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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Second spectrum of Manganese (Mn II), Part I: Fine and hyperfine structure analysis of even-parity levels

We have taken advantage of the existence of some experimental Mn II hyperfine magnetic dipole constant (A) values given in literature with low uncertainties to achieve for a first time an accurate hyperfine structure (hfs) parametric study. The monoelectronic hfs parameter values were extracted in their entirety for the alone stable {sup 55}Mn II. For example for 3d{sup 4}4s configuration we obtain: a{sub 4s}{sup 10}=198.08 mk and a{sub 3d}{sup 01}=17.14 mk. These semi-empirically extracted single-electron parameters were analyzed and compared with ab-initio calculations. In this first part of a global work, devoted particularly to even-parity levels we have at beginning studied a fine structure of two hundred levels, giving their leading eigenvector percentages and their calculated Landé-factor g{sub J}. We present also predicted singlet, triplet and quintet positions of missing experimental levels up to 120 000 cm{sup −1}, not far from Mn II ionization energy of 126 000 cm{sup −1}. We close this work by giving predicted values of magnetic dipole hfs constants of all known levels of the most relevant Mn II even-parity configuration: 3d{sup 4}4s, whose splitting is not yet measured.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Search for magnetic inelastic dark matter with XENON100

We present the first search for dark matter-induced delayed coincidence signals in a dual-phase xenon time projection chamber, using the 224.6 live days of the XENON100 science run II. This very distinct signature is predicted in the framework of magnetic inelastic dark matter which has been proposed to reconcile the modulation signal reported by the DAMA/LIBRA collaboration with the null results from other direct detection experiments. No candidate event has been found in the region of interest and upper limits on the WIMP's magnetic dipole moment are derived. The scenarios proposed to explain the DAMA/LIBRA modulation signal by magnetic inelastic dark matter interactions of WIMPs with masses of 58.0 GeV/c{sup 2} and 122.7 GeV/c{sup 2} are excluded at 3.3 σ and 9.3 σ, respectively.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1995

Radiative and Nonradiative Transitions of the Rare-Earth Ions Tm(3+) and Ho(3+) in Y3AI5O12 and LiYF4

The optical spectra of rare earth ions in solids arise primarily from electric and magnetic dipole transitions between stark split multiplets of the 4f(sup N) electronic configuration. Electric dipole transitions are parity forbidden between levels of the 4f(sup N) configuration, while those of magnetic dipole origin are allowed. It is known from experiment, however, that the significant contributions to the intensities of most transitions are electric dipole in nature. Judd and Ofelt developed the theory of forced electric dipole transitions of rare-earth ions. This study is devoted to determining electric dipole transition probabilities and branching ratios for Tm(3+) and Ho(3+) ions in Yttrium Aluminum Garnet (YAG) and Yttrium Lithium Fluoride (YLF) using the theory of Judd and Ofelt. The radiative rates determined from the Judd-Ofelt analysis are used with measured lifetimes to find nonradiative rates of relaxation.

Walsh, Brian M.↗
DOE OSTI2017

Status of the CBETA splitter common magnet design

The two common dipole magnets in each of the two CBETA splitter sections serve to direct the beams of 42, 78, 114 and 150 MeV from the linac or FFAG return loop exit into the separate splitter lines for path length adjustment and to direct the beams from the splitter into the linac or FFAG return loop entrance. Here we report the results of design and tracking studies based on the Opera V18R2 software. The choice of the H-magnet design included consideration of using the coil design developed for the internal splitter H-dipoles by Elytt Energy. Considerations of transverse space constraints and the bend angle of about 30 degrees for the 42-MeV beam led to the adoption of a T-shape for the pole. The XYZ magnet dimensions are 34 × 42 × 16 cm. The central field value is 3.6-3.9 kG, but the magnet can operate as high as 4.9 kG, allowing for tests of a beam energy as high as 54 MeV in the S1 splitter line. We include results of tracking studies showing optimal placement of the magnets based on bend angle uniformity for the four beam energies. The project now proceeds to the full engineering design and fabrication to be performed by Elytt Energy.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Search for Dark Matter Axions with CAST-CAPP

The CAST-CAPP axion haloscope, operating at CERN inside the CAST dipole magnet, has searched for axions in the 19.74 μeV to 22.47 μeV mass range. The detection concept follows the Sikivie haloscope principle, where Dark Matter axions convert into photons within a resonator immersed in a magnetic field. The CAST-CAPP resonator is an array of four individual rectangular cavities inserted in a strong dipole magnet, phase-matched to maximize the detection sensitivity. Here we report on the data acquired for 4124 h from 2019 to 2021. Each cavity is equipped with a fast frequency tuning mechanism of 10 MHz/ min between 4.774 GHz and 5.434 GHz. In the present work, we exclude axion-photon couplings for virialized galactic axions down to g aγγ = 8 × 10 –14 GeV –1 at the 90% confidence level. The here implemented phase-matching technique also allows for future large-scale upgrades.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

Electromagnetic pulse from supernovae

Upper and lower limits to the radiated electromagnetic pulse from a supernova are calculated assuming that the mass fraction of the matter expanding inside the dipole magnetic field shares energy and maintains the pressure balance in the process. A supernova model is described in which the explosion occurs in old low-mass stars containing less than 10% hydrogen in their ejecta and a remnant neutron star is produced. The analysis indicates that although the surface layer of a star of 1 g/cu thickness may be shock-accelerated to an energy factor of about 100 and may expand into the vacuum with an energy factor approaching 10,000, the equatorial magnetic field will retard this expansion so that the inner, more massive ejecta layers will effectively accelerate the presumed canonical dipole magnetic field to greater velocities than would the surface layer alone. A pulse of 10 to the 46th power ergs in a width of about 150 cm will result which will not be affected by circumstellar matter or electron self-radiation effects. It is shown that interstellar matter will attenuate the pulse, but that charge separation may reduce the attenuation and allow a larger pulse to escape.

Colgate, S. A.↗
DOE OSTI2023

A phenomenological wobbling model for isolated pulsars and the braking index

ABSTRACT An isolated pulsar is a rotating neutron star possessing a very high magnetic dipole moment, thus providing a powerful radiating mechanism. These stars loose rotational energy E through various processes, including a plasma wind originating from a highly magnetized magnetosphere and the emission of magnetic dipole radiation (MDR). Such phenomena produce a time decreasing angular velocity Ω(t) of the pulsar that is usually quantified in terms of its braking index. Although these mechanisms are widely acknowledged as the primary drivers of the spin evolution of isolated pulsars, it is plausible that other contributing factors influencing this effect have yet to be comprehensively investigated. Most of young isolated pulsars present a braking index different from that given by the MDR and plasma wind processes. Working in the weak field (Newtonian) limit, we take in this work a step forward in describing the evolution of such a system by allowing the star’s shape to wobble around an ellipsoidal configuration as a backreaction effect produced by its rotational deceleration. It is assumed that an internal damping of the oscillations occurs, thus introducing another form of energy loss in the system, and this phenomenon may be related to the deviation of the braking index from the models based on $\dot{E} \sim -\Omega ^4$ predictions. Numerical calculations suggest that the average braking index for typical isolated pulsars can be thus explained by a simple phenomenological model.

Araujo, E. C. A. (ORCID:0000000213520879)↗
DOE OSTI2017

Solitary Oxygen Dopant Emission from Carbon Nanotubes Modified by Dielectric Metasurfaces

All-dielectric metasurfaces made from arrays of high index nanoresonators supporting strong magnetic dipole modes have emerged as a low-loss alternative to plasmonic metasurfaces. Here we use oxygen-doped single-walled carbon nanotubes (SWCNTs) as quantum emitters and couple them to silicon metasurfaces to study effects of the magnetic dipole modes of the constituent nanoresonators on the photoluminescence (PL) of individual SWCNTs. We find that when in resonance, the magnetic mode of the silicon nanoresonators can lead to a moderate average PL enhancement of 0.8–4.0 of the SWCNTs, accompanied by an average increase in the radiative decay rate by a factor of 1.5–3.0. More interestingly, single dopant polarization experiments show an anomalous photoluminescence polarization rotation by coupling individual SWCNTs to silicon nanoresonators. Numerical simulations indicate that this is caused by modification of near-field polarization distribution at certain areas in the proximity of the silicon nanoresonators at the excitation wavelength, thus presenting an approach to control emission polarization. In conclusion, these findings indicate silicon nanoresonators as potential building blocks of quantum photonic circuits capable of manipulating PL intensity and polarization of single photon sources.

36 MATERIALS SCIENCE↗
NASA NTRS1995

An MHD simulation study of the poloidal mode field line resonance in the Earth's dipole magnetosphere

The poloidal mode field line resonance in the Earth's dipole magnetic field is investigated using cold plasma ideal MHD simulations in dipole geometry. In order to excite the poloidal mode resonance, we use either an initial or a continuous velocity perturbation to drive the system. The perturbation is localized at magnetic shell L = 7 with plasma flow in the radial direction (electric field component in the azimuthal direction). It is found that with the initial perturbation alone, no polodial mode resonance can be obtained and the initially localized perturbation spreads out across all magnetic L shells. With the continuous perturbation, oscillating near the poloidal resonance frequency, a global-scale poloidal cavity mode can be obtained. For the first time, a localized guided poloidal mode resonance is obtained when a radial component of electric field is added to the initial perturbation such that the curl of the electric field is everywhere perpendicular to the background dipole magnetic field. During the localized poloidal resonance, plasma vortices parallel/antiparallel to the background dipole magnetic field B(sub 0). This circular flow, elongated radially, results in twisting of magnetic field flux tubes, which, in turn, leads to the slowdown of the circular plasma flow and reversal of the plasma vortices. The energy associated with the localized poloidal resonance is conserved as it shifts back and forth between the oscillating plasma vortices and the alternately twisted magnetic flux tubes. In the simulations the eigenfunctions associated with the localized poloidal resonance are grid-scale singular functions. This result indicates that ideal MHD is inadequate to describe the underlying problem and nonideal MHD effects are needed for mode broadening.

Ding, D. Q.↗
DOE OSTI2017

Estimation of dose delivered to accelerator devices from stripping of 18.5 MeV/n 238 U ions using the FLUKA code

In Korea, a heavy ion accelerator facility (RAON) has been designed for production of rare isotopes. The 90° bending section of this accelerator includes a 1.3-μm-carbon stripper followed by two dipole magnets and other devices. An incident beam is 18.5 MeV/n 238 U 33+,34+ ions passing through the carbon stripper at the beginning of the section. The two dipoles are tuned to transport 238 U ions with specific charge states of 77+, 78+, 79+, 80+ and 81+. Then other ions will be deflected at the bends and cause beam losses. These beam losses are a concern to the devices of transport/beam line. The absorbed dose in devices and prompt dose in the tunnel were calculated using the FLUKA code in order to estimate radiation damage of such devices located at the 90° bending section and for the radiation protection. A novel method to transport multi-charged 238 U ions beam was applied in the FLUKA code by using charge distribution of 238 U ions after the stripper obtained from LISE++ code. The calculated results showed that the absorbed dose in the devices is influenced by the geometrical arrangement. The maximum dose was observed at the coils of first, second, fourth and fifth quadruples placed after first dipole magnet. The integrated doses for 30 years of operation with 9.5 pμA 238 U ions were about 2 MGy for those quadrupoles. In conclusion, the protection of devices particularly, quadruples would be necessary to reduce the damage to devices. Furthermore, results showed that the prompt radiation penetrated within the first 60 - 120 cm of concrete.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Energies and transition parameters of fusion interest in Cr-like ions between Hf XLIX and Au LVI

Using fully relativistic multiconfiguration Dirac–Fock (MCDF) wavefunctions in an active space approximation, we perform systematic calculations of the energies, wavelengths, and lifetimes for the lowest 143 levels belonging to the 3p{sup 6}3d{sup 6} and 3p{sup 5}3d{sup 7} configurations of Cr-like ions between Hf XLIX and Au LVI. Additionally, line strengths, oscillator strengths, and radiative rates for the electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1), and magnetic quadrupole (M2) transitions among these levels are reported. In the calculations, the contributions from Breit interaction (BI) and quantum electrodynamics (QED) corrections to the wave functions are taken into account (the addition of the BI and QED in CI affects both the wave functions and the level energies). For some excited states, there are no other theoretical and/or experimental data to compare with to illustrate the quality of our results/assess the accuracy. A similar calculation has been performed with the Flexible Atomic Code (FAC), using W LI as an example. The results obtained in this work are compared with the data compiled in the Atomic Spectra Database (ASD) of the National Institute of Standards and Technology (NIST) and other available theoretical/experimental information. Satisfactory agreement is found between them. The energies agree within 0.8% with the experimental results, and the M1 transition rates agree within 5% with other theoretical results. The present results are more extensive than those from previous calculations and considerably expand the existing data sets for Cr-like ions. This study should be beneficial for the analysis of experimental spectra and modeling of fusion plasmas.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Optical activity of solids from first principles

Within the framework of independent particle approximation, the optical activity tensor of solids is formulated as from different contributions: the magnetic dipole, electric quadrupole, and band dispersion terms. The first two terms have similar counterparts in the theory of finite systems, whereas the last term is unique for crystals. Further, the magnetic dipole and electric quadrupole transition moments are calculated with a sum-over-states formulation. We apply the formulation to calculate and analyze the optical rotation of elemental tellurium and the circular dichroism of the (6,4) carbon nanotube. Decomposed optical activity into different contributions is discussed. The calculated spectra agree well with experiments. As a showcase of achiral crystals, we calculate the optical activity of wurtzite GaN.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1994

Comparison of the field configurations of the magnetotails of Uranus and Neptune

The magnetic field configuration-states of the magnetotails of the planets Uranus and Neptune are compared. Earth's case is also briefly treated, as well as some related aspects of the other three magnetic planets. In Uranus' case, due to the large tilt (59 deg) of the planet's magnetic dipole with respect to its spin axis and the unusual obliquity of that axis, the angle of attack (alpha) of the solar wind with respect to dipole alignment goes through all possible angles, 0 deg to 180 deg, yielding a very broad spectrum of configuration-states of its tail. Cases are discussed where the planetary magnetic dipole is either aligned with the Sun-planet-line ('pole-on' state) or perpendicular to it and some intermediate states, for both Uranus and Neptune. Only Uranus experiences the pole-on state, which next occurs in November 1999 (+/- 2 months); last year (1993.2) it had the first 'perpendicular' state since Voyager encounter which resembles Earth's case. Neptune never has a pole-on configuration, but it gets as close as alpha = 14 deg from it; the next occurrence is early in 2003. At Voyager encounter Neptune's magnetotail apparently rapidly migrated through a broad spectrum of field structures with near extreme states resembling an Earth-like case on the one hand and a cylindrically symmetric one on the other. Magnetopause 'openness' should dramatically change in terms of the rapidly changing angle of attack throughout a planetary day for these two planets, and this has important implications for their magnetotails. Any future manetospheric mission plans for Uranus or Neptune should take in to consideration the allowed range of values for alpha for the epoch of interest; this is especially of concern for Uranus which has a pole-on state, and all possible alphas, around the middle of 2014, 20 years from now.

Lepping, R. P.↗
DOE OSTI2026

Estimation of the Required Dipole Corrector Magnetic Field for PIP-II Injection Based on Beam Studies

The Fermilab Booster will accept a 600 µs beam pulse from the new superconducting Linac for PIP-II operations. The Booster is a rapid-cycling synchrotron that uses a resonant magnet circuit ramping at 15 Hz. For PIP-II, the cycle rate will increase to 20 Hz, and the injection pulse length will expand from 40 µs to 600 µs due to the lower output current from the new Linac. Because the Booste main bending field follows a sinusoidal waveform, the magnetic field is not constant during the extended injection window. The longer pulse length and higher repetition rate modify the beam orbit and can lead to increased beam losses. The Booster contains 48 dipole-corrector packages distributed across its 24 periods. Each package includes horizontal and vertical dipoles, quadrupole, sextupole, skew-quadrupole, and skew-sextupole elements. By driving the dipole correctors with an appropriately shaped sinusoidal waveform during injection, we can compensate the changing main field and create an effectively flat bending field—referred to as flat injection. Over the past several years, machine studies have been performed to characterize the required correction fields and to determine the corresponding power-supply specifications needed for PIP-II operation. In this presentation, we will summarize the study results and discuss the estimated magnetic field requirements and power supply parameters for achieving flat injection in the Booster.

Seiya, K. [Fermilab] (ORCID:0000000250576943)↗
NASA NTRS1971

A curve of growth determination of the f-values for the fourth positive system of CO and the Lyman-Birge-Hopfield system of N2.

The curve of growth method has been employed to determine f-values for the fourth positive system of CO and the magnetic dipole and electric quadrupole components of the Lyman-Birge-Hopfield system of N2. No significant dependence on r-centroid was found. The mean value of the ratio of the electric quadrupole to magnetic dipole f-values was 0.076.

Pilling, M. J.↗
DOE OSTI2017

The Fermilab Muon g-2 experiment: laser calibration system

The anomalous muon dipole magnetic moment can be measured (and calculated) with great precision thus providing insight on the Standard Model and new physics. Currently an experiment is under construction at Fermilab (U.S.A.) which is expected to measure the anomalous muon dipole magnetic moment with unprecedented precision. One of the improvements with respect to the previous experiments is expected to come from the laser calibration system which has been designed and constructed by the Italian part of the collaboration (INFN). Furthermore, an emphasis of this paper will be on the calibration system that is in the final stages of construction as well as the experiment which is expected to start data taking this year.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Effective field theory for dark matter absorption on single phonons

Single phonon excitations, with energies in the 1–100 meV range, are a powerful probe of light dark matter (DM). Utilizing effective field theory, we derive a framework to compute DM absorption rates into single phonons starting from general DM-electron, proton, and neutron interactions. We apply the framework to a variety of DM models: Yukawa coupled scalars, axionlike particles with derivative interactions, and vector DM coupling via gauge interactions or Standard Model electric and magnetic dipole moments. We find that GaAs or Al 2 O 3 targets can set powerful constraints on a U ( 1 ) B − L model, and targets with electronic spin ordering are similarly sensitive to DM coupling to the electron magnetic dipole moment. Lastly, we make the code, (an extension of the existing code which computes general DM–single phonon scattering rates), publicly available. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗