Ellipsoidal bunches by 2D laser shaping Bas van der Geer, Jom Luiten Eindhoven University of Technology DESY Zeuthen 30 November ) Experimental progress 1) Why pancakes do not work with 1nC and 40–60 MV/m Jom Luiten Bas van der Geer work as goodas 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 , (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, (2006)

Transverse (5-D) brightness: Brightness

Source brightness Options (at fixed Q): Lower Temperature TUltra Cold Plasma cathode B.J. Claessens et al., PRL 95, (2005) Reduce Surface area ACarbon Nanotubes Needle cathodes … Reduce Pulse duration τ Pancake regime

Longitudinal phase space density Long pulsePancake 3 ps30 fs 1 nC 100 pC ~100 A/mm 2~ 1 kA/mm 2 (Both with A=π mm 2 ) z Energy Pancake Long pulse Thermal spread Longitudinal phase-space at cathode

The problem is not the high space charge density... Gaussian bunch Brightness degradation

pxpx x Gaussian bunch Space charge forces: Non-linear Slice-dependent... the real problem is the space charge density distribution.

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

Gaussian bunch Waterbag bunch pxpx 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 1929Have linear fields in all three coordinates O. D. Kellogg, Foundations of Potential Theory (Springer-Verlag, 1929). 1965Ellipsoids with uniform mass collapse into a disk (astrophysics) C.C. Lin et al., Astrophys. J. 142, 1431 (1965). Decades of use as idealized beams … 1997Pancakes evolve into approximate waterbags L. Serafini, AIP Conf. Proc. 413, 321 (1997) 2004Fundamental solution and practical recipe O.J. Luiten, S.B. van der Geer et al, PRL , (2004). O.J. Luiten, S.B. van der Geer et al, EPAC (2004).

History of uniformly charged ellipsoids 1929Have linear fields in all three coordinates O. D. Kellogg, Foundations of Potential Theory (Springer-Verlag, 1929). 1965Ellipsoids with uniform mass collapse into a disk (astrophysics) C.C. Lin et al., Astrophys. J. 142, 1431 (1965). Decades of use as idealized beams … 1997Pancakes evolve into approximate waterbags L. Serafini, AIP Conf. Proc. 413, 321 (1997) 2004Fundamental solution and practical recipe O.J. Luiten, S.B. van der Geer et al, PRL , (2004). O.J. Luiten, S.B. van der Geer et al, EPAC (2004). 2006Well received in the accelerator community J.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, (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 Bunches O.J. Luiten, S.B. van der Geer et al, PRL , (2004).

1.5 cell, 3 GHz rf-photogun + focusing solenoid E acc = 92 MV/m Q = 100 pC Waterbag bunch in a realistic field z c = 0.9 m, E = 4.5 MeV 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 MeV C. Limborg et al., NIM-A 557 (2006), p Thermal emittance! O.J. Luiten, S.B. van der Geer et al, EPAC (2004). 4 MeV

Thermal emittance! 10 fs 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, (2006), 3.5 MeV 0.7– 2.0 kA 30– 100 fs 0.7– 1.5 μm

2D 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 psOK Image charges: 36 MV/m<< 50 MV/mQuestionable

2D PITZ Settings: 50 MV/m uniform, 1 nC, R=1 mm, 2D shaping of 30 fs ‘pancake’ GPT Charge [nC] RMS Emittance [micron] Pancake

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

Emission:3D shaping2D shapingHighly non-linear fields! Lower charge densityMaintain short bunch Long pulse lengthHigh acceleration field 3D versus 2D shaping 1.5 ps: 10 μm15 fs: 1 nm

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

3D PITZ Settings: 50 MV/m uniform, 1 nC, R=1 mm, 3D shaping of 10 ps ellipsoid Pancake 3D: 3 ps 3D: 10 ps GPT Charge [nC] RMS Emittance [micron] Pancake 100 MV/m

Next Experimental progress at Eindhoven University of Technology Experimental progress at Eindhoven University of Technology Jom Luiten

2D ‘pancake’ shaping Ingredients: Ti:Sapphire 30 fs laser Transverse shaping only Ti:Saphire 30 fs laser Colinear THG 800nm → 266 nm Spatial filtering: 800 nm gaussian π shaper: Gauss → half-sphere UVSphereGauss

800 nm after spatial filtering

ideal π Shaper Laser intensity radius 01 mm π shaper Input:Gaussian beam Output: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 RR+B R+B+UV Incident beam: 1 kHz, 30 fs 800 nm, 1 mJ/pulse UV beam: 1 kHz, 30 fs 266 nm Conversion efficiency ~ 10% Colinear 3 rd harmonic generation

Cooling channel bucking magnet Tube for thermoheater Stainless steel vacuum vessel 1.5 cell S-band cavity: Clamped design

f 0 = GHz f 0 = GHz Absorption > 96 % Q = 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 2 Hz, 10 5 rf pulses 65 MV/m

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