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DOE OSTI2020

Electric field dynamics in an atmospheric pressure helium plasma jet impinging on a substrate

Time and spatially resolved electric field measurements by Stark polarization spectroscopy in a nanosecond pulsed atmospheric pressure helium jet operating in ambient air and impinging on a conductive indium tin oxide (ITO) coated glass slide are reported. An automatic fitting procedure of the Stark shifted spectra taking into consideration constraints regarding Stark components positions and intensities as well as molecular nitrogen emission subtraction was implemented. This allowed electric field vector components measurements both in the gas phase and at the interface when the jet impinges on the substrate and during the development of a surface ionization wave. The obtained results show an increase of the axial electric field in the jet effluent in the gas phase with a peak magnitude from 12 to 18 kVcm -1 before the ionization wave impinges on the substrate. A steep electric field enhancement to a peak value of about 24 kVcm -1 was observed when the ionization wave impinges on the surface. A peak radial electric field of about 27 kVcm -1 was measured off-axis in the surface ionization wave. These results are consistent with previously reported modelling predictions. While Stark polarization spectroscopy is limited to electric field measurement from regions with emission, we illustrate that the capability to measure near surface electric fields in helium makes it a valuable complementary technique for the electric field-induced second harmonic (E-FISH) technique.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Collisionless damping of circularly polarized nonlinear Alfvén waves in solar wind plasmas with and without beam protons

The damping process of field-aligned, low-frequency right-handed polarized nonlinear Alfvén waves (NAWs) in solar wind plasmas with and without proton beams is studied by using a two-dimensional ion hybrid code. The numerical results show that the obliquely propagating kinetic Alfvén waves (KAWs) excited by beam protons affect the damping of the low-frequency NAW in low beta plasmas, while the nonlinear wave-wave interaction between parallel propagating waves and nonlinear Landau damping due to the envelope modulation are the dominant damping process in high beta plasmas. The nonlinear interaction between the NAWs and KAWs does not cause effective energy transfer to the perpendicular direction. Numerical results suggest that while the collisionless damping due to the compressibility of the envelope-modulated NAW plays an important role in the damping of the field-aligned NAW, the effect of the beam instabilities may not be negligible in low beta solar wind plasmas.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

INTERSTELLAR MAGNETIC FIELDS OBSERVED BY VOYAGER 1 BEYOND THE HELIOPAUSE

Voyager 1 (V1) was beyond the heliopause between 2013.00 and 2014.41, where it was making in situ observations of the interstellar magnetic field (ISMF). The average azimuthal angle and elevation angle of the magnetic field B were (λ) = 292.°5 ± 1.°4 and (δ) = 22.°1 ± 1.°2, respectively. The angles λ and δ varied linearly at (1.°4 ± 0.°1) yr{sup –1} and (–1.°1 ± 0.°1) yr{sup –1}, respectively, suggesting that V1 was measuring the draped ISMF around the heliopause. The distributions of hourly averages of λ and δ were Gaussian distributions, with most probable values 292.°5 and 22.°1, and standard deviations (SDs) 1.°3 and 1.°1, respectively. The small SD indicates little or no turbulence transverse to B . An abrupt decrease in B from 0.50 nT on 2013/129.9 to 0.46 nT on 2013/130.6 was observed, possibly associated with a weak reverse shock or magnetoacoustic pressure wave following a burst of electron plasma oscillations. Between 2013/130.6 and 2013/365.3, (B) = 0.464 ± 0.009 nT, (λ) = 292.°6 ± 0.°8, and (δ) = 22.°1 ± 1.°1. The corresponding distribution of hourly averages of B was Gaussian with the most probable value 0.464 nT and σ = 0.009 nT. Since the uncertainty σ corresponds to the instrument and digitization noise, these observations provided an upper limit to the turbulence in the ISMF. The distributions of the hourly increments of B were Gaussian distributions with σ = 0.05 nT, 0.°4, and 0.°4, respectively, indicating that the V1 did not detect evidence of ''intermittent bursts'' of interstellar turbulence.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Cosmological magnetic fields as string dynamo seeds and axion fields in torsioned spacetime

In this paper two examples of the generation cosmological magnetic fields (CMF) are given. The first is the string dynamo seed cosmological magnetic field estimated as B{sub seed}∼10{sup -24} Gauss from a static spin polarised cylinder in Einstein-Cartan-Maxwell spacetime. The string dynamo seeds from a static spin polarised cylinder is given by B∼σ{sup 2}R{sup 2} where σ is the spin-torsion density while R is the string radius. The B-field value above is able to seed galactic dynamo. In the BBN the magnetic fields around 10{sup 12} Gauss give rise to a string radius as small as 10{sup 17}l{sub P} where l{sub P} is the Planck length. The second is the CMF from axionic torsion field which is given by B{sub seed}∼10{sup -27} Gauss which is stronger than the primordial magnetic field B{sub BICEP2}∼10{sup -30} Gauss from the BICEP2 recent experiment on primordial gravitational waves and cosmological inflation to axionic torsion. The interaction Lagrangean between axionic torsion scalar φ and magnetic fields used in this last example is given by f{sup 2}(φ)F{sub μν}F{sup μν}. A similar lagrangean has been used by K. Bamba et al. [JCAP 10 (2012) 058] so generate magnetic fields without dynamo action. Since axionic torsion can be associated with axionic domain walls both examples discussed here could be consider as topological defects examples of the generation of primordial magnetic fields in universes endowed with spacetime torsion.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Dependence of the gyrotron efficiency on the azimuthal index of non-symmetric modes

Development of MW-class gyrotrons for future controlled fusion reactors requires careful analysis of the stability of high efficiency operation in very high-order modes. In the present paper, this problem is analyzed in the framework of the non-stationary self-consistent theory of gyrotrons. Two approaches are used: the one based on the wave envelope representation of the resonator field and the second one based on representation of this field as a superposition of eigenmodes, whose fields are determined by a self-consistent set of equations. It is shown that at relatively low beam currents, when the maximum efficiency can be realized in the regime of soft self-excitation, the operation in the desired mode is stable even in the case of a very dense spectrum of competing modes. At higher currents, the maximum efficiency can be realized in the regimes with hard self-excitation; here the operation in the desired mode can be unstable because of the presence of some competing modes with low start currents. Two 170 GHz European gyrotrons for the international thermonuclear experimental reactor are considered as examples. In the first one, which is the 2 MW gyrotron with a coaxial resonator, the stability of operation in a chosen TE{sub 34,19}-mode in the presence of two sideband modes with almost equidistant spectrum is analyzed and the region of magnetic fields in which the oscillations of the central mode are stable is determined. The operation of the second gyrotron, which is the 1 MW gyrotron with a cylindrical cavity currently under development in Europe, is studied by using the wave envelope approach. It is shown that high efficiency operation of this gyrotron in the TE{sub 32,9}-mode should be stable.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2016

EXPLAINING INVERTED-TEMPERATURE LOOPS IN THE QUIET SOLAR CORONA WITH MAGNETOHYDRODYNAMIC WAVE-MODE CONVERSION

Coronal loops trace out bipolar, arch-like magnetic fields above the Sun’s surface. Recent measurements that combine rotational tomography, extreme-ultraviolet imaging, and potential-field extrapolation have shown the existence of large loops with inverted-temperature profiles, i.e., loops for which the apex temperature is a local minimum, not a maximum. These “down loops” appear to exist primarily in equatorial quiet regions near solar minimum. We simulate both these and the more prevalent large-scale “up loops” by modeling coronal heating as a time-steady superposition of (1) dissipation of incompressible Alfvén wave turbulence and (2) dissipation of compressive waves formed by mode conversion from the initial population of Alfvén waves. We found that when a large percentage (>99%) of the Alfvén waves undergo this conversion, heating is greatly concentrated at the footpoints and stable “down loops” are created. In some cases we found loops with three maxima that are also gravitationally stable. Models that agree with the tomographic temperature data exhibit higher gas pressures for “down loops” than for “up loops,” which is consistent with observations. These models also show a narrow range of Alfvén wave amplitudes: 3 to 6 km s{sup -1} at the coronal base. This is low in comparison to typical observed amplitudes of 20–30 km s{sup -1} in bright X-ray loops. However, the large-scale loops we model are believed to compose a weaker diffuse background that fills much of the volume of the corona. By constraining the physics of loops that underlie quiescent streamers, we hope to better understand the formation of the slow solar wind.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Frequency sweep rates of rising tone electromagnetic ion cyclotron waves: Comparison between nonlinear theory and Cluster observation

Resonant pitch angle scattering by electromagnetic ion cyclotron (EMIC) waves has been suggested to account for the rapid loss of ring current ions and radiation belt electrons. For the rising tone EMIC wave (classified as triggered EMIC emission), its frequency sweep rate strongly affects the efficiency of pitch-angle scattering. Based on the Cluster observations, we analyze three typical cases of rising tone EMIC waves. Two cases locate at the nightside (22.3 and 22.6 magnetic local time (MLT)) equatorial region and one case locates at the duskside (18MLT) higher magnetic latitude (λ = –9.3°) region. For the three cases, the time-dependent wave amplitude, cold electron density, and cold ion density ratio are derived from satellite data; while the ambient magnetic field, thermal proton perpendicular temperature, and the wave spectral can be directly provided by observation. These parameters are input into the nonlinear wave growth model to simulate the time-frequency evolutions of the rising tones. The simulated results show good agreements with the observations of the rising tones, providing further support for the previous finding that the rising tone EMIC wave is excited through the nonlinear wave growth process.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Recommendations on setup in simulating atmospheric gravity waves under conventionally neutral boundary layer conditions

Wind farm-induced atmospheric gravity waves have been the subject of recent research as they can impact wind farm performance. Pressure variations associated with gravity waves can contribute to the global blockage effect and wind farm wake recovery. Therefore, accurate numerical simulation of flow fields, where wind-farm-induced gravity waves may be produced, is important. Three main considerations in such simulations are the overall domain size, the use of Rayleigh damping near domain boundaries to dampen gravity waves, and advection damping at the inlet to prevent spurious oscillations. Often these considerations are treated ad hoc rather than systematically. This work aims to test and extend the systematic modelling of internal gravity waves proposed in a preliminary investigation to modelling of both internal and trapped gravity waves. The preliminary study identifies the length scales to set the domain and damping layer sizes and the time scale to configure the Rayleigh damping coefficient but under linearly stratified conditions. Large eddy simulations of flow through a wind farm canopy are performed under conventionally neutral boundary layer (CNBL) conditions to test the validity of proposed setups for CNBL conditions. Background atmospheric parameters, such as Froude number (Fr), inversion height (H i ), and inversion layer Froude number (Fr i ) control most of the atmospheric gravity wave characteristics. We validated for CBNL conditions that the effective wavelengths of the internal gravity waves are the correct length scale to configure the domain size and damping layer thickness. Likewise, the optimum damping coefficient to dampen the internal gravity waves relates to the free atmosphere's buoyancy frequency or buoyant perturbations' time scale. We infer that the damping coefficient in the inversion layer may relate to the inversion buoyancy frequency to effectively dampen the trapped gravity waves. Moreover, the advection damping length is linked to the horizontal wavelength of the trapped gravity waves in the inversion layer to prevent spurious waves at the inlet by retaining wave energy accumulation.

17 WIND ENERGY↗

DOE OSTI2022

Surface Cooper-Pair Spin Waves in Triplet Superconductors

Here, we study the electrodynamics of spin triplet superconductors including dipolar interactions, which give rise to an interplay between the collective spin dynamics of the condensate and orbital Meissner screening currents. Within this theory, we identify a class of spin waves that originate from the coupled dynamics of the spin-symmetry breaking triplet order parameter and the electromagnetic field. In particular, we study magnetostatic spin wave modes that are localized to the sample surface. We show that these surface modes can be excited and detected using experimental techniques such as microwave spin wave resonance spectroscopy or nitrogen-vacancy magnetometry, and propose that the detection of these modes offers a means for the identification of spin triplet superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2024

Progress and Challenges in Traveling-Wave SRF cavity development at Fermilab

Traveling-wave (TW) technology can push the accelerator field gradient of niobium SRF cavity to 70MV/m or higher beyond the limit of 50~60MV/m in Standing-wave (SW) technology. The early stages of TW SRF cavity developments had been funded by several SBIR grants to Euclid Techlabs and completed in collaboration with Fermilab through a 1-cell prototype and a proof-of-principle 3-cell TW cavity. The TW resonance excitation in the 3-cell TW cavity at 2K was demonstrated through the low power RF test in early 2024. A high-power test of the 3-cell in TW mode being prepared. To advance a design and technology to fabricate a novel high gradient TW SRF cavity, FNAL proposed a half-meter TW RF design and R&Ds to realize that are in progress. Here we will report the recent progress in the 3-cell TW cavity and the challenges towards a half-meter scale TW cavity.

Furuta, F.↗

DOE OSTI2024

Progress and Challenges in Traveling-Wave SRF cavity development at Fermilab

Furuta, F.↗

DOE OSTI2018

Mass, height of burst, and source–receiver distance constraints on the acoustic coda phase delay method

Here, this research uses the acoustic coda phase delay method to estimate relative changes in air temperature between explosions with varying event masses and heights of burst. It also places a bound on source–receiver distance for the method. Previous studies used events with different shapes, height of bursts, and masses and recorded the acoustic codas at source–receiver distances less than 1 km. This research further explores the method using explosions that differ in mass (by up to an order of magnitude) and are placed at varying heights. Source–receiver distances also cover an area out to 7 km. Relative air temperature change estimates are compared to complementary meteorological observations. Results show that two explosions that differ by an order of magnitude cannot be used with this method because their propagation times in the near field and their fundamental frequencies are different. These differences are expressed as inaccuracies in the relative air temperature change estimates. An order of magnitude difference in mass is also shown to bias estimates higher. Small differences in height of burst do not affect the accuracy of the method. Finally, an upper bound of 1 km on source–receiver distance is provided based on the standard deviation characteristics of the estimates.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2025

A Comparison of Battery Charge Controller Technologies for Wave Energy Converters

Wave energy is a uniquely challenging field for electrical system designers. High peak and low average power potential with a constantly varying energy input is difficult to harness and control through conventional means. To power the blue economy, low-powered wave energy converters (WECs) need batteries for energy storage. Safely and effectively charging batteries from waves requires a charge controller to properly monitor and control voltage and current going to the battery. Currently, off-the-shelf charge controllers exist for other renewable generation such as wind, hydro, and solar. Two topologies were validated: a buck converter and a pulse width modulation (PWM) charge controller. Using an in-lab dry testbed, wave energy power inputs were simulated to properly validate the effectiveness of existing charge controller technologies, identifying the shortcomings and improvements needed to effectively harness wave energy.

battery storage↗

DOE OSTI2024

A Comparison of Battery Charge Controller Technologies for Wave Energy Converters: Preprint

battery storage↗

DOE OSTI2015

Wave packet dynamics in various two-dimensional systems: A unified description

In this article we present an exact and unified description of wave packet dynamics in various 2D systems in the presence of a transverse magnetic field. We consider an initial minimum-uncertainty Gaussian wave packet and find that its long-term dynamics displays the universal phenomena of spontaneous collapse and quantum revival. We estimate the timescales associated with these phenomena based on very general arguments for various materials, whose carrier dynamics is described either by the Schrödinger equation or by the Dirac equation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

Systematic structure of the neutron drip-line {sup 22}C nucleus

In the present work we systematically discuss the nuclear structure of the the heaviest particle-bound carbon isotope, {sup 22}C. The ground state wave function of the carbon isotope is calculated using the {sup 20}C core plus two-valence neutron based on a phenomenological mean-field MF potential. We apply the deduced wave function to provide the nuclear matter density which is necessary in the calculations of the total reaction cross section. Calculations show that there is a reasonable good description of the experimental binding energy BE and root-mean square RMS radius. The exotic structure and configuration of the ground state carbon isotope is explained and a consistent explanation on the two-neutron halo (Borromean) nucleus is given.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

First Observation of Harmonics of Magnetosonic Waves in Martian Magnetosheath Region

Abstract The present study provides an evidence for the generation of harmonics of magnetosonic waves in the Martian magnetosheath region. The wave signatures are manifested in the magnetic field measurements recorded by the fluxgate magnetometer instrument onboard the Mars Atmosphere and Volatile Evolution missioN (MAVEN) spacecraft in the dawn sector around 5–10 LT at an altitude of 4,000–6,000 kms. The wave that is observed continuously from 19.1 to 20.7 UT below the proton cyclotron frequency (f ci ≈ 46 mHz) is identified as fundamental mode of the magnetosonic wave. Whereas harmonics of the magnetosonic wave are observed during 19.7–20.3 UT at frequencies that are multiple off ci . The ambient solar wind proton density and plasma flow velocity are found to vary with a fundamental mode frequency of 46 mHz. It is noticed that the fundamental mode is mainly associated with the left‐hand (LH), and higher frequency harmonics are associated with the right‐hand (RH) circular polarizations. A clear difference in the polarization and ellipticity is noticed during the time of occurrence of harmonics. The magnetosonic wave harmonics are found to propagate in the quasi‐perpendicular directions to the ambient magnetic field. The results of linear theory and Particle‐In‐Cell simulation performed here are in agreement with the observations. The present study provides a conclusive evidence for the occurrence of harmonics of magnetosonic wave in the close vicinity of the magnetosheath region of the unmagnetized planet Mars.

Astronomy & Astrophysics↗

DOE OSTI2016

Bias-free spin-wave phase shifter for magnonic logic

A design of a magnonic phase shifter operating without an external bias magnetic field is proposed. The phase shifter uses a localized collective spin wave mode propagating along a domain wall “waveguide” in a dipolarly-coupled magnetic dot array with a chessboard antiferromagnetic (CAFM) ground state. It is demonstrated numerically that the remagnetization of a single magnetic dot adjacent to the domain wall waveguide introduces a controllable phase shift in the propagating spin wave mode without significant change to the mode amplitude. It is also demonstrated that a logic XOR gate can be realized in the same system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗