Microtearing modes in the tokamak pedestal

dc.contributor.advisorHazeltine, R. D. (Richard D.)
dc.contributor.committeeMemberMahajan, Swadesh
dc.contributor.committeeMemberFitzpatrick, Richard
dc.contributor.committeeMemberMorrison, Philip
dc.creatorLarakers, Joseph Leland
dc.date.accessioned2022-08-09T23:16:52Z
dc.date.available2022-08-09T23:16:52Z
dc.date.created2021-12
dc.date.issued2022-06-24
dc.date.submittedDecember 2021
dc.date.updated2022-08-09T23:16:53Z
dc.description.abstractAn economical thermonuclear reactor has the potential to serve as an on-demand, clean, and abundant energy source. The main difficulty is confining the fusion fuel to the large pressures required for the fuel to react. The energy produced from fusion reactions must be collected and confined such that it activates further reactions. Magnetic confinement is a promising strategy. Magnetic confinement devices, such as tokamaks, have steadily improved by identifying and suppressing different mechanisms of heat transport and instability. This dissertation focuses on a single mechanism known as the microtearing mode (MTM). The microtearing mode is an electromagnetic excitation that is localized about rational magnetic surfaces and is driven unstable by electron temperature gradients. The mode tears magnetic surfaces and modifies their structure. The resulting topology relaxes the radial temperature gradient via fast parallel motion. The MTM has recently gained attention as a potentially important instability in the pedestal region of H-mode tokamaks. It is theorized to be responsible for the anomalous electron heat transport and discrete bands of magnetic fluctuations observed experimentally. Here, we revisit the conventional microtearing theory and extend it to study features pertinent to the pedestal region. In doing so, we identify a new crucial parameter for MTM linear stability. This extended theory matches with the experimental observations of magnetic fluctuations and provides an explanation of their discrete nature. With an understanding of the linear dispersion characteristics, we proceed to study the nonlinear evolution of the mode. The dispersion suggests a strong mode-mode resonance between MTM harmonics. A weak turbulence model has been developed to study the nonlinear consequences of these resonances.
dc.description.departmentPhysics
dc.format.mimetypeapplication/pdf
dc.identifier.urihttps://hdl.handle.net/2152/115163
dc.identifier.urihttp://dx.doi.org/10.26153/tsw/42064
dc.language.isoen
dc.subjectMicrotearing modes
dc.subjectMagnetic confinement
dc.subjectTearing modes
dc.subjectH-mode
dc.subjectTokamak pedestal
dc.subjectEdge localized modes
dc.titleMicrotearing modes in the tokamak pedestal
dc.typeThesis
dc.type.materialtext
thesis.degree.departmentPhysics
thesis.degree.disciplinePhysics
thesis.degree.grantorThe University of Texas at Austin
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy

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