Operational Limits in Tokamak Machines and Limiting Instabilities

The constraints for operation of a tokamak are described. The operating space is restricted by several limitations among which the plasma performance has to be optimized. Hard limits which lead to a disruption and may damage the first wall as well as soft limits resulting in a reduction of the stored energy 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.