High-Current Gas Discharge at Low Pressures

Abstract

IT has been found that the self-magnetic field associated with the flow of current in a low-pressure discharge (mercury vapour at less than 2 × 10⁻³ mm. pressure) plays an important part in determining the radial density distribution at currents as low as 30 amp. The effect of this magnetic field can be treated by adding a ‘magnetic potential’ term to the electrostatic potential V_s in the Boltzmann equation, w̄₁ being the longitudinal electron-drift velocity. The drift of electrons and ions to the tube walls is equalized at low arc currents by a radial electric field. Since the self-magnetic field tends to reduce the drift of electrons to the walls while having a negligible influence on the positive ions, increasing the arc current leads to a progressive reduction in the radial electric field.