A survey of electron Bernstein wave heating and current drive potential for spherical tokamaks

TL;DR

This paper reviews and numerically analyzes the potential of electron Bernstein waves for heating and current drive in spherical tokamaks, demonstrating their viability and controllability for plasma applications.

Contribution

It provides a comprehensive numerical study of EBW performance in spherical tokamaks, highlighting their potential for efficient and robust plasma heating and current drive.

Findings

EBWs can effectively deposit power and drive current across the plasma radius.

A universal EBW H&CD system is feasible with proper antenna positioning.

The system shows robustness and controllability in various plasma conditions.

Abstract

The electron Bernstein wave (EBW) is typically the only wave in the electron cyclotron (EC) range that can be applied in spherical tokamaks for heating and current drive (H&CD). Spherical tokamaks (STs) operate generally in high-beta regimes, in which the usual EC O- and X- modes are cut-off. In this case, EBWs seem to be the only option that can provide features similar to the EC waves---controllable localized H&CD that can be utilized for core plasma heating as well as for accurate plasma stabilization. The EBW is a quasi-electrostatic wave that can be excited by mode conversion from a suitably launched O- or X-mode; its propagation further inside the plasma is strongly influenced by the plasma parameters. These rather awkward properties make its application somewhat more difficult. In this paper we perform an extensive numerical study of EBW H&CD performance in four typical ST plasmas (NSTX L- and H-mode, MAST Upgrade, NHTX). Coupled ray-tracing (AMR) and Fokker-Planck (LUKE) codes are employed to simulate EBWs of varying frequencies and launch conditions, which are the fundamental EBW parameters that can be chosen and controlled. Our results indicate that an efficient and universal EBW H&CD system is indeed viable. In particular, power can be deposited and current reasonably efficiently driven across the whole plasma radius. Such a system could be controlled by a suitably chosen launching antenna vertical position and would also be sufficiently robust.