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

The beam dynamics simulation code V, based on the Ensemble Model, 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 the first beam position monitor (BPM1), located after the RF-gun 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 BPM 1.