Implication of DC space charge induced velocity spread on gyrotron gun performance

Summary form only given, as follows. The confinement of mirror trapped electrons under the influence of DC space charge and their effect on the velocity distribution in a configuration corresponding to a double-anode 170 GHz magnetron injection gun is investigated. Most trapped electrons escape from the gun due to pitch angle scattering by the spatially periodic electrostatic potential created by the forward propagating beam. However, a small portion scatter into orbits which are more deeply trapped and can escape only by striking the modulation anode. A loss rate due to interception with the modulation anode is obtained by assuming a small azimuthal inhomogeneity of current emission. As particles diffuse in velocity, the velocity distribution in the gun region extends towards increasing perpendicular velocity. On the other hand, the accumulation of trapped electrons near the cathode induces an additional velocity spread in the main beam. Consequently, the main beam exhibits an increased velocity spread and a reduced transverse momentum when it enters the cavity.