A 6-MeV electron beam with current of 100-200 A was used to study the hose instability of a relativistic electron stream. The growth rates of the instability were experimentally determined, and measured values displayed the trends predicted by theoretical analyses. The magnitude and position of the maximum growth rate as related to the perturbing frequency and plasma-current decay times agreed well with the predictions of both the rigid and nonrigid beam models. The general dependence of growth rate on the ratio of channel radius to beam radius was observed.

Measurements of density thresholds for an ion-cyclotron instability in a mirror-confined plasma are interpreted in terms of a boundary for Landau damping of the unstable waves. Allowing for an observed normal-mode structure, experimental threshold values are accounted for quantitatively.

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A description is given of a valve suitable for use in studies involving the acceleration of plasmas into regions of high vacua. Valve opening durations of less than 60 μsec may be attained, and amounts of gas lower than 0.01 cc STP may be introduced. Valve performance characteristics and measuring techniques are discussed.