Magnetic cusp confinement in low-β plasmas revisited

Abstract

Magnetic cusps have been used for more than 50 years to limit charged particle losses to the walls and confine the plasma in a large variety of plasma sources or ion sources. Quantification of the effective loss area has been the subject of many experimental as well as theoretical investigations in the 1970s–1990s. In spite of this effort, there is no fully reliable expression of the effective wall loss as a function of cusp magnetic field, electron temperature, ion mass, gas pressure, etc. We describe in this paper a first attempt at obtaining scaling laws for the effective loss width of magnetic cusps based on two-dimensional particle-in-cell Monte Carlo collision simulations. The results show that the calculated leak width follows a 1/B scaling in the collisionless low B limit, is approximately proportional to the hybrid gyroradius with an ion velocity equal to the Bohm velocity, and is proportional to the square root of gas pressure in the collisional limit.