Passive Thermal Stability in

A 0-dimensional model with parabolic profiles is employed to assess the use of the combination of enhanced thermal conduction loss and radial motion for passive thermal stability control of an ignited tokamak plasma. The increases in ignition requirements needed for the achievement of passive stability are determined. Both the independent thermal stabilization effects of radial motion and enhanced transport and the additional stabilizing effect of the dependence of the enhanced transport upon radial motion are considered. The enhanced thermal conduction is modeled by the addition of an ion energy loss channel to a plasma described by neoclassical ion energy transport; this additional ion loss channel is represented by an energy confinement time scaling ri,ag ~ T;-* where T is the ion temperature and e is a variable parameter. Calculations are made for tokamak plasmas where the electron energy confinement time is described by the empirical scaling law re ~ na2. The combination of the independent effects of radial motion and an enhanced transport loss with ri,dd ~ 77/2, as might be the case for increased ion thermal conductivity due to ripple trapping, can be used to obtain thermal stability for central ion temperatures greater than 15 keV with very small (< 10%) increases in the value of nr, required for ignition.