Research on EAST Reveals How RMP Suppresses ELMs

Recently, a series of investigations were conducted on EAST Tokamak in ASIPP to study the physical processes of resonant magnetic perturbation (RMP) suppressing edge localized modes (ELMs). The results bring better physical understanding on this control method, which boosts the researchers’ confidence to expand this control method to the future fusion reactors. 

Edge localized mode is one of the most frequent edge magnetohydrodynamic instabilities in high confinement operation modes in tokamaks. It brings periodic transient heat flow to the divertor and other first wall units. This is a great challenge for ITER operation and future fusion reactors’. In recent decade, RMP was found effective in mitigating or suppressing ELMs. However, the physical mechanics is still unclear. 

The research group led by Prof. Youwen SUN succeeded for the first time in the world in suppressing ELMs on EAST in the ITER-like radio frequency (rf) wave dominated heating, low torque injection condition via the recently installed RMP coils. The nonlinear transition from ELM mitigation to suppression was observed when RMP was applied. This reveals the nonlinear response of plasma to RMP and the critical role of the edge magnetic field topology change in fully suppressing ELMs.

The research is the result of long-term international and domestic collaboration, said Sun, the scientists from FZJ, Germany, CCFE, UK, DLUT and USTC, China have participated and supported the research. 

The relevant research result was published in the world leading physical journal Physical Review Letters [Sun Y., Liang Y., Liu Y. Q., et al, ‘Nonlinear Transition from Mitigation to Suppression of the Edge Localized Mode with Resonant Magnetic Perturbations in the EAST Tokamak’, Phys. Rev. Lett. 117, 115001 (2016)]. 

Article link: http://link.aps.org/doi/10.1103/PhysRevLett.117.115001 

(Wang Huihui and Jia Manni report) 

With gradually increasing RMP coil current, ELMs in rf wave heating condition were fully suppressed above a certain RMP coil current threshold.

The ELM nonlinear mitigation-to-suppression transition process due to magnetic perturbation reveals the critical role of the change in edge magnetic field topology in fully suppressing ELMs.