Computational characterization of plasma transport across magnetic filter in ROBIN using PIC-MCC simulation

Abstract

The RF based negative ion source experimental facility ROBIN has been setup to understand and investigate the different issues related to production, transport and extraction of negative hydrogen ions in negative ion sources for fusion applications. The source consists of a driver, an expansion chamber, a magnetic filter and extraction system consisting of different grids. The first phase of the ROBIN experiments have been conducted for hydrogen plasma generation and measurement of different plasma parameters without negative ion generation/ extraction. We require accurate characterization of plasma to completely understand the experimental results, the complex physics, and plasma dynamics. As a first step in this direction, we have developed an in-house parallel 2D-3v Particle-In-Cell with Monte Carlo Collision (PIC-MCC) code to understand the transport across magnetic filter under conditions similar to real ROBIN operational parameters (magnetic field, pressure, power, density etc.). Simulation results from our 2D-3v PIC-MCC code reproduces the qualitative as well as quantitative behaviors observed during the first phase of the ROBIN experiments such as decrement in electron temperature and similar plasma density profile across the magnetic filter. Our exhaustive PIC simulations helps us in quantifying the plasma transport across magnetic filter as well as the actual input power that is coupled to the plasma. Electron energy distribution function (EEDF) obtained from our simulations shows a Maxwellian distribution and is in agreement with similar experimental calculations reported in the literature. Several case studies have been performed to understand the role of the magnetic filter profile on plasma transport, which will help in planning future experiments by using the magnetic filter as a switching mechanism to achieve the required density and electron temperature profiles for efficient operation of ROBIN.