Thermal Equilibrium and Density Limit in Tokamak-Reactor

The problem of the thermal equilibrium and density limit in tokamak-reactor are analyzed. The empirical Greenwald criterion determining the critical plasma density may be exceeded in tokamaks with auxiliary heating. One may expect that the fusion power may increase the critical plasma density. The thermal balance in tokamak-reactors is discussed. The critical density is defined by the equality of heating (auxiliary plus fusion) power and radiation losses at the plasma edge. The influence of fusion power input as well as auxiliary heating on the critical density is studied. The analytic model is based on some simplifying assumptions. The auxiliary heating as well as the thermonuclear one is assumed to be localized at the center of the plasma column. The slab geometry is assumed for simplicity. It is shown that the critical density rises up increasing the fusion output drastically using the feedback control.