Start-to-End Simulations
Mikhail Krasilnikov, ASTRA Simulations for the FLASH Injector (Jan. 2009)
|
|
FLASH photo injector has been simulated (re-optimized) using a new ASTRA version (Dec. 2008).
The goal of the optimization is the projected transverse emittance after the first half of ACC1 for different bunch charges:
1nC, 0.5nC, 0.25nC. Obtained photo injector parameters are summarized in the following table:
|
|
|
Subsystem
|
Parameter
|
Unit
|
1nC
|
0.5nC
|
0.25nC
|
|
|
|
Cathode Laser
|
temporal
|
profile
|
Gaussian
|
Gaussian
|
Gaussian
|
|
Trms
|
ps
|
4.4
|
4.4
|
4.4
|
|
transverse
|
Profile
|
rad.hom.
|
rad.hom.
|
rad.hom.
|
|
XYrms
|
mm
|
0.516
|
0.381
|
0.286
|
|
Ek
|
eV
|
0.55
|
0.55
|
0.55
|
|
|
|
RF Gun
|
FB
|
|
1.13
|
1.13
|
1.13
|
|
Ecath
|
MV⁄m
|
45
|
45
|
45
|
|
phase
|
deg
|
-2
|
-2
|
-2
|
|
|
|
Gun Solenoid
|
Bmax
|
T
|
0.173188
|
0.173456
|
0.173314
|
|
zpos
|
m
|
0.276
|
0.276
|
0.276
|
|
bucking
|
|
compens.
|
compens.
|
compens.
|
|
|
ACC1
1x4TESLA
|
Emax
|
MV⁄m
|
26
|
26
|
26
|
|
phase
|
deg
|
7
|
4
|
-2
|
|
zpos*
|
m
|
3.3
|
3.3
|
3.3
|
|
|
Electron Beam
at z=8.5m
|
Charge
|
nC
|
1
|
0.5
|
0.25
|
|
kin. energy
|
MeV
|
59.7
|
60.2
|
60.6
|
|
Erms
|
keV
|
647
|
330
|
67
|
|
length
|
mm
|
2.3
|
1.9
|
1.6
|
|
XYsize
|
mm
|
0.41
|
0.41
|
0.36
|
|
proj. XY emit.
|
mm
mrad
|
1.58
|
1.04
|
0.76
|
|
Remarks:
-
Cathode laser has Gaussian temporal profile with 4.4ps rms pulse length,
transverse profile is assumed to be radial homogeneous
-
Gun cavity is shifter in 30 cm upstream
-
The booster contains first 4 TESLA cavities of ACC1,
its gradient fixed (field amplitude 26MV/m), phase tuned for a smaller emittance
-
Gun phase was not optimized and taken from 1 nC case (-2deg off-crest)
-
Thermal emittance used for these simulations is based on the optimistic theoretical model (Ek=0.55eV),
recent thermal emittance measurements at PITZ shows higher values of Ek
-
200000 ASTRA particles have been used
|
|
|
|
Electron beam properties along the photo injector:
-
Q=1nC
-
Q=0.5nC
-
Q=0.25nC
|
|
|
|
Electron beam properties at z=8.5m (after first half of ACC1)
-
-
Resulting projected emittance and peak current
|
|
|
|
Some ASTRA outputs:
-
Transverse phase space for the case Q=1nC
-
Longitudinal phase space for the case Q=1nC
-
Beam views for Q=1nC
|
|
|
|
-
Transverse phase space for the case Q=0.5nC
-
Longitudinal phase space for the case Q=0.5nC
-
Beam views for Q=0.5nC
|
|
|
|
-
Transverse phase space for the case Q=0.25nC
-
Longitudinal phase space for the case Q=0.25nC
-
Beam views for Q=0.25nC
|
|