Electron cyclotron emission in Alcator tokamak

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Abstract
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.