Exhaust assessment of a European Volumetric Neutron Source (EU-VNS) using SOLPS-ITER

EUROfusion considers a volumetric neutron source (EU-VNS) to generate a neutron wall load of about 0 . 5 M W / m 2 to qualify tritium breeding blankets early in support of EU-DEMO that mitigates the risk of a late testing for required nuclear technology. The envisaged small-scale R = 2 . 5 m D-beam/T-target driven fusion device ( P f u s ≈ 30 M W ) must exhaust helium particles and dissipate sufficient energy from the large auxiliary power required ( P a u x ≈ 50 M W ) entering in large parts the edge. A SOLPS-ITER assessment indicates that with argon seeding a finite divertor operational window exists allowing to avoid core dilution by helium and to reduce the peak heat-flux density below 10 M W / m 2 . It is shown that an extra constraint of Z e f f < 2 − 3 , required to sustain good core performance to produce the required amount of fusion neutrons, can also be met if the Greenwald-fraction f G W ≈ 0 . 5 is maintained with total T-throughputs at about half the ITER value. It is reasoned that for a EU-VNS design study the exhaust operational window can be enlarged by choosing other seeding species like Krypton, refining the balance between pellet- to gas-fuelling, and integrated core-edge modelling. • First assessment of particle and power exhaust for a conceptual European Volumetric Neutron Source (EU-VNS) successfully undertaken using the SOLPS-ITER code. • Despite large power entering the edge (50MW) in the foreseen compact sized device (R ∼ 2.5 m), a finite divertor operational window is predicted with argon seeding to reduce the peak heat-flux density on plasma-facing components below critical limits. • Core plasmas dilution by helium can be minimised by sufficient pumping in the device by maintaining neutral pressure in the divertor ∼ 10 Pa similar to ITER. Argon impurities are well compressed in the EU-VNS divertor. • Good core confinement can be sustained and thus enough fusion neutrons produced to achieve a neutron wall load of 0.5 MW/m 2 at low values Zeff < 2-3. The required core density is at 50% Greenwald fraction assuming total tritium particle throughputs ( ∼ factor 2 below ITER values). • An extension of the exhaust assessment is foreseen using krypton to enlarge operational space further and to reduce tritium throughput.