Overview of the Recent Study on ELM Mitigation Physics with Different External Actuators on HL-2A Tokamak

Mitigation of Edge localized mode(ELM) has been achieved with different external actuators such as lower hybrid wave (LHW), mixture supersonic molecular beam injection(SMBI), and laser blow-off(LBO) impurity seeding on HL-2A. During these experiments, the pedestal turbulence enhancement is commonly observed, which is found closely related to ELM mitigation. The turbulence enhancement is caused by the externally driven the velocity shear rate without change of the turbulence correlation length, but correlated to its radial wavenumber spectral shift. A common plausible mechanism for the ELM mitigation with different external source input seems to be involved. A modified theoretical model based on the turbulence radial wavenumber spectral shift is used and successfully interprets the experimental observations. The simulation suggests that a critical growth rate of the most unstable mode, also identified by the experimental results, survives in the competition of the velocity shear rate, enhancing the turbulence intensity. An example of the LHW case is used and good agreements have been found between the experimental results and simulation results.