High current (Ipmax≳ 5 MA) disruptive pulses in JET

High current (I p max ≳ 5 MA) and low beta disruptive pulses in JET have been investigated. No association was found between the disruptions and a possible triggering when the radiated power (P rad ) equalled the input power (P in ), as was reported previously for disruptions in discharges with a lower plasma current. Often, P rad remained well below P in throughout the discharge, but a disruption did occur, even though q ψ ≳ 3. These pulses were well away from the limiting boundaries associated with the high density and low-q limits in the Hugill diagram. There was evidence of MHD mode interaction as the mechanism triggering a major disruption. The m/n = 1/1 perturbation played an important role in this process. Also, a limit for these high current disruptive pulses was found by plotting the internal inductance of the plasma versus q ψ when this limit was reached, there was a very high probability for the plasma to disrupt through an MHD mode coupling process.