Space charge induced velocity spread in a gyrotron MIG

Summary form only given. Generally speaking, there are a variety of sources of velocity spread, including the initial thermal velocity spread, spread due to roughness of the surface on the cathode and spread due to the effect of beam space charge. The velocity spread caused by the first two items is difficult to eliminate in principle. We focus on the third item, the velocity spread due to the beam space charge field, and regard the effects of temperature and surface roughness as initial conditions in our simulation. It has been shown that a change in velocity spread begins during the beam´s transition from an initially laminar state to a highly nonlaminar mixed state. Our model aimed at investigating this effect. A simple model is introduced to describe the mixing process. A periodically varying potential caused by the nonuniform space charge is found to be associated with spiraling electrons, and breaks the adiabatic constancy of the magnetic moment. This space charge potential does not vanish until electrons are completely mixed. Consequently, a spread in perpendicular velocity is introduced in the mixing from the originally in phase state to the randomly mixed state.