Expansion of a multicomponent current-carrying plasma jet into vacuum
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MA DYNAMICS
Expansion of a Multicomponent Current-Carrying Plasma Jet into Vacuum V. I. Krasov and V. L. Paperny* Irkutsk State University, Irkutsk, 664003 Russia *e-mail: [email protected] Received May 27, 2016
Abstract—An expression for the ion−ion coupling in a multicomponent plasma jet is derived for an arbitrary ratio between the thermal and relative velocities of the components. The obtained expression is used to solve the problem on the expansion of a current-carrying plasma microjet emitted from the cathode surface into vacuum. Two types of plasmas with two ion components are analyzed: (i) plasma in which the ion components of equal masses are in the charge states Z1= +1 and Z2= +2 and (ii) plasma with ions in equal charge states but with the mass ratio m1 m 2 = 2 . It is shown that, for such plasmas, the difference between the velocities of the plasma components remains substantial (about 10% of the average jet velocity in case (i) and 15% in case (ii)) at distances of several centimeters from the emission center, where it can be measured experimentally, provided that its initial value at the emitting cathode surface exceeds a certain threshold. This effect is investigated as a function of the mass ratio and charge states of the ion components. DOI: 10.1134/S1063780X17030072
1. INTRODUCTION The problem on ion acceleration in a multicomponent plasma jet is not only of fundamental importance but is also of interest for many applications. In particular, this problem arises when studying the expansion of a current-carrying plasma jet emitted from the cathode of a vacuum-arc plasma source into vacuum. It is well-known that cathode jets contain ions in different charge states up to Z = +4 and with energies of up to 200 eV [1]. To better understand mechanisms of ion acceleration in such sources, it is necessary to know how the energies of ion components depend on the ion charge state. From the standpoint of applications, this dependence determines the energy of ions bombarding a substrate that is under a given bias voltage. In turn, this energy determines the structure and properties of the coating deposited on the substrate from the vacuum arc plasma [2]. The parameters of multicomponent plasma jets generated by vacuum arc sources with composite cathodes consisting of several elements with different atomic masses have been extensively studied in recent years. Such plasma sources allow one to deposit coatings with unique characteristics (see, e.g., [3, 4]). In this regard, it is important to know how the energies of different components depend not only on the ion charge but also on the ion mass. We emphasize that this dependence is determined, to a large extent, by the character of interaction between ion components.
Studies of such interaction are also of interest for plasma technologies of utilization of spent nuclear fuel (SNF), which have been actively developed in recent years [5, 6]. Within these projects, it is planned to develop an efficient method of spatial separation of ions of the SNF compo
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