High Power Electron Heating Experiments at the Plug Region of GAMMA 10

In the GAMMA 10 tandem mirror, a high power ECRH experiment at the plug region is now in progress. As the first step of this experiment, high power operation of existing gyrotrons for plug ECRH has been carried out at a power Pplug exceeding their nominal powers of 200 kW. In this step, the highest recorded value of the axial ion confining potential φc for a hot ion mode plasma is 1.4 kV at Pplug=240 kW. Then, in the second step, a newly developed high power gyrotron has been installed at one side of the both end plugs. The value of φc increased with Pplug and attained 2.1 kV at Pplug=370 kW. The potential difference ΔΦ from the plug potential to the end plate potential exceeded 5 kV. The effective temperature Teff as a mean energy of the end loss electrons reached 3 keV, and the scaling between ΔΦ and Teff has been expanded. Functions of the plug ECRH on electrons are studied from the viewpoint of velocity space diffusion, and a picture of ECRH-induced axial electron motion is presented.