1. Beam Dynamics in a Spilt SRF-Gun
M. Ferrario, W. D. Moeller, J. B. Rosenzweig, J. Sekutowicz, G.Travish
INFN, UCLA, DESY
Meeting on “ Superconducting RF Gun Simulations“
EUROFEL Work Package 5
2.-3. June 2005 at BESSY

2. Main Questions/Concerns
SUPERCONDUCTING RF PHOTO-INJECTORS
Main Advantage:
Low RF Power Losses & CW Operation
Main Questions/Concerns
Emittance Compensation ?
Q degradation due to Magnetic Field ?
High Peak Field on Cathode ?
Cathode Materials and QE ?
Laser System ?

3. Before Cool-Down B
After Cool-Down B

4. Schematic View of the Envelope Equations
HOMDYN

5. Emittance Oscillations and Growth are driven
by space charge differential defocusing
in core and tails of the beam x px
Projected Phase Space
Slice Phase Spaces

6. Emittance Compensation: Controlled Damping of Plasma Oscillation (LS-JBR)

7. Gun Working Point

8. 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

9. Homdyn movie

10. Head and tail slices carry the most pronounced energy spread

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

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

13. Envelope oscillations drive Emittance oscillations
r(z)
(z)

14. Bunch with a Linear Energy Spread Correlation

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

16. On a longer time scale

17. 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

19. Movable Emittance-Meter
envelope
Movable Emittance-Meter

20. Scaling the LCLS design from S-band to L-band
MV/m==> MV/m
1 nC ==> 2.33 nC

22. TTF VUV-FEL Photoinjector
1.3 GHz, 1.5 cell RF Gun
Main Solenoid
Bucking Solenoid

23. Y. Kim RPPT008 Emittance Damping in TTF2 Booster Linac with Gaussian Longitudinal Laser Beam Profile

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

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

26. PARMELA simulations

27. µ-metal shield solenoid stainless steel niobium He tank
Connection to tuner RT 2K
≤4K
Coupler port
130 mm
R=125 mm
500 mm
20 mGauss
(2G wo )
166 mG
320 mG

28. L-band SC gun design with coaxial coupler

29. SCRF GUN

30. Scaling with 

31. 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

32. 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

34. Is Nb the best superconductor for the photoemission ?
Cs (WF=2 .1 eV)
Pb (WF= 4.2 eV)
Nb (WF= 4.9 eV)
a /pm b /pm c /pm
α / ° β / ° γ / °  
a /pm b /pm c /pm
α / ° β / ° γ / °  
a /pm b /pm c /pm
α / ° β / ° γ / °  

35. Very preliminary results measured @ BNL Quantum Efficiency of Pb
248 nm
213 nm
1•10- 4
1.5•10-3
Puv= ƒ * (Q/ )*(h) = 4 W
4 W 213 nm (V harmonic of 1064 nm laser) can generate 1MHz nominal beam

36. Conceptual All Fiber System
Lots of development in Erbium and Ytterbium doped fiber systems
Commercially available 20W, 2MHz systems
Progress should be very rapid over next 1-2 years
Example: for UV lithography x7 and x8 of 1.5 µm Picture stolen from Nikon

37. HOMDYN Simulation n [mm-mrad] x [mm] 3.2 m Z [m] Q =0.35 nC R =1. mm
L =19.8 ps
th = 0.7 mm-mrad
Epeak = 60 MV/m (Gun)
Eacc = 11 MV/m (Cryo1)
B = 2.9 kG (Solenoid)
I = 18 A
E = 100 MeV
n = 0.76 mm-mrad n
[mm-mrad] x
[mm]
3.2 m
Z [m]

38. Velocity bunching option

39. CONCLUSIONS
Emittance compensation by external solenoid is possible
60 MV/m peak field in SC cavity have been already demonstrated
Work in BNL to demonstrate
Pb QE 200 nm
Laser System: progress should be very rapid over next 1-2 years

40. Physics and Applications of High Brightness Electron Beams
The following workshop was approved by ICFA at its meeting Feb 10-11,
2005 in Vancouver:
Physics and Applications
of High Brightness Electron Beams
Erice, Sicily, Italy, October 9-14, 2005
Organizers: L. Palumbo (Univ. Roma), J. Rosenzweig (UCLA), L. Serafini
(INFN-Milano).