Impact of an integrated core/SOL description on theRandBToptimization of tokamak fusion reactors

An updated and improved version of the 0D divertor and scrapeoff layer (hencefort SOL) model published in [1] has been coupled with the 1.5D transport code ASTRA [2,3].The resulting numerical tool has been employed for various scans in the major radius R and in the toroidal magnetic field BT -for different aspect ratios A, safety factors q, allowable loop voltages V loop and H factors -in order to identify the most convenient choices for an electricity producing tokamak.Such scenario analysis has been carried out evaluating self-consistently, and simultaneously, both the core profile and transport effects, which significantly impact on the fusion power outcome, and the divertor heat loads, which represent one of the most critical issues in view of the realization of fusion power plants [4,5].The main result is that, when divertor limits are enforced, the curves at constant electrical power output are closed on themselves in the R -BT plane, and a maximum achievable power exists -i.e.no benefits would descend from a further increase of R and BT once the optimum has been reached.This result appears as an intrinsic physical limit for all those devices where a radiative SOL is needed to deal with the power exhaust, and where a lower limit on the power crossing the separatrix (e.g. because of the L-H transition) is present.