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Low Pressure Cascaded Arc Discharge

The remote arc plasma discharge, having a wide range of technological applications [1], was ignited within the pressure range 1–25 mTorr in a long rectangular chamber between a planar vacuum arc cathode with magnetic steering of the cathodic arc spots and a remote anode in the form of rectangular plate [2]. The cathode was shielded by a set of chevron baffles defining a primary arc chamber between the main chamber walls and the chevron baffle screen. In addition, the auxiliary mid anode in the form of a rectangular plate was positioned in the middle between the chevron baffle screen and the remote anode. The current-voltage characteristics of this discharge, obtained by modeling and experimental evaluation, have demonstrated that, in comparison to low pressure glow discharge, the electron emission mechanisms (thermionic emission vs. secondary emission), as well as boundary conditions on the discharge tube walls, strongly influence both the plasma distribution and the electrical characteristics of the remote arc discharge [2], [3]. It was found that the proximate mid anode can promote the ignition of the long remote arc discharge between the cathode and the distant remote anode in cascaded arc form. The primary arc plasma generated within the cathode chamber diffuses throughout the baffle screen, forming a plasma cloud in the entire discharge tube with decreasing electron density from the baffle screen toward the remote anode, while the plasma potential increases rapidly at the baffle screen-to-remote arc plasma interface, with plasma potential in the cathode chamber defined by a typical vacuum arc voltage drop of ~20-25V, while in remote arc plasma area it is closely matching the anode potential. The modeling of the cascaded low pressure remote arc discharge was performed in drift-diffusion approximation using Plasma Module of COMSOL Multiphysics FEM commercial software package [4]. It appears that the breakdown of the remote arc discharge is due to resistance heating of electrons within the tail of diffused plasma propagating from the cathode chamber across the baffled screen toward the remote anode when the positive potential is applied either to mid anode or to remote anode or to both anodes.