Tests of advanced RF off-axis current drive techniques on DIII-D

R.I Pinsker,M.W Brookman,M Porkolab,R.J Buttery,X Chen,C.C Petty,G.M Wallace,J.M Lohr,S.J Wukitch,C.P Moeller,E Poli,J Oosterbeek,H Laqua

doi:10.1051/epjconf/201920302008

Abstract

The establishment of reactor-relevant radiofrequency heating and current drive techniques is a focus of work on DIII-D in the next five-year period. This paper gives an overview of the planned experimental work in the areas of (1) nearly vertically launched ECCD, (2) ‘helicon’ (whistlers or fast waves in the lower hybrid range of frequencies) current drive, and (3) high-field-side-launch (HFS) lower hybrid (slow wave) current drive. Each of these techniques addresses the need for efficient off-axis current drive for a steady-state tokamak reactor to supplement the bootstrap current and to provide current profile control, and each will be experimentally assessed at a coupled power level of ~1 MW on DIII-D in the next few years.

Highlights

A steady-state tokamak fusion reactor must have most of the plasma current self-driven by the bootstrap effect to be economically practical
The ARIES-RS study proposed [1] a combination of fast waves in the lower hybrid range of frequencies and lower hybrid slow waves to drive the non-inductive, non-bootstrap current in the outer half of the minor radius
The DIII-D Advanced Tokamak program is exploring multiple techniques in an effort to establish efficient means of off-axis non-inductive current drive. Three such techniques that will be explored on DIII-D in the few years are described: (1) nearly-vertically-launched electron cyclotron current drive at 110 and/or 117.5 GHz, (2) 'helicon' current drive at 0.5 GHz, and (3) high-field-side-launched slow lower hybrid wave current drive (HFS LHCD) at 4.6 GHz

Summary

Introduction

A steady-state tokamak fusion reactor must have most of the plasma current self-driven by the bootstrap effect to be economically practical. The efficiency of the current drive, both in terms of the driven current per Watt of power absorbed in the plasma core and of the efficiency of conversion of electrical power to current drive power and of coupling the power to the plasma (rf in the cases discussed here) is critical in determining the economics of the reactor. For this reason, the DIII-D Advanced Tokamak program is exploring multiple techniques in an effort to establish efficient means of off-axis non-inductive current drive. In each case, such follow-on experiments would be possible in the future on DIII-D at power levels high enough that those systems would become viable tools for the further development of the Advanced Tokamak, along with the existing off-axis neutral beam systems on DIII-D

Nearly-vertically-launched ECCD

High-field-side-launched LHCD

Findings

Summary and conclusion