Vol 62, No 7 (2019)

Plasma containing deuterium ions is used, for example, to generate neutron flows. Neutrons are generated in nuclear reactions of interaction of accelerated ion beams extracted from deuterium plasma with a solid-state target containing heavy hydrogen isotopes – deuterium or tritium. Deuterium plasma was produced in two types of arc discharge with cold cathode: in a vacuum arc with composite cathode saturated with deuterium and in a low-pressure arc with inlet of gaseous deuterium into the discharge gap. Results of studies of the mass-to-charge fractions of the plasma of these discharges are presented, and a comparative analysis of the methods of deuterium ion generation in such discharge systems is performed.

Results of using an electron beam formed by a forevacuum plasma electron source to sinter metalloceramic materials in powder form are reported. As the materials to be sintered, we used mixtures of titanium powder and an aluminum-oxide or zirconium-oxide based ceramic powder. Sintering was performed using a narrowly focused beam directed onto the surface of the metalloceramic powder. It has been shown that using a mixture of finely dispersed zirconium dioxide or aluminum oxide powder with titanium allows one, by using the electron-beam method in the forevacuum pressure region, to obtain a metalloceramic sample with a titanium concentration gradient over the volume of the sample.

The local temperatures on the surface of a ceramic coating – aluminum substrate system are measured during its irradiation with a submillisecond pulsed electron beam. Certain parameters, such as electron beam density, pulse duration, and thickness of a TiCuN-coating, are varied. The optimal modes for electron beam irradiation of the TiCuN-coating – А7-substrate system are identified.

Results are presented of a study of the stability of triggering of a six-channel seven-gap spark switch intended for switching a capacitive energy storage with a charging voltage of up to 100 kV and energy release time on the order of 100 ns. The working medium of the spark switch is air at atmospheric pressure. In the controlled triggering regime, we measured the breakdown delay time of all of the discharge gaps relative to the arrival of the voltage trigger pulse and calculated the mean square deviation of the delay time (jitter) under variation of the charging voltage and growth rate of the voltage trigger pulse. Jitter less than 1 ns was obtained for a charging voltage of 90–100 kV and a growth rate of the voltage trigger pulse ~650 kV/μs. When the growth rate of the trigger pulse is decreased, the jitter of the spark switch grows significantly. Thus, for a charging voltage of 100 kV and a trigger voltage pulse with growth rate ~200 kV/μs the jitter exceeds 20 ns, and for a voltage trigger pulse with growth rate ~100 kV/μs the jitter exceeds 30 ns. To reduce the jitter when using trigger pulses with low growth rate, blade electrodes were inserted into the spark switch, ensuring ignition of a corona discharge in the gaps during charging of the capacitive storage. It has been shown that for a growth rate of the trigger pulse of 100–200 kV/μs the corona discharge reduces the jitter by 2–3 times.

The results of experimental investigations of formation of diffuse nanosecond discharges in a nonuniform electric field in air and other gases at the pressures within 12.5–400 kPa are presented. The experiments were performed using a four-channel ICCD-camera, an ultra-fast streak-camera, and wideband oscilloscopes. It is found out that spherical streamers are formed in a sharply nonuniform electrical fields under high voltages in a pre-breakdown stage of the discharge, irrespective of the gas used (air, nitrogen, hydrogen, methane, neon, or helium). The data are obtained on the instantaneous streamer velocity in air at different voltages and on the displacement current caused by the electric field re-distribution in the gap during the streamer formation. Beams of runaway electrons are recorded. The mechanism of formation of anode- and cathode-directed streamers at high voltages is discussed.

The paper presents the results of experimental study of the discharge formed by a dual (DU) magnetron sputtering system (MSS) with aluminum targets in the mode of packet-pulse magnetron sputtering of high power (called deep oscillation magnetron sputtering (DOMS) in foreign literature). A special feature of the discharge in the DOMS mode is the use of unipolar sequence of micropulses with short durations and high powers that form macropulse duration 1000–3000 μs. This mode of sputtering was previously used only in single MSS. In this paper, the DOMS mode is first investigated with a dual magnetron sputtering system. The main plasma parameters are measured using triple and single Langmuir probes. Dependences of plasma parameters on the parameters of the pulsed discharge power supply: voltage and current amplitudes, current density, and power density on the target surface are established. The results of experiments show that the use of the dual packet-pulse magnetron sputtering can significantly increase the plasma density and the ion current density on the substrate in comparison with the traditional DC and MF modes of magnetron sputtering. The ratio of the ion flux density to the flux density of neutral atoms, characterizing the degree of ion bombardment of the growing coating in the DU DOMS mode, reached a value of 28, whereas in the DC mode it was 0.8.

The resonances of the slow-wave structure of a multiwave Cherenkov generator have been determined theoretically for a frequency range close to the π-type frequency of the lower symmetric mode. The ratio of the diameter of the slow-wave structure to the wavelength of the microwave radiation was equal to four. The resonance frequencies and Q factors of symmetric and asymmetric modes have been found in relation to the length of the drift tube. It has been shown that these relations strongly affect the spectral composition of the resonances. At some ratios of the slow-wave structure diameter to the radiation wavelength, high-Q resonances of higher oscillation types (locked modes) occur. Examples of the slow-wave structure geometries are given for which resonances of some modes have an advantage of higher Q factor.

The characteristics of sources of plasma flows formed by high-current discharges in polyethylene, teflon, and ceramic capillaries are presented that allow high-velocity flows of high-density plasma to be obtained. The influence of the initial voltage on the capillary, rate of current growth, and current amplitude on the parameters of the formed plasma bunches and on the service life of the capillaries made of the examined dielectrics is shown. Experimental data on propagation of bunches in crossed electric and magnetic fields of a magnetically insulated transmission line are presented.

The propagation of a nonlinear magnetic-field diffusion wave generated under the condition of an electrical explosion of flat conductors is investigated in the current skinning mode. Using a MIG terrawatt generator, a number of experiments are performed on electrical explosion of a copper foil, 100 μm in thickness and 5 mm in width, at the current amplitude up to 2.5 MA and its rise rate 100 ns. It is shown that under these conditions a plasma channel is formed by approximately 75-th ns from the current onset. The estimations, made considering the magnetic field enhancement on the foil edges, demonstrate that about 70–80 ns are required for the nonlinear magnetic-field diffusion wave to propagate from the foil edge to its center. A good agreement of the experimental data and the estimates suggested a conclusion that the plasma channel formation is due to the convergence of the nonlinear diffusion wave towards the longitudinal foil axis.

A wide-aperture (16 cm × 27 cm) source of e-beams for sterilization of plastic packages based on a“SINUS- 320” high-current accelerator with 450 keV energy, 9 kA current, 12 ns pulse duration, and repetition rate up to 100 Hz is described. A metal-dielectric cathode forms e-beam by explosive emission during a few nanoseconds of the voltage pulse. A high degree of e-beam uniformity can be achieved because of a large number of triple points (~800) and of electron scattering in a foil and in a 3 cm air layer for characteristic electron free paths in air up to half a meter.

The data on prebreakdown currents and static breakdown voltages measured in two-sectioned sealed-off thyratron with a cold cathode TPI1-10k/50 are presented. The temporal behavior of the anode voltage and of the voltage at the separate sections has been investigated at the prebreakdown and breakdown stages. It is demonstrated that the prebreakdown current presented in the separate sections causes redistribution of the anode voltage between the sections. Due to this effect, a maximum thyratron breakdown voltage can be obtained. The other method to increase the breakdown voltage is based on the forced distribution of the anode voltage between the sections using a capacitive divider. Special features of transition from the prebreakdown to breakdown current are discussed for different thyratron-switching circuits.

The experimental and theoretical investigations of a new form of burning of a repetitively-pulsed discharge – apokamp – are performed. It is shown that an apokampic discharge represents a narrow streamer channel, growing from the point of plasma channel bending, having a characteristic propagation velocity of tens and hundreds of meters per second, depending on the applied voltage and gas pressure and type. The conditions necessary for an apokamp to evolve are formed in a comparatively weak macroscopic electric field. The channel bend ensures a local field enhancement, which prescribes the starting orientation of the growing streamer channel. The pulse-frequency power supply regime of the discharge reproduces the streamer channel in every pulse, but the preceding framework of the ion-ion plasma ensures reproduction of the channel shape from pulse to pulse.

The paper presents the experimental study of pulsed plasma source with hollow cathode intended for bipolar electron-optical system with open-boundary plasma. The proposed configuration of the plasma source includes two ring-shaped discharge cells based on plasma thruster technology. The plasma source can operate both in a low-current high-voltage mode and a high-current low-voltage mode. The main attention is paid to the highcurrent mode which is similar to the glow discharge positive column. It is found that along with the discharge in closed electron drift the ignition of additional, non-self-sustained hollow cathode discharge with electron oscillation is possible, thus considerably reducing the voltage of the closed-drift discharge. Current–voltage characteristics of the high-current discharge are measured for these conditions. Using the double probe technique, the local plasma parameters are measured together with their spatial distribution in the discharge region. The maximum plasma density along the plasma source axis is (6.5–6.8)•10¹² сm^–3.