Experimental characterization of leading edge cracking on bulk tungsten divertor components during 2017–2019 WEST operation

• An experimental characterization of the cracks on the leading edges of non-beveled ITER-like PFUs in WEST was performed. • 133 monoblocks show cracks, or 27% of the monoblocks installed on the lower divertor of WEST. • Cracks are neat but discontinuous, with material’s bead on the sides of the crack groove. • The presence or absence of chamfer on the leading has no impact on the cracking response. During the 2017–2019 WEST operation, a set of ITER-like plasma-facing units consisting of tungsten monoblocks was installed on the lower divertor. Despite modest heating power, 27 % of these monoblocks had cracks on their poloidal leading edges, which were not protected by a toroidal bevel. A comprehensive experimental characterization of the 133 cracked monoblocks indicates that damage occurs near the plasma strike point areas where neat cracks separated by 0.15–0.5 mm in the poloidal direction were observed. Cracks are up to 1 mm long and 1 mm deep and did not affect the lower divertor ability to sustain long pulses. The most important parameter affecting crack formation is the relative vertical misalignment between components.