Analysis of hypervelocity impacts: the tungsten case

Controlling plasma-wall interactions is critical to achieve high performance in present day tokamaks, and will continue to be the case in the approach to practical fusion reactors. Tungsten (W) is the main candidate as plasma facing material for a fusion reactors and will be exclusively used in the ITER divertor [1].  Outstanding technical issues are still to be overcome, for instance erosion/redeposition from plasma sputtering and disruptions, dust and flake generation. The presence of high velocity impacts has been reported and suggested in several studies, with velocities being around 500 m/s to a few km/s [2, 3].

In this work, the atomistic mechanisms of damage initiation during high velocity (v up to 12 km/s) impacts of W projectiles on W has been investigated using molecular dynamics simulations, involving very large samples (up to 200 million atoms). Various aspects of the impact at high velocities where the projectile and part of the target materials undergo massive plastic deformation, breakup, melting or vaporization are analyzed [4]. Different stages of the penetration process are identified. Whether the damage occurring in the subsurface of the target is described by collision cascades or as effect of shock waves will be discussed.

References:

 [1] G. Federici et al 2001 Nucl. Fusion 41 1967
 [2] Castaldo C. et al 2007 Nucl. Fusion 47 L5–9
 [3] S. Ratynskaia et al 2008 Nucl. Fusion 48 015006
 [4] A. Fraile et al 2022 Nucl. Fusion 62 026034