Analytic theory of series field coil ion diodes

Abstract

Ion diodes suited to inertially confined fusion research must conduct very high currents. The magnetic fields due to these currents are comparable to the fields used to provide magnetic insulation of electrons. Because these self-fields are necessarily high at the diode boundary where the power is applied, and are zero at some other part of the diode away from the power feed, these diodes have generally been treated theoretically by two-dimensional particle-in-cell computer simulations. There is a special class of ion diodes employing series magnetic field coils which can be described by a one-dimensional model. These diodes are highly amenable to treatment by analytic theory, and therefore are easily designed and scaled to multiterawatt systems. Many features of these diodes make them very attractive as drivers for inertial-confinement fusion research. Theoretical analysis of this class, including magnetic field configuration and field coil design, electron drifts, diode efficiency, and ion focusing, is presented. Also presented is analysis of a plasma-filled version which provides ion bunching and filtering of light ion species which might otherwise have detrimental effects on target experiments.