Collisional considerations in axial-collection plasma mass filters

Abstract

The chemical inhomogeneity of nuclear waste makes chemical separations difficult, while the correlation between radioactivity and nuclear mass makes mass-based separation, and in particular plasma-based separation, an attractive alternative. Here, we examine a particular class of plasma mass filters, namely filters in which (a) species of different masses are collected along magnetic field lines at opposite ends of an open-field-line plasma device and (b) gyro-drift effects are important for the separation process. Using an idealized cylindrical model, we derive a set of dimensionless parameters which provide minimum necessary conditions for an effective mass filter function in the presence of ion-ion and ion-neutral collisions. Through simulations of the constant-density profile, turbulence-free devices, we find that these parameters accurately describe the mass filter performance in more general magnetic geometries. We then use these parameters to study the design and upgrade of current experiments, as well as to derive general scalings for the throughput of production mass filters. Importantly, we find that ion temperatures above 3 eV and magnetic fields above 104 G are critical to ensure a feasible mass filter function when operating at an ion density of 1013 cm–3.

Strategies for advantageous differential transport of ions in magnetic fusion devices

“…The transport properties of high-Z I impurities is of particular interest in fusion plasmas, where heavier elements from the wall can reduce the performance of a fusion device. They are also very important in plasma mass filters, which are designed to sort the material in a plasma based on mass [8][9][10][11][12][13][14].…”

Radial current and rotation profile tailoring in highly ionized linear plasma devices

“…Cross-field dynamics can turn out quite differently in plasmas with significant ion-neutral collisions, weak magnetization, or more complicated geometries. 7,19,20,24,[35][36][37][38][39][40] In the regime where this calculation does apply, it suggests some novel techniques with which the rotation profile might be controlled. Neutral beams, pellet injection, and electron injection can help shape the rotation profile by changing P and I.…”

Pitfalls in Modeling Walls and Neutrals Physics in Gas Discharges Using Parallel Particle-in-Cell Monte Carlo Collision Algorithms

“…In high-density plasma sources, neutral depletion [26] can be the cause of enhanced plasma transport [27], oscillations [28] and neutral-heating [29]. Neutrals can also control transport and separation capabilities in rotating plasmas [30]. In astrophysical plasmas, neutrals can lead to instabilities in interplanetary space [31,32], contribute to the tail structure of comets [33] and modify the properties of planetary atmospheres [34,35].…”