SuperKEKB Commissioning Status− Phase-3 2019 Spring Run −Y. Suetsugu
Accelerator Laboratory, KEK

B2GM 2019/6/17 KEK

1Contents• Phase-3 commissioning status (2019 spring run)
• Brief review (~6/15)• Major results and challenges• Status of several key items• Commissioning plan
• 2019 Spring run (~7/1)• Summer shutdown and 2019 Autumn run (10/15-12/12)• Winter shutdown and 2020 Spring run (1/16?-6/30?)• Summary• Detailed commissioning status and plan → Morita’s talk
• Injector linac status → Ego’s talk
B2GM 2019/6/17 KEK

2Phase-3 brief review• Phase-3 commissioning started from 11th, March, asscheduled.
• Started with a detuned optics (large b *).

• HER beam was stored on the same day.
• LER beam was stored on 13th, although some difficulties in
the injection tuning.
• Vacuum scrubbing started from 14th with 1576 bunches.

• This quick start meant that the QCS positions were wellrestored after the retraction/insertion during the shutdown.
Beam currents history

B2GM 2019/6/17 KEKRetraction/insertion work of QCS

3

Phase-3 brief review• The by* was gradually squeezed from 18th, March, andmoved to collision tuning from 20th with 789 bunches.
• The first collision event was observed on 25th, March.
• The optics with by* = 3 mm was finally established on 1st,
April, which was the same optics in Phase-2, and thephysics run had actually started.
• Unfortunately, however, we had a fire incident in the linac
building on 3rd, April. Details were reported by Tokushuku-san.
Beam currents history

B2GM 2019/6/17 KEK

b* history4

Phase-3 brief review• KEKB MR stopped during the recovery work at Linac,
with no RF and Magnet power to save electric charge.
• The Linac recovered very quickly thanks to great effort ofstaff and external contractors, and also heartfulencouragement from Belle II groups and others.

• MR operation finally restarted from 25th, just before thePlatinum week (i.e., ~10 days special national holidays
for celebrating our new emperor).
He is not the emperor

Beam currents history

B2GM 2019/6/17 KEK

New era “REIWA”

5

Phase-3 brief review• Physics run continued during this Platinum week under
non-aggressive tuning, but stably.
• Just after the holidays, the injection BG was drasticallyreduced by the elaborate tuning of collimators and new
injection tuning method, which gave a light toward thecontinuous injection mode.
Injection summary
Beam currents

Beam currents history

HER Injection efficiency
Electron charge
VXD Bw135
LER Injection efficiency
Positron charge
VXD Fwd135
Belle II Diamond

B2GM 2019/6/17 KEK

6Phase-3 brief review• Physics run continued during this Platinum week under
non-aggressive tuning, but stably.
• Just after the holidays, the injection BG was drasticallyreduced by the elaborate tuning of collimators and new
injection tuning method, which gave a light toward thecontinuous injection mode.
• LER continuous injection started from 7th, May.
• Finally, HER continuous injection started from 14th, May.
Decay mode run

Continuous injection mode run

HER beam current

LER beam current

Luminosity

Specific luminosity

B2GM 2019/6/17 KEK

7Phase-3 brief review• From 17th,owl shifts were basically served for physics run,and collision knob tunings were continued incessantly.
• Day and swing shifts were used for various accelerator
studies:• BT line and injection tuning studies• High current studies with 1576 bunches• Longitudinal feedback studies• Impedance measurements (collimators)• Beam-beam effect studies• X-ray beam size monitor calibration, etc.
Luminosity history

Beam currents history

B2GM 2019/6/17 KEK

8Phase-3 brief review• The physics run with 1576 bunches (3.06 RF bucket
spacing) started from 23rd, May.
• The beam current was increased gradually watching the
BG status since then, and along with it, the integrated
luminosity increased steadily.
• After the continuum run (DE = -60 MeV) from 28th, May to
3rd, June, the physics run on resonance restarted while
increasing the beam currents up to 660 mA (LER) and
620 mA (HER).
Luminosity history

Beam currents history

B2GM 2019/6/17 KEK

9Phase-3 brief review• The peak luminosity of 0.55x1034 cm-2s-1 was recorded
on 8th, June.
• However, a heavy QCSR quench occurred on 9 th, June,and it took approximately 3 days to recover it.

Luminosity history

Beam currents history

B2GM 2019/6/17 KEK

10Phase-3 brief review• The peak luminosity of 0.55x1034 cm-2s-1 was recorded
on 8th, June.
• However, a heavy QCSR quench occurred on 9 th, June,and it took approximately 3 days to recover it.
• Since then, the beam current has been saved to 500 mA
for safety, because the beam-dust collision at high beam
currents was suspected as a cause of the quench.
Luminosity history

Beam currents history

B2GM 2019/6/17 KEK

11

Major results and challenges• Summary of results until 15th, June

B2GM 2019/6/17 KEK

12

Major results and challenges• Achieved machine parameters
Plan (Last B2GM)
LER

HER

ex [nm]2.0

4.6

ey/ex [%]

8.0

8.0

bx* [mm]100

100

by* [mm]3

3

sz [mm]6

6

I [A] (Physics run)

1.2

1.0

Number of bunches

1576

Bunch current [mA]

0.761

.635

sy* [nm]

693

1051

0.02620.0272xy (beam-beam param.)
L [cm−2s−1]

Beam-beam parameter: xy

𝛾± 𝐼± 𝜉𝑦±𝐿=∗
2𝑒𝑟𝑒 𝛽𝑦±1.06 x 1034

L: Luminosity
I: Beam current
re: Classical electron radius
B2GM 2019/6/17 KEK

13

Major results and challenges• Achieved machine parameters
Plan (Last B2GM)

Results ~15th, June
LER

HER

ex [nm]

2.0

4.6

✔

ey/ex [%]

< 8.0

< 8.0

100

✔

bx* [mm]

100

200

3

3

✔

by* [mm]3

3

sz [mm]6

6✔

sz [mm]~6~6

I [A] (Physics run)

1.2

1.0

--

I [A] (Physics run)

0.65

0.6

✔

Number of bunches

LER

HER

ex [nm]

2.0

4.6

✔

ey/ex [%]

8.0

8.0

bx* [mm]100

by* [mm]

Number of bunches

1576

1576

Bunch current [mA]

0.761

.635

--

Bunch current [mA]

0.41

0.38

sy* [nm]

693

1051

✔

sy* [nm]

~500

~400

0.02620.0272--xy (beam beam param.)

0.02660.0165--

L [cm−2s−1]xy (beam-beam param.)
L [cm−2s−1]

1.06 x 1034

B2GM 2019/6/17 KEK

0.51034

14

Major results and challenges• Achieved luminosities
Plan (Last B2GM)
Conservative case
Lpeak limit~ 1.0 x 1034 cm-2s-1●I ~ 1200 x 1000 mA-1● L
int in 2019 Spring ~ 46 fb
w/o study-1→ Lint ~ 23 fb with 50% study●

Worst (bad BG) case
No improvements from Phase-2.
●Beam current is limited by BG.
●Sample from 2019.07.01 morning
34 cm-2s-1●Lpeak limit~ 0.2 x 10
●I ~ 290 x 270 mA→ Lint in 2019 Spring ~ 11.8 fb-1
w/o study-1→ Lint ~ 5.9 fb with 50% study●

Assumptions

Lpeak increases linearly during beam operation.
●Efficiency L
avg / Lpeak ~ 70%●Belle works 24H during beam operation.(98days for 2019 spring run)●Belle CAN take data with high beam current operation.(No BG limit)●

B2GM 2019/6/17 KEK

15

Major results and challenges• Achieved luminosities
Results ~15th, June
Conservative case
Lpeak limit~ 1.0 x 1034 cm-2s-1●I ~ 1200 x 1000 mA-1● L
int in 2019 Spring ~ 46 fb
w/o study-1→ Lint ~ 23 fb with 50% study●

Worst (bad BG) case
No improvements from Phase-2.
●Beam current is limited by BG.
●Sample from 2019.07.01 morning
34 cm-2s-1●Lpeak limit~ 0.2 x 10
●I ~ 290 x 270 mA→ Lint in 2019 Spring ~ 11.8 fb-1
w/o study-1→ Lint ~ 5.9 fb with 50% study
●

6 /fb

Fire incident

B2GM 2019/6/17 KEK

16

Major results and challenges• Decrease in Lsp with bunch current product.
𝐿𝑠𝑝 =

𝐿

𝑛𝑏 𝐼𝑏𝑒 𝐼𝑏𝑝

∝

1

𝜎𝑦∗

Lsp: Specific luminosity Ib: Bunch current
nb: Number of bunches<sy*>: Average vertical beam size at IP• If <sy*> is constant, Lsp should be constant against Ibe x Ibp.
• Actually, however, Lsp
decreases with an increase
in Ibe x Ibp.

Lsp vs Ibe x Ibp• The decrease in Lsp is causedby the beam-size blowup dueto the beam-beam effect.
• This could be one of serious
problems for increasing
luminosity in the future, if not→Next talk by Morita
solved.
B2GM 2019/6/17 KEK

17

Major results and challenges• High background – LER stored beam
• Main BG source in LER storage mode was found to be thebeam-gas Coulomb scattering from the dedicated BG
studies by Belle II group (Nakayama-san, et al.).
• This raised the base of BG,
and limited the beam
currents during physics run.

Belle Ii Background summary• A little room for BG form
injection, and some BG
bursts triggered CDC trips.

B2GM 2019/6/17 KEK

18

Major results and challenges• Status of vacuum scrubbing• Vacuum scrubbing of LER is steadily proceeding.
• At present, the average dP/dI is lower than that at the lastin Phase-2.
• But, the pressure at the upstream side of IR is still high,where new collimators were installed just before Phase-3.
• Furthermore, the number of vertical collimators is still small.
Decrease in dP/dI for LER (Phase1-3)

Location of beam collimators

New LER
collimators

by Ishibashi
B2GM 2019/6/17 KEK

19

Major results and challenges• High background – LER stored beam
• Main BG source in LER storage mode was found to be thebeam-gas Coulomb scattering from the dedicated BG
studies by Belle II group (Nakayama-san, et al.)[Countermeasures]• CDC trip threshold was raised by Belle II group.
• A vertical collimator is under manufacturing, and will be
installed during this winter shutdown.
• More collimators in the future?  Impedance issue• Optimization of betatron phases at collimator locations is
also planed.
• Expect further vacuum scrubbing. (Please be patient…)• If the source point is localized, enforcement of vacuum
pumps there might be considered, although some remodelingof beam pipes will be required.
B2GM 2019/6/17 KEK

20

Major results and challenges• High background – LER Injection beam
• Bursts of beam loss at collimators followed by beam aborts
have been frequently observed during LER injection.

• Properties are:Beam loss during injection (LER)• During injection
Injection rate,• ~10 s or longer bursts
efficiency• No correlation to collision or
Diamondnot, and to beam current
CLAWS• Loss monitor at collimators
and VXD beam dose arecorrelated.
Loss at collimators• Big horizontal kick?
• Kicker system and septum
system seem to be stable. Loss at collimators

B2GM 2019/6/17 KEK

1 minute21

Major results and challenges• High background – LER Injection beam
• Bursts of beam loss at collimators followed by beam aborts
have been frequently observed during LER injection.
Timing of VXD Diamond (Fw135) signal and[Countermeasures (tentative)]loss monitor signal at collimator (D06V2)• A program is running that inhibits thebeam injection when the VXD
Diamond level or beam losses atcollimator exceeds a specified level.
10 s⇒ Frequency of this type aborts
decreased.
• However the cause of this burst has
not been fully understood yet. The
investigation is ongoing.

B2GM 2019/6/17 KEK

22

Major results and challenges• High background – HER, LER Injection beam
• A strategy to drastically reduce the BG during HER andLER injections was developed just after the Platinum week.
• A systematic tuning of injection parameters (septum angle,
kicker height/jump, injection phase, etc.) to reduce betatronand synchrotron oscillations of the injected bunch.
• This actually makes the continuous injection available.
Position of injected bunch and it’s charge.
(5/9 HER Injection tuning by Iida and Ohnishi)

Injection summary
Electron current
HER Injection efficiency

x position

Electron charge

y position

Positron current
ChargeLER Injection efficiency
Positron charge

Turn number

by Ohnishi, Iida

Belle II Diamond

Turn number
B2GM 2019/6/17 KEK

23

Major results and challenges• High background – HER, LER Injection beam
• However, it is difficult to keep the good injection condition.
• BG as well as the injection efficiency degrades gradually,
even in a shift (8 hours).
• Sometimes, a slight tuning of injection parameters recovers
the situation.
Injection summary• Or orbit correction of linac
Electron current
can restore the injection
HER Injection efficiency
efficiency (especially forElectron charge
HER).
Positron current• Weather (temperature)
LER Injection efficiency
dependence is also
Positron charge
indicated.
Belle II Diamond• We have to find thesource of this change and
B2GM 2019/6/17 KEK
cure it.

2 days24

Major results and challenges• QCS quenches• Frequency of QCS quenches decreased compared to thatin Phase-2.
• Quick beam abort by Diamond sensor at IP.
• Narrower apertures at beam collimators than those in QCS.

• However, six quenches (two types) happened up to now.
[Type-1]: caused by theIPmalfunction of QC2LE
power supply.
Type-1[Type-2]: suspected to be
Layout of QCS magnets
caused by the steered beam
which lost energy by aIPcollision with dusts (LER).
• Heavy damages to PXD and
by Arimoto
Type-2collimator heads →Next talk by Morita
B2GM 2019/6/17 KEK

25

Major results and challenges• Heating of bellows at IP• The HER bellows at backward side of IP is heated up, andis a concern at high currents: ~50°at ~ 600 mA (nb=1576).
Bellows at IP• The behavior against beam current
changes with bunch numbers.
→not SR, but HOM (RF).
• It will be replaced to a spare usedin Phase-2 this summer.
Temperatures of bellows at IP• Inside of bellows will
be checked using afiber scope before
retracting QCSL, tocheck any troubles
during last connection
work.
• Production defect?
B2GM 2019/6/17 KEK

26

Major results and challenges• QC1L BPM connectors• Troubles were found in two coaxial cables for BPMs at
QC1L. (Reported in last BPAC)• TDR measurements suggest accidental damage at the
SMA connectors.
• Useable with three BPMs, but the accuracy will beinsufficient for the next autumn and winter commissioning.
• These BPM cables will bealso replaced to new one
during this summer
shutdown.
• The fastening toque will
be well controlled.

BPM at QC1L

by Tobiyama
B2GM 2019/6/17 KEK

27

Status of several key items• Status of damping ring (DR)Operation status of DR• DR has been working well.
• Damping of bunch:• While the beam at first blows up
just after the injection to the ring,
the longitudinal and horizontal
Longitudinal beam size (vertical) and horizontal
beam sizes well damp after 20 beam size (horizontal) after injection [Streak camera]
ms by the radiation damping.
by Ikeda• Trouble:• The power supply for extraction
septum failed once in March.
However, the symptom was not
reproduced.
• Some spare parts had beenordered.

B2GM 2019/6/17 KEK

28

Status of several key items• Status of longitudinal bunch feedback systems• Transient-domain (Excite-damp) experiments show the
feedback damping time less than 2 ms is realized.
• No spontaneous longitudinal coupled-bunch instability(CBI) was observed even with 2 RF-bucket spacings fillpattern at a beam current of 500 mA.

• Note: A longitudinal CBI was observed around 200 mA at Phase-2
Beam spectrum for 2 RF bucket spacings.
with 2 RF-bucket spacings.
No oscillation was observed.

Intensity [a.u.]

FB damping time measurement

Intensity [a.u.]

0.8Time [ms]by Tobiyama[1/ms]
rateRate(1/ms)
DampingDamping

0.7
0.6
0.5
0.4
0.3
0.2
0.1
0

0.2

0.4

0.6

0.8

1

1.2

FB gain

FB gain
B2GM 2019/6/17 KEK

Bunch number
29

Status of several key items• Status of collimators• Now we have 9 beam collimators in LER including 2 vertical
types, although the number is still smaller than HER.
Layout of collimators in Phase-3• Working well.
Vertical type collimator

Horizontal type collimator• Damage on the head:→Drastic countermeasures against
the damages by beams should be considered in long term.
• A vertical-type collimator, which is effective to reduce BG
due to beam-gas Coulomb scattering, is now under
manufacturing, and will
be installed in next winter.
B2GM 2019/6/17 KEK
30

Commissioning plan
• 2019 Spring run (~7/1)
Plan (Last B2GM)

B2GM 2019/6/17 KEK

31Commissioning plan
• 2019 Spring run (~7/1)
Actual process

Fire incident

Machin study/ Physics run• ~3 weeks loss due to the fire incident, and some tuning, BG
studies and machine studies were forced to be omitted.
B2GM 2019/6/17 KEK

32

Commissioning plan
• Summer shutdown• This 2019 Spring run will end at 9:00 on 1st, July.
• Major works during the summer shutdown• Replacement of the bellows at IP. A spare, which had beenused during Phase-2 commissioning, will be installed.
• Four new ones are to be fabricated by the end of this year.
• Replacement of QC1L BPM cables at IP, which have contact
failures at the connectors.
• These works require the retraction/insertion of QCS-L.
• Any measures against QCS quenches if available.

B2GM 2019/6/17 KEK

33

Commissioning plan
• Summer shutdown• Detailed IR schedule by Kanazawa
2019/7

2019/8

2019/92019/10

QCSL retraction
QCSL insertion

Bellows replacement
BPM cables exchange

B2GM 2019/6/17 KEK

34

Commissioning plan
• Autumn run• 2019 Autumn run will start on 15th, October and will end
on 12th, December.
• Continue the physics run and machine tunings.
2019
July
1

11

2020

August
21

1

11

21

September
1

11

21

October1

11

November

21

1

11

21

December1

Summer shutdown

11

21

January1

11

21

February
1

10/15

12/12

11

1

11

11

21

3/31

2021

August
21

1

1/16

2020
1

21

Power line work and Winter shutdown

7/1

July

11

March

21

September
1

11

21

October
1

Summer shutdown (BelleII Work)

11

November

21

1

11

21

December
1

B2GM 2019/6/17 KEK

1121

January1

11

21

February
1

11

21

March
1

11

35

21

Commissioning plan
• Autumn run• 2019 Autumn run will start on 15th, October and will end
on 12th, December.
• Continue the physics run and machine tunings.
Conservative luminosity projection(2019/10-2020/6) [Morita]

Potential:•Increase in beam-beam parameter•Fill pattern optimization
Assumptions• Operation modes
Start up: 2020/10/15 - 2019/11/11
Vacuum scrubbing: 3 weeks
Collision tuning (by* = 2.0 mm): 1 week
Luminosity run: 2020/11/11 - 2020/12/12

b y*= 3 →2 mm

1x1034 cm-2s-1• Total occupancy rate ~65%

Available operation time : 90%
Occupancy rate of machine: 85%
Occupancy rate of Belle II DAQ: 85%• Luminosity

Increase in luminosity: Sqrt[3/2] -> (3/2)
Beam-beam parameter limit: no increase
Beam current: 1.4 times until 2019 end
No machine study time

14 fb-1→Next talk by Morita
B2GM 2019/6/17 KEK

36

Commissioning plan
• Winter shutdown• 2019 Autumn run will end on 12th, December.
• Major works during the winter shutdown:• 150 kV power line work by TEPCO• The electric power in KEK was restricted to less than 50 MW.
• The MR have to be stopped. Linac, DR, and BT can be operated.

• Condenser replacement• A vertical-type collimator will be installed into LER.

B2GM 2019/6/17 KEK

37

nel)

QCS)

Commissioning plan
• 2020 Spring run• 2020 Spring run of MR will start from 16th, January,
although it is still in discussion.
• Two weeks earlier than the original plan (2/1 start).
• Compensation of loss time due to fire incident (~22 days).

• Operation in January will be for mainly BT tuning and MR
vacuum scrubbing.

• Run in March will continue as long as the budget allows.
2019

2020

December
2

6

9

13

16

January
20

23

27

1

6

10

14

17

February
20

24

27

31

3

7

10

14

17

March
21

25

28

2

6

9

13

16

19

23

27

30

Power line work and Winter shutdown
12/12

2/1

3/31

Power line work and Winter shutdown
Power line
12/12

Power line
12/28

1/16

1/24

~3/20

3/31

Linac & BT
(Limited power)

12/16

B2GM 2019/6/17 KEK

12/23
1/6

(1/6 Compressor start)

38

Commissioning plan

2019

April

May

June

• 2020 Spring run
1

11

21

1

11

21

1

11

July
21

1

11

August
21

1

11

21

September
1

11

21

October1

11

21

November
1

11

21

December
1

11• 2020 Spring run of MR will be continued until the end ofJune. (not decided)• Continue the physics run and machine tunings.
Days

Fire incident

Summer shutdown

21

1

Power line wo

162

4/3

4/26

7/1

10/15

12/12

204

rKEKB Operation Plan (Not fixed)
2020
April
1

11

May
21

1

11

June
21

1

11

July
21

1

11

August
21

1

Days

11

21

September
1

11

21

October1

11

21

November
1

11

21

December
1

11

21

1

Summer shutdown (BelleII Work)

199
7/1

167

rKEKB Operation Plan (Not fixed)
2020
April
1

Days
127

11

May
21

1

11

June
21

1

11

July
21

1

11

August
21

1

11

21

September
1

B2GM 2019/6/17Summer
KEK shutdown

11

21

October1

11

21

November
1

11

21

December
1

39

11

21

1

W

Commissioning plan
• 2020 Spring run• 2020 Spring run of MR will be continued until the end ofJune. (not decided)• Continue the physics run and machine tunings.
Conservative luminosity projection(2019/10-2020/6) [Morita]b y*=2→1.5 mm

127 fb-1

Potentials:•Increase in beam-beam parameter•Reduction of BG by additional
collimator → Higher beam current

2x1034 cm-2s-1

Assumptions• Operation modes
Start up: 2020/01/16 - 2020/02/21
Vacuum scrubbing: 2 weeks
Squeezing study (by* = 1.5 mm): 1 week
Collision tuning: 1week
Luminosity run: 2020/02/21 - 2020/07/01• Total occupancy rate ~65%

Available operation time : 90%
Occupancy rate of machine: 85%
Occupancy rate of Belle II DAQ: 85%• Luminosity

Increase in luminosity: Sqrt[2/1.5] -> (2/1.5)
Beam-beam parameter limit: no increase
Beam current: twice until 2020 summer
No machine study time

→Next talk by Morita

B2GM 2019/6/17 KEK

40

Plan after April, 2020
• 2020 summer and after• The operation schedule in FY2020 is still under discussion.
• 8 month’s run will be proposed in FY2020.

B2GM 2019/6/17 KEK

41

Summary-1• Phase-3 commissioning is now ongoing.
• Started from 11th, March 2019, as scheduled.
• In spite of approximately three weeks’ delay due to the fireincident in April, the data are being steadily accumulated byBelle II.
• The continuous injections for both rings are available inregular operation.

• Key challenges to increase luminosity• High background level• BG from stored beam and from the injection beam.
• Good after tuning, but the situation changes gradually.
• Low specific luminosity at high bunch current product• Mechanism of the beam-beam effect should beunderstood.
• Stable operation• Measures against QCS quenches• Improvement in beam abort system
B2GM 2019/6/17 KEK

42

Summary-2• Commissioning plan
• Plan until March, 2020, is almost fixed, and aim ~ 7months’ operation.
• 2019 Spring run: ~7/1
• 2019 Summer shutdown: 7/1 ~ 10/14• Replacement of bellows at IP, repair of QCS BPM.

• 2019 Autumn run: 10/15 ~ 12/12• Squeeze b y (~2 mm), increase currents with tunings• 2019 Winter shutdown: 12/12 ~2020/1/15• Power line work in Tsukuba campus• Installation of a vertical-type collimator into LER• 2020 Spring run: 2020/1/16 (not fixed) ~ (6/30)• Squeeze b y (~1.5 mm), increase currents with tuning• The schedule of 2020～2021 are under discussion.

B2GM 2019/6/17 KEK

43Thank you for your attention.

B2GM 2019/6/17 KEK

44

Backup

B2GM 2019/6/17 KEK

45

US-Japan collaboration in HEP
SLAC/Stanford:
IP feedback, Beam background, Collimators, HOM suppression, BxB
feedback, LLRF, X-ray monitor, etc.

U. Hawaii
X-ray monitor

Wayne St. Univ.
LABM

Multi-National Partnership Project (MNPP-01)
LAL: Fast luminosity monitor
CERN, IHEP : Commissioning

B2GM 2019/6/17 KEK

46

Major results and challenges• Decrease in Lsp with bunch current product.
𝐿𝑠𝑝 =

𝐿

𝑛𝑏 𝐼𝑏𝑒 𝐼𝑏𝑝

∝

1

𝜎𝑦∗

Lsp: Specific luminosity Ib: Bunch current
nb: Number of bunches<sy*>: Average vertical beam size at IP• If <sy*> is constant, Lsp should be constant against Ibe x Ibp.
• Actually, however, Lsp
decreases with an increase
in Ibe x Ibp.

Lsp vs Ibe x Ibp• The decrease in Lsp iscaused by the beam-size
blowup due to the beambeam effect.

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Major results and challenges• Decrease in Lsp with bunch current product.
• The degree of degradation of Lsp against bunch current
product improved in Phase-3 compared to that in Phase-2.
• Elaborate collision tuning• Beam-beam effect study, and development of tuning knobs.

• As a cause, the non-linear
chromatic coupling in optics
at IP is suspected.
• But, the mechanism has notbeen well understood yet.
• This could be one of serious
problems for increasing
luminosity in the future, if notsolved.
• Allow us more time tounderstand the machine.
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Lsp vs Ibe x Ibp

48

Major results and challenges• QCS quench - [Type-1]• Four quenches were caused by the malfunction of QC2LE
QCS current and loss monitor
power supply.
Beam abort• The current of QC2LE slowly
changed for ~3 ms due to themalfunction of PS until the
beam was aborted by theloss monitor signal, and thesteered beam hit QC1LE
resulting in a quench.
• Just before the beam abort(~100 ms), the high dose ofradiation entered to PXD,
and gave it heavy damage.

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Malfunction
QC1LE quench

Beam position (Libera)

Diamond detector

10 ms

49

Major results and challenges• QCS quench - [Type-1]• Four quenches were caused by the malfunction of QC2LE
power supply.
[Countermeasures]• SVD: The dynamic range was widen to detect higher dose
without saturation, and trigger the beam abort earlier.
• This change (5th) saved the SVD at the third quench!

Timing of quench• QCS: The delay time of quench
and abort trigger
detector was shorten from 16
ms to less than 3 ms on 13th,
June as a quick measure.
• Modification of PS to directly
issue an abort trigger is also in
consideration, but it will be done
after summer.
• The cause of PS malfunction is still under investigation.
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Major results and challenges• QCS quench - [Type-2]• Other two quenches were suspected to be induced bybeam-dust collision in LER.

• A pressure burst was simultaneously observed at an arc or a
Pressure burst
wiggler section in each case.
Beam abort• Horizontal shift of the beam orbit
Beam current
due to the energy loss was
20 sPressure
observed just before the abort,
although small.

• The second quench (6/9) was very
sever.

Damage of head

• High radiation dose damaged PXD.
• Collimator heads of D02_V1(vertical type collimator) wereheavily damaged.
• Liquid He of QCSR was completely
evaporated.
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Major results and challenges• QCS quench - [Type-2]• Other two quenches were suspected to be induced bybeam-dust collision in LER.
• The event was very fast.
Timing of quench and abort trigger• The first beam abort trigger
was issued from VXD
Diamond sensor.
• The beam was aborted after
30~40 ms (3~4 turns), which isalmost the fastest timing in thepresent abort system.
• But, ~150 mA out of 660 mA
was lost until the beam abort,i.e., during this 3~4 turns.

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Abort trigger

Quench52

Major results and challenges• QCS quench - [Type-2]• Other two quenches were suspected to be induced bybeam-dust collision in LER.
[Countermeasures]• We are considering to shorten the time lag between theabort trigger and the kicker firing, but it is not so easy.
• For example,• Increase the number ofabort gaps (~5 ms)

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Present abort trigger process 30 ms53

Major results and challenges• QCS quench - [Type-2]• Other two quenches were suspected to be induced bybeam-dust collision in LER.
[Countermeasures]• We are considering to shorten the time lag between theabort trigger and the kicker firing, but it is not so easy.
VXD Diamond signal• On Belle side, the fast
abort threshold of VXD
Diamond was lowered to
10 mrad/s from 70 mrad/s
to issue the trigger earlier(6/12).

• If the cause is actually the beam-dust collision ….
• It is impossible to remove all dusts from beam pipes.
• But it will be possible to reduce the probability.
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Major results and challenges• Status of pressure bursts in LER• Pressure bursts accompanied by beam aborts caused by
History of pressure bursts (LER)
possibly beam-dust collisions
Frequency
have been observed since
Phase-1, but the frequency
decreased drastically inPhase-2 and Phase-3 (up tonow).
• Aging effect? (lower
beam currents in Phase2 and 3)• Fast beam abortsystem? (VXD Diamond,narrow collimators)• Knocking of beam pipes
before Phase-2? (atTsukuba)
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Location

55

Major results and challenges• QCS quench - [Type-2]• Other two quenches were suspected to be induced bybeam-dust collision in LER.
[Countermeasures (if beam-dust collision is a cause)]• BEFORE starting the physics run, increase the beam
current and confirm the stable operation. → “Aging run”
After that, start the physics run with a somewhat lower
beam current.
• A dedicated time will be required to increase the beam
current before the physics run.

• Knock beam pipes in the ring during a long shut down, anddrop dust in advance.
• Already done at Tsukuba straight section before Phase-2.

• Any radical measures should be discussed ASAP to solve
this Type-2 quench for stable operation.
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Major results and challenges• Others• Failures in key components• For example, DR Septum PS (March), QCS PS (May, June),
QCS cryostat vacuum system (June)• Preparation of spear parts for the special component is apressing need for the stable operation, as long as the budget
allows, and some are on going.(some spare circuit for
septum PS, MR HER septum magnet, vacuum pumps, etc.)• Troubles caused by high atmospheric temperatures (evenin May)• Fluctuation of magnet cooling water sometimes exceeded theinterlock level, and it trigger the beam abort.
• The temperature of RF water load goes up near to theinterlock level, and it raised an alarm.
• These sometimes interrupt the operation, especially in day
time. → Difficulty in operating in summer.
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Status of several key items• Status of electron cloud effect (ECE) in LER• The ECE greatly deteriorates the luminosity.
• Beam-size blow up caused by single bunch instability.
Permanent magnets around beam pipes• The ECE observedin Phase-1 was
suppressed inPhase-2 using
permanent magnets
around beam pipes.

Beam sizes vs linear
current density• No indication of ECE has been observed also in Phase-3
so far, although still small linear current density.
• The ECE will be studied again in this run (end of June?).
• Effect of the permanent magnets on the beam optics is still
an concern, and has been studied.
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A juggling in 2021
• We have to reinforce the ceiling of Tsukuba Ex. Hall in 2021,
to follow the revised Building Standard Law.
• Revised after the big Tohoku earthquake in 2011.

• The work area is divided into three areas. At present, thework at the ring side is planed in 2021 summer shutdown,because a high radiation level is expected there with beam.
• The crane work is prohibited for ~2 months, and it shouldhave a big impact on the summer schedule.

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