Vacuum Chamber R

1
Vacuum Chamber RD for Super-KEKB
Y.Suetsugu, KEKB Vacuum Group
Contents

• 1. Introduction
• 2. Beam Chamber
• 3. Bellows with RF-shield
• 4. Summary and Plan

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1. Introduction

• Parameters Considered Here (Super KEKB)

LER (e-) HER (e)
Energy GeV 3.5 8.0
Beam Current A 9.4 4.1
Bunch Length mm 3 3
Bunch Number 5018 5018
Bending Radius m 16.31 104.46

• Key Points in Designing Beam Chambers and
  Components
• How to deal with intense SR?
• How to reduce beam impedance?
• How to avoid excess heating?

3
2. Beam Chamber

• Present Design Ante-chamber (arc section)

Ante-chamber
Conceptual Drawing
Pump
Beam
SR
Cooling Water
4
2.1 Ante-Chamber

• Merits of Ante-Chamber
• Weak power density of synchrotron radiation at
  wall.
• Reduction of photoelectrons in beam duct (e
  ring).
• Low impedance (no pumping port in beam duct).
• High linear pumping speed (goal 100 l/s/m)

ex. LER
170 W/mm2 at present chamber
Beam
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2.2 Basic Design of Ante-Chamber

• Typical Cross Sections for LER

B Magnets and Straight Section
Ion Pump Section
Cooling Water
Cooling Water
NEG Strip
Beam Duct
Q, SX Magnets
IP, NEG Feed through
Saw-tooth surface to reduce photoelectron yield
and reflection
Depth of ante-chamber is limited by magnet
aperture. Similar cross sections for HER
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2.3 Thermal Calculation

• Calculation by ANSYS (Temperature)
• Copper chamber, 25 C cooling water

ex. HER
lt30 C
SR
40 W/mm2
156 C
7
2.4 Structural Calculation

• Calculation by ANSYS (Stress von Mises)
• Copper chamber, 25 C cooling water

ex. HER
Deformation 0.16 mm
SR
40 W/mm2
281 MPa
The stress is below the yield strength of drawn
copper
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2.5 Ante-Chamber RD_1

• Step_1 (2001) with photon stop
• Examine Reduction of photoelectrons
• Installed in LER

Special Photon Stop
Beam
Q QF2P.33
B B2P.73
Photoelectron Monitor
3 m
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2.5 Ante-Chamber RD_1

• Measurement of electrons
• in beam duct (by K.Kanazawa)

• Number of electrons measured by a photoelectron
  monitor reduced to about 1/7 compared to the
  usual single duct.
• Solenoid is still effective to reduce number of
  electrons.

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2.6 Ante-Chamber RD_2

• Step_2 (2003) without photon stop
• High SR power density at photon stop
• -gt No photon stop design
• Verify reduction of electrons in beam duct
• Prepare NEG strip, saw-tooth surface
• Install in the present KEKB LER this year

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3. Bellows with RF-Shield

• Bellows
• ? A possible source of hardware trouble in high
  current
• An ideal solution No Bellows Design
• No heating problem by HOM
• or wall current
• No heating or discharge at
• contact point
• No impedance source
• Butthere are severe problems

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3. Bellows with RF-Shield

• Problems without bellows
• How do we connect adjacent chambers?
• No flange -gt TIG welding in situ.?
• How do we absorb manufacturing or setting errors?
• How do we absorb thermal movement of chambers??
• Control DT of beam chamber (6 m duct at 10 ? 1mm
  expansion) ?
• How to fix BPM??
• -gt Set BPM free from Q-mag. and feed back the
  position??
• Quite different design concept of beam chambers
  from conventional one should be necessary.
• Evaluation of stress, Manufacturing method

Beam chamber design with bellows
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3.1 Proposal of New RF-Shield Design

• Conceptual Design --- Comb Structure
• Merit
• High thermal strength
• Low impedance
• Low HOM leakage
• Little damage in accidental beam hitting
• Restriction
• Limiting movement
• Expansion (lt3mm)
• Bending (lt2), Offset (lt0.2mm)
• -gtsevere but manageable

• ex.
• Tooth thickness 1 mm
• Tooth length 10 mm
• Gap between tooth 2 mm
• Chamber thickness 10 mm

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3.2 New RF-Shield RD (Calculation)

• Basic Property
• Good thermal conductivity of tooth
• Tooth t1 x w10 x l10 , Cu 0.4 W/K
• lt Present finger t0.2 x w4 x l20 , Be-Cu
  0.007 W/K
• Low impedance (loss factor k)
• at sz 3 mm, k 4.2 V/pC lt 5.2 15 V/pC
  (present bellows)
• at sz 6 mm, k 0.4 V/pC lt 0.8 1.3
  V/pC

Mafia model Total length200 mm Tooth
position 95-105 mm Mesh sizex,y 0.25 mm,
z 0.5 mm Bunch length
sz 3 mm, 6 mm Calculation of k Indirect
method
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3.2 New RF-Shield RD (Calculation)

• Basic Property
• Fingers at outer side of gap between teeth and
  back of teeth
• Low current density at shield fingers
• Small HOM leakage
• Low Cost (in mass production)

Inner surface
Teeth
Teeth
Fingers
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3.2 New RF-Shield RD (Manufacturing)

• Machining is available. How about brazing?

• Test Plan

• Trial mode of RF shield
• Bench test (power test)
• using 508 MHz microwave
• Trial model of bellows with RF-shield
• Installation to LER

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3.2 New RF-Shield RD (Future)

• Application to ante-chamber
• It will be possible but further RD is necessary.
• Application to RF-shield in gate valve??

Mock-up
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4. Summary Plan

• Beam Chamber for Super-KEKB
• Basic design
• Ante-chamber without photon stop.
• Bellows connection
• No bellows is ideal but bellows connection is
  practical.
• New RF-shield structure was proposed.
• RDs in proceeding
• Ante-chamber
• A trial chamber will be installed this summer.
• Bellows
• A trial model with new RF-shield will be
  installed this summer.
• RDs to be done
• IR beam chamber
• Components Movable masks, Gate valves, ..
• How to reduce photoelectrons Coating (NEG)?,
  Solenoid,..