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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Emergent Halperin–Saslow mode, gauge glass and quenched disorders in quantum Ising magnet TmMgGaO 4

Quenched disorders could bring novel quantum excitations and models to certain quantum magnets. Motivated by recent experiments on the quantum Ising magnet TmMgGaO 4 , we explore the effects of the quenched disorder and the interlayer coupling in this triangular lattice Ising antiferromagnet. It is pointed out that the weak quenched (nonmagnetic) disorder would convert the emergent 2D Berezinskii–Kosterlitz–Thouless (BKT) phase and the critical region into a U(1) gauge glass. There will be an emergent Halperin–Saslow mode associated with this gauge glass. Using the Imry-Ma’s renormalization group result, we explain the fate of the finite-field [Formula: see text] symmetry breaking transition at the low temperatures. The ferromagnetic interlayer coupling would suppress the BKT phase and generate a tiny ferromagnetism. With quenched disorders, this interlayer coupling changes the 2D gauge glass into a 3D gauge glass, and the Halperin–Saslow mode persists. This work merely focuses on addressing a phase regime in terms of emergent U(1) gauge glass behaviors and hope to inspire future works and thoughts in weakly disordered frustrated magnets in general.

Physics↗
DOE OSTI2025

Tool Chain for Simulations of Bi-Filar Coil Winding for Fast Quench Protection

The advancement of high-field magnets utilizing high-temperature superconductors (HTS) brings about complex challenges, especially in quench detection and protection. Traditional methods often fall short due to the inherently slow quench propagation in HTS materials. One promising approach to overcome this involves using a bifilar winding configuration, where two conductors are placed side by side. Under normal operation, they function in series, but during a quench event, they switch to an anti-parallel mode. This shift reduces the differential inductance of the coil to near zero, enabling rapid current oscillations through a capacitor discharge. The resulting high-frequency current flow leads to swift, uniform heating, triggering a full-coil quench within microseconds. Moreover, the strong mutual coupling between the two windings significantly reduces electrical noise in voltage measurements. In this work, we explore the viability of this concept by designing, constructing, and testing a REBCO bifilar racetrack coil in liquid nitrogen. We also present a validated simulation model that closely mirrors the coil's dynamic behavior under these conditions, aligning well with experimental observations.

Jayathilaka, Rehan [Northern Illinois U.]↗
DOE OSTI2021

Acoustic MEMS Sensor Array for Quench Detection of CICC Superconducting Cables

A novel quench detection method using microelectro- mechanical system (MEMS) sensor technology has been investigated in use for high temperature superconducting (HTS) conductors such REBCO tape cables. The sensor array along a superconducting cable, such as a cable-in-conduit-conductor (CICC), is installed in a cooling channel. It will allow sensitive and quick detection for a local quench of a superconducting cable. This work has confirmed that a quench of a single REBCO tape can be detected in liquid nitrogen by a MEMS piezoelectric microphone sensor. The quench detection design utilizing a MEMS sensor array method is discussed for the case of a toroidal field (TF) magnets of a fusion Tokamak device.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1972

Quenching of the fluorescence of NO2

The fluorescence yield of NO2 was monitored at 25 C with incident wavelengths of 4047, 4358, and 4800A at fluorescence wavelengths of 4860, 5577, and 6300A. The NO2 pressure was varied between 0.004 and 0.080 torr. Measurements were taken both in the absence of foreign gases and in the presence of up to 30 torr. He, N2, and O2 at each NO2 pressure. In the absence of foreign gases, the self quenching follows a Stern-Volmer quenching mechanism, but foreign-gas quenching shows marked deviations from this mechanism. Both from lifetime and kinetic considerations, it is argued that the electronic state formed by absorption of the radiation cannot be the emitting state. Emission occurs from several vibrational levels of the emitting state, the various vibrational levels being formed by collisional cascade reactions. The appropriate quenching rate constant ratios were measured and tabulated. Even the two electronic state mechanism is insufficient to explain all the observations.

Braslavsky, S.↗
NASA NTRS1973

Collision quenching effects in nitrogen and helium excited by a 30-keV electron beam

The quenching cross section for the 0-0 first negative band of nitrogen is determined for temperatures between 78 K and 300 K. As the temperature increases above 78 K, the quenching reaches a maximum at approximately 140 K and then decreases as 300 K is approached. At temperatures on the order of 5000 K, quenching is reported to increase with temperature and must therefore reach a minimum at some intermediate temperature between 300 K and 5000 K. By comparison, quenching of the 5016 A helium line increases continuously over the temperature range 78 K to 300 K.

Lillicrap, D. C.↗
NASA NTRS1975

Organic synthesis by quench reactions

Study of the effects of chemical quench reactions on the formation of organic compounds at a water surface under simulated primordial earth conditions. A mixture of gaseous methane and ammonia over a water surface was exposed to an arc discharge between an electrode and the water surface, generating reactive species. Various organic molecules were formed by a subsequent quenching of these species generated on the water surface. The effects of these water-surface quench reactions were assessed by comparing the amounts of synthesized molecules to the amounts which formed during the discharge of an arc above the water level. It is concluded that the quench (or wet) discharge led to faster rates of reactions, higher-molecular-weight organic compounds, and one-order-of-magnitude larger yields than the dry discharge.

Park, W. K.↗
NASA NTRS1974

Cool flame quench distances

The results of a brief experimental investigation are presented which confirm the expectation that cool flame quenching distances should be larger than hot flame quenching distances. It is also discovered that whereas quenching distances for hot flames reach their minimum values near stoichiometric conditions, cool flame quenching distances are least under rich conditions. Rich conditions are well known to favor cool flame formation.

Ryason, P. R.↗
NASA NTRS1980

Semiclassical study of the quenching of excited-state fluorine atom by hydrogen molecule - Comparison between reactive and nonreactive processes

Semiclassical calculations are carried out for the quenching of excited-state fluorine atom by collinear collisions with hydrogen molecule. The overall quenching probability is the sum of two contributions: the reactive quenching probability associated with the formation of hydrogen fluoride and the nonreactive quenching probability leading to ground-state fluorine atom and hydrogen molecule. The reactive probability is greater in the threshold region of the collision energy, whereas the nonreactive probability dominates for energies above the threshold region.

Yuan, J.-M.↗
NASA NTRS1982

Rapid quenching effects in glassy polymers

Using a specially constructed microbalance for hydrostatic weighing, density changes in PVC thin film due to rapid quenching through the glass transition temperature were observed. The more severe the quench, the greater the free volume content. Isobaric volume recovery of PVC was also studied by volume dilatometry. Both show aging of relaxing molecular rearrangements taking place as a linear function of logarithmic aging time at room temperature. Distribution of retardation times and Primak's distributed activation energy spectra were applied to the volume recovery data. The concomitant changes in mechanical properties of PVC after quenching were monitored by tensile creep stress-stran to failure rates. All reflect the presence of excess free volume content due to rapid quenching.

Mcgarry, F. J.↗
NASA NTRS1981

Rapid quenching effects in PVC films

Using a specially constructed microbalance for hydrostatic weighing, density changes in PVC thin films (with no additives, 30-100 micrometers thick), due to rapid quenching (approximately 300 C/sec) through the glass transition temperature, have been observed. The more severe the quench, the greater is the free volume content. Isobaric volume recovery of PVC has also been studied by volume dilatometry. Both show aging of relaxing molecular rearrangements takes place as a linear function of logarithmic aging time at room temperature. Distribution of retardation times and Primak's distributed activation energy spectra have been applied to the volume recovery data. The concomitant changes in mechanical properties of PVC after quenching have been monitored by tensile creep and stress-strain to failure. All reflect the presence of excess free volume content, due to rapid quenching.

Lee, H. D.↗
NASA NTRS1985

Filamental quenching of the current-driven ion-cyclotron instability

Since their discovery by D'Angelo and Motley (1962), ion-cyclotron waves have been an area of active research. Drummond and Rosenbluth (1962) have first conducted a theoretical analysis of the current-driven ion-cyclotron wave instability, taking into account a uniform, magnetized plasma, without magnetic shear, in which electrons drift along B field lines with the same drift velocity at all points in the plasma. Bakshi et al. (1983) have found conditions for which the instability is completely quenched. This phenomenon has been referred to as filamental quenching. The present investigation is concerned with a systematic test of the filamental quenching effect. It is found that filamental quenching operates at widths of the current channel comparable to the local Larmor radius, in agreement with the conclusions of Bakshi et al.

Cartier, S. L.↗
NASA NTRS1985

The Influence of Containerless Undercooling and Rapid Solid-State Quenching on the Superconductive and Magnetic Properties of Some Clustering Alloy Systems

The potential of the 100-meter drop-tube for producing materials with new and important properties by their rapid solidification containerless undercooling was investigated. Materials produced exhibit evidence of very rapid quenching. The importance of rapid quenching in producing materials of considerable scientific and technological interest is emphasized. It is indicated that containerless undercooling, using at first a drop tube and eventually a space-shuttle-serviced orbiting laboratory, will provide another powerful approach for rapid quenching. A special advantage of the drop tube is that the microgravity condition is imposed ballistically; it is therefore possible to obtain either spherical samples by allowing solidification to take place in flight, or splats by allowing the sample material while still in undercooled liquid form to impact a stationary quench plate.

Collings, E. W.↗
NASA NTRS1991

Design and testing of an active quenching circuit for an avalanche photodiode photon detector

The photon-detection capabilities of avalanche photodiodes (APDs) operating above their theoretical breakdown voltages are described, with particular attention given to the needs and methods of quenching an avalanche once breakdown has occurred. A brief background on the motives of and previous work with this mode of operation is presented. Finally, a description of the design and testing of an active quenching circuit is given. Although the active quenching circuit did not perform as expected, knowledge was gained as to the signal amplitudes necessary for quenching and the need for a better model for the above-breakdown circuit characteristics of the Geiger-mode APD.

Arbel, D.↗
NASA NTRS1991

Temperature dependence of electronic energy transfer and quenching in copolymer films of styrene and 2-(2'-hydroxy-5'-vinylphenyl)-2H-benzotriazole

Quenching of the emission of both the polystyrene monomer and the excimer for a series of varying composition copolymer films of styrene and 2-(2'-hydroxy-5'-vinylphenyl)-2H-benzotriazole is reported. The preponderance of quenching for both the monomer and excimer emissions is due to interception of the migrating excitation at the quencher site, although additional quenching results via long-range dipole-dipole energy transfer from the monomer and excimer traps to the quencher trap. The quenching of the monomer fluorescence and phosphorescence and that of the excimer fluorescence were found to be temperature independent over the ranges 14-58 and 191-296 K, respectively. Most significantly, it is concluded that the energy migration process is temperature independent over the range 14-296 K.

O'Connor, Donald B.↗
NASA NTRS1997

The Role of Conical Intersections in Electronic Quenching of a State OH by H2 and N2

Lester and coworkers have experimentally characterized complexes of OH in the X and A states with H2 and N2. Recently, we have carried out ab initio calculations of relevant portions of the ground state and excited state potential energy surfaces for these systems, including the conical intersection regions, which are responsible for electronic quenching of the A state of OH by H2 and N2. Both of these systems have weakly bound complexes in the X state and strongly bound complexes in the A state. The OH-H2 complex is T-shaped, while the OH-N2 complex is collinear. In both cases the H end of OH is oriented toward the H2 or N2 molecule, respectively. Rotation of the OH about its center of mass involves only a small barrier and rotation by 1800 so that the 0 end of OH is oriented toward the H2 or N2 molecule leads to conical intersections with the ground state surface. Since there is about 95 kcal/mol of available energy after crossing to the ground state surface, chemical reactions on the ground state surface are possible, in addition to electronic quenching. In the case of OH-H2, the conical intersection is much lower in energy than the OH (A state) + H2 asymptotic energy and the A state complex can be characterized as a hanging well on the upper cone of the conical intersection. Passage through the conical intersection places the system on the ground state potential energy surface with the possibility of going to OH (X state) + H2 (i.e. electronic quenching) or to H2O + H (reaction). For OH-N2, the A state complex is also a hanging well on the upper cone of the conical intersection, but the conical intersection is only slightly below the OH (A state) + H2 asymptotic energy. Passage through the conical intersection can lead to OH (X state) + N2 (i.e. electronic quenching), but so far reactive pathways have not been found.

Walch, Stephen P.↗
NASA NTRS1993

The photophysics of monomeric bacteriochlorophylls c and d and their derivatives: properties of the triplet state and singlet oxygen photogeneration and quenching

Measurements of pigment triplet-triplet absorption, pigment phosphorescence and photosensitized singlet oxygen luminescence were carried out on solutions containing monomeric bacteriochlorophylls (Bchl) c and d, isolated from green photosynthetic bacteria, and their magnesium-free and farnesyl-free analogs. The energies of the pigment triplet states fell in the range 1.29-1.34 eV. The triplet lifetimes in aerobic solutions were 200-250 ns; they increased to 280 +/- 70 microseconds after nitrogen purging in liquid solutions and to 0.7-2.1 ms in a solid matrix at ambient or liquid nitrogen temperatures. Rate constants for quenching of the pigment triplet state by oxygen were (2.0-2.5) x 10(9) M-1 s-1, which is close to 1/9 of the rate constant for diffusion-controlled reactions. This quenching was accompanied by singlet oxygen formation. The quantum yields for the triplet state formation and singlet oxygen production were 55-75% in air-saturated solutions. Singlet oxygen quenching by ground-state pigment molecules was observed. Quenching was the most efficient for magnesium-containing pigments, kq = (0.31-1.2) x 10(9) M-1 s-1. It is caused mainly by a physical process of singlet oxygen (1O2) deactivation. Thus, Bchl c and d and their derivatives, as well as chlorophyll and Bchl a, combine a high efficiency of singlet oxygen production with the ability to protect photochemical and photobiological systems against damage by singlet oxygen.

NASA Discipline Number 52-30↗
NASA NTRS2011

Single photon detection with self-quenching multiplication

A photoelectronic device and an avalanche self-quenching process for a photoelectronic device are described. The photoelectronic device comprises a nanoscale semiconductor multiplication region and a nanoscale doped semiconductor quenching structure including a depletion region and an undepletion region. The photoelectronic device can act as a single photon detector or a single carrier multiplier. The avalanche self-quenching process allows electrical field reduction in the multiplication region by movement of the multiplication carriers, thus quenching the avalanche.

Zheng, Xinyu↗
NASA NTRS2015

Evolution of the Oxidation State of the Earth's Mantle: Challenges of High Pressure Quenching

The oxidation state of the Earth's mantle during formation remains an unresolved question, whether it was constant throughout planetary accretion, transitioned from reduced to oxidized, or from oxidized to reduced. We investigate the stability of Fe3+ at depth, in order to constrain processes (water, late accretion, dissociation of FeO) which may reduce or oxidize the Earth's mantle. Experiments of more mafic compositions and at higher pressures commonly form a polyphase quench intergrowth composed primarily of pyroxenes, with interstitial glass which hosts nearly all of the more volatile minor elements. In our previous experiments on shergottite compositions, variable fO2, T, and P is less than 4 GPa, Fe3+/TotFe decreased slightly with increasing P, similar to terrestrial basalt. For oxidizing experiments less than 7GPa, Fe3+/TotFe decreased as well, but it's unclear from previous modelling whether the deeper mantle could retain significant Fe3+. Our current experiments expand our pressure range deeper into the Earth's mantle and focus on compositions and conditions relevant to the early Earth. Experiments with Knippa basalt as the starting composition were conducted at 1-8 GPa and 1800 C, using a molybdenum capsule to set the fO2 near IW, by buffering with Mo-MoO3. TEM and EELS analyses revealed the run products from 7-8 GPa quenched to polycrystalline phases, with the major phase pyroxene containing approximately equal Fe3+/2+. A number of different approaches have been employed to produce glassy samples that can be measured by EELS and XANES. A more intermediate andesite was used in one experiment, and decompression during quenching was attempted after, but both resulted in a finer grained polyphase texture. Experiments are currently underway to test different capsule materials may affect quench texture. A preliminary experiment using liquid nitrogen to greatly enhance the rate of cooling of the assembly has also been attempted and this technique will be refined in further experiments.

Danielson, L. R.↗