Generation and propagation of electromagnetic waves resonantly excited by a heating wave near the electron cyclotron frequency.

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In electron cyclotron heating (ECH) of tenuous plasmas in a magnetic beach configuration, two resonant processes complicates physical analyses, i.e. divergent increase of the parallel wave number and synchronized acceleration of increasing number of resonantly gyrating electrons. In this task, we have made a new trial to look into the process in terms of frequency-spectrum-analyses of electromagnetic waves excited in the cyclotron range under the stimulation of a strong monochromatic heating wave.We have constructed a compact sensitive diagnostic system that fit in a narrow accessible pace for diagnoses of a hot plasma in a tandem mirror, We have observationally confirmed a broad-band spectrum that is attributable to cyclotron emissions by individual hot electrons.New finding in this research is a strong narrow band spectrum at a few per-cent above the heating wave frequency. The peak frequency and the width decreases with increasing power of the heating wave, and the spectral structure depends on the magnetic field profile. We conclude that this narrow-band wave is generated by a resonant group of electrons which are phase-modulated in the velocity space under ECU and spatially bunched in the magnetic slope to generate coherent emissions at the local cyclotron frequency.