Progress in RF theory: a sketch of recent evolution in selected areas

Abstract

This review of recent developments in radio-frequency (RF) theory focusses on the lower (ion-cyclotron) frequency range, although the methods described could be applied to other frequency ranges. The basic RF problem is to solve the wave propagation problem jointly with the evolution of the distribution functions (generally speaking non-Maxwellian) of the particles heated by the RF. We describe the two traditional paths towards such a solution, namely the quasi-uniform magnetic field approach and the Hamiltonian approach. We show that a theory based on the guiding-centre description of the unperturbed particle orbits can unify the two approaches and lead to a fully consistent description of the complete problem, the wave propagation and RF-induced velocity-space diffusion (quasi-linear) parts resting on identical assumptions. This guarantees that basic properties of the wave-particle interactions are preserved and that the power balance between waves and particles is automatically satisfied. The recent evolution of full-wave codes and their comparison is reviewed, and some recent puzzles are pointed out. Recent work on coupling codes is also briefly reviewed.

Wave–particle interactions in plasmas

“…When these are accounted for in Maxwell's equations, the wave equation or dispersion relation that follows is that of a plasma wave that includes both field and particles oscillations. In the simplest cases, the collective response of particles can be described as a plasma dielectric constant or tensor-in the most complicated case a dielectric tensor operator must be considered (Koch et al 1998)-and the wave-particle interaction is sort of hidden in this self-consistent picture. This dielectric property is a reactive aspect of the wave-particle interaction which takes into account the energy put into the particle's oscillations to qualify the propagation characteristics of the plasma wave but does not describe an averageor active-power transfer (at least in its simplest forms, like real dielectric tensor; complete dielectric tensors or operators contain imaginary parts that describe active power transfer).…”

The Coupling of Electromagnetic Power to Plasmas

“…Nevertheless the rigorous selfconsistent solution of the full boundary-values problem is a formidable task that can only be tackled with numerical codes. A review of the early development of sophisticated coupling codes can be found in the review [21] to which one must add reference to the RANT-3D code [20] describing coupling of recessed antennas to plasma. Both in ICANT [22] and in TOPICA [25] detailed current distributions are now computed over all antenna parts.…”

Chapter 6: Plasma auxiliary heating and current drive

“…( 7) is too complex to be solved in full toroidal geometry. Therefore, one resorts to approximation (see [92] for a review). One class of approximation is to solve the system in slab geometry (one dimensional codes).…”