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A hybrid full-wave Markov chain approach to calculating radio-frequency wave scattering from scrape-off layer filaments

Published online by Cambridge University Press:  22 October 2021

Bodhi Biswas*
Affiliation:
Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge 02193, USA
Syun'ichi Shiraiwa
Affiliation:
Princeton Plasma Physics Laboratory, Princeton 08540, USA
Seung-Gyou Baek
Affiliation:
Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge 02193, USA
Paul Bonoli
Affiliation:
Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge 02193, USA
Abhay Ram
Affiliation:
Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge 02193, USA
Anne E. White
Affiliation:
Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge 02193, USA
*
Email address for correspondence: [email protected]

Abstract

The interaction of radio-frequency (RF) waves with edge turbulence modifies the incident wave spectrum, and can significantly affect RF heating and current drive in tokamaks. Previous lower hybrid (LH) scattering models have either used the weak-turbulence approximation, or treated more realistic, filamentary turbulence in the ray tracing limit. In this work, a new model is introduced which retains full-wave effects of RF scattering in filamentary turbulence. First, a Mie-scattering technique models the interaction of an incident wave with a single Gaussian filament. Next, an effective differential scattering width is derived for a statistical ensemble of filaments. Lastly, a Markov chain solves for the transmitted wave spectrum in slab geometry. This model is applied to LH launching for current drive. The resulting wave spectrum is asymmetrically broadened in angular wavenumber space. This asymmetry is not accounted for in previous LH scattering models. The modified wave spectrum is coupled to a ray tracing/Fokker–Planck solver (GENRAY/CQL3D) to study its impact on current drive. The resulting current profile is greatly altered, and there is significant increase in the on-axis current and decrease in the off-axis peaks. This is attributed to a portion of the modified wave spectrum that is strongly dampened on-axis during the first pass.

Type
Research Article
Copyright
Copyright © The Author(s), 2021. Published by Cambridge University Press

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References

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