Yujong Kim , K. Floettmann, and T. Limberg DESY Hamburg, Germany Dongchul Son and Y. Kim

Yujong Kim, K. Floettmann, and T. Limberg DESY Hamburg, Germany

Dongchul Son and Y. KimThe Center for High Energy Physics, Daegu, Korea

[email protected], http://www.desy.de/~yjkim

New Bunch Compressors for ILC

TESLA-S2E-2004-47

November 13th-15th, 2004, KEK, Japan

2

Bunch Compressor in TESLA TDR

TeV-Energy Superconducting Linear Accelerator Projects - TTF-2, TESLA X-ray FEL, TESLA Linear Collider

- One stage : sensitive to RF jitter- Many dipoles : twelve for 3.23 deg bending six for 6.46 deg bending- ISR & CSR problem, even microbunching instability - Short-range wakefields in TESLA modules are not included in TDR BC part

BC ParametersEnergy ~ 5.0 GeVCharge = 3.2 nCInitial energy spread at DR exit = 0.13%Initial rms bunch length = 6 mmFinal rms bunch length = 0.3 mmCompression factor = 20Initial horizontal emittance = 8.0 mm.mradInitial vertical emittance = 0.02 mm.mrad

3

New BC Layout for ILC (10NOV04 Version)


Final parametersE = 6.0 GeV = 2.173%z = 300 m nx= 8.7 m, ny= 0.02 m

z = 6.00 mm 673 m 300 m

Damping Ring

ACC1 ACC2 ACC4

Q=3.2 nC e-beam

23.4 MV/m-45 deg

24.8 MV/m170.0 deg

ACC39 ACC5 ACC6ACC3BC1

E = 5.689 GeV ~ 2.4%R56 = 236 mm = 5.3 deg

E = 6.0 GeV ~ 2.174%R56 ~ 17 mm ~ 1.4 deg

BC2

13.3 MV/m-21.5 deg

Up to main Linac : ELEGANT with CSR, ISR, and geometric short-range wakefields.but without space charge

Initial parametersE = 5.000 GeV = 0.13% (small !)z = 6.0 mm nx= 8.0 m, ny= 0.02 m

1/8.9 1/2.2

4

New Bunch Compressors Layout for ILC


From various experiences in Start-To-End simulations and BC designs for TTF2, European XFEL, SCSS, PAL XFEL, we have chosen two BC stages

5

Twiss parameters along BC beamline


6

Longitudinal phase space around modules


Head

7

Longitudinal phase space around BC1


Linearization by two ACC39 modules (3.9 GHz)

8



Edges : over (or under)compression by the nonearlity due to wakefieds, T566, RF curvature

9



Edges : over (or under)compression by the nonearlity due to wakefieds, T566, RF curvature

10



From various experiences in Start-To-End simulation and BC designs for TTF2, European XFEL, SCSS, PAL XFEL, we have chosen two BC stages.

11




8.9 times reduction

2.2 times reduction

12




8.7 mm.mrad

13




Before BC1 After BC2

14





15





16

Summary


From various experiences in Start-To-End simulations and BC designs for TTF2, European XFEL, SCSS, and PAL XFEL projects, we have chosen two BC stages, we have designed one possible new BC layout for ILC.

Detail design methods will be discussed during discussion time.

Checking of possibility of 2nd harmonic modules (2.6 GHz)

We should check end effects by simulating from gun to damping ring.

See next pages, which are related with discussion.

17

Bunch Compressor (BC) Working Principle


Bunch Compressor Layout for SCSS Project - Y. Kim et al, NIMA 528 (2004) 421

chicane. bendr rectangulathefor2

3where

))/(()/()/(

56566

3256656

RT

EdEEdETEdERdzdz iiiif

)3

2(2 2

56 BB LLR

dt

dETail

Head

from precompressor linac from chicane

18

Coherent Synchrotron Radiation (CSR) in BC

In BC where dispersion is nonzero, bunch length becomes smaller.Short electron bunches in dipole can radiate coherently (CSR) at wavelength CSR from tail electrons can overtakes head electrons after the overtaking length.

CSR generates correlated energy spread along bunch:

Electrons are transversely kicked at the nonzero dispersion region or in BCHence, projected emittance is increased in BC due to CSR.

.radiusbendingis,lengthbunchrmsiswhere 243/12

OT RRL zz

3432dipole1 220 /

z/

Be,

R

NLr.


z

Electron path

CSR from tailTail

LOT Head

E

dEx

x

xx

BCin0

Dipole region

19

Coherent Synchrotron Radiation (CSR) in BC

Without CSR self-interaction

With CSR self-interaction

DM3 DM4DM2DM1

Head : energy gain by CSR

Tail : energy loss due to CSR

Head with lower energy


x

z

Projected emittance growth due to CSR

E

dEx

x

xx

BCin0

Courtesy of M. Dohlus

20

CSR Wakefield for None Uniform Beams


If there is a nonlinearity in current distribution, the local charge concentration or spike is generated during the bunch compression process. In this case, CSR is enhanced due to the local charge concentration. (R. Li, LINAC2000)

una Courtesy of Dr. R. Li

[Longitudinal Charge Distribution and CSR force for a compressed bunch]

21

LCLS CSR Microbunching Instability in BCs

Courtesy of P. Emma and M. Borland[x versus z without SC-wiggler]

[x versus z with SC-wiggler]

230 fsec14.3 GeV at undulator entrance

projected emittance growth is simply ‘steering’ of bunch head and tail

slice emittance is not altered

0.5 m

slice emittance and energy spread are changed !

ELEGANT Tracking


without space charge force

22

Action of Longitudinal Space Charge (LSC)


If there is a density modulation, space charge pushes electrons from higher density region to lower density region, creating energy modulation in the process.

Density modulation Energy modulation

Space charge oscillation frequency (Z. Huang et al, PRST-AB Volume 7, 074401, 2004) :

23

Gain of LSC Microbunching Instability – 1D


1-D longitudinal space charge impedance (LSC) per unit length & oscillation frequency are:

(Z. Huang et al, PRST-AB Volume 7, 074401, 2004).

Gain of LSC Microbunching Instability

Z is intergrated LSC impedance. (Schneidmiller et al, TESLA-FEL-2003-02).Here amplitude damping due to emittance and 2D model are ignored !

24

Slice emittanceProjected emittanceSlice energy spread Growth !!!

LSC & CSR Microbunching Instability


Initial current density modulation

Induced energy modulation

by longitudinal space charge force (LSC) in the drift & linacby coherent synchrotron radiation (CSR) in the bunch compressorby the geometric wakefields in Linac

dzf = dzi +R56(dE/E)i in BC

Amplified currentdensity modulation

1

2

denistycurrentofamp. Normalized

densitycurrentofamp. NormalizedGain

25

Beam energy : 1.0 GeV (2006)Peak current : 2.5 kArms bunch length : 50 μm ~ 166 fsBunch separation : 111 nsNumber of bunch per train : 7200Repetition rate : 10 HzSlice transverse normalized rms emittance : 2 μmrms beam size : 68 μmrms energy spread : 1 MeV @ 1.0 GeVUndulator period : 27.3 mmUndulator gap : 12 mmK-parameter : 1.17Undulator length : ~ 30 mPeak magnetic field : 0.495 TSASE source wavelength : 6.4 nm ~ 120 nmSaturation length : 27 mPeak power : 2.8 GW Average power : 40 W (Schneidmiller et al, TESLA-FEL-2003-02)FEL pulse length (FWHM) : ca. 100 fsPeak (average) spectral brightness : 2.4×1030 (3.5×1022) photons/sec/mrad2/mm2/0.1%BW

Microbunching Instability at TTF2

RF-GUN ACC1 ACC2 ACC3 ACC4 ACC5BC2 BC3

ACC6

BYPASS

UNDULATORDUMP

COLLIMATOR

LOLA

SEEDING

ACC39

E = 120.9 MeV R56 = 169.9 mmσδ = 1.03%Θ = 17.5 deg

σz = 2.09 mm 339 µm 67 µm

E = 437.9 MeV R56 = 48.7 mmσδ = 0.57%Θ = 3.8 deg


Analytically estimated maximum gain is about 320 at ~ 2.0 ps

26

New S2E Simulations on TTF2 Microbunching

RF-GUN ACC1 ACC2 ACC3 ACC4 ACC5BC2 BC3

ACC6

BYPASS

UNDULATORDUMP

COLLIMATOR

LOLA

SEEDING

ACC39

E = 120.9 MeV R56 = 169.9 mmσδ = 1.03%Θ = 17.5 deg

σz = 2.09 mm 339 µm 67 µm

E = 437.9 MeV R56 = 48.7 mmσδ = 0.57%Θ = 3.8 deg 2.0 ps modulation with 1.5 million particles

gain

projected emittance

slice emittance

Gain of Microbunching Instability at TTF2 is not so high !!!


(Yujong Kim et al, EPAC2004)

27

BC Design Concepts against Microbunching


Therefore, we choose the normal 4-bend chicane instead of S-type chicane !

Under 2.0 ps modulation with 20% amplitude,S-type chicane generates much stronger microbunching instability after BC3

Strong slice emittance growth !!!

6-bends S-type chicane 4-bends normal chicane

No strong slice emittance growth !!!

28TeV-Energy Superconducting Linear Accelerator Projects - TTF-2, TESLA X-ray FEL, TESLA Linear Collider

Strong compression at BC1 to increase uncorrelated energy spread at BC2.Large uncorrelated energy spread at BC2 by putting the BC2 at a lower energy region, which is useful to avoid over-compression at BC2 due to long. wakefields.

(Before BC) (After BC)

BC for Phase-I of SCSS Project

BC Design Concepts against Microbunching

To keep longitudinal normalized emittance during compression, uncorrelated energy spread is automatically increased by the compression factor. If we consider space charge force in BC, this is bigger ! (Private communication with M. Dohlus)

ncompressioduring inconst zu

29

Concepts against CSR & Chromatic Effects


Choosing a somewhat larger energy spread, we can choose a smaller R56

Choosing a long drift space ΔL to reduce bending angle for a required R56

chicane. bendr rectangulathefor2

3where

))/(()/()/(

56566

3256656

RT

EdEEdETEdERdzdz iiiif

)3

2(2 2

56 BB LLR

European XFEL (10AUG04 Version)

30


Linearization of longitudinal phase space with a higher harmonic cavity

number.harmonic the is and linac,frequencylowthe of gain

energy is cavity,harmonichighertheofgainenergytheiswhere

cos)/(0)(

)(

)(

12

12

12

02

21

22

n

GLGL

nGLGLdzd

dEdEd

dzd

ds

dz

Linearized range ~ 60 degree ~ 29.2 ps ~ 3.7 times of 8 ps bunch

C-band Linac + X-band Correction Cavity

Only C-band Linac

“-” means deceleration !

-70 MeV deceleration

SCSS BC

Y. Kim et al, NIMA 528 (2004) 421


31



Longer bunch length at BC1 Weaker CSR at BC1 Stronger compression at BC1

Shorter bunch length at BC2 Stronger CSR at BC2 Weaker compression at BC2

BC1 : 1.76 µm → 94 µmCompression factor = 18.7

BC2 : 94 µm → 21.5 µmCompression facto = 4.4

European XFEL (10AUG04 Version)

32

Strong focusing lattice around BCs to reduce CSR induced emittance growth



Strong focusing against CSR-functions ~ 0 -functions ~ 3

Before BC1

After BC1

33



Shorter linac with a lower frequency between BC1 and BC2 to control over-

compression and CSR at BC2 due to the short-range longitudinal wake

fields.

after BC2after BC2

after L2after L2

Courtesy of P. Emma

Over-compression after BC2 due to longitudinal wakefields in the long L2 linac

BC2 for LCLS

34



Small quadrupole length (shortest = 5 cm) around BCs to reduce chromatic effects.

1, QMyx Lk

Triplet with 5cm-10cm-5cm length for TTF2 BC2

35

BCs for European XFEL (13JAN04 Version)


ACC1 ACC2 ACC4 ACC5RF-GUN

Q=1.0 nC e-beam

0.0 m 12.0444 m

ASTRA with Space Charge

11.5 MV/m25.0 MV/m-18.3 deg

34.8 MV/m160.6 deg

ACC39

60 MV/m38 deg

ACC6ACC3BC1

z = 1.76 mm 113 m 23 m

E = 510 MeV ~ 1.89%R56 = 87 mm = 3.95 deg

E = 510 MeV ~ 1.88%R56 = 4.8 mm = 0.93 deg

ACC7 ACC8 ACC118

UNDULATOR, 200 mz = 20.5 m

1567 m

20.65 MV/m0.0 deg

All projected parameters !E = 20.0 GeV = 0.008%x= 37.3 m, y= 31.6 m, z = 20.5 m nx= 1.15 m, ny= 0.94 m

BC2

ACC9

20.5 MV/m-29.6 deg

20.65 MV/m0.0 deg

To the end of Linac : ELEGANT with CSR with geometric wakefields

without space charge

FODO MODULES

With TESLA XFEL Injector, n= 0.9 m


Longitudinal Phase Space (13JAN04 Version)


Slice Parameters at LINAC END (13JAN04)

u = 4.8E-5 before BC2, which is about four times higher than that of TTF2Therefore we are safe from the strongest microbunching with 2.0 ps period.


Slice Parameters at LINAC END (13JAN04)

RED : before BC1BLUE : LINAC END

No slice emittance growth in core !

39

BCs for LCLS

new

25-1a30-8c

21-1b21-1d X

21-3b24-6d

SC-wiggler to give u = 3.0E-5 before BC-2


Laser Heater to give u = 9.0E-5 at the undulator entrance

Without any laser heater and SC-wiggler, u = 3.0E-6 before BC-2

Over-compression at BC2 due to strong longitudinal wakefield at long L2 linac.Strong CSR at BC2 due to low compression at BC1 and high compression at BC2High beam energy at BC2 Strong microbunching instability due to small uncorrelated energy spread at BC2

40

LCLS BC Performance


Courtesy of P. Emma

Compression factor at BC 1 ~ 4.4Compression factor at BC2 ~ 8.6 → Strong CSR at BC2

41

LCLS BC Performance


Courtesy of P. Emma

after BC2after BC2

after L2after L2

BC2 ~3.2 µm

Even though projected emittance is large, slice emittance is good enough for SASE source saturation when laser heater is operated well.

projected emittance along linacwithout any heater

42

BCs for PAL XFEL (05DEC03 Version)


X1 X2 X3 K2

Q=1.0 nC e-beam

0.0 m 8.7 m

ASTRA with Space Charge

18.0 MV/m30.5 MV/m5.5/-2.5 deg

56.75 MV/m180.0 deg

120 MV/m32.02 deg

K3X2X BC1

z = 829 m 114 m 26 m

E = 442 MeV ~ 1.84%R56 = 38.9 mm = 3.5 deg

E = 700 MeV ~ 1.31%R56 = 6.7 mm = 1.45 deg

K4 K5 K12

UNDULATOR, ~ 60 m

z = 26 m

227 m

20.0 MV/m0.0 deg

All projected parameters !E = 3.389 GeV = 0.033%x= 68 m, y= 62 m, z = 26 m nx= 1.0 m, ny= 0.9 m

BC2

K6

30.0 MV/m-27.5 deg

20.0 MV/m0.0 deg

To the end of Linac : ELEGANT with CSR with geometric wakefields

without space charge

30.0 MV/m-45.0 deg

Existing PLS Linac

Existing PLS LinacNew Linac & BCs

RF-GUN

With S-band Photoinjector, n= 0.9 m

43

Parameters along PAL XFEL Linac


1.0 µm

Projected emittance

RED : before BC1BLUE : LINAC END

No slice emittance growth in core !

44

Slice Parameters at PAL XFEL LINAC END


45

LCLS TESLA XFEL PAL XFEL

BC type Two Stage One Stage Two Stage Beam energy 250 MeV 511 MeV 442 MeV Relative energy spread 1.78% 1.89% 1.84%Uncorrelated energy spread Bending angle 4.62 deg 3.95 deg 3.5 degMomentum compaction R56 35.9 mm 87 mm 38.9 mmTotal chicane length 6.56 m 20.0 m 12.2 mDipole length 0.20 m 0.30 m 0.30 m Drift length ΔL 2.6 m 8.9 m 5.0 mInitial rms bunch length 0.83 mm 1.76 mm 0.82 mm Final rms bunch length 190 m 113 m 114 mCompression factor 4.4 15.6 7.2Initial projected emittance 0.900 m 0.907 m 0.900 mFinal projected emittance 0.995 m 1.020 m 1.010 m

Initial uncorrelated energy spread is rms value which is estimated at +/- 0.1 mm core region

1st BC Performance Comparison


5100.1 6105.8 6102.9

ASTRA simulation and measured result give about 4.0 keV intial uncorrelated energy spread.

46

LCLS TESLA XFEL PAL XFEL

BC type Two Stage One Stage Two Stage Beam energy 4.54 GeV 511 MeV 700 MeV Relative energy spread 0.76% 1.88% 1.31%Uncorrelated energy spread Bending angle 1.878 deg 0.930 deg 1.450 degMomentum compaction R56 22.5 mm 4.8 mm 6.7 mmTotal chicane length 22.1 m 20.0 m 12.2 mDipole length 0.40 m 0.30 m 0.30 m Drift length ΔL 10.0 m 8.9 m 5.0 mInitial rms bunch length 195 m 113 m 114 m Final rms bunch length 22 m 20.5 m 26 mCompression factor 8.86 5.5 4.38Initial projected emittance 0.995 m 1.020 m 1.010 mFinal projected emittance 2.725 m (SW on) 1.200 m 1.116 m

All uncorrelated energy spread is estimated at +/-0.1 mm core region and without any heater !

2nd BC Performance Comparison


6100.3 5108.4 5103.4

Initial uncorrelated energy spread at BC2 is increased after compression at BC1

47

Optimized BCs for various XFEL Projects


PAL XFEL (21JUL04 Version) by Yujong Kim

European XFEL (10AUG04 Version) by Yujong Kim

48

Optimized BCs for various XFEL Projects


6 GeV SPring-8 Compact SASE Source (30SEP04 Version) by Yujong Kim

Documents

Yujong Kim , K. Floettmann, and T. Limberg DESY Hamburg, Germany Dongchul Son and Y. Kim