Mitigation of Type­I ELMs with n = 2 Fields on JET

Mitigation of type-I Edge Localized Modes (ELMs) has been observed with the application of an n = 2 field in H-mode plasmas on the JET tokamak with the ITER-like wall. In high collisionality (n*e ~2.0) H-mode plasmas, large type-I ELMs with a frequency of ~45Hz were replaced by high frequency (a few hundred Hz) small ELMs during the application of the n = 2 field. No density pump-out was observed. The influence of the n = 2 field on the core and pedestal electron pressure profiles is within the error bars and can be neglected. Splitting of the outer strike point has been observed during the strong mitigation of the type-I ELMs. The maximal surface temperature (Tmax) on the outer divertor plate was saturated and has only small variations of a few degrees due to the small mitigated ELMs. In low collisionality (n*e ~ 0.8) H-mode plasmas, the ELM frequency increased by a factor of four (from ~20 to ~80Hz). Clear density pump-out was observed during the application of the n = 2 field. The effect of ELM mitigation with the n = 2 field was seen to saturate so that the ELM frequency did not increase further above a certain IEFCC level. Multiple splitting of the outer strike point during the ELM crash has been seen, resulting in mitigation of the maximal ELM peak heat fluxes on the divertor region.
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EFDC120619 1.05 Mb