Plasma Production above Multipolar Magnetic Field Structures: From D.C. Magnetrons to Distributed ECR

Abstract

Multipolar magnetic fields, currently used for the confinement and the production of low pressure plasmas, are particularly suitable for the scaling-up of plasma sources. In such magnetic field configuration, the fast electrons, responsible for plasma excitation, oscillate within two field lines between two adjacent, opposite magnetic poles. They also undergo a drift motion perpandicular to the magnetic field, hence the interest of closing the magnetic structures onto themselves according to magnetron-like configurations. The fast electrons can be produced: i) by electron emission from negatively biased filaments; ii) by applying r.f. or negative d.c. voltages on the magnetron structure; iii) at ECR by applying microwaves in the magnetic field region. Then, the ions and the slow electrons produced along the itinerary of the fast electrons diffuse perpandicularly to the magnetic field lines under the influence of the density gradients.