Edge Localized Modes

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The steep edge gradients (of density and temperature) associated with an H-mode lead to quasi-periodic violent relaxation phenomena, known as Edge Localized Modes (ELMs), which have a strong impact on the surrounding vessel. [1] [2]

Physical mechanism

The physical mechanism of ELMs has not been fully clarified. Several possible explanations have been put forward:

ELMs and machine operation

The occurrence of an ELM leads to a significant expulsion of heat and particles, with deleterious consequences for the vessel wall and machine operation. Although Quiescent H-modes exist (without ELMs), [9] they are generally considered not convenient due to the accumulation of impurities. To achieve steady state, an ELMy H-mode is preferred and this mode of operation is proposed as the standard operating scenario for ITER, thus converting ELM mitigation into a priority. [10]

References