Development of the q = 1 advanced tokamak scenarios in hl-2 a

The advanced tokamak scenario with q close to 1 has been achived on HL-2A tokamak, which might be a internal transport barrier (ITB) at low central shear or a steady state ITB combined with H mode edge barrier. In this scenario, formation of internal transport barrier (ITB) with steep Ti profile is observed to be closely linked to the q=1 magnetic surface and MHD activitis around it, suchg as LLM or fishbone. It was found that the q-profile in the core remains flat throughout the ITB period. Such weak central magnetic shear is sustained by the LLM or fishbone activity in addition to bootstrap current, NBI-driven current. Furthermore, applying central ECRF heating and current drive to such beam heated weak shear ITB discharges shows a substantial effect on MHD stability, affecting the passage of the q profile through qmin= 1 and prolonging the weak shear phase, enhancing the strength of ITB with a stronger gradient. Moreover, a stationary advanced tokamak scenario with ITBs in combination with an H mode barrier and weak shear (qmin ~1) was maintained for 40 confinement times and several internal skin times with β N = 2.0. In the ITB/H mode scenario, (1,1) fishbones can not only clamp the current profile development near the q = 1 surface without causing energy confinement to deteriorate but also induce a polodial flow which is beneficial to the suppression of turbulence in the plasma core region.