Injector challenges

2020.2.10
M. Satoh (KEK, Acc. Lab.)for Injector Linac Group

14th annual Belle PAC Review meeting,Feb. 10-12, 2020
1

Contents• Injector operation status• e- and e+ beam sources• Accelerating structures• Beam controls– Energy and orbit feedback loops– Dispersion correction– Emittance• Summary and plan
2020/2/10

2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

100100––––66

primary e- 10

Bunch charge
(nC)
Norm.
Emittance

Phase-I

Phase-IIprimary e- 8

10.5

1310

2→

1000

130(gbe) (mmrad)

42→ 0.4

200/401400

Phase-III (final)

primary e- 10

1→1

Phase-III (interim)4

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

2222222222

Repetition rate

50 Hz

25 Hz

25 Hz

Simultaneous
top-upinjection(PPM)

3 rings(LER, HER, PF)

No top-up

Partially

2020/2/10

350 Hz50 Hz

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

Injector overview• Photocathode RF gun for HER injection• Thermionic gun for LER, PF, PF-AR
B SectorA Low emittance RF e- gun
Thermionic DC e- gun
1.1 GeV

1.5 GeVC

12 e+DR 3e+ targete-:Chicane

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

4.219 GeV
same energy

ee+ target

1.5 GeV
4CDecelerate

1PF-AR: 6.5 GeV eor 5 GeV

LER: 4 GeV e+
1.1 GeVe+2

PF: 2.5 GeV e-

345

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）

Pulsed bend rep. up to 25 Hz (LER + PF + PF-AR)(magnet coil and chamber heating issue)
It will be replaced by new one in summer shutdown 2020.
5

Simultaneous beam operation (w/ thermionic and rf e- gun)• Stable simultaneous top up injection to 4 storage rings (HER, LER,PF, and PF-AR) w/ thermionic gun, rf gun, pulsed magnets.
Hor. orbit
Ver. orbit
Bunch charge
rf gunThermionic gun and damping ringHor. orbit
Ver. orbit

Bunch charge
Thermionic gun
6Thermionic gun

Simultaneous Top-up Injections• SuperKEKB integrated luminosity improvement
17.5 /pb in 5.15 hr(5 fills)
on May. 6

41.6 /pb in 5.15 hr(top-up)
on May. 16

237%improvement
7

Low emittancerf gunRF e- gun• Yb-doped-fiber and Nd/Yb:YAG laser• IrCe cathode• QTWSC or cut disk cavities
8

M. Yoshida, SuperKEKB review, Mar. 14th, 2018

HER injection beam (rf e- gun) status• HER injection has been done w/ only rf gun from PhaseIIIday 1. (Mar. 11th , 2019)• Laser system has no significant fault.
• In summer shutdown of 2019, photocathode (Ir7Ce2) wasreplaced by new one (Ir2Ce) for aiming at better quantum
efficiency (Qe).
– Discharge, frequent VSWR, gradual decrease of bunch charge• In this winter shutdown,– Even after applying thermal cleaning of cathode, bunch charge is
not stable.
– Finally, photocathode was replaced by previous one (Ir7Ce2)
toward next run. Now, under rf conditioning.
2020/2/10

9

Before summer shutdown
5.0

Ir7Ce2

SP_A1_G1 (from rf gun)
QMD10E_M (BT)

4.5
3.5Fire accident

Bunch charge (nC)

4.0
3.0
2.5
2.0
1.5
1.0
0.5
0.0
2/1
2020/2/10

3/1

4/1

5/1
Date
10

6/1

7/1

2019

Qe of photocathode (Ir7Ce2, Ir2Ce)

M. Yoshida

2020/2/10

11

SP_A1_G1 (from rf gun)
QMD10E_M (BT)

5.0

Ir2Ce

4.5

Bunch charge (nC)

4.0
discharge

3.5
3.0
2.5

VSWR

2.0
1.5

discharge
VSWR

VSWR

VSWR

VSWR

1.0
0.5
0.0
10/1

2020/2/10

10/15

10/29

11/12

Date

11/26

12/10

2019

Lasercleaning
Thermalcleaning

M. Yoshida, B2GM, Feb. 6th, 2020

Laser cleaning ～ 30 min.

Before laser cleaning

2020/2/10

M. Yoshida, B2GM, Feb. 6th, 202014

e+ source setup 1
Positron target and capture section

DC solenoid
Large aperture S-band acc. Structures (x10)

W target + flux concentrator (FC)15

Y. Enomoto, SuperKEKB review, 2019

Pulse to pulse
e-/e+ beam switching• Pulsed steering magnet control e- beam orbit．
• Low emittance e- beam goes through a hole at center ofbeam line.
W target (F4 mm)

16hole (F2 mm)
for low emittance e- beam

12Bunch charge (nC)

6e+ beam history in 2019

Primarye- beam

Summer shut down 20198Fire accident

10

LIiBM:SP_AT_0_1:ISNGL:KBP:10S (e- gun)
LIiBM:SP_15_T_1:ISNGL:KBP:10S (W target)
LIiBM:SP_58_0_1:ISNGL:KBP:10S (Linac end)
BTpBPM:QMD13P_K_1:NC_1Hz (BT end)

42e+ beam

02/1
2020/2/10

4/1

6/1

8/1
Date
17

10/1

12/1

2019

LER
injection
beamstatus• Bunch charge– Stable and enough bunch charge in this stage– Primary e-: 11 nC (from gun), 9 nC (on W target), e+ : 1.2 nC (linac end), 0.8 nC (BT)• Flux concentrator (FC)– Previous FC was damaged by large discharge during PhaseII. It was removed inSept. 2018.
– Current FC was installed in Jan. 2019.
– 2 ～ 3 kA operation current (design 12 kA) for stable operation. no significantfault.
Requirements for material of the FC head are• Good brazing characteristic• High yield strength even after brazing• High electric and thermal conductivity– New FC made of Cu-alloy (NC50: Cu-Si-Ni) has been tested w/o fault (～ 12 kA).
– New FC will be installed in summer shutdown of 2020 for aiming at design
operation current.
2020/2/1018

After large discharge…
After large discharge

Slit gap got narrow.
Not possible to apply
high voltage unless thegap will be expanded.
Y. Enomoto, SuperKEKB review, 201919

Accelerating structures• Approx. 230 accelerating structures employed• Many aged (40 years-old) structures are degraded– Risk of 7 GeV / 4 GeV acceleration for Y(4S)– Cannot reach Y(6S)• As a 4-5 year plan, structures are being fabricated since the last year
• First tests will be performed at the assembly room
• Possibly, a couple of structures would be installed during summer

20

Feedback loops• Energy feedback (J-ARC, LTR, ECS, BT) work fine.
• Orbit feedback at some locations.
– Large drift (～ 1 mm) can be corrected
within ~ 0.1 mm w/ feedback.

0.100

Beam energy deviation (%)– Energy stability at BT line < 0.025%

Energy @ BT

ee+

0.075

0.050

0.025

0.000
00:00

05:00

10:00

15:00

20:00

HH:mm

Energy FB

Orbit FB21Dispersion measurement and correction
J-ARC

Designchicane• Horizontal dispersion leakage from J-ARC
causes the beam position jitter.
• Applying fudge factors to quads in J-ARC,dispersion is well corrected.

After correction

Before correction
Measured

Disp. correction
w/ quads

22Y. Seimiya

Residual Dispersion in the BT line
• The dispersion functions have been corrected for each
BT ARC one by one.
• Non-negligible residual dispersion is still observed
BT for e-

Straight line
(BT1)

Straight line
(BT2)

BT for e+

Straight line
(BT1)

Straight line(BT2)23

Y. Seimiya

Injection efficiency and background

Vertical emittance vs. HER Injection efficiency

Y. Ohnishi

24Injection efficiency and background

・LER
gex
[mm]

gey[mm]DR

35

BT1 BT2DR35

BT1 BT2e+ horizontal emittance has been improved after ECS bendalignment.

Y. Ohnishi

Reducing emittance is in time for by*=1mm(6/Nov/2019)(28/Jun/2019)25

2020/2/10
N. Iida, SuperKEKB workshop, 201926

Measured emittancee+ beam (Phase3.2(6.Nov.2019))

gex
[mm]

gey[mm]DR

35

BT1 BT2DR35

BT1 BT2e- beam (Phase3.2(4.Dec.2019))

e+e-gex [mm]150100gey [mm]3040sd [%]0.16(1s)0.1(1s)Emittances increase• DR → Sector3• BT1 → BT2
Beam study will be continued

Emittances increase• C→Sector3• BT1→BT2

gey[mm]gex[mm]Phase3.3

Beam study will be continuedBC３

5 BT1 BT2

N. Iida, 31. Jan., 2020

BC３5 BT1 BT227

Beam abort caused by abnormal injection beam

Y. Seimiya, F. Miyahara, T. Miura, Y. Enomoto, H. Kaji et al.

Injection beam just before abort can be monitored by,

Fast beam position monitor(BPM) in LINACa.

b.

1. Jun., 2019 19:56

LER D6V2 LM abort

LER D6V2 LM abort
No energy deviation
Dispersive point

1. Jun., 2019 21:19

Beam energy was 50 MeV lower.
Orbit deviation

Straight line

One station for the power supplies (PS) was set
to 0 [A] due to a trigger missing of the PS.

Dispersive point

Straight line

The klystron 51 was down at the time.
The estimation was -46.5 MeV which isconsistent with the beam position.

N. Iida, 31. Jan., 202028

Summary and plan
• Stable simultaneous top up injection to 4 storage rings (HER,LER, PF, and PF-AR) w/ thermionic gun, rf gun, pulsed magnets.
• HER injection has been done w/ only rf gun from PhaseIII day 1.
– Laser system has no significant fault.
– Photocathode: Ir7Ce2 => Ir2Ce (summer of 2019) for higher Qe, however,bunch charge gradually decreased.
In this winter shutdown: back to Ir7Ce2 photocathode– Laser cleaning can cure degradation of Qe• Flux concentrator for e+ beam has no significant fault.
– New flux concentrator will be installed for higher e+ bunch charge forhigher e+ bunch charge.

29

Summary and plan (cont’d)• Smaller emittance, higher injection efficiency, smaller
background.
• Emittance growth (need more beam study)– btwn BT1 - BT2 (e-, e+)– DR – Sector3 (RTL) (e+), SectorC-Sector3 (e-)– Steering magnets and BPMs will be installed in e+ capture section(solenoid section) at Sector1.
– Movable girder and precise orbit control will help for emittancepreservation.
• Single shot beam w/ bad quality (energy, orbit) could cause abort.
– Install collimator at ECS (end of linac) in this summer shutdown.
– Reduce failure rate of PS control software
30

Backup

2020/2/1031

Fire recovery• Fire at acc. structure assembly room on Apr. 3, 2019
– Southern part of the injector was much damaged as well as theassembly room

• Interim injector recovery by Apr. 26, 2019
• Full injector recovery during summer shutdown• The assembly roomcleaned up– Restoration in April– S-band structure tests andRF conditioning soon
Scaffold to clean up walls and ceilingat acc. structure assembly room32

Final target (4 nC)

Beam emittance examplee-: ex/ey 40/20 mm
e+: ex/ey 100/15 mm(~1 nC) w/ multiple wire scanners
e- emittance growth
Be+: ex/ey ～100/2 mm

A

1.1 GeV

1.5 GeV eC

e+: ex/ey ～100/6 mm

12DR

345BT
#1 straighte+: ex,y ～ 2500 mm (before DR)e-: ex,y ～20 mm

e-: ex,y ～10~20 mm
33

e-: ex,y ～ 50～80 mm
e-: ex,y ～ 50～80 mm

PF injector

KEKBTristan

2020/2/10

SuperKEKB

34

Injection efficiency and backgrounde+ vertical emittance was improved

LERgex[mm]

gey[mm]DR

35

BT1 BT2DR35

BT1 BT26.Nov.2019 3:176.Nov.2019 18:50

BGs from Vertex detectors

BG due to injection became smaller.

Signals from Loss monitors in the LER

35

Monitors• Beam position monitor (x 103)
– Four strip line electrodes (x 97)• Measurement precision ~ 10 mm– Eight strip line electrodes (x 6) (J-ARC, LTR x2, PF BT, HER BT, LER BT)• Profile monitor (x 104)
– Al2O3/CrO3 (AF995R, Demarquest Co.). (t: 1 mm, 0.1 mm), YAG:Ce (t: 0.1 mm)• Wire scanner (WS) (x 6)– SectorA, B, C, 2, 3, 5

• Streak camera (ST) (x 2)•– SectorA, C, 3
RF monitors for klystron, SLED, acc. structureSTWS

WS36

STWS

WS

WS
STWS

Pulsed magnet system• Pulsed quads (x 28) (w/ ceramic duct) and steering (x 36) were installed at Sector3 toSector5 in 2017 (on movable girder).
• Pulsed bend, additional quad and steering were installed in 2018 summer and wintershutdown.
• PXIe based control system (Windows 8.1, LabVIEW, EPICS) have worked fine w/oany serious trouble.
• Power supply stability: 0.01% (24 hours)
Pulsed magnet
BPM

37

Movable girder for pulsed magnet(remote controllable, 10 mm step)

e+ source setup 2
FC head + BC + target = FC assembly
LAS (large aperture S-band)

BC (bridge coil)targetFC(flux concentrator) head38

solenoid

Y. Enomoto, SuperKEKB review, 2019

Movable girder for accelerating structure• Six movable girders have been installed in Sector3 (in summer
shutdown of 2019).
– Four 2-m-long accelerating structures are mounted on one girder.

• It could help to suppress emittance growth due to misalignment.

5.0

SP_A1_G1 (from rf gun)- after heat cleaning of cathode -Ir2Ce

4.5

Bunch charge (nC)

4.0

One day

3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
1/11

1/12

1/13
Date

1/14

1/15

2020