Nonlinear effects in the current-voltage characteristic of a low-density Q-machine plasma: I. Related to the potential relaxation instability

We report on an investigation in the magnetized alkaline plasma of a single-ended Q-machine where the current-voltage characteristic of the cold end plate showed some new nonlinear features. The most interesting phenomena are sudden jumps of the electron saturation current which are partly accompanied by hysteresis. These new phenomena are best visible for low densities. The current jumps are explained as an indication that the well known oscillating nonlinear potential structures, which appear in the plasma column when an electron current is drawn through it, and which are known as the potential relaxation instabilities, originate from collective effects of excitation and ionization interactions produced in front of the cold plate where accelerated electrons suffer inelastic collisions with the alkaline vapour present in the plasma column.