High power RF amplifiers for accelerator applications: The Large orbit Gyrotron and the high current, space charge enhanced relativistic klystron

Abstract

Los Alamos is investigating a number of high power microwave (RPM) sources for their potential to power advanced accelerators. Included in this investigation are the large orbit gyrotron amplifier• and oscillator (LOG) arid the relativistic klystron amplifier (RKA). LOG amplifier development is newly underway. Electron beam power levels of 3 OW, 70 ns duration, are planned, with anticipated conversion efficiencies into RF on the :order of 20 percent. Ongoing investigations on this device include experimental improvement of the electron beam optics (to allow injection of a suitable fraction of the electron beam born• in the gun into the amplifier structure), and computational studies of resonator design and RF extraction. Recent RKA studies have. operated at electron beam powers into the device of 1.35 GW in microsecond duration pulses. The device has yielded modulatt',(l electron beam power approaching 300 MW using 3-5 kW of RF input drive. RF powers extracted into waveguide have been up to 70 MW, suggesting that more power is available from the device than we have converted to-date in the extractor. We have examined several aspects of operation, including beam bunching phenomena and RF power extraction techniques. In addition, investigations of the amplifier gain as a function of input drive, electron beam parameters (energy, current, and position in the device) and axial magnetic field strength also have been explored. The effect of ions formed during device operation also has been considered.