Magnetic ELM Triggering Using the Vertical Stabilization Controller in JET

Type I Edge Localized Modes (ELMs) remain a serious concern in ITER because of the high transient heat and particle flux that can be deposited on the plasma-facing components of the divertor. This has stimulated worldwide research on experimental methods to mitigate the ELM energy losses without significant degrading the confinement. Among various mitigation techniques, magnetic triggering based on a fast vertical movement of the plasma column has demonstrated that the ELM frequency (fELM) can be locked to the frequency of the externally imposed magnetic perturbation, enabling the production of more frequent, smaller ELMs. The method, first developed in TCV, has also been successfully applied in ASDEX-U and JET. In JET the plasma vertical movement relied on the vertical stabilization controller that has been modified to allow the application of a user defined voltage pulse (so called kick) at an adjustable frequency which is presently limited to a maximum value of ~60Hz due to technical constraints. This paper summarizes recent experiments on the JET tokamak devoted to study the nature of the magnetic ELM triggering mechanism and its effects on plasma performance. The experiments reported here have been carried out in high triangularity plasmas (2.2-4T/2MA, q95 = 3.6-3.9, dave = 0.43) with the outer strike position optimized for high resolution infrared measurements and additional heating dominated by NBI (PNBI = 7-12MW, PICRH = 1-2MW).
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