Nonthermal Microwave Emission Features under the Plasma Ohmic Heating and Low-hybrid Current Drive in the FT- 2 Tokamak

Study of behavior of accelerated electrons (AE) in the ohmically heated (OH) plasma and low-hybrid current drive (LHCD) in tokamak has the practical interest especially for estimations of AE radiation energy losses and solving of the non-inductive CD problem for the ITER. Studies based on measurements of non-thermal microwave radiation (MR) intensity and hard X-ray (HXR) spectra are conducted in the FT-2 tokamak having large local magnetic ripples under LHCD in the omically heated (OH) plasma with the fan instability excited. The paper presents experimental data first obtained in such conditions witnessing about some AE behavior features. Nature of MR abnormal intensity and short giant flashes together with the fast additional electron heating in the plasma core are discussed. The first high additional fast electron heating was registered together with the synchrotron radiation (SR) intensity increase. It was accompanied by short MR spikes observed in the narrow frequency range (53 ÷ 78) GHz. They arise owing to the AE transverse energy and pitch angle increase under each crossing the cyclotron auto-resonance region and SR maser gain. It is proposed the heating mechanism owing to absorption of SR and Bernstein waves arising at linear transformation the extraordinary component of intensive MR spikes in the black plasma layers. It was found that the non-thermal MR of abnormal intensity arising during OH in the frequency range (10 ÷ 40) GHz is due to the fan instability development and the substantial local magnetic ripples. MR is accompanied by short giant flashes having a narrow frequency spectrum. Together with the SR growth the less intensive MR flashes appear in the range (57 ÷ 75) GHz. In our case it becomes possible the maser amplification of both SR and collective radiation. Appearance of the giant flashes may be initiated under transition of the maser - amplifier into the self - excitation regime, when low-frequency quasi- coherent MR flashes are generated.