Experimental investigation of plasma flows in open trap with toroidal diverter under ECR discharge

The results of experimental investigations of plasma flows from an open trap with a toroidal diverter are presented. Cold plasma is generated when introducing microwave power under conditions of electron cyclotron resonance (ECR). The radiation is introduced by a waveguide through a vacuum-tight ceramic window across the axis of the device. By means of the Langmuir probes, the spatial distributions of plasma parameters are measured. The highest density is limited to a critical value n c (~1012 cm–3) for the generator frequency under use. It is found that the temperature and density of the plasma in the trap and in escaping flows are almost independent of the radius when the ECR zone is located near the open-trap confinement region and the density is close to n c. At the density n < n c, ring plasma structures, which collapse under the action of a low-frequency instability, are observed near the separatrix. The possible mechanisms of the occurrence of plasma structures and the nature of the plasma streams are discussed.