Pressure Driven Magnetohydrodynamics Instabilities in Peaked Pressure Profile Reversed Magnetic Shear Plasmas

For a reversed magnetic shear plasma formed by early neutral beam injection into the HL-2A tokamak,magnetohydrodynamics instability analysis against ideal low-n modes and resistive interchange modes is carried out.Low-n modes located in the low shear region around the shear reversal point are driven unstably by large pressure gradient,and they are of the characteristics of infernal modes.High pressure in the central negative shear region drives resistive interchange modes with the unstable window extending to r/a≈0.2,but not covering the low shear region around the shear reversal point.