Effect of Toroidal Magnetic Field on Low-Frequency Plasma Instabilities in a Multipole Machine

The effect of a finite toroidal field on the low-frequency instabilities occurring in a nonuniform plasma inside a multipole machine has been investigated. It has been found that the flute-type drift-cyclotron mode is stabilized by the introduction of a very small amount of toroidal field. Also, an unstable universal-cyclotron mode has been investigated for finite $k_{\mathrm{II}}$. These results, obtained by using a numerical solution on the Univac 1108 digital machine, have been found to be in good agreement with the findings of a recent experiment.