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Details of Ion-Temperature-Gradient-Driven Instability Saturation
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| 자료유형 | 학위논문 |
|---|---|
| 서명/저자사항 | Details of Ion-Temperature-Gradient-Driven Instability Saturation. |
| 개인저자 | Whelan, Garth G. |
| 단체저자명 | The University of Wisconsin - Madison. Physics. |
| 발행사항 | [S.l.]: The University of Wisconsin - Madison., 2019. |
| 발행사항 | Ann Arbor: ProQuest Dissertations & Theses, 2019. |
| 형태사항 | 119 p. |
| 기본자료 저록 | Dissertations Abstracts International 80-12B. Dissertation Abstract International |
| ISBN | 9781392286432 |
| 학위논문주기 | Thesis (Ph.D.)--The University of Wisconsin - Madison, 2019. |
| 일반주기 |
Source: Dissertations Abstracts International, Volume: 80-12, Section: B.
Publisher info.: Dissertation/Thesis. Advisor: Terry, Paul W. |
| 이용제한사항 | This item must not be sold to any third party vendors. |
| 요약 | Heat and particle transport due to plasma microturbulence represents a challenge in the development of commercial fusion power. Microturbulence is caused by gyroradius-scale instabilities, of which the Ion-Temperature-Gradient-Driven (ITG) instability is one. This thesis uses gyrokinetic simulations to characterize how the linear ITG instability saturates, as well as to study the turbulent state that arises.In all of the ITG parameter cases investigated here, zonal flows, which are flows constant along a flux surface, are prominent. Zonal flows are linearly damped and thus must be driven nonlinearly. Some nonlinear energy transfer from the instability sustains the flows, but the majority of the energy injected by the instability is balanced by nonlinear transfer to smaller radial-scale stable and unstable eigenmodes. Unlike Kolmogorov turbulence, the dissipation scale overlaps with the injection scale, so there is no inertial range.This thesis investigates two phenomena relating to ITG in particular, the nonlinear critical temperature-gradient upshift (the Dimits shift) and the nonlinearly enhanced transport reduction which occurs when the normalized plasma pressure 棺 is increased. It is found that, while stable modes are the primary saturation mechanism, the Dimits shift cannot be attributed to a direct reduction of the heat flux by stable modes, or to their effects on the energy injection rate. It has been suggested that energy transfer out of zonal flows, in a manner like tertiary instability, could limit their amplitude and set the nonlinear critical gradient. We find that this is not possible directly, as transfer of flow energy is into the zonal flows for all wavenumber couplings.We apply these same techniques to the nonlinearly enhanced reduction of transport with 棺. Qualitatively, the saturation process is similar throughout the range of 棺. Stable mode effects only slightly increased with 棺. Instead, the majority of the reduction is explained by better frequency matching between interacting modes, which causes energy transfer to be more efficient. This effect can be included in quasilinear mixing-length transport models, and we show that it explains 50% to 100% of the enhanced transport reduction with 棺 in five out of six test cases. |
| 일반주제명 | Physics. |
| 언어 | 영어 |
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