Preparation for 2026
Accelerator Upgrade
Makoto Tobiyama
KEK Accelerator Laboratory
9/Mar/2021
＠BPAC Review1Long-term operation plan For MEXT Roadmap 2020, we proposed to upgrade the previous
operation plan (2019) considering the current situation and theresults obtained until 2019c.
 Peak luminosity 6E35 in2028
 Integrated luminosity 50 ab1 in 2030
 Partial RF-power upgrade (2stations) in 2026
 IR upgrade in 2026
 by*=0.3mm in 2026 after IR
upgrade and 0.5mm beforethat
 Max. beam currents: LER
2.8A, HER 2.0A (1761bunches) in 2027 Basically, 8 monthsʼ
operation per year.
2Long-term operation plan Present status• MEXT updated their roadmap 2020 in Aug, 2020.
• The SuperKEKB/Belle II project was selected as one of 15 highest priority
projects with an “aa” grade (the highest).
• The actual plan will be finalized by seeing the progress of the luminosity
improvement.
• The plan was accessed by the external review committee (BPAC[2020/6] andAccelerator Review Committee (2020/7)).
• Based on the recommendation from the review committees, “Long-termoperation plan meeting” was launched in August, 2020 (Accelerator team andBelle II group) ‒most of the members are Japanese, though.

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Long-term operation plan meeting In the meeting, following issues will be discussed and examinedin these 2 or 3 years.
• Is IR upgrade really required?
• Examination of crab-waist scheme• Verification of the effect of rotatablesextupole magnets• Investigation of beam-beam effect• Understanding of background issue• βy* squeezing and luminosity• Understanding of beam lifetime• Collimators and their impedance issues• Injection efficiency• Examination of the base plan (with presentQCS)••• Is IR upgrade really possible?
• Making practical model of QCS magnet field
configuration• Making practical beam optics• The range of remodeling• Examination of technical issues• Manufacturability、Materials of SCcables、Magnet alignment method• Examination of human resources• Conflict with Belle II detector• IP chamber, Connection method• Manufacturing schedule• Commissioning after the upgrade

Short-term commissioning plan
Establish the performance model Five meetings have been held so far (17/Feb/2021)
 In IR meeting, MDI meeting and other (hardware and optics)
meeting, the upgrade related topics have been discussed.
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Example of topics in the meeting Narrow dynamic aperture/lower luminosity at high-bunch current regions
due to strong beam-beam effect•••••

A promising method to mitigate theeffect was said to be the modification ofQCS to avoid interference between thequadrupole magnetic field and the BelleII solenoid field for the LER.
Two ideas to relocate QC1P to places
farther from IP were examined at first.
However, up to now, it was found thatlittle improvement was expected even
without beam-beam effect.
On the other hand, it was also found in asimulation that the effect will be cured
using the rotatable-sextupole magnets
installed in the local correction region atTsukuba.
We will try it this during 2021 run.

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Example of topics in the meeting Narrow physical aperture in the QC1RP -1
 Enlargement of the (vertical) aperture of beam pipes in QC1RP has been
discussed.
•••

The enlargement is expected to increase the physical aperture and then increase
beam lifetime, reduce background, resulting increase the TMCI threshold.
Although little improvement in the lifetime determined by the dynamic aperture.
The aperture can be enlarged by relocating the correction magnets to outside of themain quadrupole magnets.

 It will be possible to increase the inner diameter from 13.5 mm to 18 mm
geometrically.
 The range required for the modification was examined, and it was reported thatthe modification near to the BPM and bellows near to IP is also required.

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Example of topics in the meeting Narrow physical aperture in the QC1RP -2• The R&D for the beam pipes, BPM and bellows has started.
• Required R&D• Beam pipes for QC1RP• Remodeling of connection flange at IP side（RVC）
R&D and testing together with DESY group.
• Change in the vacuum sealing mechanism
between the QCSR cryostat and the beam pipe.
(O-ring seal)• Manufacturing method of beam pipes and TiNcoating method.
• Bellows chamber with BPM• Change in the cross-section of bellows fromcircular one to an ellipse or a race-track one• Change in the flange at QCS side.

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Example of topics in the meetingExamination of the base plan (with present QCS)••

The performance with the present QCS is being examined by asimulation including beam-beam effect.
Recently it was reported that the Touschek beam lifetime will
be increased by 60% and a luminosity of around 3E35 cm-2s-1
could be achieved by introducing a “perfect match” and 40% of
the crab-waist in LER••••

Perfect injection condition, TMCI suppressed situation..

~3E35 cm-2s-1 : Extreme goal luminosity before the 2026
upgrade.
How to practically realize the “perfect match” using normalconducting quadrupole magnets, for example, is being
investigated.
Preparation of hardware need >1 years so will not be able toinstall during LS1 but will be able to install before LS2.

“Perfect match”:• Phase shifts between
SLYTRP2/SLYTLP1 and IP arejust 0.5 (x) and 0.75 (y).
• The values of βx and βy at thecenter of four SLY（SLYTLP1&2,SLYTLP1&2） are set to be thesame, respectively.

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Example of Topics in the meeting Linac long-term upgrade plan
• Replacement of aged accelerating structures (on going)• 7% of the structures will be replaced until 2023.

• Movable supports and beam collimator• Emittance preservation• ECS for electron beam
• Comments on the necessities, other method (chirp at the end of linac)• More pulse magnets• Fast kickers to make each bunch in a pulse independent• PCB measures (capacitors in the modulators, until JFY2026 by law)
• RF gun• Positron yield (Optimization of capture section)

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Example of topis in the meeting Beam transport lines, positron damping ring.
 Many aged components• Power supply (>24 years), increasing failure rate, no support from the company• Need to renew before spending the spare cards, etc.

• Cupper oxide precipitate in the hollow conductors of magnets.
• Old BPM electronics using oscilloscopes• Improvement of stability• Better Thyratron• Fast correction kicker for injection• SR monitor lines in BT

 We plan to investigate the aged components (all the acceleratorcomponents) and update them systematically.
• Urgent components will be taken care using nominal operation budget. (30MJYPper year?),• Utilize LS1 as much as possible.
• Measures for items that require long-term shutdown.

• For RF components (LLRF etc) which need much larger investment, we expect
direct support from MEXT, following the roadmap 2020.
10Other (important) topics
 RF upgrade plan
 Beam instrumentation system ?
 Improvement of energy efficiency

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Large-scale IR renovation
 Forgetting the current (physical) limitation on the space aroundIR, how much improvement of the luminosity will be expected?
 Examine the case of moving QC1Ps to L=600mm position

 Need complete different SVD/Pixel support, vacuum
connection mechanism, etc.
12Large-scale IR renovation
 LER QCS Toy model study (not using realistic magnetic fielddistribution) has shown roughly x2 improvement of lifetime onsimulation.
 Will double performance gains be worth the long construction
period and large investment?

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Upgrade plan We would like to start Linac upgrade soon.
• Before 2026 upgrade• Hoping enough budget support from MEXT for JFY2022 and after.

 Optics upgrade around IR including “Perfect matching”• Would like to start preparation of the magnets, power supplies with high priority
after fixing the modification items.

 Beam transport lines• Preparation of spare components (power supplies, magnets) with high priority

 QCS and IR upgrade• First decision to ask ARC will be made before July/2021.
• Simulation, R&D of hardware components will be needed.

 International collaboration• Depends on the COVID-19 situation. Hoping to restart direct (in-person) andlong-term contributions.
• Planning international workshop on SuperKEKB collider (Remote, Aug/2021?)• Try to ask “remote” contributions under COVID situation.

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Summary “Long-term operation plan meeting” was launched based onthe recommendation from the review committees to discuss
the detailed and practical issues in the plan.
• To date, there have been 5 (+) meetings..
• QCS, IR aperture, better optics correction scheme, Injector, Beam transport anddamping ring, beam collimators, etc.
• Linac upgrade is already on going (but without enough budget support).

 The first plan will be shown for the KEKB accelerator review on
this year.

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