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Description
The electron cyclotron maser instability (ECMI) has been considered as the mechanism of the coherent radio bursts called auroral kilometric radiation emitted from the auroral zone where the electrons are accelerated along the magnetic field line. The excitation of the ECMI is explained as the enhancement of positive 𝜕f/𝜕v⊥ as the effect of the magnetic compression. The electron cyclotron resonance heating and current drive (ECRH and ECCD) increases v⊥ of the electrons that have a specific v// to fulfill the cyclotron resonance condition. If the diffusion time in the velocity space is long enough in the low density plasma, the substantial large 𝜕f/𝜕v⊥ can be expected for the excitation of ECMI. In the heliotron J and the large helical device (LHD), we acquired intermediate frequency (IF) signals of the heterodyne radiometer for electron cyclotron emission (ECE) measurement with a fast sampling oscilloscope in discharges heated by ECH/ECCD. Fig.1 shows frequency spectrograms detected at two different ports (7.5 and 14.5) at the plasma start-up phase with oblique 70 GHz 2nd harmonic electron cyclotron (EC) wave launching with N//=0.38 in heliotron J. Upward and downward sweeping emissions from the ECRH frequency, and downward sweeping emissions which appear in the range between 56 GHz – 67 GHz are found. The time change of the frequency observed at toroidally different ports are almost the same, while the intensities of upward/downward sweeping emissions from the ECRH frequency are larger at the port near the EC wave launcher.
