Radial Transport and Electron-Cyclotron-Current Drive in the TCV and DIII-D Tokamaks

Abstract

Calculation of electron-cyclotron-current drive (ECCD) with the comprehensive CQL3D Fokker-Planck code for a TCV tokamak shot gives 550 kA of driven toroidal current, in marked disagreement with the 100-kA experimental value. Published ECCD efficiencies calculated with CQL3D in the much larger, higher-confinement DIII-D tokamak are in excellent agreement with experiment. The disagreement is resolved by including in the calculations electrostatic-type radial transport at levels given by global energy confinement in tokamaks. The radial transport of energy and toroidal current are in agreement.

Nonlocal transport in the reversed field pinch

“…where D and v are fit to observed transport in tokamaks [9][10][11][12] and reversed-field pinches (RFP) [13][14][15]. By making a detailed study of ion transport in the RFX we have found a link between pinch velocity and a magnetic chaotic topology [16].…”

Finding evidence for density fluctuation effects on electron cyclotron heating deposition profiles on DIII-D

“…Applying this correction improves agreement on deposition centers between TORAY and experimental deposition centers compared with past work [3] [7].…”

“…"# derived from ECE data using FFT or BIS analysis to compare with ray tracing analysis of ECH [2][7], these efforts found transport to be a cause of significant broadening over that of TORAY, with even high frequency modulation producing far wider experimental profiles [3].…”

“…The physics of ECH deposition has been studied on a variety of machines [1,2] and the use of predictive ray tracing is viewed as accurate when including a modeled fast radial diffusion factor [3]. However work on TCV [4], as well as theoretical work [1] and past results on DIII-D [5] suggest that !…”

Radial Transport Effects on Eccd in the TCV and Diii–d Tokamaks and on Ohmic Discharges in the MST RFP

“…At high enough power, the plasma temperature is high and the transport effects strong enough such that radial transport dominates the collisional slowing down time of the fast electrons. Our calculations [8] show that this is strongly the case for a representative full-toroidal-current-drive electron cyclotron current drive (ECCD) experiment [9] in the TCV fusion energy tokamak. Although there is little doubt as to whether plasma turbulence is responsible for the observed radial transport in excess of collisional levels [10], questions remain on the extent electrostatic (ES) or magnetic turbulence dominates [11] and also the degree of concurrence between tail electron transport and bulk plasma transport.…”