Sustained reversed magnetic shear mode of operation in the HL-2A tokamak

Realistic reversed magnetic shear (RS) discharges for the HL-2A tokamak are simulated with the TRANSP code. Early NBI heating achieves reversed shear (RS) configurations characterized by highly peaked pressure profiles and a narrow shear reversal region. To avoid excessive peaks in the pressure, and to sustain RS operation towards steady state, LHCD is used to control the current profile. The combined LH and bootstrap current create a quasi-stationary RS discharge with rmin/a » 0.6 and qmin » 2.8. A self-consistent internal transport barrier is produced, and the RS configuration is established with a wider shear reversal region and broader pressure profile that is favourable to achieving the high beta limit.