Radial patterns of instability and transport in JT-60U internal transport barrier discharges

Rewoldt, G.*; Hill, K. W.*; Nazikian, R. M.*; Tang, W. M.*; Shirai, Hiroshi; Sakamoto, Yoshiteru; Kishimoto, Yasuaki; Ide, Shunsuke; Fujita, Takaaki

One class of internal transport barrier discharge in the JT-60U tokamak is characterized by two relatively flat regions of the pressure separated by a region with very large pressure gradient. Linear growth rates for toroidal drift type modes are calculated for discharges in this class, without and with sheared rotation effects. For cases with fully developed barriers, the results with rotation are consistent with a picture in which the radial electric field generated in part by the steep pressure gradient causes local stabilization, and thus reduction of the local anomalous transport, which allows the steep pressure gradient to persist. If rotation is omitted from the calculation for these cases, or if rotation is included for cases without barriers or with partially developed barriers, the unstable region spreads into the steep pressure gradient region.