Recent Upgrade Studies ofVacuum Components
Y. Suetsugu
KEKB Vacuum GroupContents
 Introduction
 R&D for
 Beam Duct Connection Flange Bellows and Gate Valve Movable Mask (Collimator)
 Summary & Future Plan
2007/3/19

MAC2007, KEK1

Introduction
 R&D on vacuum components to meet the demands for

future high-current accelerators has been progressing
using intense beams of the KEK B-factory ring (KEKB).
 Low Energy Ring (LER): 3.5 GeV, Max.1.8A (1389 bunches) High Energy Ring (HER): 8.0 GeV, Max.1.4 A (1389 bunches) Studied Components:
 Copper beam ducts with one or two ante-chambers.
 Special connection flange with no gap at the connection point.
 Bellows chambers and gate valves with high thermal strengthand low beam impedance.
Nexttalks  Inner surfaces with a low secondary electron yield (SEY).
 Movable mask (collimator) with low beam impedance.
2007/3/19

MAC2007, KEK2

Beam Duct
 Beam duct with ante-chamber (2003 ~)Ante-chamber = additional chamber
Effective to reduce photoelectrons in the beam channel
Also effective to dilute the power density of SR Use copper

Beam duct with antechamber[NEG Strip]

BeamSR[SR Channel][Beam Channel]

2007/3/19

MAC2007, KEK3

Beam Duct Copper ducts with an antechamber for arc sections (2003~)
 Manufacturing properties were investigated.
 Installed at an arc section of the KEKB positron ring
 Electron number was estimated using a electron monitor.
 Large reduction of photoelectron was found.
Test duct (by pressing)

Installed test duct

BeamB
φ = 94 mm
ha = 112 mm
t = 6 mm2007/3/19

MAC2007, KEKElectron Monitor(DC, Collector:+100 V, Repeller:-30V)
4

Beam Duct Copper duct with two ante-chambers (2005~)Installed into the LER wiggler section~3.6 m, with NEG strips, by pressing method
Reduction of photoelectrons was again confirmed.
No problem up to 1.7 A.
Test duct (by pressing)

Installed test duct

φ = 94 mm
ha = 224 mm
t = 6 mm

InsideInside view
2007/3/19

MAC2007, KEK5

Beam Duct This year, a part of Nikko wiggler section will bereplaced by beam duct with ante-chambers.

 ~30 m in total, φ 90 mm, ha=110 mm
 Including Q-chambers with BPM
 Manufacturing is now proceeding by cold drawing method.

B

2007/3/19

BPM

Q

MAC2007, KEK

6

Beam Duct Cold drawing was successful.
 More accurate than pressing method
 Cost ?
After drawing

2007/3/19

Cut model

MAC2007, KEK

7

Beam Duct
 Beam ducts will be coated by TiN.
 Coating station is now being set up at an experimental hall.
PowerSource

2007/3/19

Power
SupplyChiller

Control Unit
MAC2007, KEK

Elevator
MachinePumping
System〜7 [m]B3 floor

Control Unit

SolenoidB2 floor

Duct

Ar + N2

Air
Heater8Connection Flange MO (Matsumot-Ohtsuka) type flange[Vacuum side](2004~)

 Seal a vacuum at only theinner surface.
 Vacuum seal doubles as RFbridge.
 No gap and step at the innersurface.
 Can follow the complicatedcross section.
Applied to beam ducts with
ante-chambers
Rectangular model (for waveguide)
2007/3/19

MAC2007, KEK9

Connection Flange Bench test (2004~)
 Stainless-steel flange and copper gasket (annealed) 180x340 for φ 94 antechamber, 28 M8-bolts along aperture Vacuum seal at a torque of ≤ 18 NmTrial models (only flanges)
 No problem after baking (200°C)
Leak rate

SS flange
Cu gasket
2007/3/19

MAC2007, KEK

Inside view
10Connection Flange Application to bellows chambers and beam ducts (2005~)
 No problem up to 1.7 A (8 flanges)
 Applied to new test chambers for wiggler sections, and will
be tested this year (28 flanges).
MO flange for beam duct

2007/3/19

MO flange for bellows chamber

MAC2007, KEK11

Bellows & Gate Valves
 Comb-type RF-shield (2003~)
 Proposed at KEK

 Nested teeth instead of fingers




High thermal strength
Small leakage of HOM（TE-mode）
Low beam impedanceApplicable to various apertures
Limited offset
Complicated structure

Finger typeBeam2007/3/19

MAC2007, KEK

BeamComb typeBeam

12

Bellows & Gate Valves
 Simplification of structure (2004~) Comb Ver.0[Outside-shield]

 Ver.0 (Original) With both outside- and back shield Circular bellows → OK

 Ver.1[Back-shield][Comb teeth] With only back-shield Racetrack bellows→ NG (Discharge)

 Ver.2
 With only outside-shield Racetrack bellows,Gate valves
 Comparable to Ver.0→ OK
2007/3/19[Finger-type][Comb-Ver.2][Comb-Ver.0]

MAC2007, KEK13

Bellows & Gate Valves Racetrack Bellows (2005~)
 150 x 50 mm racetrack, Comb-Ver.2
 No problem up to 1.4 A (HER) Temperature rise decreased to 1/3of that of the conventional bellows.
Temperature of corrugation

150x50 mm
L = 200 mmVer.2

2007/3/19

MAC2007, KEK14

Bellows & Gate Valves Bellows for a beam duct with ante-chambers (2005~)


Easy to apply to a complicated cross section (Comb-Ver.2)
No problem up to 1.7 A.
Inside was checked this winter, and no damage was found.
φ = 94 mm
ha = 224 mm
L = 200 mm
Ver.2

Comb teeth(Cu)Whole view

Inside view
2007/3/19

MAC2007, KEK15

Bellows & Gate Valves Circular gate valves (2005~)
 Comb Ver.2 = No sliding point Collaboration with VAT
Vakuumventile AG.
 Temperature rise of body decreased
to 1/3.
Temperature of body
φ = 94 mm
L = 95 mm
Ver.2

Installed gate valve

Inside view
2007/3/19

MAC2007, KEK16

Bellows & Gate Valves Racetrack gate valves (2006~)
 150x50 racetrack, Comb-Ver.2
 No problem up to 1.4 A Temperature of adjacentbellows also decreased. 160x50 mm
d: Bellows

Finger-type

L = 145 mm
Ver.2

d

Inside viewadbc

Comb-typedbbcc
aa

2007/3/19

MAC2007, KEK

17

Bellows & Gate Valves Gate valve for a beam duct with two antechambers (2007)

For the LER wiggler section, φ94
Comb-Ver.2, and MO-Flange
Will be installed this summer, and tested.

Whole view

Inside view

2007/3/19

MAC2007, KEK

18

Movable Mask
 Proposal: Stealth type [Ver.6] (2003~)

 Ceramic support →Little interference with beam
With thin metal coating to avoid unwanted charge up of head
 Ceramic or carbon head →Little damage by beam
 HOM absorber (SiC) → Damp trapped modes Similar idea to an “invisible electrode” by F. Caspers (1987)
Ver.6

Ver.4 at present
Bellows Chamber

Mask Chamber

Beam
Mask Head
2007/3/19

Bellows Chamber
MAC2007, KEK

SiC
Mask Head19

Movable Mask
 Calculation of RF properties (by Microwave Studio, Mafia)
 Impedances and Q of trapped modes, loss factors

 Ex. Trapped modes:

 Two trapped modes (Mode 1 and Mode 2) were found.
 Mode 1 (~0.7GHz) disappeared for ceramics support.
Metal Support

Mode 1(~0.7 GHz)
Mode 2(~1.4GHz)
0.5 GHz
2007/3/19

1 GHz

Mode1[S11]Ceramics Support

Mode2TE111(~1.8GHz)

1.5 GHz

Mode 2(~1.4GHz)

2 GHz

0.5 GHz

MAC2007, KEK

1 GHz

TE111
(~1.8GHz)

1.5 GHz

2 GHz
20

Movable Mask
 Ex. Calculation of longitudinal Impedances (Rs) and Q

Rs

Mode 1Q
Mode 2Rs

Q

High resistivity

 Rs decreases as increasing the resistivity of coating onsupport.
2007/3/19
MAC2007, KEK
 No CBI problem for KEKB even at full current operation.

21

Movable Mask
 Ex. Calculation of Loss factor

 Loss factor decreases as increasing the resistivity ofcoating on support.
 Loss factor is about 1/4 of the present Ver.4 mask at σz = 4mm, when the coating is 1 µm titanium, for example.

[Without SiC]

High resistivity
2007/3/19

MAC2007, KEK

22

Movable Mask
 Ex. Estimation of head temperature Total power ~ 50 W even at 10 A (#5000)→ ~ 900 °C at ε = 0.2
 May be OK, but with large ambiguity…..
 Only radiation
 Joule loss (Cu)ε1=0.2

 ~30 Wε1=0.5

 Trapped mode: Mode 2

 ~25 W (total)
ε1=0.8

 Trapped mode: Mode 1

 ~0
 High frequency components

 Will propagate……

2007/3/19

MAC2007, KEK23

Movable Mask
 Bench test using a test model An atmosphere version was manufactured to check thecalculation, and to see the manufacturing property.
 Measured behavior of trapped modes were well consistent
with the calculated one.

Mask headand support
Inside view
Setup for Q measurement
2007/3/19

MAC2007, KEK24

Movable Mask
 First trial model for beam test

Whole view

 A vertical mask for LER wasinstalled this winter.
 Al2O3 head with Cu coating (~10 µm)
 Al2O3 support with Ti coating (~1 µm)
 Beam test has just begun.
Mask HeadMaskhead

SiC

47 mm

Inside view

90 mm

5 mm x4 mm

δ/t ≥100@1.3GHz
2007/3/19

MAC2007, KEK

25

Movable Mask
 Inside view
Ver.6

Ver.4

SiC

Ti mask head

2007/3/19

Mask head

MAC2007, KEK26

Movable Mask
 Mask looked workingDecrease of beam life time was observed as the head approached to beam.

 Average temperatures of 4 bellows of 4 V-masks
 Beam current is still low, but an indicationof HOM reduction can be seen (?)
 Note: Different bunch patterns and positions

2007/3

2006/121389 bunches
Position=6 mm

51 bunches
Position=8 mm

2007/3/19

MAC2007, KEK27

Movable Mask
 Problem: Heating of head!

Radiation
thermometer Measured by a radiation thermometer Much higher than expectation:
by dozens of times!!
#31 #1389#51

Temperature
Beam Current

 T>600°C even at 40 mA (51bunches) [~2007/3/3]
 T (reading) relatively
decreased around2007/3/3 for the samecurrent→ Cu and Ti coatings
had gone??
 Input power is about 14 W
at 60 mA (51 bunches) Estimated from T decay
2007/3/19

MAC2007, KEK

after a beam abort

28

Movable Mask
 Main input power source is HOM!



T4 is proportional to I2/Nb.
T depends on the position of mask head.
Not due to SR If the loss factor is 0.2 V/pC, HOM
loss is 150 W at 60 mA (#51)→ About 10 % was absorbed byhead Affect of HOM from other masks isalso included

580 °C T depends on the position of thenext mask

 Ib = 300 mA (#300) → T =900 °C
 Ib=1600 mA (#1389) → T=1500 °C!!

2007/3/10~
65 mA (#51)
2007/3/19

MAC2007, KEK

Keep watching!
29

Movable Mask
 Further studies are required; Understand the reason of misestimation of input power High frequency HOM?, HOM from outside?
 Optimization of structure to reduce HOM loss
 Are SiC actually required?, Surface area, ε and loss?
 Optimization of materials
 Return to the original idea?
Graphite head (high emissivity and high thermal strength) and BN
support (low dielectric constant)?

 Coating will be practically no use.
 High temperature is structurally inescapable for use.
 How much is the affect of charge up?
 Long term stability ?

 Got off to a rocky start ….?
2007/3/19

MAC2007, KEK30

Summary and Future Plan
 R&D of various vacuum components to adaptable tohigh current accelerators are proceeding using KEKB.
 Beam duct with ante-chambers has beendeveloped for wiggler sections, together withbellows chambers and flanges.
 Application of bellows chambers and gate valves
with the comb type RF-shielding is expanding.
 The first trial model of a new movable mask isunder test with beam.
 Way of mask is not that easy…
2007/3/19

MAC2007, KEK31

Summary and Future Plan Next step: Replacement of the present circular beam ducts ata wiggler section (~30m) by that with antechambers [this summer], including BPMs.
 Further test and optimization of the new movablemask.
 R&D of a clearing electrode for ECI (plan).
 More practical design of beam ducts for Super B

2007/3/19

MAC2007, KEK32

End

2007/3/19

MAC2007, KEK33

Beam Duct Measured electron current can be reproduced by asimulation,

 he~0.04
 dmaxはアーク部での値と矛盾しない。
 dmax ~1.2

2007/3/19

MAC2007, KEK34

Beam Duct Measured electron current can be reproduced by asimulation,

2007/3/19

MAC2007, KEK35