INFLUENCE OF POLARITY AND RATE OF CURRENT GROWTH OF A VACUUM HIGH­CURRENT DISCHARGE ON THE CHARACTERISTICS OF PLASMA JETS

Abstract

The paper presents the results of an experimental study of plasma flows generated by a high­voltage high­current vacuum discharge initiated by a voltage of 50–70 kV over the surface of a corundum dielectric insert. Circuit modifications of capacitive storages and the range of operating voltages made it possible to change the amplitude of the oscillatory discharge current from 5 to 18 kA with half­periods of 630, 900, 1 250, and 2 500 ns (with an average rise rate of 6–50 A/ns). Measuring the velocity of the plasma flow using double probes with a reference electrode using the timeof­flight technique made it possible to establish that the plasma flow has a maximum velocity in the initial stage of discharge formation in the section of the front up to half the current amplitude. This means that the plasma jet is formed in the region of the maximum rate of current rise and its velocity increases from 5 cm/μs to 12 cm/μs with an increase in the average rate of current rise from 6 to 50 A/ns. For electrodes made of copper and aluminum, the influence of the polarity of the central electrode on the characteristics of the plasma flow was tested. With a negative polarity of the central electrode, the plasma velocity is 10–15% lower than with a positive polarity. This is due to better focusing of the plasma jet at positive polarity due to plasma compression by the discharge current’s own magnetic field. The established experimental fact confirms the importance of the role of the electrodynamic mechanism of acceleration of the current­carrying plasma of a high­current vacuum discharge