Non-Linear Modeling of RF in Tokamaks
National and international class magnetic fusion energy experiments, including DIII-D, C-Mod, NSTX, and ITER, all rely on RF heating as a principal means of achieving the requisite high temperature plasma. In these experiments, the RF power must first pass through the lower density, lower temperature edge region before it can reach the high density core of these experiments, where by design, it is deposited. But the relatively higher power density of the RF in the edge region enables non-linear processes (such as parametric decay) that can result in localized parasitic losses, thus degrading or even interrupting core performance. In this project, we propose to build upon recent progress in time-domain simulation of RF physics, in both particle and field methodologies, to improve the quantitative understanding and modeling capabilities of such non-linear processes to include 2 & amp;3D geometries, and to include full-spectrum analysis. Recent progress in particle simulations in the RF (radio frequency) range has solved one of the most perplexing difficulties associated with particle noise due to ion gyro-motions. This technique has primarily been applied to linear simulation of the plasma core, but in this project we seek to determine if the advantage will also hold for non-linear simulation of the plasma edge. Furthermore, we will test the particle approach against a more traditional fluid solve, which must first be generalized in a novel manner, in order to provide a fully competitive approach to the particle approach, in terms of physical content. This fluid generalization, a pressure closure which permits modeling of higher harmonic waves, is itself a novel development. The Phase I work will center around proof-of-principle demonstrations and degree of advantageousness determination for these two methods, on known cases involving parametric decay and parasitic losses from a launched wave. Commercial Applications and Other Benefits: This project will add to the quantitative tools and methods used to model the edge plasma region of tokamaks. The capability will allow for a better understanding of existing experimental observations, and improve the predictive capabilities, and hence confidence, in the RF systems for future experiments. This project will also offer an opportunity to benchmark the emerging Nautilus fluid solver software package, and expose it to the larger scientific community, and potential commercial customers.
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