Alfven ion-cyclotron instability in tandem-mirror plasmas. I

The linear theory of Alfven ion-cyclotron instability is studied for ion distributions that model those in tandem-mirror plasmas. The uniform-plasma approximation leads to the following qualitative stability results. Distributions that fill a mirror cell of mirror ratio R have stability limits for beta (plasma pressure/magnetic-field pressure) that increase rapidly with R. Warm ions can damp instability caused by anisotropic hot ions. Injection of neutral beams at angles far from perpendicular to the magnetic field is a method of plasma formation with good stability properties. A plasma composed of ions with different charge-to-mass ratios can achieve beta approximately twice as large as for a single-ion-species plasma. The model distributions used here are convenient also for the eikonal treatment of axially nonuniform plasmas, which are studied in a subsequent paper