The role of fast electrons for the confinement of plasma by magnetic cusps

The influence of fast primary electrons on the leak width of a plasma in a picket fence or cusp geometry in the presence of a neutral gas background is discussed theoretically. Without primary electrons a leak width of the order of an ion Larmor radius (a i ) is found, whereas with fast primary electrons a leak width of the order of a hybrid width (2 square root a i a e ) can be obtained. This is in agreement with experimental data in the literature.