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At least 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

A Search for Neutron to Mirror Neutron Oscillation Using Neutron Electric Dipole Moment Measurements

Baryon number violation is a key ingredient of baryogenesis. It has been hypothesized that there could also be a parity-conjugated copy of the standard model particles, called mirror particles. The existence of such a mirror universe has specific testable implications, especially in the domain of neutral particle oscillation, viz. the baryon number violating neutron to mirror-neutron (n−n′) oscillation. Consequently, there were many experiments that have searched for n−n′ oscillation, and imposed constraints upon the parameters that describe it. Recently, further analysis on some of these results have identified anomalies which could point to the detection of n−n′ oscillation. All the previous efforts searched for n−n′ oscillation by comparing the relative number of ultracold neutrons that survive after a period of storage for one or both of the two cases: (i) comparison of zero applied magnetic field to a non-zero applied magnetic field, and (ii) comparison where the orientation of the applied magnetic field was reversed. However, n−n′ oscillations also lead to variations in the precession frequency of polarized neutrons upon flipping the direction of the applied magnetic field. Precession frequencies are measured, very precisely, by experiments searching for the electric dipole moment. For the first time, we used the data from the latest search for the neutron electric dipole moment to constrain n−n′ oscillation. After compensating for the systematic effects that affect the ratio of precession frequencies of ultracold neutrons and cohabiting 199Hg-atoms, chief among which was due to their motion in non-uniform magnetic field, we constrained any further perturbations due to n−n′ oscillation. We thereby provide a lower limit on the n−n′ oscillation time constant of τnn′/|cos(β)|>5.7s,0.36T′

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Influence of Magnetic Confinement on the Yellow Excitons in Cuprous Oxide Subject to an Electric Field

We study the spectrum of the yellow exciton series in crossed electric and magnetic fields. The electric field, applied along the optical axis, tilts the Coulomb potential between electron and hole, so that at sufficiently high fields exciton dissociation becomes possible, roughly when the electric dipole interaction energy exceeds the binding energy of an exciton state with principal quantum number n. For an applied voltage of U = 20 V all excitons above n = 6 are dissociated. Additional application of a magnetic field normal to the optical axis introduces magnetic confinement, due to which above a threshold field strength around B = 2.5 T the exciton lines re-emerge. The complex dispersion with increasing fields suggests quantum chaotic behavior in this crossed field configuration, so that the search for exceptional points may be promising.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Nb3Sn High Field Magnets for the High Luminosity LHC Upgrade Project

The High Luminosity upgrade of the Large Hadron Collider at CERN requires a new generation of high field superconducting magnets. High field large aperture quadrupoles (MQXF) are needed for the low-beta triplets close to the ATLAS and CMS detectors, and high field two-in-one dipoles (11 T dipoles) are needed to make room for additional collimation. The MQXF quadrupoles, with a field gradient of 140 T/m in 150 mm aperture, have a peak coil field of 12.1 T at nominal current. The 11 T dipoles, with an aperture of 60 mm, have a peak coil field of 11.6 T at nominal current. Both magnets require Nb3Sn conductor and are the first applications of this superconductor to actual accelerator magnets.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

STORAGE RING AND INTERACTION REGION MAGNETS FOR A μ+μ- HIGGS FACTORY.

A low-energy Muon Collider (MC) offers unique opportunities to study the recently found Higgs boson. However, due to a relatively large beam emittance with moderate cooling in this machine, large-aperture high- field superconducting (SC) magnets are required. The magnets need also an adequate margin to operate at a large radiation load from the muon decay showers. General specifications of the SC dipoles and quadrupoles for the 125 GeV c.o.m. Higgs Factory with an average luminosity of ~2x10**31 cm-2s-1 are formulated. Magnet conceptual designs and parameters are reported. The impact of the magnet fringe fields on the beam dynamics as well as the IR and lattice magnet protection from radiation are also reported and discussed.

Zlobin, A. V.↗
DOE OSTI2013

DYNAMO ACTIVITIES DRIVEN BY MAGNETOROTATIONAL INSTABILITY AND THE PARKER INSTABILITY IN GALACTIC GASEOUS DISKS

We carried out global three-dimensional magnetohydrodynamic simulations of dynamo activities in galactic gaseous disks without assuming equatorial symmetry. Numerical results indicate the growth of azimuthal magnetic fields non-symmetric to the equatorial plane. As the magnetorotational instability (MRI) grows, the mean strength of magnetic fields is amplified until the magnetic pressure becomes as large as 10% of the gas pressure. When the local plasma {beta} (=p {sub gas}/p {sub mag}) becomes less than 5 near the disk surface, magnetic flux escapes from the disk by the Parker instability within one rotation period of the disk. The buoyant escape of coherent magnetic fields drives dynamo activities by generating disk magnetic fields with opposite polarity to satisfy the magnetic flux conservation. The flotation of the azimuthal magnetic flux from the disk and the subsequent amplification of disk magnetic field by the MRI drive quasi-periodic reversal of azimuthal magnetic fields on a timescale of 10 rotation periods. Since the rotation speed decreases with radius, the interval between the reversal of azimuthal magnetic fields increases with radius. The rotation measure computed from the numerical results shows symmetry corresponding to a dipole field.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2015

A Comparative Analysis of the Magnetic Field Signals over Impact Structures on the Earth, Mars and the Moon

An improved description of magnetic fields of terrestrial bodies has been obtained from recent space missions, leading to a better characterization of the internal fields including those of crustal origin. One of the striking differences in their crustal magnetic field is the signature of large impact craters. A comparative analysis of the magnetic characteristics of these structures can shed light on the history of their respective planetary-scale magnetic dynamos. This has motivated us to identify impact craters and basins, first by their quasi-circular features from the most recent and detailed topographic maps and then from available global magnetic field maps. We have examined the magnetic field observed above 27 complex craters on the Earth, 34 impact basins on Mars and 37 impact basins on the Moon. For the first time, systematic trends in the amplitude and frequency of the magnetic patterns, inside and outside of these structures are observed for all three bodies. The demagnetization effects due to the impact shock wave and excavation processes have been evaluated applying the Equivalent Source Dipole forward modeling approach. The main characteristics of the selected impact craters are shown. The trends in their magnetic signatures are indicated, which are related to the presence or absence of a planetary-scale dynamo at the time of their formation and to impact processes. The low magnetic field intensity at center can be accepted as the prime characteristic of a hypervelocity impact and strongly associated with the mechanics of impact crater formation. In the presence of an active internal field, the process of demagnetization due to the shock impact is associated with post-impact remagnetization processes, generating a more complex magnetic signature.

Earth↗
DOE OSTI2014

Low-energy magnetic radiation: Deviations from GOE

A pronounced spike at low energy in the strength function for magnetic radiation (LEMAR) is found by means of Shell Model calculations, which explains the experimentally observed enhancement of the dipole strength. LEMAR originates from statistical low-energy M1-transitions between many excited complex states. Re-coupling of the proton and neutron high-j orbitals generates the strong magnetic radiation. LEMAR is closely related to Magnetic Rotation. LEMAR is predicted for nuclides participating in the r-process of element synthesis and is expected to change the reaction rates. An exponential decrease of the strength function and a power law for the size distribution of the B(M1) values are found, which strongly deviate from the ones of the GOE of random matrices, which is commonly used to represent complex compound states.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS2003

Prospect of Using Numerical Dynamo Model for Prediction of Geomagnetic Secular Variation

Modeling of the Earth's core has reached a level of maturity to where the incorporation of observations into the simulations through data assimilation has become feasible. Data assimilation is a method by which observations of a system are combined with a model output (or forecast) to obtain a best guess of the state of the system, called the analysis. The analysis is then used as an initial condition for the next forecast. By doing assimilation, not only we shall be able to predict partially secular variation of the core field, we could also use observations to further our understanding of dynamical states in the Earth's core. One of the first steps in the development of an assimilation system is a comparison between the observations and the model solution. The highly turbulent nature of core dynamics, along with the absence of any regular external forcing and constraint (which occurs in atmospheric dynamics, for example) means that short time comparisons (approx. 1000 years) cannot be made between model and observations. In order to make sensible comparisons, a direct insertion assimilation method has been implemented. In this approach, magnetic field observations at the Earth's surface have been substituted into the numerical model, such that the ratio of the multiple components and the dipole component from observation is adjusted at the core-mantle boundary and extended to the interior of the core, while the total magnetic energy remains unchanged. This adjusted magnetic field is then used as the initial field for a new simulation. In this way, a time tugged simulation is created which can then be compared directly with observations. We present numerical solutions with and without data insertion and discuss their implications for the development of a more rigorous assimilation system.

Kuang, Weijia↗
DOE OSTI2016

Quench performance and field quality of FNAL twin-aperture 11 T Nb 3 Sn dipole model for LHC upgrades

A 2 m long single-aperture dipole demonstrator and two 1 m long single-aperture models based on Nb 3 Sn superconductor have been built and tested at FNAL. The two 1 m long collared coils were then assembled in a twin-aperture Nb 3 Sn dipole demonstrator compatible with the LHC main dipole and tested in two thermal cycles. This paper summarizes the quench performance of the FNAL twin-aperture Nb 3 Sn 11 T dipole in the temperature range of 1.9-4.5 K. The results of magnetic measurements for one of the two apertures are also presented. Test results are compared to the performance of coils in a single-aperture configuration. Lastly, a summary of quench propagation studies in both apertures is given.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Magneto-Mechanical Optimization of Cross-Sections for $ \text{cos}(\theta)$Accelerator Magnets

The cross-section design of cos (θ) superconducting magnets is historically developed in a two-step process: initially, the coil geometry is defined on the basis of magnetic optimizations; then, the structure is designed around the coil. The first step searches for the best coil cross-section maximizing the magnetic field, margin, field quality and conductor efficiency. The latter step aims at limiting the coil stresses and deformations. However, the coil design, defined with the initial magnetic optimization, can influence the mechanical behaviour of the magnet, altering, for example, the peak stress during operation. As the critical current is a function of the applied strain, the mechanical implications of the coil cross-section design can limit the achievable performance. In this paper we propose an integrated optimization process that targets the peak stress on the conductor in addition to the magnetic objectives. Here the results are presented for a sample high-field Nb 3 Sn dipole: a 4-layer design aiming at ultimate conductor performance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Nonradiative recombination of excitons in semimagnetic quantum dots

The mechanisms of the nonradiative recombination of excitons in neutral and charged quantum dots based on II–VI semimagnetic semiconductors are investigated. It is shown that, along with the dipole–dipole and direct-exchange mechanisms, there is one more mechanism referred to as the indirect-exchange mechanism and related to sp–d mixing. The selection rules for nonradiative recombination by exchange mechanisms are subsequently derived. The dependence of the efficiency of all recombination mechanisms on the quantum-dot size is studied. The experimentally observed growth in the intracenter photoluminescence intensity with decreasing size of dots and nanocrystals is accounted for. Methods for experimental determination of the contributions of different mechanisms to nonradiative recombination are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Accident Scenarios for IOTA Ring and Dose Distributions Calculated with MARS15 Code

The Integrable Optics Test Accelerator (IOTA) at Fermilab’s Accelerator Science and Technology (FAST) facility [1] is a storage ring for advanced high intensity beam physics research. Layout of the ring is shown in Fig. 1. A plan view of the ring with enclosure walls are shown in Fig. 2. The entire beam, stored in the IOTA ring, is assumed to be completely lost at either of the three locations shown in Fig. 2. Therefore, we will consider three separate corresponding accident scenarios. The maximal amount of electrons stored in the IOTA ring is estimated to be 2×10 10 electrons with energy of 150 MeV. At locations 1 and 2 the beam is lost on 60-deg dipole walls, while at location 3 the beam is lost on Lambertson magnet wall.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

PRECISION MØLLER POLARIMETRY AND APPLICATIONS AT JEFFERSON LABORATORY

Jefferson Lab's cutting-edge parity-violating electron scattering program has increasingly stringent requirements for systematic errors. Beam polarimetry is often one of the dominant systematic errors in these experiments. A new Møller Polarimeter in Hall A of Jefferson Lab (JLab) was installed in 2015 and has taken first measurements for a polarized scattering experiment. Upcoming parity violation experiments in Hall A include CREX, PREX-II, MOLLER and SOLID with the latter two requiring <0.5% precision on beam polarization measurements, a precision which has not been achieved to date. The polarimeter measures the Møller scattering rates of the polarized electron beam incident upon an iron target placed in a saturating magnetic field. The spectrometer consists of four quadrupoles and one momentum selection dipole. The detector is designed to measure the scattered and knock out target electrons in coincidence. Beam polarization is extracted by constructing an asymmetry from the scattering rates when the incident electron spin is parallel and antiparallel to the target electron spin. The largest systematic errors associated with Møller polarimetry comes from the precision that the target polarization and the detector acceptance is known will be discussed. Other errors including the Levchuk effect, beam stability, and target heating will be addressed.

Henry, William↗
NASA NTRS1973

Magnetic flux density environment of several electron-bombardment ion thrusters

Measurements of the external magnetic field of several electron-bombardment mercury ion thrusters were made using a single axis fluxgate magnetometer. The axial dipole moment accounted for most of the external field. In addition, residual fields from an electromagnet thruster were approximately 20 percent of the initial field. Simple degaussing of the axial magnets reduced the residual fields to 1 to 2 percent of the initial field.

Danilowicz, R. L.↗
NASA NTRS1982

Quadrupole distortions of the heliospheric current sheet in 1976 and 1977

Latitudinal variations in the position of the heliospheric current sheet were investigated using interplanetary measurements from Helios A, Helios B, IMP 8, and white light corona measurements in the period May 1976 to May 1977. The latitude of the heliospheric current sheet between 0.3 AU and I AU is consistent with that of the maximum brightness curve of white light polarization brightness at 1.75 solar radii within approximately + or - 7 deg. The combined data sets show that the four-sector magnetic sector pattern observed in the ecliptic plane for most of this epoch could be attributed to a warped current sheet whose shape near the sun resembles a saddle surface that is nearly symmetrical about the equatorial plane. The latitudinal extent of the current sheet is on the average 8 deg and the maximum extent is 15 deg (except on one rotation, when it is 20 deg). These results can be interpreted as a consequence of the solar magnetic field, the dominant components of the field being due to a dipole nearly aligned with the sun's spin axis and a quadrupole component whose strength is about 17 percent of the dipole.

Bruno, R.↗
NASA NTRS1994

On the polarization of resonantly scattered emission lines - 1. Emission and absorption coefficients in an anisotropic radiation field

Source functions and absorptions coefficients for polarized radiation in a given ansiotropic radiation field are calculated for a variety of permitted electric dipole transitions in the L-S coupling limit. Collisional, radiative and magnetic mixing of the ground sublevels are all considered. The polarization of the self-consistent, emergent radiation field is computed, using an anisotropic escape probability formalism to treat the radiative transfer. It is found that the radiative mixing can enhance the polarization for transitions with large angular momentum, and degrees of polarization less than or approximately 10 per cent are obtained for transitions with small angular momentum.

Lee, H. -W.↗
NASA NTRS2000

On Geomagnetism and Paleomagnetism I

A partial description of Earth's broad scale, core-source magnetic field has been developed and tested three ways. The description features an expected, or mean, spatial magnetic power spectrum that is approximately inversely proportional to horizontal wavenumber atop Earth's core. This multipole spectrum describes a magnetic energy range; it is not steep enough for Gubbins' magnetic dissipation range. Temporal variations of core multipole powers about mean values are to be expected and are described statistically, via trial probability distribution functions, instead of deterministically, via trial solution of closed transport equations. The distributions considered here are closed and neither require nor prohibit magnetic isotropy. The description is therefore applicable to, and tested against, both dipole and low degree non-dipole fields. In Part 1, a physical basis for an expectation spectrum is developed and checked. The description is then combined with main field models of twentieth century satellite and surface geomagnetic field measurements to make testable predictions of the radius of Earth's core. The predicted core radius is 0.7% above the 3480 km seismological value. Partial descriptions of other planetary dipole fields are noted.

Voorhies, Coerte V.↗
NASA NTRS2017

The JPL Neptune Radiation Model (NMOD)

The objective of this study is the development of a comprehensive radiation model of the Neptunian environment for JPL mission planning. The ultimate goal is to provide a description of the high-energy electron and proton environments and the magnetic field at Neptune that can be used for engineering design. The JPL Neptune Radiation Model (NMOD) models the high-energy electrons and protons between 0.025 MeV and 5 MeV based on the California Institute of Technology's Cosmic Ray Subsystem and the Applied Physics Laboratory's Low Energy Charged Particle Detector on Voyager 2. As in previous JPL radiation models, the form of the Neptunian model is based on magnetic field coordinates and requires a conversion from spacecraft coordinates to Neptunian-centered magnetic "B-L" coordinates. Two types of magnetic field models have been developed for Neptune: 1) simple "offset, tilted dipoles" (OTD), and 2) a complex, multi-pole expansion model ("O8"). A review of the existing data on Neptune and a search of the NASA Planetary Data System (PDS) were completed to obtain the most current descriptions of the Neptunian high-energy particle environment. These data were fit in terms of the O8 B-L coordinates to develop the electron and proton flux models. The flux predictions of the new model were used to estimate the total ionizing dose (TID) rate along the Neptunian equator, meridional flux contours for the electrons and protons, and for flux and dose comparisons with the other radiation belts in the Solar System.

Garrett, Henry↗