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Collisional and Electromagnetic Physics in Gyrokinetic Models
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| 자료유형 | 학위논문 |
|---|---|
| 서명/저자사항 | Collisional and Electromagnetic Physics in Gyrokinetic Models. |
| 개인저자 | Crandall, Paul Charles. |
| 단체저자명 | University of California, Los Angeles. Physics 0666. |
| 발행사항 | [S.l.]: University of California, Los Angeles., 2019. |
| 발행사항 | Ann Arbor: ProQuest Dissertations & Theses, 2019. |
| 형태사항 | 230 p. |
| 기본자료 저록 | Dissertations Abstracts International 81-06B. Dissertation Abstract International |
| ISBN | 9781392380390 |
| 학위논문주기 | Thesis (Ph.D.)--University of California, Los Angeles, 2019. |
| 일반주기 |
Source: Dissertations Abstracts International, Volume: 81-06, Section: B.
Advisor: Carter, Troy |
| 이용제한사항 | This item must not be sold to any third party vendors. |
| 요약 | One of the most challenging problems facing plasma physicists today involves themodeling of plasma turbulence and transport in magnetic confinement experiments.The most successful model to this end so far is the reduced gyrokinetic model. Such amodel cannot be solved analytically, but can be used to simulate the plasma behaviorand transport with the help of present-day supercomputers. This has lead to the developmentof many different codes which simulate the plasma using the gyrokinetic modelin various ways. These models have achieved a large amount of success in describingthe core of the plasma for conventional tokamak devices. However, numerous difficultieshave been encountered when applying these models to more extreme parameterregimes, such as the edge and scrape-off layer of the tokamak, and high plasma devices,such as spherical tokamaks. The development and application of the gyrokineticmodel (specifically with the gyrokinetic code, GENE) to these more extreme parameterranges shall be the focus of this thesis.One of the main accomplishments during this thesis project is the development ofa more advanced collision operator suitable for studying the low temperature plasmaedge. The previous collision operator implemented in the code was found to artificiallycreate free energy at high collisionality, leading to numerical instabilities when oneattempted to model the plasma edge. This made such an analysis infeasible. Thenewly implemented collision operator conserves particles, momentum, and energy tomachine precision, and is guaranteed to dissipate free energy, even in a nonisothermalscenario. Additional finite Larmor radius correction terms have also been implementedin the local code, and the global code version of the collision operator has been adaptedfor use with an advanced block-structured grid scheme, allowing for more affordablecollisional simulations.The GENE code, along with the newly implemented collision operator developedin this thesis, has been applied to study plasma turbulence and transport in the edge(tor = 0:9) of an L-mode magnetic confinement discharge of ASDEX Upgrade. Ithas been found that the primary microinstabilities at that radial position are electrondrift waves destabilized by collisions and electromagnetic effects. At low toroidal modenumbers, ion temperature gradient driven modes and microtearing modes also seem toexist. In nonlinear simulations with the nominal experimental parameters, the simulatedelectron heat flux was four times higher than the experimental reconstruction,and the simulated ion heat flux was twice as high. However, both the ion and electronsimulated heat flux could be brought into agreement with experimental values by loweringthe input logarithmic electron temperature gradient by 40%. It was also foundthat the cross-phases between the electrostatic potential and the moments agreed wellfor the part of the binormal spectrum where the dominant transport occurred, and wasfairly poor at larger scales where minimal transport occurred.Finally, a new scheme for evaluating the electromagnetic fields has been developedto address the instabilities occurring in nonlinear local and global gyrokinetic simulationsat high plasma . This new scheme is based on evaluating the electromagneticinduction explicitly, and constructing the gyrokinetic equation based on the original distribution,rather than the modified distribution which implicitly takes into account theinduction. This new scheme removes the artificial instability occurring in global simulations,enabling the study of high scenarios with GENE. The new electromagneticscheme can also be generalized to a full-f implementation, however, it would requireupdating the field matrix every time-step to avoid the cancellation problem. The newscheme (including the parallel nonlinearity) does not remove the local instability, suggestingthat that instability (caused by magnetic field perturbations shorting out zonalflows) is part of the physics of the local model. |
| 일반주제명 | Physics. |
| 언어 | 영어 |
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