Diffusion of a weakly ionized plasma in the device with a space axis

Presented are the results of a simple consideration and experimental determination of the character of plasma diffusion in an equipment with a spatial axis. It is shown that modulation of curvature and torsion in such a simple system leads to appearing of a specific group of particles similar to supertrapped particles in stellarators with screw windings. The results of measuring the parameters of a plasma-beam discharge used for producing plasma in these experiments are given; its character is found to be threshold-like according to the gas pressure and plasma density and the oscillations built up by an electron beam are shown to be essential. The method of determination of plasma particle lifetimes based on measuring the decay time of additional plasma on the background of the bulk one has been substantiated. The results of these measurements are employed for calculating the corresponding diffusion coefficients. When the effect of oscillations is minimal, the value of the diffusion coefficient and its dependence on collision frequency are shown to coincide sufficiently well with the calculated dependences in the region of transition from plateau to a collision regime. The dependence of the diffusion coefficient on magnetic field is weaker than the calculated one which is explained by plasma losses at the inlets of an electron injector