TY  - JOUR
A1  - Hülsmann, Peter
A1  - Müller, Wolfgang F. O.
A1  - Klein, Horst
T1  - The diffraction model and its applicability for wakefield calculations
T2  - Proceedings of the XX International Linac Conference, Monterey, Ca. USA, August 21 - 25, 2000
N2  - The operation of a Free Electron Laser (FEL) in the ultraviolet or in the X-ray regime requires the acceleration of electron bunches with an rms length of 25 to 50 mikrometer. The wakefields generated by these sub picosecond bunches extend into the frequency range well beyond the threshold for Cooper pair breakup (about 750 GHz) in superconducting niobium at 2 K. It is shown, that the superconducting cavities can indeed be operated with 25 mikrometer bunches without suffering a breakdown of superconductivity (quench), however at the price of a reduced quality factor and an increased heat transfer to the superfluid helium bath. This was first shown by wakefield calculations based on the diffraction model [1]. In the meantime a more conventional method of computing wake fields in the time domain by numerical methods was developed and used for the wakefield calculations [2]. Both methods lead to comparable results: the operation of TESLA with 25 mikrometer bunches is possible but leads to an additional heat load due to the higher order modes (HOMs). Therefore HOM dampers for these high frequencies are under construction [3]. These dampers are located in the beam pipes between the 9-cell cavities. So it is of interest, if there are trapped modes in the cavity due to closed photon orbits. In this paper we investigate the existence of trapped modes and the distribution of heat load over the surface of the TESLA cavity by numerical photon tracking.
Y1  - 2000
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3362
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30-20467
UR  - http://www.slac.stanford.edu/econf/C000821/
ER  -