Beam Background,Machine Detector Interface
Hiroyuki Nakayama(KEK, Belle2)

Beam Backgrounds…
1. Limit the lifetime of SuperKEKB
2. Determine survival time of Belle II detectors
3. Can lead to instantaneous damage
4. Increase Belle II hit occupancy
5. Result in non-negligible analysis background• An underestimate of phase 3 beam backgrounds could have serious consequences.
• Our goal: use phases 1 and 2 to measure each individual background type, incl. scaling
with beam parameters.

Beam BG sources at SuperKEKB
BG sources

Simulation MethodTouschekBeam-gas Bremsstrahlung

Generate scattered particles withweights and SAD tracks them.
Particles lost in IR are passed toGEANT4 fullsim.

Synchrotron Radiation

SR generator in GEANT4

Radiative Bhabha(e+e-e+ e- g)

BBBrem/BHWide generator
GEANT4

QED 2-photon(e+e-e+e-e+e-)

aafh generator  GEANT4

Injection BG

Injected particles  SAD
trackingGEANT4

Beam-gas Coulomb

Single-beam BG

Luminosity BG

Beam BG distribution
15th campaign(for phase3)

Loss wattage= loss rate onbeam pipe
* energy ofloss particleTouschek_LER
downstream
loss

Rad. Bhabha loss at|z|>65cm are stopped byshield inside QCS

Lumi-dep. BG loss at|z|<65cm are dangerous for
TOP PMT rateGlobal views

RBB LER

RBB HER

Touschek HERRBB, 2photon,SRCoulomb HER

Touschek LER

Hiroyuki Nakayama (KEK)

Higgs Factory 2014, 10th Oct. 2014, Beijing

Tungsten shields (shown in red)
inside QCS cryostat

10mm t25mm t20~70mm t

QC2REe-

QC1RE
QC1RP

20mm t (obsolete)

QC2RPe+IP

1m

10mm t~30mm te+e--1m
Major beam loss position
by Touschek or Beam-gas

Hiroyuki Nakayama (KEK)

Thick tungsten shields can significantly stopbackgroundshowers originated from |s|>65cm.
20th ARC (Feb. 23-25, 2015)

IP6BG shields outside QCS
17°Iron
VXD docks

Thick tungsten layers inside cryostat
Heavy metal shields to protect VXDfrom showers generated in cryostat

ECL

Iron

CDC

Neutron shield inside ARICH structure
Polyethylene neutron shield for CDC
elec. board (planned)

VXD docks

ECL shield, included for
ECL/ARICH simulation(Lead + Polyethylene)

Hiroyuki Nakayama (KEK)

20th ARC (Feb. 23-25, 2015)

RVC structure in front of QCS stops
showers from RBB HER loss at z=60cm
7(6cm-thick SUS steel assumed)

Single-beam BG (1)Touschek, Beam-gas– Well suppressed by movable collimators– Horizontal collimators near IP• effective for Touschek & Beam-gas Bremsstrahlung– Narrow(~2mm) vertical collimator• effective for Beam-gas Coulomb• however, we can install only one such collimator per ring (*)– Need careful collimator adjustment during operation• Miss-operation might result in x100~x1000 beam loss in the detector– Less number of collimators installed in phase2• but the BG rate is acceptable (detuned optics)(*) H. Nakayama, et. al., ``Small-Beta Collimation at SuperKEKB to Stop Beam-Gas Scattered Particles
and to Avoid Transverse Mode Coupling Instability,'' Conf.Proc. C1205201 (2012) 1104

SuperKEKBCollimators• Collimators near IR isimportant• One narrow vert.
collimator per ring
• Phase2 IR collimators• 2 horizontal• 1 vertical• KEKB type: inner only
• SuperKEKB type: bothPhase3

Installed beforephase2

HER
D01: H1, H2, H3, H4, H5
V1

Phase3

LER
D02: H1, H2, H3, H4
V1
LER

D01

Exist since
KEKB

D02

D12x x D03: H1, H2(V1, V2)

D03

HER
D12: H1, H2, H3, H4
V1, V2, V3, V4

D11

D04

D10D05

Exist since
KEKB
D09

HER
D09: H1, H2, H3, H4
V1, V2, V3, V4

D06
D08

D07

Phase3

Installedbefore
Phase1Single-beam BG (2)Synchrotron Radiation– SR fans from QCS magnets might reach VXD detectors• Simulated level is acceptable both in phase2/phase3• Beam pipe misalignment effect is also considered

Injection BG– Belle II trigger veto while injection BG is busy
• To avoid PXD high occupancy• Veto window time structure determined by injection BG– Important measurement in Phase2 (with damping ring)
Veto window

window shapedetermined bymeasurement

15th campaign

Simulated sub-Detector BG levels
CDC wire rate

PXD occupancy

ARICH neutrons

ECL crystal dose

SVD occupancy

MHz/PMTTOP PMT rate

See more details in Background parallel session
https://kds.kek.jp/indico/event/23336/session/27/?slotId=0#20170208

11

Summary for 15th campaignlisting SF<5 only
SF=Safety Factor
15th campaign resultcriteria

SFPXD occupancy

2photon:0.9% , SR:~0.2% (10th)< 3%3

CDC wire hit rate

400kHz at layer#8<200kHz

1.3

2.5

<1

1.3

250 Gy/yr<100 Gy/yr

1TOP PMT rate

5-8 MHz/PMT<1 MHz/PMT

0.3

TOP PCB n-flux*

0.35

<0.53

ARICH HAPD n-flux*

0.3

<13

ECL crystal dose

6 Gy/yr in BWD<10 Gy/yr2

ECL diode n-flux*?

<14ECL pile-up noise?

0.8 at Belle-I?

CDC Elec.Borad n-flux* (averg.)
CDC Elec.Board dose*neutron flux in unit of1011 neutrons/cm2/yr,NIEL-damage weighted
B2GM(Feb. 2017)

Beam BG まとめ• TOP PMTの半数は、 Phase3のfull-lumi数年で交換が必要– QCS と VXD の隙間からのロスが要因で、これ以上の低減は困難• その他の検出器はほぼOK (ただしmarginは少ない)• Phase2ではコリメータの数が少ないが、大丈夫• 入射BGは見積もりに含まれていないので注意– Phase2 での実測(damping ringあり)が重要• Phase2でもBG machine studyを予定– Beam-size scan, vacuum bump, collimator study– Luminosity scan
– Injection study (with damping ring)MDI communication

Topics covered- Beam Abort- Operational flags for injection control- Injection timing signal- EPICS communication
14

1. Beam abort• Beam abort should be sent via hard-wired connection• “Fast abort” sources– VXD diamond sensors– Can abort LER and HER separately• “Slow abort” sources– Solenoid quench, EH power outage– Other environmental sensors• Beam pipe temperature error, cooling system error, etc..

– Collected by ‘Uehara’ logger and give a combined abort signal– Always abort both rings Accelerator abort timing signal send back to VXD abort module– for offline abort diagnosis
1516H. Nakayamaver. 2017.6.30

Beam Abort Diagram
Abort Request
F4/F5“Fast”
abort
sourceTTL

VXD abort

TTL

opticalLER abortmoduleE/O
4lines

A8-10, E8-10“Slow”
abortsources

SKB D2 section

E-Hut

relay

Uehara system
Logger/PLC(response:~10ms)

HER abortmoduleE/O
Solenoid Quench (relay)
Solenoid Quench (relay)

E1-7

TOP
HVC
EH
power
outageAbort from otherenvironmentalmonitors
Bellesolenoid
quenchAbort Timing(for abort diagnosis)

Belle2 modules
SKB modules

ARICH HVC

Also KLM HVC?

E-Hut B2
E-Hut F4/F5

VXD abort
to freeze the ring buffer

NIM

HER/LER

Abort timing
Tobiyama-room

NIM

Discr.

Analog DCCT17BACKUP PLAN

2. Injection control- Operation flags • Accelerator status

COLLISION– COLLISION• Yes= continuous injection, No= normal injection• Collimator mode depends on this flag

PHYSICS_READY– PHYSICS_READY(can be 1 only when COLLISION is 1)• Accelerator promises not to go back to normal injection mode without
detector permission• Detector status– NORMAL_INJECTION_ENABLE• Allow normal(initial/accumulating) injection (and wild machine tuning)• TRUE when HV is STANDBY (no control from BG level assumed)– (Continuous) INJECTION_ENABLE• Allow continuous (trickle/top-up) injection• TRUE when (HV=PEAK or STANDBY)&&(no local run)&&(safe BG level)18

Y. Ohnishi(SKB)

A

B C

D

E F G

H I19

These EPICS records
should be readablefrom KEKB EPICS via CA
gatewayInjection control diagram

KEKB control room

E-hut
Continuous injection
Corresponding
NSM status

HVC= PEAKor STANDBY

Corresponding
NSM status

Not taking
local run

Normal (initial)
injection
Corresponding
NSM record

NSM/EPICS gateway

NSM status

EPICS record

TT-IO(4 NIM IN , 4 NIM OUT)

B7 rack

opticalNIM

VXD BG level issafe (diamonds)

SKB
FPGAboard

SKB
FPGAboard

Konno

opticalNIM

HVC=
STANDBY(E-hut)

opticalNIM

Physics ready
Corresponding
NSM status

Physics
ready

H. Nakayamaver. 2017.1.30(KEKB
Controlroom)

Set
B2_INJ:INJECTION:ENABLE

Set
B2_INJ:NORMAL:ENABLE

Receive
CG_OPR:PHYSICS_READY

Nakayama
Hardwarelevel signal lines

Optical lines

Softwareconnections

Belle2 modules
SKB modules

20

3.Injection timing signal• SKB beam injection timing is delivered as “Event Data”– serial link, Xilinx Rocket IO, 20bit info (timing info + α), 50Hz
– “in-advance” signal (well before injected bunch arrival)• Belle2 GDL receives “Event Data” on ut3 board– Then TTD delivers “injection veto” to sub-detectors (PXD, etc..)– PXD goes insensitive after each injection to avoid BG saturation
window shapedetermined bymeasurement

Veto window• Receiving test by ut3 ongoing (Y. Iwasaki)
PXD
SKBinjector

GDL(ut3)

TTD

CLAWS21

4. EPICS communication• Belle2-SKB communication is based on EPICS– Except several important hard-wired connection• SKBBelle2– Machine parameters, vacuum levels, injection parameters, …
– Most of them already prepared in phase1• Belle2SKB– Luminosity, vertex position, bunch luminosity, etc.. (for machine tuning)– Injection BG timing structure (for injection tuning)• See next slide– BG rates measured by sub-detectors/BG sensors (for collimator tuning)• z/phi/theta distribution of BG hits give insight on which BG we see, and which collimator
we should squeeze

22LIVE display of injection BG in phase1•••

2017/9/8

BEAST phase1 CsI crystal/CLAWS
Waveforms sent by EPICS,
updates every few seconds
Provide BG time structure for3ms after injection•This display helps SKB operator
to improve injection efficiency(periodical spikes implies badinjection phase, etc..)•We need similar displays atphase2/323

MDI まとめ• Hard-wiredのアボート信号：配線済み

佐々木氏・小林氏– アボートタイミング信号も配線済み• Hard-wiredの入射コントロール信号：配線済み• 入射タイミング信号(Event system)– Belle2 TRG/DAQグループが受信テスト中• それ以外の情報はEPICSで共有backup

Y. Ohnishi (July 11th, 2017)

Y. Ohnishi (July 11th, 2017)

Y. Ohnishi (July 11th, 2017)

Y. Ohnishi (July 11th, 2017)

Typical Run Cycle Scenario
Case study for Beam abort during Belle HV standby

A.

B.
C.
D.
E.
F.
G.
H.
I.

Enough current accumulated. KCG issues “COLLISION=1” and switches to continuous
injection. BCG switch collimators to “COLLISION” mode. KCG starts machine tuning. Since“Normal Injection Enable” flag from Belle2 is still 1, KCG can go back to COLLISION=0 ifneeded.
KCG finishes machine tuning and issues “PHYSICS_READY=1”.
Belle2 receives “PHYSICS_READY=1” and Belle2 HV starts ramp up. Any injection inhibited.
Belle2 HV reaches peak. Belle2 issues “Injection Enable=1” and continuous injection is now
allowed.
KCG issues “PHYSICS_READY=0” because machine tuning needed (beams get instable, etc.).
Note that normal injection will not start until Belle2 allow to do so (by issuing normalinjection enable)
Belle2 HV starts to ramp down.
Belle2 HV becomes standby. Belle2 issues ”NORMAL_INJECTION_ENABLE=1”. Continuous
injection resume. Now KCG can start machine tuning. (If needed, KCG switch to normal
injection and BCG switch collimators to “Injection” mode)
Beam aborted during machine tuning. Note that abort is issued during Belle HV standby, inthis case. KCG issues “COLLISION=0”. BCG switch collimators to “Injection” mode. If abort
was issued by high BG level, continuous injection is not allowed until BG get smaller.
BG becomes safe and continuous injection is enabled. Normal injection can start now.
30SuperKEKB EPICS records
we need for BEAST studies••

Accelerator status
LER/HER optics version (emittance, tune, chromaticity, steering magnet values,etc..)••

Beam currents, bunch numbers, bunch currents, beam lifetime, beam sizes,
emittance-control bump size (for Touschek study)
Vacuum pressure, partial pressure of CO, H2,.. using Q-mass (for Beam-gas
study)
Beam position/beam size/phase at each collimators, width of each collimator,
BLM(Beam Loss Monitor) info at each collimator (for Collimator study)
Injection mode, injected beam, injection rates, injection efficiency, injectedbunch number? (for Injection study)
Beam separation, etc.. (for lumi-BGstudy)•Any others?

•••

Mainly needed for background machine study, collimator study
Red: not used in KEKB . For other request items, corresponding parameter in theKEKB list (in following slide) are underlined

31

Sven Vahsen(Hawaii)

Sven Vahsen(Hawaii)3. LER collimator vs. BEAST BG
Inj. BG

Inj. BG

D06H3OUTNo inj. BG

No inj. BG

CsI BG
I_LER

Start loosing life at 16mm, aspredicted by simulation

As we change D06H3OUT width from 24mm to 17mm,BEAST CsI BG shows step-like decrease at every time collimator get narrower.

This is the clear evidence of BG suppression by the collimator!
We also observe thatinjection BG is completely stopped by the same collimator!
(at <=20mm)
2017/9/8

B-steering committe34

Carlos Marinas (Bonn)