The Modes of the Screw Instability in a Positive Column for Several Gases

The mode, frequency and wavelength of screw instability are experimentally observed for several gases. These experimental results are compared with the theory modified from that of Kadomtsev and Nedospasov. The modified theory shows good agreement with the experiment. The experimental results are divided into two cases: one is obtained in rare gas and the other is in diatomic gas discharge. For rare gas discharges the mode coincides with the Kadomtsev-Nedospasov's theory, while for diatomic gas discharges the column shows a peculiar mode transformation with increase of longitudinal magnetic field. These experimental results are explained by the modified theory.