Direct losses in the ELMO Bumpy Torus experiment

Abstract

For resonant ions in the ELMO Bumpy Torus experiment (EBT), the width of the orbits near the resonance scales like (∂Ω/∂r)−1, where Ω is the precessional drift frequency. For (∂Ω/∂r)≊0 over most of the plasma, the ions will drift vertically out of the machine due to the toroidal magnetic field. The problem of these directly lost particles is analyzed by considering collisional diffusion into a hole in velocity space. Particle and energy loss rates including boundary layer corrections due to marginally confined particles are obtained. It is shown that these direct loss rates can be comparable to diffusion rates based on banana transport.