Vacuum System for SuperKEKB(mainly for LER arc section)

Y. Suetsugu
on behalf of KEKB Vacuum GroupDesign– Upgrade strategy– Design of key components
 Beam pipes
 Movable masks (collimators)
 Countermeasures against ECPresent status and plans– Manufacturing of components– Plans
2011/2/8

Summary

KEKB Review 2011 @KEK

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Upgrade strategy_1
Goal of vacuum-system upgrade is to realize;
Ultra-high vacuum– Pressure on the order of 10-7 Pa with beam
– Maintain small emittance, Reduce background noise to detector, Avoid
ion instability [HER]Beam pipes (components) with low beam impedance– Maintain small beam emittance and short bunch length, Avoid single andmulti-bunch instabilities



Stable and robust system– Against high beam current (SR, HOM)
– Design based on established techniques, but introducing advanced
idea at the same time.

High cost efficiency– Make use of the change to the nano-beam scheme– Continuous use of vacuum systems and reuse components in KEKB
as much as possible.

2011/2/8

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Upgrade strategy_2
In concrete terms;

Infrastructures, such as electric lines, coolingwater pipes, control systems are basically reused as
it is, after maintenance.
– Cooling water pipes should be rearranged. Especially for
Wiggler section.
– Capacity of water cooling system should be enhanced.
– Radiation shielding scenario should be reconsidered aroundcollimators (Beam loss: ~20 times of KEKB).


Pumping and monitoring system– Pumps: NEG as main pump, and Ion pump as auxiliary pump:
Oil free and capture pumping system
Ion pumps are reused, and NEG is replaced with new one.
 Disconnected to atmosphere during beam operation.
– Rough pumping: Turbo molecular pump and drag pumpOil free, Rough pumping system are reused.

– Vacuum gauges (CCG), L-angle valves, thermo sensors, etc.
are reused, with some new backups.
2011/2/8

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Upgrade strategy_3Beam pipes– New beam pipe: Beam pipes with antechambers.
Low beam impedance, Higher strength against intense SR
 Less photoelectron effect to position beam [LER] : Electron-cloudformation is suppressed.
– Add more powerful countermeasures against electron
cloud (EC) effects [LER].
Solenoid field, Rough surface at side wall, TiN coating New technique: Clearing electrode, Grooved surface

Main components– Bellows chambers, gate valves, movable masks(collimators), stoppers, etc. are designed to fit the beam pipes.
Higher strength against higher beam currents

Main upgrade is the replacement of beam pipes
and other main vacuum components.
2011/2/8

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Design of key components_1
Key components presented here:Beam pipes– Beam pipes with antechambers– Aluminum-alloy beam pipe for LER– Countermeasures against electron cloud effects


Pumps– NEG strips

Connection flange– MO-type flange (Al and Cu)

Bellows and Gate valves– Comb-type RF shieldMovable mask (collimator)– Conceptual designing has just started.

2011/2/8

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Design of key components_2
Beam pipes: Beam pipes with antechambers– Small effect of photoelectrons, low beam impedance, low SR
power density– The cross section should fit to the existing magnets.
– Aluminum alloy is available for LER arc section (see next).
Copper is required for wiggler section (and HER).
– Available by cold-drawing technique (copper) or extrusion
technique (aluminum)
Concept– Copper beam pipes have been tested in KEKB.
Aluminum(A6063)

NEG strip

Conductance:~ 88 l/s/m

t6 mm

Beam
SR
BPM

Copper(OFC)

Q magnet
2011/2/8

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Design of key components_3
Aluminum-alloy beam pipe for LER– In the nano-beam scheme,Max. SR power density ~ 3 W/mm2 (ref: HER ~15 W/mm2) owing tolong curvature of bend
 Aluminum alloy is available.

– Merit (compared to copper):Cost reduction
 Easy manufacturing (TIG welding is available.) Easy handling (light)


Aluminum beam pipe with antechambers (extrusion)

2011/2/8

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Design of key components_4
Aluminum-alloy beam pipe for LER– Problems to be considered (compared to copper case):
Relatively high gas desorption and high secondary electron yield With TiN coating in any way to suppress electron cloud effect High resistive wall impedance Not so serious owing to a large aperture Vibration of beam pipe  Eddy current in Q  Beam oscillation
 A problem in Spring-8. Rigid fixing of beam pipe was effective.


Radiation issues: (T. Sanami, KEK)
Leakage of SR (εr = 1.8 keV):− Dose < 1 MGy for 10 years :OK− Checked experimentally in
KEKB.
Shielding of loss particle– No big difference between
Al and Cu in a simulation.

(by MARS15 + MCNP)

Dose rate

Al chamber
Cu chamber

Al-alloy beam pipe is adopted
for LER beam pipe
2011/2/8

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Design of key components_5
Main Pump (NEG)– Arc: Available in one of antechambers (inside of the ring) Make the most of distributed pumping system: effective
pumping.
 Effective pumping speed of ~ 80 l/s/m.
– Straight: Lumped pump ports at both antechambers.
– Ion pumps: Placed every 10 m
 Helpful at higher pressure
Arc section

Diameter φ 4 mm,
thickness 5 mm
2 row: 333 holes/m
C~2.5x10-1 m3/s/m
Seff~ 1.x10-1 m3/s/m

Straight section(Wiggler section)

Screen2011/2/8

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Design of key components_6
Flange : MO-type Flanges– Thermally strong, sure RF bridge, applicable to antechamber
scheme, low beam impedance– In addition to stain-less flanges, copper alloy and aluminumalloy flanges had been developed.
Easy welding to pipes, reduction in heating by wall loss

– Several copper flanges have been installed into the ring andtested.
Copper-alloy flange (CrCu)

2011/2/8

Aluminum-alloy flange (A2219)

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Design of key components_7
Bellows and gate valves with comb-type RF-shield– Sure RF shielding, thermally strong– Applicable to antechamber scheme– Finger-type for some cases, if flexibility is required.



Trial models has been installed into the KEKB ring andtested with beam.
– Fitting to beam pipe with antechambers– Reduction in the temperature of bellows has been
demonstrated.
Bellows chamber for antechamber

2011/2/8

Gate valve

Comb-type RF shield (Gate valve)

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Design of key components_8
Countermeasures against electron cloud (EC)effect [LER]– Serious issues for recent positron and proton storage rings.
Sections

L [m]

L [ %]Countermeasure

Material

Total

3016

100

Drift space (arc)1629 m54

TiN coating + Solenoid

Al (arc)

Steering mag.

316 m

10

TiN coating + SolenoidAl

Bending mag.

519 m

17

TiN coating + Grooved surface

Al

Wiggler mag.

154 m

5

Clearing Electrode

Q & SX mag.

254 m

9

TiN coating

Al (arc)

RF section

124 m

4

(TiN coating +) SolenoidCu

IR section

20 m

0.7

(TiN coating +) Solenoid

Cu or ?

NewCu

– By using these countermeasures, the average electron density
on the order of 1010 e-/m3 will be obtained.


Threshold of head-tail instability: ~1.6×1011 e-/m3

2011/2/8

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Design of key components_9
Some new techniques for EC mitigation

Clearing electrode for wiggler section.
– Attract electrons by electrostatic field– Very thin electrode has been developedInside view

0.1 mm tungsten on 0.2 mm Al2O3
Small impedance and effective heattransfer– Have been tested in KEKBdeveloped

Expected reduction ratio: 1/100– Also demonstrated in CesrTA– Manufacturing has already started.

0V

Equipotential lines

Beam channel(φ 90mm)+75 V~3kV/mElectrode

Antechamber+500 V
Beam pipe with clearing electrodes
2011/2/8

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Design of key components_10
Grooved surface for bending magnets section– Reduce effective SEY structurally– Have been tested in KEKB, and alsoin CesrTA– Extrusion test of aluminum beam pipe
was successful.
– With TiN coating(Roundness)

Rt

B
d

by L. Wang et al.

(Depth)Aluminum beam pipe with grooves

Grooves

Valley ：R0.1~0.12
Top ：R0.15
Angle：18~18.3°
2011/2/8

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Design of key components_11
Movable mask (collimator)– Indispensable in order to reduce background noise of BELL-II– Long R&D history in KEKBStealth type was proposed, but not yet realized.

– For SKEKB,
 High thermal strength against wall heating (~ 1 mm frombeam for vertical type) Low beam impedance (ex. Against TMC instability)
 Fitting to antechamber scheme Robust against impact of beam in case
 Placed at both sides of the ring HOM absorbers (near to masks)– Concept of Ver.4 in KEKB will
Bellows Chamber Ver.4 in KEKB
Mask Chamber
be available, at least in the
beginning stage:
Bellows Chamber
how to fit to antechamber
scheme?
Beam
One candidate: PEP-II type2011/2/8

KEKB Review 2011 @KEK

Mask Head(Ti)
15

Design of key components_12
Movable masks for KEKB (Ver.4) and PEP-II
PEP-II typePair-type(Two mask heads)“NO structural problem in this design. Intense excited HOM have heated up
bellows chambers and NEG elements near the masks.”(from M. Sullivan [SLAC])
2011/2/8

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Design of key components_13
Concept of horizontal movable mask
RF shield fingers aroundbody (GridCop?)

Pair-typed = 5~10 mm

Mask head: Graphite?
(t~1 mm?)
Length ~0.5 R.L.
Mask body: Copper

Cooling water
Mask head
φ90
2011/2/8

Tapered pipe

Reduced aperture at themask head eliminatestrapped modes.

Cooling water
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Design of key components_14Concept of vertical movable mask
Pair-type
RF shield fingers aroundbody (GridCop?)
1500

Beam

φ90
Tapered pipe
Mask headd = ~1 mm

Cooling water
2011/2/8

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Design of key components_15


Loss factors (k)– Calculated by GdfidL, 3D model– Dependence on bunch lengths (σz )Log scaled: distance between beamand mask head

（d=10 mm）

Single-type（d=5, 10 mm）

Smaller than that for
present Ver.4 (KEKB):
owing to long ramp?
Small dependence on d
No big difference
between single- andpair-type versions: Pairtype is smaller?
Single-type

Pair-type（d=3, 5 mm）(Thank to K. Shibata)
2011/2/8

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Design of key components_16
Kick factors (ky)– Calculated by GdfidL, 3D model, σz = 6 mm
– Dependence on d

Log scale

Pair-type

Large dependence on dky for pair-type isapproximately twice ofthat for single-type.

(V)
Horizontal

d = 5 mm(H)

ky = 8×1013 V/C/m
Verticald = 1 mmky = 1 ×1015 V/C/m(Thank to K. Shibata and D. Zhou)

Ref.:I. Zagorodnovet al., EUROTeV-Report-2006-074
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Design of key components_17
Threshold current for TMC (LER)– Transverse mode coupling instability (TMC)– Threshold formula (from B. Zotter, Handbook of Accelerators)

C1 f s E / e
I thresh =∑ βi k⊥i (σ z )
where



C1 ~ 8 i
fs = 2.13 ×103 Hz
E/e = 4 × 109 eV[A/bunch]β ~ 20 m (in Arc), ~1 m (in Local Correction)k⊥ (σz ) = (kick factor, V/C/m)
Σ = (total number)

Design bunch current = 1.44 mA/bunch
For 1 mask (2 heads)
d = 5 mm [H, Arc]: ky = 8×1013 V/C/m  Ith = 43 mA/bunchd = 1 mm [V, Arc]: ky = 1 ×1015 V/C/m  Ith = 3.4 mA/bunchd = 1 mm [V, LC]: ky = 1 ×1015 V/C/m  Ith = 68 mA/bunch(With non-linear collimation scheme)

4 horizontal at arc masks will be available.
1 vertical masks at LC will be OK.
2011/2/8

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Design of key components_18
Wall loss– For a beam pipe with a radius of a [m], a bunch with a length ofσz [m], the wall loss per meter is (from A. Piwinski, Handbook of Accelerators)

Γ(3 / 4) I b2C
P' = 2 3 / 2
4π aσ z 2µσ c / Z 0

Ib=Bunch current
C=Circumference(=3000m)
Z0=Vacuum impedance(= 377Ω)σc=Conductivity (1/Ω)µ = 1, Γ(3/4) = 1.225– For d = 1 mm:– If graphite (σc=2×105 1/Ωm) is used, P’=2.55 W/m. For 2500
bunches、P’= 32 kW/m. If ½ of total current concentrated in
1 mm width, P = 50 W/mm2 (32 × π/2).
 Very hard to deal
– If tungsten (σc=2×107 1/Ωm) instead, P = 5 W/mm2
 Well manageable with water cooling.
How about damage? Easy replaceable?
2011/2/8

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Design of key components_19
For movable mask;
The design has just started.
– Start with a conventional idea

To be investigated are;
– Bench marking of simulation code.
Results of GdfidL seem to Strongly depends on mesh sizes.

– Evaluation of influence on beam dynamics


TMC, Banana effect, etc.

– Choice of head material

Good electrical conductivity, High thermal strength, Easy bonding Candidates: Mo, Ta, W, Re, Rh, Ru,,,
 Simulation of heating by EGS4 has also started. (by T. Sanami)– Possibility of increasing beam sizeNon linear optics (under investigation by Y.Ohnishi)

If novel ideas are required;– Spoiler using channeling in a crystal (Si)– Collimator using Laser, Electron beam,,,,Long term has restarted again……
2011/2/8

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Present status and plans_1


R&Ds of components have almost finished.
– Conceptual design of movable masks has just begun.



Manufacturing of some beam pipes had started.
– Beam pipes with clearing electrode and Q beam pipe for LER
wiggler section is under manufacturing (~220 m).


Copper beam pipes
will be delivered this fiscal year.
Together with some bellows chambers (16 pieces)– Beam pipes and bellows chambers for LER arc sections andstraight sections will be ordered soon.
LER arc : Beam pipes for drift [S], beam pipes for bend [B],beam pipes for quad (with BPM) [Q]: ~1860 m (Al alloy)

LER straight: Chicane section and downstream of wiggler
section and wiggler beam pipes: ~135 m (Cu) Bellows chambers: 450 pieces (Al)

2011/2/8

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Present status and plans_2Delivered and ordered this year [LER](IR)

Arc section(Local Correction)

Chicane section
Wiggler section

Wiggler section(RF)

Except for
Skew SX section
Beam dump
Tapers(RF)
2011/2/8

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Present status and plans_3

Varieties of beam pipes for arc section
B beam pipe

Q beam pipe

S beam pipe

Total: 1860 m (except for bellows chambers)
Bellows chambers 450 : 90 m
2011/2/8

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Present status and plans_4Typical cross sections

Arc [S, Q]
Arc [B]
Grooved surface

Typical B beam pipe

NEG pump port
Photon mask

2011/2/8

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Present status and plans_5Typical Q beam pipe
BPM block
NEG pump port
Photon mask

Typical S beam pipe
Ion pump port
NEG pump port
Photon mask

2011/2/8

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Present status and plans_6Wiggler beam pipes (Cu)– Beam pipes and bellows chambers have been gradually
delivered.
– They will be stored for a while in a new tent.
The beam pipes are filled with dry nitrogen The packages of bellows are filled with dry nitrogenStock area of beam pipes(Thank to M. Shirai)
2011/2/8

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Present status and plans_7
Bellows chambers– Some bellows chambers for wigglers have delivered.
– Bellows chambers with aluminum body were manufacturing
for test.
– RF properties were checked by comparing a dummy pipe.

Aluminum bellows
chamber

Measurement of RF
properties (S11, S12)

(Thank to T. Abe, KEKB RF group)
2011/2/8

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Present status and plans_8Remained beam pipes [fixed plan]– Tsukuba straight sections incl. local correction sections:
165x2 = 330 m (Cu 200 m?) [LER and HER]
– Fuji cross sections [LER]: 7 m [LER]: 11 m [HER]– HER Wiggler sections: 121 m– Special beam pipes, ex. Tapered beam pipe, dump chambers,
X-ray monitor chambers [LER and HER]
– IR beam pipe [HER and LER]
– For ARES cavities (Fuji, Nikko, Oho): 182 m

Manufacturing of these chambers will start soon.
Design of special chambers, such as injection
chambers, dump chambers, X-ray monitor chambers,
will also start soon.

2011/2/8

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Present status and plans_9
Beam pipe manufacturing time schedule (preliminary)
FY2009FY2010FY2011FY2012FY2013

FY2014FY2015

LER
Cu
Wiggler
Cu
Wiggler downstream
Cu
ChicaneCu
Bellows
Arc section (regular part) Al
Al, CuBellows, GV
Al?
Tsukuba (LC)Al, CuOther beam pipes
Al, CuBellows, GV
Other components

HER
Wiggler chambers
Wiggler downstream
Bellows, GV
Tsukuba (LC)Other beam pipes
Bellows, GV
Other components
Upgrade of bellows, GV
TiN Coating
Cabling, Piping
Insallation

2011/2/8

Cu
Cu
Cu
Cu?
Al, CuCu
Cu

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Present status and plans_10
Pre-baking and TiN coating in KEK– Workflow of beam pipe assemblyTransfer of beam pipes to OHO experimental hall.
 TiN coating Assembly of NEG pumps
 Prebaking (150°C 24 hours) N2 filling Transfer of beam pipes to reservation area, or into tunnel.
– TiN coating
5 sets for Q and S beam pipe, and 2 sets for B beam pipe.
 One coating process will take 4~5 days.
 Coating for 800 beam pipes (arc section) will take ~1.5 years.


SUN
Q&S_1

MON

TUE

WED

Setting
BakingTiN coating

THU

FRI

SAT

Disassembling

Q&S_2
Q&S_3
B_1
(by K. Shibata, M. Shirai)
2011/2/8

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Present status and plans_11
Pre-baking and TiN coating facility in KEK– The facility will be set up in autumn at OHO experimental hall
this year.
– Three floors(by H. Hisamatsu)
TiN coating for B beam pipe

TiN coating for S, Q beam pipe

Baking stations

2011/2/8

KEKB Review 2011 @KEK34

SummaryUpgrade of the vacuum system for Super-KEKB has
started.
– The design basically continues the policy in KEKB,
introducing new ideas.
– Most of designs and R&Ds for key components havefinished.
Aluminum-alloy beam pipe is now adopted for LER.
 More powerful countermeasures against EC effects areembedded especially in dipole magnets.
 Further studies are required for movable masks.
 Baking and TiN coating facilities will be ready this year.
– Manufacturing of beam pipes and bellows chambers for
LER wiggler sections had started last year.
– For LER arc and straight sections, It will start this year.
– Remained parts of LER and HER will follows.
2011/2/8

KEKB Review 2011 @KEK35

Thank you for your attention

2011/2/8

KEKB Review 2011 @KEK36

Movable Mask


Possible mask locations and beam parameters (Y.
Ohnishi)***Non-linear collimation scheme
2011/2/8

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CSR (LER)

Microwave Instability (H. Ikeda, K. Oide)– For σz = 5 mm

2011/2/8

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kz and ky

Loss factors and kick factors for main components
2011/2/1 末次
Component

Resistive wall

Loss factor [V/C] Number of items
Al
Cu

Pumping port
Flange connection
Bellows
Gate valve
SR maskMovable mask
Taper
BPM
BxB FB BPM
FB kicker
IP chamber
GrooveGroove (RW x 0.14)*
Clearing ElectrodeCle Ele (RW-W)**
Cavity (ARES)
Total
Al

1.14E+09
8.22E+08
3.65E+02
1.45E+07
2.00E+09
3.00E+09
1.82E-03
1.00E+11
3.83E+08
1.63E+08
5.90E+08
5.01E+11
8.00E+08
1.00E+08
1.60E+08
2.00E+08
8.70E+08
4.35E+11* RW 50%増し x 80/(90*π)** タングステン 40mm分
2011/2/8

3000 [m]3000 [m]3000 [m]
2000
900
40
1000
8 ?
100
450
10
1
1
550 [m]
550 [m]160 [m]160 [m]18

Loss factor(total) [V/pC]
3.42

KEKB Review 2011 @KEK

1.10E-06
0.03
1.80
0.12
1.82E-120.80
3.83E-02
0.07
5.90E-03
0.50
8.00E-04
5.50E-02
8.77E-02
3.20E-02
1.39E-01
7.83
14.9 +α

Kick factor(total) [V/pC/m]

35.00

˜1000

2.50
?
5.50
27.00
1.20

39

Materials of mask headTemperature rise simulation by EGS4

2011/2/8

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