Injector linac status

Masanori Satoh (KEK, Acc. Lab.)for Injector Linac Group

B2GM, 2021/2/8
1

Contents• Operation overview• Recent progress• New accelerating structure• Summary

2021/2/82Injector: Simultaneous top-up to five rings• Photocathode RF gun for HER injection• Thermionic gun for LER (via DR), PF, PF-AR

B SectorA Low emittance RF e- gun
Thermionic DC e- gun
1.1 GeV

1.5 GeVC

12 e+DR 3e+ target

e-:Chicane

45Pulsed quads, steering magnets
HER: 7 GeV e-

4.219 GeV
same energy

ee+ target1.5 GeV
3CDecelerate

1PF-AR: 6.5 GeV eor 5 GeV

LER: 4 GeV e+
1.1 GeVe+2PF: 2.5 GeV e-

345

HERLERPF

2021/2/84AR

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: 1 nC
・PF injection: 0.3 nC
・PF-AR injection: 0.3 nC

RF e- gun
（GR_A1 for HER injection）

Beam repetition of thermal gun limit: 25 Hz => 50 Hz5(LER + PF + PF-AR)・Pulsed bends, chamber, DC quads were replaced. Two BPMs
were newly installed in merger line for precise beam tuning.
(magnet coil and chamber heating issues have been resolved.)e- beam (rf gun) improvement• Summer shutdown in 2020
– Cathode (Ir7Ce2)– Cathode type: Backside electron irradiation heating cathode =>original type
– DOE in 1st laser line for reshaping transverse laser profile– Laser position feedback has been implemented.
– Inter pulse laser cleaning has been implemented.

2021/2/86

Reshaping of rf gun laser w/ DOE• Diffractive Optical Element (DOE): Laser beam homogenizer(DOE for UV laser is a world first.)• Inside vacuum chamber (sensitive to dust). Laser power loss ～ 15%• For 1st laser line only. 2nd laser line has not enough space.

Laser position feedback

R. ZhangWire scanner (B-sector) @ 2 nC

Best emittance

M. YoshidaInter pulse laser cleaning• Laser cleaning works fine for recovering Qe.
• Usually, it takes 30 min. ～ 1 hour. (every two weeks).
• Fast switching scheme between beam on (rf on) and laser cleaning (rfoff) was tested (Jul. 2nd, 2020).
• In summer shutdown of 2020, this scheme was implemented foroperation software.
%nC

e- bunch charge (5 Hz)

Input laser power

Laser cleaning on (5 Hz)

9M. Yoshidae- bunch charge (2020a, b, c)(rf gun)(BT)

Ir7Ce22020c

2020a, bCharge feedback ON

Summershutdown

2021/2/8

10

e+ beam improvement• Flux concentrator (FC)– After large discharge in phase2, not possible to apply high voltage.

– 2019/1 ～ 2020/6: 2.5 kA operation (design operation current: 12 kA)– New FC was developed w/ Cu alloy (NC50: Cu-Si-Ni) instead of oxygen freecopper. It has worked fine in 2020c w/o any significant trouble.

• DC solenoid section in Sector1 (positron capture section)– DC steering magnets (x4) and BPMs (x4) have been installed for improving
the beam loss in DC solenoid section.
– Solenoid field is increased to design value.
2021/2/8

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FC assembly, base summary
Phase 1

Phase 2Phase 32019
autumn2020
spring2020
autumn2021
winter～delivery

removalPresent status（2020/6）

Assembly 1

Before2015

2017/3TunnelAssembly 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 for
operation

remarkFC base 5

2016/7

FC base 6

2017/11

Reserved

FC base 7*

2019/10Finished longterm test

FC base 8**

2020/5

Under test

Final version
modifiedFC base 9**2021/3

Under design

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

red： operation
blue： spare
black： test bench

Hardening(Toyama)

Y. Enomoto

Positron yield improvement• Positron yield has been increased w/ new FC.
• Stable operation w/ design current (12 kA)

simulation～ 2020b2021/2/8• New FC (design current)• Steering magnets insolenoid section mitigate
FC base8 (new FC)
beam loss in DC solenoid
in 2020c
section.
FC base5 (previous FC)• DC solenoid current canin 2020a, b
be set at design value.

2020c

Y. Enomoto
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e+ bunch charge history (2020a, b, c)(from e+ target)(before LTR)
(linac end)
2020c
(BT)

2020a, b•

Beam loss in Sector2 should be cured.
Additional steering magnet in Sector1, 2 (‘21 summer)• Some DC quads => pulsed quads in Sector1, 2(‘22 summer or later)

Summershutdown

2021/2/8

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New accelerating structure (1)• Old accelerating structures (fabricated 35 years ago) are deteriorated.
(damaged coupler, water leakage). Designed for 8 MV/m (PF injector),
now used at 20 MV/m since KEKB project.
• No good spare (Spares also suffer from power reflection and excessivefield emission)• Toward U(6s), damaged structure should be replaced.

15H. Ego, B2GM, June 2019

New accelerating structure (2)• New structure has been developed. (improved couplerdesign)• Unit energy gain is improved to 180 MeV from 160 MeV.
• In this winter (Jan.), one unit (Sector4) was replaced by newone. It works fine.
– Three units will be installedin Jan. 2023 (FY2022).

• 10.75 GeV operation in 2021c(e+ : 4.071 GeV, e- : 7.124 GeV)

– Linac: possible w/ 2 nC/bunch– BT: possible16• e+ 4.290 GeV, e- 8.465 GeV (both coil heating limit)

H. Ego, B2GM, June 2019

Summary• Simultaneous top up operation• New vertical pulsed bends and chambers in SectorA canwork up to 50 Hz. Before 2020c, it was limited up to 25 Hz(coil/chamber heating issue is fixed).
• e- beam– DOE, laser position feedback work fine.
– 2 nC operation. Best emittance ～ 11 um @ SectorB– Inter pulse laser cleaning scheme was implemented.

• e+ beam– New FC works well
– DC steering and BPM in solenoid section (Sector1)• New accelerating structure (1 unit, 4 structures) in operation17