Profile constraint in toroidal plasmas and methodologies to break leading to transport barrier

Abstract

Internal transport barriers (ITBs) observed in magnetically confined toroidal plasmas are promising for achieving high-performance burning plasmas, which are established from low-confinement L-mode plasmas dominated by anomalous transport exhibiting strong profile constraints. We studied the origin causing such L-mode plasmas using flux-driven gyro-kinetic based global toroidal simulations covering from core to edge. The simulations are incorporated with real space based statistical probability density function (PDF) approach, which directly measures the heat flux eddy distribution across the entire torus to identify the non-diffusive nature of turbulent transport with different spatio-temporal scales, such as micro-scale avalanches, macro-scale bursts, meso-scale $E\times B$ shear layers, etc., as the origin causing the constraints. Based on studies of such L-mode plasmas, we present a methodology to overcome such constraints and demonstrate ITB formations by the control of quasi-stationary global radial $E\times B$ shear through the toroidal plasma rotation driven by either externally using momentum injection and intrinsically using both ions and electron simultaneous heating.