR, the distributed production sites are qualified and the design is cleared for full production.
These reviews mark the transitions between different phases in each component’s develop-
ment and production schedule, and thus are used as key technical milestones in the overall
project schedule, discussed in Section 15.2.

The co-coordinators of each WG are responsible for the preparation of the specifications
and documentation, quality acceptance procedures, and material to be delivered to the
reviews. Each individual component that will be built into the HGTD must have a written
specification. The progress through the reviews is also used to monitor the progress of the
project and to make sure it is on track. Production procurement, especially for large quantity
items, will require a production plan and must follow procurement procedures required by
the purchasing Institution. The CERN procurement office will likely be responsible for the
procurement of large-quantity items whose CORE cost is shared across multiple funding
agencies.

15.1.4 Deliverables and WBS

The deliverables for the construction of the HGTD are organized in an hierarchical Product Breakdown Structure (PBS), with a direct correspondence to the existing first five WG activities listed above. The PBS indicates the deliverables, to be assigned to a CORE value in the MoU. The Work Breakdown Structure (WBS) is seeded by the PBS and includes the tasks required to produce the deliverables. The PBS organises the deliverables into seven primary categories (LV2), with PBS numbering from 8.1 to 8.7. The PBS is further broken down into lower levels items, shown in Table 15.3 down to level 3 (LV3). In some items, in particular item 8.3 (Luminosity, DAQ and Control), item 8.6 (Detector Assembly and QA on surface) and item 8.7 (Detector Installation and Commissioning), the structure also contains LV3 activities that only require labour effort and hence, are only part of the WBS. All PBS items have an associated CORE cost as described later in Section 15.3, while WBS-only items do not.
<table><caption>Table 15.3: Product Breakdown Structure (PBS) and Work Breakdown Structure (WBS) of the HGTD down to level 3. The WBS is seeded by the PBS and includes the tasks required to produce the deliverables. WBS-only items are mentioned explicitly when appropriate. (*) DAQ hardware deliverables are covered in the ATLAS TDAQ PBS.</caption><thead><tr><th>PBS/WBS</th><th>Deliverable</th></tr></thead><tbody><tr><td><strong>8.1</strong></td><td><strong>Sensors</strong></td></tr><tr><td>8.1.1</td><td>LGAD Sensors</td></tr><tr><td><strong>8.2</strong></td><td><strong>Electronics</strong></td></tr><tr><td>8.2.1</td><td>ASIC</td></tr><tr><td>8.2.2</td><td>Peripheral Electronics Board</td></tr><tr><td>8.2.3</td><td>High Voltage system</td></tr><tr><td>8.2.4</td><td>Low Voltage system</td></tr><tr><td><strong>8.3</strong></td><td><strong>Luminosity, DAQ and Control*</strong></td></tr><tr><td>8.3.1</td><td>Luminosity boards</td></tr><tr><td>8.3.2</td><td>DCS</td></tr><tr><td>8.3.3</td><td>Interlocks and protection system</td></tr><tr><td>8.3.4</td><td>DAQ software</td></tr><tr><td><strong>8.4</strong></td><td><strong>Modules and Detector Units</strong></td></tr><tr><td>8.4.1</td><td>Bare module hybridization</td></tr><tr><td>8.4.2</td><td>Module Flex</td></tr><tr><td>8.4.3</td><td>Modules assemblies</td></tr><tr><td>8.4.4</td><td>Detector Units</td></tr><tr><td>8.4.5</td><td>Flex Cable Tails</td></tr><tr><td><strong>8.5</strong></td><td><strong>Mechanics, Services and Infrastructure</strong></td></tr><tr><td>8.5.1</td><td>HGTD Hermetic vessel</td></tr><tr><td>8.5.2</td><td>On detector cooling system</td></tr><tr><td>8.5.3</td><td>CO2 cooling system</td></tr><tr><td>8.5.4</td><td>Water cooling system</td></tr><tr><td>8.5.5</td><td>Nitrogen system</td></tr><tr><td>8.5.6</td><td>Cables and connectors</td></tr><tr><td>8.5.7</td><td>Fibers and optical connectors</td></tr><tr><td><strong>8.6</strong></td><td><strong>Detector Assembly and QA on surface</strong></td></tr><tr><td>8.6.1</td><td>Test bench for detector certification</td></tr><tr><td>8.6.2</td><td>Tools for surface assembly</td></tr><tr><td>8.6.3</td><td>Assembly of components on cooling plates</td></tr><tr><td>8.6.4</td><td>Final integration inside vessels</td></tr><tr><td><strong>8.7</strong></td><td><strong>Installation and Commissioning</strong></td></tr><tr><td>8.7.1</td><td>Tools for transport and cavern installation</td></tr><tr><td>8.7.2</td><td>Services, patch panels and cooling installation</td></tr><tr><td>8.7.3</td><td>Back-end electronics installation in USA15</td></tr><tr><td>8.7.4</td><td>Detector installation and connectivity</td></tr><tr><td>8.7.5</td><td>Global commissioning in LS3</td></tr></tbody></table>
**15.2 Schedule and main milestones**

The HGTD installation schedule presented here uses as a reference the ATLAS TC schedule available until mid-Jan 2020. Development and optimization of the ATLAS detector installation sequence in LS3 will continue for several years. If necessary, the design of the HGTD allows for a later installation, during the following YETS, of possible missing instrumented half rings even in the presence of the beam pipe.

There are three main schedule phases for HGTD:

* 2018 – 2021 R&D

* 2021 – 2026 Construction

* 2026 – 2027 Integration, installation and commissioning

The plan is to install the HGTD detector in the Long Shutdown LS3 on the end-cap LAr calorimeter cryostat faces. This operation should take place in April 2026 and January 2027 for the A and C sides respectively.

To define the schedule of the HGTD Upgrade Project, a detailed bottom-up plan of activities has been worked out. The high-level schedule presented here comprises the reviews and main tasks that need to be undertaken between now and the completion of the project, and their dependencies, i.e. lists of tasks that have to be finished before a new task can begin.

Tables 15.4 to 15.10 show an overview schedule down to the LV3 PBS/WBS. The start points and end points of these phases are delimited by appropriate high-level milestones:

* SPR: Specifications Review;

* PDR: Prototype design meets all aspects of the specifications;

* FDR: Pre-production fabrication or build cleared to proceed;

* PRR: Full production phase cleared to proceed;

* End of the production phase: Construction Completed;

* End of the installation and commissioning phase: Installation Completed.

The schedule deliverables, detailed here up to LV3 only, are defined by the sub-project coordinators and approved by the Steering Group. It is the responsibility of sub-project coordinators to plan, implement, execute, and track the progress of their project according to the baseline schedule for their respective deliverables. They report on the progress to the Steering Group. It is the responsibility of the HGTD UPL to ensure that a comprehensive schedule is developed, to seek the necessary review process to baseline the schedule, to oversee the progress and take necessary corrective actions to ensure that the project remains on schedule, and to propose changes to the baseline as required.
<table><caption>Table 15.4: Summary of main HGTD Milestones, including the planned reviews (PDR, FDR, PRR), pre-production and production for the Sensors deliverable.</caption><thead><tr><th>PBS/WBS</th><th>Milestone</th><th>Date</th></tr></thead><tbody><tr><td><strong>8.1 Sensors</strong></td><td></td><td></td></tr><tr><td>8.1.1 LGAD Sensors</td><td>SPR</td><td>Q3 2020</td></tr><tr><td></td><td>PDR</td><td>Q1 2021</td></tr><tr><td></td><td>FDR</td><td>Q4 2021</td></tr><tr><td></td><td>Pre-production</td><td>Q1 2022 - Q3 2022</td></tr><tr><td></td><td>PRR</td><td>Q4 2022</td></tr><tr><td></td><td>Production (0-50%)</td><td>Q1 2023 - Q4 2023</td></tr><tr><td></td><td>Production (51-100%)</td><td>Q1 2024 - Q4 2024</td></tr></tbody></table>

<table><caption>Table 15.5: Summary of main HGTD Milestones, including the planned reviews (PDR, FDR, PRR), pre-production and production for the electronics deliverables.</caption><thead><tr><th>PBS/WBS</th><th>Milestone</th><th>Date</th></tr></thead><tbody><tr><td><strong>8.2 Electronics</strong></td><td></td><td></td></tr><tr><td>8.2.1 ASIC</td><td>SPR</td><td>Q3 2020</td></tr><tr><td></td><td>PDR</td><td>Q4 2021</td></tr><tr><td></td><td>FDR</td><td>Q4 2022</td></tr><tr><td></td><td>Pre-production</td><td>Q4 2022 - Q3 2023</td></tr><tr><td></td><td>PRR</td><td>Q4 2023</td></tr><tr><td></td><td>Production (0-50%)</td><td>Q4 2023 - Q2 2024</td></tr><tr><td></td><td>Production (51-100%)</td><td>Q2 2024 - Q3 2024</td></tr><tr><td>8.2.2 Peripheral Electronics Board</td><td>SPR</td><td>Q1 2021</td></tr><tr><td></td><td>PDR</td><td>Q3 2021</td></tr><tr><td></td><td>FDR</td><td>Q1 2022</td></tr><tr><td></td><td>Pre-production</td><td>Q2 2022 - Q4 2022</td></tr><tr><td></td><td>PRR</td><td>Q4 2022</td></tr><tr><td></td><td>Production (0-50%)</td><td>Q4 2022 - Q1 2024</td></tr><tr><td></td><td>Production (51-100%)</td><td>Q1 2024 - Q1 2025</td></tr><tr><td>8.2.3 High Voltage system</td><td>SPR</td><td>Q4 2021</td></tr><tr><td></td><td>PDR</td><td>Q1 2022</td></tr><tr><td></td><td>FDR</td><td>Q4 2022</td></tr><tr><td></td><td>Pre-production</td><td>Q1 2023 - Q4 2023</td></tr><tr><td></td><td>PRR</td><td>Q1 2024</td></tr><tr><td></td><td>Production (0-50%)</td><td>Q2 2024 - Q3 2025</td></tr><tr><td></td><td>Production (51-100%)</td><td>Q3 2025 - Q3 2026</td></tr><tr><td>8.2.4 Low Voltage system</td><td>SPR</td><td>Q4 2021</td></tr><tr><td></td><td>PDR</td><td>Q1 2022</td></tr><tr><td></td><td>FDR</td><td>Q4 2022</td></tr><tr><td></td><td>Pre-production</td><td>Q1 2023 - Q4 2023</td></tr><tr><td></td><td>PRR</td><td>Q1 2024</td></tr><tr><td></td><td>Production (0-50%)</td><td>Q2 2024 - Q3 2025</td></tr><tr><td></td><td>Production (51-100%)</td><td>Q3 2025 - Q3 2026</td></tr></tbody></table>
<table><caption>Table 15.6: Summary of main HGTD Milestones, including the planned reviews (PDR, FDR, PRR), pre-production and production for the Luminosity, DAQ and Control deliverables.</caption><thead><tr><th>PBS/WBS</th><th>Milestone</th><th>Date</th></tr></thead><tbody><tr><td><strong>8.3 Luminosity, DAQ and Control</strong></td><td></td><td></td></tr><tr><td>8.3.1 Luminosity boards</td><td>SPR</td><td>Q4 2021</td></tr><tr><td></td><td>PDR</td><td>Q1 2022</td></tr><tr><td></td><td>FDR</td><td>Q1 2023</td></tr><tr><td></td><td>Pre-production</td><td>Q2 2023 – Q1 2024</td></tr><tr><td></td><td>PRR</td><td>Q2 2024</td></tr><tr><td></td><td>Production (0-100%)</td><td>Q2 2024 – Q1 2025</td></tr><tr><td>8.3.2 DCS</td><td>SPR</td><td>Q4 2021</td></tr><tr><td></td><td>PDR</td><td>Q1 2022</td></tr><tr><td></td><td>FDR</td><td>Q4 2022</td></tr><tr><td></td><td>Pre-production</td><td>Q1 2023 – Q4 2023</td></tr><tr><td></td><td>PRR</td><td>Q1 2024</td></tr><tr><td></td><td>Production (0-50%)</td><td>Q2 2024 – Q2 2025</td></tr><tr><td></td><td>Production (51-100%)</td><td>Q3 2025 – Q3 2026</td></tr><tr><td>8.3.3 Interlocks and protection system</td><td>SPR</td><td>Q4 2021</td></tr><tr><td></td><td>PDR</td><td>Q1 2022</td></tr><tr><td></td><td>FDR</td><td>Q4 2022</td></tr><tr><td></td><td>Pre-production</td><td>Q1 2023 – Q4 2023</td></tr><tr><td></td><td>PRR</td><td>Q1 2024</td></tr><tr><td></td><td>Production (0-50%)</td><td>Q2 2024 – Q2 2025</td></tr><tr><td></td><td>Production (51-100%)</td><td>Q3 2025 – Q3 2026</td></tr><tr><td>8.3.4 DAQ software</td><td>SPR</td><td>Q4 2021</td></tr><tr><td></td><td>PDR</td><td>Q1 2022</td></tr><tr><td></td><td>FDR</td><td>Q4 2022</td></tr><tr><td></td><td>PRR</td><td>Q2 2023</td></tr><tr><td></td><td>Production (0-100%)</td><td>Q2 2023 – Q1 2027</td></tr></tbody></table>
<table><caption>Table 15.7: Summary of main HGTD Milestones, including the planned reviews (PDR, FDR, PRR), pre-production and production for the Module and Detector Units deliverable. The Detector Units include Support Units that will be produced ahead of the Module loading activity.</caption><thead><tr><th>PBS/WBS</th><th>Milestone</th><th>Date</th></tr></thead><tbody><tr><td><strong>8.4 Modules and Detector Units</strong></td><td></td><td></td></tr><tr><td rowspan="6">8.4.1 Bare module hybridization</td><td>SPR</td><td>Q2 2021</td></tr><tr><td>PDR</td><td>Q1 2022</td></tr><tr><td>FDR</td><td>Q4 2022</td></tr><tr><td>Pre-production</td><td>Q1 2023 - Q4 2023</td></tr><tr><td>PRR</td><td>Q4 2023</td></tr><tr><td>Production (0-50%)</td><td>Q1 2024 - Q4 2024</td></tr><tr><td></td><td>Production (51-100%)</td><td>Q3 2024 - Q1 2025</td></tr><tr><td rowspan="6">8.4.2 Module Flex</td><td>SPR</td><td>Q4 2021</td></tr><tr><td>PDR</td><td>Q2 2022</td></tr><tr><td>FDR</td><td>Q3 2022</td></tr><tr><td>Pre-production</td><td>Q4 2022 - Q1 2023</td></tr><tr><td>PRR</td><td>Q2 2023</td></tr><tr><td>Production (0-50%)</td><td>Q3 2023 - Q4 2023</td></tr><tr><td></td><td>Production (51-100%)</td><td>Q4 2023 - Q2 2024</td></tr><tr><td rowspan="6">8.4.3 Modules assemblies</td><td>SPR</td><td>Q1 2022</td></tr><tr><td>PDR</td><td>Q3 2022</td></tr><tr><td>FDR</td><td>Q2 2023</td></tr><tr><td>Pre-production</td><td>Q3 2023 - Q1 2024</td></tr><tr><td>PRR</td><td>Q1 2024</td></tr><tr><td>Production (0-50%)</td><td>Q3 2024 - Q3 2025</td></tr><tr><td></td><td>Production (51-100%)</td><td>Q3 2025 - Q3 2026</td></tr><tr><td rowspan="6">8.4.4 Detector Units</td><td>SPR</td><td>Q1 2022</td></tr><tr><td>PDR</td><td>Q4 2022</td></tr><tr><td>FDR</td><td>Q2 2023</td></tr><tr><td>Pre-production</td><td>Q2 2023 - Q1 2024</td></tr><tr><td>PRR</td><td>Q2 2024</td></tr><tr><td>Production (0-50%)</td><td>Q2 2024 - Q3 2025</td></tr><tr><td></td><td>Production (51-100%)</td><td>Q3 2025 - Q3 2026</td></tr><tr><td rowspan="6">8.4.5 Flex Cable Tails</td><td>SPR</td><td>Q1 2022</td></tr><tr><td>PDR</td><td>Q2 2022</td></tr><tr><td>FDR</td><td>Q1 2023</td></tr><tr><td>Pre-production</td><td>Q1 2023 - Q4 2023</td></tr><tr><td>PRR</td><td>Q1 2024</td></tr><tr><td>Production (0-50%)</td><td>Q1 2024 - Q4 2024</td></tr><tr><td></td><td>Production (51-100%)</td><td>Q1 2025 - Q3 2025</td></tr></tbody></table>
## 15.2 Schedule and main milestones

<table><thead><tr><th>PBS/WBS</th><th>Milestone</th><th>Date</th></tr></thead><tbody><tr><td><strong>8.5 Mechanics, Services and Infrastructure</strong></td><td></td><td></td></tr><tr><td>8.5.1 HGTD Hermetic vessel</td><td>SPR<br>PDR<br>FDR<br>PRR<br>Production (0-50%)<br>Production (51-100%)</td><td>Q1 2021<br>Q2 2021<br>Q1 2022<br>Q3 2022<br>Q3 2022 - Q3 2023<br>Q3 2023 - Q3 2024</td></tr><tr><td>8.5.2 On detector cooling system</td><td>SPR<br>PDR<br>FDR<br>PRR<br>Production (0-50%)<br>Production (51-100%)</td><td>Q1 2021<br>Q2 2021<br>Q1 2022<br>Q3 2022<br>Q3 2022 - Q3 2023<br>Q3 2023 - Q3 2024</td></tr><tr><td>8.5.3 CO<sub>2</sub> cooling system</td><td></td><td></td></tr><tr><td>8.5.3.1 CO<sub>2</sub> plants (*)</td><td>SPR<br>PDR<br>FDR+PRR (combined)<br>Production (0-100%)</td><td>Dec 2018 (passed)<br>Q4 2020<br>Q3 2021<br>Q2 2022 - Q3 2024</td></tr><tr><td>8.5.3.2 Manifold boxes</td><td>SPR<br>PDR<br>FDR<br>PRR<br>Production (0-100%)</td><td>Q1 2021<br>Q3 2021<br>Q2 2022<br>Q1 2023<br>Q1 2023 - Q2 2025</td></tr><tr><td>8.5.3.3 Cooling lines</td><td>SPR<br>PDR<br>FDR<br>PRR<br>Production (0-100%)</td><td>Q1 2021<br>Q3 2021<br>Q2 2022<br>Q1 2023<br>Q1 2023 - Q2 2025</td></tr><tr><td>8.5.4 Water cooling system</td><td>SPR<br>PDR<br>FDR<br>PRR<br>Production (0-100%)</td><td>Q1 2021<br>Q3 2021<br>Q2 2022<br>Q1 2023<br>Q1 2023 - Q2 2025</td></tr><tr><td>8.5.5 Nitrogen system</td><td>SPR<br>PDR<br>FDR<br>PRR<br>Production (0-100%)</td><td>Q1 2021<br>Q3 2021<br>Q2 2022<br>Q1 2023<br>Q1 2023 - Q2 2025</td></tr><tr><td>8.5.6 Cables and connectors</td><td>SPR<br>PDR<br>FDR<br>PRR<br>Production (0-100%)</td><td>Q3 2021<br>Q1 2022<br>Q3 2022<br>Q1 2023<br>Q2 2023 - Q3 2025</td></tr><tr><td>8.5.7 Fibers and optical connectors</td><td>SPR<br>PDR<br>FDR<br>PRR<br>Production (0-100%)</td><td>Q3 2021<br>Q1 2022<br>Q3 2022<br>Q2 2023<br>Q2 2023 - Q3 2025</td></tr></tbody></table>

Table 15.8: Summary of main HGTD Milestones, including the planned reviews (PDR, FDR, PRR), pre-production and production for PBS 8.5 Mechanics, Services and Infrastructure.

(*) The CO₂ cooling system (PBS 8.5.3) is detailed to LV4 since the CO₂ plants (PBS 8.5.3.1) will be reviewed and constructed in common with ATLAS ITk and CMS (calo, tracker, timing detectors) and much earlier than the specific HGTD CO₂ cooling items (8.5.3.2 Manifold boxes and 8.5.3.3 Cooling lines).
## 15 Project Organization, Costs, and Schedule

<table><caption>Table 15.9: Summary of main HGTD Milestones, including the planned reviews (PDR, FDR, PRR), pre-production and production for PBS 8.6 Detector Assembly and Quality Assurance on surface.</caption><thead><tr><th>PBS/WBS</th><th>Milestone</th><th>Date</th></tr></thead><tbody><tr><td><strong>8.6 Detector Assembly and QA on surface</strong></td><td></td><td></td></tr><tr><td>8.6.1 Test bench for detector certification</td><td>SPR</td><td>Q4 2021</td></tr><tr><td></td><td>PDR</td><td>Q2 2022</td></tr><tr><td></td><td>FDR</td><td>Q4 2022</td></tr><tr><td></td><td>PRR</td><td>Q2 2023</td></tr><tr><td></td><td>Production (0-100%)</td><td>Q2 2023 - Q4 2023</td></tr><tr><td>8.6.2 Tools for surface assembly</td><td>SPR</td><td>Q4 2021</td></tr><tr><td></td><td>PDR</td><td>Q2 2022</td></tr><tr><td></td><td>FDR</td><td>Q4 2022</td></tr><tr><td></td><td>PRR</td><td>Q2 2023</td></tr><tr><td></td><td>Production (0-100%)</td><td>Q2 2023 - Q4 2023</td></tr><tr><td>8.6.3 Assembly of components on cooling plates</td><td>SPR</td><td>Q2 2022</td></tr><tr><td></td><td>PDR</td><td>Q4 2022</td></tr><tr><td></td><td>FDR</td><td>Q4 2023</td></tr><tr><td></td><td>PRR</td><td>Q2 2024</td></tr><tr><td></td><td>HGTD-A assembly (0-50%)</td><td>Q3 2024 - Q4 2025</td></tr><tr><td></td><td>HGTD-C assembly (51-100%)</td><td>Q4 2025 - Q4 2026</td></tr><tr><td>8.6.4 Final integration inside vessels</td><td>SPR</td><td>Q2 2022</td></tr><tr><td></td><td>PDR</td><td>Q4 2022</td></tr><tr><td></td><td>FDR</td><td>Q4 2023</td></tr><tr><td></td><td>PRR</td><td>Q2 2024</td></tr><tr><td></td><td>HGTD-A integration (0-50%)</td><td>Q4 2024 - Q4 2025</td></tr><tr><td></td><td>HGTD-C integration (51-100%)</td><td>Q4 2025 - Q4 2026</td></tr></tbody></table>

<table><caption>Table 15.10: Summary of main HGTD Milestones, including the planned reviews (PDR, FDR, PRR), pre-production and production for PBS 8.7 Installation and Commissioning.</caption><thead><tr><th>PBS/WBS</th><th>Milestone</th><th>Date</th></tr></thead><tbody><tr><td><strong>8.7 Installation and Commissioning</strong></td><td></td><td></td></tr><tr><td>8.7.1 Tools for transport and cavern installation</td><td>SPR</td><td>Q2 2022</td></tr><tr><td></td><td>PDR</td><td>Q2 2023</td></tr><tr><td></td><td>FDR</td><td>Q4 2023</td></tr><tr><td></td><td>PRR</td><td>Q2 2024</td></tr><tr><td></td><td>Production (0-100%)</td><td>Q2 2024 - Q3 2025</td></tr><tr><td>8.7.2 Services, patch panels and cooling installation</td><td>Installation+QA (0-100%)</td><td>Q1 2025 - Q2 2026</td></tr><tr><td>8.7.3 Back-end electronics installation in USA15</td><td>Installation+QA (0-100%)</td><td>Q2 2025 - Q4 2026</td></tr><tr><td>8.7.4 Detector installation and connectivity</td><td>Schedule float (HGTD-A)<br>HGTD-A (0-50%)<br>Schedule float (HGTD-C)<br>HGTD-C (50-100%)</td><td>Q4 2025 - Q2 2026<br><strong>Q2 2026</strong><br>Q4 2026 - Q1 2027<br><strong>Q1 2027</strong></td></tr><tr><td>8.7.5 Global Commissioning in LS3</td><td>Commissioning</td><td>Q2 2026 - Q2 2027</td></tr></tbody></table>
The schedule and resources estimations take into account realistic quantities for each component, considering the yield in all production steps until the final assembled detector. A breakdown of the yield model used at the main steps of the modules construction up to its assembly in the detector is shown in Table 15.11. This model, with an overall efficiency of 74%, was used to calculate the required total quantities of the main modules components for the final production, summarised in Table 15.12.

<table><caption>Table 15.11: Yield model of the various steps of the modules construction up to installation in the detector.</caption><thead><tr><th>PBS</th><th>Production step</th><th>Yield (%)</th></tr></thead><tbody><tr><td rowspan="3">8.4.1 Bare module hybridisation</td><td>Sensor UBM</td><td>99.5</td></tr><tr><td>ASIC Bump deposition</td><td>99.5</td></tr><tr><td>Flip-chip</td><td>97</td></tr><tr><td rowspan="4">8.4.3 Module assemblies</td><td>Flex module gluing</td><td>97</td></tr><tr><td>Wire Bonding</td><td>98</td></tr><tr><td>Test</td><td>98</td></tr><tr><td>Burn-in tests</td><td>95</td></tr><tr><td rowspan="3">8.4.4 Detector Units</td><td>Loading on Detector Units</td><td>95</td></tr><tr><td>Test</td><td>98</td></tr><tr><td>Transport</td><td>99</td></tr><tr><td rowspan="2">8.6 Detector assembly and QA on surface</td><td>Assembly on cooling plates + integration</td><td>96</td></tr><tr><td>Test</td><td>99</td></tr><tr><td colspan="2"><strong>Overall yield</strong></td><td><strong>74</strong></td></tr></tbody></table>

<table><caption>Table 15.12: Estimated quantity of main deliverables needed to construct the HGTD modules. Numbers are indicated for nominal quantities, that is, for the actual items to be installed in the detector, pre-production of 5% and final production quantities. The pre-production and production numbers are corrected for the expected yield.</caption><thead><tr><th>Main components</th><th>Nominal</th><th>Pre-prod.</th><th>Production</th><th>Production comments</th></tr></thead><tbody><tr><td>8.1.1 LGAD Sensors</td><td>8032</td><td>543</td><td>10854</td><td>13 sensors/wafer</td></tr><tr><td>8.2.1 ASIC</td><td>16064</td><td>1358</td><td>27135</td><td>52 asic/wafer</td></tr><tr><td>8.4.2 Module Flex</td><td>8032</td><td>543</td><td>10854</td><td></td></tr><tr><td>8.4.4 Modules</td><td>8032</td><td>543</td><td>10854</td><td></td></tr></tbody></table>

The schedule chart for the most critical items is presented in Figure 15.2. Separated schedule charts are given for each level 2 digits PBS in Figure 15.3 up to Figure 15.9.

When possible activities are taking place in parallel, as for example the LGAD Sensors (PBS 8.1.1) and ASIC (PBS 8.2.1), while there are many activities that depend on predecessors as, for example, module hybridisation (PBS 8.4.1) that needs available sensors and ASICs, as indicated in Figure 15.2 by the vertical lines.
A more detailed description is given below for the critical deliverables, that have important dependencies and may affect the final installation milestone.

**Sensors (PBS 8.1)** A breakdown of the sensors production milestones is presented in Figure 15.3. After the R&D and prototype phases, based on the understanding of the design issues solved, the sensor PDR will be submitted in Q1 2021, followed by a market survey and the FDR in Q4 2021. The sensor pre-production (5% of the production) will take place in the first half of 2022, followed by the final production from Q1 2023 to Q4 2024. The total number of working sensors to produce is 11397 (543 for pre-production and 10854 for the final production). This last number consists of the 8032 modules that are planned to be installed in the two HGTD end-caps, divided by the overall yield of 0.74 that is assumed to be relevant for the later processing and assembly steps, as detailed in Table 15.11. The exact QA strategy is still under development but it is assumed that all sensor vendors will deliver good/tested sensors, i.e. the yield of delivered sensors is assumed to be 100%.

The various vendors will deliver sensor wafers into batches which will be further processed for bump-bonding to the HGTD front-end ASIC (PBS 8.2.1): first a metal layer will be deposited on the pixel pads (under bump-metallization or UBM), and then the wafers will be diced and connected to the ASICs in a process known as bare module hybridization (PBS 8.4.1). This will most probably be done at a dedicated hybridization company, but it might also be done by the sensor vendor.

**ASIC (PBS 8.2.1)** A first full size ASIC (ALTIROC2) with 15x15 channels and all the functionalities is expected to be submitted at the end of 2020, after the SPR, to take place in Q3 2020. It should be followed by a second real size prototype in 2021, after the PDR, that is expected in Q4 2021. The pre-production of the final chip (ALTIROC-V1) is expected between Q4 2022 and Q3 2023, just after the FDR review. The PRR, expected in Q4 2023, should give the green light for the final chip production (ALTIROC-V2). The production, including the QA to be done by the Institutes is expected to take place between Q4 2023 and Q3 2024.

ASICs will be fabricated by the TSMC foundry under an existing frame contract negotiated by CERN. The chip procurement will be done through the frame contract. ASICs are expected to be received from the vendor as 8 inches diameter silicon wafer with 52 ASICs/wafer. The wafers have to be electronically tested before an Under Bump Metallization (UBM) process and a bump deposition is applied followed by a dicing and flip chip for the bump bonding to the sensors. 27135 ASICs are needed for the final production as detailed in Table 15.12, considering an estimated yield of 80% in the ASIC manufacture up to the delivery. Both at pre-production and production, some ASICs will be tested after dicing on dedicated boards for deep measurements and irradiation tests.
**Bare module hybridisation (PBS 8.4.1)** The baseline bump-bonding technology to connect each LGAD Sensor to two ALTIROC ASICs relies on solder bumps, to be done in Industry by integrated circuit packing companies. This activity relies on the availability of sensors and ASICs, and will be done in 3 steps. After the wafers of sensors and ASICs are processed, sensor and ASICs are diced and their interconnection by flip-chipping is applied, using only the pre-selected good ASICs. The pre-production (of approx. 5%) is expected from Q1 2023 to Q4 2023. The PRR will take place in Q4 2023, giving the green light to the bare module hybridisation of 525 8-inch wafers (27135 ASIC) and 522 sensors 6-inch wafers (10854 LGAD Sensors). This is expected to take place between Q1 2024 and Q1 2025.

**Module assemblies (PBS 8.4.3)** The module assembly consist in gluing the bare module (described in PBS 8.4.1) to the Module Flex, wire bonding the two ASICs and the HV connection of the module to the flex. The last step will be the QA tests. After the FDR, expected in Q2 2023, 543 modules will be constructed in the pre-production phase from Q3 2023 to Q1 2024. This step will be used to qualify the 4-5 Institutes/sites that will participate in this activity. The final production of 10854 modules, is expected to take place between Q3 2024 and Q3 2026. The overall production rate is expected to be approximately 19 modules/working day in the first half and 22 modules per working day in the second half of the production.

**Detector Units (PBS 8.4.4)** The production of 80 support units of 6 different types will be carried out in Industry and shipped to the Institutes that will do the modules loading. The modules are loaded on the support units, to form the inner, middle and outer disks. Dedicated flex tails will be used to connect the Module Flex connector and perform electrical tests before and after the positioning and gluing of the modules. This operation is done by the same Institutes that are doing the module assemblies (PBS 8.4.3), to minimize the transport and QA time. The pre-production will take place between Q2 2023 and Q1 2024. The PRR will be in Q2 2024, followed by the production, from Q2 2024 to Q3 2026.

**Detector Assembly and QA on surface (PBS 8.6)** The detector assembly and QA will be done at CERN in a clean room using dedicated tools for the detector assembly and testbench for QA. The main activities will be the assembly of the components (Detector Units, PEB, flex tails) on the cooling plates (PBS 8.6.3) and final integration inside the vessels (PBS 8.6.4). The final integration will be done with the participation of several Institutes between Q4 2024 and Q4 2025 for HGTD-A and between Q4 2025 and Q4 2026 for HGTD-C.

**Installation and commissioning (PBS 8.7)** The detector will be moved from the CERN clean room to the ATLAS cavern and installed on the two LAr end-cap cryostats using dedicated installation tools.
15 Project Organization, Costs, and Schedule

The Installation of the HGTD-A and HGTD-C are expected in LS3, respectively on 15 April - 20 May 2026 and 4 January - 3 February 2027. After the connection of each end-cap to the respective services an intense period of commissioning will start, while there is still access to the detector. In case of significant delays in the HGTD-C construction, the following scenarios are possible. The HGTD-C will be installed in January 2027 with all available instrumented half circular disks. The missing disk(s) may still be inserted in the following 1-2 months, during the overall ATLAS commissioning period. Although the crane will not be available anymore, enough space exists between the barrel and the end-cap calorimeters to allow the installation manually (objects of ~ 35 Kg each and 1 m radius). A dedicated tool will be manufactured to transport the half instrumented disks safely without crane. The other possibility will be to install the missing instrumented disk(s) in the next YETS after LS3. This scenario will need a procedure to be developed respecting the ALARA/safety rules, to account properly for induced radiation levels.
## 15.2 Schedule and main milestones

<figure><img src="image_194.png" /><figcaption>Figure 15.2: High-level schedule for the HGTD project including the planned reviews (PDR, FDR, PRR), pre-production and production for the most time critical components.</figcaption></figure>
15 Project Organization, Costs, and Schedule

<figure><img src="image_195.png" /><figcaption>Figure 15.3: Sensors high-level schedule including the planned reviews (PDR, FDR, PRR), pre-production and production.</figcaption></figure>

<figure><img src="image_196.png" /><figcaption>Figure 15.4: Electronics high-level schedule including the planned reviews (PDR, FDR, PRR), pre-production and production.</figcaption></figure>
## 15.2 Schedule and main milestones

<figure><img src="image_197.png" /><figcaption>Figure 15.5: Luminosity, DAQ and Control high-level schedule including the planned reviews (PDR, FDR, PRR), pre-production and production.</figcaption></figure>
15 Project Organization, Costs, and Schedule

<figure><img src="image_198.png" /><figcaption>Figure 15.6: Modules and Detector Units high-level schedule including the planned reviews (PDR, FDR, PRR), pre-production and production. The pre-production and production of 8.4.1 Bare module hybridisation should be started after the pre-production and production of 8.1.1 LGAD Sensor and 8.2.1 ASIC are started, while the links are not shown in this figure.</figcaption></figure>
## 15.2 Schedule and main milestones

<figure><img src="image_199.png" /><figcaption>Figure 15.7: Mechanics, services and infrastructure high-level schedule including the planned reviews (PDR, FDR, PRR), pre-production and production.</figcaption></figure>
15 Project Organization, Costs, and Schedule

<figure><img src="image_200.png" /><figcaption>Figure 15.8: High-level schedule for the HGTD detector assembly and quality assurance on surface, including the planned reviews (PDR, FDR, PRR), pre-production and production. The production of 8.6.3 Assembly of components on cooling plates should be started after the production of 8.4.4 Detector Unit are started, while the links are not shown in this figure.</figcaption></figure>

<figure><img src="image_201.png" /><figcaption>Figure 15.9: High-level schedule for the HGTD detector installation and commissioning, including the planned reviews (PDR, FDR, PRR), pre-production and production. The Schedule Float HGTD-A of 8.7.4 Detector installation and Connectivity should be started after the HGTD-A of 8.6.4 Final integration inside vessels are finished, while the link is not shown in this figure.</figcaption></figure>
**15.3 Resources**

Many Institutes have already stated their intentions of contributing to the HGTD project, and many of them have already been working on R&D and design of various components of the system, as discussed in Section 15.1.

Surveys of the interests of Institutes and of the available resources have been performed recently. A preliminary sharing matrix showing the initial interest of the contributing Institutes toward the HGTD construction responsibilities is summarised in Table 15.13. The Institute surveys indicate that the human resources required for the HGTD project implementation are available for the full extent of the detector construction period.

The cost of the project is expected to be covered by the Institutions participating in the HGTD project, with their respective Funding Agencies. Most of the funds have been secured, and discussions among the Institutions and the Funding Agencies are ongoing in order to define the detailed list of deliverables, responsibilities, and the sharing of the project cost. These will be formalized after the project is approved, through an MoU document, insuring that all the aspects of the project are covered.
15 Project Organization, Costs, and Schedule

<table><caption>Table 15.13: Preliminary sharing matrix showing the initial interest of the contributing ATLAS Funding agencies and HGTD Institutes toward the construction responsibilities. (*) DAQ hardware deliverables are covered in the ATLAS TDAQ PBS, and they will be included in an amendment of the TDAQ MoU.</caption><thead><tr><th>Deliverable</th><th>Institutes</th></tr></thead><tbody><tr><td><strong>8.1 Sensors</strong></td><td></td></tr><tr><td>8.1.1 LGAD Sensors</td><td>CERN, IFAE, IRFU, IHEP, JSI, USTC, USP, JINR</td></tr><tr><td><strong>8.2 Electronics</strong></td><td></td></tr><tr><td>8.2.1 ASIC</td><td>IFAE, IHEP, IJCLab, JINR, LPC, OMEGA, USTC</td></tr><tr><td>8.2.2 Peripheral Electronics Board</td><td>AS, IHEP, JINR, NJU, NTHU, UIT, UH2C, UM5R, UMP, USP</td></tr><tr><td>8.2.3 High Voltage system</td><td>CERN, KTH</td></tr><tr><td>8.2.4 Low Voltage system</td><td>Giessen</td></tr><tr><td><strong>8.3 Luminosity, DAQ and Control*</strong></td><td></td></tr><tr><td>8.3.1 Luminosity boards</td><td>KTH</td></tr><tr><td>8.3.2 DCS</td><td>Giessen, UIT, UH2C, UM5R, UMP</td></tr><tr><td>8.3.3 Interlocks and protection system</td><td>to be determined</td></tr><tr><td>8.3.4 DAQ software</td><td>IHEP, LPC</td></tr><tr><td><strong>8.4 Modules and Detector Units</strong></td><td></td></tr><tr><td>8.4.1 Bare module hybridization</td><td>IFAE, IHEP, IRFU, SINANO, USTC</td></tr><tr><td>8.4.2 Module Flex</td><td>IHEP, Mainz</td></tr><tr><td>8.4.3 Modules Assemblies</td><td>IFAE, IHEP, IJCLab, IRFU, JINR, Mainz, SINANO, USTC</td></tr><tr><td>8.4.4 Detector Units</td><td>IFAE, IHEP, LPNHE, Mainz</td></tr><tr><td>8.4.5 Flex Cable Tails</td><td>IHEP, JSI, Mainz, UIT, UH2C, UM5R, UMP</td></tr><tr><td><strong>8.5 Mechanics, Services &amp; Infrustructure</strong></td><td></td></tr><tr><td>8.5.1 HGTD Hermetic vessel</td><td>IHEP, IJCLab</td></tr><tr><td>8.5.2 On detector cooling system</td><td>IJCLab, MEPhI</td></tr><tr><td>8.5.3 CO2 cooling system</td><td>CERN, IJCLab, IRFU</td></tr><tr><td>8.5.4 Water cooling system</td><td>CERN</td></tr><tr><td>8.5.5 Nitrogen system</td><td>CERN</td></tr><tr><td>8.5.6 Cables and connectors</td><td>CERN, JINR</td></tr><tr><td>8.5.7 Fibers and optical connectors</td><td>AS, KTH, NTHU</td></tr><tr><td><strong>8.6 Detector Assembly and QA</strong></td><td></td></tr><tr><td>8.6.1 Test bench for detector certification</td><td>IFAE, IHEP, LPC, USP</td></tr><tr><td>8.6.2 Tools for surface assembly</td><td>CERN, IJCLab, JINR</td></tr><tr><td>8.6.3 Assembly of components on cooling plates</td><td>CERN, IHEP, JINR, USP</td></tr><tr><td>8.6.4 Final integration inside vessels</td><td>CERN, IHEP, IJCLab, JINR, NJU</td></tr><tr><td><strong>8.7 Installation and Commissioning</strong></td><td></td></tr><tr><td>8.7.1 Tools for transport and cavern installation</td><td>IJCLab, JINR</td></tr><tr><td>8.7.2 Services, p. panels and cooling installation</td><td>CERN, USP, JINR</td></tr><tr><td>8.7.3 Back-end elect. installation in USA15</td><td>CERN, IHEP, KTH, JINR, UIT, UH2C, UM5R, UMP</td></tr><tr><td>8.7.4 Detector installation and connectivity</td><td>CERN, IHEP, IJCLab, JINR, MEPhI, NJU, SJTU, USP, USTC</td></tr><tr><td>8.7.5 Global commissioning in LS3</td><td>CERN, IHEP, JINR, KTH, LPC, MEPhI, NJU, SJTU, USP, USTC</td></tr></tbody></table>
### 15.3.1 CORE costs

Each HGTD PBS item, described in Table 15.3, has an associated CORE cost that is defined as the sum of the material value of all components making up the deliverable. The cost of generic infrastructure, prototypes, and spare components are all excluded by definition from the CORE costing, as is the cost related to personnel, such as labour or travel for personnel employed by HGTD Institutions. Specialized infrastructure, such as custom-designed tooling, is included in CORE. For items bought in industry, the material value is simply their selling price, and depending on how the vendor calculated this price, it includes some unknown fraction of labour cost at the company. This type of labour cost is included in CORE. The CORE cost of a project does not represent its full cost, and Institutions participating in HGTD have to request funds to cover both CORE and non-CORE expenditure from their Funding Agencies, in a ratio that varies from deliverable to deliverable.

The HGTD CORE cost has been estimated in a bottom-up approach and it has been calculated based on the baseline layout presented in this document. The yield model used accounts for failure and loss during the production phase, up to and including the installation of items in the ATLAS cavern, detailed for the main components in Table 15.12. The yield was estimated based on past production experience with similar or equivalent items or extrapolating from prototypes experience. In contrast, spares accounting for failure and loss during the operations phase, i.e. from the beginning of Run 4 onwards and components needed for the rings replacements are planned to be supported by maintenance and operations (M&O) funds and do not count as CORE.

The cost estimates for each item are quoted in CHF, using the exchange rates of:

* 1 Euro = 1.085 CHF

* 1 USD = 0.986 CHF

* 1 CNY = 0.1461 CHF

* 1 GBP = 1.246 CHF

* 100 JPY = 0.942 CHF

* 1 ILS = 0.2588 CHF

as in the other ATLAS phase II TDRs. The CORE estimates are based on existing contracts (ASICs), quotes from industry (sensors, FPGAs, DC-DC converters, Flex cables,...), extrapolation from other ATLAS Upgrade Phase-II projects with already signed MoU that are using the same or similar type of components (power supplies, cables, cooling station).

The price estimates for all the individual items are based on the most accurate information available at the time of the estimate, and they come with an uncertainty. The level of cost uncertainty of each item depends on the amount of technical development and design,
understanding of its procurement process, and the availability of vendor quotes. To describe the level of uncertainty of the cost, a quality factor ranging from 1 to 5 is used as summarised in Table 15.14. QF1 has the highest certainty and is based on a vendor quote for the final item or a catalogue price; QF5 has the least amount of certainty and is based on a rough estimate without any detailed design. Where items are composed of sub-items with different quality factors, a cost-weighted average quality factor is calculated.

<table><caption>Table 15.14: Quality factor (QF) definitions. QF1 has the highest precision, QF5 has the highest uncertainty.</caption><thead><tr><td>Quality Factor</td><td>Description</td></tr></thead><tbody><tr><td>QF1</td><td>Based on a vendor quote or catalogue price</td></tr><tr><td>QF2</td><td>Based on the purchase of a similar component</td></tr><tr><td>QF3</td><td>Based on an engineering design</td></tr><tr><td>QF4</td><td>Based on a conceptual design or scaled from similar systems</td></tr><tr><td>QF5</td><td>Based on a rough estimate without any detailed design</td></tr></tbody></table>

A summary of the HGTD CORE cost, detailed to the PBS level 3 is presented in Table 15.15, with a total of 9965 kCHF for the HGTD and 995 kCHF for the HGTD-DAQ related deliverables. These DAQ items are considered ATLAS TDAQ deliverables and they will be included in an amendment of the TDAQ MoU after the HGTD TDR approval.

The costs for the planned replacement of the HGTD inner and middle rings during the HL-LHC half life time are not accounted in CORE and should be accounted in the future (M&O) funds. DAQ hardware deliverables are covered in the ATLAS TDAQ PBS, and they will be included in an amendment of the TDAQ MoU.

The time profile of the CORE cost expenditures for the HGTD project, split into the main HGTD deliveries, is shown in Figure 15.10. The bulk of the expenditures will happen in 2022–2024, when most of the components need to be produced.

Basis of Estimate (BoE) documents, that describe in detail and justify the CORE cost estimate for each deliverable, have been produced. These BoEs are being reviewed in detail by the ATLAS Project Management Office in preparation of the UCG review. The HGTD cost estimate for all deliverables has an associated average cost quality factor of 2.2. The readout ASIC and LGAD Sensors, that are among the most expensive HGTD deliverables, have cost factors of 1.1 and 2.0, respectively. The CO₂ cooling system, the only other deliverable costing over 1000 kCHF has QF 2.9. The HGTD deliverables with highest QF are the Tools for surface assembly, transport and cavern installation. These have relatively low cost and are in the conceptual design stage given that they are needed later in the project. Engineering design of these tools will however accelerate in the near future.

The cost of the project is expected to be covered by the Institutes participating in the HGTD Phase-II UPR, with their respective Funding Agencies. The details of responsibility and
sharing among Institutes will be defined in an MoU to be prepared after the TDR approval.

<figure><img src="image_202.png" /><figcaption>Figure 15.10: CORE cost time profile in kCHF for the HGTD level 2 deliverables from 2020 to 2027.</figcaption></figure>

15.3.2 Required Labour Effort

Estimates of the human resources, in term of full-time equivalents FTE for the different type
of labour (physicists, engineers, technicians, students), required to complete each deliverable
have been obtained based on similar experience in other projects or sub-systems, such as the
TDAQ, and ITk Pixel and Strip projects. The estimate used a bottom-up approach based on
the detailed Work Breakdown Structure. Detailed summary information down to level 3
activities is being reviewed internally by ATLAS in preparation of the UCG review.

The labour effort needed to accomplish the construction of the detector up to the HGTD installation and commissioning is shown in Figure 15.11 as a function of time. The effort peaks, with a maximum of about 70 FTE, between 2023 and 2025 when most of the detector parts will be in the pre-production and production phases, with special emphasis to the module and Detector Units assembly. In total about 400 FTE are needed to accomplish the project, with a breakdown of approximately 20% physicists, 25% engineers, 25% technicians and 30% students. The survey mentioned earlier among participating Institutes indicates that the human resources required for the HGTD project, in all of these labor categories, is overall covered beyond the needs.
15 Project Organization, Costs, and Schedule

<table><caption>Table 15.15: Estimated CORE cost of the HGTD (in kCHF). The total cost is given with and without the costs of the DAQ. The internal and external moderator CORE costs are accounted in the ATLAS ITk common. The items listed without a cost are WBS-only items, and hence have no assigned CORE cost. (*) DAQ hardware related costs, estimated separately by TDAQ, will be included in an amendment of the TDAQ MoU.</caption><thead><tr><th>PBS/WBS</th><th>Item</th><th>CORE cost (kCHF)</th></tr></thead><tbody><tr><td>8.1</td><td><strong>Sensors</strong></td><td>2403</td></tr><tr><td>8.1.1</td><td>LGAD Sensors</td><td>2403</td></tr><tr><td>8.2</td><td><strong>Electronics</strong></td><td>3108</td></tr><tr><td>8.2.1</td><td>ASIC</td><td>1094</td></tr><tr><td>8.2.2</td><td>Peripheral Electronics Board</td><td>638</td></tr><tr><td>8.2.3</td><td>High Voltage system</td><td>955</td></tr><tr><td>8.2.4</td><td>Low Voltage system</td><td>422</td></tr><tr><td>8.3</td><td><strong>Luminosity, DAQ and Control</strong></td><td>339</td></tr><tr><td>8.3.1</td><td>Luminosity boards</td><td>260</td></tr><tr><td>8.3.2</td><td>DCS</td><td>44</td></tr><tr><td>8.3.3</td><td>Interlocks and protection system</td><td>35</td></tr><tr><td>8.3.4</td><td>DAQ software</td><td>-</td></tr><tr><td>8.4</td><td><strong>Modules and Detector Units</strong></td><td>1392</td></tr><tr><td>8.4.1</td><td>Bare module hybridization</td><td>468</td></tr><tr><td>8.4.2</td><td>Module Flex</td><td>108</td></tr><tr><td>8.4.3</td><td>Modules assemblies</td><td>318</td></tr><tr><td>8.4.4</td><td>Detector Units</td><td>142</td></tr><tr><td>8.4.5</td><td>Flex Cable Tails</td><td>356</td></tr><tr><td>8.5</td><td><strong>Mechanics, Services and Infrastructure</strong></td><td>2476</td></tr><tr><td>8.5.1</td><td>HGTD Hermetic vessel</td><td>176</td></tr><tr><td>8.5.2</td><td>On detector cooling/support plate</td><td>190</td></tr><tr><td>8.5.3</td><td>CO₂ cooling system</td><td>1167</td></tr><tr><td>8.5.4</td><td>Water cooling system</td><td>23</td></tr><tr><td>8.5.5</td><td>Nitrogen system</td><td>20</td></tr><tr><td>8.5.6</td><td>Cables and electrical connectors</td><td>691</td></tr><tr><td>8.5.7</td><td>Fibers and optical connectors</td><td>209</td></tr><tr><td>8.6</td><td><strong>Detector Assembly and QA on surface</strong></td><td>167</td></tr><tr><td>8.6.1</td><td>Test bench for detector certification</td><td>72</td></tr><tr><td>8.6.2</td><td>Tools for surface assembly</td><td>95</td></tr><tr><td>8.6.3</td><td>Assembly of components on cooling plates</td><td>-</td></tr><tr><td>8.6.4</td><td>Final integration inside vessels</td><td>-</td></tr><tr><td>8.7</td><td><strong>Installation and Commissioning</strong></td><td>80</td></tr><tr><td>8.7.1</td><td>Tools for transport and cavern installation</td><td>80</td></tr><tr><td>8.7.2</td><td>Services, patch panels and cooling installation</td><td>-</td></tr><tr><td>8.7.3</td><td>Back-end electronics installation in USA15</td><td>-</td></tr><tr><td>8.7.4</td><td>Detector installation and connectivity</td><td>-</td></tr><tr><td>8.7.5</td><td>Global commissioning in LS3</td><td>-</td></tr><tr><td colspan="2"><strong>Total HGTD</strong></td><td>9965</td></tr><tr><td colspan="2"><strong>DAQ(*)</strong></td><td>995</td></tr><tr><td colspan="2"><strong>Total w/ DAQ</strong></td><td>10960</td></tr></tbody></table>
## 15.4 Risk Analysis and Risk Mitigation

<figure><img src="image_203.png" /><figcaption>Figure 15.11: Required effort (in FTE) needed per labour type (physicists, engineers, students, technicians) over the lifetime of the project.</figcaption></figure>

## 15.4 Risk Analysis and Risk Mitigation

The HGTD project is a complex undertaking on the part of multiple Institutes, that is prone to internal and external uncertainties, the consequences of which are known as risks. These risks cannot be avoided but they must be managed. The risks associated with cost, schedule, and scope and technical performances issues in the HGTD project are managed by a structured and integrated process as defined in the HGTD Risk Management Plan (RMP). The HGTD project overall risk management process follows broadly accepted risk management standards [101], according to which, awareness of potential risks and a deliberate approach meant to prevent risks or accept and mitigate them, are key to successful risk management. The RMP defines the roles and responsibilities of the management in the process of monitoring and controlling risks throughout the project and the thresholds used to characterise risk probability and impact.

The design and construction of the HGTD Project is well within the experience and expertise of the collaborators, technical staff and physicists, who are participating. Every effort has been made to specify the project in a manner that reduces the risk to an acceptably low level. The technical risks to the project that are identified will be addressed as early as possible to assure that they do not negatively impact the timely completion of the project or stress its budget. Proactive risk identification and mitigation can therefore significantly reduce the probability of unexpected events that could require contingency and/or additional time to resolve.
15.4.1 Risk Management Process and Plan

The risk management process is an integral part of the HGTD project management, as it informs decision making at every stage. Every effort has been made to design and specify all sub-projects to reduce the risk to an acceptable low level. Risks in the HGTD project are managed by a structured and integrated process for identifying, evaluating, tracking, mitigating, and managing project risks in terms of three risk categories: cost, schedule, and scope/technical performance.

The HGTD UPLs have the ultimate responsibility for managing the project risk. The HGTD UPLs are assisted in this role by the Resources and Risk Coordinator. Similar to the HGTD UPL, the HGTD sub-project coordinators (LV2) have the ultimate responsibility to manage and oversee the risks associated with their respective WBS areas. They report to the HGTD UPLs and the Resources and Risk Coordinator. The UPL is also responsible to ensure that the respective sub-system coordinators execute the appropriate mitigation strategies to minimise the likelihood of the risk. Risks are reviewed in periodical meetings of the HGTD Coordinators in which risks are discussed, updated, and appropriate actions are taken if required.

The overall Risk Management approach consists of a five-step process:

* Identifying potential project risks,

* Analysing project risks,

* Planning risk mitigation strategies,

* Executing risk mitigation strategies, and

* Monitoring and tracking the results, revising the risk mitigation strategies as necessary.

This includes identifying appropriate risk mitigation strategies to lower the likelihood of the risk to occur and quantifying the severity of that risk. The sub-project coordinators report the potential risk to the UPLs and Risk Coordinator. It is subsequently the UPLs responsibility to approve the risks and associated actions and update the risk register. It is also the UPL responsibility to identify additional risks, including global risks that span across multiple WBS areas.

The identified risks, the associated mitigation strategy, and the response in the event that the risks were to materialize are all captured in the HGTD Risk Register. The Risk Register contains, for each risk, the following information:

* The mitigation steps that are/will be taken to minimize that risk from occurring;

* The response to the risk in the eventuality that the risk materialises;
* The quantitative impact of the risk on Cost, Schedule and Performance: The risk impact is classified as either Negligible, Low, Medium or High as shown in Table 15.16. The performance impact is based on identifying a set of Key Performance Parameters (KPP) and assessing the impact of the risks on those KPP. This risk analyses is performed by the respective sub-project coordinators and reviewed and maintained by the UPL;

* The likelihood that the identified risk will occur. The Risk Probability is identified as Low, Moderately Low, Moderately High and High based on the probability range shown in Table 15.17.

* The likely impact on the cost and schedule, and optimistic/pessimistic scenario quantifying the best/worst case scenarios.

* The overall assessment of the risk based on Table 15.17 that correlates the probability of the risk to occur and the impact of the risk. The overall risk is classified as High, Medium, or Low based on the product of the risk impact and the risk probability.

<table><caption>Table 15.16: Classification of the Risk Impact based on its impact on the cost, the schedule, and the scope/performance. The last column reflect the assessment for Scope/Performance Impact in terms of the impact on the objective Key Performance Parameters (KPP).</caption><thead><tr><th>Risk Impact</th><th>Cost impact (kCHF)</th><th>Schedule Impact (months)</th><th>Scope/performance Impact (KPP)</th></tr></thead><tbody><tr><td>Negligible</td><td>0 – 20</td><td>0 – 1</td><td>degraded &lt; 1%</td></tr><tr><td>Low</td><td>20 – 100</td><td>1 – 3</td><td>degraded 1 – 5%</td></tr><tr><td>Medium</td><td>100 – 500</td><td>3 – 6</td><td>degraded 5 – 10%</td></tr><tr><td>High</td><td>500 – &infin;</td><td>6 – &infin;</td><td>degraded &gt; 10%</td></tr></tbody></table>

<table><caption>Table 15.17: Correlation of Risk Probability (first column) and Risk Impact (remaining columns, classified as Negligible, Low, Medium and High). Considering this correlations, the identified risk is subsequently classified as Low, Medium, or High.</caption><thead><tr><th rowspan="2">Risk Probability</th><th colspan="4">Risk Impact</th></tr><tr><th>Negligible</th><th>Low</th><th>Medium</th><th>High</th></tr></thead><tbody><tr><td>30% &lt; p &le; 100%</td><td>Low</td><td>Medium</td><td>High</td><td>High</td></tr><tr><td>15% &lt; p &le; 30%</td><td>Low</td><td>Low</td><td>Medium</td><td>High</td></tr><tr><td>5% &lt; p &le; 15%</td><td>Low</td><td>Low</td><td>Medium</td><td>High</td></tr><tr><td>p &le; 5%</td><td>Low</td><td>Low</td><td>Low</td><td>Medium</td></tr></tbody></table>

### 15.4.2 Major risks and mitigation strategies

Many of the technical choices in the HGTD project were made already at the time of the Expression of Interest and Technical Proposal for the best compromise between performance
and cost. Some have since then evolved motivated by the minimization of risks. The severe
space constraints (in z, r), high radiation levels and the limited time available to implement
the project in the LS3 shutdown have been seriously considered in the optimized layout
presented in this TDR. Some major risks that have been identified and addressed in the
process of defining the scope of the HGTD project are discussed below.

**Deep ASIC characterisation and integration with sensor:** The schedule foresees two iterations of the full-size ASIC during the prototype phase (2020-2021). This ASIC is quite complex and challenging, hence demanding a deep characterisation between each iteration, including significant irradiation tests and a characterisation of the ASIC connected to the sensor. If significant problems arise, there is some risk that testing will require more time. The probability of such a risk is estimated to be 20 %. To mitigate it, intensive post layout simulations will be performed before submission to minimize the problems to be debugged when testing the ASIC. In addition additional teams will be trained and injected in the ASIC testing phase (already started recently), which could reduce this probability. The risk impact is mainly on the schedule, about 6-9 months, depending if it emerges after only the first prototype or both.

**Detector radiation performance worse than expected:** The radiation hardness of the LGAD Sensors and ALTIROC2 chips will only be fully evaluated after the respective pre-productions and the hybridization pre-production. The time is limited to react if, at this stage, the final modules underperformed in terms of radiation hardness. This might result in a detector with lower life expectancy that originally planned, specially for the inner ring. However, this scenario should have a limited impact on the overall schedule and cost. On the other hand, it may result in the need to replace the inner ring at an earlier stage than expected. If this were the case, intense R&D (with other dopant materials or bulk implantations for example) should be pursued to develop a better solution for the first replacement option. The fact that the target is to qualify and produce sensors in several fabrication sites would also help to mitigate lower performance of sensors produced in one site, or the possible low sensor yield after pre-production of one of the facilities.

**LGAD Sensor procurement:** Sensor production facilities might struggle to cope with the simultaneous requests for LGAD Sensors from ATLAS and CMS. Some vendors might even be devoted to ITk related productions or other experiment's needs. This situation will likely result in inevitable delays in the production schedule, since fabrication sites typically report a best case scenario for their delivery time and do not account for other future (possible) demands. Again, a clear mitigation factor would be the fact that the HGTD production will not rely on a single supplier, but at least in three, with whichever two sites, capable of producing the needed amount of sensors with minimal impact on the schedule. If it were the case that CMS and ATLAS both select the same vendors it may be an advantageous to be slightly ahead in the schedule and thus try to maintain a certain priority with respect to later productions.
**Periphery Electronic Boards schedule and design:** Duo to the limitation of the surface area for all components, the placement of the connectors and DC/DC blocks and the selection of the package for capacitors need to be optimized. Some prototype DC/DC blocks can be made to evaluate the physical dimension, the power efficiency, anti-magnetic ability and radiation hardness. While the delay could be absorbed in the schedule float, the precise impact on performances need to be assessed. The lpGBT, VL+ and MUX may not be available when planned. Prototype Periphery Electronic Boards can be made with commercial devices as placeholders, and there is float in the schedule to absorb an additional year of delay.

**Module production rate:** The module assembly throughput is currently based on the assumption that four assembly sites will produce modules at a rate of about 20 modules per week and that the overall yield will be better than 74%. The module assembly is an activity that extends for almost two years and thus any delay can have a significant impact on the schedule. A lower assembly yield than expected would impact cost and schedule and thus it is critical to achieve or improve the target yield. The fact that the module hybridization relies on matured and well understood processes that are commonly available in the industry gives confidence that this critical step is under control, and in any case, other companies will be approached and qualified to have options towards the final production. Problems with assembly in Institutes can be mitigated by increasing the number of assembly sites (an option that will be actively pursued and can turn into an opportunity) and by benefiting from the current R&D on more robust module concepts that could simplify the assembly process, such as using ball bonding instead of wire-binding.

**Uniform clock distribution:** The master clock will be distributed from FELIX to the lpGBT downlinks and then to the ASICs, in which a clock tree will be used to ensure the uniformity of the clock. Different contributions to the clock distribution can affect considerably the time resolution and thus having an impact on HGTD performance. Static contributions include the propagation times to distribute the clock to each ASIC while dynamic contributions can occur through a variety of mechanisms across a wide range of frequencies including high-frequency jitter. These contributions have been studied in Section 10.2 and a mitigation strategy has been shown. It will consist of computing the average the time of arrival per ASIC at L0 trigger rate and then apply this correction offline. Although conservative contributions to the clock jitter coming from FELIX, lpGBT, flex and ASIC have been taken into account in these studies; unknown or noise induced jitter sources with an irreducible clock jitter > 30ps will compromise the time resolution of the detector. The mitigation plan will include the measurement of the jitter performance at different points (FELIX, lpGBT, flex and ASIC) during pre-production in a dedicated test-bench, where the different contribution to the clock jitter can be identified. In case that any unexpected jitter contribution arises, the clock distribution might be revisited with additional clock cleaner impacting the
design of different components like the PEB and flex, and the production of these items
might be delayed by a few months.

**Increased radiation levels:** An increase of the expected radiation levels, for instance caused by further increase in the amount of ITk services in the patch panel PP1 region, can impact the HGTD performance. To mitigate this, the transition radius between the inner ring (to be replaced at each $1000 \text{ fb}^{-1}$) and the middle ring (to be replaced at $2000 \text{ fb}^{-1}$), currently at $r=230 \text{ mm}$, could be increased together with the inner radius of the permanent outer ring, currently at $r=540 \text{ mm}$.

**Schedule slippage for HGTD-C:** The schedule float for the installation of the HGTD-C in ATLAS is short. The schedule critical path is driven by the module production rate mentioned above. Modules for half of HGTD-C will take about seven months to produce. In case of delays in the construction, in spite of the mitigation measures to the module production schedule listed above, the HGTD-C will be installed in January 2027 with all available instrumented half circular disks. The missing disk(s) may still be inserted in the following 1-2 months, during the overall ATLAS commissioning period. Although the crane will not be available anymore, enough space exists between the barrel and the end-cap calorimeters to allow the installation manually (objects of ~ 35 Kg each and 1 m radius). A dedicated tool will be manufactured to transport the half instrumented disks safely without crane. The other possibility will be to install the missing instrumented disk(s) in the next YETS after LS3. This scenario will need a procedure to be developed respecting the ALARA/safety rules, to account properly for induced radiation levels. The impact in the physics performance should be small given expected lower values of instantaneous luminosity at the startup of HL-LHC, compared to the designed peak luminosity.
Acknowledgements

We thank CERN for the very successful operation of the LHC, as well as the support staff
from our institutions without whom ATLAS could not be operated efficiently.

We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS and CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF and MPG, Germany; GSRT, Greece; RGC and Hong Kong SAR, China; ISF and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russia Federation; JINR; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZŠ, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, United Kingdom; DOE and NSF, United States of America. In addition, individual groups and members have received support from BCKDF, CANARIE, Compute Canada and CRC, Canada; ERC, ERDF, Horizon 2020, Marie Skłodowska-Curie Actions and COST, European Union; Investissements d'Avenir Labex, Investissements d'Avenir Idex and ANR, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF, Greece; BSF-NSF and GIF, Israel; CERCA Programme Generalitat de Catalunya and PROMETEO Programme Generalitat Valenciana, Spain; Göran Gustafssons Stiftelse, Sweden; The Royal Society and Leverhulme Trust, United Kingdom.

The crucial computing support from all WLCG partners is acknowledged gratefully, in
particular from CERN, the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark,
Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1
(Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA), the Tier-2 facilities
worldwide and large non-WLCG resource providers. Major contributors of computing
resources are listed in Ref. [102].
<figure><img src="image_204.png" /></figure>
A Expected Energy Spectra

<figure><img src="image_205.png" /><figcaption>Figure A.1: Proton spectra averaged over the rear (outermost) and front (innermost) silicon layer of the HGTD. The uncertainties are of the order of 5%</figcaption></figure>
A Expected Energy Spectra

<figure><img src="image_206.png" /><figcaption>Figure A.2: Neutron spectra averaged over the rear (outermost) and front (innermost) silicon layer of the HGTD. The uncertainties are of the order of 5%. The fluctuations between 1 keV and 10 MeV are due to resonance.</figcaption></figure>

<figure><img src="image_207.png" /><figcaption>Figure A.3: Pion spectra averaged over the rear (outermost) and front (innermost) silicon layer of the HGTD. The uncertainties are of the order of 5%</figcaption></figure>
## B Monte Carlo samples

The simulation, digitisation and reconstruction was implemented in the ATLAS upgrade software releases<fnref n="1" />. Samples of single electrons, muons and pions as well as selected physics processes such as $t\bar{t}$, VBF $H \to Z(vv)Z(vv)$ were produced using the ATLAS production system. PYTHIA8 [26] was used together with POWHEG [21–23] for most of the samples. In the simulation step the beam spot was simulated with the nominal spread in z and time described in Section 2.1. Samples with $\langle\mu\rangle = 0$ as well as $\langle\mu\rangle = 200$ were processed. A summary of the samples is shown in Table B.1. For the minimum bias (inelastic collisions in the underlying event) samples, single neutrino events were produced to mimic the event topology at $\langle\mu\rangle = 200$.

<footnote n="1">¹ The releases used were AtlasProduction-20.20.14.4 for simulation and 20.20.14.6 for digitisation and reconstruction, both including the so-called Step 3.1 layout of ITk used for results discussed with LHCC in Nov 2019 (geometry tag ATLAS-P2-ITK-17-04-02).</footnote>
## B Monte Carlo samples

<table><caption>Table B.1: The simulated Monte Carlo samples used for the studies in this document.</caption><thead><tr><th>Sample</th><th colspan="2">Number of events</th></tr><tr><td></td><td>⟨μ⟩ = 0</td><td>⟨μ⟩ = 200</td></tr></thead><tbody><tr><td>Single particles</td><td></td><td></td></tr><tr><td>π<sup>+</sup>, p<sub>T</sub> = 5 GeV, flat η [2.3-4.3]</td><td>200000</td><td>200000</td></tr><tr><td>π<sup>+</sup>, p<sub>T</sub> = 20 GeV</td><td>200000</td><td>200000</td></tr><tr><td>π<sup>+</sup>, p<sub>T</sub> = 45 GeV</td><td>200000</td><td>200000</td></tr><tr><td>π<sup>+</sup>, flat p<sub>T</sub> [0.1-5.0] GeV, flat η [2.3-4.1]</td><td>200000</td><td>200000</td></tr><tr><td>π<sup>0</sup>, flat p<sub>T</sub> [0.1-5.0] GeV, flat η [2.3-4.1]</td><td>200000</td><td>200000</td></tr><tr><td>γ, p<sub>T</sub> = 20 GeV, flat η [2.3-4.3]</td><td>200000</td><td>200000</td></tr><tr><td>γ, p<sub>T</sub> = 45 GeV, flat η [2.3-3.2]</td><td>200000</td><td>200000</td></tr><tr><td>γ, p<sub>T</sub> = 100 GeV, flat η [2.3-3.2]</td><td>50000</td><td>50000</td></tr><tr><td>μ, p<sub>T</sub> = 45 GeV, flat θ</td><td>400000</td><td>400000</td></tr><tr><td>μ, p<sub>T</sub> = 45 GeV, flat η [2.3-3.2]</td><td>300000</td><td>300000</td></tr><tr><td>μ, p<sub>T</sub> = 45 GeV, flat η [3.2-4.3]</td><td>100000</td><td>100000</td></tr><tr><td>e, p<sub>T</sub> = 45 GeV, flat η [2.3-4.3]</td><td>400000</td><td>400000</td></tr><tr><td>e, p<sub>T</sub> = 20 GeV, flat η [2.3-4.3]</td><td>200000</td><td>200000</td></tr><tr><td>ν, for minimum-bias at ⟨μ⟩ = 200</td><td>-</td><td>1000000</td></tr><tr><td>Physics processes</td><td>Generator</td><td></td></tr><tr><td>Minimum bias, low-p<sub>T</sub></td><td>PYTHIA8</td><td>1000000</td><td>-</td></tr><tr><td>Minimum bias, high-p<sub>T</sub></td><td>PYTHIA8</td><td>1000000</td><td>-</td></tr><tr><td>Dijet, 20 GeV &lt; p̂<sub>T</sub> &lt; 60 GeV</td><td>PYTHIA8</td><td>1000000</td><td>1000000</td></tr><tr><td>Dijet, 60 GeV &lt; p̂<sub>T</sub> &lt; 160 GeV</td><td>PYTHIA8</td><td>1000000</td><td>1000000</td></tr><tr><td>Dijet, 160 GeV &lt; p̂<sub>T</sub> &lt; 400 GeV</td><td>PYTHIA8</td><td>1000000</td><td>1000000</td></tr><tr><td>Z → ee</td><td>POWHEG+PYTHIA8</td><td>100000</td><td>100000</td></tr><tr><td>Z → ττ</td><td>POWHEG+PYTHIA8</td><td>400000</td><td>400000</td></tr><tr><td>t<span style="text-decoration: overline">t</span></td><td>Powheg+Pythia8</td><td>1000000</td><td>1000000</td></tr><tr><td>VBF H → ZZ → 4ν</td><td>POWHEG+PYTHIA8</td><td>500000</td><td>500000</td></tr><tr><td>NCB beam-gas, oxygen</td><td></td><td>400000</td><td></td></tr><tr><td>NCB beam-gas, carbon</td><td></td><td>400000</td><td></td></tr><tr><td>NCB beam-gas, hydrogen</td><td></td><td>400000</td><td></td></tr></tbody></table>
C Two-ring Layout Used in Simulation

The relevant drawings concerning the two-ring detector layout used in the simulation.

<figure><img src="image_208.png" /></figure>

Figure C.1: The orientation of the readout rows for the first and second layer encountered by a particle, separately and with the overlay of both. Each layer is rotated in alternating directions by 20°. This can be compared to Figure 2.8 for the three-ring layout.
## C Two-ring Layout Used in Simulation

<figure><img src="image_209.png" /><figcaption>Figure C.2: Figures showing the placement of the modules in the (a) two-ring and (b) three-ring layouts.</figcaption></figure>

<figure><img src="image_210.png" /><figcaption>Figure C.3: The schematic drawing shows the overlap between the modules on the front and back of the cooling disk. There is a sensor overlap of 80% between sensors on front and back sides of a cooling plate at $R < 320$ mm, and 20% outside this radius. The figure can be compared to Figure 2.9.</figcaption></figure>
D Technical Drawings
<figure><img src="image_211.png" /><figcaption>Figure D.1: Sketch of the bare module (sensor and ASIC). Distances are in millimetres. The bump pads on the sensor are shifted by 250 µm on each side of the sensor, to allow a 100 µm separation between the ASICs.</figcaption></figure>
<figure><img src="image_212.png" /><figcaption>Figure D.2: Sketch of the module with the sensor, the ASICs and the Flex cable. Distances are in millimetres. Dimensions of the different components are visible, including the bumps pads, the glue and the wire-bonds.</figcaption></figure>
<figure><img src="image_213.png" /><figcaption>Figure D.3: Schematics of the design of the module flex prototype based on the ALTIROC2 pinout.</figcaption></figure>
<figure><img src="image_214.png" /><figcaption>Figure D.4: Detailed technical drawing of the external moderator part.</figcaption></figure>
<figure><img src="image_215.png" /><figcaption>Figure D.5: Detailed technical drawing of the internal moderator part.</figcaption></figure>
<figure><img src="image_216.png" /><figcaption>Figure D.6: Detailed 2D drawing of the full hermetic vessel assembly with main dimensions in R-φ & R-Z views. The CO2 transfer lines are located at 11.25° from the vertical axis as specified in the envelope study with ATLAS-TC and ITK integration team.</figcaption></figure>
<figure><img src="image_217.png" /><figcaption>Figure D.7: View of the front side of the first detector disk, placed inside the vessel. There is a tilt of 20° between the two double sided layers, detailed in the zoomed region.</figcaption></figure>
<figure><img src="image_218.png" /><figcaption>Figure D.8: Detailed 2D drawing of the full cooling loops and their manifolds inside the hermetic vessel. The R-φ front view is illustrating the cooling lines distribution and the tilt angle of 70° between the cooling plates which corresponds to 20° tilt between read out rows. The detailed views are showing the manifolds area and their restricted access space.</figcaption></figure>
<figure><img src="image_219.png" /><figcaption>Figure D.9: View of the mechanical prototype planned for the HGTD demonstrator. It includes a cooling plate, dummy modules and connectivity to peripheral electronics board (indicated in green). The heaters simulating the modules power dissipation, using dummy modules are in blue.</figcaption></figure>
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