Peculiarities of the Discharge Formation in a Plasma Accelerator and Structure of a Jet Flowing into Vacuum

Abstract

We report on results of investigation into the structure of a plasma jet generated by a coaxial plasma accelerator with conical insert in the discharge formation region. Using high-speed optoelectronic camera, we detected an inhomogeneous structure of glowing fractions of argon and deuterium jets. It was found that the jet radiation intensity oscillates with a characteristic frequency of 0.3–0.9 MHz. The argon plasma jet consisted of fragments diverging from the axis; plasma recombined 20 μs after the beginning of the discharge. The deuterium plasma jet resembled flakes. Its radiation intensity decreased significantly by 8 μs. The characteristic frequencies of radiation nonuniformities on the jet axis were about 0.09 cm–1 for argon and 0.3 cm–1 for deuterium. Analysis of the behavior of the discharge in the plasma accelerator revealed that a diffuse discharge was initiated at the base of the conical insert. After 0.5 μs, the discharge emerged at the outer boundary of the insert, was contracted, and occurred between central and external electrodes. The emergence of the discharge from the accelerator was observed 3 μs later and was accompanied with a glow of the end face of the central electrode. In the measurements of temperature of the lateral surface of external electrode using an infrared camera, it was found that heating is localized near the edge of conical insert and at the outlet of the accelerator. Results of investigations can be used for gas ionization, material irradiation, and simulation of interaction of plasma flows with the magnetic field in the outer space in laboratory conditions.