RF 電子銃の進展と入射器の現状
周 翔宇

第118回Bファクトリー計画推進委員会
2020.9.30

Linac Beam Parameters for KEKB/SuperKEKB
Stage

KEKB (final)

Beame+e–e+e–e+e–e+e–e+e–Energy

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

primary e- 10

Bunch charge
(nC)
Norm.
Emittance

Phase-I

Phase-II

Phase-III (interim)

primary e- 8

primary e- 10

1→11→ 0.4

1400

310

1000

Phase-III (final)

0.5

12

2→200/40
130(gbe)(mmrad)44

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

22222

22

2

2

2

Repetition
rate

50 Hz

25 Hz

25 Hz

50 Hz

50 Hz

Simultaneous
top-upinjection(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)

current stage

Pulse to pulse switching:rf e- gun/thermionic e- gun
QTWSC
RF-GunThermionic DC e- gun(GU_AT)・e+ production e-: 10 nC (for LERinjection)
・PF injection: 0.3 nC
・PF-AR injection: 0.3 nC

RF e- gun
（GR_A1 for HER injection）
・e- study/HER injection: 1 nC

Pulsed bends for simultaneous top up(since2018 summer)
CDS
RF-Gun3

CDS電子銃• New Cavity• New vacuum chamber

2020.9.25

Laser system development
Grating pairstretcher

Yb fiberoscillator

Nd:YAG DPSS
amplifierYb fiber
amplifierμJ

Sub nJ

Wavelength
conversion

mJ

1st line

10 ps

2nd line••…

• Final state Pump @ 808 nm 1.2 kW
Oscillator and pulse pickers
×12=14.4 kW=3.6 J DPSS (2020.7)
are synchronized with the• Output Power: ω(1030 nm):32 mJ,
RF signal
2ω(515 nm):13 mJ,
Fiber structures with no4ω(257 nm):1.8 mJ
cooling system
大型 DPSS モジュールへ交換 (2020.7)
1st line only

…

…

…

…

… 1 – 25 Hz double bunches

E.O.

SOARepetition frequency 114.24MHz
Synchronized with 2856 MHz RF trigger…

10.38MHz

Pump beam 25 Hz constant 2 beam sources 1 – 25 Hz single/double bunches selectable Several month 24h/day running without maintenance

Pockels cell1 – 25 Hz single bunch

Laser transport line
A1 ground laser hutTunnel A1 RF gun box

90o RFgun

2nd line

BBO

Delay line

HWP

1st line

Flip mirror

BBOPolarizer

HWP

HWP

Polarizer

9 m long
pipe line•Monitoring all the laser situationand synchronization state.

•Remote control system•

Realize real time UV laser beamprofile monitor•

Improve temperature stability inthe laser hut•

Beam position monitor and auto
feedback program

0o RF gunBBO
Laser roomon thegroundKLY Gallery

virtualcathodediagnostics

Laser line to RF-Gun

TunnelRF-Gun13-26

GR_A1用レーザーポジションフィードバック
制御システム (2020.9.24)
従来のやり方：X/Yを手動調整
beam profile monitor●現在のレーザーポジション●ポジションの変化履歴□この範囲から外れるとフィードバックが動作する。
・ポジションの調整はA1地上ハット内のピエゾアジャスタ付きミラーマウントで行っている。
・実際のフィードバックは EPICS IOC で行っている。
フィードバック動作確認時のポジションProfile reshaping (2019)• Aperture of the beam illustratedx’ EmittanceIxr
Laser spatial distribution

Linearity
Phase space• 秋運転から、2ndラインのみ• ビーム径を調整

Reshaping of laser spatial distribution• Laser beam homogenizer: Diffractive optical

1st line only (2020.7)

element (DOE) for flat-top distribution• Special compact vacuum chamber is designed,
due to the micro structure is weak at dust
 No electrical discharge with high chargecommissioning Laser beam stability is also improved Low emittance effect is expected
×Beam size is fixed (For high charge)

均一なプロファイル

QE & Lifetime
On line

Ir5Ce

1.5×10-4

1.5×10-5 （3-2）

Ir7Ce2 + Heating (2018)

1.0×10-4

1.5×10-5 （A1）

Ir2Ce + Heating +Better vacuum(2019)

5.0×10-4

2.0×10-4 （A1）

Ir7Ce2+ Laser Clean (2020)-1.0×10-4 （A1）

The QE dependence of the laser energy

The QE transition of the time••

QE decreasing by increase the laser energy
Beam Charge
1st laser
2nd laser
1st+2nd laser

2.5

2.0

•100

4.0E-05

Transition of quantum efficiency after laser cleaning

80

1.560

1.040

2020/3/12 15:42

3.5E-05

2020/3/26 16:04

3.0E-05

2020/4/20 16:15
2020/5/7 16:55

2.5E-05

2020/5/12 11:52
2020/5/27 10:03

2.0E-05

2020/6/3 10:59

-6



2020/2/16 17:44

Quntum Efficiency [10 ]Quntum Efficiency
1st laser
2nd laser
1st+2nd laser

120

The QE drops rapidly, from about 50 hours aftercleaning.
After that, it appears to be gradually decreasing.

QE

3.0

Beam Charge [nC]

Off line

2020/6/10 10:06
1.5E-05

0.5

2020/6/17 11:49

20
2020.03.27

0.0
0100

200
300
Laser Energy [uJ]4000500

2020/6/23 10:25

1.0E-05
5.0E-06
0:00:00

72:00:00

144:00:00

216:00:00
Timing288:00:00

360:00:00

432:00:00

Bunch Charge feedback
e- bunch charge (nC)

KEKB e- (GR_A1) CHG Feedback (2020.4)

Chargefeedback ON

1.0 nC
0.7 nC• チャージ量が指定値 となるよう、レーザーエネルギーを調整する• 調整方法:波長板を調整する。(自動・手動)

Laser cleaning / Focused laser size

Irradiation of shorter-wavelength laser (2nd laser line only)
Scan using focused laser beam without RF
Laser cleaning works for recovering QE in maintenance day (every two weeks)
Automatically running by program

2/6 Before laser cleaning Iris:2.0mm
2/6 Laser cleaning Iris:2.0mm

Charge (nC)
1.6
1.4

QE = 3.7 x 10-5

1.2

Focused laser size
1/3(1mJ/mm2)

1

QE = 2.4 x 10-5Focused laser size
1/2(0.5mJ/mm2)

0.8

0.6

QE = 1.2 x 10-5

0.4
0.2
0

2.3

2.35

2020.2

2.4

2.45

2.5

2.55

2.6

2.65

2.7

2.75

2.8

ROT-X

量子効率Mapping と Laser
Clearningプログラムを開発した

常時Laser Cleaning On(量子効率の長寿命化 )Laser energy [a.u.]

200

Laser output

Charge

1Hz150

3.5
3
2.5
2
1.5
1
0.5
05Hz(2.5nC)

Charge feedback (1nC)1005Hz50

02020/7/2 3:36

2020/7/2 8:24

2020/7/2 13:12

1Hz
2020/7/2 18:00

stop

2020/7/2 22:48

2020/7/3 3:36

2020/7/3 8:24

Time50

1.4

45

1.2

40

135

0.8

30
25

0.6

15 minutes

0.4

20
15
10:51:10

0.2
0
11:05:34

11:19:58

11:34:22

11:48:46• Adjust the laser output energy tostabilize the charge• Continuous laser cleaning between
pulses• No discharge (maybe due to DOE)
• Maintains at 2.5 nC

Charge

2nd line (clean laser) : 300μJ

1st line: ~700μJ

e- beam emittance (～ 1 nC)

・ ex,y ～15 mm at Sector-B, Sector-C• Emittance growth at BT2 in both directions.
• Emittance could be increased at around solenoid section in Sector1.

150

BC

３5

BT1 BT2

HorizontalBC

３5

BT1 BT2

Vertical

Linac

2020/9/28

14

Steering magnet and BPM in solenoidsection• There is no BPM and steering magnet between e+ target and 16_5unit.
• DC steering (x4) and BPM (x4) will be installed in this summer
shutdown.
• It could be help to cure e+ beam loss and e- beam emittance growth.
Target: e+ W target
FC_15: flux concentrator
SC: screen monitor
AC: accelerating structure
SP: BPM
SL: solenoid
BM: bend
PX: horizontal pulsed steering
PY: vertical pulsed steering

SY, BPMSX, BPMSX, BPM15
2020/9/28

No BPM and steering magnet

e+ beam emittance (～ 1 nC)• e+ beam emittance in linac and BT1 are smaller than current goal.
• Emittance growth at BT2 in both directions.
The reason for the emittance
growth from BT2 is not clear.

More studies are needed.

150

DR

35

BT1Horizontal

BT2DR

35

BT1BT2

VerticalLinac2020/9/28
2020/9/28

16

FC assembly, base summary
Phase 1

Phase 2Phase 32019
autumn2020
spring2020
autumn2021
winter～deliveryremovalPresent status（2020/6）

Assembly 1

Before 20152017/3TunnelAssembly 2

2016/3

Beam line

Assembly 3

2017/11

Test bench

FC base 1

before 2015

Trial productFC base 2

before 2015

Trial productFC base 3

before 2015

FC base 4

2017/3

Assembly 1

2018/9Tunnel2020/9Beam line foroperation

remarkFC base 5

2016/7

FC base 6

2017/11

Reserved

FC base 7*

2019/10Finished longterm test

FC base 8**

2020/5

Under testFinal version
modifiedFC base 9**2021/3

Under design

Final version
spare••*Base 7, 8, 9 (head : Cu → NC50, return yoke : SS400 → permendur)
17**Base 8, 9 Shape optimization (insulation, leakage magnetic field)

red： operation
blue： spare
black： test bench

Hardening(Toyama)

Y. EnomotoComparison FC baseMaterialShapeRemark

For e-For e+

Base 5（in operation）

OFC+SS400

Old design

12 kA in beam line
large slit gap△○

Base 7NC50+permendur

Old design

4.5 months test○○+ *Base 8NC50+permendur

New design(optimized)

Cooling water leakage was found.
(already fixed and tested during 4 days)◎○+ *All FC bases achieve 12 kA in test stand. (*) return yoke (permendur) makes higher magnetic field.
Base 8・Optimized yoke shape・Reinforced insulation (FC head support)

Base 7 and older

Test result of new FC: 2020/1 – 2020/6

Replace FC base 7 => 8During long term test, no trouble (discharge and vacuum pressure problem)
FC base 7 test: ～ May 2020
FC base 8 test: June 2020 ～Y. Enomoto19

Positron yield by FC (base 5) beam test

Y. Enomoto

Positron yield is 35% lower
than the simulation.

(July 3., 2020)?

Operation point (Run 2020a, b)(2.5 kA, yield = 0.23)

e- bunch charge @target = 8 nC・Differences between exp.
and sim. conditions.
( E/B field, primary beam
direction/position, em
shower sim. etc.)

The cause of the difference
is not clear.

We’ve started a detailed
investigation.
Ratio of bunch charge of positron at capture section exit to primaryelectron vs FC current.

There are no BPM and steering magnet until 17 m downstream of the target.
( Only 6 acc. structures and solenoids)
2 stripline BPMs and 2 BPMs for e+ and 4 steering magnets will
be installed in this summer.

Abnormal energy beam- Collimator at ECS of linac end • Klystron down or rf phase trip could cause energy change.
• In the case of e+ beam, ECS (in linac end) can correct it to a certain
extent. Beam can go through BT and into MR.
• To prevent such beam, collimator will be installed in this summer
maintenance.

2020/9/28

21Y. Okayasu

Summary Bunch charge
 Stable and enough bunch charge in this stage
 e-: 1.3 nC (from gun), 1.0 nC (linac end)
 e+: Primary e-: 11 nC (from gun), 9 nC (on W target), e+ : 2 nC (after target), 1.2 nC (linacend), 1.2 nC (BT) RF電子銃の進展
 90°CDS銃を準備した
 DOE 導入 / 1st レーザー増強• ジッターは全く無くなった• カソード寿命が長寿命化

 常時Laser Cleaning On （2nd専用レーザー）• 1, 5 Hz で Inter Pulse Laser Cleaning 実施 (300μJ)• 2.5nC で維持でき• Trigger システムを改造

 Position monitorを設置
 e+の進展 FC入り替え（High bunch charge）
 SolenoidにSteering magnet と BPMを追加• e +ビームの損失とe-ビームのエミッタンスの増加を解消するSummary 2
 Beam abort 問題の改善
 Pulsed magnet misfire (orbit)• Control software have been improved.

 Install collimator at ECS (Linac end) in this summer shutdown.
 50 Hz operationの対応
 Vertical pulsed bends and chambers will be replaced new one for 50 Hz operationof thermionic e- gun (LER, PF, PF-AR) in this summer shutdown.

 問題点
 Emittance growth at BT2
 Reproducibility
 Low emittance w/ high bunch charge (～ 2 nC)