1. Minimized emittance for high charge with multi cell superconducting guns and solenoidal focusing
D. Lipka, BESSY

2. Setup and goal for the simulation
solenoid
½ n= 1 2 3
… one module with 8 cavities
TESLA cavity
superconducting gun without RF focusing
Minimize transverse emittance at the end of the module by vary injector parameters with simplex minimization routine
06/02/2005
D. Lipka, BESSY

3. Tool for the optimization
Beam dynamic simulation with Astra
ROOT program calls Astra and reads the result
Implemented Simplex minimization routine in ROOT changes the parameters to find the minimum transverse emittance (multi dimensional minimization routine)
06/02/2005
D. Lipka, BESSY

4. Simplex
n = 1
n = 2
NELDER and MEAD
06/02/2005
D. Lipka, BESSY

5. Basic simplex
n = 2
06/02/2005
D. Lipka, BESSY

6. Simplex n = 2 reflection stretching flattening contraction 06/02/2005
D. Lipka, BESSY

7. Parameters of the simulation
Fixed parameters
Q = 2.5 nC (BESSY FEL mode)
Fall and rise time of Flat Top laser distribution = 4 ps
Emax,gun = 60 MV/m
Emax, last 4 TESLA cavities = 32 MV/m
Distance peak solenoid field to cathode (magnetic field at full cell lower than 3 mT):
n = 1: 0.6 m
n = 2: 0.7 m
n = 3: 1.0 m
Varied parameters
RMS transverse laser size (thermal emittance scaled accordingly): 0.1 – 3 mm
FWHM laser duration: 15 – 100 ps
Bmax: 0 – 0.4 T
Distance cathode to middle of first TESLA cavity (complete module is moved accordingly): 1 – 7 m
Each Emax of first 4 TESLA cavities: 5 – 33 MV/m
 8 parameters
06/02/2005
D. Lipka, BESSY

8. Result: beam size
n = 1
n = 2
n = 3
06/02/2005
D. Lipka, BESSY

9. Result: transverse emittance
Difference between n = 1,2 and n = 3 caused by larger solenoid distance
06/02/2005
D. Lipka, BESSY

10. Result: RF focusing of 3 ½ cell gun
beam size
transverse emittance
with RF focusing decrease of transverse emittance
06/02/2005
D. Lipka, BESSY

11. Summary
developed tool to minimize transverse emittance with Astra and ROOT
investigated n ½ superconducting cell guns (n = 1, 2, 3) without RF focusing with 8 parameters
solenoid has certain distance to cathode to keep superconductivity
n = 3 gives larger emittance
with RF focusing transverse emittance decreased
06/02/2005
D. Lipka, BESSY