Recent advances in characterising irradiation damage in tungsten for fusion power

Abstract

Tungsten is the front-runner candidate for building the plasma-facing armour components for future fusion reactors. However, in-service irradiation by fusion-neutrons and helium will create lattice-defects in the material, compromising its properties and lifetime. Improving the component's resilience to radiation damage and accurately predicting the lifetime of irradiated components is key for commercial feasibility of the reactor. For this purpose, understanding the creation and evolution of radiation damage is essential. This paper reviews recent advances in characterising radiation damage through experimental and modelling techniques. Tungsten-ion-and helium-ion-implantation are commonly used to mimic the damage created by neutron-and helium-irradiation respectively. Defects (> 1.5 nm) can be directly imaged using transmission electron microscopy while all defects (size-independent), may be indirectly probed by measuring lattice strains induced by them (using diffraction techniques; synchrotron X-rays or high-resolution electron-backscatter). Neutron-irradiation produces mainly ½〈111〉 prismatic loops. Loop-interaction and structural organisation evolves with changing implantation dose and temperature. Helium-irradiation, < 573 K, induces formation of small helium-vacancy clusters, which evolve into bubbles, blisters and "fuzz" structure with changing temperature and dose. Nano-indentation or micro-cantilever bending tests can be used to examine mechanical properties of ion-implanted layers. Both heliumand neutron-implantation defects induce increased hardening often followed by subsequent strain-softening and localised deformation. Such irradiation-induced alterations are detrimental to material ductility and long-term structural integrity of tungsten-based components. Development of physically-based material models that capture the physics of underlying irradiation-induced changes, inspire confidence of reliably using simulations to predict mechanical behaviour and in-service performance of irradiated engineering components in future.

Nanoscale lattice strains in self-ion implanted tungsten

“…Further hydrogen and helium will diffuse from the plasma itself [3]. These processes have been shown to alter the material properties, resulting in hardening, embrittlement, creep and lattice swelling [1,2,[4][5][6][7]. Resultant residual stresses can act as offsets to other fatigue loading, potentially reducing fatigue life, which is likely to be the limiting factor for plant service life.…”

“…The combined effects must be better understood in order to develop ways to inhibit these changes in the design of power generating plants and to estimate the lifetime of functional plasma facing components. [1][2][3]7].…”

“…Furthermore, commonly used sample preparation methods, such as Focused Ion Beam (FIB) liftout procedures for producing transmission electron microscopy samples, risk modifying the surface layer [16,17]. Secondly, free surface effects begin to play a significant role in such a thin damage layer, resulting in a deviation from the behaviour expected in a bulk sample for a similar amount of damage [7,12,18]. This has led to the general approach of using significantly higher ion energies for measurements in order to circumvent the complications associated with low ion energy implantation (e.g.…”

Band pass filter plan in fluoroscopy for high energy range

“…These cubes were positioned at a distance of 0.1 mm and represented the thickness of the filters utilized in each area. In addition, a 0.1 mm thick lead filter and a thin 0.1 mm thick tungsten target were chosen for the location where the photons pass and collide to be attenuated [29,30]. The input electron energy was assigned to 100 keV and the direction of the particles incident on the target was in the vertical direction to the Z axis.…”

Special Issue: Radiation Damage in Materials—Helium Effects

“…These 1D He nanochannels that once interconnected to form a 3D network have a potential to outgas He outside of the material in Operando when the material is continuously being implanted with He particles, and thus, effectively reduce the net He particle flux received by the material. During these studies, He implantation has emerged as a useful tool for understanding complex and diverse environments, ranging from solar winds in space [8] to 'nanofuzz' formation in fusion energy systems [9]. This Special Issue, "Radiation Damage in Materials-Helium Effects", includes three review articles and nine full length papers (12 publications in total) on new irradiation material research activities and novel material ideas focused on understanding He effects on microstructure evolution and the subsequent properties.…”