Overview of SuperKEKB Status

Y. Suetsugu
Accelerator Laboratory, KEK

The 23rd KEKB Review 2019/7/81

Contents• Brief review since the last KEKB review (2018/3/14-16)• Highlights in Phase-2 (2018/3/19-2018/7/17),
and Phase-3 2019 spring run (2019/3/11-2019/7/1)• Key challenges for higher luminosity• Specific luminosity• Background• QCS quench and beam aborts• Commissioning plan
• SummaryPhase-2 and Phase-3 2019 spring run

FY2015FY2016

2015

2016
3/2

FY2017Fy201820172018

FY2019FY202020192020

6/30

Phase-1
Belle II and QCS installation
3/197/17

Phae-2VXD Full installation

3/11 7/1
Phase-3
2019
Spring

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10/15(1/16)
12/12
2019
Autum(7/1)

2020
Spring2

Highlights in Phase-2• Phase-2 commissioning started from 19th, March, andended 17th, July, 2018.
• Aims of Phase-2:• Positron injection through the damping ring (DR)• Collision tuning with QCS (final focusing quadrupolemagnets) and Belle II detector.
• Demonstrate “nano-beam” collision scheme.
• Confirm that the background is tolerable level for the vertex
detector (VXD) to be installed in Phase-3.
Beam currents during Phase-2

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Highlights in Phase-2• The injector linac has been working stably.
• Simultaneous bean injection to five rings (HER, LER,Damping ring, PF, and PF-AR) was realized in Phase-2.
• Pulsed magnet system is working well.

• Photo-cathode RF gun has been regularly used for HERinjection.
• Flux concentrator has been also functioning as expected.
• These will be reported by Satoh-san, Zhang-san, and Enomoto-san.
Layout of injector linac

The 23rd KEKB Review 2019/7/8Flux concentrator for e+

4

Highlights in Phase-2• Commissioning of DR wasvery successful.

Operation status of DR (Phase-3)• It took only a few days forinjection, storage, andextraction.

• DR has been working wellsince Phase-2.
• Will be reported by Mori-san.

• Emittance issues in the beamtransport (BT) line have been
continuously investigated.

Longitudinal beam size (vertical) and horizontal beam
size (horizontal) after injection [Streak camera] (Phase-3)• Will be reported by Seimiya-san.
• Damping of bunch (Phase-3):

by Ikeda

While the beam at first blows up just after
the injection to the ring, the longitudinaland horizontal beam sizes well damped
after 20 ms by the radiation damping.
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Highlights in Phase-2• In MR, the collision tuning wasproceeded squeezing bx*/by* gradually.
• The first physics event was observed
on 26th, April, 2018.

The first event on 26th, April 2018.

Trends of bx* and by*Trends luminosities

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Highlights in Phase-2• Specific luminosity (Lsp) increased in proportion to 1/by*.
• This demonstrated the “nano-beamscheme” collision for the first time in apractical machine.
• But, decrease in the specific luminositywith bunch current product has beenobserved due to beam-size blowup.
Lsp vs by*

Lsp vs Ibe x Ibp

Phase-2

Phase-2*
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Highlights in Phase-2• QCS has been working stably since Phase-2.
• Lots of quenches were triggered by beams in Phase-2 .
• The quenches due to injection beams were avoided bytuning beam collimators and injection parameters.
• Narrower apertures at collimators than those in QCS.
• Fast beam abort system using VXD diamond sensors.

• The quenches, which might be induced by beam-dustcollision, occurred twice.
• The head of a beam collimator was heavily damaged.
• The similar event was again experienced in Phase-3.
List of quench events

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Damage of collimator head8

Highlights in Phase-2• Summaries of major results in Phase-2
Major results in Phase-1 and Phase-2
Phase-1(3/2/2016–6/30/2016)

Phase-2(3/19/2018–7/17/2018)

LERHER

LER

HER

Max. beam current [mA]

~1010~870~860~800

Beam dose [Ah]

775.0

661.5

337.5

340.2

--

200/3
(200/2)100/3(100/1.5)~-/10 .

~-/10(single)(single)~1.7/160(in col.)~4.6/80(in col.)

Max. bam beam param.

0.02440.0141Max. lumi. L [1033 cm−2s−1]

5.55 (@1/1576/3.06)

Specific lumi. @Max. L[1031 cm−2 s−1 mA−2]

1.43Parameters

Min. bx*/by* in physics run(non phys.) [mm/mm]
Min. ex / ey [nm/pm]

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Highlights in Phase-3 2019 Spring• Phase-3 commissioning started from 11th, March, andended 1st, July, 2019.
• Aims of Phase-3 2019 Spring run:• Starting full-scale physics run with complete VXD in Belle II.
• Accelerator and collision tunings with lower b* for higherluminosity.
Beam currents during Phase-3 2019 spring run

Fire accident in the linac building

QCS quench

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Highlights in Phase-3 2019 Spring• Fire accident in the linac building on 3rd, April.

• The fire occurred at a room separated by a wall from the injector
linac used by SuperKEKB, but lots of carbon soot in the power
pulsed-modulators should be cleaned up before restart.

• MR operation stopped for approximately 3 weeks during
the recovery work of the linac, and theoperation finally restarted from 25thand 26th.
• Details will be presented by Abe-san andFurukawa-san.
Soot at terminal block

Burnt pulse modulators

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Injector linac

11

Highlights in Phase-3 2019 Spring• by* was gradually squeezed and the optics with by* = 3
mm was established on 1st, April.
• LER and HER continuous injection started from May.
→ Increase in int. luminosity.

• Realized after successful background reduction byelaborate tunings of injection parameters and collimators.

• Most of physics run was operated with bx* = 200/100 mm(LER/HER) and by* = 3 mm.
• L ~ 0.5x1034 cm-2s-1 at ~600 mA.
Decay mode run

Continuous injection mode run
HER beam current

LER beam current

Luminosity

Specific luminosity

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Highlights in Phase-3 2019 Spring• bx*/by* were squeezed to 80/2 mm on 21st, June.
• After collision tuning, the max. luminosity of 1.23x1034
cm-2s-1 was recorded at approximately 820/830 mA(LER/HER, 1/1576/3.06RF), although the Belle II HV wasoff due to high background.
• Specific luminosity increased in proportion to 1/by*.
• Satisfied even for by* = 2 mm.
Lsp vs by*Trends luminosities

Phase-3

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Highlights in Phase-3 2019 Spring• Summary of major results
Major results in Phase-1, Phase-2 and Phas-3 2019 Spring run
Phase-1(3/2/2016–6/30/2016)

ParametersPhase-2(3/19/2018–7/17/2018)

Phase-3 2019 Spring run(3/11/2019–7/11/2019)LER

HERLERHERLER

HER

Max. beam current [mA]

~1010~870~860~800~830~940

Beam dose [Ah]

775.0

661.5

337.5

340.2

500.4

539.1

--

200/3
(200/2)100/3(100/1.5)

100/3(80/2)

100/3(80/2)~-/10 .

~-/10(single)(single)~1.7/160(in col.)~4.6/80(in col.)~2.0/88(in col.)~3.8/61(in col.)

Max. bam beam param.

0.02440.01410.03550.0197Max. lumi. L [1033 cm−2 s−1]

5.55 (@1/1576/3.06)

12.3 (@1/1576/3.06, by*=2mm)

1.43

2.9

Min. bx*/by* in physics run(non phys.) [mm/mm]
Min. ex / ey [nm/pm]

Specific lumi. @Max.
[1031 cm−2 s−1 mA−2]

L

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Key challenges for high luminosity• Decrease in Lsp with bunch current product.
• Caused by the beam-size blowup due to beam-beam effect.
• Ex. LER ey 6.1 →88 pm, HER ey 20 →61 pm. (by*=2mm, ~700 mA)• Although Lsp has been improved by elaborate collision tunings, butthe tendency does not change.

• The mechanism has not been well understood yet.
• To be reported by Ohnishi-san and Ohmi-san.
Lsp vs by*

Lsp vs by*

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Key challenges for high luminosity• High background (BG)
• From LER stored beam
• Main BG source in LER storage mode was found to be the beamgas Coulomb scattering. This raised the base of BG, and limited thebeam currents during physics run.

• Bursts from stored beam
• Induced CDC trips and/or beam aborts. Dusts?.

• Bursts from Injection beams• Induced CDC trips and/or beam aborts. Changes in energy or orbit
at the linac?

• Slow change in injection condition• BG as well as the injection efficiency degraded gradually, even in ashift (8hours), and it was difficult to keep good injection condition.
• Temperature dependence?
• Background issues will be reported by Nakayama-san and Iida-san.
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Key challenges for high luminosity• QCS quenches and beam aborts• Frequency of QCS quenches in Phase-3 decreased
compared to that in Phase-2.
• However, seven quenches (two types) happened.
• [Type-1]: Caused by the malfunction of QC2LE power
supply.
• [Type-2]: Very fast (3～4 turns) beam loss event!
Suspected to be caused by the steered or blown-up
beam which lost energy by a collision with dusts (LER).
• Stored beam was steered or blown up abruptly anddamaged a vertical-type collimator head. Similar to thecase in Phase-2.
• Also gave high radiation dose to VXD.

• Quenches, beam aborts and dust events will be reported byOhuchi-san, Ikeda-san, Nakamura-san, and Ishibashi-san
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Commissioning plan
• Summer shutdown (2019/7/1~2019/10/15)• Replacement of the bellows at IP• Replacement of QC1L BPM cables at IP• These works require the retraction/insertion of QCS-L.

• Any measures against QCS quenches if available.
• Many other works in the machine and the Belle II.

• Autumn run (2019/10/15~2019/12/12)• Continue the physics run and machine tunings.
FY2019 SuperKEKB Operation Plan (2019/4/18)
2019
April
1Days
Shutdown (scheduled)162

Operation (scheduled)204

11May21111June21

111July21

11121

1

Fire incident
4/3

2020

August1121

September
11121

October
11121

November
11121

December
1Summer shutdown

4/26

1121

January
11121

February
111March

21

11121

Power line work and Winter shutdown

7/1

10/15

12/12

1/16

3/31

FY2020 SuperKEKB Operation Plan (Not fixed)
2020
April
1

11May
21

111June21

111July
21

111Days
Shutdown (scheduled)199

Operation (scheduled)

167

2021

August21

11121

September
11121

October
11121

November
11121

December
11121January
11121February
111March21

11121

Summer shutdown (BelleII Work)
7/1

1/16

3/31

Tsukuba Exp. Hall Ceiling work

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Commissioning plan
• Winter shutdown (2019/12/12～2020/1/16(not fixed))• 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.

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

• 2020 Spring run (2020/1/16~2020/6/30 (under consideration))• Operation in January will be for mainly BT tuning andvacuum scrubbing.
• Continue the physics run and machine tunings.

FY2019 SuperKEKB Operation Plan (2019/4/18)

2019
April
1Days
Shutdown (scheduled)162

Operation (scheduled)

204

11May
21

1

11June21

111July
21

1

1121

1

Fire incident
4/3

2020

August1121

September
11121

October
11121

November
1

1121

December1

Summer shutdown

4/26

1121

January1

1121

February
1

11March

21

1

1121

Power line work and Winter shutdown

7/1

10/15

12/12

1/16

3/31

FY2020 SuperKEKB Operation Plan (Not fixed)
2020April
1

11May
21

111June21

111July
21

111DaysShutdown (scheduled)199

Operation (scheduled)

167

2021

August21

11121

September
11121

October
11121

November
1

1121

December
1

1121

January1

1121

February
111March

21

11121

Summer shutdown (BelleII Work)
7/1

1/16

3/31

Tsukuba Exp. Hall Ceiling work

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Commissioning plan
• Luminosity projection• Discussion about the strategy to increase the luminosity
has just started, on the basis of the results in this run.
• As a case study, here themachine study to squeeze by*is highly prioritized.
1 ab-1• by* is squeezed step by step
every four weeks.
• Two weeks for machine study
and two for physics run• 28 weeks operation/year• 1576 bunches.

2E35

1E35

• Notes• No improvement in beambeam parameter.
• Keep the present Lspxby*
dependence on Ib2.
• No improvement in BG
situation, i.e., Imax was limited• We need more discussions together withby the present pressure
Belle II group to find the best way.
(scrubbing effect is included).
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Summary-1• Phase-3 has just finished.
• Full-scale physics run has finally started.
• The “nano-beam scheme” collision was demonstrated up toby* = 2 mm.
• Continuous injections for both rings are available in regularoperation.
• The max. luminosity of 1.23x1034 cm-2s-1 was recorded at by*= 2 mm (LER 820 mA, HER 830 mA, 1576 bunches).
• The injector linac and DR have been working well.

• Key challenges to increase luminosity• Low specific luminosity at high bunch current product• Essential issue to realize high luminosity.
• High background• Limit beam currents.
• QCS quenches and beam aborts• Fast abort system is indispensable for stable high-current
operation.
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Summary-2• Commissioning plan
• Plan in FY2019 is almost fixed, and we will expect ~ 7months’ operation.
• 2019 Summer shutdown: 7/1 ~ 10/14• Replacement of bellows at IP, repair of QCS BPM.

• 2019 Autumn run: 10/15 ~ 12/12• 2019 Winter shutdown: 12/12 ~2020/1/16• Power line work in Tsukuba campus• Installation of a vertical-type collimator into LER• 2020 Spring run: 2020/1/16 (not fixed) ~ (7/1)• The schedule of 2020～2021 are under discussion.
• Discussion about the strategy to increase the luminosity
has just started.

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Thank you for your attention.

The 23rd KEKB Review 2019/7/823

Backup

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