Fast evaluation of the current drive efﬁciency by electron cyclotron waves for reactor studies

Emanuele Poli,Hartmut Zohm,Maximilian Müller,Michael Kovari,E Poli,H Laqua,J Oosterbeek

doi:10.1051/epjconf/201920301008

Abstract

The determination of the current driven by electron cyclotron waves is usually performed employing ray/beam tracing codes, which require as an input the magnetic equilibrium, the electron density and the electron temperature profiles on one side and the beam injection parameters on the other. In the frame of systems-code applications, however, a different approach is needed, as some of the required input quantities are not available. Here, a procedure to evaluate the achievable ECCD efficiency for given global reactor parameters is proposed. It relies on a single numerical evaluation of the current drive efficiency (based on the adjoint method and including momentum-conserving corrections) for suitably chosen input values. The results are shown to be in good agreement with the full numerical optimization of the ECCD efficiency for a number of reactor-relevant scenarios. As described in this paper, this approach does not include the effect of parasitic absorption from higher cyclotron harmonics, which becomes important starting from electron temperatures of the order of 30 keV.

Highlights

The calculation of the current driven by auxiliary heating systems is just a small part of the operations performed by systems codes like PROCESS [1, 2] in order to assess the performance of a fusion reactor for a given set of global parameters
While in most applications electroncyclotron current drive (ECCD) is calculated by ray/beam tracing codes [3] employing as an input some given values for the magnetic equilibrium, the density and the electron temperature profiles, and the EC beam parameters, in a systems code some of these data are not available
A procedure is proposed to evaluate the current driven by EC waves through a single numerical determination of the ECCD efficiency according to the adjoint method [5] for a suitably selected set of input values deduced from the global machine parameters

Summary

Introduction

The calculation of the current driven by auxiliary heating systems is just a small part of the operations performed by systems codes like PROCESS [1, 2] in order to assess the performance of a fusion reactor for a given set of global parameters. The antenna parameters which would yield the optimum current drive for a given set of global parameters are not known This makes the usual strategy based on tracing the beam path through the plasma and exploring the relevant parameter space [4] not applicable, even if the numerical burden were manageable. In this contribution, a procedure is proposed to evaluate the current driven by EC waves through a single numerical determination of the ECCD efficiency according to the adjoint method [5] for a suitably selected set of input values deduced from the global machine parameters. The computational effort of the proposed approach, which amounts basically to the numerical quadrature of two one-dimensional integrals

Theoretical background

ECCD Optimization

Evaluation of the optimum ECCD efficiency from global parameters