P1-3 ELMs, strike point jumps and SOL currents (original) (raw)

Abstract. Plasma equilibria before and after ELMs in JET are investigated. ELMs could be associated with fragile equilibria and separatrix instabilities: previously closed field lines would open up, releasing plasma current and leading to the formation of a new, smaller separatrix. This model could explain experimental observations of sudden jumps and shifts in strike point positions. Novel instability mechanisms are discussed to explain the large transient jumps observed in the strike point position: positive X-point instability, due to positive toroidal current density at the X-point and diamagnetic instability, due to negative inboard toroidal current density. 1. Theoretical background: plasma equilibrium before the ELM Plasma force balance in a magnetic confinement device with closed field lines is given by the equation: j B × =∇pGG (1) where j is the total current density, B the magnetic field and p the pressure. In tokamak equilibrium, the pressure is usually considered as a m...