Description
A study is being carried out within EUROfusion to address the feasibility of a Volumetric Neutron Source (VNS). VNS is a medium-size tokamak (R = 2.67 m, B0 = 5.6 T, A = 4.25, Ip = 2.54 MA) operating D-T plasmas, able to achieve a significant neutron wall load (approximately 0.5 MW/m2) on long pulses, to be built and operated in parallel to ITER. Purpose is to test and qualify in-vessel components, in particular the breeding blanket and the divertor, under large neutron irradiation, fluence and heat flux in a reactor-relevant environment. VNS is based on beam-target fusion reactions, which enable a significant fusion power despite the reduced device size. Neutral Beams are employed both to generate the beam-target reactions (as in JET D-T fusion energy record [Maslov, NF 2023, PPCF2026 submitted]), and to drive the plasma current to sustain the requested long pulses. Additional EC power is installed to keep the electron temperature high (a fundamental aspect in beam-target driven devices), and for control reasons. This work illustrates the design-driving criteria according to which the current VNS design point has been identified. A series of scans performed with the plasma simulator METIS [Artaud, NF 2018] coupled with the code MADE [Giannini, FED 2023] for preliminary magnets sizing is also presented. The results highlight the impact of relevant machine parameters on the VNS performance.
In addition, this work reviews the VNS plasma scenario, with focus on its critical features. This is currently being investigated with codes of different level of fidelity, both looking at some particular aspect in isolation, but also with integrated modelling – e.g. for tungsten accumulation. Further analyses deal with MHD stability (with particular attention on the interplay with energetic particles), power exhaust, fast particles confinement (both beams and alpha's) and beam deposition, as well as magnetic equilibrium and control. In the near future, a study of the dynamic phases and of the machine controllability in a broad sense via Pulse Design tools (e.g. Fenix [David, OPS 2025]) is planned, following what has recently been carried out for EU-DEMO [Di Grazia, FED 2025].