A new experimental platform at the DIII-D National Fusion Facility is being used to investigate carbon ablation and spallation under conditions relevant to both fusion divertors and atmospheric entry vehicles. According to a preprint published on arXiv, the experiments expose carbon samples to extreme parallel heat fluxes to measure material erosion, providing a unique testbed for models used in aerospace engineering. The platform leverages the high-temperature plasma environment in the tokamak's scrape-off layer and core to simulate the shock-layer conditions encountered by spacecraft, such as the Galileo probe during its entry into Jupiter's atmosphere. Source: arXiv
The study employed two complementary methods to expose the carbon samples. Stationary carbon rods, some with a wedge shape, were inserted near the divertor strike point, subjecting them to parallel heat fluxes of 30–40 MW/m² in the scrape-off layer. In a separate approach, slow-launch carbon pellets were injected vertically, traversing the edge plasma and penetrating the core. These pellets experienced significantly higher heat fluxes, estimated to be an order of magnitude greater than those at the divertor. This dual-method approach allows for the study of material response across a wide range of thermal loads within a single experimental campaign. Source: arXiv
Stationary carbon rods, some with a wedge shape, were inserted near the divertor strike point, subjecting them to parallel heat fluxes of 30–40 MW/m² in the scrape-off layer.
A comprehensive suite of diagnostics was used to characterize the material response and plasma interaction. The team utilized fast visible imaging, divertor spectroscopy, infrared thermography, CO₂ interferometry, and post-exposure profilometry. These instruments provided detailed measurements of ablation rates, surface recession, and temperature evolution throughout the exposure. The primary finding from these diagnostics was a measured mass-loss rate of (1–3)×10⁻² g·cm⁻²·s⁻¹ for the stationary samples. This direct measurement is critical for benchmarking predictive models for plasma-facing components. Source: arXiv
The experimental results show strong agreement with established semi-empirical aerospace ablation models, validating the use of a tokamak as a high-fidelity platform for studying atmospheric entry phenomena. This cross-disciplinary application provides a valuable, ground-based capability for testing heat shield materials without requiring expensive and infrequent flight tests. For the fusion community, the platform offers a robust method for studying the erosion and lifetime of candidate divertor materials under reactor-relevant heat fluxes, informing the design of future devices like ITER and commercial power plants. The work highlights the synergistic relationship between fusion science and other fields of extreme engineering. Source: arXiv