Abstract
A low-power 60 GHz gyrotron collective Thomson scattering diagnostic has been operating on TFTR to test the feasibility of detecting alpha particles when scattering perpendicular to the magnetic field. An enhanced scattered signal is predicted to result from the interaction of the energetic ions with plasma resonances in the lower hybrid frequency range. Millimeter-wave power levels at the plasma were approximately 200 W for typical pulse lengths of 50 ms. Deuterium and possible fusion product ion cyclotron frequencies and their harmonics were observed during neutral beam heating. These spectra are similar to ion cyclotron emission spectra which are detected with radio-frequency probes on TFTR at the plasma edge. Also, ion cyclotron resonance heating fundamental and harmonic fluctuations were observed. However, a signal has not been definitively detected in the lower hybrid frequency range which correlates to alpha particles. Broadband noise was observed during neutral beam heating which is greater than the predicted alpha particle signal.
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