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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

An Efficient Single Frequency Ho:YLF Laser for IPDA Lidar Applications

A highly efficient, versatile, single frequency 2-micron pulsed laser can be used in a pulsed Differential Absorption Lidar (DIAL) / Integrated Path Differential Absorption (IPDA) instrument to make precise, high-resolution measurements to investigate sources and sinks of CO2. For a direct detection IPDA lidar, the desired 2 m Ho:YLF laser should generate 30-40 mJ pulses at the repetition rate of 100 to 200 Hz, with short pulse length (<100 ns) and better than 2% wall plug efficiency. A Tm fiber laser in-band pumped Ho:YLF laser has been developed to meet this technical challenge. This Ho:YLF laser is designed in a four mirror ring resonator with bow tie configuration, which helps to obtain high beam quality. It is end-pumped by a 40 W linearly polarized Tm fiber laser at 1.94μm. The resonator length is 1.10 meters with output coupler reflectivity at 45%. The laser crystal size is 3 x 3 x 60 mm (w, h, l) with a doping concentration of 0.5% Holmium. The laser beam and pump beam are mode-matched in the active medium. Thus, the pump and laser beams have the same confocal parameters. Mode-matching is also helpful for operating the laser in a single transverse mode. The laser beam waist is slightly less than 0.5 mm at the center of the laser crystal. Based on quasi-four level modeling, pump absorption and saturation depend on laser intensity. Laser amplification and saturation also depend on the pump intensity in the crystal. The laser is injection seeded to obtain the single frequency required by an IPDA lidar measurement. The seed beam is entered into the resonator through an output coupler. The laser is mounted on a water cooled optical bench for stable and reliable operation. The size of the optical bench is 22.16 x 9.20 x 1.25 inches. It is stiffened so that the laser can be operated in any orientation of the optical bench. This packaged Ho:YLF laser is designed for either mobile trailer or airborne platform operation. The engineering prototype Ho:YLF laser has been fully characterized to demonstrate laser performance. Figure 1 shows the laser output power as a function of pump power at different pulse repetition rates from 100 Hz to 333 Hz. The threshold of the laser is less than 14 W. The slope efficiencies are 28%, 40%, 41% and 43% for pulse repetition rates of 100, 200, 250 and 333 Hz, respectively. Maximum power increases with the pulse repetition rate. Output power of 4.2 W, 6 W, 6.7 W, and 7.7 W is achieved for pulse repetition rates of 100, 200, 250 and 333Hz, respectively. This represents the optical conversion efficiency of 16.7%, 22.4%, 23.7%, and 26.5% at these various pulse repletion rates. It is the most efficient and compact Ho:YLF laser demonstrated in the high pulse energy (>20mJ) and moderate pulse repetition rate (100's Hz) operation range. As shown in Figure 1, the maximum pulse energy at 100 Hz is 42 mJ. This is limited due to optical damage. The laser stability is characterized and found to be very stable. A relative pulse energy standard deviation of 2% was measured. The beam quality of the Ho:YLF was measured by a Spiricon infrared laser beam camera. Figure 2 shows the beam profile image of the laser. Both the X-profile of the beam (horizontal direction) and the Y-profile of the beam (vertical direction) are well fitted by a Gaussian profile. The qualitative beam quality measurement shows excellent beam quality in both axis. The M-square value for the laser beam is measured at 1.06 and 1.09 for the x and y axis respectively.-

Yu, J.↗
DOE OSTI2020

Materials Data on HoAl3(BO3)4 by Materials Project

HoAl3(BO3)4 is Calcite-derived structured and crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ho3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are four shorter (2.33 Å) and two longer (2.34 Å) Ho–O bond lengths. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six O2- atoms to form edge-sharing AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.87–1.95 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form edge-sharing AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.88–1.95 Å. There are two inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.37–1.39 Å. In the second B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.38 Å) and two longer (1.39 Å) B–O bond length. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+, one Al3+, and one B3+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two Al3+ and one B3+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+, one Al3+, and one B3+ atom. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Al3+ and one B3+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+, one Al3+, and one B3+ atom. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Al3+ and one B3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

New sterically hindered polyvinylamine-containing membranes for CO 2 capture from flue gas

Amine-containing facilitated transport membranes can have both high permeability and selectivity due to the reversible reaction between CO 2 and amino groups for effective carbon capture from flue gas. In this study, we have developed an improved method for the synthesis of high-molecular-weight sterically hindered polyvinylamine (PVAm) as the new fixed-site carrier in thin-film composite membranes for CO 2 capture. Commercially available PVAm was N-monomethylated into poly-N-methyl-N-vinylamine (PVAm-CH 3 ) using the stepwise reductive amination with a highly polar fluorinated alcohol as the solvent to enhance the equilibrium shift to the formation of the imine intermediate. The method prevented over-alkylation, resulting in the increased yield of the target product. PVAm-CH 3 exhibited excellent CO 2 facilitation with a CO 2 permeability of 445.7 Barrer (1 Barrer = 3.349 x 10 –16 mol m m –2 s –1 Pa –1 ) and a CO 2 /N 2 selectivity of 70.3, which are above the Robeson 2008 upper bound. The PVAm-CH 3 solution retained a sufficiently high viscosity after incorporating the aminoacid salt, 2-(1-piperazinyl)ethylamine sarcosinate (PZEA-Sar), as the mobile carrier for the membrane coating on nanoporous polyethersulfone (PES) substrates without any penetration issues. The resultant thin-film composite PVAm-CH3/PZEA-Sar membrane with a thickness of approximately 170 nm exhibited a superior CO 2 performance of 1071 GPU (1 GPU = 3.349 x 10 –10 mol m –2 s –1 Pa –1 ) and a CO 2 /N 2 selectivity of 183 at 57°C and a feed gas pressure of 111.64 kPa (1.5 psig). This PVAm-CH 3 /PZEA-Sar membrane surpassed the latest redefined 2019 CO 2 /N 2 upper bound and outperformed other polymer-based membranes. Density functional theory calculations also demonstrated that PVAm-CH 3 showed a stronger preference, relative to PVAm, toward the more efficient bicarbonate pathway. Thus, the steric hindrance effect of PVAm-CH 3 enhanced the solubility of CO 2 in the polymer matrix and resulted in the higher CO 2 permeance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1991

Complex-coordinate calculation of D-(1,3) resonances in two-electron systems

Feshbach-type D-(1,3)resonances in two-electron systems, Z = 2-10, have been investigated using the method of complex rotation. These states lie below the n = 2 and 3 thresholds of hydrogenic systems. Wave functions containing up to 1230 Hylleraas functions have been used, giving accurate results for positions and widths. Comparisons between various calculations are given.

Ho, Y. K.↗
NASA NTRS2023

Solar Activities Associated with 3 He-rich Solar Energetic Particle Events Observed by Solar Orbiter

A series of 3 He-rich solar energetic particle (SEP) events was observed by Solar Orbiter in May 2021 at a radial distance of 0.95 AU. An isolated active region AR 12824 was likely the ultimate source of these SEP events. The period of the enhanced flux of 3He was also a period of frequent type III bursts in the decametric-hectometric range, confirming their close relationship. As in past studies, we try to find the solar activities possibly responsible for 3 He-rich SEP events, using the type III bursts close to the particle injection times estimated from the velocity dispersion. But this exercise is not as straightforward as in many of the past studies since the region produced many more type III bursts and jet-like eruptions than the SEP injections. We may generalize the solar activities for the 3 He-rich SEP events in question as coronal jets, but their appearances do not necessarily conform to classic jets that consist of a footpoint and a spire. Conversely, such jets often did not accompany type III bursts. The areas that produced jet-like eruptions changed within the active region from the first to the second set of 3 He-rich SEP events, which may be related to the extended coronal mass ejection that launched stealthily.

Sun↗
DOE OSTI2020

Materials Data on HoTl(WO4)2 by Materials Project

HoTl(WO4)2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ho3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ho–O bond distances ranging from 2.27–2.32 Å. W6+ is bonded to six O2- atoms to form a mixture of corner and edge-sharing WO6 octahedra. The corner-sharing octahedral tilt angles are 44°. There are a spread of W–O bond distances ranging from 1.83–2.14 Å. Tl1+ is bonded in a 10-coordinate geometry to ten O2- atoms. There are a spread of Tl–O bond distances ranging from 2.88–3.14 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent W6+ and two equivalent Tl1+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Ho3+, one W6+, and one Tl1+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+, two equivalent W6+, and one Tl1+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ho3+, one W6+, and one Tl1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiHo3Ge2(O4F)2 by Materials Project

LiHo3(GeO4)2F2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Li1+ is bonded in a square co-planar geometry to four O2- atoms. All Li–O bond lengths are 2.12 Å. There are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six O2- and one F1- atom to form distorted HoO6F pentagonal bipyramids that share corners with two equivalent HoO6F pentagonal bipyramids, corners with four equivalent GeO4 tetrahedra, an edgeedge with one HoO6F pentagonal bipyramid, and an edgeedge with one GeO4 tetrahedra. There are a spread of Ho–O bond distances ranging from 2.29–2.44 Å. The Ho–F bond length is 2.23 Å. In the second Ho3+ site, Ho3+ is bonded in a 8-coordinate geometry to six O2- and two equivalent F1- atoms. There are a spread of Ho–O bond distances ranging from 2.29–2.56 Å. Both Ho–F bond lengths are 2.24 Å. Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share corners with four equivalent HoO6F pentagonal bipyramids and an edgeedge with one HoO6F pentagonal bipyramid. There are a spread of Ge–O bond distances ranging from 1.76–1.81 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Ge4+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to one Li1+, two Ho3+, and one Ge4+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three Ho3+ and one Ge4+ atom. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to one Li1+, two Ho3+, and one Ge4+ atom. F1- is bonded in a bent 150 degrees geometry to two Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho4NiB13 by Materials Project

Ho4NiB13 crystallizes in the tetragonal P4/mnc space group. The structure is three-dimensional. Ho3+ is bonded in a 6-coordinate geometry to fifteen B+1.15- atoms. There are a spread of Ho–B bond distances ranging from 2.55–2.89 Å. Ni3+ is bonded in a 8-coordinate geometry to eight equivalent B+1.15- atoms. All Ni–B bond lengths are 2.18 Å. There are three inequivalent B+1.15- sites. In the first B+1.15- site, B+1.15- is bonded in a cuboctahedral geometry to four equivalent Ho3+ and eight equivalent B+1.15- atoms. All B–B bond lengths are 2.10 Å. In the second B+1.15- site, B+1.15- is bonded in a 3-coordinate geometry to six equivalent Ho3+ and three B+1.15- atoms. There is two shorter (1.77 Å) and one longer (1.91 Å) B–B bond length. In the third B+1.15- site, B+1.15- is bonded in a 9-coordinate geometry to four equivalent Ho3+, one Ni3+, and four B+1.15- atoms. Both B–B bond lengths are 1.81 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Hydration structure and energetics of iron-exchanged montmorillonite

The interaction between iron released from corroded steel canisters and bentonite is a key process influencing the long-term performance of nuclear waste repositories. In particular, the migration of Fe²⁺ into montmorillonite (Mnt) interlayers may alter its hydration, swelling, and ion-transport properties. In the present study, molecular dynamics simulations were performed to investigate the hydration behavior, structural response, and transport properties of Fe-exchanged montmorillonite (Fe-Mnt) under varying hydration states. The simulations focus on short- to intermediate-time-scale Fe 2+ and Fe 3+ interlayer exchange and hydration effects, and do not consider long-term structural substitution, Fe-bearing clay phase stabilization, or secondary iron mineral precipitation. Systems containing Na + -, Fe 2+ -, and Fe 3+ -Mnt were examined using both periodic and edge-exposed configurations to evaluate interlayer structure, ion exchange, and free energy of Fe intercalation. The results show that Fe ions influence the interlayer spacing primarily at low water contents (<1 bilayer), where Fe-Mnt exhibits a d-spacing 1–2 Å larger than Na-Mnt due to stronger hydration. The calculated hydration energies follow the order Fe 2+ $<$Fe 3+ $<$Na + . Both water and ion diffusion coefficients decrease upon Fe ion intercalation, with Fe 2+ ions diffusing an order of magnitude more slowly than those of Na + . Free energy profiles further confirm that Fe 2+ and Fe 3+ ions are thermodynamically favored in the interlayer, with Fe 3+ being the most stable. In conclusion, these findings provide molecular-scale insights into the mechanisms of Fe–Na exchange and their implications for bentonite alteration in repository environments.

clay↗
DOE OSTI2022

Anisotropic magnon damping by zero-temperature quantum fluctuations in ferromagnetic CrGeTe 3

Spin and lattice are two fundamental degrees of freedom in a solid, and their fluctuations about the equilibrium values in a magnetic ordered crystalline lattice form quasiparticles termed magnons (spin waves) and phonons (lattice waves), respectively. In most materials with strong spin-lattice coupling (SLC), the interaction of spin and lattice induces energy gaps in the spin wave dispersion at the nominal intersections of magnon and phonon modes. Here we use neutron scattering to show that in the two-dimensional (2D) van der Waals honeycomb lattice ferromagnetic CrGeTe 3 , spin waves propagating within the 2D plane exhibit an anomalous dispersion, damping, and breakdown of quasiparticle conservation, while magnons along the c axis behave as expected for a local moment ferromagnet. These results indicate the presence of dynamical SLC arising from the zero-temperature quantum fluctuations in CrGeTe 3 , suggesting that the observed in-plane spin waves are mixed spin and lattice quasiparticles fundamentally different from pure magnons and phonons.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Multipacting analysis of the SNS drift tube linac (DTL) RF vacuum window using Spark3d

An ongoing study at the Spallation Neutron Source (SNS) seeks to better understand and address potential multipacting issues associated with the Drift Tube Linac (DTL) RF vacuum windows. An analysis of several failed operational windows showed indications of excessive RF heating on the TiN-coated alumina ceramics. Coupled with vacuum bursts and arcing during conditioning and/or operational periods, these problems have been attributed to electron activity likely caused by multipacting. The status of the study, 3-D electromagnetic simulation results, mitigating techniques and a future experimental plan for studying multipacting in the SNS DTL vacuum windows are presented.

Toby, George↗
DOE OSTI2022

Gen 3 Particle Pilot Plant (G3P3) Life Cycle Management Plan (SAND report)

The National Solar Thermal Test Facility (NSTTF) at Sandia National Laboratories New Mexico (SNL/NM) developed this Life Cycle Management Plan (LCMP) to document its process for executing, monitoring, controlling and closing-out Phase 3 of the Gen 3 Particle Pilot Plant (G3P3). This plan serves as a resource for stakeholders who wish to be knowledgeable of project objectives and how they will be accomplished.

14 SOLAR ENERGY↗
NASA NTRS1983

Oscillator strengths and collision strengths for S II

Calculations are presented of the collision strengths for electron impact excitation of S II from the ground 3s(2)3p(3)(4)S0 state to excited states 3s3p(4)(4)p, 3s(2(3p(2)4s(4)P, and 3s(2)3p(2)3d(4)P. The collision strengths are calculated in a close-coupling approximate ion for the energy range up to 10 to the 6th K. In addition, oscillator strengths are given for these transitions, as well as for some UV lines which have lower states 3s(2)3p(3)(2)D(O) and 3s(2)3p(3)(2)P(0). The calculation of the collision strengths involves the use of configuration interaction target wave functions which give oscillator strengths accurate to 30 percent in most cases.

Ho, Y. K.↗
DOE OSTI2020

Materials Data on Ho4CoB13 by Materials Project

Ho4CoB13 crystallizes in the tetragonal P4/mnc space group. The structure is three-dimensional. Ho3+ is bonded in a 6-coordinate geometry to fifteen B+1.15- atoms. There are a spread of Ho–B bond distances ranging from 2.56–2.89 Å. Co3+ is bonded in a 8-coordinate geometry to eight equivalent B+1.15- atoms. All Co–B bond lengths are 2.16 Å. There are three inequivalent B+1.15- sites. In the first B+1.15- site, B+1.15- is bonded in a cuboctahedral geometry to four equivalent Ho3+ and eight equivalent B+1.15- atoms. All B–B bond lengths are 2.11 Å. In the second B+1.15- site, B+1.15- is bonded in a 3-coordinate geometry to six equivalent Ho3+ and three B+1.15- atoms. There is two shorter (1.78 Å) and one longer (1.87 Å) B–B bond length. In the third B+1.15- site, B+1.15- is bonded in a 9-coordinate geometry to four equivalent Ho3+, one Co3+, and four B+1.15- atoms. Both B–B bond lengths are 1.80 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Te(HO)6 by Materials Project

Te(OH)6 crystallizes in the orthorhombic Fmm2 space group. The structure is two-dimensional and consists of two Te(OH)6 sheets oriented in the (0, 0, 1) direction. there are three inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the second H1+ site, H1+ is bonded in a distorted single-bond geometry to two O2- atoms. There is one shorter (1.00 Å) and one longer (1.70 Å) H–O bond length. In the third H1+ site, H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.04 Å) and one longer (1.52 Å) H–O bond length. Te6+ is bonded in an octahedral geometry to six O2- atoms. There are a spread of Te–O bond distances ranging from 1.84–2.12 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to two equivalent H1+ and one Te6+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one H1+ and one Te6+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two H1+ and one Te6+ atom. In the fourth O2- site, O2- is bonded in a distorted water-like geometry to two equivalent H1+ and one Te6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Ge2O7 by Materials Project

Ho2Ge2O7 crystallizes in the tetragonal P4_12_12 space group. The structure is three-dimensional. Ho3+ is bonded to seven O2- atoms to form distorted HoO7 pentagonal bipyramids that share corners with five equivalent GeO4 tetrahedra, edges with five equivalent HoO7 pentagonal bipyramids, and an edgeedge with one GeO4 tetrahedra. There are a spread of Ho–O bond distances ranging from 2.23–2.56 Å. Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share corners with five equivalent HoO7 pentagonal bipyramids, a cornercorner with one GeO4 tetrahedra, and an edgeedge with one HoO7 pentagonal bipyramid. There are a spread of Ge–O bond distances ranging from 1.76–1.80 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Ge4+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Ge4+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three equivalent Ho3+ and one Ge4+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent Ge4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Syntheses and Crystal Structures of Rare-Earth Oxyapatites Ca 2 RE 8 (SiO 4 ) 6 O 2 (RE = Pr, Tb, Ho, Tm)

Four different rare-earth oxyapatites of Ca 2 RE 8 (SiO 4 ) 6 O 2 (RE = Pr, Tb, Ho, Tm) were synthesized using a solution-based method followed by drying, calcination, and high-temperature sintering in air. X-ray powder diffraction and Raman spectroscopy were performed on the synthesized oxyapatites. Here, the RE oxyapatites crystallize in the hexagonal space group P6 3 /m with similar unit cell parameters, increasing linearly with larger RE cations. The unit cell volumes increase linearly whereas the densities decrease nonlinearly with larger RE cations. Raman spectra showed intense bands of the symmetric bending and stretching modes of SiO 4 at ~ 400 and 860 cm -1 regions, respectively. The bands generally shifted to higher frequencies with smaller RE cations in the structures.

36 MATERIALS SCIENCE↗