FELSI Meeting 29 April 2008

Tuesday 29 Apr 2008, 14:00 → 15:00 Europe/Zurich

WBGB 020 (PSI)

14:00 → 14:20 Thomas Schietinger: Status of 3D simulations for OBLA phase I and phase II

MP: What could be the reason for the growth in slice emittance in OPAL (OBLA I)? Are the image charges considered in both Impact-T and OPAL? AA: Yes, image charges are properly implented in both codes! One needs to adjust the optics in the OPAL simulation to see whether the effect persists. AO suggests to dump the Impact-T results and pick them up with the OPAL simulation to study the problem. VS: Why is there no better agreement between simulation and measurement? What causes the bad emittance? TS: The simulated laser profile does not correspond to the measured one (will be improved in the future with OPAL). MP: The thermal emittance is missing in the simulation. If you take it into account, the disagreement is not that dramatic. The laser profile may account for the remaining discrepancy. VS: But then our emittance compensation scheme will not work! Aan: Emittance compensation does not work at such low energy anyway! YK: We will try emittance compensation at 4 MeV! Further discussion around laser profile and space charge effects. Quantum efficiency of the cathode also plays a role (discussions with Paul Emma). We can live with hot spots on the cathode, but we need to know where they are! In 4 MeV setup we should foresee a measurement of the cathode emission profile (product of laser profile and cathode quantum efficiency). RI explains the measurement at the white board: check with a mask that the electron beam indeed images the laser profile through the beam optics, then obtain the emission profile from the beam image. This is all we need to know for the simulation, we don't care whether an electron is emitted due to strong laser illumination or due to high quantum efficiency! VS urges to prepare seriously for such a measurement and come up with a step-by-step plan for the 4-MeV test stand. TS asks about official references for the beam line elements in the 4-MeV setup. MP: the present drawings are reference. The solenoid fields are identical to the ones used for the 250-MeV injector.

Slides FELSI_SH84_20080401.odp FELSI_SH84_20080401.pdf

14:20 → 14:40 Rasmus Ischebeck: OBLA / Injector lattices and repository

RI points out difficulty finding reference parameters for the various machines (OBLA, injector). There is RB's web page, which will be replaced by the “city” database, an oracle database that stores positions and other properties of all machine components. Therefore, now would be a good time to discuss what we actually want! Some disagreement whether magnet field strengths (for instance) should be in the database or not. On the one hand, these values depend on the specific optimization, therefore will change all the time (AO, YK), on the other hand it would be good to have one “reference machine” we can agree on (BS, RG). The work on the database has already started (RB with Renata Krempaska, who is in charge of the database) – we should decide soon what we want! The discussion is cut short due to a solid time constraint but should be continued in a separate meeting...