Volt-ampere characteristics of a hollow-cathode, hollow-anode discharge in hydrogen were measured by using a very fast di/dt probe. The large bandwidth of the probe enabled us to observe fast oscillations occurring at the onset of the current pulse and also at the moment of its quenching. Three different modes of operation are observed, the first with smooth voltage and current waveforms. The second mode occurs for voltages higher than 1500 V and is characterized by strong oscillations and the occurrence of current quenching. The third, mode occurs with a sharp transition and in it the current rises more rapidly to a much higher maximum value, while the oscillations are less pronounced. This mode has identical characteristics with the superdense glow mode of pseudospark discharges. At the point of transition a sudden change in the frequency of oscillations, of the impedance, and of the maximum transmitted power occur. Current quenching is observed in the second and in the third mode. The development of the superdense glow changes the character of the waveforms and current quenching while the mechanism leading to the superdense glow may be associated with the available voltage.
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