자료유형  

 학위논문

Control Number  

0016931976

International Standard Book Number  

9798379653583

Dewey Decimal Classification Number  

770

Main Entry-Personal Name  

Marcovati, Andrea.

Publication, Distribution, etc. (Imprint  

[S.l.] : Stanford University., 2023

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2023

Physical Description  

1 online resource(176 p.)

General Note  

Source: Dissertations Abstracts International, Volume: 84-12, Section: B.

General Note  

Advisor: Hara, Ken;Raitses, Yevgeny;Cappelli, Mark.

Dissertation Note  

Thesis (Ph.D.)--Stanford University, 2023.

Restrictions on Access Note  

This item must not be sold to any third party vendors.

Summary, Etc.  

요약Azimuthally 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 that are known to lead to unsteady behaviour and premature shutdown. The goal of this work is to understand the physics behind the spokes and study the conditions for their formation and control their 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 spectral analysis of the current traces using wavelet decomposition reveals the presence of higher-order harmonics, undetectable by the camera, which are sometimes observed propagating at the same phase velocity as the spokes under conditions of high obstruction.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. The different magnetization states of electrons and ions is identified to be the cause of the formation of the instability while the presence of property gradients is shown to provide the "free energy" that enables the instability to grow into distinct structures.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. At lower currents and distance between electrode plates, the propagation of the spokes is observed to be in the negative E x B direction, defined by the applied magnetic and electric fields with the latter assumed to be cathode-bound. Two distinct regimes are identified at low and high currents promoting negative and positive E xB propagating instabilities respectively. Conditions are varied to characterize how the threshold current, that separates the two regimes, varies with distance between electrodes and background pressure. The V-I characteristics obtained for the large magnetron configuration reveal a negative electrical resistance at lower currents that is believed to be caused by an anomalous flux of anodebound ions which contributes negatively to the total current. 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. Furthermore, the model suggests that the local inverted electric field increases in magnitude when the discharge current is decreased which leads to a higher anomalous ion flux at lower currents which can explain the negative electrical resistance.

Subject Added Entry-Topical Term  

Cameras.

Subject Added Entry-Topical Term  

Viscosity.

Subject Added Entry-Topical Term  

Charged particles.

Subject Added Entry-Topical Term  

Magnetic fields.

Subject Added Entry-Topical Term  

Electric fields.

Subject Added Entry-Topical Term  

Laser etching.

Subject Added Entry-Topical Term  

Plasma etching.

Subject Added Entry-Topical Term  

Atomic physics.

Subject Added Entry-Topical Term  

Electromagnetics.

Subject Added Entry-Topical Term  

Physics.

Subject Added Entry-Topical Term  

Plasma physics.

Added Entry-Corporate Name  

Stanford University.

Host Item Entry  

Dissertations Abstracts International. 84-12B.

Host Item Entry  

Dissertation Abstract International

Electronic Location and Access  

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Control Number  

joongbu:640526