Injector Linac and RF gun

Injector Linac Upgrade and RF Gun

K.F, KEK, Dec.2014.

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Linac Overview

Mission of electron/positron Injector in SuperKEKBu 40-times higher LuminosityvTwice larger storage beamà Higher beam current at Linacv20-times higher collision rate with nano-beam scheme³ à Low-emittance even at first turn³ à Shorter storage lifetimeuLinac challengesvLow emittance e-à Low-emittance beam from Linac
à Higher Linac beam current
7GeV, 20mm.mrad, 0.1%dE/E, 50Hz
5nC/bunch, 2bunches in a pulse³ with high-charge RF-gunvLow emittance e+³ with damping ringvHigher e+ beam current³ with new capture sectionvEmittance preservation³ with precise beam controlv4+1 ring simultaneous injection
Injector Linac Upgrade and RF Gun

K.F, KEK, Dec.2014.

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Energy profiles and beam propertiesB	

1.5 GeV e-	C	

10 nC x 2 (for LER)
5 nC x 2 (for HER)
0.3 nC x 1 (for AR)
0.3 nC x 1 (for PF) 	
low emittance
1.1 GeV
RF gun	A	1	2	e+	  target	  	same	  energy	DR	l e-/e+ beams are delivered to 4-rings withdifferent current & energy.
l Beam	  accelera7on	  modes	  must	  be	  switched	  by	  50	  Hz	  pulse-­‐by-­‐pulse	  for	  top-­‐up	  injec7on.	

3	4	5	e-­‐:Chicane	

4.219	  GeV	  e-	Decelerate	

1.1 GeVe+	  target	  	 e+	

HER:	  7	  GeV	  e-­‐	  	  	5	  nC	  x2	AR:	  6.5	  GeV	  e-­‐	0.3	  nC	  x1	

LER:	  2.5	  GeV	  e+	4	  nC	  x2	PF:	  2.5	  GeV	  e-­‐	0.3	  nC	  x1	

1.5	  GeV	  C	

1	2	3	

4	5	

Beam optics should satisfy the fast beam-mode switching.	
Injector Linac Upgrade and RF Gun

K.F, KEK, Dec.2014.

Pulse-to-pulse modulationu Four PPM virtual accelerators
for SuperKEKB projectmaybe withadditional PPM VAs
for stealth beammeasurements
based onDual-tier controls withEPICS and event-system

Event-based
Control System

Every
20 ms

F.B
e− GunARC

F.B

PF Injectione– (2.5GeV, 0.2nC)

F.B
e− GunARC

Damping ring

SuperKEKB-LER Injection

F.B

e– (3.5GeV, 10nC)

F.B

e+ Targete+ (4GeV, 4nC)

e− GunARC

SuperKEKB-HER Injection

F.B

e– (7GeV, 5nC)
e− GunARC

F.B

PF-AR Injection

F.B
e– (6.5GeV, 5nC)

Injector Linac Upgrade and RF Gun

K.F, KEK, Dec.2014.

45	Positron generation for SuperKEKBside	  view	
10 nC
primary e-	bridge coils	

DC QM	 spoiler	target	solenoid	
primary
e- beamLAS Accel.
structure	e+	 positronbeamhole	production
Target

5 nC injection e-	
Flux
Concentrator	

pulsed ST	pulsed QM	

FluxConcentrator
BridgeCoils

4-times more positron is required at SuperKEKB than KEKB
New positron capture section after target with
Flux concentrator (FC) and large-aperture S-band structure (LAS)
Satellite bunch (beam loss) elimination with velocity bunching
Pinhole (2mm) for electrons beside target (3.5mm)
Beam spoiler for target protection
Injector Linac Upgrade and RF Gun

e+ beam

K.F, KEK, Dec.2014.

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T.Kamitani

Positron Generation

1) Installation of positron generator for SuperKEKB in April 2014
(Beamline construction since summer 2013)(positron target, spoiler, Flux Concentrator, bridge coils, LAS structures [x6], DC solenoids [16+13],
e+/e- separator, quads [>90])

2) Commissioning of positron beam, observation of the first
positron after reconstruction for SuperKEKB, furtherimprovements expected
Primary e- [nC] Positron [nC]
June 2014
Specification(at SY2)

0.6

0.12x17

10.0

DR injection(2016?)
3)

Oct.~Dec.2014 : Linac commissioning
Jan.~Mar.2015 : Construction
Jul.~Sep.2015 : Construction

Injector Linac Upgrade and RF Gun

5.0
4.0

x42

Efficiency

Parameters

20%

FC 6.4kA, Solenoids 370A,
LAS capture field 10 MV/m

50%
40%

x2.5

FC 12kA, Solenoids 650A,
LAS capture field 14 MV/m
Energy spread acceptance
0.5%Apr.~Jun. : Linac commissioning
Oct. : LER injection
K.F, KEK, Dec.2014.

Emittance Preservationu Offset injection is required to preserve emittanceu Orbit have to be maintained preciselyu Mis-alignment should be <0.1mm locally, <0.3mm globally
Mis-alignment leads to Emittance blow-up

Orbit manipulation compensates it

100 samples
Sugimoto et al.
Injector Linac Upgrade and RF Gun

K.F, KEK, Dec.2014.

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Alignment work during summer 2014u For the first time after earthquake at downstream sectorsu Several measurements during summeru Measurement reproducibility was confirmed up to ~0.2 mmu While there existed
several conflicting
measurements,
consistent scheme~5mm
has been establishedu Movement of tunnel
by several 10’s ofmicrometer wasobserved (→ mover)~10mmu Further work necessary
in 2015, for alignmentand girder replacement
Injector Linac Upgrade and RF Gun

Higo et al.

K.F, KEK, Dec.2014.

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Photo cathode RF gun development
Yoshida et al.

Cascaded frequency doublers
Quasi traveling wave side couple cavity
Yb fiber and Yb:YAG thin disk laser

Ir5Ce
CathodeLaser system for 5Hz in 2013Injector Linac Upgrade and RF Gunu 5.6 nC / bunch was confirmedu Next step: 50-Hz beam generation
with heat dissipation
K.F, KEK, Dec.2014.

9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 fieldBeam tracking simulation result
5 nC

10 nC

Emittance 5.5 mm-mrad

Gun Exit
Size 0.4 mm

time=2.48098e-009

Energy [MeV]

11.7
11.6

Energy spread
0.6%

11.5Bunchshape

11.4
11.3

728
GPT729730z

731

732733

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 (0.2mm)

Beam SizeMechanical design and manufacturing

900

LaB6
SEM-EDX

Oxigen
OKsum

1200

LaMz

CKa

1500

LaMa

BKa

2100

CarbonCKsum OKa

2400

1800
CountsQuantum efficiency improvement
by Laser cleaning

2700

LaLa

Ir5Ce Cathode600
30000.011.01

1.51

2.01

SEM-EDX

IrMa

10000
9000

2000

CKa

4000

0.50

1.00

1.50

IrMr

5000

IrMz

6000

CeMa
OKsumFKa

7000

CKsum OKaCounts

8000

3000

3.01

3.51

4.01

4.51

keV

12000
11000

2.51

Ir5CeCarbon
No oxidization
is observed
CeLa

Lower energy density
is enough to activate Ir5Ce

0.51

1000
00.00

×２０
QE lifetime

2.00

2.50

3.00

3.50

4.00

4.50

5.00

keV

QE Enhancement of IrCe cathodeEnergy spread reduction using temporal manipulation
Energy spread of 0.1% is required for SuperKEKB synchrotron injection.

315nCt5nC10nC

2.520nC

Gaussianσ E/E (%)

21.51tSquare 5nC
10nC

0.515nC
20nC
005

10 5nC electron
15FWHM (ps)2015nC

2530

Primary beam for positron productionProperties of laser medium

Nd laser system for 3-2 RF-Gun

τ～200μs, 40%

Nd-doped○ 4-state laser is easy to operate.
SHG(532nm)
Nd:YVO4○ High power pump LD is available. LD Pump
40%(808nm)○ Large crystal is available
Nd:YAG
FHG(266nm)
× Pulse width is determined by SESAM.
808nm
20%1064nm(Gaussian)
5HG(213nm)
3%

Yb-doped○ Wide bandwidth => pulse shaping
τ～900μs, 40%○ Long fluorescent time => High power
SHG(520nm) 40%
Yb-glass○ Fiber laser oscillator => Stable
LD PumpFHG(260nm) 20%○ Small state difference
Yb:YAG(941/976nm)
5HG(208nm) 3%
× ASE
Yb:BOYS
941/976nm
1040nm
× Absorption

Ti-dopedPump τ=200μs, 40%

τ～3μs, 40%40%

Pump
Nd:YA
SHG
(808nm) 808nm
G1064nm

Ti:Sapphire

Fluorescence

800nm
532nm
○ Very wide bandwidth○ High breakdown threshold
TW laser is based on Ti-Sapphire× Low cross section
× Short fluorescent time => Q-switched laser is required for pumping

Absorption

Best for RF-Gun

Material

Nd:YAG

Yb:YAG

Ti:Sapphire

Wavelength

1064nm1030nm

660-1100nm

Fluorescent time

230ms

960ms

3.2ms

Spectral width

0.67nm

9.5nm

440nm

Fourier minimum
Pulse width
Wavelength

2.48ps

165fs

2.59fs807.5nm

941nm

488nm

Spectral width

1.5nm

21nm

200nm

Quantum efficiency

76%

91%

55%

SHG(400nm) 40%
THG(266nm) 20%
FHG(200nm) 10%

Ti:Sapphire laser system.

Yb fiber & thin disk hybrid laser system

258 nmQE = 10-4515 nm

A few mJ @ 258nm, 50Hz is required.

A-1 RF gun results 5.6 nC bunch charge
was observed.

RF gunA1 sector at KEK linac

beam size measurement for Q-scan

Q-scan emittance measurementxy

32.7 ±3.1 mm-mrad10.7 ±1.4 mm-mrad

Photo cathode RF gun improvementu Crucial for high-current low-emmittance beamu New Ir5Ce cathode and new cavity QTWSC were successfulu Basic features were confirmed at 5 Hzu Cavity: DAW (disk and washer) à QTWSC (high space charge)u Cathode: LaB6 à Ir5Ce (long life, medium q.e. >10-4)u Laser: Nd:YAG à Yb:YAG thin disk and fiber
Regenerative amp. à Multi-pass amp. w/ coolingv Yb-fiber-oscillator – stretcher – fiber-amp – fiber-amp – pulse-picker –Yb:YAG-thin-disk-multipass-amps (6-pass, 5, 5, 2, 1) – SHG – SHGu Staged laser system improvements with beam measurementsv 5-nC low-emittance stable beam for electron injectionv 10-nC beam for positron generationv 50Hz generation with heat dissipation (several possible plans)v Stability improvement, with precise synchronization (commercial oscillator)v Temporal manipulation for lower energy spread
Injector Linac Upgrade and RF Gun

K.F, KEK, Dec.2014.

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Schedule Summary (Typical)u October 2015 (Phase-1, earliest)vMR normal emittance injection for vacuum scrubbingv2bunch in a pulse, 50Hz, 1nC electron, 10nC primary electron for
positron generationu February 2017 (Phase-2, earliest?)vMR low emittance injection for collision tuningv20 mm.mrad (linac end), 2nC, 2bunch, 0.1%dE/E, 50HzvNormal emittance, 5nC, 2bunch, 50Hz for positronu October 2017 (Phase-3, earliest?)vMR low emittance injection for collision physics experimentv20 mm.mrad, 4nC (à5nC), 2bunch, 0.1%dE/E, 50HzvNormal emittance, 10nC, 2bunch, 50Hz for positron

Injector Linac Upgrade and RF Gun

K.F, KEK, Dec.2014.

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Linac Schedule Overview (autumn 2014)

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

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

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

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

Time →Location↓1 nC
Phase1: Electron: Positron: Low current electron

Injector Linac Upgrade and RF Gun

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

2 nC
Phase2

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

4 nC
Phase3PF-AR ecommiss.

K.F, KEK, Dec.2014.

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