Investigation of plasma transport across magnetic filter in low temperature plasmas using 2D 3V PICMCC simulations application to negative ion sources

Abstract

The LTP (hydrogen) based negative ion source plays an important role in the neutral beam injection system - one of the primary means of plasmaheating in magnetic fusion. In this thesis, we have performed PIC-MCCbased simulations of such plasmas wherein the ROBIN negative ion source(consisting of an LTP source with a magnetic filter) installed at IPR,Gandhinagar is taken as a testbed problem for the validation of the model.ROBIN has a driver, an expansion chamber, a magnetic filter, and extractionsystem consisting of 3 different grids. Plasma is generated in the RF driverregion, and that expands in the expansion chamber before encountering the magnetic filter field. A magnetic filter is a localized magnetic field (few tens of gauss) perpendicular to the plasma flow (diffusion flux or transport) andcontrols the plasma flux flowing from the expansion chamber to the extractionsystem. As a first step, we have performed 1D-3V PIC-MCC simulations, andwe observe a good qualitative match between the simulation and experimentalresults in terms of plasma density and electron temperature. The quantitativemismatch between the ROBIN experiment and 1D-simulation results is due tothe fact that the effect of drifts and instabilities (present in real experiments)are not captured properly in the 1D model. However, even with severallimitations, we find that 1D-3V PIC-MCC simulations can predict plasmabehavior in such LTP experiments with acceptable accuracy.As a second step in this direction, we have developed an in-house serial 2D-3VPIC-MCC code and also validated it with results available in the literature.However, stringent numerical constraints associated with a 2D PIC codemake it computationally prohibitive on CPUs in the case of real experimentalgeometry (total number of particles, number of grid points and simulationtime-scale). Therefore, we parallelized our 2D-3V PIC-MCC codes for sharedas well as distributed memory systems consisting of multi-core and many-corearchitectures (GPUs). We have also proposed a hybrid parallel..