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

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

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

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

5. 5 Coherent Synchrotron Radiation in bending magnets  Powerful radiation generates energy spread in bends  Causes bend-plane emittance growth (DESY experience)  Energy spread breaks achromatic system   x = R 16 (s)  E/E bend-plane emittance growth e–e–e–e– R zzzz coherent radiation for   z overtaking length: L 0  (24  z R 2 ) 1/3  s s xx xx  L0L0L0L0

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

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

8. 8 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 L. Serafini, “The Short Bunch Blow-out Regimein RF Photoinjectors” Pulsed photodiode + femtoseconds laser High gradient required !

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

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

11. 11

12. 12 Bullistic Bunching experiment at UCLA (Rosenzweig)

13. 13

14. 14

15. 15 Velocity bunching concept

16. 16 Quarter wavelength synchrotron oscillation

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

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

19. 19

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

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

22. 22

23. 23

24. 24

25. 25

26. 26 To be published on JJAP

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

28. 28 Stability of Velocity Bunching (-1 degree) Streak images at injection phase of –1 degree. Fluctuation is 0.4 ps (rms) for 30 shots. 1.1 psec1.4 psec0.9 psec 0.5 psec1.1 psec0.8 psec

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

30. 30

31. 31 Rectilinear Bunching Experiments Summary BNLUCLABNL-DUVFELUTNL-18LLLNL MethodeBallistic Velocity Bunching Acc. Structure S-bandPWT4 S-band 1 S-band 4 S-band Measurement zero- phasing method CTR zero-phasing method Femotsecond Streak Camera CTR Charge0.04 nC0.2 nC 1 nC0.2 nC Bunch width 0.37 ps (rms) 0.39 ps (rms) 0.5 ps (rms) 0.5 ps (rms) < 0.3 ps Comp. Ratio 615> 3> 13 10 Solenoid field No Yes

32. 32 ==> D. Giulietti talk tomorrow

33. 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. 34 HOMDYN movie

35. 35

36. 36

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

38. 38 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 Conclusions

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