gun simulations (CERN-ESRF)
CTF emittances:
100pC - 1mm.mrad
But not possible to measure directly.
Not optimizing on emittance.
0.5 MeV difference could be definition of Energy in ASTRA and RFT
ASTRA 3D model does not simulate mirror charges. From astra manual. Mirror charges help with space charge. They have an impact on beam sizes
Steffen Doebert. Expectation. Depends on the initial distribution. No expect a smallest emittance at the shortest laser pulse length. Surprised on the results of RF-Track. Short pulses blow out regime. Bunch uniforms itself because of space charge. But original reason is that not optimal initial distribution. If starting uniform distribution, would get minimum. Shortest one should not get smallest emittance. Intuition.
Blow out regime is a trick to use gaussian to get uniform.
Space charge makes the distribution uniform. If start with right uniform distribution.
Andrea Latina will share papers on measurements at CLEAR.
Easy trick to do uniform in transverse plane: cut with an aperture. Laser power limit. Cutting at 2 sigmas or 1.5sigmas. See if it helps as well. See if laser power is ok.
Flat top is a little curved is not a problem.
Optimizers : bayesian not so good for Zdenek
For optimizations, run in the cluster and start a grid of 100 optimizations with different starting points. Then pick the best. This avoids the local minima.
5nC bunch, 3.5mmmrad less for 1nC.
2.5nC probably ok.
Optimization, need to go wide. Optimal solenoid field. And keep the full injector
Emission number of steps must change
NEW PLOT:
ASTRA 2D + image charges see if it gives the same as RFT plot.
(MIRROR=True)
AND measurements would be great.
If 2.5mmmrad
For higher charge, nsteps emission larger.
Emission nsteps, at whichever time it will split in 100 steps.
https://cds.cern.ch/record/2939896/files/document.pdf
https://proceedings.jacow.org/ipac2024/pdf/WEPC03.pdf
https://indico.jacow.org/event/41/contributions/1506/
Zdenek optimize phase of first structure.
Keep emission_nsteps large (>250!)
emission_nsteps for lost particles convergence
Emission range instead is making emittance converge (7 to 6.3 mmmrad)
Also for Zdenek factor 2 larger emittance!
sc_dt_mm = 5
dt_mm =
Energy spread also different RFT vs ASTRA
Just after the gun region..
Equations are different in the gun for ASTRA and RF-Track. Different only far away from the axis.
The higher order in RF track are killers.
A Latina will check the formulas. First order are the same. RF track higher order significantly different.
Also energy is solved by 3D field maps expansion 1st order.
Try 3D field map for gun.
Solenoid on first structure could also help for COLD.
Bigger spot size. At 1mm and see where end up.
Steffen will share