Experimental investigations of the rotating magnetic field influence on an ECR discharge plasma

摘要

The effect of a weak rotating magnetic field on an ECR discharge plasma in argon has been investigated. The field was produced by an arrangement of bars surrounding the discharge vessel and carrying harmonic currents appropriately shifted in phase. Optical probes, Thomson scattering, Li beam diagnostics and a fast CCD camera were used for the investigations. A significant modulation of the election density and temperature at the plasma edge was observed. This can be assigned to an increase of the transport of electrons to the discharge vessel walls where the lines of the total B field cross them. Alteration of the transport conditions results in perturbations, which diffuse radially inwards at a velocity corresponding to that of the Bohm diffusion. A pattern of light emission develops, which rotates synchronously with the rotating field. Correlation between the total light emission from different plasma volumes was determined based on measurements made with optical probes. This shows fluctuations propagating azimuthally, anticlockwise with respect to the direction of the main B field, with a wavelength of about (7-10) x 10(-2) m. These fluctuations exist independently of the presence of the rotating magnetic field. Further investigations are still needed to answer two key questions: does the plasma rotate as a whole or is the observed effect a rotation of the plasma state only, and how does the rotating field affect fluctuations at the plasma edge?. [References: 17]