Experimental observation of ion hose instability.

A theoretically predicted instability in the ion-focus-regime (IFR) guiding of intense relativistic electron beams, known as the ion hose instability, has been definitively observed in this experiment. A 1.5-..mu..s, 1.2-kA, 2.2-MeV electron beam has been successfully injected into and propagated down a 21-meter preionized channel. Off-axis beam oscillations have been found to grow and then saturate at large amplitude. Observed growth times, real frequencies, and saturated amplitudes are in agreement with theoretical scaling predictions and with numerical simulation of ion hose instability. 8 refs., 7 figs.