Burning Plasma Relevant Fusion Materials Research Using the PISCES Linear Plasma Devices

Advances in controlled nuclear fusion research have led to where serious thought is being devoted toward the concept of a ‘burning plasma’ fusion pilot plant (FPP), as a prototype to an eventual working fusion power reactor. However, the survivability, and in-service performance of the materials that make up the plasma facing components (PFCs) are still identified as key areas of risk. To retire that risk, further scientific and engineering studies must be performed that investigate the effects of combined high heat-and-particle load plasmas on materials, in conjunction with the damaging effects and material degradation that will be caused by neutrons.<br/>PISCES plasma-materials interaction (PMI) research utilizes high-power linear-plasma devices that operate with a plasma-material-target parameter space that overlaps present day fusion confinement devices and is near to that expected in ITER and, potentially, a FPP facility. PISCES research focuses on numerous fusion materials issues such as erosion, the effects of fusion typical D and He plasma fluxes, physical and chemical changes in surface morphology, fuel retention in the material surface, and impurity transport and associated re/co-deposition. Recent lines of evidence, however, are showing that materials have unexpected responses to plasma bombardment when displacement damage is present, or, have different properties ‘in-service’ compared to that which is measured in a post-mortem state following the plasma exposure. This evidence, having implications for PFCs exposed to burning plasmas, have prompted a new focus in PISCES research to specifically address the PMI science and engineering needed for materials operation in a credible burning plasma FPP design, as well as to study of the PMI surface ‘in-service’ by a range of laser-based diagnostics capable of measuring key PMI surface parameters in-situ/operando.<br/>Material presented at the meeting will provide an overview of the PISCES program and summarize the status of ongoing PISCES research. Specific PMI topics to be discussed include, changes in tungsten PMI due to displacement damage, advances in understanding the nature of the growth of tungsten fuzz morphology (a dense layer of tungsten nano-scale tendrils out of the surface) by He implantation, the influence of surface morphology on physical sputtering, and recent findings on the hydrogen isotope retention properties of tungsten co-deposits. Results from in-situ/operando methods of studying the PMI surface will also be presented. These include, measuring PMI surface composition with laser induced breakdown spectroscopy (LIBS), measuring D retention in the PMI surface using laser induced desorption spectroscopy (LIDS), and determining the thermal diffusivity and elastic properties of tungsten PMI surfaces with transient grating spectroscopy (TGS).