Upper-hybrid Resonance Layer Research Articles

Observation of an Upper-Hybrid Soliton

A density cavity at the upper-hybrid resonance layer has been observed in the saturated stage of the trapped electrostatic field when a high-power microwave of the extraordinary mode is injected into an afterglow plasma column in a uniform magnetic field. The results can be explained by the modulational instability at the upper-hybrid frequency and the formation of an upper-hybrid soliton.

Ray-tracing in the electron-cyclotron frequency region

The tracing of the geometrical optics rays in toroidal geometry and in the electron-cyclotron frequency range has been done numerically. The results presented are relevant to the extraordinary-mode propagation and conversion at the upper-hybrid resonance layer. High-density regime refraction effects, together with strong bending of the warm Bernstein rays along the toroidal direction and resonance-cone structure generation, are the main features of the numerical output.

Electron cyclotron emission in Alcator tokamak

Radial observations of emission in the vicinity of the electron cyclotron frequency and its harmonics show the radiation to be polarized; ratio of extraordinary to ordinary mode intensity of about 2:1. In the thermal spectra the effects of cold-plasma resonances upon propagation of the radiation from emission layer to observation point are evident: (i) The extraordinary mode first harmonic is always suppressed by the upper hybrid resonance layer; (ii) The ordinary-mode first harmonic is suppressed when the plasma frequency exceeds the cyclotron frequency; (iii) For sufficiently high density the second harmonic is also affected by the hybrid cut-off. In the non-thermal spectrum the broad-band emission is polarized at high frequency but not at lower. The feature in the vicinity of the plasma frequency at intermediate density is broader than previously observed and almost entirely above ωpe. Internal sawtooth relaxations have been observed in the central temperature even up to peak densities of 7 × 1020 m−3. Temperature profiles deduced from second harmonic cyclotron emission and Thompson scattering data are compared.