Beam Loading Generated by the LOLA-IV Structure in TTF-II

The LOLA-IV transverse detecting cavity [1] is used in the Sub-Picosecond Photon Source (SPPS) as a diagnostic for measuring the length of very short bunches (with rms length on the order of tens of microns). It is envisioned to use the same structure for the same purpose in the Tesla Test Facility (TTF)-II. However, unlike the SPPS, the TTF-II may also run in multi-bunch mode, and the question arises, How serious is the beam loading that would be induced? In this report we address this question and find that, for LOLA-IV in TTF-II, the variation in beam-loading induced energy is confined to the first {approx} 80 bunches, and that the total spread in induced energy--the difference in energy between the bunch in the train with the highest energy and the one with the lowest energy--is very small, {approx} 0.03%.