Models of ion beam interactions for the stability analysis of migma

The stability of the central region of the triple delta distribution function for a migma is shown to be reducible to the analysis of fourth and sixth order ordinary differential equations for radial electrostatic modes, including axial oscillations and electron shielding effects. A normal mode study shows that a cylindrically counterstreaming ion instability appears for ωpi > ωci. This effect should be attenuated by the introduction of some spread in pθ. It is noted that a spherical system of counterstreaming beams is stable for radial modes. An instability of the Harristype is discussed with a migma slab model, which includes finite axial extent and a bias electric field. It is suggested that a microinstability observed during the Migma IV experiment was stabilized by the combined influence of small axial wavelengths and electron heating. (orig.)