Ellipsoidal bunches by 2D laser shaping

1. Ellipsoidal bunches by 2D laser shaping Bas van der Geer, Jom Luiten Eindhoven University of Technology DESY Zeuthen 30 November 2006 work as good as 3D ellipsoids 1) Why pancakes do not work with 1nC and 40–60 MV/m Bas van der Geer 2) Experimental progress Jom Luiten

2. 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)

3. Brightness Transverse (5-D) brightness:

4. Source brightness Options (at fixed Q): • Lower Temperature TUltra Cold Plasma cathodeB.J. Claessens et al., PRL 95, (2005) 164801 • Reduce Surface area ACarbon Nanotubes Needle cathodes … • Reduce Pulse duration τ Pancake regime

5. Longitudinal phase space density Longitudinal phase-space at cathode Long pulsePancake 3 ps 30 fs 1 nC 100 pC ~100 A/mm2 ~1 kA/mm2 (Both with A=πmm2) Energy Thermalspread Long pulse Pancake z

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

7. Brightness degradation px x Gaussian bunch ... the real problem is the space charge density distribution. • Space charge forces: • Non-linear • Slice-dependent

8. 1989 - 2003 px x Gaussian bunch Fighting the symptoms: • Emittance compensation (B. Carlsten) • Optimized transverse profile (L. Serafini) • Uniform temporal & radial profile (DESY, ...) • ...

9. 2004: Fundamental solution px x Gaussian bunch Waterbag bunch • Space charge forces: • Linear • Slice-independent • Space charge forces: • Non-linear • Slice-dependent Thermal-emittance-limited beam!

10. History of uniformly charged ellipsoids 1929 Have linear fields in all three coordinates O. 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 recipe O.J. Luiten, S.B. van der Geer et al, PRL 094802, (2004). O.J. Luiten, S.B. van der Geer et al, EPAC (2004).

11. History of uniformly charged ellipsoids 1929 Have linear fields in all three coordinates O. 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 recipe O.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 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, 044203 (2006), Longitudinal … ...

12. 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

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

14. Waterbag bunch in a realistic field 1.5 cell, 3 GHz rf-photogun + focusing solenoid • Eacc = 92 MV/m • Q = 100 pC zc = 0.9 m, E = 4.5 MeV O.J. Luiten, S.B. van der Geer et al, EPAC (2004).

15. Waterbag bunch in a realistic field Thermal emittance! O.J. Luiten, S.B. van der Geer et al, EPAC (2004). • 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. 106. 4 MeV

16. First waterbag bunch in a realistic field Thermal emittance! 10 fs I=50 A O.J. Luiten, S.B. van der Geer et al, EPAC (2004).

17. Longitudinal compression rf φ Laser 3.5 MeV 0.7 – 2.0 kA 30 – 100 fs 0.7 – 1.5 μm ~0.4 m S.B. van der Geer et al, PRST-AB, 9, 044203 (2006),

18. 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

19. 2D shaping @ PITZ 3.0 2.5 2.0 1.5 RMS Emittance [micron] 1.0 0.5 0.0 0.1 0.2 0.5 1 Charge [nC] GPT Settings: • 50 MV/m uniform, 1 nC, R=1 mm, 2D shaping of 30 fs ‘pancake’ Pancake

20. 3D shaping @ PITZ 3.0 2.5 2.0 1.5 RMS Emittance [micron] 1.0 0.5 0.0 0.1 0.2 0.5 1 Charge [nC] GPT Settings: • 50 MV/m uniform, 1 nC, R=1 mm, 3D shaping of 3 ps ellipsoid Pancake 3D

21. 3D versus 2D shaping Emission: 3D shaping 2D shaping Highly non-linear fields! Highly non-linear fields! Lower charge density Maintain short bunch Long pulse length High acceleration field 1.5 ps: 10 μm 15 fs: 1 nm

22. 3D shaping @ PITZ 3.0 2.5 2.0 1.5 RMS Emittance [micron] 1.0 0.5 0.0 0.1 0.2 0.5 1 Charge [nC] GPT Settings: • 50 MV/m uniform, 1 nC, R=1 mm, 3D shaping of 10 ps ellipsoid Pancake 3D: 3 ps 3D: 10 ps

23. 3D shaping @ PITZ Settings: • 50 MV/m uniform, 1 nC, R=1 mm, 3D shaping of 10 ps ellipsoid 3.0 Pancake 3D: 3 ps 2.5 2.0 3D: 10 ps 1.5 RMS Emittance [micron] Pancake 100 MV/m 1.0 0.5 0.0 0.1 0.2 0.5 1 Charge [nC] GPT

24. Next Experimental progress atEindhoven University of TechnologyJom Luiten

25. 2D ‘pancake’ shaping Ingredients: • Ti:Sapphire 30 fs laser • Transverse shaping only Spatial filtering: 800 nm gaussian π shaper: Gauss → half-sphere Colinear THG 800nm → 266 nm Ti:Saphire 30 fs laser Gauss Sphere UV

26. 800 nm after spatial filtering

27. π shaper ideal Laser intensity πShaper 0 1 mm radius Input: Gaussian beam Output: Half-sphere laser intensity profile (without losses)

28. Colinear 3rd harmonic generation Zero order retardation plate 0.15 mm BBO SHG 2.5 mm BBO Delay 0.04 mm BBO THG R+B R+B R+B+UV R R+B Incident beam: 1 kHz, 30 fs pulse @ 800 nm, 1 mJ/pulse UV beam: 1 kHz, 30 fs pulse @ 266 nm Conversion efficiency ~ 10%

29. 1.5 cell S-band cavity: Clamped design Cooling channel bucking magnet Tube for thermoheater Stainless steel vacuum vessel

30. 1.5 cell cavity: measured resonances p-mode Lorentzian fits f0=2.9980 GHz Absorption > 96 % 0-mode f0=2.9918 GHz Q = 7600

31. 1.5 cell cavity: field profile π-mode Superfish ♦ measured Design and machining precision better than 5 μm

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

33. END