Stochastic Ripple Diffusion of Energetic Particles in Reversed Magnetic Shear Tokamak

The stochastic ripple diffusion is investigated in a realistic reversed magnetic shear discharge. Rippled field produces variations in the velocity of trapped particles leading to excursion of the tip position for successive banana bounces. When the excursion is large enough, the trapped energetic particles are lost rapidly via stochastic banana diffusion. The ripple diffusion of fast ions produced during the neutral beam injection is calculated by assuming that the trapped ions are lost if their turning points are in regions where the ripple exceeds a threshold for the stochastic ripple loss. As the safety factor is of higher value inside the reversed magnetic shear plasma, the ripple loss in a modelled reversed magnetic shear discharge of HL-2A is much stronger than that in a non-RS discharge.