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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on ThH28C12(N2O3)6 by Materials Project

Th(CO2)8(CN3H6)4(H2O)2 crystallizes in the monoclinic C2/c space group. The structure is one-dimensional and consists of sixteen guanidinium molecules; eight water molecules; and two Th(CO2)8 ribbons oriented in the (0, 0, 1) direction. In each Th(CO2)8 ribbon, Th4+ is bonded in a 10-coordinate geometry to ten O2- atoms. There are a spread of Th–O bond distances ranging from 2.45–2.62 Å. There are four inequivalent C+3.33+ sites. In the first C+3.33+ site, C+3.33+ is bonded in a bent 120 degrees geometry to two O2- atoms. Both C–O bond lengths are 1.27 Å. In the second C+3.33+ site, C+3.33+ is bonded in a bent 120 degrees geometry to two O2- atoms. There is one shorter (1.25 Å) and one longer (1.29 Å) C–O bond length. In the third C+3.33+ site, C+3.33+ is bonded in a bent 120 degrees geometry to two O2- atoms. There is one shorter (1.24 Å) and one longer (1.29 Å) C–O bond length. In the fourth C+3.33+ site, C+3.33+ is bonded in a bent 120 degrees geometry to two O2- atoms. There is one shorter (1.25 Å) and one longer (1.29 Å) C–O bond length. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one C+3.33+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one C+3.33+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to one C+3.33+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one C+3.33+ atom. In the fifth O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one C+3.33+ atom. In the sixth O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one C+3.33+ atom. In the seventh O2- site, O2- is bonded in a single-bond geometry to one C+3.33+ atom. In the eighth O2- site, O2- is bonded in a single-bond geometry to one C+3.33+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ThAlRh by Materials Project

ThRhAl crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. Th is bonded in a 5-coordinate geometry to five Rh atoms. All Th–Rh bond lengths are 3.01 Å. There are two inequivalent Rh sites. In the first Rh site, Rh is bonded in a 9-coordinate geometry to three equivalent Th and six equivalent Al atoms. All Rh–Al bond lengths are 2.67 Å. In the second Rh site, Rh is bonded in a 9-coordinate geometry to six equivalent Th and three equivalent Al atoms. All Rh–Al bond lengths are 2.84 Å. Al is bonded in a 4-coordinate geometry to four Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ThP2H2CO8 by Materials Project

Th(PO3)2CH2O2 crystallizes in the orthorhombic Pna2_1 space group. The structure is three-dimensional and consists of four hydrogen peroxide;methane molecules and one Th(PO3)2 framework. In the Th(PO3)2 framework, Th4+ is bonded in an octahedral geometry to six O2- atoms. There are a spread of Th–O bond distances ranging from 2.28–2.37 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. All P–O bond lengths are 1.54 Å. In the second P5+ site, P5+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There is one shorter (1.54 Å) and two longer (1.55 Å) P–O bond length. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one P5+ atom. In the second O2- site, O2- is bonded in a distorted linear geometry to one Th4+ and one P5+ atom. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a distorted linear geometry to one Th4+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ThUTe2 by Materials Project

UThTe2 is Caswellsilverite-like structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. U is bonded to six Te atoms to form UTe6 octahedra that share corners with six equivalent UTe6 octahedra, edges with four equivalent UTe6 octahedra, and edges with eight equivalent ThTe6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (3.12 Å) and two longer (3.13 Å) U–Te bond lengths. Th is bonded to six Te atoms to form ThTe6 octahedra that share corners with six equivalent ThTe6 octahedra, edges with four equivalent ThTe6 octahedra, and edges with eight equivalent UTe6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (3.12 Å) and two longer (3.13 Å) Th–Te bond lengths. There are two inequivalent Te sites. In the first Te site, Te is bonded to four equivalent U and two equivalent Th atoms to form a mixture of edge and corner-sharing TeTh2U4 octahedra. The corner-sharing octahedral tilt angles are 0°. In the second Te site, Te is bonded to two equivalent U and four equivalent Th atoms to form TeTh4U2 octahedra that share corners with six equivalent TeTh4U2 octahedra and edges with twelve TeTh2U4 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf3Th by Materials Project

ThHf3 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Th is bonded to twelve Hf atoms to form ThHf12 cuboctahedra that share corners with six equivalent ThHf12 cuboctahedra, corners with twelve equivalent HfHf8Th4 cuboctahedra, edges with eighteen HfHf8Th4 cuboctahedra, faces with eight equivalent ThHf12 cuboctahedra, and faces with twelve HfHf8Th4 cuboctahedra. There are six shorter (3.33 Å) and six longer (3.34 Å) Th–Hf bond lengths. There are two inequivalent Hf sites. In the first Hf site, Hf is bonded to four equivalent Th and eight Hf atoms to form HfHf8Th4 cuboctahedra that share corners with four equivalent ThHf12 cuboctahedra, corners with fourteen HfHf8Th4 cuboctahedra, edges with six equivalent ThHf12 cuboctahedra, edges with twelve HfHf8Th4 cuboctahedra, faces with four equivalent ThHf12 cuboctahedra, and faces with sixteen HfHf8Th4 cuboctahedra. There are a spread of Hf–Hf bond distances ranging from 3.10–3.55 Å. In the second Hf site, Hf is bonded to four equivalent Th and eight equivalent Hf atoms to form HfHf8Th4 cuboctahedra that share corners with four equivalent ThHf12 cuboctahedra, corners with fourteen HfHf8Th4 cuboctahedra, edges with six equivalent ThHf12 cuboctahedra, edges with twelve equivalent HfHf8Th4 cuboctahedra, faces with four equivalent ThHf12 cuboctahedra, and faces with sixteen HfHf8Th4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaNa6Th(CO4)6 by Materials Project

Na6BaTh(CO4)6 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. Na is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Na–O bond distances ranging from 2.33–2.85 Å. Ba is bonded to twelve O atoms to form BaO12 cuboctahedra that share faces with two equivalent ThO12 cuboctahedra. There are six shorter (2.89 Å) and six longer (2.95 Å) Ba–O bond lengths. Th is bonded to twelve O atoms to form ThO12 cuboctahedra that share faces with two equivalent BaO12 cuboctahedra. There are six shorter (2.53 Å) and six longer (2.71 Å) Th–O bond lengths. C is bonded in a trigonal planar geometry to three O atoms. There is one shorter (1.29 Å) and two longer (1.30 Å) C–O bond length. There are four inequivalent O sites. In the first O site, O is bonded in a distorted single-bond geometry to three equivalent Na, one Th, and one C atom. In the second O site, O is bonded in a 1-coordinate geometry to one Na, one Ba, one Th, and one C atom. In the third O site, O is bonded in a distorted T-shaped geometry to two equivalent Na and one C atom. In the fourth O site, O is bonded in a distorted T-shaped geometry to two equivalent Na and one Ba atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y2Th8O19 by Materials Project

Th8Y2O19 is alpha bismuth trifluoride-derived structured and crystallizes in the tetragonal P-4m2 space group. The structure is three-dimensional. there are four inequivalent Th4+ sites. In the first Th4+ site, Th4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Th–O bond distances ranging from 2.35–2.46 Å. In the second Th4+ site, Th4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Th–O bond distances ranging from 2.39–2.42 Å. In the third Th4+ site, Th4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are two shorter (2.39 Å) and six longer (2.40 Å) Th–O bond lengths. In the fourth Th4+ site, Th4+ is bonded in a body-centered cubic geometry to eight O2- atoms. All Th–O bond lengths are 2.39 Å. Y3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Y–O bond distances ranging from 2.23–2.48 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded to four Th4+ atoms to form a mixture of edge and corner-sharing OTh4 tetrahedra. In the second O2- site, O2- is bonded to four Th4+ atoms to form a mixture of edge and corner-sharing OTh4 tetrahedra. In the third O2- site, O2- is bonded to four Th4+ atoms to form a mixture of edge and corner-sharing OTh4 tetrahedra. In the fourth O2- site, O2- is bonded to four equivalent Th4+ atoms to form a mixture of edge and corner-sharing OTh4 tetrahedra. In the fifth O2- site, O2- is bonded to two equivalent Th4+ and two equivalent Y3+ atoms to form OY2Th2 tetrahedra that share corners with twelve OY2Th2 tetrahedra and edges with six OTh4 tetrahedra. In the sixth O2- site, O2- is bonded to four Th4+ atoms to form OTh4 tetrahedra that share corners with sixteen OTh4 tetrahedra and edges with six OY2Th2 tetrahedra. In the seventh O2- site, O2- is bonded to two equivalent Th4+ and two equivalent Y3+ atoms to form OY2Th2 tetrahedra that share corners with fourteen OTh4 tetrahedra and edges with five OY2Th2 tetrahedra. In the eighth O2- site, O2- is bonded to four equivalent Y3+ atoms to form a mixture of edge and corner-sharing OY4 tetrahedra. In the ninth O2- site, O2- is bonded to four Th4+ atoms to form a mixture of edge and corner-sharing OTh4 tetrahedra. In the tenth O2- site, O2- is bonded to four Th4+ atoms to form a mixture of edge and corner-sharing OTh4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Search for the production of a Higgs boson in association with a single top quark in pp collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

A search for the production of a Higgs boson in association with a single top quark, tH, is presented. The analysis uses proton-proton collision data corresponding to an integrated luminosity of 140 fb −1 at a centre-of-mass energy of 13 TeV, collected by the ATLAS detector at the LHC. The search targets Higgs-boson decays into $b\bar{b}$, WW * , ZZ * , and ττ, accompanied by an isolated lepton (electron or muon) from the top-quark decay. Multivariate techniques are employed to enhance the separation between signal and background processes. The observed signal strength, μ tH , defined as the ratio between the measured cross-section and the predicted Standard Model value, is μ tH = 8.1 ± 2.6 (stat.) ± 2.0 (syst.). The significance of the observed (expected) signal above the background-only expectation is 2.8 (0.4) standard deviations. The corresponding observed (expected) upper limit at the 95% confidence level on the tH cross-section is found to be 13.9 (6.1) times the value predicted by the Standard Model. An interpretation with an inverted sign of the top-quark Yukawa coupling is performed, and the signal strength and corresponding limit are reported.

Hadron-Hadron Scattering↗
DOE OSTI2023

Results from a controlled depleted uranium metal casting experiment designed to investigate nuclear Forensic Radiochronometry Signatures

The accurate interpretation of uranium metal 230 Th/ 234 U and 231 Pa/ 235 U radiochronometry model ages requires an understanding of how uranium parent nuclides and decay progeny ( 230 Th and 231 Pa) behave during uranium metal casting. In order to directly measure the spatial distribution of 230 Th and 231 Pa in uranium metal before and after vacuum induction melting (VIM), Los Alamos National Laboratory identified uranium metal feedstock, characterized the metal feedstock, conducted a controlled casting experiment of an approximately 120 kg uranium metal rod, and characterized the cast metal. Herein this study presents radiochronometry results and quantified 230 Th and 231 Pa VIM separation factors from bulk uranium.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2024

Optimizing iodine adsorption in functionalized metal-organic frameworks via an unprecedented positional isomerism strategy

Porous metal–organic frameworks (MOFs) have emerged as highly promising adsorbents for capturing radioiodine, a predominant fission product released during nuclear fuel reprocessing. However, systematic investigations into the correlation between MOF structure and iodine uptake capacity remain scarce. Here, we present a novel approach to enhance the iodine adsorption capacity of MOFs by optimizing linker functionalization. Using ligand-functionalized thorium-based MOFs as a structural platform, we demonstrate that ortho-amino-substitution near the node of the dicarboxylate linker significantly increases iodine adsorption capacity compared to meta-amino-substitution, where the amino groups are directed away from the node. Specifically, ortho-substituted Th-UiO-68-3,3”-(NH 2 ) 2 exhibits higher iodine uptake capacities than the meta-substituted Th-UiO-68-2,2”-(NH 2 ) 2 via both vapor diffusion-based (2.042 vs. 1.087 g/g) and solution-based (0.841 vs. 0.784 g/g) processes. Notably, the I 2 vapor adsorption capacity (2.042 g/g) of Th-UiO-68-3,3”-(NH 2 ) 2 represents the second highest among all reported Th-MOFs. Pair distribution function (PDF) studies reveal that the superior iodine uptake performance of ortho-functionalized MOFs can be attributed to the reduced steric hindrance of the amino groups compared with the meta-substituted variants. Finally, this research highlights how positional isomerism and its subtle alterations can significantly influence host–guest interactions, extending beyond simple structural considerations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Estimation of stress and stress-induced permeability change in a geological nuclear waste repository in a thermo-hydrologically coupled simulation

Geologic disposal is a promising solution for a safe permanent isolation of accumulated high-level nuclear waste from nuclear powerplants. The behavior of host rock is highly coupled thermally, hydromechanically, and chemically. Numerical simulations of such coupled phenomena for the extremely long term (>100,000 years) and large length scale (>1 km) of geologic disposal remain to be computationally challenging. In this study, a methodology has been developed to approximate stress and stress-induced permeability change in host rock using only thermo-hydrological (TH) variables. A coupled thermo-hydromechanical (THM) simulation is carried out using TOUGH-FLAC simulator to model THM behaviors of a generic nuclear waste repository, in order to evaluate the performance of the developed methodology, which is implemented in a coupled TH simulation. Results show that stress and permeability change estimated by the developed methodology in the TH-coupled simulation match those calculated in the THM-coupled simulation over the simulated timeframe of over 10,000 years. Details about errors in stress and permeability estimates accrued by the developed methodology are discussed here. The developed methodology will help incorporate stress-induced permeability change into existing TH simulators for the long-term radionuclide transport in geologic disposal.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

f-Element complexes with benzyl and cyclohexyl substituted trihydroborates

Actinide complexes containing the simplest borohydrides (BH 4 ) 1- and (MeBH 3 ) 1- can exhibit remarkably highly volatility, which creates unique hazards and handling challenges, especially when making measurements on solid samples under vacuum. Here we describe efforts to prepare new actinide borohydride complexes with attenuated volatility by adding bulkier benzyl (Bn) and cyclohexyl (Cy) substituents to boron. Reactions of ThCl 4 , UI 3 (thf) 4 , and NdI 3 with the mixed alkali metal salt Li/K(BnBH 3 )(thf) n yielded Th(BnBH 3 ) 4 (thf) 2 , U(BnBH 3 ) 4 (thf) 2 , and K[Nd(BnBH 3 ) 4 ], respectively. Notable amongst these, the reaction with UI 3 (thf) 4 proceeds via oxidation of U(III) to U(IV) despite the presence of reducing borohydride ligands. Similarly, reactions of the same metal halides with four equivalents of Li(CyBH 3 )(Et 2 O) n yielded Th(CyBH 3 ) 4 , U(CyBH 3 ) 4 (thf) 2 , and [Li(Et 2 O) 3 ][Nd(CyBH 3 ) 4 ]. Single crystal X-ray diffraction studies of the M(BnBH 3 ) 4 (thf) 2 complexes with M = Th and U confirmed their formulations. Furthermore, the complexes have approximate D 2d point group symmetry and adopt bicapped hexagonal antiprismatic coordination geometries with axial thf ligands and κ 3 -BnBH 3 ligands bound in the equatorial plane. K[Nd(BnBH 3 ) 4 ] and [Li(Et 2 O) 3 ][Nd(CyBH 3 ) 4 ], which were prepared for comparison to U(III) complexes that were unsuccessfully targeted, were also structurally characterized to reveal complex anions with tetrahedral arrangements of trihydroborate ligands bound to Nd(III). Crystals obtained for Th(CyBH 3 ) 4 and U(CyBH 3 ) 4 (thf) 2 were not suitable for XRD studies, but 1 H and 11 B NMR spectra were consistent with their formulations. Collectively, these complexes represent rare examples of structurally characterized f-element trihydroborate complexes with carbon substituents other than methyl.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Leveraging Nitrogen Linkages in the Formation of a Porous Thorium–Organic Nanotube Suitable for Iodine Capture

We report the synthesis, characterization, and iodine capture application of a novel thorium–organic nanotube, TSN-626, [Th 6 O 4 (OH) 4 (C 6 H 4 NO 2 ) 7 (CHO 2 ) 5 (H 2 O) 3 ]·3H 2 O. The classification as a metal–organic nanotube (MONT) distinguishes it as a rare and reduced dimensionality subset of metal–organic frameworks (MOFs); the structure is additionally hallmarked by low node connectivity. TSN-626 is composed of hexameric thorium secondary building units and mixed O/N-donor isonicotinate ligands that demonstrate selective ditopicity, yielding both terminating and bridging moieties. Because hard Lewis acid tetravalent metals have a propensity to bind with electron donors of rival hardness (e.g., carboxylate groups), such Th–N coordination in a MOF is uncommon. However, the formation of key structural Th–N bonds in TSN-626 cap some of the square antiprismatic metal centers, a position usually occupied by terminal water ligands. TSN-626 was characterized by using complementary analytical and computational techniques: X-ray diffraction, vibrational spectroscopy, N 2 physisorption isotherms, and density functional theory. TSN-626 satisfies design aspects for the chemisorption of iodine. The synergy between accessibility through pores, vacancies at the metal–oxo nodes, and pendent N-donor sites allowed a saturated iodine loading of 955 mg g –1 by vapor methods. Furthermore, the crystallization of TSN-626 diversifies actinide–MOF linker selection to include soft electron donors, and these Th–N linkages can be leveraged for the investigation of metal-to-ligand bonding and unconventional topological expressions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A Uranium(II) Arene Complex That Acts as a Uranium(I) Synthon

We report two-electron reduction of the amidate-supported U(III) mono(arene) complex U(TDA) 3 (2) with KC 8 yields the anionic bis(arene) complex [K[2.2.2]cryptand][U(TDA) 2 ] (3) (TDA = N-(2,6-di-isopropylphenyl)pivalamido). EPR spectroscopy, magnetic susceptibility measurements, and calculations using DFT as well as multireference CASSCF methods all provide strong evidence that the electronic structure of 3 is best represented as a 5f 4 U(II) metal center bound to a monoreduced arene ligand. Reactivity studies show 3 reacts as a U(I) synthon by behaving as a two-electron reductant toward I 2 to form the dinuclear U(III)–U(III) triiodide species [K[2.2.2]cryptand][(UI(TDA) 2 ) 2 (μ-I)] (6) and as a three-electron reductant toward cycloheptatriene (CHT) to form the U(IV) complex [K[2.2.2]cryptand][U(η 7 -C 7 H 7 )(TDA) 2 (THF)] (7). The reaction of 3 with cyclooctatetraene (COT) generates a mixture of the U(III) anion [K[2.2.2]cryptand][U(TDA) 4 ] (1-crypt) and U(COT) 2 , while the addition of COT to complex 2 instead yields the dinuclear U(IV)–U(IV) inverse sandwich complex [U(TDA) 3 ] 2 (μ-η 8 :η 3 -C 8 H 8 ) (8). Two-electron reduction of the homoleptic Th(IV) amidate complex Th(TDA) 4 (4) with KC 8 gives the mono(arene) complex [K[2.2.2]cryptand][Th(TDA) 3 (THF)] (5). The C–C bond lengths and torsion angles in the bound arene of 5 suggest a direduced arene bound to a Th(IV) metal center; this conclusion is supported by DFT calculations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Concurrence of quantum anomalous Hall and topological Hall effects in magnetic topological insulator sandwich heterostructures

The quantum anomalous Hall (QAH) effect is a consequence of non-zero Berry curvature in momentum space. The QAH insulator harbours dissipation-free chiral edge states in the absence of an external magnetic field. Yet, the topological Hall (TH) effect, a hallmark of chiral spin textures, is a consequence of real-space Berry curvature. Herein, by inserting a topological insulator (TI) layer between two magnetic TI layers, we realized the concurrence of the TH effect and the QAH effect through electric-field gating. The TH effect is probed by bulk carriers, whereas the QAH effect is characterized by chiral edge states. The appearance of the TH effect in the QAH insulating regime is a consequence of chiral magnetic domain walls that result from the gate-induced Dzyaloshinskii–Moriya interaction and occurs during the magnetization reversal process in the magnetic TI sandwich samples. The coexistence of chiral edge states and chiral spin textures provides a platform for proof-of-concept dis- sipationless spin-textured spintronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Structural chemistry of penta- and hexanitrato thorium($\tiny{IV}$) complexes isolated using N–H donors

In this study, a series of fifteen tetravalent thorium phases were prepared. The compounds were isolated from acidic aqueous nitrate solutions using protonated nitrogen heterocycles of varying hydrogen-bond donation strength. Structural analysis via single crystal X-ray diffraction showed that the structures are built from pentanitrato, [Th(NO 3 ) 5 (H 2 O) 2 ] 1- , and hexanitrato, [Th(NO 3 ) 6 ] 2- , molecular units, with the latter being far more prevalent in the solid state. The vibrational properties of the compounds were examined using Raman and IR spectroscopy; the spectra are dominated by stretches characteristic of nitrate and the organic ions. The relative energetics of nitrate complexation was examined using electronic structure theory. These results confirmed that there are clear thermodynamic sinks for the penta- and hexanitrato structural units that were observed experimentally. Additionally, electrostatic surface potentials (ESPs) were calculated in an effort to better understand the counterion stabilization of the complexes. The ESP surfaces showed that the position of the water and nitrate molecules and the coordination geometry of the metal complex had a clear effect on the polarizability of the two structural motifs. Despite limited speciation of the Th–nitrate structural units, the compounds exhibit rich supramolecular chemistry resulting from hydrogen bonding of the Th complexes with the organic N–H donors and π–π stacking interactions from the protonated N-heterocycles.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Statistical analysis of magnetic divertor configuration influence on H-mode transitions

DIII-D plasmas are compared for two upper divertor configurations: with the outer strike point on the small angle slot (SAS) divertor target and with the outer strike point on the horizontal divertor target (HT). Scanning the vertical distance between the magnetic null point and the divertor target over a range 0.10–0.16 m is shown to increase the threshold power, $P_\mathrm{th}$, and edge plasma power, $P_\mathrm{Loss},$ for the low-to-high confinement (L–H) and H–L transitions respectively, by up to a factor of 1.4. The X-point height scans were performed at three L-mode core plasma line average electron densities, $\bar{n}_\mathrm{e} = $ 1.2, 2.2 and 3.6 $\times 10^{19}\,\mathrm{m}^{-3}$, to investigate the density dependence of divertor magnetic configuration influence on $P_\mathrm{th}$. The X-point height, $Z_\textrm{x-pt}$, was further extended across the range 0.16–0.22 m with the more open HT divertor configuration, for which a clear decrease in $P_\mathrm{th}$ with increasing $Z_\textrm{x-pt}$ is observed. The dependence of $P_\textrm{th}$ on divertor magnetic geometry is further investigated using a time-dependent probability density function (PDF) model and information geometry to elucidate the roles played by pedestal plasma turbulence and perpendicular velocity flows. The degree of stochasticity of the plasma turbulence is observed to be sensitive to the plasma heating rate. The calculated square of the information rate shows changes in the relative density fluctuations and perpendicular velocity PDFs begin 2–5 ms prior to the L–H transition for three plasmas; providing a crucial measurement of the dynamic timescale of external transport barrier formation. Additionally, both information length and rate provide potential predictors of the L–H transition for these plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Investigating the role of edge neutrals in exciting tearing mode activity and achieving flat temperature profiles in LTX-β

Abstract We present observations, numerical simulations, and analysis from experiments in the Lithium Tokamak Experiment-Beta (LTX- β ) in which the electron temperature profile ( T e ( r )) shifts from flat to peaked and a tearing mode is also destabilized when the average density ( n e ave ) exceeds ∼10 19 m −3 . Flat T e ( r ) is obtained routinely in LTX- β , with a lithium coated, low-recycling first wall, once the external fueling is stopped and density decays [Boyle et al 2023 Nucl. Fusion 63 056020]. In the present experiment, flat T e profiles can be sustained while maintaining constant n e ave below a line averaged density threshold ( n e ave th ) of ∼10 19 m −3 . Above n e ave th , T e ( r ) shifts from flat to peaked and a tearing mode is destabilized. Due to low recycling, the achieved n e ave can be controlled precisely by external fueling and hence, a certain threshold of the edge neutral inventory from the external fueling is experimentally manifested through n e ave th . The goal of the present work is to investigate the role of edge neutrals in determining T e ( r ) and MHD stability in the unique low-recycling regime of LTX- β . Our hypothesis is that the peaking of T e ( r ) beyond n e ave th is due ultimately to the edge cooling by the cold neutrals beyond a critical fueling flux. At lower fueling flux, flat T e ( r ) results in broader pressure profile and lower resistivity, which in turn stabilizes the tearing mode. This hypothesis is supported by edge neutral density estimation by DEGAS 2 code. Mode analysis by singular value decomposition confirms the tearing mode structure to be m / n = 2/1 ( m and n being the poloidal and toroidal mode numbers). Linear tearing stability analysis with M3D-C1 predicts that plasmas with n e ave > 10 19 are highly susceptible to a n = 1 tearing mode. ORBIT simulations, however, confirmed that the tearing modes do not contribute to the loss of fast ions from neutral beam injection. This study shows for the first time that the neutral inventory at the edge could be one of the deciding factors for the achievability of the unique operation regime of flat T e ( r ) and the excitation of tearing activity that could be disruptive for the plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗