MDI-related topics in 2020ab
Hiroyuki NAKAYAMA (KEK)

Satellite MDI session on June 18th
https://kds.kek.jp/indico/event/34633/

2020/6/22 B2GM plenary1Latest beam background status*limited by injection

June 21st, 2020

• LER 720mA, HER 610mA*, 978 bunch• Delivered peak luminosity record

ALD• 2.402x1034/cm2/s (June 21st, 2020)• on-resonance, with Belle IIconventional• TOP PMT rates: still below limit ☺
• CDC HV trips: not frequent anymore ☺
• Injection rate: LER 22Hz, HER 25Hz

TOP limit (relaxed since June 20th)
1.0MHz + lumi → 1.2MHz + lumi

• Injection veto deadtime: 7~8% (mainly LER)

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Major MDI improvements in 2020ab• New LER vertical collimator (D6V1)• New LINAC/BT orbit monitor• New injection BG monitors (CDC/TRG)

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Improvement: D6V1 and beam-gas BG• A new LER vertical collimator: D6V1
(good phase, large beta_y)• We use D6V1 as “primary” (=narrowest),
to protect downstream collimators (D2V1)• D6V1 head will be replaced with carbon inthis summer• TOP BG by LER Beam-gas has reducedby factor x~2 since 2019c, thanks to:- new collimator (D6V1),- tighter settings of other collimators,- and vacuum baking progress.

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Koga, Nakagiri,

Improvements: injection BG monitoring
Injection BG duration monitor
ECLTRG (#cluster>6)

These plots are shown in the front display of SKB control room.
Also available as PVs. Very useful for injection tuning by machine operators.
2020/6/22 B2GM plenary5Improvements: LINAC/BT monitoring
LINAC/BT orbit trend

Miyahara,Seimiya, Kaji,etc..

BT orbit web

2020/06/15 20:48
Diamond abort
Pulse Magnet failure(PC_6,181)

Easy to detect injector problems when bad injections are observed.
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Major MDI issues in 2020ab• QCS quenches (May 24th, June 20th)• Beam aborts → machine down time
• Injection BG duration → injection veto dead time

• PXD SR during HER injection• Collimator issues (activation, impedance)

2020/6/22 B2GM plenary7Issues: QCS quench on May 27th, 2020
What happened?
• LER was aborted first. Diamond abort was not issued.
• Diamond system received the abort acknowledge signal
and started the data dump.
• Diamond was blind during this data dump, while still
HER is circulating the ring.
• ~0.7 sec later, iBump fast FB strongly kicked HER
beam and caused HER beam loss.
• It resulted in QCS quench and damage on PXD.

PXD after QCS quench in May 27thSolutions• Diamond system is modified.
• Dump the data only when both beams are aborted.
• iBump fast FB is also modified• Add the limiter on the FB power supply controller

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Another QCS quench occurred on June 20th. Diamondabort was issued. Caused by small LER vacuum burst?
8H. Ikeda

Issues: beam aborts• “Beam abort” taskforce, led by Hitomi Ikeda, to investigate the possible cause ofbeam aborts and improve integrated luminosity by reducing machine downtime• Beam aborts in-sync with injection has
significantly decreased thanks to LINAC
group’s effort• HER beam loss aborts not-in-sync withinjections are dominant now.
••No clear correlation with injection timing→ Not caused by “delayed” injection losses
Small vacuum bursts? Or any unknown causes?

HER aborts by bad injections
have disappeared since Apr. 9th2020/6/22 B2GM plenary

9ECLTRG (#cluster>6)

T. Koga

Injection BG duration• Typical duration: LER: 6~12ms, HER:1~6ms• Single beam: BG duration∝bunch current• Colliding beams: BG duration longer than single-beam• beam-beam effect• However, luminosity scan w/ v-offset didn’t change BG duration...
• Crab waist strength: no clear dependence• beta*y squeeze: BG duration longer with small beta*y• Dedicated machine study shows:• Not only the injected bunch, but also later bunches are lost
• However, “blank-shot” injections don’t give any BG duration→ coupling btw an injected bunch and later bunches?
“blank-shot” injection: kickers are fired but no charge is injected
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10Issues: PXD SR during HER injection

Carsten• SR hit pattern on PXD forward –X modules• Only visible during HER injections• Becomes stronger when HER beta*_x was squeezed• SR NOT observed with “blank-shot” HER injections•••

HER horizontal tune adjustment shows no significant improvement within
acceptable tune range
HER D01H collimator adjustment didn’t improve SRSR increased with the smaller HER H angle (May 15-31), so we went
back to the original angle• SR rate PV is now available.
• BCG/PXD experts monitors it.

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PXD SR is not critical right now, but we need to keep our eyes on it.

11Issues: LER D6V2 “mystery”• When we opened D6V2, injection BG duration (and injection BG on diamonds) improved.
• Now we use ~400um wider D6V2 settings.
Why?
• Tip-scattering of injection charge? → seems unlikely to reach IR from D6 or affect BG duration.
• Collimator impedance issue? (why only in D6V2?)
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12Ongoing projects for further improvements
Carbon collimator head for D6V1

• Collimator works in mid-September 2020
• Replace D6V1 with carbon head, install LER D3V1 collimator• Simulation study including tip-scattering is ongoing• LINAC works aiming for higher beam currents• LER injection at 18Hz, 2-bunch injections• Increase injection charge while keeping good emittance• Additional shield around QCS bellows• Further BG reduction for TOP/CDC• K. Nakamura’s report in background session

QCS remodeling• QCS remodeling• Wider beam pipe aperture. More space to add tungsten shied?
• Ohuchi-san’s report at MDI session• VXD diamond & beam abort system upgrade (RMBA task force)• A dedicated B2GM parallel session on June 24th
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Summary• New LER collimator(D6V1)→ works very well to reduce BG• QCS quench → problems found and already fixed• Beam aborts → much less injection-related aborts• Injection BG duration → better understandings now• Several projects ongoing, for further BG improvement(new collimators, additional shield, QCS remodeling, etc..)

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backup

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Machine study plan in remaining 2020b run• HER/LER single-beam BG studies + lumi-BG study (June 27th day)• Similar with May 9th study, but with the latest optics (hopefully at beta*y=0.8mm)• Will be used to background extrapolation for future optics• Collimator study (June 18th)• Try to open collimators with large activation• Injection tuning with wider collimator settings (use Belle II diamond as a tuning guide)• Injection studies (June 24th swing)• 2-bunch injection challenge• LER BTend feedback using the average orbit of 1st/2nd bunch• PXD SR vs. injection charge, iBump height• Synchrotron injection challenge (2020c?)

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MDIIssues in 2020abImprovement plans• Beam aborts• Collimator enforcement• Machine down time ➔luminosity loss
• Aborts by bad injections are significantly decreased• HER aborts not-in-sync with injection are dominant(causes still unknown)• Injection BG duration• Veto deadtime ➔ luminosity loss
• Trying to understand its mechanics by systematicmachine studies• QCS quench on May 27th
• Problem in machine FB system and diamond abortsystem are already fixed• PXD SR• PXD sensors on -X side see SR hit pattern, backscattering from +Z?

• Collimator activation• LER D6V1 → carbon head
• Add LER D3V1

• Higher beam currents• 2-bunch injection, LER 18Hz injection• Larger injection charges with good emittance• Add QCS bellows shield• Mechanical design/ simulation ongoing• Radiation monitor/beam abort upgrade• RMBA taskforce• QCS remodeling• Luminosity improvement• Less single-beam BG• Collimator impedance issue?

2020/6/22 B2GM plenary17Issues: activation of collimators• LER survey (June 2020)
D06H3：400 uSv/h
D06V1：400 uSv/h
D06V2：260 uSv/h
D02V1: 130 uSv/h
D02H3: 950 uSv/h

Tanaka, Terui• D6V1: “primary”(=narrowest) LER verticalcollimator• D2V1: Low activation isthanks to D6V1

• HER survey (Apr. 2020)
D09V4 : 80µSv/h
D09H4 : 60µSv/h
D09V3 : 40µSv/h
D09H3 : 9µSv/h
D09V1 : 380µSv/h
D09V2 : 15µSv/h
D09H1 : 25µSv/h
D09H2 : 75µSv/h
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D12V1 200µSv/h
D12H115µSv/h
D12V235µSv/h
D12H220µSv/h
D12H365µSv/h
D12V3 350µSv/h
D12H4 45µSv/hD12V42µSv/h• HER D09V1(and D12V1,3) show large activation,
but the loss monitors at those collimators show
small values• Several collimators are opened, especially ones
with higher activation, by carefully looking atinjection BG
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Issues: injection-related beam aborts

Sato• Pulsed magnet misfire events caused many (HER) beam aborts in March/early April.

• The control software replacement on April 9th → misfire reduced significantly.
• HER aborts in-sync with injection have completely disappeared.
• LER aborts in-sync with injection still exist. Some are due to LINAC Klystron down.
RF gun pressure bursts cause HER
injection spikes in VXD diamonds, butthey do not cause beam aborts so far.

Pulse magnet failure
disappeared after Apr. 9th
During June 11-16th, pulse magnet
misfire event appeared again We see
LER aborts due to bad injections.

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Weekly beam abort counts
HER aborts in-sync with injections due toLINAC pulse magnet misfires (till April 9th)

Nakayama
LER aborts in-sync with injection due toLINAC Klystron down or other unknown reasons

4/24~ HER CW start

5/11~14 off resonance
5/14~31 HER angle
5/21~ LER high εx
6/11 D6V2 open
6/10~16 off resonance

What is the cause of
those HER aborts
not in-sync withinjections?
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Due to higher beam currents?
or D6V2 open on 6/11?

LINAC pulse magnet misfires
appeared again (June 11-)20

CDC HV trips – much less frequent now

2020/6/22 B2GM plenary•Only few CDC HV trips in 2020ab(using higher trip thresholds)•Inner layers(∈SL0) were tripped•

Mostly caused by HER injections•

Trip frequency seems to bedecreasing over time, although
the beam currents gets higher•

Still acceptable trip rates at higher
beam currents?

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VXD abort modification after QCS quench
Yifan Jin

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Andrii NATOCHII

Beam loss simulation with collimator tip-scattering

Simulated IR loss rate of HER Touschek/Coulomb significantly increases byusing realistic collimator shape and adding tip-scatting effect
Link to Andrii’s slides at
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MDI meeting, June 11th23

Diamond abort with large loss

Small pressure burst (~5.5E-8 Pa) at HER D01_H10

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Small pressure burst(~8E-8 Pa) at HER D01_H1524

Beam orbit drift on LER D2V1
D6V1

D6V2

D2V1

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50um

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MR collimator installation plans(from Ishibashi-san)• We plan to replace D06V1 during this summer shutdown.
However, the delivery date of the low-Z heads is this mid-September, and we want tobake-out the collimator in-situ after the installation (it takes for about 1-2 weeks), so
there is a possibility that it won’t install the low-Z heads depending on the startingtime of 2020c run.

• We have started manufacturing a vertical collimator for LER and plan to install it at
D03V1 during this summer shutdown (mid-September maybe) so far. Then, we canchange the installation site if required.

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Long-term Radiation Monitor & Beam Abort w.g.
• RMBA working group, started in Feb. 2020 at the 35th B2GM
Membership:
representatives from Belle II subsystems and SuperKEKB; open to participation
coordinated by L.Vitale (INFN and Univ. Trieste)

Charge:study of long-term future of beam-loss (BL) radiation monitoring and beamabort in the interaction region
Initial focus: upgrade of the diamond system electronics

Preliminary work plan:
Review of existing BLM systems at colliders; update of requirements andspecifications for Belle II / SuperKEKB; comparison of upgrade options• Documentation, meetings, mailing list
https://confluence.desy.de/display/BI/Longterm+future+of+Radiation+Monitoring+and+Beam+Abort
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RMBA working group: meetings•

1st meeting, May 29th, 2020: https://indico.belle2.org/event/2287
W. Viganò, E.Calvo Giraldo (CERN): “The BLM system of the LHC injector complex”
I. Popov (MPI Munich): “CLAWS for beam abort in SuperKEKB”•

2nd meeting, June 11th, 2020: https://indico.belle2.org/event/2373
M.Tortora, P.Scarbolo (CAENels): “MTCA beam abort at IBS and future developments”•

Next meeting (B2GM): June 24th,2020 at 14:00 JST
H. Ikeda (KEK): “Beam loss monitor and beam abort at SuperKEKB”(discussion: drafts of requirements for upgrades; organization)•

Main present discussion topics:
Diamond electronics upgrade: dynamic range in current measurements, access to buffer memories
without disabling beam abort, synchronization and integration with SuperKEKB
Update of requirements, comparison of upgrade options
New opportunities, for instance CLAWS beam abort

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