Authors: K. Przygoda, T. Pozniak, A. Napieralski, P. Sekalski, M. Grecki
Affilation: Technical University of Lodz, Poland
Pages: 349 - 352
Keywords: piezoelectric actuator, SC cavity
The main part of linear accelerator (linac), used for driving the Free-Electron Laser (FEL) machine, is superconducting (SC) resonant cavity. The SC cavity is very susceptible to small changes in dimension because of a very narrow radio frequency (RF) resonance bandwidth (~300 Hz) and a high quality factor (~10^6). The detuned cavity reflects more input power, and as a result, it needs more RF control effort to achieve desired FEL conditions. The cavity can be tuned to a resonance frequency using fast frequency tuners. The fast frequency tuners, commonly based on piezoelectric materials, are used for active compensation of cavity detuning during the RF pulse. The piezo elements, considered as a capacitive load (~5 uF), need a very sophisticated driving circuits. The voltage range that can be applied to piezo tuners is also limited to several tens of volts. The paper presents the SC cavities fast tuning system commissioning at the Free Electron Laser in Hamburg (FLASH) linear accelerator. The tuning system has been operated in both AC and DC modes and the main results from its performance during high gradient, high current experiment carried out at Deutsches Elektronen-Synchrotron are summarized.