Linac Upgrade for SuperKEKB
SuperKEKB Int’l review
7 February 2011
T. Higo (KEK)Contents on Linac Upgrade• Gross scope– Required changes– General strategy• High‐charge positron source– L‐band and/or LAS and capture magnePc ﬁeld

• High‐charge low‐emiRance electron gun– Eﬀort to judge best combinaPon of cathode, cavity and laser• EmiRance preservaPon  Yoshida– Finding causes for the growth and suppression strategy• Schedule– Present status and strategy preparing commissioning and laterimprovements
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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Simultaneous injecPon for 3 rings+ AR injecPon
e‐e+HER
7GeVLER
4GeV

2011/2/7

PF
2.5~3 GeVSuperKEKB
AR
36.5 GeV

Linac Upgrade for SuperKEKB (Higo)

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Parameter changes for Linac Upgrade
KEKB
obtained(e+ / e-)SuperKEKB
required(e+ / e-)Beam energy

3.5 GeV / 8.0 GeV

4.0 GeV / 7.0 GeV

Bunch chargee- e+ / ee-  e+ / e10  1.0 nC / 1.0 nC 10  4.0 nC / 5.0 nC

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

2011/2/7

Linac Upgrade for SuperKEKB (Higo)

6 µm / 20 µm

4Injector Upgrade strategy(e-)

 High charge

Photo RF gun

 Low emittance(e+)

AMD + Large aperture acc.

 High charge
 Low emittanceDR( ε ) Emittance

Identify relevant factors
Alignment, dispersion, wake, CSR

preservation(simultaneous injection)

 Pulse-to-pulse optics

2011/2/7

Pulse magnet

Linac Upgrade for SuperKEKB (Higo)5e–SuperKEKB Injector complex
AB

光RF gunRF gun1.7 GeV@J‐arc

1C

2target bypass
bump orbite+

A1 gunCA
Target @1‐41
3.5 GeV
10nC x 2

2011/2/7345e‐ bypass line for
DC separaTon bend

A1 gun 10nC e–

Bfor PF
2.5 GeV
0.1nC x 1

Nominal acceleraTon
S‐band 160MeV / RF unit
+ C‐band 8m at 4‐42ECSfor ARe– or e+ ?

For both e+ and e‐
EmiZance preservaTon
through whole linac

DR
1.1 GeV@DRBCS

for HER
7.0 GeV
5nC x 2

3Capt. and accel.
Linac Upgrade for SuperKEKB (Higo)

4C‐band

5for LER
4.0 GeV
4nC x 2ECS

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Positron source

2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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Positron source• To high charge– Higher focus ﬁeld with AMD (AdiabaPc matchingdevice)– Large aperture acc & associated focus system– SimulaPon gives 6‐7nC with large aperture• Low emiRance– DR + emiRance preservaPon• 1.1GeV injecPon energy→target shib to upstream

2011/2/7

Linac Upgrade for SuperKEKB (Higo)8

Configuration change of positronsource for introduction of DR
Present layout around e+ target

Each block is an accelerator module.

target
1-4

1-5

1-6

1-7

1-8

2-1

2-2

2-3

2-4

2-6

2-7

2-8

solenoid focusingSuperKEKB： Layout with L/LAS capture secTontarget

target moved for DR inj. energy margine– bypass through target holeDR

L/LAS modules
1-4

1-5

1-6

1-7

1-8

2-1

2-2

2-3

2-4

2-6

2-7

2-8

solenoid focusing

2011/2/7

Linac Upgrade for SuperKEKB (Higo)

9Strategy and R&D’s• Increasing focus magnePc ﬁeld with AMD– FLC（Flux concentrator） under development aiming at 10T– Development for stable system in mind

• Satellite in S‐band bucket– Need to be suppressed because it results in DR injecPon loss
associated with DR radiaPon problem– Inclusion of L‐band system is considered to suppress• Method of electron bypass– No independent line because too expensive and less energy gain
– EmiRance growth with oﬀset beam should be suppressed• Reduce construcPon cost
– Need to reduce iniPal construcPon cost large aperture accelerator
with large magnet
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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FLC development in collaboraPon with BINP

Field was measured
Long-term operation under test
Beam test in coming March
Actual one is to be designed and madePower supply is to be made in Japan
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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FLC Bz field measurement
TargetposiTon

Bz field was measured in air.
Bz at target = 45% of Bz max
due to 5.5mm separation
Slope is steeper than AMDrequirement

2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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FLC Bt field measurement
Measured with Bz=3.1T

Bt（Horizontal ）Bt（VerTcal）

Bx/Bz=0.13T / 3.1T= 4.2 %not negligible, ~agrees with calculaTon
Results in Bz center shic by 1mm
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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How to transport electron
Bypass inside FLC
Make electron
passage route andsuppression ofemiRance growth

FLC aperture
φ8

Bypass in thepresenttarget

2011/2/7

e+ φ31㎜ oﬀset（Mag. center)e‐ φ32.5㎜ oﬀset

Linac Upgrade for SuperKEKB (Higo)Oﬀ‐centeredpositronproducPon point
and yield
esPmaPon

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Iida, Nov. 9, 2010

An example
Lx2+LASx4+LASx8+Normal

Summary ofyield and loss
ChargeCapt Next Boost
DR[nC]
4m 8m 16mloss [%]@DR

OpPcs from target to LTR

LL

LAS

6.60.05

LLAS

LAS

6.3

0.27

LAS LAS

LAS

6.3

0.40

DR injecPon

6~7 nC is esPmated in various conﬁguraPons with large aperture.
2011/2/7

Linac Upgrade for SuperKEKB (Higo)15

L‐band preparaPon
L‐band 1st structure was delivered.
Waveguide components are being
prepared.
High power test will be early next JFY.
Focus magnets were foundvery expensive which accept
large bore aperture.
Minimize the large sizearea.
Make focus magnets in acheap manner.
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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SCS to be tested at B8 in March

Found: Average heaPng is important rather than pulse heaPng.
Considering the progress and available Pme Pll commissioning,
SCS development will be interrupted aber ongoing studies.
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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Positron source plan
JFY2011

JFY2012

JFY2013

JFY2014

JFY2015

FLC beam study
FLC actual
Solenoid, etc
Q、STCommissioning

L‐band acc str
Large aperture S‐band acc str
SCS study

2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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Electron source

2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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General strategy on electron source• Requirement– Low enough emiRance at the beginning of commissioning,with at least 1nC– Then improve for longer‐term stability and higher current• Strategy– We expect big diﬃculty, though should do if needed, toimprove the actual system in operaPon– Therefore, basic studies on cathode, cavity and laser tojudge the best conﬁguraPon should carefully be proceeded
beforehand– One system is quickly installed based on LaB6+DAW• Used for emiRance study• And for gepng the operaPonal experience

2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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ExisPng RF gun• ExisPng RF guns
– SLAC： Cu cathode life ~1 yr, 0.25〜1nC, <1πμm,TiSa 266nm, S‐band, 60Hz
– ATF：CsTe, <5nC, 4πμm＠4nC, YAG 266nm, S‐band,1.56Hz– DESY : 8nC, 15πµm with L‐band• We need long‐term stability– Maintenance free > 50Hz * 1yr or easy exchange– No established technology exists
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

21Performance of improved ATF RF Gun

Terunuma, 27 July 2010

Dark
current

2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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R&D items• Cathode life

– Material choice– Get operaPon experience and establish long life

• Laser stability– No laser specialist, yet to be developed– Get operaPon experience to understand the issues• Establishment of low emiRance– Low emiRance at high charge should be provenexperimentally– SimulaPon and long‐term beam test is urged• Strategy– These should be developed in parallel but independentlyof linac operaPon

2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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Studies on cathode, cavity and laser
We start with conﬁguraPons, blue & green below,
though other combinaPons can actually be applied.

• Cathode– Cu → study with 200nm– Cs2Te  266~205nm– LaB6 , Ir5Ce  Thermal＋337~266nm• Cavity– 1.6‐cell ATF (BNL) type and ½‐cell type in high gradient– DAW in medium gradient with bunching in cavity• Laser– TiSa 3rd 266nm and 4th 200nm– YVO4  337~266nm
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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DAW + LaB6 (or Ir5Ce)• For long‐term stable operaPon
Maintenance Free / Long Life
/ Purged into airCavity : Lower Electric Field‐ Stable operaPon‐ Short Ageing Time: 60 MV / m (on cathode): 100 MV / m (maximum)

This RF‐Gun( DAW +LaB6 thermal) was
already in operaPonat Tokyo University ofSciencesince 2008.
Stable cathode : LaB6 or Ir5Ce‐ Not acPve, Solid (not thin ﬁlm), High MelPng Temperature : life Pme >> Cs2Te‐ WorkfuncPon φ =2.8 eV(LaB6), 2.57 eV(Ir5Ce): laser power << metal
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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YVO4 Laser under development start assembling
114.2 MHz : λ/2 = 1.3125 m, 30 ps, 1.5 mJ
YVO4LD (10W, 808 nm)

1064nmSESAMPockels Cell
YVO4

YVO4
Halfwave plate

Pockels Cell
YVO4

YVO4

1064 → 266nm
BBO

Polarizer:
Mirror:Dichroic Mirror:
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

26

TiSa laser system under procurement
PerformanceConﬁguraTon••••••••CENTAURUS ampliﬁer
Compact stretcher (ofner type,graPng base)
RegeneraPve ampliﬁer (2 pockelscell type)
Nd:YAG pump laser(output>110mJ, 532nm, 100Hz)
MulP‐pass ampliﬁer
Gen pulse (SynchronizaPonmodule)High power opPcal compressor
Harmonic generator (3rd and 4th )••••••••

Rep rate 100Hz
Ti:Sa center wave length 800nm
Output power > 6mJ abercompression ＠800nm
Energy stability <2% RMS ＠
800nm in +:/‐ 1degC
Pulse width < 2psec ＠800nm(typical 1ps)
Band width <1,5 Pmes transform
limit ＠800nm
Beam proﬁle Gaussian
Output pulse energy > 100 μJ ＠FHG 200nm

To be delivered by the end of this JFY, in acouple of months.
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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Planning• Test with installing one system into A1– System with DAW+ LaB6 by YVO4 laser– InstallaPon at A1 from April 2011
• Low‐emiRance beam for emiRance growth study• EvaluaPon of RF gun property and potenPal• Eﬀorts to study feasibility of key components– TiSa 4th 200nm, 100µJ– High gradient RF gun (Half‐cell or 1.6‐cell)– Import Cs2Te technology and gun cavity from ATF– Study Ir5Ce
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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RF Gun installaPon to A1

2011.04 : RF‐Gun installaPon => will be tested by summer shutdown
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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One system at A1 gun areaand parallel eﬀorts in various areas
1st acc str

Free spacefor RF gun

Buncher

A1 bunching secTon

2011/2/7

Area planned for RF gun
development

Linac Upgrade for SuperKEKB (Higo)

30

Photo‐RF gun for electron source
plan
JFY2011

JFY2012

JFY2013

JFY2014

JFY2015

Cavity & cathodeDevelopments for more stable and higher charge

Laser
RF gun development
Test system
at A1

System at A1 for study use
Establish A1 system
Commissioning
Low‐intensity beam from A1 for studies

3‐1 gun2011/2/7

3‐2 gun

Linac Upgrade for SuperKEKB (Higo)

A‐1 gun31

EmiRance preservaPon
Refer to the following talk by Yoshida2011/2/7

Linac Upgrade for SuperKEKB (Higo)

32

Source of growth and strategy• Possible sources– Dispersion– RF kick mostly from cavity– Wake ﬁeld
– CSR＠J‐ARC• Strategy– Improve alignment– Measurement of slice emiRance andcompensaPon– BeRer BPM resoluPon for BBA– 3‐ring simultaneous injecPon should be inmind

2011/2/7

Linac Upgrade for SuperKEKB (Higo)

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 Yoshida’s talkEmiRance growth as of now
EmiRance Measurement @2009.07.01
AB
J‐ARCCWire scannerGun213Emittance Measurement

Emittance Measurement

800350600

γεx500
400

1nC

300

1nC

3nC

250

3nC

5nC

200

5nC

γεy

700

300

1502001001005000B

C5B

C5SectorSector

2011/2/7

54Linac Upgrade for SuperKEKB (Higo)

34

Alignment: status and strategy• As of KEKB startup– Laser alignment 0.1㎜ was not established– Sector A,B,C were added but not fully tuned / measured• Present– Sector C misalignment of ~mm– Sector 2 positron secPon is kinked in ~0.3mrad• For SuperKEKB– SpeciﬁcaPon ~0.1㎜ in mind, actual value under evaluaPon– Global alignment with convenPonal techniques– Misalignments will be corrected locally by laser tracker, etc.
– Establish alignment method as a base for BBA
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

35

EmiRance strategy and R&D’s• Improve alignment where possible– ConvenPonal method is applied  < 1mm• Growth source should be idenPﬁed– Measurement of emiRance• Add more measurement points• Measurement of slice emiRance• Suppression and/or correcPon– Dispersion correcPon– Wake ﬁeld suppression and compensaPon withoﬀset injecPon– Proceed BBA with beRer BPM resoluPon
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

36

EmiRance preservaPon plan
JFY2011

JFY2012

JFY2013Growth source
idenTﬁcaiton
ConstrucTon ofmeasurement line
Local re‐alignment withconvenTonal method

JFY2014

JFY2015

Commissioning
Pulse ST, Q anddeﬂector etc.
Re‐alignment and new supports

BPM resoluTon improvement
BBA
Establish emiZance preservaTon
Low‐intensity beam from A1 for studies
3‐1 gun2011/2/7

3‐2 gun

Linac Upgrade for SuperKEKB (Higo)

A‐1 gun37

AcPon plan in JFY2011• Positron– FLC beam test and stability conﬁrmaPon– Large aperture accelerator structures– Design of bypass for electron beam

• Electron– Install RF gun at A1 and get operaPonal experience– RF gun caviPes are developed– Cathode materials are evaluated– Laser development is proceeded• EmiRance– Improve local alignment– Reinforce emiRance measurement– IdenPfy source of growth– Try suppression and compensaPon
2011/2/7

Linac Upgrade for SuperKEKB (Higo)

38

Injector upgrade
JFY2011

JFY2012

JFY2013

JFY2014

ConstrucTon of HER, LER, DRAMD

System integraTonLarge aperture acc

JFY2015

Commissioning

Commissioning
Higher intensity

Study of cathode, cavity and laser
System at A1 used for study
Improvements in stability & intensity

EmiZance study
ConvenTonal alignment
BPM resoluTon and BBA

Total system
Improvements
PF, AR injecTon 3‐1 gun
2011/2/7

3‐2 gun
Linac Upgrade for SuperKEKB (Higo)

A‐1 gun39Longer scope to 2014

• Positron in higher charge– Develop a system for 1 nC in a cost eﬀecPve manner witha conﬁguraPon extendible to higher charge• Electron for higher charge and stable operaPon– Establish an RF gun at A1 serving >1nC with low emiRance– Study results are introduced to improve the system tohigher charge and stable operaPon• EmiRance in high charge– Growth source is idenPﬁed and compensated– Alignment is developed as required– Independent opPcs will be realized to fully control three
diﬀerent beams from pulse‐to‐pulse basis, as budget
allows2011/2/7

Linac Upgrade for SuperKEKB (Higo)40