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All sources NASA NTRS DOE OSTI

DOE OSTI2025

Erosion of high-Z refractory coatings for helicon plasma source window

Proto-MPEX (Materials Plasma Exposure eXperiment), a linear plasma device (LPD), using a high power radio frequency (RF) (⩾100 kW, 13.56 MHz) helicon plasma source, has suffered RF sheath-induced window erosion. The sputtered impurities from the window surface transport toward the downstream target affecting plasma-material interaction studies. The rectified sheath voltage formed was high enough to cause window erosion by light ions due to its low-Z components (e.g. Si 3 N 4 and AlN). Hence, we are proposing impurity mitigation strategies, which involve the application of a Faraday screen to lower the rectified sheath voltage and the application of high-Z refractory coatings on the existing window plasma-facing surface. In this work, we report the erosion of two different coatings, i.e., tantalum oxide (Ta 2 O 5 ) and hafnium oxide (HfO 2 ) on a silicon nitride (Si 3 N 4 ) window material under conditions of low-energy deuterium (D) ion impact, well below the Ta 2 O 5 sputtering energy threshold (i.e. 250 eV). The test samples were RF-biased and exposed to a high D-ion fluence (∼10 26 m −2 ) in Plasma Interaction with Surface Component Experimental Station (PISCES-A) LPD. The experimentally measured sputtering yields of the high-Z refractory coatings below the sputtering energy threshold of Ta 2 O 5 indicate an increased erosion due to the plasma impurities, especially due to oxygen. Improving the vacuum level could reduce the oxygen impurities and increase the lifespan of the coated helicon window for plasma operation. Post-surface analysis indicates no preferential erosion of oxygen or enrichment of the high-Z surface component. This is likely due to an effective energy transfer from the impurity ion for sputtering of the high-Z component in the coating. With the reduced rectified sheath voltage at the window surface and improved vacuum conditions, the proposed high-Z refractory coatings offer a promising solution for reducing window erosion in future MPEX plasma operations at ORNL.

RF bias↗

DOE OSTI2025

FLAW STABILITY ANALYSIS OF SURFACE CRACKS IN DOE STANDARD CANISTERS UNDER OPERATION LOADS AND WELDING RESIDUAL STRESSES

There are over 3000 commercial spent nuclear fuel (SNF) storage canisters that are made of stainless steel and planned for multi-purpose functions of SNF handling: interim storage, transportation, and ultimate disposal at a future SNF disposition location. To date, many multi-purpose canisters (MPC) are located in coastal regions for long-term storage. The canisters are fabricated by welding, and post-welding heat treatment is not required for relieving welding residual stresses (WRS). As a result, these canisters may be susceptible to chloride induced stress corrosion cracking (CISCC) due to the chloride-bearing marine salts. The flaw stability analysis of MPC canisters was performed at SRNL (i.e., PVP2016-4935 and PVP2016-63887) for through-wall flaws and for surface flaws respectively, where WRS was considered, and the failure assessment diagram (FAD)-based fracture mechanics method codified by API 579-1/ASME FFS-1-2007 Edition was adopted.

DOE standard canister↗

DOE OSTI2023

Offshore wind energy forecasting sensitivity to sea surface temperature input in the Mid-Atlantic

Abstract. As offshore wind farm development expands, accurate wind resource forecasting over the ocean is needed. One important yet relatively unexplored aspect of offshore wind resource assessment is the role of sea surface temperature (SST). Models are generally forced with reanalysis data sets, which employ daily SST products. Compared with observations, significant variations in SSTs that occur on finer timescales are often not captured. Consequently, shorter-lived events such as sea breezes and low-level jets (among others), which are influenced by SSTs, may not be correctly represented in model results. The use of hourly SST products may improve the forecasting of these events. In this study, we examine the sensitivity of model output from the Weather Research and Forecasting model (WRF) 4.2.1 to different SST products. We first evaluate three different data sets: the Multiscale Ultrahigh Resolution (MUR25) SST analysis, a daily, 0.25∘ × 0.25∘ resolution product; the Operational Sea Surface Temperature and Ice Analysis (OSTIA), a daily, 0.054∘ × 0.054∘ resolution product; and SSTs from the Geostationary Operational Environmental Satellite 16 (GOES-16), an hourly, 0.02∘ × 0.02∘ resolution product. GOES-16 is not processed at the same level as OSTIA and MUR25; therefore, the product requires gap-filling using an interpolation method to create a complete map with no missing data points. OSTIA and GOES-16 SSTs validate markedly better against buoy observations than MUR25, so these two products are selected for use with model simulations, while MUR25 is at this point removed from consideration. We run the model for June and July of 2020 and find that for this time period, in the Mid-Atlantic, although OSTIA SSTs overall validate better against in situ observations taken via a buoy array in the area, the two products result in comparable hub-height (140 m) wind characterization performance on monthly timescales. Additionally, during hours-long flagged events (< 30 h each) that show statistically significant wind speed deviations between the two simulations, both simulations once again demonstrate similar validation performance (differences in bias, earth mover's distance, correlation, and root mean square error on the order of 10−1 or less), with GOES-16 winds validating nominally better than OSTIA winds. With a more refined GOES-16 product, which has been not only gap-filled but also assimilated with in situ SST measurements in the region, it is likely that hub-height winds characterized by GOES-16-informed simulations would definitively validate better than those informed by OSTIA SSTs.

17 WIND ENERGY↗

DOE OSTI2021

ExoMars Mars Organic Molecule Analyzer (MOMA) Laser Desorption/Ionization Mass Spectrometry (LDI-MS) Analysis of Phototrophic Communities from a Silica-Depositing Hot Spring in Yellowstone National Park, USA

The Mars Organic Molecule Analyzer (MOMA) is a key scientific instrument on the ExoMars Rover mission. MOMA is designed to detect and characterize organic compounds, over a wide range of volatility and molecular weight, in samples obtained from up to two meters below the martian surface. Thorough analog sample studies are required to best prepare to interpret MOMA data collected on Mars. We present here the MOMA characterization of Mars analog samples collected from an alkaline silica depositing hot spring in Yellowstone National Park, WY, USA. These samples contain microbial streamer communities composed primarily of oxygenic and anoxygenic phototrophs. Additionally, in a study focused on detection of key classes of nonvolatile organics, samples of microbial streamers and their total lipid extract (TLE) have been measured on a MOMA Engineering Test Unit (ETU) instrument using its laser desorption/ionization mass spectrometry (LDI-MS) mode. MOMA LDI-MS detected a variety of lipids and pigments in the TLE sample. Species such as chlorophyll a were also detected from the streamer sample with the help of mass isolation. The results add to the LDI-MS sample characterization database, as well as demonstrate the benefit of using mass isolation on the MOMA instrument to reveal the presence of complex organics, and potential biomarkers, preserved in a natural sample, providing guidance to the in situ analysis of surface samples during Mars operations.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2025

In-service corrosion and grain boundary oxidation in neutron-irradiated 316 stainless steel baffle-former bolts

Reactor core internal components such as baffle-former bolts (BFBs) are subjected to significant mechanical stress, corrosive environment, and neutron irradiation from the reactor core during the plant operation. Over the long operation period, these conditions lead to potential degradation and of the bolts. In this work, characterization was performed on the oxidized surface of stainless steel BFBs harvested from a commercial pressurized water reactor (PWR) after 40 years of operation. The analysis shows that a complex multilayered surface oxide with six identified layers formed that is different from 2-layer structure commonly observed in model experiments. The oxide varies by composition – predominantly Fe, Cr, and Ni, grain size, and phase, and has features resembling both unirradiated and radiation/ corrosion experiments likely due to the low radiation flux compared to ion-irradiation or the test reactor radiation. In addition, grain boundary oxidative attack featured a pathway for Fe and other elements to move from the metal matrix to the outermost oxide. In conclusion, the results help assess PWR lifetime extension, put into context previous experimental studies, and provide input for designing experiments combining radiation and corrosion effects.

Baffle-former bolt↗

DOE OSTI2020

Constraints on low-mass, relic dark matter candidates from a surface-operated SuperCDMS single-charge sensitive detector

This article presents an analysis and the resulting limits on light dark matter inelastically scattering off of electrons, and on dark photon and axionlike particle absorption, using a second-generation SuperCDMS high-voltage eV-resolution detector. The 0.93 g Si detector achieved a 3 eV phonon energy resolution; for a detector bias of 100 V, this corresponds to a charge resolution of 3% of a single electron-hole pair. The energy spectrum is reported from a blind analysis with 1.2 g-days of exposure acquired in an above-ground laboratory. With charge carrier trapping and impact ionization effects incorporated into the dark matter signal models, the dark matter-electron cross section σ ¯ e is constrained for dark matter masses from 0.5 to 10 4 MeV / c 2 ; in the mass range from 1.2 to 50 eV / c 2 the dark photon kinetic mixing parameter ϵ and the axioelectric coupling constant g a e are constrained. The minimum 90% confidence-level upper limits within the above-mentioned mass ranges are σ ¯ e = 8.7 × 10 - 34 cm 2 , ϵ = 3.3 × 10 - 14 , and g a e = 1.0 × 10 - 9 .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2022

Stability and Activity of Cobalt Antimonate for Oxygen Reduction in Strong Acid

Guided by computational Pourbaix screening and high-throughput experiments aimed at the development of precious-metal-free fuel cells, we investigate rutile CoSb 2 O 6 as an electrocatalyst for oxygen reduction in 1 M sulfuric acid. Following 4 h of catalyst conditioning at 0.7 V vs RHE, operation at this potential for 20 h yielded an average current density of –0.17 mA cm –2 with corrosion at a rate of 0.04 nm hour –1 that is stoichiometric with catalyst composition. Surface Pourbaix analysis of the (111) surface identified partial H coverage under operating conditions. The Sb active site has an HO* binding free energy of 0.49 eV, which is near the peak of the kinetic 4e – ORR volcano for transition-metal oxides in acidic conditions. Furthermore, the experimental demonstration of operational stability and computational identification of a reaction pathway with favorable energetics place rutile CoSb 2 O 6 among the most promising precious-metal-free electrocatalysts for oxygen reduction in acidic media.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Intrinsic (Trap‐Free) Transistors Based on Epitaxial Single‐Crystal Perovskites

Abstract The first experimental realization of the intrinsic (not dominated by defects) charge conduction regime in lead‐halide perovskite field‐effect transistors (FETs) is reported. The advance is enabled by: i) a new vapor‐phase epitaxy technique that results in large‐area single‐crystalline cesium lead bromide (CsPbBr 3 ) films with excellent structural and surface properties, including atomically flat surface morphology, essentially free from defects and traps at the level relevant to device operation; ii) an extensive materials analysis of these films using a variety of thin‐film and surface probes certifying the chemical and structural quality of the material; and iii) the fabrication of nearly ideal (trap‐free) FETs with characteristics superior to any reported to date. These devices allow the investigation of the intrinsic FET and (gated) Hall‐effect carrier mobilities as functions of temperature. The intrinsic mobility is found to increase on cooling from ≈30 cm 2 V −1 s −1 at room temperature to ≈250 cm 2 V −1 s −1 at 50 K, revealing a band transport limited by phonon scattering. Establishing the intrinsic (phonon‐limited) mobility provides a solid test for theoretical descriptions of carrier transport in perovskites, reveals basic limits to the technology, and points to a path for future high‐performance perovskite electronic devices.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Surface Heat Load Analysis Due to Plasma Thermal Radiation on Equatorial Port 09

This paper reports calculated surface heat load owing to plasma thermal radiation, which will be applied to the surfaces of Equatorial Port 09 (EP09) diagnostic shield modules (DSMs) for thermal analysis during normal operation. The calculation assumes that the thermal energy will deposit uniformly in all directions from the plasma to the adjacent components and environment (i.e. gray body radiation). Assuming the temperature for the plasma surface, calculated view factors are used to determine the allocation of thermal energy to each component. The analysis provides an initial assessment of the thermal radiation heat load on the DSMs to be checked in structural/thermal analyses to verify significance. In conclusion, the designs of the EP09 components are still in the early preliminary phase, and changes are expected in the future.

ANSYS↗

DOE OSTI2022

A Novel Steam Condenser with Loop Thermosyphons and Film-Forming Agents for Improved Heat Transfer Efficiency and Durability

In this DOE/NETL BAA program, Advanced Cooling Technologies, Inc. (ACT), with Suez Water Technologies & Solutions (Suez), developed film-forming amine coatings applied to condenser surfaces that incorporated loop thermosyphons to enhance steam surface condenser performance and efficiency for coal-fired power plants. The condensation phenomenon resulting from these coatings promotes efficient dropwise condensation without additional thermal resistance through the use of film-forming amines (FFA). The loop thermosyphon technology was being developed to supplant current pumped cooling water systems to reduce operations and maintenance issues, reduce energy use, and promote high thermal performance. Both of ACT’s advanced coating and loop thermosyphon technologies were developed for application to wet cooling and indirect dry cooling systems. Internal steam condensation and subsequent heat dissipation complete the thermodynamic power cycle used by power plant cooling systems. The successful 3-year project period delved into understanding the experimental performance gain using film-forming amines applied to flat and tubular condenser surfaces under realistic operating conditions. The performance gain was used to create a technoeconomic analysis to more clearly understand the market value for power plants using FFA coatings to achieve dropwise condensation on condenser surfaces. A tall (50 ft.) loop thermosyphon was designed, fabricated, and tested to optimize the performance characteristics by tuning the working fluid charge and determining the temperature drop across the loop at different heat loads. Commercialization opportunities were explored to transition the loop thermosyphon work into the building HVAC market.

20 FOSSIL-FUELED POWER PLANTS↗

DOE OSTI2023

Analysis of Tank 38h (HTF-38-23-19, -20) and Tank 43H (HTF-43-23-21, -22) Samples for Support of the Enrichment Control and Corrosion Control Programs

SRNL analyzed samples from Tank 38H and Tank 43H to support ECP and CCP. The results indicate the concentrations of most soluble species in the Tank 38H surface sample decreased significantly from the previous surface sample. The Tank 38H sub-surface sample shows changes in concentration for soluble species in the solution with some increasing and some decreasing. The current Thank 38H sub-surface sample contains visible sludge solids similar to the previous sample, i.e., less than 1%, based on visual appearance. The significant differences in the concentrations of major components between the Tank 38H surface and sub-surface samples indicate significant stratification of solution species between these two locations within the tank. Savannah River Mission Completion personnel indicate that ~ 150,000 gallons of Tank 22 supernate were received in Tank 38H since its last analysis during which time the 2H evaporator was not operated, so the observed stratification is expected. The Tank 43H surface and sub-surface samples are similar in composition to the previous samples. The similar solution compositions measured in the Tank 43H surface and sub-surface samples indicate a minimal stratification within the tank. The total uranium and plutonium in the current Tank 38H surface sample remains similar to the previous analysis. The Tank 38H sub-surface sample shows an increase in uranium and plutonium concentrations compared to the previous sample likely because of an increase in sludge solids in the current sample. The total uranium concentration in the Tank 43H surface sample is similar to the previous sample results while the plutonium in the Tank 43H sub-surface sample increased relative to the previous analysis. The sum of the major cations versus the sum of the major anions shows a difference of <10% for both samples from Tank 38H sub-surface sample (174 mg/L) increased compared with the previous sample. The Tank 38H surface sample silicon concentrations (27.5 mg/L) is one-half of the previous sample results. The Tank 43H surface sample silicon concentrations compared to the previous sample results indicate Si in the concentration range of 60 to 83 mg/L. Thus, these current samples analyzed from Tanks 38H and 43H show overall silicon concentrations ranging from 27.5 to 174 mg/L.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2023

Platinum Surface Oxide and Oxygen Reduction Reaction Kinetics during Transient Fuel Cell Operation

Pt surface oxide coverage (POC) and Oxygen Reduction Reaction (ORR) were measured under a range of operating conditions in a Proton Exchange Membrane Fuel Cell (PEMFC). Sensitivity analysis suggests that adsorption of sulfonate groups of the ionomer on the Pt surface plays an important role in POC and ORR kinetics. Although both Pt oxide growth and ORR activity decay follow a logarithm of time behavior, it is found that ORR kinetics are affected by at least two different types of Pt oxide. A semi-empirical ORR kinetic model is proposed taking into account the effect of ionomer and Pt oxide types. The model is capable of providing a quantitative prediction of POC and ORR activity over a range of potential, temperature, relative humidity, and time that is relevant to normal PEMFC operation.

Electrochemistry↗

DOE OSTI2023

Adsorbate-Induced Strong Metal–Support Interactions: Implications for Catalyst Design

Since the discovery of strong metal–support interactions (SMSIs) over supported metal catalysts in the 1970s, researchers have studied ways to harness this type of catalyst reconstruction to achieve enhanced stability of metal particles against sintering and to create catalytic sites with novel electronic and bonding properties. The motivation to elucidate performance–structure relationships in catalytic transformations has led researchers to take a closer look into catalytic surfaces under reaction conditions rather than a postreaction analysis. These investigations of operating catalysts have made it clear that SMSIs are more common than initially thought. Recent reports show how various adsorbed species, rather than traditional H 2 /O 2 treatment, can promote SMSI in various catalytic systems, a phenomenon named adsorbate-induced SMSI (A-SMSI). Researching the occurrence of A-SMSI has allowed fundamental understanding of catalyst stability, catalytic rates, and product selectivity. The present Perspective discusses the state-of-the-art regarding A-SMSI, the current challenges, and the opportunities ahead in heterogeneous catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

The Effect of Pressure on NO x Entitlement and Reaction Timescales in a Premixed Axial Jet-In-Crossflow

This paper investigates the pressure dependency of a lean premixed jet injected into a lean vitiated crossflow with an experimentally verified detailed chemistry computational fluid dynamics (CFD) model and 53 species considered. Experimental data were taken in an axially staged combustor with an optically accessible test section, allowing the use of particle image velocimetry (PIV) and CH* chemiluminescence techniques as well as point measurement of species concentration, temperature, and pressure. The experimental data cases at one, three, and five atmospheres were selected to describe the flame stabilization dependency on pressure and gain the required knowledge for an extrapolation to engine condition. Simulated exit nitrogen oxide levels were validated with experimental emission data, and a global emission trend for the NO reduction at elevated pressure and constant turbine inlet temperature level was defined. The nitrogen oxide benefit at elevated operating pressure was justified with the significantly smaller flame surface area: the analysis of the simulated spanwise and top-view profiles showed a relatively short receded core flame with nitrogen oxide production in the center at high pressure relative to a longer and larger shear layer flame at atmospheric condition that produced NO toward the inner and outer side of the flame. Furthermore, decomposition of the Damköhler number revealed the strong influence of the reaction timescales with higher reaction rates at elevated pressure, along with a moderate influence of the turbulent timescales, showing higher turbulence intensity in the lee-side recirculation zone at lower pressure.

03 NATURAL GAS↗

DOE OSTI2023

Towards operational atmospheric correction of airborne hyperspectral imaging spectroscopy: Algorithm evaluation, key parameter analysis, and machine learning emulators

Atmospheric correction of airborne hyperspectral imaging spectroscopy (AHIS) to obtain high-quality surface reflectance is the prerequisite for remote sensing applications. Over the last decades, different atmospheric correction methods have been developed based on radiative transfer models (RTMs), however, the relative performances of different algorithms are unclear. Automated operational atmospheric correction methods to process large-volume AHIS data in a high-accurate and high-throughput manner are still lacking. Therefore, this study proposed an operational atmospheric correction pipeline for deriving surface reflectance from AHIS data. To ensure the accuracy and efficiency of the pipeline, we focused on three specific aspects: (1) selecting a suitable RTM for the development of atmospheric lookup tables (LUTs) by comparing the commercial MODerate resolution atmospheric TRANsmission (MODTRAN) and open-sourced Library for Radiative TRANsfer (LibRadTRAN) models, where the widely-used software, Atmospheric/Topographic Correction for Airborne Imagery (ATCOR), was used as benchmarks; (2) identifying key atmospheric correction parameters and determining suitable sources for parameter retrievals including AHIS, Moderate Resolution Imaging Spectroradiometer (MODIS), and AErosol RObotic NETwork (AERONET); and (3) testing the performance of using machine learning emulators to speed up the RTM-based atmospheric correction. Results indicate that (1) atmospheric correction based on MODTRAN LUTs can produce surface reflectance accurately with mean absolute errors < 0.05 and cosine similarities > 0.98 compared to field measurements, which is comparable to the software ATCOR and slightly outperforms the LibRadTRAN LUTs; (2) sobol global sensitivity analysis demonstrates that in the atmospheric correction, visibility and water vapor are two key parameters that can be accurately derived from AHIS in contrast to MODIS or AERONET data; and (3) Random Forest emulators can produce accurate estimations of surface reflectance with mean absolute errors < 0.03 and cosine similarities > 0.98 for higher processing efficiency and determine a suitable set of wavelengths for retrieving atmospheric visibility and water vapor. In conclusion, the proposed atmospheric correction pipeline also improved the four-stream radiative transfer theory for airborne applications by considering adjacent effects from airborne surrounding pixels and can also be applied for atmospheric correction of hyperspectral data from spaceborne missions.

47 OTHER INSTRUMENTATION↗

DOE OSTI2022

A new perspective on the initial hydrogenation of $\mathrm{TiFe_{0.9}M_{0.1}}$ ($\mathrm{M = V, Cr, Fe, Co, Ni}$) gained from surface oxide analysis and nucleation thermodynamics

Despite the promise of TiFe-based alloys as low-cost solid-state hydrogen storage materials with mild operating conditions and reasonable hydrogen capacity, their initial hydrogenation process is difficult, hindering broad utilization. The effect of alloying element on the initial hydrogenation kinetics of TiFe alloys, TiFe 0.9 M 0.1 (M = V, Cr, Fe, Co and Ni), was evaluated by analyzing changes to the passivating surface oxide layer that inhibits hydrogen permeation, as well as the ease of initial-stage hydrogen absorption into the underlying matrix. X-ray photoelectron spectroscopy and atom probe tomography revealed key variations in surface oxide compositions and thinning of the passivating oxide layer compared to pure TiFe, which suggests suppressed oxide growth by alloying-induced elemental redistribution. At the same time, density functional theory calculations predicted exothermic formation of hydride nuclei when alloying with V or Cr, as well as a reduced nucleation barrier when alloying with Co or Ni. Overall, these results are consistent with the observed experimental trend of the activation kinetics. We propose that improvements in activation kinetics of TiFe with alloying arises from the combined effect of reduced passivating oxide thickness and easier hydride nucleation, offering a starting point for alloy design strategies towards further improvement.

25 ENERGY STORAGE↗

DOE OSTI2026

Quasi-In-Situ Analysis of Electrode Top Atomic Layers via High-Sensitivity Low-Energy Ion Scattering and Potential-Controlled Sample Transfer

Electrocatalytic reactions involve interfacial interactions between the surfaces of electrodes and reactive species at an electrolyte interface. There are presently no universal or unambiguous methods to directly assay the active top atomic layer composition that influences the reactivity of these electrodes under relevant operating conditions. Low-energy ion scattering (LEIS) spectroscopy is a surface characterization technique that yields compositional analysis of the outermost atomic layer of a material, but it must be performed in ultrahigh vacuum (UHV). Application of LEIS measurements to electrochemical materials that are removed from ambient liquid-phase environments thus leaves an open question as to whether the surface that is transferred to UHV is truly the surface that manifested during the electrochemical reaction. Toward the goal of preserving the active surface state, we developed a sample transfer workflow for LEIS enabling air-free removal and drying of an electrode from an electrochemical cell while maintaining control of the potential using an auxiliary electrode. The potential-controlled emersion method was demonstrated to give distinct potential-dependent surface compositions for a Cu−Pd alloy relative to removal after uncontrolled return to open-circuit potential. A Cu-enriched surface was found at anodic potential and a Pd-enriched surface at cathodic potential, suggesting that the approach can be used to retain representative atomic configurations during transfer. Since adsorbates will often persist from the reaction environment, conventional sample pretreatment methods for removal, including atomic O and atomic H exposure, were also contrasted. Both methods were found to differ with results from incidental low-dose depth profiling by the LEIS primary ion source, which removes adventitious species and surface atoms during the course of repeated measurements. These depth profiles were found to be sensitive to sample history and thus qualitatively informative, despite the possible changes induced by ion damage. The results exhibit (i) the need for complete control over the polarization state of the sample at all times (no excursions to open circuit during transfer) and (ii) the utility of low-dose depth profiling to capture changes in the near-surface composition.

Alloys↗

DOE OSTI2024

Net lithium deposition and dominant self-sputtering in lithium tokamak experiment-β with a liquid lithium wall

We observed enhanced net lithium deposition and lithium erosion, possibly dominated by physical sputtering of lithium by lithium-ion bombardment, on the outer plasma-facing surface in the Lithium Tokamak eXperiment-β (LTX-β) during liquid lithium wall operations. Silicon crystal samples with micro-trenches (30 μm × 30 μm × 2–7 μm deep) were exposed to hydrogen plasmas in LTX-β for solid and liquid lithium wall operations. Post-mortem analysis using X-ray photoelectron spectroscopy combined with argon ion sputtering measured net lithium deposition of 8.2 or 21 nm on the silicon crystal surface exposed for ~ 50 repeated shots of ~ 50-ms hydrogen plasma discharges during the liquid lithium wall operations at a vessel temperature of 475 K. Energy dispersive X-ray spectroscopy measured oxygen concentration patterns on the micro-trench floors, which were due to oxidized lithium deposition. Using the inhomogeneous oxygen concentration pattern caused by an ion-shadowing effect associated with the micro-trench’s geometric structure, we determined a polar incident ion direction of 68.4 ± 1.6° referenced to the surface normal direction. This observation was well-explained by the hypothesis that self-sputtering of Li was a dominant lithium erosion source in addition to lithium sputtering by hydrogen bombardment.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗