STABILITY OF A PLASMA CONFINED IN A DIPOLE FIELD

Plasma confined in a magnetic dipole field is stabilized by the expans ion of the magnetic flux. The stability of low beta electrostatic mode s in a magnetic dipole field is examined when the distribution functio n is Maxwellian to lowest order. It is shown using a Nyquist analysis that for sufficiently gentle density and temperature gradients the con figuration would be expected to be stable to both magnetohydrodynamic and collisionless interchange modes. Furthermore, it is shown that whe n it is stable to the interchange mode it is also stable to ion temper ature gradient and collisionless trapped particle modes, as well as mo des driven by parallel dynamics such as the ''universal'' instability. (C) 1998 American Institute of Physics. [S1070-664X(98)02610-X].