Comparison of DTT conventional and advanced divertor configurations

The role of the DTT facility [1] is to bridge the gap between today's proof-of-principle experiments and DEMO [2]. It will help the development of a reliable solution for the power and particle exhaust in a reactor. To this aim DTT has been designed to study a large suite of alternative divertor magnetic configurations in order to ensure acceptable conditions at the walls while maintaining sufficient core performance. All of the present more promising alternative divertor configurations are realizable in DTT: the flux flaring towards the target (X divertor), the increasing of the outer target radius (Super-X) and the movement of a secondary x-point inside the vessel (X-point target) as well as the entire range of Snowflake (SF) configurations [3] and the presently reconsidered double null (DN). Most of previous configurations are produced using out-of-vessel coils but in DTT it is also possible a fine tuning of the magnetic field in the divertor region by small in-vessel coils. Here, we present a first comparative power exhaust study of conventional Single Null (SN) and alternative configurations by using the SOLEDGE2D-EIRENE [4] code which is one of the few codes able to deal with all presently envisaged divertor configurations. Closed divertors, with a full W wall, no impurity seeding and a level of power crossing the separatrix PSOL|25MW, have been considered in the simulations. In addition, the transport coefficient has been set up constant and an outer midplane decay length of 3 mm in SN attached condition has been assumed. A density scan for both the conventional and advanced configurations has been performed in order to investigate the behaviour of the different magnetic divertor solutions realized on the same vessel and divertor targets. In SND high power loads are foreseen by the code independently from the density, with a peak values higher than 20 MW/m2. Lower peak power has been obtained in the alternative configurations. Furthermore, the codes predict detachment conditions for lower value of the upstream density. This behaviour is probably related to the benefit deriving from the geometrical feature of alternative configurations like the increase in the flux expansion and connection length.