Control of Alfvén eigenmodes and its impact on fast-ion confinement in KSTAR high poloidal beta discharges*

In high poloidal beta (β_P) discharges accompanying the toroidal Alfven eigenmodes (TAE) with broad q-profile, degradations of plasma performance as well as neutron emission rate are often observed. It has been found on KSTAR that ECRH deposition on the optimal location where the TAE gap can be formed could mitigate the TAEs successfully. Modeled fast-ion pressure profile during the TAE mitigation period is matched well to the case of classical (D_fast ~ 0 m²/s) profile, and the modeling is supported by comparison with the neutron emission rate and the total stored energy. Mechanism of TAE mitigation in this high β_P discharge with monotonic broad q-profile is to align the ECRH deposition location on the existing TAE gap location, and is verified by NOVA calculations. Another consideration for control of TAEs in high β_P discharges is that mismatched ECRH application is able to excite different TAEs or tearing modes at different radial locations, and neutron emission rate does not elevate much as a result. It implies that the AE control actuators on high β_P discharges should be optimized and depend on the q-profile and the beam-ion distributions.