外部磁場によるプラズマの圧縮機構

抄録

Contraction process of plasma in azimuthal pinch experiment is investigated and over-all picture of the process is examined. On the assumption that a plasma column with a well-defined radius is compressed as a whole by external magnetic field, relevant parameters of the process are considered to be the following: B=the rate of field increase, a₀=the tube radius, and p₀=the initial gas pressure. Characteristic quantities of the process, such as the time-scale of contraction, the kinetic temperature of plasma at the maximum contraction, etc., are estimated in terms of these parameters, It is also inferred that the column radius at the maximum contraction is independent of B and p₀. The snow-plow model is used to find the change of column radii with time.
The experiment is performed with B=several×10⁸ gausses/sec, a₀=6cm, and p₀=(1-250)μHg, using hydrogen, nitrogen, air, and argon gases. Current and voltage oscillograms and streak camera photographs are used to obtain and analyse the results. The rather lower values of B than those used in experiments at other places are to be stressed, and the condition for the induced breakdown is briefly described. Although the range of parameters is not quite wide, it is found that the over-all picture represents the actual process with a reasonable correctness. It it indicated, however, that some other phenomena not taken into account in the picture do exist, such as the reverse magnetic field remaining trapped in the plasma, which could have important effects on the contraction in certain conditions. This point as well as the radial oscillation of the compressed plasma column will be dealt with in other papers.