The ion cyclotron instabilities in the PHOENIX high energy injection mirror machine have been suppressed by applying oscillating electric fields. Two instabilities appear to be present. One is suppressed by energy spreading and the suppression of the other appears to be due to the effect of the applied electric fields on the electrons.

We study the containment of particles in the loss cone of a magnetic-mirror machine by means of rf fields whose frequency slightly exceeds the maximum value of the ion cyclotron frequency within the plasma. We report computations which verify the adiabatic theory of this confinement system.

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The ion cyclotron drift loss-cone instability is studied for the case of steep particle density gradients [(l/n)(dn/dr)ai « -0.3], magnetic field gradients and finite plasma dimensions. Computational results show that there are no high density stable regimes. It is found that for a mirror velocity distribution the magnetic well field gradient is de-stabilizing, in contrast to the stabilizing effect found by Krall and Fowler for a near-Maxwellian velocity distribution. Potential distributions and critical densities are found for a slab model using appropriate boundary conditions to determine the modes. The threshold densities for the boundary value case are only slightly higher than that given by the usual local approximation. Frequencies and growth rates as functions of azimuthal wave number are found for the instability for typical PHOENIX II and ALICE parameters. 0-0 0-1 0-2 0-3 FIG.8. Plot of density against fig for the result from local approximation and for 4 = 0 , 1.