Effect of L-H and H-L Transitions on Tokamak-reactor Operation

Abstract

The effect of L-H and H-L transitions on the tokamak-reactor operation is considered. Both initial modes are considered as quasi-equilibrium states with the same thermal energy for constant total toroidal currents. A method has been developed for quantification the change in neutron yield in a tokamak- reactor during these transitions occurring over times much shorter than the plasma energy confinement time. The method is based on the use of duality of solutions of the Grad-Shafranov equation. The arbitrary functions included in this equation were found as a result of approximation of the normalized plasma pressure profiles, presented versus on the radial flow coordinate obtained at the DIII-D facility. To calculate changes in neutron fluxes during L-H and back H-L transitions, we used these plasma pressure distributions for the ITER device parameters presented in Cartesian coordinates. A numerical calculation showed that in the back H-L transition, a large spike on the global neutron production is possible, which was previously discovered experimentally (ALCATOR-C-Mode, 2001). Since such an increase in neutron fluxes during tokamak-reactor ITER operation poses a serious threat to both the personnel and the facility itself, it is necessary to exclude the possibility of such transitions. Thus, it is necessary to develop such a reactor design that would make it possible to obtain a self-sustaining thermonuclear reaction in the L-mode operation.