A New diagnostic method for electromagnetic field patterns of fast waves during FWCD experiments in JFT-2M

Saigusa, Mikio*; Kanazawa, Sadayoshi*; Ogawa, Toshihide; Kawashima, Hisato; Kikuchi, Kazuo; Ido, Takeshi*; Fukuyama, Atsushi*

A new diagnostic method is proposed for direct measurements of electromagnetic field patterns of fast waves in toroidal plasmas. The fluctuation of ponderomotive potential at a beat wave frequency between the two frequency fast waves produces the actual potential fluctuation via electron and ion motions. A heavy ion beam probe (HIBP) detected the potential fluctuation patterns at a beat wave frequency during the fast wave pulse. The amplitude of potential fluctuations decreases with increasing an electron temperature in fast wave current drive (FWCD) experiments of JFT-2M, due to the improvement of wave absorption via electron Landau damping. The measured potential fluctuation does not contradict with the prediction using a full wave code calculations.