The dielectric body in a channel of electromagnetic launcher (EML) accelerates under action of pressure of plasma. There are severe enough basis to consider that in a channel of constant cross section the velocity of plasma flow can not surpass a velocity of sound in plasma. Accordingly, the maximum accessible velocity of throwing projectiles in EML is limited to a velocity of sound. The velocity of sound in plasma is determined by its composition and temperature. The plasma in a channel of EML is usually produced due to erosion of walls of the channel. Under typical conditions of EML operation the velocity of sound in plasma is 5-7 km/s that coincides with values of throwing velocity obtained experimentally. The increase of a velocity of throwing can be reached only at increase of the velocity of sound in plasma. The probable solutions permitting to raise the velocity of sound till 10-12 km/s are discussed. Probably, it is impossible to receive values of sound velocity above 15-20 km/s for the working conditions of EML, therefore the velocity of throwing at a level 12-15 km/s is limiting for EML.One of methods of increase of a sound velocity in EML is the using of the massive initiators from lithium and graphite. The results of experimental study of the EML characteristics with such initiators have been presented. It has been shown, that at usage of such initiators erosion of walls of a channel essentially decreases, and the high values of conversion of electromagnetic energy brought to a channel, in a kinetic energy of projectile (about 20 %) have been reached.

A diffuse (spotless) vacuum arc was investigated on a hot cathode made from cerium dioxide. The discharge is obtained in the following range of current, voltage, and cathode temperature of I = 15–150 A, Va = 9–14 V, and Tc = 2.1–2.4 kK. The main characteristics of the plasma flow in space behind the anode with a hole were determined: it was found that the electron temperature at the working parameters lies in the range of 0.4–1 eV, the ions are predominantly singly charged, the average charge of the outgoing heavy particles reaches 0.9 e (elementary charge), and the most probable kinetic energy of the ions does not exceed 9 eV. Potentially found regimes of vacuum arc operation are promising for use in the work on implementation of the plasma method for spent nuclear fuel and/or radioactive waste reprocessing.

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The paper presents a diffuse vacuum arc with heated cathode made of ceramic (CeO 2 ) and metal (Cr) mixture, initiated and studied for the first time. Plasma sources of multicomponent mixtures are demanded for plasma based methods of rare-earths recycling and spent nuclear fuel reprocessing, which are currently under development. The discharge current-voltage characteristic was measured for different cathode temperatures (1950-2250 K); in the range of the arc current 30-100 A the voltage varied from 6 to 11 V. A cooling effect of the mixed cathode due to the thermionic emission at presence of the arc plasma was found; the effect reached about 150 W at the arc current of 30 A. The cooling effect and the current-voltage characteristic distinguish the discharge from the diffuse vacuum arcs with single-component cathodes made of cerium dioxide and chromium. The plasma parameters and optical emission spectra were analyzed for various cathode temperatures and arc currents (electron temperature was 0.4-0.6 eV, local particle densities in plasma near the cathode were in range 10 11 -10 13 cm −3 ). The study is of interest for plasma sources development and increase of their efficiency as well as for the tasks aimed at ionization of multicomponent mixtures.