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.
The authors analyse the specific properties of the plasmascope as a device for investigating the processes which occur in a closed-end plasma chamber immersed in a magnetic field. They indicate its advantages and possibilities, and assess how much information can be obtained with it.
The design elements of the plasmascope are described, together with certain techniques employed in its construction.
The results are presented of plasmascope experiments with a low-temperature plasma obtained by means of gaseous discharge with an incandescent cathode. On the basis of these results it is possible to estimate the directed-motion velocities of the plasma, the plasma potential and the electric fields, and to obtain a picture of the instantaneous plasma density distribution over the transverse cross-section of the discharge. It is shown that the characteristic states of a discharge can be identified with the help of plasmagrams.
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