Repetitive bursting of neoclassical tearing modes in EAST under boronization wall conditions

Neoclassical tearing modes (NTMs) are critical magneto-hydrodynamic (MHD) instabilities in tokamak plasmas, significantly impacting plasma confinement and potentially leading to disruptions. In the Experimental Advanced Superconducting Tokamak (EAST) with boronization wall conditions, the repetitive bursting phenomena of NTMs are observed experimentally in the high confinement mode plasma with metal impurity accumulation. The evolution characteristics of NTM behaviors are investigated in the article. The m / n = 2/1 NTMs are excited by mode couple with ideal kink modes. The NTMs exhibited two distinct growth phases: a rapid growth phase (phase A) with small saturated amplitude and a secondary growth phase (phase B) characterized by a slow growth rate but larger saturated amplitude. Plasma confinement is enhanced during NTM phase A but degraded in phase B. The phase B of NTMs can lead to fast electron loss and H–L transitions. In addition, the NTMs are observed to periodically recur on a timescale of approximately 200 ms. It is found that the high-Z impurity radiation is also modulated synchronously by the long-period NTM behavior. A strong radiation region near the m / n = 2/1 magnetic island develops in NTM phase B due to outward impurity transport and the radiation profile becomes hollow. The effect of metal impurity radiation on NTM dynamics is worth further investigating for fusion devices with full tungsten wall like ITER.