# ATLAS PIXEL LOCAL SUPPORTS - DESIGN STATUS

# Introduction

This notes summarizes the design status and measurements on prototypes
of the ATLAS Pixel Local Supports. A proposed plan of work leading up to
the Production Readiness Review(PRR) is also provided. The note is
divided into three major sections: design status of the barrel-region
local supports(staves), design status of the disk-region local
supports(sectors) and the plan of work leading to the PRR. This note
assumes familiarity with the ATLAS Pixel System[^1] and the
corresponding local-support requirements.[^2]

# Barrel Staves

# Disk Sectors

## Design and Prototype History and Status

### Overview

Three different types of disk sectors have been designed and prototypes
fabricated. Tests have been performed on these prototypes to determine
if the designs meet the requirements. The design concept for each of
these prototypes is summarized here. A more detailed description of the
fabrication process for two of the designs - those based on aluminum
cooling tubes and sealed carbon-carbon tubes - is available.[^3] All
disk sector designs share the common feature of having carbon-carbon
faceplates. Pixel modules are mounted on both sides of the sector.
Coolant is contained in a tube between the faceplates that is arranged
to meet the thermal requirements with the minimum material (for each
design). The three different designs differ in the composition of the
cooling tube, how the tube is attached to the faceplates and how
structural stiffness is maintained for the finished sector.

A complete set of measurements does not yet exist to demonstrate that
all requirements can be met. An enumeration of outstanding issues and a
plan to address them are included in this note.

### Carbon-tube Design 

The carbon tube design was developed by Energy Sciences Laboratory, Inc
(ESLI)[^4] under a direct contract from the US Department of Energy. The
coolant tube is a glassy carbon tube that can be formed as shown in
Error: Reference source not found. The tube is mechanically and
thermally connected to the faceplates by using high-thermal-conductivity
fibers that are \"flocked\" onto the carbon tube and machined flat,
using a proprietary process from ESLI. The concept is illustrated in
Error: Reference source not found. The resulting structure is then
thermally and otherwise processed to provide an all-carbon structure
with good matching of the coefficients of thermal expansion among the
various sub-components.

ESLI developed a number of generations of these prototypes. Nine
prototypes were manufactured to develop the technique. These prototypes
have been used in three critical tests to assess the ability to meet the
design requirements. One, evaporative cooling tests(with C~4~F~10~) were
performed in four different orientations of the sector to determine if
gravity affected the evaporative cooling concept using a cooling tube
with multiple bends. No significant differences were observed. Two, a
later generation of prototype was used with evaporative cooling(also
with C~4~F~10~) to understand operating margins and compare with
theoretical calculations. These tests are described in more detail
later. Third, ESLI produced an additional twelve prototype sectors(of
which two developed leaks during handling) that were mounted on a
prototype disk support ring. Extensive stability measurements were
performed on this complete disk at simulated operating conditions. These
tests are also described later.

ESLI is not currently considered to be a viable alternative for
production of the disk sectors. The reasons for not considering them
include cost, reliability of the design under pressure fault conditions,
reliability of the fabrication process and schedule.

+-----------------------------------+-----------------------------------+
| ![](media/image1.                 | ![](media/image2                  |
| png){width="3.0868055555555554in" | .png){width="2.060416666666667in" |
| height="3.201388888888889in"}     | height="3.2in"}                   |
|                                   |                                   |
| Figure 1. Glassy carbon tube      | Figure 2. Glassy carbon tube with |
| manufactured by ESLI. See text    | fibers attached.                  |
| for description.                  |                                   |
+-----------------------------------+-----------------------------------+

### Sealed-tube Design

The tube in this design has been developed by HYTEC, Inc[^5] under
direct contract from the US Department of Energy. The tube is a
resin-sealed carbon-carbon tube developed by Hytec, Inc[^6] and
illustrated in Error: Reference source not found and Figure 4. It is
attached to the faceplates with a rigid epoxy and there is no material
other than the tube between the faceplates. There is a very good match
of coefficients of thermal expansion between the carbon-carbon tube and
the carbon-carbon faceplates.

+-----------------------------------+-----------------------------------+
| ![](media/image3.                 | ![](media/image3.                 |
| wmf){width="3.1729166666666666in" | wmf){width="3.1729166666666666in" |
| height="2.7215277777777778in"}    | height="2.7215277777777778in"}    |
|                                   |                                   |
| Figure 3. Placeholder.            | Figure 4. Placeholder             |
+-----------------------------------+-----------------------------------+

NNN sectors of this type have been fabricated (as of early June 2000).
The basic parameters of these prototypes are summarized in Table 1. Test
results for these sectors are reported below. A full disk of twelve
sectors with a second-generation support ring is under assembly.

Table 1. Summary of sealed-tube prototype sectors.

This sector design remains an option for final production of the disk
sectors.

### Aluminum-tube Design

The tube in this design is a bent, rectangular aluminum tube - see
Error: Reference source not found. The thermal contact with the
faceplates is provide by thermally conductive compound (CGL-7018 from AI
Technologies) as shown in Error: Reference source not found and tube is
captured by carbon foam and a few carbon-carbon hard points that are
rigidly bonded to the faceplates as also shown in Error: Reference
source not found. These sectors have been designed and fabricated at
Lawrence Berkeley National Laboratory.

  ---------------------------------------------------- -----------------------------------
  ![](media/image4.png){width="3.1666666666666665in"   ![](media/image5.png)**Figure 6.
  height="2.1125in"}**Figure 5. Aluminum tube for disk Tube in foam showing
  sectors.**                                           construction.**

  ---------------------------------------------------- -----------------------------------

Ten prototypes of this design have been fabricated (as of early June
2000). The basic parameters of these prototypes are summarized in Table
2. Test results for some of these sectors are reported below. Prototypes
#1 and #2 were fabricated some years ago for disk layouts that are no
longer relevant. Prototype #5 was poorly made and rebuilt to become
prototype #6.

+--------+----------------+-------------+----------------+------------+
| Number | Facing         | Fill        | fill to c-c    | Al-tube    |
|        | thickness      | material    | adhesive       |            |
|        |                |             |                |            |
|        |                | carbon foam |                |            |
+--------+----------------+-------------+----------------+------------+
| 3      | 0.50 mm        | 0.05 gm/cc  | 3M-9460        | Round      |
|        |                |             |                |            |
|        |                |             |                | 3.6 mm ID  |
|        |                |             |                |            |
|        |                |             |                | 0.20 mm    |
|        |                |             |                | wall       |
+--------+----------------+-------------+----------------+------------+
| 4      | 0.30           | 0.10        | Cyanate ester  | Round      |
|        |                |             |                | /flattened |
|        |                |             |                |            |
|        |                |             |                | 3.6 mm ID  |
|        |                |             |                |            |
|        |                |             |                | 0.20 mm    |
|        |                |             |                | wal        |
+--------+----------------+-------------+----------------+------------+
| 5      | 0.30           | 0.10        | Cyanate ester  | R          |
|        |                |             |                | ectangular |
|        |                |             |                |            |
|        |                |             |                | ID         |
|        |                |             |                | 1.69x4.06  |
|        |                |             |                | mm         |
|        |                |             |                |            |
|        |                |             |                | 0.20 mm    |
|        |                |             |                | wall       |
+--------+----------------+-------------+----------------+------------+
| 6      | 0.30           | 0.10        | Cyanate ester  | R          |
|        |                |             |                | ectangular |
|        |                |             |                |            |
|        |                |             |                | ID         |
|        |                |             |                | 1.69x4.06  |
|        |                |             |                | mm         |
|        |                |             |                |            |
|        |                |             |                | 0.20 mm    |
|        |                |             |                | wall       |
+--------+----------------+-------------+----------------+------------+
| 7 and  | 0.420.03       | 0.10        | Cyanate ester  | R          |
| 8      |                |             |                | ectangular |
|        |                |             |                |            |
|        |                |             |                | ID         |
|        |                |             |                | 1.69x4.06  |
|        |                |             |                | mm         |
|        |                |             |                |            |
|        |                |             |                | 0.29 mm    |
|        |                |             |                | wall       |
+--------+----------------+-------------+----------------+------------+
| 9 and  | 0.420.03       | 0.10        | Cyanate ester  | R          |
| 10     |                |             |                | ectangular |
|        |                |             |                |            |
|        |                |             |                | ID         |
|        |                |             |                | 2.74x4.19  |
|        |                |             |                | mm         |
|        |                |             |                |            |
|        |                |             |                | 0.29 mm    |
|        |                |             |                | wall       |
+--------+----------------+-------------+----------------+------------+

Table 2 Summary of aluminum-tube prototype sectors.

This design is the current baseline for the disk sectors and thus is an
option for the final production.

## Thermal Performance

### Introduction

The essential thermal requirement is to maintain the pixel silicon
sensor temperature below -6^o^C with a uniformity across the sector of
??^o^C under all conditions. The thermal performance of the sectors has
been assessed by attaching dummy heat loads to the sectors to simulate
the heat load introduced by the pixel electronics. This has been done by
evaporating thin platinum on 0.300 mm silicon in a pattern that
simulates the pixel electronics heat load. These resistive heaters are
attached to the sectors in a manner similar to that expected for actual
pixel module attachment. Thus the actual heat loads are simulated as
well as can be done in the absence of real pixel modules.

Thermal measurements are done by infrared(IR) thermography coupled with
measurements at discrete points using RTD or other devices. The IR
measurements are normalized to the single point measurements. The
overall absolute accuracy in the temperature scale is estimated to be
1.5^o^C. Two different types of IR cameras have been used so far.

The thermal performance of the sectors depends on a number of factors.
These include the coolant temperature, the coolant flow rate, the
temperature differential between the coolant and the surface of the
sector faceplates and the differential between the faceplate and the
simulated pixel module. The last item is an interface to the sector, and
imposes requirements on the module attachment that are not directly
addressed here.

The current baseline coolant system is evaporative C~3~F~8~. Thermal
performance tests on disk sector prototypes have been done with
water/alcohol mixes, liquid fluorinert(C~6~F~14~) and evaporative
C~4~F~10~ but NO tests have been done on disk sectors with the baseline
coolant. First tests with the baseline coolant are planned in June 2000.
Our test results exhibit a good correlation between the thermal
performance measured with different fluids, in particular the
temperature differential between the local coolant (or coolant pipe) and
the surface of the sector faceplates. Thus we believe measurements made
with coolants other than evaporative C~3~F~8~ are reliable indicators of
thermal performance.

### Test Samples and Single Sectors

Thermal measurements have been done on single prototypes of the disk
sectors and smaller test pieces used for pre- and post-irradiation
comparisons. [^7] These test pieces were constructed in a manner similar
to the sectors.

#### Normal Operating Conditions

The measurement of thermal performance of an aluminum-tube sector is
illustrated in Figure 7 and Figure 8. The IR measurements are
cross-referenced to measurements using RTDs at a few points on the
platinum-plated, silicon dummy heaters. Measurements without power are
taken to determine a base state and then measurements are taken at
different power levels and coolant conditions. The coolant used in this
example was a water/methanol mixture. Error: Reference source not found
and Error: Reference source not found also show reference
surfaces(points 3 and 4) that are used to calibrate the measurements.
The measurements on aluminum-tube prototypes #4 and #5 can by summarized
briefly as follows:

-   the temperature differential between the bulk coolant temperature
    and the surface of the silicon simulated heaters can be kept 12^o^C
    at full power(50 W) in the worst locations for flow conditions that
    are believed to approximate those that would prevail in evaporative
    C~3~F~8~ cooling;

-   the uniformity of temperature can be 7^o^C under the same
    conditions; and

-   these temperature differentials are linear in the power, for fixed
    coolant temperature and flow.

The maximum temperature differential occurs near the edges of the
sector, and additional design modifications (small movements of the
aluminum tube) are being implemented to reduce further the maximum
temperature differential.

+-----------------------------------+-----------------------------------+
| ![](media/image6.j                | ![](media/image7.                 |
| peg){width="3.1993055555555556in" | jpeg){width="3.176388888888889in" |
| height="2.6902777777777778in"}    | height="2.676388888888889in"}     |
|                                   |                                   |
| Figure 7. Infrared image of       | Figure 8. Infrared image of       |
| aluminum-tube prototype# 4        | aluminum-tube prototype#4 at 48W  |
| without power at 10 cc/sec flow   | of power with 10 cc/sec flow of   |
| of coolant.                       | coolant.                          |
+-----------------------------------+-----------------------------------+

#### After Temperature Cycling

Temperature cycling measurements occur naturally as the thermal
performance is measured although usually over a restricted range of
temperature. Aluminum-tube prototype #4 was cycled between room
temperature(22^O^C and -18^O^C) without heaters attached, the heaters
attached and the thermal performance measured(also after the pressure
cycling described in the next section). The thermal performance met the
requirements. The temperatures measured at discrete points for low
temperature operation are shown in . Thermal measurement were repeated
on this sector using liquid C~6~F~14~ coolant that resulted in
temperature cycling multiple times from room temperature to about
-20^o^C. No degradation in thermal performance has been observed after
temperature cycling from room temperature to about -20^o^C for
aluminum-tube prototypes measured so far. However, it should be noted
that in all cases the dummy heaters were attached solely with CGL7018,
which has a very, very low shear modulus and decouples any CTE mismatch
between the silicon and the sector structure. Measurements are just
starting on thermal cycling effects with dummy heaters attached both
with CGL-7018 and with small tacks of UV epoxy that are required to
prevent long-term creep using CGL-7018 alone. This will couple the

![](media/image8.png)Sealed tube measurements\.....

#### After Pressure Cycling

The thermal performance after pressure cycling has been measured on
aluminum-tube prototypes #4 and #5. Prototype #4 was cycled from
atmospheric pressure to 5 bar absolute 24 times and then heaters
attached. It was then cycled to 3.7 bar absolute 20 times with the
heaters attached. The thermal performance of this prototype before and
after cycling with heaters attached is shown in Figure 10 and Figure 11,
respectively. The power was 60 W, the coolant was water at 11^o^C and
the flow rate 20 cc/sec. No significant change in thermal performance
was observed. Similar results were obtained with prototype #6, cycled to
5 bar absolute 140 times without heaters attached.

Sealed tube results here\....

+----------------------------------+-----------------------------------+
| ![](media/image9.jp              | ![](media/image10.                |
| eg){width="3.1993055555555556in" | jpeg){width="3.277083333333333in" |
| height="2.6902777777777778in"}   | height="2.686111111111111in"}     |
|                                  |                                   |
| Figure 10. Aluminum-tube         | Figure 11. Aluminum-tube          |
| prototype #4 before pressure     | prototype #4 after pressure       |
| cycling(see text).               | cycling(see text).                |
+----------------------------------+-----------------------------------+

#### After Irradiation

The thermal performance of aluminum-tube prototype sector #3 was
measured before and after irradiation with a Co^60^ source to 22 MRad.
The before and after comparison is shown in Figure 12 and Figure 13,
respectively. The power level was 36 W, the coolant was water at 23^o^C
and the flow rate was 15(after) and 17(before) cc/sec. The temperature
differential between the bulk coolant temperature and the silicon heater
surface was the same within about 1^o^C, and even this small difference
can be attributed to slightly different flow conditions. Thus there was
no evidence of effects from radiation at 22 MRad.

Irradiation of test pieces that simulate one-third of an aluminum-tube
sector are\.....insert results if available otherwise underway. Similar
tests on sample pieces of the sealed-carbon-carbon tube are also
underway.

+-----------------------------------+-----------------------------------+
| ![](media/image11.                | ![](media/image12.                |
| png){width="3.1743055555555557in" | png){width="3.1743055555555557in" |
| height="1.9965277777777777in"}    | height="1.9965277777777777in"}    |
|                                   |                                   |
| Figure 12. Before 22 MRad         | Figure 13. After 22 MRad          |
| irradiation.                      | irradiation.                      |
+-----------------------------------+-----------------------------------+

#### After Transient and Fault Conditions

![](media/image13.jpeg){width="2.9993055555555554in"
height="1.8888888888888888in"}

Figure 14. Aluminum-tube prototype #4 after pressure conditions
described in the text.

Thermal measurements on aluminum-tube prototype #6 were made after
cycling to 7 bar absolute without heaters attached. This followed the
cycling to 5 bar absolute described previously. The thermal performance
of this prototype met requirements, as can be seen in Error: Reference
source not found. The power level was 50 W, the coolant was
water/methanol at 11^o^C and the flow rate 10/cc/sec.

Measurement have not yet been done at 8 bar absolute, the recently
established single fault maximum pressure. Measurements to simulate
no-flow conditions also have not yet been done.

#### Measurements with Evaporative Cooling

![](media/image14.png){width="2.1041666666666665in"
height="2.875in"}~4~F~10~ but with a design configuration corresponding
to an obsolete disk layout - see Figure 16. A direct comparison to
measurements using water/methanol was made. These measurements were made
about one year ago. A good correlation was observed between the thermal
performance using water/methanol at the exhaust temperature used in the
C~4~F~10~ measurements.

More here later\....

## Stability Performance

### Introduction

The stability performance of the disk sectors has been assessed by
performing thermal cycling measurements and pressure cycling
measurements. In each case the motion, primarily out-of-plane, of the
sectors has been measured. This has been done using optical targets
attached to the sectors and two types of optical coordinate measurement
machines. Each of these optical CMMs has an accuracy of approximately
0.002 mm(rms) in the plane of the sector faceplate and about 0.005
mm(rms) in the out-of-plane(Z) measurements. More precise measurements
of the Z motion has been done at Hytec, Inc using TV Holography, which
has an intrinsic accuracy of about 0.00025 mm in the Z coordinate. The
TV holographic technique has not been used so far for in-plane
measurements but is being adapted for this purpose.

### Test Samples and Single Sectors

Measurements have been done on a variety of single sectors and on a few
test samples that simulate the sector construction techniques.

#### Thermal Effects

#### Pressure Effects

#### Dynamic Motion

#### Transient and Fault Conditions

### Prototype Disk

## Material

The radiation length of a disk sector, averaged over the active region,
is desired to be 0.7% X~o~, assuming other requirements can be met. The
radiation length of aluminum-tube prototype sector #6, based on measured
weights, is summarized in Table 3. A number of fabrication options for
aluminum-tube sectors remain and the impact of these on the radiation
length, scaling from the measured weights of prototype #6, are given in
Table 4. The radiation length of the sealed carbon-carbon tube
sectors\...\...\...\...\.....(to be added).

Table 3 Radiation Length of Aluminum-tube Prototype Sector #6.

Table 4 Radiation Length of Options for Aluminum Tube Sectors.

## Miscellaneous 

## Summary of Status and Critical Outstanding Issues

# Work Plan

# Introduction

The critical outstanding issues for the barrel staves and disk sectors
have been identified above. We briefly summarize below our plan for
addressing these issues before a Production Readiness Review and the
corresponding schedules.

# Barrel Staves

# Disk Sectors

Bulletized list of critical items and short list of actions to be taken

Project \'98 schedule to go along with this.

[^1]: Overview of the ATLAS Pixel System - Final Design Review.

[^2]: ATLAS Pixel Local Support Requirements - Final Design Review.

[^3]: ATLAS Disk Sector Fabrication and Specifications - Final Design
    Review

[^4]: Energy Sciences Laboratory, Inc \...\...\...\...\...\...

[^5]: HYTEC, Inc, 110 Eastgate Dr., Los Alamos NM 87544.

[^6]: HYTEC-TN-DOE/SBIR-04, January 2000.

[^7]: Smaller test pieces for studies after irradiation were used
    because of size limitations of the Co^60^ source that was used in
    the irradiation.