Beam Loss Simula-on at
SuperKEKB
Y. Funakoshi
KEKB Review
2013. 03. 05

Beam Loss Simula-on• Needs of simula-on on loss distribu-on aroundthe ring– Es-ma-on of detector beam background (Y.
Nakayama)– Design of radia-on shield– Design of beam loss monitor• Simula-on– Touschek: Y. Ohnishi– Beam‐gas Coulomb: Y. Funakoshi– Radia-ve Bhabbha: Y. Funakoshi

Comparison of beam loss
KEKB (design)

KEKB (achieved)

SuperKEKB

LER

HER

LER

HER

LER

HER

Radia-veBhabha

21.3h

9.0h

6.6h

4.5h

28min.

20min.

Beam‐gas45ha)

45ha)

24.5min.b)

46min. b)

Touschek

10h‐10min.

10min.

Total

5.9h

7.4h

~133min.

~200min.

6min.

6min.

Beamcurrent

2.6A

1.1A

1.6A

1.1A

3.6A

2.6A

Loss Rate

0.12mA/s

0.04mA/s

0.23mA/s

0.11mA/s

10mA/s

7.2mA/sa) Bremsstrahlungb) Coulomb scaYering, sensi-ve to mask se[ngBeam loss accompanied with the beam injec-on should be added.

Beam‐gas Coulomb simula-onCross sec-on of Beam‐Gas scaYering(Coulomb scaYering)• Diﬀeren-al cross sec-on– ScaYering angle: θ– Azimuthal angle: φ! Z (Z +1)rd! G =1 gas
2i2ei"2+1 comes from Mφller scaYering.
No energy loss is considered.

! Z (Z +1)r#cot 3 d# d$ " d! G = % gas
2ii"2• Total cross sec-on" Z (Z +1)r # 1!

d! Gd! = 2! gas! c d!

!G = !

!G "1 $y=# c2 Aci!22e#
cot 3 d#2Gas: COγ = 4GeV/511keV– θ > θci2e!c &2 "ccot+lnsin%(22 '$2θcBeam Life-me from Coulomb
scaYering against residual gas• Parameters (LER)– Gas: CO– Pressure: 1 x 10‐7 Pa– Temperature: 300°K– AcceptanceLife-me ~ 1468 sec
ver-cal mask: 2.0mm (βym ~ 104.57m)• Ver-cal: QC1: 13.5mm (βym ~ 2888m)• Horizontal: 20 σx! y " 47.9m• Life-me
1= cnG!C

4 " re2 # Z(Z +1)
gas$21
2% c ( s)1! c ( s)2" x " xm " y " ym=+222axm
2aym– Life-me calculated = 1961 sec (@QC1ap=13.5mm), 1186
sec (@QC1ap=10.5mm)

HER integral of ver-cal beta func-on
HER:
average ver-cal beta func-on = 52.78m

The area (IP +/‐ 100m) causes 68% of beam loss
from beam‐gas Coulomb scaYering if the vacuum
pressure is constant around the ring.

The area (IP +/‐ 4m) causes ~7% beam loss. If the vacuum
pressure in this region gets worse by a factor 10, the beamloss increases by about 63%.

LER integral of ver-cal beta func-on
LER:
average ver-cal beta func-on = 47.90m

Tracking• Star-ng points: each SAD element (minimum distance:50cm)• # of turns: 3~10 turns (tracking of 30 turns is underway)• Minimum scaYering angle（θc） depends on ringposi-on!c =Ap" ys " yAp# 3% $y % $y =&y"y– Azimuthal angle φ : uniform distribu-on• # of par-cles– ~0.2 ~ 2 x 106 par-cles in the ring

• Consider beam size distribu-on• Mask se[ng– Op-mized for Touschek backgroundSe[ng values for masks
Y. Ohnishi

Loss distribu-on HER
beam‐gas Coulomb

sher_5753

V‐maskH‐maskTracking: 3 turns

IR Loss (‐4m < s < 4m)~1.09MHz (28 events)

H‐mask｛｛H‐mask

Total lost par-cles in simula-on:
1.16x106 (45.4 GHz)
Analy-c calcula-on: 59GHz

Loss distribu-on LER
beam‐gas Coulomb

sler_1684

V‐maskH‐mask｛H‐maskTracking: 10 turns

IR Loss (‐4m < s < 4m)~141MHz (108 events)

Total lost par-cles in simula-on:
0.097x106(126.6GHz)
Analy-c calcula-on: 197GHz

3 turns

15 turns

10 turns

30 turns

Element name: APT.6002
S [m] = 2934.3069853702323
BX = 16.68318748342323
BY = 142.88788115847524
sigmax = .00023463699345008804
sigmapx = 1.4064278405024721e‐05
sigmay = 4.3429483433398944e‐05
sigmapy = 3.0394098562656846e‐07
sigmaz = .006
sigmae = .000809
Theta_c = 1.8337874570821454e‐05
Length which element represent for [m] =5.098814615590072
Number of par-cles = 146

Radia-ve Bhabha simula-onRadia-ve Bhabha (LER)

0.5% < ΔE < 100%: using analy-c formula

1 turn tracking
Mul-‐turn eﬀects are small.

sler_1684

Radia-ve Bhabha (LER)
beam loss rate per m
H‐maskCoordinateBeamLoss2013_3_5_1_18_32.dat

Loss rate = 2.04mA/s ‐> τ = 29.4min. (3.6A)

Radia-ve Bhabha (HER)

sher_5753

Radia-ve Bhabha (HER)
beam loss rate per m
H‐maskCoordinateBeamLoss2013_3_5_0_28_36.dat

Loss rate = 2.14mA/s ‐> τ = 20.2min. (2.6A)

Touschek Beam LossY. Ohnishi

sler_1672_5 loss distribu-on

Y. Ohnishi

sher_5745_1 loss distribu-on

Y. OhnishiSum of 3 processes

Beam loss rate (LER)
sum of 3 processes

H‐maskV‐maskBeam loss rate (HER)
sum of 3 processes

H‐maskV‐maskHow to use the simula-on results• IR loss– Touschek, Radia-ve Bhabha ‐> already Nakayama
san uses data for Belle II background es-ma-on– Beam‐gas Coulomb ‐> to be sent to Nakayama san• Other loss
– I already passed a preliminary results of LER toradia-on safety sec-on. They started anes-ma-on. Arer ﬁnishing the beam‐gassimula-on under way, I will send them the results.

Phase‐1 LER

1 mA/bunch, 1 nTorr k = 10%28

Y. Ohnishi

Phase‐1 HER

1 mA/bunch, 1 nTorr k = 10%29

Y. Ohnishi

BackupBeam loss power (LER)
sum of 2 processes (beam‐gas, radia-ve Bhabah)Total cross sec-on

Correc-on for ﬁnite beam size is included.

σ(ε>1.5%)= 1.55 x 10-25 cm2σ(ε>5.0%)= 1.05 x 10-25 cm2σ(ε>20%) = 0.51 x 10-25 cm2σ(ε>50%) = 0.20 x 10-25 cm2Assuming particles are lost with energy loss of ε>1.5%,
Beam lifetime = 30.15 min. (L=8x1035 /cm2/s, Ib=3.6A, LER case)
Loss rate 1.99mA/s

Correc-on for cross sec-on due toﬁnite beam size

Energy acceptance = 1.0%

~60nm (SuperKEKB, κ=0.4%)

Created distribu-on of Coulomb
scaYering angles

Loss distribu-on (power) HER
beam‐gas Coulomb

V‐maskRadia-ve Bhabha (HER)

0.5% < ΔE < 100%: using analy-c formula

1 turn tracking
Mul-‐turn eﬀects are small.

Phase‐1 LER

φ40 mm38

Phase‐1 HER39

φ40 mmSummaryTotal beam loss / bunch

Phase
1NbHER

Touschek Coulomb

Brems.

TotalPPS

PPS

PPS

PPS

6.28x1010

1.41x106

6.17x104

2.94x105

1.76x106LER

6.28x1010

8.74x106

9.95x104

2.72x105

9.11x106

condition

1 mA/bunch

10 %coupling

sher_5755_beast
sler_1684_beast
40

Pave= 1 nTorr
w/o movable masks#bunches = 1000 ‐ 2000
Pave = 1 nTorr ‐ 10 nTorr

1.09x107

Phase‐2 LER

41

Touschek lossPhase‐2 HER

42

Touschek loss