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

In the GAMMA 10 tandem mirror device, an experimental plan of high power ECRH is now under way. As the first step, operation of existing gyrotrons for plug ECRH has been carried out at a power exceeding their nominal powers of 200 kW. In this step, the highest recorded value of [varphi]_c for a hot ion mode plasma is 1.4 kV at P_plug = 240 kW. The effective temperature T_eff of the end loss electrons as a scaling factor of the axial potential distribution has attained to 3 keV at a heating power of 260 kW and the potential difference between the plug to the end plate has exceeded 5 kV. Then, the potential range of the scaling between and T_eff has been expanded. Use of a new gyrotron delivering much higher power is the second step. The first experimental campaign with this gyrotron has just started.