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Reinterpreting radio frequency heating and current drive theory in a tokamak

Published online by Cambridge University Press:  25 October 2024

Peter J. Catto Open the ORCID record for Peter J. Catto [Opens in a new window]
Peter J. Catto*
Affiliation:
Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
*
† Email address for correspondence: [email protected]
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Abstract

Quasilinear treatments are widely used for tokamaks to evaluate radio frequency (rf) heating and current drive. Even though the core of a tokamak plasma is weakly collisional, the solution of the linearized kinetic equation is evaluated using unperturbed collisionless trajectories while often treating successive poloidal circuits of the passing (and trapped) particles as uncorrelated or nearly so. In addition, the most important effect of tokamak geometry, the mirror force, is usually mistreated or ignored when obtaining the solution. These concerning aspects of rf treatments are clarified by considering lower hybrid heating and current drive to illustrate that the electrons in resonance with the applied rf are enclosed by narrow collisional boundary layers, and that tokamak geometry makes it necessary to retain poloidal variation when solving a weakly collisional linearized kinetic equation. Other aspects such as collisional boundary layers at the trapped–passing boundary, cyclotron resonances, and the limitations of quasilinear theory are also considered. The new insights lead to a fundamentally different formulation and interpretation of the solution of the linearized Fokker–Planck equation used for rf quasilinear theory in a tokamak, while retaining many of the features that have contributed to its successful application to rf heating and current drive.

Keywords

fusion plasmaplasma heatingplasma waves
Type
Research Article
Information
Journal of Plasma Physics , Volume 90 , Issue 5 , October 2024 , 905900508
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Creative Commons
This is a work of the US Government and is not subject to copyright protection within the United States. Published by Cambridge University Press.
Copyright
Copyright © United states Government, 2024

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