Development of a Reconstruction Procedure for the Halo Current Distribution

In magnetic-confinement toroidal machines, only a limited number of first wall modules can be equipped with current sensors, giving partial information about the distribution of the "halo" current (HC) injected into the vessel when the plasma hits the wall during disruptions. The knowledge of the complete distribution of the HC is necessary for evaluating the JxB loads exerted on the vessel structure. Since the pattern of contact areas of plasma with the wall during disruptions is spatially discontinuous, the HCs injected in the first wall (FW) cannot be efficiently fitted using harmonic functions. A procedure has been developed and implemented for estimating all the currents injected in vessel on the basis of a limited number of current sensors on the FW modules. The results obtained in the case of a numerical machine model with simplified geometry indicate that the procedure can be successfully applied to machines with more complex HC distribution, such as ITER.