Kinetic stability of electrostatic plasma modes in a dipolar magnetic field

An axially symmetric plasma immersed in a poloidal magnetic field with clos ed lines is considered. Low-frequency electrostatic modes are studied kinet ically for an "intermediate collisionality" ordering, in which the particle collision frequency is much smaller than the transit or bounce frequency, but much larger than the mode, magnetic drift, and diamagnetic drift freque ncies. This ordering is appropriate for the Levitated Dipole Experiment (LD X) [J. Kesner , 17th IAEA Fusion Energy Conference, Yokahama, Japan (IAEA, Vienna, 1999)] and some other closed field line devices. "High-frequency" m agnetohydrodynamic-like and "low-frequency" entropy modes are found and sta bility boundaries are determined. Collisional effects are considered and th e corresponding ion gyro-relaxation effects are evaluated. These effects in troduce dissipation (or inverse dissipation) and are shown to modify the st ability picture considerably, while leaving large stability regions in the d, eta parametric space, where eta is the ratio of the gradients of tempera ture and density and d is the ratio of the diamagnetic and magnetic drift f requencies. (C) 2001 American Institute of Physics.