Electric potential in a magnetically confined virtual cathode fusion device

Abstract

The magnetically confined virtual cathode (MCVC) is an approach to nuclear fusion in which multipole magnetic traps are used to confine a dense cloud of electrons and thereby establish a deep electrostatic potential well for the heating and trapping of ions. We describe preliminary studies conducted in MCVC-0, a two-coil, biconic cusp trap, in which high impedance, floating Langmuir probe measurements were used to characterize the electrostatic potential. Contrary to previous studies in six-coil “polywell” devices, no potential well formation was observed and this is attributed to the particular configuration of magnetic fields within the new device. A computational model was developed, based on the anisotropic electrical conductivity of discharge plasmas within magnetic fields, and shown to accurately describe the obtained experimental results. Electrostatic boundaries that were intersected by magnetic field lines were found to strongly dominate the form of the electric potential within the device, with strong implications for the design of future MCVC/polywell machines.