Vertical displacement events and halo currents

This review examines results from all non-circular tokamaks with a distinct emphasis on investigations in ASDEX-Upgrade. There a major fraction of the experimental time has been dedicated studying vertical displacement events of single null plasmas over a large range of q-values in an attempt to obtain the scaling of both the displacement dynamics and the splitting of forces between those associated with poloidal and toroidal plasma currents as a function of q and Bt. These studies on different tokamaks are accompanied by simulations with-among other codes-the tokamak simulation code TSC, in a version where halo currents flowing in the plasma scrape-off layer (SOL) evolve self-consistently. The technical consequences of VDEs for the machine design, measures taken and first predictions are discussed. Safety setups that have been developed and possible avoidance strategies are briefly described.