The feasibility of resonance induced instabilities in the magnetic filter region of low temperature plasma based negative ion sources

Abstract

Low pressure, low-temperature plasma (LTP) with a spatially varying transverse magnetic filter field configuration has a wide range of applications. In such devices, the magnetic field value is low enough that it magnetizes only the electrons and not the ions, and works as an electron filter by limiting the flux of hot electrons. Due to the gradient of the transverse magnetic filter field, the electron cyclotron frequencies are also changing with location and in some places it comes close to different collision frequencies. A parallel 2D-3V Particle-in-Cell Monte Carlo Collision (PIC MCC) kinetic model based code has been developed to study plasma transport in a negative ion source where a spatially varying transverse magnetic filter field is considered in a source geometry similar to that of ROBIN (RF Operated Beam source in INdia). Various collision dependent physical phenomena, having different time scales and length scales are studied. In this article, we are reporting instabilities, observed near the filter field region. It is also observed that the frequencies of those instabilities are close to some of the electronic and ionic collision frequencies which may create resonant phenomena in the magnetic filter region and influence the cross-field transport, and heating.