Implementation of the forced landing scheme under off-normal events in KSTAR

Disruption avoidance is one of the most critical issues in KSTAR due to its high current, temperature and long operation characteristics of the superconducting tokamak. To minimize possible damages to the machine, we imposed a real time handling algorithm of off-normal events, named “forced landing” to ramp down the plasma with well-controlled plasma current and position. Two different plasma control schemes are implemented for different purposes and situations. Both schemes have been successfully demonstrated with careful classifications of actions on the machine in real experiments and they show routine performance with effective reduction of impacts on the machine. Such “machine-protection” schemes enable more aggressive operations such as mega-ampere or high beta experiment, resulting in an expansion of the KSTAR operation regime due to reduced less concerns regarding mechanical safety issues.