Operational Limits in Tokamaks and Limiting Instabilities

The constraints for operation of tokamaks are described. The operating space is restricted by several limitations among which the plasma performance has to be optimized. Hard limits which lead ultimately to a disruption and may damage the first wall as well as soft limits resulting in a reduction of the energy content of the plasma can occur. The operational limits can be summarized in two general groups: excessive radiation from the plasma, and global as well as local violation of MHD stability.