Injector Linac Status
Fusashi Miyahara (KEK, Acc. Lab.)for Injector Linac Group

B2GM, Oct. 18, 2021

4+1 ring simultaneous injection
Beam injection to each accelerator has been stable.
Bunch charge [nC/bunch]
60 Klystron units

8-sectors (A-C,1-5)

Energy Knob

1.1 GeV e+Damping Ring

Thermionic gun

B

A

2LER

210 e- for e+ production

PhotocathodeRF gunJ-Arc
1.5 GeVHER

PF/PF-ARBCSECSC

12e+e+ capture section
target34chicane

5

Energy Knob

4.2 GeV

1.1 GeV

1.5 GeVC

12Acceleration3ECS

PF-AR

HER LERLER 4 GeV e+Stand-bye+ target e+PF

HER 7GeV
PF-AR 6.5 GeV

Acceleration

e-0.34Deceleration

5Beam energies for each beam modes after the J-Arc.

PF 2.5 GeV

Linac Beam Parameters for SuperKEKB
Stage

KEKB (final)

Beam
Energye+e–e+e–e+e–e+e–e+e–

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 GeVStored current

1.6 A

1.1 A

1.0 A

1.0 A––

1.8 A

1.3 A

3.6 A

2.6 A

Life time (min.)

150

200

100

100––––

66

Bunch charge
(nC)
Norm.
Emittance

Phase-Iprimary e10

primary e- 8→1→ 0.4

1

Phase-II

Phase-III (interim)

primary e- 10

10.5

1200/40
1400

310

1000

Phase-III (final)

130(γβε) (mmrad)

2.5

2100/60100/80100/1540/20(Hor./Ver.)(Hor./Ver.)(Hor./Ver.)(Hor./Ver.)

→

44

150
(Hor./Ver.)

Energy spread

0.13%

0.13%

0.50%

0.50%

0.16%

0.10%

0.16%

0.10%

0.16%

0.07%

Bunch / Pulse

2222222222

Repetition rate

50 Hz

25 Hz

25 Hz

50 Hz50 HzSimultaneous
top-up injection(PPM)

3 rings(LER, HER, PF)

No top-up

Partially

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

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

Photocathode RF gun
Diffractive optical element (DOE) was installed in 1st laser line from 2020c.
･ Elliptical flat-top (uniform) spatial distribution on
the surface of photocathode･ Low emittance e- beam generation･ High stability (Shot-by-shot variation ↓, Discharge ↓)･ No discharges due to strong convergence of laser

R. Zhang

without DOE

Before installationAfter installation
Goal

Electron beam emittance at BT1 (2nC, only 1st laser)(γεx , γεy )= (40,20)
q= 4 nC

DOE

Very low emittancebeam at BT1 wasachieved.

with DOELaser profiles onthe cathode.

Emittance at B-sector ( the end of first straight section)e- emittance history
M. Satoh
Current requirement: (γεx , γεy )= (100,80), 2 nC

Feedback systems (RF phase, energy, laserposition) have been enhanced, but preservationof low emittance beam is an issue.

Upgrade in this summer･ DOE for 2nd laser line has been installed･ New pulsed steering magnets have been installedDOE for 2nd laser line

Beam tuning is still in the process

A new DOE for 2nd laser line has been
installed this summer.

2nd line laser profile with DOE
Emittance measurement at B-sector for e- beam with DOSs (1st + 2nd)γεx = 14.6±1.6 [µm]γεy = 4.7±3.1 [µm]2 nC/bunchPositron Beam Status

Positron capture section

Y. Enomoto

Large Aperture S-band acc. structure (LAS)
Bridge Coil (BC)IFC= 12 kA

Solenoid
Tungsten target

Stable, no failure3.5 GeV e- beam

Flux Concentrator (FC)Current history of the FC

Positron yield

Y. Enomoto
design2020ab(運転)2020ab(study)

2020c

2021a

2021b

2020/7/1

2020/7/2

2020/10/12

2021/2/12

2021/7/6

Energy (e-)*

3.46 GeV

3.01 GeV

3.01 GeV

2.87 GeV

2.89 GeV

2.92 GeV

TargetBunch charge (e-)

10 nC

8.2 nC

8.3 nC

8.1 nC

8 nC

9.0 nC

CaptureSec. exit

e+/e- @ SP_16_5

0.58

0.23

0.38

0.51

0.55

0.59

e+ @ SP_16_5

5.8 nC

1.9 nC

3.2 nC

4.1 nC

4.4 nC

5.3 nC

2-sec. end

e+ @ SP_28_4-

1.6 nC

2.4 nC

2.5 nC

3.2 nC

3.5 nCDR to linac

e+ @ SP_DC_4-

1.3 nC

1.9 nC

2.1 nC

2.5 nC

3.0 nC

Linac end

e+ @ SP_58_4

4 nC

1.3 nC

1.9 nC

2.1 nC

2.5 nC

3.0 nCLER BTe+ @QMF8P_K**

4 nC

2.77 nC

2.95 nC

Plan to increase yields

e+ Capture Section exit
2-sector end
5-sector end
LER BT

Change in bunch charge at major point

Yields at exit of thecapture section almost
reached the design value• Increase primary electron• Decrease beam loss after thecapture section• Optimization of FC shape, etc.

FC current and positron yielde+ emittance history• Vertical emittance is kept low in BT1• Emittance becomes large in BT2(Explained in a later slide)Stability, Upgrades

Upgrade of Low level RFT. Miura

MO feedback system
Linac master oscillator feedback
system was introduced to makethe Linac RF phase follow the SuperKEKB ring rf phase.
FB OffFB On

Phase shifter for linac downstream (3-5 sector)
 Increase the number of rf bucket which synchronized with linac

Beam position variation upstream(green) / downstream (red) of acavity for bunch compression system(BCS) which located in the transportline between DR and linac.

RF phase feedback system
Phase feedback system stabilizes rf phases at exit of accelerating structures by monitoring rf of No Injection
Mode (NIM).
T. Miura

BeforeThe beam cannot be emitted until the temperatureof the acc. structures are stabilized if all klystrons areturned off.
= Waiting ~1 hour
After installation of the rf phase feedback
Beam operation is possible in ~3 minutes from RF ON.
In case of entering the linac tunnel, the operation
can be started within 10 minutes of leaving thetunnel.
Until the temperature is stabilized, it is necessary toinclude NIM in the injection pattern.

Variation of rf phase and temperature ofaccelerating structure

T. MiuraPulsed magnets
1) New pulsed steering magnets have been installed in this summer.

Y. Enomoto
Current stability of pulsed magnet
Required

Measured

Quad.

0.1%

< ~0.006%

Steering

0.01%< ~0.003%

2) DCCT monitors for pulsed magnet power supply have been replaced to high resolution them.
Upgrade plan

･ Adding more pulsed magnets  Increase the flexibility of beam tuning for each beam mode.
･ Development of a quadrupole magnet with large bore radius and its power supply.
･ Development of a fast pulsed steering magnet which acts only on the 1st or 2nd bunch.

Feedback Systems in Linac
Laser
Position feedback

Major feedback systems that contribute to bam stabilization

Laser line

Status

1stOK

Beam

Beam

StatusJ-Arc energy feedbacke-: 1st, e+: 1stOK

3-5 sector orbit feedbacke-: 1st + 2nd, e+: 1st + 2ndOKLinac end orbit feedbacke-: 1st + 2nd, e+: 1st + 2ndOKSY3 energy feedbacke+: 1st + 2ndOKBT energy feedbacke-: 1st, e+: 1stOK

A-sector orbit feedback (new)e-: 1st + 2nd, e+: 1st + 2nd

Installed in 2021c

C-sector orbit feedback (new)e-: 1st + 2nd, e+: 1st + 2nd

Installed in 2021c

RFObjectStatusMaster Oscillator (MO) feedback

RF phase between LER/HER and LinacOKRF phase

RF phase of acc. structure, rf-gunOKBeam orbit stabilitypositron (•1st bunch,◦2nd bunch)electron (only 1st bunch)

After DR
Linac end

Before DR

J-Arc
Linac end

Gun exit

Beam position at a particular
bpm shows correlation with theinjection efficiency

Injection efficiency and beam orbit variation (10 minutes average) in 25 days (June 2021) at major point.
The RMS of beam position is shown in gray line.

Room for improvement
・Suppressing Daily variation
・Match the orbits of the 1stand 2nd bunch
The causes are under investigation• The 2nd line DOE may
reduce the variation atgun exit
• Orbit feedback using newpulsed steering magnets

Energy MarginBeam mode and Energy
Measured maximum beam energy at Linac end [GeV].

H. EgoNormalOperation

Additional Unit (Normally in standby mode)
KL38

KL38, KL57

KL38, KL57, KL11

KL38, KL57, KL11, KL15

KBE (e-) (1.9 nC)

6.943

7.130

7.311

7.438

7.458

KBP(e+) (1.2 nC)

4.000

4.160

4.320--･ RF unit (KL*) provides rf to 4 accelerating structures.
･ Energy gain in a unit is ~160 MeV.
･ The actual beam energy is slightly lower than the maximum
value in order to align energy of bunch head and tail.
Standby units

Beam test of higher energy operationLER

HER

Linac status10.579(Normal)

4.000

7.007

OK

10.657

4.029

7.059

OK

10.706

4.048

7.091

OK

10.751

4.065

7.121

OK

10.810

4.087

7.160

OK

𝒔𝒔 [GeV] ##: Crossing angle: 83 mrad

Energy knob :KL51, KL52
Standby  Acc. : KL57
Standby:
KL38
Higher energy operations keep one standby unit (KL38).

Current issue

Emittance growth of electron 2nd bunch
Bean injection of electron 2nd bunch is difficult due tothe large emittance

1st bunch

Emittances measured in HER BT
1st bunch

2nd bunch

Horizontal: γεx [µm]16.4±2.045.9±3.6

Vertical: γεy [µm]9.6±1.867.7±6.5

2nd bunch

thicker than 1st bunch

Beam profiles at 3-sector measured by wire scanner

The degradation of emittance may be occurring downstream from positron capture section.
The cause is still under investigation.

M. YoshidaLarge emittance growth in BT

BT2

BT1

HER BT（e-)

LER BT (e+)

Emittances of 1st bunch measured in BT1(wire), BT2(OTR) (Example)

2021.6.10

WS at BT1γεx [µm]

29.8±6.4

γεy [µm]

48.6±8.6

OTR at BT2BT2/BT1

82.8±3.3x 1.7

Emittances measured in BT1(wire), BT2(OTR) (Example)

BTp1

1st bunch

2nd bunchγεy [µm]

2.21±0.62

3.53±0.26

N. Iida, T. Mori

BTp2

1st bunch

BT2/BT1

2nd bunch

BT2/BT1γεy [µm]62.7±13.5x2959.9±7.1x17

Degradation of accelerating structures
Electrical discharge and leakage of cooling water have been occurred due to degradation over time.
At August 2021

H. EgoWater leakage

One accelerating structure failure leads to stop of 1 unit = 4 acc. structure = ~160 MeV.
･ 12 new accelerating structures are in production.
･ Degraded acc. structures are scheduled to be replaced starting in the summer of 2022.
(Replacement will be done on a unit-by-unit basis)･ More new acc. structures will be manufactured, but the quantity will depend on the budget.

惠郷Appendix

Assembly, base management (2021/1 ver.)Y. Enomoto
Phase 1

Phase 2Phase 32019 Q4

2020 ab2020cdeliveredremovedpresent

Assembly 1<20152017/3

In tunnel

Assembly 2

2016/3In operationAssembly 3

2017/11

Test bench

FC base 1<2015

Test

FC base 2<2015

Test

FC base 3<2015

FC base 4

2017/3In tunnel

2018/9In tunnel

2020/9In tunnel

NoteFC base 5

2016/7

FC base 6

2017/11

Test bench

bad quality

2019/10

Test bench(back up)

New material

FC base 8

2020/6In operationFinal version

FC base 9

2021/3

Test bench

Saper for Finalversion

FC base 7

Material test started in 2018/10

9号機以降は当面製作予定なし

in operation
spare
test bench

26

Correlation between position and injection efficiency (KBE)
There is a correlation between beam position atthe gun exit and injection efficiency.
Variation of bunch profile (transverse/longitudinal)?
Data: 6/5-6/30

Correlation at SP_61_H1 with large dispersion function.

Data: 6/5-6/16

Correlation between SP_A1_G / SP_61_H1 andinjection efficiency. The correlation coefficient are
shown at the top of the figure.

Correlations with other BPMs are givenin the appendix.
There is no clear correlation in other BPM.
(Not all BPMs have been checked.)Correlation between position and injection efficiency (KBP)

Correlation between yposition of 2nd bunch at
SP_61_3 and injection
efficiency.

Correlation between SP_DC_4 (1st BPM in
Linac after DR) and injection efficiency.

The cause of the difference inthe orbit after the DR needs tobe investigated carefully.