Vacuum
The 27th KEKB Accelerator Review Committee
26th March 2024
Kyo Shibata
On behalf of KEKB Vacuum GroupInter-University Research Institute Corporation High Energy Accelerator Research Organization (KEK)
大学共同利用機関法人 高エネルギー加速器研究機構 (KEK)Contents• Introduction• Major Vacuum works during LS1• MR works• Collimator works & status• DR works• MR vacuum status after LS1• DR vacuum status after LS1• Summary
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The 27th KEKB Accelerator Review Committee

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Vacuum works during LS1 at a glance (MR): Area open to dry nitrogen or atmosphere

LER

Collimator head replacement (D02V1)
Collimator relocation(D03V1 -> D05V1)

Collimator head replacement (D01V1)

IR works

Temporary countermeasure against
vacuum leak from beam pipe welding line
Installation of new bellows
chambers with SR masks
NEG pump feedthrough replacement(Vacuum leak)

Removal and reinstallation of
kicker ceramic chambers formagnetic field measurement
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HER

IR works
Gate valve & bellows chamber
replacement

NLC (D05V1) systemconstruction
Collimator head replacement(D05V1)

Bellows chamber replacement(vacuum leak)Ion pump feedthrough replacement(Abnormal discharge, Vacuum leak)

Collimator head replacement(D06V1, D06H3)
Installation of HOM absorberchamber
Collimator head replacement(D06H3, D06H4)
Collimator relocation(D06H1 -> D06H4)

Collimator head replacement(D09V1)

Injection septum &chamber replacement

The 27th KEKB Accelerator Review Committee

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Vacuum works during LS1 at a glance (BT&DR): Area open to dry nitrogen or atmosphere

BT

Installation of V-offset bellows chambers (BTp)Installation of CSR monitor chamber (BTp)DR

Installation of OTR screen monitor (BTp)Removal and reinstallation of
bellows chambers for magnet
alignment (BTe & BTp)

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RF cavity work (by RF group)
Removal and reinstallation of Ext. kicker
chambers for Kicker PS work

The 27th KEKB Accelerator Review Committee

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List of major works during LS1 (MR)
Vacuum work

• IR work (LER&HER)• Replacement of IP bellows chambers• QCS cryostat modification• NLC system construction (LER)• Removal and reinstallation of kicker ceramic chambers for magnetic field measurement (LER)• Replacement of beam pipes at HER Injection point (HER)
Will be reported in this talk
• Installation of new bellows chamber with SR mask at Wiggler sections (LER)(works mainly for vacuum system)• Countermeasure against vacuum issues
•
•
•
•
•

NEG pump feedthrough replacement (countermeasure against vacuum leak, LER)
Ion pump feedthrough replacement (x4, countermeasure against abnormal discharge & vacuum leak, HER)
Bellows chamber replacement (countermeasure against vacuum leak, HER)
Temporary countermeasure against vacuum leak from beam pipe welding line (countermeasure against vacuum leak, LER)
Gate valve and bellows chamber replacement (countermeasure against pressure spike, HER)

• Collimator works (LER&HER)
•
•
•
•
•

Collimator relocation (LER:D03V1 -> D05V1(NLC), D06H1 -> D06H4)
Collimator head replacement (LER:D02V1, D05V1(NLC), D06V1, D06H3, D06H4, HER:D01V1, D09V1)
Installation HOM absorber chamber near D06V1 (LER)
Installation of permanent magnet on SuperKEKB-type horizontal collimators (countermeasure against SBL, LER&HER)
Upgrade of KEKB-type driving mechanism (HER:D09V1, D12V3)
Not vacuum work

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List of major works during LS1 (BT&DR)• Removal and reinstallation of bellows chambers for magnet alignment (BTe & BTp)
• Installation of V-offset bellows chambers (BTp)• Installation of CSR monitor chamber (BTp)• Installation of OTR screen monitor (BTp)

Requirements for vacuum system are less severe.

• Removal and reinstallation of Ext. kicker chambers for Kicker PS work (DR)Will be reported in this talk(First vacuum work after start of beam operation)

Vacuum work

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The 27th KEKB Accelerator Review Committee

6Major vacuum works during LS1 (MR) #1• Vacuum work at LER wiggler sections (LER)

Temp [°C]70

Already reported in last KEKB Review• Countermeasure against temperature rise ofbeam pipes downstream of Wiggler Sections

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40

Bellows chamber
replacement
w/o → w/ SR masks

30

w/ → w/o SR masks

70

Nikko wiggler section (D10, D11)60

@1400 mA

50
40
30
20

beam

D10 D11e+Installation of new bellows
chambers with SR masks
Wiggler
sections

D04 D05• Air and water cooling of the bellows chamberwith SR masks were also enforced.

Wiggler removal
For NLC50

beam• Rearrangement of bellows chambers• Larger SR power locations:
From bellows chamber w/o SR masks to w/ SR
masks (9 chambers)• Smaller SR power locations:
From bellows chamber w/ SR masks to w/o SR
masks (8 chambers)

60@1400 mA

20

Temp [°C]• Beam current will be increased after LS1.
• Magnetic field of wiggler magnets might beincreased to compensate the reduction due toremoved wiggler magnets for NLC systemconstruction.
• Strong SR should be absorbed by SR masks in the
bellows chambers.
• Locations of SR masks were optimized.

Oho wiggler section (D04, D05)

NLC

The 27th KEKB Accelerator Review Committeee+

SR masks in bellow chamber
7

Major vacuum works during LS1 (MR) #2• NEG pump feedthrough replacement (LER)

LER beam pipe

NEG pump• Countermeasure against vacuum leak during LS1• It was found that a vacuum switch at D09 Arc Section in LER indicatedabnormally high pressure. (2022/12/28)• Vacuum gauges and Ion pumps were turned off by I/L.
• Unfortunately, data logging had been accidentally stopped, so
pressure history was unknown.
• D09 Arc Section was filled with air up to low vacuum at least.
• Vacuum leak from NEG pump feedthrough was detected by vacuum
leak test.

• Replacement and investigation of NEG pump feedthrough• Faulty feedthrough was replaced with new one.
• It was found that vacuum leak was occurred at the brazed part
between the ceramic and stainless steel.
• Investigation with X-rays revealed a crack in the ceramic part.
• Ceramic tube inside vacuum was also broken.
• It is still unclear why the ceramic parts were damaged at this time.
• No work near this feedthrough & no NEG activation at this time.
• Remaining excessive force during installation?
• No further countermeasure against this issue

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NEG pump feedthroughThe 27th KEKB Accelerator Review Committee

D09
Feedthrough tip

NEG pump
NEG pump is installedbehind ceramic part
Broken ceramic tube

Leak point

8Major vacuum works during LS1 (MR) #3• Countermeasure against abnormal discharge and vacuum
leak during LS1• Pressure at D12 Arc Section of HER suddenly increased to ∼10−4 Pa.
(2023/8/25)• It was found that abnormal discharge occurred in HV connector of an ion
pump.
•

There was abnormal sound from it and abnormal high temperature on it.

• Discharge in the connector resulted in vacuum leak.

Pressure [Pa]• Ion pump feedthrough replacement (x4, HER)

10-3
10-5
10-6
10-8
10-9

0:00 12:00 0:00 12:00 0:00 12:00 0:00
8/28
8/26
8/27
8/25/2023••

Similar issues has occurred several times over the past 20 years.

D09

Ion pump feedthrough (discharged)• Faulty feedthrough was replaced with new one. (Vacuum work)• Feedthroughs and connectors of other ion pumps were checked.
• It was found that abnormal discharge occurred in some connectors at
D09 & D12 Arc Sections.

Three feedthroughs in D09 & D12 Arc Sections were replaced with new ones.
(Vacuum work)
Others were reused after cleaning. (Not vacuum work)

Vacuumleak

10-7• Replacement of HV feedthrough and investigation of otherfeedthroughs

•

D12

10-4

Connector (discharged)

Ion pump feedthrough(healthy)• Similar issues occurred during LS1 although they did not result in vacuum
leaks fortunately.
• They may be due to an increase in humidity due to the air conditioner
stopping.

Ion pump• Further countermeasures:• R&D of humidity-resistant HV feedthrough and connector was started.
•

Since the feedthrough is no longer in production and difficult to obtain,
alternative feedthrough must be developed.

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The 27th KEKB Accelerator Review Committee

Ion pump feedthrough (discharged)

Connector (discharged)9

Major vacuum works during LS1 (MR) #4• Countermeasure against vacuum leak during LS1• Pressure at D03 Arc Section of HER gradually increased to∼7×10−7 Pa. (from 2023/12/13)• Leak test revealed that a vacuum leak occurred at the brazing
line of a bellows chamber.
• Faulty bellows chamber was replaced with new one.

Pressure [Pa]• Bellows chamber replacement (HER)

×10-7
7
D03

6
5
4
3
2
1

0:00 12/14 12/16 12/18 12/20
12/12/2023• It was installed into KEKB in 1997.

Leaked bellows chamber• Still unclear why the vacuum leak occurred at thisbellows chamber at this time
• If vacuum leak occurs at other bellows chamber, it will be
replaced with spare bellows chambers.
• There are spare bellows chambers.

He gas was sprayed with a syringe to locate the leak point

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Major vacuum works during LS1 (MR) #5• To make orbit length the same as before removal of wiggler
magnets in NLC section, beam pipes in Nikko chicane section
were moved horizontally by up to 24 mm.
• The BPM block of the Q-chamber, which had not been fixed
for unknown reason, was fixed to the Q-magnet.
(2023/4/28)• Vacuum leak occurred from the welding line of the BPM
block. (2023/6/3)•••

Leak rate was ∼10−9 Pam3/s at this point.
This chamber was deformed during TiN coating process and repaired
before installation into the SuperKEKB.
Stress due to repair work might be a cause of the vacuum leak.

• Countermeasure against vacuum leak:10-5

Vac seal

10-6
10-7
10-8

0:00 6/11 6/21
6/1/2023

7/1

7/11

7/21

e+

8/1

24 mm
Vacuum bag sealant tape

• At first, the vacuum leak was stopped by “Vac seal”, however
it could not be stopped by “Vac seal” in the end.
• The vacuum leak was stopped by “Vacuum bag sealant tape”.

• Further countermeasure• New beam pipe is currently being fabricated and is scheduled to bedelivered on 27th March (tomorrow).

26th March 2024

Leak rate : ∼10−9 Pam3/s
Vac bag sealant tape

D11
Nikko chicane• Re-alignment of beam pipes in Nikko Chicane
Section (not vacuum work)

10-4

Pressure [Pa]• Temporary countermeasure against vacuum
leak from beam pipe welding line (LER)

The 27th KEKB Accelerator Review Committee

Vac sealQ-mag.

BPM Block
BPM support

BPM block is fixed to Q-magnet
by BPM support

11

Major vacuum works during LS1 (MR) #6

Pressure [Pa]• Abnormal pressure spikes near a gate valve were observed
at HER D12 Arc Section (2022ab).
• Abnormal temperature rise of the gate valve was also
observed.
• Internal visual check revealed that the groove for the RF
contact of the bellows chamber connected to the gate
valve was 1 mm deeper than designed. (Vacuum work)• Possible cause is discharge at small gap due to poor
contact between gate valve and bellows chamber.

Beam current [mA]

• Replacement of gate valve and bellows
Already reported in last KEKB Review
chamber (HER)• Countermeasure against abnormal pressure spike

Gate valve

M. Shirai

Beam current

Bellows chamber
D12

Y. Suetsugu• Gate valve and bellows chamber were replaced with newones.
• It was confirmed that the depth of the groove for the RF
contact of installed bellows chamber was designed value.
• It was also confirmed that the pressures and temperaturesof other HER gate valves were normal.
• The depth of the other bellows chamber grooves seems tobe as designed.
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RF contact

Vacuum seal
12Collimator works during LS1 #1• Collimator relocation and head replacement:• Replacement of damaged heads of verticalcollimators

Damaged head

D02

M. Shirai

D03• LER : D02V1, D06V1• HER : D01V1, D09V1

D05• Relocation and head replacement for NLC

D06• LER : D03V1 -> D05V1(NLC)• Head was replaced with shorter one (Ta, 5 mm) for scratch
resistant• D06V1 (Ti, 10 mm) can be used as a spoiler for SBL• Countermeasure against injection kicker
accidental firing (Horizontal collimators)

D01

D09

New head with Cu coating

T. Ishibashi• LER : D06H3

Carbon head
(Before Cu coating)• Head was replaced with Low-Z one (C, 16mm) for robustness• Spoiler against inj. kicker accidental firing.

• LER : D06H1(upstream of D06H3) -> D06H4 (downstreamof D06H3)• W head was replaced with Ta head (10mm) to suppress dust
generation when damaged.
• Absorber against inj. kicker accidental firing.

S. TeruiCarbon head
(After Cu coating)• LER Inj. Kicker accidentally mis-fired several times in 2024arun, and Low-Z collimator seemed to work as expected.
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The 27th KEKB Accelerator Review Committee

e+
LER

eHER
13

Collimator works during LS1 #2• Other collimator related works:

M. Shirai

D06V1• Installation of HOM absorber chamber (LER)• Beam pipe with HOM absorbers was installed near D06V1 collimator in LER.
• For future high current beam operation.
• HOM generated at collimator have not been serious issues so far.

• Installation of permanent magnet on SuperKEKB-type horizontal
collimators (LER&HER)

HOM absorberchamber
Permanent magnet• For suppression of electron cloud which may be the cause of SBL.
• All SuperKEKB-type horizontal collimators have permanent magnets on it.

• Precise alignment of collimators by Magnet Group.

• For SuperKEKB-type Vertical collimators whose heads were replaced during LS1

T. Ishibashi• HER : D01V1• LER : D02V1, D05V1, D06V1• Upgrade of KEKB-type driving mechanism• For more precise and stable position control• HER : D09V1, D12V3
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M. Shirai

The 27th KEKB Accelerator Review Committee

Conventional driving
mechanism

New driving
mechanism
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Status of LER collimator after LS1
T. Ishibashi• Vertical collimator
Name

Type

Tip Material

Cu coating

Tip condition

D02V1

SuperKEKB

Ta (160 mm)

〇

〇

D05V1

SuperKEKBTa (4 mm)

〇

〇

D06V1

SuperKEKB

Ti (10 mm)

〇

〇

D06V2

SuperKEKB

Hybrid (3 mm)〇〇• Horizontal collimator
Name

Type

Tip Material

Cu coating

Tip condition

D02H1-H4

SuperKEKBW (10 mm)

×

〇

D03H1

SuperKEKBW (10 mm)

×

〇

D06H3

SuperKEKB

C (160 mm)

〇

〇

D06H4

SuperKEKB

Ta (10 mm)

×〇• Remarks• D06H3 and D06H4 work as spoiler and absorber against
inj. kicker accidental firings.
• All collimator heads are healthy (Not damaged).
• All vertical collimator heads are coated with Cu.
• All horizontal collimator have permanent magnets.

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Status of HER collimator after LS1• Vertical collimator
Name

Type

Tip Material

Cu coating

Tip condition

D01V1

SuperKEKB

Ta (10 mm)〇〇

D12V1, V2

KEKB

Ti (40 mm)〇

×D12V3, V4

KEKB

Ti (40 mm)〇〇

D09V1-V4

KEKB

Ti (40 mm)〇〇• Horizontal collimator
Name

Type

Tip Material

Cu coating

Tip condition

D01H3-H5

SuperKEKBW (10 mm)×〇D12H1, H3

KEKB

Ti (40 mm)

×

〇

D12H2

KEKB

Ti (40 mm)

〇

×

D12H4

KEKB

Ti (40 mm)〇〇

D09H1-H4

KEKB

Ti (40 mm)〇

×T. Ishibashi• Remarks• Drive mechanism of some KEKB-type collimators has
been upgraded for precise and stable adjustment.
•

D09V1, D12V1, D12V3, D12V4

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Major vacuum works during LS1 (DR)• Two beam pipes were disassembled and reinstalled for Ext.
Kicker PS work.
• First vacuum work after DR construction• West Arc Section was filled with dry nitrogen.
• Ceramic beam pipe for Ext. kicker and a beam pipe next to it weredisassembled to remove Kicker PS.
• These two beam pipes were filled with dry nitrogen and reinstalled into DR
about 10 months later.
• Remaining area of West Arc Section was also filled with dry nitrogen forabout 10 months.

• Other sections covered by Vacuum Group were kept in vacuum.
• East Arc Section• North Straight Section• Sought Straight Section

DR

Removal and reinstallationof Ext. kicker chambers for
Kicker PS work

RF cavity work (by RF group)• RF Group also performed vacuum work at RF section during LS1• Vacuum system of RF section is covered by RF Group.
• Pressure of RF section was improved by this work.
• Pressures of West Arc Section and Sought Straight Section were also
improved by this work.

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The 27th KEKB Accelerator Review Committee

Ext. kicker and its PS

Disassembled beam pipes
17

Beam dose & Maximum beam currents (MR)• Beam dose integrated in 2024a run (1/29 ∼ 3/23)

HER

Whole ring

• HER : 308 Ah• LER : 358 Ah• No more dedicated vacuum scrubbing is required.

Arc sections

Pressure measurement limit
Beam current• Max. beam current in 2024a run (1/29 ∼ 3/23)

640 mA• HER : 640 mA• LER : 800 mA• Max. beam current
so farLER

Whole ring
Arc sections• HER : 1145 mA• LER : 1455 mA

Pressure measurement limit
Beam current

1455 mA
800 mA

Phase1

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1145 mA

The 27th KEKB Accelerator Review Committee

Phase22019c
2020c 2021c
2019ab 2020ab 2021ab 2022ab

LS1

Phase3182024ab

Vacuum scrubbing status (MR)
• Vacuum scrubbing is proceeding steadily in both rings.
• ∆p/∆I is decreasing steadily as beam dose increases.
• ∆p/∆I is higher in LER than HER.
• Less memory effect in LER• More vacuum works in LER during LS12024ab (This run)
Whole ring
Arc sections
Imax

LER

2024ab (This run)
Whole ring
Arc sections
Imax

Whole ring
Arc sections
2022ab (Previous run)
Imax

26th March 2024

HER

Whole ring
Arc sections
2022ab (Previous run)Imax

The 27th KEKB Accelerator Review Committee

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Vacuum scrubbing status (MR)
• Vacuum scrubbing status from Phase-I to Phase-III 2024ab run (∼3/22)

LER
Phase22024ab

2020c
2021c

Phase1∆p/∆I & η
for arc sections
2019ab26th March 2024

2020ab2021ab2022ab∆p/∆I for whole ring

Phase22019c

2024ab2020c
2021c

Phase1∆p/∆I & η
for arc sections

The 27th KEKB Accelerator Review Committee

2019ab2020ab2021ab2022ab20

η @Arc sect. [molec./photon]

2019cη @Arc sect. [molec./photon]∆p/∆I
for whole ring

HER

Beam dose & Pressure (DR)• Beam dose (until 3/22 0:00)

East Arc Section
West Arc Section(Vacuum work during LS1)
North Straight Section
Sough Straight Section
RF Section(Vacuum work during LS1
by RF Group)• 73.0 Ah (from start of beam operation)• 5.4 Ah (after LS1)

• Pressure• RF Section work during LS1 has significantly reduced the average pressurein West Arc Section and South Straight Section.

Average pressure measured by ion pumps
Sough Straight Section
Beam doseWest Arc Section
East Arc Section
North Straight
SectionCurrent
Current
Current

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Vacuum scrubbing status (DR)• Vacuum scrubbing of West Arc Section is proceeding steadily after LS1.

• To eliminate the influence of pressure in RF section, average pressure measured by ion pumps excluding one near RF
Section was shown as West Arc Section.
• ∆p/∆I is decreasing steadily as beam dose increases.

• ∆p/∆I of West Arc Section is still higher than that of East Arc Section• Gap between West Arc Section and East Arc Section is narrowing.
• Impact of long vacuum work in West Arc Section on the beam operation is not large.
After LS1

West Arc Section

DR

West Arc Section

East Arc Section

East Arc Section

Beam Dose after LS1 [Ah]26th March 2024

The 27th KEKB Accelerator Review Committee

Removal and reinstallationof Ext. kicker chambers for
Kicker PS work

RF cavity work (by RF group)22Other activities• Investigation on beam pipe deformation due to SR heating in SLY section.
• Measurement of deformation of beam pipes due and displacement of BPM and
Q-magnet in SLY section• Simulation of deformation of beam pipes and displacement of BPM and Qmagnet in SLY section• Fabrication of new BPM supports to isolate BPM block from Q-mag.

M.L. Yao• They will be installed near future.

• Development of pressure anomaly detection method applying machinelearning• Trial operation of pressure anomaly detection program from this month (March
2024).

S. Terui• Collimator R&D• R&D of more robust head material such as MoGr
• R&D of collimator with revolver heads• And so on.
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The 27th KEKB Accelerator Review Committee

23Summary• A lot of vacuum works were done during LS1, and mainly vacuum works related to thevacuum system and collimator were reported.
• Installation of new bellows chambers with SR mask at Wiggler Sections• NEG pump feedthrough replacement• Ion pump feedthrough replacement• Bellows chamber replacement• Temporary countermeasure against vacuum leak with vacuum sealant tape
• Gate valve and bellows chamber replacement• Collimator relocation• Collimator head replacement• Installation HOM absorber chamber• Removal and reinstallation of Ext. kicker chambers (DR)• All vacuum works planned during LS1 were successfully completed.
• Vacuum scrubbing is proceeding steadily.
• No more dedicated vacuum scrubbing is required.

• Vacuum system is ready for higher beam current operation!!
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Fin.

Thank you for your attention.

Inter-University Research Institute Corporation High Energy Accelerator Research Organization (KEK)
大学共同利用機関法人 高エネルギー加速器研究機構 (KEK)Backup• Vacuum Bag Sealant Tape
• https://www.generalsealants.com/vacuum-bag-sealants/#1568264193156-000f6158-0e49

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The 27th KEKB Accelerator Review Committee26