Repetitive ＇Snakes＇ and Their Damping Effect on Core Toroidal Rotation in EAST Plasmas with Multiple H-L-H Transitions

Repetitive impurity snake modes are observed after H-L mode transitions （high to low confinement modes） in EAST plasmas exhibiting multiple H-L-H transitions. Such snake modes are observed to lower the core plasma toroidal rotation. A critical impurity strength factor associated with snake-mode formation is estimated to be as high as αz,c = nz,cZ^2/ne - 0.75. These observations have implications for ITER H-mode sustainability when the heating power is only slightly above the H-mode power threshold.