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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Coil Creep and Skew-Quadrupole Field Components in the Tevatron

During the start-up of Run II of the Tevatron Collider program, several issues surfaced which were not present, or not seen as detrimental, during Run I. These included the repeated deterioration of the closed orbit requiring orbit smoothing every two weeks or so, the inability to correct the closed orbit to desired positions due to various correctors running at maximum limits, regions of systematically strong vertical dipole corrections, and the identification of very strong coupling between the two transverse degrees-of-freedom. It became apparent that many of the problems being experienced operationally were connected to a deterioration of the main dipole magnet alignment, and remedial actions were undertaken. However, the alignment alone was not enough to explain the corrector strengths required to handle transverse coupling. With one exception, strong coupling had generally not been an issue in the Tevatron during Run I. Based on experience with the Main Ring, the Tevatron was designed with a very strong skew quadrupole circuit to compensate any quadrupole alignment and skew quadrupole field errors that might present themselves. The circuit was composed of 48 correctors placed evenly throughout the arcs, 8 per sector, evenly placed in every other cell. Other smaller circuits were installed but not initially needed or commissioned. These smaller circuits were composed of individual skew quadrupole correctors on either side of the long straight sections. These circuits were tuned by first bringing the horizontal and vertical tunes near each other. The skew quadrupoles were then adjusted to minimize tune split, usually to less than 0.003. Initially, the main skew quad circuit (designated T:SQ) could accomplish this global decoupling with only 4% of its possible current, and the smaller circuits were not required at all. The start-up of Run Ib was complicated by what was later discovered to be a rolled triplet quadrupole magnet in one of the Interaction Regions. This led to a reduction in luminosity of nearly 50%, as well as operational confusion until it was uncovered. By the time Collider Run II began, the current needed on the main SQ circuit had increased to 60% of its maximum value. Some of the smaller circuits were also needed to fully decouple the tunes. With this history, several studies were performed early in Run II to search for strong local coupling sources like the triplet quadrupole, but without success. The strong corrector settings were indicative of a much larger problem than a single rolled magnet, and the locality of the error was hard to deduce from the setting of a global correction system. Several possible reasons for the increase in coupling were investigated.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

THE ROLE OF ACTIVE REGION LOOP GEOMETRY. I. HOW CAN IT AFFECT CORONAL SEISMOLOGY?

We present numerical results of coronal loop oscillation excitation using a three-dimensional (3D) MHD model of an idealized active region (AR) field. The AR is initialized as a potential dipole magnetic configuration with gravitationally stratified density and contains a loop with a higher density than its surroundings. We study different ways of excitation of vertical kink oscillations of this loop by velocity: as an initial condition, and as an impulsive excitation with a pulse of a given position, duration, and amplitude. We vary the geometry of the loop in the 3D MHD model and find that it affects both the period of oscillations and the synthetic observations (difference images) that we get from oscillations. Due to the overestimated effective length of the loop in the case of loops which have maximum separation between their legs above the footpoints (>50% of observed loops), the magnetic field obtained from coronal seismology can also be overestimated. The 3D MHD model shows how the accuracy of magnetic field strength determined from coronal seismology can be improved. We study the damping mechanism of the oscillations and find that vertical kink waves in 3D stratified geometry are damped mainly due to wave leakage in the horizontal direction.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1995

Consideration of the Martian magnetotail as evidence for an intrinsic magnetic field

It has been suggested by Verigin et al. (1993) that the response of the Martian magnetotail to changes in the solar wind ram pressure indicates the presence of an intrinsic dipole magnetic field. 3-D hybrid particle simulations of Mars were performed including the magnetotail regions. The simulations are in agreement with published Phobos 2 data from the 3 elliptical orbits and reproduce the magnetopause diameter dependence on the solar wind ram pressure reported by Verigin et al. (1993). However, the simulations were performed with no intrinsic field present, indicating that the dependence of the magnetotail width on ram pressure, is not a discriminator for the presence of the intrinsic field.

Brecht, Stephen H.↗
NASA NTRS2018

In Situ Observation of Magnetic Reconnection Between an Earthward Propagating Flux Rope and the Geomagnetic Field

It has been proposed that, in the near-Earth magnetotail, earthward propagating flux ropes can merge with the Earth's dipole magnetic field and dissipate its magnetic energy. However, the reconnection diffusion region related to this process has not been identified. Here we report the first in situ observation of magnetic reconnection between an earthward propagating flux rope and the closed magnetic field lines connecting to Earth. Magnetospheric Multiscale (MMS) spacecraft crossed a vertical current sheet between the leading edge of the flux rope (negative B(sub z)) and the geomagnetic field (positive B(sub z)). The subion-scale current sheet, super-Alfvénic electron outflow, Hall magnetic and electric field, conversion of magnetic energy to plasma energy (J·E > 0), and magnetic null were observed during the crossing. All the above signatures indicate that MMS detected the reconnection diffusion region. This result is also relevant to other planets with intrinsic magnetosphere.

Magnetospheric Multiscale↗
DOE OSTI2023

Dipole-lattice nanoparticle resonances in finite arrays

We investigate how the periodic lattices define the collective optical characteristics of the silicon and titanium nanoparticle arrays. We examine the effects of dipole lattice on the resonances of optical nanostructures, including those made of lossy materials, such as titanium. Our approach involves employing coupled-electric-magnetic-dipole calculations for finite-size arrays, as well as lattice sums for effectively infinite arrays. Our model shows that the convergence to the infinite-lattice limit is faster when the resonance is broad, requiring fewer array particles. Our approach differs from previous works by altering the lattice resonance through modifications in the array period. We observed that a higher number of nanoparticles is necessary to achieve convergence to the infinite-array limit. Additionally, we observe that the lattice resonances excited next to higher diffraction orders (such as second order) converge more quickly toward the ideal case of an infinite array than the lattice resonances related to the first diffraction order. This work reports on the significant advantages of using a periodic arrangement of lossy nanoparticles and the role of collective excitation in enhancing response from transition metals, such as titanium, nickel, tungsten, and so on. The periodic arrangement of nanoscatterers allows for the excitation of strong dipoles, boosting the performance of nanophotonic devices and sensors by improving the strength of localized resonances.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Is Proxima Centauri b Habitable? A Study of Atmospheric Loss

We address the important question of whether the newly discovered exoplanet, Proxima Centauri b (PCb), is capable of retaining an atmosphere over long periods of time. This is done by adapting a sophisticated multi-species MHD model originally developed for Venus and Mars and computing the ion escape losses from PCb. The results suggest that the ion escape rates are about two orders of magnitude higher than the terrestrial planets of our Solar system if PCb is unmagnetized. In contrast, if the planet does have an intrinsic dipole magnetic field, the rates are lowered for certain values of the stellar wind dynamic pressure, but they are still higher than the observed values for our solar system’s terrestrial planets. These results must be interpreted with due caution since most of the relevant parameters for PCb remain partly or wholly unknown.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

Theoretical electric dipole moments of SiH, GeH and SnH

Accurate theoretical dipole moments have been computed for the X2Pi ground states of Si(-)H(+) (0.118 D), Ge(+)H(-) (0.085 D), and Sn(+)H(-) (0.357 D). The trend down the periodic table is regular and follows that expected from the electronegativities of the group IV atoms. The dipole moment of 1.24 + or - 0.1 D for GeH recently derived by Brown, Evenson and Sears (1985) from the relative intensities of electric and magnetic dipole transitions in the 10-micron spectrum of the X2Pi state is seriously questioned.

Pettersson, L. G. M.↗
NASA NTRS1999

Discovery of a Magnetar Associated with the Soft Gamma Repeater SGR 1900+14

The soft gamma repeater SGR 1900+14 became active again in June 1998 after a long period of quiescence; it remained at a low state of activity until August 1998, when it emitted a series of extraordinarily intense outbursts. We have observed the source with the Rossi X-Ray Timing Explorer twice, during the onset of each active episode. We confirm the pulsations at the 5.16 s period reported earlier from SGR 1900+14. Here we report the detection of a secular spin-down of the pulse period at an average rate of 1.1 x 10(exp -10)s/s. In view of the strong similarities between SGRs, we attribute the spin-down of SGR 1900+14 to magnetic dipole radiation, possibly accelerated by a quiescent flux, as in the case of SGR 1806-20. This allows an estimate of the pulsar dipolar magnetic field, which is (2-8) x 10(exp 14) G. Our results confirm that SGRs are magnetars.

Kouveliotou, C.↗
NASA NTRS1999

Discovery of a Magnetar Associated with the Soft Gamma Repeater SGR 1900 + 14

The soft-gamma repeater (SGR) 1900 + 14 became active again on June 1998 after a long period of quiescence; it remained at a low state of activity until August 1998, when it emitted a series of extraordinarily intense outbursts. We have observed the source with RXTE twice, during the onset of each active episode. We confirm the pulsations at the 5.16 s period reported earlier from SCR 1900 + 14 . Here we report the detection of a secular spindown of the pulse period at an average rate of 1.1 x 10(exp -10) s/s. In view of the strong similarities between SGRs, we attribute the spindown of SGR 1900 + 14 to magnetic dipole radiation, possibly accelerated by a quiescent flux, as in the case of SGR 1806 - 20. This allows an estimate of the pulsar dipolar magnetic field, which is 2 - 8 x 10(exp 14) G. Our results confirm that SGRs are magnetars.

Kouveliotou, Chryssa↗
DOE OSTI2025

Charge radii and electromagnetic moments of 214−218 Bi : Exploring the “southern” border of the 𝑍 > 82 octupole-deformation region

The changes in the mean-squared charge radii relative to 209 Bi 126 (𝛿⁢⟨𝑟 2 ⟩ 𝑁,126 ) and the magnetic dipole and electric quadrupole moments in 214−218 Bi have been measured using the in-source resonance-ionization spectroscopy technique at ISOLDE (CERN). Magnetic moments of odd-odd bismuth nuclei have been analyzed by the additivity relation. Previous tentative spin-parity and configuration assignments based on the 𝛽-decay feeding patterns have been supported. A normal odd-even staggering in charge radii of bismuth isotopes with 𝑁>126 has been observed. The new data for the 𝛿⁡⟨𝑟 2 ⟩ of bismuth isotopes allow a study of the isotonic dependencies in the charge radii, revealing jumps in 𝛿⁢⟨𝑟 2 ⟩ 132,126 and 𝛿⁢⟨𝑟 2 ⟩ 134,126 at 𝑍 = 84. This pattern could be explained by a sudden onset of octupole deformation at 𝑁 = 132 and 134 when going from polonium (𝑍 = 84) to astatine (𝑍 = 85).

fundamental symmetries↗
DOE OSTI2014

timesphere6.f software

Solves the electromagnetic forward problem for a plane wave or magnetic dipole fields impingent on a set of spherical shells in a whole space of uniform resistivity, relative permeability , and relative permitivity for electric fields and magnetic fields of internal origin at nrcv receivers and nf frequencies. For receivers outside the largest sphere these are standard secondary fields. Results are given in either time or frequency domain. Time domain results allow modelling turn-on or turn-off step function transmitter wave forms, or square pulse and half sine pulse wave funcitons with arbitrary pulse length and repetition rate. Pulses may be either uni-modal or bi-modal (alternating sign each half period).

Smith, Jeremy↗
DOE OSTI2019

Improved Momentum Spread for Precision Physics Experiments Using Wedges

High precision experiments have become key in the search for physics beyond the Standard Model. Measurements that can be made in order to expand our knowledge of the Standard Model are the precise measurement of the magnetic dipole moment (MDM) of the muon and searches for a non-zero value of its electric dipole moment (EDM). In order to perform precise measurements of this type, the storage of particles with a precisely known momentum in a highly uniform magnetic field is required. This thesis is focused on how one may use a wedge of energy absorbing material and the optical parameters of an accelerator lattice to improve upon the amount of particles delivered into a storage ring. This thesis will rely on computer simulations to determine ideal optics parameters as well as to study how the beam parameters change as the beam traverses a lattice. As a case study, this thesis will look to the M4 and M5 lines in the Fermilab Muon g-2 experiment, where a wedge of energy absorbing material will be used to reduce the energy spread of a muon beam.

43 PARTICLE ACCELERATORS↗
NASA NTRS1994

A three-dimensional ring current decay model

This work is an extension of a previous ring current decay model. In the previous work, a two-dimensional kinetic model was constructed to study the temporal variations of the equatorially mirroring ring current ions, considering charge exchange and Coulomb drag losses along drift paths in a magnetic dipole field. In this work, particles with arbitrary pitch angle are considered. By bounce averaging the kinetic equation of the phase space density, information along magnetic field lines can be inferred from the equator. The three-dimensional model is used to simulate the recovery phase of a model great magnetic storm, similar to that which occurred in early February 1986. The initial distribution of ring current ions (at the minimum Dst) is extrapolated to all local times from AMPTE/CCE spacecraft observations on the dawn and dusk sides of the inner magnetosphere spanning the L value range L = 2.25 to 6.75. Observations by AMPTE/CCE of ring current distributions over subsequent orbits during the storm recovery phase are compared to model outputs. In general, the calculated ion fluxes are consistent with observations, except for H+ fluxes at tens of keV, which are always over-estimated. A newly-invented visualization idea, designated as a chromogram, is used to display the spatial and energy dependence of the ring current ion differential flux. Important features of storm-time ring current, such as day-night asymmetry during injection and drift hole on the dayside at low energies (less than 10 keV), are manifested in the chromogram representation. The pitch angle distribution is well fit by the function, j(sub o)(1+Ay(exp n)), where y is sine of the equatorial pitch angle. The evolution of the index n is a combined effect of charge exchange loss and particle drift. At low energies (less than 30 keV), both drift dispersion and charge exchange are important in determining n.

Fok, Mei-Ching↗
NASA NTRS1995

Three-dimensional ring current decay model

This work is an extension of a previous ring current decay model. In the previous work, a two-dimensional kinetic model was constructed to study the temporal variations of the equatorially mirroring ring current ions, considering charge exchange and Coulomb drag losses along drift paths in a magnetic dipole field. In this work, particles with arbitrary pitch angle are considered. By bounce averaging the kinetic equation of the phase space density, information along magnetic field lines can be inferred from the equator. The three-dimensional model is used to simulate the recovery phase of a model great magnetic storm, similar to that which occurred in early February 1986. The initial distribution of ring current ions (at the minimum Dst) is extrapolated to all local times from AMPTE/CCE spacecraft observations on the dawnside and duskside of the inner magnetosphere spanning the L value range L = 2.25 to 6.75. Observations by AMPTE/CCE of ring current distributions over subsequent orbits during the storm recovery phase are compared to model outputs. In general, the calculated ion fluxes are consistent with observations, except for H(+) fluxes at tens of keV, which are always overestimated. A newly invented visualization idea, designated as a chromogram, is used to display the spatial and energy dependence of the ring current ion differential flux. Important features of storm time ring current, such as day-night asymmetry during injection and drift hole on the dayside at low energies (less than 10 keV), are manifested in the chromogram representation. The pitch angle distribution is well fit by the function, J(sub o)(1 + Ay(sup n)), where y is sine of the equatorial pitch angle. The evolution of the index n is a combined effect of charge exchange loss and particle drift. At low energies (less than 30 keV), both drift dispersion and charge exchange are important in determining n.

Fok, Mei-Ching↗
DOE OSTI2014

Capacitive energy storage and recovery for synchrotron magnets

Feasibility studies on capacitive energy storage and recovery in the main-ring synchrotron of the Japan Proton Accelerator Research Complex were conducted by circuit simulation. The estimated load fluctuation was 96 MVA in total for dipole magnets, which is likely to induce a serious disturbance in the main grid. It was found that the energy stored in the magnets after the excitation period can be recovered to the storage capacitor by controlling the voltage across the energy-storage capacitor using a pulse-width-modulation converter and reused in the next operational cycle. It was also found that the power fluctuation in the main grid can be reduced to 12 MVA. An experimental evaluation of an aluminum metalized film capacitor revealed that capacitance loss was induced by a fluctuating voltage applied to the storage capacitor when applying the proposed method. The capacitance loss was induced by corona discharge around the edges of segmented electrodes of a self-healing capacitor. The use of aluminum-zinc alloy was evaluated as a countermeasure to mitigate the effect induced by the corona discharge. For a zinc content of 8%, which was optimized experimentally, a capacitor with a sufficient life time expectancy of 20 years and a working potential gradient of 250 V/μm was developed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Perturbation analysis of trapped-particle dynamics in axisymmetric dipole geometry

The bounce-action-angle coordinates (J,{zeta}) for charged particles trapped in an axisymmetric dipole magnetic field are constructed by perturbation analysis. First, the lowest-order bounce-action-angle coordinates (J{sub 0},{zeta}{sub 0}) are derived for deeply trapped particles in the harmonic-oscillator approximation. Next, the Lie-transform perturbation method is used to derive higher-order anharmonic action-angle corrections (J=J{sub 0}+{epsilon}{sub t}J{sub 1}, {zeta}={zeta}{sub 0}+{epsilon}{sub t{zeta}1}), where the dimensionless parameter {epsilon}{sub t{identical_to}}(s{sub b}/r{sub e}){sup 2}<<1 is defined as the ratio of the turning-point distance |s{sub b}| (measured from the equator) along a magnetic field line labeled by the equatorial distance r{sub e}. Explicit expressions (with anharmonic corrections) for the canonical parallel coordinates s(J,{zeta}) and p{sub ||}(J,{zeta}) are presented, which satisfy the canonical identity {l_brace}s,p{sub ||{r_brace}{identical_to}}1. Lastly, analytical expressions for the bounce and drift frequencies (which include anharmonic corrections) yield excellent agreement with exact numerical results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Cryogenic and safety design of the future high field cable test facility at Fermilab

The HFVMTF (High Field Vertical Magnet Test Facility) is a new experimental facility under development at Fermi National Accelerator Laboratory (FNAL) to test large superconducting magnets (up to 20 tons weight and 1.3 m diameter) in a double bath superfluid helium cryostat (1.9 K and 1.2 bar). Coupled with a superconducting dipole magnet fabricated by Lawrence Berkeley National Laboratory (LBNL), this facility will be able to test future high-temperature superconductor (HTS) cables under a background magnetic field of 15 T for fusion magnets. This paper describes the design of the cryostat and its 1.4-meter diameter lambda plate, as well as the different components for a safe operation of the facility, even during critical events such a magnet quench or a vacuum breaking situation. The project is funded by US DOE Offices of Science, High Energy Physics (HEP), and Fusion Energy Sciences (FES).

43 PARTICLE ACCELERATORS↗