Ion hose instability of REB in a self-generated plasma channel

Ion hose (or ion resonance) has been identified as an important instability in the propagation of an intense relativistic electron beam in a tenous plasma channel. This mode has been experimentally shown to be disruptive to the propagation of a relativistic E-beam over short distances (≅ 0.5m) in a tenous plasma. The cause for this instability has been understood to be the electrostatically transverse coupling between the beam and channel ions oscillations. Analytic and numerical models have been developed to study this mode, where the usual assumption has been that the neutralization fraction f (ions to beam line density ratio) is a constant from beam head to tail. Therefore, these studies are not applicable to the important case when the channel is generated by the relativistic beam itself, i.e. f varies as a function of the distance from the beam head. The authors present an analytic study in which both the beam and channel ions are assumed to be rigid pencil beams, with the ion density varies as a function of time. Thus the instability initially grows and eventually saturates. Growth rates and saturation threshold are presented and discussed