Speaker
Description
Tungsten (W) is widely used as a plasma-facing material in fusion devices due to its high melting point, low sputtering yield, and excellent thermal conductivity [1]. However, due its mechanical behaviour it is prone to crack under harsh experimental fusion environments: high heat fluxes (cycling steady state loading, ELMs & disruption) [2], light impurities bombardment (H, D, He) [3]. Experiments run in high heat flux test facilities for the qualification of plasma facing components (PFCs) using tungsten as armor material highlighted macro-crack propagation through the tungsten monoblocks during steady state cyclic solicitations [4]. The presence of cracks not only degrades the structural integrity of tungsten components but may also limit the power plant availability and the plasma performance.
Since the first experiments in ASDEX-U (end of 90’s) [5], the use of tungsten as plasma facing material has become a standard practice for divertor PFC application (JET, ASDEX-U, EAST, KSTAR, WEST…). In some devices, tungsten is also used as plasma facing material for first wall limiter (EAST, WEST,…). These fusion devices accumulated hours of plasma in this configuration and report systematic cracking of tungsten elements [6-7-8]. This overview aims at presenting the cracking phenomenology (pattern, types, quantity, localisation...) observed after plasma solicitation in several fusion device environments at the divertor & the first wall regions. Rationale (thermal cycling, energetic events, …) regarding their occurrence is also discussed based on cracking patterns observation, metallographic analysis and crack initiation / propagation modelling. The impact of such cracking patterns on the dust collection process, the high impurities sources, the plasma operation and maintenance scheme are discussed. Off-normal events such as disruptions or runaway electrons may also induced a larger variety of damage patterns than cracks. Recrystallization, delamination and local melting are finally also discussed based on divertor and first wall post-mortem analysis available.
*Corresponding author e-mail: alan.durif@cea.fr
[1] Abernethy, R. G. 2016. MST, 33(4), 388-399
[2] M. Wirtz et al, NME, 12 (2017) 148-155
[3] Y. Li et al 2021 Nucl. Fusion 61 046018
[4] S. Nogami et al, FED 120 (2017) 49-60
[5] K. Krieger et al, JNM 266 -269 (1999) 207-216
[6] Chuannan Xuan et al 2025 Nucl. Fusion 65 046027
[7] Dahuan Zhu et al 2022 Nucl. Fusion 62 056004
[8] M. Diez et al, NME, Vol 41, 2024, 101746