Injector status
2021.06.21
Mitsuhiro Yoshdia

1Linac Beam Property Requirements

Linac Beam Parameters for KEKB/SuperKEKB
Stage

KEKB (final)

Beame+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––––

66

primary e- 10

Bunch charge
(nC)
Norm.
Emittance

Phase-I (achieved)

Phase-II (achieved)

Phase-III (interim)

primary e- 8

primary e- 10

1→11→ 0.4

1400

310

1000

Phase-III (final)

0.5

1224→4200/40
130(gbe) (mrad)

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

22222

22222

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

2

Recent injection
by*=1mm
The injection
efficiency andBG are notbad for thistotal current.

2-bunchinjection
23Hz injection

Loss monitor at the injection point
was high.
The septum positionis effective to theinjection

The measured emittances inthe upper part of e-line have
kept lower level.

2-bunch injection orbits
LERHER

5

HER 2-bunch injection
Theemittances of
the 1st bunch
arevery small.

1st bunch

2nd bunchgex [mm]16.4±2.045.9±3.6BMAGx

1.00

1.13

gey [mm]

9.63±1.78

67.7±6.5

BMAGy

1.31

1.35

Theemittances ofthe 2nd bunch
are large.

6May/18

The injection rate was almost
same as 1-bunch injection
even with 2-bunch.

(6.25Hz)May/26
Injection efficiency of 2nd bunch
Injection efficiency of 1st bunch

1-bunch 2-bunch(6.25Hz) (6.25Hz)

Injection rate

Injection rate
repetition rate

2-bunch1-bunch(12.5Hz)(25Hz)
The injection rate became
twice just due to the double
repetition rate

The injection efficiencies of 1st and 2nd bunches
7were 70% and 40%

LER 2-bunch injection study
Bunch-1

Bunch-2

T. Mori

BT1BT2y only

• Although there is still an enlargement of emittance from BT1 to BT2,8ndstStatus of 2 bunch is comparable to 1 bunch.

LER 23Hz injection• The injection
efficiency fromBCM at 23Hz
becomes lower
than that at 12.5Hz.

9

Injection BG in LER 23 Hz w/ DR 2-pulse operation
H. Sugimura

23 Hz 1-pulse
12.5 Hz 1-pulse

23 Hz 2-pulse•

stored time in 23 Hz• 40 ms at 1-pulse• 80 ms at 2-pulse→ 23Hz 2-pulse is lower BG than 1-pulse→ Damping time is longer thanthat of design value

Now the 2-pulse operation in the DR is availab
10Positron generation

11

Positron generation• Update from previous B2GM (2021/2 = before 2021a)– Charge is increased by beam adjustment• No hardware change• 5.4 nC after target, linac end 2.9 nC with primary electron charge of 9.6 nC• Future upgrade for 4 nC
– Improve target to DR transportation efficiency• 1-5 acceleration gradient is half than design.
– Dummy load problem => Improved dummy load development is ongoing (Ego)• Pulse magnet installtion– Increase pulse steering (2021)– Replacement from DC Q to pulsed Q (2022)– Positron generation efficiency improvemnet• Increase the FC current (Upgrade the power supply by RF group at 2022)– Primary electron (Injector )• Limited by PF dark current
12• Test plan for the maximum charge of primary electron at 2021/7

SuperKEKB positron source
FC head + BC + target = FC assembly
LAS (large aperture S-band)

BC (bridge coil)
W targetFC(flux concentrator) headsolenoid13

Positron yield vs FC current
Design (0.58)
Present(Further tuning was done
after this measurement.
Now the yield almost
reached design value.
See next page)

Before upgrade(To avoid discharge,
FC current was limited very low)14

Recent status (2021ab)••

Primary electron

e+/e- design•

Before DR

After DRFirst BMP after target

Linac end

Primary beam
– 96% (9.6 nC / 10 nC)
Positron yield（e+/e-）– 100% (0.58 / 0.58)
transport– Target to DR• Should be improved– DR to Linac end• Little loss

Hardware upgrade
Further beam tuning
design2020ab2020c2021a2021b

Energy (e-)

3.5 GeV

3.5 GeV

3.5 GeV

3.5 GeV

3.5 GeV

primary charge (e-)

10 nC

8.4 nC

8 nC

9 nC

9.6 nC

e+/e-

0.58

0.24

0.51

0.58

0.58

e+ @ first BPM after the target

5.8 nC

2.0 nC

4.1 nC

5.1 nC

5.4 nCe+ @ before DR-

1.6 nC

2.5 nC

3.2 nC

3.3 nCe+ @ after DR-

1.4 nC

2.1 nC

2.9 nC

3.0 nCe+ @ Linac end

4 nC

1.4 nC

2.1 nC

2.9 nC

2.9 nC

Transport optimization
is not sufficient

15Gradient after the target
nameDesign gradient(MV/m)

Operation gradient(MV/m)
2020/10/30

Max gradient @ KLY
power = 40 MW

AC_15_1

14.0

7.3

17.0

AC_15_2

14.0

7.3

17.0

AC_16_1

10.0

11.3

12.2

AC_16_2

10.0

11.3

12.2

AC_16_3

10.0

11.3

12.2

AC_16_4

10.0

11.3

12.2

Data from H. Ego

Due to the load problem, gradient of the first andsecond acc. structure after the target is low.
This may cause poor bunching which can be one of thereason for large beam loss during transportation to theDR.
https://www.pasj.jp/web_publish/pasj2014/proceedings/PDF/SAP0/SAP045.pdf
https://doi.org/10.18429/JACoW-IPAC2014-THPRI047
16

Transport between Target and DR – replace DC Q with pulsed Q
Surrounding Acc. Structure = impossible to be pulsed

Between Acc. Structure = possible to be pulsed

Replace several DC Q magnets with pulsed Q magnets (2022～).
Also important for preserving electron emittance.
17

Short term plans（1～2 years）
Major upgrade was done in 2020 summer shutdown
Increase positrons up to 4 nC by several minor improvements.
Now, it’s time to consider new strategy for long term goal.

••••

•

Increase Acc. Gradient at 1-5 unit（H. Ego）
– New load for the Acc. structure（under development）
Install pulsed magnets between target and DR（T. Natsui、K. Yokoyama、Y. Okayasu、T.
Kamitani、Y. Enomoto）– Increase steering magnets（2021）– Replace DC Q magnets with pulsed Q magnets（2022）
Fast BPM （T. Suwada、F. Miyahara、A. Rehman）– Under test
Increase FC current（RF group）– Thanks to new material, higher current operation may be possible.
• Stable operation has been confirmed up to13 kA at test bench.
– Upgrade of the power supply is necessary（2021～）
Increase primary electron charge（Yoshida）– It’s not difficult to increase current by increasing heater current– Dark current to the PF ring issue have to be solved

Electron generation

19

Pulse to pulse switching:rf e- gun/thermionic e- gun

Thermionic DC e- gun (GU_AT)
w/ 2 subharmonic bunchers and 2 bunchers

・e+ production e-: 10 nC (for LERinjection)・e- study/HER injection: 2 nC
・PF injection: 0.3 nC
・PF-AR injection: 0.3 nC

RF e- gun
（GR_A1 for HERinjection）
Beam repetition of thermal gun limit: 25 Hz => 50 Hz(LER + PF + PF-AR)・Pulsed bends, chamber, DC quads were replaced. Two BPMs
were newly installed in merger line for precise beam tuning.
20(magnetcoil and chamber heating issues have been resolved.)

RF-Gun• Newly improved Ir7Ce2 cathode keeps to generate
2 nC electron without cleaning.
(QE was decreased by human error at the end ofMarch, and currently 1.5nC by one side laser. )• Stable operation with low field operation(Es=35.5kV, 866ns)

Quantum efficiency of IrCe

2-bunch (Es=35.5kV, 866ns)

Wire scanner (BT) 4/26 lowest emittanceFuture upgrade of RF-Gun for 4 nC
• New RF-Gun cavity– Vacuum improved and short pulse RF-Gun (Travelling wave
cut disk structure with cathode choke cell)• Improve IrCe cathode– KEK made Ir7Ce2 cathode– Development of the cleaning method• Laser upgrade– Power up and DOE installation of 2nd laser– Yb:YAG rod laser for lower energy spread• Laser upgrade– Power up and DOE installation of 2nd lase

New RF-Gun cavity
RFVacuum improved andshort pulse RF-Gun(Travelling wave cut disk structurewith cathode choke cell)

Coupling cavity(no field)

VacuumPump

Travelling wave

RF Double choke

Laser upgrade of FY2021- Higher power and multi-purpose usage of 2nd laser
HERInjection(KBE)

4 nC generation• High power laser module (15kW pump)• DOE

DOE for2nd laser

2ndlaserIntermediatecathode laser
cleaning

PF / PF-AR
Thermal electron gun can be optimized
for positron generaion.

- Yb:YAG rod laser for lower energy spread=> Lower emittance and energy spreadFuture LINAC upgrade planChallenges in Linac upgrade• Achieving the both of higher injection beam charge and lower
transverse/longitudinal emittance• Maintaining higher availability and stability• Establishing injection energy for higher resonances• Solutions with upgraded hardware– Precise pulsed magnets and kickers– Movable girders for quads and structures– Energy compression system (ECS)– Accelerating structures to replace aged ones
– Low emittance and high charge RF gun– High efficiency positron capturing– Replacement of capacitors including PCB at power converters• Polarized electron beam design for the futureUpgrade plan (2022 – 2026)
BA1C2345Injector

Fast pulsed kicker

RF-Gun upgradeMoverBT

PCB capacitor replacement

Positron capture section

Electron-ECS

Accelerating structure
replacement• Recent injection

Summary– HER:
• 1.5nC injection for lower emittance and higher injection efficiency• 2nd-bunch injection efficiency is low (Beam blow up at 1-sector)– LER:• 2nC injection and 2-bunch injection is stabele• 23Hz injection is ready to use• Short term upgrade for 4nC generation– LER : New RF-Gun and laser upgrade– HER : High efficiency positron capturing– Transportation upgrade (pulse steering etc,.)• LINAC upgrade 2022-2026– Precise pulsed magnets and kickers– Movable girders for quads and structures– Energy compression system (BTe-ECS)– Accelerating structures to replace aged ones
– Replacement of capacitors including PCB at power converters