Reconsideration of ELMs

The Edge Localized Modes (ELMs) have been observed in the H-mode [1]. The ELM bursts have been conventionally imagined as MHD activities (except ‘dither’, which is considered as limit cycles of turbulence and meso-mean plasma parameters [2,3]). A majority line of thought on the type-I ELMs employs the peeling-ballooning (P-B) mode as a central player (See, e.g., a review [4]). Nevertheless, essential problems remain, i.e., the identification the mechanism(s) of the trigger, the reason why the so-called ‘resonant magnetic (RM) field’ [5] is effective in suppression, etc.
Driven by these motivations, here we report new discoveries (type-III ELM on HL-2A [6] and type-I ELM on JT-60U [7]) that could rewrite the conventional picture of trigger mechanisms of ELMs.
In this presentation, I would explain these new discoveries as well as new way of thinking to understand them. These two examples urge us to reconsider the trigger mechanisms of ELMs. Results here provide a hope to formulate a dependable guideline to control them.

Acknowledgements:
Major part of the presented novel work was performed in collaboration with Dr. K. Kamiya (QST), whom the author cordially acknowledges. Collaboration with Drs. J. Cheng, J. Q. Dong, K. J. Zhao is also acknowledged. This work is dedicated to the memory of late Prof. Sanae-I. Itoh.

References:
[1] ASDEX Team: Nucl. Fusion 29 (1989) 1959
[2] S.-I. Itoh, et al.: Phys. Rev. Lett. 67 (1991) 2485
[3] E. J. Kim, et al.: Phys. Rev. Lett. 90 (2003) 185006
[4] H. R. Wilson, et al.: Plasma Phys. Contr. Fusion 48 (2006) A71
[5] T. Evans, et al.: Nature Physics 2 (2006) 419
[6] J. Cheng, et al.: Nuclear Fusion 60 (2020) 086014
[7] K. Kamiya, et al.: Nature. Comm., in review, doi.org/10.21203/rs.3.rs-3222302/v1 (2023)