Observation of the limit cycle in asymmetric plasma divided by a magnetic filter

Abstract

An asymmetric plasma divided by a magnetic filter is numerically simulated by the one-dimensional particle-in-cell code VSIM1D ͓Koga et al., J. Phys. Soc. Jpn. 68, 1578 ͑1999͔͒. Depending on the asymmetry, the system behavior is static or dynamic. In the static state, the potentials of the main plasma and the subplasma are given by the sheath potentials, M ϳ3T Me /e and S ϳ3T Se /e, respectively, with e being an electron charge and T Me and T Se being electron temperatures (T Me ϾT Se ). In the dynamic state, while M ϳ3T Me /e, S oscillates periodically between S,min ϳ3T Se /e and S,max ϳ3T Me /e. The ions accelerated by the time varying potential gap get into the subplasma and excite the laminar shock waves. The period of the limit cycle is determined by the transit time of the shock wave structure.

Magnetic filter operation in hydrogen plasmas

“…Its effect for cooling the electrons has been proved both experimentally [3,6,7,13,[20][21][22][23][24][25][26], by probe diagnostics and measurements of the current density of the extracted negative ions, and theoretically [6][7][8][9][10][11][12]15,27] by modelling and discussions on the mechanisms governing the operation of the filter. The fluid-plasma models [6][7][8][9][10]15] of the magnetic filter involve importance of the transport processes.…”

“…Obviously, when description of the total source of negative ion beams is aimed to be completed, such simplifying assumptions are unavoidable. Numerical simulations [12,18,27] based on particle-in-cell and Monte Carlo methods, also developed, stress mechanisms of the filter operation related to instabilities, turbulent diffusion and potential gaps accelerating the ions.…”

“…In general, the sources of negative hydrogen ions with volume-production based processes as well as the hybrid sources where surface production is employed are tandem-type sources with a construction ensuring space separation of regions of high and low electron temperature [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Thus, electron cooling in the discharge is needed and this is provided by a magnetic filter.…”

Particle-in-cell with Monte Carlo collision modeling of the electron and negative hydrogen ion transport across a localized transverse magnetic field

“…1͒, where lower temperature plasma is needed for en-hancement of the negative ion production. 5 Later, this phenomenon was studied also experimentally [9][10][11][12][13][14][15] and theoretically [15][16][17][18][19][20][21][22][23][24] by several researchers.…”

“…The highenergy electrons are supposed to diffuse slower across the filter than the low-energy ones because they "average out the fine scale fluctuations of the electric field." 18 The purpose of this paper is to study the electron and negative ion transport in the magnetic filter by means of kinetic PIC with Monte Carlo collisions ͑PIC-MCCs͒ model with proper account for the collisional processes for several different cases. First we will discuss the electron transport across the magnetic filter without negative ions and for boundary conditions of grounded walls.…”