Operational Limits in Tokamak Machines

Abstract

Different operational limits of tokamaks are reviewed. The finally limiting processes are hard or soft plasma disruptions or a strong x-ray source. The underlying events are explained as far as the physical causes are known. Treated are the density limit, the low-q-limit, the runaway limit, the β–-limit, and the vertical displacement limit. In addition, the spontaneous MHD-instability and a hollow temperature profile situation are presented. The graphical displays are experimental results from the TEXTOR tokamak.VIII. SUMMARYA number of practical limitations for tokamak operation was briefly discussed. These limits play an important role for the operation of future large tokamak devices. They must be avoided by all means to minimize the risk of technical defects on machine and electrical components. The physical mechanisms involved and the precursors to coming disruptions must be known and should be studied on existing experiments today. Strategies to bring the future machines into a safe state, whenever a known precursor to a tokamak disruption is detected, must be developed. Tokamak plasmas are susceptible to disruptive behaviour in the limiting parameter regimes.