IMPLICATION OF DC-SPACE-CHARGE-INDUCED VELOCITY SPREAD ON GYROTRON GUN PERFORMANCE

The confinement of mirror-trapped electrons under the influence of de space charge and their effect on the velocity distribution in a magnet ron injection gun is investigated theoretically and computationally. M ost trapped electrons are found to escape from the gun due to pitch an gle scattering by the spatially periodic electrostatic potential creat ed by the forward propagating beam, However, a small portion scatters into orbits which are more deeply trapped and can escape only by strik ing the modulation anode. As electrons diffuse in velocity, the veloci ty distribution in the gun region extends toward increasing perpendicu lar velocity. On the other hand, the accumulation of trapped particles near the cathode induces an additional velocity spread in the main be am. Consequently, the main beam exhibits an increased velocity spread and a reduced transverse momentum when it enters the cavity.