Analysis of the performances of a fusion reactor in a reduced H-mode confinement

The feasibility of a tokamak fusion reactor working in a reduced H-mode confinement, typical of the type III (or grassy) ELMs regime is here analyzed with two codes. The first is COREDIV that provides an integrated and self-consistent description of both the core and SOL plasma. The analysis is complemented by the 2D code TECXY which models the SOL more accurately and can then provide better estimates of the power deposited on the divertor targets. As for the present version of the EU-DEMO, the auxiliary power is fixed at 50 MW and q95 = 3.5, while the energy confinement time is downgraded to 0.6 times the standard H-mode. The major radius R is increased by 1 m step from 9 up to 12 m and the toroidal magnetic field BT by 1 T step from 6 up to 8 T, with density kept at its Greenwald limit. An interesting working window around R = 11 m and BT = 7 is identified with the fusion gain Q ≈ 30. The impurity seeding by either Xe or Kr, which can reduce the power input into the SOL and hence the load on the plates, can however affect the sustainment of the H-mode, even if degraded. Argon is then considered for enhancing the radiated power inside the SOL. The TECXY analysis of this issue shows that the loads on to the target can be maintained at a very acceptable level, still preserving the core performance. Using liquid tin as divertor target material can be very advantageous for exhausting the power entering the divertor chamber provided argon is used in conjunction. In conclusion the option of a reactor working in a safer and simpler low confinement mode should not be put aside prematurely.