1. Superconducting High Brightness RF Photoinjector Design
M. Ferrario, J. B. Rosenzweig, J. Sekutowicz,
G.Travish, W. D. Moeller
INFN, UCLA, DESY

2. Main Questions/Concerns
Emittance Compensation ?
High Peak Field on Cathode ?
Cathode Materials and QE ?
Q degradation due to Magnetic Field ?

4. Before Cool-Down B
After Cool-Down B

6. No independent tuning of accelerating field and RF focusing effects
Transverse non linearities

8. LCLS GUN + SOLENOID

9. Gun Working Point

10. these slices also carry the most pronounced energy spread

11. Matching Conditions with the Linac

12. Linac Working Point
The emittance compensation occuring in the booster when the invariant envelope matching conditions are satisfied is actually limited by the head and tail slice behavior

13. Splitting Acceleration and Focusing
25 cm
10 cm
50 cm
The Solenoid can be placed downstream the cavity
Switching on the solenoid when the cavity is cold prevent any trapped magnetic field

14. Scaling the LCLS design from S-band to L-band
(JBR)
MV/m==> MV/m
1 nC ==> 2.33 nC

15. L-band SC gun design with coaxial coupler
J. Sekutowicz

17. HOMDYN Simulation en [mm-mrad] 3.3 m Z [m] Q =1 nC R =1.69 mm
L =19.8 ps
eth = 0.45 mm-mrad
Epeak = 60 MV/m (Gun)
Eacc = 13 MV/m (Cryo1)
B = 3 kG (Solenoid)
I = 50 A
E = 120 MeV
en = 0.6 mm-mrad en
[mm-mrad]
Z [m]
HOMDYN Simulation
6 MeV
3.3 m

18. PARMELA simulations
J. B. Rosenzweig

19. SCRF GUN

20. BNL All-Niobium SC Gun No contamination from cathode particles
1/2 cell, 1.3 GHz
Maximum Field: 45 MV/m
Q.E. of 248 nm
with laser cleaning
before: 2 x 10-7
after: x 10-5
T. Srinivasan-Rao et al., PAC 2003
I. Ben-Zvi, Proc. Int. Workshop, Erlangen, 2002

21. Extrapolation to Higher Field
Measurements at room T on a dedicated DC system
Extrapolation to Higher Field
SCRF GUN
Measured
Limited by the available voltage

23. CONCLUSIONS
RF focusing is not necessary
60 MV/m peak field in SC cavity have been already demonstrated
Work in BNL to demonstrate Nb QE 60 MV/m plus new ideas
Multibunch effects
The new working point for a Split Photoinjector can be easily adopted by a SCRF gun

24. Simple Case: Transport in a Long Solenoid
==> Equilibrium solution ? ==>
g(x)

25. Small perturbations around the equilibrium solution
Same Plasma Frequencies
Different Amplitudes

26. Envelope oscillations drive Emittance oscillations
sr(z)
e(z)

27. Bunch with a Linear Energy Spread Correlation

28. A Spread in Plasma Frequencies drives a Beating in Emittance Oscillations

29. On a longer time scale

30. increasing the initial envelope offset the emittance evolution is dominated by the beating term and the original minimum is recovered only after a longer period