자료유형  

 학위논문

Control Number  

0017163890

International Standard Book Number  

9798383697368

Dewey Decimal Classification Number  

530

Main Entry-Personal Name  

Duff, Joseph M.

Publication, Distribution, etc. (Imprint  

[S.l.] : The University of Wisconsin - Madison., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

249 p.

General Note  

Source: Dissertations Abstracts International, Volume: 86-02, Section: B.

General Note  

Advisor: Hegna, Chris C.

Dissertation Note  

Thesis (Ph.D.)--The University of Wisconsin - Madison, 2024.

Summary, Etc.  

요약The interplay between magnetic field shaping and turbulent transport in toroidal magnetic confinement fusion must be understood to design new devices to elevate fusion energy to a competitive solution to humanity's energy needs. In this thesis, the turbulence properties of both axisymmetric shaping and three-dimensional shaping of magnetic fields that are local to a flux surface were studied using the gyrokinetic code GENE. Gyrokinetics is a high-fidelity model, where the dimensionality is reduced from a Vlasov-Maxwell system by averaging out the fast gyromotion of the charged particles in the plasma.The effect of triangularity and sign of geodesic curvature Kx on ion-temperaturegradient (ITG)-driven turbulence was investigated, covering both extreme positive and negative triangularities. Triangularity had a substantial impact on linear and nonlinear physics, and reversing Kx significantly impacted turbulence saturation. Negative triangularity reduced peak linear growth rates and broadened the growth rate spectrum as a function of radial wavenumber kx. Positive triangularity increased peak growth rates that shifted to finite kx and narrowed the growth rate spectrum. Reversing the sign of Kx slightly lowered linear growth rates, except for δ = 0.85, where the growth rates decreased significantly. The effect of triangularity on linear instability properties at low perpendicular wavenumbers can be explained through its impact on magnetic polarization and curvature. The nonlinear heat flux was weakly dependent on triangularity for −0.5 ≤ δ ≤ 0, increasing significantly with extreme δ, regardless of sign. When Kx was reversed, the heat flux decreased, became weakly dependent on triangularity for |δ| ≤ 0.5, and decreased significantly at extreme triangularity, regardless of sign. Zonal modes play an important role in nonlinear saturation for the configurations studied, and artificially suppressing zonal modes increased the nonlinear heat flux by a factor of at least two and a half, with negative triangularities having a larger increase. When Kx was reversed, so did the trend of heat flux ratios with triangularity. Proxies for zonal-flow damping and drive suggest that zonal flows are enhanced with increasing positive δ in both Kx scenarios. Conventional quasilinear models did not capture the nonlinear heat flux trends, but, by using a reduced three-field fluid model for ITGs, the effect of unstable modes coupling to stable modes via zonal modes was added to the quasilinear model. This three-wave-interaction corrected quasilinear model was only able to capture the nonlinear trends in triangularity when Kx was reversed. The failure of the modified quasilinear model to estimate the nonlinear trend for the physical equilibria was likely due to the nonlinear heat flux spectra extending into scales where the fluid model is not valid.Optimizations resulted in two three-dimensionally-shaped magnetic configurations with suppressed trapped-electron-mode (TEM)-driven turbulence. Initial equilibria had flux surface shapes with a helically rotating negative triangularity (NT) and positive triangularity (PT). The optimization targeted quasihelical symmetry and the available energy of trapped electrons. In electron-temperature-gradientdriven scenarios, the most unstable linear modes of the TEM-optimized configurations were inconsistent with TEMs, and the nonlinear simulations showed no significant fluctuations at ion scales. When a density gradient was present, the most unstable modes at low ky were toroidal universal inabilities (UIs) in the NT case and slab UIs in the PT geometry. Nonlinear simulations showed that UIs drove substantial heat flux in the NT and PT configurations. Increasing the ratio of plasma pressure to magnetic pressure to β = 4 x 10−3 significantly reduced linear instability at low ky, halved the nonlinear heat flux for the NT case, and almost completely suppressed the turbulence in the PT configuration.

Subject Added Entry-Topical Term  

Plasma physics.

Subject Added Entry-Topical Term  

Theoretical physics.

Subject Added Entry-Topical Term  

Physics.

Subject Added Entry-Topical Term  

Nuclear engineering.

Index Term-Uncontrolled  

Magnetic field shaping

Index Term-Uncontrolled  

Optimization

Index Term-Uncontrolled  

Plasma

Index Term-Uncontrolled  

Stellarators

Index Term-Uncontrolled  

Tokamak

Index Term-Uncontrolled  

Turbulence

Added Entry-Corporate Name  

The University of Wisconsin - Madison Physics

Host Item Entry  

Dissertations Abstracts International. 86-02B.

Electronic Location and Access  

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Control Number  

joongbu:656872