Current losses induced by edge localized modes in JET tokamak plasmas

We have investigated the effect of edge localized modes (ELMs) on the total plasma current in JET tokamak plasmas using the earth leakage current detection circuit connected to the in-vessel saddle coils. These measurements, and the geometry of the saddle coil circuit, indicate that, in typical H-mode plasmas, up to similar to 300 A (corresponding to a maximum of similar to 150 A per MA of plasma current) can be deposited at each ELM in regions rather far away (similar to 50 cm) from the strike point position and divertor target plates. These current losses decrease with increasing ELM frequency (f(ELM)), being practically below or around the detection limit for f(ELM) > 60 Hz, and show some saturation for increasing diamagnetic energy losses for 'slow' Type-l ELMs at f(ELM) < 10Hz. The measurements reported here are consistent with the ELM phenomenon being associated to a peeling of the edge magnetic flux surfaces.