Internal transport barrier triggered by non-linear lower hybrid wave deposition under condition of beam-driven toroidal rotation

Abstract

By using gyro-Landau fluid transport model (GLF23), time-dependent integrated modeling is carried out using TRANSP to explore the dynamic process of internal transport barrier (ITB) formation in the neutral beam heating discharges. When the current profile is controlled by LHCD (lower hybrid current drive), with appropriate neutral beam injection, the nonlinear interplay between the transport determined gradients in the plasma temperature (T i,e ) and toroidal velocity (V / ) and the EÂB flow shear (including q-profile) produces transport bifurcations, generating spontaneously a stepwise growing ITB. In the discharge, the constraints imposed by the wave propagation condition causes interplay of the LH driven current distribution with the plasma configuration modification, which constitutes non-linearity in the LH wave deposition. The non-linear effects cause bifurcation in LHCD, generating two distinct quasi-stationary reversed magnetic shear configurations. The change of current profile during the transition period between the two quasi-stationary states results in increase of the EÂB shearing flow arising from toroidal rotation. The turbulence transport suppression by sheared EÂB flow during the ITB development is analysed, and the temporal evolution of some parameters characterized the plasma confinement is examined. Ample evidence shows that onset of the ITB development is correlated with the enhancement of EÂB shearing rate caused by the bifurcation in LHCD. It is suggested that the ITB triggering is associated with the non-linear effects of the LH power deposition. V C 2015 AIP Publishing LLC. [http://dx.

Bifurcation in lower hybrid wave absorption induced by modification of electron temperature and formation of steady internal transport barrier

“…Although several tools have been identified that modify transport directly, the effect of the current profile on transport is large and remains an important transport control feature. Improvement of the plasma performance through active modification of the current density in advanced plasma regimes with ITBs has been the goal of intense research [28][29][30][31][32]. To establish steady state operation of high performance tokamak, real-time control of the plasma current profile will be an essential aspect.…”