자료유형  

 학위논문

Control Number  

0016935022

International Standard Book Number  

9798380413794

Dewey Decimal Classification Number  

530

Main Entry-Personal Name  

Yerger, Evan Lowell.

Publication, Distribution, etc. (Imprint  

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

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2023

Physical Description  

1 online resource(136 p.)

General Note  

Source: Dissertations Abstracts International, Volume: 85-04, Section: B.

General Note  

Advisor: Kunz, Matthew W.

Dissertation Note  

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

Restrictions on Access Note  

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

Summary, Etc.  

요약The regulation of conductive heat transport in high-β, weakly collisional, magnetized plasma by microscale electromagnetic instabilities is investigated. The transport mediated by these instabilities can be a small fraction of the value expected by particle collisions and is particularly important to the macroscale physics of a number of astrophysical systems, including the intracluster medium of galaxy clusters, radiatively inefficient accretion flows, and the solar wind. Heat conduction ultimately determines how thermal energy is distributed throughout these systems and can have implications for their large-scale stability and structure. Transport in high-β, weakly collisional, magnetized plasma is generally anisotropic, (i.e. rapid along the field and suppressed perpendicular to it), corresponding to perturbations in the distribution function that can drive waves unstable. For example, a temperature gradient oriented along a mean magnetic field can induce a heat flux that provides the free energy for a number of kinetic microscale instabilities, including the electron-heat-flux-driven whistler instability (HWI), whistler heat-flux instability (WHFI), ion-heat-flux-driven slow mode instability (HSI), and ion-heat-flux-driven gyrothermal instability (GTI). Each of these instabilities has an associated wave mode that can back-react on the transport by scattering the relevant particle species and reducing the free energy in the distribution function - and thus the associated transport - to a value that is marginally stable.I provide analytic arguments showing that many of these instabilities have marginally stable values of heat flux that scale with β; in particular, ∼β −1 in the case of the HWI and HSI, and ∼β −1/2 in the case of the GTI. While these arguments lend confidence that these instabilities will exist in astrophysical plasmas, they do not guarantee that the instabilities will in fact be able to limit the heat flux to marginally stable values. Fortunately, first-principles numerical simulations can both assess whether transport saturates at the marginally stable values as well as detail the specific physical mechanisms that result in this saturation. The main thrust of the numerical analysis presented in this thesis pertains to the HWI. Previous analytical and numerical studies have shown that the heat flux for the saturated HWI scales as the analytic calculations predict: ∝βe−1 . These numerical studies, however, had limited scale separation and, consequently, large fluctuation amplitudes, which calls into question the relevancy of the presented analytic arguments in explaining the simulation results, and vice-versa. I ran a number of electromagnetic particle-in-cell (PIC) simulations of the HWI for two distinct initial conditions across a range of βe and temperature-gradient length scales in an attempt to increase scale separation and lower fluctuation amplitudes. I found that, even out to the largest heretofore performed simulations, the steady-state heat flux scales as ∼βe−1 . I also present preliminary results using hybrid-PIC simulations of ion-heat-flux-driven micro-scale instabilities, which show the presence of the GTI for the first time; however, the saturated value of the heat flux is yet to be ascertained.In order to investigate how the HWI saturates as a function of βe and scale separation, I used a number of methods to infer from the simulations an effective collision operator describing interactions between electrons and the HWI fluctuations. The first method leverages a Chapman-Enskog expansion of the kinetic equation under the assumption that the waves pitch-angle scatter particles in a frame moving at their phase velocity. Using distribution functions measured in simulations, the collision operator is inverted to solve for the dependence of the pitch-angle scattering frequency as a function of velocity-space variables. The second method employed is the construction of a quasilinear operator from the electromagnetic spectrum measured in simulations, under the assumption of purely resonant wave-particle scattering. Under the further assumption that the wave phase speed is much less than the thermal velocity of the species, I demonstrate that this operator is equivalent to the operator assumed in the first method. Finally, I employ data from a large number of tracked particles in simulations to construct a Fokker-Planck operator, which I show also adopts the form of a pitch-angle scattering operator in the frame of the wave phase velocity. All of the methods presented in this thesis are either novel or are significant refinements of existing methods, and are therefore results in their own right.The exact form of the collision frequency differs between each of the methods; however, each result motivates different key physical ingredients, which I incorporate and synthesize into a model for the pitch-angle scattering frequency of the saturated HWI. The model, which is that of a resonance-broadened quasi-linear operator, shows that the HWI can regulate heat flux to the observed ∼βe−1 scaling in the limit of astrophysical scale separation. Resonance broadening is a crucial ingredient for this extrapolation. I argue that without this feature, electrons with sub-thermal parallel velocities do not have any physical means by which to be scattered by waves, resulting in a large, unphysical heat flux that would deviate from the scaling. Finally, I show that the presence of resonance broadening also explains much of the difference between the model operators that I have inferred from simulations, and that the entirety of the analysis represents a self-consistent picture.

Subject Added Entry-Topical Term  

Plasma physics.

Subject Added Entry-Topical Term  

Astrophysics.

Subject Added Entry-Topical Term  

Electromagnetics.

Index Term-Uncontrolled  

Effective collision operator

Index Term-Uncontrolled  

Heat flux

Index Term-Uncontrolled  

Intracluster medium

Index Term-Uncontrolled  

Whistler waves

Index Term-Uncontrolled  

Heat transport

Added Entry-Corporate Name  

Princeton University Astrophysical Sciences-Plasma Physics Program

Host Item Entry  

Dissertations Abstracts International. 85-04B.

Host Item Entry  

Dissertation Abstract International

Electronic Location and Access  

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Control Number  

joongbu:642443