Maximum Q in feedback controlled subignited tokamak fusion plasmas

For high Q operation in feedback controlled subignited tokamak fusion plasmas, the operating temperature must be close to the ignition temperature. The authors discuss the technological and physical effects which may restrict this temperature difference. The investigation is based on a simplified, yet accurate, 0-D analytical analysis of the maximum Q of a subignited system. Particular emphasis is put on sawtooth oscillations which complicate the interpretation of diagnostic neutron emission data for determining the plasma temperatures and may imply an inherent lower bound on the deviation of the temperature from the ignition point. For a tokamak fusion reactor, the estimated maximum Q is found to be marginal (Q=10-20). (author). Letter-to-the-editor. 9 refs, 1 fig