Beam BackgroundContents:• Improved monitoring and diagnostics• Phase 3 Background composition• How to reduce backgrounds further?
• Data versus MC• Extrapolation for 2020
Hiro NAKAYAMA (KEK)The 23rd Accelerator Review Committee (July 8th, 2019)
Most of slides are taken from 33rd B2GM Plenary report by Sven Vahsen

1Beam Backgrounds: developments since February• Improved BG monitoring– Online: Belle II rates– Online: Vertex distributions– Offline: Automated summary files• Four new LER collimators• Established continuous injection inboth rings• BG mitigation & study May 9-14
(Nakayama et al.)• Beam currents increased up to
600-700 mA
2

Beam Background “big picture”(as of mid. June 2019)• Machine parameters– beta_y*=3mm, 1576bunch, 650+650mA, L~0.5*1034• Our bottle-neck is CDC (and TOP)LER single-beam study
I=450mA, beta_y* = 3mm• Dominant source: LER beam-gas BG– Touschek BG is small enough, thanks to newly-installedhorizontal collimators after phase2• Keep good injection condition is very important

CDC current [uA]

– CDC HV trips with large BG (storage + injection)– TOP PMT photocathode lifetime get shorter– To avoid CDC HV trip
– To avoid loss monitor aborts at collimators (and allow us toclose the collimators even narrower)

At the end of June, we moved to beta_y*=2mm optics. When L~1.2*1034 isachieved with 800mA, BG was three times too high to turn on Belle2.
(Note that we didn’t have enough time for collimator optimization with 2mm optics)

Touschek
Beam-gas

Touschek scaling(beam size scan)New: Online Rate Monitoring (BCG)

Schueler et al.

June 18, 2019, 500+500 mA• Total (storage + injection) bkg compared against 100% “alarm limits”• Clear how much headroom we have to raise beam currents• Detect when bkg conditions (e.g., injection backgrounds) deteriorate→ take immediate action• Most detectors: safety factors order 5-10. Exceeding 100% implies soft
performance degradation, but not physical danger• CDC and TOP <= 2, currently limiting beam currents• CDC: >100% can occur during injection spikes, causing HV trips,
significant downtime• TOP: >100% leads to unacceptable deterioration of PMT photocathodeand efficiency loss before 2020 (or 2021)

Limit is raised
to 200uA4

βy*=3mm, 1576 bunches, 600+600mA, L~0.5*1034

Fulsom, Spruck, et al.

x (cm)

New: Online Monitoringof Background Spatial Distribution (DQM)
Phase3 r1976(Lumi run)

Track vertex distributions

horizontal

horizontal

verticalz (cm)• Monitor for scraping beams• We suspect incoming-LER scraping (at this position or at upstream QC1)
• Optimizing beam vertical steering at IP (dedicated study on June 20th)
achieved 10~15% BG reduction in CDC/TOP!
5

Improved: fitting of single-beam storage backgrounds

Beam-gas• background studies performed
May 11, 12, 14• beam size scans and fill patternscans now agree (LER),
providing unambiguous
estimate of backgroundcomposition• diamonds, PXD, SVD, TOP,
analyzed in detail• KLM, CDC groups have first
results• others detectors still
forthcoming

Touschek

Tanigawa

Touschek

𝑅𝑎𝑡𝑒 = 𝑇 ×

𝐼2
𝜎𝑦 𝑛𝑏

Beam-gas+ B × IPvary both 𝜎𝑦 and 𝑛𝑏 to change Touschek bkg normalization

6

Tanigawa (SVD)

Diamonds, SVD, TOP well described by simple beam-gas + Touschek model
PXD not yet fully understood, suspect due to Synchrotron Radiation
7

Updated Beam Background Composition
May background studies, HER 320mA, LER 350mA, 789 bunches

TOP, Tsuzuki
SVD, Tanigawa• Exact composition depends on collimator settings and detector, but…
• LER storage bkg >> HER storage bkg. Ratio LER/HER >= 4
– LER beam gas dominates (~70% of total)– LER Touschek small in SVD, negligible in TOP
8

From beam lifetime

Data vs. MC• bkg simulation perfect  data/mc = 1• Typically, data/mc >1. We use data/mc ascorrection factor for simulation, for instance toestimate backgrounds at design luminosity• Three groups have results– Diamonds: observe data/MC ~ 1– SVD/TOP: shown to right

•
•
•
•

Tanigawa, Tsuzuki
Data/MC in SVD,TOP
total loss

SVD L3(SVD L4-6)

TOP

LER beam-gas

1.9-4.1

12-13(5.4-6.9)

12

LER Touschek

1.3-1.8

1.0-1.1(0.87-1.1)

0.16

HER beam-gas

1016(19-27)

7.7

HER Touschek

3

1600

(760-900)

510

Total loss rate data/MC <=10. SAD simulation reasonably accurate.
LER Touschek: good.
HER Touschek: suspect simulation problem (Data rate is small. MC rate is toooo small).
Beam gas: data/mc high even for total loss rate. Note that dynamic pressure is already accounted for in theseratios and does not include measured Zeff. Need to investigate beam-gas normalization. Gas injection study?

9Major issue: LER Dynamic Pressure
Touschek• Why is LER beam gas bkg so high?
• Because dynamic pressure is high inall of LER, especially in D02, where
we installed collimators after
Phase2• We need to replace the collimator
head of D02V1 damaged by June 9th
accident.
• Intensive vacuum scrubbing after
the replacement is important!

Beam-gas

𝐼2
𝑅𝑎𝑡𝑒 = 𝑇 ×+ B × IP𝜎𝑦 𝑛𝑏
𝐼2
2𝑅𝑎𝑡𝑒 = 𝑇 ×+ B’𝑍𝑒𝑓𝑓
× I(𝑃0 +I dP/dI)
𝜎𝑦 𝑛𝑏

LiptakVacuum scrubbing goal10

Another major issue: Severe Background burst
June 9thx40!

Severe damage on
inner detectors

L. Vitale

Can we minimize this delay?
See Ikeda-san’s talk later11

Latest SKB roadmap till 2020
recently updated at 33rd B2GM

In this slide, we assume
2019 winter: 0.84/0.77A, beta_y*=2.0mm, L=1.0*10^342020 summer: 1.20/1.10A, beta_y*=1.5mm, L=2.0*10^34
12

BG extrapolation toward 2020 summer
This extrapolation based on the scaling the latest BG measurement using machine parameters.
Another approach is being prepared, to scale the BG simulation with future optics, using latest Data/MC ratio.

In this slide, we assume
2019 winter: 0.84/0.77A, beta_y*=2.0mm, L=1.0*10^342020 summer: 1.20/1.10A, beta_y*=1.5mm, L=2.0*10^34

LER Touschek•

2019 winter2020 summer

x2(0.84A)

x4(1.2A)

Collimator reduction factor

x1

x1

Total

x2

x4

Beam current (I^2)

LER Beam-gas

2019 winter2020 summer

x2(0.84A)

x4(1.2A)

1/beta_y*

x1.5

x2

Vacuum scrubbing (dP/dI) *

x2/3

x1/2

Collimator reduction factor **

x1

x1

Total

x2

x4

Beam current(I^2)* My personal guess** “x1” might be optimistic. Vertical collimation at squeezed optics will be more difficult••

HER Touschek, HER Beam-gas are assumed to bemuch smaller than LER also in 2020.
Lumi-BG is not yet measured in Phase3. We
expect x2(x4) lumi-BG in 2019(2020) than now,which we assume to be smaller than LER BG.
Based on these assumptions, LER beam-gas will
be still a dominant background source in 2020

Simply increasing beam currents willlead to intolerable BG, even withvacuum scrubbing- New LER collimator(s)- Optics adjustments- Intensive vacuum scrubbing

13

Possible Background Mitigation• Possible options for reducing LER beam-gas– reduce dynamic pressure(dP/dI)– adjust IP beam steering → it might also improve luminosity– modify optics to match existing collimator phases better– add LER vertical collimator(s) → Add D06V1 in 2019 winter shutdown. Add D03V1 next.

• Recommendation: pursue all four options• Dynamic pressure reduction via– Intensive vacuum scrubbing period with detuned beams, Belle II off– Beam pipe heating– Additional / improved pumping (need beam pipe modification)

14

Summary• Status– Horizontal collimators are added after Phase2, and they suppress Touschek bkg– LER beam gas bkg now dominates (>= 70% of total background)– CDC and TOP limit max beam currents– Injection bkg bursts are a persistent problem, causing CDC HV trips– QCS and (we think) beam-dust related background bursts endanger detectors• Recommendations– LER beam gas reduction: beam steering study, optics modification, new vertical collimators,
intense LER vacuum scrubbing– Improve HER simulation for improved long-term bkg prognosis– Check beam-gas normalization with gas injection study– Improve injection further, especially for HER– Improved / faster / redundant abort system (See Ikeda-san’s talk later)

15

backup16

High Level Status
Generally speaking, we want to measure, fully understand,and mitigate the following beam background components to
Background Component
Simulation Method
safe levels
Measured in early phase3.
Touschek

Too high for going higher currents.
Large data/mc discrepancy

Beam-gas Bremsstrahlung

SAD (accelerator tracking code)
generates and tracks scattered particles.
If lost near IP: passed to GEANT4.

Radiative Bhabha

BBBrem/BHWide → GEANT4

QED 2-photon

Aafh → GEANT4

Synchrotron Radiation

SR generation in GEANT4

Expected to dominate at higher Luminosity
Marginal observation in early phase3
Lowest simulation uncertainty.
measured in early phase3. ~OK

Injection BG

Injection particles provided byaccelerator group→ SAD →GEANT4

Beam dust-

Neutrons

All of above

Beam-gas Coulomb

measured in early phase3
LER injection BG is very clean
mitigation is purely experimental(injection tuning is not simulation based)17

Backgrounds: The road ahead
Still would like to
Additional studies already requested by Nakayama• check if collimator effectiveness canbe improved• confirm simulated origin points ofthe dominant LER beam-gas storage
background, and measure uncertain
normalization factor Z2
Phase3 r1976• optimize beam steering near IP, to (Lumi run)
reduce apparent new scraping
backgrounds•

1. Vacuum bump study (1shift), LER only , Belle2 HV=STANDBY(6/13 owl shift
2. IR orbit adjustment (~0.5 shift), Collision Beams, Belle2 HV=PEAK
3. LER D06V2 vertical phase adjustment(~1.0 shift), LER only,
Belle2 HV=STANDBY

4a. Quick LER beam-size scan study (~0.5 shift) after all adjustments,
LER only, Belle2 HV=PEAK,(4b. Quick HER beam-size scan study (~0.5 shift) after all
adjustments, HER only, Belle2 HV=PEAK)(5. N2 gas injection on LER D03 region?)

Then, decide on best strategy: increase beam currents or change optics?
18

My *PERSONAL* understandings/guesson the current BG situation•••

LER beam-gas scattered particles are lost vertically inside QC1RP, at z=+1.1m. Simulation can reliably predict it.
Showers generated at z+1m develops toward –z direction and reaches to QCS bellows at z=0.6m. If the showers are still localized in +y or –y direction at
z=0.6m (should be confirmed by Geant4 simulation), it can explain observed V0 vertex distribution
There are no shielding around z=0.6m, so the secondary particles generated at the material in that region (bellows flanges etc.) can be directly seen byouter detectors (CDC,TOP,…) and therefore becomes dominant BG source•

We observe D02V1BTM is more effective to suppress BG rates than D02V1TOP. Since LER D02V1 and QC1RP have opposite nu_y, D02V1BTM can
suppress +y loss at QC1RP. This supports the hypothesis the hot spots on bellows are originated from loss in QC1RP.

•

Data/MC ratio should be revisited after using section-by-section pressure values in MC. Z_eff difference should also be taken into accounty[cm]

QCS FW bellows
QC1RP

QC1RP
Showerescapesfrom QCS

19

e+ lossy[cm]Effect of new collimators• Simulation: IR loss rates in MHz

Paladino

Phase 2Phase 3
LER: 5/14
HER: 5/12

ChangeLER beam-gas

188

45

75% ⬇

Coulomb
Brehms

186
2

44
1

LER Touschek

160

37.6

• Measurement: SVD occupancy in % Tanigawa

*)

75% ⬇

Assume 1nTorr for entire ring

• Compared to Phase 2, LER Touschek reduced by factor 2-3 with new horizontal collimators.
• LER vertical collimators also reduce LER Coulomb beam gas component effectively*) Measure increase is due to the increased pressure around D02 section

20

KLM: LER neutron cavern backgrounds• But, now see neutron bkg in theouter, forward KLM endcap• Extra shielding may be required– Inside polyethylene square– Is current square thick enough?

concrete

Piilonen

Cosmics

Poly-shield• KLM generally robust against bkg

NoshieldPiilonen21

Neutron source? Touschek!?
Schueler
Data points are averaged over 300s

𝑁𝑏 = 395

𝑁𝑏 = 789
𝑁𝑏 = 1576

Knob 0Touschek

Recoil RateHz
𝐼𝑃𝑍𝑒2mA⋅Pa⋅e2• TPC fast neutron detectors
now mounted inaccelerator tunnel• Suggest KLM endcap
neutrons originate from
Touschek background(surprise!)• Generated at upstream
collimators? More workneeded to investigate.

Beam-gas𝐼
mA
𝑃𝜎𝑦 𝑁𝑏 𝑍𝑒2 Pa⋅𝜇m⋅e2
22

Beam BG extrapolation
toward 2020 summer
H. Nakayama (KEK)2019 June BPAC
23

Latest roadmap toward 2020
Updated by SKB group at the 33rd B2GM last week.

In this slide, we assume
2019 winter: 0.84/0.77A, beta_y*=2.0mm, L=1.0*10^342020 summer: 1.20/1.10A, beta_y*=1.5mm, L=2.0*10^34
24

Extrapolation methods
The smaller beta_y* optics files are notprepared by SuperKEKB optics group yet.

• Method 1:– Run beam-loss simulation using future optics files– Apply the latest data/MC ratio on simulated loss rates
Analysis of May 2019 BG study is ongoing• Method 2:– Calculate extrapolation factor using machine parameters(*)– Apply the factor on the latest BG measurement
What I can show today is based on method 2.

25

Extrapolation based on machine parameters• Touschek BG:– Proportional to I^2– Assume the same collimator reduction factor• LER horizontal collimators should be narrowed (bx*: 200mm to 100mm)• Re-optimization seems possible• Beam-gas Coulomb BG:– Proportional to P * I * / by*. (Note that P=P0+dP/dI *I, almost proportional to I)• Vacuum scrubbing can reduce IR loss
• Assume factor 2/3 for 2019 winter and factor 1/2 for 2020 summer (my personal guess!)• Installing a new collimator makes the vacuum worse– Assume the same collimator reduction factor(*)• We need to further close LER vertical collimators as by* goes 3.0→2.0→1.5mm• LER vertical collimators are already very tight. Can we really close them further without beam instability or injection
loss monitor abort?? This assumption might be optimistic.

26

BG extrapolation toward 2020 summer
In this slide, we assume
2019 winter: 0.84/0.77A, beta_y*=2.0mm, L=1.0*10^342020 summer: 1.20/1.10A, beta_y*=1.5mm, L=2.0*10^34

LER Touschek

2019 winter2020 summer

x2(0.84A)

x4(1.2A)

Collimator reduction factor

x1

x1

Total

x2

x4

Beam current (I^2)

LER Beam-gas

2019 winter2020 summer

x2(0.84A)

x4(1.2A)

1/beta_y*

x1.5

x2

Vacuum scrubbing (dP/dI)

x2/3

x1/2

Collimator reduction factor

x1*

x1*

Total

x2

x4

Beam current(I^2)•

HER Touschek, HER Beam-gas are assumed to bemuch smaller than LER also in 2020.

•

Lumi-BG is not yet measured in Phase3. We
expect x2(x4) lumi-BG in 2019(2020) than now,which we assume to be smaller than LER BG.

•

Based on these assumptions, LER beam-gas will
be still a dominant background source in 2020

Simply increasing beam currents will leadto intolerable BG, even with vacuum
scrubbing- New LER collimator(s)- Optics adjustments

27

Mitigation ideas?
• IR orbit adjustment– 10~15% reduction seen during vertical orbit scan (June 20th)• Add more LER vertical collimator(s)– It could reduce LER beam-gas BG.
– The location of the new collimator is being discussed (D06V1/D03V1/D03V2)• Intensive vacuum scrubbing at LER D02 section– Still worse vacuum (breached by collimator work before 2019 spring run)
– Reinforcement on pumping? (need beam pipe remodeling work)• LER D06V2 vertical phase adjustment– Change wiggler section phase advance to adjust D06V2 phase– A big work, study is postponed to winter run or later• LER D02V1 vertical phase improves as beta_y* squeezed– Not a big effect at beta_y* = 2mm or 1.5mm

IR orbit adjustment

29

Phase3 r1976 (Lumi run)Vertical loss(+y) around z=+60cm
contributes outer detector BG(no shielding material around here)BG reduction by IR orbit vertical scanJune 20th (TODAY)

Vertical orbit angle shift

LER upstream orbit is moved downward by
0.4~0.5mm around QC1
TOP/CDC/ECL rates decreased by 10~15%
QCS_FWD diamonds rate decreased by
40%
PXD/SVD occupancies did not change
significantly

2019/7/5

33rd B2GM

31

Vo vertex x-y view at z=+60cm
before/after vertical IR orbit scan
Run 2747

Dy=0

Run 2750

1hour
10~15% BG reduction in
TOP/CDC!!

Dy=-0.4mm

0.5hourNEW LER collimators33

(2.0/1.5mm optics)

D6V1

Add LER V collimator for 2020

D2V1
D3V1
D6V2
D3V2

• D06V1– Pro: Good phase, can effectively reduce IR loss and reduce burden on D02V1– Pro: Large beta_y (easier handling)
Vacuum bump study on June 13th suggests
beam-gas scattering at D01/D12-D07 can– Con: far from IP (no impact on particles scattered in D06-D03)
contribute to IR loss

• D03V1

Con: impedance budget issue at design optics and full current– Pro: near from IP– Con: unmatched phase, but might have some impact on particles scattered in D06-D03• D03V2– Pro: completely unmatched phase, might be effective to protect IR from crazy beam
– Pro?: near from IP, but it does not help because of ↓– Con: completely unmatched phase, expect no impact on particles scattered in D06-D03
I propose to install D06V1 in 2019 winter shutdown.
For the next opportunity, I propose to install D03V1.

Simulated scattered positions of IR loss
LER beam-gas Coulomb

June 1st, 500mA
D02_LER 13.9E-08
D03_LER 4.3E-08
D04_LER 7.7E-08
D05_LER 4.1E-08
D06_LER 4.9E-08
D07_LER 8.7E-08
D08_LER 9.1E-06
D09_LER 2.4E-08
D10_LER 5.7E-08
D11_LER 4.4E-08
D12_LER 1.7E-08
D01_LER 7.7E-08

IPe+
D06V1 D06V2

e+
D03V1

D02V1

May 14th setting
D06V2=3.1mm
D02V1=2.1mm

1nTorr uniform pressure
assumed(should be scaled usingpressures at eachsection )Single-turnloss only

Suppressed only
by vacuum
scrubbing

Partially suppressed byadding D03V1

D07

D06

D05

D04

D03

D02

D01 D12Can be suppressed byadding D06V1

D11

Scattering at D02 is dominant source of IR loss.

D10

D09

D08

Summary• Simple extrapolation using machine parameters shows:– x2 BG rates at 0.84/0.77A, beta_y*=2mm (2019 winter)– x4 BG rates in 1.20/1.10A, beta_y*=1.5mm (2020 summer)– Preparing detailed extrapolation using latest data/MC ratio• Further BG reduction is necessary to achieve higher currents
planned for 2020.
• New LER V collimator(s), intensive LER vacuum scrubbing, andoptics adjustments are important.
36

Additional LER V collimator for 2020
Candidate location: D06V1, D03V1, D03V2
Vertical betatron phaseat beta_y*=2mm (0.27mm)

beta_yDistance from IP

D06V1+0.04 (+0.10)61m

Far(-1146m)

D03V1+0.12 (+0.17)17m

Near(-301m)

D03V2+0.28 (+0.34)17m

Near(-225m)

Comment

Closer phase with QC1R? →D06V1 preferred.
Diversity in phase to stop crazy
beam? → D03V1/V2

D06V1 can be used with wider
width, but we face impedance
budget issue with large beta_y atfull current.

Beam-gas scattering at nearsection can only be stopped bynear collimators (single-turnloss).

D06V2: +0.18 (+0.24)
D02V1: +0.06 (+0.01)

D06V2:
19m
D02V1: 20m (110m)

beta_y*=2mm
D6V1

D06V2: -1026m
D02V1: -82m

D2V1
D3V1
D6V2
D3V2

Phase adjustment for D06
collimators is really possible?

Possibility to move D06V2
to other place?

LER vertical collimators at different beta_y*
beta_y*=2mm

beta_y*=3mm

Dnu
beta_ynu_y61.43 28.90 +0.04
19.24 30.53 +0.17
16.96 41.47 +0.11
16.96 42.63 +0.27
21.57 44.93 +0.07
260.7 46.36 +0

Phase2.1.7
PMD06V1
PMD06V2
PMD03V1
PMD03V2
PMD02V1QC1RP995

Phase2.1.7
PMD06V1
PMD06V2
PMD03V1
PMD03V2
PMD02V1QC1RP995

d[mm]
6.6
3.7
3.4
3.4
3.9
13.5

Dnu
beta_ynu_y61.43 28.90 +0.04
19.24 30.54 +0.18
16.96 41.47 +0.12
16.96 42.63 +0.28
20.81 44.91 +0.06
391.1 46.35 +0

d[mm]
5.4
3.0
2.8
2.8
3.1
13.5

D6V1
D6V1
D2V1

D2V1
D3V1

D6V2

D3V2

…

D3V1

beta_y*=0.27mm (design)

Phase3
PMD06V1
PMD06V2
PMD03V1
PMD03V2
PMD02V1QC1RP995

beta_ynu_y Dnu
61.43 28.92 +0.10
19.24 30.56 +0.24
16.96 41.49 +0.17
16.96 42.66 +0.34
111.75 44.83 +0.01
2794.00 46.32 +0

D6V2

d[mm]
D3V2

2.0
1.1
1.1
1.1
2.7
13.5

D2V1
D6V1

D3V1
D3V2
D6V2

38

Beam abort

39

VXD abort diamond setup for Phase 3

28 diamonds installed for phase3
8: beam pipe (BP)12: SVD cones (SVD)
8: QCS bellows (QCS)
Added in Phase3

QCS bellows diamonds show good correlation with outerdetector background rates. Very useful tomonitoring/tuning of beam BG !!
“The more eyes, the better”

40

VXD abort diamonds~lessons from recent QCS quench accidents~• Two severe QCS quenches in Phase 3– QCS quench on May 28th: caused by QCS power supply failure– QCS quench on June 9th : probably caused by “beam-dust” event– Serious damage on Belle2 sensors and collimator head

A tiny dust in the beam pipe
vacuum falls onto the beamand get trapped• Protection by VXD diamond– At May 28th event, diamonds were saturated and didn’t issue the beam abort.
• accelerator loss monitors issued the abort earlier than diamonds– Diamond gain/threshold were adjusted on June 6th– At June 9th event, diamonds issued the beam abort !
• earliest abort among all abort sensors in the ring

• however.. (see next page)41

L. Vitale

x40!

Can we minimize this delay?

Severe damage on
inner detectors

42

Beam abort delays
H. Ikeda

Detector response time
Diamond needs 0~10us from thestart of beam loss to detection(100kHz reading)Distance to KEKB control:
10ms for D1/D2(near IP)
2ms for D7/D8

Wait for the abort gap: 0~10us+ delay in kicker module: 4/3us+ etc..

Need 1 turn (10us)
to kick out all bunches

43

Ideas for minimizing the abort delay
Shorter detector response time
– Lower threshold on loss monitor PINs (need to veto injection spikes)– Faster VXD diamond sampling rate (for example, 200kHz sampling) → 0~5us faster

SKB side
Belle2 side

Shorter distance to KEKB control– Beam loss detection by a monitor near KEKB control, not IP → 0~8us faster

Shorter waiting time for abort gap– Increase abort gap from 1 to 2 → 0~5us faster (~1year to update the system)

All possibilities are under active
discussion in MDI group44

Recent BG studies

45

th
LER single-beam study on June 9 , 2019

H. Nakayama(KEK)SKB:VALCLM:D06H1OUT:CSS:SET_POS1 11.5
SKB:VALCLM:D06H1IN:CSS:SET_POS1 -11.5
SKB:VALCLM:D06H3OUT:CSS:SET_POS1 13
SKB:VALCLM:D06H3IN:CSS:SET_POS1 -13
SKB:VALCLM:D03H1OUT:CSS:SET_POS1 12
SKB:VALCLM:D03H1IN:CSS:SET_POS1 -12
SKB:VALCLM:D02H1OUT:CSS:SET_POS1 9
SKB:VALCLM:D02H1IN:CSS:SET_POS1 -9
SKB:VALCLM:D02H2OUT:CSS:SET_POS1 11
SKB:VALCLM:D02H2IN:CSS:SET_POS1 -11
SKB:VALCLM:D02H3OUT:CSS:SET_POS1 23
SKB:VALCLM:D02H3IN:CSS:SET_POS1 -23
SKB:VALCLM:D02H4OUT:CSS:SET_POS1 10.5
SKB:VALCLM:D02H4IN:CSS:SET_POS1 -10.5
SKB:VALCLM:D06V2TOP:CSS:SET_POS1 2.6
SKB:VALCLM:D06V2BTM:CSS:SET_POS1 -2.3
SKB:VALCLM:D02V1TOP:CSS:SET_POS1 2.1
SKB:VALCLM:D02V1BTM:CSS:SET_POS1 -1.8

LER single-beam study on June 9th
Run type=beam, Trg type=gdl
run 2255 starting at 8:26, ECK=0, I=450mA->350mA
run 2257 starting at 8:43, ECK=+1, I=450mA->390mA
run 2258 starting at 8:53, ECK=+2, I=450mA->448mA (very short, stopped by PXD Error)

run 2255

run 2257

run 2258

Belle2 rates vs. beam size
LER single-beam study on June 9th, I=450mA

At 450mA and 100um(nominal beam size
during collision), LER Touschek is <10% in outerdetectors and QCS_FW diamonds, ~17% in PXD
and BP diamonds

LER Vacuum bump study
on June 13th
Hiro Nakayama (KEK)LER Vacuum bump study on June 13th

Pressures are shown in log scale!!

- NEG heating at all (tried) sections had impact on diamond rates as predicted by simulation→ installing D06V1 (far from IP) can still suppress loss from D07-D12, D01- D02, D06, D11 seems more sensitive than other sections- Diamonds on beam pipe, QCS_FW bellows, QCS_BW bellows showed proportional increase in most cases,
but the response was different for D02 bump (near IP).
- Beam pipe diamonds directly sees interaction with beam and gas in IP beam-pipe?

Simulated scattered positions of IR loss
LER beam-gas Coulomb

June 1st, 500mA
D02_LER 13.9E-08
D03_LER 4.3E-08
D04_LER 7.7E-08
D05_LER 4.1E-08
D06_LER 4.9E-08
D07_LER 8.7E-08
D08_LER 9.1E-06
D09_LER 2.4E-08
D10_LER 5.7E-08
D11_LER 4.4E-08
D12_LER 1.7E-08
D01_LER 7.7E-08

IPe+
D06V1 D06V2

e+
D03V1

D02V1

May 14th setting
D06V2=3.1mm
D02V1=2.1mm

1nTorr uniform pressure
assumed(should be scaled usingpressures at eachsection )Single-turnloss only

Suppressed only
by vacuum
scrubbing

Partially suppressed byadding D03V1

D07

D06

D05

D04

D03

D02

D01 D12Can be suppressed byadding D06V1

D11

Scattering at D02 is dominant source of IR loss.

D10

D09

D08

D02 RGA
D02L13-16
NEG heating

D02L18-24
NEG heating

D02L01-09
NEG heating

D02L25
NEG heating

No response
on D02RGA

No response on D02RGARGA is only
sensitive to very
narrow region

D06 RGANo response
on D06RGALER orbit scan study
on June 20th, 2019
Hiro Nakayama (KEK)LER orbit scan study on June 20th
dx=+0.3mm@QC1
Horizontal orbit position
Vertical orbit position

dy=-0.4mm@QC1
Lumi
Dia(BP)
Dia(FW)
TOP
CDC
SVD
PXD

Run 2747

Run 2750

dpy=-1.0mrad (move LER upstream orbit vertically downward)--> Diamond(QCS_FW) decreased by 30%, CDC/TOP decreased by ~15%, SVDL3/PXDL1 didn't change.
--> Luminosity becomes better (HER size smaller)--> V0 hotspot at z=60cm moved from +Y to -Y.
dpx=-0.3mrad (move LER upstream/downstream orbit closer to Belle2 solenoid axis)--> no significant change in Belle2/diamond rates, V0 hot spot, luminosity.

Run 2755

Phase3 MDI/BG topics

6. V0 vertex display ~ a powerful tool to show “hot spots” ~Loss at -y

Loss at +x, -x

Phase2Phase2 r3565(LER
r3565(LER only)
only)

Loss at +y

Hot spots on ridges?

Phase3 r1976 (Lumi run)
7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

COLZ range is chosen by handto enhance non-IP clusters

Loss at +x

LER “hotspot” is different from phase2 → IR
orbit adjustment might reduce IR loss? Studyplanned in this week.

Loss at -x

Loss at +y

Loss at +y29

Phase3 r1976 (Lumi run)

x-y view at z=+60cm
before/after vertical IR orbit scan
Run 2747

Dy=0

Run 2750

1hour

Dy=-0.4mm

0.5hourPhase3 Beast detectors

58

BEAST Detectors in Phase 3• Most of “BEAST” retired• A few dedicated BG detectors remain• Diamonds• CLAWS++ on QCS• PINs on QCS• He-3 in tunnel• TPCs in tunnel• BEAST online DAQ for BG monitoring via
EPICS will keep running• We will display rates + rate limits of all Belle II and BEAST detectors
in SuperKEKB control room (see BCG meeting talk by Jeff Schueler)• BCG Shifters will monitor BEAST, call experts if there is trouble

59Phase 3 TPC System

60

BWD SideFWD Side

= TPC
= He3
61