Development of an in operando uniaxial fatigue testing regime for the linear plasma device Magnum-PSI

• A novel proof-of-concept low-cycle fatigue testing regime has been developed for the linear plasma device Magnum-PSI. • Controlled thermomechanical cycling with simultaneous plasma exposure has been achieved. • Finite element analyses are used to define experimental parameters for Magnum-PSI experiments, based on a DEMO strikepoint sweeping regime. • This new method enables the synergistic effects of plasma-material interactions on the fatigue cracking behaviour of plasma-facing components to be explored. • Initial findings demonstrate a reliable and robust method, and surface roughness effects on fatigue cracking behaviour are qualitatively explored. Tokamak divertors may be exposed to cyclic thermomechanical loads during service, giving rise to the fatigue cracking of plasma-facing monoblocks. Fatigue is a surface-sensitive dislocation-mediated degradation phenomenon, and monoblock fatigue life may be affected by plasma-material interactions such as D/T/He implantation, blistering, fuzz, and ELMs that modify the morphology, microstructure and mechanical response of the plasma-facing surface. To investigate the synergistic effects of plasma-material interactions on fatigue cracking, a novel experimental method has been developed for the Magnum-PSI linear plasma device that combines cyclic thermomechanical loading with simultaneous plasma exposure. A DEMO strikepoint sweeping scenario (45 MW m −2 at 1 Hz over 100 mm span) is translated into experimental parameters via time-dependent thermal–mechanical finite element modelling of a monoblock, which calculated the uniaxial strain imposed at the centre of the plasma-facing surface to be 0.648%. The cyclic thermal loading of ITER-grade W targets is achieved in Magnum-PSI via sinusoidal modulation of the plasma source, with real-time monitoring via synchronous Thomson scattering, optical emission spectroscopy, pyrometry, and infrared thermography. Initial results are presented which demonstrate a proof-of-concept in operando fatigue testing method, qualitatively explore surface roughness/treatment effects, and indicate that strikepoint sweeping may significantly contribute to plasma-facing surface cracking.