BEAM DIVERGENCE DUE TO CONVECTIVE DRIFT INSTABILITIES IN AN APPLIED-B ION DIODE

A low-frequency instability is identified, which is convected through an applied-B ion diode by the ion beam, is driven by the cross-field flow of electrons relative to drifting ions, and produces a spread in beam velocity. The consequences of this convective instability are explored in detail, and many of the aspects needed for application to ion beam physics are calculated and combined into a single unified theory. Many aspects of this instability agree with the frequency range, growth properties, spatial structure, saturation level, and beam spread seen in experiments and computer simulations.