International Task Force (ITF)
Activity summary
Mika Masuzawa

Contents• Introduction• Summary from each group• Optics• Beam-beam• TMCI• LINAC• SBL• Next26th ARC, Dec.14, 2022

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• Introduction

ITF activities
International Task Force (ITF) for SuperKEKB
Goal
Find a realistic way to achieve 1035cm-2s-1 after LS1 without major modification
Consider ideas to achieve 6x1035cm-2s-1 with larger-scale modification at LS2
The kickoff meeting was held on July 28, 2021
Three working groups were originally organized.
① Optics (A. Morita/H. Koiso)② Beam-beam (D. Zhou/K. Ohmi)③ TMCI (M. Migliorati/T. Ishibashi)④ LINAC (M. Satoh/S. Matsumoto) was organized later⑤ SBL (H. Ikeda/H. Nakayama) was organized recently
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• Introduction

ITF
Y. Suetsugu

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• Introduction

We had 7 general meetings

ITF activities

One year activity
reportMid-term review
by ARC

Kickoff meeting

2021
7ITF general meeting

○89○

2022
10○

1112○

kick off

123○

45○

6789101112○

ARC

ITF report○○ARC review○○

SuperKEKB operation

Activity period
Coming one year

One year (or more) extension
New chair: Y. Ohnishi

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Summary from each group
The activity report with• comments from the reviers• responses from each group
Is uploaded here
https://kds.kek.jp/event/44835/
and distributed.
26th ARC, Dec.14, 20225• Summary from each group

ITF activities① Optics activities (A. Morita (KEK)/H. Koiso(KEK))• Report on “Orbit drift at the SLY magnets (The sextupoles for local chromaticity correction and for
creating CW) causes linear optics deformation.” by H. Sugimoto.
• Two schemes, suggested by ITF optics meetings, were tried for DA optimizations:• Yunhai Cai's sextupole parameter set was tried during 2021/12/20 swing shift.
→ (see next page).
• Trial simulation study to insert IP phase weak sextupole to SuperKEKB LER,which was inspired
by Pantaleo Raimondi talk, was performed.
→ No significant improvement of optimized Touschek lifetime is observed crab-waist single
beam optics.

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6• Summary from each group

ITF activities① Optics

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ITF activities① Optics

26th ARC, Dec.14, 20228• Summary from each group

ITF activities

There were 12 beam-beammeetings held.

② Beam-beam activities (D. Zhou (KEK)/K. Ohmi (KEK))
1)The critical issues investigated and key conclusions drawn from the ITF-BB sub-workgroupʼs activities andinteractions with other ITF sub-workgroups
1.1) Crab waist: It is a must for the nano-beam collision scheme.
1.2) Interactions among beam-beam, lattice nonlinearity, and crab waist effects are show-stoppers with by*~0.3mm
but do not set a limit if > 0.6mm.
1.3) Single-bunch impedance (longitudinal monopole, transverse monopole, dipole, and quadrupole terms) sets a
limit on machine performances. The interaction between BxB feedback and vertical impedance in LER was affecting
luminosity performance until April 2022. This problem was relaxed after BxB was fine-tuned but remains as apotential source of mild vertical emittance blowup.
1.4) Beam-beam simulation codes:
Strong-strong simulation codes are a must for reliable predictions of luminosity at SuperKEKB. Benchmarks among
various codes presented good agreements in general. On the other hand, the effects of multiple beam dynamics(beam-beam, impedances, lattice imperfections, and BxB feedback) must be included. Efforts being made.

Beam-beam talk by D. Zhou after this talk.

9• Summary from each group
There were 12 beam-beammeetings held.

ITF activities② Beam-beam activities (From the summary repot by D. Zhou)
2) Responses to the comments and recommendations from ARC members

2.1) “The high momentum compaction optics (when/once available) should be tried in operation before the shutdown.”
Machine tunings were focused on achieving a new record luminosity beyond 5x34 cm-2s-1 before LS1. Machine
tunings with high a is time-consuming and we had to give up trying this.
2.2) “Clarify the performance reach of the crab waist scheme, its operational range in usable strength and its impact
on reachable specific luminosity and on dynamic aperture .”Trying different crab waist ratio…
Because of the same reason, machine tunings by varying crab waist strengths were not tried before LS1.

•

Beam-beam talk by D. Zhou after this talk.

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Ohmi-sanʼs talk this morning

ITF activities

There were 7 TMCI
meetings held by the endof April.

③ TMCI• A TMCI-like single-bunch instability in the LER was identified as a “-1 mode instability.
The “-1 mode instability” causes a vertical blow-up with a bunch-current threshold of~1 mA in LER. Fine-tuning the FB system helped suppress this instability.

0.3mA/bunch

0.5mA/bunch

0.7mA/bunch

The signal appears at
ny-ns (-1 mode).
This is why we callthis instability“-1 mode”

0.9mA/bunch
1.1mA/bunch

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1.1mA/bunch11• Summary from each group

ITF activities

D06V1 collimator setting

Ohmi-sanʼs talk this morning③ TMCI (M. Migliorati (Università di Roma)/T. Ishibashi (KEK))
Narrower• The TMCI sub-group investigated and studies the workaround andmechanism of the vertical beam size blowup at ~1 mA/bunch in LER,
by machine studies and simulations.
• Remodeling of the impedance in LER and HER was carried out
through the activities in this group.
• Observations are• beam size blowup is due to a single bunch effect.
• -1 mode (ny-ns) signals are observed when the blowups occur.
• the bunch current threshold increases by opening the aperture of
the vertical collimator and decreasing the vertical impedance, and• BxB FB gain needs to be adjusted properly.
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Wider

BxB FB gain

FB onFB gain
adjusted
FB off12• Summary from each group

ITF activities

Ishibashi-sanʼs and Ohmi-sanʼs talk this morning③ TMCI (M. Migliorati (Università di Roma)/T. Ishibashi (KEK))

Workarounds for the instability suppression found through machine studies are:1) Proper tuning of BxB FB gain
2) Higher vertical tune
3) Higher vertical chromaticity
4) Reducing vertical impedance2) & 3) Injection efficiency drops…

4) A new collimation scheme “non-linear collimator scheme” to reduce the vertical impedance
was proposed, and it is being installed now and will be completed during Long Shutdown 1 (LS1).

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• Summary from each group

ITF activities④ Linac (M. Satoh(KEK)/S. Matsumoto(KEK)), has not been active.

• The Injector linac sub-group was formed at the 2nd ITF general meeting on Sep. 2, after
receiving a recommendation to increase the number of focused task-force groups to the otherkey areas.
• Unfortunately, there wasnʼt any members from overseas joining us who showed interest in joining
the group in the first few months. And we could not gain momentum as an international team
as we became busier with the daily commissioning of the linac for SuperKEKB/PF-AR/PF.
• We regret that there is not much to report as an ITF group this time.
• The injector linac activities, operation summary and the future plan were reported yesterday,• Making a smaller, better-defined working groups may help activate international collaboration.

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ITF activities

Ikeda-sanʼs talk this morning

There were 2 SBL
meetings held already.

⑤ Sudden Beam Loss (H. Ikeda (KEK)/H. Nakayama (KEK)), organized recently after the 2022b run.

••••Sudden beam loss (SBL) is one of the obstacles for machine tuning and beam current increase.
The SBL mechanism is not understood.
SBL causes collimator (and other component) damages, QCS quenches, and large B.G. to Belle-II.
The ITF SBL working group was launched at the ITF meeting held on July 22 this year.

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Next

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• Next

ITF activities
The first-round ITF activities end today.
It was not too easy to operate ITF while machine was running.

Y. Ohnishi is the new chairperson and re-organize working groups.

New ITF
During and after LS1

Thank you for your support

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