The authors present results of the investigation of an incandescent-cathode discharge in an equipotential volume in a magnetic field of 2000 Oe. In the pressure range studied, 2 × 10−6 to 10−4 Torr, there is formed a plasma column negatively charged in relation to the surrounding walls. It is established that, when the pressure of the neutral gas is increased, such a discharge becomes unstable. A plasma torch is formed which rotates steadily in the direction of the electrons and escapes from the region of the primary beam. The torch is a result of plasma polarisation in the primary electron beam when there is azimuthal non-uniformity of density and a difference between the ion and electron drift velocities. If the pressure is increased further the steady rotation vanishes and intensive oscillations with a continuous frequency spectrum develop in the discharge. The fundamental principles underlying this discharge behaviour are explained. By means of a simplified model an expression for the rotation frequency of the torch is obtained and confirmed qualitatively by experiment.

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UDC 533.951 Results are presented on electron-beam instability for azimuthal mode m = i. The measurements have been made at residual-gas pressures from 6 x 10 -~ tort to 10 -2 tort at a beam current of 27 A, electron energy 300 keV, and pulse length up to 500 sec. The instability is of standing-wave form when developed, the frequency varying with pressure and the transport system length over the range 0.4-4 MHz. The nature of the instability is discussed.One of the most characteristic instabilities for an electron beam in a plasma produced by it is the position one associated with the excitation of paired transverse oscillations and plasma ions and electrons.Although there have been some advances in the theory [1-3], few experiments have been performed on dipole instability, and those mainly for low currents (Ib~lO0 uA) [4].We have examined beam instability for azimuthal mode m = 1 with the following parameters: beam diameter 2a = 0.4 cm, energy E = 300 keV, current I b = 27 A, electron concentration n 4 x I0 *~ cm -s, and pulse length ~--800 usec.

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