RF‐Gun and beam transport
Mitsuhiro Yoshida

SuperKEKB upgradefor low emittance electron beam
High charge low emittance isrequired for SuperKEKB.
SuperKEKBKEKB obtained(e+ / e-)SuperKEKB
required (e+ / e-)

Beam energy

3.5 GeV / 8.0 GeV

4.0 GeV / 7.0 GeV

Bunch chargee- Æe+ / e10 Æ 1.0 nC / 1.0 nC

e- Æ e+ / e10 Æ 4.0 nC / 5.0 nC

Beam emittance(γε)[1σ]2100 μm / 300 μm

6 μm / 20 μm

5 nC 10 mm‐mrad electron beam generated by RF gun.
+ 10mm‐mrad emittance ppreservation is required.
qPreliminaryy test at 3‐2due to earthquake• RF‐GunRF G– Design of RF‐Gun cavity• Disk‐And‐Washer (DAW)• Quasi travelling wave side couple– Cathode– Laser– Test stand and schedule• Emittance preservation– Alignment– Beam transport– Beam diagnostics

RF‐Gun for 5 nC
20

• Space charge is dominant.
• Stable operation is required.
– Lower electric field : < 100MV/m• Focusing field must be required
required.

emittance(SC)_x@5nC&90MV/m

16
Emittance (mm mrad)– Longer pulse length : 20 ‐ 30 psemittance(RF)_x@5nC&90MV/m
itt(RF) @5 C&90MV/

18emittance(total)_x@5nC&90MV/m

1412108Total

64Space charge
RF20010203040

Tlaser (ps)– Solenoid focus causes the emittance growth.
– Electricli fifield
ld ffocus preserve theh emittance.
i
Epxial coupled cavity : BNL
Annular coupled cavity : Disk and washer / Side couple

50

DAW (Disk and Washer) type RF‐Gun
Electric field focus

Large coupling

Strong focussing field
Curved surface cathodefor low emittance.

CathodeLow electric fieldEmittance
6 mmmm‐mradmrad（5 nC）

Beam size (σ)
1.2 mmBunch length (σ)
8 psecFabrication

Network analyzer measurement and adjustmentof resonant frequency

Result from smith chart

Adjust with spacer
on cathode rod

Reflection ratio

G = 0.119

Coupling

β = 1.27

Q factor

Q0 = 6007.3

Loaded Q

QL = 2646.4

Design of a quasi traveling wave side couple
RF gun for A1 sector
Quasi travelingg wave side couple
p has stronger
g focusingg
and accelerated gradient than DAW.

Quasi traveling wave sidecouple structure

Normal side couple
structurestuctu e2D Designing of the quasi traveling wave side couple RF gun

Optimize 1st cell by using
downhill simplex method.

Surface E‐field is limited at 120 MV/m

1st cell dimensional parameter

IImprovedd surfacef
E fi ld 120 MV/m
E‐fieldMV/

RF‐Gun comparison
Quasi traveling wave side couple RF gun(100 MV/m, 6mm‐mrad, 13.5 MeV)
DAW‐typeyp RF ggun
(90 MV/m, 5 mm‐mrad, 3.2 MeV)
BNL‐type RF gun(120 MV/m, 11.0 mm‐mrad, 5.5 MeV)

BNL (3.8 mm)
DAW (1.7 mm)
QTW (0.2 mm)

Beam Size• RF‐GunRF G– Design of RF‐Gun cavity– Cathode• Advantage of LaB6
• Measurement equipment of quantum efficiency• Laser cleaning & Heat treatment– Laser– Test stand and schedule• Emittance preservation– Alignment– Beam transport– Beam diagnostics

Cathode : Advantage of LaB6
Justin Jimenez, A Systematic Cathode Study , Ph.D Thesis, Monterery, California•••

Low Workfunction (2.8 eV)and enough QE (10‐4)
at room temperature.
Inactive in air
Recover by heating orlaser cleaning

Best choicefor SuperKEKB 5 nClongg time operationpPhysica Scripta.
Scripta Vol.
Vol T71
T71, 39
39‐45,45 1997.
1997
Cathodes for Electron Guns
G. I. Kuznetsov

Quantum Efficiency Measurement with laser cleaning
Parameter

value

Repetition Rate(Hz)10Energy per Pulse(mJ)

75

Pulse Width(ns)5～7Beam Diameter(mm)7COMPACT 10/10 SHG (THALES)

75mJ/pulse
lensiris

λ λ
4 2

Dichroic
Mi
Mirror

18mJ/pulse

Polariser
BBO
Dichroic
Mirror20×20mmScan area
3mm×3mm
Cathode(LaB6)

Reason for using
the Nd:YAG 2nd Harmonic・Strong absorption of 532nm
・ReuseRoff 532532nm

Results of Laser Cleaning
0.00050.00040.00030.0002

Reflectivity wavelength vs Reflectivity
1.0000.900 Material ; LaB6
0.800
0.700
0.600
0.500
0 400
0.400
0.300
0.200
0.100
λ[nm]
0.000350

450QE

550

650750850

M Q.E=3.499×10Max
Q E 3 499×10‐440.0001
5E 05
5E‐05

Laser Power ; 250μJ(266nm)μ()Total Charge ; 20 nC×60
0.307mJ/mm20.443mJ/mm2
1.635mJ/mm2
2.49mJ/mm2

0 00001
0.00001
0.000004

1.0×1010×10‐6Pa
16kV
024Time6(min)81012[SUPER‐KEKB e Linac]
Laser Power ; 63μJ/pulseμ /p（λ=266nm）
Target value ; 5nC

Results of Heater Treatment
0.003

Treatment Condition
・Temperature ； 1673 K・Time ； 75 minute

Q.E

0.002

×100 001
0.001

Max Q.E =3.058×10‐3×20.0005

Laser Power ; 50μJ(266nm)
Total Charge ; 30 nC
1400℃(75min)
Laser Cleaning(3mJ/mm2)

0 00010.00010200

400600Temperature （℃）

8001000[SUPER‐KEKB e Linac]
Laser Power ; 8μJ/pulse（λ=266nm）
Target value ; 5nC

Lifetime of LaB65Q (nC)

43Laser Power
1.3mJ/pulse×62After Laser Cleaning
Before Laser Cleaning
100200400600800TiTime(min)( i )Laser Power ; 1.4mJ/pulse → total charge ; 4nC
No decreasement of the total charge for 1000min.
1000min

10001200• RF‐GunRF G– Design of RF‐Gun cavity– Cathode– Laser• Nd:YVO4 / Nd:YAG Solid state laser• Yb fiber laser– Test stand and schedule• Emittance preservation– Alignment– Beam transport– Beam diagnostics

Laser• Solid state (Nd:YVO4 + Nd:YAG)– Pulse width is determined by SESAM.
– Highg powerppumpp p LD is available.
– No abosorption at emission wavelength.

• Fiber + solid state amplifier (Yb(Yb:glassglass + Yb:KGW)
Yb KGW)– Wide bandwidth with non‐linear polarization=> pulse shaping– Stable / Highg efficiencyy– Difficulties : Self start, ASE, AbsorptionOscillator & Regenerative amplifier
O ill t (AOscillator(Active‐passivetii hybrid
h b id modelocking)d l ki )RF OFFRF ON

Regenerative amplifier for 2
2‐bunchbunch

Beam current
Laser output
Regenerative amplifierOscillator output

Solid state laser for preliminary test
Oscillator(114 MHz)

RegenerativeAmplifier

Nd:YAG (2‐pass)

60mJ@1064nm

Nd:YAG (4‐pass)

20mJ@532nm

100μJ

5mJ@266nm5mJ

Yb‐fiber & Yb solid state laser development
Yb Fiber Main-Amplifier
70W

LD
Pump

λ/4 λ/2

2.5μJ

Yb Fiber Pre-Amplifier

Solid-state Amplifier Yb:KGW

100Hz

LD
200W
10W

Pump Laser
3mJ

Frequency doubling LBO
517nm

BBO

Yb Fiber Oscillator
LD~30ps
0.5mJ
Spectral Range
Adjustment

1035nmWDM

Prism Pair

Intensity [a.u.]

Spectrum of Seed (52MHz)

980

990

1000

1010

1020 1030 1040
Wavelength [nm]

1050

1060

1070

1080

Oscillator & pre‐amplifier are already working.

259nm

• RF‐Gun– Designg of RF‐Gun cavityy– Cathode– Laser– Test stand and schedule• 3‐2 RF‐Gun for preliminary test & PF injection• A‐1 RF‐Gun• Emittance preservation– Alignment– Beam transport– BeamBdiagnostics
diti

3‐2 RF gun installation• DAW type RF‐Gun was installed due to earth quake.
• Designing the injection beam line on the angle forcontinuous PF injection.
injectionLinac beam line

Present situation of RF‐Gun commissioning
from 2011.10‐2012.02
2011 10 2012 02• RF‐Gun cavity– Ageing
A i process was fifinishedi h d ffor onlyl one week.
k• Cathode– Room temperature 6mmφ LaB6 cathode was installed.
– Laser cleaning was tested.

• Laser & Control

Thermal cathode is under development
development.

– Synchronization: almost achieved.
– Pulse picker: almost achieved.
– Pointing fluctuation : feedback system will be installed.
– Power: YAG module will be added.
Fight with destruction is necessary.

A1 new RF gun install schedule

Exist DC gun(Positron beam primary)

SH buncher

Pre buncher,Buncher

Install new RF gun between A1
DC gun buncherb h andd 2 m llinac
by using injection line on theangle.
lInstall in this year
2 m Acc.

A1 sector

• RF‐Gun– Design
g of RF‐Gun cavityy– Cathode– Laser– Test stand and schedule• Emittance preservation– Alignment– Beam transport– BeamBdiagnostics
ditiOverview of emittance source and growth
Current charge & emittance:e- :1 nC, 300 mm mrade+ :1 nC,nC 2100 mm mrad

Longer bunch can reduce
space charge effect inside RF‐GunRF Gun
and also CSR at J‐ARC.

GunBJCSRC

1.1GeV@DRAPF

Target @1‐43.5 GeV 10nC x 2

12BCSECS

345ECS

Beam diagnostic
stationC‐bandDue to mis‐alignment:‐ Dispersion
p‐ Short range wakefieldfor HEROne feed coupler (x480)
7.0 GeV 5nC x 2
causes of RF emittance.
emittance
ε < 20 mm mrad(Δγε ~ 1.2 mm mrad is estimated) yRequirement:

for LER
4 0 GeV 4nC x 2
4.0
εy < 6 mm mrad

Emittance measurement
Wire scanner should install more.

Existing wire scannerA

B

PF Injection

DC‐GunJ‐ARCCγεx [mm mrad]

1200
1000
800

3254800

0.5nC
1 C
1nC
3nC
5nC
1.0nC
3.0nC
5.0nC
7.0nC

700
600

γεy [mm mrad]

1400

1600
400

500
400

00.5nC
5 C
1nC
3nC
5nC
1.0nC
3.0nC
5.0nC
. C
7.0nC

300
200

200

10000
B

CSector

5B

C

Sector5• RF‐Gun– Design
g of RF‐Gun cavityy– Cathode– Laser– Test stand and schedule• Emittance preservation– Alignment– Beam transport– BeamBdiagnostics
ditiAlignment SystemL
LaserTTracker
kTarget holder on coupler

Laser alignment system(w/ quadrant‐segmented photodiode (PD))

• RF‐Gun– Designg of RF‐Gun cavityy– Cathode– Laser– Test stand and schedule• Emittance preservation– Alignment– Beam transport– BeamB
diagnostics
ditiTest for emittance preservation
Dispersion reduction using weak lens
(C to 5 sector)

Wakefield compensation by initial offset(A to B sector)

600

500

400

300

200

1000020406080100120

C to ２ sector Q-magnet[ % ]RF-Deflector => bunch slice emittance
TM110 Cavity ChainhDispersion compensation
RF‐Deflector => Initial offsetz

Simulation for emittance preservation• Simulation test for A‐B sector• Mis‐alignment of 0.3 mm• Initial emittance : 6 mm mrad

Initial offset

BNS damping• RF‐Gun– Designg of RF‐Gun cavityy– Cathode– Laser– Test stand and schedule• Emittance preservation– Alignment– Beam transport– BeamB
diagnostics
ditiMeasurement precision of stripline BPM‐‐‐ Results of 3BPM method (w/ 0.1 nC e‐e beam) ‐‐‐DAQ system

Currentsystem(Oscilloscope)

Libera Brilliance Single Pass

Horizontal (μm)

56.84

20.24

Vertical (μm)

54.37

19.12
30000

ADC counts

20000
10000
0-10000
20000-20000-30000
0••••Real time sampling 10 GSa/s
Precision is limited by 8 bits ADC.
••

50

100t (ns)150

Band‐pass sampling w/ SAW filter
ADC: 125 MHz, 16 bits
Target precision: < 10 μm
UUpgraded off Libera
Lib(based‐on Libera Brilliance plus)

200

RF‐Deflector for transverse wakefield measurementz⎛ eVdeflectorωRF Δt ⎞ ⎛π⎞Δxscreen = β deflector β screen ⎜⎟ sin ⎜ φdeflector → screen = ⎟Ebeam
2⎠⎝⎠ ⎝σ x = β screenε screen

X‐band RF‐Deflector (U.S. / SLAC)‐11 m structuret t
same as theth RF‐deflector
RF d fl t ffor LCLSΔxscreen / σ x =β deflector ⎛ eVdeflectorωRF Δt ⎞⎜⎟ε screen ⎝Ebeam⎠

Vdeflector = 10 MV , f RF = 2.856GHz , Δt = 10 ps, β deflector = 10m→ Δxscreen / σ x = 3
Vdeflector = 15MV , f RF = 11.424GHz , Δt = 10 ps, β deflector = 10m→ Δxscreen / σ x = 18Input Power : 10MW
Deflectingg Voltageg : 15 MV

1.5 m RF ‐ Deflector
X‐band Klystron (KEK)‐ 250 kV, ηP=0.7‐ 10 MW output‐ 2 window

1 m RF‐deflector
Wi dWindow

10 MWKlystronSchedule

SY3
Beamdiagnostics

A-1 RF-Gun
Low Emittancestudy

3-2 RF-Gun

2011
Q1

FY2011Q2
Q3
Q4
complete
LaB6, Ir5Ce
compkete

DAW-GunCathode development (LaB6, Ir5Ce, Cs2Te)
Quantum efficiency measurement
Solid state laser system
3-2 RF-Gun injection beam line
Beam test using DAW-Gun
Laser system for PF injection
PF injection
3-2 reconstruction
Quasi travelling wave side couple
Fiber laser development
Design for A-1
Low emittance study
Laser development for SuperKEKB operation
Backup RF-Gun for A-1

2012
Q1

FY2012Q2Q3Heater assembly

2013
Q1

Q4

FY2013Q2Q3Q4SuperKEKB operation cathodecomplete completetest

operation

Oscillator

X-band RF-Deflector (SLAC)
Ｘ-band 10MW klystron (Japan)
Power supply / LLRF / WaveguideHigh power test
Beam line construction
Beam monitor / bunch analyzer
BPM DAQ upgrade
Alignment using laser tracker
Laser alignment

ＳＬＡＣcomplete

Beam test Beam test
Cpmleted

Sector AB

Sector C-5

AchievementRF‐Gun•

RF‐Gun cavity––••

Emittance preservation

Disk and washer
Quasi TW side couple

Cathode (LaB6)
Laser
––

Nd:YVO4 + YAG Solid state
Yb Fiber laser

completepunder design

QE > 10‐450 %25 %•Alignment––••

Laser tracker
Laser alignment

Emittance preservation
Beam diagnostics––

BPM
Beam diagnostic station

Tested for 3‐5 sector recoveryy
Tested in 3‐5 sector

20 μm (should reduce to 10 μm)
RF deflector development
RF‐deflector
under US‐Japan collaboration.