Injector Overview
Masanori Satoh (Acc. Lab. Div. V, KEK)
on behalf of Injector Linac Group and Linac Commissioning GroupKEKB Accelerator Review Committee, Mar. 25-27, 2024

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Contents• Injector outline• e- beam status and issue• e+ beam status and issue• Upgrade work and progress during LS1• Summary

KEKB Accelerator Review Committee, Mar. 25-27, 2024

Outline

Injector Linac Layout

・Two electron sources:
RF gun: HER injection
Thermionic DC gun: LER, PF, PF-AR・Sector 3-5:
All magnets are pulsed magnets.
Continuous orbit feedback
1.1 GeV e+Damping Ring ・DC magnet settings are same for different beam mode・Simultaneous top up injection for SuperKEKB andlight sources since 2018

60 klystron units
240 accelerating structures (S-band 2-m-long)

8 Sectors (A-C,1-5)
Energy Knob

Thermionic gun
PhotocathodeRF gunJ-ARC
1.5 GeV

B

ABCS
ECS

C

123e+e+ capture section
target

45PF
ECS

PF-AR

LER

chicaneEnergy KnobHER
HER 7GeV
PF-AR 6.5 or 5 GeV

Acceleration
4.2 GeVee+ target

LER 4 GeV e+Stand-byDeceleration

1.1 GeVe+

PF 2.5 GeV

Acceleration1.5 GeVC12345

Beam energy variation
forAccelerator
each beammode along
thebeam line after J-ARC
KEKB
Review Committee,
Mar. 25-27,
2024

3

Pulse to pulse beam switching:rf e- gun/thermionic e- gun
In injector section(double decker beam line)

Thermionic DC e- gun (GU_AT)

Outlinew/ 2 subharmonic bunchers (114 MHz, 571 MHz) and 2bunchers.

・e+ production e-: 10 nC (for LER injection)・e- study/HER injection: 1 nC
・PF injection: 0.1 - 0.3 nC
・PF-AR injection: 0.1 - 0.3 nC

RF e- gun
（GR_A1 for HER injection）

Pulsed bend
Schematic side view

KEKB Accelerator Review Committee, Mar. 25-27, 2024

4Injector operation statistics
KEKB

SuperKEKBKEKB Accelerator Review Committee, Mar. 25-27, 2024

OutlineOutline

Injector beam loss time statistics(FY2020 – FY2022)
0.6%
0.1%

1%
20.9%

33.8%

10.6%
2%
11.3%

6.4%

4% 9.2%

FY2020: 1.58%

RF
MagnetAcc. Structure
Cooling water
VacuumControl
TimingGun
Facility
Earthquake
Etc

3.8% 0%RF
MagnetAcc. Structure
Cooling water
VacuumControl
TimingGun
Facility
Earthquake
Etc

1.9%
20.7%

40.7%

10.3%
3.4%
5.7%
8.5% 4.5% 0.4%

FY2021: 1.83%••••RF
MagnetAcc. Structure
Cooling water
VacuumControl
TimingGun
Facility
Earthquake
Etc

0.5% 5.2%
9.8%
5.2%

24.4%

39.2%
1.3%

12%

1.7%

0.6%

0.1%

FY2022: 0.81%

Beam operation could be interrupted by some different reasons. (RF, magnet powers supply, control software failure, …)
Beam loss time ratio is less than 2%.
Most beam loss time are caused by RF and e- gun related troubles.
In FY2022, beam loss time is less than 1%.
• In 2022b, 2022c, 2023a, SuperKEKB was not in operation because of LS1.
• Linac klystron operation mode was changed from 50 Hz to 25 Hz.
• In FY2022, most of beam loss time are caused by magnet trouble.
• Pulsed magnet controller problem.
KEKB Accelerator Review Committee, Mar. 25-27, 2024

e- beam status and issue

KEKB Accelerator Review Committee, Mar. 25-27, 2024

Low emittance photocathoderf e- (0gun
QTW RF gun or operationdeg. Line)RF e- gunIr7Ce2 cathode

Photocathode(metale- beam statusLaser system• Photocathode:
7Ce2
CDS RF Irgun
for backup (90 deg. Line)• Cavity:
QTWSC (Quasi Travelling Wave Side Coupler)– Strong focusing electric fieldshort drift space
Secondary RF gun
for test and backup

M. Yoshida et al.

KEKB Accelerator Review Committee, Mar. 25-27, 20248

e- beam status

Hybrid laser system for rf e- gun•

Yb doped fiber and Nd:YAG DPSS module Amplifier••••

Output Power:ω (1064 nm): 30 mJ
2ω ( 532 nm): 15 mJ
4ω ( 266 nm): 1 mJ

1st laser
2nd laser

Laser roomon theground virtualKLY Gallery

cathodediagnostics

Laser line to RFGunTunnel

RF-GunR. Zhang,
X. Zhou et al.

Optics layout
the Reviewtunnel
KEKBinAccelerator
Committee, Mar. 25-27, 2024

Laser transport line9DOE for reshaping of laser spatial distribution
2019.06 without DOE & beam position sensor

H 2σ: 48.04±0.51, V 2σ: 46.08±0.69

Pointing stability
can be improved.
DOE is installed in vacuum
chamber filled with Argon gas.

e- beam status

2021.06 with DOE & beam position sensor

H 2σ: 24.30±3.06, V 2σ: 10.08±0.46

DOE (diffractive optical element) were installedat 1st /2nd (in summer ‘20/‘21) line laser: Laser beamhomogenizer for low emittance beam with thehigh intensity bunch charge.

DOEs were replaced by newone (F8 mm from F6 mm)
for high bunch charge
operation.
Forworld first DOE application in UV laser

KEKB Accelerator Review Committee, Mar. 25-27, 2024

R. Zhang

e- beam statuse- bunch charge history (2020a to 2024a)(from rf gun)(BT end)2020a,b2020c

2021a,b2021c

2022a,b2022c

High bunchcharge study

2023a,b2023c

2024aLS1discharge

KEKB Accelerator Review Committee, Mar. 25-27, 202411

e- beam summary and issue

e- beam issue• Thermionic DC e- gun has worked fine for light source (PF, PF-AR) injection and e+ production primarye- beam (10 nC).
• Photocathode rf e- gun• Laser system and the new DOE (F8 mm) element have worked fine without any significant trouble.

• Increase of bunch charge• High bunch charge of 5 nC e- from gun was demonstrated w/ previous DOE (F6 mm).
• Further high bunch charge e- beam study will be conducted w/ new DOE.

• Issue• Breakdown rate of rf gun cavity gradually increased. New cavity should be installed in the near future.
• Best emittance at the linac end and BT1 (before Arc1) is almost satisfied the final goal while bunch charge (2nC) is less than final goal (4 nC).
• However, emittance at BT2 is increased due to ISR, CSR, and some other reasons.
• Increase of 2nd bunch injection efficiency and improvement of its stability are important issues.
• In this run 2024a, 2nd bunch emittance is improved. It is almost comparable to 1st bunch one. Two bunch
Emittance measured
injection will be tested soon.
on Mar. 10th, 2024e- emittance

Measured enx,nxy (2 nC) : 20/20 mm (at BT1)
Goal: enx,nxy (4 nC) : 40/20 (H/V) mｍst

1 bunch@ BT1 Review Committee, Mar. 25-27, 2024
KEKBAccelerator

2nd bunch @ BT1

e+ beam status and issue

KEKB Accelerator Review Committee, Mar. 25-27, 2024

e+ beam status

Positron source setup at Sector1
Positron target and capture section

DC solenoid
Large aperture S-band acc. Structures (x10)

W target + flux concentrator (FC)KEKB Accelerator Review Committee, Mar. 25-27, 2024

Y. Enomoto et al.

e+ beam status

Positron Capture Section: Flux concentrator, bridge coil, solenoid
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)
IFC= 12 kA
KEKB Accelerator Review Committee, Mar. 25-27, 2024

Y. Enomoto et al.

e+ beam statuse+ bunch charge history (2020a to 2024a)(after e+ target)(before DR)(Linac end)(BT end)

2020a,b2020c

2021a,b・Solenoid current (SL_16_)optimization・beam tuning (primary e- bunch charge ↑)2022c

2021c
2022a,b2023a,bLS1

・beam tuning

・Steering, BPM
in Unit 1-5, 1-6
・beam tuning
・New FC
・Solenoidcurrent↑・decrease bunch charge(MR request)

KEKB Accelerator Review Committee, Mar. 25-27, 2024

2023c

2024a

e+ beam summary and issue

e+ beam issue• e+ bunch charge is almost achieved (final target: 4 nC)• 3.5 nC at linac end and BT• Machine learning based automatic tuning can help to increase the e+ bunch charge at end of Sector2 (upto around 5.5 nC).
• Measured e+ production efficiency (65%) is comparable to the simulation result (60%).
• Flux concentrator operation has been very stable.

• Issue• Emittance at linac end and BT1 (before Arc1) are almost satisfied the final goal.
• However, emittance at BT2 is increased. It could be caused by some magnetic errors.
(“Injection” report by T. Yoshimoto san)• Horizontal emittance after DR is larger than design value. Low emittance DR optics will be tested after LS1.
e+ emittance

Measured enx,nxy (3 nC) : 103.5/4.7 mm (at BT1)
Goal: enx,nxy (4 nC) : 100/15 (H/V) mｍ

KEKB Accelerator Review Committee, Mar. 25-27, 2024

Upgrade work and progress
during LS1

KEKB Accelerator Review Committee, Mar. 25-27, 2024

Upgrade during LS1

Upgrade work and progress during LS1• Pulsed Quads• at J-ARC• at Sector1, 2• Control software upgrade• Fast kicker for 2nd bunch orbit control (J-ARC, linac end, e- BT)• New accelerating structure• Automatic beam tuning

KEKB Accelerator Review Committee, Mar. 25-27, 2024

Pulsed Quads at J-ARC and Sector1, 2Upgrade during LS1• Additional pulsed quads at J-ARC and Sector1, 2 were installed in 2023 summer maintenance.
• J-ARC: dedicated beam matching for each injection beam (HER/LER/PF/PF-AR)• Sector1, 2: low beta optics for HER injection beam (mitigate emittance growth)• At J-ARC, newly designed pulsed quad (K. Yokoyama) and pulsed power supply driver (T. Natsui)
were installed in the 2023 summer maintenance.
Seven pulsed quads were installed.

Four DC quads were replaced by pulsed one.
KEKB Accelerator Review Committee, Mar. 25-27, 2024

Pulsed magnet control system (1)••••••Upgrade during LS1=== PXI-based controller ===PCIe-8381 & PXIe-8381, PXI Remote Control Module
PXI 6733 DAC
PXIe 6356 ADC
MRF EVR-230=== cRIO ===Interlock system
Data logging

ADC

KEKB Accelerator Review Committee, Mar. 25-27, 2024

DAC

EVR

Di Wang et al.

Pulsed magnet control system (2)Upgrade during LS1• Windows/LabVIEW/PXI system– Started since 2017– Sometimes control PC or LabVIEW program
freeze.
– It takes 20 minutes for restarting system.
(Large # of variable should be initialized inLabVIEW software)

DACADC• Development history– Decided to migrate to Linux/EPICS IOC(2022/12)– NI DAC&ADC driver (2023/02)– EVR driver (2023/03)– EPICS IOC (2023/04)– OPI & Monitoring (2023/05)– Experiment (2023/06)– Revision (2023/07)– Stability test (2023/07)

EVR• 8 of 17 control system were replaced by
new software since 2023c.
– They have worked well w/o trouble.
– In this summer maintenance, remaining
KEKB Accelerator Review Committee, Mar. 25-27, 2024
system also will be replaced by new one.

Di Wang et al.

Upgrade during LS1

Fast kicker for 2nd bunch orbit correction• Based on “ceramics chamber with integrated pulsed magnet“ developed by C. Mitsuda (PF)• J-ARC (’22 summer), end of linac and e- BT (‘23 summer/winter) for 2nd bunch orbitcorrection• It could help to increase the injection efficiency of e- 2nd bunch.

Fast kicker (J-ARC)

Fast kicker(linac end)

PF (Mitsuda, Shinohara,Naito)，Linac
Y. Enomoto, Natsui)
KEKB
Accelerator Review (Kamitani,Committee, Mar. Okayasu,25-27, 2024

e+ beam test w/ fast kicker (linac end)

Upgrade during LS1• Fast kicker can correct the 2nd bunch beam position and reduce the orbit difference(1st and 2nd bunch).
• However, it increase the beam position jitter. It should be corrected for beam operation.
e+ BT vertical beam position at BPM QMD5P(1st bunch)(2nd bunch)

Fast kicker ON

Fast kicker OFF

KEKB Accelerator Review Committee, Mar. 25-27, 2024

24

New accelerating structure

Upgrade during LS1• Mitigation of accelerating structure failures• Originally designed for 8 MeV/m (PF injector), but used at 20 MeV/m (KEKB upgrade)• Degradation is leading to high field emission rate and discharges.
• Water leaks, field emission , discharge in waveguide, and so on (29 of 60 units have some problems)• Not only future Y(6S) but even Y(4S) could be suffered

Damaged iris

• 5-year upgrade plan to fabricate and install new accelerator structures (FY2018 –FY2022)• 4 units (16 acc. structures) have been replaced by new one.
• New acc. structure: acc. gain ↑7%, surface field ↓20% (reduce breakdown)• New pulse compressor (SCPC) was also developed and installed in Unit#44.

Colling water leakage

New pulse compressor

New S-band 2-m-long TW acc. structure KEKB Accelerator Review
Committee,Mar.
25-27, 2024
Spherical-Cavity
PulseCompressor(SCPC)

H. EgoAutomatic beam tuning

Upgrade during LS1• Automatic beam tuning approach with machine learning is recent trend in accelerator operation.
• Bayesian Optimization approach is now under test by using the beam of injector Linac.
• Implementation using GPyOpt Python library (T. Natsui) / In-house developed implementation (G. Mitsuka, S. Kato)• Automatic beam tuning test started in 2022c.
• Both of Bayesian optimization and downhill simplex method areavailable.
• Preliminary test was started by using only 4 control variables(pulsed steering magnets) to improve e+ bunch charge.
• After continuous study and software improvement, the number ofcontrol variables increased to around 16.
• This automatic tuning is also applied to dispersion correction at JARC .
• Currently, any linac operators can easily used this automatic beamtuning software.
KEKB Accelerator Review Committee, Mar. 25-27, 2024

Automatic tuning GUI# of trial

Beam orbit and bunch charge during automatic tuning

Hor.
(mm)

Ver.
(mm)

RTL

I(nC)
e+target (W)
KEKB Accelerator Review Committee, Mar. 25-27, 2024

LTR

Automatic tuning for increasing e+ bunch charge• Measured data (Oct. 25the, 2023) of e+ bunch charge in Sector2 almost agreewith the simulation result.
• Pulsed Quads at J-ARC (installed in 2023 summer) and automatic beam tuning
software can help to increase the e+ bunch charge.
simulated e+ bunch charge
measured e+ bunch charge

e+ 1st bunch charge

Simulation by Y. Seimiya
KEKB Accelerator Review Committee, Mar. 25-27, 2024

Summary•••

Simultaneous top up injection has been successfully conducted.
e- beam• Laser system has worked fine without any significant trouble.
• New DOEs (F8 mm) have been installed at both of 1st and 2nd laser, and they have worked fine.
• 5 nC from gun was demonstrated w/ previous DOE (F6 mm). Further beam study will be conducted w/new DOE.
e+ beam• e+ generation system (flux concentrator, power supply, DC solenoid) has worked fine.
• e+ bunch charge of 3.5 nC at BT end are archived (final design 4 nC).
• Machine learning based automatic tuning can help to increase the e+ bunch charge at end of Sector2(up to around 5.5 nC).

• Upgrade work and progress during LS1• Pulsed quads at J-ARC and Sector1, 2 have been successfully installed and worked fine.
• New control software for pulsed magnet• New accelerating structure• Fast kicker for 2nd bunch orbit correction (J-ARC, Linac end, e- BT)• Automatic beam tuning is deployed for daily operation.
• Issues• Emittance growth at end of BT for both of e- and e+ beam (Injection report)• Low e- injection efficiency of 2nd bunch so far. Fast kicker system could help to improve it.
• Increase the e- bunch charge while keeping small emittance w/ new DOE.
KEKB Accelerator Review Committee, Mar. 25-27, 2024