Injector LINAC Status

Kazuro Furukawa for Injector LINAC<http://www-linac.kek.jp/linac-paper/general/>
Information from all injector group members

Injector linac status

K.Furukawa, Feb.2022

1

Improved Precision/Flexibility Injections
HER: 800mA, 12.5 – 25 Hz,
1.4 nC, 1 bunch
LER: 1000mA, 12.5 – 25 Hz,
3.0 nC, 1-2 bunch
PF ring: 450mA, <1 Hz,
0.25 nC
PF-AR: 50mA, <1 Hz,
0.3 nC
vred: Ring current (mA)vblue: Bunch charge (nC)vgreen: Injection rate (mA/s)

Typical 1-day Injections

Event-based
Control System
Every
20 ms

Injector operation hours and failure rates
8
Operation hours (hour)
Limited injection (%)
Beam stop rate (%)

Hours

7,000

F.B
7

6,000

6

5,000

5

4,000

4

3,000

3

2,000

2

1,000

1

(Achieved 200 thousand hours ofoperation at the middle of 2020)
0e− GunARC

Rates (%)

8,000

0
1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020

PF Injection

The injector provide high availability with advanced high-current andlow-emittance injections for SuperKEKB as well as light source rings

Injector linac statuse– (2.5GeV, 0.2nC)

F.B
e− GunARC

Damping ring

SuperKEKB-LER Injection

F.B

e– (3.5GeV, 10nC)

F.B

e+ Targete+ (4GeV, 4nC)

e− GunARC

SuperKEKB-HER Injection

F.B

Fiscal year

uF.B

e– (7GeV, 4nC)
e− GunARC

F.B

Four virtual
injectors haveenabled highefficiency
simultaneous
top-upinjections

PF-AR Injection

F.B
e– (6.5GeV, 0.2nC)

K.Furukawa, Feb.2022

2

Recent LINAC Development and Progress
Positron production yield reaching designed valueu Copper-Nickel alloy was applied to flux-concentrator andresolved the discharge issues
u Optimized with newly installed correctors and monitors
u 3 nC/bunch enough for present SuperKEKB operation

Present operation

Positron yield

top view

u Planning to replace damaged 40 year-old 7% in
230 accelerating structuresu Succeeded to achieve high acceleration field andlow discharge rate with the first 4 structures
u Will install 12 more structures in 2023
bridge coils
solenoidu Can reach Υ (6S)

DC quad
10 nC
spoilertargetprimary e-

LAS Accel.
structuree+injection e-

beam
hole
Flux
Concentrator

Operation up to the last year

New accelerating structures were designed
and are being fabricatedDesign to achieve high performance

H. Egopulsed corr.
pulsed quad

Y. Enomoto
Flux concentrator

Steady progress of
positron beam

4 new structures installed

Injector linac status

K.Furukawa, Feb.2022

3

Electron Beam from RF gun
u Beam emittancev Present requirement γεx 100 µm, γεy 40 µm
v Stability improvements³ DOE for 2nd laser³ Stabilization closed loops³ 7 additional pulsed
correctors

At 1.5 GeV

v Emittance blow-up
in later part of BT³ Needs further studies³ CSR is suspected
w Vertical blow-up ?
w Blow-up behavior withmodified optics condition ?

1st half of BT³ Orbit stability
w To avoid sextupole field
fluctuation from bends
w Mitigation by permanent
magnet sextupole correctors
Injector linac status

K.Furukawa, Feb.2022

4

Injection-1. Improvement of HER injection
βy*=8mm

βy*=1mm

Energy scan

HER “raw” injection efficiency reached 80-90 % !
N. IidaInjection study①Nov.9 Optics
matching BTe1
②Nov.18, Septum ③Dec.1, Septum
Angle:2.57→2.68 Angle: 2.6→2.5④Nov.18 Energy adjustedwith TbT-BPM

1. HER injection for βy*=1mm has improved, achieved from 60% to 80%.
Injector linac status

K.Furukawa, Feb.2022

5

Injection-2. Understanding the injection orbit

3.5

M. Kikuchi, Feb.4

2.85

2.96

v The horizontal orbit of the injection beam for HER has little room to the wall of theinjection point chamber.
v Fairly high residual radioactivity here is observed.
v It is planned that this chamber will be replaced with a wider one during LS1.
Injector linac status

K.Furukawa, Feb.2022

6

Injection-3. “Injection-BPM” became a good reference
The horizontal position at “Injection-BPM”, so-called“Mitsuka-monitor”, has a correlation with the ”raw”
injection efficiency.

X inj-BPM

X inj-BPM“raw” efficiency“raw” efficiency

HER

Charge at “Inj-BPM”

Septum angle:
2.55→2.68

Smaller fluctuation of the X of the “Inj-BPM” is better.

Septum angle wastuned so as toincrease thecharge at “InjBPM”.

Nov.18G. Mitsuka, T. Mori, Y. Ohnishi, S. Ogasawara, N. Iida

v The injection tuning panel for the septum magnets has been redesigned considering
the design orbit that reduced beam losses at the injection point.
v The signal of the special beam position monitor (“Injection-BPM”) for the injected beam
became clear, which helped the injection tuning so much.
Injector linac status

K.Furukawa, Feb.2022

7

Injection-4. Emittance blowup in the BT lines

N. IidaOTR
WS

Horizontal
OTR

ElectronPositronWS

Vertical

WS

OTR

WS measurements
may includes beamjitters.
OTR

4. The emittance blowups between BT1 and BT2 are still unresolved.
v The horizontal emittance blowup is now observed not only in e- BT but also in e+ BT byincreasing beam charge.
v A coherent synchrotron radiation (CSR) is now the most suspected.
v We are investigating whether the emittance blowup has charge dependence.
Injector linac status

K.Furukawa, Feb.2022

8

Injector Linac Improvementsu Short term：Summer 2021
v Optical element and amplifier for 2nd Laser of Rf-gun
v Photo cathode and laser window replacementv Core/Edge network switch upgrade
Laser stabilization with DOE elementv 7 pulsed corrector magnet additionv Solid-state amplifiers replacing mid-power klystronv Damaged waveguide renewal
v Beam position monitor just after positron target
v Improved secondary RF-gun as backup
New beam position monitor
v Improved protection against AC 50Hz fluctuation

Secondary RF-gun

Core network switchesu Mid-term：up to 2026
v Pulsed magnets & kicker
v Precision girder mover
Pulsed magnets
High-precision mover
PCB capacitor renewal
Energy compression
v Energy compression systemv Improved RF-gun
v Improved positron generationv Accelerating structure upgrade
Accelerating structure
Positron generation
RF gunv PCB capacitor renewal
Injector linac status

K.Furukawa, Feb.2022

9

Injector Linac Upgrade Items 2022 - 2026
Thermionic gun with 10 nC

B
J-arc

ARF gun with 4 nC

PF ring
2.5 GeV
0.2 nC

1.1 GeV positron
damping ring

1.5 GeV
Bunch compression

3.2 GeV, 10nC x 2

C

1 Positron
generation 2

LER positron
4.0 GeV
Energy compression 4 nC x 2

Energy compression

3

4

5

PF-AR
6.5 GeV
0.2 nCHER electron
7.0 GeV
4 nC x 2

Pulsed magnets/kickers High precision movers PCB capacitor renewal New energy compressor

RF gunInjector linac status

Positron capture section

Accelerating structure
K.Furukawa, Feb.2022

10

Pulsed Magnet, Kicker and Mover
Injector linac injects beams into SuperKEKB HER, LER as well as light sources PF, PFAR with adequate beam properties at 50 Hz maximum in simultaneous top-up injection
scheme. Pulsed magnets, kicker magnets and girder movers will be installed in order tosuppress emittance blow-up caused by wakefield in accelerator structure with 4 nC perbunch. Kicker magnets may correct beam orbits separated by only 96 ns. Girder movers
may compensate 2-mm annual floor drift at less than 10 microns.
Ceramics chamber integrated
kicker development C. Mitsuda

Pulsed magnets and power
supplies Y. Enomoto, T. NatsuiHigh-precision girder movers
Y. Enomoto

Injector linac status

K.Furukawa, Feb.2022

11

Higher Energy Injection and Collisionu Mitigation of accelerator structure issuesv Originally designed for 8 MeV/m, but has been used at 20 MeV/mv Degradation that lead to high field emission rate and discharges
v Water leaks
v Not only Y(6S) but even Y(4S) could be endangered

u 4-year plan to fabricate and install new accelerator structures

Demands for light source
operation may delay the
installation until summer
2023

Injector linac status

K.Furukawa, Feb.2022

12

New Accelerating Structuresand ECS for Electron Beam
7% of 230 accelerating structures will be
replaced for mitigation of 40-years ofdegradation by discharges and water leaks.

Energy compression system (ECS) for
electron beam will be installed at the
beginning of the beam transport line.

電子銃空洞と光陰極

回折光学素子による形状補正

E

Additional replacement will be necessary
in near future.
Injector linac status

E

H
H

E
HE

E
H

E

E
H

E

K.Furukawa, Feb.2022

13

Capacitors with PCB contamination
Capacitors (up to 1200) in power modulatorswith low-level PCB produced before 1991 will be
replaced following the law.
Capacitors in high-power
klystron modulators

Injector linac status

Injector linac continues to improve withhardware upgrade in 7 category regions
from 2022 to 2026.

K.Furukawa, Feb.2022

14

Further Injector Improvement Possibilitiesu After injector upgrade in 7 categories
v Difficult to foresee now which parameter to improve furtheru Under considerationv Further increase in positron bunch charge³ LER stored current is higher and beam lifetime is shorter³ Several possible plans exist

v Beam transport line thru the direct tunnel³ May relax CSR, etc³ May interfere with PF-AR operationv Even higher energy³ Not difficult in ring hardware up to 12 GeV with different energy ratio³ Collision optics design should be investigated³ Quite expensive modification at LINAC and beam transport linev Polarization³ Physics demand³ R&D for resources, space, meaningful bunch chargev…
Injector linac status

K.Furukawa, Feb.2022

15

Positron Generation Improvements
u Improvement
at summer 2020v Cu-Ni alloy forflux concentratorv Routine 12 kA operationv Correctors inside of
15-m solenoid sectionv Accelerating structure & loadv Stable 3 nC positron delivery
in 2021

Injector linac statusbridge coils

top view
10 nC
primary e-

DC quadspoilersolenoid
LAS Accel.
structuretarget

e+
beam
hole

4 nC injection eFlux
Concentrator

pulsed corr.
pulsed quad

K.Furukawa, Feb.2022

16

Further Positron Enhancementu Optimization of capturing and bunchingvAccelerating voltage gradually increasing³ Long-term RF conditioning³ Discharge in dummy loads and waveguides being resolved

vSeveral beam monitors and correctors were added

New BPM that measures electron
and positron separately just after
the target before the electron
separator.
This helps understand positron
behavior in solenoidal field.

Signal

³ Spiral beam orbit behavior in solenoid with large energy spread³ Normal bunching or velocity (decelerating) bunching

PositronTime

Injector linac status

Electron
Monitor head

K.Furukawa, Feb.2022

17

Further Positron Enhancement (II)u Successful resolution of discharge at flux concentrator
vIntroduction of copper-nickel alloyu Successful mitigation of spike waveformvSimulation of equivalent circuit with detailed stray capacitance
T. Natsui

Simulation with improved equivalent circuit and the new design

Actual application of the new designu Higher current and higher magnetic field possibility
v With power modulator upgrade
Injector linac status

K.Furukawa, Feb.2022

18

Further Positron Enhancement (III)u Positron beam not at the center of solenoid / structurev In order to pass electron beam at the center of structure with lower wakefieldv The target is 3.5 mm away from the center of structure and 1.5 mm away fromthe center of flux concentrator, responsible for spiral beam and lower mag fieldu Solenoidal field gap between flux concentrator and structurev For maintainability at high radiation regionv After several years of experience, shorter gap possibility

Top view
Rear viewu Both are the sources of positron loss, and new design is underway
Injector linac status

K.Furukawa, Feb.2022

19

Carbon Neutral Activities at Injector LINACHigh Performance Simultaneous Top-up Injections

69% Power Recovery from Pulsed Magnet Coils

High Power Conversion Efficiency at Magnet Power Supplies

High Efficiency RF Power Distribution

Injector linac status

K.Furukawa, Feb.2022

20

Responses to previous BPAC Commentsu Although the current injection rate is adequate, improvements will be needed to achieve
higher stored beam currents and shorter ring lifetime.
v Much improved with a new beam injection monitor. Several possible ideas are being investigated,
including physical aperture, optics matching, magnetic field compensation, mitigation of CSR by
new beam duct, more synchronized beam instrumentations, etc.

u The positron yield is below the design value. The positron yield needs to be improved inorder to keep up with the expected short lifetime of the LER as beam currents increase.
v Several possible scenarios were presented in this presentation. Presently, it is said to be large
enough for the bucket charge quantization.

u The HER injection rate also is low and there is still the emittance increase in the BT to thering.
v We are slowly studying the beam behavior between collision operation.

u Further studies on the two-bunch injection for the HER is encouraged, most likely requiring
dedicated machine time.
v Thanks for the recommendation, we will balance it with collision operation and ring study.

u The committee encourages expanding the effort to improve the modelling of the current BT
in order to understand where the emittance blowup is occurring; e.g. how much a latticeerror needs to be increased in order to induce the observed emittance blowup.
v We began to understand where the blowup starts, etc. with limited instrumentations.

Injector linac status

K.Furukawa, Feb.2022

21

Summaryu Injector LINAC continues reasonable injections insimultaneous top-up injection mode.
u Emittance blow-up at the 2nd half of beam transport line isstill under investigation, but is partially relaxed recently
with finer parameter tuning to make injection and storage
beams match.
u The injector upgrade was discussed and will be
implemented in 7 categories for the final beam
parameters with higher bunch charges and lower
transverse and longitudinal emittances. Further upgrade
is also investigated.
Injector linac status

K.Furukawa, Feb.2022

22

Thank you

Injector linac status

K.Furukawa, Feb.2022

23

BackupInjector linac status

K.Furukawa, Feb.2022

24

Injector linac status

K.Furukawa, Feb.2022

25

DR Optics Change
H. Sugimoto(A) Optics using the operation (B) Low emittance optics (C) Half-low-emittance optics(Failed in Apr.2021)(Feb.2022)<latexit sha1_base64="y9SdN5Mg3oDttcIKPuHQG98LMzY=">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</latexit>"x = 24.8 nm↵p = 0.0080(⌫x , ⌫y ) = (9.38, 6.28)

Injector linac status

K.Furukawa, Feb.2022

Linac Beam Property Requirements

Linac Beam Parameters for KEKB/SuperKEKB
Stage

KEKB (final)

Beam

e+

e–

e+

e–

e+

e–

e+

e–

e+

e–

EnergyStoredcurrent
Life time(min.)

3.5 GeV

8.0 GeV

4.0 GeV

7.0 GeV

4.0 GeV

7.0 GeV

4.0 GeV

7.0 GeV

4.0 GeV

7.0 GeV

1.6 A

1.1 A

1.0 A

1.0 A

–

–

1.8 A

1.3 A

3.6 A

2.6 A

150

200

100

100

–

–

–

–

6

6

primary e- 10

Bunch charge
(nC)
Norm.
Emittance

Phase-II (achieved)

310

Phase-III (final)

primary e- 10

1

0.5

1

2

2

→ 0.4

4
→4

200/401400

Phase-III (interim)

primary e- 81→1

Phase-I (achieved)

1000

130

(γβε) (mrad)

150/30100/40100/1540/20(Hor./Ver.)(Hor./Ver.)(Hor./Ver.)(Hor./Ver.)150(Hor./Ver.)

Energyspread

0.13%

0.13%

0.50%

0.50%

0.16%

0.10%

0.16%

0.10%

0.16%

0.07%

Bunch / Pulse

2

2

2

2

2

2

2

2

2

2

Repetition
rate

50 Hz

25 Hz

25 Hz

Simultaneous
top-upinjection(PPM)

3 rings(LER, HER, PF)

No top-up

Partially

50 Hz

50 Hz

4+1 rings (LER, HER, DR, 4+1 rings (LER, HER, DR,
PF, PF-AR)
PF, PF-AR)

u Gradual improvements keeping light source injections
Injector linac status

K.Furukawa, Feb.2022

27

Alignment

Emittance Preservation
u Offset injection may solve the issueu Orbit have to be maintained preciselyu Mis-alignment should be <0.1mm locally, <0.3mm globally
Mis-alignment leads to Emittance blow-up

Orbit manipulation compensates it

100 samples
Sugimoto et al.
Injector linac status

K.Furukawa, Feb.2022

28

Alignment

Floor vertical movement
in a half year from summer to winter

C3

Injector linac status

11

18

28

38

Higo et al.

48

K.Furukawa, Feb.202229