EFFECT OF PARTICLE TRANSPORT ON THE MEASURED ELECTRON CYCLOTRON CURRENT DRIVE PROFILE

Abstract

There are several important applications on ITER for the localized non-inductive current generated by electron cyclotron (EC) waves, including suppression of neoclassical tearing modes. While the strong absorption of EC waves guarantees that the power deposition is localized, radial transport of the current carrying electrons can make the resulting current drive profile significantly broader. For example, studies on the small TCV tokamak showed that CQL3D quasilinear Fokker-Planck modeling could be brought in line with measurements only by including radial transport at levels similar to the thermal energy transport. 1 This decreased the predicted electron cyclotron current drive (ECCD) magnitude by a factor of 5 and substantially broadened the ECCD profile. Conversely, experiments on the large JT-60U tokamak found that the ECCD profile determined using a motional Stark effect (MSE) diagnostic was in agreement with CQL3D modeling with radial transport turned off. 2 A well diagnosed series of ECCD experiments on the DIII-D tokamak have explored the intermediate size regime between TCV and JT-60U. Studies at low relative power density (QEC/ ne < 1, where QEC is the EC power density in MW/m 3 and ne is the electron density in units of 10 19 m -3 ) found that the width of the ECCD profile determined from MSE signals was consistent with the calculated width from CQL3D in the absence of radial transport. 3