High-βp scenario realized by the integration of internal and external transport barriers in the HL-2A tokamak

Abstract

High-βp scenario addresses needs for an attractive tokamak fusion reactor design, where βp is the normalized plasma poloidal beta. High-βp experiments have been performed during recent years in the HL-2A tokamak. The high-performance region is realized by the integration of internal and external transport barriers which are dubbed as ITBs and ETBs, namely, double transport barriers (DTBs), with the high-power NBI heating. Generally, the ITB forms and becomes strong after the NBI injection on HL-2A. Subsequently, the edge ion temperature and toroidal rotation increase, as a result that the ETB or pedestal creates and L-H transition occurs. A high-βp (βp∼3) scenario is obtained with Ip∼110 kA and q95∼5, and another high-βp (βp∼2.7) scenario is also realized with Ip∼160 kA and q95∼4.2. The two high-βp scenarios are both characterized by a large-radius ITB and an ETB. However, the two scenarios are different. For the former there are strong large-radius ITB and weak ETB on radial ion temperature profiles, but for the later there are weak large-radius ITB and strong ETB. Although two high-βp scenarios on HL-2A have been accessed, however they are both transient. In addition, MHD instabilities in high-βp scenarios are also present for a high fusion gain and reactor relevant high fusion-density plasma.