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,cZ2/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.