OBLA simulations

Simulation software: IMPACT-T, written by Ji Qiang (LBNL), modified by Andreas Adelmann and Christof Kraus (PSI)
Visualization: H5PartROOT
Setup: based on FEL-PM84-005-01 (Marco Pedrozzi)

State of the art

Latest IMPACT-T version with Andreas' gun and fixed image charges. The gun simulation is run separately with a time step of 0.1 ps and produces a restart file with particle distributions at 15 mm. The actual OBLA simulation takes over from there with a time-step of 1 ps (see table below).

Default parameters for IMPACT-T:

time step:1 ps*
number of particles:100k
mesh size:32 × 32 × 32
current:0.329 Amp** (= 5.5 A * 40 ps * 1498.95 MHz)
kinetic energy:500 keV
* except in scans, where time step is increased to 4 ps
** except for case 3 (low-current case): 0.00598 A

Plots for phase I

case 1 case 2 case 3 case 3a
standard plot:
emittance and
RMS beam size
(ROOT macro)

pdf

pdf

pdf

pdf
comparison to
Homdyn and GPT
(ROOT macro)

pdf

pdf

pdf

pdf
slice study
(emittance and
rms beam size)
(ROOT macro)

pdf

pdf

pdf

pdf
B field scan
(python script,
ROOT macro)

pdf

pdf

pdf
(see case 3)
misalignment study
(python script,
ROOT macro)

pdf

pdf

pdf

pdf
movie (mpeg)

Convergence study

pdf IMPACT-T simulation for case 1: comparison between simulations with time step 1 ps (0.1 ps for the first 15 mm) and 0.1 ps (0.01 ps for the first 15 mm). There is no perceptible difference.

Duetto gun

Short pulse (20 µJ) has 6.5 ps width (Gaussian sigma). Simulation of (longitudinally) Gaussian gun now possible thanks to Ji Qiang's fix. The bunch charge is 370 pC (according to A. Anghel, 26.7.2007) or 20 pC (according to R. Ganter, 26.10.2007.

Simulation parameters are:

time step:0.1 (gun) / 1 ps (rest)
number of particles:100k
mesh size:32 × 32 × 32
current:0.329 Amp** (= 5.5 A * 40 ps * 1498.95 MHz)
kinetic energy at cathode:1 eV (i.e. 593 nm/ps)
emission slices (gun):390
energy bins (gun):39

I played around with SP1 and SP3/SP4 (i.e. using only two solenoids at a time) and tried to find settings where there is a clear minimum in projected emittance, roughly coinciding with the beam waist following the solenoids. With SP1 and SP3 only, the minimum is too early for the emittance monitor, the best solutions are found with SP1 and SP4.

370 pC 20 pC
SP1: 165 SP3: 95 [mT] SP1: 130 SP4: 60 [mT]
standard plot:
emittance and
RMS beam size
(ROOT macro)

pdf

pdf
slice study
(emittance and
rms beam size)
(ROOT macro)

pdf

pdf
movie (mpeg)
Watch me programming in ImpactT!

Meeting August 16

Kevin's presentation on phase 2 (4 MeV).

Other plots

Comparison before/after image charge correction (and to Homdyn/GPT) (pdf)
Comparison 0.25/0.3 mm gun (and to Homdyn/GPT) (pdf)

Older stuff

April/May 2007

Bo Liu's simulations: Bo's main conclusions for the OBLA-I setup (most of them still applicable to current IMPACT-T version):



Last update:

Thomas.Schietinger@psi.ch