Long-term SuperKEKB operation andupgrade plan
Y. Suetsugu, M. Tobiyama and K. Furukawa, KEK
B2GM plenary
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SuperKEKB project timeline
Construction: 2011-2016
Phase 1 Test run 2016.2 – 2016.6
Phase 2 Pilot run 2018.3-2018.7
Phase 3 Physics run 2019.3.11-present

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SuperKEKB achievements to date

• SuperKEKB is already exploring uncharted territory!
• It is very challenging to improve the machine further to achieve the design goal.
2.96 10 cm s(world record)∗2021/6/21

0.8 mm(world record)

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187fb(as of May, 2021)

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Long-term luminosity profile
Current profile = MEXT Roadmap 20202021/6/21• The current goal is to achieve~6 10 !" # and50ab by around 2031,
which requires an intermediate machine
upgrade around 2026 that improves theluminosity by a factor of 2-3.
• The plan and profiles were assessed by
the external review committees (BPAC(2020/6, 2021/3) and Accelerator Review
Committee (ARC, 2020/7)).
• A variety of ideas to realize the plan havebeen proposed and discussed not only inthe Long-term operation plan meeting but
also other meetings, such as MDI meetingand IR technical meeting.

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Limitations found so far• While we have been confronting various difficulties during operation, the underlying
issues became evident in 2020c. Identified challenges are as follows:• Shorter beam lifetime than expected• As a result, the maximum bunch currents are limited by the balance between thelifetime and the injection power.

• Lower bunch-current limit due to TMCI than expected• Due to higher impedance of beam collimators, in which the apertures are smaller
than the design values to suppress high background.

• Beam-beam effect (vertical beam size blow-up)• Relaxed by the crab-waist collision scheme, but still remains.

• Low operation efficiency• Operation efficiency during 2021a, b is almost 0.5, lower than expected one, 0.65.
• Machine tunings, machine troubles, maintenance, etc.

• Aging of hardware and facilities, and so on.
• Various measures to solve these challenges have been also discussed at the sametime.
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Planned countermeasures
AimIncrease injection(1) power (efficiency)

Possible countermeasures

Linac upgrade to designed specification

Large physical aperture at electron injection point (HER)
Linac upgrade beyond designed specification
Rotatable sextuplole magnets(2) Improve dynamicaperture

Perfect matching
QCS modification (Option#1): Move QC1RP to far side of IP
Large scale QCS modification (Option #8)

Lower BG
(3) Improve physicalaperture

QCS cryostat front panel modification and additional shield to IP bellows(4) Relax TMCI limit

Non-linear collimator

Optimization of collimator location
QCSR beam pipe enlargement (Option#3)(5) Improve stability

Robust collimator(6) Anti-aging measures

Preparation of standby machines and spares, repair of facilities, etc.

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Upgrade of beam abort system and loss monitor system

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Planned countermeasures• High-priority countermeasures before LS2
AimPossible
countermeasures

Expected improvement

Ready status

Increase
Linac upgrade toOn going sequentially.
injection power
Full spec injection
designed specification(efficiency)
Improve
Rotatable sextupole
Beam-beam parameter
Ready. Preparation of tuningdynamicMagnets(emittance), beam lifetime knob.
aperture
Improvestability

Robust collimator

Improvestability

Beam abort system andOperation stability
loss monitor system

Anti-aging
measuresAnti-aging measures

Sustainability

LS1LS22021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031~

Need R&D and beam test
On going sequentially.

On going sequentially.
Operation efficiency(standby machine, repair Especially for long shut down
periodsof facilities)• Essential to achieve ~2x1035 cm-2s-1 before LS2.

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Planned countermeasures• Possible countermeasures in LS1
AimIncrease
injection power(efficiency)

Possiblecountermeasures
Large physical aperture
at electron injection
point (HER)

Improve dynamic
Perfect matching
aperture

Expected improvement
HER Injection rate x #?

Ready status

LS1

LS2

LS1

LS22021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031~

Need further estimation,
design of pipes

Need further simulation,
LER beam lifetime x ~1.5. design, manufacturing ofmagnets and pipes

QCS cryostat front panel
Improve physical
Background, Physicalmodification andWill be ready by 2022.
apertureaperture, TMCI limit x ~1.2
additional shield to IP
Lower BG
bellows
Improve physical
Optimization of collimator Background x ~1/2
Need further simulation,
aperture
manufacturing of pipes
location(Storage beam)
Lower BG
Need further simulation,
Background x ~3/5
design, manufacturing ofRelax TMCI limit Non-linear collimator(Storage beam)magnets and pipes• Possible countermeasures in LS2
AimImprove
dynamic
aperture
Improve
physical
aperture
Lower BG

Possible countermeasures

Expected improvement

Ready status

QCS modification(Option#1): Move QC1RP to Found to be no effect.
Will be not adopted
far side of IP
13.5 mm -> 15 or 18 mm,
Need design, manufacturing
QCSR beam pipe
βy*=0.3 will be possible, noof correction magnets andenlargement (Option#3)
effect on dynamic aperture,
pipes
TMCI limit x ~1.5.

2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031~

8Preliminary luminosity estimation• Estimated luminosity with these countermeasures
Lp [x1034 cm-2s-1]

Int. L [fb-1]

RM2020
RM2020~2

Estimation~3

W/O LS2

W/O LS2

Estimation• The luminosity will be lower than expected considering various limitations.
• The ideas of the intermediate upgrade of IR around 2026 we have planed so far are notsatisfactory from the viewpoint of int. luminosity as given in RM2020, and therefore we arecontinuing the effort to find more effective measures(x2~3), not limited to the IR but also toother parts of the MR and Linac.
• Ideas of a more revolutionary upgrade including some modification of Belle II should beconsidered to reach even higher luminosity; this may require a longer time for R&D (~203x).
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9Plan• We continue to find more effective measures, not only limited to the IR but
also including the MR, other parts and Linac to maintain the target
luminosity profile.
• Inaugurate an international taskforce under the management of the KEK
Accelerator Lab. to pursue effective measures for recovering the luminosity
profile and reaching target luminosity.
• The results of ongoing studies will be reported at the next ARC, scheduledin September.
• Some practical conclusion should be obtained before LS1 on the feasibility
and contents of the upgrade around 2026.
• The actual long-term plan will be revised based on the progress of theongoing luminosity improvement.
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We greatly appreciate your continued support!

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Back up

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Planned countermeasures• For reference, proposed countermeasures after LS2 (~2031?)• Still preliminary discussion
Aim

Possible
Expected improvement
countermeasures
Large scale QCS andalso Belle II modification LER beam lifetime x ~2.2(Option #8)

Improvedynamicaperture
Increase
Linac upgrade beyondinjection power
designed specification(efficiency)

Injectin power x ~2?

Ready status

LS1

LS22021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031~

Need further simulation
Need furtherinvesitgation• With these countermeasures• L = ~2x1035 cm-2s-1 -> ~4x1035 cm-2s-1

IR modification (option #8) including Belle II (SVD etc.)

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Limitations found so far(3) Low operation efficiency• Operation efficiency during 2021a, b is almost 0.5, lower than expected one, 0.65.
• Main reasons (analyzed by K. Matsuoka):
Operation statistics(including suspension
by beam abort etc.)• Note that the efficiency was ~66% during 5/11~5/25, where the beam currents were kept
constant, and the operation was dedicated to physics run.
• A key point is how to keep the stability of machine.
• Hardware trouble due to aging can be avoided by planned and prepared updating orreplacing old hardware.
• Preparation of standby machines and spares, and anti-aging measure for facilities and oldhardware are urgent matters.

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Luminosities expected under these limitations• These challenges add new bunch current limits in the operation, and will limit
the luminosity.
•Lifetime (injection power) limit based on the formula presented by K. Oide.
1HI&'(1HI
J( +( 9:K(1 ∗ @1HI&'.'•TMCI limit

/,01
&'(

1.4 "3 &'/,01

1.5 "3•RF power limit)*&'(+(, .'&')*•Hardware limit (for example by BPM)+, .'2 "3&'4 56• Luminosity formula

4 56&'(J +1HI

9:

K1

∗

@.'+(, - =2.59 A, + , - = 1.87 A before LS2+(, - =2.82 A, + , - = 2.04 A after LS22 "3.' &'( &'1∗
478 9: sin=0 >?
@A2021/6/21

B±28D> ∗∓ +± G ± B± +± G ±1+ ∗~(when limited by beam-beam parameter, ξy)∗>28D ∗ ±±B2GM 2021/6

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Luminosities expected under these limitations• The luminosities under these bunch current limitations were estimated by H.
Nakayama and K. Nakamura.

• Reported in MDI meeting, IR technical meeting, and LTOP meeting.
• Here, the maximum luminosity was searched by scanning Nb (500~2500) for each βy*.
• Assumptions:
Background does not matter.
Beam-beam parameter (ξy) and emittance (εy) are constant (no dependence on βy*).
Beam lifetime is determined by Touschek lifetime (due to dynamic aperture).
Luminosity+(, - 2.59 A
Beam current ratio of HER to LER is free.
limited by• The calculation is not astrict simulation, butwill give some
Luminosity
limited by
guideline of achievable beam-beameffectluminosities under
Luminosity
these limitations.
limited byTMCIRF power

Luminosity [cm-2s-1]••••

beam-beam
TMCI

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0.075

Max. beam currents
Bunch lengthMax. number of bunches
Vertical emittanceLER ver. beam-beam
parameter

3.6 10O
Lifetime parameter1.2 10T
1HI
Inj. efficiency
J 1HI 0.8
J(1HI
1HI
Inj.
bunchcharge
P
4 nCP(1HI
1HI.'
2 Inj. number of bunches.'(Inj. power

βy* [mm]

G ,( K(1K1Max.

.'
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RF power

Luminosity
limited byinjection
power+ , - 1.87 A>? 6.5 mm.', - 2500
@20 pm

1HIMax.
luminosityunder alllimitations

1HI

25 Hz Inj. repetition rate95(95&(4 562 mA& 4 562 mA&(/,01

1.4 mA & /,01

1.5 mA

Hardware limit

16

TMCI limit

Luminosities expected under these limitations• The maximum luminosities before and after LS2 were calculated using possible
parameters basically following their methods.

• Note here, we assumed the full-power injection, that is, 4 nc/bunch, 2 bunches, 25 Hz
injection with an efficiency of 80%.

• Preliminary results;
Before LS2(βy* ≥ 0.5 mm), L = 1.9x1035 [cm-2s-1]

Luminosity [cm-2s-1]

Before LS2

beam-beam
TMCI

RF power
Inj. power+(, -2021/6/211663

βy* [mm]0.075

K(13.610O

K1

1.210T

J(1HI
P(1HI.'(1HI.'

After LS2

1.87 A>? 6.5 mm.', - 2500@
20 pm
G ,( -95(&(4 56&(/,01

After LS2(βy* ≥ 0.3 mm), L = 2.3x1035 [cm-2s-1]

2.59 A+, -1HIMin. L•J 1HI 0.8
P1HI 4 nC
1HI.'
295

1HI

25 Hz

2 mA& 4 56

1.4 mA & /,01

Luminosity [cm-2s-1]•2 mA
1.5 mA

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beam-beam

TMCI+(, -RF power
Inj. power.'1980

βy* [mm]2.04 A>? 6.5 mm.', - 2500
@10 pmG ,( -3.610O

K1

1.210T

1HI

J 1HI 0.8
P1HI 4 nC
1HI.'
21HI951HI

25 Hz

2 mA & 4 56
1.4 mA & /,012 mA

95(&(4 56&(/,010.081

K(1J(1HIP(
1HI.'(Min. L

2.82 A+, -17

1.5 mA

Luminosities expected under these limitations• Re-estimated luminosities was much lower than that presented in RM2020.
• Operation efficiency should be also improved to accumulate the expected luminosity.
• To improve luminosity• Increase injection power (injection efficiency, bunch charge)
or improve beam lifetime (dynamic aperture and also physical aperture)• Lower background -> Wide collimator aperture (physical aperture) -> Long beam
lifetime, Low impedance -> Relax TMCI limit• Relax TMCI limit (important if emittance is still large).
• Improve beam-beam parameter (low emittance, )• To improve operation efficiency (Integrated luminosity)••••Increase efficiency of beam tuning (improvement tuning knobs)
Improve stability of machines
Prepare standby machine and spares
Execute anti-aging plans for facilities

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