Dynamics of rotating structures in a magnetized plasma discharge
Abstract/Contents
- Abstract
- Azimuthally propagating instabilities, in the form of regions of higher plasma density, are sometimes seen propagate in Hall thrusters and other magnetized discharges. These structures, termed spokes, have been linked to an increase in axial electron mobility and are thought to play a role in breathing mode oscillations. The goal of this work is to understand the physics behind the spokes and study the conditions for their formation and propagation. Two small ring-shaped magnetized discharges (5 mm and 19 mm in diameter) form inside two configurations, that differ only in size, of a device designed to promote the exclusive growth of the same spokes observed in Hall thrusters while being much easier to operate. Two main diagnostic techniques are used: high-speed imaging, through a transparent layer of Indium Tin Oxide (ITO) constituting the anode, and anode segmentation current measurements, obtained by segmenting the anode into electrically isolated regions. Both diagnostic techniques reveal the presence of spokes azimuthally propagating along the discharge ring in the frequency range 100 kHz to 10 MHz when operating with argon gas. A theoretical framework is developed to model the propagation of the spokes as a saturated instability wave. The linear perturbation analysis of the equations leads to an analytical form of the wave dispersion relation which reveals the instability conditions and is shown to be in agreement with experimental results. Experimentally, operating conditions are varied to characterize how the propagation of these plasma structures is influenced by the various parameters. Discharge current and distance between electrodes are found to be the parameters to which their propagation is most sensitive. A spectral analysis of the segmented anode currents reveals the presence of a threshold current under which the direction of propagation of the spokes reverses. A theoretical model suggests this rotation inversion to be caused by the large density gradients that are promoted by low currents and can lead to an inversion of the local electric field.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2023; ©2023 |
| Publication date | 2023; 2023 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Marcovati, Andrea |
|---|---|
| Degree supervisor | Cappelli, Mark A. (Mark Antony) |
| Thesis advisor | Cappelli, Mark A. (Mark Antony) |
| Thesis advisor | Hara, Ken |
| Thesis advisor | Raitses, Yevgeny |
| Degree committee member | Hara, Ken |
| Degree committee member | Raitses, Yevgeny |
| Associated with | Stanford University, School of Engineering |
| Associated with | Stanford University, Department of Mechanical Engineering |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Andrea Marcovati. |
|---|---|
| Note | Submitted to the Department of Mechanical Engineering. |
| Thesis | Thesis Ph.D. Stanford University 2023. |
| Location | https://purl.stanford.edu/xc308gw6135 |
Access conditions
- Copyright
- © 2023 by Andrea Marcovati
- License
- This work is licensed under a Creative Commons Attribution 3.0 Unported license (CC BY).
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