Beam-based alignment of TTF RF-gun using V-Code

The beam dynamics simulation code V [1,2], based on the Ensemble Model [3], is being developed for on-line simulations. One practical application of the V-Code is the beam-based alignment (BBA) of accelerator (TESLA Test Facility) elements. Before we started with BBA thefirst beam position monitor (BPM1), located after the RFgun cavity, showed non-zero readings. Moreover the readings depended on RF-power, RF-phase and primary and secondary solenoid currents. This effect could be explained by misalignments of the gun and the solenoids. Such beam offsets must be compensated by means of steering coils but such a procedure can be one of the sources of increased emittances. Based on the V-Code solver a dedicated utility was developed for alignment studies. The laser beam mismatch at the cathode, as well as the primary and secondary solenoid displacements were considered as probable reasons for the misalignment of the beam. A new method for the correction of these misalignments combines a sequence of measurements, simulations and the elimination of the largest imperfections. This semi-automatic method applied to the TTF RF-gun yields a centering of the beam within the accuracy of the BPM1

Investigation of TTF injector alignment with the simulation Code V

The exact alignment of accelerator components is of crucial importance for the production of low emittance beams. Once a beam-line section is set up, a supplementary correction of misalignments implies the knowledge of its magnitude which is difficult to determine using conventional adjusting instruments. An excellent alternative to measure existing misalignments of accelerator components is to vary machine parameters and compare the behaviour of the beam with results obtained from a simulation. It is obvious that time consuming particle tracking programmes are notappropriate to reach this aim. Regarding computing time, the on-line simulation code V is advantageous compared to other beam dynamics programmes. The theoretical basis of V-Code, the “Ensemble Model”, consists of selfconsistent equations for the ensemble parameters that arederived from the Vlasov equation. The requirement to simulate misalignments such as offsets and tilts led to the development of the ALIGNMENT UTILITY which utilizes the solver of V-Code. The new utility enabled us to investigate the beam-line alignment of the TESLA Test Facility injector.This contribution presents the theoretical background and an illustrating example of the optimization process

BEAM DYNAMICS SIMULATIONS FOR THE PITZ RF-GUN

The Photo Injector Test Facility at DESY Zeuthen (PITZ) is dedicated to the optimisation of laser driven RF guns as applied for free electron lasers (FELs) and linear colliders. The RF gun currently under study is a 1.5 cell copper cavity operated in the π-mode at 1.3 GHz. It is designed for operation as electron source at the TESLA Test Facility (TTF). Beam dynamics simulations deliver an essential contribution to the understanding of the emittance growth within the gun hence assisting in the achievement of high quality beams. We investigated in our simulations possible reasons for emittance growth of which we present here the influence of initial transverse beam offsets with respect to the field symmetry axis. For our simulations we used the TS2 and TS3 modules of the MAFIA programme which are particle in cell (PIC) codes for two and three dimensions