The Stabilizing Effect of the Conducting Walls on the Instabilities of the Magnetized Positive Column

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In the present paper, the effects of conducting walls on the aoomalous diffusion of the magnetized positive column are examined experimentally. We can expect that the conducting walls of the inner surface of tube, in general, have the stabilizing effect on the anomalous diffusion, because the azimuthal component of the electric field, and consequently also the normal component of the electric drift, will be cancelled in boundary layer at the wall. The investigation on this effect has scarcely been done. In our experiments, the discharge tubes of inner radius 1.1 cm and 1.8 cm andboth 9O cm long, are placed in a solenoidal magnetic coil which has the uniform part of the field 30 cm long. In order to measure the longitudinal electric field, two ring probes are inserted in the tube at the interval of 20 cm. Also modes of a oscillation of the floating potential are measured by two pairs of Langmuir probes, which are mounted at the wall in the identical cross section of the tube. First, the measurements are carried out on the tube of non conducting wall, next on the tube of conducting walls which are painted with the low resistance graphite sol, circularly 2 mm widths, 1 mm apart each other. The experimental results, in the former case (Fig. 3), are in good agreements with the theory given by B. B. Kadomtsev, as shown in Fi9. 1. The experimental results in the latter case are shown in Fig. 2 and Fig. 3. When only the part of the wall between two ring probes is conductive (the tube radius 1.8 cm), the screw instabilities are observed (Fig. 2). The effect of the conducting wall the longitudinal electric field in the magnetic field, above which the instabilities will occur, becames less sensitive than that of non conducting wall.However when the wall in full length is conductive (the tube radius 1・1 cm), the anomalous diffusion can scarcely be observed (Fig.3). A luminous of the positive is strongly focused near the axis of the tube.
社団法人日本物理学会の論文
1964-06-05

The Stabilizing Effect of the Conducting Walls on the Instabilities of the Magnetized Positive Column

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