RFgun and Electron Beam
SuperKEKB review @ 14, June, 2016

SuperKEKB upgradefor low emiAance electron beam
High charge low emiAance isrequired for SuperKEKB.

KEKB obtained(e+ / e-)SuperKEKB
required (e+ / e-)

Beam energy

3.5 GeV / 8.0 GeV

4.0 GeV / 7.0 GeV

Bunch chargee- àe+ / e10 à 1.0 nC / 1.0 nC

e- à e+ / e10 à 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 emiAance preservaMon is required.
Quasi –travelling side couple RF-Gun
with Yb-ﬁber and Nd/Yb solid laser system

BJ-ARCA 10ps30ps

Cut Disk Structure RF-Gun
will be installed

C

1

2

Preliminary test using DAW RF-Gun
with Nd laser system => Yb-ﬁber &Nd:YAG
due to earthquake

3

4

5

Schedule• Last Year

– Reconﬁgure thermal gun for positron generaMon– Step by step RF-Gun RF ageing.

• DoneFollowing the RF-Gunreviewer’s comments– SuperKEKB injecMon using stabilized exisMng undergroud laser (25Hz)– New laser system in 3-2 and A-1 ground laser room
• Increase stability & pulse energy from ﬁber laser• Simplify the laser system (Nd/Yb RegeneraMve ampliﬁer)• On going(Postponed the pulse shaping un<l Phase-III )– Third RF-Gun (nomal laser injecMon / cavity modiﬁcaMon / cathode change)– Simple Nd ampliﬁer for Phase-I & II stable injecMon

G R_32RF-G unB eam line
C athode
Laser
C om issioning

SuperKEKBInjectionRF-G un
B eam line
C athode
Laser
C om issioning

G R_A 110 ps gaussian is enough for Phase-I (1nC) & II (2nC), postponed the pulse shaping un<l Phase-III
FY2011Q2 Q32012 FY2012
Q4 Q1 Q2 Q3
D AW

Ir5C e

LaB 6
N d Laser1Q4

2013 FY2013
Q1 Q2 Q3

Q42014 FY2014
Q1 Q2 Q3

Q42015 FY2015
Q1 Q2 Q3

Q4

2016 FY2016
Q1 Q2 Q3

Q42017 FY2017
Q1 Q2 Q3

Q4

2018 FY2018
Q1 Q2 Q3

Q42019Q1Ir5C e
N d Laser2

D AW
Ir5C eYb Laser1 5H z

Yb-Fiber+N d:YAG

SC -Q TW
C hicane
Ir5C e25H z

Phase-1Phase-2Phase-3

SC -Q TW 2

C D S w ith 90deg ARC

N ew IrC e cathodeYb Laser (underground)
Therm al G un

Q E im provem ent
N d Am plifier (50H z)
Yb Laser3(C ryogenic)

1nC injection
2nC low em ittance
4nC low em ittanceD esign
D evelopm ent
Installation
O peration

RF-Gun for 5 nC
20

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

em ittance(S C )_x@ 5nC & 90M V /m

16

Em ittance (m m m rad)– Longer pulse length : 20 - 30 ps

em ittance(R F)_x@ 5nC & 90M V /m

18em ittance(total)_x@ 5nC & 90M V /m1412108Total

64Space charge
RF20010203040

T laser (ps)– Solenoid focus causes the emiAance growth.
– Electric ﬁeld focus preserve the emiGance.
Epaxial coupled cavity : BNL
Annular coupled cavity : Disk and washer / Side couple

50

S-band RF-Gun development strategy for SuperKEKB• Cavity : Strong electric ﬁeld focusing structure– Disk And Washer (DAW)=> 3-2– Quasi Traveling Wave Side Couple => A-1– Cut Disk Structure => A-1 90 deg line and normal laser injec<on=> Reduce beam divergence and projected emiAance diluMon• Cathode : Long term stable cathode– Middle QE (QE=10-4～10-3 @266nm) and long lifeMme– Solid material (no thin ﬁlm) => Metal composite cathode=> Started from LaB6 (short life Mme)=> Ir5Ce has very long life <me and QE>10-4 @266nm• Laser : Stable laser without/with temporal manipulaMon– LD pumped laser medium• Nd doped solid laser=> 3-2• Yb doped ﬁber and Nd/Yb solid hybrid laser => A-1– Temporal manipulaMon => Yb (posteponded unMl Phase-III)=> Minimum energy spread

Pill-box cavity

Annular coupled cavity with nose

AcceleraMng ﬁeld

AcceleraMng ﬁeld
加速電場ビーム
BeamBeam=> Strong focus

Field

Ez,Er/rEz,Er/r=> Weak focus

Field
Focussing ﬁeldzAcceleraMng ﬁeld

Focussingﬁeld
Given forcez

Focussingﬁeld

AcceleraMng ﬁeld

Ez,Er/rEz,Er/r

AcceleraMng ﬁeldz

AcceleraMng ﬁeld

Given force

zFocussing
ﬁeld

6Closed gap makes focus ﬁeld
Side coupled cavity is one candidate (or DAW / ACS / CDS …)

Concentrated ﬁeld
has focusing eﬀect

This structure has long dril space

This structure has focusing ﬁeld.
Long dril space is problem.
7

Design of a quasi traveling wave side couple RF gun
Normal side couple structure

Quasi traveling wave sidecouple structure

Quasi traveling wave side couple has stronger focusing andaccelerated gradient than DAW.

RF-Gun comparison
Quasi traveling wave side couple RF gun(100 MV/m, 6mm-mrad, 13.5 MeV)
DAW-type RF gun(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Cavity design
Field calculaMon
RF90 deghcathode
beamcoupling caviMes

acceleraMng
cavityNo reﬂec<on to klystronybridMechanical design and manufacturing

Cathode : Advantage of metal composite cathode(LaB6 or Ir5Ce )JusMn Jimenez, A SystemaMc Cathode Study , Ph.D Thesis, Monterery, California•••Low WorkfuncMon (2.8 eV)and enough QE (10-4)
at room temperature.
InacMve in air
Recover by heaMng orlaser cleaning

Best choicefor SuperKEKB 5 nClong <me opera<onPhysica Scripta. Vol. T71, 39-45, 1997.
Cathodes for Electron Guns
G. I. Kuznetsov

LifeMme measurement（LaB6 / Ir5Ce）
10QE-4IrCe
LaB610-505101520253035

Life<me (hour)

Condi&on
Con<nuous pulse laser 200μJ@266nm)
Irrada<on => 2.5 nC emission

404550Condi<on
HV = 16kV
Vacuum ; 5.8×10-6 Pa
Cleaning Mme ; 10 min

Quantum eﬃciency improvement
by Laser cleaning

QE

1500
1200

LaMz

900

LaB6
SEM-EDX

Oxigen
OKsum

Counts1800

Carbon
LaMa

BKa

2100

CKsum OKa

2400

CKa

2700

10-4

LaLa

Ir5Ce Cathode

600

00.01

1.51

2.01

2.51

3.01

3.51

4.01

4.51

keV

Ir5CeCarbon

8000

CKa

4000
3000
2000

0.50

1.00

1.50

IrMr

5000

IrMz

6000

CeMa
OKsumFKa

7000

CeLa

10000

IrMa

SEM-EDX

11000
9000

Ir5Ce@266nm

1.01

12000

LaB6@266nm
LaB6@532nm

0.51

CKsum OKa

×２０300Counts

10-5

Lower energy densityis enough to acMvate Ir5Ce

1000
00.00

10-602.00

2.50

3.00

3.50

4.00

4.50

keV

1000
2000
3000
4000
Energy density of cleaning laser(μJ/mm2)

Non acMvaMon
QE = 5.00×10-6×20Laser cleaning
Max QE = 1.00×10-45000

No oxidizaMon is observed[SUPER-KEKB e Linac]
Laser Power ; 233μJ/pulse（λ=266nm）
Target value ; 5nC

5.00

Cavity RF condiMoning
CondiMoning progress was too slow aroung 12 MW input.
Frequently brake down was big problem.
Cathode rod contact?
Cathode material ﬁxaMon?
Cathode material spuAering due to laser?
We have to separate causes of brake down.
1. Cavity condiMoning, used dummy cathode rod without
cathode material (all Cu).
2. Replace new cathode rod with material (new ﬁxaMon isshrinkage ﬁt).
3. For reduce mulMpactoring eﬀect, another cathode cell
design is required.

Current cathode

Build 6-1 ageing standA-1 RF-Gun
Third RF-Gun cavity

New cathodeshrinkage ﬁt

History of GR_A1 RF condiMoning
20

Reduce RF-Gun powerfor dummy load RF condiMoning

18
16

RF-Gun Pf (MW)14121086420
2015/9/23

2015/9/25

2015/9/28

2015/10/3

2015/10/8

2015/10/13

2015/10/15

2015/10/18

Curent injector beam line on up and down.
Thermionic DC gun was installed to upper beam line.

10 nC
for positron primary

70 MeV
Acc.tubebuncher

prebuncher

SHB2

SHB1

Thermionic
DC gunEnergy slope
Chicane10 psec

30 MeVBunch
25 pseccompression

Acc.tube

RF gun1 nC (Phase-I)
2 nC (Phase-II)
5 nC Low emiAance (Phase-III)

Current setup of unit A1• Thermionic e- gun has been temporarily back in the end of May,2015.
– Radiation control license inspection– 10 nC e- beam for e+ production• Beam line remodeling– Keep the rf gun beam line almost unchanged (1st acc. stracture was removed)– Thermionic e- gun beam line: 1200 mm to 1950 mm– Spare magnets have been used for the merger beam line.
Merger line

Thermionic e- gunRF e- gun beam line
181200 mm

1950 mm

Recent achievement• Successful injecMon from RF-Gun to SuperKEKB HER
ring with stabilized exisMng underground lasersystem.
• RF-Gun– The ageing process of the choke structure was done at 6-1
ageing staMon.
• Improvement on laser system(Zhou)– Yb ﬁber laser=> 25 ps pulse length is obtained by strecher adjustment.
Nd solid laser (3-2)– Yb solid laser (A-1 underground)SuperKEKB HER (electron) injecMon
GR_A1 (RF-Gun)

GU_AT (Thermal Electron Gun)

Current(blue)：2016/06/10 02:01、GR_A1 KEKB HER e- injecMon
Ref(green)：2016/05/21 03:26、GU_AT KEKB HER e- injecMon

Current(blue)：2016/05/30 16:43、GU_AT KEKB HER e- injecMon
Ref(green)：2016/05/21 03:26、GU_AT KEKB HER e- injecMon

GR_A1 KEKB HER e- injecMon

GU_AT KEKB HER e- injecMon

GR_A1 (RF-Gun) screen at J-ARC

GU_AT (Thermal Gun) screen at J-ARC

SC_R0_31

SC_R0_31

SC_61_H

SC_61_H

7 hours beam charge stability. (5/19)

PoinMng stabilityX
1σ : 0.44 mm

y
1σ : 0.23 mm

EmiAance measurement (Q scan method)

A1 chicane
A1 M
B sector dump

Horizontal (projec<on)

Ver<cal(projec<on)28.3 (31.8)
20.3 (20.8)
48.5 (52.7)

26.4 (29.4)
17.7 (18.3)
21.7 (22.2)

Should improve- Laser Proﬁle & jiAer- Perpendicular laser injecMon- QE uniformity of IrCe cathodeOn-going R&D for RF-Gun• RF-Gun– New CDS-type RF-Gun is under fabricaMon
Larger beam aperture
Simple structure enough for 5 nC generaMon– Second RF-Gun installaMon with 90-degree arc
secMon.

• Cathode– QE improvement of IrCe cathode :Ir7Ce2=> beAer uniformity
Single Crystal => beAer QE– Thermal assist for higher QE & cathode cleaningSimple cavity RF gun is developed for test

Cut Disk Structure(CDS)

In the simulaMon, 5 nC beam generaMon is possible

Second RF gun on the 45 degree line
Normal laser injec<on

RF condi<ning at 6-1 is on going
before installa<on.
AngledStudies onlaser- Improved RF-Gun cavity
injec<on- Normal laser injecMon- Changeable cathode including alkaline cathodeSchedule• Last Year

– Reconﬁgure thermal gun for positron generaMon– Step by step RF-Gun RF ageing.

• DoneFollowing the RF-Gunreviewer’s comments– SuperKEKB injecMon using stabilized exisMng undergroud laser (25Hz)– New laser system in 3-2 and A-1 ground laser room
• Increase stability & pulse energy from ﬁber laser• Simplify the laser system (Nd/Yb RegeneraMve ampliﬁer)• On going(Postponed the pulse shaping un<l Phase-III )– Third RF-Gun (nomal laser injecMon / cavity modiﬁcaMon / cathode change)– Simple Nd ampliﬁer for Phase-I & II stable injecMon

G R_32RF-G unB eam line
C athode
Laser
C om issioning

SuperKEKB
InjectionRF-G un
B eam line
C athode
Laser
C om issioning

G R_A 110 ps gaussian is enough for Phase-I (1nC) & II (2nC), postponed the pulse shaping un<l Phase-III
FY2011Q2 Q32012 FY2012
Q4 Q1 Q2 Q3
D AW

Ir5C e

LaB 6N d Laser1Q42013 FY2013
Q1 Q2 Q3

Q42014 FY2014
Q1 Q2 Q3

Q42015 FY2015
Q1 Q2 Q3

Q4

2016 FY2016
Q1 Q2 Q3

Q42017 FY2017
Q1 Q2 Q3Q42018 FY2018
Q1 Q2 Q3Q42019
Q1

Ir5C eN d Laser2

D AW
Ir5C eYb Laser1 5H z

Yb-Fiber+N d:YAG

SC -Q TW
C hicane
Ir5C e25H z

Phase-1
Phase-2Phase-3SC -Q TW 2

C D S w ith 90deg ARC

N ew IrC e cathodeYb Laser (underground)
Therm al G un

Q E im provem ent
N d Am plifier (50H z)
Yb Laser3(C ryogenic)

1nC injection
2nC low em ittance
4nC low em ittanceD esign
D evelopm ent
Installation
O peration