Relativistic klystron research for two-beam accelerators

We have tested a high-power 11.4-GHz rf generator which consists of a 5.7-GHz transverse modulating system and two 11.4-Ghz traveling-wave output structures. The device was designed to generate 500 MW of pulsed rf power when driven by a 1-kA, 3-MeV induction accelerator beam. Transverse beam instability due to rf coupling between the two output structures has limited the width of the rf output pulse for currents above 600 amperes. Short rf pulses of total output power of up to 420 MW have been produced. Using a single output structure, rf output pulses with stable phase (< +/- 2 degree(s)) and amplitude (< +/- 2%) have been achieved for widths comparable to the beam width. We have modified and tested an output structure to decrease the growth of fields causing transverse instabilities. During the next year our experimental program will include both studies of rf power extraction and reacceleration of modulated electron beams. In support of reacceleration experiments, we are developing a time dependent computer code for the simulation of transverse instabilities due to dipole modes in the rf structures, and are upgrading the induction beam to 5 MeV.