JET disruption simulations

The JET tokamak is a main source of information about the poss ible effects of disruptions [1, 2] in ITER. JET measurements indicate large forces will be gen erated on conducting structures surrounding the plasma. It was also found in JET that the halo current, and hence the wall force, rotates during disruptions. This is potentially important if the force oscillations are resonant with the mechanical response of the external structure. Rece ntly JET disruption simulations using the M3D code [3] were carried out, initialized with an e quilibrium reconstruction of a disruption shot [1]. The equilibrium reconstruction shows that q ? 0 . 8 at the magnetic axis just before the disruption. The equilibrium is unstable both to a n internal ( 1 , 1 ) sawtooth and to a vertical displacement event (VDE). The large scale ( 1 , 1 ) mode destabilizes or drives other modes, causing a turbulent state and producing a thermal que nch (TQ), which occurs on a rapid timescale. This is followed by the VDE which evolves on the sl ow resistive wall penetration timescale. During the VDE, the magnetic surfaces heal, but t here remains a large saturated ( 1 , 1 ) perturbation. This causes a large asymmetric wall force to b e produced. The direction of the force in the midplane rotates [5, 6] at a rate consistent w ith experimental observation [1]. This is also consistent with the net toroidal velocity seen i n the simulations. The simulations also show asymmetries of the toroidal current [1] and of the t oroidal magnetic flux [2]. These effects are related to magnetic penetration of the resistiv e wall [6]. Further details will be presented.