Electron and Ion Transport across a Magnetic Field in an Arc Diffusion Experiment

Abstract

The effective ion-diffusion coefficient can be determined from the radial density profile, which in a plasma of finite length is given by the ion transport across and unhindered ion losses along the magnetic field to the conducting end walls. In addition, the electron-diffusion coefficient can be determined from the electron-temperature profile, which depends on the diffusion rate of electrons across the magnetic field, energy dissipation by collisions, and particle losses to the end walls. The measured electron-temperature profile is considerably flatter than expected from collisional diffusion and agrees with the one calculated for Bohm diffusion. The electron-temperature gradient causes a radial electric field which contributes to the ion transport across the field. Taking the ion mobility term into consideration, it is possible to explain the apparent large ion-diffusion coefficients in previous arc diffusion experiments, which were deduced by neglecting electron-temperature gradients and radial electric fields.