Edge Localised Mode, ELM
An instability which occurs in short periodic bursts during the H-mode in divertor tokamaks. It causes sudden outbursts of the plasma thus expelling particles and depositing large heat flux onto the vessel wall. The plasma loses severe amounts of energy. In high-power fusion devices such as ITER or DEMO, ELMs are so powerful that they will cause erosion at the vessel wall. Finding methods to mitigate or supress ELMs is therefore a hot topic in current fusion research.