Fast two-dimensional potential measurement at the thermal barrier region of the tandem mirror Gamma 10

A gold neutral beam probe system was improved by adopting a multichannel ion detector and adding sweeping functions of beam energy, deflector voltage, and electrode voltage of the analyzer to the system to measure the fluctuations and time evolution of the two-dimensional space potentials with fast resolving time during one shot. Positions of the beam spot on the multichannel detector corresponding to the ionizing points of the beam in the plasma were simulated precisely as a function of the beam energy and the injection angle. A potential derivation formula was determined taking into consideration both the numerical and experimental results, and the reproducibility of the potential profile was checked. Two-dimensional potential profiles were measured in the optimization experiment of the microwave injection angles for formation of the plug potential.