EFFECT OF PARTICLE TRANSPORT ON THE MEASURED ELECTRON CYCLOTRON CURRENT DRIVE PROFILE
This work was supported by the US Department of Energy under DE-FC02-04ER54698, DE-FG03-97ER54415, DE-FG03-99ER54541, and DE-AC52-07NA27344.
Radial transport of the current carrying electrons can broaden the profile of electron cyclotron current drive (ECCD), with potentially detrimental effects for applications that reply on strong localization of the noninductive current. Early experiments on the DIII-D tokamak did not observe any clear effects of particle transport on the ECCD profile. However, more recent experiments at high ECCD power, low density, and radiation temperatures above 20 keV clearly demonstrate that the ECCD profile is reduced and broadened compared to CQL3D predictions assuming no radial transport. At high relative power densities, a diffusion coefficient of ≈0.4 m2/s is required in CQL3D to reproduce the experimental ECCD profile, while smaller diffusion coefficients are needed to model the ECCD profile at low relative power densities. This level of transport is an order of magnitude less than the electron thermal diffusivity but is comparable to the effective particle transport rate needed to maintain the density profile.
