> TD-02-017

05 /02

**CONCEPT OF THE FIRST VLHC PHOTON STOP CRYOGENIC DESIGN EXPERIMENT**

P. Bauer, C. Darve\*, K. Ewald, P. Limon, T. Nicol

Fermilab, Technical Division

\*Fermilab, Beams Division

As part of Fermilab's recent Very Large Hadron Collider (VLHC)
feasibility study, a water-cooled photon stop was proposed as a possible
device to intercept the intense synchrotron radiation in the high field
stage VLHC with minimal plug-power. The photon stop, if feasible,
promises not only significant savings in cooling power compared to a
solution in which the synchrotron radiation is extracted from a beam
screen at cryogenic temperatures, but also virtually removes the
synchrotron radiation limitation to beam energy and luminosity in a
future VLHC.

Among the technological challenges regarding photon stops is their
cryo-design. The photon stop is water-cooled and operates in a cryogenic
environment. A careful cryo-design is therefore essential to enable
operation at minimum heat transfer between the room temperature sections
and the cryogenic parts. A photon stop cryo-design was developed and is
being presented here. An experiment, presented in this note, is being
prepared that will allow verification of the thermal model and the
proposed cryo-design.

1)  **INTRODUCTION**

A very large hadron collider (VLHC) is being proposed as a possible
successor to the large hadron collider (LHC). The latest set of general
characteristics of the second stage of this machine, as recently studied
\[1\], is listed in Table 1. The second stage VLHC, referred to as VLHC2
in the ongoing text, will produce protons at energies more than 10 times
larger than the LHC. Unlike the first stage, the VLHC2 beams will emit
considerable synchrotron radiation power, when steered through the high
field magnets.

  ---------------------------------------------------- ----- ----------------
  Energy per proton E~p~ @ collision(TeV)                    87.5

  Gamma γ                                                    93284

  Peak luminosity L (cm^-2^s^-1^)                            2⋅10^34^

  Total circumference C (km)                                 233

  Arc bending radius ρ (km)                                  29.9

  Dipole field B @ collision (T)                             9.7

  Number of bunches N~b~                                     37152

  Initial Nr. of protons per bunch N~p/b~                    7.5⋅10^9^

  Initial beam current I~b~ (mA)                             57.4

  Bunch spacing t~b~ (ns)                                    18.8

  Radiation damping time τ~R~ (hrs)                    2.5   

  Revolution frequency f~0~ (Hz)                             1286

  Normal. (round) beam emittance ε~N~ @ collis. (rms)        0.08⋅π
  (mm-mrad)                                                  
  ---------------------------------------------------- ----- ----------------

Table 1: VLHC2 machine parameters \[1\].

The synchrotron radiation power radiated by the stage 2 beam, calculated
with the parameters of Table 1, is listed in Table 2 together with the
other synchrotron radiation characteristics. A more detailed description
of the calculations is given in \[2\],\[3\]. The synchrotron radiation
power in this particular VLHC2 scenario amounts to \~5 W/m per beam.

  ------------------------------------------------------------ ------------
  Synchrotron radiation power per m, per beam (W/m)            4.7

  Critical energy E~crit~ (keV)                                8.03

  Number of incident photons per meter Γ (m^-1^s^-1^)          1.2⋅10^16^

  Incidence angle of synchrotron radiation (mrad)              1.31

  Azimuthal (rms) width of synchr. rad. strip on beam tube /   0.5
  photon stop\* (mm)                                           

  Radial (rms) width of synchr. rad. strip on the photon       10
  stop\* (mm)                                                  
  ------------------------------------------------------------ ------------

Table 2: Synchrotron radiation parameters in the VLHC2. \*Calculated for
14 m long magnets and 3 m long magnet inter-connects.

The synchrotron radiation power in the VLHC2, with the operational
parameters listed in Table 1, is \~50 times larger than in the case of
the LHC. The cost at the plug for removing this synchrotron radiation
heat load from low temperature surfaces is considerable. A more detailed
discussion of the cooling issues is given in \[4\], \[5\], \[6\]. The
plug power requirement for extracting the synchrotron radiation heat
load can be significantly reduced by photon stops operating at room
temperature. Photon stops (Figure 1) are water-cooled absorbers that
protrude into the beam tube at the end of each bending magnet and scrape
off the synchrotron light beam emitted in the second magnet up-stream
from their location. Radiation fan geometry and cooling requirements
demand a certain minimum photon stop surface area \[7\]. To increase the
cooling surface area and reduce reflectivity, the absorber uses a
wedge-shaped cavity to trap the synchrotron radiation light beam. The
synchrotron radiation power deposited on the photon stop in a VLHC2 is
of the order of 100 W. The shape of the photon stop mainly responds to
stipulations regarding its impedance. A detailed discussion of the
impedance related implications of the photon stop and the results of
numerical impedance calculations are reported elsewhere \[8\]. The
general implications of photon stops for VLHC's are discussed in \[9\].
A first photon stop prototype was designed and manufactured (Figure 1).

![](media/image3.jpeg){width="2.4930555555555554in"
height="2.077777777777778in"}![](media/image4.jpeg){width="2.9125in"
height="2.064583333333333in"}![](media/image5.jpeg){width="2.522222222222222in"
height="2.14375in"}![](media/image6.jpeg){width="2.5965277777777778in"
height="1.8166666666666667in"}

Figure 1: Conceptual design of the VLHC photon stop: illustration of
assembly in magnet interconnect (upper left), cryo-module assembly
(upper right), close-up on absorber in beam tube (lower left),
endpiece - absorber (lower right).

Figure 1 shows a conceptual sketch of a complete photon stop assembly in
the accelerator magnet interconnect. A beam screen and the outer
cryostat jacket are shown. The photon stop insert, i.e. the part
containing the cooling pipes and the radiation absorber, is at room
temperature or above, while the environment is at cold-mass (\~4.5 K) or
beam screen (\~100 K) temperatures. The absorber enters the beam screen
through a rectangular hole from the side. To limit the thermal
interference and thus minimize thermal losses, an optimal
cryo-engineering design is crucial. To test the cryo-design, experiments
should be conducted in a magnet interconnect mock-up, consisting of a
vacuum vessel, a 4.2 K bore and a tube cooled by a helical LN~2~ heat
exchanger representing the high temperature beam-screen. The complete
photon-stop cryo-assembly will be mounted into the vacuum vessel in the
same way it would be in the magnet interconnect cryostat in an
accelerator. The heat transfer between the cold tube and the warm photon
stop, i.e. the thermal loss rate, can be measured with an array of
temperature sensors, mounted on various sections of the photon stop and
via a measurement of the cryogen boil-off rates. The synchrotron
radiation heating will be simulated with an electrical heater mounted to
the tip of the photon stop. This experiment would as well allow us to
investigate the risk of freezing in the cooling water lines in the
absence of synchrotron radiation heating. The cryo-design, the
cryo-design calculations and the concept of a first cryo-test of the
photon stop prototype will be discussed next.

2)  **PHOTON STOP / BEAM SCREEN ASSEMBLY DESIGN FOR CRYO-TEST**

*2.1) Introduction*

A first pass engineering design of the photon stop for the VLHC study
was presented in \[7\]. The design has evolved since to address some key
issues such as vacuum and HOM trapping. One of the major new elements of
the design was the introduction of an intermediate, so-called inner
shield (\~80 K) to thermally shield the 4.2 K environment from the room
temperature parts of the photon stop. Another major design change is
that the design assumes a large cold bore OD (\~80 mm), which is \~2
times the VLHC2 coil aperture. This design change considerably
facilitates the cryo-assembly, because the outer shield can be welded
directly to the cold-bore tube with no need for diameter-adaptors.
Figure 2 shows a cut through the photon stop cryo assembly model. The
cryo assembly consists of the water cooled radiation absorber in the
center, surrounded by an inner and an outer shield. The cryo-assembly as
well includes a 60" long dummy beam screen / cold bore section. The 1.5"
∅ dummy beam screen is cooled to \~80 K, while the cold bore is cooled
to \~4.5 K. The core of the photon-stop is inserted into the inner
thermal shield, which is made from a 1.5" ∅ tube, actively cooled to
\~80 K throughout the bottom half, and negotiating a temperature drop
from room temperature to \~80 K through a long bellows along its upper
portion. The lower, 80 K, part of the inner shield in turn is surrounded
by a 3"∅ outer shield, which, through a similar bellows, negotiates a
temperature drop from \~80 K at its top to \~4.5 K at the bottom, where
it is welded to the 3"∅ cold bore.

To facilitate the temperature control the dummy beam screen and cold
bore tubes are made of copper. For the sake of simplicity, the inner and
outer shield tubes are made from copper as well. The bellows with their
flanges are made of stainless steel. The bellows are fixed to the shield
tubes through mixed steel/copper flanges. The photon stop insert is made
from copper entirely (except for the water tubes) and uses a simplified
design, consisting of a copper tube with a radiation absorber mock-up
welded to its end. Other simplifying design elements, that would not be
permissible in a real accelerator setting, is the use of mixed material
flanges (not vacuum tight) and a water to vacuum weld at the photon stop
tip. The former would not be an issue in a real accelerator setting in
which all parts would be made from steel. The latter can easily be
avoided. A detailed view of the center of the photon stop cryo-test
assembly is shown in Figure 3.

![](media/image7.wmf)

Figure 2: Cut through photon stop cryo-test assembly.

![](media/image8.wmf)

Figure 3: Cross-section through photon stop assembly for cryo-testing,
detail.

*2.1) Absorber*

![](media/image9.jpeg){width="2.1222222222222222in"
height="3.5208333333333335in"}Unlike an accelerator compatible photon
stop design, the cryo-test photon stop will be simpler because of
reduced concern regarding possible water leaks. The absorber insert,
shown in Figure 4, consists of a 1.25" ∅, 19.75" long copper tube,
welded at one end to the absorber and at the other end to a disc with
two holes for the 0.5" ∅ stainless steel water tubes (0.03" wall
thickness). The brazing between the copper tube and the bottom absorber
would not be permissible in a real accelerator setting. At the top the
copper tube is closed up by a disc, containing two holes for the water
tubes. The stainless steel disc will be gold-brazed to the copper tube.
In addition, the simplified cryo-test version of the absorber does not
include a cavity to reduce reflectivity. Three press-fitted G10-pins,
placed at 120 degrees around the bottom of the absorber will serve to
center the absorber within the inner shield tube with minimum heat
transfer. The pins are not shown in Figure 4.

![](media/image10.jpeg){width="2.167361111111111in"
height="3.8805555555555555in"}*2.2) Inner Shield*

The photon stop thermal shield (so called "inner shield") has to
negotiate a temperature drop from ambient to 100 K (or less) and absorb
the thermal radiation from the 300 K insert in its core. To shield the
cryogenic environment from the room temperature radiation, the shield is
assembled around the water cooled photon stop insert. Figure 5 shows a
sketch of the inner thermal shield. The shield consists of a 1.5" ∅
copper tube (wall thickness=0.03") with a brazed copper cooling spiral
as the lower part and a stainless steel bellows (with flanges) as the
top part, connected by a mixed steel/copper flange. At the bottom the
inner shield is welded to the 1.5" ∅ dummy beam screen. At the top end
the shield is at room temperature and bolted to the top flange of the
water-cooled photon stop. The upper part of the inner shield is not
surrounded by any outer shield. A 7.25" long stainless steel bellows
negotiates the temperature drop from ambient at the top to \~80 K in the
middle by increasing the thermal length. It also provides mechanical
flexibility and therefore facilitates assembly and system alignment. The
lower section of the inner shield is thermalized at the beam screen
temperature of \~80 K with a cooling spiral made from copper tubing. In
the cryo-test the spiral will contain LN~2~, whereas in a VLHC it would
contain GHe from the cold-mass thermal shield. The LN~2~ cooling system
enters the shield through the brazed copper flange and spirals down
along the inner shield tube. The cooling spiral is brazed to the inner
shield tube to improve the thermal contact. The spiral pitch is 0.75",
the copper cooling tube ∅ is 0.25" (0.03" wall thickness). The brazed
copper flange connects (and thus thermalizes) as well the inner shield
to the outer shield, which ends in the 80 K mid-section. At the bottom
the inner shield tube passes through a hole in the cold-bore tube and is
welded to the 1.5" ∅ dummy beam screen. In the cryo-test assembly the
inner shield cooling spiral does not wind around the beam-screen.
Instead, a separate LN~2~ cooling tube is brazed to the beam screen tube
from the inside (see Figure 7).

*2.3) Outer Shield*

![](media/image11.jpeg){width="2.0006944444444446in"
height="2.8055555555555554in"}∅ copper tube, stainless steel flanges and
a stainless steel bellows. It is bolted to the copper flange on top and
is welded to the cold bore at the bottom. This copper flange is welded
to the inner shield. A 7.25" long stainless steel bellows negotiates the
temperature drop from \~80 K at one end to the cold-bore temperature
(\~4.5 K) at the other end. To prevent a copper/steel weld the steel
bellows is fixed at the top and bottom via flanges. At the top the
bellows are bolted to the inner shield copper flange, which in turn is
welded to the inner shield. This flange is as well crossed by the LN~2~
tubing for the inner shield cooling. In the cryo-test assembly the cold
bore tube OD is 3", such that a straight-forward brazing between outer
shield and the dummy cold bore tube is possible.

*2.4) Beam-Screen Assembly*

The 60" long dummy beam screen (copper) tube (1.5" ∅) is inserted into
the dummy cold-bore (copper) tube (3" ∅), supported with G10 spiders at
both extremities. A schematic of the beam-screen assembly is shown in
Figure 7. The spider is shown separately in Figure 8. The cold-bore tube
is cooled from the outside by a 0.75" pitch, 0.25" ∅ cooling tube spiral
with LHe flow. In the cryo-test assembly the inner tube (beam screen) is
maintained at LN~2~ temperature with a copper cooling duct welded to it
along its entire length. The spider, which is a critical part of the
cryo-design, is the only mechanical connection between the 80 K and 4.2
K systems.

![](media/image12.jpeg){width="3.30625in"
height="1.8993055555555556in"}One spider of the type shown in Figure 8
will be installed at each extremity of the dummy beam screen assembly.
As will be shown in part 3), thermal model calculations indicate that a
spider of the type shown in Figure 8 restricts the 80 K to 4.2 K heat
flux to less than 0.43 W. The spider thickness is 0.1875", the three
contact pins are 0.125" (0.3"?) wide.

*2.5) Test Cryostat*

![](media/image13.jpeg){width="1.75in" height="1.75in"}~2~ and cooling
water circuits are not explicitly shown. The helium transfer lines enter
the cryostat through the top access window. Water and LN~2~ circuits
enter through the small side-ports in the middle of the cryostat. The
cryogens as well as the water will be directed to the connection ports
on the photon stop / beam screen assembly with copper tubing. VCO
fittings will be used to connect the tubes to the ports. The pipes
within the cryostat will be equipped with union fittings in order to
facilitate the assembly and disassembly of the system. The wiring of the
temperature sensors and heaters will be routed through the lateral
windows in the cryostat mid-section. The LHe will be provided from
dewars. A flow diagram is given in Figure 13.

*2.6) Photon Stop Cryo-Test Assembly Procedure*

![](media/image15.jpeg){width="5.9944444444444445in"
height="5.518055555555556in"}

Figure 11: Schematic showing how photon stop is assembled into cryostat
thermal shield.

The photon stop assembly could be installed into the cryostat described
in 2.5. The total weight of the assembly is approximately 25 kg. After
soldering the cooling spiral to the cold bore tube and the straight
cooling tube to the beam screen tube, the dummy beam screen is slid into
the cold bore and supported with the G10 spiders in the ends (Figure 7).
Then, the inner shield is assembled, that is, the copper flange and the
cooling spiral are brazed to the inner shield tube. Before welding of
the shield assembly to the dummy beam screen assembly, the outer shield
(bellows) is bolted to the copper flange. Retracting the outer shield
bellows, the inner shield can then be welded to the beam screen through
the hole in the cold-bore tube. The next step consists in welding the
outer shield to the cold-bore tube. Next, the beam screen / cold bore --
inner / outer shield assembly is placed into the cryostat (Figure 11)
and positioned with the large G10 spiders shown in Figure 12. The top
part (bellows) of the inner shield can then be attached to the
mid-section flange on the inner shield through the top access window of
the cryostat

![](media/image16.jpeg){width="5.991666666666666in"
height="4.085416666666666in"}

Figure 12: Schematic of photon stop cryo-test assembly in cryostat
thermal shield.

(Figure 11). The photon stop insert is introduced into the inner shield
and the inner shield bellows is bolted to the insert top flange. The top
spider, which prevents the photon stop from tilting, is bolted to the
top flange as well. The plumbing for the different cooling circuits
(LHe, LN~2~, H~2~O) is then connected with flexible tubing. Finally the
vacuum tight top-flange ("dome") and the side and end caps are put in
place to seal the vacuum vessel.

3)  **MODEL CALCULATIONS**

*3.1) Introduction*

The theoretical model allows to specify the thermo-mechanical design of
the photon stop, to limit the heat load to the 4.5 K (dummy cold bore)
and 77 K (shielding) temperature levels. In addition, the model allows
to simulate dynamical conditions by adding heat loads and computing the
ensuing changes of temperature. The model was used to support the design
presented in 2). The theoretical model will be completed and validated
during the experiment, which will provide temperature measurements in
static and dynamic heat load conditions. Table 1 summarizes the photon
stop design parameters and temperatures.

  ------------------------------------------------------- ---------------
  Temperature of the dummy cold bore (K)                  5

  Temperature of the dummy beam screen (K)                80

  Temperature of the dummy (absorber) photon-stop (K)     300-350

  Temperature of photon stop, inner shield (K)            80-300

  Temperature of photon stop, outer shield (K)            5-80

  Length of the vacuum vessel, dummy beam screen and cold 60
  bore (in)                                               

  Length of the bellows (in) (thermal length is twice     7.5
  longer)                                                 

  Total length of the photon stop inner shield (in)       12.75

  Total length of the photon stop outer shield (in)       8.5 (to check)

  Length of the photon stop-absorber insert (in)          19.75
  ------------------------------------------------------- ---------------

Table 3: Summary of the design parameters and temperatures.

The vacuum is estimated to 10^-4^ Pa. Materials considered are copper
and stainless steel, their thermal and mechanical properties are taken
from literature \[10\].

*3.2) The LN~2~ Temperature Level*

There are three major components operating at LN~2~ temperature in the
photon-stop cryo-test set-up: the cryostat thermal shield, the photon
stop inner shield and the dummy beam-screen. The cryostat thermal shield
is mainly receiving thermal radiation from the outer, room temperature
walls of the cryo vacuum-vessel. The photon stop inner shield absorbs
mostly the thermal radiation from the water cooled, room temperature
photon stop insert. The dummy beam screen absorbs some radiation from
the \~350 K photon stop tip, where the synchrotron radiation heat load
is absorbed (simulated by a heater in the cryo-test).

The vacuum vessel thermal shield consists of a copper shield, cooled
with a LN~2~ spiral and surrounded by a wrap of 30 layers of MLI.
Radiation and conduction into residual gas need to be estimated. The
conditions were similar in the LHC main magnet cryostat thermal model,
therefore the calculation takes into account results of measurements
performed on the LHC main magnet cryostat at CERN, \[11\]. Equation (1)
relates the contribution of radiation and residual gas conduction to the
heat load from room temperature to the 80 K cryostat thermal shield.

$Q = A\left\lbrack a\left( \frac{T_{v}^{2} - T_{\text{ts}}^{2}}{2} \right) + b\left( T_{v}^{4} - T_{\text{ts}}^{4} \right) \right\rbrack$
(1)

where a=4.7⋅10^-6^ W/m^2^/K^2^ and b= 1.25⋅10^-10^ W/m^2^/K^4^.

T~v~ and T~ts~ are the temperatures of the vacuum vessel (300 K) and the
thermal shield (\~80 K) respectively. The heat load calculated from the
ambient to the cryostat thermal shield is 2.8 Watt (if we would consider
no MLI wrap it would be 64.3 Watt).

The photon stop inner shield absorbs the thermal radiation from the
water cooled, room temperature photon stop insert. The radiation heat
load can be calculated from the Stefan-Boltzmann law
(σ=5.67⋅10^-8^W/m^2^/K^4^) (2):

$Q = e\sigma S\left( T_{\text{ps}}^{4} - T_{\text{psts}}^{4} \right)$
(2)

With, e the emissivity and S the surface of the emitting object. The
heat load on the inner shield due to the radiation from the photon stop
insert is 3.6 W.

The photon stop insert is not free-floating within the inner shields,
rather it is spread from the shield through a guiding support consisting
of three G10 pins, 2 mm in diameter, press-fitted into the nose-piece
(at the bottom) of the photon stop insert. The annular gap between the
insert and the inner shield is 1.65 mm. The heat load via conduction
from the absorber to the inner shield is less than 1 W.

The conduction heat load through the inner shield top bellows (7.25"
length, 0.03" wall thickness, thermal length enhancement factor 2) from
ambient to the 80 K level is only 60 mW.

The radiation heat load from ambient to the beam screen tip is
negligible given the small emitting surface area.

The total static heat load on the LN~2~ system is thus expected to be
\~4.61 W.

*3.3) The LHe Temperature Level*

The photon stop cryo-test design uses a tube with a LH~2~ cooling spiral
to simulate the magnet cold-bore. The heat loads by radiation from the
80 K cryostat thermal shield and the \~ 80 K dummy beam screen to the
cold bore, calculated with Stefan-Boltzmann, are 75 and 25 mW,
respectively. The radiative heat transfer from the vacuum vessel axial
end-cap is less then 0.2 W.

The largest heat load to the LH~2~ system is a result of conduction from
a) the dummy beam screen and outer shield to the cold bore via the
support spiders shown in Figure 8 and b) the photon stop outer shield
bellows. The heat load by conduction is calculated with the Fourier
equation:

$Q = \int_{T_{\text{cold}}}^{T_{\text{warm}}}{k_{G\text{10}}(T)\text{dT}\frac{A}{L}}$
(3)

where A and L are the cross-sectional area and thermal length of the
heat transfer element (the G10 spider or stainless steel bellows). The
ratio of G10 / steel thermal conductivity assumed is 3.5 at 5 K, \[10\].

The thermal length and the cross-sectional area of the G10 spider were
optimized in order to limit the conduction. The objective was to limit
the heat load to less then 0.3 W. The thickness / width of the spider
support therefore is 0.1875 mm / 0.33 mm. In order to limit the
conduction from the photon stop inner thermal shield to the dummy cold
bore through the outer shield stainless steel bellows (and copper
"adaptor"), the bellows thermal length / wall thickness was specified to
be 14.5" / 0.03" mm. This heat load can increase considerably in case
the middle flange is not at 80 K. If the bellows is at 300 K this heat
load can increase up to 1.2 W. The bellows heat load is thus reduced to
less than 0.15 W. Hence the 5 K dummy cold bore receives a total of less
than 1 W (less than 2.2 W in the worst case).

4)  **PHOTON STOP CRYO-TEST PLAN**

*4.1) Experimental Model and Instrumentation*

The goal of the test campaign are to 1) check the feasibility of the
current photon stop cryo design, 2) measure the contribution of the
different components to the system heat load, 3) validate the model used
to predict the heat loads for various conditions, 4) check the
distribution of the temperature at various points of interest. A flow
diagram for the cryogenic circuits is shown in Figure 13.

The heat load to the liquid helium and liquid nitrogen temperature
levels will be determined by the heater technique. This technique uses
the measurement of a temperature change along the cooling duct as a
result of a heater power Q~el~ applied to the cooling duct, according to
the heat balance equation (4).

$Q_{\text{el}} + Q_{0} = \overset{˙}{m}C_{p}\left( T_{\text{out}} - T_{\text{in}} \right)$
(4)

The linearity of this relation allows extrapolation to ∆T=0, in which
case the factor Q~0~, the static heat load can be determined. Various
accelerator load configurations are simulated by an electrical heater
mounted to the absorber tip. The heater technique will be used to
determine the resulting heat loads on each of the components for varying
heat load on the absorber.

The instrumentation (see flow diagram in Figure 13) is mainly composed
of Cernox and Platinum temperature sensors mounted with Stycast to the
piping (vacuum side). 4 Cernox are mounted at each extremity of the
copper cooling spiral of the dummy cold bore tube. Since this
measurement is of prime importance, the sensors are duplicated. In
addition, eight PT102 temperature sensors are mounted at each extremity
of the cooling system of the photon stop thermal shield, cryostat
thermal shield and dummy beam screen and photon stop insert (water
circuit). To improve the accuracy of the measurement a flow-meter will
be provided for the LHe circuit.

Heaters are made of Nickel wiring encapsulated in Kapton foils. They are
fixed with STYCAST to the LHe and LN~2~ piping loops, on the vacuum
side. Appropriate heaters are located along the dummy beam screen and at
the absorber extremity. A specific attention is driven by the contact
between the heater and the piping. Heaters are located also around and
in the water loop in order to prevent freezing.

Pressure transducers are available in the A0 North LHe supply system.

The wires of each sensor which are located in the vacuum space are
routed to the lateral exit ports of the cryostat. Maganin wires are
preferred in order to limit the load to the sensors and cold media. The
thermometry technique and the 19-pins connectors are similar to these
used for LHC thermal model \[13\]. The connectors are welded to the
flanges and transfer the signal to the DAQ system. The instrumentation
measurement are read-out with a scanner / multimeter system available at
the TD. An existing Labview program can be modified for the DAQ.

A tentative program could be:

1.  Installation and commissioning of the cryo-test and DAQ

2.  Measurement of the A0 North cave (or other test stand) capacity

3.  Measurements of the static heat leaks and temperature distribution

4.  Measurements of effect of heating on photon stop tip

![](media/image17.wmf){width="5.979861111111111in"
height="3.272222222222222in"}

Figure 13: Flow schematic and connection flanges for cryogenic fluid
circuits.

*4.2) Schedule*

The schedule is partially constrained by the necessity to free the test
cryostat before fall 2002. Therefore the test campaigns are planned for
summer 2002. The design and update of the test cryostat, is estimated to
take one month. The procurement, production and assembly of the cryo
design component will have to be completed within 2 months. Drawings can
be finalized in 2-3 weeks. The installation and the test itself will be
conducted in the A0 North cave facility, if possible.

*4.3) Cost Estimate*

Estimated Total \~ \$ 8,500 (not including assembly labor).

Table 4: Cost estimate for photon stop cryo-experiment.

+---+-----------------------------------------------+------+-----+-----+
| \ | Item Description                              | Pr   | Qty | Pr  |
| # |                                               | ice/ |     | ice |
|   |                                               | Qty  |     | to  |
|   |                                               | (\$) |     | tal |
|   |                                               |      |     | (   |
|   |                                               |      |     | \$) |
+---+-----------------------------------------------+------+-----+-----+
|   | **Mechanical**                                |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 1 | ¼" copper tubing for heat exchanger (80 ft    | 0.   | 200 | 100 |
|   | min) and piping (80 ft min)                   | 5/ft | ft  |     |
+---+-----------------------------------------------+------+-----+-----+
| 2 | ½" stainless steel tubing for water pipes (80 | 0.2  | 80  | 1   |
|   | ft min)                                       | 3/ft | ft  | 8.4 |
+---+-----------------------------------------------+------+-----+-----+
| 3 | 1,5" copper tube, inner shield, dummy beam    |      | 10  | 200 |
|   | screen                                        |      | ft  |     |
+---+-----------------------------------------------+------+-----+-----+
| 4 | 3" copper tubing, outer shield, dummy cold    |      | 10  | 250 |
|   | bore                                          |      | ft  |     |
+---+-----------------------------------------------+------+-----+-----+
| 5 | 1¼" copper tubing, photon stop insert         |      | X   | 100 |
|   |                                               |      | ft  |     |
+---+-----------------------------------------------+------+-----+-----+
| 6 | 1¼" solid copper billet                       |      | X   | 50  |
|   |                                               |      | ft  |     |
+---+-----------------------------------------------+------+-----+-----+
| 7 | 1½" ∅ bellows (7.5" long) with 2.75/4"        |      | 1   | 300 |
|   | flanges bottom/top, how-about MDC ?           |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 8 | 3" ∅ bellows (7.5" long) with 4" flanges      |      | 1   | 400 |
|   | top/bottom how-about MDC ?                    |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 9 | 4" ∅ copper billet for 3 flanges, (outer      | ?    | 1   | 50  |
|   | shield - bottom & top, insert - top)          |      | .5" |     |
+---+-----------------------------------------------+------+-----+-----+
| 1 | 2.75" ∅ copper billet for inner shield        | ?    | 5   | 50  |
| 0 | mid-section flange                            |      | /8" |     |
+---+-----------------------------------------------+------+-----+-----+
| 1 | G10 for 3 large spiders, ¼" thick, 14" ∅      |      | 3   | 50  |
| 1 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 1 | G10 for 2 small spiders, 3/16" thick, 3" ∅    |      | 2   | 10  |
| 1 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 1 | Water flange, 6" OD, with H~2~O 2-way         | 80   | 1   | 100 |
| 2 | feed-through,                                 |      |     |     |
|   |                                               |      |     |     |
|   | 2x19 wires feed-through                       |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 1 | LN~2~ flange, 6" OD, with LN~2~ 2-way         | 80   | 1   | 100 |
| 3 | feed-through, 2x19 wires feed-through         |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 1 | Bulkhead SS-4-VCO-61 LN~2~-loop               | 11.5 | 4   | 46  |
| 4 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 1 | Socket weld gland SS-4-VCO-3 LN~2~-loop       | 1    | 15  | 15  |
| 5 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 1 | Gasket SS-4-VCO-2 GR LN~2~-loop               | 1    | 15  | 15  |
| 6 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 1 | SS nut SS-4-VCO-1 LN~2~-loop                  | 4    | 4   | 16  |
| 7 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 1 | Union Gasket SS-4-VCO-2 GR LN~2~-loop         | 1    | 15  | 15  |
| 8 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 1 | Union SS nut SS-4-VCO-4 LN~2~-loop            | 5    | 4   | 20  |
| 9 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 2 | Union body socket weld conn. SS-4-VCO-1       | 5    | 8   | 41  |
| 0 | LN~2~-loop                                    |      | .25 |     |
+---+-----------------------------------------------+------+-----+-----+
| 2 | Bulkhead SS-8-VCO-61 H~2~O-loop               | 11.5 | 4   | 46  |
| 1 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 2 | Socket weld gland SS-8-VCO-3 H~2~O loop       | 1    | 15  | 15  |
| 2 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 2 | Gasket SS-8-VCO-2 GR H~2~O loop               | 1    | 15  | 15  |
| 3 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 2 | SS nut SS-8-VCO-1 H~2~O-loop                  | 4    | 4   | 16  |
| 4 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 2 | Union Gasket SS-8-VCO-2 GR H~2~O loop         | 4    | 1   | 4   |
| 5 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 2 | Union SS nut SS-8-VCO-4 H~2~O loop            | 2    | 4   | 8   |
| 6 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 2 | Union body socket weld conn. SS-8-VCO-1 H~2~O | 2    | 8   | 16  |
| 7 | loop                                          |      | .25 |     |
+---+-----------------------------------------------+------+-----+-----+
| 2 | Bulkhead SS-8-VCR-61 LHe-loop                 | 11.5 | 2   | 23  |
| 8 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 2 | Socket weld gland SS-4-VCR-3 LHe-loop         | 1    | 4   | 4   |
| 9 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 3 | Gasket SS-4-VCR GR LHe loop                   | 1    | 4   | 4   |
| 0 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 3 | SS nut SS-4-VCR-1 LHe-loop                    | 2    | 4   | 8   |
| 1 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 3 | Union Gasket SS-4-VCR-2 GR LHe-loop           | 4    | 1   | 4   |
| 2 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 3 | Union SS nut SS-4-VCR-4 LHe loop              | 2    | 4   | 8   |
| 3 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 3 | Union body socket weld conn. SS-4-VCR-1 LHe   | 2    | 8   | 16  |
| 4 | loop                                          |      | .25 |     |
+---+-----------------------------------------------+------+-----+-----+
| 3 | SS Flange for return adaptor OD 2 3/16 LHe    | 1    | 16  | 16  |
| 5 | loop                                          |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 3 | 1½" OD, #810-61 Bulkhead Union                | 12   | 2   | 24  |
| 6 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 3 | 1¼" OD, #401-PC Port Connector                | 4    | 20  | 80  |
| 7 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 3 | 1½" OD, #811-PC Port Connector                | 4    | 20  | 80  |
| 8 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 3 | 1¼" OD, #400-6 Union                          | 0.83 | 10  | 83  |
| 9 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 4 | 1½" OD, #810-6 Union                          | 0.83 | 10  | 83  |
| 0 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 4 | ¼" tubing strap #9434T13                      | 1    | 20  | 20  |
| 1 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 4 | ½" Screw socket, #6-32 to bolt flanges,       | 0.25 | 20  | 5   |
| 2 | enough?                                       |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 4 | Screw socket MA-364149 M3x6mm, R.H.M.S.       | 0.2  | 20  | 10  |
| 3 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 4 | Screw socket HD SS #6-32 x 0.5"               | 0.25 | 20  | 5   |
| 4 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
|   | Sum Mechanical                                |      |     | 2   |
|   |                                               |      |     | 470 |
+---+-----------------------------------------------+------+-----+-----+
|   | **Labor (\$ 70/hr)**                          |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 4 | Photon Stop insert                            | 70   | 4   | 280 |
| 5 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 4 | G10 Spiders                                   | 70   | 6   | 420 |
| 6 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 4 | Beam Screen                                   | 70   | 3   | 210 |
| 7 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 4 | Cold Bore                                     | 70   | 1   | 70  |
| 8 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 4 | Heat Exchangers                               | 70   | 4   | 280 |
| 9 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 5 | ½" stainless steel tubing ????                | 70   | 2   | 140 |
| 0 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 5 | Cu Flanges                                    | 70   | 10  | 700 |
| 1 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 5 | Plumbing                                      | 70   | 7   | 500 |
| 2 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 5 | Welding                                       | 70   | 12  | 840 |
| 3 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
|   | Sum Labor                                     |      |     | 3   |
|   |                                               |      |     | 430 |
+---+-----------------------------------------------+------+-----+-----+
|   | **Instrumentation**                           |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 5 | PT102, temperature sensor                     | 72   | 8   | 576 |
| 4 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 5 | CX-1050-SD, temperature sensor                | 156  | 4   | 624 |
| 5 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 5 | Stycast 2850 FT                               | 165  | 2   | 330 |
| 6 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 5 | 150 Watt Heater                               | 29   | 7   | 203 |
| 7 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 5 | Manganin wire                                 | 1/ft | 20  | 20  |
| 8 |                                               |      | ft  |     |
+---+-----------------------------------------------+------+-----+-----+
| 5 | Connectors, 19 pin female                     | 19   | 4   | 76  |
| 9 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 6 | Connectors, 19 pin male                       | 19   | 4   | 76  |
| 0 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 6 | O-rings #2-021                                | 0.2  | 20  | 10  |
| 1 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
| 6 | Doppler flowmeter                             | 600  | 1   | 600 |
| 2 |                                               |      |     |     |
+---+-----------------------------------------------+------+-----+-----+
|   | Sum Instrumentation                           |      |     | 2   |
|   |                                               |      |     | 540 |
+---+-----------------------------------------------+------+-----+-----+

**References:**

\[1\] P. Limon et al., "*Design Study for a Staged Very Large Hadron
Collider*", Fermilab-TM-2149, June 2001.

\[2\] M. Pivi, W.C. Turner, P. Bauer, P. Limon, "*Synchrotron Radiation
and Beam Tube Vacuum in a Very Large Hadron Collider, Stage 1 and Stage
2*", Proceedings to the Particle Accelerator Conference 2001, Chicago,
Sept. 2001

\[3\] P. Bauer et al., "*Synchrotron Radiation Issues in the VLHC*",
Proceedings to the Particle Accelerator Conference 2001, Chicago, Sept.
2001

\[4\] P. Bauer, C. Darve, I. Terechkine, "*Synchrotron Radiation Issues
in Future Hadron Colliders*", to be published in the proceedings of the
2001 Particle Physics conference at Snowmass

\[5\] P. Bauer, C. Darve, I. Terechkine, "*Synchrotron Radiation Issues
in Future Hadron Colliders*", Summary of the contributions to the T2 WG
at the Snowmass 2001 conference, Fermilab, Technical Division note
TD-01-061, August 2001

\[6\] C. Darve et al: "*VLHC beam-screen cooling*", Fermilab, Technical
Division Note TD-01-005, Feb. 2001

\[7\] P. Bauer et al. "*A Photon Stop for the VLHC-2, Engineering Design
1*", Fermilab, Technical Division note, TD-01-023, April 2001

\[8\] N. Solyak, "*Photon stop for the VLHC-2 -- Impedance
Calculations*", Fermilab, Technical Division Note TD-01-014

\[9\] P. Bauer et al., "*Accelerator Physics and Technology Limitations
in Stage II -- type Very Large Hadron Colliders*", Summary of the
contributions to the M4 WG at the Snowmass 2001 conference, Fermilab,
Technical Division note, TD-01-062, October 2001

\[10\] Institute International du Froid / IIR, "*Les techniques de
l'ingenieur*".

\[11\] C. Darve et al, "*Thermal performance measurements for a 10 meter
LHC dipole prototype (Cryostat Thermal Model 2)"*, CERN,
LHC-Project-Note-112, November 1997.

\[12\] C. Darve et al, "*Measurements of temperature on LHC thermal
models*", Cryogenics Vol 41, Issues 5-6.