The direct measurements of the plasma electric potential by heavy ion beam probe on T-10 tokamak - Does T-10 obtain the H-mode?

The Heavy Ion Beam Probe (HIBP) diagnostics on T-10 tokamak was modified to measure the local values of the plasma potential in ECRH plasma. The Tl+ ion beam with the energy up to 240 keV and intensity about a few dozens muA was used in experiments. The clear fall of the potential in the range of -200 + -600 V was observed during the phase of the improvement of plasma confinement in the outer region with respect to EC resonance. The fall-down of the potential is accompanied by the fall of D-alpha and the density increase. The time evolution of the spatial profile demonstrates the formation of a thin (about 1 cm) area near the limiter with a strong E-r (similar to300 V/cm) that proves the H-mode.