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DOE OSTI2020

Diffusivity and Structure of Room Temperature Ionic Liquid in Various Organic Solvents

Room-temperature ionic liquids (RTILs) hold promise for applications in electric double layer capacitors (EDLCs), owing to a much wider potential window, lower vapor pressure, and better thermal and chemical stabilities compared to conventional aqueous and organic electrolytes. However, because the low diffusivity of ions in neat RTILs negates the EDLCs’ advantage of high power density, the ionic liquids are often used in mixture with organic solvents. In this study, we measured the diffusivity of cations and anions in RTIL, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) ([BMIM + ][TFSI – ]), mixed with 10 organic solvents, by using the pulsed-field gradient NMR method. The ion diffusivity was found to follow that of neat solvents and in most studied solvents showed an excellent agreement with the predicted values reported in the recent molecular dynamics (MD) study [Thompson, M. W.; J. Phys. Chem. B 2019, 123, 1340-1347]. In two solvents consisting of long-chain molecules, however, the MD simulations predictions slightly underestimated the ionic diffusivities. The degree of ion dissociation was also estimated for each solvent by comparing the ionic conductivity with the molar conductivity derived from the diffusion measurements. The degree of ion dissociation and the hydrodynamic radius of ions suggest that the ions are coordinated by ~1 solvent molecule. Finally, the scarcity of solvent–ion interactions explains the fact that the diffusivity of ions in the mixture significantly depends on the viscosity of the solvent.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

First-principles study of an S = 1 quasi one-dimensional quantum molecular magnetic material

We use density functional theory to study the structural, magnetic, and electronic structures of the organometallic quantum magnet NiCl 2-4 SC (NH 2 ) 2 (DTN). Recent work has demonstrated the quasi one-dimensional nature of the molecular crystal and studied its quantum phase transitions at low temperatures. The system includes a magnetoelectric (ME) coupling and, when doped with Br, the presence of an exotic Bose-glass state. Using the generalized gradient approximation with inclusion of a van der Waals term to account for weak intermolecular forces and by introducing a Hubbard U term to the total energy, we systematically show that our calculations reproduce the magnetic anisotropy, the intermolecular exchange coupling strength, and the magnetoelectric effect in DTN, which have been observed in previous experiments. Further analysis of the electronic structure gives insight into the underlying magnetic interactions, including what mechanisms may be causing the ME effect. Using this computationally efficient model, we predict what effect applying an electric field might have on the magnetic properties of this quantum magnet.

1-dimensional spin chains↗

NASA NTRS1979

Stable dielectric charge distributions from field enhancement of secondary mission

The emission of secondary electrons from dielectrics subject to numerous effects of electric field which are experimentally difficult to control is discussed. Measurements are reported using pulse techniques such that local fields do not build to significant levels, but measurements with fields present are also of interest. A specific series of measurements under controlled conditions are described and their implications in terms of fields, magnitude and angle, near the dielectric surface were examined. The measurements were made for a charged fluorinated-ethylene-propylene surface near a grounded aluminum half-round resting on the surface. The geometry produced a stable surface-charge gradient being controlled by a strongly enhanced secondary emission for which a model is constructed. Observations of surface flashovers under various conditions confirm the predictions of some scaling exercises.

Robinson, J. W.↗

NASA NTRS2005

Novel Applications of Magnetic Fields for Fluid Flow Control and for Simulating Variable Gravity Conditions

Static and dynamic magnetic fields have been used to control convection in many materials processing applications. In most of the applications, convection control (damping or enhancement) is achieved through the Lorentz force that can be tailored to counteract/assist dominant system flows. This technique has been successfully applied to liquids that are electrically conducting, such as high temperature melts of semiconductors, metals and alloys, etc. In liquids with low electrical conductivity such as ionic solutions of salts in water, the Lorentz force is weak and hence not very effective and alternate ways of flow control are necessary. If the salt in solution is paramagnetic then the variation of magnetic susceptibility with temperature and/or concentration can be used for flow control. For thermal buoyancy driven flows this can be accomplished in a temperature range below the Curie point of the salt. The magnetic force is proportional to the magnetic susceptibility and the product of the magnetic field and its gradient. By suitably positioning the experiment cell in the magnet, system flows can be assisted or countered, as desired. A similar approach can be extended to diamagnetic substances and fluids but the required magnetic force is considerably larger than that required for paramagnetic substances. The presentation will provide an overview of work to date on a NASA fluid physics sponsored project that aims to test the hypothesis of convective flow control using strong magnetic fields in protein crystal growth. The objective is to understand the nature of the various forces that come into play, delineate causative factors for fluid flow and to quantify them through experiments, analysis, and numerical modeling. The seminar will report specifically on the experimental results using paramagnetic salts and solutions in magnetic fields and compare them to analytical predictions. Applications of the concept to protein crystallization studies will be discussed. The use of strong magnetic fields for terrestrially simulating variable gravity environments and applications supporting the NASA Exploration Initiative will also be briefly discussed.

Ramachandran, N.↗

DOE OSTI2026

Ion Transport and Crystal Rotation in Plastic Crystal Electrolytes Under Applied Electric Fields

Organic ionic plastic crystal electrolytes, containing a plastic crystal and lithium salt, offer a potential balance between mechanical and electrochemical properties for solid state lithium-ion battery electrolytes. These electrolytes contain multiple mobile ionic species (three or four), resulting in complex transport mechanisms which have not yet been established. Plastic crystals are defined by long-range positional order and short-range rotational disorder. It is therefore necessary to quantify changes in the local crystal structure of the electrolyte as current flows through it. Herein, we examine the electrochemical properties of pyrrolidinium-based plastic crystal electrolytes containing lithium salt and zwitterion additives, including measurements of current fraction and limiting current. We obtain species-specific insight into electrolyte transport using pulsed-field gradient nuclear magnetic resonance spectroscopy and find that, while the zwitterion additive increases ionic conductivity, it decreases lithium diffusivity with respect to other ionic components. With operando spatiotemporally resolved wide-angle X-ray scattering we observe location-specific crystal rotations due to the passage of ionic current. In conclusion, we posit that reducing energy dissipation due to rotation is essential for using plastic crystal electrolytes in practical applications.

Yap, Kyra M. K. [University of California, Berkele↗

NASA NTRS1986

A three-dimensional MHD simulation of the interaction of the solar wind with the earth's magnetosphere - The generation of field-aligned currents

The time-dependent interaction of the solar wind with the earth's magnetosphere is simulated using a three-dimensional MHD model. The bow shock, magnetopause, magnetotail, and plasma sheet of the magnetosphere and Birkeland field-aligned currents that are dependent on the polarity of the z component of the IMF are produced. Twin convection cells and a dawn to dusk electric potential of 30-100 kV are detected at the equator in the magnetosphere. Four types of field-aligned currents are observed: region 1, region 2, dayside magnetopause currents in the dayside cusp region, and the dayside cusp currents for southward IMF. Region 1 and 2 field-aligned currents generated for all IMF conditions are 0.6-1.0 x 10 to the 6th A and 0.15-0.61 x 10 to the 6th A, respectively. The relationship between region 1 currents and field-aligned vorticity, and region 2 currents and pressure gradients are studied. The simulated data are compared with a theoretical analysis of the field-aligned currents and good correlation is observed.

Ogino, T.↗

NASA NTRS2003

Cluster electric current density measurements within a magnetic flux rope in the plasma sheet

On August 22, 2001 all 4 Cluster spacecraft nearly simultaneously penetrated a magnetic flux rope in the tail. The flux rope encounter took place in the central plasma sheet, Beta(sub i) approx. 1-2, near the leading edge of a bursty bulk flow. The "time-of-flight" of the flux rope across the 4 spacecraft yielded V(sub x) approx. 700 km/s and a diameter of approx.1 R(sub e). The speed at which the flux rope moved over the spacecraft is in close agreement with the Cluster plasma measurements. The magnetic field profiles measured at each spacecraft were first modeled separately using the Lepping-Burlaga force-free flux rope model. The results indicated that the center of the flux rope passed northward (above) s/c 3, but southward (below) of s/c 1, 2 and 4. The peak electric currents along the central axis of the flux rope predicted by these single-s/c models were approx.15-19 nA/sq m. The 4-spacecraft Cluster magnetic field measurements provide a second means to determine the electric current density without any assumption regarding flux rope structure. The current profile determined using the curlometer technique was qualitatively similar to those determined by modeling the individual spacecraft magnetic field observations and yielded a peak current density of 17 nA/m2 near the central axis of the rope. However, the curlometer results also showed that the flux rope was not force-free with the component of the current density perpendicular to the magnetic field exceeding the parallel component over the forward half of the rope, perhaps due to the pressure gradients generated by the collision of the BBF with the inner magnetosphere. Hence, while the single-spacecraft models are very successful in fitting flux rope magnetic field and current variations, they do not provide a stringent test of the force-free condition.

Slavin, J. A.↗

NASA NTRS1972

Electrostatic waves in the magnetosphere.

Electric dipole antennas on magnetospheric spacecraft measure E field components of many kinds of electromagnetic waves. In addition, lower hybrid resonance emissions are frequently observed well above the ionosphere. The Ogo 5 plasma wave experiment has also detected new forms of electrostatic emissions that appear to interact very strongly with the local plasma particles. Greatly enhanced wave amplitudes have been found during the expansion phases of substorms, and analysis indicates that these emissions produce strong pitch angle diffusion. Intense broadband electrostatic turbulence is also detected at current layers containing steep magnetic field gradients. This current-driven instability is operative at the bow shock and also at field null regions just within the magnetosheath, and at the magnetopause near the dayside polar cusp. The plasma turbulence appears to involve ion acoustic waves, and the wave particle scattering provides an important collisionless dissipation mechanism for field merging.

Scarf, F. L.↗

DOE OSTI2021

Higher Ion Selectivity with Lower Energy Usage Promoted by Electro-osmotic Flow in the Transport through Conical Nanopores

The tradeoff between selectivity and throughput presents fundamental challenges to improve desalination and charge storage, salinity gradient-based energy harvesting, memory device/circuit development, and so forth. The well-known ion-current rectification and the recently resolved time-dependent transport hysteresis in conical nanopores or asymmetric nanointerfaces offer new opportunities for the selective transport of matter. This report shows that electro-osmotic flow (EOF) is an overlooked factor that increases ion selectivity while maintaining enhanced transport throughput in rectified nanoscale electrokinetic transport. The increased selectivity originates primarily from the suppression of anion flux by the fluid flow in the opposite direction under the applied electrical field. By solving the Poisson and Nernst–Planck (PNP) equations without and with coupled Navier–Stokes (PNP–NS) equations, the EOF effects on cation and anion transport are unequivocally revealed in asymmetric nanopipettes. The flux of cations and anions as well as the transference number and flow velocity are elucidated using the models and boundary conditions validated by previous experiments. A dimensionless parameter, radius over the Debye length, reveals optimal ion selectivity and energy cost at intermediate ion concentrations and nanopore sizes, up to hundreds of millimolars and tens of nanometers under time-dependent potential stimulus. Furthermore, the fundamental insights into EOF at nanointerfaces suggest new routes/strategies for better separation, analysis, and energy applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1992

Reversible electron heating vs. wave-particle interactions in quasi-perpendicular shocks

The energy necessary to explain the electron heating in quasi-perpendicular collisionless shocks can be derived either from the electron acceleration in the d.c. cross shock electric potential, or by the interactions between the electrons and the waves existing in the shock. A Monte Carlo simulation has been performed to study the electron distribution function evolution through the shock structure, with and without particle diffusion on waves. This simulation has allowed us to clarify the relative importance of the two possible energy sources; in particular it has been shown that the electron parallel temperature is determined by the d.c. electromagnetic field and not by any wave-particle-induced heating. Wave particle interactions are effective in smoothing out the large gradients in phase space produced by the 'reversible' motion of the electrons, thus producing a 'cooling' of the electrons.

Veltri, P.↗

NASA NTRS1996

Studies of Westward Electrojets and Field-Aligned Currents in the Magnetotail During Substorms: Implications for Magnetic Field Models

This section outlines those tasks undertaken in the final year that contribute integrally to the overarching project goals. Fast, during the final year, it is important to note that the project benefited greatly with the addition of a Boston University graduate student, Ms. Karen Hirsch. Jointly, we made substantial progress on the development of and improvements to magnetotail magnetic field and plasma models. The ultimate aim of this specific task was to assess critically the utility of such models for mapping low-altitude phenomena into the magnetotail (and vice-versa). The bulk of this effort centered around the finite-width- magnetotail convection model developed by and described by Spence and Kivelson (J. Geophys. Res., 98, 15,487, 1993). This analytic, theoretical model specifies the bulk plasma characteristics of the magnetotail plasma sheet (number density, temperature, pressure) across the full width of the tail from the inner edge of the plasma sheet to lunar distances. Model outputs are specified by boundary conditions of the source particle populations as well as the magnetic and electric field configuration. During the reporting period, we modified this code such that it can be interfaced with the auroral particle precipitation model developed by Dr. Terry Onsager. Together, our models provide a simple analytic specification of the equatorial distribution of fields and plasma along with their low-altitude consequences. Specifically, we have built a simple, yet powerful tool which allows us to indirectly 'map' auroral precipitation signatures (VDIS, inverted-V's, etc.) measured by polar orbiting spacecraft in the ionosphere, to the magnetospheric equatorial plane. The combined models allow us to associate latitudinal gradients measured in the ion energy fluxes at low-altitudes with the large-scale pressure gradients in the equatorial plane. Given this global, quasi-static association, we can then make fairly strong statements regarding the location of discrete features in the context of the global picture. We reported on our initial study at national and international meetings and published the results of our predictions of the low-altitude signatures of the plasma sheet. In addition, the PI was invited to contribute a publication to the so-called 'Great Debate in Space Physics' series that is a feature of EOS. The topic was on the nature of magnetospheric substorms. Specific questions of the when and where a substorm occurs and the connection between the auroral and magnetospheric components were discussed in that paper. This paper therefore was derived exclusively from the research supported by this grant. Attachment: Empirical modeling of the quite time nightside magnetosphere.' 'CRRES observations of particle flux dropout event.' The what, where, when, and why of magnetospheric substorm triggers'. and 'Low altitude signature of the plasma sheet: model prediction of local time dependence'.

Spence, Harlan E.↗

DOE OSTI2025

Turbulence and transport in mirror geometries in the Large Plasma Device

Thanks to advances in plasma science and enabling technology, mirror machines are being reconsidered for fusion power plants and as possible fusion volumetric neutron sources. However, cross-field transport and turbulence in mirrors remains relatively understudied compared with toroidal devices. Turbulence and transport in mirror configurations were studied utilizing the flexible magnetic geometry of the Large Plasma Device (LAPD). Multiple mirror ratios from $M=1$ to $M=2.68$ and three mirror-cell lengths from $L=3.51$ to $L=10.86$ m were examined. Langmuir and magnetic probes were used to measure profiles of density, temperature, potential and magnetic field. The electric field-fluctuation-driven ${\tilde {\boldsymbol{E}}} \times {\boldsymbol{B}}$ particle flux, where $\boldsymbol{B}$ is the background field, was calculated from these quantities. Two probe correlation techniques were used to infer wavenumbers and two-dimensional structure. Cross-field particle flux and density fluctuation power decreased with increased mirror ratio. Core density and temperatures remain similar with mirror ratio, but radial line-integrated density increased. The physical expansion of the plasma in the mirror cell by using a higher field in the source region may have led to reduced density fluctuation power through the increased gradient scale length. This increased scale length reduced the growth rate and saturation level of rotational interchange and drift-like instabilities. Despite the introduction of magnetic curvature, no evidence of mirror-driven instabilities – interchange, velocity space or otherwise – were observed. For curvature-induced interchange, many possible stabilization mechanisms were present, suppressing the visibility of the instability.

Travis, Phil (ORCID:0000000343170432)↗

NASA NTRS1972

Unipolar interaction of Mercury with the solar wind - The steady state bow shock problem.

The steady state electromagnetic interaction of the solar wind with the planet Mercury is computed for a spectrum of electrical conductivity functions using the assumption that no atmosphere or planetary magnetic field prohibits the direct interaction. The form of the induction is described by the unipolar effect and corresponds to the zero frequency limit of a transverse magnetic (TM) mode. Calculations are included to determine the effective surface temperature of the planet. These calculations include the apparent motion of the sun in the Hermean sky. It is shown that a significant interaction, detectable by a space probe, is plausible for reasonable conductivity functions. The strength of the interaction is considered in terms of the subsurface thermal gradient, and computations are given relating the strength of the solar wind interaction with the conductivity parameters.

Colburn, D. S.↗

NASA NTRS1983

Hydromagnetic vortices. I - The 11 December 1977 event

Through a synthesis of magnetometer, plasma, energetic particle and electric field data from the ISEE satellite pair, the characteristics of the initial (11 December 1977) magnetotail plasma vortex event reported by Hones et al. (1978), are described. The event is associated with a hot (beta is approximately unity) compressional hydromagnetic wave and apparent vortical motion is seen because at two points in the flow cycle the flow is field-aligned. The behavior of the energetic ions receives special study: when combined with the thermal flow measurements energy dispersion is evident in the field-aligned flow, while the large pitch angle energetic ions reveal the presence of gradients. It is argued that these gradients are wave-induced, and the data are used to determine the perpendicular wave wavelength together with the speed and direction of transverse wave propagation.

Saunders, M. A.↗

NASA NTRS2008

Remote Sensing of the Ionosphere and Plasmasphere from Space Using Radiowaves

Topics include the scientific context, trans-ionospheric and sounding, small-scale structure, plasmasphere, fast and slow tomography, and pseudo-imaging. Individual slides focus on where geospace science stands today, variability in inner magnetosphere electric fields, Appleton-Hartree formula, phase and range ionospheric observables, examples of leveling, large ionization changes during storms, new mid-latitude phenomena, ionospheric sounding, COSMIC CERTO/Tri-band beacon, LEO-ground radio tomography, irregularity measurements, COSMIC, critical sensor data from COSMIC GPS limb sounding, occultation geometry, comparison of calibrated slant TEC measurements for 26 June 2006, historic examples of Abel electron density profiles, comparison of UCAR and JPL Able profiles of 26 June 2006, validating UCAR and JPL Abel profiles using Arecibo ISR measurements for 26 June 2006, E-region from GPS/MET 1995, Abel versus gradient assisted retrieval, 3000 profiles/day, plasmasphere, JASON TEC above satellite, GPS equatorial plasmasphere measurements, April 2002 geomagnetic storm, and space-based GPS tomography.

ionosphere↗

NASA NTRS2016

Plasma Oscillation Characterization of NASA's HERMeS Hall Thruster via High Speed Imaging

The performance and facility effect characterization tests of NASA's 12.5-kW Hall Effect Rocket with Magnetic Shielding had been completed. As a part of these tests, three plasma oscillation characterization studies were performed to help determine operation settings and quantify margins. The studies included the magnetic field strength variation study, background pressure effect study, and cathode flow fraction study. Separate high-speed videos of the thruster including the cathode and of only the cathode were recorded. Breathing mode at 10-15 kHz and cathode gradient-driven mode at 60-75 kHz were observed. An additional high frequency (40-70 kHz) global oscillation mode with sinusoidal probability distribution function was identified.

Ground Tests↗

NASA NTRS1973

Speed and thickness of the magnetopause.

We have used the finite gyroradius of protons with energies greater than 140 keV to determine the location of the magnetopause when the satellite is within the adjacent steep proton flux gradient. This steep gradient region is usually two to four 140-keV proton gyroradii, or about 1000 to 4000 km thick. The measurements described here were made within 45 deg of the earth-sun line on moderately disturbed days, when proton fluxes were unusually high. On these days, the magnetopause usually moves at a speed of less than 20 km/sec. The magnetopause velocity sometimes changes abruptly, while remaining below 20 km/sec. Very rapid (about 50 km/sec) radial motion appears to be associated with the propagation of single, isolated waves along the magnetopause. The thickness of the electric current sheet that produces the magnetic field rotation in the magnetopause is usually on the order of 10 times the gyroradius of a 1-keV proton, or about 1000 km.

Kaufmann, R. L.↗

NASA NTRS1992

Field and thermal plasma observations of ULF pulsations during a magnetically disturbed interval

A ULF pulsation event is discussed on the basis of experimental observations of electric and magnetic field measurements as well as particle measurements from the DE 1 spacecraft. The observations were made near the magnetic equator in a space covering a large range of L shells and magnetic latitudes, and comparisons are made to ground observations. Azimuthal oscillations are observed following gradually decaying long-period compressional waves. Weak interaction between magnetic shells indicates that the source is probably weak, and ground data on magnetic pulsations showed strong signals that did not necessarily correspond to the quasisinusoidal pulsations observed in space. Azimuthal pulsations observed by the spacecraft indicate that there was a plasma density gradient beyond the plasmapause. The ULF pulsations were probably affected by changes in the magnetic field and solar-wind dynamic pressure, and their periods are found to be linked to geomagnetic latitude.

Lin, N.↗