Status of SuperKEKB Ring
Contents•••••

Brief review of 2021a/b runs
Works during summer shut down
Status of 2021c run
Near-term operation planLong-term operation plan andInternational task force for SuperKEKB upgrade• ARC report• Summaries

Y. Suetsugu
KEK
11/8/2021

BPAC, 11/09/2021

1

Contents
•
•
•
•
•

Brief review of 2021a/b runs
Works during summer shut down
Status of 2021c run
Near-term operation planLong-term operation plan andInternational task force for SuperKEKB upgrade (ITF)• ARC report• Summaries

11/8/2021

BPAC, 11/09/2021

2

Brief review of 2021a/b runs
• 2021ab operation summary

Y. Ohnishi, ARC, 2021

•

•

•
•

•
•

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The 2021a/b run started on 16th
February and operated for 140
days.
The maximum beam currents were
940 mA and 1000 mA for HER and
LER, respectively. (during baking
runs)
The peak luminosity was 3.12x1034
cm-2s-1.
HER D01V1 jaw was replacedsince wrong type had been used inMay.
LER D02V1 jaw was replaced due
to damage in June.
Many aborts occurred from 20th
April to 3rd May due to noises in
BxB FB system, which was fixed
finally.
3

Brief review of 2021a/b runs
• Machine parameters (2020b and 2021b)

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Y. Ohnishi, ARC, 2021

4

Brief review of 2021a/b runs
• Specific luminosity• Definition of specific luminosity
Y. Ohnishi, ARC, 2021

• Specific luminosity for βy* = 1 mm is
improved compared to that of 2020ab.
• x-y couplings at IP are improved byusing local correctors with luminosity
optimization.
• We also use chromatic x-y couplingcorrectors.
• Bunch current product is achievedlarger than 0.5 mA2 with crab waist
scheme.

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Brief review of 2021a/b runs
• Major challenges in 2021a/b runs

Y. Ohnishi, ARC, 2021

• Beam background and beam aborts due to beam loss
• Caused by stored beam and injection beam
• Resulted in high radiation dose (serious) at collimators, collimator damage, Belle IIdetector damage→ Risks for increasing beam currents• Collimator impedance : TMCI threshold• High impedance due to narrow collimator aperture (physical aperture)• The lower threshold limits of bunch current than expected.
• Short lifetime• Due to mall dynamic aperture and/or small physical aperture (collimators, QCS
aperture, etc.)• Beam-beam blowup• Is the source of blowup the chromatic X-Y couplings ?
• Single beam blowup or multi bunch effect ? How about BxB FB gain ?
→ Those enhance beam-beam blowup ? How about BBHT(XZ) ?
• Insufficient understanding of injection beam
• Emittance, orbit fluctuation, energy spread, stability of injector linac
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Brief review of 2021a/b runs
• Operation statistics• The ratio of “Physics run” reached 60~70%.
• The percentage is increasing gradually.
• 2020c run had a problem of heavy TMCI etc..
• “Troubles” + “Maintenance” ~ 10 %• “Machine tuning” 20 ~ 30 %• Reducing these percentage is a key to improve
efficiency.

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Contents
•
•
•
•
•

Brief review of 2021a/b runs
Works during summer shut down
Status of 2021c run
Near-term operation planLong-term operation plan andInternational task force for SuperKEKB upgrade (ITF)• ARC report• Summaries

11/8/2021

BPAC, 11/09/2021

8

Works during summer shutdown• Regular maintenance (Water flow meters, Power supplies for RF and magnets, etc.
• Collimators (see also next page)• Installation of new collimator heads with 3 mm Tantalum and graphite (at LER arc).
• Robust against damages from beam.

• Relocation of LER D02V1 collimators• Replacement of 2 collimator heads (HER).
• Upgrade of driving device of 2 collimators (HER)• LER injection kicker• Exchange of all thyratrons to those with higher withstanding voltage to avoid unexpectedfiring.
• Rewiring of trigger cables to control each kicker timing separately.

• Exchange of the mirror and its folder of SR beam size monitor for LER.
• Installation of a HOM absorber at RF section (HER Nikko).
• BT• Installation of beam profile monitors with OTR screen.
• Installation of a beam shutter in LER injection line.

• Installation of a strip-line kicker into RTL line at DR• Anti-aging measures• Replacement of HV (66 kV and 6.6 kV) power cables.
• Repair of water leak from roof of some power stations.
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Works during summer shutdown• Works for beam collimators

11/8/2021

K. Shibata

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10

Contents
•
•
•
•
•

Brief review of 2021a/b runs
Works during summer shut down
Status of 2021c run
Near-term operation planLong-term operation plan andInternational task force for SuperKEKB upgrade (ITF)• ARC report• Summaries

11/8/2021

BPAC, 11/09/2021

11

Status of 2021c run• 2021c run has started as scheduled from 19th October.

As of 8th November
•
•
•
•
•
•

βy* = 8 mm

Vacuum scrubbing
Beam studies
NEG
Injection studies activation

βy* -> 1 mm
Vacuumscrubbing

Physicsrun•

Physicsrun••
Unexpectedfiring of LER
kicker#1-2
11/8/2021

Unexpected Unexpectedfiring of LER firing of LER
kicker#1-1
kicker#2-2

Unexpectedfiring of LER
kicker#1-1
BPAC, 11/09/2021

2021c run has started on 19th October.
Vacuum scrubbing was performed until
27th at with βy* = 8 mm.
Unexpected firing of LER injection kickers
occurred on 21st.
Various beam studies, such as on TMCI,
beam injection, were carried out during
this period.
βy* was squeezed to 1 mm after regular
maintenance on 27th.
Unexpected firing of the LER injection
kickers recurred on 28th.
Physics run started once from 29th, but
stopped next day since unexpected firingof the LER injection kickers has occurredagain and moved to vacuum scrubbing.
QCS power supply turned off due to an
earthquake on 1st November.
Physics run restarted on 2nd, the beam
currents were increased gradually. But thebeam currents were again decreased on
5th due to unexpected firing of the LER
injection kickers.
12

Status of 2021c run• 2021c run has started as scheduled from 19th October.
Y. Ohnishi, Commissioning meeting

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Status of 2021c run• Troubles - Leak at QCSR insulation vacuum tank •••In the examination of the QCS system in the summer shut-down, the degradation of thevacuum condition for the thermal insulation in the QCSR cryostat was found.
The residual gas indicated a clear air leak. The leak rate was 3.8 ×10-4 Pa m3 s-1.
Helium leak test of the accessible cryostat parts was performed, but no detection.
•••

In October, the temperature successfully reached to 4 K in approximately 1.5 days.
The cooling down succeeded this time, but the risk would remain until LS1. We hope theleak do not get worse….
••

The most suspicious part is red squares in the bottom figure.

Heat load with the leak after cooling the magnets at 4 K for the He refrigerator < 1 W @4 K, while the marginof He ref. cooling capacity = 40 W @ 4 K. We have still enough margin.

We will perform a detailed leak check next summer, by opening End yoke and (if necessary)
End cap.
Withadditionalpump

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Status of 2021c run• Troubles - unexpected-firing of LER injection kicker•

On 21st October, unexpected-firing occurred at LER injection kicker #1-2••

Since we have exchanged all of thyratrons of the kicker PSs to those with a higher withstandvoltage during the last summer shutdown, noises to the trigger cables are suspected as apossible cause at first.
We have configured a “coincident circuit” to avoid fake trigger signal on 22nd.
However, the unexpected-firing again occurred at the kicker #1-1 and #1-2 on 28th.
The thyratron of kicker #1-2 was replaced with that had been used in #2-2. A thyratron stored
at 30 years at PF was used to #2-2 instead. Furthermore, the running voltage was lowered forkickers #1.
The unexpected-firing occurred at kicker #2-2 on 30th. The kicker #2-2 was turned off.

•

The unexpected-firing occurred at kicker #1-1 on 5th November.

•
•
•

•

11/8/2021

Kicker #2 is available with two kicker magnets.
Kicker- Thyratron

Before 2021c#1 - 130y (unused)#1 – 230y (unused)#1 – 330y (unused)#2 – 1

Spare (new)#2 – 21y (unused)#2 - 3

Spare (new)

10/21

X

10/22

Coincident circuit•

Pressure burst at D06_H3 was observed at the same time. Damaged?

10/28

10/30

X -> V↘

11/5

11/8

X -> V↘

-> Used (~2021b)

X -> 1y V↘
->

V↘

->30y(unused)

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X -> OFF
15

Status of 2021c run• Troubles - unexpected-firing of LER injection kicker•••

Considering these situation, it seems that the thyratrons stored for 30 years unused were
deteriorated, although the reason is unknown.
Then the thyratron of kicker #1-1 was replaced with used one which had been used until
2021b on 8th.
Short-term countermeasures• Select available thyratrons among those we have now, in any way.
• Install new two thyratrons that we are now manufacturing as soon as we received.
• Order more spares.
Mid-term, Long-term countermeasures• Set up a real test stand to check the property of thyratron before installing into the ring.
• Rewire the system to use a common power supply for #1 and #2 kickers, as
recommended in the last ARC. Need correction kickers and some tests.
• Develop a semiconductor switch to replace with a thyratron. Need extensive R&D.

11/8/2021

Kicker- Thyratron

Before 2021c#1 - 130y (unused)#1 – 230y (unused)#1 – 330y (unused)#2 – 1

Spare (new)#2 – 21y (unused)#2 - 3

Spare (new)

10/21

X

10/22

Coincident circuit

•

10/28

10/30

X -> V↘

11/5

11/8

X -> V↘

-> Used (~2021b)

X -> 1y V↘
->

V↘

-> 30y(unused)

BPAC, 11/09/2021

X -> OFF16

Contents
•
•
•
•
•

Brief review of 2021a/b runs
Works during summer shut down
Status of 2021c run
Near-term operation planLong-term operation plan andInternational task force for SuperKEKB upgrade (ITF)• ARC report• Summaries

11/8/2021

BPAC, 11/09/2021

17

Near-term operation plan ~2024• Near-term operation plan was re-considered.
• Considering the recent rise of electricity charge, the starting time of 2022a waspostponed from 9th to 21st February.
• Total operation period in this fiscal year will be approximately 6.6 months.
• The period depends on the increase rate of electric charge in the future.
2021

2022

4

5

FY2021

6

7

8

9

10

12

1

2

~3.2M

7/5

10/19

~2.2M

10

11

3
2022a

2021c

2021b
4/1

11

12/23

2/9

Total

~1.7M ~7.0M/yHalf a year delay (2021/10/22)
2021
4FY2021

6

7

8

9

~3.2M

12

7/5

10/19

~2.2M

BPAC, 11/09/2021

1

2

3
2022a

2021c

2021b
4/1

11/8/2021

2022
5

12/23

2/21 ~1.2M

Total~6.6M/y18

Near-term operation plan ~2024• We decided to postpone the LS1 by a half year.
• The LS1 will start from January, 2023.
• A detailed leak check of QCSR cryostat vacuum tank is scheduled in summer
shutdown 2022.
7/5

4/1

2022
4

5

FY2022

6

8

9

10

11

12

1

2

3
Total

2022b

LS1 (PXD, TOP exchange)

~3.5M

4/1

7/15

2023
4

FY20235

6

7

5/16 ~2M

8

9

10

4

FY2022

7/14

5

6

10/11

5

7

8

9

7/4

6

1

2

~2.5M

3
2024a

10

7

8

9

11

12

1

2

~2.8M

Total

10

11

12

~6.0M/y2024
12~1.9M 12/25
10/31

2/6

• Influence of Covid-19• Fabrication of a new IP chamber• Integrated luminosity until LS1• QCSR leak
• Availability of expertise especiallyin PXD.

• Requested budget is compatible
with 6 months operation.

3
2024a

2023c

LS1 (PXD, TOP exchange)

3

LS1
12/26

• Items to be considered~6.6M/y

2022c
10/4

Total

~1.7M ~6.2M/y

2/8

12/22

2/21

QCSR leak check

~3.2M

2023
4

12

2023

2022b
4/1

11
2023c

7/5

2022

~3.5M/y

2024

2023b

LS1

4/1

FY2023

2023
7

Total

~1.8M ~3.7M/y• The schedule will be discussed again in May 2022, considering the situation at thattime.
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Near-term Luminosity profile ~2024• Luminosity profile

~820
~1
~610
~0.8

~9

~1.6

~1.4
~6

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Works planed during LS1• QCS cryostat front panel modification and additional shield to IP bellows••••

Make rooms for cables of Belle II detectors.
Exchange plate material from tungsten to stainless-steel to reduce the beam background.
Add new radiation shield inside the cryostat.
FWD and BWD bellows shields were also developed. In the current mechanics, there is no beam BG
shield around the bellows pipes and a fraction of BG go into CDC and TOP from these regions.
• The preparation for LS1 is on going together with Belle II group.
K. Nakamura

11/8/2021

K. Shibata 2021/3/4

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Works planed during LS1• Non-linear collimator• A vertical-type collimator, called “non-linear collimator”, is located between a pair of specified skewsextupole magnets. The non-linear vertical kicks by the magnet are utilized to enlarge the verticaldisplacement of particles at small βy section, which will reduce the collimator impedance and mitigate
TMCI (K. Oide).
• Vertical phase advance of 0.25 between the sextupole magnets and the IP is possible, which reduces
beam background (A. Natochii).
• It can be uses as a primary collimator instead of D06_V1 at present.
• The dynamic aperture looks fine so far by simulation.
• The preparation has started to install the non-linear collimator during LS1.
IP

K. OideOHO

T. Ishibashi
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Contents
•
•
•
•
•

Brief review of 2021a/b runs
Works during summer shut down
Status of 2021c run
Near-term operation planLong-term operation plan andInternational task force for SuperKEKB upgrade (ITF)• ARC report• Summaries

11/8/2021

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23

Long-term operation plan
• Current operation plan (luminosity profile)••

The current goal is to achieve~6 10 cm s and
50 ab by around 2031,
which requires an intermediate machine
upgrade around 2026 (LS2) that improves theluminosity by a factor of 2-3.
The plan was adopted in the MEXT roadmap
2020.

•

The plan and profiles were assessed by theexternal review committees (Accelerator
Review Committee (ARC and BPAC)•

βy* [mm]
Recommendation in the last ARC, 2020
• Over the next year or so, perform beam measurements to determine if the proposed
upgrades are absolutely necessary to get to the design luminosity.
• Determine which technical studies need to be carried out now, before a decision canbe made, within about 2 years.

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Long-term operation plan
• To solve the confronting challenges and to realize the plan, a variety ofcountermeasures have been proposed and discussed over the last year in various
meetings, such as “Long-term operation plan meeting” (internal), MDI (Machine
Detector Interface) meeting, BITF (Beam Injection Task Force) meeting and IR
technical meeting, and so on.
• Although various kind of measures have been proposed to improve beam lifetime, relax
TMCI, improve dynamic aperture, etc., no effective method to boost up the luminosity by
LS2 has not been found so far.
• An international task force was created under the
management of the KEK Accelerator Lab. and B
promotion office (BPO) to pursue effective
measures for recovering the luminosity profile andreaching target luminosity.
• Find more effective (x2~3) measures, not limited to the IR
but also to other parts of the MR and Linac, Ideas of amore revolutionary upgrade including some modification of
Belle II should be considered to reach even higher
luminosity; this may require a longer time for R&D (~203x).
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International task force for SuperKEKB upgrade• ITF members
International Task Force members
2021/7/27
International members
Maria Enrica Biagini
Georg Hoffstaetter
Evgeny Levichev
Mark Palmer
Yunhai Cai
Rogelio Tomas
Pantaleo Raimondi
Katsunobu Oide

INFN
Cornell
BINP
BNL
SLAC
CERN
ESRF
CERN/KEKKEK ACCL members
Mika Maszawa (Chair)
Yukiyoshi Ohnishi
Akio Morita
Hiroshi Sugimoto
Renjun Yang
Haruyo Koiso
Yoshihiro Funakoshi
Tsukasa Miyajima
Kazuhito Ohmi
Demin Zhou
Kentaro Harada

SKEKB
SKEKB
SKEKB
SKEKB
SKEKB
SKEKB
SKEKB
SKEKB
SKEKB
SKEKB
KEK-PF

Belle II members
Hiroyuki Nakayama
Francesco Forti

Belle II
Belle IIBPO members
Masanori Yamauchi
Tadashi Koseki
Makoto Tobiyama
Kazuro Furukawa
Kyo Shibata
Yusuke Suetsugu

KEK
ACCL
SKEKB
SKEKB
SKEKB
SKEKB

Naohito Saito
Shoji Uno
Yutaka Ushiroda
Toru Iijima
Kodai Matsuoka

IPNS
Belle II
Belle II
Belle II
Belle II

• Three ITF meeting were held so far, 28th July (kick off), 2nd September (Joint with
ARC) and 16th October.
• Four working groups (sub-groups) were organized and their indico sites were created.
• Optics (Contact person: Akio Morita & Sub: Haruyo Koiso)• Beam-beam (Contact person: Demin Zhou & Sub: Kazuhito Ohmi)• TMCI and impedance matters (Contact person: Mauro Migliorati & Sub: Takuya Ishibashi)• Linac (Contact person: Masanori Satoh & Sub: Shuji Matsumoto• Indico site https://kds.kek.jp/category/2242/
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International task force for SuperKEKB upgrade• Recent activities and topics• Beam-beam sub-group• Meetings: 24th August, 28th September, 28th October• Some observed properties of the beam-size blow up could be explained by the beam-beam head
tail instability (BBHTI), but not satisfactory. A consistent and predictable model for beam-beamsimulation is necessary.
• Luminosity predicted by the strong-weak simulation with beam-beam effects agrees well with thepresent situation.
• Proposals to move the working point to a higher point in the betatron tune diagram. It will be tried
during 2021c run.
• Re-evaluation of beam impedances for various vacuum components are on going for more precise
simulations, together with TMCI sub-group.

• TMCI sub-group• Meetings: 27th August, 2nd September, 1st October, 9th November (scheduled),• Mystery of the lower bunch current threshold of TMCI than that expected by the simple formula.
Localized impedance? Mode coupling between higher modes?
• Need to develop an impedance model which can reproduce the observations. Re-evaluation ofbeam impedances for collimators is on going.
• Machine studies, such as betatron tune scan, chromaticity, etc., are proposed, and partiallyalready done during 2021c run.
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International task force for SuperKEKB upgrade• Recent activities and topics• Optics sub-group• 22nd September, 13th October• Comprehensive summaries about optics measurement so far was presented.
• Limitations of the optics correction using the present tools were pointed out.
• It was reported that elaborate optics matching (“semi-perfect matching”) using existing magnets
will give a comparable improvement in dynamic aperture with “perfect matching” proposed before.
• It was also reported that additional sextupole magnets at IR was effective to improve the dynamic
aperture for SuperB in a simulation. The effectiveness is under investigation using SuperKEKB
lattice.
• The conversion of lattice formats, that is, from SAD to MAD8, LEGO, etc., are on going. Somebasic reproducibility will be reported soon.

• Linac sub-group• Just started.
• First meeting will be held soon, where the upgrade plan was explained first of all.

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Contents
•
•
•
•
•

Brief review of 2021a/b runs
Works during summer shut down
Status of 2021c run
Near-term operation planLong-term operation plan andInternational task force for SuperKEKB upgrade (ITF)• ARC report• Summaries

11/8/2021

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29

ARC report• The 25th KEKB Accelerator Review Committee (ARC) meeting was held remotely on
1-2 September 2021.
• Slides of the presentations and the report are available athttps://superkekb.kek.jp/event/131/

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ARC report• General comments• Remarkably, this progress was achieved with a limited, and shrinking, number of staff members, andduring the covid-19 pandemic.
• The important advances accomplished, the remaining large challenges and the noticeable task-force
support from the international accelerator community underline that SuperKEKB is a highly innovative
facility, of critical importance for particle physics and for the world-wide progress in colliders.
• We support the KEK management in making every possible effort to ensure a highest priority for
SuperKEKB and to maximize available staff support, such that the required substantial workload canbe accomplished.

• The most important challenges at present• The top-up injection efficiency and injection stability, including HER beam blow up in the transfer line,
mitigating the consequences of accidental kicker-pulser misfiring, problematic HER two-bunch
injection, septum drifts, etc.
• Collimation and machine protection strategy, including overcoming the present bunch intensity
limitations due to TMCI; developing a strategy for safe beam current increase; and understanding andavoiding yet unexplained sudden large beam losses in the LER• Medium and long-term plan including possible upgrade paths.
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ARC report• Most significant recommendations and our actions - 1• Sufficient beam time should be allocated for beam studies (other than routine tuning) to better
understand and characterize the machines and their limitations, and to develop solutions or mitigation
measures. More beam diagnostics would be helpful. Planned, dedicated machine study periods would
also enable remote participation by Task Force members and other foreign experts.
→We are now discussing with Belle II group to increase the machine study time. We are also
considering possible measure to participate the studies remotely.
• Check the RF gun timing and perform careful RF conditioning of the QTW RF gun to recover the RF
pulse width and, possibly, to improve the 2ndbunch emittance.
→ The timing has been checked. We succeeded in securing enough pulse width by careful conditioning.
• Develop refined procedures including triggers so that Belle II can operate closer to the backgroundlimits of its sub-detectors.
• The six LER kickers should be rewired to use a common power supply, or three power supplies each ofwhich feeds a pair of upstream and downstream magnets, to avoid problems related to thyratron
misfiring and injection impact on circulating bunches.
→ The reconfiguration of the kicker system is quite difficult. We replaced all thyratrons of LER to otherones with higher withstand voltage. The new circuit to avoid mis-firing by noise was also introduced.
• Localize, identify and eliminate the source of vertical coupling in the HER injection line.
→ Various studies and analysis are on going.
• Develop a safe plan for increasing beam intensity in documented phases/machine states, that are eachformally verified for optimized performance, background and adequate machine protection.
→ We are working on a plan with the cooperation of the commission group and Belle II group.
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ARC report• Most significant recommendations and our actions - 2• Establish a realistic model of the transverse impedance including accurate collimator wake fields andcorrect weighting with local beta functions; assess TMCI threshold for this model.
• Measure the single-bunch tune shift created by each collimator as a function of its gap, compare withtheoretical expectation and verify that collimator contributions to the impedance are correctly
understood.
→ We are planning to investigate in detail the difference between the results of the current model andthe measurement through machine studies, and build a more realistic model.
• Further develop and study the non-linear collimation scheme (including the removal of some wiggler
sections) and quantify its implications on beam optics and beam dynamics.
→ Detailed studies are underway on both beam optics and hardware aiming to install it during LS1.
• Carry out more comprehensive beam-beam simulations, incl. crab waist, impedance, lattice errors, etc.,
to guide the upgrade path.
→ Detailed discussion has started in the beam-beam sub-group of ITF.
• Consider increasing the number of focused task-force groups to other key areas such as linac, injection,
collimation and machine protection.
• Invite external international task-force members to share organization efforts for the ITF sub-task
groups.
→ Linac sub-group has been established. We would like to search for various ways to make the task
force work effectively including the above plan.

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Contents
•
•
•
•
•

Brief review of 2021a/b runs
Works during summer shut down
Status of 2021c run
Near-term operation planLong-term operation plan andInternational task force for SuperKEKB upgrade (ITF)• ARC report• Summaries

11/8/2021

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34

Summaries• The performance of SuperKEKB has been steadily improving.
• Peak luminosity : 3.12x1034cm−2s−1, with βy*= 1mm, Beam current [mA]= 790 (LER)/687(HER)• Total integrated luminosity : 213.5 fb−1, Maximum Daily integrated luminosity (delivered) = 2.233 fb−1

• Various challenges, however, still remained, and should be solved to further improve themachine to achieve the goal.
• Vertical beam size blow-up, short beam lifetime, TMCI, low machine stability, aging of hardware andfacilities, low injection efficiency (HER), etc.

• The near-term operation plan was reconsidered recently considering recent situations.
• LS1 will start from January, 2023.

• Various countermeasures have been discussed in various meetings to solve lots ofchallenges facing us to realize the current Long-term operation plan.
• International Task Force to address the challenges and find ways to boost up theluminosity using LS2 was organized this summer.
• Enthusiastic discussion is taking place in four sub-groups : Optics, Beam-beam, TMCI, and Linac• Some proposed beam studies will be performed in 2021c run.

• Lots of useful comments and recommendation was reported from ARC. The action plan
is now under discussion.
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35

We greatly appreciate your corporation!
End

11/8/2021

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36

Backup

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37

Major results of 2021ab run• Projection of specific luminosity in 2021ab• Definition of specific luminosity
Y. Ohnishi, ARC, 2021•

Max. of nbIb+Ib- is 540 mA2(840 mA/818 mA, nb = 1272)• Target of 2021b: 700 mA2• LER / HER : 1.1 A / 1.0 A, nb =1565

• L > 4x1034 cm-2s-1

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38

SuperKEKB achievements so far• The performance has been improved steadily.
• SuperKEKB is already exploring uncharted territory!

#$∗

3.12 10 ! cm s
(world record)

0.8 mm(world record)
213.5 fb
(July, 2021)

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39

Status of 2021c run• 2021c run has started as scheduled from 19th October.

As of 1st November
•
•
•

•

•
βy* = 8 mm

Vacuum scrubbing
Beam studies

βy* -> 1 mm

NEG
activation

Vacuumscrubbing••Unexpectedfiring of LER
kicker
11/8/2021

Unexpected
Unexpectedfiring of LER
firing of LER
kickerkicker
BPAC, 11/09/2021•

2021c run has started on 19th October.
Vacuum scrubbing was performed until
27th at with βy* = 8 mm.
Unexpected firing of LER injection
kickers occurred on 21st, and the beam
current was increased carefully after
that, less than 300 mA
Various beam studies, such as on
TMCI, beam injection, were carried out
during this period.
βy* was squeezed to 1 mm after
regular maintenance on 27th.
Unexpected firing of the LER injection
kickers recurred on 28th.
Physics run started once from 29th, but
stopped next day since unexpectedfiring of the LER injection kickers has
occurred again and moved to vacuum
scrubbing.
QCS power supply turned off due to an
earthquake on 1st November.
40

Status of 2021c run• Troubles - unexpected-firing of LER injection kicker•

On 21st October, unexpected-firing of LER injection kicker (#1) occurred.
•

•
•
•
•
•
•

Pressure burst at D06_H3 was observed at the same time. Damaged?

Since we have exchanged all of thyratrons of the kicker PSs to those with a higher withstandvoltage during the last summer shutdown, noises to the trigger cables are suspected as apossible cause at first.
We have added a trigger line (optical fiber) connected directly to the event generator (EVR),
and configured a “coincident circuit” before the kicker PSs to avoid fake trigger signal on 22nd.
However, the unexpected-firing again occurred at the kicker #1-1 and #1-2 on 28th.
The thyratron of kicker #1-1 was replaced with that had been used in #2-2. A thyratron stored
at PF was used to #2-2 instead. Furthermore, the reservoir voltages were lowered by 0.1~0.2
V and the bias voltages of grid#2 were also increased by 20 V for all thyratrons of kickers #1.
The unexpected-firing occurred at the kicker #2-2 on 30th. The kicker #2-2 was turned off.
LER beam current will be increased carefully watching the situation.

New trigger line

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41

Luminosity profile for present plan
Integrated luminosity (delivered)Present plan (Aug. 2021)
2021
4

FY2021

2022
5

6

8

9

10

7/5

2022
4

FY2022

5

11

12

1

2

6

10/19

~2.2M

10

11

12/23

8

9

12

1

2

3
Total

2022b

LS1 (PXD, TOP exchange)

~3.5M

4/1

7/15

2023
4

FY2023

5

6

7

2024
4

FY2024

5/16 ~2M

5

6

8

9

10

~3.4M

βy*

11

12

1

2

7/14

7

10/11

8

9

10

~2.5M
11

12/22

12

2025
1

2

7/12

10/16

~2.3M

12/25

2/6

~510

3
2025a

2024c

Total

~1.7M ~6.2M/y

2/8

~890

~650

3
2024a

2023c

2024b
4/1

~3.5M/y

2024

2023b

LS1

~1230

Total

~1.7M ~7.0M/y

2/9

2023
7

3
2022a

2021c

~3.2M

4/1

11/8/2021

7

2021b

Total

~1.8M ~7.5M/yBeam current

BPAC, 11/09/2021

Luminosity

42

Luminosity profile for half a year delay plan
~2024bIntegrated
luminosity (delivered)Half a year delay (2021/10/22)
2021
4FY2021

2022
5

6

7

8

9

10

~3.2M

7/5

2022
4

FY2022

5

6

4

~3.2M
5

10/19

~2.2M

8

9

10

11

7/4

6

7

8

9

~2.8M

10

11

2/21 ~1.2M

12/23

1

2

12/26

12

FY2024567

8~1.9M 12/25
10/31
9

10

2

~3.4M

βy*

11

12

2025
1

2

7/12

10/16

~2.3M

2/6

Total

~610

3
2025a

12/25

~920

3
~1.8M ~3.7M/y

2/6

~820

~6.0M/y

2024a

2024c

2024b
4/1

Total

2024
1

~1290

Total

~6.6M/y

3

LS1

2023c

LS1 (PXD, TOP exchange)

4

3
2022a

12

10/4

2024

11/8/2021

2

2022c

QCSR leak check2023

FY2023

1

2023
7

2022b
4/1

12

2021c

2021b
4/1

11

Total

~1.8M ~7.5M/yBeam current

BPAC, 11/09/2021

Luminosity

43

Luminosity profile for one year delay plan
Integrated luminosity (delivered)

One year delay (2021/10/22)
2021
4FY2021

2022
5

6

9

10

4

FY2022

5

10/19

7/5

2022
6

7

5

8

9

6

5

10

11

12

1

2

7

8

9

10

11

12

6

7

9

10

11

12

1

2

10/10

~2.5M

Total

~840
~810

3
~3.5M/y

1

2

3
2025a

12/25

~1150

Total

2024c
7/12

~1110

3

2025
8

Total

~6.6M/y~2.1 M ~5.8M/y

1/28

7/14

5/14 ~2M

βy*2/21 ~1.2M

12/23

2023a

2024b

LS1

~2.2M

3
2022a

LS1 (PXD exchange)

~3.5M

2024
4

2

2024

2023b
4/1

1

TOP Exchange

7/19

2023
4

12

QCSR leak check~3.7M

FY2023

11

2023

2022b
4/1

11/8/2021

8

2021c

~3.2M

4/1

FY2024

7

2021b

2/6

Total

~1.8M ~6.3M/yBeam current

BPAC, 11/09/2021

Luminosity

44Time until the liquid He starts to accumulate

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45

International task force for SuperKEKB upgrade• Charges• Consider effective ideas to realize luminosity of ~6x1035 cm-2 s-1 as a result of anintermediate upgrade around 2026, which could include modifications of IR, final focus
systems, injectors, but without changing the boundary to the Belle II detectors.
• Find a realistic way before long shutdown 1 (LS1) scheduled to start Jul/2022 in order toachieve luminosity of the order of 1035 cm-2 s-1 without large modification of accelerator
components.
• Consider longer-term alternative idea to achieve ~6x1035 cm-2 s-1 or more, even by largely
modifying the IR and the Belle II detector.

• Activity period• Coming one year, before the LS1.

• Rough schedule• (Online) meeting per month basically.
• Meetings are basically open, but may occasionally have closed sessions.
• Special review by ARC per ~6 months.
• Final report is to be submitted by the end of July, 2022.
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46

Long-term operation plan
• To improve the machine further to achieve the goal, however, various challenges asfollows should be solved:
1) Severe beam-beam effect (vertical beam size blow-up)••

Vertical beam size (vertical emittance) blow-up has been observed at high bunch currents.
Relaxed by the crab-waist collision scheme, but it still remains.

2) Shorter beam lifetime than expected in the design phase.

The maximum bunch currents are limited by the balance between the lifetime and theinjection power.
• The dynamic aperture is very small due to the beam-beam effect and crab-waist sextupoles,
while the physical aperture is limited by the beam collimators.
•

3) Lower bunch-current limit due to TMCI than expected.
•

The cause is higher impedance of beam collimators, where the apertures are smaller thanthe design values to suppress high background to Belle II.

4) Low machine stability••

Abnormal beam aborts, sometimes leading to the damage of collimators.
Operation efficiency during 2021ab, for example, was almost 0.5, lower than expected one,
0.65. (Main causes: machine tunings, machine troubles, maintenance, etc.).

5) Low injection efficiency especially in HER••High residual radiation at injection point and beam collimators.
Large emittance of injected beam6) Aging of hardware and facilities, and so on.
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End

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