Microwrinkle structures on refractory metal surfaces irradiated with noble gas plasma species

Abstract

Microwrinkle structures with a pitch of less than 100 nm and up to 600 nm on refractory metals like tungsten (W) and molybdenum, which are irradiated by noble gas ions such as neon and helium, have been studied systematically. The wrinkle formation mechanism is thought to be a buckling of the hard surface layer supported by the soft elastic substrate, which is induced by a penetration of noble gas species from the irradiated surface. Microwrinkle forms on this structure under lateral compressive strain/stress fields coming from thermal constriction on the way to substrate cooling. Such a process should be anticipated when walls in a fusion reactor are attacked by heat pulses such as edge localized modes and/or vertical displacement events, and therefore might be an initial stage of W surface damage.

Effects of nitrogen-seeded deuterium plasma on tungsten surfaces

“…Instead, nitrogen atoms diffused deep into the surface layer and took a pinning role against dislocation movement, leading to the formation of a hard surface layer. This observation is consistent with the buckling model of a hard surface layer supported by soft bulk material, favoring a microwrinkle structure formation [9].…”

“…Introducing nitrogen gas in deuterium plasmas at a similar surface temperature changed the W surface morphology drastically, as shown in figures 5(b) and (c). The microwrinkle with a pitch of 150-200 nm is clearly observed, similar to these observed in deuterium and Ne mixed-gas discharge plasmas [9]. According to the buckling model of the hard surface layer supported by a soft elastic substrate, nitrogen also seems to contribute the surface hardening.…”

“…The formation mechanisms for the abovementioned two cases seem to be quite different: for W fuzz formation, the physical processes would be very important [8], while in the present nitrogen case a chemical reaction would be of importance so that we put great attention on the surface temperature. Microwrinkle formation is a popular phenomenon, due to Ne [9] as well as D [10,11], and possibly due to the presence of another atom, such as He. In this study, the contribution of nitrogen to microwrinkle formation is also examined.…”

Hydrogen interactions with low-index surface orientations of tungsten

“…The tungsten divertor in ITER will experience massive heat loads (10-20 MW m −2 ) and particle fluxes (10 24 m −2 s −1 ), which can cause significant microstructural and morphological changes [1]. It has been shown that tungsten, under simultaneous implantation to both low energy hydrogen and helium ions within the temper ature range of 1000-2000 K, experiences surface roughening and the formation of a tendril-like fuzz in certain combinations of temper ature and helium fluence [2][3][4]. The formation of this fuzz and other damage effects are especially concerning because they may lead to the formation of high Z dust, as well as enhanced fuel retention [5,6].…”

“…Whether hydrogen isotopes impinge on materials from the plasma side or diffuse out from the bulk, all particles will interact with the surface. H, in the form of deuterium and tritium isotopes, is the primary fuel source in fusion reactors and will be continuously implanted into the near-surface region of PFCs contributing to deleterious effects such as the formation of bubbles, surface blistering, and changes in the thermal and mechanical properties of the material [1][2][3][4][5][6]. The behavior of hydrogen on various surfaces of tungsten, in particular the (1 1 0) and (1 0 0) surfaces and to a lesser extent the (1 1 1) surface, have been studied both theoretically [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] and experimentally [6,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40].…”