The contribution of plasma dielectric properties to the cyclotron radiation spectrum from a tokamak plasma

Abstract

The effects of the dielectric properties of the plasma on the cyclotron radiation spectrum from a tokamak discharge are investigated for propagation perpendicular to the magnetic field. At the cut-offs and at the upper hybrid resonance the cold-plasma dispersion relation is assumed to be valid. It is shown that the presence of evanescent regions, cut-off surfaces, and an upper hybrid resonance surface in the plasma distorts the line shape at the lower harmonics when ωp ∼ ωc. The first-harmonic extraordinary-mode emission is suppressed as ωp/ωc at the centre of the discharge increases owing to the de-coupling of the electromagnetic wave from the plasma electrons. A computer study is made of the changes in the spectrum as (ωp/ωc)r=0 is increased. The anisotropy of the cyclotron radiation spectrum about the minor axis of the torus is also investigated. Both line width and shape depend on the viewing direction.