Double layer formation in a magnetised laboratory plasma

Abstract

Double layers in a current-carrying magnetised argon plasma are studied experimentally. The layer evolves from an unstable anode sheath when the anode voltage has reached a critical value which depends on the neutral gas pressure. The double layer is an oscillating, three-dimensional structure enclosing both axially and radially a plasma at higher potential which is maintained by a low rate of ionisation due to the accelerated electrons. Axially accelerated electrons and radially accelerated ions have been detected, but not axially accelerated ions. High frequency is detected on the anode side of the layer. Double layers have also been observed in helium and xenon plasmas. Time independent numerical solutions of Maxwell's equation div D= rho in one dimension including ionisation are discussed.