Tungsten-Diamond Composites for Fusion Plasmas?

The current reference material for plasma-facing components in ITER and fusion power plant projects is tungsten. However, when subjected to the extreme heat fluxes of these machines, its mechanical properties deteriorate. The combination of tungsten and diamond—which has very high thermal conductivity—is an approach being developed at CEA-IRFM to create a composite that can combine the advantages of both tungsten and diamond. A patent has been filed, initial samples have been manufactured, and the first tests have shown promising results.

The armor materials for plasma-facing components currently under consideration for magnetic confinement fusion machines typically involve “high-Z” refractory metals such as tungsten (W) [1]. Despite its high melting point, its low tritium retention [2] , and good erosion resistance, W is prone to recrystallization, cracking, and/or melting under thermal shocks due to limitations in its thermomechanical properties [3].

Carbon, in the form of graphite or fiber-reinforced composites, is no longer considered a plasma-facing material, primarily due to its high tritium retention capacity [4]. However, carbon in the form of diamond obtained by chemical vapor deposition (CVD) [5] has a low retention level after exposure to plasmas [6] and demonstrates exceptional performance under thermal shock [7] thanks to its excellent thermal conductivity (20 times greater than that of W at 300 K). Unfortunately, diamond in this form tends to erode almost as easily as graphite [8,9].

For this reason, a tungsten-diamond composite was developed consisting of a millimeter-thick CVD diamond substrate, to ensure rapid and uniform heat distribution at the expected heat flux, with a tungsten coating approximately ten microns thick on its surface to act as protection against erosion.

This material, its applications as armor under high heat flux, and its manufacturing process are now the subject of a patent filed with the National Institute of Industrial Property [WO2026008640A1].

This is the result of a study during which 10×10 mm W-diamond samples were fabricated and tested under high heat flux at the CHAUCOLASE laser station [10] at the Fresnel Institute at the University of Marseille. These tests confirmed the material’s good performance under various thermal loads representative of those expected in ITER (¹⁰⁴ cycles of 1 ms at 2 ^GW·m⁻², 20 cycles of 1 s at 100 ^MW·m⁻²) [11]. The PIIM laboratory at Aix-Marseille University, responsible for the characterization, observed no cracks, melting, or delamination. By comparison, test samples made of solid tungsten all cracked or melted on the surface upon exposure to even the lowest thermal stresses (see example in Figure 1). The next step in this development is to propose a complete plasma-facing component that can be tested in WEST.

Figure 1:
a) W-diamond sample after 1 to 20 cycles (in the indicated regions) at 1 s at 100 MW^·m⁻².
The central region was subjected to a single event of continuous power deposition for 10 s at 100 ^MW·m⁻².
b) Electron microscope images of the surface in the middle of the power deposition zone (after 20 cycles) and of an unexposed surface.
c) Same as a) for a solid W sample.
d) Optical microscope imaging of a solid W surface subjected to the lowest heat load.