Investigation of boron distribution and material migration on the W7-X divertor by picosecond LIBS

One set of horizontal target elements of the Test Divertor Units (TDU), retrieved from the Wendelstein 7-X (W7-X) vessel after the end of second divertor Operation Phase (OP1.2B) in Hydrogen (H), were investigated by picosecond Laser-Induced Breakdown Spectroscopy (ps-LIBS). The Boron (B) distribution, H pattern and the material erosion/deposition pattern on these target elements were analyzed with high depth resolution and mapped in the poloidal direction of W7-X. From the spectroscopic analysis, B, H, Carbon (C) and Molybdenum (Mo) were clearly identified. A non-uniformly distributed B pattern on these divertor target elements was determined by the combination of B layer deposition during the three boronizations and W7-X plasma operation with multiple erosion and deposition steps of B. Like the TDU, the analyzed target elements are made of fine grain graphite, but have two marker layers which allow us to determine the material migration via the ps-LIBS technique. Two net erosion zones including one main erosion zone with a peak erosion depth of 6.5 μm and one weak erosion with a peak erosion of 1.3 μm were determined. Between two net erosion zones, a net deposition zone with width of 135 mm and a thickness up to 3.5 μm at the peak deposition location was determined by the ps-LIBS technique. The B distributions are correlated with the erosion/deposition pattern and the operational time in standard magnetic configuration of W7-X in the phases after the boronizations. The thickness of the containing B layer on these target elements also correlates with the erosion/deposition depth, in which the thickness of the containing B layer varies spatially in poloidal direction between 0.1 μm and 6 μm. Complementary, Focused Ion Beam combined with Scanning Electron Microscopy (FIB-SEM) was employed also to verify and investigate the deposition layer thicknesses at typical net erosion and net deposition zones as well as to identify the three boronizations in depth.

Handheld LIBS for Li Exploration: An Example from the Carolina Tin-Spodumene Belt, USA

Laser-induced breakdown spectroscopy (LIBS), which has recently emerged as tool for geochemical analysis outside the traditional laboratory setting, is an ideal tool for Li exploration because it is the only technique that can measure Li in minerals, rocks, soils, and brines in-situ in the field. In addition to being used in many products essential to modern life, Li is a necessary element for a reduced carbon future and Li–Cs–Ta (LCT) granitic pegmatites are an important source of Li. Such pegmatites can have varying degrees of enrichment in Li, Rb, Cs, Be, Sn, Ga, Ta>Nb, B, P, and F. We focus here on the LCT pegmatites of the Carolina Tin-Spodumene Belt (CTSB) situated in the Kings Mountain Shear Zone, which extends from South Carolina into North Carolina. The CTSB hosts both barren and fertile pegmatites, with Li-enriched pegmatites containing spodumene, K-feldspar, albite, quartz, muscovite, and beryl. We illustrate how handheld LIBS analysis can be used for real-time Li analysis in the field at a historically important CTSB pegmatite locality in Gaston County, N.C. in four contexts: (i) elemental detection and identification; (ii) microchemical mapping; (iii) depth profiling; and (iv) elemental quantitative analysis. Finally, as an example of a practical exploration application, we describe how handheld LIBS can be used to measure K/Rb ratios and Li contents of muscovite and rapidly determine the degree of pegmatite fractionation. This study demonstrates the potential of handheld LIBS to drastically reduce the time necessary to acquire geochemical data relevant to acquiring compositional information for pegmatites during a Li pegmatite exploration program.