Impact of an integrated core/SOL modelling on the optimization of tokamak fusion reactors

Full text: A 0D divertor and scrape-off layer (SOL) model, which provides the heat flux and the temperature at the plates for given upstream conditions and seeded impurity concentrations, has been coupled to the 1.5D core transport code ASTRA. The resulting numerical tool has been employed for various parameter scans in order to identify the most convenient choices for the operation of electricity producing tokamak devices. The main result we found is that the curves at constant electrical power output are closed on themselves in the R B_T plane, i.e. no improvement would be achieved by further increasing R or B_T once the maximum has been reached. In particular, for high R and B_T , the need of auxiliary power to compensate the large synchrotron radiation losses from the main plasma is such to overcome any increase in the generated fusion power. Viceversa, at low B_T and large R, the necessary impurity concentrations for the divertor compatibility lead to a significant dilution of the main plasma, thus compromising the total fusion outcome - unless unrealistically high divertor compression factors are assumed. Also, some preliminary considerations about the presence of a hysteresis on the required impurity concentration for divertor detachment are reported.