Injector Commissioning Masanori Satoh (Accelerator Laboratory, KEK) for the Injector Linac...

Injector CommissioningInjector Commissioning

Injector Commissioning

Masanori Satoh

(Accelerator Laboratory, KEK)

for the Injector Linac Commissioning Group

The 20th KEKB Accelerator Review Committee, Feb. 23-25, 2015


Contents

1. Injector upgrade overview

2. Energy spread/low emittance preservation

3. Simultaneous top-up for 4-rings

4. Progress of electron commissioning

5. Issues and Schedule

6. Summary

2


Injector upgrade overview• Injector linac

– Provide e-/e+ for 4 independent storage rings– 600-m-long, 50 Hz, two bunch operation (96 ns interval)

• Collider rings (top-up):– KEKB (shut down in 30 Jun. 2010)

• HER(e-): 8 GeV, 1 nC• LER(e+): 3.5 GeV, 1 nC

– SuperKEKB• HER: 7 GeV, 5 nC• LER: 4 GeV, 4 nC (w/ damping ring)

• Two light Sources:– PF: e-, 2.5 GeV, 0.3 nC (top-up)– PF-AR: e-, 3 GeV, 0.3 nC (twice daily injection)

3


Injector upgrade items

4

• Low emittance photo-cathode rf gun – e-: 1 nC, 100 mmmrad => 5 nC, 20/50 mmmrad (Ver./Hor.)– e+: 1 nC, 2100 mmmrad => 4 nC, 20/100 mmmrad (Ver./Hor.)

– Component alignment and fine beam control for low emittance preservation

• New positron capture system (Flux concentrator, Large aperture S-band structure), and damping ring

• New timing system (bucket selection for DR/MR)• Fast RF monitor, high precision BPM readout and other new

subsystems• Simultaneous top-up injection

– Including PF-AR via new beam transport. Pulsed Quads, steering magnets (Sector3-Sector5)

• Main ring commissioning: Jan. of 2016


low emittanceRF gun

AB

C 1 2 3 4 5

1.5 GeV e-

e+ target e-:Chicane

10 nC x 2 bunches x 50 Hz (for LER) 5 nC x 2 bunches x 50 Hz (for HER) 5 nC x 1 bunch x 5 Hz (for PF-AR)0.3 nC x 1 bunch x 25 Hz (for PF)

1.1 GeV

DR

Decelerate

e+ target

54321C

e-

e+1.1 GeV

4.219 GeV

1.5 GeV

same energy

e-/e+ beams are delivered to 4-rings with different bunch charge and energy.

Beam acceleration modes must be switched by 50 Hz pulse-by-pulse for top-up injection.

HER: 7 GeV e-

PF-AR: 6.5 GeV e-

PF: 2.5 GeV e-

LER: 2.5 GeV e+

5 nC x2

5 nC x1

0.3 nC x1

4 nC x2

Energy profiles and beam properties

Pulsed Quad (Doublet) for pulse-by-pulse switching

Compatible settings for e-/e+ beams (DC Quads)


Energy spread requirement• Energy spread should be less than 0.1%.• Uniform beam distribution is necessary for mitigation longitudinal

wakefield and reduce energy spread.• Temporal manipulation of laser system

Gaussian

Uniform

0.1%

Gaussian w/ S-band

Uniform w/ S-band

Uniform w/ X-band


Emittance growth due to component misalignment

Sector Cto5: -10 deg rf phaseR56 =-0.20

• Simulation results from 100 different seeds.• Misalignment of Quadrupole magnets and Accelerating structure:

• s < 0.1 mm: bge 20 mm·mrad is almost satisfied.• >s 0.1 mm: emittance preservation is required by some methods.

20 mm·mrad

<Emittance growth>

・ quadratic curve as a function of misalignment

・ strongly depend on error seeds

Nor

m. p

roje

cted

rm

s em

itta

nce

(m

mm

rad

)

Misalignment s (mm)

SimulationSAD code, ElegantInitial bunch charge: 5 nCInitial emittance: 6 mmmradInitial bunch length: 10 ps (FWHM)Initial energy spread : 0.4%Initial beam energy: 20 MeVUniform longitudinal beam distribution


Offset injection for emittance preservation• Low emittance electron beam should be delivered to MR w/o

damping ring.• Emittance preservation is key issue for e- beam.• Low emittance rf gun• Offset injection: intentional change of misalignment seed. • Control the steering magnet at the beginning of Sector C

Bunch compression Offset injection


Offset injection (simulation)

Sector Cto5: -10 deg rf phaseR56 =-0.20

• Kick angle is relatively small.• Need a high-precision and stable orbit control.


風間スライド挿入

10


Low emittance electron issue• Component alignment is important

• s < 0.1 mm: enough for emittance (alignment is very difficult)• > 0.1 s mm: beam manipulation is necessary.

• Simulation w/ misalignment s ～ 0.3 mm (100 error seeds)• Emittance can be preserved by

• J-ARC: Bunch compression• Sector C: Offset injection

• Alignment requirement:• < 0.3 s mm for global (whole Linac)• < 0.1 s mm for local (one Sector ̴ 100 m)


e-/e+ beam fast switching (SuperKEKB)

12

• Fixed positron target with a hole (e- beam pass through inside a hole)• A hole is at the center of beam line for low emittance e- beam.• Same scheme was successful in KEKB operation.


Simultaneous top-up injection for three rings• Stored beam current stability in 2000.

- KEKB: 300 mA (~ 50 %)

- PF: 240 mA (~ 53 %)

13

• Stored beam current stability in Apr. 2010.- KEKB: 1 mA (~ 0.05%) : e-: 12.5 Hz, e+: 25 Hz

- PF: 0.05 mA (~ 0.01%) : 0.5 Hz

KEKB e-

KEKB e+

Luminosity

PF

• PF-AR injection (twice daily) interrupt KEKB injection.

• Big issue for SuperKEKB operation.• Beam lifetime ~ 6 min.)


Simultaneous top-up including PF-AR injection• PF-AR and KEKB share the long part of beam transport line.• Existing tunnel space is very tight.• New tunnel has been constructed in Mar. of 2014.• Pulsed bend will be installed at #3 switch yard of Linac.• New BT will be available in Jan. of 2017.

H. Takaki (KEKB review 2013)


Injector commissioning- Our goal -• Beam charge/emittance

– e- 5 nC: 20/50 mmmrad w/o DR (Ver./Hor.) – e+ 4nC : 20/100 mmmrad w/ DR (Ver./Hor.)

• Emittance preservation at end of Linac– Bunch compression at A1 unit/J-ARC– Offset injection/wakefield bump (High precision orbit measurement/control)

• Beam stability – Charge– Position– Energy– Energy spread– Emittance

• Simultaneous top-up for 4 rings15


Injector commissioning• Injector commissioning has been started in Oct.

of 2013.

16


Beam orbit example

17

Injector CommissioningCharge history

0.58 nC

5.6 nC


Beam diagnostics• Beam position measurement

– BPMs x 90 (strip-line type electrodes)• Beam profile/Emittance measurement

– Fluorescent screen monitors x100– Single wire scanner x1– Multiple wire scanner x5

• Bunch length measurement– Streak camera x3

19


Typical beam charge stability

20

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.00

50

100

150

200

250

300

350

400

Cou

nts

I (nC)

I = 1.13 +/- 0.144 (nC)1 hour

sI: 10% ~ 20%~ 2.5% (KEKB operation)


Shot-by-shot beam profile stability

21


Two bunch operation example

22


Emittance measurement example (A1 unit)

23

• Quadrupole scan• Screen monitor at chicane

Horizontalbgenx: 15.43 mm·mrad

Verticalbgeny: 9.42 mm·mrad

Chicane


Emittance measurement example (Sector B)

24

• Multiple wire scanner at the end of Sector B• Typical result (1 nC):

– en,x: 66.006 ± 10.755 mmmrad– en,y: 77.309 ± 14.522 mmmrad

• Charge stability is not so small. Software is under development for subtracting shot-by-shot beam fluctuation.


Emittance history

25

• Emittance at Gun and Sector B were measured by Quad scan and multiple wire scanner.

• In Nov. and Dec. of 2014


Emittance

26

• Emittance plot as function of bunch charge


Offset Injection (experiment)

27

• Feasibility of offset injection was studied w/ bunch charge of 0.3 nC.


Bunch compression at A1 unit

28 A1 RF F -30°: 10 ～ 15 psA1 RF F 0°: 30 ～ 40 ps

w/o bunch compression w/ bunch compression

10 ps40 ps

First Accelerating structureChicane


Bunch compression @ J-ARC

29

• Isochronous, R56 = -0.3 m• w/ different RF F in SectorA/B

Isochronous R56 = -0.3 m


Preliminary result of bunch compression @ J-ARC

30

• Isochronous (w/o bunch compression), R56 = -0.3 m (w/ bunch compression) w/ different RF F in SectorA/B

• Clear bunch compression has not yet been measured.• Emittance measurement by multiple wire scanner at Sector2 w/ and w/o J-ARC

bunch compression.

Streak camera at SectorC

-6 -4 -2 0 2 4 610

12

14

16

18

20

Bu

nch

leng

th (

ps)

RF (deg.)

w/o compression w/ compression


e+ beam measurement• First e+ beam was measured by current system at Jun. 9th 2014.• Primary e- beam charge: 0.5 nC• e+ charge: 0.02 nC @ SP_28_4

31

e- beam e+ beam

x (mm)

y (mm)

I (nC)

target


Beam injection study (new timing system)

32

Beam orbit for PF injection (new system)Beam orbit for PF injection (current system)

• Beam injection to PF/PF-AR w/ new EVG


R16, R36 elements at J-ARC

33

Design value w/ fudge factors

• R16, R36 values were measured at J-ARC and SectorC.• w/ and w/o fudge factors (B’ = Afudge x B’model )

• Find suitable fudge factors– Typical fudge factors used for KEKB operation are 1% ~ 5%.


Chicane at Unit-A1

34


Unit A1 (remodeling)

35

• Previous thermionic e- gun will be temporarily back in end of this Apr. for radiation facility test.– Left the beam line for rf gun in current position.– Beam line level of beam line will be changed from 1200 mm to 1950 mm.– Spare magnets will be used for new beam line.

• Commissioning will be started in early May.

RF e- gun beam line

Thermionic e- gun

1950 mm

1200 mm

Merger line


Design drawing of A1 beam line

36


Optics design

37

• Quadrupole triplets will be installed in merger line.

(mm)

𝜂𝑥(𝑚𝑚)

Ver. beam size (mm)

Hor. beam size (mm)

Beam energy (MeV)

Merger line


Summary of e- commissioning

38

Item Requirement Current status

Beam charge (nC) 5 　 (10 for e+ primary) 5.6 (first BPM)0.58 (Linac end)

Beam energy (GeV) 7 7

Normalized emittance (mmmrad)

50/20 (Hor./Ver.)(at the end of Linac)

20/7 (Hor./Ver.) (from RF gun)

Bunch charge stability 2.5% (KEKB) 10% ~ 20%

Bunch compression @ A1 unit 30 ps => 10 ps 30 ~ 40 ps ~ 10 ~ 15 ps

Bunch compression @ J-ARC 10 ps => 5 ps n/a

Temporal manipulation of laser Uniform shape n/a

Emittance preservation 20 mmmrad (Linac end) n/a

Max. beam repetition 50 25

# of bunches 2 2

Operation Simultaneous top-up n/a


Issues• Injector commissioning

– Oct. ~ Dec. of 2013/ Apr. ~ Jun. of 2014/ Oct. ~ Dec. of 2014– Not enough time for injector commissioning– e+ commissioning:

• Installation of flux concentrator has delayed from Dec. of 2013 to May of 2014.

• First e+ beam was measured in Jun. of 2014.• Progress in LAS RF conditioning (x10) is slow.• Twice accidents in Dec. of 2013 and Dec. 2014 (cable burned)• Not yet enough primary e- bunch charge

– e- commissioning:• Beam stability (charge, position) is not yet enough.

39

Injector CommissioningSummary

40

• Commissioning stage 1: (Oct. 2013 Mar. 2014)– New RF gun commissioning (laser tuning and cavity conditioning)– High intensity charge– Prepare beam diagnostics and commissioning tools– New Photo-cathode RF gun has successfully manufactured and

installed. (Summer 2014)• 5.6 nC from New RF Gun• 0.58 nC at end of Linac

• Stage 2: (Apr. 11 Jul. 1, 2014)– Emittance preservation of e- at the end of Sector B, Sector 5

• Bunch compression at J-ARC, offset injection, wake field bump,…..

– Positron beam commissioning (May 2014 )– Beam stability

• Charge, Position, Energy, Energy spread, Emittance

Injector Commissioning Masanori Satoh (Accelerator Laboratory, KEK) for the Injector Linac...

Documents

Transcript of Injector Commissioning Masanori Satoh (Accelerator Laboratory, KEK) for the Injector Linac...