Comparison between measurements of the poloidal distribution of magnetic fluctuations and predictions of theoretical models during TAE activity

W.W Heidbrink,A Jaun,H.A Holties

doi:10.1088/0029-5515/37/10/i07

Abstract

Fluctuations produced by beam-driven toroidicity-induced Alfven eigenmode (TAE) activity in the DIII-D tokamak are measured by a poloidal array of magnetic probes and compared with the wavefields computed by two theoretical models. Fluid resistive models compute continuum damped TAEs. A kinetic plasma model that retains Landau damping and finite Larmor radius effects computes global drift-kinetic Alfven eigenmodes. The phases of the probes disagree with both theoretical predictions, while the amplitudes agree best with the kinetic model

Highlights

Toroidicity induced Alfvh eigenmodes (TAEs) are potentially dangerous instabilities that could be destabilized by alpha particles in a tokamak fusion reactor
The only published comparison of measurements of the mode structure with a theoretical prediction was performed by Durst et al [7],who found that the poloidal mode number inferred from beam emission spectroscopy was consistent with the predictions of ideal MHD within -50% uncertainties
We find that the wave fields at the edge are sensitive to the global eigenfunction predicted by the theoretical models, so the probe data are useful as a diagnostic of the mode structure

Summary

INTRODUCTION

Toroidicity induced Alfvh eigenmodes (TAEs) are potentially dangerous instabilities that could be destabilized by alpha particles in a tokamak fusion reactor. There have been numerous measurements of the frequency and toroidal mode number of TAE activity [l],measurements of the radial and poloidal mode structure are relatively rare. The only published comparison of measurements of the mode structure with a theoretical prediction was performed by Durst et al [7],who found that the poloidal mode number inferred from beam emission spectroscopy was consistent with the predictions of ideal MHD within -50% uncertainties. The ideal MHD model [8]is widely employed, but both plasma kinetic [9-121 and energetic particle [ll,13-15] effects modify the predicted eigenfunction. We find that the wave fields at the edge are sensitive to the global eigenfunction predicted by the theoretical models, so the probe data are useful as a diagnostic of the mode structure. We find that a model that includes kinetic effects gives better agreement with experiment than the resistive MHD models

APPARATUS

THEORETICAL MODELLING

RESULTS

DISCUSSION AND CONCLUSIONS