Collisional and thermal effects on liquid lithium sputtering

Abstract

The lithium sputtering yield from lithium and tin-lithium surfaces in the liquid state under bombardment by low-energy, singly charged particles as a function of target temperature is measured by using the Ion-surface Interaction Experiment facility. Total erosion exceeds that expected from conventional collisional sputtering after accounting for lithium evaporation for temperatures between 200 and 400°C. Lithium surfaces treated with high-fluence D atoms are bombarded by H + , D + , He + , and Li + at energies between 200 and 1000 eV and 45°incidence. Erosion measurements account for temperature-dependent evaporation. For example, 700 eV He + particles bombarding the D-treated liquid Li surface at room temperature result in a sputter yield of 0.12 Li/ion and at temperatures ϳ2.0T m ͑where T m is the melting temperature of the sample͒, a yield near and above unity. The enhancement of lithium sputtering is observed to be a strong function of temperature and moderately on particle energy. Bombardment of a low-vapor-pressure lithium alloy ͑0.8 Sn-Li͒, used for comparison, also results in nonlinear rise of lithium erosion as a function of temperature. Measurements on both pure liquid Li and the alloy indicate a weak dependence with surface temperature of the secondary ion-induced secondary ion emission. Treatment of liquid Li surfaces with D, yields reduced sputtering under He + impact by a factor of 5-6 when measured at room temperature due to preferential sputtering effects.

Experimental studies of lithium-based surface chemistry for fusion plasma-facing materials applications

“…Fig. 1 shows the sputter yield of Li-C by energetic He ions compared to other lithium-treated or lithium-based surfaces including: pure lithium, alloyed lithium with tin, deuterated lithium, and lithium deposited on ATJ graphite [12]. Comparing these results we find that depending on the state of lithium bonding the yield of sputtered atoms can vary by almost two orders of magnitude near the sputter threshold region.…”

“…The first, in situ lithiated graphite experiments under particle irradiation and lithium deposition with simultaneous surface analysis. The second, ex situ lithium depositions and high-intensity deuterium exposures conducted in the IIAX experiment [12] at the University of Illinois and post-mortem characterization in facilities of the Birck Nanotechnology Center at Purdue University. The third, post-mortem analysis of NSTX ATJ graphite tiles.…”

“…bonding with impurity species), (2) any alloying with other metals, and (3) whether the surface is in the solid or liquid state [12]. The hydrogen retention level can also affect particle sputtering.…”

Full toroidal imaging of non-axisymmetric plasma material interaction in the National Spherical Torus Experiment divertor

“…Heated LLD segments also clearly show enhanced neutral and singly ionized lithium influxes (up to 2×). This can be interpreted as a result of the temperature dependence of lithium physical sputtering yield 7 . Again, the cold LLD segment shows influxes comparable to the nearby graphite tile.…”

“…Toroidal asymmetries in local lithium influxes are generally observed and are enhanced during transient divertor heat loads, such as ELMs. The transient heat load causes differential heating of coatings with different thickness and a consequently different lithium sputtering response 7 . In Figure 3 (top), the simulated lithium toroidal distribution is shown.…”