Sudden Beam Loss (SBL)
2024/6/3 B2GM H. Ikeda
SuperKEKB : T. Abe, H. Fukuma, Y. Funakoshi, T. Ishibashi, H. Kaji, T. Kobayashi, H. Koiso,
G. Mitsuka, T. Mitsuhashi, M. Nishiwaki, S. Ogasawara, S. Sasaki, Y. Suetsugu, S. Terui,
M. Tobiyama, T. Yamaguchi
Belle II : M. Aversano, T. Koga, A. Maeda, K. Matsuoka, S. Mitra, H. Nakayama, Y. Liu, R.
Nomaru, I. Okada, X. Shi, K. Uno, B. Urbschat, K. Yoshihara

Contents• What is “SBL”?
• Observations (Run1)• Works during LS1• Observations (Run2)• SBL events with QCS Quench/Belle II damage• Causes of SBL from observation• Knocker study• SummaryWhat is “Sudden Beam Loss” ?
Beam loss that occurs suddenly within
1 turn (10µs) without precursory
phenomena. ＝ Sudden Beam Loss
（SBL）
• The cause of SBL has been unknown.
• A significant percentage of the beam
is before the abort trigger is issued
and stored beam is dumped→ Harmful effects of SBL;

Beam signal measured by
Bunch Oscillation Recorder(BOR) & Bunch Current Monitor(BCM)• Damage to collimators and otheraccelerator components,• Quench of the final focusing
superconducting magnets (QCS),• Large backgrounds to the Belle-II detector,• Inability to store high current due tobeam abort.
3

Observations (Run1)• A large fraction of the stored beam is suddenly lost before the abort.
• Beam loss occurs in both HER and LER, but the damage to the hardware is particularly large
when the loss occurs in LER.
• We don't know if it will happen even with a single beam or low current beam because wehaven't operated for a long time under such a conditions.
• The starting point of beam loss depends on the collimator setting and is not limited to a specificlocation.
• Just before the beam loss begins, the orbit appears to move, but the displacement is small～O(0.1 mm).
• After the start of the beam loss, orbit displacement is <O(1mm).
• No oscillations that could be precursors to beam loss are observed.
• Pressure bursts have been observed all over the place and rarely occur in the same place except
at the collimator sections.
• At D06H3 and D06H1 collimators, we observed rapid and nonlinear pressure increase as westored more beam current.
4Works during LS1
To Mitigate SBL• Replaced damaged collimator heads.
• Copper coating of collimator heads (D6H3, D6V1, D5V1, D2V1). （Cover material with a high sublimation point,
which could be the seed of a fireball, with material with a low sublimation point.)• Installed permanent magnets in all SuperKEKB-type horizontal collimators. （In order to reduce the electron
cloud effect…）• LER D02H4, D02H3, D02H2, D02H1, D03H1, D06H3, D06H4• HER D01H3, D01H4, D01H5
To Investigate the cause of SBL• Installed more loss monitors for timing analysis.
• Added BORs (Bunch Oscillation Recorders) to investigate beam orbit change in locations that may be the causeof SBL.
• Measure the orbit at two different locations with phase differences. ：Existing BOR• Add a simplified version to measure in phase with the collimator, although with less accuracy. ：New BOR• Installed acoustic sensors to detect acoustic waves due to thermal shock generated by vacuum arc forinvestigation the cause of LER SBL.(D2V1:minimum physical aperture, D5V1:new collimator, QCS, D6V2 andD6V1 after starting run2)
5

Loss Monitor for Timing analysis• To gain more information aboutbeam aborts, especially SBL, some
PMT/EMT are installed during LS1.
• We shall analysis the waveform ofeach sensors to determine thesignal time and synchronize all the
sensors.

Example of loss monitor timing analysis• The vertical dashline is the signal
time determined by‘bi-threshold’ .
• For this abort, firstsignal is seen on
D5V1. Then insame turn, signal isseen in D2V1. Then
IR has huge dose.
• The collimators in
the upstream of D5
won’t help for thisabort.
• The D5V1 was fully
opened. (Wasclosed to 5mm at
3/26.
(X. Shi)• For the 5 aborts start D2V1, average IR
dose is 726 mRad (including one QCS
quench).
• For aborts start D6V1, average IR doseis 64 mRad, thanks to the collimators
btw IR and D6V1.
• Maybe there are multi-sources of SBL?
As the initial position is not always insame region(X. Shi)Location of BOR

D1

TL 筑波 TR

D2

12C
D01H5 (TL18)
D02H4 (TR14)
D02H2 (TR120)
D01H4 (TL34)
D02H3 (TR67)
D02H1 (TR142)
D01H3 (TL47)
D02V1 (TR80)
D03V1 (TR300)
D01V1 (TL60)
D12V4 (NR354)
D03H1 (OL352)
D12H4 (NR307)
D12V3 (NR285)
D12H3 (NR274)
D12H2 (NR236)
D12V2 (NR209)
D12H1 (NR199)
D12V1 (NR134)

D11

3C

D4 D4RF

Beam Dump
BOR/BCM

D5 C • Readout: oscilloscope → RFSoC

OL

赤：LER
青：HER

日光

NL

D10

• Use original FB monitor(upstream anddownstream).
• Readout:BOR/iGp12

9C

D05V1

B

D
E
F

New BOR/BCM

D09V4 (NL156)
D09H4 (NL203)
D09V3 (NL232)
D09H3 (NL236)
D09H2 (NL279)
D09H1 (NL307)

D06V2(OR271)
D06V1 (FL362)

D09V2 (FR354)

D06H3 (FL276)

D09V1 (FR209)

D06H1 (FL200)
6C

D8

H•
G
F

Use BPM that is upstream of the collimatorin phase with the collimator head.
• Same vertical betatron phase as
大穂
D2V1 : MQN1OP D5 BM2 66.7m
D5RF • Same vertical betatron phase asOR
A
D6V1 : MQD5P26 D7 BM3 144.4

NR

FR 富士 FL

D7

BOR timing analysis (May 5th, QCS quench event)• Beam orbit deviation timings found in BOR plots are overlayed on the loss monitor timing diagram• BOR/iGp12: Horizontal orbit deviation started 3.5turns before abort. Vertical orbit deviation and beam loss atcollimators started in the next turn.
• RFSoC: Horizontal orbit deviation was not seen in the first turn. This gives implication for the phase of oscillation.
• Since the oscillation was not observed at D6 in the first turn, we cannot select the ring section for SBL origin.

(H. Nakayama)Acoustic-Emission Sensors for D02V1 collimator
Acoustic loss monitor

On the undersidein the same manner

I. Okada,
K. Uno, and
T. AbeCan hear AE around the head.

(mechanically isolated)

Can hear particle showers

In the same manner for D05V1 collimator (NCL)

(T. Abe)(T. Abe)Observation (Run2)• We are investigating the beam conditions and information from various sensors when an SBL
abort occurs.
↓• For the aborts until 05/29, most of them start in in region of [D6V1, D5V1]. If beam loss happens
in D6V1, less IR does.
• Horizontal oscillations are often initially invoked.
• So far, no acoustic observation clearly considered a vacuum arc at any collimator of D02V1, D05V1,(D06V2, or D06V1) when SBL occurred. Further analysis on-going.
• SBL can occur with both single beam and collision beam.
• SBL occurs both at β*=1mm or 3mm.
• Vertical Beam Size increases when SBL occurs compared to other abort.
• The vacuum pressure spiked at D04 or D10 in the most cases when LER beam aborts of unknown
cause happened.
• Aging effect might be seen.
14

0.2

200
0.1

0
0

Beam Current
Bunch Current
QCS quench
knocker study

2024/5/31 0:00

2024/5/29 0:00

2024/5/27 0:00

2024/5/25 0:00

2024/5/23 0:00

2024/5/21 0:00

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2024/5/5 0:00

2024/5/3 0:00

2024/5/1 0:00

2024/4/29 0:00

2024/4/27 0:00

2024/4/25 0:00

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2024/4/21 0:00

2024/4/19 0:00

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2024/4/15 0:00

2024/4/13 0:00

2024/4/11 0:00

2024/4/9 0:00

2024/4/7 0:00

2024/4/5 0:00

2024/4/3 0:00

2024/4/1 0:00

2024/3/30 0:00

2024/3/28 0:00

2024/3/26 0:00

2024/3/24 0:00

2024/3/22 0:00

2024/3/20 0:00

2024/3/18 0:00

2024/3/16 0:00

2024/3/14 0:00

2024/3/12 0:00

2024/3/10 0:00

1600
β*=3mm0.7

1400
Single beam
0.6

1200
0.5

1000

800
0.4

600
0.3

Bunch Current[mA]

400

2024/3/8 0:00

Beam Current [mA]

SBL statistics
The beam current which SBL occurs looks increasing.
SBL abort

SBL: Mar.1st – June. 2nd
118 LER SBLs (incl. SBL with QCS quench) + 11 HER SBLs

𝑰𝐋𝐄𝐑 [mA]#LER SBL

Max. Dose [mRad]#LER SBL

May.9th※ -[0.0, 300]

1[0.0, 100]87

38

[300,500]

4[100,300]14

6[500,800]

34 (incl. 2 quench)[300,500]71[800,1000]

27 (incl. 5 quench)[500,800]

10[1000, 1200]

31[800, 1000]

10[1200, ]21[1000, ]8

1Knocker study※ Closed LER horizontal collimators on May 9th
2024/06/03

16

#SBL/hour

Beam current dependency
Mar.1st - May. 22 at 19:00

0.4
0.35
0.3

March

𝑰𝐋𝐄𝐑 [mA]

April

Frequency depends on 𝐼

May

[300, 700]#LER SBL

Operation time
331
[hour]#SBL/hour 0.027 ± 0.009#LER SBL

5

Operation time
April
159
[hour]#SBL/hour 0.031 ± 0.014

0.2
0.15

#LER SBL

2

Operation timeMay
76[hour]#SBL/hour 0.026 ± 0.019

0.1
0.05

200

9

March

Sum

0.25

0

[700, 900]

400

600

800

1000

[900, 1000][1000, ]

10

0

0

114

0

0

0.088 ± 0.028

−

−

13

8

20

120

114

110

0.101 ± 0.003

0.07 ± 0.025

0.18 ± 0.04

2

6

30

24

115

159

0.083 ± 0.059

0.05 ± 0.021

0.19 ± 0.03

1200
1400
ILER [mA]• Frequency (#SBL/hour) depends on the LER beam current• It seems no aging effect.. (hard to say something about it)
2024/06/03

17

D1

Beam size measurement @SBL
• A beam image at the abort timing wasmeasured using a D8 SRM gated camera.
• trigger：Abort trigger• Gate width：10us• When the Abort trigger is sent to the kicker, asignal is also sent to D8.
• The beam goes in the order of D8 → BOR →Abort kicker, so we should be able to see theimage of the last turn.
↓• Vertical Beam Size increases when SBL occurs
compared to other abort.
Reason:• due to beam loss? (Loss amount is relatively
small)• Beam size increase due to some kind of kick(collision with dust? discharge?), resulting inbeam loss at the collimator?

D12V4(NR354)
D12H4(NR307)
D12V3(NR285)
D12H3 (NR274)
D12H2 (NR236)
D12V2 (NR209)
D12H1 (NR199)
D12V1 (NR134)

D11
NR

日光

D01H5
D02H4 (TR14)D02H2 (TR120)(TL18)
D02H3 (TR67)D02H1 (TR142)
D01H4
D02V1 (TR80)D03V1 (TR300)(TL34)D03H1
D01H3 (TL47)(OL352)
D01V1 (TL60)

赤：LER
青：HER

3C

D05V1

Beam Dump

NL

BOR/BCM

D109C

New BOR/BCM
D09V4 (NL156)
SRM
D09H4 (NL203)
D09V3 (NL232)
D09H3
D06V2(OR271)(NL236)
D09H1 (NL307)
D06V1 (FL362)
D09H2
D09V2 (FR354)
D06H3 (FL276)(NL279)
D06H1 (FL200)
D09V1 (FR209)
6C
D8

Injection

TL 筑波 TR D2

12C

FR 富士 FL D7

SBL

D4 D4RF
H
OL G
F
大穂
D5RF
OR A
B
D5 C
D
E
F

Pressure Burst• D05V1 has a burst near 1200mA. Previously, it occurred at a lower beam current.
It looks aging effect.
• Aging effect at D6H3&H4 also appears.
• There are many vacuum bursts in the Wiggler(D10/D4) section, but they also occur
when SBL is not occurring.
• LM(PIN) were installed downstream of the Wiggler section, but no beam loss wasobserved.
• Anomaly detection to investigate the cause of sudden beam loss (K. Matsuoka)• The vacuum pressure spiked at D04 or D10 in the most cases (145/161) when LER beamaborts of unknown cause happened.
• The spike never coincided in D04 and D10.
• The spike never coincided at different locations within D04 or D10.

(Y. Suetsugu)

(Y. Suetsugu)

D06_H3はまだエージングが進んでいるよう(Y. Suetsugu)

#SBL events

LER SBL vs Pressure burst
120

100

96

80

60

40

36

20

D4_L*

D10_L*

10

D4_L*

22
20
18
16

> 300 mRad
10 events/36

14
12

5
others

D11_L*#SB L events/100 m R ad

#SB L events/100 m Rad

0

D10_L*

70
60> 300 mRad
8 events/96

50
40

10
30

8
6

20

4

10

2

2024/06/03

00

500

1000

1500

2000

2500

3000

Max. diamond dose [mRad]

0

0

500

1000

1500

2000

2500

3000

Max. diamond dose [mRad]23

SBL events with QCS Quench/Belle II damage• 2024-04-18 10:00:12 (796mAx6.0%) orbit of D2V1 was off by ~100um.
• 2024-04-19 07:58:25 (896mAx12%) orbit of D2V1 was off by ~100um.
• 2024-04-19 13:45:10 (946x19.4%) orbit of D2V1 was off by ~100um.
• 2024-04-22 23:55:08 (796x13.9%) β*y=3mm(LER)/1mm(HER),• 2024-05-05 05:25:45 (996x4.7%)• 2024-05-06 21:25:11 (997x5.8%)

QCS quench:
4/18, 4/19 quench case

• Optics correction after maintenance revealed that the orbit of D2V1
was off by ~100um.
• Because of that, D2V1's Aperture was narrowest condition.
• It was a normal SBL, but an unstable beam hit D2V1 and wasscattered in the IR direction, causing a QCS quench.
• After that, we adjusted the collimator to match the orbit, so thequench doesn't seem to occur.

2024-04-22 23:55:08 (796mA) Case;

CLAWS D05V1→LM D6 (Optical Fiber)→Belle2 CLAWS→LM(D6V1V2collimator)

SBL/QCS quench

QCS quench:
4/22,5/5,6 quench case2024-04-22 23:55:08• D6V1/V2 had a narrower aperture, but the beam passed through it and hit D2V1, causing a large
dose and QCS quench.
• Based on this experience, we decided to close the D5V1 collimator as much as possible andoperate in a way that the unstable beam would not cause loss at D2V1.
2024-05-05 05:25:45
2024-05-06 21:25:11• Beam loss at D2V1 was small, but…
• After passing through the vertical collimator, the horizontal oscillation was coupled to the verticalvibration.?
• We closed horizontal collimator’s after these events.

SBL with large doses due to LER did not occur after PXD OFF,D6V1close,D6V2open, D5V1close(bottom), Horizontal collimator close.

Causes of SBL from observation• No. of SBL depend on LER current.
• Aging effect might be seen.
• The vacuum pressure spiked at D04 or D10 (Wiggler section ) were
happened for most of SBL events.
• Vertical Beam Size increases when SBL occurs compared to otherabort.
↓
What does this mean?
• We're back to the possibilities of dust.

Nikko straight section
concrete shield

Wiggler section（Place where beam pipe with clearing electrode is installed）

真空計
D10_L07e+ beam
D1

TL 筑波 TR

D2

12C

3C

D11

D4

NR

OL

日光

赤：LER
青：HER

NL

Beam Dump

OR

D10

BOR/BCM

D5

D05V1

大穂

OHO straight section
e+ beam
真空計
D04_L07concrete shield

New BOR/BCM
SRM

9C

6C
D8

FR 富士 FL

D7

Wiggler section（Place where beam pipe with clearing electrode is installed）

Dust event (reminder)• At the Phase-1, pressure bursts with beam loss were frequently observed in the LER, which
was an obstacle to beam current increase.

 When a loss monitor was triggered and issued abort, the pressure momentarily jumps to the 10-7-10-6 Parange in some parts of the ring at the same time.
 The beam was lost over several 100 μs, and oscillations in the beam phase were observed.

• Estimating the location of pressure bursts from the CCG indications, most of the pressure
bursts occurred in the vicinity of the grooved aluminum beam pipes in the bending magnets.
• The beam current at which pressure bursts occurred increased with the maximum beam
current at that time. The frequency of pressure bursts tended to decrease after a while ofoperation at the same maximum beam current (aging effect).

（T. Ishibashi）

Dust event (reminder)• We speculated that this phenomenon was caused by dusts trapped in groove
structures falling into the beam. To verify this, a knocker was installed in the LER beampipe.
• When this knocker was operated during beam operation and the beam pipe wasstruck, the above phenomenon was reproduced.
• As a countermeasure for Phase-2 operation, the grooved aluminum beam pipe was
knocked around with a knocker during the shutdown period. As a result, thefrequency of pressure bursts with beam loss was dramatically reduced.
• However, the frequency of occurrence has not been reduced to zero. Then,sometimes dust events occur even at low beam currents.

（T. Ishibashi）

Similarities between SBL and dust event• The frequency of SBL (Sudden Beam Loss) in LER increased after LS1(?)

 During LS1, there was vacuum work in about 2/3 of the LER, and dusts may have moved significantly
through the beam pipe in that section due to nitrogen purging and pumping, etc. (groove structure retraps dusts?) .

• Pressure bursts are sometimes observed along with SBLs.
 Similar to dust events• The beam current that SBL occurs is gradually increasing(?)
 Aging effect, similar to dust events.

• However, in the case of dust events, slow beam loss and aborts with oscillations in the
beam phase were observed, but no such phenomena were observed in the SBL.
• However, at some point (Phase-3?), the abort itself with slow beam loss and oscillations in
the beam phase did not occur at all.
• Since there is still a myriad of dusts in the beam pipe, it is also unnatural that no dust
events have occurred at all.
 Are some of the unexplained aborts now due to dust events? Are some of the unexplained aborts
occurring now due to dust events?
 Is it possible that the SBLs is caused by dusts, and that squeezing the y* has changed the way we see
dust events?

（T. Ishibashi）

Knocker study• We would like to reinstall the knocker to the beam pipe and see how the abort
due to the current dust event is observed.
It may be possible to determine some of the many non-SBL aborts as dust events even if
they are not observed as SBLs.

• Knocker installation locations• Where there is vacuum work during LS1 and dusts are likely to be re-trapped in the grooves.
And where the collimator passes from the Belle II and QCS safety point of dust generation
to the IP.
 Aluminum beam pipe with grooves in bending magnet in D06 arc section• A location where pressure often jumps and is suspicious when SBL occurs. And where thecollimator passes from the Belle II and QCS dust generation point to the IP for safety
reasons.
 Beam pipe with clearing electrode in D10 Nikko Wiggler section ： Electrodes are formed by spraying
alumina and tungsten onto copper beam pipes (electrodes are on top of the beam) .

Detailed location of knocker installation
D06

Where there is a groove structure in the chamber
D07_L20(CCG)

B2P59 and 60

Detailed location of knocker installation
D10
BW0NNLP.16 and BW0NLMP.14

Where there is a clearing electrode in the chamber

D06:B2P.59 groove point

B2P.59 aborted on the knock count =3.
However, it was not an SBL.
Pressure burst observed.

Later knocks had pressure bursts larger than the pressure burst at abort,
but were not aborted.

Beam abort
Small amount of Beam Loss only ＠ D5V1

Knock count
1,2,3

1->0 is Knock timing

D06:B2P.60 groove point
Manual beam abort

No beam abort andpressure burst at knock timingD10: BW0NNLP.16 clearing electrode point
No SBLNo SBLSBL

SBL

I kept knocking and the abort stopped happening.
Aging effect?

Losses are not proportional tothe amplitude of the pressure burst.

D10: BW0NLMP.14 clearing electrode point
SBL

SBL

SBL

SBL

we knocked on this place a lot(about 30 times) when there
was no beam current.
At 50 mA, pressure bursts
occur, but no abort. Pressure
bursts are also small.
Aborts when knocking at over 500mA.
The aging effect is not visibleat this location.

• 2024/5/17 Knocker study was performed.
• Aluminum beam pipe with grooves in bending magnet in D06 arc section：Abort x1• Beam Loss is small only in D5V1.
• Then only vacuum bursts occurred, but stopped as the knocking continued.
• No beam abort and pressure burst at knock timing @another beam pipe.
• Beam pipe with clearing electrode in D10 Nikko Wiggler section• Up to 800mA, small amount of Beam Loss Abort at D6V2/D5V1.
• SBL Abort occurred with beam loss at all around in the ring by increasing to 1000mA.
• After that, the amount of Loss decreased and eventually vacuum bursts no longer
occurred.
• When the Chamber was changed, SBL Abort occurred even at 500 mA, and thenknocked several tens of times, but no aging effect was observed. However, at 50 mA,
vacuum bursts were seen but not abort.
• In both cases, the magnitude of the vacuum burst is not particularly proportional to themagnitude of Beam Loss.

There seems to be a
problem with the beam
pipe with clearing
electrode, so the vacuum
group investigated in theexperimental room with
test-chamber （Chamberwith electrodes taken out
for D5V1 collimator
installation) and came up
with a countermeasure.
*It was sent for chemical
analysis, but no alumina
or tungsten was detectedin the dust.

5/29 Maintenance• We knocked the D10（almost）/D11(3) wigller chamber with aknocker (about 100 times each).

2024/5/30 : knocker study• knocked the chamber upstream of D11 (to see the effect ).
• where there is less vacuum burst (&SBL) at lower current, but bursts can be seen
when the beam current is high• saw the current dependence by knocking D10 chamber.
• applied voltage to the electrode.
*Fill pattern is changed for each current to keep the bunch current constant.

D10

D11
③

①

②

①

②

QCS quench BW0NRP3 （D11①）
Abort signal

Loss monitor

QCS quench BW0NRP3 (2024/5/30 )Abort : RF D04H(HER)→Belle2 CLAWS→ LM(D5V1 collimator)→

Beam current dependent BW0NRP3（D11①）
400mA
Maybe aging observed
Beam current
200mA

VXD
Knocker
50mA

100mA

VXD burst observed at knocker timing, but not abort.

Beam current dependent BW0NRP3（D11①）

Pressure burst observed

Beam current dependent BW0NRMP2（D11②）
No SBL

600mA

400mA

200mA

100mA

Pressure burst observed
Only 1 abortBeam current dependent BW0NRMP2（D11②）

VXD burst observedClearing electrode On/Off dependent
BW0NLP13(D10①)
On(500V)

Strange orbit

Off(10V)Clearing electrode On/Off dependent
BW0NLP13(D10①)
On

OffClearing electrode On/Off dependent
BW0NRP5(D11③)
On

OffFill change(->2346)

2346 Bunch BW0NLP11(D10②)

SBL

SBL

500V

10V

Clearing electrode voltage change(D10②)
SBL

SBL

Discharge?

Not knocked

SBL• D11-①• Knocked D11 chamber which is less Pressure burst →QCS quench @1A• Check the current dependence（50,100,200,400mA）• VXD burst observed at knocker timing, but not abort.
• Pressure burst was observed at any current.

• D11-② （100,200,400,600mA）• Abort（not SBL）＠100mA• Pressure burst @ 400mA, After that, the pressure burst disappeared？

• D10-①：Clearing electrode On/Off dependent• No difference was seen between ON (500V)/OFF (10V) (both without Abort)• D11-③Clearing electrode On/Off dependent• No difference was seen between ON (500V)/OFF (10V) (both without Abort)• changed the Fill Pattern, but it already disappeared?

• D10-②Clearing electrode On/Off dependent• No difference was seen between ON/OFF (both SBL Abort)• When the voltage is increased to 800V, Abort occurs without knocking.

• There was also an Abort where a phenomenon similar to discharge was observed.

• At low currents, even if an Abort occurs, it did not reach SBL.

Further investigation• There seems to be a problem with the beam pipe with clearing electrode, so thevacuum group continues to perform measurements using particle counter, etc. in
the experimental room with test-chamber （Chamber with electrodes taken out
for D5V1 collimator installation) and come up with a countermeasure.
• On the maintenance day on May 29th, we reinstalled the knocker in the D10
section and knocked almost all chambers with electrodes.
→If it works and we get less serious SBL, we may knock on other places too.
• Since the mechanism by which dust falls and interacts with the beam is not clear,turning the beam pipe upside down may not be very effective, so we are carefully
considering it.

Summary• We had been suffering from SBL before LS1, and were working hard
to find out the cause.
• Although there are signs of a causal relationship between dust and
SBL, the mechanism is still unclear.
• The observed event depends on the type of dust, the location where
it falls, and the beam current.
• There seems to be a problem with the beam pipe with clearing
electrode, so the Vacuum group investigation underway.

backup

1400

0.6

1200

0.5

1000

0.4

800
0.3
600
0.2

400
200

0.1

0

0

Beam Current

Bunch Current

Bunch Current [mA]

Beam Current [mA]HER SBL

(H. Nakayama)

LM

D12V1
PMT

D12V3
PMT

D02V1
PMT
D01V1
PMT

D05V1
PMT

D09V3
PMT
D06V2
EMT

D09H2
PMT
D09V1
EMT

D07 injEMT
D08 inj
EMT

D06V1
PMT

D06H3
EMT
D06H4
EMT

(K. Uno et al.)62

Knocker study
OPI
Control room
Tunnel

24V PSIOC (raspberry pi) with relay

Valve

Knocker
https://www.technos-serve.com/mgk-knocker

Compressor

日時

knock

Current[mA]

Abort

SBL

D05 CLAWS

2024-05-17 10:56:40

D6

594

LM(D5V1 collimator)→RF D04G

ON

2024-05-17 13:45:56

D10-①

598

CLAWS D05V1→LM(D5V1 collimator)ON

2024-05-17 14:05:45

D10-①

792

CLAWS D05V1

ON

2024-05-17 14:29:42

D10-①

995

RF D04G→Belle2 CLAWS→LM(D5V1 collimator)

✓大

OFF

2024-05-17 14:54:54

D10-①

994

LM（D6V1V2collimator）→RF D04G→Belle2 CLAWS→✓

OFF

2024-05-17 16:36:00

D10-②

995

LM D6 (Optical Fiber)→RF D04G→Belle2 CLAWS→✓

OFF

2024-05-17 16:52:46

D10-②

492

LM（D6V1V2collimator）→RF D04G→LM(D5V1
collimator)→

✓

OFF

50

--------

OFF

2024-05-17 17:10:34

D10-②

495

LM（D6V1V2collimator）✓

OFF

2024-05-17 17:25:10

D10-②

495

CLAWS D05V1→LM（D6V1V2collimator）✓

ON

Possible Reasons for SBL•

Damage of vacuum component (RF Finger) @KEKB & PEP-II• Beam phase changes (beam energy losses) observed ms to several hundred μs before aborts.
→ The time scale differs from that of SBL.
• Abnormal temperature rise at bellows chambers had been observed and the catastrophic damages in
the RF-ﬁnger had been conﬁrmed. → We could not find that damage.

• Interaction with Dust : Early stage @ SuperKEKB• Beam aborts accompanied by local pressure bursts. → not observed the burst that causes it in SBL• Beam loss lasted a few ms before the beam abort. → me scale is diﬀerent• Vacuum chambers were cleaned or tapped to remove as much dust as possible and fixed the problem.
• Vertical abort kicker misfire• We are using the same thyratron for horizontal kicker.
• FB kicker trouble or lack of power : measured @ BEPC II• Sinch the growth time of coupled bunch instability might be O(～several 10 turns), our sbl was notcaused by FB system problem.
65

2024-05-17 10:56:40 594mA
LM(D5V1 collimator)→RF D04G
D6 knock
Small amount of Beam Loss only ＠ D5V1

2024-05-17 14:29:42 995mA
RF D04G→Belle2 CLAWS→LM(D5V1 collimator)
D10-①
SBL 全周でLossNLC建設のためのビームパイプ撤去作業の様子

NLC建設のためのビームパイプ撤去作業の様子

Component analysis of collected dust

Possible Reasons for SBL•

Equilibrium of tuners, piezo's parameter, LLRF, noise from transmitter, 50Hz filter of RF system could cause
sudden beam loss. : measured @ BEPC II, DAFNE•
RF system are monitored at each abort, and were not seen abnormal signal.

•

Electron Cloud• SBL should be measured only in LER.→ SBL is also measured in the HER beam.
• Curious behavior of the pressure in D06H3 collimator may suggest the formation of a discharge orelectron cloud.
• Simulations show that the electron density distribution changes with time and a maximum electron
density is on the order of 1E13/m3 to 1E14/m3 → How this relates to SBL?

•

Fireball : Measured @ RF cavity• The vacuum chamber is made of copper with low sublimation point and collimator head is made oftungsten or tantalum with high sublimation point.
• → The situa on has the poten al for a ﬁreball to be formed.
• This fireball hypothesis could explain SBL (~μs) due to the fast plasma evolution (~100 ns at the fastest).
71Candidate Reasons for SBL :Damage of vacuum component• Damage of vacuum
component (RF Finger)@KEKB & PEP-II• Beam phase changes (beam energy
losses) observed ms to several
hundred μs before aborts.
→ The time scale differs from that of
SBL.
• Abnormal temperature rise at bellows
chambers had been observed and thecatastrophic damages in the RF-finger
had been conﬁrmed. → We could not
find that damage.
72(Y.Suetsugu)

Candidate Reasons for SBL : Interaction withDust
• Dust : Early stage @ SuperKEKB• Beam aborts accompanied by local pressure bursts. → not observed the burst that causes it in SBL• Beam loss lasted a few ms before the beam abort. → time scale is different• Vacuum chambers were cleaned or tapped to remove as much dust as possible and fixed the problem.

73Candidate Reasons for SBL :• Vertical abort kicker misfire• We are using the same thyratron for horizontal kicker. X• FB kicker trouble or lack of power : measured @ BEPC II• Sinch the growth time of coupled bunch instability might be O(～several 10 turns), our sbl was
not caused by FB system problem. X• Equilibrium of tuners, piezo's parameter, LLRF, noise from transmitter, 50Hz filter of RF system
could cause sudden beam loss. : measured @ BEPC II, DAFNE• RF system are monitored at each abort, and were not seen abnormal signal. X

74

Candidate Reasons for SBL : Electron Cloud•

Electron Cloud• SBL should be measured only in LER.→ SBL is also measured in the HER beam.
• Curious behavior of the pressure in D06H3 collimator may suggest the formation of adischarge or electron cloud.
• Simulations show that the electron density distribution changes with time and a maximum
electron density is on the order of 1E13/m3 to 1E14/m3 → How this relates to SBL? △75

Candidate Reasons for SBL : Fireball• Fireball : Measured @ RF cavity• The vacuum chamber is made of copper withlow sublimation point and collimator head ismade of tungsten or tantalum with highsublimation point.
→ The situa on has the poten al for a ﬁreball to
be formed.
• This fireball hypothesis could explain SBL (~μs)
due to the fast plasma evolution (~100 ns at thefastest).

76