Vacuum
Collimator will be presented by Ishibashi_san (14th Dec.)

The 26th KEKB Accelerator Review Committee
13th Dec. 2022
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• MR• Vacuum System Status• Major troubles (from 2019c to 2022ab*)• DR• DR Vacuum System Status• Vacuum works during LS1• Summary
Last vacuum status report was made by Ishibashi_san at 23rd KEKB Review* (immediately
after 2019ab run).
13th Dec. 2022

The 26th KEKB Accelerator Review Committee2MR : HER pressure and beam current• HER pressure is decreasing steadily
although beam current is increasing
gradually.

• Maximum beam current : 1145 mA• Pressures with beam at the end of 2022ab:∼5×10-8 Pa (1145 mA, 2249 bunches)• Base pressure without beam: ∼3×10-8 Pa

Arc

Arc

Arc

Arc

HER

Whole ring

Arc sections∼5×10-8 Pa(1145 mA, 2249 bunches)(Measurement limit in cold cathode gauges)• Pressure is approaching measurement limit.
• Accurate pressure measurement is difficult.

Beam current

Pressure measurement limit

1145 mA• HER pressure is lower than LER pressure
due to memory effect.

• See following slides.
• ∼82% of beam pipes, bellows chambers,
and pumps were reused.

Phase1

Phase22019ab2019c

2020ab2020c

2021ab2021c

2022abPhase313th Dec. 2022

The 26th KEKB Accelerator Review Committee3MR : LER pressure and beam current• LER pressure is decreasing steadily althoughbeam current is increasing gradually.
• Maximum beam current : 1455 mA• Pressures with beam at the end of 2022ab:∼2×10-7 Pa (1.455 mA, 2249 bunches)• Base pressure without beam: ∼3×10-8 Pa

Whole ring

Arc

Arc

Arc

Arc

Arc sections(Measurement limit in cold cathode gauges)• LER pressure is higher than HER pressure.

• ∼ 93% of beam pipes and bellows chambers,
and pumps were renewed. (no memory
effect)• More vacuum works have been done in LER
than HER.

Beam current

Phase12019ab2019c∼2×10-7 Pa(1455 mA, 2249 bunches)

1455 mA

Pressure measurement limit

Phase2

LER

2020ab2020c

2021ab2021c

2022abPhase313th Dec. 2022

The 26th KEKB Accelerator Review Committee4MR : pressure and beam current• Comparison between LER and HER

LER

Whole ring

Arc sections

Arc sections

Beam current

Phase1Pressure measurement limit

Phase22019abBeam current

2022ab2020ab2021ab
2019c
2020c
2021c

Phase1

Phase313th Dec. 2022

HER

Whole ring

The 26th KEKB Accelerator Review Committee

Phase22019ab2022ab2020ab2021ab
2019c
2020c
2021c
Phase35

MR : HER vacuum scrubbing• For HER, ∆p/∆I and η show thevacuum scrubbing is progressing
steadily.

Photon dose [photons/m]
1024
1025

1023
-4
10

10-4

∆p/∆I
for whole ring10-5

• ∆p/∆I = (3 × pmeasure – pbase) / beam current• η [molec./photon]: photon-stimulated gas
desorption rate at arc sections as a function ofphoton dose• η [molec./photon]= 94.7 × ∆p/∆I [Pa/A] × S [m3s-1m-1]∆p/∆I [Pa/A]

pmeasure : pressure measured by CCG at pumping port
3 × pmeasure : estimated pressure in beam channel(3 is conversion factor from pressure at CCG
to pressure in the beam channel)
pbase : base pressure (3.0×10-8 Pa)

10-5
Phase2

10-6
10-7
10-8

2019c 2020c 2021c

Phase1• At the end of 2022ab (at 5.7×1025 photons/m), ηreached 2×10-8 molec./photon

13th Dec. 2022

10-7∆p/∆I & η
for arc sections

S [m3s-1m-1] : Pumping speed per unit length(0.03 m3s-1m-1 for HER)

10-6

10-9

101

The 26th KEKB Accelerator Review Committee

2×10-82019ab2020ab102
103
Beam dose [Ah]2021ab10-82022ab104

6

η @Arc sect. [molec./photon]• ∆p/∆I [Pa/A]: pressure rise per unit beam
current as function of the beam dose

HER

MR : LER vacuum scrubbing• For LER, ∆p/∆I and η show the vacuum
scrubbing is progressing steadily, but
still much larger than those for HER.

10-4

•

At the end of 2022ab (at 3.9×1025 photons/m), ηreached 4×10-7 molec./photon• ∆p/∆I evaluation by fitting curve:

2019c 2020c 2021c

10-4
10-5

10-6
∆p/∆I & η
for arc sections

Phase1

10-6

10-7

4×10-7

3.3×10-7

2019ab• ∆p/∆I [Pa/A] = 5.3×10-5×(beam dose)-0.8• At 1×104 Ah, ∆p/∆I [Pa/A] will reach 3.3×10-7 Pa/A.

2020ab10-8
10-9 110

13th Dec. 2022

Phase210-5∆p/∆I [Pa/A]

S [m3s-1m-1] : Pumping speed per unit length(0.06 m3s-1m-1 for LER)LER

The 26th KEKB Accelerator Review Committee

102

Beam dose [Ah]1032021ab10-72022ab

η @Arc sect. [molec./photon]∆p/∆I
for whole ring• η [molec./photon]: photon-stimulated gas
desorption rate at arc sections as a function ofphoton dose• η [molec./photon]= 166 × ∆p/∆I [Pa/A] × S [m3s-1m-1]

1023

Photon dose [photons/m]
1024
1025

10-8
104

∆𝑝𝑝
= 5.3 × 10−5 × Beam dose −0.8
∆𝐼𝐼7

MR : vacuum scrubbing• Comparison between LER and HER
10-4

10-4

LER

10-6
10-7

10-5
∆p/∆I [Pa/A]∆p/∆I [Pa/A]

10-5

10-6
10-7

10-8

10-8

10-9

10-9

13th Dec. 2022

HER

The 26th KEKB Accelerator Review Committee8MR : maximum beam current and beam dose
• Beam dose during Phase3
2022ab• HER : ∼1450 Ah• LER : ∼1800 Ah• ∼122 days

2022abLER Imax : 1455 A∼1800 Ah during 2022ab∼1450 Ah during 2022ab

HER Imax : 1145 A

LER total beam dose : ∼7300 Ah
Phase1
Phase2Phase32019ab2021ab 2021c

2019c

HER total beam dose : ∼6200 Ah

2020ab2020c

For LER• ∼ 2.3×10−3 months/Ah• It will take ∼2.3 months toaccumulate 1000 Ah more.

More 6.2 months are required
to accumulate 104 Ah in total.

10-5

10-5
∆p/∆I [Pa/A]• It will take ∼6.2 months
more to accumulate 104 Ah
in total and reach ∼3.3×10-7
Pa/A.

10-6

10-6

10-7

10-7
3.3×10-7

10-8

10-8

10-9 110

13th Dec. 2022

10-4

LER

The 26th KEKB Accelerator Review Committee

η @Arc sect.
[molec./photon]

10-4

102

103

104

Beam dose [Ah]9MR : beam current dependence of pressure• LER Pressure rise is not in proportional to the total beam current (I) recently.
• Pressure rise rate becomes larger at higher beam currents.
• Pressure depends on the number of bunches (Nb).

• It seems that pressure is determined by thermal desorption (TD) and photon-stimulated desorption (PSD).

• Measured pressures are well reproduced by the regression curve with following assumption and experimental result.
• Regression curve : 𝑝𝑝 = 𝑝𝑝0 + ∆𝑝𝑝p + ∆𝑝𝑝t = 𝑝𝑝0 + 𝐶𝐶p 𝐼𝐼 + 𝐶𝐶t 𝐼𝐼2 ⁄𝑁𝑁b 2 = 2.42 × 10−8 + 7.64 × 10−11 𝐼𝐼 + 7.64 × 10−11 𝐼𝐼2 ⁄𝑁𝑁b 2• Assumption (PSD): ∆𝑝𝑝p ∝ 𝐼𝐼
• Experimental result (TD): ∆𝑝𝑝t ∝ ∆𝑇𝑇 2 → ∆𝑝𝑝t ∝ 𝐼𝐼2 ⁄𝑁𝑁b 2• Constants (p0, Cp, Ct) were determined by multi regression analysis using data for LER.

• There may be some vacuum components heated by HOM?
Measurement

Calculation byregression curve

Y. Suetsugu

13th Dec. 2022

The 26th KEKB Accelerator Review Committee10MR : contribution to beam lifetime• Recent single beam lifetime is not limited by only pressures but also the Touschek effect (Touschek lifetime).
• Pressures have been decreasing steadily though the apertures are strongly restricted by beam collimators.
• Beam emittance is small (εy = ∼20 pm) and bunch length is short (σz = ∼6 mm).

• Contribution of the pressure to beam lifetime (τ) was estimated by multi regression analysis for LER.
• Measured lifetime are well reproduced by the regression curve with following assumption.
• Regression curve : 1⁄𝜏𝜏 = 1⁄𝜏𝜏𝑝𝑝 + 1⁄𝜏𝜏𝑡𝑡 = 𝐶𝐶p 𝑝𝑝 + 𝐶𝐶t 𝐼𝐼⁄ 𝑁𝑁𝑏𝑏 𝜎𝜎𝑧𝑧 = 2.61 × 105 𝑝𝑝 + 0.979𝐼𝐼⁄ 𝑁𝑁𝑏𝑏 𝜎𝜎𝑧𝑧

• Assumption1 (beam lifetime due to pressure): 𝜏𝜏𝑝𝑝 ∝p• Assumption2 (Touschek lifetime) : 𝜏𝜏𝑡𝑡 ∝ 𝐼𝐼⁄ 𝑁𝑁𝑏𝑏 𝜎𝜎𝑧𝑧
• Dependence on the emittances was not included in the Touschek effect here, since the measured emittances were scattered.
• Constants (Cp, Ct) were determined by multi regression analysis using data for LER.

• For LER single beam, approximately 60-80% of the total lifetime is determined by Touschek lifetime at present.
• For HER single beam, approximately 100% of the total lifetime is determined by Touschek effect.
τ vs. I for different Nb∆P/∆I and Iτ vs. beam dose

Ratio of 1/τp to 1/τt vs. bunch current
Y. Suetsugu

Measurement

13th Dec. 2022

Calculation byregression curve

The 26th KEKB Accelerator Review Committee11MR : electron cloud effect• At present, any obvious signs of electron cloud effect are not observed in usual collisionexperiments.
• Current linear density is now over 0.53 mA/bunch/RF-bucket

Y. Suetsugu

Magnet units attached to beam pipes
Vertical beam size vs. current
density in Phase-1

Bunch by bunch luminosity along
a train by ADLM (S. Uehara)

Vertical beam size vs. current
density in Phase-3

Phase-3

Phase-1

>0.53
~0.2

13th Dec. 2022

The 26th KEKB Accelerator Review Committee12MR : major troubles #1
Beam current
pressure• Vacuum leak was stopped by “flange
refastening” and “Vac seal injection”.

• We tried refastening the suspect flanges
without identifying the leak location on
maintenance day.
• It was confirmed that vacuum leakage had
occurred at flange connection.
• Vac seal was injected into the flange
connection.

Vacuum leak during 2020ab

Vacuum leak during 2022ab
SR mask
Air cooling fan

Vac seal injection• Countermeasure• Bellows chambers were replaced to new ones
with SR masks.
• Air and water cooling were reinforced.
• See page 24.

13th Dec. 2022

Pressure [×10-7 Pa]• Possible cause was thermal expansion due tostrong SR irradiation.
• Pressure was still low enough to continue
beam operation.

Pressure [×10-7 Pa]• Abnormal pressure rises due to vacuum leakwere observed immediately after beam abort.

pressureBeam current [mA]

• Vacuum leaks at LER D04 wiggler sections(2020ab, 2022ab)

Beam current [mA]

• Vacuum leak (from 2019c) #1&2:

Beam current

The 26th KEKB Accelerator Review Committee

Bellows chamber w/ SR masks

Air cooling reinforcement13MR : major troubles #2
Beam current• Cooling water stopped due to pump failure, but beam
operation was continued for a few minutes.
• “Low water flow” alarm did not issue beam abort
request because flow meters often failed.
• At final, beam abort was requested by “hightemperature & low water flow” alarm.

Pressure [Pa]• Vacuum leaks at LER D10 wiggler section (2020c)

Beam current [mA]

• Vacuum leak (from 2019c) #3:• After cooling water flow was made by sub pump, beam
operation was resumed.
• Some vacuum gauges at D10 wiggler section showed
higher pressures than usual.

Pump failed• Leak test was performed on the next maintenance day.

D10 wiggler
section• Pressures were still low enough to continue beam
operation.
•

beam

Nikko Lab.

D11 wiggler
section

It was found that vacuum leaks occurred at 9 flange
connections.

• Vacuum leaks were stopped by “flange refastening” and“Vac seal injection”.

• Countermeasure

Suspected leak point• Interlock modification• When several “Low water flow” alarms are issued
simultaneously, beam abort is requested.
• Water flow rate of main pipe was newly monitored by
vacuum group.
• When cooling water flow rate of main pipe drops,
beam abort is requested.

13th Dec. 2022

The 26th KEKB Accelerator Review Committee

Leak rate[Pam3s-1]
Cooling water stopped

Y. Suetsugu
14MR : major troubles #3
NEG conditioning• Vacuum leak (from 2019c) #4:

Water drain

Re-increase
Vac seal• Gradual pressure increase at LER D04 weak bend
section• Pressure increase had been observed since the startof 2021 run.
• NEG pump conditioning was effective to temporarily
reduce pressure, but pressure gradually increased
again.
• Vacuum leak test had been carried out several times,
but no vacuum leak had been detected.
• Pressure dropped when cooling water was drained
from cooling channel for leak test.

Beam current• Leak test showed no vacuum leaks from thecooling channel.
• Abnormal pressure increase stopped after that.

Beam current

pressure

Vac seal injection• Large pressure increase was observed with low
beam current during 2022ab.
• At final, vacuum leak from the cooling channel was
detected.
• “Vac seal” was injected into the cooling channel by
an injector.

13th Dec. 2022

The 26th KEKB Accelerator Review Committee

Beam current [mA]

• Vacuum leak from cooling channel at LER D04
weak bend section

Pressure [Pa]• Abnormal pressure re-increased during 2022ab.

15

MR : major troubles #4• Abnormal pressure rise #1• Cause of improvement is still unknown.
• Countermeasures were taken, but their effects
were not clear.

Pressure [Pa]• Pressure did not depend on beam current.
• Abnormal pressure rise seemed to have
improved.

• Permanent magnets to suppress multipactor
effect.
• Air cooling reinforcement

Beam current

Beam current [mA]

• Abnormal pressure rise near gate valve wasobserved at HER inj. section (2020ab).

Air cooling fan

Permanent magnet
Disassembled gate valve• Possible cause of abnormal pressure rise isabnormal heating of gate valve.

• During summer shutdown after 2020ab run, thesuspected gate valve was replacement withdummy pipe.
• No abnormal pressure rise has been observed
after that.
• Removed gate valve was disassembled andchecked, but no obvious abnormality was found.
• Is there small gap at opening and closing
mechanism of gate valve? (See next slide)13th Dec. 2022

The 26th KEKB Accelerator Review Committee16MR : major troubles #5• Abnormal pressure rise #2:• Abnormal temperature rise of gate valve was also
observed.

• During LS1, bellows chambers connected to the gate
valve were disassembled for internal check.

Beam current• It was found that some parts were discolored probably
due to heating and/or discharge.
• RF shield of the gate valve• RF contact installed between the gate valve andbellows chamber

Gate valve

Beam current [mA]

• Abnormal pressure rise near gate valve wasobserved at HER D12 arc section (2022ab).

Pressure [Pa]M. Shirai

Bellows chamber• It was also found that groove for the RF contact on the
bellows chamber was 1 mm deeper than design.
• Possible cause is small gap due to poor contact between
gate valve and bellows chamber.

• Gate valve and bellows chamber were replaced withnew ones.

• It was confirmed that the groove for the RF contact on the
bellows chamber is correct.
• It was confirmed that the pressure and temperature of other
HER gate valves are normal.
••

Pressure at this gate valve was a little similar to pressure
at the gate valve at HER inj. section. (see previous page)
Gate valve at HER inj. Section had a similar problem?

13th Dec. 2022

RF contact

Vacuum seal

Y. Suetsugu

The 26th KEKB Accelerator Review Committee17MR : major troubles #6• Troubles of vacuum system are decreasing:• The ratio of troubles of vacuum system was less than 4%.
• Main troubles are repairs of vacuum leaks and exchanges of damaged vacuum components.
Total operation time, the ratio of no-operation time resulted fromtroubles to the total operation time, and those related to vacuum system

Y. Suetsugu

13th Dec. 2022

The 26th KEKB Accelerator Review Committee18

DR : vacuum status• Average pressure of the two arc sections and two straight sections since Phase2(excluding RF section).
• The pressures in the arc sections are sufficiently low.
•

In the west arc section, 2 beam pipes are temporarily disassembled for Ext. kicker works during LS1.

•

Elastomer gaskets in the RF section were replaced with metal gaskets during LS1 by RF group.

• High pressures near the RF section indicate higher pressure in the RF section, but it is still acceptable.

East arc section
West arc section 1 *West arc section 2 **North straight section
Sough straight section

Beam current

Phase213th Dec. 2022

2019ab

2019c 2020ab

2020c

2021ab2021c

2022abThe 26th KEKB Accelerator Review Committee* Average over all IPs** Average over IPs excluding one
near RF sect.
19

DR : vacuum scrubbing• ∆p/∆I and η for arc sections show the vacuum scrubbing
is progressing steadily.

DR Vacuum scrubbing status• At the end of 2022ab:• Total beam dose : 67.6 Ah (photon dose : 3.5×1024 photons/m )• η : 2×10-6 molec./photon

East arc
west arc∼28 mA

67.6 Ah

Beam dose
2×10-6

Beam current

13th Dec. 2022

The 26th KEKB Accelerator Review Committee

20

Vacuum works during LS1
Collimator head replacement(D02V1)

LER

Collimator head replacement(D01V1)HER

Collimator relocation(D03V1 -> D05V1)
Gate valve & bellows chamber
replacement (GV_D01H3)
Installation of new bellows
to suppress temperature rise
Collimator head replacement(D09V1)

NLC (D05V1)

Magnetic field measurement in
K1 and K2 ceramic chambers
13th Dec. 2022

Collimator head replacement(D06V1, D06H3)
Collimator relocation(D06H1 -> D06H4)

Injection chamber replacement

The 26th KEKB Accelerator Review Committee

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Major vacuum works during LS1 #1• Vacuum work at IR:• IP bellows chambers will be
replaced with new ones of thesame design.

• Fiberscope observations show that RFshield fingers are discolored but
appear to be healthy.
• More detailed check will be done after
removing IP chamber. (March 2023?)• Front cap (R-side) and front plate (Lside) of QCS cryostat will be replacedwith new one with a different material.

• For background noise reduction,material will be changed from W to
SUS.
• Tip of QCS-R cryostat will be smaller toallow more space for Belle II cables.
• For this work, it is necessary todisassemble QCS cryostat and QCS
beam pipes.

13th Dec. 2022

QCS cryostat

Y. Arimoto

Current front cap

New front cap

The 26th KEKB Accelerator Review Committee

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Major vacuum works during LS1 #2• Vacuum works for NLC:

S. Nakamura• Beam pipe replacement are required within arange of ∼50 m.
• Removal : 16 beam pipes & 18 bellows chambers• 10 Wiggler-mag. beam pipes with electron clearing
electrode, 5 Q-mag. beam pipes, 1 taper pipe, 1straight pipe, 18 bellows chambers• Installation : 1 collimator, 13 beam pipes, 22 bellows
chambers∼ 50 m• 1 Collimator (relocation from D03V1), 2 new beam pipes,
2 modified beam pipes, 4 reused beam pipes, 15 sparebeam pipes, 22 bellows chambers• TiN coating & baking at laboratory:• TiN coating: 2 new beam pipes, 2 modified beam pipes• Baking : 19 beam pipes excluding 4 reused beam pipes• Others:• New chamber support, Cooling water piping, Pb
radiation shield, concrete shield removal and installation,etc.

• Schedule••••

Production & modification : ∼ March/2023
Wiggler-Mag beam pipes removal : done
Collimator installation : ∼ March/2023
Beam pipe baking and TiN coating at laboratory : Nov./2022∼
May/2023• Beam pipe installation : May/2023 ∼ July/2023?

13th Dec. 2022

The 26th KEKB Accelerator Review Committee

23

Major vacuum works during LS1 #3• From bellows chamber w/o SR masks to w/ SR
masks : 9 chambers• From bellows chamber w/ SR masks to w/o SR
masks : 8 chambers• As a countermeasure against temperature riseof beam pipes downstream of the wiggler
sections• Beam current will be increased after LS1.
• Magnetic field of wiggler magnets will be
increased by the amount of decreased wiggler
magnets.
• Strong SR should be absorbed by SR masks in the
bellows chambers.
• Bellows chambers w/ SR masks installed inlocations where strong SR would not be irradiatedwere replaced with bellows chambers w/o SR
masks

Temp [°C]• Replacement of bellows chambers

60
50

Oho wiggler section (D04, D05)

@1400 mA

Wiggler removal

Bellows chamber
replacement
w/o → w/ SR masks

40
30
20

w/ → w/o SR masks

beam

70

Temp [°C]• Vacuum work at LER wiggler sections:

70

60

Nikko wiggler section (D10, D11)

@1400 mA

50
40
30
20

beam

SR mask• Air and water cooling of the bellows chamberwith SR masks were also enforced.
13th Dec. 2022

The 26th KEKB Accelerator Review Committee

24

Major vacuum works during LS1 #4• Vacuum work at HER injection
section:• 3 beam pipes are replaced withnew ones to increase injectionrate.
• Orbit clearance from chamber wall isenlarged by changing wall position
along beam axis.
• Wall length along the beam axis is
shorten as much as possible.

M. Kikuchi

wall
too smallclearance
New wall• Pumping port will be removed toshorten wall length if possible.

Y. Suetsugu• New BPM for injected beam is installed
for precise injection tuning.

• Schedule• Production : JFY2022 (∼ March/2023)• Beam pipe replacement : JFY2023(April/2023 ∼)13th Dec. 2022

The 26th KEKB Accelerator Review Committee

25

Summary• MR and DR vacuum systems have been working mostly well.
• Vacuum scrubbing progressed steadily.
• Troubles of vacuum system are decreasing.
• No clear indication of ECE has been observed.

• Recent behaviors of pressure against beam current are explained including
thermal desorption (heating by wall current and HOM) as well as PSD.
• Recent single beam lifetime is mostly limited by the Touschek effect rather
than pressure (the Rutherford scattering).
• Large vacuum works are ongoing during LS1.
• NLC construction at LER D05• IR vacuum works for modification of Belle II detector and QCS cryostat.
• Installation of bellows with SR masks at LER D04 and D10• Replacement of HER injection chambers• Many collimator works (not mentioned in this talk)• Etc.

13th Dec. 2022

The 26th KEKB Accelerator Review Committee

26

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)Backup13th Dec. 2022

The 26th KEKB Accelerator Review Committee

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