Increased ion beam throughput with reduced beam divergence in a dipole magnet

摘要

Spreading of an ion beam when passing through a dipole magnet is reduced or suppressed by electrostatic ion beam confinement which supplements magnetic confinement which may be provided. The magnetic confinement is enhanced by the provision of a magnetic mirror through concentration and localized increase of the dipole field with a concave profile of the pole pieces faces and/or provision of permanent magnets or localized regions of material of increased permeability to form magnetic cusps. Pitch and geometry of convex portions of the pole piece faces are adjusted to increase the mirror ratio and the location of the maximum mirror field relative to the thickness of a graphite or insulating liner which may be employed. Electrostatic confinement elements in the form of negatively charged electrodes and/or electrically isolated electrodes or insulators which assume a negative charge. Ionization of plasma between the pole pieces may be enhanced by application of a VHF/UHF field having a frequency of about 40 MHz to 100 MHZ or higher.