Ellipsoidal bunches by 2D laser shapingEllipsoidal bunches by 2D laser shaping

Bas van der Geer, Jom LuitenEindhoven University of Technology

DESY Zeuthen30 November 2006

2) Experimental progress

1) Why pancakes do not work with 1nC and 40–60 MV/m

Jom Luiten

Bas van der Geer

work as good as 3D ellipsoids

Waterbags

• Transverse phase-space– No space-charge induced emittance degradation– No ‘slice’ dependence– O.J. Luiten, S.B. van der Geer et al, PRL 094802, (2004).– Confirmed by J. Rosenzweig and C. Limborg in NIM-A 557 (2006)

• Longitudinal phase-space– Ideal for linear compression– Manipulation possible at low energy– Energy spread can be recovered– S.B. van der Geer et al,

PRST-AB, 9, 044203 (2006)

Transverse (5-D) brightness:

Brightness

kTJmcI

B p

ynxn

p

2

,,2)2(

Eznynxn

Bmc

Q 2,,,

3)2(

B

2mc QBk T A

Source brightness

Options (at fixed Q):

• Lower Temperature T Ultra Cold Plasma cathodeB.J. Claessens et al., PRL 95, (2005)

164801

• Reduce Surface area A Carbon NanotubesNeedle cathodes…

• Reduce Pulse duration τ Pancake regime

Longitudinal phase space density

Long pulse Pancake3 ps 30 fs1 nC 100 pC~100 A/mm2 ~1 kA/mm2

(Both with A=π mm2)z

Energy

Pancake

Long pulse

Thermalspread

Longitudinal phase-spaceat cathode

kTJmcI

B p

ynxn

p

2

,,2)2(

The problem is not the highspace charge density ...

Gaussian bunch

Brightness degradation

Brightness degradation

px

x

Gaussian bunch

Space charge forces:• Non-linear• Slice-dependent

... the real problem is the space charge density distribution.

px

x

Gaussian bunch

1989 - 2003

Fighting the symptoms:• Emittance compensation (B. Carlsten)• Optimized transverse profile (L. Serafini)• Uniform temporal & radial profile (DESY, ...)• ...

Gaussian bunchWaterbag bunch

px

x

Space charge forces:• Non-linear• Slice-dependent

Space charge forces:• Linear• Slice-independent

Thermal-emittance-limited beam!

2004: Fundamental solution

History of uniformly charged ellipsoids

1929 Have linear fields in all three coordinatesO. D. Kellogg, Foundations of Potential Theory (Springer-Verlag, 1929).

1965 Ellipsoids with uniform mass collapse into a disk (astrophysics)C.C. Lin et al., Astrophys. J. 142, 1431 (1965).

Decades of use as idealized beams…

1997 Pancakes evolve into approximate waterbags L. Serafini, AIP Conf. Proc. 413, 321 (1997)

2004 Fundamental solution and practical recipeO.J. Luiten, S.B. van der Geer et al, PRL 094802, (2004).O.J. Luiten, S.B. van der Geer et al, EPAC (2004).

History of uniformly charged ellipsoids

1929 Have linear fields in all three coordinatesO. D. Kellogg, Foundations of Potential Theory (Springer-Verlag, 1929).

1965 Ellipsoids with uniform mass collapse into a disk (astrophysics)C.C. Lin et al., Astrophys. J. 142, 1431 (1965).

Decades of use as idealized beams…

1997 Pancakes evolve into approximate waterbags L. Serafini, AIP Conf. Proc. 413, 321 (1997)

2004 Fundamental solution and practical recipeO.J. Luiten, S.B. van der Geer et al, PRL 094802, (2004).O.J. Luiten, S.B. van der Geer et al, EPAC (2004).

2006 Well received in the accelerator communityJ.B. Rosenzweig et al., NIM-A 557 (2006), Emittance compensation …C. Limborg et al., NIM-A 557 (2006), Optimum electron distributions …S.B. van der Geer et al, PRST-AB, 9, 044203 (2006), Longitudinal …...

2D Waterbag bunch recipe

Femtosecond photoexcitation of pancake bunch • Half-sphere transverse laser intensity profile• Temporal laser profile is irrelevant

Automatic evolution into 3D, uniform ellipsoid

fs laser

Ellipsoid creation

How to Realize Uniform Three-Dimensional Ellipsoidal Electron BunchesO.J. Luiten, S.B. van der Geer et al, PRL 094802, (2004).

1.5 cell, 3 GHz rf-photogun + focusing solenoid• Eacc = 92 MV/m• Q = 100 pC

Waterbag bunch in a realistic field

zc = 0.9 m, E = 4.5 MeV

-0.4 -0.2 0.0 0.2 0.4GPT z-zc [mm]

-2

-1

0

1

2

x [m

m]

O.J. Luiten, S.B. van der Geer et al, EPAC (2004).

Waterbag bunch in a realistic field

• Confirmed at higher energies– Compatible with SPARC emittance compensation, 85 MeV

J. Rosenzweig et al., NIM-A 557 (2006), p. 87.

– 50% improvement on transverse emitance for LCLS, 63 MeVC. Limborg et al., NIM-A 557 (2006), p. 106.

0

0.2

0.4

0.6

0.8

1

0 200 400 600 800 1000

z [mm]

RM

S e

mitt

ance

[μm

]

Thermal emittance!

O.J. Luiten, S.B. van der Geer et al, EPAC (2004).

4 MeV

-0.4 -0.2 0.0 0.2 0.4GPT z-zc [mm]

4.1

4.2

4.3

4.4

4.5

4.6

4.7

Ene

rgy

[MeV

]

0

0.2

0.4

0.6

0.8

1

0 200 400 600 800 1000

z [mm]

RM

S e

mitt

ance

[μm

]

Thermal emittance!

10 fs

-0.4 -0.2 0.0 0.2 0.4GPT z-zc [mm]

-2

-1

0

1

2

x [m

m]

First waterbag bunch in a realistic field

O.J. Luiten, S.B. van der Geer et al, EPAC (2004).

I=50 A

Longitudinal compression

~0.4 m

Laser

rf φ

S.B. van der Geer et al, PRST-AB, 9, 044203 (2006),

3.5 MeV0.7 – 2.0 kA 30 – 100 fs0.7 – 1.5 μm

2D shaping @ PITZ

Limitations of 2D ‘pancake’ shaping:• Laser-pulse duration << Asymptotic bunch length• Fields of image charges << Acceleration field

PITZ: 1 nC, 50 MV/m, R=1 mm:• Pulse duration: 30 fs << 25 ps OK• Image charges: 36 MV/m << 50 MV/m Questionable

2D shaping @ PITZ

Settings:• 50 MV/m uniform, 1 nC, R=1 mm, 2D shaping of 30 fs ‘pancake’

0.1 0.2 0.5 1GPT Charge [nC]

0.0

0.5

1.0

1.5

2.0

2.5

3.0

RM

S E

mitt

ance

[mic

ron]

Pancake

3D shaping @ PITZ

Settings:• 50 MV/m uniform, 1 nC, R=1 mm, 3D shaping of 3 ps ellipsoid

Pancake3D

0.1 0.2 0.5 1GPT Charge [nC]

0.0

0.5

1.0

1.5

2.0

2.5

3.0

RM

S E

mitt

ance

[mic

ron]

Emission: 3D shaping 2D shaping

Highly non-linear fields! Highly non-linear fields!

Lower charge density Maintain short bunch

Long pulse lengthHigh acceleration field

3D versus 2D shaping

1.5 ps: 10 μm 15 fs: 1 nm

3D shaping @ PITZ

Settings:• 50 MV/m uniform, 1 nC, R=1 mm, 3D shaping of 10 ps ellipsoid

Pancake3D: 3 ps

3D: 10 ps

0.1 0.2 0.5 1GPT Charge [nC]

0.0

0.5

1.0

1.5

2.0

2.5

3.0

RM

S E

mitt

ance

[mic

ron]

3D shaping @ PITZ

Settings:• 50 MV/m uniform, 1 nC, R=1 mm, 3D shaping of 10 ps ellipsoid

Pancake3D: 3 ps

3D: 10 ps

0.1 0.2 0.5 1GPT Charge [nC]

0.0

0.5

1.0

1.5

2.0

2.5

3.0

RM

S E

mitt

ance

[mic

ron]

Pancake100 MV/m

Next

Experimental progress atExperimental progress atEindhoven University of TechnologyEindhoven University of Technology

Jom Luiten

2D ‘pancake’ shaping

Ingredients:• Ti:Sapphire 30 fs laser• Transverse shaping only

Ti:Saphire30 fs laser

Colinear THG800nm → 266 nm

Spatial filtering:800 nm gaussian

π shaper:Gauss → half-sphere

UVSphereGauss

800 nm after spatial filtering

ideal

π Shaper

Laser intensity

radius0 1 mm

π shaper

Input: Gaussian beamOutput: Half-sphere laser intensity profile (without losses)

0.15 mm BBO SHG

2.5 mm BBO Delay

Zero order retardation plate

0.04 mm BBO THG

R R+B R+B R+B R+B+UV

Incident beam:

1 kHz, 30 fs pulse @ 800 nm, 1 mJ/pulse

UV beam:

1 kHz, 30 fs pulse @ 266 nm Conversion efficiency ~ 10%

Colinear 3rd harmonic generation

Cooling channelbucking magnet

Tube for thermoheater

Stainless steel vacuum vessel

1.5 cell S-band cavity: Clamped design

f0=2.9918 GHz

f0=2.9980 GHzAbsorption

> 96 %

Q = 7600

0-mode

-mode

1.5 cell cavity: measured resonances

Lorentzian fits

1.5 cell cavity: field profile π-mode

Superfish♦ measured

Design and machining precision better than 5 μm

Cavity training

First results (November 2006)• 15 hours @ 2 Hz, 105 rf pulses• 65 MV/m

END