Limiting beam current in gyrotrons due to space charge depression

Gyrotrons operating at millimeter wavelengths in megawatt power levels will require electron beam currents of tens of amperes in highly overmoded cavities. The limiting current will be determined by space charge depression, either by modifying the velocity space loss cone to produce mirroring or by causing the Brillouim limit to be exceeded. Our computer simulations have demonstrated that previous estimates of the limiting current are overly pessimistic. Comparative results will be presented.