Plasma flow and acceleration in the magnetic mirror and nozzle geometries
Date
2025-01-14
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0009-0009-1603-7100
Type
Thesis
Degree Level
Masters
Abstract
This thesis investigates key physics governing transonic plasma flow within converging-diverging magnetic field (magnetic nozzle) configurations as used in fusion open mirror systems and plasma propulsion applications. In such configurations, plasma is accelerated from subsonic to supersonic velocities somewhat similar to the effects of the Laval nozzle. The Magnetohydrodynamic (MHD) fluid code {\it PLUTO} and the Particle-in-Cell (PIC) code {\it {\it VSim}} are employed to simulate plasma dynamics in both the nozzle and its expander region.
The first part of the study utilizes the {\it PLUTO} MHD code to analyze the axial acceleration and density gradients characteristic of the magnetic nozzle. Not much work has been done on the analysis of the transonic acceleration in the magnetic nozzle using the MHD description. The observed acceleration profile demonstrates strong and remarkable agreement with a theoretical one-dimensional model, remaining valid for radii up to half the nozzle's injection width. To extend the analysis, an azimuthal velocity component was introduced in the injected plasma to simulate centrifugal confinement, a mechanism used in magnetic confinement devices to enhance confinement. Preliminary results indicate improved plasma confinement near the nozzle axis and increased axial acceleration along the centerline.
The investigation continues with {\it {\it VSim}}, where a trapping condition for particles was derived, and the mirror effect was confirmed using test particles. Simulations of ion injection into the nozzle reveal transonic acceleration and density gradients across three energy injection scenarios. Notably, the acceleration profiles reached the sound speed at the nozzle throat, a phenomenon typically observed in fluid models but remarkable in the particle framework, where collisions and electromagnetic interactions are not explicitly included.
In the final section, the dynamics of ions in the expander region are explored with {\it {\it VSim}}. An external electric field was introduced to account for the presence of electrons. Including electrons results in an enhanced azimuthal velocity due to the {$\mathbf{E \times B}$} drift. Theoretical calculations of the modified flux surface are validated by simulations, which further reveal increased ion confinement near the nozzle axis and detachment from magnetic field lines.
Description
Keywords
Plasma, magnetic nozzle, Magnetohydrodynamics, Centrifugal confinement
Citation
Degree
Master of Science (M.Sc.)
Department
Physics and Engineering Physics
Program
Physics