Sample records for hall current ionslip

  1. Global well-posedness and asymptotic behavior of solutions for the three-dimensional MHD equations with Hall and ion-slip effects

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaopeng; Zhu, Mingxuan

    2018-04-01

    In this paper, we consider the small initial data global well-posedness of solutions for the magnetohydrodynamics with Hall and ion-slip effects in R^3. In addition, we also establish the temporal decay estimates for the weak solutions. With these estimates in hand, we study the algebraic time decay for higher-order Sobolev norms of small initial data solutions.

  2. Faster Hall-Effect Current-Measuring Circuit

    NASA Technical Reports Server (NTRS)

    Sullender, Craig C.; Johnson, Daniel D.; Walker, Daniel D.

    1993-01-01

    Current-measuring circuit operates on Hall-effect-sensing and magnetic-field-nulling principles similar to those described in article, "Nulling Hall-Effect Current-Measuring Circuit" (LEW-15023), but simpler and responds faster. Designed without feedback loop, and analog pulse-width-modulated output indicates measured current. Circuit measures current at frequency higher than bandwidth of its Hall-effect sensor.

  3. Nulling Hall-Effect Current-Measuring Circuit

    NASA Technical Reports Server (NTRS)

    Sullender, Craig C.; Vazquez, Juan M.; Berru, Robert I.

    1993-01-01

    Circuit measures electrical current via combination of Hall-effect-sensing and magnetic-field-nulling techniques. Known current generated by feedback circuit adjusted until it causes cancellation or near cancellation of magnetic field produced in toroidal ferrite core by current measured. Remaining magnetic field measured by Hall-effect sensor. Circuit puts out analog signal and digital signal proportional to current measured. Accuracy of measurement does not depend on linearity of sensing components.

  4. A non-invasive Hall current distribution measurement system for Hall Effect thrusters

    NASA Astrophysics Data System (ADS)

    Mullins, Carl Raymond

    A direct, accurate method to measure thrust produced by a Hall Effect thruster on orbit does not currently exist. The ability to calculate produced thrust will enable timely and precise maneuvering of spacecraft---a capability particularly important to satellite formation flying. The means to determine thrust directly is achievable by remotely measuring the magnetic field of the thruster and solving the inverse magnetostatic problem for the Hall current density distribution. For this thesis, the magnetic field was measured by employing an array of eight tunneling magnetoresistive (TMR) sensors capable of milligauss sensitivity when placed in a high background field. The array was positioned outside the channel of a 1.5 kW Colorado State University Hall thruster equipped with a center-mounted electride cathode. In this location, the static magnetic field is approximately 30 Gauss, which is within the linear operating range of the TMR sensors. Furthermore, the induced field at this distance is greater than tens of milligauss, which is within the sensitivity range of the TMR sensors. Due to the nature of the inverse problem, the induced-field measurements do not provide the Hall current density by a simple inversion; however, a Tikhonov regularization of the induced field along with a non-negativity constraint and a zero boundary condition provides current density distributions. Our system measures the sensor outputs at 2 MHz allowing the determination of the Hall current density distribution as a function of time. These data are shown in contour plots in sequential frames. The measured ratios between the average Hall current and the discharge current ranged from 0.1 to 10 over a range of operating conditions from 1.3 kW to 2.2 kW. The temporal inverse solution at 2.0 kW exhibited a breathing mode of 37 kHz, which was in agreement with temporal measurements of the discharge current.

  5. Non-invasive Hall current distribution measurement in a Hall effect thruster

    NASA Astrophysics Data System (ADS)

    Mullins, Carl R.; Farnell, Casey C.; Farnell, Cody C.; Martinez, Rafael A.; Liu, David; Branam, Richard D.; Williams, John D.

    2017-01-01

    A means is presented to determine the Hall current density distribution in a closed drift thruster by remotely measuring the magnetic field and solving the inverse problem for the current density. The magnetic field was measured by employing an array of eight tunneling magnetoresistive (TMR) sensors capable of milligauss sensitivity when placed in a high background field. The array was positioned just outside the thruster channel on a 1.5 kW Hall thruster equipped with a center-mounted hollow cathode. In the sensor array location, the static magnetic field is approximately 30 G, which is within the linear operating range of the TMR sensors. Furthermore, the induced field at this distance is approximately tens of milligauss, which is within the sensitivity range of the TMR sensors. Because of the nature of the inverse problem, the induced-field measurements do not provide the Hall current density by a simple inversion; however, a Tikhonov regularization of the induced field does provide the current density distributions. These distributions are shown as a function of time in contour plots. The measured ratios between the average Hall current and the average discharge current ranged from 6.1 to 7.3 over a range of operating conditions from 1.3 kW to 2.2 kW. The temporal inverse solution at 1.5 kW exhibited a breathing mode frequency of 24 kHz, which was in agreement with temporal measurements of the discharge current.

  6. Non-invasive Hall current distribution measurement in a Hall effect thruster.

    PubMed

    Mullins, Carl R; Farnell, Casey C; Farnell, Cody C; Martinez, Rafael A; Liu, David; Branam, Richard D; Williams, John D

    2017-01-01

    A means is presented to determine the Hall current density distribution in a closed drift thruster by remotely measuring the magnetic field and solving the inverse problem for the current density. The magnetic field was measured by employing an array of eight tunneling magnetoresistive (TMR) sensors capable of milligauss sensitivity when placed in a high background field. The array was positioned just outside the thruster channel on a 1.5 kW Hall thruster equipped with a center-mounted hollow cathode. In the sensor array location, the static magnetic field is approximately 30 G, which is within the linear operating range of the TMR sensors. Furthermore, the induced field at this distance is approximately tens of milligauss, which is within the sensitivity range of the TMR sensors. Because of the nature of the inverse problem, the induced-field measurements do not provide the Hall current density by a simple inversion; however, a Tikhonov regularization of the induced field does provide the current density distributions. These distributions are shown as a function of time in contour plots. The measured ratios between the average Hall current and the average discharge current ranged from 6.1 to 7.3 over a range of operating conditions from 1.3 kW to 2.2 kW. The temporal inverse solution at 1.5 kW exhibited a breathing mode frequency of 24 kHz, which was in agreement with temporal measurements of the discharge current.

  7. Intrinsic superspin Hall current

    NASA Astrophysics Data System (ADS)

    Linder, Jacob; Amundsen, Morten; Risinggârd, Vetle

    2017-09-01

    We discover an intrinsic superspin Hall current: an injected charge supercurrent in a Josephson junction containing heavy normal metals and a ferromagnet generates a transverse spin supercurrent. There is no accompanying dissipation of energy, in contrast to the conventional spin Hall effect. The physical origin of the effect is an antisymmetric spin density induced among transverse modes ky near the interface of the superconductor arising due to the coexistence of p -wave and conventional s -wave superconducting correlations with a belonging phase mismatch. Our predictions can be tested in hybrid structures including thin heavy metal layers combined with strong ferromagnets and ordinary s -wave superconductors.

  8. Bending strain engineering in quantum spin hall system for controlling spin currents

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Huang, Bing; Jin, Kyung-Hwan; Cui, Bin

    Quantum spin Hall system can exhibit exotic spin transport phenomena, mediated by its topological edge states. The concept of bending strain engineering to tune the spin transport properties of a quantum spin Hall system is demonstrated. Here, we show that bending strain can be used to control the spin orientation of counter-propagating edge states of a quantum spin system to generate a non-zero spin current. This physics mechanism can be applied to effectively tune the spin current and pure spin current decoupled from charge current in a quantum spin Hall system by control of its bending curvature. Moreover, the curvedmore » quantum spin Hall system can be achieved by the concept of topological nanomechanical architecture in a controllable way, as demonstrated by the material example of Bi/Cl/Si(111) nanofilm. This concept of bending strain engineering of spins via topological nanomechanical architecture affords a promising route towards the realization of topological nano-mechanospintronics.« less

  9. Bending strain engineering in quantum spin hall system for controlling spin currents

    DOE PAGES

    Huang, Bing; Jin, Kyung-Hwan; Cui, Bin; ...

    2017-06-16

    Quantum spin Hall system can exhibit exotic spin transport phenomena, mediated by its topological edge states. The concept of bending strain engineering to tune the spin transport properties of a quantum spin Hall system is demonstrated. Here, we show that bending strain can be used to control the spin orientation of counter-propagating edge states of a quantum spin system to generate a non-zero spin current. This physics mechanism can be applied to effectively tune the spin current and pure spin current decoupled from charge current in a quantum spin Hall system by control of its bending curvature. Moreover, the curvedmore » quantum spin Hall system can be achieved by the concept of topological nanomechanical architecture in a controllable way, as demonstrated by the material example of Bi/Cl/Si(111) nanofilm. This concept of bending strain engineering of spins via topological nanomechanical architecture affords a promising route towards the realization of topological nano-mechanospintronics.« less

  10. Hall Current Plasma Source Having a Center-Mounted or a Surface-Mounted Cathode

    NASA Technical Reports Server (NTRS)

    Martinez, Rafael A. (Inventor); Moritz, Jr., Joel A. (Inventor); Williams, John D. (Inventor); Farnell, Casey C. (Inventor)

    2018-01-01

    A miniature Hall current plasma source apparatus having magnetic shielding of the walls from ionized plasma, an integrated discharge channel and gas distributor, an instant-start hollow cathode mounted to the plasma source, and an externally mounted keeper, is described. The apparatus offers advantages over other Hall current plasma sources having similar power levels, including: lower mass, longer lifetime, lower part count including fewer power supplies, and the ability to be continuously adjustable to lower average power levels using pulsed operation and adjustment of the pulse duty cycle. The Hall current plasma source can provide propulsion for small spacecraft that either do not have sufficient power to accommodate a propulsion system or do not have available volume to incorporate the larger propulsion systems currently available. The present low-power Hall current plasma source can be used to provide energetic ions to assist the deposition of thin films in plasma processing applications.

  11. Field-aligned current and auroral Hall current characteristics derived from the Swarm constellation

    NASA Astrophysics Data System (ADS)

    Huang, Tao; Wang, Hui; Hermann, Luehr

    2017-04-01

    On the basis of field-aligned currents (FACs) and Hall currents derived from high-resolution magnetic field data of the Swarm constellation the average characteristics of these two current systems in the auroral regions are comprehensively investigated by statistical methods. This is the first study considering both current types simultaneously and for both hemispheres. The FAC distribution, derived from the Swarm dual-spacecraft approach, reveals the well-known features of Region 1 (R1) and Region 2 (R2) FACs. At high latitudes, Region 0 (R0) FACs appear on the dayside. Their direction depends on the orientation of the interplanetary magnetic field (IMF) By component. Of particular interest is the distribution of auroral Hall currents. The most prominent auroral electrojets are found to be closely controlled by the solar wind input. But there is no dependence on the IMF By orientation. The eastward electrojet is about twice as strong in summer as in winter. Conversely, the westward electrojet shows less dependence on season. Part of the electrojet current is closed over the polar cap. Here the seasonal variation of conductivity mainly controls the current density. There is a clear channeling of return currents over the polar cap. Depending on IMF By orientation most of the current is flowing either on the dawn or dusk side. The direction of Hall currents in the noon sector depends directly on the orientation of the IMF By. This is true for both signs of the IMF Bz component. But largest differences between summer and winter seasons are found for northward IMF Bz. Around the midnight sector the westward substorm electrojet is dominating. As expected, it is highly dependent on magnetic activity, but shows only little response to the IMF By polarity.

  12. Another Nulling Hall-Effect Current-Measuring Circuit

    NASA Technical Reports Server (NTRS)

    Thibodeau, Phillip E.; Sullender, Craig C.

    1993-01-01

    Lightweight, low-power circuit provides noncontact measurement of alternating or direct current of many ampheres in main conductor. Advantages of circuit over other nulling Hall-effect current-measuring circuits is stability and accuracy increased by putting both analog-to-digital and digital-to-analog converters in nulling feedback loop. Converters and rest of circuit designed for operation at sampling rate of 100 kHz, but rate changed to alter time or frequency response of circuit.

  13. Anomalous Hall resistance in bilayer quantum Hall systems

    NASA Astrophysics Data System (ADS)

    Ezawa, Z. F.; Suzuki, S.; Tsitsishvili, G.

    2007-07-01

    We present a microscopic theory of the Hall current in the bilayer quantum Hall system on the basis of noncommutative geometry. By analyzing the Heisenberg equation of motion and the continuity equation of charge, we demonstrate the emergence of the phase current in a system where the interlayer phase coherence develops spontaneously. The phase current arranges itself to minimize the total energy of the system, as it induces certain anomalous behaviors in the Hall current in the counterflow geometry and also in the drag experiment. They explain the recent experimental data for anomalous Hall resistances due to Kellogg [Phys. Rev. Lett. 88, 126804 (2002); 93, 036801 (2004)] and Tutuc [Phys. Rev. Lett. 93, 036802 (2004)] at ν=1 .

  14. A programmable quantum current standard from the Josephson and the quantum Hall effects

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Poirier, W., E-mail: wilfrid.poirier@lne.fr; Lafont, F.; Djordjevic, S.

    We propose a way to realize a programmable quantum current standard (PQCS) from the Josephson voltage standard and the quantum Hall resistance standard (QHR) exploiting the multiple connection technique provided by the quantum Hall effect (QHE) and the exactness of the cryogenic current comparator. The PQCS could lead to breakthroughs in electrical metrology like the realization of a programmable quantum current source, a quantum ampere-meter, and a simplified closure of the quantum metrological triangle. Moreover, very accurate universality tests of the QHE could be performed by comparing PQCS based on different QHRs.

  15. Low operational current spin Hall nano-oscillators based on NiFe/W bilayers

    NASA Astrophysics Data System (ADS)

    Mazraati, Hamid; Chung, Sunjae; Houshang, Afshin; Dvornik, Mykola; Piazza, Luca; Qejvanaj, Fatjon; Jiang, Sheng; Le, Tuan Q.; Weissenrieder, Jonas; Åkerman, Johan

    2016-12-01

    We demonstrate highly efficient spin Hall nano-oscillators (SHNOs) based on NiFe/β-W bilayers. Thanks to the very high spin Hall angle of β-W, we achieve more than a 60% reduction in the auto-oscillation threshold current compared to NiFe/Pt bilayers. The structural, electrical, and magnetic properties of the bilayers, as well as the microwave signal generation properties of the SHNOs, have been studied in detail. Our results provide a promising path for the realization of low-current SHNO microwave devices with highly efficient spin-orbit torque from β-W.

  16. Experimental Investigation of a Hall-Current Accelerator. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Plank, G. M.

    1983-01-01

    The Hall-current accelerator is being investigated for use in the 1000-2000 sec. range of specific impulse. Three models of this thruster were tested. The first two models had three permanent magnets to supply the magnetic field and the third model had six magnets to supply the field. The third model thus had approximately twice the magnetic field of the first two. The first and second models differ only in the shape of the magnetic field. All other factors remained the same for the three models except for the anode-cathode distance, which was changed to allow for the three thrusters to have the same magnetic field integral between the anode and the cathode. These Hall thrusters were tested to determine the plasma properties, the beam characteristics, and the thruster characteristics. The thruster operated in three modes: (1) main cathode only, (2) main cathode with neutralizer cathode, and (3) neutralizer cathode only. The plasma properties were measured along an axial line, 1 mm inside the cathode radius, at a distance of 0.2 to 6.2 cm from the anode. Results show that the current used to heat the cathode produced nonuniformities in the magnetic field, hence also in the plasma properties. In a Hall thruster this general design appears to provide the most thrust when operated at a magnetic field less than the maximum value studied.

  17. Effects of Hall current and electrical resistivity on the stability of gravitating anisotropic quantum plasma

    NASA Astrophysics Data System (ADS)

    Bhakta, S.; Prajapati, R. P.

    2018-02-01

    The effects of Hall current and finite electrical resistivity are studied on the stability of uniformly rotating and self-gravitating anisotropic quantum plasma. The generalized Ohm's law modified by Hall current and electrical resistivity is used along with the quantum magnetohydrodynamic fluid equations. The general dispersion relation is derived using normal mode analysis and discussed in the parallel and perpendicular propagations. In the parallel propagation, the Jeans instability criterion, expression of critical Jeans wavenumber, and Jeans length are found to be independent of non-ideal effects and uniform rotation but in perpendicular propagation only rotation affects the Jeans instability criterion. The unstable gravitating mode modified by Bohm potential and the stable Alfven mode modified by non-ideal effects are obtained separately. The criterion of firehose instability remains unaffected due to the presence of non-ideal effects. In the perpendicular propagation, finite electrical resistivity and quantum pressure anisotropy modify the dispersion relation, whereas no effect of Hall current was observed in the dispersion characteristics. The Hall current, finite electrical resistivity, rotation, and quantum corrections stabilize the growth rate. The stability of the dynamical system is analyzed using the Routh-Hurwitz criterion.

  18. Global characteristics of auroral Hall currents derived from the Swarm constellation: dependences on season and IMF orientation

    NASA Astrophysics Data System (ADS)

    Huang, Tao; Lühr, Hermann; Wang, Hui

    2017-11-01

    On the basis of field-aligned currents (FACs) and Hall currents derived from high-resolution magnetic field data of the Swarm constellation, the average characteristics of these two current systems in the auroral regions are comprehensively investigated by statistical methods. This is the first study considering both current types determined simultaneously by the same spacecraft in both hemispheres. The FAC distribution, derived from the novel Swarm dual-spacecraft approach, reveals the well-known features of Region 1 (R1) and Region 2 (R2) FACs. At high latitudes, Region 0 (R0) FACs appear on the dayside. Their flow direction, up or down, depends on the orientation of the interplanetary magnetic field (IMF) By component. Of particular interest is the distribution of auroral Hall currents. The prominent auroral electrojets are found to be closely controlled by the solar wind input, but we find no dependence of their intensity on the IMF By orientation. The eastward electrojet is about 1.5 times stronger in local summer than in winter. Conversely, the westward electrojet shows less dependence on season. As to higher latitudes, part of the electrojet current is closed over the polar cap. Here the seasonal variation of conductivity mainly controls the current density. During local summer of the Northern Hemisphere, there is a clear channeling of return currents over the polar cap. For positive (negative) IMF By a dominant eastward (westward) Hall current circuit is formed from the afternoon (morning) electrojet towards the dawn side (dusk side) polar cap return current. The direction of polar cap Hall currents in the noon sector depends directly on the orientation of the IMF By. This is true for both signs of the IMF Bz component. Comparable Hall current distributions can be observed in the Southern Hemisphere but for opposite IMF By signs. Around the midnight sector the westward substorm electrojet is dominating. As expected, it is highly dependent on magnetic

  19. Optically adjustable valley Hall current in single-layer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Sengupta, Parijat; Pavlidis, Dimitris; Shi, Junxia

    2018-02-01

    The illumination of a single-layer transition metal dichalcogenide with an elliptically polarized light beam is shown to give rise to a differential rate of inter-band carrier excitation between the valence and conduction states around the valley edges, K and K' . This rate with a linear dependence on the beam ellipticity and inverse of the optical gap manifests as an asymmetric Fermi distribution between the valleys or a non-equilibrium population which under an external field and a Berry curvature induced anomalous velocity, results in an externally tunable finite valley Hall current. Surface imperfections that influence the excitation rates are included through the self-consistent Born approximation. Further, we describe applications centered around circular dichroism, quantum computing, and spin torque via optically excited spin currents within the framework of the suggested formalism. A closing summary points to the possibility of extending the calculations to composite charged particles like trions. The role of the substrate in renormalizing the fundamental band gap and moderating the valley Hall current is also discussed.

  20. Current-Nonlinear Hall Effect and Spin-Orbit Torque Magnetization Switching in a Magnetic Topological Insulator

    NASA Astrophysics Data System (ADS)

    Yasuda, K.; Tsukazaki, A.; Yoshimi, R.; Kondou, K.; Takahashi, K. S.; Otani, Y.; Kawasaki, M.; Tokura, Y.

    2017-09-01

    The current-nonlinear Hall effect or second harmonic Hall voltage is widely used as one of the methods for estimating charge-spin conversion efficiency, which is attributed to the magnetization oscillation by spin-orbit torque (SOT). Here, we argue the second harmonic Hall voltage under a large in-plane magnetic field with an in-plane magnetization configuration in magnetic-nonmagnetic topological insulator (TI) heterostructures, Crx (Bi1 -ySby )2 -xTe3 /(Bi1 -ySby )2Te3 , where it is clearly shown that the large second harmonic voltage is governed not by SOT but mainly by asymmetric magnon scattering without macroscopic magnetization oscillation. Thus, this method does not allow an accurate estimation of charge-spin conversion efficiency in TI. Instead, the SOT contribution is exemplified by current pulse induced nonvolatile magnetization switching, which is realized with a current density of 2.5 ×1010 A m-2 , showing its potential as a spintronic material.

  1. Current-Nonlinear Hall Effect and Spin-Orbit Torque Magnetization Switching in a Magnetic Topological Insulator.

    PubMed

    Yasuda, K; Tsukazaki, A; Yoshimi, R; Kondou, K; Takahashi, K S; Otani, Y; Kawasaki, M; Tokura, Y

    2017-09-29

    The current-nonlinear Hall effect or second harmonic Hall voltage is widely used as one of the methods for estimating charge-spin conversion efficiency, which is attributed to the magnetization oscillation by spin-orbit torque (SOT). Here, we argue the second harmonic Hall voltage under a large in-plane magnetic field with an in-plane magnetization configuration in magnetic-nonmagnetic topological insulator (TI) heterostructures, Cr_{x}(Bi_{1-y}Sb_{y})_{2-x}Te_{3}/(Bi_{1-y}Sb_{y})_{2}Te_{3}, where it is clearly shown that the large second harmonic voltage is governed not by SOT but mainly by asymmetric magnon scattering without macroscopic magnetization oscillation. Thus, this method does not allow an accurate estimation of charge-spin conversion efficiency in TI. Instead, the SOT contribution is exemplified by current pulse induced nonvolatile magnetization switching, which is realized with a current density of 2.5×10^{10}  A m^{-2}, showing its potential as a spintronic material.

  2. Development and Testing of High Current Hollow Cathodes for High Power Hall Thrusters

    NASA Technical Reports Server (NTRS)

    Kamhawi, Hani; Van Noord, Jonathan

    2012-01-01

    NASA's Office of the Chief Technologist In-Space Propulsion project is sponsoring the testing and development of high power Hall thrusters for implementation in NASA missions. As part of the project, NASA Glenn Research Center is developing and testing new high current hollow cathode assemblies that can meet and exceed the required discharge current and life-time requirements of high power Hall thrusters. This paper presents test results of three high current hollow cathode configurations. Test results indicated that two novel emitter configurations were able to attain lower peak emitter temperatures compared to state-of-the-art emitter configurations. One hollow cathode configuration attained a cathode orifice plate tip temperature of 1132 degC at a discharge current of 100 A. More specifically, test and analysis results indicated that a novel emitter configuration had minimal temperature gradient along its length. Future work will include cathode wear tests, and internal emitter temperature and plasma properties measurements along with detailed physics based modeling.

  3. Evaluation of a Magnetically-Filtered Faraday Probe for Measuring the ion Current Density Profile of a Hall Thruster

    DTIC Science & Technology

    2004-07-01

    The ability of a magnetically-filtered Faraday probe (MFFP) to obtain the ion current density profile of a Hall thruster is investigated. The MFFP is...MFFP, boxed Faraday probe (BFP), and nude Faraday probe are used to measure the ion current density profile of a 5 kW Hall thruster operated over the

  4. Magnetically Filtered Faraday Probe for Measuring the Ion Current Density Profile of a Hall Thruster

    DTIC Science & Technology

    2006-01-01

    Hall thruster is investigated. The MFFP is designed to eliminate the collection of low-energy, charge-exchange (CEX) ions by using a variable magnetic field as an ion filter. In this study, a MFFP, Faraday probe with a reduced acceptance angle (BFP), and nude Faraday probe are used to measure the ion current density profile of a 5 kW Hall thruster operating over the range of 300-500 V and 5-10 mg/s. The probes are evaluated on a xenon propellant Hall thruster in the University of Michigan Large Vacuum Test Facility at operating

  5. Hall current effects in the Lewis magnetohydrodynamic generator

    NASA Technical Reports Server (NTRS)

    Nichols, L. D.; Sovie, R. J.

    1972-01-01

    Data obtained in a magnetohydrodynamic generator are compared with theoretical values calculated by using the Dzung theory. The generator was operated with cesium-seeded argon as the working fluid. The gas temperature varied from 1800 to 2100 K, the gas pressure from 19 to 22 N/sq cm, the Mach number from 0.3 to 0.5, and the magnetic field strength from 0.2 to 1.6 T. The analysis indicates that there is incomplete seed vaporization and that Hall current shorting paths (through the working fluid to ground at both the entrance and exit of the channel) limit generator performance.

  6. Spin Hall effects

    NASA Astrophysics Data System (ADS)

    Sinova, Jairo; Valenzuela, Sergio O.; Wunderlich, J.; Back, C. H.; Jungwirth, T.

    2015-10-01

    Spin Hall effects are a collection of relativistic spin-orbit coupling phenomena in which electrical currents can generate transverse spin currents and vice versa. Despite being observed only a decade ago, these effects are already ubiquitous within spintronics, as standard spin-current generators and detectors. Here the theoretical and experimental results that have established this subfield of spintronics are reviewed. The focus is on the results that have converged to give us the current understanding of the phenomena, which has evolved from a qualitative to a more quantitative measurement of spin currents and their associated spin accumulation. Within the experimental framework, optical-, transport-, and magnetization-dynamics-based measurements are reviewed and linked to both phenomenological and microscopic theories of the effect. Within the theoretical framework, the basic mechanisms in both the extrinsic and intrinsic regimes are reviewed, which are linked to the mechanisms present in their closely related phenomenon in ferromagnets, the anomalous Hall effect. Also reviewed is the connection to the phenomenological treatment based on spin-diffusion equations applicable to certain regimes, as well as the spin-pumping theory of spin generation used in many measurements of the spin Hall angle. A further connection to the spin-current-generating spin Hall effect to the inverse spin galvanic effect is given, in which an electrical current induces a nonequilibrium spin polarization. This effect often accompanies the spin Hall effect since they share common microscopic origins. Both can exhibit the same symmetries when present in structures comprising ferromagnetic and nonmagnetic layers through their induced current-driven spin torques or induced voltages. Although a short chronological overview of the evolution of the spin Hall effect field and the resolution of some early controversies is given, the main body of this review is structured from a pedagogical

  7. Bulk electron spin polarization generated by the spin Hall current

    NASA Astrophysics Data System (ADS)

    Korenev, V. L.

    2006-07-01

    It is shown that the spin Hall current generates a nonequilibrium spin polarization in the interior of crystals with reduced symmetry in a way that is drastically different from the previously well-known “equilibrium” polarization during the spin relaxation process. The steady state spin polarization value does not depend on the strength of spin-orbit interaction offering possibility to generate relatively high spin polarization even in the case of weak spin-orbit coupling.

  8. Tunneling Anomalous and Spin Hall Effects.

    PubMed

    Matos-Abiague, A; Fabian, J

    2015-07-31

    We predict, theoretically, the existence of the anomalous Hall effect when a tunneling current flows through a tunnel junction in which only one of the electrodes is magnetic. The interfacial spin-orbit coupling present in the barrier region induces a spin-dependent momentum filtering in the directions perpendicular to the tunneling current, resulting in a skew tunneling even in the absence of impurities. This produces an anomalous Hall conductance and spin Hall currents in the nonmagnetic electrode when a bias voltage is applied across the tunneling heterojunction. If the barrier is composed of a noncentrosymmetric material, the anomalous Hall conductance and spin Hall currents become anisotropic with respect to both the magnetization and crystallographic directions, allowing us to separate this interfacial phenomenon from the bulk anomalous and spin Hall contributions. The proposed effect should be useful for proving and quantifying the interfacial spin-orbit fields in metallic and metal-semiconductor systems.

  9. Ion Current Density Study of the NASA-300M and NASA-457Mv2 Hall Thrusters

    NASA Technical Reports Server (NTRS)

    Huang, Wensheng; Shastry, Rohit; Herman, Daniel A.; Soulas, George C.; Kamhawi, Hani

    2012-01-01

    NASA Glenn Research Center is developing a Hall thruster in the 15-50 kW range to support future NASA missions. As a part of the process, the performance and plume characteristics of the NASA-300M, a 20-kW Hall thruster, and the NASA-457Mv2, a 50-kW Hall thruster, were evaluated. The collected data will be used to improve the fidelity of the JPL modeling tool, Hall2De, which will then be used to aid the design of the 15-50 kW Hall thruster. This paper gives a detailed overview of the Faraday probe portion of the plume characterization study. The Faraday probe in this study is a near-field probe swept radially at many axial locations downstream of the thruster exit plane. Threshold-based integration limits with threshold values of 1/e, 1/e2, and 1/e3 times the local peak current density are tried for the purpose of ion current integration and divergence angle calculation. The NASA-300M is operated at 7 conditions and the NASA-457Mv2 at 14 conditions. These conditions span discharge voltages of 200 to 500 V and discharge power of 10 to 50 kW. The ion current density profiles of the near-field plume originating from the discharge channel are discovered to strongly resemble Gaussian distributions. A novel analysis approach involving a form of ray tracing is used to determine an effective point of origin for the near-field plume. In the process of performing this analysis, definitive evidence is discovered that showed the near-field plume is bending towards the thruster centerline.

  10. Ion Current Density Study of the NASA-300M and NASA-457Mv2 Hall Thrusters

    NASA Technical Reports Server (NTRS)

    Huang, Wensheng; Shastry, Rohit; Herman, Daniel A.; Soulas, George C.; Kamhawi, Hani

    2012-01-01

    NASA Glenn Research Center is developing a Hall thruster in the 15-50 kW range to support future NASA missions. As a part of the process, the performance and plume characteristics of the NASA-300M, a 20-kW Hall thruster, and the NASA-457Mv2, a 50-kW Hall thruster, were evaluated. The collected data will be used to improve the fidelity of the JPL modeling tool, Hall2De, which will then be used to aid the design of the 15-50 kW Hall thruster. This paper gives a detailed overview of the Faraday probe portion of the plume characterization study. The Faraday probe in this study is a near-field probe swept radially at many axial locations downstream of the thruster exit plane. Threshold-based integration limits with threshold values of 1/e, 1/e(sup 2), and 1/e(sup 3) times the local peak current density are tried for the purpose of ion current integration and divergence angle calculation. The NASA-300M is operated at 7 conditions and the NASA-457Mv2 at 14 conditions. These conditions span discharge voltages of 200 to 500 V and discharge power of 10 to 50 kW. The ion current density profiles of the near-field plume originating from the discharge channel are discovered to strongly resemble Gaussian distributions. A novel analysis approach involving a form of ray tracing is used to determine an effective point of origin for the near-field plume. In the process of performing this analysis, definitive evidence is discovered that showed the near-field plume is bending towards the thruster centerline.

  11. Numerical Study of Current Driven Instabilities and Anomalous Electron Transport in Hall-effect Thrusters

    NASA Astrophysics Data System (ADS)

    Tran, Jonathan

    Plasma turbulence and the resulting anomalous electron transport due to azimuthal current driven instabilities in Hall-effect thrusters is a promising candidate for developing predictive models for the observed anomalous transport. A theory for anomalous electron transport and current driven instabilities has been recently studied by [Lafluer et al., 2016a]. Due to the extreme cost of fully resolving the Debye length and plasma frequency, hybrid plasma simulations utilizing kinetic ions and quasi-steady state fluid electrons have long been the principle workhorse methodology for Hall-effect thruster modeling. Using a reduced dimension particle in cell simulation implemented in the Thermophysics Universal Research Framework developed by the Air Force Research Lab, we show collective electron-wave scattering due to large amplitude azimuthal fluctuations of the electric field and the plasma density. These high-frequency and short wavelength fluctuations can lead to an effective cross-field mobility many orders of magnitude larger than what is expected from classical electron-neutral momentum collisions in the low neutral density regime. We further adapt the previous study by [Lampe et al., 1971] and [Stringer, 1964] for related current driven instabilities to electric propulsion relevant mass ratios and conditions. Finally, we conduct a preliminary study of resolving this instability with a modified hybrid simulation with the hope of integration with established hybrid Hall-effect thruster simulations.

  12. An Investigation of Hall Currents Associated with Tripolar Magnetic Fields During Magnetospheric Kelvin Helmholtz Waves

    NASA Astrophysics Data System (ADS)

    Sturner, A. P.; Eriksson, S.; Newman, D. L.; Lapenta, G.; Gershman, D. J.; Plaschke, F.; Ergun, R.; Wilder, F. D.; Torbert, R. B.; Giles, B. L.; Strangeway, R. J.; Russell, C. T.; Burch, J. L.

    2016-12-01

    Kinetic simulations and observations of magnetic reconnection suggest the Hall term of Ohm's Law is necessary for understanding fast reconnection in the Earth's magnetosphere. During high (>1) guide field plasma conditions in the solar wind and in Earth's magnetopause, tripolar variations in the guide magnetic field are often observed during current sheet crossings, and have been linked to reconnection Hall magnetic fields. Two proposed mechanisms for these tripolar variations are the presence of multiple nearby X-lines and magnetic island coalescence. We present results of an investigation into the structure of the electron currents supporting tripolar guide magnetic field variations during Kelvin-Helmholtz wave current sheet crossings using the Magnetosphere Multiscale (MMS) Mission, and compare with bipolar magnetic field structures and with kinetic simulations to understand how these tripolar structures may be used as tracers for magnetic islands.

  13. Dissipationless Hall current in dense quark matter in a magnetic field

    DOE PAGES

    Ferrer, Efrain J.; de la Incera, V.

    2017-03-29

    Here, we show the realization of axion electrodynamics within the Dual Chiral Density Wave phase of dense quark matter in the presence of a magnetic field. This system exhibits an anomalous dissipationless Hall current perpendicular to the magnetic field and an anomalous electric charge density. This connection to topological insulators and 3D optical lattices, as well as possible implications for heavy-ion collisions and neutron stars are outlined.

  14. Nondestructive hall coefficient measurements using ACPD techniques

    NASA Astrophysics Data System (ADS)

    Velicheti, Dheeraj; Nagy, Peter B.; Hassan, Waled

    2018-04-01

    Hall coefficient measurements offer great opportunities as well as major challenges for nondestructive materials characterization. The Hall effect is produced by the magnetic Lorentz force acting on moving charge carriers in the presence of an applied magnetic field. The magnetic perturbation gives rise to a Hall current that is normal to the conduction current but does not directly perturb the electric potential distribution. Therefore, Hall coefficient measurements usually exploit the so-called transverse galvanomagnetic potential drop effect that arises when the Hall current is intercepted by the boundaries of the specimen and thereby produce a measurable potential drop. In contrast, no Hall potential is produced in a large plate in the presence of a uniform normal field at quasi-static low frequencies. In other words, conventional Hall coefficient measurements are inherently destructive since they require cutting the material under tests. This study investigated the feasibility of using alternating current potential drop (ACPD) techniques for nondestructive Hall coefficient measurements in plates. Specifically, the directional four-point square-electrode configuration is investigated with superimposed external magnetic field. Two methods are suggested to make Hall coefficient measurements in large plates without destructive machining. At low frequencies, constraining the bias magnetic field can replace constraining the dimensions of the specimen, which is inherently destructive. For example, when a cylindrical permanent magnet is used to provide the bias magnetic field, the peak Hall voltage is produced when the diameter of the magnet is equal to the diagonal of the square ACPD probe. Although this method is less effective than cutting the specimen to a finite size, the loss of sensitivity is less than one order of magnitude even at very low frequencies. In contrast, at sufficiently high inspection frequencies the magnetic field of the Hall current induces a

  15. Levitation of current carrying states in the lattice model for the integer quantum Hall effect.

    PubMed

    Koschny, T; Potempa, H; Schweitzer, L

    2001-04-23

    The disorder driven quantum Hall to insulator transition is investigated for a two-dimensional lattice model. The Hall conductivity and the localization length are calculated numerically near the transition. For uncorrelated and weakly correlated disorder potentials the current carrying states are annihilated by the negative Chern states originating from the band center. In the presence of correlated disorder potentials with correlation length larger than approximately half the lattice constant the floating up of the critical states in energy without merging is observed. This behavior is similar to the levitation scenario proposed for the continuum model.

  16. Resonant Hall effect under generation of a self-sustaining mode of spin current in nonmagnetic bipolar conductors with identical characters between holes and electrons

    NASA Astrophysics Data System (ADS)

    Sakai, Masamichi; Takao, Hiraku; Matsunaga, Tomoyoshi; Nishimagi, Makoto; Iizasa, Keitaro; Sakuraba, Takahito; Higuchi, Koji; Kitajima, Akira; Hasegawa, Shigehiko; Nakamura, Osamu; Kurokawa, Yuichiro; Awano, Hiroyuki

    2018-03-01

    We have proposed an enhancement mechanism of the Hall effect, the signal of which is amplified due to the generation of a sustaining mode of spin current. Our analytic derivations of the Hall resistivity revealed the conditions indispensable for the observation of the effect: (i) the presence of the transverse component of an effective electric field due to spin splitting in chemical potential in addition to the longitudinal component; (ii) the simultaneous presence of holes and electrons each having approximately the same characteristics; (iii) spin-polarized current injection from magnetized electrodes; (iv) the boundary condition for the transverse current (J c, y = 0). The model proposed in this study was experimentally verified by using van der Pauw-type Hall devices consisting of the nonmagnetic bipolar conductor YH x (x ≃ 2) and TbFeCo electrodes. Replacing Au electrodes with TbFeCo electrodes alters the Hall resistivity from the ordinary Hall effect to the anomalous Hall-like effect with an enhancement factor of approximately 50 at 4 T. We interpreted the enhancement phenomenon in terms of the present model.

  17. Observation of a superfluid Hall effect

    PubMed Central

    Jiménez-García, Karina; Williams, Ross A.; Beeler, Matthew C.; Perry, Abigail R.; Phillips, William D.; Spielman, Ian B.

    2012-01-01

    Measurement techniques based upon the Hall effect are invaluable tools in condensed-matter physics. When an electric current flows perpendicular to a magnetic field, a Hall voltage develops in the direction transverse to both the current and the field. In semiconductors, this behavior is routinely used to measure the density and charge of the current carriers (electrons in conduction bands or holes in valence bands)—internal properties of the system that are not accessible from measurements of the conventional resistance. For strongly interacting electron systems, whose behavior can be very different from the free electron gas, the Hall effect’s sensitivity to internal properties makes it a powerful tool; indeed, the quantum Hall effects are named after the tool by which they are most distinctly measured instead of the physics from which the phenomena originate. Here we report the first observation of a Hall effect in an ultracold gas of neutral atoms, revealed by measuring a Bose–Einstein condensate’s transport properties perpendicular to a synthetic magnetic field. Our observations in this vortex-free superfluid are in good agreement with hydrodynamic predictions, demonstrating that the system’s global irrotationality influences this superfluid Hall signal. PMID:22699494

  18. B-periodic oscillations in the Hall-resistance induced by a dc-current-bias under combined microwave-excitation and dc-current bias in the GaAs/AlGaAs 2D system.

    PubMed

    Liu, Han-Chun; Reichl, C; Wegscheider, W; Mani, R G

    2018-05-18

    We report the observation of dc-current-bias-induced B-periodic Hall resistance oscillations and Hall plateaus in the GaAs/AlGaAs 2D system under combined microwave radiation- and dc bias excitation at liquid helium temperatures. The Hall resistance oscillations and plateaus appear together with concomitant oscillations also in the diagonal magnetoresistance. The periods of Hall and diagonal resistance oscillations are nearly identical, and source power (P) dependent measurements demonstrate sub-linear relationship of the oscillation amplitude with P over the span 0 < P ≤ 20 mW.

  19. On Multiple Hall-Like Electron Currents and Tripolar Guide Magnetic Field Perturbations During Kelvin-Helmholtz Waves

    NASA Astrophysics Data System (ADS)

    Sturner, Andrew P.; Eriksson, Stefan; Nakamura, Takuma; Gershman, Daniel J.; Plaschke, Ferdinand; Ergun, Robert E.; Wilder, Frederick D.; Giles, Barbara; Pollock, Craig; Paterson, William R.; Strangeway, Robert J.; Baumjohann, Wolfgang; Burch, James L.

    2018-02-01

    Two magnetopause current sheet crossings with tripolar guide magnetic field signatures were observed by multiple Magnetosphere Multiscale (MMS) spacecraft during Kelvin-Helmholtz wave activity. The two out-of-plane magnetic field depressions of the tripolar guide magnetic field are largely supported by the observed in-plane electron currents, which are reminiscent of two clockwise Hall current loop systems. A comparison with a three-dimensional kinetic simulation of Kelvin-Helmholtz waves and vortex-induced reconnection suggests that MMS likely encountered the two Hall magnetic field depressions on either side of a magnetic reconnection X-line. Moreover, MMS observed an out-of-plane current reversal and a corresponding in-plane magnetic field rotation at the center of one of the current sheets, suggesting the presence of two adjacent flux ropes. The region inside one of the ion-scale flux ropes was characterized by an observed decrease of the total magnetic field, a strong axial current, and significant enhancements of electron density and parallel electron temperature. The flux rope boundary was characterized by currents opposite this axial current, strong in-plane and converging electric fields, parallel electric fields, and weak electron-frame Joule dissipation. These return current region observations may reflect a need to support the axial current rather than representing local reconnection signatures in the absence of any exhausts.

  20. Development Status of the Helicon Hall Thruster

    DTIC Science & Technology

    2009-09-15

    Hall thruster , the Helicon Hall Thruster , is presented. The Helicon Hall Thruster combines the efficient ionization mechanism of a helicon source with the favorable plasma acceleration properties of a Hall thruster . Conventional Hall thrusters rely on direct current electron bombardment to ionize the flow in order to generate thrust. Electron bombardment typically results in an ionization cost that can be on the order of ten times the ionization potential, leading to reduced efficiency, particularly at low

  1. Synchronization of spin-transfer torque oscillators by spin pumping, inverse spin Hall, and spin Hall effects

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Elyasi, Mehrdad; Bhatia, Charanjit S.; Yang, Hyunsoo, E-mail: eleyang@nus.edu.sg

    2015-02-14

    We have proposed a method to synchronize multiple spin-transfer torque oscillators based on spin pumping, inverse spin Hall, and spin Hall effects. The proposed oscillator system consists of a series of nano-magnets in junction with a normal metal with high spin-orbit coupling, and an accumulative feedback loop. We conduct simulations to demonstrate the effect of modulated charge currents in the normal metal due to spin pumping from each nano-magnet. We show that the interplay between the spin Hall effect and inverse spin Hall effect results in synchronization of the nano-magnets.

  2. Thermally driven anomalous Hall effect transitions in FeRh

    NASA Astrophysics Data System (ADS)

    Popescu, Adrian; Rodriguez-Lopez, Pablo; Haney, Paul M.; Woods, Lilia M.

    2018-04-01

    Materials exhibiting controllable magnetic phase transitions are currently in demand for many spintronics applications. Here, we investigate from first principles the electronic structure and intrinsic anomalous Hall, spin Hall, and anomalous Nernst response properties of the FeRh metallic alloy which undergoes a thermally driven antiferromagnetic-to-ferromagnetic phase transition. We show that the energy band structures and underlying Berry curvatures have important signatures in the various Hall effects. Specifically, the suppression of the anomalous Hall and Nernst effects in the antiferromagnetic state and a sign change in the spin Hall conductivity across the transition are found. It is suggested that the FeRh can be used as a spin current detector capable of differentiating the spin Hall effect from other anomalous transverse effects. The implications of this material and its thermally driven phases as a spin current detection scheme are also discussed.

  3. The electrical MHD and Hall current impact on micropolar nanofluid flow between rotating parallel plates

    NASA Astrophysics Data System (ADS)

    Shah, Zahir; Islam, Saeed; Gul, Taza; Bonyah, Ebenezer; Altaf Khan, Muhammad

    2018-06-01

    The current research aims to examine the combined effect of magnetic and electric field on micropolar nanofluid between two parallel plates in a rotating system. The nanofluid flow between two parallel plates is taken under the influence of Hall current. The flow of micropolar nanofluid has been assumed in steady state. The rudimentary governing equations have been changed to a set of differential nonlinear and coupled equations using suitable similarity variables. An optimal approach has been used to acquire the solution of the modelled problems. The convergence of the method has been shown numerically. The impact of the Skin friction on velocity profile, Nusslet number on temperature profile and Sherwood number on concentration profile have been studied. The influences of the Hall currents, rotation, Brownian motion and thermophoresis analysis of micropolar nanofluid have been mainly focused in this work. Moreover, for comprehension the physical presentation of the embedded parameters that is, coupling parameter N1 , viscosity parameter Re , spin gradient viscosity parameter N2 , rotating parameter Kr , Micropolar fluid constant N3 , magnetic parameter M , Prandtl number Pr , Thermophoretic parameter Nt , Brownian motion parameter Nb , and Schmidt number Sc have been plotted and deliberated graphically.

  4. NASA's Hall Thruster Program 2002

    NASA Technical Reports Server (NTRS)

    Jankovsky, Robert S.; Jacobson, David T.; Pinero, Luis R.; Manzella, David H.; Hofer, Richard R.; Peterson, Peter Y.

    2002-01-01

    The NASA Hall thruster program currently supports a number of tasks related to high power thruster development for a number of customers including the Energetics Program (formerly called the Space-based Program), the Space Solar Power Program, and the In-space Propulsion Program. In program year 2002, two tasks were central to the NASA Hall thruster program: 1) the development of a laboratory Hall thruster capable of providing high thrust at high power-, and 2) investigations into operation of Hall thrusters at high specific impulse. In addition to these two primary thruster development activities, there are a number of other on-going activities supported by the NASA Hall thruster program. These additional activities are related to issues such as high-power power processor architecture, thruster lifetime, and spacecraft integration.

  5. Autonomous Method and System for Minimizing the Magnitude of Plasma Discharge Current Oscillations in a Hall Effect Plasma Device

    NASA Technical Reports Server (NTRS)

    Hruby, Vladimir (Inventor); Demmons, Nathaniel (Inventor); Ehrbar, Eric (Inventor); Pote, Bruce (Inventor); Rosenblad, Nathan (Inventor)

    2014-01-01

    An autonomous method for minimizing the magnitude of plasma discharge current oscillations in a Hall effect plasma device includes iteratively measuring plasma discharge current oscillations of the plasma device and iteratively adjusting the magnet current delivered to the plasma device in response to measured plasma discharge current oscillations to reduce the magnitude of the plasma discharge current oscillations.

  6. ION ACOUSTIC TURBULENCE, ANOMALOUS TRANSPORT, AND SYSTEM DYNAMICS IN HALL EFFECT THRUSTERS

    DTIC Science & Technology

    2017-06-30

    17394 4 / 13 HALL EFFECT THRUSTERS Hall Effect Thrusters (HET): Traditionally Modeled in R-Z Named for Hall Current in θ Uses Quasi -1D Electron Fluid...HET): Traditionally Modeled in R-Z Named for Hall Current in θ Uses Quasi -1D Electron Fluid Solve Ohm’s Law→ No e−-momentum Zθ Unrolled to YZ...Current in θ Uses Quasi -1D Electron Fluid Solve Ohm’s Law→ No e−-momentum Zθ Unrolled to YZ Electron ExB Drift Unmagnetized Ions Results in Hall Current

  7. Wire-positioning algorithm for coreless Hall array sensors in current measurement

    NASA Astrophysics Data System (ADS)

    Chen, Wenli; Zhang, Huaiqing; Chen, Lin; Gu, Shanyun

    2018-05-01

    This paper presents a scheme of circular-arrayed, coreless Hall-effect current transformers. It can satisfy the demands of wide dynamic range and bandwidth current in the distribution system, as well as the demand of AC and DC simultaneous measurements. In order to improve the signal to noise ratio (SNR) of the sensor, a wire-positioning algorithm is proposed, which can improve the measurement accuracy based on the post-processing of measurement data. The simulation results demonstrate that the maximum errors are 70%, 6.1% and 0.95% corresponding to Ampère’s circuital method, approximate positioning algorithm and precise positioning algorithm, respectively. It is obvious that the accuracy of the positioning algorithm is significantly improved when compared with that of the Ampère’s circuital method. The maximum error of the positioning algorithm is smaller in the experiment.

  8. Time-domain detection of current controlled magnetization damping in Pt/Ni{sub 81}Fe{sub 19} bilayer and determination of Pt spin Hall angle

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ganguly, A.; Haldar, A.; Sinha, J.

    2014-09-15

    The effect of spin torque from the spin Hall effect in Pt/Ni{sub 81}Fe{sub 19} rectangular bilayer film was investigated using time-resolved magneto-optical Kerr microscopy. Current flow through the stack resulted in a linear variation of effective damping up to ±7%, attributed to spin current injection from the Pt into the Ni{sub 81}Fe{sub 19}. The spin Hall angle of Pt was estimated as 0.11 ± 0.03. The modulation of the damping depended on the angle between the current and the bias magnetic field. These results demonstrate the importance of optical detection of precessional magnetization dynamics for studying spin transfer torque due to spinmore » Hall effect.« less

  9. Remnant Geometric Hall Response in a Quantum Quench.

    PubMed

    Wilson, Justin H; Song, Justin C W; Refael, Gil

    2016-12-02

    Out-of-equilibrium systems can host phenomena that transcend the usual restrictions of equilibrium systems. Here, we unveil how out-of-equilibrium states, prepared via a quantum quench in a two-band system, can exhibit a nonzero Hall-type current-a remnant Hall response-even when the instantaneous Hamiltonian is time reversal symmetric (in contrast to equilibrium Hall currents). Interestingly, the remnant Hall response arises from the coherent dynamics of the wave function that retain a remnant of its quantum geometry postquench, and can be traced to processes beyond linear response. Quenches in two-band Dirac systems are natural venues for realizing remnant Hall currents, which exist when either mirror or time-reversal symmetry are broken (before or after the quench). Its long time persistence, sensitivity to symmetry breaking, and decoherence-type relaxation processes allow it to be used as a sensitive diagnostic of the complex out-of-equilibrium dynamics readily controlled and probed in cold-atomic optical lattice experiments.

  10. Extrinsic spin Hall effect in graphene

    NASA Astrophysics Data System (ADS)

    Rappoport, Tatiana

    The intrinsic spin-orbit coupling in graphene is extremely weak, making it a promising spin conductor for spintronic devices. In addition, many applications also require the generation of spin currents in graphene. Theoretical predictions and recent experimental results suggest one can engineer the spin Hall effect in graphene by greatly enhancing the spin-orbit coupling in the vicinity of an impurity. The extrinsic spin Hall effect then results from the spin-dependent skew scattering of electrons by impurities in the presence of spin-orbit interaction. This effect can be used to efficiently convert charge currents into spin-polarized currents. I will discuss recent experimental results on spin Hall effect in graphene decorated with adatoms and metallic cluster and show that a large spin Hall effect can appear due to skew scattering. While this spin-orbit coupling is small if compared with what it is found in metals, the effect is strongly enhanced in the presence of resonant scattering, giving rise to robust spin Hall angles. I will present our single impurity scattering calculations done with exact partial-wave expansions and complement the analysis with numerical results from a novel real-space implementation of the Kubo formalism for tight-binding Hamiltonians. The author acknowledges the Brazilian agencies CNPq, CAPES, FAPERJ and INCT de Nanoestruturas de Carbono for financial support.

  11. Hall viscosity and electromagnetic response of electrons in graphene

    NASA Astrophysics Data System (ADS)

    Sherafati, Mohammad; Principi, Alessandro; Vignale, Giovanni

    The Hall viscosity is a dissipationless component of the viscosity tensor of an electron liquid with broken time- reversal symmetry, such as a two-dimensional electron gas (2DEG) in the quantum Hall state. Similar to the Hall conductivity, the Hall viscosity is an anomalous transport coefficient; however, while the former is connected with the current response, the latter stems from the stress response to a geometric deformation. For a Galilean-invariant system such as 2DEG, the current density is indeed the generator of the geometric deformation: therefore a connection between the Hall connectivity and viscosity is expected and by now well established. In the case of graphene, a non-Galilean-invariant system, the existence of such a connection is far from obvious, as the current operator is essentially different from the momentum operator. In this talk, I will first present our results of the geometric Hall viscosity of electrons in single-layer graphene. Then, from the expansion of the nonlocal Hall conductivity for small wave vectors, I demonstrate that, in spite of the lack of Galilean invariance, an effective mass can be defined such that the relationship between the Hall conductivity and the viscosity retains the form it has in Galilean-invariant systems, not only for a large number of occupied Landau levels, but also, with very high accuracy, for the undoped system.

  12. Magnetic field deformation due to electron drift in a Hall thruster

    NASA Astrophysics Data System (ADS)

    Liang, Han; Yongjie, Ding; Xu, Zhang; Liqiu, Wei; Daren, Yu

    2017-01-01

    The strength and shape of the magnetic field are the core factors in the design of the Hall thruster. However, Hall current can affect the distribution of static magnetic field. In this paper, the Particle-In-Cell (PIC) method is used to obtain the distribution of Hall current in the discharge channel. The Hall current is separated into a direct and an alternating part to calculate the induced magnetic field using Finite Element Method Magnetics (FEMM). The results show that the direct Hall current decreases the magnetic field strength in the acceleration region and also changes the shape of the magnetic field. The maximum reduction in radial magnetic field strength in the exit plane is 10.8 G for an anode flow rate of 15 mg/s and the maximum angle change of the magnetic field line is close to 3° in the acceleration region. The alternating Hall current induces an oscillating magnetic field in the whole discharge channel. The actual magnetic deformation is shown to contain these two parts.

  13. NASA's Hall Thruster Program

    NASA Technical Reports Server (NTRS)

    Jankovsky, Robert S.; Jacobson, David T.; Rawlin, Vincent K.; Mason, Lee S.; Mantenieks, Maris A.; Manzella, David H.; Hofer, Richard R.; Peterson, Peter Y.

    2001-01-01

    NASA's Hall thruster program has base research and focused development efforts in support of the Advanced Space Transportation Program, Space-Based Program, and various other programs. The objective of the base research is to gain an improved understanding of the physical processes and engineering constraints of Hall thrusters to enable development of advanced Hall thruster designs. Specific technical questions that are current priorities of the base effort are: (1) How does thruster life vary with operating point? (2) How can thruster lifetime and wear rate be most efficiently evaluated? (3) What are the practical limitations for discharge voltage as it pertains to high specific impulse operation (high discharge voltage) and high thrust operation (low discharge voltage)? (4) What are the practical limits for extending Hall thrusters to very high input powers? and (5) What can be done during thruster design to reduce cost and integration concerns? The objective of the focused development effort is to develop a 50 kW-class Hall propulsion system, with a milestone of a 50 kW engineering model thruster/system by the end of program year 2006. Specific program wear 2001 efforts, along with the corporate and academic participation, are described.

  14. Nonlinear dynamics induced anomalous Hall effect in topological insulators

    PubMed Central

    Wang, Guanglei; Xu, Hongya; Lai, Ying-Cheng

    2016-01-01

    We uncover an alternative mechanism for anomalous Hall effect. In particular, we investigate the magnetisation dynamics of an insulating ferromagnet (FM) deposited on the surface of a three-dimensional topological insulator (TI), subject to an external voltage. The spin-polarised current on the TI surface induces a spin-transfer torque on the magnetisation of the top FM while its dynamics can change the transmission probability of the surface electrons through the exchange coupling and hence the current. We find a host of nonlinear dynamical behaviors including multistability, chaos, and phase synchronisation. Strikingly, a dynamics mediated Hall-like current can arise, which exhibits a nontrivial dependence on the channel conductance. We develop a physical understanding of the mechanism that leads to the anomalous Hall effect. The nonlinear dynamical origin of the effect stipulates that a rich variety of final states exist, implying that the associated Hall current can be controlled to yield desirable behaviors. The phenomenon can find applications in Dirac-material based spintronics. PMID:26819223

  15. Nonlinear dynamics induced anomalous Hall effect in topological insulators.

    PubMed

    Wang, Guanglei; Xu, Hongya; Lai, Ying-Cheng

    2016-01-28

    We uncover an alternative mechanism for anomalous Hall effect. In particular, we investigate the magnetisation dynamics of an insulating ferromagnet (FM) deposited on the surface of a three-dimensional topological insulator (TI), subject to an external voltage. The spin-polarised current on the TI surface induces a spin-transfer torque on the magnetisation of the top FM while its dynamics can change the transmission probability of the surface electrons through the exchange coupling and hence the current. We find a host of nonlinear dynamical behaviors including multistability, chaos, and phase synchronisation. Strikingly, a dynamics mediated Hall-like current can arise, which exhibits a nontrivial dependence on the channel conductance. We develop a physical understanding of the mechanism that leads to the anomalous Hall effect. The nonlinear dynamical origin of the effect stipulates that a rich variety of final states exist, implying that the associated Hall current can be controlled to yield desirable behaviors. The phenomenon can find applications in Dirac-material based spintronics.

  16. Current Driven Instabilities and Anomalous Mobility in Hall-effect Thrusters

    NASA Astrophysics Data System (ADS)

    Tran, Jonathan; Eckhardt, Daniel; Martin, Robert

    2017-10-01

    Due to the extreme cost of fully resolving the Debye length and plasma frequency, hybrid plasma simulations utilizing kinetic ions and quasi-steady state fluid electrons have long been the principle workhorse methodology for Hall-effect thruster (HET) modeling. Plasma turbulence and the resulting anomalous electron transport in HETs is a promising candidate for developing predictive models for the observed anomalous transport. In this work, we investigate the implementation of an anomalous electron cross field transport model for hybrid HET simulations such a HPHall. A theory for anomalous transport in HETs and current driven instabilities has been recently studied by Lafleur et al. This work has shown collective electron-wave scattering due to large amplitude azimuthal fluctuations of the electric field. We will further adapt the previous results for related current driven instabilities to electric propulsion relevant mass ratios and conduct a preliminary study of resolving this instability with a modified hybrid (fluid electron and kinetic ion) simulation with the hope of integration with established hybrid HET simulations. This work is supported by the Air Force Office of Scientific Research award FA9950-17RQCOR465.

  17. The Kelvin-Helmhotz instability and thin current sheets in the MHD and Hall MHD formalisms

    NASA Astrophysics Data System (ADS)

    Chacon, L.; Knoll, D.

    2005-12-01

    Sheared magnetic fields and sheared flows co-exist in many space, astrophysical, and laboratory plasmas. In such situations the evolution of the Kelvin-Helmhotz instability (KHI) can have a significant impact on the topology of the magnetic field. In particular, it can result in current sheet thinning [2,3], which may allow Hall scales to become relevant and result in fast reconnection rates [1]. There are a number of interesting applications of this phenomena in the magnetosphere. We will discuss some of our recent work in this area [1,2,3] with special focus on Hall MHD effects on the KHI [1]. As an example, we will discuss the parameter regime in which the 2-D parallel KHI can evolve for sub-Alfvenic flows [1]. This may have important implication for dayside reconnection in the magnetopause. [1] Chacon, Knoll, and Finn, Phys. Lett. A, vol. 308, 2003 [2] Knoll and Chacon, PRL, vol. 88, 2002 [3] Brackbill and Knoll, PRL, vol. 86, 2001

  18. Complex Terahertz and Direct Current Inverse Spin Hall Effect in YIG/Cu1-xIrx Bilayers Across a Wide Concentration Range.

    PubMed

    Cramer, Joel; Seifert, Tom; Kronenberg, Alexander; Fuhrmann, Felix; Jakob, Gerhard; Jourdan, Martin; Kampfrath, Tobias; Kläui, Mathias

    2018-02-14

    We measure the inverse spin Hall effect of Cu 1-x Ir x thin films on yttrium iron garnet over a wide range of Ir concentrations (0.05 ⩽ x ⩽ 0.7). Spin currents are triggered through the spin Seebeck effect, either by a continuous (dc) temperature gradient or by ultrafast optical heating of the metal layer. The spin Hall current is detected by electrical contacts or measurement of the emitted terahertz radiation. With both approaches, we reveal the same Ir concentration dependence that follows a novel complex, nonmonotonous behavior as compared to previous studies. For small Ir concentrations a signal minimum is observed, whereas a pronounced maximum appears near the equiatomic composition. We identify this behavior as originating from the interplay of different spin Hall mechanisms as well as a concentration-dependent variation of the integrated spin current density in Cu 1-x Ir x . The coinciding results obtained for dc and ultrafast stimuli provide further support that the spin Seebeck effect extends to terahertz frequencies, thus enabling a transfer of established spintronic measurement schemes into the terahertz regime. Our findings also show that the studied material allows for efficient spin-to-charge conversion even on ultrafast time scales.

  19. Tunnelling anomalous and planar Hall effects (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Matos-Abiague, Alex; Scharf, Benedikt; Han, Jong E.; Hankiewicz, Ewelina M.; Zutic, Igor

    2016-10-01

    We theoretically show how the interplay between spin-orbit coupling (SOC) and magnetism can result in a finite tunneling Hall conductance, transverse to the applied bias. For two-dimensional tunnel junctions with a ferromagnetic lead and magnetization perpendicular to the current flow, the detected anomalous Hall voltage can be used to extract information not only about the spin polarization but also about the strength of the interfacial SOC. In contrast, a tunneling current across a ferromagnetic barrier on the surface of a three-dimensional topological insulator (TI) can induce a planar Hall response even when the magnetization is oriented along the current flow[1]. The tunneling nature of the states contributing to the planar Hall conductance can be switched from the ordinary to the Klein regimes by the electrostatic control of the barrier strength. This allows for an enhancement of the transverse response and a giant Hall angle, with the tunneling planar Hall conductance exceeding the longitudinal component. Despite the simplicity of a single ferromagnetic region, the TI/ferromagnet system exhibits a variety of functionalities. In addition to a spin-valve operation for magnetic sensing and storing information, positive, negative, and negative differential conductances can be tuned by properly adjusting the barrier potential and/or varying the magnetization direction. Such different resistive behaviors in the same system are attractive for potential applications in reconfigurable spintronic devices. [1] B. Scharf, A. Matos-Abiague, J. E. Han, E. M. Hankiewicz, and I. Zutic, arXiv:1601.01009 (2016).

  20. Tunable-φ Josephson junction with a quantum anomalous Hall insulator

    NASA Astrophysics Data System (ADS)

    Sakurai, Keimei; Ikegaya, Satoshi; Asano, Yasuhiro

    2017-12-01

    We theoretically study the Josephson current in a superconductor/quantum anomalous Hall insulator/superconductor junction by using the lattice Green function technique. When an in-plane external Zeeman field is applied to the quantum anomalous Hall insulator, the Josephson current J flows without a phase difference across the junction θ . The phase shift φ appearing in the current-phase relationship J ∝sin(θ -φ ) is proportional to the amplitude of Zeeman fields and depends on the direction of Zeeman fields. A phenomenological analysis of the Andreev reflection processes explains the physical origin of φ . In a quantum anomalous Hall insulator, time-reversal symmetry and mirror-reflection symmetry are broken simultaneously. However, magnetic mirror-reflection symmetry is preserved. Such characteristic symmetry properties enable us to have a tunable φ junction with a quantum Hall insulator.

  1. Optical determination of Shockley-Read-Hall and interface recombination currents in hybrid perovskites

    PubMed Central

    Sarritzu, Valerio; Sestu, Nicola; Marongiu, Daniela; Chang, Xueqing; Masi, Sofia; Rizzo, Aurora; Colella, Silvia; Quochi, Francesco; Saba, Michele; Mura, Andrea; Bongiovanni, Giovanni

    2017-01-01

    Metal-halide perovskite solar cells rival the best inorganic solar cells in power conversion efficiency, providing the outlook for efficient, cheap devices. In order for the technology to mature and approach the ideal Shockley-Queissier efficiency, experimental tools are needed to diagnose what processes limit performances, beyond simply measuring electrical characteristics often affected by parasitic effects and difficult to interpret. Here we study the microscopic origin of recombination currents causing photoconversion losses with an all-optical technique, measuring the electron-hole free energy as a function of the exciting light intensity. Our method allows assessing the ideality factor and breaks down the electron-hole recombination current into bulk defect and interface contributions, providing an estimate of the limit photoconversion efficiency, without any real charge current flowing through the device. We identify Shockley-Read-Hall recombination as the main decay process in insulated perovskite layers and quantify the additional performance degradation due to interface recombination in heterojunctions. PMID:28317883

  2. Comment on "Effects of Magnetic Field Gradient on Ion Beam Current in Cylindrical Hall Ion Source

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Raitses, Y.; Smirnov A.; Fisch, N.J.

    It is argued that the key difference of the cylindrical Hall thruster (CHT) as compared to the end-Hall ion source cannot be exclusively attributed to the magnetic field topology [Tang et al. J. Appl. Phys., 102, 123305 (2007)]. With a similar mirror-type topology, the CHT configuration provides the electric field with nearly equipotential magnetic field surfaces and a better suppression of the electron cross-field transport, as compared to both the end-Hall ion source and the cylindrical Hall ion source of Tang et al.

  3. Low-Cost, High-Performance Hall Thruster Support System

    NASA Technical Reports Server (NTRS)

    Hesterman, Bryce

    2015-01-01

    Colorado Power Electronics (CPE) has built an innovative modular PPU for Hall thrusters, including discharge, magnet, heater and keeper supplies, and an interface module. This high-performance PPU offers resonant circuit topologies, magnetics design, modularity, and a stable and sustained operation during severe Hall effect thruster current oscillations. Laboratory testing has demonstrated discharge module efficiency of 96 percent, which is considerably higher than current state of the art.

  4. What do you measure when you measure the Hall effect?

    NASA Astrophysics Data System (ADS)

    Koon, D. W.; Knickerbocker, C. J.

    1993-02-01

    A formalism for calculating the sensitivity of Hall measurements to local inhomogeneities of the sample material or the magnetic field is developed. This Hall weighting function g(x,y) is calculated for various placements of current and voltage probes on square and circular laminar samples. Unlike the resistivity weighting function, it is nonnegative throughout the entire sample, provided all probes lie at the edge of the sample. Singularities arise in the Hall weighting function near the current and voltage probes except in the case where these probes are located at the corners of a square. Implications of the results for cross, clover, and bridge samples, and the implications of our results for metal-insulator transition and quantum Hall studies are discussed.

  5. Current-driven dynamics of skyrmions stabilized in MnSi nanowires revealed by topological Hall effect

    PubMed Central

    Liang, Dong; DeGrave, John P.; Stolt, Matthew J.; Tokura, Yoshinori; Jin, Song

    2015-01-01

    Skyrmions hold promise for next-generation magnetic storage as their nanoscale dimensions may enable high information storage density and their low threshold for current-driven motion may enable ultra-low energy consumption. Skyrmion-hosting nanowires not only serve as a natural platform for magnetic racetrack memory devices but also stabilize skyrmions. Here we use the topological Hall effect (THE) to study phase stability and current-driven dynamics of skyrmions in MnSi nanowires. THE is observed in an extended magnetic field-temperature window (15–30 K), suggesting stabilization of skyrmions in nanowires compared with the bulk. Furthermore, we show in nanowires that under the high current density of 108–109 A m−2, the THE decreases with increasing current densities, which demonstrates the current-driven motion of skyrmions generating the emergent electric field in the extended skyrmion phase region. These results open up the exploration of skyrmions in nanowires for fundamental physics and magnetic storage technologies. PMID:26400204

  6. Inverse spin Hall effect in a closed loop circuit

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Omori, Y.; Auvray, F.; Wakamura, T.

    We present measurements of inverse spin Hall effects (ISHEs), in which the conversion of a spin current into a charge current via the ISHE is detected not as a voltage in a standard open circuit but directly as the charge current generated in a closed loop. The method is applied to the ISHEs of Bi-doped Cu and Pt. The derived expression of ISHE for the loop structure can relate the charge current flowing into the loop to the spin Hall angle of the SHE material and the resistance of the loop.

  7. HEDSA Town Hall Meeting

    NASA Astrophysics Data System (ADS)

    Afeyan, Bedros

    2017-10-01

    HEDSA will hold its Town Hall meeting on Wednesday October 25 at 12:30pm in the Wisconsin Center. The new steering committee members and HEDSA leadership will be announced. A report will be given on 2017 HEDSA activities. Program Managers from Federal Funding Agencies such as OFES, NNSA, AFOSR and NSF will provide updates on the state of sponsored research in HED plasmas, and to engage the community in an open dialogue. The HEDSA Town Hall is a ``bring your own lunch'' meeting. Current members of HEDSA and all graduate students are strongly encouraged to attend. To join HEDSA please visit HEDSA.org

  8. Contactless measurement of alternating current conductance in quantum Hall structures

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Drichko, I. L.; Diakonov, A. M.; Malysh, V. A.

    2014-10-21

    We report a procedure to determine the frequency-dependent conductance of quantum Hall structures in a broad frequency domain. The procedure is based on the combination of two known probeless methods—acoustic spectroscopy and microwave spectroscopy. By using the acoustic spectroscopy, we study the low-frequency attenuation and phase shift of a surface acoustic wave in a piezoelectric crystal in the vicinity of the electron (hole) layer. The electronic contribution is resolved using its dependence on a transverse magnetic field. At high frequencies, we study the attenuation of an electromagnetic wave in a coplanar waveguide. To quantitatively calibrate these data, we use themore » fact that in the quantum-Hall-effect regime the conductance at the maxima of its magnetic field dependence is determined by extended states. Therefore, it should be frequency independent in a broad frequency domain. The procedure is verified by studies of a well-characterized p-SiGe/Ge/SiGe heterostructure.« less

  9. Coupling intensity between discharge and magnetic circuit in Hall thrusters

    NASA Astrophysics Data System (ADS)

    Wei, Liqiu; Yang, Xinyong; Ding, Yongjie; Yu, Daren; Zhang, Chaohai

    2017-03-01

    Coupling oscillation is a newly discovered plasma oscillation mode that utilizes the coupling between the discharge circuit and magnetic circuit, whose oscillation frequency spectrum ranges from several kilohertz to megahertz. The coupling coefficient parameter represents the intensity of coupling between the discharge and magnetic circuits. According to previous studies, the coupling coefficient is related to the material and the cross-sectional area of the magnetic coils, and the magnetic circuit of the Hall thruster. However, in our recent study on coupling oscillations, it was found that the Hall current equivalent position and radius have important effects on the coupling intensity between the discharge and magnetic circuits. This causes a difference in the coupling coefficient for different operating conditions of Hall thrusters. Through non-intrusive methods for measuring the Hall current equivalent radius and the axial position, it is found that with an increase in the discharge voltage and magnetic field intensity, the Hall current equivalent radius increases and its axial position moves towards the exit plane. Thus, both the coupling coefficient and the coupling intensity between the discharge and magnetic circuits increase. Contribution to the Topical Issue "Physics of Ion Beam Sources", edited by Holger Kersten and Horst Neumann.

  10. Current-driven second-harmonic domain wall resonance in ferromagnetic metal/nonmagnetic metal bilayers: A field-free method for spin Hall angle measurements

    NASA Astrophysics Data System (ADS)

    Hajiali, M. R.; Hamdi, M.; Roozmeh, S. E.; Mohseni, S. M.

    2017-10-01

    We study the ac current-driven domain wall motion in bilayer ferromagnetic metal (FM)/nonmagnetic metal (NM) nanowires. The solution of the modified Landau-Lifshitz-Gilbert equation including all the spin transfer torques is used to describe motion of the domain wall in the presence of the spin Hall effect. We show that the domain wall center has a second-harmonic frequency response in addition to the known first-harmonic excitation. In contrast to the experimentally observed second-harmonic response in harmonic Hall measurements of spin-orbit torque in magnetic thin films, this second-harmonic response directly originates from spin-orbit torque driven domain wall dynamics. Based on the spin current generated by domain wall dynamics, the longitudinal spin motive force generated voltage across the length of the nanowire is determined. The second-harmonic response introduces additionally a practical field-free and all-electrical method to probe the effective spin Hall angle for FM/NM bilayer structures that could be applied in experiments. Our results also demonstrate the capability of utilizing FM/NM bilayer structures in domain wall based spin-torque signal generators and resonators.

  11. Spin Hall Effects in Metallic Antiferromagnets

    DOE PAGES

    Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; ...

    2014-11-04

    In this paper, we investigate four CuAu-I-type metallic antiferromagnets for their potential as spin current detectors using spin pumping and inverse spin Hall effect. Nontrivial spin Hall effects were observed for FeMn, PdMn, and IrMn while a much higher effect was obtained for PtMn. Using thickness-dependent measurements, we determined the spin diffusion lengths of these materials to be short, on the order of 1 nm. The estimated spin Hall angles of the four materials follow the relationship PtMn > IrMn > PdMn > FeMn, highlighting the correlation between the spin-orbit coupling of nonmagnetic species and the magnitude of the spinmore » Hall effect in their antiferromagnetic alloys. These experiments are compared with first-principles calculations. Finally, engineering the properties of the antiferromagnets as well as their interfaces can pave the way for manipulation of the spin dependent transport properties in antiferromagnet-based spintronics.« less

  12. New pathways towards efficient metallic spin Hall spintronics

    DOE PAGES

    Jungfleisch, Matthias Benjamin; Zhang, Wei; Jiang, Wanjun; ...

    2015-11-16

    Spin Hall effects (SHEs) interconvert spin- and charge currents due to spin- orbit interaction, which enables convenient electrical generation and detection of diffusive spin currents and even collective spin excitations in magnetic solids. Here, we review recent experimental efforts exploring efficient spin Hall detector materials as well as new approaches to drive collective magnetization dynamics and to manipulate spin textures by SHEs. As a result, these studies are also expected to impact practical spintronics applications beyond their significance in fundamental research.

  13. Roles of nonlocal conductivity on spin Hall angle measurement

    NASA Astrophysics Data System (ADS)

    Chen, Kai; Zhang, Shufeng

    2017-10-01

    Spin Hall angle characterizes the rate of spin-charge current conversion and it has become one of the most important material parameters for spintronics physics and device application. A long-standing controversy is that the spin Hall angles for a given material measured by spin pumping and by spin Hall torque experiments are inconsistent and they could differ by as much as an order of magnitude. By using the linear response spin transport theory, we explicitly formulate the relation between the spin Hall angle and measured variables in different experiments. We find that the nonlocal conductivity inherited in the layered structure plays a key role to resolve conflicting values of the spin Hall angle. We provide a generalized scheme for extracting spin transport coefficients from experimental data.

  14. A Planar Hall Thruster for Investigating Electron Mobility in ExB Devices (Preprint)

    DTIC Science & Technology

    2007-08-24

    Hall thruster that emits and collects the Hall current across a planar discharge channel is described. The planar Hall thruster (PHT) is being investigated for use as a test bed to study electron mobility in ExB devices. The planar geometry attempts to de-couple the complex electron motion found in annular thrusters by using simplified geometry. During this initial test, the PHT was operated at discharge voltages between 50-150 V to verify operability and stability of the device. Hall current was emitted by hollow cathode electron sources and

  15. Optimum Design Rules for CMOS Hall Sensors

    PubMed Central

    Crescentini, Marco; Biondi, Michele; Romani, Aldo; Tartagni, Marco; Sangiorgi, Enrico

    2017-01-01

    This manuscript analyzes the effects of design parameters, such as aspect ratio, doping concentration and bias, on the performance of a general CMOS Hall sensor, with insight on current-related sensitivity, power consumption, and bandwidth. The article focuses on rectangular-shaped Hall probes since this is the most general geometry leading to shape-independent results. The devices are analyzed by means of 3D-TCAD simulations embedding galvanomagnetic transport model, which takes into account the Lorentz force acting on carriers due to a magnetic field. Simulation results define a set of trade-offs and design rules that can be used by electronic designers to conceive their own Hall probes. PMID:28375191

  16. Optimum Design Rules for CMOS Hall Sensors.

    PubMed

    Crescentini, Marco; Biondi, Michele; Romani, Aldo; Tartagni, Marco; Sangiorgi, Enrico

    2017-04-04

    This manuscript analyzes the effects of design parameters, such as aspect ratio, doping concentration and bias, on the performance of a general CMOS Hall sensor, with insight on current-related sensitivity, power consumption, and bandwidth. The article focuses on rectangular-shaped Hall probes since this is the most general geometry leading to shape-independent results. The devices are analyzed by means of 3D-TCAD simulations embedding galvanomagnetic transport model, which takes into account the Lorentz force acting on carriers due to a magnetic field. Simulation results define a set of trade-offs and design rules that can be used by electronic designers to conceive their own Hall probes.

  17. Observation of the Zero Hall Plateau in a Quantum Anomalous Hall Insulator

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Feng, Yang; Feng, Xiao; Ou, Yunbo

    We report experimental investigations on the quantum phase transition between the two opposite Hall plateaus of a quantum anomalous Hall insulator. We observe a well-defined plateau with zero Hall conductivity over a range of magnetic field around coercivity when the magnetization reverses. The features of the zero Hall plateau are shown to be closely related to that of the quantum anomalous Hall effect, but its temperature evolution exhibits a significant difference from the network model for a conventional quantum Hall plateau transition. We propose that the chiral edge states residing at the magnetic domain boundaries, which are unique to amore » quantum anomalous Hall insulator, are responsible for the novel features of the zero Hall plateau.« less

  18. Plume Characteristics of the BHT-HD-600 Hall Thruster (Preprint)

    DTIC Science & Technology

    2006-07-01

    Hall thruster on spacecraft, a number of plume properties have been measured. These include current density using a Faraday probe, ion energy distribution using a retarding potential analyzer, and ion species fractions using an E x B probe. The BHT-HD-600 Hall thruster is a nominally 600 W xenon Hall thruster developed by Busek Co. Inc. for the U.S. Air Force Research Laboratory. Plume characterization of Hall thrusters is required to fully understand the impacts of thruster operation on spacecraft. Much of these plume data are

  19. 5. View of Community Hall, first floor interior, entrance hall ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. View of Community Hall, first floor interior, entrance hall on east side of building, facing southeast. Ticket booth center foreground, stairway to auditorium right foreground. - Community Hall, Rainier Avenue & View Drive, Port Gamble, Kitsap County, WA

  20. Macroscopic Quantum Phase-Locking Model for the Quantum Hall = Effect

    NASA Astrophysics Data System (ADS)

    Wang, Te-Chun; Gou, Yih-Shun

    1997-08-01

    A macroscopic model of nonlinear dissipative phase-locking between a Josephson-like frequency and a macroscopic electron wave frequency is proposed to explain the Quantum Hall Effect. It is well known that a r.f-biased Josephson junction displays a collective phase-locking behavior which can be described by a non-autonomous second order equation or an equivalent 2+1-dimensional dynamical system. Making a direct analogy between the QHE and the Josephson system, this report proposes a computer-solving nonlinear dynamical model for the quantization of the Hall resistance. In this model, the Hall voltage is assumed to be proportional to a Josephson-like frequency and the Hall current is assumed related to a coherent electron wave frequency. The Hall resistance is shown to be quantized in units of the fine structure constant as the ratio of these two frequencies are locked into a rational winding number. To explain the sample-width dependence of the critical current, the 2DEG under large applied current is further assumed to develop a Josephson-like junction array in which all Josephson-like frequencies are synchronized. Other remarkable features of the QHE such as the resistance fluctuation and the even-denominator states are also discussed within this picture.

  1. Ion properties in a Hall current thruster operating at high voltage

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Garrigues, L., E-mail: laurent.garrigues@laplace.univ-tlse.fr

    2016-04-28

    Operation of a 5 kW-class Hall current Thruster for various voltages from 400 V to 800 V and a xenon mass flow rate of 6 mg s{sup −1} have been studied with a quasi-neutral hybrid model. In this model, anomalous electron transport is fitted from ion mean velocity measurements, and energy losses due to electron–wall interactions are used as a tuned parameter to match expected electron temperature strength for same class of thruster. Doubly charged ions production has been taken into account and detailed collisions between heavy species included. As the electron temperature increases, the main channel of Xe{sup 2+} ion production becomes stepwisemore » ionization of Xe{sup +} ions. For an applied voltage of 800 V, the mass utilization efficiency is in the range of 0.8–1.1, and the current fraction of doubly charged ions varies between 0.1 and 0.2. Results show that the region of ion production of each species is located at the same place inside the thruster channel. Because collision processes mean free path is larger than the acceleration region, each type of ions experiences same potential drop, and ion energy distributions of singly and doubly charged are very similar.« less

  2. Diagnostics Systems for Permanent Hall Thrusters Development

    NASA Astrophysics Data System (ADS)

    Ferreira, Jose Leonardo; Soares Ferreira, Ivan; Santos, Jean; Miranda, Rodrigo; Possa, M. Gabriela

    This work describes the development of Permanent Magnet Hall Effect Plasma Thruster (PHALL) and its diagnostic systems at The Plasma Physics Laboratory of University of Brasilia. The project consists on the construction and characterization of plasma propulsion engines based on the Hall Effect. Electric thrusters have been employed in over 220 successful space missions. Two types stand out: the Hall-Effect Thruster (HET) and the Gridded Ion Engine (GIE). The first, which we deal with in this project, has the advantage of greater simplicity of operation, a smaller weight for the propulsion subsystem and a longer shelf life. It can operate in two configurations: magnetic layer and anode layer, the difference between the two lying in the positioning of the anode inside the plasma channel. A Hall-Effect Thruster-HET is a type of plasma thruster in which the propellant gas is ionized and accelerated by a magneto hydrodynamic effect combined with electrostatic ion acceleration. So the essential operating principle of the HET is that it uses a J x B force and an electrostatic potential to accelerate ions up to high speeds. In a HET, the attractive negative charge is provided by electrons at the open end of the Thruster instead of a grid, as in the case of the electrostatic ion thrusters. A strong radial magnetic field is used to hold the electrons in place, with the combination of the magnetic field and the electrostatic potential force generating a fast circulating electron current, the Hall current, around the axis of the Thruster, mainly composed by drifting electrons in an ion plasma background. Only a slow axial drift towards the anode occurs. The main attractive features of the Hall-Effect Thruster are its simple design and operating principles. Most of the Hall-Effect Thrusters use electromagnet coils to produce the main magnetic field responsible for plasma generation and acceleration. In this paper we present a different new concept, a Permanent Magnet Hall

  3. Performance Characteristics of a 5 kW Laboratory Hall Thruster

    DTIC Science & Technology

    1996-07-01

    Characteristics of a 5 kW Laboratory Hall Thruster James M. Haas’, Frank S. Gulczinski III%, and Alec D. Gallimoret Plasmadynamics and Electric Propulsion...the information learned from the study of this thruster applicable to the understanding of its commercial counterparts. INTRODUCTION Hall thrusters are...few in number at this time; and those that do exist are intended primarily Current generation Hall thruster research has for flight qualification

  4. Anisotropic anomalous Hall effect in triangular itinerant ferromagnet Fe3GeTe2

    NASA Astrophysics Data System (ADS)

    Wang, Yihao; Xian, Cong; Wang, Jian; Liu, Bingjie; Ling, Langsheng; Zhang, Lei; Cao, Liang; Qu, Zhe; Xiong, Yimin

    2017-10-01

    Magnetic frustrated materials are of great interest for their novel spin-dependent transport properties. We report an anisotropic anomalous Hall effect in the triangular itinerant ferromagnet Fe3GeTe2 . When the current flows along the a b plane, Fe3GeTe2 exhibits the conventional anomalous Hall effect below the Curie temperature Tc, which can be depicted by Karplus-Luttinger theory. On the other hand, the topological Hall effect shows up below Tc with current along the c axis. The enhancement of Hall resistivity can be attributed to the chiral effect during the spin-flop process.

  5. Hall effect on magnetohydrodynamic instabilities at an elliptic magnetic stagnation line

    NASA Astrophysics Data System (ADS)

    Spies, Günther O.; Faghihi, Mustafa

    1987-06-01

    To answer the question whether the Hall effect removes the unphysical feature of ideal magnetohydrodynamics of predicting small wavelength kink instabilities at any elliptic magnetic stagnation line, a normal mode analysis is performed of the motion of an incompressible Hall fluid about cylindrical Z-pinch equilibria with circular cross sections. The eigenvalue loci in the complex frequency plane are derived for the equilibrium with constant current density. Every particular mode becomes stable as the Hall parameter exceeds a critical value. This value, however, depends on the mode such that it increases to infinity as the ideal growth rate decreases to zero, implying that there always remains an infinite number of slowly growing instabilities. Correspondingly, the stability criterion for equilibria with arbitrary current distributions is independent of the Hall parameter.

  6. Proton Knock-Out in Hall A

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kees de Jager

    Proton knock-out is studied in a broad program in Hall A at Jefferson Lab. The first experiment performed in Hall A studied the {sup 16}O(e,e'p) reaction. Since then proton knock-out experiments have studied a variety of aspects of that reaction, from single-nucleon properties to its mechanism, such as final-state interactions and two-body currents, in nuclei from {sup 2}H to {sup 16}O. In this review the results of this program will be summarized and an outlook given of future accomplishments.

  7. Spin torque efficiency of Ta, W, and Pt in metallic bilayers evaluated by harmonic Hall and spin Hall magnetoresistance measurements

    NASA Astrophysics Data System (ADS)

    Lau, Yong-Chang; Hayashi, Masamitsu

    2017-08-01

    We investigate the efficiency of current-induced torque, i.e., the spin torque efficiency, in in-plane magnetized heavy metal/CoFeB/MgO heterostructures (heavy metals = Pt, W, and Ta) using the harmonic Hall technique and the spin Hall magnetoresistance. We find that the amplitude of the external magnetic field has a strong influence on the spin torque efficiency evaluation by the harmonic Hall measurements. This can be corrected by measuring the corresponding Hall resistance susceptibility. The sign and magnitude of the resulting Slonczewski-like spin torque efficiencies are in agreement with previous reports and the measurements utilizing the spin Hall magnetoresistance, except for the Pt underlayer films. The origin of the discrepancy for the Pt underlayer films is unclear. The field like torque efficiencies, upon subtracting the Oersted field contribution, are quite low or negligible. This is in significant contrast to what has been found for the field like torque in heterostructures with perpendicular magnetization. These results suggest that a more advanced model is required in order to describe accurately spin transport and momentum transfer at metallic interfaces.

  8. Direct observation of the skyrmion Hall effect

    DOE PAGES

    Jiang, Wanjun; Zhang, Xichao; Yu, Guoqiang; ...

    2016-09-19

    The well-known Hall effect describes the transverse deflection of charged particles (electrons/holes) as a result of the Lorentz force. Similarly, it is intriguing to examine if quasi-particles without an electric charge, but with a topological charge, show related transverse motion. Magnetic skyrmions with a well-defined spin texture with a unit topological charge serve as good candidates to test this hypothesis. In spite of the recent progress made on investigating magnetic skyrmions, direct observation of the skyrmion Hall effect has remained elusive. Here, by using a current-induced spin Hall spin torque, we experimentally demonstrate the skyrmion Hall effect, and the resultantmore » skyrmion accumulation, by driving skyrmions from the creep-motion regime (where their dynamics are influenced by pinning defects) into the steady-flow-motion regime. Lastly, the experimental observation of transverse transport of skyrmions due to topological charge may potentially create many exciting opportunities, such as topological selection.« less

  9. Plasmon Geometric Phase and Plasmon Hall Shift

    NASA Astrophysics Data System (ADS)

    Shi, Li-kun; Song, Justin C. W.

    2018-04-01

    The collective plasmonic modes of a metal comprise a simple pattern of oscillating charge density that yields enhanced light-matter interaction. Here we unveil that beneath this familiar facade plasmons possess a hidden internal structure that fundamentally alters its dynamics. In particular, we find that metals with nonzero Hall conductivity host plasmons with an intricate current density configuration that sharply departs from that of ordinary zero Hall conductivity metals. This nontrivial internal structure dramatically enriches the dynamics of plasmon propagation, enabling plasmon wave packets to acquire geometric phases as they scatter. At boundaries, these phases accumulate allowing plasmon waves that reflect off to experience a nonreciprocal parallel shift. This plasmon Hall shift, tunable by Hall conductivity as well as plasmon wavelength, displaces the incident and reflected plasmon trajectories and can be readily probed by near-field photonics techniques. Anomalous plasmon geometric phases dramatically enrich the nanophotonics toolbox, and yield radical new means for directing plasmonic beams.

  10. Direct observation of the skyrmion Hall effect

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jiang, Wanjun; Zhang, Xichao; Yu, Guoqiang

    The well-known Hall effect describes the transverse deflection of charged particles (electrons/holes) as a result of the Lorentz force. Similarly, it is intriguing to examine if quasi-particles without an electric charge, but with a topological charge, show related transverse motion. Magnetic skyrmions with a well-defined spin texture with a unit topological charge serve as good candidates to test this hypothesis. In spite of the recent progress made on investigating magnetic skyrmions, direct observation of the skyrmion Hall effect has remained elusive. Here, by using a current-induced spin Hall spin torque, we experimentally demonstrate the skyrmion Hall effect, and the resultantmore » skyrmion accumulation, by driving skyrmions from the creep-motion regime (where their dynamics are influenced by pinning defects) into the steady-flow-motion regime. Lastly, the experimental observation of transverse transport of skyrmions due to topological charge may potentially create many exciting opportunities, such as topological selection.« less

  11. Determination of intrinsic spin Hall angle in Pt

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wang, Yi; Deorani, Praveen; Qiu, Xuepeng

    2014-10-13

    The spin Hall angle in Pt is evaluated in Pt/NiFe bilayers by spin torque ferromagnetic resonance measurements and is found to increase with increasing the NiFe thickness. To extract the intrinsic spin Hall angle in Pt by estimating the total spin current injected into NiFe from Pt, the NiFe thickness dependent measurements are performed and the spin diffusion in the NiFe layer is taken into account. The intrinsic spin Hall angle of Pt is determined to be 0.068 at room temperature and is found to be almost constant in the temperature range of 13–300 K.

  12. The effect of inertia on the Dirac electron, the spin Hall current and the momentum space Berry curvature

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chowdhury, Debashree, E-mail: debashreephys@gmail.com; Basu, B., E-mail: sribbasu@gmail.com

    2013-02-15

    We have studied the spin dependent force and the associated momentum space Berry curvature in an accelerating system. The results are derived by taking into consideration the non-relativistic limit of a generally covariant Dirac equation with an electromagnetic field present, where the methodology of the Foldy-Wouthuysen transformation is applied to achieve the non-relativistic limit. Spin currents appear due to the combined action of the external electric field, the crystal field and the induced inertial electric field via the total effective spin-orbit interaction. In an accelerating frame, the crucial role of momentum space Berry curvature in the spin dynamics has alsomore » been addressed from the perspective of spin Hall conductivity. For time dependent acceleration, the expression for the spin polarization has been derived. - Highlights: Black-Right-Pointing-Pointer We study the effect of acceleration on the Dirac electron in the presence of an electromagnetic field, where the acceleration induces an electric field. Black-Right-Pointing-Pointer Spin currents appear due to the total effective electric field via the total spin-orbit interaction. Black-Right-Pointing-Pointer We derive the expression for the spin dependent force and the spin Hall current, which is zero for a particular acceleration. Black-Right-Pointing-Pointer The role of the momentum space Berry curvature in an accelerating system is discussed. Black-Right-Pointing-Pointer An expression for the spin polarization for time dependent acceleration is derived.« less

  13. Are quantum spin Hall edge modes more resilient to disorder, sample geometry and inelastic scattering than quantum Hall edge modes?

    PubMed

    Mani, Arjun; Benjamin, Colin

    2016-04-13

    On the surface of 2D topological insulators, 1D quantum spin Hall (QSH) edge modes occur with Dirac-like dispersion. Unlike quantum Hall (QH) edge modes, which occur at high magnetic fields in 2D electron gases, the occurrence of QSH edge modes is due to spin-orbit scattering in the bulk of the material. These QSH edge modes are spin-dependent, and chiral-opposite spins move in opposing directions. Electronic spin has a larger decoherence and relaxation time than charge. In view of this, it is expected that QSH edge modes will be more robust to disorder and inelastic scattering than QH edge modes, which are charge-dependent and spin-unpolarized. However, we notice no such advantage accrues in QSH edge modes when subjected to the same degree of contact disorder and/or inelastic scattering in similar setups as QH edge modes. In fact we observe that QSH edge modes are more susceptible to inelastic scattering and contact disorder than QH edge modes. Furthermore, while a single disordered contact has no effect on QH edge modes, it leads to a finite charge Hall current in the case of QSH edge modes, and thus a vanishing of the pure QSH effect. For more than a single disordered contact while QH states continue to remain immune to disorder, QSH edge modes become more susceptible--the Hall resistance for the QSH effect changes sign with increasing disorder. In the case of many disordered contacts with inelastic scattering included, while quantization of Hall edge modes holds, for QSH edge modes a finite charge Hall current still flows. For QSH edge modes in the inelastic scattering regime we distinguish between two cases: with spin-flip and without spin-flip scattering. Finally, while asymmetry in sample geometry can have a deleterious effect in the QSH case, it has no impact in the QH case.

  14. Valley Hall effect and Nernst effect in strain engineered graphene

    NASA Astrophysics Data System (ADS)

    Niu, Zhi Ping; Yao, Jian-ming

    2018-04-01

    We theoretically predict the existence of tunneling valley Hall effect and Nernst effect in the normal/strain/normal graphene junctions, where a strained graphene is sandwiched by two normal graphene electrodes. By applying an electric bias a pure transverse valley Hall current with longitudinal charge current is generated. If the system is driven by a temperature bias, a valley Nernst effect is observed, where a pure transverse valley current without charge current propagates. Furthermore, the transverse valley current can be modulated by the Fermi energy and crystallographic orientation. When the magnetic field is further considered, we obtain a fully valley-polarized current. It is expected these features may be helpful in the design of the controllable valleytronic devices.

  15. Spin wave amplification using the spin Hall effect in permalloy/platinum bilayers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gladii, O.; Henry, Y.; Bailleul, M.

    2016-05-16

    We investigate the effect of an electrical current on the attenuation length of a 900 nm wavelength spin-wave in a permalloy/Pt bilayer using propagating spin-wave spectroscopy. The modification of the spin-wave relaxation rate is linear in current density, reaching up to 14% for a current density of 2.3 × 10{sup 11} A/m{sup 2} in Pt. This change is attributed to the spin transfer torque induced by the spin Hall effect and corresponds to an effective spin Hall angle of 0.13, which is among the highest values reported so far. The spin Hall effect thus appears as an efficient way of amplifying/attenuating propagating spin waves.

  16. Effects of an Internally-Mounted Cathode on Hall Thruster Plume Properties

    NASA Technical Reports Server (NTRS)

    Hofer, Richard R.; Johnson, Lee K.; Goebel, Dan M.; Fitzgerald, Dennis J.

    2006-01-01

    The effects of cathode position on the plume properties of an 8 kW BHT-8000 Busek Hall thruster are discussed. Experiments were conducted at the Jet Propulsion Laboratory (JPL) in a vacuum chamber suitable for the development and qualification of high-power Hall thrusters. Multi-mode Hall thruster operation was demonstrated at operating conditions ranging from 200-500 V discharge voltage, 10-40 A discharge current, and 2-8 kW discharge power. Reductions in plume divergence and increased near-field plume symmetries were found to result from the use of an internally-mounted cathode instead of the traditional externally-mounted configuration. High-current hollow cathodes developed at JPL utilizing lanthanum hexaboride (LaB6) emitters were also demonstrated. Discharge currents up to 100 A were achieved with the cathode operating alone and up to 40 A during operation with the Hall thruster. LaB6 cathodes were investigated because of their potential to reduce overall system cost and risk due to less stringent xenon purity and handling requirements.

  17. Ion and electron dynamics generating the Hall current in the exhaust far downstream of the reconnection x-line

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Fujimoto, Keizo, E-mail: keizo.fujimoto@nao.ac.jp; Takamoto, Makoto

    2016-01-15

    We have investigated the ion and electron dynamics generating the Hall current in the reconnection exhaust far downstream of the x-line where the exhaust width is much larger than the ion gyro-radius. A large-scale particle-in-cell simulation shows that most ions are accelerated through the Speiser-type motion in the current sheet formed at the center of the exhaust. The transition layers formed at the exhaust boundary are not identified as slow mode shocks. (The layers satisfy mostly the Rankine-Hugoniot conditions for a slow mode shock, but the energy conversion hardly occurs there.) We find that the ion drift velocity is modifiedmore » around the layer due to a finite Larmor radius effect. As a result, the ions are accumulated in the downstream side of the layer, so that collimated ion jets are generated. The electrons experience two steps of acceleration in the exhaust. The first is a parallel acceleration due to the out-of-plane electric field E{sub y} which has a parallel component in most area of the exhaust. The second is a perpendicular acceleration due to E{sub y} at the center of the current sheet and the motion is converted to the parallel direction. Because of the second acceleration, the electron outflow velocity becomes almost uniform over the exhaust. The difference in the outflow profile between the ions and electrons results in the Hall current in large area of the exhaust. The present study demonstrates the importance of the kinetic treatments for collisionless magnetic reconnection even far downstream from the x-line.« less

  18. Spontaneous Hall effect in a chiral p-wave superconductor

    NASA Astrophysics Data System (ADS)

    Furusaki, Akira; Matsumoto, Masashige; Sigrist, Manfred

    2001-08-01

    In a chiral superconductor with broken time-reversal symmetry a ``spontaneous Hall effect'' may be observed. We analyze this phenomenon by taking into account the surface properties of a chiral superconductor. We identify two main contributions to the spontaneous Hall effect. One contribution originates from the Bernoulli (or Lorentz) force due to spontaneous currents running along the surfaces of the superconductor. The other contribution has a topological origin and is related to the intrinsic angular momentum of Cooper pairs. The latter can be described in terms of a Chern-Simons-like term in the low-energy field theory of the superconductor and has some similarities with the quantum Hall effect. The spontaneous Hall effect in a chiral superconductor is, however, nonuniversal. Our analysis is based on three approaches to the problem: a self-consistent solution of the Bogoliubov-de Gennes equation, a generalized Ginzburg-Landau theory, and a hydrodynamic formulation. All three methods consistently lead to the same conclusion that the spontaneous Hall resistance of a two-dimensional superconducting Hall bar is of order h/(ekFλ)2, where kF is the Fermi wave vector and λ is the London penetration depth; the Hall resistance is substantially suppressed from a quantum unit of resistance. Experimental issues in measuring this effect are briefly discussed.

  19. Modeling of anomalous electron mobility in Hall thrusters

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Koo, Justin W.; Boyd, Iain D.

    Accurate modeling of the anomalous electron mobility is absolutely critical for successful simulation of Hall thrusters. In this work, existing computational models for the anomalous electron mobility are used to simulate the UM/AFRL P5 Hall thruster (a 5 kW laboratory model) in a two-dimensional axisymmetric hybrid particle-in-cell Monte Carlo collision code. Comparison to experimental results indicates that, while these computational models can be tuned to reproduce the correct thrust or discharge current, it is very difficult to match all integrated performance parameters (thrust, power, discharge current, etc.) simultaneously. Furthermore, multiple configurations of these computational models can produce reasonable integrated performancemore » parameters. A semiempirical electron mobility profile is constructed from a combination of internal experimental data and modeling assumptions. This semiempirical electron mobility profile is used in the code and results in more accurate simulation of both the integrated performance parameters and the mean potential profile of the thruster. Results indicate that the anomalous electron mobility, while absolutely necessary in the near-field region, provides a substantially smaller contribution to the total electron mobility in the high Hall current region near the thruster exit plane.« less

  20. Concert hall acoustics

    NASA Astrophysics Data System (ADS)

    Schroeder, Manfred

    2004-05-01

    I will review some work at Bell Laboratories on artificial reverberation and concert hall acoustics including Philharmonic Hall (Lincoln Center for the Performing Arts, New York). I will also touch on sound diffusion by number-theoretic surfaces and the measurement of reverberation time using the music as played in the hall as a ``test'' signal.

  1. Tutorial: Physics and modeling of Hall thrusters

    NASA Astrophysics Data System (ADS)

    Boeuf, Jean-Pierre

    2017-01-01

    Hall thrusters are very efficient and competitive electric propulsion devices for satellites and are currently in use in a number of telecommunications and government spacecraft. Their power spans from 100 W to 20 kW, with thrust between a few mN and 1 N and specific impulse values between 1000 and 3000 s. The basic idea of Hall thrusters consists in generating a large local electric field in a plasma by using a transverse magnetic field to reduce the electron conductivity. This electric field can extract positive ions from the plasma and accelerate them to high velocity without extracting grids, providing the thrust. These principles are simple in appearance but the physics of Hall thrusters is very intricate and non-linear because of the complex electron transport across the magnetic field and its coupling with the electric field and the neutral atom density. This paper describes the basic physics of Hall thrusters and gives a (non-exhaustive) summary of the research efforts that have been devoted to the modelling and understanding of these devices in the last 20 years. Although the predictive capabilities of the models are still not sufficient for a full computer aided design of Hall thrusters, significant progress has been made in the qualitative and quantitative understanding of these devices.

  2. Exchange magnon induced resistance asymmetry in permalloy spin-Hall oscillators

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Langenfeld, S.; Walter Schottky Institut and Physik-Department, Technische Universität München, 85748 Garching; Tshitoyan, V.

    2016-05-09

    We investigate magnetization dynamics in a spin-Hall oscillator using a direct current measurement as well as conventional microwave spectrum analysis. When the current applies an anti-damping spin-transfer torque, we observe a change in resistance which we ascribe mainly to the excitation of incoherent exchange magnons. A simple model is developed based on the reduction of the effective saturation magnetization, quantitatively explaining the data. The observed phenomena highlight the importance of exchange magnons on the operation of spin-Hall oscillators.

  3. Superconducting quantum spin-Hall systems with giant orbital g-factors

    NASA Astrophysics Data System (ADS)

    Hankiewicz, Ewelina; Reinthaler, Rolf; Tkachov, Grigory

    Topological aspects of superconductivity in quantum spin-Hall systems (QSHSs) such as thin layers of three-dimensional topological insulators (3D Tis) or two-dimensional Tis are in the focus of current research. Here, we describe a novel superconducting quantum spin-Hall effect (quantum spin Hall system in the proximity to the s-wave superconductor and in the orbital in-plane magnetic field), which is protected against elastic backscattering by combined time-reversal and particle-hole symmetry. This effect is characterized by spin-polarized edge states, which can be manipulated in weak magnetic fields due to a giant effective orbital g-factor, allowing the generation of spin currents. The phenomenon provides a novel solution to the outstanding challenge of detecting the spin-polarization of the edge states. Here we propose the detection of the edge polarization in the three-terminal junction using unusual transport properties of superconducting quantum Hall-effect: a non-monotonic excess current and a zero-bias conductance splitting. We thank for the financial support the German Science Foundation (DFG), Grants No HA 5893/4-1 within SPP 1666, HA5893/5-2 within FOR1162 and TK60/1-1 (G.T.), as well the ENB graduate school ``Topological insulators''.

  4. Dynamics of antiferromagnetic skyrmion driven by the spin Hall effect

    NASA Astrophysics Data System (ADS)

    Jin, Chendong; Song, Chengkun; Wang, Jianbo; Liu, Qingfang

    2016-10-01

    Magnetic skyrmion moved by the spin-Hall effect is promising for the application of the generation racetrack memories. However, the Magnus force causes a deflected motion of skyrmion, which limits its application. Here, we create an antiferromagnetic skyrmion by injecting a spin-polarized pulse in the nanostripe and investigate the spin Hall effect-induced motion of antiferromagnetic skyrmion by micromagnetic simulations. In contrast to ferromagnetic skyrmion, we find that the antiferromagnetic skyrmion has three evident advantages: (i) the minimum driving current density of antiferromagnetic skyrmion is about two orders smaller than the ferromagnetic skyrmion; (ii) the velocity of the antiferromagnetic skyrmion is about 57 times larger than the ferromagnetic skyrmion driven by the same value of current density; (iii) antiferromagnetic skyrmion can be driven by the spin Hall effect without the influence of Magnus force. In addition, antiferromagnetic skyrmion can move around the pinning sites due to its property of topological protection. Our results present the understanding of antiferromagnetic skyrmion motion driven by the spin Hall effect and may also contribute to the development of antiferromagnetic skyrmion-based racetrack memories.

  5. Magnetic Reconnection and Modification of the Hall Physics Due to Cold Ions at the Magnetopause

    NASA Technical Reports Server (NTRS)

    Andre, M.; Li, W.; Toldeo-Redondo, S.; Khotyaintsev, Yu. V.; Vaivads, A.; Graham, D. B.; Norgren, C.; Burch, J.; Lindqvist, P.-A.; Marklund, G.; hide

    2016-01-01

    Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohms law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the v x B drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.

  6. Computational manipulation of a radiative MHD flow with Hall current and chemical reaction in the presence of rotating fluid

    NASA Astrophysics Data System (ADS)

    Alias Suba, Subbu; Muthucumaraswamy, R.

    2018-04-01

    A numerical analysis of transient radiative MHD(MagnetoHydroDynamic) natural convective flow of a viscous, incompressible, electrically conducting and rotating fluid along a semi-infinite isothermal vertical plate is carried out taking into consideration Hall current, rotation and first order chemical reaction.The coupled non-linear partial differential equations are expressed in difference form using implicit finite difference scheme. The difference equations are then reduced to a system of linear algebraic equations with a tri-diagonal structure which is solved by Thomas Algorithm. The primary and secondary velocity profiles, temperature profile, concentration profile, skin friction, Nusselt number and Sherwood Number are depicted graphically for a range of values of rotation parameter, Hall parameter,magnetic parameter, chemical reaction parameter, radiation parameter, Prandtl number and Schmidt number.It is recognized that rate of heat transfer and rate of mass transfer decrease with increase in time but they increase with increasing values of radiation parameter and Schmidt number respectively.

  7. Hall Thruster With an External Acceleration Zone

    DTIC Science & Technology

    2005-09-14

    Hall Thruster in a high vacuum environment. The ionized propellant velocities were measured using laser induced fluorescence of the excited state xenon ionic transition at 834.7 nm. Ion velocities were interrogated from the channel exit plane to a distance 30 mm from it. Both axial and cross-field (along the electron Hall current direction) velocities were measured. The results presented here, combined with those of previous work, highlight the high sensitivity of electron mobility inside and outside the channel, depending on the background gas density, type of wall

  8. Efficiency Analysis of a High-Specific Impulse Hall Thruster

    NASA Technical Reports Server (NTRS)

    Jacobson, David (Technical Monitor); Hofer, Richard R.; Gallimore, Alec D.

    2004-01-01

    Performance and plasma measurements of the high-specific impulse NASA-173Mv2 Hall thruster were analyzed using a phenomenological performance model that accounts for a partially-ionized plasma containing multiply-charged ions. Between discharge voltages of 300 to 900 V, the results showed that although the net decrease of efficiency due to multiply-charged ions was only 1.5 to 3.0 percent, the effects of multiply-charged ions on the ion and electron currents could not be neglected. Between 300 to 900 V, the increase of the discharge current was attributed to the increasing fraction of multiply-charged ions, while the maximum deviation of the electron current from its average value was only +5/-14 percent. These findings revealed how efficient operation at high-specific impulse was enabled through the regulation of the electron current with the applied magnetic field. Between 300 to 900 V, the voltage utilization ranged from 89 to 97 percent, the mass utilization from 86 to 90 percent, and the current utilization from 77 to 81 percent. Therefore, the anode efficiency was largely determined by the current utilization. The electron Hall parameter was nearly constant with voltage, decreasing from an average of 210 at 300 V to an average of 160 between 400 to 900 V. These results confirmed our claim that efficient operation can be achieved only over a limited range of Hall parameters.

  9. Generation of magnetic skyrmion bubbles by inhomogeneous spin Hall currents

    DOE PAGES

    Heinonen, Olle; Jiang, Wanjun; Somaily, Hamoud; ...

    2016-03-07

    Recent experiments have shown that magnetic skyrmion bubbles can be generated and injected at room temperature in thin films. In this study, we demonstrate, using micromagnetic modeling, that such skyrmions can be generated by an inhomogeneous spin Hall torque in the presence of Dzyaloshinskii-Moriya interactions (DMIs). In the experimental Ta-Co 20Fe 60B 20 thin films, the DMI is rather small; nevertheless, the skyrmion bubbles are stable, or at least metastable on observational time scales.

  10. Strong Intrinsic Spin Hall Effect in the TaAs Family of Weyl Semimetals

    NASA Astrophysics Data System (ADS)

    Sun, Yan; Zhang, Yang; Felser, Claudia; Yan, Binghai

    2016-09-01

    Since their discovery, topological insulators are expected to be ideal spintronic materials owing to the spin currents carried by surface states with spin-momentum locking. However, the bulk doping problem remains an obstacle that hinders such an application. In this work, we predict that a newly discovered family of topological materials, the Weyl semimetals, exhibits a large intrinsic spin Hall effect that can be utilized to generate and detect spin currents. Our ab initio calculations reveal a large spin Hall conductivity in the TaAs family of Weyl materials. Considering the low charge conductivity of semimetals, Weyl semimetals are believed to present a larger spin Hall angle (the ratio of the spin Hall conductivity over the charge conductivity) than that of conventional spin Hall systems such as the 4 d and 5 d transition metals. The spin Hall effect originates intrinsically from the bulk band structure of Weyl semimetals, which exhibit a large Berry curvature and spin-orbit coupling, so the bulk carrier problem in the topological insulators is naturally avoided. Our work not only paves the way for employing Weyl semimetals in spintronics, but also proposes a new guideline for searching for the spin Hall effect in various topological materials.

  11. Reversed Hall effect and plasma conductivity in the presence of charged impurities

    NASA Astrophysics Data System (ADS)

    Yaroshenko, V. V.; Lühr, H.

    2018-01-01

    The Hall conductivity of magnetized plasma can be strongly suppressed by the contribution of negatively charged particulates (referred further as "dust"). Once the charge density accumulated by the dust exceeds a certain threshold, the Hall component becomes negative, providing a reversal in the Hall current. Such an effect is unique for dust-loaded plasmas, and it can hardly be achieved in electronegative plasmas. Further growth of the dust density leads to an increase in both the absolute value of the Hall and Pedersen conductivities, while the field-aligned component is decreased. These modifications enhance the role of transverse electric currents and reduce the anisotropy of a magnetized plasma when loaded with charged impurities. The findings provide an important basis for studying the generation of electric currents and transport phenomena in magnetized plasma systems containing small charged particulates. They can be relevant for a wide range of applications from naturally occurring space plasmas in planetary magnetospheres and astrophysical objects to laboratory dusty plasmas (Magnetized Dusty Plasma Experiment) and to technological and fusion plasmas.

  12. The ``cinquefoil" resistive/Hall measurement geometry

    NASA Astrophysics Data System (ADS)

    Koon, Daniel W.

    2000-03-01

    This talk begins by analyzing the charge transport weighting functions -- the sensitivity of resistive and Hall measurements to local macroscopic inhomogeneities -- of bridge-shaped transport specimens. As expected, such measurements sample only that region of the specimen between the central voltage electrodes, in the limit of narrow current channels connected by even narrower arms to the voltage electrodes. The bridge geometry has a few advantages over the van der Pauw cloverleaf geometry -- including ease in zeroing out the null-field Hall voltage -- but also some disadvantages. The talk concludes with an analysis of a hybrid geometry, the “cinquefoil” or five-leafed clover, which combines the best features of both.

  13. Observations of Hall Reconnection Physics Far Downstream of the X Line.

    PubMed

    Mistry, R; Eastwood, J P; Haggerty, C C; Shay, M A; Phan, T D; Hietala, H; Cassak, P A

    2016-10-28

    Observations made using the Wind spacecraft of Hall magnetic fields in solar wind reconnection exhausts are presented. These observations are consistent with the generation of Hall fields by a narrow ion inertial scale current layer near the separatrix, which is confirmed with an appropriately scaled particle-in-cell simulation that shows excellent agreement with observations. The Hall fields are observed thousands of ion inertial lengths downstream from the reconnection X line, indicating that narrow regions of kinetic dynamics can persist extremely far downstream.

  14. Nonequilibrium Fractional Hall Response After a Topological Quench

    NASA Astrophysics Data System (ADS)

    Unal, Nur; Mueller, Erich; Oktel, M. O.

    When a system is suddenly driven between two topologically different phases, aspects of the original topology survive the quench, but most physical observables (edge currents, Hall conductivity) appear to be non-universal. I will present the non-equilibrium Hall response of a Chern insulator following a quench where the mass term of a single Dirac cone changes sign. In the limit where the physics is dominated by a single Dirac cone, we theoretically find that the Hall conductivity universally changes by two-thirds of the quantum of conductivity. I will analyze this universal behavior by considering the Haldane model, and discuss experimental aspects for its observation in cold atoms. This work is supported by TUBITAK, NSFPHY-1508300, ARO-MURI W9111NF-14-1-0003.

  15. Anomalous Hall effect in semiconductor quantum wells in proximity to chiral p -wave superconductors

    NASA Astrophysics Data System (ADS)

    Yang, F.; Yu, T.; Wu, M. W.

    2018-05-01

    By using the gauge-invariant optical Bloch equation, we perform a microscopic kinetic investigation on the anomalous Hall effect in chiral p -wave superconducting states. Specifically, the intrinsic anomalous Hall conductivity in the absence of the magnetic field is zero as a consequence of Galilean invariance in our description. As for the extrinsic channel, a finite anomalous Hall current is obtained from the impurity scattering with the optically excited normal quasiparticle current even at zero temperature. From our kinetic description, it can be clearly seen that the excited normal quasiparticle current is due to an induced center-of-mass momentum of Cooper pairs through the acceleration driven by ac electric field. For the induced anomalous Hall current, we show that the conventional skew-scattering channel in the linear response makes the dominant contribution in the strong impurity interaction. In this case, our kinetic description as a supplementary viewpoint mostly confirms the results of Kubo formalism in the literature. Nevertheless, in the weak impurity interaction, this skew-scattering channel becomes marginal and we reveal that an induction channel from the Born contribution dominates the anomalous Hall current. This channel, which has long been overlooked in the literature, is due to the particle-hole asymmetry by nonlinear optical excitation. Finally, we study the case in the chiral p -wave superconducting state with a transverse conical magnetization, which breaks the Galilean invariance. In this situation, the intrinsic anomalous Hall conductivity is no longer zero. Comparison of this intrinsic channel with the extrinsic one from impurity scattering is addressed.

  16. A Monolithic CMOS Magnetic Hall Sensor with High Sensitivity and Linearity Characteristics

    PubMed Central

    Huang, Haiyun; Wang, Dejun; Xu, Yue

    2015-01-01

    This paper presents a fully integrated linear Hall sensor by means of 0.8 μm high voltage complementary metal-oxide semiconductor (CMOS) technology. This monolithic Hall sensor chip features a highly sensitive horizontal switched Hall plate and an efficient signal conditioner using dynamic offset cancellation technique. An improved cross-like Hall plate achieves high magnetic sensitivity and low offset. A new spinning current modulator stabilizes the quiescent output voltage and improves the reliability of the signal conditioner. The tested results show that at the 5 V supply voltage, the maximum Hall output voltage of the monolithic Hall sensor microsystem, is up to ±2.1 V and the linearity of Hall output voltage is higher than 99% in the magnetic flux density range from ±5 mT to ±175 mT. The output equivalent residual offset is 0.48 mT and the static power consumption is 20 mW. PMID:26516864

  17. A Monolithic CMOS Magnetic Hall Sensor with High Sensitivity and Linearity Characteristics.

    PubMed

    Huang, Haiyun; Wang, Dejun; Xu, Yue

    2015-10-27

    This paper presents a fully integrated linear Hall sensor by means of 0.8 μm high voltage complementary metal-oxide semiconductor (CMOS) technology. This monolithic Hall sensor chip features a highly sensitive horizontal switched Hall plate and an efficient signal conditioner using dynamic offset cancellation technique. An improved cross-like Hall plate achieves high magnetic sensitivity and low offset. A new spinning current modulator stabilizes the quiescent output voltage and improves the reliability of the signal conditioner. The tested results show that at the 5 V supply voltage, the maximum Hall output voltage of the monolithic Hall sensor microsystem, is up to ±2.1 V and the linearity of Hall output voltage is higher than 99% in the magnetic flux density range from ±5 mT to ±175 mT. The output equivalent residual offset is 0.48 mT and the static power consumption is 20 mW.

  18. An evaluation of krypton propellant in Hall thrusters

    NASA Astrophysics Data System (ADS)

    Linnell, Jesse Allen

    Due to its high specific impulse and low price, krypton has long sparked interest as an alternate Hall thruster propellant. Unfortunately at the moment, krypton's relatively poor performance precludes it as a legitimate option. This thesis presents a detailed investigation into krypton operation in Hall thrusters. These findings suggest that the performance gap can be decreased to 4% and krypton can finally become a realistic propellant option. Although krypton has demonstrated superior specific impulse, the xenon-krypton absolute efficiency gap ranges between 2 and 15%. A phenomenological performance model indicates that the main contributors to the efficiency gap are propellant utilization and beam divergence. Propellant utilization and beam divergence have relative efficiency deficits of 5 and 8%, respectively. A detailed characterization of internal phenomena is conducted to better understand the xenon-krypton efficiency gap. Krypton's large beam divergence is found to be related to a defocusing equipotential structure and a weaker magnetic field topology. Ionization processes are shown to be linked to the Hall current, the magnetic mirror topology, and the perpendicular gradient of the magnetic field. Several thruster design and operational suggestions are made to optimize krypton efficiency. Krypton performance is optimized for discharge voltages above 500 V and flow rates corresponding to an a greater than 0.015 mg/(mm-s), where alpha is a function of flow rate and discharge channel dimensions (alpha = m˙alphab/Ach). Performance can be further improved by increasing channel length or decreasing channel width for a given flow rate. Also, several magnetic field design suggestions are made to enhance ionization and beam focusing. Several findings are presented that improve the understanding of general Hall thruster physics. Excellent agreement is shown between equipotential lines and magnetic field lines. The trim coil is shown to enhance beam focusing

  19. Electron Transport in Hall Thrusters

    NASA Astrophysics Data System (ADS)

    McDonald, Michael Sean

    Despite high technological maturity and a long flight heritage, computer models of Hall thrusters remain dependent on empirical inputs and a large part of thruster development to date has been heavily experimental in nature. This empirical approach will become increasingly unsustainable as new high-power thrusters tax existing ground test facilities and more exotic thruster designs stretch and strain the boundaries of existing design experience. The fundamental obstacle preventing predictive modeling of Hall thruster plasma properties and channel erosion is the lack of a first-principles description of electron transport across the strong magnetic fields between the cathode and anode. In spite of an abundance of proposed transport mechanisms, accurate assessments of the magnitude of electron current due to any one mechanism are scarce, and comparative studies of their relative influence on a single thruster platform simply do not exist. Lacking a clear idea of what mechanism(s) are primarily responsible for transport, it is understandably difficult for the electric propulsion scientist to focus his or her theoretical and computational tools on the right targets. This work presents a primarily experimental investigation of collisional and turbulent Hall thruster electron transport mechanisms. High-speed imaging of the thruster discharge channel at tens of thousands of frames per second reveals omnipresent rotating regions of elevated light emission, identified with a rotating spoke instability. This turbulent instability has been shown through construction of an azimuthally segmented anode to drive significant cross-field electron current in the discharge channel, and suggestive evidence points to its spatial extent into the thruster near-field plume as well. Electron trajectory simulations in experimentally measured thruster electromagnetic fields indicate that binary collisional transport mechanisms are not significant in the thruster plume, and experiments

  20. Mode transition of a Hall thruster discharge plasma

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hara, Kentaro, E-mail: kenhara@umich.edu; Sekerak, Michael J., E-mail: msekerak@umich.edu; Boyd, Iain D.

    2014-05-28

    A Hall thruster is a cross-field plasma device used for spacecraft propulsion. An important unresolved issue in the development of Hall thrusters concerns the effect of discharge oscillations in the range of 10–30 kHz on their performance. The use of a high speed Langmuir probe system and ultra-fast imaging of the discharge plasma of a Hall thruster suggests that the discharge oscillation mode, often called the breathing mode, is strongly correlated to an axial global ionization mode. Stabilization of the global oscillation mode is achieved as the magnetic field is increased and azimuthally rotating spokes are observed. A hybrid-direct kinetic simulationmore » that takes into account the transport of electronically excited atoms is used to model the discharge plasma of a Hall thruster. The predicted mode transition agrees with experiments in terms of the mean discharge current, the amplitude of discharge current oscillation, and the breathing mode frequency. It is observed that the stabilization of the global oscillation mode is associated with reduced electron transport that suppresses the ionization process inside the channel. As the Joule heating balances the other loss terms including the effects of wall loss and inelastic collisions, the ionization oscillation is damped, and the discharge oscillation stabilizes. A wide range of the stable operation is supported by the formation of a space charge saturated sheath that stabilizes the electron axial drift and balances the Joule heating as the magnetic field increases. Finally, it is indicated from the numerical results that there is a strong correlation between the emitted light intensity and the discharge current.« less

  1. Direct current modulation of spin-Hall-induced spin torque ferromagnetic resonance in platinum/permalloy bilayer thin films

    NASA Astrophysics Data System (ADS)

    Hirayama, Shigeyuki; Mitani, Seiji; Otani, YoshiChika; Kasai, Shinya

    2018-06-01

    We examined the spin-Hall-induced spin torque ferromagnetic resonance (ST-FMR) in platinum/permalloy bilayer thin films under bias direct current (DC). The bias DC modulated the symmetric components of the ST-FMR spectra, while no dominant modulation was found in the antisymmetric components. A detailed analysis in combination with simple model calculations clarified that the major origin of the modulation can be attributed to the DC resistance change under the precessional motion of magnetization. This effect is the second order contribution for the precession angle, even though the contribution can be comparable to the rectification voltage under some specific conditions.

  2. Discharge Oscillations in a Permanent Magnet Cylindrical Hall-Effect Thruster

    NASA Technical Reports Server (NTRS)

    Polzin, K. A.; Sooby, E. S.; Raitses, Y.; Merino, E.; Fisch, N. J.

    2009-01-01

    Measurements of the discharge current in a cylindrical Hall thruster are presented to quantify plasma oscillations and instabilities without introducing an intrusive probe into the plasma. The time-varying component of the discharge current is measured using a current monitor that possesses a wide frequency bandwidth and the signal is Fourier transformed to yield the frequency spectra present, allowing for the identification of plasma oscillations. The data show that the discharge current oscillations become generally greater in amplitude and complexity as the voltage is increased, and are reduced in severity with increasing flow rate. The breathing mode ionization instability is identified, with frequency as a function of discharge voltage not increasing with discharge voltage as has been observed in some traditional Hall thruster geometries, but instead following a scaling similar to a large-amplitude, nonlinear oscillation mode recently predicted in for annular Hall thrusters. A transition from lower amplitude oscillations to large relative fluctuations in the oscillating discharge current is observed at low flow rates and is suppressed as the mass flow rate is increased. A second set of peaks in the frequency spectra are observed at the highest propellant flow rate tested. Possible mechanisms that might give rise to these peaks include ionization instabilities and interactions between various oscillatory modes.

  3. Current-Driven Dynamics of Skyrmions Stabilized in MnSi Nanowires Revealed by Topological Hall Effect

    NASA Astrophysics Data System (ADS)

    Liang, Dong; Degrave, John; Stolt, Matthew; Tokura, Yoshinori; Jin, Song

    2015-03-01

    Skyrmions, novel topologically stable spin vortices, hold promise for next-generation high-density magnetic storage technologies due to their nanoscale domains and ultralow energy consumption. One-dimensional (1D) nanowires are ideal hosts for skyrmions since they not only serve as a natural platform for magnetic racetrack memory devices but also can potentially stabilize skyrmions. We use the topological Hall effect (THE) to study the phase stability and current-driven dynamics of the skyrmions in MnSi nanowires. The THE was observed in an extended magnetic field-temperature window (15 to 30 K), suggesting stabilization of skyrmion phase in nanowires compared with the bulk (27 to 29.5 K). Furthermore, we study skyrmion dynamics in this extended skyrmion phase region and found that under the high current-density of 108-109Am-2 enabled by nanowire geometry, the THE decreases with increasing current densities, which demonstrates the current-driven motion of skyrmions generating the emergent electric field. These results open up the exploration of nanowires as an attractive platform for investigating skyrmion physics in 1D systems and exploiting skyrmions in magnetic storage concepts. This work is supported by US National Science Foundation (ECCS-1231916) and JSPS Grant-in-Aid for Scientific Research No. 24224009.

  4. The Influence of Current Density and Magnetic Field Topography in Optimizing the Performance, Divergence, and Plasma Oscillations of High Specific Impulse Hall Thrusters

    NASA Technical Reports Server (NTRS)

    Hofer, Richard R.; Jankovsky, Robert S.

    2003-01-01

    Recent studies of xenon Hall thrusters have shown peak efficiencies at specific impulses of less than 3000 s. This was a consequence of modern Hall thruster magnetic field topographies, which have been optimized for 300 V discharges. On-going research at the NASA Glenn Research Center is investigating this behavior and methods to enhance thruster performance. To conduct these studies, a laboratory model Hall thruster that uses a pair of trim coils to tailor the magnetic field topography for high specific impulse operation has been developed. The thruster-the NASA-173Mv2 was tested to determine how current density and magnetic field topography affect performance, divergence, and plasma oscillations at voltages up to 1000 V. Test results showed there was a minimum current density and optimum magnetic field topography at which efficiency monotonically increased with voltage. At 1000 V, 10 milligrams per second the total specific impulse was 3390 s and the total efficiency was 60.8%. Plume divergence decreased at 400-1000 V, but increased at 300-400 V as the result of plasma oscillations. The dominant oscillation frequency steadily increased with voltage, from 14.5 kHz at 300 V, to 22 kHz at 1000 V. An additional oscillatory mode in the 80-90 kHz frequency range began to appear above 500 V. The use of trim coils to modify the magnetic field improved performance while decreasing plume divergence and the frequency and magnitude of plasma oscillations.

  5. Topological Hall and Spin Hall Effects in Disordered Skyrmionic Textures

    NASA Astrophysics Data System (ADS)

    Ndiaye, Papa Birame; Akosa, Collins; Manchon, Aurelien; Spintronics Theory Group Team

    We carry out a throughout study of the topological Hall and topological spin Hall effects in disordered skyrmionic systems: the dimensionless (spin) Hall angles are evaluated across the energy band structure in the multiprobe Landauer-Büttiker formalism and their link to the effective magnetic field emerging from the real space topology of the spin texture is highlighted. We discuss these results for an optimal skyrmion size and for various sizes of the sample and found that the adiabatic approximation still holds for large skyrmions as well as for few atomic size-nanoskyrmions. Finally, we test the robustness of the topological signals against disorder strength and show that topological Hall effect is highly sensitive to momentum scattering. This work was supported by the King Abdullah University of Science and Technology (KAUST) through the Award No OSR-CRG URF/1/1693-01 from the Office of Sponsored Research (OSR).

  6. Quantum Nonlinear Hall Effect Induced by Berry Curvature Dipole in Time-Reversal Invariant Materials.

    PubMed

    Sodemann, Inti; Fu, Liang

    2015-11-20

    It is well known that a nonvanishing Hall conductivity requires broken time-reversal symmetry. However, in this work, we demonstrate that Hall-like currents can occur in second-order response to external electric fields in a wide class of time-reversal invariant and inversion breaking materials, at both zero and twice the driving frequency. This nonlinear Hall effect has a quantum origin arising from the dipole moment of the Berry curvature in momentum space, which generates a net anomalous velocity when the system is in a current-carrying state. The nonlinear Hall coefficient is a rank-two pseudotensor, whose form is determined by point group symmetry. We discus optimal conditions to observe this effect and propose candidate two- and three-dimensional materials, including topological crystalline insulators, transition metal dichalcogenides, and Weyl semimetals.

  7. Facility Focus: Residence Halls.

    ERIC Educational Resources Information Center

    College Planning & Management, 2002

    2002-01-01

    Describes residence halls seeking to meet needs beyond traditional mass housing for the 18- to 22-year-old students: Whittemore Hall at the Tuck School of Business at Dartmouth College (for older students); Small Group Housing at Washington University (grouping students with common interests); and the renovation of the residence hall at Boston's…

  8. Astronaut Hall of Fame

    NASA Image and Video Library

    2018-04-21

    Scott D. Altman, second from left, is inducted into the Astronaut Hall of Fame (AHOF) during a ceremony inside the Space Shuttle Atlantis attraction at NASA's Kennedy Space Center Visitor Complex in Florida. At far left, Hall of Famer Curt Brown, board chairman, Astronaut Scholarship Foundation (ASF), inducts Altman into the Hall of Fame Class of 2018. At right is Hall of Famer John Grunsfeld, who spoke on Altman's behalf during the ceremony. At far right is Thomas D. Jones, Ph.D., who also was inducted into the AHOF Class of 2018. Inductees into the Hall of Fame are selected by a committee of Hall of Fame astronauts, former NASA officials, flight directors, historians and journalists. The process is administered by the Astronaut Scholarship Foundation. To be eligible, an astronaut must have made his or her first flight at least 17 years before the induction. Candidates must be a U.S. citizen and a NASA-trained commander, pilot or mission specialist who has orbited the earth at least once. Including Altman and Jones, 97 astronauts have been inducted into the AHOF.

  9. Astronaut Hall of Fame

    NASA Image and Video Library

    2018-04-21

    Thomas D. Jones, Ph.D., in the center, is inducted into the Astronaut Hall of Fame (AHOF) during a ceremony inside the Space Shuttle Atlantis attraction at NASA’s Kennedy Space Center Visitor Complex in Florida. At left, Hall of Famer Curt Brown, board chairman, Astronaut Scholarship Foundation (ASF), inducts Jones into the Hall of Fame Class of 2018. At right is Hall of Famer Storey Musgrave, who spoke on Jones behalf during the ceremony. Also inducted was retired astronaut Scott D. Altman. Inductees into the Hall of Fame are selected by a committee of Hall of Fame astronauts, former NASA officials, flight directors, historians and journalists. The process is administered by the Astronaut Scholarship Foundation. To be eligible, an astronaut must have made his or her first flight at least 17 years before the induction. Candidates must be a U.S. citizen and a NASA-trained commander, pilot or mission specialist who has orbited the earth at least once. Including Altman and Jones, 97 astronauts have been inducted into the AHOF.

  10. NASA's 2004 Hall Thruster Program

    NASA Technical Reports Server (NTRS)

    Jacobson, David T.; Manzella, David H.; Hofer, Richard R.; Peterson, Peter Y.

    2004-01-01

    An overview of NASA's Hall thruster research and development tasks conducted during fiscal year 2004 is presented. These tasks focus on: raising the technology readiness level of high power Hall thrusters, developing a moderate-power/ moderate specific impulse Hall thruster, demonstrating high-power/high specific impulse Hall thruster operation, and addressing the fundamental technical challenges of emerging Hall thruster concepts. Programmatic background information, technical accomplishments and out year plans for each program element performed under the sponsorship of the In-Space Transportation Program, Project Prometheus, and the Energetics Project are provided.

  11. Use of the 'Hall technique' for management of carious primary molars among Scottish general dental practitioners.

    PubMed

    Dean, A A; Bark, J E; Sherriff, A; Macpherson, L M D; Cairns, A

    2011-06-01

    To assess the current awareness, usage and opinion of the Hall technique as a restorative option for primary molars in Scottish general dental practice; and to identify preferences for methods of further training, if desired, for those not currently using the technique. A postal questionnaire was sent to a random sample of Scottish general dental practitioners (GDPs) (n= 1207). Half of all GDPs within each health board were mailed. All analyses have been carried out in Minitab (version 15). The study is primarily descriptive and uses frequency distributions and cross-tabulations. Percentages are reported with p5% confidence intervals. Characteristics of the whole sample were reported. However when reporting the use of the Hall technique, only those GDP's reporting to treat children, at least sometimes are considered. Following two mail-shots, the overall response rate was 59% (715/1207). Eighty-six percent (616/715) of respondents were aware of the Hall technique as a method of restoring primary molars and 48 % (n=318) were currently using the Hall technique. Of those GDPs who never used the Hall technique (51% of total respondents; n=340), 46% (n=157) indicated they were either 'very interested' or 'interested' in adopting the Hall technique into their clinical practice. The preferred source for further training was via a section 63 continuing professional development (CPD) course, incorporating a practical element. Of those GDPs in Scotland who responded to the questionnaire, an unexpectedly high number were already using the Hall technique in their practice, and among those not currently using it, there is a demand for training.

  12. Direct comparison of fractional and integer quantized Hall resistance

    NASA Astrophysics Data System (ADS)

    Ahlers, Franz J.; Götz, Martin; Pierz, Klaus

    2017-08-01

    We present precision measurements of the fractional quantized Hall effect, where the quantized resistance {{R}≤ft[ 1/3 \\right]} in the fractional quantum Hall state at filling factor 1/3 was compared with a quantized resistance {{R}[2]} , represented by an integer quantum Hall state at filling factor 2. A cryogenic current comparator bridge capable of currents down to the nanoampere range was used to directly compare two resistance values of two GaAs-based devices located in two cryostats. A value of 1-(5.3  ±  6.3) 10-8 (95% confidence level) was obtained for the ratio ({{R}≤ft[ 1/3 \\right]}/6{{R}[2]} ). This constitutes the most precise comparison of integer resistance quantization (in terms of h/e 2) in single-particle systems and of fractional quantization in fractionally charged quasi-particle systems. While not relevant for practical metrology, such a test of the validity of the underlying physics is of significance in the context of the upcoming revision of the SI.

  13. Development and Characterization of High-Efficiency, High-Specific Impulse Xenon Hall Thrusters

    NASA Technical Reports Server (NTRS)

    Hofer, Richard R.; Jacobson, David (Technical Monitor)

    2004-01-01

    This dissertation presents research aimed at extending the efficient operation of 1600 s specific impulse Hall thruster technology to the 2000 to 3000 s range. Motivated by previous industry efforts and mission studies, the aim of this research was to develop and characterize xenon Hall thrusters capable of both high-specific impulse and high-efficiency operation. During the development phase, the laboratory-model NASA 173M Hall thrusters were designed and their performance and plasma characteristics were evaluated. Experiments with the NASA-173M version 1 (v1) validated the plasma lens magnetic field design. Experiments with the NASA 173M version 2 (v2) showed there was a minimum current density and optimum magnetic field topography at which efficiency monotonically increased with voltage. Comparison of the thrusters showed that efficiency can be optimized for specific impulse by varying the plasma lens. During the characterization phase, additional plasma properties of the NASA 173Mv2 were measured and a performance model was derived. Results from the model and experimental data showed how efficient operation at high-specific impulse was enabled through regulation of the electron current with the magnetic field. The electron Hall parameter was approximately constant with voltage, which confirmed efficient operation can be realized only over a limited range of Hall parameters.

  14. Throttling Impacts on Hall Thruster Performance, Erosion, and Qualification for NASA Science Missions

    NASA Technical Reports Server (NTRS)

    Dankanich, John W.; DeHoyos, Amado

    2007-01-01

    With the SMART-1, Department of Defense, and commercial industry successes in Hall thruster technologies, NASA has started considering Hall thrusters for science missions. The recent Discovery proposals included a Hall thruster science mission and the In-Space Propulsion Project is investing in Hall thruster technologies. As the confidence in Hall thrusters improve, ambitious multi-thruster missions are being considered. Science missions often require large throttling ranges due to the 1/r(sup 2) power drop-off from the sun. Deep throttling of Hall thrusters will impact the overall system performance. Also, Hall thrusters can be throttled with both current and voltage, impacting erosion rates and performance. Last, electric propulsion thruster lifetime qualification has previously been conducted with long duration full power tests. Full power tests may not be appropriate for NASA science missions, and a combination of lifetime testing at various power levels with sufficient analysis is recommended. Analyses of various science missions and throttling schemes using the Aerojet BPT-4000 and NASA 103M HiVHAC thruster are presented.

  15. Overview of NASA Iodine Hall Thruster Propulsion System Development

    NASA Technical Reports Server (NTRS)

    Smith, Timothy D.; Kamhawi, Hani; Hickman, Tyler; Haag, Thomas; Dankanich, John; Polzin, Kurt; Byrne, Lawrence; Szabo, James

    2016-01-01

    NASA is continuing to invest in advancing Hall thruster technologies for implementation in commercial and government missions. The most recent focus has been on increasing the power level for large-scale exploration applications. However, there has also been a similar push to examine applications of electric propulsion for small spacecraft in the range of 300 kg or less. There have been several recent iodine Hall propulsion system development activities performed by the team of the NASA Glenn Research Center, the NASA Marshall Space Flight Center, and Busek Co. Inc. In particular, the work focused on qualification of the Busek 200-W BHT-200-I and development of the 600-W BHT-600-I systems. This paper discusses the current status of iodine Hall propulsion system developments along with supporting technology development efforts.

  16. Resistive and Hall weighting functions in three dimensions

    NASA Astrophysics Data System (ADS)

    Koon, D. W.; Knickerbocker, C. J.

    1998-10-01

    The authors extend their study of the effect of macroscopic impurities on resistive and Hall measurements to include objects of finite thickness. The effect of such impurities is calculated for a series of rectangular parallelepipeds with two current and two voltage contacts on the corners of one square face. The weighting functions display singularities near these contacts, but these are shown to vanish in the two-dimensional limit, in agreement with previous results. Finally, it is shown that while Hall measurements principally sample the plane of the electrodes, resistivity measurements sample more of the interior of an object of finite thickness.

  17. A highly sensitive CMOS digital Hall sensor for low magnetic field applications.

    PubMed

    Xu, Yue; Pan, Hong-Bin; He, Shu-Zhuan; Li, Li

    2012-01-01

    Integrated CMOS Hall sensors have been widely used to measure magnetic fields. However, they are difficult to work with in a low magnetic field environment due to their low sensitivity and large offset. This paper describes a highly sensitive digital Hall sensor fabricated in 0.18 μm high voltage CMOS technology for low field applications. The sensor consists of a switched cross-shaped Hall plate and a novel signal conditioner. It effectively eliminates offset and low frequency 1/f noise by applying a dynamic quadrature offset cancellation technique. The measured results show the optimal Hall plate achieves a high current related sensitivity of about 310 V/AT. The whole sensor has a remarkable ability to measure a minimum ± 2 mT magnetic field and output a digital Hall signal in a wide temperature range from -40 °C to 120 °C.

  18. Role of casson fluid on MHD natural convective flow towards vertically inclined plate with hall current

    NASA Astrophysics Data System (ADS)

    Prasad, D. V. V. Krishna; Chaitanya, G. S. Krishna; Raju, R. Srinivasa

    2018-05-01

    The aim of the present investigation is to study the steady magnetohydrodynamic free convective Casson fluid flow of an electrically conducting gray gas near equilibrium in the optically thin limit along an infinite vertical plate in the presence of strong transverse magnetic field imposed perpendicularly to the plate, taking hall current and thermal radiation into account. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. Using the non-dimensional quantities, the governing equations have been transformed into a set of ordinary differential equations. The influence of different pertinent parameters on the flow properties is studied. A comparison is made with the available results in the literature, and our numerical results are in very good agreement with the analytical results.

  19. Ion Velocity Measurements in a Linear Hall Thruster (Postprint)

    DTIC Science & Technology

    2005-06-14

    Hall Thruster in a high vacuum environment. The ionized propellant velocities were measured using laser induced fluorescence of the excited state xenon ionic transition at 834.7 nm. Ion velocities were interrogated from the channel exit plane to a distance 30 mm from it. Both axial and cross-field (along the electron Hall current direction) velocities were measured. The results presented here, combined with those of previous work, highlight the high sensitivity of electron mobility inside and outside the channel, depending on the background gas density, type of wall

  20. Investigations of an Environmentally Induced Long Duration Hall Thruster Start Transient (PREPRINT)

    DTIC Science & Technology

    2006-02-06

    Hall thruster start transient is produced by exposure of the thruster to ambient laboratory atmosphere. This behavior was first observed during operation of a cluster of four 200 W BHT-200 Hall effect thrusters where large anode discharge fluctuations, visible as increased anode current and a diffuse plume structure, occurred in an apparently random manner. During operation of a single thruster, the start transient appears as a quickly rising and later smoothly decaying elevated anode current with a diffuse plume that persists for less than 500 seconds. The start transient

  1. Ionization oscillations in Hall accelerators

    NASA Astrophysics Data System (ADS)

    Barral, S.; Peradzyński, Z.

    2010-01-01

    The underlying mechanism of low-frequency oscillations in Hall accelerators is investigated theoretically. It is shown that relaxation oscillations arise from a competition between avalanche ionization and the advective transport of the working gas. The model derived recovers the slow progression and fast recession of the ionization front. Analytical approximations of the shape of current pulses and of the oscillation frequency are provided for the case of large amplitude oscillations.

  2. Impact of the Hall effect on high-energy-density plasma jets.

    PubMed

    Gourdain, P-A; Seyler, C E

    2013-01-04

    Using a 1-MA, 100 ns-rise-time pulsed power generator, radial foil configurations can produce strongly collimated plasma jets. The resulting jets have electron densities on the order of 10(20) cm(-3), temperatures above 50 eV and plasma velocities on the order of 100 km/s, giving Reynolds numbers of the order of 10(3), magnetic Reynolds and Péclet numbers on the order of 1. While Hall physics does not dominate jet dynamics due to the large particle density and flow inside, it strongly impacts flows in the jet periphery where plasma density is low. As a result, Hall physics affects indirectly the geometrical shape of the jet and its density profile. The comparison between experiments and numerical simulations demonstrates that the Hall term enhances the jet density when the plasma current flows away from the jet compared to the case where the plasma current flows towards it.

  3. Astronaut Hall of Fame

    NASA Image and Video Library

    2018-04-21

    Inside the Space Shuttle Atlantis attraction at NASA’s Kennedy Space Center Visitor Complex in Florida, two space explorers, Scott D. Altman, second from left, and Thomas D. Jones, Ph.D., far right, are inducted into the U.S. Astronaut Hall of Fame Class of 2018. At far left is Hall of Famer Curt Brown, board chairman, Astronaut Scholarship Foundation, who inducted Altman and Jones into the AHOF. Second from right is Hall of Famer John Grunsfeld, who spoke on behalf of Altman during the ceremony. Inductees into the Hall of Fame are selected by a committee of Hall of Fame astronauts, former NASA officials, flight directors, historians and journalists. The process is administered by the Astronaut Scholarship Foundation. To be eligible, an astronaut must have made his or her first flight at least 17 years before the induction. Candidates must be a U.S. citizen and a NASA-trained commander, pilot or mission specialist who has orbited the earth at least once. Including Altman and Jones, 97 astronauts have been inducted into the AHOF.

  4. Role of chiral quantum Hall edge states in nuclear spin polarization.

    PubMed

    Yang, Kaifeng; Nagase, Katsumi; Hirayama, Yoshiro; Mishima, Tetsuya D; Santos, Michael B; Liu, Hongwu

    2017-04-20

    Resistively detected NMR (RDNMR) based on dynamic nuclear polarization (DNP) in a quantum Hall ferromagnet (QHF) is a highly sensitive method for the discovery of fascinating quantum Hall phases; however, the mechanism of this DNP and, in particular, the role of quantum Hall edge states in it are unclear. Here we demonstrate the important but previously unrecognized effect of chiral edge modes on the nuclear spin polarization. A side-by-side comparison of the RDNMR signals from Hall bar and Corbino disk configurations allows us to distinguish the contributions of bulk and edge states to DNP in QHF. The unidirectional current flow along chiral edge states makes the polarization robust to thermal fluctuations at high temperatures and makes it possible to observe a reciprocity principle of the RDNMR response. These findings help us better understand complex NMR responses in QHF, which has important implications for the development of RDNMR techniques.

  5. Comment on 'Effects of magnetic field gradient on ion beam current in cylindrical Hall ion source' [J. Appl. Phys. 102, 123305 (2007)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Raitses, Y.; Smirnov, A.; Fisch, N. J.

    It is argued that the key difference in the cylindrical Hall thruster (CHT) as compared to the end-Hall ion source cannot be exclusively attributed to the magnetic field topology [Tang et al., J. Appl. Phys. 102, 123305 (2007)]. With a similar mirror-type topology, the CHT configuration provides the electric field with nearly equipotential magnetic field surfaces and a better suppression of the electron cross-field transport, as compared to both the end-Hall ion source and the cylindrical Hall ion source of [Tang et al., J. Appl. Phys. 102, 123305 (2007)].

  6. Inverse spin Hall effect from pulsed spin current in organic semiconductors with tunable spin-orbit coupling.

    PubMed

    Sun, Dali; van Schooten, Kipp J; Kavand, Marzieh; Malissa, Hans; Zhang, Chuang; Groesbeck, Matthew; Boehme, Christoph; Valy Vardeny, Z

    2016-08-01

    Exploration of spin currents in organic semiconductors (OSECs) induced by resonant microwave absorption in ferromagnetic substrates is appealing for potential spintronics applications. Owing to the inherently weak spin-orbit coupling (SOC) of OSECs, their inverse spin Hall effect (ISHE) response is very subtle; limited by the microwave power applicable under continuous-wave (cw) excitation. Here we introduce a novel approach for generating significant ISHE signals in OSECs using pulsed ferromagnetic resonance, where the ISHE is two to three orders of magnitude larger compared to cw excitation. This strong ISHE enables us to investigate a variety of OSECs ranging from π-conjugated polymers with strong SOC that contain intrachain platinum atoms, to weak SOC polymers, to C60 films, where the SOC is predominantly caused by the curvature of the molecule's surface. The pulsed-ISHE technique offers a robust route for efficient injection and detection schemes of spin currents at room temperature, and paves the way for spin orbitronics in plastic materials.

  7. Not your grandfather's concert hall

    NASA Astrophysics Data System (ADS)

    Cooper, Russell; Malenka, Richard; Griffith, Charles; Friedlander, Steven

    2004-05-01

    The opening of Judy and Arthur Zankel Hall on 12 September 2003, restores Andrew Carnegie's original 1891 concept of having three outstanding auditoriums of different sizes under one roof, and creates a 21st-century venue for music performance and education. With concerts ranging from early music to avant-garde multimedia productions, from jazz to world music, and from solo recitals to chamber music, Zankel Hall expands the breadth and depth of Carnegie Hall's offerings. It allows for the integration of programming across three halls with minifestivals tailored both to the size and strengths of each hall and to the artists and music to be performed. The new flexible space also provides Carnegie Hall with an education center equipped with advanced communications technology. This paper discusses the unique program planned for this facility and how the architects, theatre consultants, and acousticians developed a design that fulfilled the client's expectations and coordinated the construction of the facility under the floor of the main Isaac Stern Auditorium without having to cancel a single performance.

  8. Investigation of the Effects of Facility Background Pressure on the Performance and Voltage-Current Characteristics of the High Voltage Hall Accelerator

    NASA Technical Reports Server (NTRS)

    Kamhawi, Hani; Huang, Wensheng; Haag, Thomas; Spektor, Rostislav

    2014-01-01

    The National Aeronautics and Space Administration (NASA) Science Mission Directorate In-Space Propulsion Technology office is sponsoring NASA Glenn Research Center to develop a 4 kW-class Hall thruster propulsion system for implementation in NASA science missions. A study was conducted to assess the impact of varying the facility background pressure on the High Voltage Hall Accelerator (HiVHAc) thruster performance and voltage-current characteristics. This present study evaluated the HiVHAc thruster performance in the lowest attainable background pressure condition at NASA GRC Vacuum Facility 5 to best simulate space-like conditions. Additional tests were performed at selected thruster operating conditions to investigate and elucidate the underlying physics that change during thruster operation at elevated facility background pressure. Tests were performed at background pressure conditions that are three and ten times higher than the lowest realized background pressure. Results indicated that the thruster discharge specific impulse and efficiency increased with elevated facility background pressure. The voltage-current profiles indicated a narrower stable operating region with increased background pressure. Experimental observations of the thruster operation indicated that increasing the facility background pressure shifted the ionization and acceleration zones upstream towards the thrusters anode. Future tests of the HiVHAc thruster are planned at background pressure conditions that are expected to be two to three times lower than what was achieved during this test campaign. These tests will not only assess the impact of reduced facility background pressure on thruster performance, voltage-current characteristics, and plume properties; but will also attempt to quantify the magnitude of the ionization.

  9. Critical current density measurement of striated multifilament-coated conductors using a scanning Hall probe microscope

    NASA Astrophysics Data System (ADS)

    Li, Xiao-Fen; Kochat, Mehdi; Majkic, Goran; Selvamanickam, Venkat

    2016-08-01

    In this paper the authors succeeded in measuring the critical current density ({J}{{c}}) of multifilament-coated conductors (CCs) with thin filaments as low as 0.25 mm using the scanning hall probe microscope (SHPM) technique. A new iterative method of data analysis is developed to make the calculation of {J}{{c}} for thin filaments possible, even without a very small scan distance. The authors also discussed in detail the advantage and limitation of the iterative method using both simulation and experiment results. The results of the new method correspond well with the traditional fast Fourier transform method where this is still applicable. However, the new method is applicable for the filamentized CCs in much wider measurement conditions such as with thin filament and a large scan distance, thus overcoming the barrier for application of the SHPM technique on {J}{{c}} measurement of long filamentized CCs with narrow filaments.

  10. Quantum Hall resistance standard in graphene devices under relaxed experimental conditions

    NASA Astrophysics Data System (ADS)

    Ribeiro-Palau, R.; Lafont, F.; Brun-Picard, J.; Kazazis, D.; Michon, A.; Cheynis, F.; Couturaud, O.; Consejo, C.; Jouault, B.; Poirier, W.; Schopfer, F.

    2015-11-01

    The quantum Hall effect provides a universal standard for electrical resistance that is theoretically based on only the Planck constant h and the electron charge e. Currently, this standard is implemented in GaAs/AlGaAs, but graphene's electronic properties have given hope for a more practical device. Here, we demonstrate that the experimental conditions necessary for the operation of devices made of high-quality graphene grown by chemical vapour deposition on silicon carbide can be extended and significantly relaxed compared with those for state-of-the-art GaAs/AlGaAs devices. In particular, the Hall resistance can be accurately quantized to within 1 × 10-9 over a 10 T wide range of magnetic flux density, down to 3.5 T, at a temperature of up to 10 K or with a current of up to 0.5 mA. This experimental simplification highlights the great potential of graphene in the development of user-friendly and versatile quantum standards that are compatible with broader industrial uses beyond those in national metrology institutes. Furthermore, the measured agreement of the quantized Hall resistance in graphene and GaAs/AlGaAs, with an ultimate uncertainty of 8.2 × 10-11, supports the universality of the quantum Hall effect. This also provides evidence of the relation of the quantized Hall resistance with h and e, which is crucial for the new Système International d'unités to be based on fixing such fundamental constants of nature.

  11. The Hall-induced stability of gravitating fluids

    NASA Astrophysics Data System (ADS)

    Karmakar, P. K.; Goutam, H. P.

    2018-05-01

    We analyze the stability behavior of low-density partially ionized self-gravitating magnetized unbounded dusty plasma fluid in the presence of the Hall diffusion effects (HDEs) in the non-ideal magnetohydrodynamic (MHD) equilibrium framework. The effects of inhomogeneous self-gravity are methodically included in the basic model tapestry. Application of the Fourier plane-wave perturbative treatment decouples the structuration representative parameters into a linear generalized dispersion relation (sextic) in a judicious mean-fluid approximation. The dispersion analysis shows that the normal mode, termed as the gravito-magneto-acoustic (GMA) mode, is drastically modified due to the HDEs. This mode is highly dispersive, and driven unstable by the Hall current resulting from the symmetry-breaking of electrons and ions relative to the magnetic field. The mode feature, which is derived from a modified induction with the positive Hall, is against the ideal MHD. It is further demonstrated that the HDEs play stabilizing roles by supporting the cloud against gravitational collapse. Provided that the HDEs are concurrently switched off, the collapse occurs on the global spatial scale due to enhanced inward accretion of the gravitating dust constituents. It is seen explicitly that the enhanced dust-charge leads to stabilizing effects. Besides, the Hall-induced fluctuations, as propagatory wave modes, exhibit both normal and anomalous dispersions. The reliability checkup of the entailed results as diverse corollaries and special cases are illustratively discussed in the panoptic light of the earlier paradigmatic predictions available in the literature.

  12. Quantum anomalous Hall effect in time-reversal-symmetry breaking topological insulators

    NASA Astrophysics Data System (ADS)

    Chang, Cui-Zu; Li, Mingda

    2016-03-01

    The quantum anomalous Hall effect (QAHE), the last member of Hall family, was predicted to exhibit quantized Hall conductivity {σyx}=\\frac{{{e}2}}{h} without any external magnetic field. The QAHE shares a similar physical phenomenon with the integer quantum Hall effect (QHE), whereas its physical origin relies on the intrinsic topological inverted band structure and ferromagnetism. Since the QAHE does not require external energy input in the form of magnetic field, it is believed that this effect has unique potential for applications in future electronic devices with low-power consumption. More recently, the QAHE has been experimentally observed in thin films of the time-reversal symmetry breaking ferromagnetic (FM) topological insulators (TI), Cr- and V- doped (Bi,Sb)2Te3. In this topical review, we review the history of TI based QAHE, the route to the experimental observation of the QAHE in the above two systems, the current status of the research of the QAHE, and finally the prospects for future studies.

  13. The Role of Social Influence on How Residence Hall Inhabitants Respond to Fire Alarms

    ERIC Educational Resources Information Center

    Leytem, Michael; Stark, Emily

    2016-01-01

    College resident halls pose a threat for a catastrophic event in the case of fire, but little research has examined potential influences on students' responses to fire alarms, particularly the role of social influence in affecting their behaviors. In the current study, residence hall inhabitants reported their knowledge about fire safety, their…

  14. Interlayer tunneling in double-layer quantum hall pseudoferromagnets.

    PubMed

    Balents, L; Radzihovsky, L

    2001-02-26

    We show that the interlayer tunneling I-V in double-layer quantum Hall states displays a rich behavior which depends on the relative magnitude of sample size, voltage length scale, current screening, disorder, and thermal lengths. For weak tunneling, we predict a negative differential conductance of a power-law shape crossing over to a sharp zero-bias peak. An in-plane magnetic field splits this zero-bias peak, leading instead to a "derivative" feature at V(B)(B(parallel)) = 2 pi Planck's over 2 pi upsilon B(parallel)d/e phi(0), which gives a direct measurement of the dispersion of the Goldstone mode corresponding to the spontaneous symmetry breaking of the double-layer Hall state.

  15. Scanning micro-Hall probe mapping of magnetic flux distributions and current densities in YBa2Cu3O7 thin films

    NASA Technical Reports Server (NTRS)

    Xing, W.; Heinrich, B.; Zhou, HU; Fife, A. A.; Cragg, A. R.; Grant, P. D.

    1995-01-01

    Mapping of the magnetic flux density B(sub z) (perpendicular to the film plane) for a YBa2Cu3O7 thin-film sample was carried out using a scanning micro-Hall probe. The sheet magnetization and sheet current densities were calculated from the B(sub z) distributions. From the known sheet magnetization, the tangential (B(sub x,y)) and normal components of the flux density B were calculated in the vicinity of the film. It was found that the sheet current density was mostly determined by 2B(sub x,y)/d, where d is the film thickness. The evolution of flux penetration as a function of applied field will be shown.

  16. Driving and detecting ferromagnetic resonance in insulators with the spin Hall effect

    DOE PAGES

    Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.; ...

    2015-11-06

    We demonstrate the generation and detection of spin-torque ferromagnetic resonance in Pt/Y 3Fe 5O 12 (YIG) bilayers. A unique attribute of this system is that the spin Hall effect lies at the heart of both the generation and detection processes and no charge current is passing through the insulating magnetic layer. When the YIG undergoes resonance, a dc voltage is detected longitudinally along the Pt that can be described by two components. One is the mixing of the spin Hall magnetoresistance with the microwave current. The other results from spin pumping into the Pt being converted to a dc currentmore » through the inverse spin Hall effect. The voltage is measured with applied magnetic field directions that range in-plane to nearly perpendicular. In conclusion, we find that for magnetic fields that are mostly out-of-plane, an imaginary component of the spin mixing conductance is required to model our data.« less

  17. Concert halls with strong lateral reflections enhance musical dynamics.

    PubMed

    Pätynen, Jukka; Tervo, Sakari; Robinson, Philip W; Lokki, Tapio

    2014-03-25

    One of the most thrilling cultural experiences is to hear live symphony-orchestra music build up from a whispering passage to a monumental fortissimo. The impact of such a crescendo has been thought to depend only on the musicians' skill, but here we show that interactions between the concert-hall acoustics and listeners' hearing also play a major role in musical dynamics. These interactions contribute to the shoebox-type concert hall's established success, but little prior research has been devoted to dynamic expression in this three-part transmission chain as a complete system. More forceful orchestral playing disproportionately excites high frequency harmonics more than those near the note's fundamental. This effect results in not only more sound energy, but also a different tone color. The concert hall transmits this sound, and the room geometry defines from which directions acoustic reflections arrive at the listener. Binaural directional hearing emphasizes high frequencies more when sound arrives from the sides of the head rather than from the median plane. Simultaneously, these same frequencies are emphasized by higher orchestral-playing dynamics. When the room geometry provides reflections from these directions, the perceived dynamic range is enhanced. Current room-acoustic evaluation methods assume linear behavior and thus neglect this effect. The hypothesis presented here is that the auditory excitation by reflections is emphasized with an orchestra forte most in concert halls with strong lateral reflections. The enhanced dynamic range provides an explanation for the success of rectangularly shaped concert-hall geometry.

  18. Mesoscopic spin Hall effect in semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Zarbo, Liviu

    The spin Hall effect (SHE) is a name given to a collection of diverse phenomena which share two principal features: (i) longitudinal electric current flowing through a paramagnetic semiconductor or metallic sample leads to transverse spin current and spin accumulation of opposite sign at opposing lateral edges; (ii) SHE does not require externally applied magnetic field or magnetic ordering in the equilibrium state of the sample, instead it relies on the presence of spin-orbit (SO) couplings within the sample. This thesis elaborates on a new type of phenomenon within the SHE family, predicted in our recent studies [Phys. Rev. B 72, 075361 (2005); Phys. Rev. Lett. 95, 046601 (2005); Phys. Rev. B 72, 075335 (2005); Phys. Rev. B 73 , 075303 (2006); and Europhys. Lett. 77, 47004 (2007)], where pure spin current flows through the transverse electrodes attached to a clean finitesize two-dimensional electron gas (2DEG) due to unpolarized charge current injected through its longitudinal leads. If transverse leads are removed, the effect manifests as nonequilibrium spin Hall accumulation at the lateral edges of 2DEG wires. The SO coupling driving this SHE effect is of the Rashba type, which arises due to structural inversion asymmetry of semiconductor heterostructure hosting the 2DEG. We term the effect "mesoscopic" because the spin Hall currents and accumulations reach optimal value in samples of the size of the spin precession length---the distance over which the spin of an electron precesses by an angle pi. In strongly SO-coupled structures this scale is of the order of ˜100 nm, and, therefore, mesoscopic in the sense of being much larger than the characteristic microscopic scales (such as the Fermi wavelength, screening length, or the mean free path in disordered systems), but still much smaller than the macroscopic ones. Although the first theoretical proposal for SHE, driven by asymmetry in SO-dependent scattering of spin-up and spin-down electrons off impurities

  19. Effective anomalous Hall coefficient in an ultrathin Co layer sandwiched by Pt layers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang, Peng; Wu, Di; Jiang, Zhengsheng

    2014-02-14

    Anomalous Hall effect in Co/Pt multilayer is important to study the effect of interface with strong spin-orbit coupling. However, the shunting effect of the layers in such system and the circuit in the plane perpendicular to the injected current were overlooked in most works and thus, anomalous Hall coefficient in Co/Pt multilayer has not been determined accurately. Considering the shunting effect and the equivalent circuit, we show that the effective anomalous Hall coefficient of a 0.5 nm thick Co layer sandwiched by Pt layers R{sub S} is 0.29 ± 0.01 μΩ cm/T at the zero temperature limit and increases to about 0.73 μΩ cm/T at the temperaturemore » of 300 K. R{sub S} is one order larger than that in bulk Co film, indicating the large contribution of the Co/Pt interface. R{sub S} increases with the resistivity of Co as well as a resistivity independent contribution of −0.23 ± 0.01 μΩ cm/T. The equivalent anomalous Hall current in the Co layer has a maximum of 1.1% of the injected transverse current in the Co layer around the temperature of 80 K.« less

  20. Influence of the carrier mobility distribution on the Hall and the Nernst effect measurements in n-type InSb

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Madon, B.; Wegrowe, J.-E.; Drouhin, H.-J.

    2016-01-14

    In this study, we report magneto-resistance measurements on an n-doped InSb film, to separate the contributions of the electrical currents from the heat currents. We have demonstrated a prototype for a magnetic field sensor which is powered by heat currents and does not require any electrical current. We fabricated two Hall bars, where a low frequency (f = 0.05 Hz) AC current, was applied between the two contacts in one of the Hall bars. Separating the f and 2f components of the voltage measured across the second Hall bar was used to distinguish between the electrical and the heat contributions to the electronmore » currents. Our observations can be modeled using a Gaussian distribution of mobility within the sample.« less

  1. Particle-in-cell simulations of Hall plasma thrusters

    NASA Astrophysics Data System (ADS)

    Miranda, Rodrigo; Ferreira, Jose Leonardo; Martins, Alexandre

    2016-07-01

    Hall plasma thrusters can be modelled using particle-in-cell (PIC) simulations. In these simulations, the plasma is described by a set of equations which represent a coupled system of charged particles and electromagnetic fields. The fields are computed using a spatial grid (i.e., a discretization in space), whereas the particles can move continuously in space. Briefly, the particle and fields dynamics are computed as follows. First, forces due to electric and magnetic fields are employed to calculate the velocities and positions of particles. Next, the velocities and positions of particles are used to compute the charge and current densities at discrete positions in space. Finally, these densities are used to solve the electromagnetic field equations in the grid, which are interpolated at the position of the particles to obtain the acting forces, and restart this cycle. We will present numerical simulations using software for PIC simulations to study turbulence, wave and instabilities that arise in Hall plasma thrusters. We have sucessfully reproduced a numerical simulation of a SPT-100 Hall thruster using a two-dimensional (2D) model. In addition, we are developing a 2D model of a cylindrical Hall thruster. The results of these simulations will contribute to improve the performance of plasma thrusters to be used in Cubesats satellites currenty in development at the Plasma Laboratory at University of Brasília.

  2. Pt thickness dependence of spin Hall effect switching of in-plane magnetized CoFeB free layers studied by differential planar Hall effect

    NASA Astrophysics Data System (ADS)

    Mihajlović, G.; Mosendz, O.; Wan, L.; Smith, N.; Choi, Y.; Wang, Y.; Katine, J. A.

    2016-11-01

    We introduce a differential planar Hall effect method that enables the experimental study of spin orbit torque switching of in-plane magnetized free layers in a simple Hall bar device geometry. Using this method, we study the Pt thickness dependence of switching currents and show that they decrease monotonically down to the minimum experimental thickness of ˜5 nm, while the critical current and power densities are very weakly thickness dependent, exhibiting the minimum values of Jc0 = 1.1 × 108 A/cm2 and ρJc0 2=0.6 ×1012 W/cm 3 at this minimum thickness. Our results suggest that a significant reduction of the critical parameters could be achieved by optimizing the free layer magnetics, which makes this technology a viable candidate for fast, high endurance and low-error rate applications such as cache memories.

  3. Nanoconstriction spin-Hall oscillator with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Divinskiy, B.; Demidov, V. E.; Kozhanov, A.; Rinkevich, A. B.; Demokritov, S. O.; Urazhdin, S.

    2017-07-01

    We experimentally study spin-Hall nano-oscillators based on [Co/Ni] multilayers with perpendicular magnetic anisotropy. We show that these devices exhibit single-frequency auto-oscillations at current densities comparable to those for in-plane magnetized oscillators. The demonstrated oscillators exhibit large magnetization precession amplitudes, and their oscillation frequency is highly tunable by the electric current. These features make them promising for applications in high-speed integrated microwave circuits.

  4. The rotation of discs around neutron stars: dependence on the Hall diffusion

    NASA Astrophysics Data System (ADS)

    Faghei, Kazem; Salehi, Fatemeh

    2018-01-01

    In this paper, we study the dynamics of a geometrically thin, steady and axisymmetric accretion disc surrounding a rotating and magnetized star. The magnetic field lines of star penetrate inside the accretion disc and are twisted due to the differential rotation between the magnetized star and the disc. We apply the Hall diffusion effect in the accreting plasma, because of the Hall diffusion plays an important role in both fully ionized plasma and weakly ionized medium. In the current research, we show that the Hall diffusion is also an important mechanism in accreting plasma around neutron stars. For the typical system parameter values associated with the accreting X-ray binary pulsar, the angular velocity of the inner regions of disc departs outstandingly from Keplerian angular velocity, due to coupling between the magnetic field of neutron star and the rotating plasma of disc. We found that the Hall diffusion is very important in inner disc and increases the coupling between the magnetic field of neutron star and accreting plasma. On the other word, the rotational velocity of inner disc significantly decreases in the presence of the Hall diffusion. Moreover, the solutions imply that the fastness parameter decreases and the angular velocity transition zone becomes broad for the accreting plasma including the Hall diffusion.

  5. Magnetic field configurations on thruster performance in accordance with ion beam characteristics in cylindrical Hall thruster plasmas

    NASA Astrophysics Data System (ADS)

    Kim, Holak; Choe, Wonho; Lim, Youbong; Lee, Seunghun; Park, Sanghoo

    2017-03-01

    Magnetic field configuration is critical in Hall thrusters for achieving high performance, particularly in thrust, specific impulse, efficiency, etc. Ion beam features are also significantly influenced by magnetic field configurations. In two typical magnetic field configurations (i.e., co-current and counter-current configurations) of a cylindrical Hall thruster, ion beam characteristics are compared in relation to multiply charged ions. Our study shows that the co-current configuration brings about high ion current (or low electron current), high ionization rate, and small plume angle that lead to high thruster performance.

  6. Nonlocal Polarization Feedback in a Fractional Quantum Hall Ferromagnet.

    PubMed

    Hennel, Szymon; Braem, Beat A; Baer, Stephan; Tiemann, Lars; Sohi, Pirouz; Wehrli, Dominik; Hofmann, Andrea; Reichl, Christian; Wegscheider, Werner; Rössler, Clemens; Ihn, Thomas; Ensslin, Klaus; Rudner, Mark S; Rosenow, Bernd

    2016-04-01

    In a quantum Hall ferromagnet, the spin polarization of the two-dimensional electron system can be dynamically transferred to nuclear spins in its vicinity through the hyperfine interaction. The resulting nuclear field typically acts back locally, modifying the local electronic Zeeman energy. Here we report a nonlocal effect arising from the interplay between nuclear polarization and the spatial structure of electronic domains in a ν=2/3 fractional quantum Hall state. In our experiments, we use a quantum point contact to locally control and probe the domain structure of different spin configurations emerging at the spin phase transition. Feedback between nuclear and electronic degrees of freedom gives rise to memristive behavior, where electronic transport through the quantum point contact depends on the history of current flow. We propose a model for this effect which suggests a novel route to studying edge states in fractional quantum Hall systems and may account for so-far unexplained oscillatory electronic-transport features observed in previous studies.

  7. Hall viscosity of hierarchical quantum Hall states

    NASA Astrophysics Data System (ADS)

    Fremling, M.; Hansson, T. H.; Suorsa, J.

    2014-03-01

    Using methods based on conformal field theory, we construct model wave functions on a torus with arbitrary flat metric for all chiral states in the abelian quantum Hall hierarchy. These functions have no variational parameters, and they transform under the modular group in the same way as the multicomponent generalizations of the Laughlin wave functions. Assuming the absence of Berry phases upon adiabatic variations of the modular parameter τ, we calculate the quantum Hall viscosity and find it to be in agreement with the formula, given by Read, which relates the viscosity to the average orbital spin of the electrons. For the filling factor ν =2/5 Jain state, which is at the second level in the hierarchy, we compare our model wave function with the numerically obtained ground state of the Coulomb interaction Hamiltonian in the lowest Landau level, and find very good agreement in a large region of the complex τ plane. For the same example, we also numerically compute the Hall viscosity and find good agreement with the analytical result for both the model wave function and the numerically obtained Coulomb wave function. We argue that this supports the notion of a generalized plasma analogy that would ensure that wave functions obtained using the conformal field theory methods do not acquire Berry phases upon adiabatic evolution.

  8. Astronaut Hall of Fame

    NASA Image and Video Library

    2018-04-21

    Kelvin Manning, associate director of NASA's Kennedy Space Center in Florida, welcomes guests to the 2018 U.S. Astronaut Hall of Fame (AHOF) Induction inside the Space Shuttle Atlantis attraction at the Kennedy Space Center Visitor Complex (KSCVC). Two veteran space explorers were inducted into the Hall of Fame Class of 2018. They are Scott D. Altman and Thomas D. Jones, Ph.D. Inductees into the Hall of Fame are selected by a committee of Hall of Fame astronauts, former NASA officials, flight directors, historians and journalists. The process is administered by the Astronaut Scholarship Foundation. To be eligible, an astronaut must have made his or her first flight at least 17 years before the induction. Candidates must be a U.S. citizen and a NASA-trained commander, pilot or mission specialist who has orbited the earth at least once. Including Altman and Jones, 97 astronauts have been inducted into the AHOF.

  9. Astronaut Hall of Fame

    NASA Image and Video Library

    2018-04-21

    Former astronauts and space explorers Scott D. Altman, at left, and Thomas D. Jones, Ph.D., are inducted into the U.S. Astronaut Hall of Fame Class of 2018 during a ceremony inside the Space Shuttle Atlantis attraction at NASA’s Kennedy Space Center Visitor Complex in Florida. They unveiled their plaques, which will be placed in Hall of Fame at the visitor complex. At far right is Master of Ceremonies, John Zarella, former CNN space correspondent. Inductees into the Hall of Fame are selected by a committee of Hall of Fame astronauts, former NASA officials, flight directors, historians and journalists. The process is administered by the Astronaut Scholarship Foundation. To be eligible, an astronaut must have made his or her first flight at least 17 years before the induction. Candidates must be a U.S. citizen and a NASA-trained commander, pilot or mission specialist who has orbited the earth at least once. Including Altman and Jones, 97 astronauts have been inducted into the AHOF.

  10. Astronaut Hall of Fame

    NASA Image and Video Library

    2018-04-21

    Former astronauts and space explorers Scott D. Altman, at left, and Thomas D. Jones, Ph.D., are inducted into the U.S. Astronaut Hall of Fame Class of 2018 during a ceremony inside the Space Shuttle Atlantis attraction at NASA’s Kennedy Space Center Visitor Complex in Florida. They unveiled their plaques, which will be placed in the Hall of Fame at the visitor complex. At far right is Master of Ceremonies, John Zarella, former CNN space correspondent. Inductees into the Hall of Fame are selected by a committee of Hall of Fame astronauts, former NASA officials, flight directors, historians and journalists. The process is administered by the Astronaut Scholarship Foundation. To be eligible, an astronaut must have made his or her first flight at least 17 years before the induction. Candidates must be a U.S. citizen and a NASA-trained commander, pilot or mission specialist who has orbited the earth at least once. Including Altman and Jones, 97 astronauts have been inducted into the AHOF.

  11. Investigation of the Effects of Facility Background Pressure on the Performance and Voltage-Current Characteristics of the High Voltage Hall Accelerator

    NASA Technical Reports Server (NTRS)

    Kamhawi, Hani; Huang, Wensheng; Haag, Thomas; Spektor, Rostislav

    2014-01-01

    The National Aeronautics and Space Administration (NASA) Science Mission Directorate In-Space Propulsion Technology office is sponsoring NASA Glenn Research Center to develop a 4 kW-class Hall thruster propulsion system for implementation in NASA science missions. A study was conducted to assess the impact of varying the facility background pressure on the High Voltage Hall Accelerator (HiVHAc) thruster performance and voltage-current characteristics. This present study evaluated the HiVHAc thruster performance in the lowest attainable background pressure condition at NASA GRC Vacuum Facility 5 to best simulate space-like conditions. Additional tests were performed at selected thruster operating conditions to investigate and elucidate the underlying physics that change during thruster operation at elevated facility background pressure. Tests were performed at background pressure conditions that are three and ten times higher than the lowest realized background pressure. Results indicated that the thruster discharge specific impulse and efficiency increased with elevated facility background pressure. The voltage-current profiles indicated a narrower stable operating region with increased background pressure. Experimental observations of the thruster operation indicated that increasing the facility background pressure shifted the ionization and acceleration zones upstream towards the thruster's anode. Future tests of the HiVHAc thruster are planned at background pressure conditions that are expected to be two to three times lower than what was achieved during this test campaign. These tests will not only assess the impact of reduced facility background pressure on thruster performance, voltage-current characteristics, and plume properties; but will also attempt to quantify the magnitude of the ionization and acceleration zones upstream shifting as a function of increased background pressure.

  12. Development and characterization of high-efficiency, high-specific impulse xenon Hall thrusters

    NASA Astrophysics Data System (ADS)

    Hofer, Richard Robert

    This dissertation presents research aimed at extending the efficient operation of 1600 s specific impulse Hall thruster technology to the 2000--3000 s range. While recent studies of commercially developed Hall thrusters demonstrated greater than 4000 s specific impulse, maximum efficiency occurred at less than 3000 s. It was hypothesized that the efficiency maximum resulted as a consequence of modern magnetic field designs, optimized for 1600 s, which were unsuitable at high-specific impulse. Motivated by the industry efforts and mission studies, the aim of this research was to develop and characterize xenon Hall thrusters capable of both high-specific impulse and high-efficiency operation. The research divided into development and characterization phases. During the development phase, the laboratory-model NASA-173M Hall thrusters were designed with plasma lens magnetic field topographies and their performance and plasma characteristics were evaluated. Experiments with the NASA-173M version 1 (v1) validated the plasma lens design by showing how changing the magnetic field topography at high-specific impulse improved efficiency. Experiments with the NASA-173M version 2 (v2) showed there was a minimum current density and optimum magnetic field topography at which efficiency monotonically increased with voltage. Between 300--1000 V, total specific impulse and total efficiency of the NASA-173Mv2 operating at 10 mg/s ranged from 1600--3400 s and 51--61%, respectively. Comparison of the thrusters showed that efficiency can be optimized for specific impulse by varying the plasma lens design. During the characterization phase, additional plasma properties of the NASA-173Mv2 were measured and a performance model was derived accounting for a multiply-charged, partially-ionized plasma. Results from the model based on experimental data showed how efficient operation at high-specific impulse was enabled through regulation of the electron current with the magnetic field. The

  13. Influence of Hall Current and Viscous Dissipation on Pressure Driven Flow of Pseudoplastic Fluid with Heat Generation: A Mathematical Study.

    PubMed

    Noreen, Saima; Qasim, Muhammad

    2015-01-01

    In this paper, we study the influence of heat sink (or source) on the peristaltic motion of pseudoplastic fluid in the presence of Hall current, where channel walls are non-conducting in nature. Flow analysis has been carried out under the approximations of a low Reynolds number and long wavelength. Coupled equations are solved using shooting method for numerical solution for the axial velocity function, temperature and pressure gradient distributions. We analyze the influence of various interesting parameters on flow quantities. The present study can be considered as a mathematical presentation of the dynamics of physiological organs with stones.

  14. Cross-field diffusion in Hall thrusters and other plasma thrusters

    NASA Astrophysics Data System (ADS)

    Boeuf, J. P.

    2012-10-01

    Understanding and quantifying electron transport perpendicular to the magnetic field is a challenge in many low temperature plasma applications. Hall effect thrusters (HETs) provide an excellent example of cross-field transport. The HET is a very successful concept that can be considered both as a gridless ion source and an electromagnetic thruster. In HETs, the electric field E accelerating the ions is a consequence of the Lorentz force due to an external magnetic field B acting on the ExB Hall electron current. An essential aspect of HETs is that the ExB drift is closed, i.e. is in the azimuthal direction of a cylindrical channel. In the first part of this presentation we will discuss the physics of cross-field electron transport in HETs, and the current understanding (or non-understanding) of the possible role of turbulence and wall collisions on cross-field diffusion. We will also briefly comment on alternative designs of ion sources based on the same principles as the conventional HET (Anode Layer Thruster, Diverging Cusp Field Thrusters, End-Hall ion sources). In a second part of the presentation we show that the Lorentz force acting on diamagnetic currents (associated with the ∇PexB term in the electron momentum equation) can also provide thrust. This is the case for example in helicon thrusters where the plasma expands in a magnetic nozzle. We will report and discuss recent work on helicon thrusters and other devices where the diamagnetic current is dominant (with some examples where the ∇PexB current is not closed and is directed toward a wall!).

  15. Performance Evaluation of a 50kW Hall Thruster

    NASA Technical Reports Server (NTRS)

    Jacobson, David T.; Jankovsky, Robert S.

    1999-01-01

    An experimental investigation was conducted on a laboratory model Hall thruster designed to operate at power levels up to 50 kW. During this investigation the engine's performance was characterized over a range of discharge currents from 10 to 36 A and a range of discharge voltages from 200 to 800 V Operating on the Russian cathode a maximum thrust of 966 mN was measured at 35.6 A and 713.0 V. This corresponded to a specific impulse of 3325 s and an efficiency of 62%. The maximum power the engine was operated at was 25 kW. Additional testing was conducted using a NASA cathode designed for higher current operation. During this testing, thrust over 1 N was measured at 40.2 A and 548.9 V. Several issues related to operation of Hall thrusters at these high powers were encountered.

  16. Mini array of quantum Hall devices based on epitaxial graphene

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Novikov, S.; Lebedeva, N.; Hämäläinen, J.

    2016-05-07

    Series connection of four quantum Hall effect (QHE) devices based on epitaxial graphene films was studied for realization of a quantum resistance standard with an up-scaled value. The tested devices showed quantum Hall plateaux R{sub H,2} at a filling factor v = 2 starting from a relatively low magnetic field (between 4 T and 5 T) when the temperature was 1.5 K. The precision measurements of quantized Hall resistance of four QHE devices connected by triple series connections and external bonding wires were done at B = 7 T and T = 1.5 K using a commercial precision resistance bridge with 50 μA current through the QHE device. The results showed thatmore » the deviation of the quantized Hall resistance of the series connection of four graphene-based QHE devices from the expected value of 4×R{sub H,2} = 2 h/e{sup 2} was smaller than the relative standard uncertainty of the measurement (<1 × 10{sup −7}) limited by the used resistance bridge.« less

  17. The Hall Instability of Weakly Ionized, Radially Stratified, Rotating Disks

    NASA Astrophysics Data System (ADS)

    Liverts, Edward; Mond, Michael; Chernin, Arthur D.

    2007-09-01

    Cool weakly ionized gaseous rotating disks are considered by many models to be the origin of the evolution of protoplanetary clouds. Instabilities against perturbations in such disks play an important role in the theory of the formation of stars and planets. Thus, a hierarchy of successive fragmentations into smaller and smaller pieces as a part of the Kant-Laplace theory of formation of the planetary system remains valid also for contemporary cosmogony. Traditionally, axisymmetric magnetohydrodynamic (MHD) and, recently, Hall-MHD instabilities have been thoroughly studied as providers of an efficient mechanism for radial transfer of angular momentum and of radial density stratification. In the current work, the Hall instability against nonaxisymmetric perturbations in compressible rotating fluid in external magnetic field is proposed as a viable mechanism for the azimuthal fragmentation of the protoplanetary disk and, thus, perhaps initiates the road to planet formation. The Hall instability is excited due to the combined effect of the radial stratification of the disk and the Hall electric field, and its growth rate is of the order of the rotation period. This family of instabilities is introduced here for the first time in an astrophysical context.

  18. Exact law for homogeneous compressible Hall magnetohydrodynamics turbulence

    NASA Astrophysics Data System (ADS)

    Andrés, N.; Galtier, S.; Sahraoui, F.

    2018-01-01

    We derive an exact law for three-dimensional (3D) homogeneous compressible isothermal Hall magnetohydrodynamic turbulence, without the assumption of isotropy. The Hall current is shown to introduce new flux and source terms that act at the small scales (comparable or smaller than the ion skin depth) to significantly impact the turbulence dynamics. The law provides an accurate means to estimate the energy cascade rate over a broad range of scales covering the magnetohydrodynamic inertial range and the sub-ion dispersive range in 3D numerical simulations and in in situ spacecraft observations of compressible turbulence. This work is particularly relevant to astrophysical flows in which small-scale density fluctuations cannot be ignored such as the solar wind, planetary magnetospheres, and the interstellar medium.

  19. Familial Pallister-Hall in adulthood.

    PubMed

    Talsania, Mitali; Sharma, Rohan; Sughrue, Michael E; Scofield, R Hal; Lim, Jonea

    2017-10-01

    Pallister Hall syndrome is autosomal dominant disorder usually diagnosed in infants and children. Current diagnostic criteria include presence of hypothalamic hamartoma, post axial polydactyly and positive family history, but the disease has variable manifestations. Herein we report Pallister Hall syndrome diagnosed in a family where both patients were adults. A 59 year old man developed seizures 4 years prior to our evaluation of him, at which time imaging showed a hypothalamic hamartoma. The seizures were controlled medically. He did well until he had visual changes after a traumatic head injury. Repeat MRI showed slight expansion of the mass with formal visual field testing demonstrating bitemporal hemianopsia. There was no evidence of pituitary dysfunction except for large urine volume. He underwent surgery to debulk the hamartoma and the visual field defects improved. There was no hypopituitarism post-operatively, and the polydyspia resolved. His 29 year old daughter also had seizures and hypothalamic hamartoma. Both patients had had polydactyly with prior surgical correction in childhood. The daughter underwent genetic testing, which revealed a previously undescribed heterozygous single base pair deletion in exon 13 of the GLI3 gene causing a frameshift mutation. Further investigation into family history revealed multiple members in previous generations with polydactyly and/or seizures. Pallister-Hall syndrome is caused by an inherited autosomal dominant or de novo mutation in GLI3 gene. This rare syndrome has not had prevalence defined, however. Generally, diagnoses are made in the pediatric population. Our report adds to the few cases detected in adulthood.

  20. Electron Transport and Ion Acceleration in a Low-power Cylindrical Hall Thruster

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    A. Smirnov; Y. Raitses; N.J. Fisch

    2004-06-24

    Conventional annular Hall thrusters become inefficient when scaled to low power. Cylindrical Hall thrusters, which have lower surface-to-volume ratio, are therefore more promising for scaling down. They presently exhibit performance comparable with conventional annular Hall thrusters. Electron cross-field transport in a 2.6 cm miniaturized cylindrical Hall thruster (100 W power level) has been studied through the analysis of experimental data and Monte Carlo simulations of electron dynamics in the thruster channel. The numerical model takes into account elastic and inelastic electron collisions with atoms, electron-wall collisions, including secondary electron emission, and Bohm diffusion. We show that in order to explainmore » the observed discharge current, the electron anomalous collision frequency {nu}{sub B} has to be on the order of the Bohm value, {nu}{sub B} {approx} {omega}{sub c}/16. The contribution of electron-wall collisions to cross-field transport is found to be insignificant. The plasma density peak observed at the axis of the 2.6 cm cylindrical Hall thruster is likely to be due to the convergent flux of ions, which are born in the annular part of the channel and accelerated towards the thruster axis.« less

  1. Hall effect of copper nitride thin films

    NASA Astrophysics Data System (ADS)

    Yue, G. H.; Liu, J. Z.; Li, M.; Yuan, X. M.; Yan, P. X.; Liu, J. L.

    2005-08-01

    The Hall effect of copper nitride (Cu3N) thin films was investigated in our work. Cu3N films were deposited on glass substrates by radio-frequency (RF) magnetron sputtering at different temperatures using pure copper as the sputtering target. The Hall coefficients of the films are demonstrated to be dependent on the deposition gas flow rate and the measuring temperature. Both the Hall coefficient and resistance of the Cu3N films increase with the nitrogen gas flow rate at room temperature, while the Hall mobility and the carrier density of the films decrease. As the temperature changed from 100 K to 300 K, the Hall coefficient and the resistivity of the films decreased, while the carrier density increased and Hall mobility shows no great change. The energy band gap of the Cu3N films deduced from the curve of the common logarithm of the Hall coefficient against 1/T is 1.17-1.31 eV.

  2. Semiclassical theory of Hall viscosity

    NASA Astrophysics Data System (ADS)

    Biswas, Rudro

    2014-03-01

    Hall viscosity is an intriguing stress response in quantum Hall systems and is predicted to be observable via the conductivity in an inhomogeneous electric field. This has been studied extensively using a range of techniques, such as adiabatic transport, effective field theories, and Kubo formulae. All of these are, however, agnostic as to the distinction between strongly correlated quantum Hall states and non-interacting ones, where the effect arises due to the fundamental non-commuting nature of velocities and orbit positions in a magnetic field. In this talk I shall develop the semiclassical theory of quantized cyclotron orbits drifting in an applied inhomogeneous electric field and use it to provide a clear physical picture of how single particle properties in a magnetic field contribute to the Hall viscosity-dependence of the conductivity.

  3. Faraday Probe Analysis, Part 2: Evaluation of Facility Effects on Ion Migration in a Hall Thruster Plume (Preprint)

    DTIC Science & Technology

    2010-02-24

    A nested Faraday probe was designed and fabricated to assess facility effects in a systematic study of ion migration in a Hall thruster plume...Current density distributions were studied at 8, 12, 16, and 20 thruster diameters downstream of the Hall thruster exit plane with four probe configurations...measurements are a significant improvement for comparisons with numerical simulations and investigations of Hall thruster performance.

  4. Hall Thruster Thermal Modeling and Test Data Correlation

    NASA Technical Reports Server (NTRS)

    Myers, James; Kamhawi, Hani; Yim, John; Clayman, Lauren

    2016-01-01

    The life of Hall Effect thrusters are primarily limited by plasma erosion and thermal related failures. NASA Glenn Research Center (GRC) in cooperation with the Jet Propulsion Laboratory (JPL) have recently completed development of a Hall thruster with specific emphasis to mitigate these limitations. Extending the operational life of Hall thursters makes them more suitable for some of NASA's longer duration interplanetary missions. This paper documents the thermal model development, refinement and correlation of results with thruster test data. Correlation was achieved by minimizing uncertainties in model input and recognizing the relevant parameters for effective model tuning. Throughout the thruster design phase the model was used to evaluate design options and systematically reduce component temperatures. Hall thrusters are inherently complex assemblies of high temperature components relying on internal conduction and external radiation for heat dispersion and rejection. System solutions are necessary in most cases to fully assess the benefits and/or consequences of any potential design change. Thermal model correlation is critical since thruster operational parameters can push some components/materials beyond their temperature limits. This thruster incorporates a state-of-the-art magnetic shielding system to reduce plasma erosion and to a lesser extend power/heat deposition. Additionally a comprehensive thermal design strategy was employed to reduce temperatures of critical thruster components (primarily the magnet coils and the discharge channel). Long term wear testing is currently underway to assess the effectiveness of these systems and consequently thruster longevity.

  5. Chiral Maxwell demon in a quantum Hall system with a localized impurity

    NASA Astrophysics Data System (ADS)

    Rosselló, Guillem; López, Rosa; Platero, Gloria

    2017-08-01

    We investigate the role of chirality on the performance of a Maxwell demon implemented in a quantum Hall bar with a localized impurity. Within a stochastic thermodynamics description, we investigate the ability of such a demon to drive a current against a bias. We show that the ability of the demon to perform is directly related to its ability to extract information from the system. The key features of the proposed Maxwell demon are the topological properties of the quantum Hall system. The asymmetry of the electronic interactions felt at the localized state when the magnetic field is reversed joined to the fact that we consider energy-dependent (and asymmetric) tunneling barriers that connect such state with the Hall edge modes allow the demon to properly work.

  6. Quenching of the Quantum Hall Effect in Graphene with Scrolled Edges

    NASA Astrophysics Data System (ADS)

    Cresti, Alessandro; Fogler, Michael M.; Guinea, Francisco; Castro Neto, A. H.; Roche, Stephan

    2012-04-01

    Edge nanoscrolls are shown to strongly influence transport properties of suspended graphene in the quantum Hall regime. The relatively long arclength of the scrolls in combination with their compact transverse size results in formation of many nonchiral transport channels in the scrolls. They short circuit the bulk current paths and inhibit the observation of the quantized two-terminal resistance. Unlike competing theoretical proposals, this mechanism of disrupting the Hall quantization in suspended graphene is not caused by ill-chosen placement of the contacts, singular elastic strains, or a small sample size.

  7. Jefferson Lab Experimental Hall C

    NASA Astrophysics Data System (ADS)

    Carlini, Roger D.

    1996-10-01

    Jefferson Lab's Hall C went into initial operation in November 1995. The hall has a short orbit spectrometer (SOS) for short-lived particles such as pions and kaons and a high-momentum spectrometer (HMS) usually used for electrons. The SOS can also be used for protons. The HMS can range to 7 GeV/c. Both the SOS and HMS have typical resolutions of (10-3). Experiments for this hall range from measuring the neutron electric form factor, to color transparency, to creating strange nuclei. This paper will present the optical capabilities of the spectrometers, the parameters of the detection systems, and the overall beam line characteristics of the hall as determined from the results from the recent physics experiments along with the upcoming experimental schedule. Additional information is available at URL http://www.cebaf.gov/hallc.html.

  8. Development of scanning graphene Hall probes for magnetic microscopy

    NASA Astrophysics Data System (ADS)

    Schaefer, Brian T.; Wang, Lei; McEuen, Paul L.; Nowack, Katja C.

    We discuss our progress on developing scanning Hall probes fabricated from hexagonal boron nitride (hBN)-encapsulated graphene, with the goal to image magnetic fields with submicron resolution. In contrast to scanning superconducting quantum interference device (SQUID) microscopy, this technique is compatible with a large applied magnetic field and not limited to cryogenic temperatures. The field sensitivity of a Hall probe depends inversely on carrier density, while the primary source of noise in the measurement is Johnson noise originating from the device resistance. hBN-encapsulated graphene demonstrates high carrier mobility at low carrier densities, therefore making it an ideal material for sensitive Hall probes. Furthermore, engineering the dielectric environment of graphene by encapsulating in hBN reduces low-frequency charge noise and disorder from the substrate. We outline our plans for adapting these devices for scanning, including characterization of the point spread function with a scanned current loop and fabrication of a deep-etched structure that enables positioning the sensitive area within 100 nanometers of the sample surface.

  9. Fault Detection and Diagnosis In Hall-Héroult Cells Based on Individual Anode Current Measurements Using Dynamic Kernel PCA

    NASA Astrophysics Data System (ADS)

    Yao, Yuchen; Bao, Jie; Skyllas-Kazacos, Maria; Welch, Barry J.; Akhmetov, Sergey

    2018-04-01

    Individual anode current signals in aluminum reduction cells provide localized cell conditions in the vicinity of each anode, which contain more information than the conventionally measured cell voltage and line current. One common use of this measurement is to identify process faults that can cause significant changes in the anode current signals. While this method is simple and direct, it ignores the interactions between anode currents and other important process variables. This paper presents an approach that applies multivariate statistical analysis techniques to individual anode currents and other process operating data, for the detection and diagnosis of local process abnormalities in aluminum reduction cells. Specifically, since the Hall-Héroult process is time-varying with its process variables dynamically and nonlinearly correlated, dynamic kernel principal component analysis with moving windows is used. The cell is discretized into a number of subsystems, with each subsystem representing one anode and cell conditions in its vicinity. The fault associated with each subsystem is identified based on multivariate statistical control charts. The results show that the proposed approach is able to not only effectively pinpoint the problematic areas in the cell, but also assess the effect of the fault on different parts of the cell.

  10. Substorm Birkeland currents and Cowling channels in the ionosphere

    NASA Astrophysics Data System (ADS)

    Fujii, R.

    2016-12-01

    Field-aligned current (FAC) connects electromagnetically the ionosphere with the magnetosphere and plays important roles on dynamics and energetics in the magnetosphere and the ionosphere. In particular, connections between FACs in the ionosphere give important information on various current sources in the magnetosphere and the linkage between them, although the connection between FACs in the ionosphere does not straightforwardly give that in the magnetosphere. FACs in the ionosphere are closed to each other through ionospheric currents determined with the electric field and the Hall and Pedersen conductivities. The electric field and the conductivities are not independently distributed, but rather they are harmonized with each other spatially and temporarily in a physically consistent manner to give a certain FAC. In particular, the divergence of the Hall current due to the inhomogeneity of the Hall conductivity either flows in/out to the magnetosphere as a secondary FAC or accumulates excess charges that produce a secondary electric field. This electric field drives a current circuit connecting the Hall current with the Pedersen current; a Cowling channel current circuit. The FAC (the electric field) we observe is the sum of the primary and secondary FACs (electric fields). The talk will present characteristics of FACs and associated electric field and auroras during substorms, and the ionospheric current closures between the FACs. A statistical study has shown that the majority of region 1 currents are connected to their adjacent region 2 or region 0 currents, indicating the Pedersen current closure rather than the Hall current closure is dominant. On the other hand, the Pedersen currents associated with surge and substorm-related auroras often are connected to the Hall currents, forming a Cowling channel current circuit within the ionosphere.

  11. Precision Electron Beam Polarimetry in Hall C at Jefferson Lab

    NASA Astrophysics Data System (ADS)

    Gaskell, David

    2013-10-01

    The electron beam polarization in experimental Hall C at Jefferson Lab is measured using two devices. The Hall-C/Basel Møller polarimeter measures the beam polarization via electron-electron scattering and utilizes a novel target system in which a pure iron foil is driven to magnetic saturation (out of plane) using a superconducting solenoid. A Compton polarimeter measures the polarization via electron-photon scattering, where the photons are provided by a high-power, CW laser coupled to a low gain Fabry-Perot cavity. In this case, both the Compton-scattered electrons and backscattered photons provide measurements of the beam polarization. Results from both polarimeters, acquired during the Q-Weak experiment in Hall C, will be presented. In particular, the results of a test in which the Møller and Compton polarimeters made interleaving measurements at identical beam currents will be shown. In addition, plans for operation of both devices after completion of the Jefferson Lab 12 GeV Upgrade will also be discussed.

  12. Hall Thruster Plume Measurements On-Board the Russian Express Satellites

    NASA Technical Reports Server (NTRS)

    Manzella, David; Jankovsky, Robert; Elliott, Frederick; Mikellides, Ioannis; Jongeward, Gary; Allen, Doug

    2001-01-01

    The operation of North-South and East-West station-keeping Hall thruster propulsion systems on-board two Russian Express-A geosynchronous communication satellites were investigated through a collaborative effort with the manufacturer of the spacecraft. Over 435 firings of 16 different thrusters with a cumulative run time of over 550 hr were reported with no thruster failures. Momentum transfer due to plume impingement was evaluated based on reductions in the effective thrust of the SPT-100 thrusters and induced disturbance torques determined based on attitude control system data and range data. Hall thruster plasma plume effects on the transmission of C-band and Ku-band communication signals were shown to be negligible. On-orbit ion current density measurements were made and subsequently compared to predictions and ground test data. Ion energy, total pressure, and electric field strength measurements were also measured on-orbit. The effect of Hall thruster operation on solar array performance over several months was investigated. A subset of these data is presented.

  13. High Power Hall Thrusters

    NASA Technical Reports Server (NTRS)

    Jankovsky, Robert; Tverdokhlebov, Sergery; Manzella, David

    1999-01-01

    The development of Hall thrusters with powers ranging from tens of kilowatts to in excess of one hundred kilowatts is considered based on renewed interest in high power. high thrust electric propulsion applications. An approach to develop such thrusters based on previous experience is discussed. It is shown that the previous experimental data taken with thrusters of 10 kW input power and less can be used. Potential mass savings due to the design of high power Hall thrusters are discussed. Both xenon and alternate thruster propellant are considered, as are technological issues that will challenge the design of high power Hall thrusters. Finally, the implications of such a development effort with regard to ground testing and spacecraft intecrati'on issues are discussed.

  14. Microscopic model of quasiparticle wave packets in superfluids, superconductors, and paired Hall states.

    PubMed

    Parameswaran, S A; Kivelson, S A; Shankar, R; Sondhi, S L; Spivak, B Z

    2012-12-07

    We study the structure of Bogoliubov quasiparticles, bogolons, the fermionic excitations of paired superfluids that arise from fermion (BCS) pairing, including neutral superfluids, superconductors, and paired quantum Hall states. The naive construction of a stationary quasiparticle in which the deformation of the pair field is neglected leads to a contradiction: it carries a net electrical current even though it does not move. However, treating the pair field self-consistently resolves this problem: in a neutral superfluid, a dipolar current pattern is associated with the quasiparticle for which the total current vanishes. When Maxwell electrodynamics is included, as appropriate to a superconductor, this pattern is confined over a penetration depth. For paired quantum Hall states of composite fermions, the Maxwell term is replaced by a Chern-Simons term, which leads to a dipolar charge distribution and consequently to a dipolar current pattern.

  15. Electrochemistry of the Hall-Heroult Process for Aluminum Smelting.

    ERIC Educational Resources Information Center

    Haupin, W. E.

    1983-01-01

    Nearly all aluminum is produced by the electrolysis of alumina dissolved in a molten cryolite-based electrolyte, the Hall-Heroult Process. Various aspects of the procedure are discussed, focusing on electrolyte chemistry, dissolution of alumina, electrode reactions, current efficiency, and cell voltage. Suggestions for graduate study related to…

  16. Classical Hall Effect without Magnetic Field

    NASA Astrophysics Data System (ADS)

    Schade, Nicholas; Tao, Chiao-Yu; Schuster, David; Nagel, Sidney

    We show that the sign and density of charge carriers in a material can be obtained without the presence of a magnetic field. This effect, analogous to the classical Hall effect, is due solely to the geometry of the current-carrying wire. When current flows, surface charges along the wire create small electric fields that direct the current to follow the path of the conductor. In a curved wire, the charge carriers must experience a centripetal force, which arises from an electric field perpendicular to the drift velocity. This electric field produces a potential difference between the sides of the wire that depends on the sign and density of the charge carriers. We experimentally investigate circuits made from superconductors or graphene to find evidence for this effect.

  17. High-Power Hall Thruster Technology Evaluated for Primary Propulsion Applications

    NASA Technical Reports Server (NTRS)

    Manzella, David H.; Jankovsky, Robert S.; Hofer, Richard R.

    2003-01-01

    High-power electric propulsion systems have been shown to be enabling for a number of NASA concepts, including piloted missions to Mars and Earth-orbiting solar electric power generation for terrestrial use (refs. 1 and 2). These types of missions require moderate transfer times and sizable thrust levels, resulting in an optimized propulsion system with greater specific impulse than conventional chemical systems and greater thrust than ion thruster systems. Hall thruster technology will offer a favorable combination of performance, reliability, and lifetime for such applications if input power can be scaled by more than an order of magnitude from the kilowatt level of the current state-of-the-art systems. As a result, the NASA Glenn Research Center conducted strategic technology research and development into high-power Hall thruster technology. During program year 2002, an in-house fabricated thruster, designated the NASA-457M, was experimentally evaluated at input powers up to 72 kW. These tests demonstrated the efficacy of scaling Hall thrusters to high power suitable for a range of future missions. Thrust up to nearly 3 N was measured. Discharge specific impulses ranged from 1750 to 3250 sec, with discharge efficiencies between 46 and 65 percent. This thruster is the highest power, highest thrust Hall thruster ever tested.

  18. Ultra-sensitive Hall sensors based on graphene encapsulated in hexagonal boron nitride

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Dauber, Jan; Stampfer, Christoph; Peter Grünberg Institute

    2015-05-11

    The encapsulation of graphene in hexagonal boron nitride provides graphene on substrate with excellent material quality. Here, we present the fabrication and characterization of Hall sensor elements based on graphene boron nitride heterostructures, where we gain from high mobility and low charge carrier density at room temperature. We show a detailed device characterization including Hall effect measurements under vacuum and ambient conditions. We achieve a current- and voltage-related sensitivity of up to 5700 V/AT and 3 V/VT, respectively, outpacing state-of-the-art silicon and III/V Hall sensor devices. Finally, we extract a magnetic resolution limited by low frequency electric noise of less than 50more » nT/√(Hz) making our graphene sensors highly interesting for industrial applications.« less

  19. The Hall effect in star formation

    NASA Astrophysics Data System (ADS)

    Braiding, C. R.; Wardle, M.

    2012-05-01

    Magnetic fields play an important role in star formation by regulating the removal of angular momentum from collapsing molecular cloud cores. Hall diffusion is known to be important to the magnetic field behaviour at many of the intermediate densities and field strengths encountered during the gravitational collapse of molecular cloud cores into protostars, and yet its role in the star formation process is not well studied. We present a semianalytic self-similar model of the collapse of rotating isothermal molecular cloud cores with both Hall and ambipolar diffusion, and similarity solutions that demonstrate the profound influence of the Hall effect on the dynamics of collapse. The solutions show that the size and sign of the Hall parameter can change the size of the protostellar disc by up to an order of magnitude and the protostellar accretion rate by 50 per cent when the ratio of the Hall to ambipolar diffusivities is varied between -0.5 ≤ηH/ηA≤ 0.2. These changes depend upon the orientation of the magnetic field with respect to the axis of rotation and create a preferred handedness to the solutions that could be observed in protostellar cores using next-generation instruments such as ALMA. Hall diffusion also determines the strength and position of the shocks that bound the pseudo and rotationally supported discs, and can introduce subshocks that further slow accretion on to the protostar. In cores that are not initially rotating (not examined here), Hall diffusion can even induce rotation, which could give rise to disc formation and resolve the magnetic braking catastrophe. The Hall effect clearly influences the dynamics of gravitational collapse and its role in controlling the magnetic braking and radial diffusion of the field merits further exploration in numerical simulations of star formation.

  20. A Comparative Study of the Efficacy of Intervention Strategies on Student Electricity Use in Campus Residence Halls

    ERIC Educational Resources Information Center

    Wisecup, Allison K.; Grady, Dennis; Roth, Richard A.; Stephens, Julio

    2017-01-01

    Purpose: The purpose of this study was to determine whether, and how, electricity consumption by students in university residence halls were impacted through three intervention strategies. Design/methodology/approach: The current investigation uses a quasi-experimental design by exposing freshman students in four matched residence halls and the…

  1. Scanning micro-Hall probe mapping of magnetic flux distributions and current densities in YBa{sub 2}Cu{sub 3}O{sub 7}

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Xing, W.; Heinrich, B.; Zhou, H.

    1994-12-31

    Mapping of the magnetic flux density B{sub z} (perpendicular to the film plane) for a YBa{sub 2}Cu{sub 3}O{sub 7} thin-film sample was carried out using a scanning micro-Hall probe. The sheet magnetization and sheet current densities were calculated from the B{sub z} distributions. From the known sheet magnetization, the tangential (B{sub x,y}) and normal components of the flux density B were calculated in the vicinity of the film. It was found that the sheet current density was mostly determined by 2B{sub x,y}/d, where d is the film thickness. The evolution of flux penetration as a function of applied field willmore » be shown.« less

  2. Domain wall in a quantum anomalous Hall insulator as a magnetoelectric piston

    NASA Astrophysics Data System (ADS)

    Upadhyaya, Pramey; Tserkovnyak, Yaroslav

    2016-07-01

    We theoretically study the magnetoelectric coupling in a quantum anomalous Hall insulator state induced by interfacing a dynamic magnetization texture to a topological insulator. In particular, we propose that the quantum anomalous Hall insulator with a magnetic configuration of a domain wall, when contacted by electrical reservoirs, acts as a magnetoelectric piston. A moving domain wall pumps charge current between electrical leads in a closed circuit, while applying an electrical bias induces reciprocal domain-wall motion. This pistonlike action is enabled by a finite reflection of charge carriers via chiral modes imprinted by the domain wall. Moreover, we find that, when compared with the recently discovered spin-orbit torque-induced domain-wall motion in heavy metals, the reflection coefficient plays the role of an effective spin-Hall angle governing the efficiency of the proposed electrical control of domain walls. Quantitatively, this effective spin-Hall angle is found to approach a universal value of 2, providing an efficient scheme to reconfigure the domain-wall chiral interconnects for possible memory and logic applications.

  3. Spin-Hall Switching of In-plane Exchange Biased Heterostructures

    NASA Astrophysics Data System (ADS)

    Mann, Maxwell; Beach, Geoffrey

    The spin Hall effect (SHE) in heavy-metal/ferromagnet bilayers generates a pure transverse spin current from in-plane charge current, allowing for efficient switching of spintronic devices with perpendicular magnetic anisotropy. Here, we demonstrate that an AFM deposited adjacent to the FM establishes a large in-plane exchange bias field, allowing operation at zero HIP. We sputtered Pt(3nm)/Co(0.9nm)/Ni80Co20O(tAF) stacks at room-temperature in an in-plane magnetic field of 3 kOe. The current-induced effective field was estimated in Hall cross devices by measuring the variation of the out-of-plane switching field as a function of JIP and HIP. The spin torque efficiency, dHSL/dJIP, is measured versus HIP for a sample with tAF =30 nm, and for a control in which NiCoO is replaced by TaOx. In the latter, dHSL/dJIP varied linearly with HIP. In the former, dHSL/dJIP varied nonlinearly with HIP and exhibited an offset indicating nonzero spin torque efficiency with zero HIP. The magnitude of HEB was 600 Oe in-plane.

  4. Star Formation and the Hall Effect

    NASA Astrophysics Data System (ADS)

    Braiding, Catherine

    2011-10-01

    Magnetic fields play an important role in star formation by regulating the removal of angular momentum from collapsing molecular cloud cores. Hall diffusion is known to be important to the magnetic field behaviour at many of the intermediate densities and field strengths encountered during the gravitational collapse of molecular cloud cores into protostars, and yet its role in the star formation process is not well-studied. This thesis describes a semianalytic self-similar model of the collapse of rotating isothermal molecular cloud cores with both Hall and ambipolar diffusion, presenting similarity solutions that demonstrate that the Hall effect has a profound influence on the dynamics of collapse. ... Hall diffusion also determines the strength of the magnetic diffusion and centrifugal shocks that bound the pseudo and rotationally-supported discs, and can introduce subshocks that further slow accretion onto the protostar. In cores that are not initially rotating Hall diffusion can even induce rotation, which could give rise to disc formation and resolve the magnetic braking catastrophe. The Hall effect clearly influences the dynamics of gravitational collapse and its role in controlling the magnetic braking and radial diffusion of the field would be worth exploring in future numerical simulations of star formation.

  5. Quantum Hall effect breakdown in two-dimensional hole gases

    NASA Astrophysics Data System (ADS)

    Eaves, L.; Stoddart, S. T.; Wirtz, R.; Neumann, A. C.; Gallagher, B. L.; Main, P. C.; Henini, M.

    2000-02-01

    The breakdown of dissipationless current flow in the quantum Hall effect is studied for a two-dimensional hole gas at filling factors i=1 and 2. At high currents, the magnetoresistance curves at breakdown exhibit a series of steps accompanied by hysteresis and intermittent noise. These are compared with similar data for electron systems and are discussed in terms of a hydrodynamic model involving inter-Landau level scattering at the sample edge.

  6. Reduced Spin Hall Effects from Magnetic Proximity.

    DOE PAGES

    Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; ...

    2015-03-26

    We investigate temperature-dependent spin pumping and inverse spin Hall effects in thin Pt and Pd in contact with Permalloy. Our experiments show a decrease of the spin Hall effect with decreasing temperature, which is attributed to a temperature-dependent proximity effect. The spin Hall angle decreases from 0.086 at room temperature to 0.042 at 10 K for Pt and is nearly negligible at 10 K for Pd. By first-principle calculations, we show that the spin Hall conductivity indeed reduces by increasing the proximity-induced spin magnetic moments for both Pt and Pd. This work highlights the important role of proximity-induced magnetic orderingmore » to spin Hall phenomena in Pt and Pd.« less

  7. Residence Hall Seating That Works.

    ERIC Educational Resources Information Center

    Wiens, Janet

    2003-01-01

    Describes the seating chosen for residence halls at the Massachusetts Institute of Technology and the University of New England. The seating required depends on ergonomics, aesthetics, durability, cost, and code requirements. In addition, residence halls must have a range of seating types to accommodate various uses. (SLD)

  8. Study on the influences of ionization region material arrangement on Hall thruster channel discharge characteristics

    NASA Astrophysics Data System (ADS)

    Xiang, HU; Ping, DUAN; Jilei, SONG; Wenqing, LI; Long, CHEN; Xingyu, BIAN

    2018-02-01

    There exists strong interaction between the plasma and channel wall in the Hall thruster, which greatly affects the discharge performance of the thruster. In this paper, a two-dimensional physical model is established based on the actual size of an Aton P70 Hall thruster discharge channel. The particle-in-cell simulation method is applied to study the influences of segmented low emissive graphite electrode biased with anode voltage on the discharge characteristics of the Hall thruster channel. The influences of segmented electrode placed at the ionization region on electric potential, ion number density, electron temperature, ionization rate, discharge current and specific impulse are discussed. The results show that, when segmented electrode is placed at the ionization region, the axial length of the acceleration region is shortened, the equipotential lines tend to be vertical with wall at the acceleration region, thus radial velocity of ions is reduced along with the wall corrosion. The axial position of the maximal electron temperature moves towards the exit with the expansion of ionization region. Furthermore, the electron-wall collision frequency and ionization rate also increase, the discharge current decreases and the specific impulse of the Hall thruster is slightly enhanced.

  9. 75 FR 22770 - Gary E. Hall and Rita Hall; Notice of Availability of Environmental Assessment

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-30

    ... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Project No. 13652-000-Montana] Gary E. Hall and Rita Hall; Notice of Availability of Environmental Assessment April 22, 2010. In accordance with the National Environmental Policy Act of 1969, as amended, and the Federal Energy Regulatory...

  10. Charge carrier coherence and Hall effect in organic semiconductors

    DOE PAGES

    Yi, H. T.; Gartstein, Y. N.; Podzorov, V.

    2016-03-30

    Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force actingmore » on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Lastly, our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor.« less

  11. Charge carrier coherence and Hall effect in organic semiconductors.

    PubMed

    Yi, H T; Gartstein, Y N; Podzorov, V

    2016-03-30

    Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force acting on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor.

  12. Charge carrier coherence and Hall effect in organic semiconductors

    PubMed Central

    Yi, H. T.; Gartstein, Y. N.; Podzorov, V.

    2016-01-01

    Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force acting on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor. PMID:27025354

  13. Current-induced switching in a magnetic insulator

    NASA Astrophysics Data System (ADS)

    Avci, Can Onur; Quindeau, Andy; Pai, Chi-Feng; Mann, Maxwell; Caretta, Lucas; Tang, Astera S.; Onbasli, Mehmet C.; Ross, Caroline A.; Beach, Geoffrey S. D.

    2017-03-01

    The spin Hall effect in heavy metals converts charge current into pure spin current, which can be injected into an adjacent ferromagnet to exert a torque. This spin-orbit torque (SOT) has been widely used to manipulate the magnetization in metallic ferromagnets. In the case of magnetic insulators (MIs), although charge currents cannot flow, spin currents can propagate, but current-induced control of the magnetization in a MI has so far remained elusive. Here we demonstrate spin-current-induced switching of a perpendicularly magnetized thulium iron garnet film driven by charge current in a Pt overlayer. We estimate a relatively large spin-mixing conductance and damping-like SOT through spin Hall magnetoresistance and harmonic Hall measurements, respectively, indicating considerable spin transparency at the Pt/MI interface. We show that spin currents injected across this interface lead to deterministic magnetization reversal at low current densities, paving the road towards ultralow-dissipation spintronic devices based on MIs.

  14. Laurance David Hall.

    PubMed

    Coxon, Bruce

    2011-01-01

    An account is given of the life, scientific contributions, and passing of Laurance David Hall (1938-2009), including his early history and education at the University of Bristol, UK, and the synthesis and NMR spectroscopy of carbohydrates and other natural products during ∼20 years of research and teaching at the University of British Columbia in Vancouver, Canada. Lists of graduate students, post-doctoral fellows, and sabbatical visitors are provided for this period. Following a generous endowment by Dr. Herchel Smith, Professor Hall built a new Department of Medicinal Chemistry at Cambridge University, UK, and greatly expanded his researches into the technology and applications of magnetic resonance imaging (MRI) and zero quantum NMR. MRI technology was applied both to medical problems such as the characterization of cartilage degeneration in knee joints, the measurement of ventricular function, lipid localization in animal models of atherosclerosis, paramagnetic metal complexes of polysaccharides as contrast agents, and studies of many other anatomical features, but also to several aspects of materials analysis, including food analyses, process control, and the elucidation of such physical phenomena as the flow of liquids through porous media, defects in concrete, and the visualization of fungal damage to wood. Professor Hall's many publications, patents, lectures, and honors and awards are described, and also his successful effort to keep the Asilomar facility in Pacific Grove, California as the alternating venue for the annual Experimental NMR Conference. Two memorial services for Professor Hall are remembered. Copyright © 2011 Elsevier Inc. All rights reserved.

  15. The first vineyard concert hall in North America

    NASA Astrophysics Data System (ADS)

    Jaffe, Christopher; Rivera, Carlos

    2002-11-01

    The first vineyard or surround concert hall designed and built in the Western Hemisphere is the Sala Nezahualcoyotl in Mexico City. The Hall was completed in 1976 and is part of the Cultural Center at the Universidad Nacional Autonoma de Mexico. The hall was named after a Toltec poet, architect, and musician who lived in the 15th century and was the Renaissance man of his day. In order to provide the familiar traditional sound of the rectangular (shoebox) European Hall, the acoustic designers set the criteria for reverberation times through the frequency spectrum and the Initial Time Delay Gap at every seat in the house to match the measurements taken at the Grosser Musik vereinssaal in Vienna and Boston Symphony Hall. In this paper we discuss the techniques used to create the traditional sound in a vineyard hall and the reaction of musicians and audiences to the completed facility. The Sala was the model for Suntory Hall in Japan which in turn spawned a number of vineyard halls in Japan. Most recently, the vineyard style seems to be appealing to more and more symphonic organizations in Europe and North America.

  16. Modeling an anode layer Hall thruster and its plume

    NASA Astrophysics Data System (ADS)

    Choi, Yongjun

    This thesis consists of two parts: a study of the D55 Hall thruster channel using a hydrodynamic model; and particle simulations of plasma plume flow from the D55 Hall thruster. The first part of this thesis investigates the xenon plasma properties within the D55 thruster channel using a hydrodynamic model. The discharge voltage (V) and current (I) characteristic of the D55 Hall thruster are studied. The hydrodynamic model fails to accurately predict the V-I characteristics. This analysis shows that the model needs to be improved. Also, the hydrodynamic model is used to simulate the plasma flow within the D55 Hall thruster. This analysis is performed to investigate the plasma properties of the channel exit. It is found that the hydrodynamic model is very sensitive to initial conditions, and fails to simulate the complete domain of the D55 Hall thruster. However, the model successfully calculates the channel domain of the D55 Hall thruster. The results show that, at the thruster exit, the plasma density has a maximum value while the ion velocity has a minimum at the channel center. Also, the results show that the flow angle varies almost linearly across the exit plane and increases from the center to the walls. Finally, the hydrodynamic model results are used to estimate the plasma properties at the thruster nozzle exit. The second part of the thesis presents two dimensional axisymmetric simulations of xenon plasma plume flow fields from the D55 anode layer Hall thruster. A hybrid particle-fluid method is used for the simulations. The magnetic field near the Hall thruster exit is included in the calculation. The plasma properties obtained from the hydrodynamic model are used to determine boundary conditions for the simulations. In these simulations, the Boltzmann model and a detailed fluid model are used to compute the electron properties, the direct simulation Monte Carlo method models the collisions of heavy particles, and the Particle-In-Cell method models the

  17. Turbulence Measurements in a Tropical Zoo Hall

    NASA Astrophysics Data System (ADS)

    Eugster, Werner; Denzler, Basil; Bogdal, Christian

    2017-04-01

    The Masoala rainforest hall of the Zurich Zoo, Switzerland, covers a ground surface area of 10,856 m2 and reaches 30 m in height. With its transparent ETFE foiled roof it provides a tropical climate for a large diversity of plants and animals. In combination with an effort to estimate dry deposition of elemental mercury, we made an attempt to measure turbulent transfer velocity with an ultrasonic anemometer inside the hall. Not surprising, the largest turbulence elements were on the order of the hall dimension. Although the dimensions of the hall seem to be small (200,000 m3) for eddy covariance flux measurements and the air circulation inside the hall was extremely weak, the spectra of wind velocity components and virtual (sonic) temperature obeyed the general statistical description expected under unconstrained outdoor measurement conditions. We will present results from a two-week measurement campaign in the Masoala rainforest hall and make a suggestion for the deposition velocity to be used to estimate dry deposition of atmospheric components to the tropical vegetation surface.

  18. Covariant Conservation Laws and the Spin Hall Effect in Dirac-Rashba Systems

    NASA Astrophysics Data System (ADS)

    Milletarı, Mirco; Offidani, Manuel; Ferreira, Aires; Raimondi, Roberto

    2017-12-01

    We present a theoretical analysis of two-dimensional Dirac-Rashba systems in the presence of disorder and external perturbations. We unveil a set of exact symmetry relations (Ward identities) that impose strong constraints on the spin dynamics of Dirac fermions subject to proximity-induced interactions. This allows us to demonstrate that an arbitrary dilute concentration of scalar impurities results in the total suppression of nonequilibrium spin Hall currents when only Rashba spin-orbit coupling is present. Remarkably, a finite spin Hall conductivity is restored when the minimal Dirac-Rashba model is supplemented with a spin-valley interaction. The Ward identities provide a systematic way to predict the emergence of the spin Hall effect in a wider class of Dirac-Rashba systems of experimental relevance and represent an important benchmark for testing the validity of numerical methodologies.

  19. Inverse spin Hall and spin rectification effects in NiFe/FeMn exchange-biased thin films

    NASA Astrophysics Data System (ADS)

    Garcia, W. J. S.; Seeger, R. L.; da Silva, R. B.; Harres, A.

    2017-11-01

    Materials presenting high spin-orbit coupling are able to convert spin currents in charge currents. The phenomenon, known as inverse spin Hall effect, promises to revolutionize spintronic technology enabling the electrical detection of spin currents. It has been observed in a variety of systems, usually non-magnetic metals. We study the voltage emerging in exchange biased Ta/NiFe/FeMn/Ta thin films near the ferromagnetic resonance. Measured signals are related to both inverse spin Hall and spin rectification effects, and two distinct protocols were employed to separate their contributions.The curve shift due to the exchange bias effect may enable high frequency applications without an external applied magnetic field.

  20. Effects of Ionospheric Hall Polarization on Magnetospheric Configurations and Dynamics in Global MHD Simulation

    NASA Astrophysics Data System (ADS)

    Nakamizo, A.; Yoshikawa, A.; Tanaka, T.

    2017-12-01

    We investigate how the M-I coupling and boundary conditions affects the results of global simulations of the magnetosphere. More specifically, we examine the effects of ionospheric Hall polarization on magnetospheric convection and dynamics by using an MHD code developed by Tanaka et al. [2010]. This study is motivated by the recently proposed idea that the ionospheric convection is modified by the ionospheric polarization [Yoshikawa et al., 2013]. We perform simulations for the following pairs of Hall conductance and IMF-By; Hall conductance set by αH = 2, 3.5, 5, and uniform distribution (1.0 [S] everywhere), where RH is the ratio of Hall to Pedersen conductance, and IMF-By of positive, negative, and zero. The results are summarized as follows. (a) Large-scale structure: In the cases of uniform Hall conductance, the magnetosphere is completely symmetric under the zero IMF-By. In the cases of non-uniform Hall conductance, the magnetosphere shows asymmetries globally even under the zero IMF-By. Asymmetries become severe for larger αH. The results indicate that ionospheric Hall polarization is one of the important factors to determine the global structure. (b) Formation of NENL: The location becomes closer to the earth and timing becomes earlier for larger RH. The difference is considered to be related to the combined effects of field lines twisting due to ionospheric Hall polarization and M-I energy/current closures. (c) Near-earth convection: In the cases of non-uniform Hall conductance, an inflection structure is formed around premidnight sector on equatorial plane inside 10 RE. Considering that the region 2 FAC is not sufficiently generated in MHD models, the structure corresponds to a convection reversal often shown in the RCM. Previous studies regard the structure as the Harang Reversal in the magnetosphere. In the cases of uniform Hall conductance, by contrast, such structure is not formed, indicating that the Harang Reversal may not be formed without the

  1. The Other Hall Effect: College Board Physics

    ERIC Educational Resources Information Center

    Sheppard, Keith; Gunning, Amanda M.

    2013-01-01

    Edwin Herbert Hall (1855-1938), discoverer of the Hall effect, was one of the first winners of the AAPT Oersted Medal for his contributions to the teaching of physics. While Hall's role in establishing laboratory work in high schools is widely acknowledged, his position as chair of the physics section of the Committee on College Entrance…

  2. Chapin Hall Center for Children.

    ERIC Educational Resources Information Center

    Chicago Univ., IL. Chapin Hall Center for Children.

    This document consists of two separate publications: (1) "The Power of Knowing", a brief 12-page description of the Chapin Hall Center for Children, and (2) "Projects and Publications", a 67-page list of the center's projects and publications as of Autumn 1997. "The Power of Knowing" describes the Chapin Hall Center…

  3. Unidirectional spin Hall magnetoresistance in topological insulator/ferromagnetic layer heterostructures

    NASA Astrophysics Data System (ADS)

    Kally, James; Lv, Yang; Zhang, Delin; Lee, Joon Sue; Samarth, Nitin; Wang, Jian-Ping; Department of Electrical; Computer Engineering, University of Minnesota, Minneapolis Collaboration; Department of Physics, Pennsylvania State University Collaboration

    The surface states of topological insulators offer a potentially very efficient way to generate spins and spin-orbit torques to magnetic moments in proximity. The switching by spin-orbit torque itself only requires two terminals so that a charge current can be applied. However, a third terminal with additional magnetic tunneling junction structure is needed to sense the magnetization state if such devices are used for memory and logic applications. The recent discovery of unidirectional spin Hall magnetoresistance in heavy metal/ferromagnetic and topological insulator/magnetically doped topological insulator systems offers an alternative way to sense magnetization while still keeping the number of terminals to minimal two. The unidirectional spin Hall magnetoresistance in topological insulator/strong ferromagnetic layer heterostructure system has yet not been reported. In this work, we report our experimental observations of such magnetoresistance. It is found to be present and comparable to the best result of the previous reported Ta/Co systems in terms of magnetoresistance per current density per total resistance.

  4. The influence of the Hall term on the development of magnetized laser-produced plasma jets

    NASA Astrophysics Data System (ADS)

    Hamlin, N. D.; Seyler, C. E.; Khiar, B.

    2018-04-01

    We present 2D axisymmetric simulation results describing the influence of the Hall term on laser-produced plasma jets and their interaction with an applied magnetic field parallel to the laser axis. Bending of the poloidal B-field lines produces an MHD shock structure surrounding a conical cavity, and a jet is produced from the convergence of the shock envelope. Both the jet and the conical cavity underneath it are bound by fast MHD shocks. We compare the MHD results generated using the extended-MHD code Physics as an Extended-MHD Relaxation System with an Efficient Upwind Scheme (PERSEUS) with MHD results generated using GORGON and find reasonable agreement. We then present extended-MHD results generated using PERSEUS, which show that the Hall term has several effects on the plasma jet evolution. A hot low-density current-carrying layer of plasma develops just outside the plume, which results in a helical rather than a purely poloidal B-field, and reduces magnetic stresses, resulting in delayed flow convergence and jet formation. The flow is partially frozen into the helical field, resulting in azimuthal rotation of the jet. The Hall term also produces field-aligned current in strongly magnetized regions. In particular, we find the influence of Hall physics on this problem to be scale-dependent. This points to the importance of mitigating the Hall effect in a laboratory setup, by increasing the jet density and system dimensions, in order to avoid inaccurate extrapolation to astrophysical scales.

  5. Hall Thruster Technology for NASA Science Missions

    NASA Technical Reports Server (NTRS)

    Manzella, David; Oh, David; Aadland, Randall

    2005-01-01

    The performance of a prototype Hall thruster designed for Discovery-class NASA science mission applications was evaluated at input powers ranging from 0.2 to 2.9 kilowatts. These data were used to construct a throttle profile for a projected Hall thruster system based on this prototype thruster. The suitability of such a Hall thruster system to perform robotic exploration missions was evaluated through the analysis of a near Earth asteroid sample return mission. This analysis demonstrated that a propulsion system based on the prototype Hall thruster offers mission benefits compared to a propulsion system based on an existing ion thruster.

  6. Numerical analysis of Hall effect on the performance of magnetohydrodynamic heat shield system based on nonequilibrium Hall parameter model

    NASA Astrophysics Data System (ADS)

    Li, Kai; Liu, Jun; Liu, Weiqiang

    2017-01-01

    Magnetohydrodynamic (MHD) heat shield system, a novel thermal protection technique in the hypersonic field, has been paid much attention in recent years. In the real flight condition, not only the Lorentz force but also the Hall electric field is induced by the interaction between ionized air post shock and magnetic field. In order to analyze the action mechanisms of the Hall effect, numerical methods of coupling thermochemical nonequilibrium flow field with externally applied magnetic field as well as the induced electric field are constructed and validated. Based on the nonequilibrium model of Hall parameter, numerical simulations of the MHD heat shield system is conducted under two different magnetic induction strengths (B0=0.2 T, 0.5 T) on a reentry capsule forebody. Results show that, the Hall effect is the same under the two magnetic induction strengths when the wall is assumed to be conductive. For this case, with the Hall effect taken into account, the Lorentz force counter stream diminishes a lot and the circumferential component dominates, resulting that the heat flux and shock-off distance approach the case without MHD control. However, for the insulating wall, the Hall effect acts in different ways under these two magnetic induction strengths. For this case, with the Hall effect taken into account, the performance of MHD heat shield system approaches the case neglecting the Hall effect when B0 equals 0.2 T. Such performance becomes worse when B0 equals 0.5 T and the aerothermal environment on the capsule shoulder is even worse than the case without MHD control.

  7. Hall mobility in multicrystalline silicon

    NASA Astrophysics Data System (ADS)

    Schindler, F.; Geilker, J.; Kwapil, W.; Warta, W.; Schubert, M. C.

    2011-08-01

    Knowledge of the carrier mobility in silicon is of utmost importance for photovoltaic applications, as it directly influences the diffusion length and thereby the cell efficiency. Moreover, its value is needed for a correct quantitative evaluation of a variety of lifetime measurements. However, models that describe the carrier mobility in silicon are based on theoretical calculations or fits to experimental data in monocrystalline silicon. Multicrystalline (mc) silicon features crystal defects such as dislocations and grain boundaries, with the latter possibly leading to potential barriers through the trapping of charge carriers and thereby influencing the mobility, as shown, for example, by Maruska et al. [Appl. Phys. Lett. 36, 381 (1980)]. To quantify the mobilities in multicrystalline silicon, we performed Hall measurements in p-type mc-Si samples of various resistivities and different crystal structures and compared the data to majority carrier Hall mobilities in p-type monocrystalline floatzone (FZ) silicon. For lack of a model that provides reliable values of the Hall mobility in silicon, an empirical fit similar to existing models for conductivity mobilities is proposed based on Hall measurements of monocrystalline p-type FZ silicon. By comparing the measured Hall mobilities obtained from mc silicon with the corresponding Hall mobilities in monocrystalline silicon of the same resistivity, we found that the mobility reduction due to the presence of crystal defects in mc-Si ranges between 0% and 5% only. Mobility decreases of up to 30% as reported by Peter et al. [Proceedings of the 23rd European Photovoltaic Solar Energy Conference, Valencia, Spain, 1-5 September 2008], or even of a factor of 2 to 3 as detected by Palais et al. [Mater. Sci. Eng. B 102, 184 (2003)], in multicrystalline silicon were not observed.

  8. Prospect of quantum anomalous Hall and quantum spin Hall effect in doped kagome lattice Mott insulators.

    PubMed

    Guterding, Daniel; Jeschke, Harald O; Valentí, Roser

    2016-05-17

    Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.

  9. A Gift for Reading Hall No. 1

    ERIC Educational Resources Information Center

    MacWilliams, Bryon

    2009-01-01

    In this article, the author describes Reading Hall No. 1 of the Russian State Library. He was placed in the first reading hall in the mid-1990s, when the Russian government still honored Soviet traditions of granting certain privileges to certain foreigners. In the first hall, the rules are different. He can request as many books as he wants. He…

  10. Quantum hall ferromagnets

    NASA Astrophysics Data System (ADS)

    Kumar, Akshay

    We study several quantum phases that are related to the quantum Hall effect. Our initial focus is on a pair of quantum Hall ferromagnets where the quantum Hall ordering occurs simultaneously with a spontaneous breaking of an internal symmetry associated with a semiconductor valley index. In our first example ---AlAs heterostructures--- we study domain wall structure, role of random-field disorder and dipole moment physics. Then in the second example ---Si(111)--- we show that symmetry breaking near several integer filling fractions involves a combination of selection by thermal fluctuations known as "order by disorder" and a selection by the energetics of Skyrme lattices induced by moving away from the commensurate fillings, a mechanism we term "order by doping". We also study ground state of such systems near filling factor one in the absence of valley Zeeman energy. We show that even though the lowest energy charged excitations are charge one skyrmions, the lowest energy skyrmion lattice has charge > 1 per unit cell. We then broaden our discussion to include lattice systems having multiple Chern number bands. We find analogs of quantum Hall ferromagnets in the menagerie of fractional Chern insulator phases. Unlike in the AlAs system, here the domain walls come naturally with gapped electronic excitations. We close with a result involving only topology: we show that ABC stacked multilayer graphene placed on boron nitride substrate has flat bands with non-zero local Berry curvature but zero Chern number. This allows access to an interaction dominated system with a non-trivial quantum distance metric but without the extra complication of a non-zero Chern number.

  11. Towards Thermal Reading of Magnetic States in Hall Crosses

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Petit-Watelot, S.; Polewczyk, V.; Parent, G.; Montaigne, F.; Wegrowe, J.-E.; Mangin, S.; Lacroix, D.; Hehn, M.; Lacour, D.

    2018-03-01

    The 3 ω method is a standard way to measure the thermal conductivity of thin films. In this study, we apply the method to read the magnetic state of a perpendicularly magnetized CoTb ferrimagnetic Hall cross using a thermal excitation. In order to generate the thermal excitation, an oscillating current at an ω frequency is applied to the Hall cross using different geometries. The magnetic signals oscillating at ω , 2 ω , and 3 ω are probed using a lock-in technique. From the analysis of the power dependence, we can attribute the 3 ω response to the temperature oscillation and the 2 ω to the temperature-gradient oscillation. Finally, the frequency dependence of the magnetic signals can be understood by considering the heat diffusion in a two-dimensional model.

  12. Overview of Hall D Complex

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chudakov, Eugene A.

    Hall D is a new experimental hall at Jefferson Lab, designed for experiments with a photon beam. The primary motivation for Hall D is the GlueX experiment [1,2], dedicated to meson spectroscopy. The Hall D complex consists of: An electron beam line used to extract the 5.5-pass electrons from the accelerator into the Tagger Hall. The designed beam energy is E e = 12 GeV;The Tagger Hall, where the electron beam passes through a thin radiator (~0.01% R.L.) and is deflected into the beam dump. The electrons that lost >30% of their energy in the radiator are detected with scintillatormore » hodoscopes providing a ~0.1% energy resolution for the tagged photons. Aligned diamond radiators allow to produce linearly polarized photons via the Coherent Bremsstrahlung. The beam dump is limited to 60 kW (5 µA at 12 GeV); The Collimator Cave contains a collimator for the photon beam and dipole magnets downstream in order to remove charged particles. The 3.4 mm diameter collimator, located about 75 m downstream of the radiator, selects the central cone of the photon beam increasing its average linear polarization, up to ~40%in the coherent peak at 9 GeV; Hall D contains several elements of the photon beam line, and themain spectrometer. A Pair Spectrometer consists of a thin converter, a dipole magnet, and a two-arm detector used to measure the energy spectrum of the photon beam. The main spectrometer is based on a 2-T superconducting solenoid, 4 m long and 1.85 m bore diameter. The liquid hydrogen target is located in the front part the solenoid. The charged tracks are detected with a set of drift chambers; photons are detected with two electromagnetic calorimeters. There are also scintillator hodoscopes for triggering and time-of-flight measurements. The spectrometer is nearly hermetic in an angular range of 1° < θ < 120 •. The momentum resolution is σ p /p ~ 1 ₋ ₋3% depending on the polar angle θ. The energy resolution of the electromagnetic calorimeters is about 7

  13. Giant spin Hall angle from topological insulator BixSe(1 - x) thin films

    NASA Astrophysics Data System (ADS)

    Dc, Mahendra; Jamali, Mahdi; Chen, Junyang; Hickey, Danielle; Zhang, Delin; Zhao, Zhengyang; Li, Hongshi; Quarterman, Patrick; Lv, Yang; Mkhyon, Andre; Wang, Jian-Ping

    Investigation on the spin-orbit torque (SOT) from large spin-orbit coupling materials has been attracting interest because of its low power switching of the magnetization and ultra-fast driving of the domain wall motion that can be used in future spin based memory and logic devices. We investigated SOT from topological insulator BixSe(1 - x) thin film in BixSe(1 - x) /CoFeB heterostructure by using the dc planar Hall method, where BixSe(1 - x) thin films were prepared by a unique industry-compatible deposition process. The angle dependent Hall resistance was measured in the presence of a rotating external in-plane magnetic field at bipolar currents. The spin Hall angle (SHA) from this BixSe(1 - x) thin film was found to be as large as 22.41, which is the largest ever reported at room temperature (RT). The giant SHA and large spin Hall conductivity (SHC) make this BixSe(1 - x) thin film a very strong candidate as an SOT generator in SOT based memory and logic devices.

  14. Astronaut Hall of Fame

    NASA Image and Video Library

    2018-04-21

    Former astronauts and space explorers, Thomas D. Jones, Ph.D., and Scott D. Altman, front row, center, left and right, respectively, were inducted into the U.S. Astronaut Hall of Fame Class of 2018 during a ceremony inside the Space Shuttle Atlantis attraction at NASA’s Kennedy Space Center Visitor Complex in Florida. They are standing with previous Hall of Famers, including, Curt Brown, back row, far left, chairman of the board, Astronaut Scholarship Foundation. Brown performed the induction ceremony. Also in the group is former astronaut and NASA administrator Charlie Bolden, in the center, behind Jones and Altman. In the back row, second from left is John Grunsfeld, who spoke on behalf of Altman during the ceremony. Directly behind Altman is Storey Musgrave, who spoke on behalf of Jones during the ceremony. Inductees into the Hall of Fame are selected by a committee of Hall of Fame astronauts, former NASA officials, flight directors, historians and journalists. The process is administered by the Astronaut Scholarship Foundation. To be eligible, an astronaut must have made his or her first flight at least 17 years before the induction. Candidates must be a U.S. citizen and a NASA-trained commander, pilot or mission specialist who has orbited the earth at least once. Including Altman and Jones, 97 astronauts have been inducted into the AHOF.

  15. Dr. Hall and the work cure.

    PubMed

    Reed, Kathlyn L

    2005-01-01

    Herbert James Hall, MD (1870-1923), was a pioneer in the systematic and organized study of occupation as therapy for persons with nervous and mental disorders that he called the "work cure." He began his work in 1904 during the early years of the Arts and Crafts Movement in the United States. His primary interest was the disorder neurasthenia, a condition with many symptoms including chronic fatigue, stress, and inability to work or perform everyday tasks. The prevailing treatment of the day was absolute bed rest known as the "rest cure." Hall believed that neurasthenia was not caused by overwork but by faulty living habits that could be corrected through an ordered life schedule and selected occupations. He identified several principles of therapy that are still used today including graded activity and energy conservation. Dr. Adolph Meyer credits Hall for organizing the ideas on the therapeutic use of occupation (Meyer, 1922). Hall also provided the name American Occupational Therapy Association for the professional organization and served as the fourth president. For his many contributions to the profession Hall deserves to be recognized as a major contributor to the development and organization of occupational therapy.

  16. Method for analyzing E x B probe spectra from Hall thruster plumes.

    PubMed

    Shastry, Rohit; Hofer, Richard R; Reid, Bryan M; Gallimore, Alec D

    2009-06-01

    Various methods for accurately determining ion species' current fractions using E x B probes in Hall thruster plumes are investigated. The effects of peak broadening and charge exchange on the calculated values of current fractions are quantified in order to determine the importance of accounting for them in the analysis. It is shown that both peak broadening and charge exchange have a significant effect on the calculated current fractions over a variety of operating conditions, especially at operating pressures exceeding 10(-5) torr. However, these effects can be accounted for using a simple approximation for the velocity distribution function and a one-dimensional charge exchange correction model. In order to keep plume attenuation from charge exchange below 30%, it is recommended that pz < or = 2, where p is the measured facility pressure in units of 10(-5) torr and z is the distance from the thruster exit plane to the probe inlet in meters. The spatial variation of the current fractions in the plume of a Hall thruster and the error induced from taking a single-point measurement are also briefly discussed.

  17. From rotating atomic rings to quantum Hall states.

    PubMed

    Roncaglia, M; Rizzi, M; Dalibard, J

    2011-01-01

    Considerable efforts are currently devoted to the preparation of ultracold neutral atoms in the strongly correlated quantum Hall regime. However, the necessary angular momentum is very large and in experiments with rotating traps this means spinning frequencies extremely near to the deconfinement limit; consequently, the required control on parameters turns out to be too stringent. Here we propose instead to follow a dynamic path starting from the gas initially confined in a rotating ring. The large moment of inertia of the ring-shaped fluid facilitates the access to large angular momenta, corresponding to giant vortex states. The trapping potential is then adiabatically transformed into a harmonic confinement, which brings the interacting atomic gas in the desired quantum-Hall regime. We provide numerical evidence that for a broad range of initial angular frequencies, the giant-vortex state is adiabatically connected to the bosonic ν = 1/2 Laughlin state.

  18. Effect of quantum tunneling on spin Hall magnetoresistance

    NASA Astrophysics Data System (ADS)

    Ok, Seulgi; Chen, Wei; Sigrist, Manfred; Manske, Dirk

    2017-02-01

    We present a formalism that simultaneously incorporates the effect of quantum tunneling and spin diffusion on the spin Hall magnetoresistance observed in normal metal/ferromagnetic insulator bilayers (such as Pt/Y3Fe5O12) and normal metal/ferromagnetic metal bilayers (such as Pt/Co), in which the angle of magnetization influences the magnetoresistance of the normal metal. In the normal metal side the spin diffusion is known to affect the landscape of the spin accumulation caused by spin Hall effect and subsequently the magnetoresistance, while on the ferromagnet side the quantum tunneling effect is detrimental to the interface spin current which also affects the spin accumulation. The influence of generic material properties such as spin diffusion length, layer thickness, interface coupling, and insulating gap can be quantified in a unified manner, and experiments that reveal the quantum feature of the magnetoresistance are suggested.

  19. Magnet/Hall-Effect Random-Access Memory

    NASA Technical Reports Server (NTRS)

    Wu, Jiin-Chuan; Stadler, Henry L.; Katti, Romney R.

    1991-01-01

    In proposed magnet/Hall-effect random-access memory (MHRAM), bits of data stored magnetically in Perm-alloy (or equivalent)-film memory elements and read out by using Hall-effect sensors to detect magnetization. Value of each bit represented by polarity of magnetization. Retains data for indefinite time or until data rewritten. Speed of Hall-effect sensors in MHRAM results in readout times of about 100 nanoseconds. Other characteristics include high immunity to ionizing radiation and storage densities of order 10(Sup6)bits/cm(Sup 2) or more.

  20. Analysis of Wien filter spectra from Hall thruster plumes.

    PubMed

    Huang, Wensheng; Shastry, Rohit

    2015-07-01

    A method for analyzing the Wien filter spectra obtained from the plumes of Hall thrusters is derived and presented. The new method extends upon prior work by deriving the integration equations for the current and species fractions. Wien filter spectra from the plume of the NASA-300M Hall thruster are analyzed with the presented method and the results are used to examine key trends. The new integration method is found to produce results slightly different from the traditional area-under-the-curve method. The use of different velocity distribution forms when performing curve-fits to the peaks in the spectra is compared. Additional comparison is made with the scenario where the current fractions are assumed to be proportional to the heights of peaks. The comparison suggests that the calculated current fractions are not sensitive to the choice of form as long as both the height and width of the peaks are accounted for. Conversely, forms that only account for the height of the peaks produce inaccurate results. Also presented are the equations for estimating the uncertainty associated with applying curve fits and charge-exchange corrections. These uncertainty equations can be used to plan the geometry of the experimental setup.

  1. 2017 Astronaut Hall of Fame Induction Ceremony

    NASA Image and Video Library

    2017-05-19

    In the Space Shuttle Atlantis facility at the Kennedy Space Center Visitor Complex in Florida, Astronaut Scholarship Foundation Chairman Dan Brandenstein, left, also a Hall of Fame astronaut, presents inductee Michael Foale with his hall of fame medal. Former NASA Administrator Charlie Bolden, right, a Hall of Fame member, presented Foale for induction. During this year's ceremonies, space shuttle astronaut Ellen Ochoa also was enshrined.

  2. 2017 Astronaut Hall of Fame Induction Ceremony

    NASA Image and Video Library

    2017-05-19

    In the Space Shuttle Atlantis facility at the Kennedy Space Center Visitor Complex in Florida, Astronaut Scholarship Foundation Chairman Dan Brandenstein, left, also a Hall of Fame astronaut, presents inductee Ellen Ochoa with her hall of fame medal. Former Johnson Space Center Director Mike Coats, right, a Hall of Fame member, presented Ochoa for induction. During this year's ceremonies, space shuttle astronaut Michael Foale also was enshrined.

  3. Analytical theory and possible detection of the ac quantum spin Hall effect

    DOE PAGES

    Deng, W. Y.; Ren, Y. J.; Lin, Z. X.; ...

    2017-07-11

    Here, we develop an analytical theory of the low-frequency ac quantum spin Hall (QSH) effect based upon the scattering matrix formalism. It is shown that the ac QSH effect can be interpreted as a bulk quantum pumping effect. When the electron spin is conserved, the integer-quantized ac spin Hall conductivity can be linked to the winding numbers of the reflection matrices in the electrodes, which also equal to the bulk spin Chern numbers of the QSH material. Furthermore, a possible experimental scheme by using ferromagnetic metals as electrodes is proposed to detect the topological ac spin current by electrical means.

  4. The Impact of Harness Impedance on Hall Thruster Discharge Oscillations

    NASA Technical Reports Server (NTRS)

    Pinero, Luis R.

    2017-01-01

    Hall thrusters exhibit characteristic discharge voltage and current oscillations during steady-state operation. The lower frequency breathing-mode current oscillations are inherent to each thruster and could impact thruster operation and power processing unit (PPU) design. The design of the discharge output filter, in particular, the output capacitor is important because it supplies the high peak current oscillations that the thruster demands. However, space-rated, high-voltage capacitors are not readily available and can have significant mass and volume. So, it is important for a PPU designer to know what is the minimum amount of capacitance required to operate a thruster. Through Simulation Program with Integrated Circuit Emphasis modeling and electrical measurements on the Hall Effect Rocket with Magnetic Shielding thruster, it was shown that the harness impedance between the power supply and the thruster is the main contributor towards generating voltage ripple at the thruster. Also, increasing the size of the discharge filter capacitor, as previously implemented during thruster tests, does not reduce the voltage oscillations. The electrical characteristics of the electrical harness between the discharge supply and the thruster is crucial to system performance and could have a negative impact on performance, life and operation.

  5. The Impact of Harness Impedance on Hall Thruster Discharge Oscillations

    NASA Technical Reports Server (NTRS)

    Pinero, Luis R.

    2017-01-01

    Hall thrusters exhibit characteristic discharge voltage and current oscillations during steady-state operation. The lower frequency breathing-mode current oscillations are inherent to each thruster and could impact thruster operation and PPU design. The design of the discharge output filter, in particular, the output capacitor is important because it supplies the high peak current oscillations that the thruster demands. However, space-rated, high-voltage capacitors are not readily available and can have significant mass and volume. So, it is important for a PPU designer to know what is the minimum amount of capacitance required to operate a thruster. Through SPICE modeling and electrical measurements on the Hall Effect Rocket with Magnetic Shielding (HERMeS) thruster, it was shown that the harness impedance between the power supply and the thruster is the main contributor towards generating voltage ripple at the thruster. Also, increasing the size of the discharge filter capacitor, as previously implemented during thruster tests, does not reduce the voltage oscillations. The electrical characteristics of the electrical harness between the discharge supply and the thruster is crucial to system performance and could have a negative impact on performance, life and operation.

  6. Effect of IrMn inserted layer on anomalous-Hall resistance and spin-Hall magnetoresistance in Pt/IrMn/YIG heterostructures

    NASA Astrophysics Data System (ADS)

    Shang, T.; Yang, H. L.; Zhan, Q. F.; Zuo, Z. H.; Xie, Y. L.; Liu, L. P.; Zhang, S. L.; Zhang, Y.; Li, H. H.; Wang, B. M.; Wu, Y. H.; Zhang, S.; Li, Run-Wei

    2016-10-01

    We report an investigation of anomalous-Hall resistance (AHR) and spin-Hall magnetoresistance (SMR) in Pt/Ir20Mn80/Y3Fe5O12 (Pt/IrMn/YIG) heterostructures. The AHR of Pt/IrMn/YIG heterostructures with an antiferromagnetic inserted layer is dramatically enhanced as compared to that of the Pt/YIG bilayer. The temperature dependent AHR behavior is nontrivial, while the IrMn thickness dependent AHR displays a peak at an IrMn thickness of 3 nm. The observed SMR in the temperature range of 10-300 K indicates that the spin current generated in the Pt layer can penetrate the IrMn layer (≤3 nm) to interact with the ferromagnetic YIG layer. The lack of conventional anisotropic magnetoresistance (AMR) implies that the insertion of the IrMn layer between Pt and YIG could efficiently suppress the magnetic proximity effect (MPE) on induced Pt moments by YIG.

  7. Pseudo-Hall Effect in Graphite on Paper Based Four Terminal Devices for Stress Sensing Applications

    NASA Astrophysics Data System (ADS)

    Qamar, Afzaal; Sarwar, Tuba; Dinh, Toan; Foisal, A. R. M.; Phan, Hoang-Phuong; Viet Dao, Dzung

    2017-04-01

    A cost effective and easy to fabricate stress sensor based on pseudo-Hall effect in Graphite on Paper (GOP) has been presented in this article. The four terminal devices were developed by pencil drawing with hand on to the paper substrate. The stress was applied to the paper containing four terminal devices with the input current applied at two terminals and the offset voltage observed at other two terminals called pseudo-Hall effect. The GOP stress sensor showed significant response to the applied stress which was smooth and linear. These results showed that the pseudo-Hall effect in GOP based four terminal devices can be used for cost effective, flexible and easy to make stress, strain or force sensors.

  8. Remote Diagnostic Measurements of Hall Thruster Plumes

    DTIC Science & Technology

    2009-08-14

    This paper describes measurements of Hall thruster plumes that characterize ion energy distributions and charge state fractions using remotely...charge state. Next, energy and charge state measurements are described from testing of a 200 W Hall thruster at AFIT. Measurements showed variation in...position. Finally, ExB probe charge state measurements are presented from a 6-kW laboratory Hall thruster operated at low discharge voltage levels at AFRL

  9. The Influence of the Hall Term on the Development of Magnetized Laser-Produced Plasma Jets

    DOE PAGES

    Hamlin, N.D.; Seyler, C. E.; Khiar, B.

    2018-04-29

    We present 2D axisymmetric simulation results describing the influence of the Hall term on laser-produced plasma jets and their interaction with an applied magnetic field parallel to the laser axis. Bending of the poloidal B-field lines produces an MHD shock structure surrounding a conical cavity, and a jet is produced from the convergence of the shock envelope. Both the jet and the conical cavity underneath it are bound by fast MHD shocks. We compare the MHD results generated using the extended-MHD code Physics as an Extended-MHD Relaxation System with an Efficient Upwind Scheme (PERSEUS) with MHD results generated using GORGONmore » and find reasonable agreement. We then present extended-MHD results generated using PERSEUS, which show that the Hall term has several effects on the plasma jet evolution. A hot low-density current-carrying layer of plasma develops just outside the plume, which results in a helical rather than a purely poloidal B-field, and reduces magnetic stresses, resulting in delayed flow convergence and jet formation. The flow is partially frozen into the helical field, resulting in azimuthal rotation of the jet. The Hall term also produces field-aligned current in strongly magnetized regions. In particular, we find the influence of Hall physics on this problem to be scale-dependent. In conclusion, this points to the importance of mitigating the Hall effect in a laboratory setup, by increasing the jet density and system dimensions, in order to avoid inaccurate extrapolation to astrophysical scales.« less

  10. The Influence of the Hall Term on the Development of Magnetized Laser-Produced Plasma Jets

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hamlin, N.D.; Seyler, C. E.; Khiar, B.

    We present 2D axisymmetric simulation results describing the influence of the Hall term on laser-produced plasma jets and their interaction with an applied magnetic field parallel to the laser axis. Bending of the poloidal B-field lines produces an MHD shock structure surrounding a conical cavity, and a jet is produced from the convergence of the shock envelope. Both the jet and the conical cavity underneath it are bound by fast MHD shocks. We compare the MHD results generated using the extended-MHD code Physics as an Extended-MHD Relaxation System with an Efficient Upwind Scheme (PERSEUS) with MHD results generated using GORGONmore » and find reasonable agreement. We then present extended-MHD results generated using PERSEUS, which show that the Hall term has several effects on the plasma jet evolution. A hot low-density current-carrying layer of plasma develops just outside the plume, which results in a helical rather than a purely poloidal B-field, and reduces magnetic stresses, resulting in delayed flow convergence and jet formation. The flow is partially frozen into the helical field, resulting in azimuthal rotation of the jet. The Hall term also produces field-aligned current in strongly magnetized regions. In particular, we find the influence of Hall physics on this problem to be scale-dependent. In conclusion, this points to the importance of mitigating the Hall effect in a laboratory setup, by increasing the jet density and system dimensions, in order to avoid inaccurate extrapolation to astrophysical scales.« less

  11. Long-range mutual synchronization of spin Hall nano-oscillators

    NASA Astrophysics Data System (ADS)

    Awad, A. A.; Dürrenfeld, P.; Houshang, A.; Dvornik, M.; Iacocca, E.; Dumas, R. K.; Åkerman, J.

    2017-03-01

    The spin Hall effect in a non-magnetic metal with spin-orbit coupling injects transverse spin currents into adjacent magnetic layers, where the resulting spin transfer torque can drive spin wave auto-oscillations. Such spin Hall nano-oscillators (SHNOs) hold great promise as extremely compact and broadband microwave signal generators and magnonic spin wave injectors. Here we show that SHNOs can also be mutually synchronized with unprecedented efficiency. We demonstrate mutual synchronization of up to nine individual SHNOs, each separated by 300 nm. Through further tailoring of the connection regions we can extend the synchronization range to 4 μm. The mutual synchronization is observed electrically as an increase in the power and coherence of the microwave signal, and confirmed optically using micro-Brillouin light scattering microscopy as two spin wave regions sharing the same spectral content, in agreement with our micromagnetic simulations.

  12. A Preliminary Investigation of Hall Thruster Technology

    NASA Technical Reports Server (NTRS)

    Gallimore, Alec D.

    1997-01-01

    A three-year NASA/BMDO-sponsored experimental program to conduct performance and plume plasma property measurements on two Russian Stationary Plasma Thrusters (SPTs) has been completed. The program utilized experimental facilitates at the University of Michigan's Plasmadynamics and Electric Propulsion Laboratory (PEPL). The main features of the proposed effort were as follows: (1) Characterized Hall thruster (and arcjet) performance by measuring ion exhaust velocity with probes at various thruster conditions; (2) Used a variety of probe diagnostics in the thruster plume to measure plasma properties and flow properties including T(sub e) and n(sub e) ion current density and ion energy distribution, and electric fields by mapping plasma potential; (3) Used emission spectroscopy to identify species within the plume and to measure electron temperatures. A key and unique feature of our research was our collaboration with Russian Hall thruster researcher Dr. Sergey A Khartov, Deputy Dean of International Relations at the Moscow Aviation Institute (MAI). His activities in this program included consulting on and participation in research at PEPL through use of a MAI-built SPT and ion energy probe.

  13. A Comprehensive Investigation of Facility Effects on the Testing of High-Power Monolithic and Clustered Hall Thruster Systems

    DTIC Science & Technology

    2004-09-02

    path for developing high-power EP systems is somewhat certain given NASA’s recent success with its 70+ kW NASA-457M Hall thruster , it is clear that...current density distribution, and summarize findings from cold- and hot-flow pressure map data of our vacuum chamber for a number of Hall thruster mass flow rates.

  14. Advanced Hall Electric Propulsion for Future In-space Transportation

    NASA Technical Reports Server (NTRS)

    Oleson, Steven R.; Sankovic, John M.

    2001-01-01

    The Hall thruster is an electric propulsion device used for multiple in-space applications including orbit raising, on-orbit maneuvers, and de-orbit functions. These in-space propulsion functions are currently performed by toxic hydrazine monopropellant or hydrazine derivative/nitrogen tetroxide bi-propellant thrusters. The Hall thruster operates nominally in the 1500 sec specific impulse regime. It provides greater thrust to power than conventional gridded ion engines, thus reducing trip times and operational life when compared to that technology in Earth orbit applications. The technology in the far term, by adding a second acceleration stage, has shown promise of providing over 4000s Isp, the regime of the gridded ion engine and necessary for deep space applications. The Hall thruster system consists of three parts, the thruster, the power processor, and the propellant system. The technology is operational and commercially available at the 1.5 kW power level and 5 kW application is underway. NASA is looking toward 10 kW and eventually 50 kW-class engines for ambitious space transportation applications. The former allows launch vehicle step-down for GEO missions and demanding planetary missions such as Europa Lander, while the latter allows quick all-electric propulsion LEO to GEO transfers and non-nuclear transportation human Mars missions.

  15. Hall thruster with grooved walls

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li Hong; Ning Zhongxi; Yu Daren

    2013-02-28

    Axial-oriented and azimuthal-distributed grooves are formed on channel walls of a Hall thruster after the engine undergoes a long-term operation. Existing studies have demonstrated the relation between the grooves and the near-wall physics, such as sheath and electron near-wall transport. The idea to optimize the thruster performance with such grooves was also proposed. Therefore, this paper is devoted to explore the effects of wall grooves on the discharge characteristics of a Hall thruster. With experimental measurements, the variations on electron conductivity, ionization distribution, and integrated performance are obtained. The involved physical mechanisms are then analyzed and discussed. The findings helpmore » to not only better understand the working principle of Hall thruster discharge but also establish a physical fundamental for the subsequent optimization with artificial grooves.« less

  16. Spin pumping and inverse spin Hall effects—Insights for future spin-orbitronics (invited)

    DOE PAGES

    Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; ...

    2015-03-13

    Quantification of spin-charge interconversion has become increasingly important in the fast-developing field of spin-orbitronics. Pure spin current generated by spin pumping acts a sensitive probe for many bulk and interface spin-orbit effects, which has been indispensable for the discovery of many promising new spin-orbit materials. Here, we apply spin pumping and inverse spin Hall effect experiments, as a useful metrology, and study spin-orbit effects in a variety of metals and metal interfaces. We also quantify the spin Hall effects in Ir and W using the conventional bilayer structures, and discuss the self-induced voltage in a single layer of ferromagnetic permalloy.more » Finally, we extend our discussions to multilayer structures and quantitatively reveal the spin current flow in two consecutive normal metal layers.« less

  17. Performance characteristics of No-Wall-Losses Hall Thruster

    NASA Astrophysics Data System (ADS)

    Ding, Yongjie; Peng, Wuji; Sun, Hezhi; Wei, Liqiu; Zeng, Ming; Wang, Fufeng; Yu, Daren

    2017-08-01

    A 200 W No-Wall-Losses Hall Thruster (NWLHT-200 W) is designed and processed to verify the technology of pushing down magnetic field with two permanent magnetic rings. To create a magnetic field, NWLHT-200 W uses two permanent magnetic rings (inner and outer) in the absence of magnetic screen or magnetic component. The anode is at the internal magnetic separatrix position, and the thruster shell is hollow to enhance the heat dissipation of ceramics. The magnetic field strength at the channel outlet is 90% of the maximum magnetic field. In this study, the experimental results concerning the thrust, discharge current, specific impulse, and efficiency are presented and examined. Our experiments show that "no erosive discharge" of wall is achieved within the range of 120-460 W; the maximum efficiency of the anode may reach 49%. The thruster designed can work stably for a long time, without any auxiliary heat dissipation equipment (heat pipe or radiator), which significantly prolongs the life of Hall thrusters.

  18. Valley-chiral quantum Hall state in graphene superlattice structure

    NASA Astrophysics Data System (ADS)

    Tian, H. Y.; Tao, W. W.; Wang, J.; Cui, Y. H.; Xu, N.; Huang, B. B.; Luo, G. X.; Hao, Y. H.

    2016-05-01

    We theoretically investigate the quantum Hall effect in a graphene superlattice (GS) system, in which the two valleys of graphene are coupled together. In the presence of a perpendicular magnetic field, an ordinary quantum Hall effect is found with the sequence σxy=ν e^2/h(ν=0,+/-1,+/-2,\\cdots) . At the zeroth Hall platform, a valley-chiral Hall state stemming from the single K or K' valley is found and it is localized only on one sample boundary contributing to the longitudinal conductance but not to the Hall conductivity. Our findings may shed light on the graphene-based valleytronics applications.

  19. Nonlinearity in the effect of an inhomogeneous Hall angle

    NASA Astrophysics Data System (ADS)

    Koon, Daniel W.

    2007-03-01

    The differential equation for the electric potential in a conducting material with an inhomogeneous Hall angle is extended to the large-field limit. This equation is solved for a square specimen, using a successive over-relaxation [SOR] technique for matrices of up to 101x101 size, and the Hall weighting function -- the effect of local pointlike perturbations on the measured Hall angle -- is calculated as both the unperturbed Hall angle, θH, and the perturbation, δθH, exceed the linear, small angle limit. Preliminary results show that the Hall angle varies by no more than 5% if both | θH |<1 and | δθH |<1. Thus, previously calculated results for the Hall weighting function can be used for most materials in all but the most extreme magnetic fields.

  20. Plasma oscillation effects on nested Hall thruster operation and stability

    NASA Astrophysics Data System (ADS)

    McDonald, M. S.; Sekerak, M. J.; Gallimore, A. D.; Hofer, R. R.

    High-power Hall thrusters capable of throughput on the order of 100 kW are currently under development, driven by more demanding mission profiles and rapid growth in on-orbit solar power generation capability. At these power levels the nested Hall thruster (NHT), a new design that concentrically packs multiple thrusters into a single body with a shared magnetic circuit, offers performance and logistical advantages over conventional single-channel Hall thrusters. An important area for risk reduction in NHT development is quantifying inter-channel coupling between discharge channels. This work presents time- and frequency-domain discharge current and voltage measurements paired with high-speed video of the X2, a 10-kW class dual channel NHT. Two “ triads” of operating conditions at 150 V, 3.6 kW and 250 V, 8.6 kW were examined, including each channel in individual operation and both channels in joint operation. For both triads tested, dual-channel operation did not noticeably destabilize the discharge. Partial coupling of outer channel oscillations into the inner channel occurred at 150 V, though oscillation amplitudes did not change greatly. As a percentage of mean discharge current, RMS oscillations at 150 V increased from 8% to 13% on the inner channel and decreased from 10% to 8% on the outer channel from single- to dual-channel operation. At 250 V the RMS/mean level stayed steady at 13% on the inner channel and decreased from 7% to 6% on the outer channel. The only mean discharge parameter noticeably affected was the cathode floating potential, which decreased in magnitude below ground with increased absolute cathode flow rate in dual-channel mode. Rotating spokes were detected on high-speed video across all X2 operating cases with wavelength 12-18 cm, and spoke velocity generally increased from single- to dual-channel operation.

  1. Giant Hall Photoconductivity in Narrow-Gapped Dirac Materials

    NASA Astrophysics Data System (ADS)

    Song, Justin C. W.; Kats, Mikhail A.

    2016-12-01

    Carrier dynamics acquire a new character in the presence of Bloch-band Berry curvature, which naturally arises in gapped Dirac materials (GDMs). Here we argue that photoresponse in GDMs with small band gaps is dramatically enhanced by Berry curvature. This manifests in a giant and saturable Hall photoconductivity when illuminated by circularly polarized light. Unlike Hall motion arising from a Lorentz force in a magnetic field, which impedes longitudinal carrier motion, Hall photoconductivity arising from Berry curvature can boost longitudinal carrier transport. In GDMs, this results in a helicity-dependent photoresponse in the Hall regime, where photoconductivity is dominated by its Hall component. We find that the induced Hall conductivity per incident irradiance is enhanced by up to six orders of magnitude when moving from the visible regime (with corresponding band gaps) to the far infrared. These results suggest that narrow-gap GDMs are an ideal test-bed for the unique physics that arise in the presence of Berry curvature, and open a new avenue for infrared and terahertz optoelectronics.

  2. Topological Valley Currents in Gapped Dirac Materials

    NASA Astrophysics Data System (ADS)

    Lensky, Yuri D.; Song, Justin C. W.; Samutpraphoot, Polnop; Levitov, Leonid S.

    2015-06-01

    Gapped 2D Dirac materials, in which inversion symmetry is broken by a gap-opening perturbation, feature a unique valley transport regime. Topological valley currents in such materials are dominated by bulk currents produced by electronic states just beneath the gap rather than by edge modes. The system ground state hosts dissipationless persistent valley currents existing even when topologically protected edge modes are absent. Valley currents induced by an external bias are characterized by a quantized half-integer valley Hall conductivity. The undergap currents dominate magnetization and the charge Hall effect in a light-induced valley-polarized state.

  3. Air temperature gradient in large industrial hall

    NASA Astrophysics Data System (ADS)

    Karpuk, Michał; Pełech, Aleksander; Przydróżny, Edward; Walaszczyk, Juliusz; Szczęśniak, Sylwia

    2017-11-01

    In the rooms with dominant sensible heat load, volume airflow depends on many factors incl. pre-established temperature difference between exhaust and supply airflow. As the temperature difference is getting higher, airflow volume drops down, consequently, the cost of AHU is reduced. In high industrial halls with air exhaust grids located under the ceiling additional temperature gradient above working zone should be taken into consideration. In this regard, experimental research of the vertical air temperature gradient in high industrial halls were carried out for the case of mixing ventilation system The paper presents the results of air temperature distribution measurements in high technological hall (mechanically ventilated) under significant sensible heat load conditions. The supply airflow was delivered to the hall with the help of the swirl diffusers while exhaust grids were located under the hall ceiling. Basing on the air temperature distribution measurements performed on the seven pre-established levels, air temperature gradient in the area between 2.0 and 7.0 m above the floor was calculated and analysed.

  4. The Enhancement of spin Hall torque efficiency and Reduction of Gilbert damping in spin Hall metal/normal metal/ferromagnetic trilayers

    NASA Astrophysics Data System (ADS)

    Nguyen, Minh-Hai; Pai, Chi-Feng; Ralph, Daniel C.; Buhrman, Robert A.

    2015-03-01

    The spin Hall effect (SHE) in ferromagnet/heavy metal bilayer structures has been demonstrated to be a powerful means for producing pure spin currents and for exerting spin-orbit damping-like and field-like torques on the ferromagnetic layer. Large spin Hall (SH) angles have been reported for Pt, beta-Ta and beta-W films and have been utilized to achieve magnetic switching of in-plane and out-of-plane magnetized nanomagnets, spin torque auto-oscillators, and the control of high velocity domain wall motion. For many of the proposed applications of the SHE it is also important to achieve an effective Gilbert damping parameter that is as low as possible. In general the spin orbit torques and the effective damping are predicted to depend directly on the spin-mixing conductance of the SH metal/ferromagnet interface. This opens up the possibility of tuning these properties with the insertion of a very thin layer of another metal between the SH metal and the ferromagnet. Here we will report on experiments with such trilayer structures in which we have observed both a large enhancement of the spin Hall torque efficiency and a significant reduction in the effective Gilbert damping. Our results indicate that there is considerable opportunity to optimize the effectiveness and energy efficiency of the damping-like torque through engineering of such trilayer structures. Supported in part by NSF and Samsung Electronics Corporation.

  5. Preliminary Study of Arcjet Neutralization of Hall Thruster Clusters (Postprint)

    DTIC Science & Technology

    2007-01-18

    Clustered Hall thrusters have emerged as a favored choice for extending Hall thruster options to very high powers (50 kW - 150 kW). This paper...examines the possible use of an arcjet to neutralize clustered Hall thrusters, as the hybrid arcjet- Hall thruster concept can fill a performance niche...and helium, and then demonstrate the first successful operation of a low power Hall thruster -arcjet neutralizer package. In the surrogate anode studies

  6. Hall Thruster

    NASA Image and Video Library

    2017-03-06

    NASA Glenn engineer Dr. Peter Peterson prepares a high-power Hall thruster for ground testing in a vacuum chamber that simulates the environment in space. This high-powered solar electric propulsion thruster has been identified as a critical part of NASA’s future deep space exploration plans.

  7. Inhibitory Control in a Notorious Brain Teaser: The Monty Hall Dilemma

    ERIC Educational Resources Information Center

    Saenen, Lore; Heyvaert, Mieke; Van Dooren, Wim; Onghena, Patrick

    2015-01-01

    The Monty Hall dilemma (MHD) is a counterintuitive probability problem in which participants often use misleading heuristics, such as the equiprobability bias. Finding the optimal solution to the MHD requires inhibition of these heuristics. In the current study, we investigated the relation between participants' equiprobability bias and their MHD…

  8. The quantum Hall effects: Philosophical approach

    NASA Astrophysics Data System (ADS)

    Lederer, P.

    2015-05-01

    The Quantum Hall Effects offer a rich variety of theoretical and experimental advances. They provide interesting insights on such topics as gauge invariance, strong interactions in Condensed Matter physics, emergence of new paradigms. This paper focuses on some related philosophical questions. Various brands of positivism or agnosticism are confronted with the physics of the Quantum Hall Effects. Hacking's views on Scientific Realism, Chalmers' on Non-Figurative Realism are discussed. It is argued that the difficulties with those versions of realism may be resolved within a dialectical materialist approach. The latter is argued to provide a rational approach to the phenomena, theory and ontology of the Quantum Hall Effects.

  9. Hall devices improve electric motor efficiency

    NASA Technical Reports Server (NTRS)

    Haeussermann, W.

    1979-01-01

    Efficiency of electric motors and generators is reduced by radial magnetic forces created by symmetric fields within device. Forces are sensed and counteracted by Hall devices on excitation or control windings. Hall generators directly measure and provide compensating control of anu asymmetry, eliminating additional measurements needed for calibration feedback control loop.

  10. Coping Behaviors of Residence Hall Directors

    ERIC Educational Resources Information Center

    Wilkes, Ben

    2017-01-01

    This mixed-methods study examined tertiary-level residence-hall directors' reported coping behaviors for three systems of stress: environmental, personal, and work. It surveyed a convenience sample of 128 respondents using the Brief COPE scale (Carver, 1997). Reported length of service, genders, and hall populations were matched with 28 types of…

  11. Performance of a Cylindrical Hall-Effect Thruster Using Permanent Magnets

    NASA Technical Reports Server (NTRS)

    Polzin, Kurt A.; Raitses, Y.; Merino, E.; Fisch, N. J.

    2009-01-01

    While annular Hall thrusters can operate at high efficiency at kW power levels, it is difficult to construct one that operates over a broad envelope from 1 kW down to 100 W while maintaining an efficiency of 45-55%. Scaling to low power while holding the main dimensionless parameters constant requires a decrease in the thruster channel size and an increase in the magnetic field strength. Increasing the magnetic field becomes technically challenging since the field can saturate the miniaturized inner components of the magnetic circuit and scaling down the magnetic circuit leaves very little room for magnetic pole pieces and heat shields. In addition, the central magnetic pole piece defining the interior wall of the annular channel can experience excessive heat loads in a miniaturized Hall thruster, with the temperature eventually exceeding the Curie temperature of the material and in extreme circumstances leading to accelerated erosion of the channel wall. An alternative approach is to employ a cylindrical Hall thruster (CHT) geometry. Laboratory model CHTs have operated at power levels ranging from 50 W up to 1 kW. These thrusters exhibit performance characteristics that are comparable to conventional, annular Hall thrusters of similar size. Compared to the annular Hall thruster, the CHTs insulator surface area to discharge chamber volume ratio is lower. Consequently, there is the potential for reduced wall losses in the channel of a CHT, and any reduction in wall losses should translate into lower channel heating rates and reduced erosion, making the CHT geometry promising for low-power applications. This potential for high performance in the low-power regime has served as the impetus for research and development efforts aimed at understanding and improving CHT performance. Recently, a 2.6 cm channel diameter permanent magnet CHT (shown in Fig. 1) was tested. This thruster has the promise of reduced power consumption over previous CHT iterations that employed

  12. Iodine Hall Thruster Propellant Feed System for a CubeSat

    NASA Technical Reports Server (NTRS)

    Polzin, Kurt A.

    2014-01-01

    There has been significant work recently in the development of iodine-fed Hall thrusters for in-space propulsion applications.1 The use of iodine as a propellant provides many advantages over present xenon-gas-fed Hall thruster systems. Iodine is a solid at ambient temperature (no pressurization required) and has no special handling requirements, making it safe for secondary flight opportunities. It has exceptionally high ?I sp (density times specific impulse), making it an enabling technology for small satellite near-term applications and providing system level advantages over mid-term high power electric propulsion options. Iodine provides thrust and efficiency that are comparable to xenonfed Hall thrusters while operating in the same discharge current and voltage regime, making it possible to leverage the development of flight-qualified xenon Hall thruster power processing units for the iodine application. Work at MSFC is presently aimed at designing, integrating, and demonstrating a flight-like iodine feed system suitable for the Hall thruster application. This effort represents a significant advancement in state-of-the-art. Though Iodine thrusters have demonstrated high performance with mission enabling potential, a flight-like feed system has never been demonstrated and iodine compatible components do not yet exist. Presented in this paper is the end-to-end integrated feed system demonstration. The system includes a propellant tank with active feedback-control heating, fill and drain interfaces, latching and proportional flow control valves (PFCV), flow resistors, and flight-like CubeSat power and control electronics. Hardware is integrated into a CubeSat-sized structure, calibrated and tested under vacuum conditions, and operated under under hot-fire conditions using a Busek BHT-200 thruster designed for iodine. Performance of the system is evaluated thorugh accurate measurement of thrust and a calibrated of mass flow rate measurement, which is a function of

  13. Comparisons and Evaluation of Hall Thruster Models

    DTIC Science & Technology

    2002-03-20

    COVERED (FROM - TO) 20-04-2001 to 20-04-2002 4. TITLE AND SUBTITLE comparisons and Evaluation of Hall Thruster Models Unclassified 5a. CONTRACT NUMBER...TITLE AND SUBTITLE Comparisons and Evaluation of Hall Thruster Models 5c. PROGRAM ELEMENT NUMBER 5d. PROJECT NUMBER 5d. TASK NUMBER 6. AUTHOR(S...evaluation of Hall thruster models G. J. M. Hagelaar, J. Bareilles, L. Garrigues, and J.-P. Boeuf CPAT, Bâtiment 3R2, Université Paul Sabatier 118 Route

  14. Modeling Electron Transport within the Framework of Hydrodynamic Description of Hall Thrusters (Preprint)

    DTIC Science & Technology

    2008-06-16

    Framework of Hydrodynamic Description of Hall Thrusters (Preprint) 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) M . keidar (The George...within the framework of hydrodynamic description of Hall thrusters (PREPRINT) M . Keidar 1 and L. Brieda 2 1) Department of Mechanical and...the electron current density: y yw y m ew y w z w ew dV V y kT mV kT e kT e kT m B E nj y )sin() 2 exp()exp()exp( 2 2 2 2 2/1 0 (2) In this case, a

  15. The shear-Hall instability in newborn neutron stars

    NASA Astrophysics Data System (ADS)

    Kondić, T.; Rüdiger, G.; Hollerbach, R.

    2011-11-01

    Aims: In the first few minutes of a newborn neutron star's life the Hall effect and differential rotation may both be important. We demonstrate that these two ingredients are sufficient for generating a "shear-Hall instability" and for studying its excitation conditions, growth rates, and characteristic magnetic field patterns. Methods: We numerically solve the induction equation in a spherical shell, with a kinematically prescribed differential rotation profile Ω(s), where s is the cylindrical radius. The Hall term is linearized about an imposed uniform axial field. The linear stability of individual azimuthal modes, both axisymmetric and non-axisymmetric, is then investigated. Results: For the shear-Hall instability to occur, the axial field must be parallel to the rotation axis if Ω(s) decreases outward, whereas if Ω(s) increases outward it must be anti-parallel. The instability draws its energy from the differential rotation, and occurs on the short rotational timescale rather than on the much longer Hall timescale. It operates most efficiently if the Hall time is comparable to the diffusion time. Depending on the precise field strengths B0, either axisymmetric or non-axisymmetric modes may be the most unstable. Conclusions: Even if the differential rotation in newborn neutron stars is quenched within minutes, the shear-Hall instability may nevertheless amplify any seed magnetic fields by many orders of magnitude.

  16. Piezo-Hall effect and fundamental piezo-Hall coefficients of single crystal n-type 3C-SiC(100) with low carrier concentration

    NASA Astrophysics Data System (ADS)

    Qamar, Afzaal; Dao, Dzung Viet; Dinh, Toan; Iacopi, Alan; Walker, Glenn; Phan, Hoang-Phuong; Hold, Leonie; Dimitrijev, Sima

    2017-04-01

    This article reports the results on the piezo-Hall effect in single crystal n-type 3C-SiC(100) having a low carrier concentration. The effect of the crystallographic orientation on the piezo-Hall effect has been investigated by applying stress to the Hall devices fabricated in different crystallographic directions. Single crystal n-type 3C-SiC(100) and 3C-SiC(111) were grown by low pressure chemical vapor deposition at 1250 °C. Fundamental piezo-Hall coefficients were obtained using the piezo-Hall effect measurements as P11 = (-29 ± 1.3) × 10-11 Pa-1, P12 = (11.06 ± 0.5)× 10-11 Pa-1, and P44 = (-3.4 ± 0.7) × 10-11 Pa-1. It has been observed that the piezo-Hall coefficients of n-type 3C-SiC(100) show a completely different behavior as compared to that of p-type 3C-SiC.

  17. Batch-fabricated high-performance graphene Hall elements

    PubMed Central

    Xu, Huilong; Zhang, Zhiyong; Shi, Runbo; Liu, Honggang; Wang, Zhenxing; Wang, Sheng; Peng, Lian-Mao

    2013-01-01

    Hall elements are by far the most widely used magnetic sensor. In general, the higher the mobility and the thinner the active region of the semiconductor used, the better the Hall device. While most common magnetic field sensors are Si-based Hall sensors, devices made from III-V compounds tend to favor over that based on Si. However these devices are more expensive and difficult to manufacture than Si, and hard to be integrated with signal-processing circuits for extending function and enforcing performance. In this article we show that graphene is intrinsically an ideal material for Hall elements which may harness the remarkable properties of graphene, i.e. extremely high carrier mobility and atomically thin active body, to create ideal magnetic sensors with high sensitivity, excellent linearity and remarkable thermal stability. PMID:23383375

  18. Safety halls--an evaluation.

    PubMed

    Nyberg, Anders; Gregersen, Nils Petter; Nolén, Sixten; Engström, Inger

    2005-01-01

    In most countries, drivers licensing systems usually include teaching some aspects of using safety equipment (e.g., airbags and seat belts). However, there is now evidence worldwide that such education is inadequate, as indicated by, for example, the overrepresentation of young drivers who do not use seat belts. A randomized controlled study was conducted in Sweden to evaluate the effects of visiting a facility known as a "safety hall" in combination with the mandatory skid training. The results were assessed to determine the effects of the knowledge and attitudes of learner drivers in the following subjects: airbags, securing loads, seat belts, sitting posture, speed, and tires. An experimental group and a control group comprising 658 and 668 learners, respectively, answered identical questionnaires on three different occasions (pretest, posttest 1, and posttest 2). The results show that, for most of the topics considered, knowledge and attitudes in both groups were better at posttest 2 than at the pretest, and in general, the best knowledge and attitudes were found in the experimental group. The combined safety/skid training seems to have had the greatest effect on seat belts and loads. The findings also indicate that the safety halls can be further improved to achieve an even better effect. The use of safety halls has improved the knowledge and attitudes of learner drivers concerning several important areas related to traffic safety. Since knowledge and attitudes are important predictors of behavior, implementing safety halls can be expected to lead to improvements, especially regarding the use of safety belts and securing loads.

  19. High magnetic field test of bismuth Hall sensors for ITER steady state magnetic diagnostic.

    PubMed

    Ďuran, I; Entler, S; Kohout, M; Kočan, M; Vayakis, G

    2016-11-01

    Performance of bismuth Hall sensors developed for the ITER steady state magnetic diagnostic was investigated for high magnetic fields in the range ±7 T. Response of the sensors to the magnetic field was found to be nonlinear particularly within the range ±1 T. Significant contribution of the planar Hall effect to the sensors output voltage causing undesirable cross field sensitivity was identified. It was demonstrated that this effect can be minimized by the optimization of the sensor geometry and alignment with the magnetic field and by the application of "current-spinning technique."

  20. Sheath oscillation characteristics and effect on near-wall conduction in a krypton Hall thruster

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang, Fengkui, E-mail: fengkuizhang@163.com; Kong, Lingyi; Li, Chenliang

    2014-11-15

    Despite its affordability, the krypton Hall-effect thruster in applications always had problems in regard to performance. The reason for this degradation is studied from the perspective of the near-wall conductivity of electrons. Using the particle-in-cell method, the sheath oscillation characteristics and its effect on near-wall conduction are compared in the krypton and xenon Hall-effect thrusters both with wall material composed of BNSiO{sub 2}. Comparing these two thrusters, the sheath in the krypton-plasma thruster will oscillate at low electron temperatures. The near-wall conduction current is only produced by collisions between electrons and wall, thereby causing a deficiency in the channel current.more » The sheath displays spatial oscillations only at high electron temperature; electrons are then reflected to produce the non-oscillation conduction current needed for the krypton-plasma thruster. However, it is accompanied with intensified oscillations.« less

  1. Particle-in-cell simulations of asymmetric guide-field reconnection: quadrupolar structure of Hall magnetic field

    NASA Astrophysics Data System (ADS)

    Schmitz, R. G.; Alves, M. V.; Barbosa, M. V. G.

    2017-12-01

    One of the most important processes that occurs in Earth's magnetosphere is known as magnetic reconnection (MR). This process can be symmetric or asymmetric, depending basically on the plasma density and magnetic field in both sides of the current sheet. A good example of symmetric reconnection in terrestrial magnetosphere occurs in the magnetotail, where these quantities are similar on the north and south lobes. In the dayside magnetopause MR is asymmetric, since the plasma regimes and magnetic fields of magnetosheath and magnetosphere are quite different. Symmetric reconnection has some unique signatures. For example, the formation of a quadrupolar structure of Hall magnetic field and a bipolar Hall electric field that points to the center of the current sheet. The different particle motions in the presence of asymmetries change these signatures, causing the quadrupolar pattern to be distorted and forming a bipolar structure. Also, the bipolar Hall electric field is modified and gives rise to a single peak pointing toward the magnetosheat, considering an example of magnetopause reconnection. The presence of a guide-field can also distort the quadrupolar pattern, by giving a shear angle across the current sheet and altering the symmetric patterns, according to previous simulations and observations. Recently, a quadrupolar structure was observed in an asymmetric guide-field MR event using MMS (Magnetospheric Multiscale) mission data [Peng et al., JGR, 2017]. This event shows clearly that the density asymmetry and the guide-field were not sufficient to form signatures of asymmetric reconnection. Using the particle-in-cell code iPIC3D [Markidis et al, Mathematics and Computers in Simulation, 2010] with the MMS data from this event used to define input parameters, we found a quadrupolar structure of Hall magnetic field and a bipolar pattern of Hall electric field in ion scales, showing that our results are in an excellent agreement with the MMS observations. To our

  2. Ion Engine and Hall Thruster Development at the NASA Glenn Research Center

    NASA Technical Reports Server (NTRS)

    Domonkos, Matthew T.; Patterson, Michael J.; Jankovsky, Robert S.

    2002-01-01

    NASA's Glenn Research Center has been selected to lead development of NASA's Evolutionary Xenon Thruster (NEXT) system. The central feature of the NEXT system is an electric propulsion thruster (EPT) that inherits the knowledge gained through the NSTAR thruster that successfully propelled Deep Space 1 to asteroid Braille and comet Borrelly, while significantly increasing the thruster power level and making improvements in performance parameters associated with NSTAR. The EPT concept under development has a 40 cm beam diameter, twice the effective area of the Deep-Space 1 thruster, while maintaining a relatively-small volume. It incorporates mechanical features and operating conditions to maximize the design heritage established by the flight NSTAR 30 cm engine, while incorporating new technology where warranted to extend the power and throughput capability. The NASA Hall thruster program currently supports a number of tasks related to high power thruster development for a number of customers including the Energetics Program (formerly called the Space-based Program), the Space Solar Power Program, and the In-space Propulsion Program. In program year 2002, two tasks were central to the NASA Hall thruster program: 1.) the development of a laboratory Hall thruster capable of providing high thrust at high power; 2.) investigations into operation of Hall thrusters at high specific impulse. In addition to these two primary thruster development activities, there are a number of other on-going activities supported by the NASA Hall thruster program, These additional activities are related to issues such as thruster lifetime and spacecraft integration.

  3. The effect of segmented anodes on the performance and plume of a Hall thruster

    NASA Astrophysics Data System (ADS)

    Kieckhafer, Alexander W.

    Development of alternative propellants for Hall thruster operation is an active area of research. Xenon is the current propellant of choice for Hall thrusters, but can be costly in large thrusters and for extended test periods. Condensible propellants may offer an alternative to xenon, as they will not require costly active pumping to remove from a test facility, and may be less expensive to purchase. A method has been developed which uses segmented electrodes in the discharge channel of a Hall thruster to divert discharge current to and from the main anode and thus control the anode temperature. By placing a propellant reservoir in the anode, the evaporation rate, and hence, mass flow of propellant can be controlled. Segmented electrodes for thermal control of a Hall thruster represent a unique strategy of thruster design, and thus the performance of the thruster must be measured to determine the effect the electrodes have on the thruster. Furthermore, the source of any changes in thruster performance due to the adjustment of discharge current between the shims and the main anode must be characterized. A Hall thruster was designed and constructed with segmented electrodes. It was then tested at anode voltages between 300 and 400 V and mass flows between 4 and 6 mg/s, as well as 100%, 75%, 50%, 25%, and <5% of the discharge current on the shim electrodes. The level of current on the shims was adjusted by changing the shim voltage. At each operating point, the thruster performance, plume divergence, ion energy, and multiply charged ion fraction were measured. Thruster performance exhibited a small change with the level of discharge current on the shim electrodes. Thrust and specific impulse increased by as much as 6% and 7.7%, respectively, as discharge current was shifted from the main anode to the shims at constant anode voltage. Thruster efficiency did not change. Plume divergence was reduced by approximately 4 degrees of half-angle at high levels of current on

  4. Numerical study of magnetohydrodynamic viscous plasma flow in rotating porous media with Hall currents and inclined magnetic field influence

    NASA Astrophysics Data System (ADS)

    Bég, O. Anwar; Sim, Lik; Zueco, J.; Bhargava, R.

    2010-02-01

    A numerical solution is developed for the viscous, incompressible, magnetohydrodynamic flow in a rotating channel comprising two infinite parallel plates and containing a Darcian porous medium, the plates lying in the x-z plane, under constant pressure gradient. The system is subjected to a strong, inclined magnetic field orientated to the positive direction of the y-axis (rotational axis, normal to the x-z plane). The Navier-Stokes flow equations for a general rotating hydromagnetic flow are reduced to a pair of linear, viscous partial differential equations neglecting convective acceleration terms, for primary velocity (u‧) and secondary velocity (v‧) where these velocities are directed along the x and y axes. Only viscous terms are retained in the momenta equations. The model is non-dimensionalized and shown to be controlled by a number of dimensionless parameters. The resulting dimensionless ordinary differential equations are solved using a robust numerical method, Network Simulation Methodology. Full details of the numerics are provided. The present solutions are also benchmarked against the analytical solutions presented recently by Ghosh and Pop [Ghosh SK, Pop I. An analytical approach to MHD plasma behaviour of a rotating environment in the presence of an inclined magnetic field as compared to excitation frequency. Int J Appl Mech Eng 2006;11(4):845-856] for the case of a purely fluid medium (infinite permeability). We study graphically the influence of Hartmann number (Ha, magnetic field parameter), Ekman number (Ek, rotation parameter), Hall current parameter (Nh), Darcy number (Da, permeability parameter), pressure gradient (Np) and also magnetic field inclination (θ) on primary and secondary velocity fields. Additionally we investigate the effects of these multiphysical parameters on the dimensionless shear stresses at the plates. Both primary and secondary velocity are seen to be increased with a rise in Darcy number, owing to a simultaneous

  5. Integration Tests of the 4 kW-Class High Voltage Hall Accelerator Power Processing Unit with the HiVHAc and the SPT-140 Hall Effect Thrusters

    NASA Technical Reports Server (NTRS)

    Kamhawi, Hani; Pinero, Luis; Haag, Thomas; Huang, Wensheng; Ahern, Drew; Liang, Ray; Shilo, Vlad

    2016-01-01

    NASA's Science Mission Directorate is sponsoring the development of a 4 kW-class Hall propulsion system for implementation in NASA science and exploration missions. The main components of the system include the High Voltage Hall Accelerator (HiVHAc), an engineering model power processing unit (PPU) developed by Colorado Power Electronics, and a xenon flow control module (XFCM) developed by VACCO Industries. NASA Glenn Research Center is performing integrated tests of the Hall thruster propulsion system. This paper presents results from integrated tests of the PPU and XFCM with the HiVHAc engineering development thruster and a SPT-140 thruster provided by Space System Loral. The results presented in this paper demonstrate thruster discharge initiation along with open-loop and closed-loop control of the discharge current with anode flow for both the HiVHAc and the SPT-140 thrusters. Integrated tests with the SPT-140 thruster indicated that the PPU was able to repeatedly initiate the thruster's discharge, achieve steady state operation, and successfully throttle the thruster between 1.5 and 4.5 kW. The measured SPT-140 performance was identical to levels reported by Space Systems Loral.

  6. Integration Tests of the 4 kW-class High Voltage Hall Accelerator Power Processing Unit with the HiVHAc and the SPT-140 Hall Effect Thrusters

    NASA Technical Reports Server (NTRS)

    Kamhawi, Hani; Pinero, Luis; Haag, Thomas; Huang, Wensheng; Ahern, Drew; Liang, Ray; Shilo, Vlad

    2016-01-01

    NASAs Science Mission Directorate is sponsoring the development of a 4 kW-class Hall propulsion system for implementation in NASA science and exploration missions. The main components of the system include the High Voltage Hall Accelerator (HiVHAc), an engineering model power processing unit (PPU) developed by Colorado Power Electronics, and a xenon flow control module (XFCM) developed by VACCO Industries. NASA Glenn Research Center is performing integrated tests of the Hall thruster propulsion system. This presentation presents results from integrated tests of the PPU and XFCM with the HiVHAc engineering development thruster and a SPT-140 thruster provided by Space System Loral. The results presented in this paper demonstrate thruster discharge initiation, open-loop and closed-loop control of the discharge current with anode flow for both the HiVHAc and the SPT-140 thrusters. Integrated tests with the SPT-140 thruster indicated that the PPU was able to repeatedly initiate the thrusters discharge, achieve steady state operation, and successfully throttle the thruster between 1.5 and 4.5 kW. The measured SPT-140 performance was identical to levels reported by Space Systems Loral.

  7. Spin-pumping and spin-Hall magnetoresistance (SMR) at transition metal interfaces: case of (Co/Pt) (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Jaffres, Henri; George, Jean-Marie; Laczowski, Piotr; Reyren, Nicolas; Vila, Laurent

    2016-10-01

    Spintronic phenomena are made possible via the diffusion of spin-currents or the generation of spin-accumulation. Spinorbitronics uses the electronic spin-orbit coupling (SOC) and emerges as a new route to create spin-currents in the transverse direction of the charge flow. This is made possible via the intrinsic spin Hall conduction (SHE) of heavy metals or extrinsic spin-Hall effect of metallic alloys. SHE borrows its concept from the anomalous Hall effect (AHE) where the relativistic spin-orbit coupling (SOC) promotes an asymmetric deflection of the spin-current. SHE is now at the base of magnetization commutation and domain wall moving via spin-orbit torque (SOT) and spin-transfer torque operations in the FMR regime. However, the exact anatomy of SOT at spin-orbit active interfaces like Co/Pt is still missing. In the case of Pt, recent studies have put forward the major role played by i) the spin-memory loss (SML) and the electronic transparency at 3d/5d interfaces and ii) the inhomogeneity of the conductivity in the current-in-plane (CIP) geometry to explain the discrepancy in the SHE. Ingredients to consider then are the profiles of both the conductivity and spin-current across the multilayers and spin-transmission. In this talk, we will present robust SMR measurements observed on NiCo/Pt multilayer stacks characterized by a perpendicular magnetic anisotropy (PMA). The SMR occurs for both in-plane magnetization rotation or from nominal out-of-plane to the in-plane direction transverse to the current flow. This clearly departs from standard AMR or pure interfacial anisotropic-AMR symmetries. We analyze in large details our SMR signals for the whole series of samples owing to two main guidelines: i) we consider the exact conductivity profile across the multilayers, in particular near the Co/Pt interface, via the Camley-Barnas approach and ii) we derive the spin current profile generated by SHE along the perpendicular direction responsible for SMR. We consider

  8. Simmons Hall, Massachusetts.

    ERIC Educational Resources Information Center

    Amelar, Sarah

    2003-01-01

    Describes the design of Simmons Hall, an undergraduate dormitory at the Massachusetts Institute of Technology, including the educational context and design goals. Includes information on the architects, as well as floor plans and photographs. (EV)

  9. The spin-Hall effect and spin-orbit torques in epitaxial Co2FeAl/platinum bilayers

    NASA Astrophysics Data System (ADS)

    Peterson, T. A.; Liu, C.; McFadden, T.; Palmstrøm, C. J.; Crowell, P. A.

    We have performed magnetoresistance measurements on epitaxially grown Co2FeAl/platinum (CFA/Pt) ultrathin ferromagnet/heavy metal bilayers to study the spin-Hall effect in Pt and the accompanying spin-orbit torque (SOT) exerted on the magnetic CFA layer. Specifically, we measure the spin-Hall magnetoresistance in the Pt layer by changing the orientation of the CFA magnetization with respect to the spin current orientation created in the Pt, and we determine the SOT efficiency using a second-harmonic detection technique. Because the latter of the two measurements is proportional to the spin-Hall ratio θSHE while the former is proportional to θSHE2, we are able to extract the bare Pt spin-Hall ratio with no assumptions about the CFA/Pt interface spin mixing conductance. Furthermore, by varying the Pt thickness we show that the results are consistent with resistivity-independent spin-Hall conductivity. Finally, the two measurements in combination allow us to infer a spin-mixing conductance at the CFA/Pt interface of 2 +/- 1 ×1015Ω-1m-2 . The combination of spin-Hall magnetoresistance and SOT measurements allows for a determination of the spin-mixing conductance using only low-frequency transport techniques. This work was supported by STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

  10. A Behavioral Weight Control Program for Residence Hall Students.

    ERIC Educational Resources Information Center

    Domke, Jane A.; And Others

    1981-01-01

    Compared a weight control treatment specifically tailored to the needs of residence hall students with a standardized behavioral procedure. Although posttreatment results indicated a very slight and nonsignificant advantage for the residence hall condition, this was not true at follow-up. Suggests the residence hall procedure may be overly…

  11. Experimental and Numerical Examination of a Hall Thruster Plume (Preprint)

    DTIC Science & Technology

    2007-07-31

    Hall thruster has been characterized through measurements from various plasma electrostatic probes. Ion current flux, plasma potential, plasma density, and electron temperatures were measured from the near-field plume to 60 cm downstream of the exit plane. These experimentally derived measurements were compared to numerical simulations run with the plasma plume code DRACO. A major goal of this study was to determine the fidelity of the DRACO numerical simulation. The effect of background pressure on the thruster plume was also examined using ion current flux measurements

  12. Topological Hall Effect in Skyrmions: A Nonequilibrium Coherent Transport Approach

    NASA Astrophysics Data System (ADS)

    Yin, Gen; Zang, Jiadong; Lake, Roger

    2014-03-01

    Skyrmion is a topological spin texture recently observed in many materials with broken inversion symmetry. In experiments, one effective method to detect the skyrmion crystal phase is the topological Hall measurement. At adiabatic approximation, previous theoretical studies show that the Hall signal is provided by an emergent magnetic field, which explains the topological Hall effect in the classical level. Motivated by the potential device application of skyrmions as digital bits, it is important to understand the topological Hall effect in the mesoscopic level, where the electron coherence should be considered. In this talk, we will discuss the quantum aspects of the topological Hall effect on a tight binding setup solved by nonequilibrium Green's function (NEGF). The charge distribution, Hall potential distribution, thermal broadening effect and the Hall resistivity are investigated in detail. The relation between the Hall resistance and the DM interaction is investigated. Driven by the spin transferred torque (SST), Skyrmion dynamics is previously studied within the adiabatic approximation. At the quantum transport level, this talk will also discuss the non-adiabatic effect in the skyrmion motion with the presence of the topological Hall effect. This material is based upon work supported by the National Science Foundation under Grant Nos. NSF 1128304 and NSF 1124733. It was also supported in part by FAME, one of six centers of STARnet, an SRC program sponsored by MARCO and DARPA.

  13. Training Top 10 Hall of Fame

    ERIC Educational Resources Information Center

    Training, 2012

    2012-01-01

    Microsoft Corporation and SCC Soft Computer are the newest inductees into the Training Top 10 Hall of Fame, joining the ranks of the 11 companies named to the hall since its inception in 2008 (Wyeth Pharmaceuticals subsequently was acquired by Pfizer Inc. in 2009). These 11 companies held Top 10 spots in the Training Top 50, Top 100, and now Top…

  14. Compact High Current Rare-Earth Emitter Hollow Cathode for Hall Effect Thrusters

    NASA Technical Reports Server (NTRS)

    Goebel, Dan M. (Inventor); Watkins, Ronnie M. (Inventor); Hofer, Richard R. (Inventor)

    2012-01-01

    An apparatus and method for achieving an efficient central cathode in a Hall effect thruster is disclosed. A hollow insert disposed inside the end of a hollow conductive cathode comprises a rare-earth element and energized to emit electrons from an inner surface. The cathode employs an end opening having an area at least as large as the internal cross sectional area of the rare earth insert to enhance throughput from the cathode end. In addition, the cathode employs a high aspect ratio geometry based on the cathode length to width which mitigates heat transfer from the end. A gas flow through the cathode and insert may be impinged by the emitted electrons to yield a plasma. One or more optional auxiliary gas feeds may also be employed between the cathode and keeper wall and external to the keeper near the outlet.

  15. 5. ROOFTOPS, ISHERWOOD HALL (BUILDING NO. 104), GRIFFIN (BUILDING NO. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. ROOFTOPS, ISHERWOOD HALL (BUILDING NO. 104), GRIFFIN (BUILDING NO. 110), MELVILLE HALL (BUILDING NO. 116) LOOKING WEST FROM CLOCK TOWER OF MAHAN HALL - U.S. Naval Academy, Annapolis, Anne Arundel County, MD

  16. Persistent Hall voltages across thin planar charged quantum rings on the surface of a topological insulator

    NASA Astrophysics Data System (ADS)

    Durganandini, P.

    2015-03-01

    We consider thin planar charged quantum rings on the surface of a three dimensional topological insulator coated with a thin ferromagnetic layer. We show theoretically, that when the ring is threaded by a magnetic field, then, due to the Aharanov-Bohm effect, there are not only the well known circulating persistent currents in the ring but also oscillating persistent Hall voltages across the thin ring. Such oscillating persistent Hall voltages arise due to the topological magneto-electric effect associated with the axion electrodynamics exhibited by the surface electronic states of the three dimensional topological insulator when time reversal symmetry is broken. We further generalize to the case of dipole currents and show that analogous Hall dipole voltages arise. We also discuss the robustness of the effect and suggest possible experimental realizations in quantum rings made of semiconductor heterostructures. Such experiments could also provide new ways of observing the predicted topological magneto-electric effect in three dimensional topological insulators with time reversal symmetry breaking. I thank BCUD, Pune University, Pune for financial support through research grant.

  17. Anomalous Hall effect in calcium-doped lanthanum cobaltite and gadolinium

    NASA Astrophysics Data System (ADS)

    Baily, Scott Alan

    The physical origin of the anomalous (proportional to magnetization) Hall effect is not very well understood. While many theories account for a Hall effect proportional to the magnetization of a material, these theories often predict effects significantly smaller than those found in ferromagnetic materials. An even more significant deficiency of the conventional theories is that they predict an anomalous Hall resistivity that is proportional to a power of the resistivity, and in the absence of a metal insulator transition cannot account for the anomalous Hall effect that peaks near TC. Recent models based on a geometric, or Berry, phase have had a great deal of success describing the anomalous Hall effect in double-exchange systems (e.g., lanthanum manganite and chromium dioxide). In gadolinium, as in double-exchange magnets, the exchange interaction is mediated by the conduction electrons and the anomalous Hall effect may therefore resemble that of CrO2 and other metallic double-exchange ferromagnets. Lanthanum cobaltite is similar to manganite in many ways, but a strong double-exchange interaction is not present. Calcium-doped lanthanum cobaltite films were found to have the largest anomalous Hall effect of any ferromagnetic metal. The primary purpose of this study is to gain insight into the origin of the anomalous Hall effect with the hope that these theories can be extended to account for the effect in other materials. The Hall resistivity, magnetoresistance, and magnetization of a Gadolinium single crystal were measured in fields up to 30 T. Cobaltite films were grown via laser ablation and characterized by a variety of techniques. Hall resistivity, magnetoresistance, magnetization, and magnetothermopower of L 1-xCaxCoO3 samples with 0.15 < x < 0.4 were measured in fields up to 7 T. The Gd results suggest that Berry's phase contributes partially to the Hall effect near TC. Berry's phase theories hold promise for explaining the large anomalous Hall effect in

  18. Performance of an 8 kW Hall Thruster

    DTIC Science & Technology

    2000-01-12

    For the purpose of either orbit raising and/or repositioning the Hall thruster must be capable of delivering sufficient thrust to minimize transfer...time. This coupled with the increasing on-board electric power capacity of military and commercial satellites, requires a high power Hall thruster that...development of a novel, high power Hall thruster , capable of efficient operation over a broad range of Isp and thrust. We call such a thruster the bi

  19. Kinetic Alfven wave explanation of the Hall signals in magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Dai, L.; Wang, C.; Zhang, Y.; Duan, S.; Lavraud, B.; Burch, J. L.; Pollock, C.; Torbert, R. B.

    2017-12-01

    Magnetic reconnection is initiated in a small diffusion region but can drive global-scale dynamics in Earth's magnetosphere, solar flares, and astrophysical systems. Understanding the processes at work in the diffusion region remains a main challenge in space plasma physics. Recent in-situ observations from MMS and THEMIS reveal that the electric field normal to the reconnection current layer, often called the Hall electric field (En), is mainly balanced by the ion pressure gradient. Here we present theoretical explanations indicating that this observation fact is a manifestation of Kinetic Alfven Waves (KAW) physics. The ion pressure gradient represents the finite gyroradius effect of KAW, leading to ion intrusion across the magnetic field lines. Electrons stream along the magnetic field lines to track ions, resulting in field-aligned currents and the associated pattern of the out-of-plane Hall magnetic field (Bm). The ratio En/Bm is on the order of the Alfven speed, as predicted by the KAW theory. The KAW physics further provides new perspectives on how ion intrusion may trigger electric fields suitable for reconnection to occur.

  20. Effect of segmented electrode length on the performances of Hall thruster

    NASA Astrophysics Data System (ADS)

    Duan, Ping; Chen, Long; Liu, Guangrui; Bian, Xingyu; Yin, Yan

    2016-09-01

    The influences of the low-emissive graphite segmented electrode placed near the channel exit on the discharge characteristics of Hall thruster are studied using the particle-in-cell method. A two-dimensional physical model is established according to the Hall thruster discharge channel configuration. The effects of electrode length on potential, ion density, electron temperature, ionization rate and discharge current are investigated. It is found that, with the increasing of segmented electrode length, the equipotential lines bend towards the channel exit, and approximately parallel to the wall at the channel surface, radial velocity and radial flow of ions are increased, and the electron temperature is also enhanced. Due to the conductive characteristic of electrodes, the radial electric field and the axial electron conductivity near the wall are enhanced, and the probability of the electron-atom ionization is reduced, which leads to the degradation of ionization rate in discharge channel. However, the interaction between electrons and the wall enhances the near wall conductivity, therefore the discharge current grows along with the segmented electrode length, and the performance of the thruster is also affected.

  1. Anomalous spin Hall magnetoresistance in Pt/Co bilayers

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Masashi; Towa, Daiki; Lau, Yong-Chang; Takahashi, Saburo; Hayashi, Masamitsu

    2018-05-01

    We have studied the spin Hall magnetoresistance (SMR), the magnetoresistance within the plane transverse to the current flow, of Pt/Co bilayers. We find that the SMR increases with increasing Co thickness: the effective spin Hall angle for bilayers with thick Co exceeds the reported values of Pt when a conventional drift-diffusion model is used. An extended model including spin transport within the Co layer cannot account for the large SMR. To identify its origin, contributions from other sources are studied. For most bilayers, the SMR increases with decreasing temperature and increasing magnetic field, indicating that magnon-related effects in the Co layer play little role. Without the Pt layer, we do not observe the large SMR found for the Pt/Co bilayers with thick Co. Implementing the effect of the so-called interface magnetoresistance and the textured induced anisotropic scattering cannot account for the Co thickness dependent SMR. Since the large SMR is present for W/Co but its magnitude reduces in W/CoFeB, we infer that its origin is associated with a particular property of Co.

  2. Spin injection and detection via the anomalous spin Hall effect of a ferromagnetic metal

    NASA Astrophysics Data System (ADS)

    Das, K. S.; Schoemaker, W. Y.; van Wees, B. J.; Vera-Marun, I. J.

    2017-12-01

    We report a spin injection and detection mechanism via the anomalous Hall effect in a ferromagnetic metal. The anomalous spin Hall effect (ASHE) refers to the transverse spin current generated within the ferromagnet. We utilize the ASHE and its reciprocal effect to electrically inject and detect magnons in a magnetic insulator (yttrium iron garnet) in a nonlocal geometry. Our experiments reveal that permalloy has a comparable spin injection and detection efficiency to that of platinum, owing to the ASHE. We also demonstrate the tunability of the ASHE via the orientation of the permalloy magnetization, thus creating possibilities for spintronic applications.

  3. Redundant speed control for brushless Hall effect motor

    NASA Technical Reports Server (NTRS)

    Nola, F. J. (Inventor)

    1973-01-01

    A speed control system for a brushless Hall effect device equipped direct current (D.C.) motor is described. Separate windings of the motor are powered by separate speed responsive power sources. A change in speed, upward or downward, because of the failure of a component of one of the power sources results in a corrective signal being generated in the other power source to supply an appropriate power level and polarity to one winding to cause the motor to be corrected in speed.

  4. Measured Early Lateral Energy Fractions in Concert Halls and Opera Houses

    NASA Astrophysics Data System (ADS)

    BARRON, M.

    2000-04-01

    In the 30 years since early lateral reflections were first suggested as important for concert halls, spatial impression and source broadening have become almost universally accepted as essential characteristics of halls with good acoustics. Two objective measures of source broadening have been proposed. Measured values of the best defined of these measures, the early lateral energy fraction (LF), are considered here. Results from two independent measurement surveys are discussed. Comparisons of LF values by hall show a significant link between hall mean LF and hall width. There is however considerable overlap between measured LF values in different halls so the relevance of describing halls by their mean early lateral energy fraction values is questionable. The behaviour of LF values within auditoria is discussed for different concert hall plan forms and within opera houses. A measure of source broadening including sound level is proposed and results considered in the context of auditorium design.

  5. Destruction of the Fractional Quantum Hall Effect by Disorder

    DOE R&D Accomplishments Database

    Laughlin, R. B.

    1985-07-01

    It is suggested that Hall steps in the fractional quantum Hall effect are physically similar to those in the ordinary quantum Hall effect. This proposition leads to a simple scaling diagram containing a new type of fixed point, which is identified with the destruction of the fractional states by disorder. 15 refs., 3 figs.

  6. 27. FIRST FLOOR CENTRAL HALL, EAST WALL, DETAIL OF ENTABLATURE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    27. FIRST FLOOR CENTRAL HALL, EAST WALL, DETAIL OF ENTABLATURE SHOWING EGG AND DART OVOLO AND GUTTAE OF THE THIRD MUTULE FROM THE SOUTHEAST CORNER - Independence Hall Complex, Independence Hall, 500 Chestnut Street, Philadelphia, Philadelphia County, PA

  7. Intrinsic quantum spin Hall and anomalous Hall effects in h-Sb/Bi epitaxial growth on a ferromagnetic MnO2 thin film.

    PubMed

    Zhou, Jian; Sun, Qiang; Wang, Qian; Kawazoe, Yoshiyuki; Jena, Puru

    2016-06-07

    Exploring a two-dimensional intrinsic quantum spin Hall state with a large band gap as well as an anomalous Hall state in realizable materials is one of the most fundamental and important goals for future applications in spintronics, valleytronics, and quantum computing. Here, by combining first-principles calculations with a tight-binding model, we predict that Sb or Bi can epitaxially grow on a stable and ferromagnetic MnO2 thin film substrate, forming a flat honeycomb sheet. The flatness of Sb or Bi provides an opportunity for the existence of Dirac points in the Brillouin zone, with its position effectively tuned by surface hydrogenation. The Dirac points in spin up and spin down channels split due to the proximity effects induced by MnO2. In the presence of both intrinsic and Rashba spin-orbit coupling, we find two band gaps exhibiting a large band gap quantum spin Hall state and a nearly quantized anomalous Hall state which can be tuned by adjusting the Fermi level. Our findings provide an efficient way to realize both quantized intrinsic spin Hall conductivity and anomalous Hall conductivity in a single material.

  8. Establishment of a Hall Thruster Cluster

    DTIC Science & Technology

    2004-02-01

    DURIP funds were used to develop a Hall thruster cluster test facility centered around the University of Michigan Large Vacuum Test Facility and a 2x2 cluster of BUSEK 600 W BHT-600 Hall thrusters. This capability will facilitate our three-year program to address the issue of high-power CDT operation and to provide insight on how chamber effects influence CDT engine/cluster characteristics.

  9. Current sheet extension and reconnection scaling in collisionless, hyperresistive, Hall MHD

    NASA Astrophysics Data System (ADS)

    Sullivan, B. P.; Bhattacharjee, A.; Huang, Y. M.

    2009-11-01

    We present Sweet-Parker type scaling arguments in the context of collisionless, hyper-resistive, Hall magnetohyrdodynamics (MHD). The predicted steady state scalings are consistent with those found by Chac'on et al. [PRL 99, 235001 (2007)], and Uzdensky, [PoP 16, 040702 (2009)], though our methods differ slightly. As with those studies, no prediction of electron dissipation region length is made. Numerical experiments confirm that both cusp like & extended geometries are realizable. Importantly, the length of the electron dissipation region (taken as a parameter by several recent studies) is found to depend on the level of hyper-resistivity. Although hyper-resistivity can produce modestly extended dissipation regions, the dissipation regions observed here are much shorter than those seen in many kinetic studies. The thickness of the dissipation region scales in a similar way as the length,so that the reconnection rate is not strongly sensitive to the level of hyperresistivity. The length of the electron dissipation region depends on electron inertia as well.The limitations of scaling theories that do not predict the length of the electron dissipation region are emphasized.

  10. Instabilities and transport in Hall plasmas with ExB drift

    NASA Astrophysics Data System (ADS)

    Smolyakov, Andrei

    2016-10-01

    Low temperature plasma with moderate magnetic field, where the ions are not or just weakly magnetized, i.e. the ion Larmor radius being larger or comparable to the characteristic length scale of interest (e.g. the size ofthe system), have distinctly different properties from strongly magnetized plasmas such as that for fusion applications. Such parameters regimes are generally defined here as Hall plasmas. The natural scale separation between the ion and electron Larmor radii in Hall plasma, further exploited by the application of the external electric field, offers unique applications in various plasma devices for material processing and electric propulsion. Plasmas in such devices are in strongly non-equilibrium state making it prone to a number of instabilities. This talk presents physics description of the dominant unstable modes in ExB Hall plasmas resulting in highly turbulent state with nonlinear coherent structures and anomalous electron current. Since ions are un-magnetized, fundamental instabilities operating in low temperature Hall plasmas are very different from much studied gradients (density, temperature and magnetic field) driven drift-wave turbulence in strongly magnetized plasmas for fusion applications. As a result the nonlinear saturation mechanisms, role of the ExB shear flows are also markedly different in such plasmas. We review the basic instabilities in these plasmas which are related to the ion-sound, low-hybrid and anti-drift modes, discuss nonlinear saturation and anomalous transport mechanisms. The advanced nonlinear fluid model for such plasmas and results of nonlinear simulations of turbulence and anomalous transport performed within a modified BOUT++ framework will be presented. Research supported by NSERC Canada and US AFOSR FA9550-15-1-0226.

  11. Non-volatile logic gates based on planar Hall effect in magnetic films with two in-plane easy axes.

    PubMed

    Lee, Sangyeop; Bac, Seul-Ki; Choi, Seonghoon; Lee, Hakjoon; Yoo, Taehee; Lee, Sanghoon; Liu, Xinyu; Dobrowolska, M; Furdyna, Jacek K

    2017-04-25

    We discuss the use of planar Hall effect (PHE) in a ferromagnetic GaMnAs film with two in-plane easy axes as a means for achieving novel logic functionalities. We show that the switching of magnetization between the easy axes in a GaMnAs film depends strongly on the magnitude of the current flowing through the film due to thermal effects that modify its magnetic anisotropy. Planar Hall resistance in a GaMnAs film with two in-plane easy axes shows well-defined maxima and minima that can serve as two binary logic states. By choosing appropriate magnitudes of the input current for the GaMnAs Hall device, magnetic logic functions can then be achieved. Specifically, non-volatile logic functionalities such as AND, OR, NAND, and NOR gates can be obtained in such a device by selecting appropriate initial conditions. These results, involving a simple PHE device, hold promise for realizing programmable logic elements in magnetic electronics.

  12. L'effet Hall Quantique

    NASA Astrophysics Data System (ADS)

    Samson, Thomas

    Nous proposons une methode permettant d'obtenir une expression pour la conductivite de Hall de structures electroniques bidimensionnelles et nous examinons celle -ci a la limite d'une temperature nulle dans le but de verifier l'effet Hall quantique. Nous allons nous interesser essentiellement a l'effet Hall quantique entier et aux effets fractionnaires inferieurs a un. Le systeme considere est forme d'un gaz d'electrons en interaction faible avec les impuretes de l'echantillon. Le modele du gaz d'electrons consiste en un gaz bidimensionnel d'electrons sans spin expose perpendiculairement a un champ magnetique uniforme. Ce dernier est decrit par le potentiel vecteur vec{rm A} defini dans la jauge de Dingle ou jauge symetrique. Conformement au formalisme de la seconde quantification, l'hamiltonien de ce gaz est represente dans la base des etats a un-corps de Dingle |n,m> et exprime ainsi en terme des operateurs de creation et d'annihilation correspondants a_sp{ rm n m}{dag} et a _{rm n m}. Nous supposons de plus que les electrons du niveau fondamental de Dingle interagissent entre eux via le potentiel coulombien. La methode utilisee fait appel a une equation mai tresse a N-corps, de nature quantique et statistique, et verifiant le second principe de la thermodynamique. A partir de celle-ci, nous obtenons un systeme d'equations differentielles appele hierarchie d'equations quantique dont la resolution nous permet de determiner une equation a un-corps, dite de Boltzmann quantique, et dictant l'evolution de la moyenne statistique de l'operateur non-diagonal a _sp{rm n m}{dag } a_{rm n}, _{rm m}, sous l'action du champ electrique applique vec{rm E}(t). C'est sa solution Tr(p(t) a _sp{rm n m}{dag} a_{rm n},_ {rm m}), qui definit la relation de convolution entre la densite courant de Hall vec{rm J}_{rm H }(t) et le champ electrique vec {rm E}(t) dont la transformee de Laplace-Fourier du noyau nous fournit l'expression de la conductivite de Hall desiree. Pour une valeur de

  13. Deficiency of the bulk spin Hall effect model for spin-orbit torques in magnetic-insulator/heavy-metal heterostructures

    NASA Astrophysics Data System (ADS)

    Li, Junxue; Yu, Guoqiang; Tang, Chi; Liu, Yizhou; Shi, Zhong; Liu, Yawen; Navabi, Aryan; Aldosary, Mohammed; Shao, Qiming; Wang, Kang L.; Lake, Roger; Shi, Jing

    2017-06-01

    Electrical currents in a magnetic-insulator/heavy-metal heterostructure can induce two simultaneous effects, namely, spin Hall magnetoresistance (SMR) on the heavy-metal side and spin-orbit torques (SOTs) on the magnetic-insulator side. Within the framework of a pure spin current model based on the bulk spin Hall effect (SHE), the ratio of the spin Hall-induced anomalous Hall effect (SH-AHE) to SMR should be equal to the ratio of the fieldlike torque (FLT) to the dampinglike torque (DLT). We perform a quantitative study of SMR, SH-AHE, and SOTs in a series of thulium iron garnet/platinum or T m3F e5O12/Pt heterostructures with different T m3F e5O12 thicknesses, where T m3F e5O12 is a ferrimagnetic insulator with perpendicular magnetic anisotropy. We find the ratio between the measured effective fields of FLT and DLT is at least two times larger than the ratio of the SH-AHE to SMR. In addition, the bulk SHE model grossly underestimates the spin-torque efficiency of FLT. Our results reveal deficiencies of the bulk SHE model and also address the importance of interfacial effects such as the Rashba and magnetic proximity effects in magnetic-insulator/heavy-metal heterostructures.

  14. Piezo Voltage Controlled Planar Hall Effect Devices

    PubMed Central

    Zhang, Bao; Meng, Kang-Kang; Yang, Mei-Yin; Edmonds, K. W.; Zhang, Hao; Cai, Kai-Ming; Sheng, Yu; Zhang, Nan; Ji, Yang; Zhao, Jian-Hua; Zheng, Hou-Zhi; Wang, Kai-You

    2016-01-01

    The electrical control of the magnetization switching in ferromagnets is highly desired for future spintronic applications. Here we report on hybrid piezoelectric (PZT)/ferromagnetic (Co2FeAl) devices in which the planar Hall voltage in the ferromagnetic layer is tuned solely by piezo voltages. The change of planar Hall voltage is associated with magnetization switching through 90° in the plane under piezo voltages. Room temperature magnetic NOT and NOR gates are demonstrated based on the piezo voltage controlled Co2FeAl planar Hall effect devices without the external magnetic field. Our demonstration may lead to the realization of both information storage and processing using ferromagnetic materials. PMID:27329068

  15. Piezo Voltage Controlled Planar Hall Effect Devices.

    PubMed

    Zhang, Bao; Meng, Kang-Kang; Yang, Mei-Yin; Edmonds, K W; Zhang, Hao; Cai, Kai-Ming; Sheng, Yu; Zhang, Nan; Ji, Yang; Zhao, Jian-Hua; Zheng, Hou-Zhi; Wang, Kai-You

    2016-06-22

    The electrical control of the magnetization switching in ferromagnets is highly desired for future spintronic applications. Here we report on hybrid piezoelectric (PZT)/ferromagnetic (Co2FeAl) devices in which the planar Hall voltage in the ferromagnetic layer is tuned solely by piezo voltages. The change of planar Hall voltage is associated with magnetization switching through 90° in the plane under piezo voltages. Room temperature magnetic NOT and NOR gates are demonstrated based on the piezo voltage controlled Co2FeAl planar Hall effect devices without the external magnetic field. Our demonstration may lead to the realization of both information storage and processing using ferromagnetic materials.

  16. Hall viscosity and geometric response in the Chern-Simons matrix model of the Laughlin states

    NASA Astrophysics Data System (ADS)

    Lapa, Matthew F.; Hughes, Taylor L.

    2018-05-01

    We study geometric aspects of the Laughlin fractional quantum Hall (FQH) states using a description of these states in terms of a matrix quantum mechanics model known as the Chern-Simons matrix model (CSMM). This model was proposed by Polychronakos as a regularization of the noncommutative Chern-Simons theory description of the Laughlin states proposed earlier by Susskind. Both models can be understood as describing the electrons in a FQH state as forming a noncommutative fluid, i.e., a fluid occupying a noncommutative space. Here, we revisit the CSMM in light of recent work on geometric response in the FQH effect, with the goal of determining whether the CSMM captures this aspect of the physics of the Laughlin states. For this model, we compute the Hall viscosity, Hall conductance in a nonuniform electric field, and the Hall viscosity in the presence of anisotropy (or intrinsic geometry). Our calculations show that the CSMM captures the guiding center contribution to the known values of these quantities in the Laughlin states, but lacks the Landau orbit contribution. The interesting correlations in a Laughlin state are contained entirely in the guiding center part of the state/wave function, and so we conclude that the CSMM accurately describes the most important aspects of the physics of the Laughlin FQH states, including the Hall viscosity and other geometric properties of these states, which are of current interest.

  17. Acoustic Requirements for a Multi-Purpose Hall.

    ERIC Educational Resources Information Center

    Schulte, W. Allen

    2002-01-01

    This case study examines the proposed design of a new lecture/recital hall in Centennial Hall at Lynchburg College that will be used for lectures, public events, a film studies course, and musical recitals. It explores the audio-visual challenges presented by the differing acoustical requirements for the building. (EV)

  18. A milliKelvin scanning Hall probe microscope for high resolution magnetic imaging

    NASA Astrophysics Data System (ADS)

    Khotkevych, V. V.; Bending, S. J.

    2009-02-01

    The design and performance of a novel scanning Hall probe microscope for milliKelvin magnetic imaging with submicron lateral resolution is presented. The microscope head is housed in the vacuum chamber of a commercial 3He-refrigerator and operates between room temperature and 300 mK in magnetic fields up to 10 T. Mapping of the local magnetic induction at the sample surface is performed by a micro-fabricated 2DEG Hall probe equipped with an integrated STM tip. The latter provides a reliable mechanism of surface tracking by sensing and controlling the tunnel currents. We discuss the results of tests of the system and illustrate its potential with images of suitable reference samples captured in different modes of operation.

  19. Experimental test of 200 W Hall thruster with titanium wall

    NASA Astrophysics Data System (ADS)

    Ding, Yongjie; Sun, Hezhi; Peng, Wuji; Xu, Yu; Wei, Liqiu; Li, Hong; Li, Peng; Su, Hongbo; Yu, Daren

    2017-05-01

    We designed a 200 W Hall thruster based on the technology of pushing down a magnetic field with two permanent magnetic rings. Boron nitride (BN) is an important insulating wall material for Hall thrusters. The discharge characteristics of the designed Hall thruster were studied by replacing BN with titanium (Ti). Experimental results show that the designed Hall thruster can discharge stably for a long time under a Ti channel. Experiments were performed to determine whether the channel and cathode are electrically connected. When the channel wall and cathode are insulated, the divergence angle of the plume increases, but the performance of the Hall thruster is improved in terms of thrust, specific impulse, anode efficiency, and thrust-to-power ratio. Ti exhibits a powerful antisputtering capability, a low emanation rate of gas, and a large structural strength, making it a potential candidate wall material in the design of low-power Hall thrusters.

  20. Effect of multiply charged ions on the performance and beam characteristics in annular and cylindrical type Hall thruster plasmas

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kim, Holak; Lim, Youbong; Choe, Wonho, E-mail: wchoe@kaist.ac.kr

    2014-10-06

    Plasma plume and thruster performance characteristics associated with multiply charged ions in a cylindrical type Hall thruster (CHT) and an annular type Hall thruster are compared under identical conditions such as channel diameter, channel depth, propellant mass flow rate. A high propellant utilization in a CHT is caused by a high ionization rate, which brings about large multiply charged ions. Ion currents and utilizations are much different due to the presence of multiply charged ions. A high multiply charged ion fraction and a high ionization rate in the CHT result in a higher specific impulse, thrust, and discharge current.

  1. Magnetometry of micro-magnets with electrostatically defined Hall bars

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lachance-Quirion, Dany; Camirand Lemyre, Julien; Bergeron, Laurent

    2015-11-30

    Micro-magnets are key components for quantum information processing with individual spins, enabling arbitrary rotations and addressability. In this work, characterization of sub-micrometer sized CoFe ferromagnets is performed with Hall bars electrostatically defined in a two-dimensional electron gas. Due to the ballistic nature of electron transport in the cross junction of the Hall bar, anomalies such as the quenched Hall effect appear near zero external magnetic field, thus hindering the sensitivity of the magnetometer to small magnetic fields. However, it is shown that the sensitivity of the diffusive limit can be almost completely restored at low temperatures using a large currentmore » density in the Hall bar of about 10 A/m. Overcoming the size limitation of conventional etched Hall bars with electrostatic gating enables the measurement of magnetization curves of 440 nm wide micro-magnets with a signal-to-noise ratio above 10{sup 3}. Furthermore, the inhomogeneity of the stray magnetic field created by the micro-magnets is directly measured using the gate-voltage-dependent width of the sensitive area of the Hall bar.« less

  2. Magnesium Hall Thruster

    NASA Technical Reports Server (NTRS)

    Szabo, James J.

    2015-01-01

    This Phase II project is developing a magnesium (Mg) Hall effect thruster system that would open the door for in situ resource utilization (ISRU)-based solar system exploration. Magnesium is light and easy to ionize. For a Mars- Earth transfer, the propellant mass savings with respect to a xenon Hall effect thruster (HET) system are enormous. Magnesium also can be combusted in a rocket with carbon dioxide (CO2) or water (H2O), enabling a multimode propulsion system with propellant sharing and ISRU. In the near term, CO2 and H2O would be collected in situ on Mars or the moon. In the far term, Mg itself would be collected from Martian and lunar regolith. In Phase I, an integrated, medium-power (1- to 3-kW) Mg HET system was developed and tested. Controlled, steady operation at constant voltage and power was demonstrated. Preliminary measurements indicate a specific impulse (Isp) greater than 4,000 s was achieved at a discharge potential of 400 V. The feasibility of delivering fluidized Mg powder to a medium- or high-power thruster also was demonstrated. Phase II of the project evaluated the performance of an integrated, highpower Mg Hall thruster system in a relevant space environment. Researchers improved the medium power thruster system and characterized it in detail. Researchers also designed and built a high-power (8- to 20-kW) Mg HET. A fluidized powder feed system supporting the high-power thruster was built and delivered to Busek Company, Inc.

  3. 20th Annual Residence Hall Construction Report

    ERIC Educational Resources Information Center

    Agron, Joe

    2009-01-01

    Even in difficult economic times, colleges and universities continue to invest in residence hall construction projects as a way to attract new students and keep existing ones on campus. According to data from "American School & University"'s 20th annual Residence Hall Construction Report, the median new project completed in 2008 was…

  4. Residence Hall Fires.

    ERIC Educational Resources Information Center

    Wright, Dorothy

    1999-01-01

    Discusses how one college's experience with a tragic fire in one of its residence halls prompted a reevaluation of its fire-prevention-and-response strategies. Staff training, sprinkler installation, new alarm systems, and exit hardware to help make building exiting more efficient are discussed. (GR)

  5. NASA HERMeS Hall Thruster Electrical Configuration Characterization

    NASA Technical Reports Server (NTRS)

    Peterson, Peter Y.; Kamhawi, Hani; Huang, Wensheng; Yim, John; Herman, Daniel; Williams, George; Gilland, James; Hofer, Richard

    2015-01-01

    The NASA Hall Effect Rocket with Magnetic Shielding (HERMeS) 12.5 kW Technology Demonstration Unit-1 (TDU-1) Hall thruster has been the subject of extensive technology maturation in preparation for development into a flight ready propulsion system. Part of the technology maturation was to test the TDU-1 thruster in several ground based electrical configurations to assess the thruster robustness and suitability to successful in-space operation. The ground based electrical configuration testing has recently been demonstrated as an important step in understanding and assessing how a Hall thruster may operate differently in-space compared to ground based testing, and to determine the best configuration to conduct development and qualification testing. This paper describes the electrical configuration testing of the HERMeS TDU-1 Hall thruster in NASA Glenn Research Center's Vacuum Facility 5. The three electrical configurations examined were 1) thruster body tied to facility ground, 2) thruster floating, and 3) thruster body electrically tied to cathode common. The HERMeS TDU-1 Hall thruster was also configured with two different exit plane boundary conditions, dielectric and conducting, to examine the influence on the electrical configuration characterization.

  6. Perception of music dynamics in concert hall acoustics.

    PubMed

    Pätynen, Jukka; Lokki, Tapio

    2016-11-01

    Dynamics is one of the principal means of expressivity in Western classical music. Still, preceding research on room acoustics has mostly neglected the contribution of music dynamics to the acoustic perception. This study investigates how the different concert hall acoustics influence the perception of varying music dynamics. An anechoic orchestra signal, containing a step in music dynamics, was rendered in the measured acoustics of six concert halls at three seats in each. Spatial sound was reproduced through a loudspeaker array. By paired comparison, naive subjects selected the stimuli that they considered to change more during the music. Furthermore, the subjects described their foremost perceptual criteria for each selection. The most distinct perceptual factors differentiating the rendering of music dynamics between halls include the dynamic range, and varying width of sound and reverberance. The results confirm the hypothesis that the concert halls render the performed music dynamics differently, and with various perceptual aspects. The analysis against objective room acoustic parameters suggests that the perceived dynamic contrasts are pronounced by acoustics that provide stronger sound and more binaural incoherence by a lateral sound field. Concert halls that enhance the dynamics have been found earlier to elicit high subjective preference.

  7. Graphene/Si CMOS hybrid hall integrated circuits.

    PubMed

    Huang, Le; Xu, Huilong; Zhang, Zhiyong; Chen, Chengying; Jiang, Jianhua; Ma, Xiaomeng; Chen, Bingyan; Li, Zishen; Zhong, Hua; Peng, Lian-Mao

    2014-07-07

    Graphene/silicon CMOS hybrid integrated circuits (ICs) should provide powerful functions which combines the ultra-high carrier mobility of graphene and the sophisticated functions of silicon CMOS ICs. But it is difficult to integrate these two kinds of heterogeneous devices on a single chip. In this work a low temperature process is developed for integrating graphene devices onto silicon CMOS ICs for the first time, and a high performance graphene/CMOS hybrid Hall IC is demonstrated. Signal amplifying/process ICs are manufactured via commercial 0.18 um silicon CMOS technology, and graphene Hall elements (GHEs) are fabricated on top of the passivation layer of the CMOS chip via a low-temperature micro-fabrication process. The sensitivity of the GHE on CMOS chip is further improved by integrating the GHE with the CMOS amplifier on the Si chip. This work not only paves the way to fabricate graphene/Si CMOS Hall ICs with much higher performance than that of conventional Hall ICs, but also provides a general method for scalable integration of graphene devices with silicon CMOS ICs via a low-temperature process.

  8. A free-trailing vane flow direction indicator employing a linear output Hall effect transducer

    NASA Technical Reports Server (NTRS)

    Zell, Peter T.; Mcmahon, Robert D.

    1988-01-01

    The Hall effect vane (HEV) was developed to measure flow angularity in the NASA 40-by-80-foot and 80-by-120-foot wind tunnels. This indicator is capable of sensing flow direction at air speeds from 5 to 300 knots and over a + or - 40 deg angle range with a resolution of 0.1 deg. A free-trailing vane configuration employing a linear output Hall effect transducer as a shaft angle resolver was used. The current configuration of the HEV is designed primarily for wind tunnel calibration testing; however, other potential applications include atmospheric, flight or ground research testing. The HEV met initial design requirements.

  9. Magnon Spin Hall Magnetoresistance of a Gapped Quantum Paramagnet.

    PubMed

    Ulloa, Camilo; Duine, R A

    2018-04-27

    Motivated by recent experimental work, we consider spin transport between a normal metal and a gapped quantum paramagnet. We model the latter as the magnonic Mott-insulating phase of an easy-plane ferromagnetic insulator. We evaluate the spin current mediated by the interface exchange coupling between the ferromagnet and the adjacent normal metal. For the strongly interacting magnons that we consider, this spin current gives rise to a spin Hall magnetoresistance that strongly depends on the magnitude of the magnetic field, rather than its direction. This Letter may motivate electrical detection of the phases of quantum magnets and the incorporation of such materials into spintronic devices.

  10. Optical Emission Characterization of High-Power Hall Thruster Wear

    NASA Technical Reports Server (NTRS)

    WIlliams, George J.; Kamhawi, Hani

    2013-01-01

    Optical emission spectroscopy is employed to correlate BN insulator erosion with high-power operation of the NASA 300M Hall-effect thruster. Actinometry leveraging excited xenon states is used to normalize the emission spectra of ground state boron as a function of thruster operating condition. Trends in the strength of the boron signal are correlated with thruster power, discharge voltage, discharge current and magnetic field strength. The boron signals are shown to trend with discharge current and show weak dependence on discharge voltage. The trends are consistent with data previously collected on the NASA 300M and NASA 457M thrusters but are different from conventional wisdom.

  11. Magnon Spin Hall Magnetoresistance of a Gapped Quantum Paramagnet

    NASA Astrophysics Data System (ADS)

    Ulloa, Camilo; Duine, R. A.

    2018-04-01

    Motivated by recent experimental work, we consider spin transport between a normal metal and a gapped quantum paramagnet. We model the latter as the magnonic Mott-insulating phase of an easy-plane ferromagnetic insulator. We evaluate the spin current mediated by the interface exchange coupling between the ferromagnet and the adjacent normal metal. For the strongly interacting magnons that we consider, this spin current gives rise to a spin Hall magnetoresistance that strongly depends on the magnitude of the magnetic field, rather than its direction. This Letter may motivate electrical detection of the phases of quantum magnets and the incorporation of such materials into spintronic devices.

  12. Comparison of Hall Thruster Plume Expansion Model with Experimental Data

    DTIC Science & Technology

    2006-05-23

    focus of this study, is a hybrid particle- in-cell ( PIC ) model that tracks particles along an unstructured tetrahedral mesh. * Research Engineer...measurements of the ion current density profile, ion energy distributions, and ion species fraction distributions using a nude Faraday probe, retarding...Vol.37 No.1. 6 Oh, D. and Hastings, D., “Three Dimensional PIC -DSMC Simulations of Hall Thruster Plumes and Analysis for Realistic Spacecraft

  13. Localization in a quantum spin Hall system.

    PubMed

    Onoda, Masaru; Avishai, Yshai; Nagaosa, Naoto

    2007-02-16

    The localization problem of electronic states in a two-dimensional quantum spin Hall system (that is, a symplectic ensemble with topological term) is studied by the transfer matrix method. The phase diagram in the plane of energy and disorder strength is exposed, and demonstrates "levitation" and "pair annihilation" of the domains of extended states analogous to that of the integer quantum Hall system. The critical exponent nu for the divergence of the localization length is estimated as nu congruent with 1.6, which is distinct from both exponents pertaining to the conventional symplectic and the unitary quantum Hall systems. Our analysis strongly suggests a different universality class related to the topology of the pertinent system.

  14. Hall effects on hydromagnetic free convection flow along a porous flat plate with mass transfer

    NASA Astrophysics Data System (ADS)

    Hossain, M. A.; Rashid, R. I. M. A.

    1987-01-01

    Effect of Hall current on the unsteady free convection flow of a viscous incompressible and electrically conducting fluid, in presence of foreign gases (such as H2, CO2, H2O, NH3), along an infinite vertical porous flat plate subjected to a transpiration velocity inversely proportional to the square-root of time is investigated in the presence of a uniform transverse magnetic field. The results are discussed with the effects of the parameters Gc (the Grashof number for mass transfer), m (the Hall parameter) and Sc (the Schmidt number) for Pr = 0.71, which represents air.

  15. Effects of Hall current and electron temperature anisotropy on proton fire-hose instabilities

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hau, L.-N.; Department of Physics, National Central University, Jhongli, Taiwan; Wang, B.-J.

    The standard magnetohydrodynamic (MHD) theory predicts that the Alfvén wave may become fire-hose unstable for β{sub ∥}−β{sub ⊥}>2. In this study, we examine the proton fire-hose instability (FHI) based on the gyrotropic two-fluid model, which incorporates the ion inertial effects arising from the Hall current and electron temperature anisotropy but neglects the electron inertia in the generalized Ohm's law. The linear dispersion relation is derived and analyzed which in the long wavelength approximation, λ{sub i}k→0 or α{sub e}=μ{sub 0}(p{sub ∥,e}−p{sub ⊥,e})/B{sup 2}=1, recovers the ideal MHD model with separate temperature for ions and electrons. Here, λ{sub i} is the ionmore » inertial length and k is the wave number. For parallel propagation, both ion cyclotron and whistler waves become propagating and growing for β{sub ∥}−β{sub ⊥}>2+λ{sub i}{sup 2}k{sup 2}(α{sub e}−1){sup 2}/2. For oblique propagation, the necessary condition for FHI remains to be β{sub ∥}−β{sub ⊥}>2 and there exist one or two unstable fire-hose modes, which can be propagating and growing or purely growing. For large λ{sub i}k values, there exists no nearly parallel FHI leaving only oblique FHI and the effect of α{sub e}>1 may greatly enhance the growth rate of parallel and oblique FHI. The magnetic field polarization of FHI may be reversed due to the sign change associated with (α{sub e}−1) and the purely growing FHI may possess linear polarization while the propagating and growing FHI may possess right-handed or left-handed polarization.« less

  16. Traveling waves in Hall-magnetohydrodynamics and the ion-acoustic shock structure

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hagstrom, George I.; Hameiri, Eliezer

    Hall-magnetohydrodynamics (HMHD) is a mixed hyperbolic-parabolic partial differential equation that describes the dynamics of an ideal two fluid plasma with massless electrons. We study the only shock wave family that exists in this system (the other discontinuities being contact discontinuities and not shocks). We study planar traveling wave solutions and we find solutions with discontinuities in the hydrodynamic variables, which arise due to the presence of real characteristics in Hall-MHD. We introduce a small viscosity into the equations and use the method of matched asymptotic expansions to show that solutions with a discontinuity satisfying the Rankine-Hugoniot conditions and also anmore » entropy condition have continuous shock structures. The lowest order inner equations reduce to the compressible Navier-Stokes equations, plus an equation which implies the constancy of the magnetic field inside the shock structure. We are able to show that the current is discontinuous across the shock, even as the magnetic field is continuous, and that the lowest order outer equations, which are the equations for traveling waves in inviscid Hall-MHD, are exactly integrable. We show that the inner and outer solutions match, which allows us to construct a family of uniformly valid continuous composite solutions that become discontinuous when the diffusivity vanishes.« less

  17. Precision Tests of a Quantum Hall Effect Device DC Equivalent Circuit Using Double-Series and Triple-Series Connections

    PubMed Central

    Jeffery, A.; Elmquist, R. E.; Cage, M. E.

    1995-01-01

    Precision tests verify the dc equivalent circuit used by Ricketts and Kemeny to describe a quantum Hall effect device in terms of electrical circuit elements. The tests employ the use of cryogenic current comparators and the double-series and triple-series connection techniques of Delahaye. Verification of the dc equivalent circuit in double-series and triple-series connections is a necessary step in developing the ac quantum Hall effect as an intrinsic standard of resistance. PMID:29151768

  18. Facilty Focus: Residence Halls.

    ERIC Educational Resources Information Center

    Hunnewell, James F., Jr.

    2002-01-01

    Describes the Western Ridge Residence at Colorado College and Beard Hall at Wheaton College. The buildings feature multiple levels that take advantage of views and also help create a "homey" feeling. (EV)

  19. A holographic model for the fractional quantum Hall effect

    NASA Astrophysics Data System (ADS)

    Lippert, Matthew; Meyer, René; Taliotis, Anastasios

    2015-01-01

    Experimental data for fractional quantum Hall systems can to a large extent be explained by assuming the existence of a Γ0(2) modular symmetry group commuting with the renormalization group flow and hence mapping different phases of two-dimensional electron gases into each other. Based on this insight, we construct a phenomenological holographic model which captures many features of the fractional quantum Hall effect. Using an -invariant Einstein-Maxwell-axio-dilaton theory capturing the important modular transformation properties of quantum Hall physics, we find dyonic diatonic black hole solutions which are gapped and have a Hall conductivity equal to the filling fraction, as expected for quantum Hall states. We also provide several technical results on the general behavior of the gauge field fluctuations around these dyonic dilatonic black hole solutions: we specify a sufficient criterion for IR normalizability of the fluctuations, demonstrate the preservation of the gap under the action, and prove that the singularity of the fluctuation problem in the presence of a magnetic field is an accessory singularity. We finish with a preliminary investigation of the possible IR scaling solutions of our model and some speculations on how they could be important for the observed universality of quantum Hall transitions.

  20. A New Definition in Atlanta: Q&A with Beverly Hall

    ERIC Educational Resources Information Center

    Crow, Tracy

    2010-01-01

    Beverly Hall has been superintendent of Atlanta Public Schools since 1999. Before coming to Atlanta, Hall was state district superintendent of Newark Public Schools, deputy chancellor for instruction of New York City Public Schools, superintendent of Community School District 27 in New York City, and a principal in Brooklyn. Hall chairs Harvard…

  1. Unsteady Heat and Mass Transfer of Chemically Reacting Micropolar Fluid in a Porous Channel with Hall and Ion Slip Currents

    PubMed Central

    2014-01-01

    This paper presents an incompressible two-dimensional heat and mass transfer of an electrically conducting micropolar fluid flow in a porous medium between two parallel plates with chemical reaction, Hall and ion slip effects. Let there be periodic injection or suction at the lower and upper plates and the nonuniform temperature and concentration at the plates are varying periodically with time. The flow field equations are reduced to nonlinear ordinary differential equations using similarity transformations and then solved numerically by quasilinearization technique. The profiles of velocity components, microrotation, temperature distribution and concentration are studied for different values of fluid and geometric parameters such as Hartmann number, Hall and ion slip parameters, inverse Darcy parameter, Prandtl number, Schmidt number, and chemical reaction rate and shown in the form of graphs. PMID:27419211

  2. Hollow Cathode Assembly Development for the HERMeS Hall Thruster

    NASA Technical Reports Server (NTRS)

    Sarver-Verhey, Timothy R.; Kamhawi, Hani; Goebel, Dan M.; Polk, James E.; Peterson, Peter Y.; Robinson, Dale A.

    2016-01-01

    To support the operation of the HERMeS 12.5 kW Hall Thruster for NASA's Asteroid Redirect Robotic Mission, hollow cathodes using emitters based on barium oxide impregnate and lanthanum hexaboride are being evaluated through wear-testing, performance characterization, plasma modeling, and assessment of system implementation concerns. This paper will present the development approach used to assess the cathode emitter options. A 2,000-hour wear-test of development model barium-oxide-based (BaO) hollow cathode is being performed as part of the development plan. The cathode was operated with an anode that simulates the HERMeS hall thruster operating environment. Cathode discharge performance has been stable with the device accumulating 740 hours at the time of this report. Cathode operation (i.e. discharge voltage and orifice temperature) was repeatable during period variation of discharge current and flow rate. The details of the cathode assembly operation during the wear-test will be presented.

  3. Quasiparticle-mediated spin Hall effect in a superconductor.

    PubMed

    Wakamura, T; Akaike, H; Omori, Y; Niimi, Y; Takahashi, S; Fujimaki, A; Maekawa, S; Otani, Y

    2015-07-01

    In some materials the competition between superconductivity and magnetism brings about a variety of unique phenomena such as the coexistence of superconductivity and magnetism in heavy-fermion superconductors or spin-triplet supercurrent in ferromagnetic Josephson junctions. Recent observations of spin-charge separation in a lateral spin valve with a superconductor evidence that these remarkable properties are applicable to spintronics, although there are still few works exploring this possibility. Here, we report the experimental observation of the quasiparticle-mediated spin Hall effect in a superconductor, NbN. This compound exhibits the inverse spin Hall (ISH) effect even below the superconducting transition temperature. Surprisingly, the ISH signal increases by more than 2,000 times compared with that in the normal state with a decrease of the injected spin current. The effect disappears when the distance between the voltage probes becomes larger than the charge imbalance length, corroborating that the huge ISH signals measured are mediated by quasiparticles.

  4. Quantum Hall Ferroelectrics and Nematics in Multivalley Systems

    NASA Astrophysics Data System (ADS)

    Sodemann, Inti; Zhu, Zheng; Fu, Liang

    2017-10-01

    We study broken symmetry states at integer Landau-level fillings in multivalley quantum Hall systems whose low-energy dispersions are anisotropic. When the Fermi surface of individual pockets lacks twofold rotational symmetry, like in bismuth (111) [Feldman et al. , Observation of a Nematic Quantum Hall Liquid on the Surface of Bismuth, Science 354, 316 (2016), 10.1126/science.aag1715] and in Sn1 -xPbxSe (001) [Dziawa et al., Topological Crystalline Insulator States in Pb1 -xSnxSe , Nat. Mater. 11, 1023 (2012), 10.1038/nmat3449] surfaces, interactions tend to drive the formation of quantum Hall ferroelectric states. We demonstrate that the dipole moment in these states has an intimate relation to the Fermi surface geometry of the parent metal. In quantum Hall nematic states, like those arising in AlAs quantum wells, we demonstrate the existence of unusually robust Skyrmion quasiparticles.

  5. Conducting wall Hall thrusters in magnetic shielding and standard configurations

    NASA Astrophysics Data System (ADS)

    Grimaud, Lou; Mazouffre, Stéphane

    2017-07-01

    Traditional Hall thrusters are fitted with boron nitride dielectric discharge channels that confine the plasma discharge. Wall properties have significant effects on the performances and stability of the thrusters. In magnetically shielded thrusters, interactions between the plasma and the walls are greatly reduced, and the potential drop responsible for ion acceleration is situated outside the channel. This opens the way to the utilization of alternative materials for the discharge channel. In this work, graphite walls are compared to BN-SiO2 walls in the 200 W magnetically shielded ISCT200-MS and the unshielded ISCT200-US Hall thrusters. The magnetically shielded thruster shows no significant change in the discharge current mean value and oscillations, while the unshielded thruster's discharge current increases by 25% and becomes noticeably less stable. The electric field profile is also investigated through laser spectroscopy, and no significant difference is recorded between the ceramic and graphite cases for the shielded thruster. The unshielded thruster, on the other hand, has its acceleration region shifted 15% of the channel length downstream. Lastly, the plume profile is measured with planar probes fitted with guard rings. Once again the material wall has little influence on the plume characteristics in the shielded thruster, while the unshielded one is significantly affected.

  6. Nonequilibrium Hall Response After a Topological Quench

    NASA Astrophysics Data System (ADS)

    Unal, F. Nur; Mueller, Erich; Oktel, M. O.

    2017-04-01

    We theoretically study the Hall response of a lattice system following a quench where the topology of a filled band is suddenly changed. In the limit where the physics is dominated by a single Dirac cone, we find that the change in the Hall conductivity is two-thirds of the quantum of conductivity. We explore this universal behavior in the Haldane model, and discuss cold-atom experiments for its observation. Beyond linear response, the Hall effect crosses over from fractional to integer values. We investigate finite-size effects, and the role of the harmonic confinement. Furthermore, we explore the magnetic field quenches in ladders formed in synthetic dimensions. This work is supported by TUBITAK, NSFPHY-1508300, ARO-MURI W9111NF-14-1-0003.

  7. Diffusion in plasma: The Hall effect, compositional waves, and chemical spots

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Urpin, V., E-mail: Vadim.urpin@uv.es

    2017-03-15

    Diffusion caused by a combined influence of the electric current and Hall effect is considered, and it is argued that such diffusion can form inhomogeneities of a chemical composition in plasma. The considered mechanism can be responsible for the formation of element spots in laboratory and astrophysical plasmas. This current-driven diffusion can be accompanied by propagation of a particular type of waves in which the impurity number density oscillates alone. These compositional waves exist if the magnetic pressure in plasma is much greater than the gas pressure.

  8. Tuning the stability and the skyrmion Hall effect in magnetic skyrmions by adjusting their exchange strengths with magnetic disks

    NASA Astrophysics Data System (ADS)

    Sun, L.; Wu, H. Z.; Miao, B. F.; Wu, D.; Ding, H. F.

    2018-06-01

    Magnetic skyrmion is a promising candidate for the future information technology due to its small size, topological protection and the ultralow current density needed to displace it. The applications, however, are currently limited by its narrow phase diagram and the skyrmion Hall effect which prevents the skyrmion motion at high speed. In this work, we study the Dzyaloshinskii-Moriya interaction induced magnetic skyrmion that exchange coupled with magnetic nano-disks utilizing the micromagnetic simulation. We find that the stability and the skyrmion Hall effect of the created skyrmion can be tuned effectively with the coupling strength, thus opens the space to optimize the performance of the skyrmion based devices.

  9. End-hall thrusters

    NASA Technical Reports Server (NTRS)

    Kaufman, H. R.; Robinson, R. S.; Day, M. L.; Haag, T. W.

    1990-01-01

    The end-Hall thruster can provide electric propulsion with fixed masses, specific impulses, and power-to-thrust ratios intermediate of an arcjet and a gridded (electrostatic) ion thruster. With these characteristics, this thruster is a candidate for missions of intermediate difficulty, such as the north-south stationkeeping of geostationary satellites.

  10. Optical Diagnostic Characterization of High-Power Hall Thruster Wear and Operation

    NASA Technical Reports Server (NTRS)

    Williams, George J., Jr.; Soulas, George C.; Kamhawi, Hani

    2012-01-01

    Optical emission spectroscopy is employed to correlate BN insulator erosion with high-power Hall thruster operation. Specifically, actinometry leveraging excited xenon states is used to normalize the emission spectra of ground state boron as a function of thruster operating condition. Trends in the strength of the boron signal are correlated with thruster power, discharge voltage, and discharge current. In addition, the technique is demonstrated on metallic coupons embedded in the walls of the HiVHAc EM thruster. The OES technique captured the overall trend in the erosion of the coupons which boosts credibility in the method since there are no data to which to calibrate the erosion rates of high-power Hall thrusters. The boron signals are shown to trend linearly with discharge voltage for a fixed discharge current as expected. However, the boron signals of the higher-power NASA 300M and NASA 457Mv2 trend with discharge current and show an unexpectedly weak to inverse dependence on discharge voltage. Electron temperatures measured optically in the near-field plume of the thruster agree well with Langmuir probe data. However, the optical technique used to determine Te showed unacceptable sensitivity to the emission intensities. Near-field, single-frequency imaging of the xenon neutrals is also presented as a function of operating condition for the NASA 457 Mv2.

  11. Magnetic bilayer-skyrmions without skyrmion Hall effect

    NASA Astrophysics Data System (ADS)

    Zhang, Xichao; Zhou, Yan; Ezawa, Motohiko

    2016-01-01

    Magnetic skyrmions might be used as information carriers in future advanced memories, logic gates and computing devices. However, there exists an obstacle known as the skyrmion Hall effect (SkHE), that is, the skyrmion trajectories bend away from the driving current direction due to the Magnus force. Consequently, the skyrmions in constricted geometries may be destroyed by touching the sample edges. Here we theoretically propose that the SkHE can be suppressed in the antiferromagnetically exchange-coupled bilayer system, since the Magnus forces in the top and bottom layers are exactly cancelled. We show that such a pair of SkHE-free magnetic skyrmions can be nucleated and be driven by the current-induced torque. Our proposal provides a promising means to move magnetic skyrmions in a perfectly straight trajectory in ultra-dense devices with ultra-fast processing speed.

  12. Intrinsic Spin-Hall Effect in n-Doped Bulk GaAs

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bernevig, B.Andrei; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-01-15

    We show that the bulk Dresselhauss (k{sup 3}) spin-orbit coupling term leads to an intrinsic spin-Hall effect in n-doped bulk GaAs, but without the appearance of uniform magnetization. The spin-Hall effect in strained and unstrained bulk GaAs has been recently observed experimentally by Kato et. al. [1]. We show that the experimental result is quantitatively consistent with the intrinsic spin-Hall effect due to the Dresselhauss term, when lifetime broadening is taken into account. On the other hand, extrinsic contribution to the spin-Hall effect is several orders of magnitude smaller than the observed effect.

  13. Determination of the spin Hall angle in single-crystalline Pt films from spin pumping experiments

    NASA Astrophysics Data System (ADS)

    Keller, Sascha; Mihalceanu, Laura; Schweizer, Matthias R.; Lang, Philipp; Heinz, Björn; Geilen, Moritz; Brächer, Thomas; Pirro, Philipp; Meyer, Thomas; Conca, Andres; Karfaridis, Dimitrios; Vourlias, George; Kehagias, Thomas; Hillebrands, Burkard; Papaioannou, Evangelos Th

    2018-05-01

    We report on the determination of the spin Hall angle in ultra-clean, defect-reduced epitaxial Pt films. By applying vector network analyzer ferromagnetic resonance spectroscopy to a series of single crystalline Fe (12 nm) /Pt (t Pt) bilayers we determine the real part of the spin mixing conductance (4.4 ± 0.2) × 1019 m‑2 and reveal a very small spin diffusion length in the epitaxial Pt (1.1 ± 0.1) nm film. We investigate the spin pumping and ISHE in a stripe microstucture excited by a microwave coplanar waveguide antenna. By using their different angular dependencies, we distinguish between spin rectification effects and the inverse spin Hall effect. The relatively large value of the spin Hall angle (5.7 ± 1.4)% shows that ultra-clean e-beam evaporated non-magnetic materials can also have a comparable spin-to-charge current conversion efficiency as sputtered high resistivity layers.

  14. Graphene/Si CMOS Hybrid Hall Integrated Circuits

    PubMed Central

    Huang, Le; Xu, Huilong; Zhang, Zhiyong; Chen, Chengying; Jiang, Jianhua; Ma, Xiaomeng; Chen, Bingyan; Li, Zishen; Zhong, Hua; Peng, Lian-Mao

    2014-01-01

    Graphene/silicon CMOS hybrid integrated circuits (ICs) should provide powerful functions which combines the ultra-high carrier mobility of graphene and the sophisticated functions of silicon CMOS ICs. But it is difficult to integrate these two kinds of heterogeneous devices on a single chip. In this work a low temperature process is developed for integrating graphene devices onto silicon CMOS ICs for the first time, and a high performance graphene/CMOS hybrid Hall IC is demonstrated. Signal amplifying/process ICs are manufactured via commercial 0.18 um silicon CMOS technology, and graphene Hall elements (GHEs) are fabricated on top of the passivation layer of the CMOS chip via a low-temperature micro-fabrication process. The sensitivity of the GHE on CMOS chip is further improved by integrating the GHE with the CMOS amplifier on the Si chip. This work not only paves the way to fabricate graphene/Si CMOS Hall ICs with much higher performance than that of conventional Hall ICs, but also provides a general method for scalable integration of graphene devices with silicon CMOS ICs via a low-temperature process. PMID:24998222

  15. Formulation of the relativistic quantum Hall effect and parity anomaly

    NASA Astrophysics Data System (ADS)

    Yonaga, Kouki; Hasebe, Kazuki; Shibata, Naokazu

    2016-06-01

    We present a relativistic formulation of the quantum Hall effect on Haldane sphere. An explicit form of the pseudopotential is derived for the relativistic quantum Hall effect with/without mass term. We clarify particular features of the relativistic quantum Hall states with the use of the exact diagonalization study of the pseudopotential Hamiltonian. Physical effects of the mass term to the relativistic quantum Hall states are investigated in detail. The mass term acts as an interpolating parameter between the relativistic and nonrelativistic quantum Hall effects. It is pointed out that the mass term unevenly affects the many-body physics of the positive and negative Landau levels as a manifestation of the "parity anomaly." In particular, we explicitly demonstrate the instability of the Laughlin state of the positive first relativistic Landau level with the reduction of the charge gap.

  16. Hole mobilities and the effective Hall factor in p-type GaAs

    NASA Astrophysics Data System (ADS)

    Wenzel, M.; Irmer, G.; Monecke, J.; Siegel, W.

    1997-06-01

    We prove the effective Hall factor in p-GaAs to be larger than values discussed in the literature up to now. The scattering rates for the relevant scattering mechanisms in p-GaAs have been recalculated after critical testing the existing models. These calculations allow to deduce theoretical drift and theoretical Hall mobilities as functions of temperature which can be compared with measured data. Theoretical Hall factors in the heavy and light hole bands and an effective Hall factor result. The calculated room temperature values of the drift mobility and of the effective Hall factor are 118 cm2/V s and 3.6, respectively. The fitted acoustic deformation potential E1=7.9 eV and the fitted optical coupling constant DK=1.24×1011 eV/m are close to values published before. It is shown that the measured strong dependence of the Hall mobility on the Hall concentration is not mainly caused by scattering by ionized impurities but by the dependence of the effective Hall factor on the hole concentration.

  17. 4. MESS HALL, FRONT DETAIL OVER DOOR, LOOKING EAST. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. MESS HALL, FRONT DETAIL OVER DOOR, LOOKING EAST. - NIKE Missile Base C-84, Mess Hall, North of Launch Area Entrance Drive, east of Officers' Quarters & Administration Building, Barrington, Cook County, IL

  18. 3. MESS HALL, REAR SIDE, LOOKING NORTH. NIKE Missile ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. MESS HALL, REAR SIDE, LOOKING NORTH. - NIKE Missile Base SL-40, Mess Hall, East central portion of base, southeast of Barracks No. 2, northwest of Administration Building, Hecker, Monroe County, IL

  19. 2. MESS HALL, RIGHT SIDE, LOOKING EAST. NIKE Missile ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. MESS HALL, RIGHT SIDE, LOOKING EAST. - NIKE Missile Base SL-40, Mess Hall, East central portion of base, southeast of Barracks No. 2, northwest of Administration Building, Hecker, Monroe County, IL

  20. Modeling an Iodine Hall Thruster Plume in the Iodine Satellite (ISAT)

    NASA Technical Reports Server (NTRS)

    Choi, Maria

    2016-01-01

    An iodine-operated 200-W Hall thruster plume has been simulated using a hybrid-PIC model to predict the spacecraft surface-plume interaction for spacecraft integration purposes. For validation of the model, the plasma potential, electron temperature, ion current flux, and ion number density of xenon propellant were compared with available measurement data at the nominal operating condition. To simulate iodine plasma, various collision cross sections were found and used in the model. While time-varying atomic iodine species (i.e., I, I+, I2+) information is provided by HP Hall simulation at the discharge channel exit, the molecular iodine species (i.e., I2, I2+) are introduced as Maxwellian particles at the channel exit. Simulation results show that xenon and iodine plasma plumes appear to be very similar under the assumptions of the model. Assuming a sticking coefficient of unity, iodine deposition rate is estimated.

  1. 5. MESS HALL, RIGHT AND REAR SIDES, LOOKING NORTHEAST. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. MESS HALL, RIGHT AND REAR SIDES, LOOKING NORTHEAST. - NIKE Missile Base SL-40, Mess Hall, East central portion of base, southeast of Barracks No. 2, northwest of Administration Building, Hecker, Monroe County, IL

  2. 6. PHOTOCOPY, PLAN AND SCHEDULE DRAWING OF MESS HALL. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. PHOTOCOPY, PLAN AND SCHEDULE DRAWING OF MESS HALL. - NIKE Missile Base SL-40, Mess Hall, East central portion of base, southeast of Barracks No. 2, northwest of Administration Building, Hecker, Monroe County, IL

  3. 7. PHOTOCOPY, ELEVATION AND SECTION DRAWING OF MESS HALL. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. PHOTOCOPY, ELEVATION AND SECTION DRAWING OF MESS HALL. - NIKE Missile Base SL-40, Mess Hall, East central portion of base, southeast of Barracks No. 2, northwest of Administration Building, Hecker, Monroe County, IL

  4. 4. MESS HALL, FRONT AND LEFT SIDES, LOOKING SOUTHWEST. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. MESS HALL, FRONT AND LEFT SIDES, LOOKING SOUTHWEST. - NIKE Missile Base SL-40, Mess Hall, East central portion of base, southeast of Barracks No. 2, northwest of Administration Building, Hecker, Monroe County, IL

  5. Anomalous Hall hysteresis in T m3F e5O12/Pt with strain-induced perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Tang, Chi; Sellappan, Pathikumar; Liu, Yawen; Xu, Yadong; Garay, Javier E.; Shi, Jing

    2016-10-01

    We demonstrate robust interface strain-induced perpendicular magnetic anisotropy in atomically flat ferrimagnetic insulator T m3F e5O12 (TIG) films grown with pulsed laser deposition on a substituted G d3G a5O12 substrate which maximizes the tensile strain at the interface. In bilayers consisting of Pt and TIG, we observe large squared Hall hysteresis loops over a wide range of thicknesses of Pt at room temperature. When a thin Cu layer is inserted between Pt and TIG, the Hall hysteresis magnitude decays but stays finite as the thickness of Cu increases up to 5 nm. However, if the Cu layer is placed atop Pt instead, the Hall hysteresis magnitude is consistently larger than when the Cu layer with the same thickness is inserted in between for all Cu thicknesses. These results suggest that both the proximity-induced ferromagnetism and spin current contribute to the anomalous Hall effect.

  6. Performance of a Low-Power Cylindrical Hall Thruster

    NASA Technical Reports Server (NTRS)

    Polzin, Kurt A.; Markusic, Thomas E.; Stanojev, Boris J.; Dehoyos, Amado; Raitses, Yevgeny; Smirnov, Artem; Fisch, Nathaniel J.

    2007-01-01

    Recent mission studies have shown that a Hall thruster which operates at relatively constant thrust efficiency (45-55%) over a broad power range (300W - 3kW) is enabling for deep space science missions when compared with slate-of-the-art ion thrusters. While conventional (annular) Hall thrusters can operate at high thrust efficiency at kW power levels, it is difficult to construct one that operates over a broad power envelope down to 0 (100 W) while maintaining relatively high efficiency. In this note we report the measured performance (I(sub sp), thrust and efficiency) of a cylindrical Hall thruster operating at 0 (100 W) input power.

  7. Intrinsic Dawn-Dusk Asymmetry of Magnetotail Thin Current Sheet

    NASA Astrophysics Data System (ADS)

    Lu, S.; Pritchett, P. L.; Angelopoulos, V.; Artemyev, A.

    2017-12-01

    Magnetic reconnection and its related phenomena (flux ropes, dipolarization fronts, bursty bulk flows, particle injections, etc.) occur more frequently on the duskside in the Earth's magnetotail. Magnetohydrodynamic simulations attributed the asymmetry to the nonuniform ionospheric conductance through global scale magnetosphere-ionosphere interaction. Hybrid simulations, on the other hand, found an alternative responsible mechanism: the Hall effect in the magnetotail thin current sheet, but left an open question: What is the physical origin of the asymmetric Hall effect? The answer could be the temperature difference on the two sides and/or the dawn-dusk transportation of magnetic flux and plasmas. In this work, we use 3-D particle-in-cell simulations to further explore the magnetotail dawn-dusk asymmetry. The magnetotail equilibrium contains a dipole magnetic field and a current sheet region. The simulation is driven by a symmetric and localized (in the y direction) high-latitude electric field, under which the current sheet thins with a decrease of Bz. During the same time, a dawn-dusk asymmetry is formed intrinsically in the thin current sheet, with a smaller Bz, a stronger Hall effect (indicated by the Hall electric field Ez), and a stronger cross-tail current jy on the duskside. The deep origin of the asymmetry is also shown to be dominated by the dawnward E×B drift of magnetic flux and plasmas. A direct consequence of this intrinsic dawn-dusk asymmetry is that it favors magnetotail reconnection and related phenomena to preferentially occur on the duskside.

  8. Using nutrition labeling as a potential tool for changing eating habits of university dining hall patrons.

    PubMed

    Driskell, Judy A; Schake, Marian C; Detter, Hillary A

    2008-12-01

    The purpose of this cross-sectional study was to examine the influence of the nutritional labeling Nutrition Bytes on the eating habits of adults eating in dining halls at a Midwestern university and to assess differences between sexes. Dining hall patrons (114 men, 91 women) 19 years of age or older voluntarily completed a descriptive 15-item written questionnaire that examined the use and nonuse of Nutrition Bytes, which contains much of the information included in the Nutrition Facts label. A significantly higher percentage of women than men patrons reported currently using Nutrition Bytes labels (P<0.001). Predominant reasons for using Nutrition Bytes labels were: general knowledge, concern about overall health, calorie counting, and concern about a certain nutrient(s). Predominant reasons given for not using Nutrition Bytes labels were: will not change my mind about food items selected and not enough time. Reasons given by men and women for using or not using Nutrition Bytes labels were similar. Significantly higher percentages of women than men using Nutrition Bytes labels indicated being interested in having serving sizes (P<0.005) and ingredients (P<0.0005) listed, whereas higher percentages of men than women indicated being interested in having protein listed (P<0.05). The percentages of users who indicated nearly always and sometimes changing their food choices after reading Nutrition Bytes labels inside the dining halls were 12% and 80%, respectively, whereas 23% and 65%, respectively, indicated changing their food choices after reading the nutrition label when eating outside the dining halls. Nutrition Bytes labeling seemed to positively impact food choices of these adult dining hall patrons, and likely would do so at other dining halls.

  9. Cylindrical geometry hall thruster

    DOEpatents

    Raitses, Yevgeny; Fisch, Nathaniel J.

    2002-01-01

    An apparatus and method for thrusting plasma, utilizing a Hall thruster with a cylindrical geometry, wherein ions are accelerated in substantially the axial direction. The apparatus is suitable for operation at low power. It employs small size thruster components, including a ceramic channel, with the center pole piece of the conventional annular design thruster eliminated or greatly reduced. Efficient operation is accomplished through magnetic fields with a substantial radial component. The propellant gas is ionized at an optimal location in the thruster. A further improvement is accomplished by segmented electrodes, which produce localized voltage drops within the thruster at optimally prescribed locations. The apparatus differs from a conventional Hall thruster, which has an annular geometry, not well suited to scaling to small size, because the small size for an annular design has a great deal of surface area relative to the volume.

  10. Master equation for open two-band systems and its applications to Hall conductance

    NASA Astrophysics Data System (ADS)

    Shen, H. Z.; Zhang, S. S.; Dai, C. M.; Yi, X. X.

    2018-02-01

    Hall conductivity in the presence of a dephasing environment has recently been investigated with a dissipative term introduced phenomenologically. In this paper, we study the dissipative topological insulator (TI) and its topological transition in the presence of quantized electromagnetic environments. A Lindblad-type equation is derived to determine the dynamics of a two-band system. When the two-band model describes TIs, the environment may be the fluctuations of radiation that surround the TIs. We find the dependence of decay rates in the master equation on Bloch vectors in the two-band system, which leads to a mixing of the band occupations. Hence the environment-induced current is in general not perfectly topological in the presence of coupling to the environment, although deviations are small in the weak limit. As an illustration, we apply the Bloch-vector-dependent master equation to TIs and calculate the Hall conductance of tight-binding electrons in a two-dimensional lattice. The influence of environments on the Hall conductance is presented and discussed. The calculations show that the phase transition points of the TIs are robust against the quantized electromagnetic environment. The results might bridge the gap between quantum optics and topological photonic materials.

  11. Iodine Plasma Species Measurements in a Hall Effect Thruster Plume

    DTIC Science & Technology

    2013-04-01

    direction f = species fraction 0g = gravitational constant at Earth’s surface, 9.81 m/s 2 I = current, subscripts b for beam, c for cathode, d for...Hall effect thruster uses crossed electric and magnetic fields to generate and accelerate ions. The gas in the discharge is partially ionized, although...early 1960s.10 Ions are weakly magnetized and most are accelerated directly out of the channel, forming the ion beam. The bulk of the cathode

  12. Comparison of Hall Thruster Plume Expansion Model with Experimental Data (Preprint)

    DTIC Science & Technology

    2006-07-01

    Cartesian mesh. AQUILA, the focus of this study, is a hybrid PIC model that tracks particles along an unstructured tetrahedral mesh. COLISEUM is capable...measurements of the ion current density profile, ion energy distributions, and ion species fraction distributions using a nude Faraday probe...Spacecraft and Rockets, Vol.37 No.1. 6 Oh, D. and Hastings, D., “Three Dimensional PIC -DSMC Simulations of Hall Thruster Plumes and Analysis for

  13. Astronaut Hall of Fame Induction Ceremony

    NASA Image and Video Library

    2017-05-19

    In a ceremony set beneath Space Shuttle Atlantis, veteran astronauts C. Michael Foale and Ellen Ochoa are inducted into the U.S. Astronaut Hall of Fame. Foale and Ochoa make up the 16th group of space shuttle astronauts to be inducted into the Hall of Fame, and their addition to the group brings the total number of inductees to 95. More than 20 legendary astronauts were on hand to welcome the inductees, including: Robert Cabana, Dan Brandenstein, Al Worden, Charlie Duke, Charles Bolden, Michael Coats, Robert Crippen, Rhea Seddon, and Fred Gregory.

  14. Hall Sweet Home

    ERIC Educational Resources Information Center

    Oguntoyinbo, Lekan

    2011-01-01

    Many urban and commuter universities have their sights set on students who are unlikely to connect with the college and likely to fail unless the right strategies are put in place to help them graduate. In efforts to improve retention rates, commuter colleges are looking to an unusual suspect: residence halls. The author discusses how these…

  15. Hall Effect Spintronics

    DTIC Science & Technology

    2014-01-01

    ferromagnetic films with perpendicular anisotropy were examined, and finally, the magnetoresistance and Hall effect in Manganese- doped Germanium was...interest in ferromagnetic semiconductors. Germanium doped with Mn is particularly interesting Distribution A: Approved for public release...unavoidable, and doped films are strongly inhomogeneous with GexMny, metallic precipitates coexisting with Mn-rich regions and Mn dilute matrix

  16. G. Stanley Hall, Child Study, and the American Public.

    PubMed

    Young, Jacy L

    2016-01-01

    In the final decades of the 19th century psychologist Granville Stanley Hall was among the most prominent pedagogical experts in the nation. The author explores Hall's carefully crafted persona as an educational expert, and his engagements with the American public, from 1880 to 1900, arguably the height of his influence. Drawing from accounts of Hall's lecture circuit in the popular press, a map of his talks across the nation is constructed to assess the geographic scope of his influence. These talks to educators on the psychology underlying childhood and pedagogy, and his views and research on child life more generally, were regularly discussed in newspapers and popular periodicals. The venues in which Hall's ideas were disseminated, discussed, and in some cases, dismissed are described. His efforts to mobilize popular support for, and assistance with, his research endeavors in child study are also discussed. Such efforts were controversial both within the burgeoning field of psychology and among the public. Through his various involvements in pedagogy, and concerted efforts to engage with the American public, Hall helped establish psychology's relevance to parenting and educational practices.

  17. Observation of anomalous Hall effect in a non-magnetic two-dimensional electron system

    PubMed Central

    Maryenko, D.; Mishchenko, A. S.; Bahramy, M. S.; Ernst, A.; Falson, J.; Kozuka, Y.; Tsukazaki, A.; Nagaosa, N.; Kawasaki, M.

    2017-01-01

    Anomalous Hall effect, a manifestation of Hall effect occurring in systems without time-reversal symmetry, has been mostly observed in ferromagnetically ordered materials. However, its realization in high-mobility two-dimensional electron system remains elusive, as the incorporation of magnetic moments deteriorates the device performance compared to non-doped structure. Here we observe systematic emergence of anomalous Hall effect in various MgZnO/ZnO heterostructures that exhibit quantum Hall effect. At low temperatures, our nominally non-magnetic heterostructures display an anomalous Hall effect response similar to that of a clean ferromagnetic metal, while keeping a large anomalous Hall effect angle θAHE≈20°. Such a behaviour is consistent with Giovannini–Kondo model in which the anomalous Hall effect arises from the skew scattering of electrons by localized paramagnetic centres. Our study unveils a new aspect of many-body interactions in two-dimensional electron systems and shows how the anomalous Hall effect can emerge in a non-magnetic system. PMID:28300133

  18. Nonlinear excitation of long-wavelength modes in Hall plasmas

    NASA Astrophysics Data System (ADS)

    Lakhin, V. P.; Ilgisonis, V. I.; Smolyakov, A. I.; Sorokina, E. A.

    2016-10-01

    Hall plasmas with magnetized electrons and unmagnetized ions exhibit a wide range of small scale fluctuations in the lower-hybrid frequency range as well as low-frequency large scale modes. Modulational instability of lower-hybrid frequency modes is investigated in this work for typical conditions in Hall plasma devices such as magnetrons and Hall thrusters. In these conditions, the dispersion of the waves in the lower-hybrid frequency range propagating perpendicular to the external magnetic field is due to the gradients of the magnetic field and the plasma density. It is shown that such lower-hybrid modes are unstable with respect to the secondary instability of the large scale quasimode perturbations. It is suggested that the large scale slow coherent modes observed in a number of Hall plasma devices may be explained as a result of such secondary instabilities.

  19. Performance Potential of Plasma Thrusters: Arcjet and Hall Thruster Modeling

    DTIC Science & Technology

    1993-09-17

    FUNDING NUMBERS Performance Potential of Plasma Thrusters: \\ Arcjet and Hall Thruster Modeling FQ 8671-9300908 S ,,G-AFOSR-91-0256 6. AUTHOR(S) Manuel...models for the internal physics and the performance of hydrogen arcjets and Hall thrusters , respectively. These are thought to represent the state of...work. 93-24268 14. SUBJECT TERMS IS. NUMBER OF PAGES Electric Propulsion, Arcjets, Hall Thrusters 15 16. PRICE COOE 17. SECURITY CLASSIFICATION I18

  20. Spin Hall Effect in Doped Semiconductor Structures

    NASA Astrophysics Data System (ADS)

    Tse, Wang-Kong; Das Sarma, S.

    2006-02-01

    In this Letter we present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump and skew-scattering contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show that their effects scale as σxySJ/σxySS˜(ℏ/τ)/ɛF, with τ being the transport relaxation time. Motivated by recent experimental work we apply our theory to n- and p-doped 3D and 2D GaAs structures, obtaining σs/σc˜10-3-10-4, where σs(c) is the spin Hall (charge) conductivity, which is in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)]SCIEAS0036-807510.1126/science.1105514 in n-doped 3D GaAs system.

  1. Spin Hall Effect in Doped Semiconductor Structures

    NASA Astrophysics Data System (ADS)

    Tse, Wang-Kong; Das Sarma, Sankar

    2006-03-01

    We present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump (SJ) and skew-scattering (SS) contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show their effects scale as σxy^SJ/σxy^SS ˜(/τ)/ɛF, where τ being the transport relaxation time. Motivated by recent experimental work we apply our theory to n-doped and p-doped 3D and 2D GaAs structures, obtaining analytical formulas for the SJ and SS contributions. Moreover, the ratio of the spin Hall conductivity to longitudinal conductivity is found as σs/σc˜10-3-10-4, in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)] in n-doped 3D GaAs system.

  2. Anomalous Hall Resistance in Bilayer Electron Systems

    NASA Astrophysics Data System (ADS)

    Ezawa, Z. F.; Suzuki, S.; Tsitsishvili, G.

    2007-04-01

    Interlayer phase coherence has revealed various novel features in bilayer quantum Hall (QH) systems. It is shown to make the QH resistance vanish instead of developing a Hall plateau in a bilayer counterflow geometry. It also induces another anomalous QH resistance discovered in a drag experiment. These theoretical results explain recent experimental data due to Kellogg et al. [PRL 93 (2004) 036801;PRL 88 (2002) 126804] and Tutuc et al.[PRL 93 (2004) 036802].

  3. Interior detail of dispatch boards in main hall, facing west ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Interior detail of dispatch boards in main hall, facing west - International Longshoremen's & Warehousemen's Union Hall, Naval Civil Engineering Laboratory, Port Hueneme Road, Port Hueneme, Ventura County, CA

  4. Giant spin Hall effect in graphene grown by chemical vapour deposition

    NASA Astrophysics Data System (ADS)

    Balakrishnan, Jayakumar; Koon, Gavin Kok Wai; Avsar, Ahmet; Ho, Yuda; Lee, Jong Hak; Jaiswal, Manu; Baeck, Seung-Jae; Ahn, Jong-Hyun; Ferreira, Aires; Cazalilla, Miguel A.; Neto, Antonio H. Castro; Özyilmaz, Barbaros

    2014-09-01

    Advances in large-area graphene synthesis via chemical vapour deposition on metals like copper were instrumental in the demonstration of graphene-based novel, wafer-scale electronic circuits and proof-of-concept applications such as flexible touch panels. Here, we show that graphene grown by chemical vapour deposition on copper is equally promising for spintronics applications. In contrast to natural graphene, our experiments demonstrate that chemically synthesized graphene has a strong spin-orbit coupling as high as 20 meV giving rise to a giant spin Hall effect. The exceptionally large spin Hall angle ~0.2 provides an important step towards graphene-based spintronics devices within existing complementary metal-oxide-semiconductor technology. Our microscopic model shows that unavoidable residual copper adatom clusters act as local spin-orbit scatterers and, in the resonant scattering limit, induce transverse spin currents with enhanced skew-scattering contribution. Our findings are confirmed independently by introducing metallic adatoms-copper, silver and gold on exfoliated graphene samples.

  5. View of north front and west sides of hall, facing ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View of north front and west sides of hall, facing south - International Longshoremen's & Warehousemen's Union Hall, Naval Civil Engineering Laboratory, Port Hueneme Road, Port Hueneme, Ventura County, CA

  6. Mixed-state Hall effect of high-T(c) superconductors

    NASA Astrophysics Data System (ADS)

    Kang, Byeongwon

    In this dissertation, we presented the study on the mixed-state Hall effect of high-Tc superconductors (HTSs). In order to understand the mechanisms of the puzzling phenomena in the mixed-state Hall effect of HTSs, the Hall sign anomaly and scaling behavior, Hall measurements are conducted in several HTS thin films. We investigate the mechanism of the sign reversal of the Hall resistivity in Tl-2201 films when the electronic band structure is varied through the underdoped, optimally doped, and overdoped regions. It is found that the Hall sign reversals are an intrinsic property of HTSs and determined by electronic band structure. Although pinning is not found to be the mechanism behind sign reversals, pinning can suppress the appearance of the Hall sign reversal. Therefore, it is concluded that two (or more) sign reversals are a generic behavior of HTSs. From a systematic study of the vortex phase diagram, we discover several new features of the vortex liquid. In the presence of pinning, the vortex-liquid phase can be divided into two regions, a glassy liquid (GL) where vortices remain correlated as manifested in non-Ohmic resistivity, and a regular liquid (RL) where resistivity becomes Ohmic as vortices become uncorrelated. The field dependence of the Hall angle is found to be linear in the RL and nonlinear in the GL. Generally the decoupling line (Hk- T), which is defined as a boundary between the GL and the RL, is lower than the depinning line (Hd-T). As pinning increases the Hk-T may approach the Hd-T, thus vortices are decoupled and depinned nearly simultaneously. For a weak pinning system, on the other hand, the Hk-T and the Hd-T are well separated so that single vortices remain pinned in the region Hk ≤ H ≥ Hd. The behavior of s xy is also investigated in the GL and the RL. In the GL s xy is observed to strongly depend on pinning due to the inter-vortex correlation whereas in the RL s xy is independent of pinning since the pinning effect is scaled out.

  7. Probing the thermal Hall effect using miniature capacitive strontium titanate thermometry

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tinsman, Colin; Li, Gang; Asaba, Tomoya

    2016-06-27

    The thermal Hall effect is the thermal analog of the electrical Hall effect. Rarely observed in normal metals, thermal Hall signals have been argued to be a key property for a number of strongly correlated materials, such as high temperature superconductors, correlated topological insulators, and quantum magnets. The observation of the thermal Hall effect requires precise measurement of temperature in intense magnetic fields. Particularly at low temperature, resistive thermometers have a strong dependence on field, which makes them unsuitable for this purpose. We have created capacitive thermometers which instead measure the dielectric constant of strontium titanate (SrTiO{sub 3}). SrTiO{sub 3}more » approaches a ferroelectric transition, causing its dielectric constant to increase by a few orders of magnitude at low temperature. As a result, these thermometers are very sensitive at low temperature while having very little dependence on the applied magnetic field, making them ideal for thermal Hall measurements. We demonstrate this method by making measurements of the thermal Hall effect in Bismuth in magnetic fields of up to 10 T.« less

  8. Accelerating 3D Hall MHD Magnetosphere Simulations with Graphics Processing Units

    NASA Astrophysics Data System (ADS)

    Bard, C.; Dorelli, J.

    2017-12-01

    The resolution required to simulate planetary magnetospheres with Hall magnetohydrodynamics result in program sizes approaching several hundred million grid cells. These would take years to run on a single computational core and require hundreds or thousands of computational cores to complete in a reasonable time. However, this requires access to the largest supercomputers. Graphics processing units (GPUs) provide a viable alternative: one GPU can do the work of roughly 100 cores, bringing Hall MHD simulations of Ganymede within reach of modest GPU clusters ( 8 GPUs). We report our progress in developing a GPU-accelerated, three-dimensional Hall magnetohydrodynamic code and present Hall MHD simulation results for both Ganymede (run on 8 GPUs) and Mercury (56 GPUs). We benchmark our Ganymede simulation with previous results for the Galileo G8 flyby, namely that adding the Hall term to ideal MHD simulations changes the global convection pattern within the magnetosphere. Additionally, we present new results for the G1 flyby as well as initial results from Hall MHD simulations of Mercury and compare them with the corresponding ideal MHD runs.

  9. Theoretical study of spin Hall effect in conjugated Organic semiconductors

    NASA Astrophysics Data System (ADS)

    Mahani, M. R.; Delin, A.

    The spin Hall effect (SHE), a direct conversion between electronic and spin currents, is a rapidly growing branch of spintronics. The study of SHE in conjugated polymers has gained momentum recently due to the weak spin-orbit couplings and hyperfine interactions in these materials. Our calculations of SHE based on the recent work, are the result of the misalignment of pi-orbitals in triads consisting of three molecules. In disordered organics, where the electronic conduction is through hopping of the electrons among randomly oriented molecules, instead of identifying a hopping triad to represent the entire system, we numerically solve the master equations for electrical and spin hall conductivities by summing the contributions from all triads in a sufficiently large system. The interference between the direct and indirect hoppings in these triads leads to SHE proportional to the orientation vector of molecule at the first order of spin-orbit coupling. Hence, our results show, the degree of molecular alignment as well as the strength of the spin-orbit coupling can be used to control the SHE in organics.

  10. Quantum transport in graphene Hall bars: Effects of side gates

    NASA Astrophysics Data System (ADS)

    Petrović, M. D.; Peeters, F. M.

    2017-05-01

    Quantum electron transport in side-gated graphene Hall bars is investigated in the presence of quantizing external magnetic fields. The asymmetric potential of four side-gates distorts the otherwise flat bands of the relativistic Landau levels, and creates new propagating states in the Landau spectrum (i.e. snake states). The existence of these new states leads to an interesting modification of the bend and Hall resistances, with new quantizing plateaus appearing in close proximity of the Landau levels. The electron guiding in this system can be understood by studying the current density profiles of the incoming and outgoing modes. From the fact that guided electrons fully transmit without any backscattering (similarly to edge states), we are able to analytically predict the values of the quantized resistances, and they match the resistance data we obtain with our numerical (tight-binding) method. These insights in the electron guiding will be useful in predicting the resistances for other side-gate configurations, and possibly in other system geometries, as long as there is no backscattering of the guided states.

  11. Comparison of two data acquisition and processing systems of Moller polarimeter in Hall A of Jefferson Lab

    DOE PAGES

    Vereshchaka, Vadym V.; Glamazdin, Oleksandr V.; Pomatsalyuk, Roman I.

    2014-07-01

    Two data acquisition and processing systems are used simultaneously to measure electron beam polarization by Moller polarimeter in Hall A of Jefferson Lab (Newport News, VA, USA). The old system (since 1997) is fully functional, but is not repairable in case of malfunction (system modules arenot manufactured anymore). The new system (since 2010) based on flash-ADC is more accurate, but currently requires more detailed adjustment and further improvement. Description and specifications of two data acquisition and processing systems have been given. The results of polarization measurements during experiments conducted in Hall A from 2010 to 2012 are compared.

  12. Hall effect and fine structures in magnetic reconnection with high plasma {beta}

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jin, S.P.; Yang, H.A.; Wang, X.G.

    2005-04-15

    Magnetic reconnection with various plasma {beta} (the ratio of plasma pressure to the magnetic pressure) is studied numerically using a 2.5 dimensional Hall magnetohydrodynamics (MHD) code developed from a multistep implicit scheme. The initial state of the Hall MHD simulation is an equilibrium Harris sheet with L{sub c}=0.5d{sub i} (where L{sub c} is the half-width of the equilibrium current layer and d{sub i} is the ion inertial length) and a zero guide field (i.e., B{sub y0}=0 at t=0). Driven by a constant boundary inflow a quasisteady fast reconnection occurs in the plasma with a low uniform resistivity. The out-of-plane magneticmore » field component B{sub y} is then spontaneously generated and its quadrupolar structure is shown around the X point. It is demonstrated by the comparing studies that the reconnection dynamics is controlled by the Hall effect and the effect of scalar electron pressure gradient is negligible in the generalized Ohm's law. It is also found that the openness of the magnetic separatrix angle and associated quadrupolar B{sub y} structure is enlarged as {beta} increases. When {beta}>2.0 fine structures of B{sub y} contours with reversed sign emerge. The numerical results indicate that the variations in electron velocity V{sub e} are greater than those in ion velocity V{sub i} and the decoupling of electron and ion occurs in larger scale lengths than d{sub i} as {beta} increases. Clearly, the reserve current, which is associated with the relative motion between electrons and ions, generates the fine structures of B{sub y} contours in the outflow region. Then the corresponding profile of B{sub y} component exhibits a static whistler wave signature. Enhanced wave activities observed during a Cluster crossing of the high-{beta} exterior cusp region [Y. Khotyaintsev, A. Vaivads, Y. Ogawa, B. Popielawska, M. Andre, S. Buchert, P. Decreau, B. Lavraud, and H. Reme, Ann. Geophys. 22, 2403 (2004)] might be related to the Hall effects of magnetic

  13. Note: Broadband low-noise photodetector for Pound-Drever-Hall laser stabilization

    NASA Astrophysics Data System (ADS)

    Potnis, Shreyas; Vutha, Amar C.

    2016-07-01

    The Pound-Drever-Hall laser stabilization technique requires a fast, low-noise photodetector. We present a simple photodetector design that uses a transformer as an intermediary between a photodiode and cascaded low-noise radio-frequency amplifiers. Our implementation using a silicon photodiode yields a detector with 50 MHz bandwidth, gain >105 V/A, and input current noise <4 pA/ √{ Hz } , allowing us to obtain shot-noise-limited performance with low optical power.

  14. Timber Creek bunkhouse and mess hall, Rocky Mountain National Park. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Timber Creek bunkhouse and mess hall, Rocky Mountain National Park. Interior, kitchen and dining area, viewing north. - Timber Creek Bunkhouse & Mess Hall, Trail Ridge Road, Grand Lake, Grand County, CO

  15. Developments in Scanning Hall Probe Microscopy

    NASA Astrophysics Data System (ADS)

    Chouinard, Taras; Chu, Ricky; David, Nigel; Broun, David

    2009-05-01

    Low temperature scanning Hall probe microscopy is a sensitive means of imaging magnetic structures with high spatial resolution and magnetic flux sensitivity approaching that of a Superconducting Quantum Interference Device. We have developed a scanning Hall probe microscope with novel features, including highly reliable coarse positioning, in situ optimization of sensor-sample alignment and capacitive transducers for linear, long range positioning measurement. This has been motivated by the need to reposition accurately above fabricated nanostructures such as small superconducting rings. Details of the design and performance will be presented as well as recent progress towards time-resolved measurements with sub nanosecond resolution.

  16. Hall effect spintronics for gas detection

    NASA Astrophysics Data System (ADS)

    Gerber, A.; Kopnov, G.; Karpovski, M.

    2017-10-01

    We present the concept of magnetic gas detection by the extraordinary Hall effect. The technique is compatible with the existing conductometric gas detection technologies and allows the simultaneous measurement of two independent parameters: resistivity and magnetization affected by the target gas. Feasibility of the approach is demonstrated by detecting low concentration hydrogen using thin CoPd films as the sensor material. The Hall effect sensitivity of the optimized samples exceeds 240% per 104 ppm at hydrogen concentrations below 0.5% in the hydrogen/nitrogen atmosphere, which is more than two orders of magnitude higher than the sensitivity of the conductance detection.

  17. High-performance LED luminaire for sports hall

    NASA Astrophysics Data System (ADS)

    Lee, Xuan-Hao; Yang, Jin-Tsung; Chien, Wei-Ting; Chang, Jung-Hsuan; Lo, Yi-Chien; Lin, Che-Chu; Sun, Ching-Cherng

    2015-09-01

    In this paper, we present a luminaire design with anti-glare and energy-saving effects for sports hall. Compared with traditional lamps using in a badminton court, the average illuminance on the ground of the proposed LED luminaire is enhanced about 300%. Besides, the uniformity is obviously enhanced and improved. The switch-on speed of lighting in sports hall is greatly reduced from 5-10 minutes to 1 second. The simulation analysis and the corresponding experiment results are demonstrated.

  18. Kids in the Hall.

    ERIC Educational Resources Information Center

    Swanquist, Barry

    2000-01-01

    Discusses resident hall furniture design that meets student needs as well as the needs of administrators and parents. Furniture design issues examined include the higher expectations of students in their living environment, the need for greater flexibility in space utilization, and adaptability to technology. (GR)

  19. Detail of main hall porch on east elevation; camera facing ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Detail of main hall porch on east elevation; camera facing west. - Mare Island Naval Shipyard, Wilderman Hall, Johnson Lane, north side adjacent to (south of) Hospital Complex, Vallejo, Solano County, CA

  20. Interior detail of platform in main hall, with desk, flag, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Interior detail of platform in main hall, with desk, flag, and banners, facing south - International Longshoremen's & Warehousemen's Union Hall, Naval Civil Engineering Laboratory, Port Hueneme Road, Port Hueneme, Ventura County, CA

  1. Useful Pedagogical Applications of the Classical Hall Effect

    ERIC Educational Resources Information Center

    Houari, Ahmed

    2007-01-01

    One of the most known phenomena in physics is the Hall effect. This is mainly due to its simplicity and to the wide range of its theoretical and practical applications. To complete the pedagogical utility of the Hall effect in physics teaching, I will apply it here to determine the Faraday constant as a fundamental physical number and the number…

  2. Rule-based fault diagnosis of hall sensors and fault-tolerant control of PMSM

    NASA Astrophysics Data System (ADS)

    Song, Ziyou; Li, Jianqiu; Ouyang, Minggao; Gu, Jing; Feng, Xuning; Lu, Dongbin

    2013-07-01

    Hall sensor is widely used for estimating rotor phase of permanent magnet synchronous motor(PMSM). And rotor position is an essential parameter of PMSM control algorithm, hence it is very dangerous if Hall senor faults occur. But there is scarcely any research focusing on fault diagnosis and fault-tolerant control of Hall sensor used in PMSM. From this standpoint, the Hall sensor faults which may occur during the PMSM operating are theoretically analyzed. According to the analysis results, the fault diagnosis algorithm of Hall sensor, which is based on three rules, is proposed to classify the fault phenomena accurately. The rotor phase estimation algorithms, based on one or two Hall sensor(s), are initialized to engender the fault-tolerant control algorithm. The fault diagnosis algorithm can detect 60 Hall fault phenomena in total as well as all detections can be fulfilled in 1/138 rotor rotation period. The fault-tolerant control algorithm can achieve a smooth torque production which means the same control effect as normal control mode (with three Hall sensors). Finally, the PMSM bench test verifies the accuracy and rapidity of fault diagnosis and fault-tolerant control strategies. The fault diagnosis algorithm can detect all Hall sensor faults promptly and fault-tolerant control algorithm allows the PMSM to face failure conditions of one or two Hall sensor(s). In addition, the transitions between health-control and fault-tolerant control conditions are smooth without any additional noise and harshness. Proposed algorithms can deal with the Hall sensor faults of PMSM in real applications, and can be provided to realize the fault diagnosis and fault-tolerant control of PMSM.

  3. Interior of Mess Hall, showing original columns and quarry tile ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Interior of Mess Hall, showing original columns and quarry tile floor - U.S. Naval Base, Pearl Harbor, Barracks & Mess Hall, Hornet Avenue between Liscome Bay & Enterprise Streets, Pearl City, Honolulu County, HI

  4. Contextual view of ILWU Hall, facing northwest with commercial port ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Contextual view of ILWU Hall, facing northwest with commercial port buildings visible in the background - International Longshoremen's & Warehousemen's Union Hall, Naval Civil Engineering Laboratory, Port Hueneme Road, Port Hueneme, Ventura County, CA

  5. Contextual view of ILWU Hall, facing southsouthwest, with ocean bank ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Contextual view of ILWU Hall, facing south-southwest, with ocean bank visible in the background - International Longshoremen's & Warehousemen's Union Hall, Naval Civil Engineering Laboratory, Port Hueneme Road, Port Hueneme, Ventura County, CA

  6. Development of internal magnetic probe for current density profile measurement in Versatile Experiment Spherical Torus

    NASA Astrophysics Data System (ADS)

    Yang, J.; Lee, J. W.; Jung, B. K.; Chung, K. J.; Hwang, Y. S.

    2014-11-01

    An internal magnetic probe using Hall sensors to measure a current density profile directly with perturbation of less than 10% to the plasma current is successfully operated for the first time in Versatile Experiment Spherical Torus (VEST). An appropriate Hall sensor is chosen to produce sufficient signals for VEST magnetic field while maintaining the small size of 10 mm in outer diameter. Temperature around the Hall sensor in a typical VEST plasma is regulated by blown air of 2 bars. First measurement of 60 kA VEST ohmic discharge shows a reasonable agreement with the total plasma current measured by Rogowski coil in VEST.

  7. First demonstration of HF-driven ionospheric currents

    NASA Astrophysics Data System (ADS)

    Papadopoulos, K.; Chang, C.-L.; Labenski, J.; Wallace, T.

    2011-10-01

    The first experimental demonstration of HF driven currents in the ionosphere at low ELF/ULF frequencies without relying in the presence of electrojets is presented. The effect was predicted by theoretical/computational means in a recent letter and given the name Ionospheric Current Drive (ICD). The effect relies on modulated F-region HF heating to generate Magneto-Sonic (MS) waves that drive Hall currents when they reach the E-region. The Hall currents inject ELF waves into the Earth-Ionosphere waveguide and helicon and Shear Alfven (SA) waves in the magnetosphere. The proof-of-concept experiments were conducted using the HAARP heater in Alaska under the BRIOCHE program. Waves between 0.1-70 Hz were measured at both near and far sites. The letter discusses the differences between ICD generated waves and those relying on modulation of electrojets.

  8. NASA HERMeS Hall Thruster Electrical Configuration Characterization

    NASA Technical Reports Server (NTRS)

    Peterson, Peter; Kamhawi, Hani; Huang, Wensheng; Yim, John; Herman, Daniel; Williams, George; Gilland, James; Hofer, Richard

    2016-01-01

    NASAs Hall Effect Rocket with Magnetic Shielding (HERMeS) 12.5 kW Technology Demonstration Unit-1 (TDU-1) Hall thruster has been the subject of extensive technology maturation in preparation for development into a flight ready propulsion system. Part of the technology maturation was to test the TDU-1 thruster in several ground based electrical configurations to assess the thruster robustness and suitability to successful in-space operation. The ground based electrical configuration testing has recently been demonstrated as an important step in understanding and assessing how a Hall thruster may operate differently in space compared to ground based testing, and to determine the best configuration to conduct development and qualification testing. This presentation will cover the electrical configuration testing of the TDU-1 HERMeS Hall thruster in NASA Glenn Research Centers Vacuum Facility 5. The three electrical configurations examined are the thruster body tied to facility ground, thruster floating, and finally the thruster body electrically tied to cathode common. The TDU-1 HERMeS was configured with two different exit plane boundary conditions, dielectric and conducting, to examine the influence on the electrical configuration characterization.

  9. Inverse spin Hall effect by spin injection

    NASA Astrophysics Data System (ADS)

    Liu, S. Y.; Horing, Norman J. M.; Lei, X. L.

    2007-09-01

    Motivated by a recent experiment [S. O. Valenzuela and M. Tinkham, Nature (London) 442, 176 (2006)], the authors present a quantitative microscopic theory to investigate the inverse spin-Hall effect with spin injection into aluminum considering both intrinsic and extrinsic spin-orbit couplings using the orthogonalized-plane-wave method. Their theoretical results are in good agreement with the experimental data. It is also clear that the magnitude of the anomalous Hall resistivity is mainly due to contributions from extrinsic skew scattering.

  10. Contextual view of ILWU Hall, facing east, with the city ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Contextual view of ILWU Hall, facing east, with the city of Port Hueneme visible in the background - International Longshoremen's & Warehousemen's Union Hall, Naval Civil Engineering Laboratory, Port Hueneme Road, Port Hueneme, Ventura County, CA

  11. G. Stanley Hall and The Journal of Genetic Psychology: A Note.

    PubMed

    Hogan, John D

    2016-01-01

    The Journal of Genetic Psychology (originally called The Pedagogical Seminary) has a complicated history. Known primarily as a journal of development psychology, it was originally intended to be a journal of higher education. In addition, G. Stanley Hall created it, at least in part, to curry favor with Jonas Clark, the benefactor of Clark University. The journal had a cumbersome start, with irregular issues for most of its first decade. Hall was a hands-on editor, often contributing articles and reviews as well as the texts of many of his speeches. A substantial number of additional articles were written by Clark University faculty and fellows where Hall was president. After Hall.s death, the editor became Carl Murchison who eventually left Clark University with the journal and continued to publish it privately until his death. Through the years, the journal has been the source for many classic articles in developmental psychology.

  12. Enhanced spin Hall ratios by Al and Hf impurities in Pt thin films

    NASA Astrophysics Data System (ADS)

    Nguyen, Minh-Hai; Zhao, Mengnan; Ralph, Daniel C.; Buhrman, Robert A.

    The spin Hall effect (SHE) in Pt has been reported to be strong and hence promising for spintronic applications. In the intrinsic SHE mechanism, which has been shown to be dominant in Pt, the spin Hall conductivity σSH is constant, dependent only on the band structure of the spin Hall material. The spin Hall ratio θSH =σSH . ρ , on the other hand, should be proportional to the electrical resistivity ρ of the spin Hall layer. This suggests the possibility of enhancing the spin Hall ratio by introducing additional diffusive scattering to increase the electrical resistivity of the spin Hall layer. Our previous work has shown that this could be done by increasing the surface scattering by growing thinner Pt films in contact with higher resistivity materials such as Ta. In this talk, we discuss another approach: to introduce impurities of metals with negligible spin orbit torque into the Pt film. Our PtAl and PtHf alloy samples exhibit strong enhancement of the spin Hall torque efficiency with impurity concentration due to increased electrical resistivity. Supported in part by Samsung Electronics.

  13. Very-Near-Field Plume Model of a Hall Thruster

    DTIC Science & Technology

    2003-07-20

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP014988 TITLE: Very-Near-Field Plume Model of a Hall Thruster DISTRIBUTION...numbers comprise the compilation report: ADP014936 thru ADP015049 UNCLASSIFIED am 46 Very-Near-Field Plume Model of a Hall Thruster F. Taccogna’, S. LongoŖ

  14. High Life: 17th Annual Residence Hall Construction Report

    ERIC Educational Resources Information Center

    Agron, Joe

    2006-01-01

    Residence hall construction continues to be a priority for colleges and universities. With enrollments on the upswing, higher-education institutions are spending more and building larger facilities to entice students to live on campus. This article presents the findings of "American School & University's" 17th annual Residence Hall Construction…

  15. Pure spin-Hall magnetoresistance in Rh/Y3Fe5O12 hybrid

    NASA Astrophysics Data System (ADS)

    Shang, T.; Zhan, Q. F.; Ma, L.; Yang, H. L.; Zuo, Z. H.; Xie, Y. L.; Li, H. H.; Liu, L. P.; Wang, B. M.; Wu, Y. H.; Zhang, S.; Li, Run-Wei

    2015-12-01

    We report an investigation of anisotropic magnetoresistance (AMR) and anomalous Hall resistance (AHR) of Rh and Pt thin films sputtered on epitaxial Y3Fe5O12 (YIG) ferromagnetic insulator films. For the Pt/YIG hybrid, large spin-Hall magne toresistance (SMR) along with a sizable conventional anisotropic magnetoresistance (CAMR) and a nontrivial temperature dependence of AHR were observed in the temperature range of 5-300 K. In contrast, a reduced SMR with negligible CAMR and AHR was found in Rh/YIG hybrid. Since CAMR and AHR are characteristics for all ferromagnetic metals, our results suggest that the Pt is likely magnetized by YIG due to the magnetic proximity effect (MPE) while Rh remains free of MPE. Thus the Rh/YIG hybrid could be an ideal model system to explore physics and devices associated with pure spin current.

  16. Spin-Hall effect and emergent antiferromagnetic phase transition in n-Si

    NASA Astrophysics Data System (ADS)

    Lou, Paul C.; Kumar, Sandeep

    2018-04-01

    Spin current experiences minimal dephasing and scattering in Si due to small spin-orbit coupling and spin-lattice interactions is the primary source of spin relaxation. We hypothesize that if the specimen dimension is of the same order as the spin diffusion length then spin polarization will lead to non-equilibrium spin accumulation and emergent phase transition. In n-Si, spin diffusion length has been reported up to 6 μm. The spin accumulation in Si will modify the thermal transport behavior of Si, which can be detected with thermal characterization. In this study, we report observation of spin-Hall effect and emergent antiferromagnetic phase transition behavior using magneto-electro-thermal transport characterization. The freestanding Pd (1 nm)/Ni80Fe20 (75 nm)/MgO (1 nm)/n-Si (2 μm) thin film specimen exhibits a magnetic field dependent thermal transport and spin-Hall magnetoresistance behavior attributed to Rashba effect. An emergent phase transition is discovered using self-heating 3ω method, which shows a diverging behavior at 270 K as a function of temperature similar to a second order phase transition. We propose that spin-Hall effect leads to the spin accumulation and resulting emergent antiferromagnetic phase transition. We propose that the length scale for Rashba effect can be equal to the spin diffusion length and two-dimensional electron gas is not essential for it. The emergent antiferromagnetic phase transition is attributed to the site inversion asymmetry in diamond cubic Si lattice.

  17. Hall-effect Thruster Channel Surface Properties Investigation (PREPRINT)

    DTIC Science & Technology

    2011-03-03

    Article 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Hall-effect Thruster Channel Surface Properties Investigation 5b...13. SUPPLEMENTARY NOTES For publication in the AIAA Journal of Propulsion and Power. 14. ABSTRACT Surface properties of Hall-effect thruster...incorporated into thruster simulations, and these models must account for evolution of channel surface properties due to thruster operation. Results from

  18. The Hall Effect in Hydrided Rare Earth Films

    NASA Astrophysics Data System (ADS)

    Koon, D. W.; Azofeifa, D. E.; Clark, N.

    We describe two new techniques for measuring the Hall effect in capped rare earth films during hydriding. In one, we simultaneously measure resistivity and the Hall coefficient for a rare earth film covered with four different thicknesses of Pd, recovering the charge transport quantities for both materials. In the second technique, we replace Pd with Mn as the covering layer. We will present results from both techniques.

  19. 71. FIRST FLOOR, ROOM 101, ENTRANCE HALL (SIDE WITH FIRE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    71. FIRST FLOOR, ROOM 101, ENTRANCE HALL (SIDE WITH FIRE DETECTOR), ARCHWAY TO STAIR HALL 100, LOOKING UP, DETAIL OF ARCHWAY SOFFIT. - Octagon House, 1799 (1741) New York Avenue, Northwest, Washington, District of Columbia, DC

  20. Design and Testing of a Hall Effect Thruster with Additively Manufactured Components

    NASA Astrophysics Data System (ADS)

    Hopping, Ethan

    The UAH-78AM is a low-power Hall effect thruster developed at the University of Alabama in Huntsville to study the application of low-cost additive manufacturing in the design and fabrication of Hall thrusters. The goal of this project is to assess the feasibility of using unconventional materials to produce a low-cost functioning Hall effect thruster and consider how additive manufacturing can expand the design space and provide other benefits. The thruster features channel walls and a propellant distributor that were manufactured using 3D printing with a variety of materials including ABS, ULTEM, and glazed ceramic. A version of the thruster was tested at NASA Glenn Research Center to obtain performance metrics and to validate the ability of the thruster to produce thrust and sustain a discharge. The design of the thruster and the transient performance measurements are presented here. Measured thrust ranged from 17.2 mN to 30.4 mN over a discharge power of 280 W to 520 W with an anode Isp range of 870 s to 1450 s. Temperature limitations of materials used for the channel walls and propellant distributor limit the ability to run the thruster at thermal steady-state. While the current thruster design is not yet ready for continuous operation, revisions to the device that could enable longer duration tests are discussed.

  1. Universal DC Hall conductivity of Jain's state ν = N/2N +/- 1

    NASA Astrophysics Data System (ADS)

    Nguyen, Dung; Son, Dam

    We present the Fermi-liquid theory of the fractional quantum Hall effect to describe Jain's states with filling fraction ν =N/2 N +/- 1 , that are near half filling. We derive the DC Hall conductivity σH (t) in closed form within the validity of our model. The results show that, without long range interaction, DC Hall conductivity has the universal form which doesn't depend on the detail of short range Landau's parameters Fn. When long range interaction is included, DC Hall conductivity depends on both long range interaction and Landau's parameters. We also analyze the relation between DC Hall conductivity and static structure factor. This work was supported by the Chicago MRSEC, which is funded by NSF through Grant DMR-1420709.

  2. Temperature dependence of the enhanced inverse spin Hall voltage in Pt/Antiferromagnetic/ Y3Fe5O12

    NASA Astrophysics Data System (ADS)

    Brangham, J. T.; Lee, A. J.; Cheng, Y.; Yu, S. S.; Dunsiger, S. R.; Page, M. R.; Hammel, P. C.; Yang, F. Y.

    The generation, propagation, and detection of spin currents are of intense interest in the field of spintronics. Spin current generation by FMR spin pumping using Y3Fe5O12 (YIG) and spin current detection by the inverse spin Hall effect (ISHE) in metals such as Pt have been well studied. This is due to YIG's exceptionally low damping and insulating behavior and the large spin Hall angle of Pt. Previously, our group showed that the ISHE voltages are significantly enhanced by adding a thin intermediate layer of an antiferromagnet (AFM) between Pt and YIG at room temperature. Recent theoretical work predicts a mechanism for this enhancement as well as the temperature dependence of the ISHE voltages of metal/AFM/YIG trilayers. The predictions show a maximum in the ISHE voltages for these systems near the magnetic phase transition temperature of the AFM. Here we present experimental results showing the temperature dependence for Pt/AFM/YIG structures with various AFMs. DOE Grant No. DE-SC0001304.

  3. Kelvin-Helmholtz versus Hall magnetoshear instability in astrophysical flows.

    PubMed

    Gómez, Daniel O; Bejarano, Cecilia; Mininni, Pablo D

    2014-05-01

    We study the stability of shear flows in a fully ionized plasma. Kelvin-Helmholtz is a well-known macroscopic and ideal shear-driven instability. In sufficiently low-density plasmas, also the microscopic Hall magnetoshear instability can take place. We performed three-dimensional simulations of the Hall-magnetohydrodynamic equations where these two instabilities are present, and carried out a comparative study. We find that when the shear flow is so intense that its vorticity surpasses the ion-cyclotron frequency of the plasma, the Hall magnetoshear instability is not only non-negligible, but it actually displays growth rates larger than those of the Kelvin-Helmholtz instability.

  4. 68. TURBINE HALL, LOOKING DOWN FROM THE CONTROL ROOM INTO ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    68. TURBINE HALL, LOOKING DOWN FROM THE CONTROL ROOM INTO TURBINE HALL AT UNITS 3, 5, AND 2) - Delaware County Electric Company, Chester Station, Delaware River at South end of Ward Street, Chester, Delaware County, PA

  5. Residence Hall Discipline as a Function of Personality Type.

    ERIC Educational Resources Information Center

    Williams, W. C.; Nelson, Susan Innmon

    1986-01-01

    Administered personality measures to residence hall personnel (N=48) to test assertive, nonassertive, or hostile responses to describe residence hall disciplinary situations. Found that not all personnel were well suited to college student disciplining and that the personality tests could be used to identify individuals who may be best suited for…

  6. Implementing Proactive Network Management Solutions in the Residence Halls

    ERIC Educational Resources Information Center

    Bedi, Param

    2005-01-01

    This paper discusses how to implement networking solutions in residence halls at Arcadia University in Philadelphia. Sections of the paper include: (1) About Arcadia University; (2) Residence Halls Network; (3) How Campus Manager Helped Arcadia University; (4) What Is Campus Manager; (5) How Campus Manager Works; (6) Campus Manager Remediation…

  7. An End-to-End Model of a Hall Thruster

    DTIC Science & Technology

    2000-09-01

    and deposition of sputtered material, simulation of the operator of a Hall Thruster in a vacuum tank and the extension to the near-plume of a...sophisticated Hall thruster transient hybrid PlC model which had been previously used only to describe the internal flow. The first two items have been

  8. High Performance Power Module for Hall Effect Thrusters

    NASA Technical Reports Server (NTRS)

    Pinero, Luis R.; Peterson, Peter Y.; Bowers, Glen E.

    2002-01-01

    Previous efforts to develop power electronics for Hall thruster systems have targeted the 1 to 5 kW power range and an output voltage of approximately 300 V. New Hall thrusters are being developed for higher power, higher specific impulse, and multi-mode operation. These thrusters require up to 50 kW of power and a discharge voltage in excess of 600 V. Modular power supplies can process more power with higher efficiency at the expense of complexity. A 1 kW discharge power module was designed, built and integrated with a Hall thruster. The breadboard module has a power conversion efficiency in excess of 96 percent and weighs only 0.765 kg. This module will be used to develop a kW, multi-kW, and high voltage power processors.

  9. Interior view, groundfloor dining hall extending across the rotunda extension ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Interior view, ground-floor dining hall extending across the rotunda extension from it's northern exterior wall to its southern exterior wall, from the north. - U. S. Naval Asylum, Biddle Hall, Gray's Ferry Avenue, Philadelphia, Philadelphia County, PA

  10. Suitable reverberation times for halls for rock and pop music.

    PubMed

    Adelman-Larsen, Niels Werner; Thompson, Eric R; Gade, Anders C

    2010-01-01

    The existing body of literature regarding the acoustic design of concert halls has focused almost exclusively on classical music, although there are many more performances of popular music, including rock and pop. Objective measurements were made of the acoustics of 20 rock music venues in Denmark and a questionnaire was used in a subjective assessment of those venues with professional rock musicians and sound engineers as expert listeners. Correlations between the measurements show that clarity, including bass frequencies down to 63 Hz, is important for the general impression of the acoustics of the hall. The best-rated halls in the study have reverberation times that are approximately frequency independent from 0.6 to 1.2 s for hall volumes from 1000 to 6000 m(3). The worst rated halls in the study had significantly higher reverberation times in the 63 and 125 Hz bands. Since most audiences at rock concerts are standing, absorption coefficients were measured with a standing audience from 63 Hz to 4 kHz. These measurements showed that a standing audience absorbs about five times as much energy in mid-/high-frequency bands as in low-frequency bands.

  11. Measuring the Hall weighting function for square and cloverleaf geometries

    NASA Astrophysics Data System (ADS)

    Scherschligt, Julia K.; Koon, Daniel W.

    2000-02-01

    We have directly measured the Hall weighting function—the sensitivity of a four-wire Hall measurement to the position of macroscopic inhomogeneities in Hall angle—for both a square shaped and a cloverleaf specimen. Comparison with the measured resistivity weighting function for a square geometry [D. W. Koon and W. K. Chan, Rev. Sci. Instrum. 69, 12 (1998)] proves that the two measurements sample the same specimen differently. For Hall measurements on both a square and a cloverleaf, the function is nonnegative with its maximum in the center and its minimum of zero at the edges of the square. Converting a square into a cloverleaf is shown to dramatically focus the measurement process onto a much smaller portion of the specimen. While our results agree qualitatively with theory, details are washed out, owing to the finite size of the magnetic probe used.

  12. A Small Modular Laboratory Hall Effect Thruster

    NASA Astrophysics Data System (ADS)

    Lee, Ty Davis

    Electric propulsion technologies promise to revolutionize access to space, opening the door for mission concepts unfeasible by traditional propulsion methods alone. The Hall effect thruster is a relatively high thrust, moderate specific impulse electric propulsion device that belongs to the class of electrostatic thrusters. Hall effect thrusters benefit from an extensive flight history, and offer significant performance and cost advantages when compared to other forms of electric propulsion. Ongoing research on these devices includes the investigation of mechanisms that tend to decrease overall thruster efficiency, as well as the development of new techniques to extend operational lifetimes. This thesis is primarily concerned with the design and construction of a Small Modular Laboratory Hall Effect Thruster (SMLHET), and its operation on argon propellant gas. Particular attention was addressed at low-cost, modular design principles, that would facilitate simple replacement and modification of key thruster parts such as the magnetic circuit and discharge channel. This capability is intended to facilitate future studies of device physics such as anomalous electron transport and magnetic shielding of the channel walls, that have an impact on thruster performance and life. Preliminary results demonstrate SMLHET running on argon in a manner characteristic of Hall effect thrusters, additionally a power balance method was utilized to estimate thruster performance. It is expected that future thruster studies utilizing heavier though more expensive gases like xenon or krypton, will observe increased efficiency and stability.

  13. Laser characterization of electric field oscillations in the Hall thruster breathing mode

    NASA Astrophysics Data System (ADS)

    Young, Christopher; Lucca Fabris, Andrea; MacDonald-Tenenbaum, Natalia; Hargus, William, Jr.; Cappelli, Mark

    2016-10-01

    Hall thrusters are a mature technology for space propulsion applications that exhibit a wide array of dynamic behavior, including plasma waves, instabilities and turbulence. One common low frequency (10-50 kHz) discharge current oscillation is the breathing mode, a cycle of neutral propellant injection, strong ionization, and ion acceleration by a steep potential gradient. A time-resolved laser-induced fluorescence diagnostic non-intrusively captures this propagating ionization front in the channel of a commercial BHT-600 Hall thruster manufactured by Busek Co. Measurements of ion velocity and relative ion density (using the 5 d[ 4 ] 7 / 2 - 6 p[ 3 ] 5 / 2 Xe II transition at 834.95 nm, vacuum) reveal a dynamic electric field structure traversing the channel throughout the breathing mode cycle. This work is sponsored by the U.S. Air Force Office of Scientific Research, with Dr. M. Birkan as program manager. C.Y. acknowledges support from the DOE NSSA Stewardship Science Graduate Fellowship under contract DE-FC52-08NA28752.

  14. Influence of Hall Effect on Magnetic Control of Stagnation Point Heat Transfer

    NASA Astrophysics Data System (ADS)

    Poggie, Jonathan; Gaitonde, Datta

    2001-11-01

    Electromagnetic control is an appealing possibility for mitigating the thermal loads that occur in hypersonic flight. There was extensive research on this technique in the past (up to about 1970), but enthusiasm waned because of problems of system cost and weight. Renewed interest has arisen recently due to developments in the technology of super-conducting magnets and the understanding of the physics of weakly-ionized, non-equilibrium plasmas. A problem of particular interest is the reduction of stagnation point heating during atmospheric entry by magnetic deceleration of the flow in the shock layer. For the case of hypersonic flow over a sphere, a reduction in heat flux has been observed with the application of a dipole magnetic field (Poggie and Gaitonde, AIAA Paper 2001-0196). The Hall effect has a detrimental influence on this control scheme, tending to rotate the current vector out of the circumferential direction and to reduce the impact of the applied magnetic field on the fluid. In the present work we re-examine this problem by using modern computational methods to simulate flow past a hemispherical-nosed vehicle in which a axially-oriented magnetic dipole has been placed. The deleterious effects of the Hall current are characterized, and are observed to diminish when the surface of the vehicle is conducting.

  15. A Preliminary Investigation of Hall Thruster Technology

    NASA Technical Reports Server (NTRS)

    Gallimore, Alec D.

    1997-01-01

    A three-year, NASA/BMDO-sponsored experimental program to conduct performance and plume plasma property measurements on two Russian Stationary Plasma Thrusters (SPTs) has been completed. The program utilized experimental facilitates at the University of Michigan's Plasmadynamics and Electric Propulsion Laboratory (PEPL). The main features of the proposed effort were as follows: We Characterized Hall thruster [and arcjet] performance by measuring ion exhaust velocity with probes at various thruster conditions. Used a variety of probe diagnostics in the thruster plume to measure plasma properties and flow properties including T(sub e) and n(sub e), ion current density and ion energy distribution, and electric fields by mapping plasma potential. Used emission spectroscopy to identify species within the plume and to measure electron temperatures.

  16. 3D Quantum Hall Effect of Fermi Arc in Topological Semimetals

    NASA Astrophysics Data System (ADS)

    Wang, C. M.; Sun, Hai-Peng; Lu, Hai-Zhou; Xie, X. C.

    2017-09-01

    The quantum Hall effect is usually observed in 2D systems. We show that the Fermi arcs can give rise to a distinctive 3D quantum Hall effect in topological semimetals. Because of the topological constraint, the Fermi arc at a single surface has an open Fermi surface, which cannot host the quantum Hall effect. Via a "wormhole" tunneling assisted by the Weyl nodes, the Fermi arcs at opposite surfaces can form a complete Fermi loop and support the quantum Hall effect. The edge states of the Fermi arcs show a unique 3D distribution, giving an example of (d -2 )-dimensional boundary states. This is distinctly different from the surface-state quantum Hall effect from a single surface of topological insulator. As the Fermi energy sweeps through the Weyl nodes, the sheet Hall conductivity evolves from the 1 /B dependence to quantized plateaus at the Weyl nodes. This behavior can be realized by tuning gate voltages in a slab of topological semimetal, such as the TaAs family, Cd3 As2 , or Na3Bi . This work will be instructive not only for searching transport signatures of the Fermi arcs but also for exploring novel electron gases in other topological phases of matter.

  17. 12. BUILDING 324, INTERIOR, ENTRY HALL AND STAIRWAY, FROM SOUTH ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    12. BUILDING 324, INTERIOR, ENTRY HALL AND STAIRWAY, FROM SOUTH ENTRY, LOOKING NORTH, WITH HALL LEADING TO GARAGE TO RIGHT OF STAIRWAY. - Oakland Naval Supply Center, Commanding Officers Residences, Between E & F Streets, West of Fourth Street, Oakland, Alameda County, CA

  18. 24. BEDROOM #1 INTERIOR SHOWING OPEN DOOR TO HALL WITH ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    24. BEDROOM #1 INTERIOR SHOWING OPEN DOOR TO HALL WITH HALL LINEN CLOSETS VISIBLE IN BACKGROUND, AND PARTIALLY OPEN DOOR TO CLOSET. VIEW TO EAST. - Big Creek Hydroelectric System, Powerhouse 8, Operator Cottage, Big Creek, Big Creek, Fresno County, CA

  19. Mary E. Hall: Dawn of the Professional School Librarian

    ERIC Educational Resources Information Center

    Alto, Teresa

    2012-01-01

    A century ago, a woman named Mary E. Hall convinced school leaders of the need for the professional school librarian--a librarian who cultivated a love of reading, academic achievement, and independent learning skills. After graduating from New York City's Pratt Institute Library School in 1895, Hall developed her vision for the high school…

  20. First Firing of a 100-kW Nested-Channel Hall Thruster

    DTIC Science & Technology

    2013-09-01

    Technical Paper 3. DATES COVERED (From - To) September 2013- December 2013 4. TITLE AND SUBTITLE First Firing of a 100-kW Nested-Channel Hall Thruster 5a...STATEMENT A: Approved for public release; distribution unlimited. 1 First Firing of a 100-kW Nested-channel Hall Thruster IEPC-2013-394...converting electrical power to directed kinetic power I. Introduction ESTING the channels of Hall thrusters has proven to be a viable method to increase

  1. Multifunctional semiconductor micro-Hall devices for magnetic, electric, and photo-detection

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gilbertson, A. M.; Cohen, L. F.; Sadeghi, Hatef

    2015-12-07

    We report the real-space voltage response of InSb/AlInSb micro-Hall devices to local photo-excitation, electric, and magnetic fields at room temperature using scanning probe microscopy. We show that the ultrafast generation of localised photocarriers results in conductance perturbations analogous to those produced by local electric fields. Experimental results are in good agreement with tight-binding transport calculations in the diffusive regime. The magnetic, photo, and charge sensitivity of a 2 μm wide probe are evaluated at a 10 μA bias current in the Johnson noise limit (valid at measurement frequencies > 10 kHz) to be, respectively, 500 nT/√Hz; 20 pW/√Hz (λ = 635 nm) comparable to commercial photoconductive detectors;more » and 0.05 e/√Hz comparable to that of single electron transistors. These results demonstrate the remarkably versatile sensing attributes of simple semiconductor micro-Hall devices that can be applied to a host of imaging and sensing applications.« less

  2. Judy Estes Hall (1940-2015).

    PubMed

    Sammons, Morgan T; Boucher, Andrew

    2016-01-01

    Presents an obituary for Judy Estes Hall, who passed away on November 24, 2015. Hall served as the Executive Officer of the National Register of Health Service Psychologists until her retirement in 2013. She is a recognized expert in the development of education and training standards for the profession of psychology, she also made significant contributions in the field of international psychology, where she was a renowned expert in cross-national credentialing and an advocate for commonality in licensing standards. She was the coauthor of one edited volume and author of more than 60 journal articles, book chapters, and professional publications. A passionate advocate for the advancement of women in psychology, a devoted mother and grandmother, a connoisseur of wine and international traveler extraordinaire, she touched the personal and professional lives of many. (PsycINFO Database Record (c) 2016 APA, all rights reserved).

  3. Electron dynamics in Hall thruster

    NASA Astrophysics Data System (ADS)

    Marini, Samuel; Pakter, Renato

    2015-11-01

    Hall thrusters are plasma engines those use an electromagnetic fields combination to confine electrons, generate and accelerate ions. Widely used by aerospace industries those thrusters stand out for its simple geometry, high specific impulse and low demand for electric power. Propulsion generated by those systems is due to acceleration of ions produced in an acceleration channel. The ions are generated by collision of electrons with propellant gas atoms. In this context, we can realize how important is characterizing the electronic dynamics. Using Hamiltonian formalism, we derive the electron motion equation in a simplified electromagnetic fields configuration observed in hall thrusters. We found conditions those must be satisfied by electromagnetic fields to have electronic confinement in acceleration channel. We present configurations of electromagnetic fields those maximize propellant gas ionization and thus make propulsion more efficient. This work was supported by CNPq.

  4. Integration Test of the High Voltage Hall Accelerator System Components

    NASA Technical Reports Server (NTRS)

    Kamhawi, Hani; Haag, Thomas; Huang, Wensheng; Pinero, Luis; Peterson, Todd; Dankanich, John

    2013-01-01

    NASA Glenn Research Center is developing a 4 kilowatt-class Hall propulsion system for implementation in NASA science missions. NASA science mission performance analysis was completed using the latest high voltage Hall accelerator (HiVHAc) and Aerojet-Rocketdyne's state-of-the-art BPT-4000 Hall thruster performance curves. Mission analysis results indicated that the HiVHAc thruster out performs the BPT-4000 thruster for all but one of the missions studied. Tests of the HiVHAc system major components were performed. Performance evaluation of the HiVHAc thruster at NASA Glenn's vacuum facility 5 indicated that thruster performance was lower than performance levels attained during tests in vacuum facility 12 due to the lower background pressures attained during vacuum facility 5 tests when compared to vacuum facility 12. Voltage-Current characterization of the HiVHAc thruster in vacuum facility 5 showed that the HiVHAc thruster can operate stably for a wide range of anode flow rates for discharge voltages between 250 and 600 volts. A Colorado Power Electronics enhanced brassboard power processing unit was tested in vacuum for 1,500 hours and the unit demonstrated discharge module efficiency of 96.3% at 3.9 kilowatts and 650 volts. Stand-alone open and closed loop tests of a VACCO TRL 6 xenon flow control module were also performed. An integrated test of the HiVHAc thruster, brassboard power processing unit, and xenon flow control module was performed and confirmed that integrated operation of the HiVHAc system major components. Future plans include continuing the maturation of the HiVHAc system major components and the performance of a single-string integration test.

  5. The inverse hall-petch relation in nanocrystalline metals: A discrete dislocation dynamics analysis

    NASA Astrophysics Data System (ADS)

    Quek, Siu Sin; Chooi, Zheng Hoe; Wu, Zhaoxuan; Zhang, Yong Wei; Srolovitz, David J.

    2016-03-01

    When the grain size in polycrystalline materials is reduced to the nanometer length scale (nanocrystallinity), observations from experiments and atomistic simulations suggest that the yield strength decreases (softening) as the grain size is decreased. This is in contrast to the Hall-Petch relation observed in larger sized grains. We incorporated grain boundary (GB) sliding and dislocation emission from GB junctions into the classical DDD framework, and recovered the smaller is weaker relationship observed in nanocrystalline materials. This current model shows that the inverse Hall-Petch behavior can be obtained through a relief of stress buildup at GB junctions from GB sliding by emitting dislocations from the junctions. The yield stress is shown to vary with grain size, d, by a d 1 / 2 relationship when grain sizes are very small. However, pure GB sliding alone without further plastic accomodation by dislocation emission is grain size independent.

  6. Redistributing Chern numbers and quantum Hall transitions in multi-band lattices

    NASA Astrophysics Data System (ADS)

    Yu, H. L.; Zhai, Z. Y.; Jiang, C.

    2018-07-01

    We numerically study the integer quantum Hall effect (IQHE) on m-band lattices. With continuous modulating the next-nearest-neighbor hopping integral t' , it is found that the full band is divided into 2 m - 1 regions. There are m - 1 critical regions with pseudogaps induced by the merging between the two adjacent subbands, where both Chern numbers of the correlating Landau subbands and the corresponding Hall plateau are not well-defined. The other m regions with different well-defined Chern numbers are separated by the above m - 1 critical regions. Due to the redistributing Chern numbers of system induced by the merging of subbands, the Hall conductance exhibits a peculiar phase transition, which is characterized by the direct change of Hall plateau state.

  7. Effect of azimuthal diversion rail on an ATON-type Hall thruster

    NASA Astrophysics Data System (ADS)

    Xu, Zhang; Liqiu, Wei; Liang, Han; Yongjie, Ding; Daren, Yu

    2017-03-01

    A newly designed azimuthal diversion rail (ADR) is studied and used to enhance the ionization process in an ATON-type Hall thruster. The diversion rail efficiently reduces the neutral flow axial velocity, and hence, increases the resistance time of atoms in the discharge channel of the Hall thruster. Thrust performances, in terms of thrust, anode efficiency and ion beam divergence, are found to be improved because of the application of the diversion rail, especially at low mass flow rate conditions. Experiment results reveal that the ADR increases the mass utilization under insufficient mass flow rate operating conditions. The design of the ADR broadens the efficient operating range of Hall thrusters and has significant contribution to multi-mode Hall thruster development.

  8. Magnetotransport properties of 8-Pmmn borophene: effects of Hall field and strain.

    PubMed

    Islam, S K Firoz

    2018-07-11

    The polymorph of 8-Pmmn borophene is an anisotropic Dirac material with tilted Dirac cones at two valleys. The tilting of the Dirac cones at two valleys are in opposite directions, which manifests itself via the valley dependent Landau levels in presence of an in-plane electric field (Hall field). The valley dependent Landau levels cause valley polarized magnetotransport properties in presence of the Hall field, which is in contrast to the monolayer graphene with isotropic non-tilted Dirac cones. The longitudinal conductivity and Hall conductivity are evaluated by using linear response theory in low temperature regime. An analytical approximate form of the longitudinal conductivity is also obtained. It is observed that the tilting of the Dirac cones amplifies the frequency of the longitudinal conductivity oscillation (Shubnikov-de Haas). On the other hand, the Hall conductivity exhibits graphene-like plateaus except the appearance of valley dependent steps which are purely attributed to the Hall field induced lifting of the valley degeneracy in the Landau levels. Finally we look into the different cases when the Hall field is applied to the strained borophene and find that valley dependency is fully dominated by strain rather than Hall field. Another noticeable point is that if the real magnetic field is replaced by the strain induced pseudo magnetic field then the electric field looses its ability to cause valley polarized transport.

  9. Hall thruster microturbulence under conditions of modified electron wall emission

    NASA Astrophysics Data System (ADS)

    Tsikata, S.; Héron, A.; Honoré, C.

    2017-05-01

    In recent numerical, theoretical, and experimental papers, the short-scale electron cyclotron drift instability (ECDI) has been studied as a possible contributor to the anomalous electron current observed in Hall thrusters. In this work, features of the instability, in the presence of a zero-electron emission material at the thruster exit plane, are analyzed using coherent Thomson scattering. Limiting the electron emission at the exit plane alters the localization of the accelerating electric field and the expected drift velocity profile, which in turn modifies the amplitude and localization of the ECDI. The resulting changes to the standard thruster operation are expected to favor an increased contribution by the ECDI to electron current. Such an operation is associated with a degradation of thruster performance and stability.

  10. Contextual view of the Hall of Transportation from Yerba Buena ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Contextual view of the Hall of Transportation from Yerba Buena Island, showing Palace of Fine and Decorative Arts (Building 3) at far right, camera facing northwest - Golden Gate International Exposition, Hall of Transportation, 440 California Avenue, Treasure Island, San Francisco, San Francisco County, CA

  11. Plasma Properties in the Plume of a Hall Thruster Cluster

    DTIC Science & Technology

    2003-06-04

    The Hall thruster cluster is an attractive propulsion approach for spacecraft requiring very high-power electric propulsion systems. This article...probes in the plume of a low-power, four-engine Hall thruster cluster. Simple analytical formulas are introduced that allow these quantities to be

  12. Spin-hall-active platinum thin films grown via atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Schlitz, Richard; Amusan, Akinwumi Abimbola; Lammel, Michaela; Schlicht, Stefanie; Tynell, Tommi; Bachmann, Julien; Woltersdorf, Georg; Nielsch, Kornelius; Goennenwein, Sebastian T. B.; Thomas, Andy

    2018-06-01

    We study the magnetoresistance of yttrium iron garnet/Pt heterostructures in which the Pt layer was grown via atomic layer deposition (ALD). Magnetotransport experiments in three orthogonal rotation planes reveal the hallmark features of spin Hall magnetoresistance. To estimate the spin transport parameters, we compare the magnitude of the magnetoresistance in samples with different Pt thicknesses. We check the spin Hall angle and the spin diffusion length of the ALD Pt layers against the values reported for high-quality sputter-deposited Pt films. The spin diffusion length of 1.5 nm agrees well with that of platinum thin films reported in the literature, whereas the spin Hall magnetoresistance Δ ρ / ρ = 2.2 × 10 - 5 is approximately a factor of 20 smaller compared to that of our sputter-deposited films. Our results demonstrate that ALD allows fabricating spin-Hall-active Pt films of suitable quality for use in spin transport structures. This work provides the basis to establish conformal ALD coatings for arbitrary surface geometries with spin-Hall-active metals and could lead to 3D spintronic devices in the future.

  13. Higher (odd) dimensional quantum Hall effect and extended dimensional hierarchy

    NASA Astrophysics Data System (ADS)

    Hasebe, Kazuki

    2017-07-01

    We demonstrate dimensional ladder of higher dimensional quantum Hall effects by exploiting quantum Hall effects on arbitrary odd dimensional spheres. Non-relativistic and relativistic Landau models are analyzed on S 2 k - 1 in the SO (2 k - 1) monopole background. The total sub-band degeneracy of the odd dimensional lowest Landau level is shown to be equal to the winding number from the base-manifold S 2 k - 1 to the one-dimension higher SO (2 k) gauge group. Based on the chiral Hopf maps, we clarify the underlying quantum Nambu geometry for odd dimensional quantum Hall effect and the resulting quantum geometry is naturally embedded also in one-dimension higher quantum geometry. An origin of such dimensional ladder connecting even and odd dimensional quantum Hall effects is illuminated from a viewpoint of the spectral flow of Atiyah-Patodi-Singer index theorem in differential topology. We also present a BF topological field theory as an effective field theory in which membranes with different dimensions undergo non-trivial linking in odd dimensional space. Finally, an extended version of the dimensional hierarchy for higher dimensional quantum Hall liquids is proposed, and its relationship to quantum anomaly and D-brane physics is discussed.

  14. Unusual Thermal Hall Effect in a Kitaev Spin Liquid Candidate α -RuCl3

    NASA Astrophysics Data System (ADS)

    Kasahara, Y.; Sugii, K.; Ohnishi, T.; Shimozawa, M.; Yamashita, M.; Kurita, N.; Tanaka, H.; Nasu, J.; Motome, Y.; Shibauchi, T.; Matsuda, Y.

    2018-05-01

    The Kitaev quantum spin liquid displays the fractionalization of quantum spins into Majorana fermions. The emergent Majorana edge current is predicted to manifest itself in the form of a finite thermal Hall effect, a feature commonly discussed in topological superconductors. Here we report on thermal Hall conductivity κx y measurements in α -RuCl3 , a candidate Kitaev magnet with the two-dimensional honeycomb lattice. In a spin-liquid (Kitaev paramagnetic) state below the temperature characterized by the Kitaev interaction JK/kB˜80 K , positive κx y develops gradually upon cooling, demonstrating the presence of highly unusual itinerant excitations. Although the zero-temperature property is masked by the magnetic ordering at TN=7 K , the sign, magnitude, and T dependence of κx y/T at intermediate temperatures follows the predicted trend of the itinerant Majorana excitations.

  15. Finite element study of three dimensional radiative nano-plasma flow subject to Hall and ion slip currents

    NASA Astrophysics Data System (ADS)

    Nawaz, M.; Zubair, T.

    In this article, we developed a computer code of Galerikan Finite Element method (GFEM) for three dimensional flow equations of nano-plasma fluid (blood) in the presence of uniform applied magnetic field when Hall and ion slip current are significant. Lorentz force is calculated through generalized Ohm's law with Maxwell equations. A series of numerical simulations are carried out to search ηmax and algebraic equations are solved by Gauss-Seidel method with simulation tolerance 10-8 . Simulated results for special case have an excellent agreement with the already published results. Velocity components and temperature of the nano-plasma (blood) are influenced significantly by the inclusion of nano-particles of Copper (Cu) and Silver (Ag). Heat enhancement is observed when copper and silver nonmagnetic nanoparticles are used instead of simple base fluid (conventional fluid). Radiative nature of nano-plasma in the presence of magnetic field causes a decrease in the temperature due to the transfer of heat by the electromagnetic waves. In contrast to this, due to heat dissipated by Joule heating and viscous dissipation phenomena, temperature of nano-plasmaincreases as thermal radiation parameter is increased. Thermal boundary layer thickness can be controlled by using radiative fluid instead of non-radiative fluid. Momentum boundary layer thickness can be reduced by increasing the intensity of the applied magnetic field. Temperature of plasma in the presence magnetic field is higher than the plasma in the absence of magnetic field.

  16. Pair spectrometer hodoscope for Hall D at Jefferson Lab

    DOE PAGES

    Barbosa, Fernando J.; Hutton, Charles L.; Sitnikov, Alexandre; ...

    2015-09-21

    We present the design of the pair spectrometer hodoscope fabricated at Jefferson Lab and installed in the experimental Hall D. The hodoscope consists of thin scintillator tiles; the light from each tile is collected using wave-length shifting fibers and detected using a Hamamatsu silicon photomultiplier. Light collection was measured using relativistic electrons produced in the tagger area of the experimental Hall B.

  17. Pair spectrometer hodoscope for Hall D at Jefferson Lab

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Barbosa, Fernando J.; Hutton, Charles L.; Sitnikov, Alexandre

    We present the design of the pair spectrometer hodoscope fabricated at Jefferson Lab and installed in the experimental Hall D. The hodoscope consists of thin scintillator tiles; the light from each tile is collected using wave-length shifting fibers and detected using a Hamamatsu silicon photomultiplier. Light collection was measured using relativistic electrons produced in the tagger area of the experimental Hall B.

  18. Study and Developement of Compact Permanent Magnet Hall Thrusters for Future Brazillian Space Missions

    NASA Astrophysics Data System (ADS)

    Ferreira, Jose Leonardo; Martins, Alexandre; Cerda, Rodrigo

    2016-07-01

    . The main difficulty to reach these minor bodies is related to their specific orbits with high eccentricity and inclination. A good example is the case for sample return missions to NEOs-Near Earth Objects. They are small bodies consisting of primitive left over building blocks of the Solar System formation processes. These missions can be accomplished by using low thrust trajectories with spacecrafts propelled by plasma thrusters with total thrust below 0.5 N, and a specific impulse around2500 s. In this work, we will show the brazilian contribution to the development of a compact electrical propulsion engine named PHALL III, designed with DCFH and foreseen to be used in future cubesats microsatellites but with possible applications in geostationary attitude control systems and on low thrust trajectory missions to the Near Earth Asteroids region. We will show a particular new permanent magnet field designed for PHALL III . Computer based simulation codes such as VSIM are also used on the design of this new proposed cuped magnet field Hall Thruster. Based on the first results wee believed PHALL III will also allow a good spacecraft performance of long duration space missions for small size spacecrafts with limited low electric source power consumption. The PHALL III plasma source characterization is presented together with the ejected plasma plume ion current intensity, ion energy and plasma flow velocity parameters measured by an integrated Plasma Diagnostic Bench (BID). Based on plasma source and plume ejected parameters a merit figure of PHALL III is constructed and compared to computer calculated low thrust transfer requirements. From these results it is goig to be possible to analyse the potential use of PHALL III on future brazillian space missions , its working parameters are compared with parameters of existing space tested plasma thrusters already used on moon , deep space missions and also on satellite geostationary positioning using low thrust orbit

  19. Admittance of multiterminal quantum Hall conductors at kilohertz frequencies

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hernández, C.; Consejo, C.; Chaubet, C., E-mail: christophe.chaubet@univ-montp2.fr

    2014-03-28

    We present an experimental study of the low frequency admittance of quantum Hall conductors in the [100 Hz, 1 MHz] frequency range. We show that the frequency dependence of the admittance of the sample strongly depends on the topology of the contacts connections. Our experimental results are well explained within the Christen and Büttiker approach for finite frequency transport in quantum Hall edge channels taking into account the influence of the coaxial cables capacitance. In the Hall bar geometry, we demonstrate that there exists a configuration in which the cable capacitance does not influence the admittance measurement of the sample. In thismore » case, we measure the electrochemical capacitance of the sample and observe its dependence on the filling factor.« less

  20. Modeling a Hall Thruster from Anode to Plume Far Field

    DTIC Science & Technology

    2008-12-31

    Two dimensional ax symmetric simulations of xenon plasma plume flow fields from a D55 Anode layer Hall thruster is performed. A hybrid particle-fluid...method is used for the Simulations. The magnetic field surrounding the Hall thruster exit is included in the Calculation. The plasma properties

  1. Hybrid-PIC Modeling of a High-Voltage, High-Specific-Impulse Hall Thruster

    NASA Technical Reports Server (NTRS)

    Smith, Brandon D.; Boyd, Iain D.; Kamhawi, Hani; Huang, Wensheng

    2013-01-01

    The primary life-limiting mechanism of Hall thrusters is the sputter erosion of the discharge channel walls by high-energy propellant ions. Because of the difficulty involved in characterizing this erosion experimentally, many past efforts have focused on numerical modeling to predict erosion rates and thruster lifespan, but those analyses were limited to Hall thrusters operating in the 200-400V discharge voltage range. Thrusters operating at higher discharge voltages (V(sub d) >= 500 V) present an erosion environment that may differ greatly from that of the lower-voltage thrusters modeled in the past. In this work, HPHall, a well-established hybrid-PIC code, is used to simulate NASA's High-Voltage Hall Accelerator (HiVHAc) at discharge voltages of 300, 400, and 500V as a first step towards modeling the discharge channel erosion. It is found that the model accurately predicts the thruster performance at all operating conditions to within 6%. The model predicts a normalized plasma potential profile that is consistent between all three operating points, with the acceleration zone appearing in the same approximate location. The expected trend of increasing electron temperature with increasing discharge voltage is observed. An analysis of the discharge current oscillations shows that the model predicts oscillations that are much greater in amplitude than those measured experimentally at all operating points, suggesting that the differences in oscillation amplitude are not strongly associated with discharge voltage.

  2. 1000 Hours of Testing Completed on 10-kW Hall Thruster

    NASA Technical Reports Server (NTRS)

    Mason, Lee S.

    2001-01-01

    Between the months of April and August 2000, a 10-kW Hall effect thruster, designated T- 220, was subjected to a 1000-hr life test evaluation. Hall effect thrusters are propulsion devices that electrostatically accelerate xenon ions to produce thrust. Hall effect propulsion has been in development for many years, and low-power devices (1.35 kW) have been used in space for satellite orbit maintenance. The T-220, shown in the photo, produces sufficient thrust to enable efficient orbital transfers, saving hundreds of kilograms in propellant over conventional chemical propulsion systems. This test is the longest operation ever achieved on a high-power Hall thruster (greater than 4.5 kW) and is a key milestone leading to the use of this technology for future NASA, commercial, and military missions.

  3. Quantum Hall effect in graphene with interface-induced spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Cysne, Tarik P.; Garcia, Jose H.; Rocha, Alexandre R.; Rappoport, Tatiana G.

    2018-02-01

    We consider an effective model for graphene with interface-induced spin-orbit coupling and calculate the quantum Hall effect in the low-energy limit. We perform a systematic analysis of the contribution of the different terms of the effective Hamiltonian to the quantum Hall effect (QHE). By analyzing the spin splitting of the quantum Hall states as a function of magnetic field and gate voltage, we obtain different scaling laws that can be used to characterize the spin-orbit coupling in experiments. Furthermore, we employ a real-space quantum transport approach to calculate the quantum Hall conductivity and investigate the robustness of the QHE to disorder introduced by hydrogen impurities. For that purpose, we combine first-principles calculations and a genetic algorithm strategy to obtain a graphene-only Hamiltonian that models the impurity.

  4. Preliminary Evaluation of a 10 kW Hall Thruster

    NASA Technical Reports Server (NTRS)

    Jankovsky, Robert S.; McLean, Chris; McVey, John

    1999-01-01

    A 10 kW Hall thruster was characterized over a range of discharge voltages from 300-500 V and a range of discharge currents from 15-23 A. This corresponds to power levels from a low of 4.6 kW to a high of 10.7 kW. Over this range of discharge powers, thrust varied from 278 mN to 524 mN, specific impulse ranged from 1644 to 2392 seconds, and efficiency peaked at approximately 59%. A continuous 40 hour test was also undertaken in an attempt to gain insight with regard to long term operation of the engine. For this portion of the testing the thruster was operated at a discharge voltage of 500 V and a discharge current of 20 A. Steady-state temperatures were achieved after 3-5 hrs and very little variation in performance was detected.

  5. Observation of the fractional quantum Hall effect in graphene.

    PubMed

    Bolotin, Kirill I; Ghahari, Fereshte; Shulman, Michael D; Stormer, Horst L; Kim, Philip

    2009-11-12

    When electrons are confined in two dimensions and subject to strong magnetic fields, the Coulomb interactions between them can become very strong, leading to the formation of correlated states of matter, such as the fractional quantum Hall liquid. In this strong quantum regime, electrons and magnetic flux quanta bind to form complex composite quasiparticles with fractional electronic charge; these are manifest in transport measurements of the Hall conductivity as rational fractions of the elementary conductance quantum. The experimental discovery of an anomalous integer quantum Hall effect in graphene has enabled the study of a correlated two-dimensional electronic system, in which the interacting electrons behave like massless chiral fermions. However, owing to the prevailing disorder, graphene has so far exhibited only weak signatures of correlated electron phenomena, despite intense experimental and theoretical efforts. Here we report the observation of the fractional quantum Hall effect in ultraclean, suspended graphene. In addition, we show that at low carrier density graphene becomes an insulator with a magnetic-field-tunable energy gap. These newly discovered quantum states offer the opportunity to study correlated Dirac fermions in graphene in the presence of large magnetic fields.

  6. Quantum Hall physics: Hierarchies and conformal field theory techniques

    NASA Astrophysics Data System (ADS)

    Hansson, T. H.; Hermanns, M.; Simon, S. H.; Viefers, S. F.

    2017-04-01

    The fractional quantum Hall effect, being one of the most studied phenomena in condensed matter physics during the past 30 years, has generated many ground-breaking new ideas and concepts. Very early on it was realized that the zoo of emerging states of matter would need to be understood in a systematic manner. The first attempts to do this, by Haldane and Halperin, set an agenda for further work which has continued to this day. Since that time the idea of hierarchies of quasiparticles condensing to form new states has been a pillar of our understanding of fractional quantum Hall physics. In the 30 years that have passed since then, a number of new directions of thought have advanced our understanding of fractional quantum Hall states and have extended it in new and unexpected ways. Among these directions is the extensive use of topological quantum field theories and conformal field theories, the application of the ideas of composite bosons and fermions, and the study of non-Abelian quantum Hall liquids. This article aims to present a comprehensive overview of this field, including the most recent developments.

  7. Scanning hall probe microscopy (SHPM) using quartz crystal AFM feedback.

    PubMed

    Dede, M; Urkmen, K; Girişen, O; Atabak, M; Oral, A; Farrer, I; Ritchie, D

    2008-02-01

    Scanning Hall Probe Microscopy (SHPM) is a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations such as ferromagnetic domains with high spatial and magnetic field resolution of approximately 50 nm and 7 mG/Hz(1/2) at room temperature. In the SHPM technique, scanning tunneling microscope (STM) or atomic force microscope (AFM) feedback is used to keep the Hall sensor in close proximity of the sample surface. However, STM tracking SHPM requires conductive samples; therefore the insulating substrates have to be coated with a thin layer of gold. This constraint can be eliminated with the AFM feedback using sophisticated Hall probes that are integrated with AFM cantilevers. However it is very difficult to micro fabricate these sensors. In this work, we have eliminated the difficulty in the cantilever-Hall probe integration process, just by gluing a Hall Probe chip to a quartz crystal tuning fork force sensor. The Hall sensor chip is simply glued at the end of a 32.768 kHz or 100 kHz Quartz crystal, which is used as force sensor. An LT-SHPM system is used to scan the samples. The sensor assembly is dithered at the resonance frequency using a digital Phase Locked Loop circuit and frequency shifts are used for AFM tracking. SHPM electronics is modified to detect AFM topography and the frequency shift, along with the magnetic field image. Magnetic domains and topography of an Iron Garnet thin film crystal, NdFeB demagnetised magnet and hard disk samples are presented at room temperature. The performance is found to be comparable with the SHPM using STM feedback.

  8. Scanning tunneling microscopy measurements of the spin Hall effect in tungsten films by using iron-coated tungsten tips

    NASA Astrophysics Data System (ADS)

    Xie, Ting; Dreyer, Michael; Bowen, David; Hinkel, Dan; Butera, R. E.; Krafft, Charles; Mayergoyz, Isaak

    2018-05-01

    Scanning tunneling microscopy experiments using iron-coated tungsten tips and current-carrying tungsten films have been conducted. An asymmetry of the tunneling current with respect to the change of the direction of the bias current through a tungsten film has been observed. It is argued that this asymmetry is a manifestation of the spin Hall effect in the current-carrying tungsten film. Nanoscale variations of this asymmetry across the tungsten film have been studied by using the scanning tunneling microscopy technique.

  9. Orbital Magnetization of Quantum Spin Hall Insulator Nanoparticles.

    PubMed

    Potasz, P; Fernández-Rossier, J

    2015-09-09

    Both spin and orbital degrees of freedom contribute to the magnetic moment of isolated atoms. However, when inserted in crystals, atomic orbital moments are quenched because of the lack of rotational symmetry that protects them when isolated. Thus, the dominant contribution to the magnetization of magnetic materials comes from electronic spin. Here we show that nanoislands of quantum spin Hall insulators can host robust orbital edge magnetism whenever their highest occupied Kramers doublet is singly occupied, upgrading the spin edge current into a charge current. The resulting orbital magnetization scales linearly with size, outweighing the spin contribution for islands of a few nm in size. This linear scaling is specific of the Dirac edge states and very different from Schrodinger electrons in quantum rings. By modeling Bi(111) flakes, whose edge states have been recently observed, we show that orbital magnetization is robust with respect to disorder, thermal agitation, shape of the island, and crystallographic direction of the edges, reflecting its topological protection.

  10. A Comparative Analysis of Student Engagement, Learning, and Satisfaction in Lecture Hall and Online Learning Settings

    ERIC Educational Resources Information Center

    Rabe-Hemp, Cara; Woollen, Susan; Humiston, Gail Sears

    2009-01-01

    The current study involves a comparison of student levels of engagement, ability to learn autonomously, and interaction with peers and faculty in two different learning settings: a large lecture hall and online. Results suggest that learning mechanism drives the styles of learning and teaching practiced in traditional and online learning settings.…

  11. Hall Effect–Mediated Magnetic Flux Transport in Protoplanetary Disks

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bai, Xue-Ning; Stone, James M.

    2017-02-10

    The global evolution of protoplanetary disks (PPDs) has recently been shown to be largely controlled by the amount of poloidal magnetic flux threading the disk. The amount of magnetic flux must also coevolve with the disk, as a result of magnetic flux transport, a process that is poorly understood. In weakly ionized gas as in PPDs, magnetic flux is largely frozen in the electron fluid, except when resistivity is large. When the disk is largely laminar, we show that the relative drift between the electrons and ions (the Hall drift), and the ions and neutral fluids (ambipolar drift) can playmore » a dominant role on the transport of magnetic flux. Using two-dimensional simulations that incorporate the Hall effect and ambipolar diffusion (AD) with prescribed diffusivities, we show that when large-scale poloidal field is aligned with disk rotation, the Hall effect rapidly drags magnetic flux inward at the midplane region, while it slowly pushes flux outward above/below the midplane. This leads to a highly radially elongated field configuration as a global manifestation of the Hall-shear instability. This field configuration further promotes rapid outward flux transport by AD at the midplane, leading to instability saturation. In quasi-steady state, magnetic flux is transported outward at approximately the same rate at all heights, and the rate is comparable to the Hall-free case. For anti-aligned field polarity, the Hall effect consistently transports magnetic flux outward, leading to a largely vertical field configuration in the midplane region. The field lines in the upper layer first bend radially inward and then outward to launch a disk wind. Overall, the net rate of outward flux transport is about twice as fast as that of the aligned case. In addition, the rate of flux transport increases with increasing disk magnetization. The absolute rate of transport is sensitive to disk microphysics, which remains to be explored in future studies.« less

  12. Coherent radar estimates of high latitude field-aligned currents: the importance of conductance gradients

    NASA Astrophysics Data System (ADS)

    Kosch, M.; Nielsen, E.

    Two bi-static VHF radar systems STARE and SABRE have been employed to estimate ionospheric electric field distributions in the geomagnetic latitude range 61 1 - 69 3 degrees over Scandinavia corresponding to the global Region 2 current system 173 days of data from all four radars have been analysed during the period 1982 to 1986 The average magnetic field-aligned currents have been computed as a function of the Kp and Ae indices using an empirical model of ionospheric Pedersen and Hall conductance taking into account conductance gradients The divergence of horizontal Pedersen currents and Hall conductance gradients have approximately the same importance for generating the Region 2 field-aligned currents Pedersen conductance gradients have a significant modifying effect A case study of field-aligned currents has been performed using the STARE radar system to obtain the instantaneous ionospheric electric field distribution in the vicinity of an auroral arc The instantaneous Hall conductance was estimated from the Scandinavian Magnetometer Array This study clearly shows that even for quiet steady state geomagnetic conditions conductance gradients are important modifiers of magnetic field-aligned currents

  13. Topological Phase Transitions in the Photonic Spin Hall Effect

    DOE PAGES

    Kort-Kamp, Wilton Junior de Melo

    2017-10-04

    The recent synthesis of two-dimensional staggered materials opens up burgeoning opportunities to study optical spin-orbit interactions in semiconducting Dirac-like systems. In this work, we unveil topological phase transitions in the photonic spin Hall effect in the graphene family materials. It is shown that an external static electric field and a high frequency circularly polarized laser allow for active on-demand manipulation of electromagnetic beam shifts. The spin Hall effect of light presents a rich dependence with radiation degrees of freedom, and material properties, and features nontrivial topological properties. Finally, we discover that photonic Hall shifts are sensitive to spin and valleymore » properties of the charge carriers, providing an unprecedented pathway to investigate spintronics and valleytronics in staggered 2D semiconductors.« less

  14. Electrical control of the anomalous valley Hall effect in antiferrovalley bilayers

    NASA Astrophysics Data System (ADS)

    Tong, Wen-Yi; Duan, Chun-Gang

    2017-08-01

    In analogy to all-electric spintronics, all-electric valleytronics, i.e., valley manipulation via electric means, becomes an exciting new frontier as it may bring revolutions in the field of data storage with ultra-high speed and ultra-low power consumption. The existence of the anomalous valley Hall effect in ferrovalley materials demonstrates the possibility of electrical detection for valley polarization. However, in previously proposed valley-polarized monolayers, the anomalous valley Hall effect is controlled by external magnetic fields. Here, through elaborate structural design, we propose the antiferrovally bilayer as an ideal candidate for realizing all-electric valleytronic devices. Using the minimal k.p model, we show that the energy degeneracy between valley indexes in such system can be lifted by electric approaches. Subsequently, the anomalous valley Hall effect strongly depends on the electric field as well. Taking the bilayer VSe2 as an example, all-electric tuning and detecting of anomalous valley Hall effect is confirmed by density-functional theory calculations, indicating that the valley information in such antiferrovalley bilayer can be reversed by an electric field perpendicular to the plane of the system and easily probed through the sign of the Hall voltage.

  15. G. Stanley Hall, Child Study, and the Teaching of Geography

    ERIC Educational Resources Information Center

    Koelsch, William A.

    2002-01-01

    G. Stanley Hall (1844-1924), founding president of Clark University, was a leader in the child study movement and a significant figure in psychology and education in the late nineteenth and early twentieth centuries. Hall had pronounced opinions on many educational subjects, including the teaching of geography. His criticisms and program for the…

  16. Improvement of the low frequency oscillation model for Hall thrusters

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wang, Chunsheng, E-mail: wangcs@hit.edu.cn; Wang, Huashan

    2016-08-15

    The low frequency oscillation of the discharge current in Hall thrusters is a major aspect of these devices that requires further study. While the existing model captures the ionization mechanism of the low frequency oscillation, it unfortunately fails to express the dynamic characteristics of the ion acceleration. The analysis in this paper shows this is because of the simplification of the electron equation, which affects both the electric field distribution and the ion acceleration process. Additionally, the electron density equation is revised and a new model that is based on the physical properties of ion movement is proposed.

  17. NASA Chief Technologist Hosts Town Hall

    NASA Image and Video Library

    2010-05-24

    NASA's Chief Technologists, Bobby Braun, hosts a Town Hall meeting to discuss agency-wide technology policy and programs at NASA Headquarters on Tuesday, May 25, 2010, in Washington. Photo Credit: (NASA/Carla Cioffi)

  18. Cabana inducted into Hall of Fame

    NASA Image and Video Library

    2008-05-03

    Former astronaut Al Worden (left) presents Stennis Space Center Director Bob Cabana with a gold medallion signifying his induction into the U.S. Astronaut Hall of Fame at Kennedy Space Center in Florida.

  19. Moiré assisted fractional quantum Hall state spectroscopy

    DOE PAGES

    Wu, Fengcheng; MacDonald, A. H.

    2016-12-14

    Intra-Landau level excitations in the fractional quantum Hall regime are not accessible via optical absorption measurements. Here we point out that optical probes are enabled by the periodic potentials produced by a moire pattern. Our observation is motivated by the recent observations of fractional quantum Hall incompressible states in moire-patterned graphene on a hexagonal boron nitride substrate, and is theoretically based on f-sum rule considerations supplemented by a perturbative analysis of the influence of the moire potential on many-body states.

  20. Non-Intrusive, Time-Resolved Hall Thruster Near-Field Electron Temperature Measurements

    DTIC Science & Technology

    2011-08-01

    With the growing interest in Hall thruster technology, comes the need to fully characterize the plasma dynamics that determine performance. Of...instabilities characteristic of Hall thruster behavior, time resolved techniques must be developed. This study presents a non-intrusive method of

  1. AGU Position Statements Addressed at Fall Meeting Town Hall

    NASA Astrophysics Data System (ADS)

    Hankin, Erik

    2013-01-01

    The AGU Outreach Committee and Public Affairs staff held a town hall at the 2012 Fall Meeting to discuss AGU position statements. The town hall, "AGU Position Statements: Announcing New Submission and Review Methods," held on Monday, 3 December, provided background on AGU position statements, recent changes to the review and writing processes, updates on statements under revision, and ways for members to utilize and impact position statements.

  2. Note: An approach to measurement of low frequency oscillation amplitude of discharge current of in-orbit Hall thruster.

    PubMed

    Han, Liang; Ding, Yongjie; Wei, Liqiu; Yu, Daren

    2014-06-01

    This paper provides a method to measure the amplitude of low frequency oscillation under the on-track working condition, and realizes the sampling by means of adding the circuit design of sampling, low pass filtering by 3 dB at 48.2 kHz, detection and integrating in the filtering unit. The experimental results prove that the measuring device of merely 0.8 g can quantitatively reflect the amplitude of low frequency oscillation in Hall thruster and the maximum deviation of experiment data and theory data is 10% FS.

  3. ENCOURAGING ELECTRICITY SAVINGS IN A UNIVERSITY RESIDENTIAL HALL THROUGH A COMBINATION OF FEEDBACK, VISUAL PROMPTS, AND INCENTIVES

    PubMed Central

    Bekker, Marthinus J; Cumming, Tania D; Osborne, Nikola K.P; Bruining, Angela M; McClean, Julia I; Leland, Louis S

    2010-01-01

    This experiment investigated the combined use of visual prompts, daily feedback, and rewards to reduce electricity consumption in a university residential hall. After a 17-day baseline period, the experimental intervention was introduced in the intervention hall, and no change was made in the control hall. Energy usage decreased in the intervention hall, but energy usage did not change appreciably in the control hall. In the intervention hall, mean daytime and nighttime savings were 16.2% and 10.7%, respectively, compared to savings of 3.8% (day) and 6.5% (night) in the control hall. PMID:21119909

  4. Spin-independent transparency of pure spin current at normal/ferromagnetic metal interface

    NASA Astrophysics Data System (ADS)

    Hao, Runrun; Zhong, Hai; Kang, Yun; Tian, Yufei; Yan, Shishen; Liu, Guolei; Han, Guangbing; Yu, Shuyun; Mei, Liangmo; Kang, Shishou

    2018-03-01

    The spin transparency at the normal/ferromagnetic metal (NM/FM) interface was studied in Pt/YIG/Cu/FM multilayers. The spin current generated by the spin Hall effect (SHE) in Pt flows into Cu/FM due to magnetic insulator YIG blocking charge current and transmitting spin current via the magnon current. Therefore, the nonlocal voltage induced by an inverse spin Hall effect (ISHE) in FM can be detected. With the magnetization of FM parallel or antiparallel to the spin polarization of pure spin currents ({{\\boldsymbol{σ }}}sc}), the spin-independent nonlocal voltage is induced. This indicates that the spin transparency at the Cu/FM interface is spin-independent, which demonstrates that the influence of spin-dependent electrochemical potential due to spin accumulation on the interfacial spin transparency is negligible. Furthermore, a larger spin Hall angle of Fe20Ni80 (Py) than that of Ni is obtained from the nonlocal voltage measurements. Project supported by the National Basic Research Program of China (Grant No. 2015CB921502), the National Natural Science Foundation of China (Grant Nos. 11474184 and 11627805), the 111 Project, China (Grant No. B13029), and the Fundamental Research Funds of Shandong University, China.

  5. Computed versus measured ion velocity distribution functions in a Hall effect thruster

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Garrigues, L.; CNRS, LAPLACE, F-31062 Toulouse; Mazouffre, S.

    2012-06-01

    We compare time-averaged and time-varying measured and computed ion velocity distribution functions in a Hall effect thruster for typical operating conditions. The ion properties are measured by means of laser induced fluorescence spectroscopy. Simulations of the plasma properties are performed with a two-dimensional hybrid model. In the electron fluid description of the hybrid model, the anomalous transport responsible for the electron diffusion across the magnetic field barrier is deduced from the experimental profile of the time-averaged electric field. The use of a steady state anomalous mobility profile allows the hybrid model to capture some properties like the time-averaged ion meanmore » velocity. Yet, the model fails at reproducing the time evolution of the ion velocity. This fact reveals a complex underlying physics that necessitates to account for the electron dynamics over a short time-scale. This study also shows the necessity for electron temperature measurements. Moreover, the strength of the self-magnetic field due to the rotating Hall current is found negligible.« less

  6. Protecting Your Residence Hall Furniture Investment.

    ERIC Educational Resources Information Center

    Wiens, Janet

    2003-01-01

    Asserting that residence hall furniture takes abuse simply through use, discusses a three-part approach--student involvement and education, creating the right environment, and ongoing maintenance--that helps reduce normal wear and tear. (EV)

  7. Room temperature quantum spin Hall insulators with a buckled square lattice.

    PubMed

    Luo, Wei; Xiang, Hongjun

    2015-05-13

    Two-dimensional (2D) topological insulators (TIs), also known as quantum spin Hall (QSH) insulators, are excellent candidates for coherent spin transport related applications because the edge states of 2D TIs are robust against nonmagnetic impurities since the only available backscattering channel is forbidden. Currently, most known 2D TIs are based on a hexagonal (specifically, honeycomb) lattice. Here, we propose that there exists the quantum spin Hall effect (QSHE) in a buckled square lattice. Through performing global structure optimization, we predict a new three-layer quasi-2D (Q2D) structure, which has the lowest energy among all structures with the thickness less than 6.0 Å for the BiF system. It is identified to be a Q2D TI with a large band gap (0.69 eV). The electronic states of the Q2D BiF system near the Fermi level are mainly contributed by the middle Bi square lattice, which are sandwiched by two inert BiF2 layers. This is beneficial since the interaction between a substrate and the Q2D material may not change the topological properties of the system, as we demonstrate in the case of the NaF substrate. Finally, we come up with a new tight-binding model for a two-orbital system with the buckled square lattice to explain the low-energy physics of the Q2D BiF material. Our study not only predicts a QSH insulator for realistic room temperature applications but also provides a new lattice system for engineering topological states such as quantum anomalous Hall effect.

  8. Performance of a Permanent-Magnet Cylindrical Hall-Effect Thruster

    NASA Technical Reports Server (NTRS)

    Polzin, K. A.; Sooby, E. S.; Kimberlin, A. C.; Raites, Y.; Merino, E.; Fisch, N. J.

    2009-01-01

    The performance of a low-power cylindrical Hall thruster, which more readily lends itself to miniaturization and low-power operation than a conventional (annular) Hall thruster, was measured using a planar plasma probe and a thrust stand. The field in the cylindrical thruster was produced using permanent magnets, promising a power reduction over previous cylindrical thruster iterations that employed electromagnets to generate the required magnetic field topology. Two sets of ring-shaped permanent magnets are used, and two different field configurations can be produced by reorienting the poles of one magnet relative to the other. A plasma probe measuring ion flux in the plume is used to estimate the current utilization for the two magnetic topologies. The measurements indicate that electron transport is impeded much more effectively in one configuration, implying higher thrust efficiency. Thruster performance measurements on this configuration were obtained over a power range of 70-350 W and with the cathode orifice located at three different axial positions relative to the thruster exit plane. The thrust levels over this power range were 1.25-6.5 mN, with anode efficiencies and specific impulses spanning 4-21% and 400-1950 s, respectively. The anode efficiency of the permanent-magnet thruster compares favorable with the efficiency of the electromagnet thruster when the power consumed by the electromagnets is taken into account.

  9. Effect of Time Dependent Bending of Current Sheets in Response to Generation of Plasma Jets and Reverse Currents

    NASA Astrophysics Data System (ADS)

    Frank, Anna

    Magnetic reconnection is a basis for many impulsive phenomena in space and laboratory plasmas accompanied by effective transformation of magnetic energy. Reconnection processes usually occur in relatively thin current sheets (CSs), which separate magnetic fields of different or opposite directions. We report on recent observations of time dependent bending of CSs, which results from plasma dynamics inside the sheet. The experiments are carried out with the CS-3D laboratory device (Institute of General Physics RAS, Moscow) [1]. The CS magnetic structure with an X line provides excitation of the Hall currents and plasma acceleration from the X line to both side edges [2]. In the presence of the guide field By the Hall currents give rise to bending of the sheet: the peripheral regions located away from the X line are deflected from CS middle plane (z=0) in the opposite directions ±z [3]. We have revealed generation of reverse currents jy near the CS edges, i.e. the currents flowing in the opposite direction to the main current in the sheet [4]. There are strong grounds to believe that reverse currents are generated by the outflow plasma jets [5], accelerated inside the sheet and penetrated into the regions with strong normal magnetic field component Bz [4]. An impressive effect of sudden change in the sign of the CS bend has been disclosed recently, when analyzing distributions of plasma density [6] and current away from the X line, in the presence of the guide field By. The CS configuration suddenly becomes opposite from that observed at the initial stage, and this effect correlates well with generation of reverse currents. Consequently this effect can be related to excitation of the reverse Hall currents owing to generation of reverse currents jy in the CS. Hence it may be concluded that CSs may exhibit time dependent vertical z-displacements, and the sheet geometry depends on excitation of the Hall currents, acceleration of plasma jets and generation of reverse

  10. Outdoor concert hall sound design: idea and possible solutions

    NASA Astrophysics Data System (ADS)

    Kim, Yang-Hann; Lee, Jung-Min; Kim, Wanjung; Kim, Hwan; Choi, Jung-Woo; Wang, Semyung

    Sound design of outdoor concert halls needs to satisfy two contradictory objectives: good sound reproduction within the hall, as well as the minimization of external sound radiation. Outdoor concert hall usually has open space, therefore good sound for the listeners can be bad sound for its neighborhood. It would be a good attempt to have a virtual sound wall that can reflect all sound, therefore making a relatively quiet zone in the outside. This attempt can be possible if we could produce invisible but very high impedance mismatch around the hall, for a selected frequency band. This can be possible if we can generate an acoustically bright zone inside and a dark (quite) zone outside. Earlier work [Choi, J.-W. and Kim, Y.-H. (2002). J. Acoust. Soc. Am. 111, 1695-1700], at least, assures it is possible for a selected region and frequencies. Simulations show that it is possible for a two-dimensional case. Experimental verification has been also tried. The discrepancies have been explained in terms of the number of loudspeakers, their spatial distributions, spacing with regard to wavelength. The dependency of its performances with respect to the size of bright and dark zone scaled by wavelength of interest has also been explained.

  11. NASA Chief Technologist Hosts Town Hall

    NASA Image and Video Library

    2010-05-24

    Bobby Braun, NASA's Chief Technologist, answers questions during a Town Hall meeting to discuss agency-wide technology policy and programs at NASA Headquarters on Tuesday, May 25, 2010, in Washington. Photo Credit: (NASA/Carla Cioffi)

  12. A Residential Paradox?: Residence Hall Attributes and College Student Outcomes

    ERIC Educational Resources Information Center

    Bronkema, Ryan; Bowman, Nicholas A.

    2017-01-01

    The researchers of this brief observed that few environments have the potential to shape the outcomes of college students as much as residence halls. As a result, residence halls have the capacity to foster a strong sense of community as well as other important outcomes such as college satisfaction and academic achievement. However, given the high…

  13. 30. VIEW OF DRILL HALL FROM SECOND FLOOR EAST BALCONY ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    30. VIEW OF DRILL HALL FROM SECOND FLOOR EAST BALCONY FACING WEST. SHOWS ALTERNATE BAY X BRACING OF ROOF TRUSSES. ALSO SHOWS TRUSSES, WINDOWS IN THE MONITOR, STAIRWAY AT THE SOUTHWEST CORNER OF THE DRILL HALL AND THE THREE LEVELS OF BENCHES ON THE BALCONY. - Yakima National Guard Armory, 202 South Third Street, Yakima, Yakima County, WA

  14. Interior and Exterior Laser-Induced Fluorescence and Plasma Measurements within a Hall Thruster (Postprint)

    DTIC Science & Technology

    2002-02-01

    ionized xenon in the plume and interior portions of the acceleration channel of a Hall thruster plasma discharge operating at powers ranging from 250...performed in the interior of the Hall thruster with resonance fluorescence collection. Optical access to the interior of the Hall thruster is

  15. Study of electron transport in a Hall thruster by axial–radial fully kinetic particle simulation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Cho, Shinatora, E-mail: choh.shinatora@jaxa.jp; Kubota, Kenichi; Funaki, Ikkoh

    2015-10-15

    Electron transport across a magnetic field in a magnetic-layer-type Hall thruster was numerically investigated for the future predictive modeling of Hall thrusters. The discharge of a 1-kW-class magnetic-layer-type Hall thruster designed for high-specific-impulse operation was modeled using an r-z two-dimensional fully kinetic particle code with and without artificial electron-diffusion models. The thruster performance results showed that both electron transport models captured the experimental result within discrepancies less than 20% in thrust and discharge current for all the simulated operation conditions. The electron cross-field transport mechanism of the so-called anomalous diffusion was self-consistently observed in the simulation without artificial diffusion models;more » the effective electron mobility was two orders of magnitude higher than the value obtained using the classical diffusion theory. To account for the self-consistently observed anomalous transport, the oscillation of plasma properties was speculated. It was suggested that the enhanced random-walk diffusion due to the velocity oscillation of low-frequency electron flow could explain the observed anomalous diffusion within an order of magnitude. The dominant oscillation mode of the electron flow velocity was found to be 20 kHz, which was coupled to electrostatic oscillation excited by global ionization instability.« less

  16. Multiscale Currents Observed by MMS in the Flow Braking Region

    NASA Astrophysics Data System (ADS)

    Nakamura, Rumi; Varsani, Ali; Genestreti, Kevin J.; Le Contel, Olivier; Nakamura, Takuma; Baumjohann, Wolfgang; Nagai, Tsugunobu; Artemyev, Anton; Birn, Joachim; Sergeev, Victor A.; Apatenkov, Sergey; Ergun, Robert E.; Fuselier, Stephen A.; Gershman, Daniel J.; Giles, Barbara J.; Khotyaintsev, Yuri V.; Lindqvist, Per-Arne; Magnes, Werner; Mauk, Barry; Petrukovich, Anatoli; Russell, Christopher T.; Stawarz, Julia; Strangeway, Robert J.; Anderson, Brian; Burch, James L.; Bromund, Ken R.; Cohen, Ian; Fischer, David; Jaynes, Allison; Kepko, Laurence; Le, Guan; Plaschke, Ferdinand; Reeves, Geoff; Singer, Howard J.; Slavin, James A.; Torbert, Roy B.; Turner, Drew L.

    2018-02-01

    We present characteristics of current layers in the off-equatorial near-Earth plasma sheet boundary observed with high time-resolution measurements from the Magnetospheric Multiscale mission during an intense substorm associated with multiple dipolarizations. The four Magnetospheric Multiscale spacecraft, separated by distances of about 50 km, were located in the southern hemisphere in the dusk portion of a substorm current wedge. They observed fast flow disturbances (up to about 500 km/s), most intense in the dawn-dusk direction. Field-aligned currents were observed initially within the expanding plasma sheet, where the flow and field disturbances showed the distinct pattern expected in the braking region of localized flows. Subsequently, intense thin field-aligned current layers were detected at the inner boundary of equatorward moving flux tubes together with Earthward streaming hot ions. Intense Hall current layers were found adjacent to the field-aligned currents. In particular, we found a Hall current structure in the vicinity of the Earthward streaming ion jet that consisted of mixed ion components, that is, hot unmagnetized ions, cold E × B drifting ions, and magnetized electrons. Our observations show that both the near-Earth plasma jet diversion and the thin Hall current layers formed around the reconnection jet boundary are the sites where diversion of the perpendicular currents take place that contribute to the observed field-aligned current pattern as predicted by simulations of reconnection jets. Hence, multiscale structure of flow braking is preserved in the field-aligned currents in the off-equatorial plasma sheet and is also translated to ionosphere to become a part of the substorm field-aligned current system.

  17. Multiscale Currents Observed by MMS in the Flow Braking Region.

    PubMed

    Nakamura, Rumi; Varsani, Ali; Genestreti, Kevin J; Le Contel, Olivier; Nakamura, Takuma; Baumjohann, Wolfgang; Nagai, Tsugunobu; Artemyev, Anton; Birn, Joachim; Sergeev, Victor A; Apatenkov, Sergey; Ergun, Robert E; Fuselier, Stephen A; Gershman, Daniel J; Giles, Barbara J; Khotyaintsev, Yuri V; Lindqvist, Per-Arne; Magnes, Werner; Mauk, Barry; Petrukovich, Anatoli; Russell, Christopher T; Stawarz, Julia; Strangeway, Robert J; Anderson, Brian; Burch, James L; Bromund, Ken R; Cohen, Ian; Fischer, David; Jaynes, Allison; Kepko, Laurence; Le, Guan; Plaschke, Ferdinand; Reeves, Geoff; Singer, Howard J; Slavin, James A; Torbert, Roy B; Turner, Drew L

    2018-02-01

    We present characteristics of current layers in the off-equatorial near-Earth plasma sheet boundary observed with high time-resolution measurements from the Magnetospheric Multiscale mission during an intense substorm associated with multiple dipolarizations. The four Magnetospheric Multiscale spacecraft, separated by distances of about 50 km, were located in the southern hemisphere in the dusk portion of a substorm current wedge. They observed fast flow disturbances (up to about 500 km/s), most intense in the dawn-dusk direction. Field-aligned currents were observed initially within the expanding plasma sheet, where the flow and field disturbances showed the distinct pattern expected in the braking region of localized flows. Subsequently, intense thin field-aligned current layers were detected at the inner boundary of equatorward moving flux tubes together with Earthward streaming hot ions. Intense Hall current layers were found adjacent to the field-aligned currents. In particular, we found a Hall current structure in the vicinity of the Earthward streaming ion jet that consisted of mixed ion components, that is, hot unmagnetized ions, cold E × B drifting ions, and magnetized electrons. Our observations show that both the near-Earth plasma jet diversion and the thin Hall current layers formed around the reconnection jet boundary are the sites where diversion of the perpendicular currents take place that contribute to the observed field-aligned current pattern as predicted by simulations of reconnection jets. Hence, multiscale structure of flow braking is preserved in the field-aligned currents in the off-equatorial plasma sheet and is also translated to ionosphere to become a part of the substorm field-aligned current system.

  18. NASA Chief Technologist Hosts Town Hall

    NASA Image and Video Library

    2010-05-24

    Bobby Braun, right, NASA's Chief Technologist, answers questions during a Town Hall meeting to discuss agency-wide technology policy and programs at NASA Headquarters on Tuesday, May 25, 2010, in Washington. Photo Credit: (NASA/Carla Cioffi)

  19. Study of Energy Loss Mechanisms in the BPT-4000 Hall Thruster

    DTIC Science & Technology

    2003-06-30

    Aerojet has developed a high performance multi-mode flightweight Hall thruster for orbit raising and stationkeeping on geo-synchronous satellites. In...order to further understand and improve upon the performance of this state of the art Hall thruster and other next generation thrusters being planned

  20. 25. CURRENT METERS: GURLEY MODEL NO. 665 AT CENTER, GURLEY ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    25. CURRENT METERS: GURLEY MODEL NO. 665 AT CENTER, GURLEY MODEL NO. 625 'PYGMY' CURRENT METER AT LEFT, AND WES MINIATURE PRICE-TYPE CURRENT METER AT RIGHT. - Waterways Experiment Station, Hydraulics Laboratory, Halls Ferry Road, 2 miles south of I-20, Vicksburg, Warren County, MS