Scattering of ECRF waves by edge density fluctuations and blobs

¹ Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139. USA
² National Technical University of Athens (part of HELLAS), School of Electrical and Computer Engineering, Association EURATOM - Hellenic Republic, GR-15773, Greece

^a e-mail: abhay@mit.edu
^b e-mail: kyriakos@central.ntua.gr

Published online: 12 March 2015

Abstract

The scattering of electron cyclotron waves by density blobs embedded in the edge region of a fusion plasma is studied using a full-wave model. The full-wave theory is a generalization of the usual approach of geometric optics ray scattering by blobs. While the latter allows for only refraction of waves, the former, more general formulation, includes refraction, reflection, and diffraction of waves. Furthermore, the geometric optics, ray tracing, model is limited to blob densities that are slightly different from the background plasma density. Observations in tokamak experiments show that the fluctuating density differs from the background plasma density by 20% or more. Thus, the geometric optics model is not a physically realistic model of scattering of electron cyclotron waves by plasma blobs. The differences between the ray tracing approach and the full-wave approach to scattering are illustrated in this paper.