Experiments were performed in the Pilot-PSI linear plasma device to study the formation of helium-induced nanostructures under high heat fluxes (>10MWm−2), the erosion of a tungsten surface at the ...elevated temperatures where those structures typically form and most importantly the behavior of a helium-induced fibreform structure during ELM-like pulses. A strong correlation between the characteristic size of the helium-induced morphology and the size of the voids observed in the near-surface region has been found, and both increase in size with increasing temperatures. Temperature-dependent erosion of tungsten surfaces was observed despite the ion energy being below the sputtering threshold, with an exponential increase of the erosion for temperatures higher than 2400°C. The same effect was observed during ELM-like plasma pulses. Finally, a complete disappearance of the tungsten fibreform structure was observed after only one plasma pulse for energy densities higher than 0.5MJm−2.
Growth of tungsten nano-tendrils (“fuzz”) has been observed for the first time in the divertor region of a high-power density tokamak experiment. After 14 consecutive helium L-mode discharges in ...Alcator C-Mod, the tip of a tungsten Langmuir probe at the outer strike point was fully covered with a layer of nano-tendrils. The depth of the W fuzz layer (600±150nm) is consistent with an empirical growth formula from the PISCES experiment. Re-creating the C-Mod exposures as closely as possible in Pilot-PSI experiment can produce nearly-identical nano-tendril morphology and layer thickness at surface temperatures that agree with uncertainties with the C-Mod W probe temperature data. Helium concentrations in W fuzz layers are measured at 1–4at.%, which is lower than expected for the observed sub-surface voids to be filled with several GPa of helium pressure. This possibly indicates that the void formation is not pressure driven.
Helium (He) concentration depth profiles of evolving tungsten (W) nanostructures have been measured for the first time using in situ Elastic Recoil Detection (ERD) throughout plasma irradiation. ...Exposures resulting in fuzzy and non-fuzzy surfaces were analyzed in order to illuminate the role of He during the development of these surface morphologies. ERD was performed on samples with surface temperatures from Ts=530–1100K and irradiated by He flux densities of ΓHe∼1020–1022 m−2s−1. He concentration profiles in samples that developed either non-fuzzy or fuzzy surfaces are uniformly shaped with concentrations of 1.5–7at.%, which is presumed to be too low for pressure driven growth models. Therefore, surface morphology changes are not perpetuated by continuous bubble bursting deformation. Also, a threshold in He flux density above 1020m−2s−1 is suggested by using in situ ERD to monitor the depth profile evolution of the He-rich layer while changing the flux during exposure.
Protein−carbohydrate interactions play a critical role in many biological recognition events. Multivalent therapeutic agents that utilize protein−carbohydrate interactions have proven difficult to ...design, primarily because the fundamental requirements of protein−carbohydrate interactions are not well understood. Here, we report a systematic study of the effect on lectin binding of varying the loading of mannose surface residues on generations three through six PAMAM dendrimers. The degree of mannose functionalization was controlled by stoichiometric addition, and dendrimers were characterized using NMR and MALDI-TOF MS. Hemagglutination assays and quantitative precipitation assays were performed to determine the relative activity of the dendrimers. Using the mannose/hydroxyl-functionalized dendrimers reported here, we could systematically control both the degree of lectin clustering and the overall activity of the lectin with the dendrimer.
•Porous tungsten made via spark plasma sintering.•Incorporation of liquid lithium in porous W investigated.•liquid Li percolation into porous W substrate.•Enhanced liquid Li wetting on Li-percolated ...porous W substrate.•Deuterium found in bulk of hybrid porous W/liquid Li.
This work explores the concept of a hybrid material system designed to protect the plasma from high-Z material emission while also protecting an underlying high-Z wall material from erosion by integrating a low-Z component in the liquid phase. Plasma-surface interaction properties of a porous tungsten (W)-liquid metal hybrid system, having the favorable bulk thermomechanical properties of W while serving as a scaffold for a liquid metal with self-healing and radiative vapor shielding characteristics, are examined. W-substrates with 70% density of bulk W and 1–5 μm sized pores have been fabricated with 50-nm W powders using spark plasma sintering. Enhanced lithium (Li) wettability, driven by percolation through the porous W architecture, is demonstrated with in-situ liquid Li drop measurements. Results show complete wetting of liquid Li at 250 °C in the porous W, 100 °C lower temperature than what has been observed on traditional W surfaces. In operando ion beam analysis of Li films deposited on porous W substrates provides microscopic evidence of Li percolation into the substrate and a first look at D retention up to a depth of 100 nm after plasma exposure at a flux of 1020 m−2s−1, 250 eV/amu D+ plasma to a fluence of 1.16 × 1023 m−2 at a temperature of 200 °C.
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