Introduction of Linac Operation Status& Progress of Injector GroupThe 120th B Factory Project Committee
Rui Zhang (ACCL 5, Injector Group)

On behalf of all the ACCL 5 members, 2021.09.22.

CONTENTS• Linac status during 2021ab commissioning• Injector group status• Achievements and issues in 2021ab• Upgrades• Summary

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LINAC STATUS in 2021ab COMMISIONING
General Introduction of Linac Injector

All members of linac and MSC

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LINAC STATUS in 2021ab COMMISIONING
Electron Source PartTop view

Thermionic DC e- gun (GU_AT)
Pulse bends in 24o line:
Pulse to pulse beam switchingfor RF e- gun/thermionic e- gun・e+ production e-: 10 nC (for LER injection)・e- study: 1 nC
・PF injection: 0.1 - 0.3 nC
・PF-AR injection: 0.1 - 0.3 nC

Side view

M. Yoshida, X.Y. Zhou, R. Zhang

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LINAC STATUS in 2021ab COMMISIONING
Electron Source Part

0o RF Gun••••

Primary RF gun
QTWSC cavity
Two laser beams 60º
oblique incidence
Ir7Ce2 photocathodeSide view
M. Yoshida, X.Y. Zhou, R. Zhang

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Positron Target and Capture Section

Tungsten Target & Flux Concentrator
Y. Enomoto, et.al

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LINAC STATUS in 2021ab COMMISIONING
Positron Target and Capture Section

Large Aperture S-band acc. structure (LAS)
Bridge Coil (BC)Solenoid
Tungsten target

3.5 GeV e- beam

Flux Concentrator (FC)Cu-alloy (NC50: Cu-Si-Ni)

Y. Enomoto, LCG, 2020.07

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LINAC STATUS in 2021ab COMMISIONING
Electron Beam (HER) for SuperKEKB in 2021ab• Installed DOE (Diffractive Optical Element) in 1st laser line from 2020c• Elliptical flat-top spatial distribution on the surface of photocathode (LA6mm SA3mm) for
low emittance e- generation and avoiding discharge• Single laser incidence in 2020c and 2021ab (No installation space for 2nd laser)
Without DOE

6mm

With DOE

3mm

R. Zhang, LCG, 2020.07

Laser beam profile monitor

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LINAC STATUS in 2021ab COMMISIONING
Electron Beam (HER) for SuperKEKB in 2021ab

1st BMP after RF gun
BT BMP

M. Satoh, KEKB ARC, 2021.09

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LINAC STATUS in 2021ab COMMISIONING
Electron Beam (HER) for SuperKEKB in 2021ab

1st BMP after RF gun
BT BMPDischarge••

Mis-operation under the statusof feedback on
2 nC → 1.5 nC

Temperature fluctuation••

Air-conditioner of A1 laser hut
A1 Klystron gallery

Beam tuning•••

Exchange of air-conditioner
Laser phase adjustment
Beam adjustment

Performance degradation••

Quantum efficiency ofphotocathodeRF gun vacuum window for
laser incidence
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LINAC STATUS in 2021ab COMMISIONING
Electron Beam (HER) for SuperKEKB in 2021ab

1st BMP after RF gun
BT BMP

2 lasers
incidence

1 laser incidence

2/1 laser incidence•••

DOE in 1st laser line
No DOE in 2nd laser linePhotocathode QE increased

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LINAC STATUS in 2021ab COMMISIONING
Electron Beam (HER) for SuperKEKB in 2021ab

1st BMP after RF gun
BT BMPW/ laser cleaning/WO lasercleaning*

2/1 laser incidence•••

DOE in 1st laser line
No DOE in 2nd laser line
Photocathode QE increased

W/WO laser cleaning••

Essential to keep QE*Laser cleaning tested in
2021ab but inefficient

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LINAC STATUS in 2021ab COMMISIONING
Electron Beam (HER) for SuperKEKB in 2021ab

1st BMP after RF gun
BT BMP

Ir2Ce PhotocathodeIr7Ce2
Photocathode2/1 laser incidence•••

DOE in 1st laser line
No DOE in 2nd laser line
Photocathode QE increased

W/WO laser cleaning••

Essential to keep QE*Laser cleaning tested in2021ab but inefficient

Ir2Ce / Ir7Ce2•••

QE: Ir2Ce < Ir7Ce2
Lifetime: to be estimatedLaser cleaning: Ir2Ce >> Ir7Ce2

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LINAC STATUS in 2021ab COMMISIONING
Electron Beam (HER) Emittance History in 2021ab

Emittance of electron beam••••••
N. Iida, KEKB ARC, 2021.09

Unstable γεy@Sector B (e- charge 1.5~2.0 nC)→ Newly added pulse steering magnets in upstream
and orbit feedback system (2021c)
Reason unknow on blowup of vertical emittance→ Under investigating
Horizontal emittance increased by synchrotron
radiation→ Under simulation
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LINAC STATUS in 2021ab COMMISIONING
Electron Beam (HER) Injection History in 2021ab

Injection of electron beam•

High injection efficiency under βy*=2 mm•

Poor injection efficiency for βy*=1 mm case•Reason unknow on poor efficiency(Simulation result: ~70% under the sameemittance level)→Under simulation
Frequent setting adjustment for injection
septum→Please consult other experts
Unachievable 2-bunch injection (Injection
efficiency of the 2nd bunch is almost 0)→To do sufficient RF conditioning andadjust the RF pulse width, improve theemittance of the 2nd bunch beam

•
••
•

•

N. Iida, KEKB ARC, 2021.09

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LINAC STATUS in 2021ab COMMISIONING
Positron Beam (LER) for SuperKEKB 2021ab

M. Satoh, KEKB ARC, 2021.09

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LINAC STATUS in 2021ab COMMISIONING
Positron Beam (LER) for SuperKEKB 2021ab

Positron beamγεx / γεy (2.3 nC)
99.7/3.2 μm @BT••••

5 nC positron beam achieved after the positron target
3 nC is realized after DR and linac end
High positron yield closes to the simulation result
Qualified emittance at BT

Y. Enomoto, LCG, 2021.07

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LINAC STATUS in 2021ab COMMISIONING
Positron Beam (LER) Beam Charge History in 2021ab

after e+ target
before DR
Linac endBT

15_T : before e+ target
16_5 : after e+ target
28_4 : before DR
DC_4 : after DR
58_4 : Linac end

Positron beam charge history••••••Stable charge operationTiny loss between Linac end and BT
Charge increased efficiently and closes
to the 4 nC design value→Newly installed Q & steering magnets→Increase the gradient of AC_15_1[2]→Increase FC and DC solenoid field

Y. Enomoto, LCG, 2021.07
M. Satoh, KEKB ARC, 2021.09

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LINAC STATUS in 2021ab COMMISIONING
Positron Beam (LER) Beam Emittance History in 2021ab

Positron emittance history••••

N. Iida, KEKB ARC, 2021.09

Stable low emittance thanks to effective
DRBlowup problem (BTp1→BTp2)→Newly added Quad in the center of
SY3 chicane to decrease leak dispersion→Installation of skew quads in theARC2-3 of e+ BT line for improving
vertical emittance blowup

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LINAC STATUS in 2021ab COMMISIONING
Positron Beam (LER) Injection History in 2021ab

Injection of Positron beam

N. Iida, KEKB ARC, 2021.09•

High injection efficiency•Successful double bunch injection•Injection status of the 2nd bunch is worse•

Large beam background of Belle II

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LINAC STATUS in 2021ab COMMISIONING
Other Improvement of Linac in 2021ab

RF phase feedback-T. Miura•

Application in manylocations•

Fast recovery frommaintenance status

T. Miura, LCG, 2021.03

Synchronized measurement-F. Miyahara

J-arc synchrotron radiation Monitor-R. Zhang•

Available to BPM, RF, pulsed magnet•

RF phase correction•

Large data storage (ASCII→gzip)•

Measurement of transverse beam size•

Abnormal event analysis for MR abort•

For orbit feedback in the future

F. Miyahara, LCG, 2021.04

R. Zhang, Linac Technology Meeting, 2021.04.20
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LINAC STATUS in 2021ab COMMISIONING
Smooth 4-Ring Simultaneous Top-up Injection

22-35M. Satoh, KEKB ARC, 2021.09

INJECTOR GROUP STATUS
Achievements and Issues in 2021ab

R. Zhang, Linac TechnologyMeeting, 2020.12.22

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INJECTOR GROUP STATUS
Achievements and Issues in 2021ab

QE of PhotocathodeR. Zhang, Linac Technology Meeting, 2020.12.22•

QE Ranking:
KEK Ir7Ce2 >KOBELCO Ir2Ce >KOBELCO Ir7Ce2 >KEK Ir2Ce•

Discharge Probability
KEK Ir7Ce2 <KOBELCO Ir2Ce•

Adoption of KEK Ir7Ce2 from 2021ab•Achievable bigger size

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INJECTOR GROUP STATUS
Achievements and Issues in 2021ab

Improvement of Laser Shutter for HER Gate•••

Application of new synchronization circuit
Light weighting of physical shutter
Removal of ambiguous injection beam which is potential
cause of HER beam abort

M. Yoshida, LCG, 2021.04.26

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INJECTOR GROUP STATUS
Achievements and Issues in 2021ab
2019.06 without DOE & beam
position sensor

Laser System for RF gun•

Application of DOE in 1st laser line•

Energy upgrade of 1st laser line•

Laser beam position sensor for point stabilityfeedback•

Trouble-free continuous laser operation

H 2σ: 48.04±0.51, V 2σ: 46.08±0.69
2.1 nC@A1: 10.636 ± 7.215, 13.276 ± 5.026

2021.06 with DOE & beam position sensor

H 2σ: 24.30±3.06, V 2σ: 10.08±0.46
1.8 nC@BT: 19.343± 26.848, 18.742 ± 3.158

R. Zhang, Linac Technology Meeting, 2021.06.29

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INJECTOR GROUP STATUS
Achievements and Issues in 2021ab

Arisen issues in 2021ab•

Serous discharge → Uniform laser intensity distribution and smooth RF conditioning•

Performance deterioration of RF-gun window → Component analysis of deposits•

Unavailable 2-bunch injection → Sufficient RF conditioning and adjust the RF pulse width, improve theemittance of the 2nd bunch beam•

Not achieved charge at BT end > 2 nC → Next page

Photocathode used in 2021ab
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Gun window used in 2021ab

M. Yoshida, Linac Technology Meeting, 2021.08

R. Zhang, 2021.08

INJECTOR GROUP STATUS
Upgrade for Higher Charge from 2021c

Higher Charge
Two lasers incidence case in 2019

Electron charge @BT-end > 2 nC andfor higher HER injection efficiency

01
Higher Laser Energy

Space in RFGun Box

06

Extremely overcrowded

02
Two Tier LaserConfiguration

A. Two lasers
incidence
B. Upgrade of 2nd laserline 5th amplifier
modulePowerful amplifier module

03

05
DOE for 2nd laser line
Uniform flat-top laser
beam pattern

A. For uniform laser intensity
distribution after laser energy
upgrade of 2nd laser line
B. Keeping laser cleaning function

Higher Photocathode QE
Available laser cleaningmode during commissioning

04
Discharge Problem

Focused small laser
beam pattern

Non-uniform powerful laser beam
induces discharge easily

Laser cleaning needs small laser beam spot wo DOE
KBE operation requires big and uniform laser beam with DOE

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INJECTOR GROUP STATUS
Upgrade for Higher Charge from 2021c

Red line: 1st laser line
Blue line: 2nd laser line

R. Zhang, Linac Technology Meeting, 2021.06.29

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INJECTOR GROUP STATUS
Upgrade for Higher Charge from 2021c

150mm
65mm
1st Flip mirror:
for switching laser to KBE modeor cleaning mode

R. Zhang, Linac Technology Meeting, 2021.06.29

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INJECTOR GROUP STATUS
Upgrade for Higher Charge from 2021c

The 2nd tier for DOE
150mm

R. Zhang, Linac Technology Meeting, 2021.06.29

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INJECTOR GROUP STATUS
Upgrade for Higher Charge from 2021c

Uniform laser beam
for commissioning
2nd Switching flip
mirrorR. Zhang, Linac Technology
Meeting, 2021.06.29

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INJECTOR GROUP STATUS
Upgrade for Higher Charge from 2021c

Uniform laser beam
for commissioning
2nd Switching flip
mirrorLaser with small beam
spot for cleaning
R. Zhang, Linac Technology
Meeting, 2021.06.29

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INJECTOR GROUP STATUS
Two Tier Laser Configuration

2nd tier of 2nd laser: KBE or QFE with DOE
1st laser line: KBE or for GR_AS
1st tier of 2nd laser: Cleaning mode wo DOE
R. Zhang, Linac Technology Meeting, 2021.06.29

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SUMMARY• Smooth linac operation in 2021ab• e-: 1.5 nC @BT and unachievable double bunch injection• e+: increased charge smoothly and working well
• Successful 4-ring simultaneous top-up injection• Others effective improvements for efficient operation from all groups• Injector group status• Laser systems working well in 2021ab commissioning• Upgrade of laser system for high performance operation from 2021c

THANKS！
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