<title>Beam breakup instability experiments on long-pulse electron-beam transport through rf cavities</title>

Abstract

Experiments designed to investigate the beam breakup (BBU) instability have been performed using the long-pulse MELBA electron-beam generator (0.5 - 1.5 microsecond(s) , 0.7 - 0.8 MV, ldiode equals 1 - 15 kA, lextracted equals 0.1 - 0.5 kA). The experiment consists of 10 identical pillbox cavities each containing a small microwave loop antenna designed to detect the TM110 beam breakup mode. For our cavity design the TM110 resonant frequency occurs at approximately 2.5 GHz. The cavities are connected by small diameter tubes which attenuate the RF cavity-to-cavity crosstalk. The MELBA diode and subsequent cavity system are immersed in a solenoidal magnetic field (0.8 - 3 kG). Microwaves of 2.5 GHz (1 - 4 kW), whose pulselength exceeds the beam pulse, can be injected into the initial cavity in order to prime the BBU instability. BBU instability growth is measured through the growth of 2.5 GHz RF between the first (or second) and tenth cavities. The BBU growth is compared with predictions made by beam-cavity coupled-mode theory.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.