Speaker
Description
Tungsten is the preferred candidate as plasma-facing material for future power plants like DEMO. However, current W materials produced by industry like ITER-Grade Tungsten (IGW) will most likely not meet their requirements. New advanced armor concepts are being studied to withstand those steady state and transients heat loads [1]. One of the methods to simulate the heats loads expected in a device as DEMO is by a high-energy fiber laser as in OLMAT High Heat Flux (HHF) facility, described in [2]. Laser methods are very well suited as a fast and cheap screening test, and the only possibility to simulate certain heat loads.
In this work a small overview of the optimization of the high-energy fiber laser system will be first given. The installation has not been straightforward due to its high energy: laser beam shape characterization to find a flat-top profile, special viewports, beam dump for reflections, laser absorption quantification, etc.
The second, and main part, of this work is to compare different types of advanced W materials —2 types of Wf/W, WCrYZr self-passivating alloy, W-W2C— against IGW from 4 suppliers/batches as a reference material. They have been subjected to heats loads simulating disruptions (150-1000 MW/m2) at the edges of the armor (critical part), and small-ELMs regimes (50-300 MW/m2, 50-2000 Hz, up to 107 pulses) at the surface. Most materials were not damaged if the small-ELMs regimes were under 200 Hz and 106 pulses (being recent Wf/W the best suited), but were damaged with disruptions of >450 MW/m2 at the edges, but not if impacted at the surface (being IGW the more resilient against thermal shocks). However, the cracks at the edges were nucleated/originated by small cracks produced during fabrication at all non-polished sides (only the surface was). This indicates that in a future reactor there must be found a compromise in at least a rough polishing to eliminate those cracks and the high cost of it. Finally, future upgrades to overcome some of the problems found will also be presented.
[1] F.Maviglia et al. Nucl. Mat. Ener. 26, 100897 (2021)
[2] D.Alegre et al. J. Fus. Energy. 39, 411 (2020)