Boundary condition for toroidal plasma flow imposed at the separatrix in high confinement JT-60U plasmas with edge localized modes and the physics process in pedestal structure formation

Kamiya, Kensaku; Honda, Mitsuru; Urano, Hajime; Yoshida, Maiko; Kamada, Yutaka; Ito, Kimitaka*; JT-60 Team

Modulation Charge eXchange Recombination Spectroscopy (MCXRS) measurements with high spatial and temporal resolution have made the evaluation of the toroidal plasma flow of fully stripped carbon impurity ions in the JT-60U tokamak peripheral region (including in particular separatrix) possible with a better signal-to-noise ratio. Boundary condition of Vt imposed at the separatrix in ELMy H-mode plasmas has been identified, comparing between co- and counter-NBI discharges. The Vt value at the separatrix is not held fixed at the zero, varying with momentum input direction, but being not strongly affected by the ELM event. A non-zero Vt value at the separatrix might be connected to fast ion losses due to toroidal field ripple that results in formation of a negative radial electric field (Er) layer having almost zero (or very weak positive) Er-shear value at the separatrix. Improved understanding of physics process in pedestal structure formation for the Vt and Er is also discussed.