IR Vacuum Chamber and Assembly

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The 16th KEKB Accelerator Review Committee, KEK, 7-9 February 2011
Ken-ichi Kanazawa
KEKB Vacuum GroupIR Technical Meeting Member
IR Installation Meeting Member
SVD/IR Mechanics Meeting Member

Contents
1. Beam Pipes in the Cryostat
Overview – Aperture – BPM – Pumping and Cooling – Connection to the IP
Chamber – Summary

2. IP Chamber
Design Features of the inner shape – Cut View - Central Part – Ridge – Loss factor– Longitudinal Wake Potential – Stress Analysis – Summary

3. Installation
Overview – Structure of SVD4 – Stress Analysis of SVD4 – Basic Steps – Step 1 –Step 2 – Summary

1. Beam Pipes in the CryostatOverview
Beam pipes are part of the cryostat.
Two kinds of beam pope will be manufactured.
• Dummy beam pipe for the magnetic field measurement：Stainless steel, 2-3 mm thick.
• Beam pipe for machine operation: Ta is suggested, 4mm thick except BPM• NEG coating (Inside, Ti-Zr-V, Thickness: 1µm, Activation temperature: 150-180℃)• BPM• Cooling channel, heater (for NEG activation), thermosensor.

Beam pipes are fixed tothe cryostat.

• Pick-ups for BPM are screwed
after the beam pipes are inserted
into the cryostat using service
ports.
• Leaf support• Rooting of signal cables• Beam pipes and the cryostat body is intervened
with bellows.
• Cooling pipes, heater, thermosensor will be fed
through the end flange.

1. Beam Pipes in the Cryostat
Aperture
Recently proposed aperture
Aperture requirement
appeared this January
Aperture assumed till the endof 2010. (The beam loss
simulation by Ohnishi used
this aperture.)

The aperture of thebeam pipe will bedetermined fromthe beam stayclear, the beamloss acceptable tothe detector, andmechanical designof the cryostat.
Not fixed yet.

1. Beam Pipes in the Cryostat
BPM• The thick part of thebeam pipe to screw BPM
pick-ups is available bymaking use of the aperture
difference before andbehind BPM.
• This part will besupported by a leaf
support.
Whether QCS design
allows these issues or not
is still under consideration.

1. Beam Pipes in the Cryostat
Pumping and Cooling
Example: QCSR

Beam pipe

In‐coming positronOut‐going electron

Major heat source

Direct SR from BL0RP: 1.4
Wall loss a): 0.8

Wall loss a): 0.4

kW

Temperature rise of 12water b)

2℃

Major gas source

Photo‐desorpHon: 0.13η

Thermal desorpHonPa m3Pressure c)~10‐6<10‐7Paa) For Tab) ~2.6 l min-1 with the velocity of 2 m sec-1c) Pumping speed of NEG ~ 10-4 Pa m3 (1cm2) and η = 10-5

At a pressure of 10-6 Pa, NEG will saturate within one day. High capacity coatingmust be studied.

1. Beam Pipes in the Cryostat
Connection to IP Chamber• IP chamber and the cryostat is connected withbellows chamber to absorb a possible motion of thecryostat after exciting magnetic fields.
• The bellows has a finger type rf-bridge to ensure
flexibility.
• The bellows is water-cooled on both ends.
• The bellows and BPM is integrated into a shortpipe. This makes it easy to replace them.
• The position of bellows is fixed to IP chamber.
The sealing mechanism on both ends of the pipe isdesigned using reduced number of screws. A model
chamber to test the sealing mechanism is now being
prepared.

BellowsCryostatbodyBeam pipein thecryostat

BPM“Neckstopper”

Summary for the Beam Pipes in the Cryostat•••••••

As material for the beam pipe, Ta is suggested at present from the view point of detector background.
The basic connecting structure to the cryostat on the IP side is fixed.
For the other side, a bellows is necessary. And feedthroughs for water, heater, and thermosensor must be incorporated. The design for this part will be proposed till the end of this fiscal
year.
To install pick-ups of BPM, accessibility from outside of the cryostat is necessary.
The possibility of leaf support and of increasing the bore of beam duct at the position of QC2E
must be feed backed from the cryostat design.
The manufacturing of Ta pipe and its high capacity NEG coating will be tested in FY 2011.
The connecting structure between the cryostat and IP chamber will be tested within this fiscal
year.
The application of NEG coating is criticized in the Domestic Review last month, because it is nota perfect solution. Recent studies require a larger aperture than before for the beam pipe. This maychange the condition for the design of pumping scheme.

2. IP Chamber
Design features of the inner shape
WL:85W

WL: 70W
SRQ: fewW

WL: 68W
SRQ:~50W
SRB: 100W

TaBe+ StainlessSteel

WL: 57W

WL: 97W
SRQ: ?W
SRB: 130W

Ta• Minimize the creation andthe trap of HOM.
• The pipe for incoming beam
start from ID20 mm. Then ID
is gradually reduced to about 9mm to mask SR.
• The central part is a ID20mm
straight pipe.
• The central part and thebranch for out going beam
constitute a bent pipe ofID20mm.
• The inner surface of a pipefor incoming beam has ridges
to prevent scattered light fromhitting the central part.
• All inner surface will becoated by 10~100mm thickAu.

2. IP Chamber
Cut View
Electron(Koike)

PositronDiaphragm to absorb
the change of thelength of Be pipes.

2. IP Chamber
CentralPart
Be double tube

• The central part of thecentral part is a Be double
tube. The gap is a space fora coolant.
• The coolant is paraffin.
The flow of paraffin canabsorb a heat of ~270W fora temperature rise of 10℃.
(Estimated heat load fromthe beam is less than 100W.)• Both ends of be double
tube are manifolds made ofstainless steal. Ta is attachedto stainless steal by HIP toconnect a branched part byEBW.
(Kohriki) • In this design, it ispermitted to put a weld
seam between paraffin andvacuum.

Mock-up model for cooling test

2. IP Chamber
Ridge

Thin wall around here cannot has aridge structure. However, scatteredphotons from this part enter thecentral pipe with a shallow angle
and give no serious effect.

A disk with adiameter of 24mm.
The position is thenearest end of aphoton production
region.

The narrowest aperture must be a ridge, of course.
Only single scattering is taken into account. Test machining is in progress.

A disk with adiameter of
24mm in frontof the Be pipe.
This disk
should be freefrom scatteredphotons.

2. IP Chamber
Loss Factor (of HER beam)
Loss factor [V/C]
Bunch length[mm]With Ridge

Without Ridge

42.87E+10

1.31E+105

1.67E+10

9.92E+09

6

1.10E+108.28E+09

87.38E+09

6.62E+09

10

6.73E+09

5.78E+09

3With Ridge

Power loss [W](current : 2.62 A, bunch spacing:4 ns)

Without Ridge

Bunch length[mm]With Ridge

Without Ridge

47.88E+02

3.60E+02

5

4.58E+02

2.72E+02

6

3.03E+02

2.27E+02

8

2.03E+02

1.82E+02

10

1.85E+02

1.59E+02

3(Shibata)2. IP Chamber
Longitudinal Wake Potential (of HER beam)
With Ridges

No Ridges

Bunch length = 6 mm(Shibata)With a ridge structure, a long oscillating wake appears. The effect of this wake is now understudy.
The estimation of the transverse impedance is also to be done.

2. IP ChamberStress Analysis(Koike)

Results of stress analysis of the IP chamber• Even if the chamber is horizontally supported at one end , the maximum stress in the Be part
(157 MPa) is less than its yield strength (245 MPa). (It doesn’t break!)• If the chamber is supported at both ends, the central part bend down 0.44 mm, and the stress in
the Be tube is 39 MPa.
• If the chamber is supported at the proper position of the Y-shaped part, the central part bend
down only 0.026 mm (above picture), and the stress of Be pipe becomes as small as 3.5 MPa.
Therefore, though IP chamber has a delicate built structure, it is not so weak as to require a help of aspecial supporting tool in handling.

Summary for IP chamber••••

A basic design of the IP chamber has been proposed.
In FY 2011, the test of most of technical issues will be over and the final
design will appear.
The ridges in a beam pipe induces a long standing wake. The effect will bestudied.
According to stress analysis, IP chamber is not so weak as to need a help ofa special supporting tool in handling.

3. Installation
Overview
Find a solution for installing this IR structure.
~ Establish a reasonable procedure to connect vacuum chamber flanges.
• IP chamber is supported by SVD frame.
• SVD is supported by CDC.
• QCS cryostats can move out.

Connection flanges for vacuumchambers.

Top view

Some work spaces toaccess flanges.
It will be possible to
make use of thesespaces.

CDC

Little work space toaccess flanges.
It is impossible toconnect flanges in thisconfiguration.

Top View

3. Installation
The structure of SVD4
End flange

End ring302

Heavy Metal
support940
Silicon wafer

CFRP 1mm(Koike)
IP chamber is supported around here.

The total amount of Heavy Metal is not fixed yet.
The total weight of SVD4 unit will be close to 100 kg.

3. Installation
Stress Analysis of SVD4The outside CFRP
and heavy-metal
structure in eachhalf are always
separated.

Heavy-Metal
Density: 18g/cm3
Young Modulus：360GPa
Poisson ratio：0.285

AlAl(Koike)s:This surface
is fixed to theother half.
Backward

Forward
Supportpoint

Supportpoint

Weight of IP chamber:
20 kg eachs:This surface is fixed tothe other half.

CFRP：1 mm
Young modulus: 200GPaTensile strength: ~GPa

Total weight~78 kg3. Installation
Stress Analysis of SVD4 - Results(Koike)

Equivalent stress：Max 25MPa
The SVD unit is self-supporting with the IP chamber. However, the effect ofa pressing force from the cryostat is not studied yet.

Maximum displacement: 0.015mm

The results for CFRP are shown.
• Deformation is very small.
• Stress is much less than the tensile
strength.
SVD4 keeps its shape when supported at bothends.

Principal stress：Max 15MPa

3. Installation
Basic Steps
Top view

L-sideR-side

1. Connect IP chamber withSVD4 to the QCSR cryostat.
2. The QCSR cryostat moves in.
3. The QCSL cryostat moves in.
4. Connect the flanges in front of
the QCSL cryostat.
To support SVD4, a gutter is used.
Both sides of IP chamber are
fixed to the SVD4 frametransversally and are freelongitudinally.
The R-side of SVD4 is aligned
transversally and is freelongitudinally.
The L-side of SVD4 is fixed toCDC.

3. Installation
Step 1 – Ready to go•The gutter is attached to SVD4. The other side of SVD4 is supported by the QCSRcryostat.
•SVD4 must hold by itself. During move-in of the QCSR cryostat, SVD4 is pushed by thecryostat.

(Kohriki)3. Installation
Step 1- ongoing(Kohriki)3. Installation
Step 1 - ongoing(Kohriki)3. Installation
Step 1 - ongoing(Kohriki)3. Installation
Step 1 – SVD4 arrives at the goal position
The junction between
SVD4 and the cryostat
must be loosened so thata possible motion of thecryostat after exciting
magnets may not exert aforce on SVD4.

The transverse positionof SVD4 forward end
must be fixed in thisconfiguration.

(Kohriki)3. Installation
Step 1 – Loosen the junction between SVD4and QCSR
QCS‐SVD‐joint
SVD4 armPin（φ10）
本体QCS arm

Screw bolt（M8）Nut-cramp （M8）
(Kohriki)Ring-cramp（φ8.2）

3. Installation
Step 1 – Fix the forward end of SVD4transversally
Position setting
mechanism(Kohriki)3. Installation
Step 1 - Complete(Kohriki)3. Installation
Step 2In the step 2, these flanges must be
tightened using available spaces inthis drawing.

•If the flanges are accessible by hands,
screws or a quick disconnect system
can be used.
•As an option in case the flanges
cannot be accessible by hands, an idea
to provide the cryostat with channels(along the red lines in the figure) for atightening rod is proposed.

Side view
Request for a wider space isunder consideration in thedesign of CDC.

The use of ion yoke for QC2E
made this option practicallyimpossible.

Summary for Installation
•

•

•
•
•

In the R-side of Belle II detector, there are no spaces available forconnecting vacuum chamber flanges after the QCSR cryostat moves in. On
the other hand, some working space seems to be available for the L-side
after the QCSL cryostat moves in.
An IR installation procedure adopted in our working group consists of twosteps.
• Step 1: IP chamber with SVD4 is connected to the QCSR cryostat.
Then QCSR cryostat moves in.
• Step 2: The QCSL cryostat moves in. Then the flanges in front of theQCSL cryostat are tighten up.
For the step 1, a gutter is attached to the SVD4 unit. A mechanical strength
more than self-supporting one is required for the SVD4 unit.
For the step 2, negotiation on the work space is still going on.
The final scenario will appear before the end of March 2011.