Simulation of MHD activity during density disruptions on JET
This report presents a simulation study of density limit disruptions in which radiation losses were specified according to experimental data from a disruption in JET. The MHD activity was simulated by a reduced MHD-code with a simple transport model. The simulations reproduce the sequence of events observed during density limit disruptions in JET, starting with m=3/n=1 activity, followed by strong growth of the m=2/n=1 mode, a sequence of minor disruptions and, finally, a major disruption, in which the current profile flattens over almost the entire plasma, leading to a large drop in internal inductance, and an accompanying negative voltage spike. The major disruption occurs in two steps. First, a large fraction of the central temperature is lost in an "energy quench", which occurs as a sawtooth modified by the large amplitude 2/1 mode. At the end of the energy quench, the magnetic field in the central q=1 region becomes stochastic because of the simultaneous presence of modes with different helicities, notably 2/1, 1/1, and 3/2. In a major disruption, good flux surfaces are never restored again, the kinetic energy of several modes continues to grow and, in the final phase, the activity is dominated by the 2/1 and a rapidly growing 3/1 mode.
Bibliographic Reference: Paper presented: 17th EPS Conference on Controlled Fusion and Plasma Heating, Amsterdam (NL), June 25-29, 1990
Availability: Available from (1) as Paper EN 35298 ORA
Record Number: 199011553 / Last updated on: 1994-12-02
Original language: en
Available languages: en