Contribution of the electrostatic fluctuation to the particle and energy fluxes in the edge region of STP-3(M) reversed field pinch plasma

The analysis of particle and energy fluxes was made by using electrostatic probes in the edge region of STP-3(M) reversed field pinch plasma. One of the new findings is that the plasma potential profile in the case of high current plasma indicates an increase in radial electric field Er (= -∇Vs) in the region where 0.92 < r/a < 1.00, which implies the generation of Er x Bp velocity shear. The electrostatic part of the particle flux was observed to decrease in the shear region, while the electron density and temperature profiles remained unchanged. Thus, spontaneous generation of velocity shear suppresses the electrostatic particle flux locally, but transition to global confinement improvement is not realized. The contribution of electrostatic fluctuations to energy flux in the edge is estimated as about 50%, and of stochastic diffusion is estimated as about 50%. (author)