Abstract Details
Abstracts
Author: Ilya Y. Dodin
Requested Type: Pre-Selected Invited
Submitted: 2019-02-22 10:27:19
Co-authors: D. E. Ruiz, K. Yanagihara, Y. Zhou, S. Kubo
Contact Info:
PPPL
PO Box 451, MS 28
Princeton, 08543
USA
Abstract Text:
Full-wave modeling of mm waves in fusion plasmas is computationally demanding due to the small ratio of their wavelengths to the plasma size. Reduced models rooted in traditional geometrical optics (GO) are faster but do not resolve the wave-beam quasioptical structure and cannot capture mode conversion, unless they rely on semi-analytic models with limited applicability. We report a modernized version of GO, termed extended geometrical optics (XGO), which does not suffer from the said limitations. XGO allows for a general dispersion operator and expands its, using Weyl calculus in a curved ray-based metric, in the GO parameter; then, a tractable envelope equation is obtained for the coupled-mode amplitudes by a straightforward reduction. The first-order XGO predicts general fundamental corrections to the ray equations. Special cases of these corrections include spin-orbital interactions in quantum mechanics and the Hall effect of light in optics but have not been explicitly identified for classical plasma waves until recently [Ruiz and Dodin, Phys. Plasmas 24, 055704 (2017)]. The second-order XGO yields a quasioptical model of mode-converting beams. Without assuming a particular ansatz for the beam structure, this formulation leads to a parabolic PDE for a certain projection of the wave field. The number of components of this projection equals the number of the resonantly-coupled modes, so mode conversion is naturally resolved (Dodin et al, arXiv:1901.00268). A new quasioptical code PARADE (PAraxial RAy Description) has been developed based on this theory. Using this code, the dynamics of mm-wave beams in inhomogeneous plasma with and without mode conversion has been simulated, particularly in application to the Large Helical Device (Yanagihara et al, in preparation). The numerical results show good agreement of PARADE predictions with one-dimensional full-wave modeling, conventional ray tracing, and analytic formulas from Gaussian-beam optics.
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