A steady state regime for the tokamak-based DEMO Fusion Neutron Source (DEMO-FNS) with parameters R/a = 3.2 m/1.0 m, B = 5 Т, Ipl = 4–5 MA, PNBI = 30 MW and РECR = 6 МW is studied using coupled simulations of the central and divertor plasma. In our analysis, the divertor plasma state is determined by the values of the heat flux PSOL, the pressure of the neutrals in the divertor p n and the total number of neon particles NNe outside the separatrix. As the boundary conditions for the core plasma, we use the values at the separatrix of the electron density, ne_sep, and temperatures of the ions, Ti_sep, and electrons, Te_sep, the concentration of the neon impurity normalized to the electron density at the separatrix, cNe = ∑ nNe/ne_sep and the hydrogen neutral influx into the core plasma, Γ0sep. In the divertor region, all the values are calculated using the SOLPS4.3 code for a number of operating points (~150 in our case) with different values of PSOL, p n and NNe. Then the calculation results are approximated by analytical formulas. Power balance in the core plasma is calculated using the ASTRA and NUBEAM codes. The hydrogen (deuterium and tritium) density is modelled taking into account the sources generated by the neutrals originating from the divertor region, as well as by injection of fast atoms and pellet injection. The neon density and radiation in the main plasma are simulated using the STRAHL code.As the result of the simulations, the operational regime of DEMO-FNS is determined, in which the heat loading onto the divertor targets remains at the acceptable level below 10 MW m−2, the divertor plasma does not transit into the 'full detachment' mode and the plasma in a double-null separatrix configuration is kept up–down symmetric. Variations of these conditions versus the impurity level and confinement parameters are investigated and discussed.
Optimization of isotope composition of fusion plasmas