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All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Parametric study of Alfvénic instabilities driven by runaway electrons during the current quench in DIII-D

Abstract To avoid or mitigate runaway electron (RE) beams in ITER, RE-driven instabilities are actively studied as a complimentary technique to massive material injection. In this work we report experimental dependencies of Alfvénic instabilities driven by REs during the current quench in DIII-D on plasma and material injection parameters. These instabilities, observed in the frequency range of 0.1–3 MHz, correlate with increased RE loss and thus may play a role in non-sustained RE beams. It was found that as the toroidal magnetic field ( B T ) decreases, the RE population becomes more energetic, the energy of instabilities increases, and no RE beam is observed when the maximum energy of REs exceeds 15 MeV (or when B T is below 1.8 T). Analysis of disruptions at plasma core temperature ( T e ) of 1 keV and 8 keV shows that the RE population is much less energetic (with the maximum energy of only about 3 MeV) when T e is high, and no instabilities are observed in this case. Besides disruptions above caused by Ar injection, cases with Ne and D 2 injections were also studied. Both Ne and D 2 injections cause no sustained RE beams, however, for different reasons. Measurements of the instability polarization indicate that it is of predominantly compressional nature at the edge, which is consistent with modeling suggesting excitation of compressional Alfvén eigenmodes. However, drive of global Alfvén eigenmodes is also possible at low frequencies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Variability of MHD instabilities in benign termination of high-current runaway electron beams in the JET and DIII-D tokamaks

Benign termination, in which magnetohydrodynamic (MHD) instabilities deconfine runaway electrons (REs) following hydrogenic injections, is a promising strategy for mitigating dangerous RE loads after disruptions. Recent experiments on the Joint European Torus (JET) have explored this scenario at higher pre-disruptive plasma currents than are achievable on other devices, revealing challenges in obtaining benign terminations at I p ≥2.5 MA. This work analyzes the evolution of these high-current RE beams and their terminating MHD events using fast magnetic sensor measurements and EFIT equilibrium reconstructions for approximately 40 JET and 20 DIII-D tokamak discharges. On JET, unsuccessful non-benign terminations occur at low edge safety factor (q edge ≈ 2), and are preceded by intermittent, non-terminating MHD events at higher rational qedge. Trends in the internal inductance I i indicate more peaked RE current profiles in the high-I p non-benign population, which may hinder successful recombination through re-ionization of the companion plasma. In contrast, benign terminations on JET typically occur at higher q edge ≥3 and exhibit less peaked RE current profiles. DIII-D displays a broader range of terminating edge safety factors, again correlated with the measured values. Across both tokamaks, the RE current peaking is therefore found to determine which MHD instability boundary is encountered, a result confirmed by linear resistive MHD modeling with the CASTOR3D code. Measured growth rates are similar for benign and non-benign cases, indicating that ideal MHD timescales at low density after hydrogenic injection do not alone explain efficient RE deconfinement. Instead, non-benign cases are most readily characterized by their comparably lower overall MHD perturbation amplitudes δB. These observations suggest that the interplay between ideal and resistive dynamics governs the termination process, with implications for extrapolating benign RE termination to high-I p reactor scenarios.

MHD instabilities↗
DOE OSTI2020

Direct CP violation and the ΔI=1/2 rule in K→ππ decay from the standard model

We present a lattice QCD calculation of the Δ I = 1 / 2 , K → π π decay amplitude A 0 and ϵ ' , the measure of direct C P violation in K → π π decay, improving our 2015 calculation [1] of these quantities. Both calculations were performed with physical kinematics on a 32 3 × 64 lattice with an inverse lattice spacing of a - 1 = 1.3784 ( 68 ) GeV . However, the current calculation includes nearly 4 times the statistics and numerous technical improvements allowing us to more reliably isolate the π π ground state and more accurately relate the lattice operators to those defined in the standard model. We find Re ( A 0 ) = 2.99 ( 0.32 ) ( 0.59 ) × 10 - 7 GeV and Im ( A 0 ) = - 6.98 ( 0.62 ) ( 1.44 ) × 10 - 11 GeV , where the errors are statistical and systematic, respectively. The former agrees well with the experimental result Re ( A 0 ) = 3.3201 ( 18 ) × 10 - 7 GeV . These results for A 0 can be combined with our earlier lattice calculation of A 2 [2] to obtain Re ( ϵ ' / ϵ ) = 21.7 ( 2.6 ) ( 6.2 ) ( 5.0 ) × 10 - 4 , where the third error represents omitted isospin breaking effects, and Re ( A 0 ) / Re ( A 2 ) = 19.9 ( 2.3 ) ( 4.4 ) . The first agrees well with the experimental result of Re ( ϵ ' / ϵ ) = 16.6 ( 2.3 ) × 10 - 4 . A comparison of the second with the observed ratio Re ( A 0 ) / Re ( A 2 ) = 22.45 ( 6 ) , demonstrates the standard model origin of this “ Δ I = 1 / 2 rule” enhancement.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Maximizing Strength: The Stimuli and Mediators of Strength Gains and Their Application to Training and Rehabilitation

Abstract Spiering, BA, Clark, BC, Schoenfeld, BJ, Foulis, SA, and Pasiakos, SM. Maximizing strength: the stimuli and mediators of strength gains and their application to training and rehabilitation. J Strength Cond Res 37(4): 919–929, 2023—Traditional heavy resistance exercise (RE) training increases maximal strength, a valuable adaptation in many situations. That stated, some populations seek new opportunities for pushing the upper limits of strength gains (e.g., athletes and military personnel). Alternatively, other populations strive to increase or maintain strength but cannot perform heavy RE (e.g., during at-home exercise, during deployment, or after injury or illness). Therefore, the purpose of this narrative review is to (a) identify the known stimuli that trigger gains in strength; (b) identify the known factors that mediate the long-term effectiveness of these stimuli; (c) discuss (and in some cases, speculate on) potential opportunities for maximizing strength gains beyond current limits; and (d) discuss practical applications for increasing or maintaining strength when traditional heavy RE cannot be performed. First, by conceptually deconstructing traditional heavy RE, we identify that strength gains are stimulated through a sequence of events, namely: giving maximal mental effort, leading to maximal neural activation of muscle to produce forceful contractions, involving lifting and lowering movements, training through a full range of motion, and (potentially) inducing muscular metabolic stress. Second, we identify factors that mediate the long-term effectiveness of these RE stimuli, namely: optimizing the dose of RE within a session, beginning each set of RE in a minimally fatigued state, optimizing recovery between training sessions, and (potentially) periodizing the training stimulus over time. Equipped with these insights, we identify potential opportunities for further maximizing strength gains. Finally, we identify opportunities for increasing or maintaining strength when traditional heavy RE cannot be performed.

Sport Sciences↗
DOE OSTI2021

Synthesis and Single Crystals of Refractory Oxides of Lanthanides and Thorium

At the completion of this program, we can report that we developed a considerable degree of technical improvements in our ability to perform hydrothermal reactions at high temperatures and pressures. We can now routinely perform reactions at 700-750°C and 200 MPa. Currently we are in the process of exploiting this new technology synthesizing a range of exotic new materials investigating relatively poorly understood materials. Our initial efforts focused on the chemistry of rare earth oxides with tetravalent and pentavalent oxides. We recently published a study of the lanthanides with Nb 5+ and Ta 5+ ions, where we grew oxides such as RENdO 4 and RETaO 4 as high quality single crystals. These compounds were targeted as potential hosts for luminescent and scintillation materials, particularly given that they are among the densest oxide hosts and hence have good potential as absorbers for high energy radiation like X-rays and gamma rays. We also isolated a range of unusual new rare earth tantalates with very complex structures. indicating that the chemistry is very sensitive to conditions. We performed some fairly comprehensive examinations of the solid-state chemistry of rare earth ions with various tetravalent metal ions especially Si 4+ , Ge 4+ , Sn 4+ and Ti 4+ . Given the potential role of rare earth silicates in immobilizing radioactive waste elements in long-term storage, and the similarity of our hydrothermal fluids with known geological conditions, this chemistry continues to be relevant. We prepared an extensive series of new lanthanide germanates (e.g. RE 13 Ge 6 O 31 (OH), BaRE 10 (GeO 4 ) 4 O 8 ). and found that there is there is almost no overlap between the chemistry of the rare earth silicates. Stannic oxide (SnO 2 ) is much more refractory and requires higher temperatures and of mineralizer concentrations. One significant result is the growth of RE 2 Sn 2 O 7 pyrochlore single crystals. These are of interest because the rare earth stannate pyrochlores are known to display a wide range of magnetic frustration such as spin ice behavior. We grew high quality single crystals of rare earth germanate and stannate pyrochlores and this led to a collaboration with Professor Kate Ross at Colorado State. Preliminary measurements, indicate that the crystals contain no detectable defects or site disorder. Initial neutron diffraction on single crystals was performed at Oak Ridge, and more detailed experiments involving the Ross group are underway at both NIST and ORNL. This particular chemistry has turned out to be the most potentially significant work on this project and the collaborative effort with Prof. Ross is the topic of a DoE renewal project on quantum materials. Our initial foray into the hydrothermal chemistry of rare earth titanates has also been very promising and a range of cubic and polar ferroic phases of the light rare earths RE 2 Ti 2 O 7 (RE = La - Pr) in the P2 1 phase. We also discovered an interesting new phase Ce 2 Ti 4 O 11 that can have implications in heavy metal immobilization and storage. along with a series of new rare earth titanates (La 5 Ti 4 O 15 (OH) Sm 3 TiO 5 (OH) 3 and Lu 5 Ti 2 O 11 (OH) with exceptionally complex structures. One interesting sidelight has been high temperature hydrothermal chemistry terbium, including the growth of large crystals of TbO(OH). This is not a new compound but it is the first time it has been grown as large single crystals. The Tb atom density is almost as high as that in Tb 2 O 3 and has a very high Verdet constant (ca. 70), making it a very attractive candidate as a Faraday rotator. Unfortunately it is not in a cubic structure but he material is hard, stable, pure and inexpensive, so should still be an attractive Faraday oscillator. We recently received a patent on this material. We also synthesized K 2 Tb(Ge 2 O 7 ) containing stable octahedral Tb 4+ ions, which appears to be the first example of a well-characterized Tb 4+ complex. Given that Tb 4+ has been proposed as a benign surrogate for more treacherous tetravalent ions such as Cf 4+ and Bk 4+ , we think that Tb 4+ silicates can be a particularly useful study for actinide immobilization and related work. We also began reaction studies with rare earths and both ReO 2 and RuO 2 . These resulted in large single crystals of species like RE 5 Ru 2 O 12 , RE 4 Re 2 O 11 , REReO 4 and RE 2 ReO 5 . Several of these samples have already been sent to ORNL for magnetic and neutron diffraction studies.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Neutral rhenium(i) tricarbonyl complexes with sulfur-donor ligands: anti-proliferative activity and cellular localization

Rhenium(I) tricarbonyl complexes are widely studied for their cell imaging properties and anticancer and anti-microbial activities, but the complexes with S-donor ligands remain relatively unexplored. A series of six fac-[Re(NN)(CO) 3 (SR)] complexes, where (NN) is 2,2'-bipyridyl (bipy) or 1,10-phenanthroline (phen), and RSH is a series of thiocarboxylic acid methyl esters, have been synthesized and characterized. Cellular uptake and anti-proliferative activities of these complexes in human breast cancer cell lines (MDA-MB-231 and MCF-7) were generally lower than those of the previously described fac-[Re(NN)(CO) 3 (OH 2 )] + complexes; however, one of the complexes, fac-[Re(CO) 3 (phen)(SC(Ph)CH 2 C(O)OMe))] (3b), was active (IC 50 ~ 10 μM at 72 h treatment) in thiol-depleted MDA-MB-231 cells. Moreover, unlike fac- [Re(CO) 3 (phen)(OH 2 )] + , this complex did not lose activity in the presence of extracellular glutathione. Taken together these properties show promise for further development of 3b and its analogues as potential anti-cancer drugs for co-treatment with thiol-depleting agents. Conversely, the stable and non-toxic complex, fac-[Re(bipy)(CO) 3 (SC(Me)C(O)OMe)] (1a), predominantly localized in the lysosomes of MDA-MB-231 cells, as shown by live cell confocal microscopy (λ ex = 405 nm, λ em = 470-570 nm). It is strongly localized in a subset of lysosomes (25 μM Re, 4 h treatment), as shown by co-localization with a Lysotracker dye. Longer treatment times with 1a (25 μM Re for 48 h) resulted in partial migration of the probe into the mitochondria, as shown by co-localization with a Mitotracker dye. These properties make complex 1a an attractive target for further development as an organelle probe for multimodal imaging, including phosphorescence, carbonyl tag for vibrational spectroscopy, and Re tag for X-ray fluorescence microscopy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Land of Opportunity: Potential for Renewable Energy on Federal Lands

Renewable energy (RE) in the United States has historically been deployed primarily on private lands, but the growing interest in RE development, generally across the country and specifically on federal lands, raises questions about the potential for RE on public lands. This study seeks to estimate RE technical potential on federal lands and project the amount of RE to be developed on federal lands under decarbonization scenarios for the contiguous United States. The study applied a combination of high-resolution geospatial analysis and power sector modeling and relied on multiple partner federal agencies and land administrators from the Bureau of Land Management, the U.S. Fish and Wildlife Service, the U.S. Forest Service, the U.S. Department of Defense, and the U.S. Department of Energy. In our reference siting access case, we estimate 44 million acres of federal land across the contiguous United States is potentially suitable for UPV development, which corresponds to a capacity technical potential of 5,750 gigawatts (GW) (Figure ES-1). Federal land area available for wind development is similar to UPV but wind’s generating capacity technical potential is lower (875 GW). The technical potential is estimated for two geothermal technologies, hydrothermal and enhanced geothermal systems (EGS), both of which have a smaller amount of federal land available for development (12 and 27 million acres, respectively). However, in terms of capacity, the technical potential for EGS (975 GW) is approximately equal to wind’s technical potential and there is an estimated 130 GW of hydrothermal potential. We also developed cases with more-limited land available for UPV and wind (for federal and non-federal lands) resulting in 96% reduction of wind capacity potential and 70% reduction for UPV. In a case with additional constraints applied to non-federal lands only (Limited Private), the overall (federal and non-federal) technical potential declines but the share of that technical potential on federal lands is higher than in the other siting cases. The technical potential is the maximum amount that could be developed, but only a small fraction would be developed or needed in the future. Across seven scenarios that achieve 100% carbon-free electricity by 2035, we estimate 26 GW to 270 GW of RE capacity could be deployed on federal lands by 2035. The three central scenarios have 51–84 GW of RE deployed by 2035 and requiring about 500,000 to 1,000,000 acres of total land area. Direct land consumption is less than total land use required, thus enabling co-use opportunities. The large technical potential estimates and the increasing deployment projections from the collection of scenarios show the opportunities for RE development on federal lands. Capturing these opportunities-while minimizing conflicts with other land uses, federal department or agency missions, and public interest, and simultaneously maximizing the economic, grid, and social value of the projects-would require collaborative planning among federal land administrators, grid planners, project developers, the public, and other stakeholders.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2024

Electromagnetic Design Optimization Integrated with Mechanical Stress Analysis of PM-Assisted Synchronous Reluctance Machine Topologies Enabled with a Blend of Magnets

Permanent Magnet-Assisted Synchronous Reluctance Machines (PMASynRM) provide a low-cost alternative to Surface PM Machines due to the use of relatively lower grades of rare-earth (RE) or RE-free magnets, as the performance degradation due to weaker magnets is compensated by the presence of reluctance torque. However, the weaker magnets suffer from a high risk of demagnetization, leading to unreliable motor operation. Using a blend of RE and RE-free magnets has the potential to overcome this issue. This paper proposes to blend different grades of various rare-earth (RE) and rare-earth-free (RE-free) magnets in six different combinations and utilizes them in two-layer and three-layer U-shaped PMASynRM topologies with both eight-pole and six-pole variations. The rotor of the various designs is then optimized using a differential evolution (DE) based optimization algorithm to obtain low-cost designs with reduced RE magnet volume and minimum demagnetization risk. The optimization of each design is also integrated with the evaluation of mechanical stresses in the rotor laminations so as to maintain the stresses below the material yield strength. Furthermore, the various performance metrics, such as toque–speed/power–speed characteristics, demagnetization, and efficiency maps, are evaluated for each of the optimized and mechanically feasible designs. A quantitative comparison of the various optimized designs is also obtained to highlight the various trade-offs. The results indicate the feasibility of meeting the baseline torque requirement across the entire speed range, even with a 100% reduction in RE magnet volume and less than 5% demagnetization risk, while achieving a cost reduction exceeding 50%. Moreover, the two-layer, eight-pole designs exhibit relatively higher performance, whereas the three-layer, eight-pole designs are found to be the most economical option.

design optimization↗
DOE OSTI2020

Materials Data on KBa2Re by Materials Project

KBa2Re crystallizes in the cubic F-43m space group. The structure is three-dimensional. K is bonded in a distorted body-centered cubic geometry to four equivalent Ba and four equivalent Re atoms. All K–Ba bond lengths are 3.64 Å. All K–Re bond lengths are 3.64 Å. There are two inequivalent Ba sites. In the first Ba site, Ba is bonded to four equivalent Ba and four equivalent Re atoms to form distorted edge-sharing BaBa4Re4 tetrahedra. All Ba–Ba bond lengths are 3.64 Å. All Ba–Re bond lengths are 3.64 Å. In the second Ba site, Ba is bonded in a 4-coordinate geometry to four equivalent K, four equivalent Ba, and six equivalent Re atoms. All Ba–Re bond lengths are 4.21 Å. Re is bonded in a distorted body-centered cubic geometry to four equivalent K and ten Ba atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K15Re7N19 by Materials Project

K15Re7N19 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are sixteen inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 6-coordinate geometry to six N3- atoms. There are a spread of K–N bond distances ranging from 2.77–3.41 Å. In the second K1+ site, K1+ is bonded in a 6-coordinate geometry to six N3- atoms. There are a spread of K–N bond distances ranging from 2.78–3.24 Å. In the third K1+ site, K1+ is bonded to four N3- atoms to form distorted KN4 tetrahedra that share corners with four ReN4 tetrahedra and an edgeedge with one KN6 pentagonal pyramid. There are a spread of K–N bond distances ranging from 2.76–2.96 Å. In the fourth K1+ site, K1+ is bonded in a 6-coordinate geometry to six N3- atoms. There are a spread of K–N bond distances ranging from 2.70–3.22 Å. In the fifth K1+ site, K1+ is bonded in a 4-coordinate geometry to four N3- atoms. There are a spread of K–N bond distances ranging from 2.72–3.03 Å. In the sixth K1+ site, K1+ is bonded in a 4-coordinate geometry to four N3- atoms. There are a spread of K–N bond distances ranging from 2.77–3.13 Å. In the seventh K1+ site, K1+ is bonded to six N3- atoms to form distorted KN6 pentagonal pyramids that share corners with two ReN4 tetrahedra, an edgeedge with one KN6 pentagonal pyramid, an edgeedge with one KN4 tetrahedra, and edges with three ReN4 tetrahedra. There are a spread of K–N bond distances ranging from 2.78–3.11 Å. In the eighth K1+ site, K1+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of K–N bond distances ranging from 2.72–3.10 Å. In the ninth K1+ site, K1+ is bonded in a 6-coordinate geometry to six N3- atoms. There are a spread of K–N bond distances ranging from 2.84–3.30 Å. In the tenth K1+ site, K1+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of K–N bond distances ranging from 2.83–3.34 Å. In the eleventh K1+ site, K1+ is bonded in a 4-coordinate geometry to four N3- atoms. There are a spread of K–N bond distances ranging from 2.64–3.05 Å. In the twelfth K1+ site, K1+ is bonded in a 6-coordinate geometry to six N3- atoms. There are a spread of K–N bond distances ranging from 2.79–3.33 Å. In the thirteenth K1+ site, K1+ is bonded in a 3-coordinate geometry to three N3- atoms. There are a spread of K–N bond distances ranging from 2.68–2.81 Å. In the fourteenth K1+ site, K1+ is bonded in a 3-coordinate geometry to five N3- atoms. There are a spread of K–N bond distances ranging from 2.60–3.29 Å. In the fifteenth K1+ site, K1+ is bonded in a hexagonal planar geometry to six N3- atoms. There are a spread of K–N bond distances ranging from 2.87–3.12 Å. In the sixteenth K1+ site, K1+ is bonded in a distorted hexagonal planar geometry to six N3- atoms. There are a spread of K–N bond distances ranging from 2.98–3.27 Å. There are seven inequivalent Re6+ sites. In the first Re6+ site, Re6+ is bonded to four N3- atoms to form ReN4 tetrahedra that share a cornercorner with one KN6 pentagonal pyramid, a cornercorner with one KN4 tetrahedra, corners with three ReN4 tetrahedra, and an edgeedge with one KN6 pentagonal pyramid. There are a spread of Re–N bond distances ranging from 1.79–1.93 Å. In the second Re6+ site, Re6+ is bonded to four N3- atoms to form corner-sharing ReN4 tetrahedra. There are a spread of Re–N bond distances ranging from 1.79–1.95 Å. In the third Re6+ site, Re6+ is bonded to four N3- atoms to form corner-sharing ReN4 tetrahedra. There are a spread of Re–N bond distances ranging from 1.78–1.90 Å. In the fourth Re6+ site, Re6+ is bonded to four N3- atoms to form corner-sharing ReN4 tetrahedra. There are a spread of Re–N bond distances ranging from 1.80–1.92 Å. In the fifth Re6+ site, Re6+ is bonded to four N3- atoms to form corner-sharing ReN4 tetrahedra. There are a spread of Re–N bond distances ranging from 1.77–1.95 Å. In the sixth Re6+ site, Re6+ is bonded to four N3- atoms to form ReN4 tetrahedra that share corners with two equivalent KN4 tetrahedra, corners with two ReN4 tetrahedra, and an edgeedge with one KN6 pentagonal pyramid. There are a spread of Re–N bond distances ranging from 1.80–1.99 Å. In the seventh Re6+ site, Re6+ is bonded to four N3- atoms to form ReN4 tetrahedra that share a cornercorner with one KN6 pentagonal pyramid, a cornercorner with one KN4 tetrahedra, corners with two ReN4 tetrahedra, and an edgeedge with one KN6 pentagonal pyramid. There are a spread of Re–N bond distances ranging from 1.81–1.93 Å. There are nineteen inequivalent N3- sites. In the first N3- site, N3- is bonded in a 1-coordinate geometry to five K1+ and one Re6+ atom. In the second N3- site, N3- is bonded in a distorted linear geometry to four K1+ and two Re6+ atoms. In the third N3- site, N3- is bonded in a 1-coordinate geometry to five K1+ and one Re6+ atom. In the fourth N3- site, N3- is bonded in a 2-coordinate geometry to three K1+ and two Re6+ atoms. In the fifth N3- site, N3- is bonded in a 2-coordinate geometry to three K1+ and two Re6+ atoms. In the sixth N3- site, N3- is bonded in a 1-coordinate geometry to four K1+ and one Re6+ atom. In the seventh N3- site, N3- is bonded in a 1-coordinate geometry to five K1+ and one Re6+ atom. In the eighth N3- site, N3- is bonded in a 2-coordinate geometry to four K1+ and two Re6+ atoms. In the ninth N3- site, N3- is bonded in a 1-coordinate geometry to five K1+ and one Re6+ atom. In the tenth N3- site, N3- is bonded in a 6-coordinate geometry to five K1+ and one Re6+ atom. In the eleventh N3- site, N3- is bonded in a 2-coordinate geometry to three K1+ and two Re6+ atoms. In the twelfth N3- site, N3- is bonded in a 1-coordinate geometry to four K1+ and one Re6+ atom. In the thirteenth N3- site, N3- is bonded in a 2-coordinate geometry to three K1+ and two Re6+ atoms. In the fourteenth N3- site, N3- is bonded in a 2-coordinate geometry to four K1+ and two Re6+ atoms. In the fifteenth N3- site, N3- is bonded in a 1-coordinate geometry to five K1+ and one Re6+ atom. In the sixteenth N3- site, N3- is bonded in a 2-coordinate geometry to three K1+ and two Re6+ atoms. In the seventeenth N3- site, N3- is bonded in a 2-coordinate geometry to two K1+ and two Re6+ atoms. In the eighteenth N3- site, N3- is bonded in a 1-coordinate geometry to five K1+ and one Re6+ atom. In the nineteenth N3- site, N3- is bonded in a 1-coordinate geometry to four K1+ and one Re6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na15Re7N19 by Materials Project

Na15Re7N19 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are sixteen inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six N3- atoms. There are a spread of Na–N bond distances ranging from 2.57–2.91 Å. In the second Na1+ site, Na1+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of Na–N bond distances ranging from 2.38–2.86 Å. In the third Na1+ site, Na1+ is bonded to four N3- atoms to form distorted NaN4 tetrahedra that share corners with four ReN4 tetrahedra. There are a spread of Na–N bond distances ranging from 2.55–2.63 Å. In the fourth Na1+ site, Na1+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of Na–N bond distances ranging from 2.39–3.06 Å. In the fifth Na1+ site, Na1+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of Na–N bond distances ranging from 2.41–2.83 Å. In the sixth Na1+ site, Na1+ is bonded in a 3-coordinate geometry to five N3- atoms. There are a spread of Na–N bond distances ranging from 2.37–3.08 Å. In the seventh Na1+ site, Na1+ is bonded in a 4-coordinate geometry to four N3- atoms. There are a spread of Na–N bond distances ranging from 2.39–2.53 Å. In the eighth Na1+ site, Na1+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of Na–N bond distances ranging from 2.38–2.85 Å. In the ninth Na1+ site, Na1+ is bonded in a 3-coordinate geometry to four N3- atoms. There are a spread of Na–N bond distances ranging from 2.39–3.04 Å. In the tenth Na1+ site, Na1+ is bonded in a distorted pentagonal planar geometry to five N3- atoms. There are a spread of Na–N bond distances ranging from 2.53–2.80 Å. In the eleventh Na1+ site, Na1+ is bonded in a 4-coordinate geometry to four N3- atoms. There are a spread of Na–N bond distances ranging from 2.38–2.72 Å. In the twelfth Na1+ site, Na1+ is bonded in a 4-coordinate geometry to four N3- atoms. There are a spread of Na–N bond distances ranging from 2.49–2.66 Å. In the thirteenth Na1+ site, Na1+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of Na–N bond distances ranging from 2.48–2.99 Å. In the fourteenth Na1+ site, Na1+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of Na–N bond distances ranging from 2.40–2.89 Å. In the fifteenth Na1+ site, Na1+ is bonded in a distorted linear geometry to four N3- atoms. There are two shorter (2.34 Å) and two longer (3.00 Å) Na–N bond lengths. In the sixteenth Na1+ site, Na1+ is bonded to six N3- atoms to form distorted NaN6 octahedra that share corners with six ReN4 tetrahedra and edges with two equivalent ReN4 tetrahedra. There are a spread of Na–N bond distances ranging from 2.73–3.00 Å. There are seven inequivalent Re6+ sites. In the first Re6+ site, Re6+ is bonded to four N3- atoms to form ReN4 tetrahedra that share a cornercorner with one NaN6 octahedra, a cornercorner with one NaN4 tetrahedra, and corners with three ReN4 tetrahedra. The corner-sharing octahedral tilt angles are 76°. There are a spread of Re–N bond distances ranging from 1.79–1.93 Å. In the second Re6+ site, Re6+ is bonded to four N3- atoms to form corner-sharing ReN4 tetrahedra. There are a spread of Re–N bond distances ranging from 1.78–1.97 Å. In the third Re6+ site, Re6+ is bonded to four N3- atoms to form corner-sharing ReN4 tetrahedra. There are a spread of Re–N bond distances ranging from 1.79–1.89 Å. In the fourth Re6+ site, Re6+ is bonded to four N3- atoms to form corner-sharing ReN4 tetrahedra. There are a spread of Re–N bond distances ranging from 1.80–1.92 Å. In the fifth Re6+ site, Re6+ is bonded to four N3- atoms to form ReN4 tetrahedra that share a cornercorner with one NaN6 octahedra, corners with three ReN4 tetrahedra, and an edgeedge with one NaN6 octahedra. The corner-sharing octahedral tilt angles are 3°. There are a spread of Re–N bond distances ranging from 1.78–1.92 Å. In the sixth Re6+ site, Re6+ is bonded to four N3- atoms to form ReN4 tetrahedra that share corners with two equivalent NaN4 tetrahedra and corners with two ReN4 tetrahedra. There are a spread of Re–N bond distances ranging from 1.79–2.00 Å. In the seventh Re6+ site, Re6+ is bonded to four N3- atoms to form ReN4 tetrahedra that share a cornercorner with one NaN6 octahedra, a cornercorner with one NaN4 tetrahedra, and corners with two ReN4 tetrahedra. The corner-sharing octahedral tilt angles are 74°. There is two shorter (1.80 Å) and two longer (1.91 Å) Re–N bond length. There are nineteen inequivalent N3- sites. In the first N3- site, N3- is bonded to five Na1+ and one Re6+ atom to form distorted corner-sharing NNa5Re octahedra. In the second N3- site, N3- is bonded in a 6-coordinate geometry to four Na1+ and two Re6+ atoms. In the third N3- site, N3- is bonded in a 6-coordinate geometry to five Na1+ and one Re6+ atom. In the fourth N3- site, N3- is bonded in a 4-coordinate geometry to two Na1+ and two Re6+ atoms. In the fifth N3- site, N3- is bonded in a 2-coordinate geometry to two Na1+ and two Re6+ atoms. In the sixth N3- site, N3- is bonded in a 5-coordinate geometry to four Na1+ and one Re6+ atom. In the seventh N3- site, N3- is bonded in a 6-coordinate geometry to five Na1+ and one Re6+ atom. In the eighth N3- site, N3- is bonded to three Na1+ and two Re6+ atoms to form distorted NNa3Re2 trigonal bipyramids that share a cornercorner with one NNa3Re2 trigonal bipyramid and an edgeedge with one NNa5Re octahedra. In the ninth N3- site, N3- is bonded in a 4-coordinate geometry to four Na1+ and one Re6+ atom. In the tenth N3- site, N3- is bonded to five Na1+ and one Re6+ atom to form distorted edge-sharing NNa5Re octahedra. In the eleventh N3- site, N3- is bonded in a 2-coordinate geometry to three Na1+ and two Re6+ atoms. In the twelfth N3- site, N3- is bonded to four Na1+ and one Re6+ atom to form distorted NNa4Re trigonal bipyramids that share corners with two equivalent NNa5Re octahedra, a cornercorner with one NNa4Re trigonal bipyramid, and an edgeedge with one NNa4Re trigonal bipyramid. The corner-sharing octahedra tilt angles range from 33–73°. In the thirteenth N3- site, N3- is bonded in a 4-coordinate geometry to two Na1+ and two Re6+ atoms. In the fourteenth N3- site, N3- is bonded in a 6-coordinate geometry to four Na1+ and two Re6+ atoms. In the fifteenth N3- site, N3- is bonded in a 5-coordinate geometry to four Na1+ and one Re6+ atom. In the sixteenth N3- site, N3- is bonded in a 2-coordinate geometry to four Na1+ and two Re6+ atoms. In the seventeenth N3- site, N3- is bonded in a 4-coordinate geometry to two Na1+ and two Re6+ atoms. In the eighteenth N3- site, N3- is bonded in a 4-coordinate geometry to five Na1+ and one Re6+ atom. In the nineteenth N3- site, N3- is bonded in a 5-coordinate geometry to four Na1+ and one Re6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ga3Re by Materials Project

Ga3Re crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Re is bonded in a 9-coordinate geometry to one Re and eight Ga atoms. The Re–Re bond length is 2.67 Å. There are a spread of Re–Ga bond distances ranging from 2.52–2.67 Å. There are two inequivalent Ga sites. In the first Ga site, Ga is bonded in a distorted linear geometry to two equivalent Re atoms. In the second Ga site, Ga is bonded in a 1-coordinate geometry to three equivalent Re atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

DFT-based investigation of solvation of Nd(III)/Yb(III) cations in room-temperature ionic-liquid

We report a DFT study on the solvation of bare rare-earth (RE) cations [Nd(III) and Yb(III)] in the room-temperature ionic-liquid (RTIL) based on 1,3-dimethyl-imidazolium + , PF 6 - , [MMI][PF 6 ]. In the present article, we aim to investigate whether the chosen RTIL can preferentially solvate any of the RE cations under study. First, the RTIL binding to the RE cation is studied in the gas phase, and then explored with continuum solvation model employing RTIL parameters. First, we considered the formation of the first solvation shell, where the PF 6 - anions directly bond with the Ln(III) cation. We then further surrounded the first solvation shell with [MMI]+ cations to form the second solvation shell. The stability of PF 6 - coordinated complexes is studied by calculating the binding energy values. The number of PF 6 - anions for both Ln(III) cations starts with three ligands and goes until the maximum binding energy in the RTIL medium is reached. The coordination number and binding modes of PF 6 - depend on the size of the RE cation. Comparing the binding energy values between the RE cations for the first solvation shell complexes, it is noticed that Yb-complexes have relatively greater binding energy than Nd-complexes. We have further performed a Boltzmann population analysis to find out the most dominant conformer among each category of PF 6 - coordinated complexes. A study using Natural Population Analysis shows that after complexation with PF 6 - the charge on the Yb-centers lower to a greater extent than Nd-centers, implying stronger bonding between Yb and PF 6 - , which is in harmony with the binding energy analysis. Overall, the computational investigation provides an in-depth understanding of the complexation phenomena of RE cations in RTIL, which can be useful for the practical separation of RE cations using RTIL.

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

Spatially dependent modeling and simulation of runaway electron mitigation in DIII-D

New simulations with the Kinetic Orbit Runaway electron (RE) Code (KORC) show RE deconfinement losses to the wall during plasma scrape off are the primary current dissipation mechanism in DIII-D experiments with high-Z impurity injection, and not collisional slowing down. The majority of simulations also exhibit an increase in the RE beam energy due to acceleration by the induced toroidal electric field, even while the RE beam current is decreasing. In this study, KORC integrates RE orbits using the relativistic guiding center equations of motion and incorporates time-sequenced, experimental reconstructions of the magnetic and electric fields and line integrated electron density to construct spatiotemporal models of electron and partially ionized impurity transport in the companion plasma. Comparisons of experimental current evolution and KORC results demonstrate the importance of including Coulomb collisions with partially ionized impurity physics, initial RE energy, pitch angle, and spatial distributions, and spatiotemporal electron and partially ionized impurity transport. The research presented here provides an initial quantification of the efficacy of RE mitigation via injected impurities and identification of the critical role played by loss of confinement due to plasma scrape off on the inner wall as compared to the relatively slow collisional damping.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Diffusion–convection model of runaway electrons due to large magnetohydrodynamic perturbations in post-thermal quench plasmas

Systematic test particle tracing simulations for runaway electrons (REs) are performed for six post-thermal quench equilibria from DIII-D and ITER, where large scale, kink-like n = 1 (n is the toroidal mode number) magnetohydrodynamic (MHD) instabilities are found. The modeled particle guiding center orbits allow extraction of the effective diffusion–convection coefficients of REs in the presence of large three-dimensional (3D) perturbations up to 10% of the equilibrium toroidal field. With a fixed spatial distribution of the field perturbation, the RE transport coefficients along the plasma radial coordinate track reasonably well with the surface-averaged perturbation level. A substantial variation in the value of the transport coefficients—by three orders of magnitude in most cases, however, occurs with varying launching location of REs along the plasma radius. Large 3D perturbations almost always lead to comparable diffusion and convection processes, meaning that diffusion alone is insufficient to describe the particle motion. At lower (but still high) level of perturbation, the RE convection is found to be dominant over diffusion. A similar observation is made when the perturbation is too strong. In the presence of large perturbation, the dependence of the RE transport on the particle energy is sensitive to the spatial distribution of the perturbation. Based on numerically obtained RE transport coefficients, an analytic fitting model is proposed to quantify the particle diffusion and convection processes due to large MHD events in post-thermal quench plasmas. The model is shown to reasonably well reproduce the direct test particle tracing results for the RE loss fraction and can, thus, be useful for incorporating into other kinetic RE codes in order to simulate the RE beam evolution in the presence of large 3D perturbations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

On the minimum transport required to passively suppress runaway electrons in SPARC disruptions

In Izzo et al (2022 Nucl. Fusion 62 096029), state-of-the-art modeling of thermal and current quench (CQ) magnetohydrodynamics (MHD) coupled with a self-consistent evolution of runaway electron (RE) generation and transport showed that a non-axisymmetric (n = 1) in-vessel coil could passively prevent RE beam formation during disruptions in SPARC, a compact high-field tokamak projected to achieve a fusion gain Q > 2 in DT plasmas. However, such suppression requires finite transport of REs within magnetic islands and re-healed flux surfaces; conservatively assuming zero transport in these regions leads to an upper bound of RE current ~1MA compared to ~8.7MA of pre-disruption plasma current. Further investigation finds that core-localized electrons, within r/a < 0.4 and with kinetic energies ~0.2–15 MeV, contribute most to the RE plateau formation. Yet only a relatively small amount of transport, i.e. a diffusion coefficient ~18 m 2 s -1 , is needed in the core to fully mitigate these REs. Properly accounting for (a) the CQ electric field's effect on RE transport in islands and (b) the contribution of significant RE currents to disruption MHD may help achieve this.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Measurement of post-disruption runaway electron kinetic energy and pitch angle during final loss instability in DIII-D

Post-disruption runaway electron (RE) kinetic energy K and pitch angle sin$\vartheta$ are critical parameters for determining resulting first wall material damage during wall strikes, but are very challenging to measure experimentally. During the final loss instability, confined RE K and sin$\vartheta$ are reconstructed during center-post wall strikes for both high impurity (high-Z) and low impurity (low-Z) plasmas by combining soft x-ray, hard x-ray, synchrotron emission, and total radiated power measurements. Deconfined (wall impacting) RE sin$\vartheta$ is then reconstructed for these shots by using time-decay analysis of infra-red imaging. Additionally, deconfined RE K and sin$\vartheta$ are reconstructed for a low-Z downward loss shot by analyzing resulting damage to a sacrificial graphite dome limiter. The damage analysis uses multi-step modeling simulating plasma instability, RE loss orbits, energy deposition, and finally material expansion (MARS-F, KORC, GEANT-4, and finally COMSOL). Overall, mean kinetic energies are found to be in the range $\langle$$K$$\rangle$ $≈ 3-4$ MeV for confined REs. KORC simulations indicate that the final loss instability process does not change individual RE kinetic energy K. In conclusion, confined RE pitch angles are found to be fairly low initially pre-instability, $\langle$sin$\vartheta$$\rangle$ $≈ 0.1 – 0.2$, but appear to increase roughly 2x, to $\langle$sin$\vartheta$$\rangle$ $≈ 0.3 – 0.4$ for both confined and deconfined REs during instability onset in the low-Z case; this increase is not observed in the high-Z case.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗