eefact2016
58th ICFA Advanced Beam Dynamics Workshop
on High Luminosity Circular e+e-Colliders
24-27 October 2016
CockcroS InsTtute at Daresbury Laboratory, UKInjector linac upgrade and new RFgun development for SuperKEKB
Takuya Natsui
KEK

Contents• Injector linac in KEK and upgrade for SuperKEKB• RF gun development• Phase1 commissioning in RF gun• Conclusion

Mission of electron/positron Injector in SuperKEKB• 40-Tmes higher Luminosity• 20-Tmes higher collision rate with nano-beam scheme• à Low-emiZance even at ﬁrst turn à Low-emiZance beam from Linac• à Shorter storage lifeTme• Twice larger storage beamà Higher beam current from Linac• Linac challenges• Low emiZance e-• with high-charge RF-gun• Low emiZance e+• with damping ring

• Higher e+ beam current• with new capture secTon• EmiZance preservaTon• with precise beam control• 4+1 ring simultaneous injecTon

Required injector beam parameters for SuperKEKB
KEKB obtained(e+ / e-)SuperKEKB required(e+ / e-)Energy3.5 GeV / 8.0 GeV

4.0 GeV / 7.0 GeVChargee- à e+ / e10 à 1.0 nC / 1.0 nCe- à e+ / e10 à 4.0 nC / 5.0 nC

EmiFance [mm-mrad]

2100 / 300

20 / 20

low emittanceRF gunand DC gun
3.5 GeV
10nC x 2 (prim. e-)
5nC x 2 (inj. e-)

Bunch
Compressor

S-bandlinac

1.1 GeV
Damping Ringcirc. 136 m
Energy-spread
Compression System
3TRF gun

50 Hz (e+ or e-)pulse-by-pulse
mode switchingPF
2.5 GeV e0.1nC x 1

AR (later)
6.5 GeV e-

LER, AR

4.0 GeV e+
4nC x 2ECSe+ target &LAS capture section

7.0 GeV e5nC x 2 HER

4 ring injecTon and Virtual Accelerator(VA)
We have to inject to diﬀerent 4 rings with one beam line, simultaneous injecTon.

ParKcleEnergy [GeV]Charge [nC]SuperKEKB HER

Electron

75 x2

SuperKEKB LER

Positron

44 x2

PFElectron

2.5

0.3 x1

PF-AR

Electron

6.55 x1

e-:Chicane
4.219 GeV

same energye+ target
1.5 GeV

Deceleratee-LER: 4 GeV e+
4 nC x2
PF: 2.5 GeV e-

1.1 GeVe+

HER: 7 GeV e5 nC x2
PF-AR: 6.5 GeV e5 nC x1

0.3 nC x1
C1234550 Hz pulse-to-pulse control system is required.
Developing pulse magnets and pulse to pulse LLRF control system.

Flux concentrator (FC)The positron bunch intensity is boosted from 1 nC
to 4 nC by eﬃcient FC capture.
This FC based on the SLAC-IHEP model design.
Primary beam: 3.3 GeV 10 nC e-.
EmiZance will be reduce by using the new
damping ring.
bridge coils

primary e-

DC QM

spoilertargetprimarye- beam
positronproduction
Targete+ beamsolenoidAccel.
structure

FluxConcentrator
targetdiameter
4.0 mmtargetoffset
3.5 mm

e+
beam
hole

FluxConcentrator

pulse ST
pulse QM

side view

injection e-2.0 mm
FC offset

holediameter
2.0 mm
7.0 mm
FC aperture

rear view•••••

EmiZance PreservaTon

Linac is 600 m. Misalignment can not avoid
Transverse kick due to wakeﬁeld increases slice emiZance
Oﬀset injecTon may solve the issue
Orbit have to be maintained precisely
Misalignment should be <0.1mm locally, <0.3mm globally
Mis-alignment leads to EmiZance blow-up

Orbit manipulaTon compensates it

100 samples
7Sugimoto et al.

Double electron gun system
convenTonal thermionic DC gun
merged tonormal line
New RF gun

This thermionic gun was used for Phase1
positron primary beam and normal operaTon.
RF gun beam line was used for study in Phase1.

RF gun development

Why we need advanced RF gun?
Normal RF gun

5 nC beam tracking simulaTon.
Beam size will be too large for our use.

Normal RF gun does not have focusing E-ﬁeld.
5 nC beam charge has much higher space charge.
We need advanced RF gun.

developed cavityrr

normal cavity

E-ﬁeldEz, Er/r

accelerate

Ez, Er/r

E-ﬁeld on-axis

E-ﬁeld on-axis
focus

zz

focus

accelerate

EﬀecTve E-ﬁeld on-axis
accelerate

Ez, Er/r

Ez, Er/r

E-ﬁeld

EﬀecTve E-ﬁeld
on-axisaccelerate
zz

focus

focus
11

normal cavity

developed cavity

E-ﬁeld

加速電場
E-ﬁeld
ビーム
Beam

Beam

focus：Strong

Ez, Er/r

accelerate

Ez, Er/r

E-ﬁeld on-axis

E-ﬁeld on-axis
focus

zz

focus

accelerate

EﬀecTve E-ﬁeld on-axis
accelerate

Ez, Er/r

Ez, Er/r

focus: WeakEﬀecTve E-ﬁeld
on-axisacceleratezz

focus

focus
12

Annular coupling caviTes makes narrow acceleraTng gap

Close nose make narrowacceleraTon ﬁeld

Long driS space causes the beam defocus

The close nose makes focus ﬁeld. Side coupled cavity can be madethe close nose. But, long driS space is problem. One solution is touse tow standing wave cavity.
13

Quasi traveling wave side coupled caviTes
Normal side coupled caviTes

Whole caviTes design
This RF gun has total of seven acceleration cavities. These are divided into twostanding wave structure of 3 and 4 side coupled cavities respecTvely.

First cavity (Cathode cell)
Maximum E-ﬁeld at
surface: 120 MV/m

Regular cell
Maximum E-ﬁeld at surface: 100 MV/m

EmiZance: 5.5 mm-mrad @ 5 nC
This RF gun can generate 10 nC beam
15

Beam tracking simulaTon result （5 nC）
EmiZance 5.5 mm-mrad

time=2.48098e-009

Energy [MeV]11.7

Gun Exit

11.6
11.5
11.4

Bunch shape

11.3

Size 0.4 mm

728
GPTEnergy spread 0.6%729730731732z

5 nC 11.5 MeV parallel beam7333D design
RFbeamcathodecoupling caviTes

90 deghybrid

acceleraTngcavity

17

Installed RF gun at A1
Cathode90 degHybridLaser port

18

Layout for 25 Hz Yb:YAG Laser system
SynchronizaTonsystem
Yb-doped ﬁber
oscillator withTransmission graTng
51.9 MHz51.9 MHz and 2856 MHz LLRF
Yb-dopedﬁber preampliﬁer

Transmission
graTng pairstretcher

0.2 nJ @ 1037 nm>µJ @ 1037 nm

Yb:YAG thin-disk
mulTpass ampliﬁer
SHG(BBO)

Yb-dopedﬁber pre
ampliﬁer

FHG
517 nm (BBO)

Yb-doped ﬁber
main ampliﬁer

259 nmRF GUN

Pulse picker
25 HzSingle or Double bunch

Yb-dopedﬁber mainampliﬁer

Layout for 25 Hz Yb:YAG Laser system

Yb:YAG thin disk

2ω

Laser injecTon to RF gun

telescope4ω

BBO

Laser injecTon component near the RF gun.
Laser pulse is transported as 2nd harmonics, and convert to 4th harmonics by BBO.
InjecTon angle is adjusted with remote control mirror to angled laser port.

Phase 1 commissioning in RF gun

Beam charge stability• Target of RF gun study in Phase1 was HER injecTon at 1 nC.
• Charge stability is most important point.
7 hours beam charge stability. (5/19)

1.724 +/- 0.07 nC

We achieve 5% charge stability at 1 nC.

Laser and beam proﬁle stability

Laser proﬁleLaser proﬁle should be improved.
PosiTon jiZer is also one of problem. (Horizontal 0.5 mm, VerTcal 0.2 mm)

Beam proﬁleA1-M screen

EmiZance measurement by using Q scan method
1 nC beam

A1 chicane
A1 M
B sector dump

Horizontal (projecKon)

VerKcal(projecKon)

28.3 (31.8)
20.3 (20.8)
48.5 (52.7)

26.4 (29.4)
17.7 (18.3)
21.7 (22.2)[mm-mrad]

Measurement emiZance is larger thansimulated emiZance.
Due to laser pulse quality.

A1 chicane Q scan
Horizontal
EmiZance 28.3 (31.8) mm-mrad

VerTcalEmiZance 26.4 (29.4) mm-mrad

HER injecTon with RF gun
We achieved HER injecTon with RF gun.
It was conTnuous 10 days injecTon.
Beam quality and stability are almost same as thermionic gun.

Eﬃciency isalmost 100 %Conclusion• In KEK injector, several upgrade was carried out.
• Thermionic gun was used for Phase1. Charge ofelectron beam is 1 nC. Charge of positron beam is
1 nC with FC.
• We achieved charge of 1 nC beam generaTon byusing the new RF gun.
• Laser power stability is acceptable. (chargestability : 5%)• PosiTon stability is sTll not so good at RF gun.
• EmiZance is approximately 20 mm-mrad.
• SuperKEKB HER Ring injecTon test was succeededwith the RF gun. We achieved 10 days stableinjecTon.

Schedule

RF-Gun e- beamcommissioning
at A,B-sector

e- commiss.
at A,B,J,C,1

Linac Schedule Overview
e+ commiss.
at 1,2 sector (FC, DCS, Qe- 50%)e- commiss.
at 1,2,3,4,5 sector

Phase1: high emiZance beam for vacuum scrub
Phase2,3: low emiZance beam for collision

Time →LocaKon↓
Beam
Licensesin steps

Low EmiFance
Beams

4+1 Ring
InjecKons

DRCommiss.
1 nC
Phase1

Without Top-up: Electron: Positron: Low current electron29

non damped e+ commiss.
at 1,2, 3,4,5 sectors
e- commiss. at A→5 sectors

2 nC
Phase24 nC
Phase3

Direct PF-AR BT
damped e+ commiss.
at 1→5 Qe+ = 1~4nC
e- commiss.
at A→5 Qe- = 1~5nC

Improved
RF gunThank you for your a,en.on