Tungsten control in type-I ELMy H-mode plasmas on EAST

The first experimental investigation of the tungsten behavior in ELMy H-mode plasmas with co-/counter neutral beam injection (NBI) and unfavorable/favorable B t was performed on EAST. Tungsten was found to accumulate easily in ELMy H-mode plasma with co-NBI heating and unfavorable B t . Thus, in this case the tungsten concentration can exceed 10 −4 , resulting in degradation of the plasma confinement and periodic H–L transitions. To reduce the tungsten concentration in steady-state type-I ELMy H-mode operation, counter-NBI is applied to modify the density and temperature and brake the plasma toroidal rotation. The applied counter-NBI decreases the PHZ + E r inward pinch velocity and reverses the direction of neoclassical inward convection, thus decreasing the tungsten concentration from ~ 7 × 10 −5 to ~ 2 × 10 −5 in type-I ELMy H-mode plasma with favorable B t . A comparison of the effects of different B t directions on the tungsten behavior also shows that favorable B t is beneficial for reducing the tungsten concentration in the core plasma. These results imply that counter-NBI with favorable B t can effectively prevent tungsten accumulation and expand the operating window for exploring steady-state type-I ELMy H-mode operation of EAST.