Design of a single-stage, depressed collector for a 1 MW, CW gyrotron

Summary form only given. 1 MW, CW millimeter-wave gyrotron oscillators are being developed for electron cyclotron resonance heating (ECRH) of plasma in fusion experiments. These gyrotrons have to operate at very high order operating modes due to high frequencies and high power levels. The electron beam in such a gyrotron is very thin compared to the beam radius and carries about 2.5-3.0 MW of DC beam power. The tight helical trajectories of the electrons have to be unwound and spread out in the collector region to get peak power density on the collector wall below 1000 W/cm/sup 2/. High power density in the incoming electron beam makes it a challenging task to design a collector under such operating conditions. With a single-stage, depressed collector the overall efficiency of the gyrotron is increased and power deposited by the beam on collector walls is lowered. We have analyzed different operating schemes for a single-stage depressed collector for a 1 MW, CW gyrotron. Iron shield and collector coils are used to steer the electron trajectories in the collector region.