Plasma instability in ECR heated ion sources

Summary form only given. In an experimental program on Constance B and Tara Anchor at the MIT Plasma Fusion Center, electron cyclotron resonance (ECR)-heated plasmas in magnetic quadrupole mirrors were investigated. Experiments were conducted at microwave frequencies between 10.5 and 18 GHz and ECR heating powers between 1 and 5 kW. It is found that the confinement of highly charged ions along the magnetic field lines is principally electrostatic; in the perpendicular direction, ion diffusion varies approximately as B^-2, although at rates considerably greater than classical. Increasing ECR frequency and heating power produces higher densities of multiply charged ions, although strong low-frequency instabilities were observed which affected ion confinement. A theoretical model suggests that the instability is of the drift-wave type. A qualitative comparison between the instability model and experimental results shows good agreement