Speaker
Description
The EUROfusion programme is advancing the design of the Volumetric Neutron Source (VNS), a compact tokamak facility dedicated to testing in-vessel components under high neutron flux and fluence, to be built in parallel to ITER. The VNS concept relies on beam–target fusion, with 120 keV deuterium neutral beams injected into a tritium plasma to maximize fusion reaction, following a strategy similar to that successfully demonstrated during the JET record fusion pulses (DTE-2 and DTE-3) [1]. To achieve a Neutron Wall Load of ~0.5 MW m⁻² while limiting tritium consumption, the device is designed with a major radius of R = 2.67 m. The NBI fully drives the current and should sustain the requested long-pulse operation, inevitably leading to strong plasma rotation. In addition, tungsten plasma-facing components are foreseen for long-pulse operation.
A key question for the feasibility of this concept is whether high-performance operation can be sustained without deleterious tungsten accumulation. Strong beam-driven rotation can enhance impurity peaking, while tungsten radiation may significantly degrade the core electron temperature, reducing fusion power and potentially leading to plasma termination.
To assess scenario feasibility, predictive simulations were performed with the high-fidelity integrated modelling code ASTRA [2]. The model self-consistently includes turbulent and neoclassical transport (TGLF-SAT2 [3], FACIT [4]), NBI particle and power deposition via RABBIT, and neutral particle effects. Plasma rotation is estimated using the Zimmermann model [5], and pedestal transport is treated with the Puchmayr scaling [6] from ρ = 0.95 outwards. Preliminary pedestal pressure values were informed by IPED runs.
Model validation on experimental results from the JET DTE-2 campaign has been performed, focusing on the key transport mechanisms expected to be critical for VNS operation. Based on this, predictive simulations of the VNS were carried out. The main results are presented, with a focus on tungsten accumulation and its interplay with high rotation levels, and on overall plasma performance, including fusion power production for a 10/90 D/T plasma mixture. Finally, perspectives for further optimization of both the modelling approach and fusion performance are discussed.