Short Electron Pulses from RF Photoinjectors Massimo Ferrario INFN - LNF

1. Short Electron Pulses from RF Photoinjectors Massimo Ferrario INFN - LNF

2. Schematic View of the Envelope Equations (HOMDYN model)

3. Emittance Compensation: Controlled Damping of Plasma Oscillation 100 A ==> 150 MeV Brillouin Flow L. Serafini, J. B. Rosenzweig, Phys. Rev. E 55 (1997) Hokuto Iijima

4. Matching onto the Local Emittance Max., Final emittance = 0.4 mm Example of an optimized matching M. Ferrario et al., “HOMDYN Study For The LCLS RF Photo-Injector”, Proc. of the 2nd ICFA Adv. Acc. Workshop on “The Physics of High Brightness Beams”, UCLA, Nov., 1999, also in SLAC-PUB-8400

5. Powerful radiation generates energy spread in bends • Energy spread breaks achromatic system • Causes bend-plane emittance growth (DESY experience) bend-plane emittance growth coherent radiation for > z z  E/E = 0 L0 s R x e– E/E < 0 x = R16(s)E/E overtaking length: L0  (24zR2)1/3  Coherent Synchrotron Radiation in bending magnets

6. Talk Outline Pulsed photodiodes Ballistic bunching Velocity bunching Bunch slicing

7. Q = 20-100 pC z < ~ 250 m ==> z = 20 m x ~ 20-30 m ==> nx < 5 m  < 1 % ~ ~150 MeV e- beam requirements

8. Pulsed photodiode + femtoseconds laser maximum amount of charge that can be extracted from a photocathode illuminated by a laser the induced rms energy spread on the electron bunch: the actual beam current at the gun exit will be almost independent on the initial peak current High gradient required ! L. Serafini, “The Short Bunch Blow-out Regimein RF Photoinjectors”

9. 2 MV HV 1 ns pulse on a 2 mm diode gap: 1 GV/m , 100 pC ==> 200 fs bunch,

10. Bullistic Bunching Provide a correlated energy spread enough to produce, in a drift of length Ldrift a path difference equal to half the bunch length Lo

12. Bullistic Bunching experiment at UCLA (Rosenzweig)

15. Velocity bunching concept

16. Quarter wavelength synchrotron oscillation

17. Limitation: longitudinal emitance growth induced by RF non-linearities

18. OVER- COMPRESSION HIGH COMPRESSION MEDIUM COMPRESSION LOW COMPRESSION Average current vs RF compressor phase

20. B. Spataro et al, PAC05 ==>

21. <I> = 860 A nx = 1.5 m C. Ronsivalle et al. , “Optimization of RF compressor in the SPARX injector”, PAC05

26. To be published on JJAP

27. Streak Images of Electron Bunch Injected Phase -70O Injected Phase -1O 50 psec range 200 psec range Minimum!

28. 1.1 psec 1.4 psec 0.9 psec 0.5 psec 1.1 psec 0.8 psec Stability of Velocity Bunching (-1 degree) Streak images at injection phase of –1 degree. Fluctuation is 0.4 ps (rms) for 30 shots.

29. Current sensitivity for 1 degree error in the RF compressor phase with IV harmonic cavity D. Alesini, PAC05

31. Rectilinear Bunching Experiments Summary

32. PLASMON X ==> D. Giulietti talk tomorrow

33. Exercise for this workshop z= 200 m ==> < 25 m x =175 m ==> < 20 m = 0.2% , nx < 0.3 m Q = 20 pC

34. HOMDYN movie

37. PLASMON X Bunch slicing Q = 1nC ==> 25pC Lb=10 ps ==> 100 fs x = 0.5 mm ==> 5 m < 0.2% C. Vaccarezza et al., EPAC_04

38. Conclusions Short pulses delivered by RF photoinjectors could meet the plasma acceleretor requirements Within a quite short time more experimental data will be available on RF compression in optimized layout

39. Physics and Applications of High Brightness Electron Beams Organizers: L. Palumbo (Univ. Roma), J. Rosenzweig (UCLA), L. Serafini (INFN-Milano).