Cathode Laser Pulse Shaping For High Brightness Electron Sources (PITZ Experience)

Cathode Laser Pulse Shaping For High Brightness Electron Sources

(PITZ Experience)Mikhail Krasilnikov (DESY) for the PITZ Team

Content:• Photo cathode laser system at PITZ• Temporal pulse shaping – flat-top profile:

• rise/fall time impact• flat-top modulations studies

• Transverse laser distribution influence• Advanced pulse shaping of the cathode laser: 3D ellipsoid• Summary

ICFA Workshop on Future Light Sources, March 5-9, 2012Thomas Jefferson National Accelerator Facility, Newport News, VA

Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 2

Yb:YAG laser at PITZ with integrated optical sampling system

Two-stage Yb:YAG double-pass amplifier

G ~ 40

Emicro= 0.002 mJ

Emicro~ 80 mJ

Emicro= 0.002 mJ

Emicro~ 2 mJ

LBO BBO

UV output pulsesEmicro~ 10 mJ

Optical Sampling System (OSS)

scanning amplifier(Yb:KGW)Yb:YAG power regen

G ~ 106

Pulseselector

pulse shaper

Highly-stable Yb:YAG oscillator

pulse selector Nonlinear

fiber amplifier Resolution: t < 0.5…1 ps

t ~ 1.7 ps

PITZ Photo cathode laser (Max-Born-Institute, Berlin)


Multicrystal birefringent pulse shaper containing 13 crystals

FWHM = 25 ps

edge10-90 ~ 2.2 ps

edge10-90 ~ 2 ps

birefringent shaper, 13 crystals

OSS signal (UV)

temperature controlled

birefringent crystal

motorized rotationstage

Gaussianinput

pulses

Shaped ouput

pulses

Will, Klemz, Optics Express 16 (2008) , 4922-14935

Photo cathode laser: temporal pulse shaping

FWHM ~ 11 ps

FWHM ~7 ps

FWHM ~ 17 ps

FWHM ~ 2 ps

FWHM ~ 11 ps

FWHM ~7 ps

FWHM ~ 17 ps

FWHM ~ 2 ps

Gaussian:

FWHM ~ 20 ps

Simulated pulse-stacker FWHM ~ 24 ps

FWHM ~ 24 ps


Photo cathode laser: flat-top temporal pulse profiles

Laser temporal profile used for the emittance optimization at various bunch charge levels

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 140

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

02.05.2011, 2nC-optimization

07.05.2011, 1nC-optimization

12.04.2011, 0.25nC-optimization



t, ps

norm

. las

er in

tens

ity, a

.u.

FWHM=(21.20±0.33)psrise time=(2.02±0.11)psfall time=(2.62±0.13)ps


0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

2 3 4 5 6 7rise/fall time, ps

emitt

, mm

mra

d

measured XY-emittance

simulated XY-emittance

Check effect on rise/fall time – results of 2009

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

2 3 4 5 6 7rise/fall time, ps

emitt

, mm

mra

d

EmXEmY

• Q=1nC• Imainoptimized• Gun: +6deg off-crest• Booster: on-crest• Laser: temp FWHM~20ps, BSA=1.5mm

• In 2009 it was not possible to measure the effect with current machine stability

•After the improvement of the phase stability the effect is planned to be rechecked (this year)

Best measurements(22.08.2009M)

http://pitzlb.ifh.de:8080/PITZelog/data/2009/37/09.09_a/2009-09-09T21:12:11-00.ps


http://pitzlb.ifh.de:8080/PITZelog/data/2009/37/10.09_M/2009-09-10T10:09:33-00.ps


-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 160,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

Temporal laser shapesused for the simulation

flat top 5 % 10 % 20 % 30 % 40 % 50 % 75 % 100%

inte

nsity

, Q n

orm

.

time, ps

-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 160,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

flat top 5 % 10 % 20 % 30 % 40 % 50 % 75 % 100%


inte

nsity

, Q n

orm

.

time, ps

-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 160,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

flat top 5 % 10 % 20 % 30 % 40 % 50 % 75 % 100%


inte

nsity

, Q n

orm

.

time, ps

-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 160,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0 flat top 5 % 10 % 20 % 30 % 40 % 50 % 75 % 100%


inte

nsity

, Q n

orm

.

time, ps

Various laser temporal flat-top modulationsSimulations

0,0 0,2 0,4 0,6 0,8 1,00,60

0,65

0,70

0,75

0,80

0,85

0,90

0,95

1,00

1,05

1,10

1,15

1,20

2 peaks 3 peaks 4 peaks 5 peaks

emitt

ance

(mm

mra

d)

modulation depth

0

10

20

30

40

50

60

70

80

Simulated optimum emittance vs.modulation depth

em

ittan

ce c

hang

e (%

)

• higher modulation frequency larger emittance growth rate• reliable simulations for modulations with >5 peaks are

difficult

simulations with gun on-crest, other parameters optimized

2 peaks

3 peaks

4 peaks

5 peaks


Laser temporal profile modulationsExperiment: measurements in 2009

0 20 40 60 80 1000,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

2,2simulation

2 peaks 3 peaks 4 peaks

experiment2 peaks on crest +6 deg3 peaks on crest +6 deg4 peaks on crest +6 deg

emitt

ance

(mm

mra

d)

modulation depth (%)

Experimental results compared to simulations

2 peaks

3 peaks

4 peaks

default

In 2009 it was not possible to measure the effect with the current machine stability

http://pitzlb.ifh.de:8080/PITZelog/data/2009/33/13.08_n/2009-08-14T01:25:39-00.ps











Measurements with / without modulations on the temporal laser distribution

with modulationswithout modulations

Approach detuning of an aligned pulse shaper, i.e. by purpose introducing modulations on the flat-top of the temporal laser distribution and measuring momentum distribution in HEDA

Laser temporal profiles

Electron beam longitudinal momentum distribution

Electron beam longitudinal momentum distribution

Machine conditions: gun: on-crest booster: +10deg off-crest bunch charge: 500pC

(5 laser pulses used) (1 laser pulse used)


• Resonantly driven plasma wave high tranformation ratio 5 Bunchlets inside the bunch:

Studies for Particle Driven Plasma Acceleration @PITZ

• Self-modulation without seed but with flat-top modulation:

• Self-modulation with seed pulse:

to be sent to bunch compres-sor

mradmmxy 448.0

mradmmxy 471.0

,45.48 mxy m

,25.83 mxy m

mmz 311.0

mmLb 05.4,50pCQ

,10pCQ

Flat-top:

Gauss:

1231 1069.3][ cmnb

1332 1005.1][ cmnb

1bn2bn

Photo cathode laser distributions

Output parameters for 2 sub-bunches @6.28m from cathode:

probe bunch

V

V


Photo cathode laser: transverse pulse shaping

laser spot at “virtual cathode”

Beam Shaping Aperture (BSA) plate is now replaced by an iris with remotely tunable opening

imaging of the BSA onto the photo cathode

laser beam steering



Photo cathode laser: transverse distributions

BSA=1.2mm (1nC)

RMS sizes (no Gaussian fit!)x=0.30 mm and y=0.29 mm

RMS sizes (no Gaussian fit!)x=0.13 mm and y=0.12 mm

BSA=0.5mm (0.1nC)


“Fresh Cathode Effect” studies 07.05.2011 > 07.05.2011M – “Old” cathode (#110.2) best 1nC machine setup (+cathode measurements: dark current, QE maps)> 07.05.2011N – “New” (fresh) cathode (#11.3) best 1nC machine setup (+cathode measurements : dark current, QE maps)

Old cathode #110.2 QE-map New cathode #11.3 QE-mapCathode laser Cathode laser

07.05.2011M3x3 stat:X-emit=0.742±0.021Y-emit=0.782±0.028XY-emit=0.761±0.022

07.05.2011N: 3x3 stat:Xemit=0.724±0.056Y-emit=0.603±0.038XY-emit=0.661±0.046

e-beam at EMSY1

e-beam at EMSY1










Laser pulse shaping studies for further improvement of the electron beam quality in a photo injector

cylindrical 3D ellipsoidal

temporallyGaussian

(e.g. FLASH)Trms=4.4ps

Flat-top(e.g PITZ)

FWHM~20ps, rt~2ps

222SpChRFcath

min :shapelaser cathode SpCh

Beam dynamics (ASTRA) simulations for PITZ-1.8 setup


BD simulations for bunch charge 1 nC

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 2 4 6 8 10z, m

mm

mra

d

Xemit (Gaussian 4.4ps)

Xemit (flat-top)

Xemit (ellipsoid)

Slice parameters at z=5.74m

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-6 -4 -2 0 2 4 6z-<z>, mm

sl.e

mitt

ance

, mm

mra

d

0

10

20

30

40

50

60

beam

cur

rent

, A

XYemit (Gaussian, 4.4ps) XYemit (f lat-top)

XYemit (ellipsoid) current (Gaussian 4.4ps)

current (flat-top) current (ellipsoid)

1.02

0.65

0.42

0.62

0.44

0.34

0.50

0.37

0.290.35

0.260.21

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

Trms=4.4ps 20ps/2ps Trms=Trms(f-t)

Gaussian flat-top Ellipsoid

100%

95%

90%

80%

Core emittance

3D ellipsoidal

temporal profile Gaussian Flat-top

transverse distribution

Trms ps 4,4 5,8 5,8

XYrms mm 0,427 0,415 0,389

Ek eV

th.emit. mm mrad 0,36 0,35 0,33

Ecath MV/m

phase deg -3,1 -1,9 -2,8

maxBz T -0,2253 -0,2258 -0,2277

maxE 18,5 19,1 19,1

phase deg

charge nC

energy MeV 22,3 22,7 22,8

proj.emit. mm mrad 1,02 0,65 0,42th./proj.em. % 36% 54% 78%<sl.emit.> mm mrad 0,82 0,58 0,41

51 106 270

RF-

gun

3D ellipsoidal

cylindrical

laser shape type

radial homogen.

e-be

am @

EM

SY

1

B~Ipeak/em 2̂

1

0CD

S

boos

t

parameter unit

0,55cath

ode

lase

r

60


15

BD simulations for bunch charge 1 nC

Transverse phase space at z=5.74m

reduced beam halo almost no beam halo

Projected emittance (1nC) at EMSY1

100%60%

39%0%

20%40%60%80%

100%


rel.e

mitt

ance

Electron beam transverse distribution at z=5.74m


BD simulations for bunch charge 1 nC Projected emittance (1nC) at EMSY1

168%100%

65%0%

50%

100%

150%


rel.e

mitt

ance

Electron beam (Z-X) shape at z=5.74m

Longitudinal phase space (Z-Pz) at z=5.74m

less nonlinearity


Conclusions> Cathode laser pulse shaping is one of the key parameters for a high

brightness photo injector> Nominal temporal pulse shape at PITZ – a flat-top of ~ 20ps FWHM

Short rise/fall time, first trials were performed in 2009, to be checked soon Flat-top modulations: no large impact onto the transverse phase space, but longitudinal

phase space modulations

> Transverse laser distribution: Laser transport and imaging to the cathode “Fresh cathode” effect homogeneous emission area

> Beam dynamics simulations applying a 3D pulse shaping (ellipsoid) for the PITZ injector yield :

significant reduction in beam projected and slice emittance reduced beam halo and less sensitivity to machine parameters less nonlinear longitudinal phase spacepractical realization BMBF project with IAP, Nizhniy Novgorod, Russia


The End


BD simulations for bunch charge 100 pC

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 2 4 6 8 10z, m

mm

mra

d

Xemit (Gaussian 4.4ps)

Xemit (flat-top)

Xemit (ellipsoid)

Slice parameters at z=5.74m

0

0.05

0.1

0.15

0.2

0.25

-6 -4 -2 0 2 4 6z-<z>, mm

sl.e

mitt

ance

, mm

mra

d

0

1

2

3

4

5

6

7

8

9

10

beam

cur

rent

, A

XYemit (Gaussian 4.4ps) XYemit (flat-top)XYemit (ellipsoid) current (Gaussian 4.4ps)current (flat-top) current (ellipsoid)

0.32

0.18

0.13

0.2

0.130.11

0.16

0.110.09

0.11

0.08 0.07

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35


100%

95%

90%

80%

Core emittance

3D ellipsoidal

temporal profile Gaussian Flat-top

transverse distribution

Trms ps 4,4 5,8 5,8

XYrms mm 0,175 0,154 0,125

Ek eV

th.emit. mm mrad 0,15 0,13 0,11

Ecath MV/m

phase deg -1,5 1,4 0,8

maxBz T -0,2245 -0,2250 -0,2240

maxE 16,7 21,3 16,9

phase deg

charge nC

energy MeV 20,7 24,7 20,8

proj.emit. mm mrad 0,320 0,182 0,128th./proj.em. % 46% 72% 83%<sl.emit.> mm mrad 0,17 0,14 0,12

81 165 368

parameter unit

0,55cath

ode

lase

r

60

e-be

am @

EM

SY

1

B~Ipeak/em^2

RF-

gun

3D ellipsoidal

cylindrical

laser shape type

radial homogen.

0,1

0CD

S

boos

t


-1 -0.5 0 0.5 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

x, mm

y, m

m

20

BD simulations for bunch charge 100 pC

Transverse phase space at z=5.74m

almost no beam halo

Projected emittance (100pC) at EMSY1

100%57% 40%

0%20%40%60%80%

100%


rel.e

mitt

ance

-1 -0.5 0 0.5 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

x, mm

y, m

m

-1 -0.5 0 0.5 1-25

-20

-15

-10

-5

0

5

10

15

20

25

x, mm

px, m

rad


BD simulations for bunch charge 100 pC Projected emittance (100pC) at EMSY1

175%100% 70%

0%

50%

100%

150%

200%


rel.e

mitt

ance

Electron beam (Z-X) shape at z=5.74m

Longitudinal phase space (Z-Pz) at z=5.74m


BD simulations for bunch charge 1 nC Tolerances

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-1.0% -0.8% -0.6% -0.4% -0.2% 0.0% 0.2% 0.4% 0.6% 0.8% 1.0%

solenoid detuning

emitt

ance

gro

wth

Gauss

flat-top

Ellipsoid

optimain

optimainmain III )(

In the case of the ellipsoidal shaping the electron beam quality is less sensitive to machine parameters (e.g. main solenoid peak field)

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Cathode Laser Pulse Shaping For High Brightness Electron Sources (PITZ Experience)

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