Density limits in tokamaks

Analysis of the stability of the radial temperature and density profiles against radial collapse leads to predictive algorithms for plasma and neutral fueling density limits in tokamaks. The predicted plasma density limit agrees with the Greenwald limit in magnitude and parameter scaling for Ohmic plasmas. Auxiliary-heated plasmas are predicted to have a higher plasma density limit than comparable Ohmic-heated plasmas, but fusion alpha-heated plasmas are predicted to have a lower plasma density limit than comparable Ohmic-heated plasmas. Model problem calculations indicate a rather complex dependence of the predicted density limit on the plasma parameters; under certain conditions the weak sensitivity seen in experiments to edge temperature, impurity concentration, and heating power is found, but under other conditions a stronger sensitivity is predicted than is seen in experiments.