Beam-induced Background

Hiroyuki NAKAYAMA (KEK)
ARC(Mar. 3rd, 2014)

Topics reported last year
• Beam loss simulation:– Touschek/Beam-gas: SAD-based (Ohnishi, Funakoshi)– Radiatibe Bhabha: BBBREM generator– 2-photon: “BDK” generator– SR: Geant4 SR physics model• Full-detector simulation (5th campaign)– PXD occupancy 2~3%: close to limit– TOP PMT lifetime: new PMTs are OK, still ~x2 reductionneeded for old PMTs (lifetime: ~1C/cm2)• Injection BG study
ARC (Mar. 3, 2014)

What’s new in this review• RBB cross section update– Less cross section due to “beam size effect”• Full detector simulation (8th campaign)– Detector performance, radiation dose, neutron flux withthe updated loss distribution– New shielding ideas (near ARICH/ECL)– Forward QCS design• Monitor DAQ diagram– Beam abort, collimator control

ARC (Mar. 3, 2014)

BG loss distribution

Ver. 2013.6.12(6th campaign)
Loss wattage= loss rate
* energy of loss particle

For 7th/8thcampaign
we scale RBBcomponents
By x0.8HER(e-)

LER(e+)

1GeV ,1GHz= 0.16W
LER (4GeV e+)HER (7GeV e-)Rad. Bhabha

0.63 W (eff. 0.98GHz) 0.88W (eff. 0.78GHz)

Touschek

0.07 W (0.11GHz)

0.02 W (0.02 GHz)

Coulomb

0.07 W (0.10GHz)

0.001W (0.001GHz)

ARC (Mar. 3, 2014)

Rad. Bhabha cross section:“beam size effect”

ARC (Mar. 3, 2014)

Rad.Bhabha: beam size effect
BBBREM paper: R. Kleiss, H. Burkhardt arXiv:hep-ph/9401333• Theoretically calculated RBB cross section is larger
than measured cross section at machine.
• This is explained by assuming only “impactparameter < beam size” range contributes to themeasured cross section, while the theoretical
calculation assume infinite impact parameter range.
• This effect was not included in default BBBREM
which is used for 6th campaign

ARC (Mar. 3, 2014)

d(beam size)

Impactparameter

BBBREM cross sectionmb
LER sigma_y*: 48nm
HER sigma_y*:63nm

Min frac

1e-6

1%2%5%

no cut1077 mb

266 mb215 mb

153 mbhard cut

521 mb

161 mb131 mb96 mbsoft cut

501 mb

152 mb

125 mb

92 mb

ARC (Mar. 3, 2014)no cuthard cut (LER)
hard cut (HER)
soft cut (LER)

Minimum
photon energy
Fraction

RBB HER loss distribution
Tracking by SAD-- no cut-- hard cut
edecreased, as expectede-mIP
ARC (Mar. 3, 2014)

Full-detector simulation

ARC (Mar. 3, 2014)

New shielding ideas 17°
Iron
VXD docks

Heavy metal shields to protect VXDfrom showers generated in cryostat

150°
ECL
Iron

CDC

Neutron shield inside ARICH structure(ARICH: 8ring 7 ring)
Neutron shield for CDC elec. board.
(B4C/Polyethylene)

VXD docks

Neutron/shower shield
to mitigate ARICH/ECL BG rate.
(Lead + Polyethylene)
RVC structure in front of QCS stops
showers from RBB HER loss at z=60cm
ARC (Mar. 3, 2014)

Forward QCS cryostat design
6th campaign

Red: Tungsten

New(type-1)

New (type2)

Do we really need thispart to be Tungsten?

Type-1 is preferred frombackground viewpoint
RC (Mar.detector3, 2014)

Full-detector simulation summary• Full simulation(8th campaign)– PXD occupancy: 2-photon:0.8%, SR~0.1%– TOP: old PMTs killed in few years w/ full lumi.
– CDC/ARICH neutron rate: suppressed by shields• We prefer type2 (more tungsten)– slightly less BG in most of sub-dets– slight increase in CDC rate, but it can be handled anyway
See each sub-detector report at this B2GM
http://kds.kek.jp/conferenceTimeTable.py?confId=14531#20140206

ARC (Mar. 3, 2014)

TOP

Tara Natut (7th campaign)

TOP PMT rates

New PMTs(7C/cm2), half gain, 80/ab

2MHz/PMT, 50/ab
4C/cm2 (full-gain)
2C/cm2 (half-gain)
We assume
10 years x full lumi.

2MHz/PMT, 80/ab
6.4C/cm2 (full-gain)
3.2C/cm2 (half-gain)

Old PMTs(1C/cm2), half gain, 80/ab

Measured photocathode lifetime-New PMTs: 7C/cm2-Old PMTs : 1.5C/cm2 (best)
1C/cm2 (ave.)

New PMTs with half-gain survives 80/ab (with x2 margin)
Old PMTs with half-gain can only survive 3years x full-lumi.
ARC (Mar. 3, 2014)

Beam loss position which
create TOP PMT hits

HER RBB loss at z=60cm is dominantsource of TOP PMT background. Quick
study shows material for Remote
Vacuum Connection (RVC) gives ~20%
TOP BG reduction, assuming RVC isequivalent to 60mm thick iron.

ARC (Mar. 3, 2014)

R~12cmRecent news on RBB• We used a wrong lattice file for beam loss
simulation for RBB_LER– Dipole component of solenoid field was artificiallyswitched off in that lattice file

• Beam loss at z=-50cm was underestimated,
where shield thickness is limited• Impact on TOP PMT BG is now under detailed
investigation (increase x2?)

ARC (Mar. 3, 2014)

IP beam pipee-e+TiBeTi

10um Au plating on inner surface of Be/Ti pipe
ARC (Mar. 3, 2014)

Latest SR simulation

LER (per bunch crossing)

Occupancy

Y. Soloviev(DESY)

HER (per bunch crossing)

Occupancy
ARC (Mar. 3, 2014)

Also need to study halo/misalignment effectSummary for 8th campaign* Not including halo ,mis-alignment effect

SF=Safety Factor

8th campaign resultlimitSF

PXD occupancy

2photon:0.8% (from 7th), SR:~0.1%*< 3%<3CDC wire hit rate

~100kHz<200kHz2

CDC Elec.Borad n-flux*

0.8

<11

CDC Elec.Board dose

~20Gy/yr<100 Gy/yr

5TOP PMT rate

2MHz/PMT<1 MHz/PMT

0.5

TOP PCB n-flux*

0.5

<12

ARICH HAPD n-flux*

0.65

<11

ECL crystal dose

13Gy/yr<10 Gy/yr

1ECL diode n-flux*

1.2

<11

ECL pile-up noise

5/1MeV

0.8/0.2MeV at
Belle-I?

KLMs are not included
showing SF<5 only
(SVD is not shown ‘cause it’s very save)

With “combined”
shield inside ECL

ARC (Mar. 3, 2014)*neutron flux in unit of1011 neutrons/cm2/yr,
NIEL-damage weighted

Belle2-SuperKEKB DAQ interface
Beam abort,
Collimator control, etc..

ARC (Mar. 3, 2014)

Monitor DAQ diagram

Proposed byNakayama

KLM
Via Input Output Controller(IOC) on B3 control roomat ~1HzECL
Belle2
NSM

PID

KEKB
EPICS

CDC
Softwareabort

VXD(EPICS)“interlockbox”

BP-BGmonhardware logic
insideLonger cableto tunnel
DCCT
Or digital path?

Hard-wired
abort cable

Abortloggers
Record info. just before
abort (for 100ms) with
0.2/1Mz

Abortkicker

Collimator
control

KEKB control roommonitors for BCG

Collimator control systems• Careful operation is important at SuperKEKB/Belle-II– Keep IR loss <1GHz, while total collimator loss >600GHz– Miss-operation of collimator(espc. vertical ones) easily resultsin x10 or even x100 detector background level– Aim to develop semi-automatic control algorithm• Input information:– beam lifetime, loss rates at collimators, sub-detector BG levels,
injection efficiency, and IR loss distributions, etc..

• IR loss rate distribution gives insight on which BG source andtherefore which collimator we should adjust• IR loss monitor R&D has started

BPAC (Sep. 10, 2013)

SuperKEKB collimators

e-e+~20 Horizontal collimators
2 Vertical collimators
Each collimator can be asymmetric
Optimization of ~50 parameters

BPAC (Sep. 10, 2013)

IR loss monitors around cryostat- For example, loss at z=+1.2m is strongly correlated with Touschek/Coulomb- 6 or 8 sensors in phi direction at each z positions- Type of sensor is under discussion- PIN diodes? Diamonds? Thin plastic scintillators to issue veto? Neutron sensors?
- Should be prepared before summer ‘14 and tested at BEAST phase-1- Collaboration with BEAST group !!
23Summary• Detector simulations are updated every 4 month• New shielding ideas confirmed to be effective, nowstart realistic design• TOP PMT lifetime is still the biggest concern• Propose to develop semi-automatic collimatorcontrol– Vertical collimator is very sensitive to IR background level– Detector BG information should be provided to thecollimator control algorithm
ARC (Mar. 3, 2014)

Backup

ARC (Mar. 3, 2014)

Background pictureVer. 2014.3.3

RBB LER

Touschek HER
SRCoulomb HER
Touschek LER

Neutrons (rad. Bhabha)

RBB HERElectron energy (lab)Can be lostin |s|<4mGeV
ARC (Mar. 3, 2014)

Items omitted in the DAQ diagram
to keep it simple• Belle solenoid field, power outage should also issue beam abort• “injection_inhibit” signal to tell accelerator that BG level is
uncomfortable, but not so bad to abort beam
• Analog path for real time monitoring by shifters– CDC leak current limiter (beep sound in KEKB control room at Belle1)– ECL BG level / TOP rate/ Injection veto timing measured by oscilloscope(send display image by CATV line)– We need similar ones for Belle2, also in digitized way to give to collimatorsemi-automatic control algorithm• Timing signals from/to KEKB• ZDLMs– Need much faster path for bunch-by-bunch feedbackDetail to do lists••••

QED spent e+/e- could contribute to CDC?
Secondary showers from collimator
Shield around collimators/beam loss positions
SR emitted at |s|>4m (final bending magnet)– Speed up mag-field calculation in simulation• Feasibility study for IR loss monitors to feedback collimator control• Realistic injection background (need e- gun group involved)• Tunnel neutron BG on BKLM edges– Polyethylene shield thickness requirement attached to end-yoke• Dose estimation on QCS components• CDC neutron shield design (by CDC group)• etc..

ARC (Mar. 3, 2014)

BG levels at each sub-detectors
7th/8th campaign
Disclaimer:- We assume 10 Snow-Mass years of operation
with the design luminosity.
- Neutron flux are normalized to 1MeVequivalent neutron rate using NIEL-damage.

☺

Safety margin>2
Safety margin>1
Safety margin<1
ARC (Mar. 3, 2014)

PXD

Pit VanhoeferSR: ~0.1% at one half (+z) ladder in #1 layer
need to see halo/miss-alignment impact with latest
results (were <1% previously)
Yuri Soloviev
Close to limit (3%)

ARC (Mar. 3, 2014)

SVD
Peter Kvasnicka (7th campaign)

Well below 10%. OK
ARC (Mar. 3, 2014)☺

CDC
Don van Thanh(7th campaign)☺
☺

With this rate, “unrecoverable error” happens every ~7hours in one ofFPGAs and we need to stop the data-taking
taking to download FPGA firmware.
It is still acceptable but less neutrons rate is desired.

ARC (Mar. 3, 2014)

ARICH
Removed innermost ring

8 rings

7 rings

Luka Santelj☺

☺

ARC (Mar. 3, 2014)

Beam pipe aperture change for SR

r=7.15 5.0mm

r=4.8 5.0mm

IPr=3.2 5.0mm

Now this cylinder part
points at (z,x) =(0, -0.5)mm

10um Au plating extended to Ti: (z=-3.7~5.9cm
ARC (Mar. 3, 2014)

r=5.8 5.0mm

Now this cylinder part
points at (z,x) =(0, -0.5)mm-6.55~+10.5 cm)

Only used for stopping
power calculation

Lead shield at Belle-I5cm

We can put more thickness than
5cm, as long as there areenough space and its weight
can be mechanically supported.

5cm
lead+Poly
lead (Belle-I)

polyethylene
orARC (Mar. 3, 2014)5cm

Lead shield at Belle-I

5cm

We can put more thickness than
5cm, as long as there areenough space and its weight
can be mechanically supported.

5cm

lead+Poly preferred• Unfortunately previous shield was already discarded• But we are in contact with the same company who fabricated previous ones.
ARC (Mar. 3, 2014)

ARICH shield study
Luka Santelj(6th campaign)

5th campaignlead(Belle-I)
5cmpolyethylene

lead+Poly

Lead+poly2
Even half (2.5cm) of polyethylene shield gives sizable
reduction. Neutron shields inside ARICH structure(extended to +z) is also known to be effective.
ARC (Mar. 3, 2014)

ECL

Sam de Jong

Crystal radiation dose/ diode Neutron flux becomes OK,
with “combined” shielding option.
ARC (Mar. 3, 2014)