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NASA NTRS2016

Observations of Large-Amplitude, Parallel, Electrostatic Waves Associated with the Kelvin-Helmholtz Instability by the Magnetospheric Multiscale Mission

On 8 September 2015, the four Magnetospheric Multiscale spacecraft encountered a Kelvin-Helmholtz unstable magnetopause near the dusk flank. The spacecraft observed periodic compressed current sheets, between which the plasma was turbulent. We present observations of large-amplitude (up to 100 mVm) oscillations in the electric field. Because these oscillations are purely parallel to the background magnetic field, electrostatic, and below the ion plasma frequency, they are likely to be ion acoustic-like waves. These waves are observed in a turbulent plasma where multiple particle populations are intermittently mixed, including cold electrons with energies less than 10 eV. Stability analysis suggests a cold electron component is necessary for wave growth.

Wilder, F. D.↗

NASA NTRS1988

Resonant geomagnetic field oscillations and Birkeland currents in the morning sector

The relationship between large-scale Birkeland currents and resonant oscillations of the geomagnetic field is investigated on the basis of Viking magnetic-field, electric-field, and particle measurements and AMPTE-CEE and IMP-8 magnetic-field measurements obtained during April 23-25, 1986. The data are presented in extensive graphs and characterized in detail. The 3-16-mHz 5-60-nT magnetic-field oscillations detected by Viking are also seen by AMPTE-CEE below L = 8.8 and extend from the lower L shells to the boundary between regions 1 and 2 of the Birkeland-current system, and this boundary is shown to be closely related to the interface between the low-latitude boundary layer and the central plasma sheet. It is suggested that the magnetospheric oscillations may be driven by several different solar-wind features, possibly depending on the direction of the IMF.

Potemra, T. A.↗

DOE OSTI2022

Parametric studies of stream instability-induced higher harmonics in plasma ionization breakdown near an emissive dielectric surface

Here, in this work, we comprehensively investigate the generation of higher harmonic (HH) electric fields normal to the applied rf electric field in multipactor-coexisting plasma breakdown by fully kinetic particle-in-cell (PIC) simulations and a theoretical model. Firstly, a base case at driving frequency 1 GHz, transverse rf electric field amplitude 3 MV m –1 , and background gas pressure 0.2 Torr, is studied in detail. The enhanced harmonic frequency observed is around ten times the fundamental rf frequency, significantly lower than the Langmuir frequency. A theoretical model reveals that the fundamental mechanism of HHs generation is stream–plasma instability, which originates from stream-like secondary electron emission interacting with plasma. The resulting HH frequency and the growth rate of its oscillating amplitude from the theoretical model, agree well with the PIC simulations. With increasing pressure, the HH oscillations are found to be significantly reduced. This is because at higher pressure the gas ionization rate is higher, which causes a more rapidly increasing plasma density, leaving less time for the growth of instability. Furthermore, the parameter space in terms of background gas pressure and rf field amplitude within which the HHs appear is revealed. Finally, the effect of the driving rf frequency on HHs is also investigated, and it is found that the instability-induced oscillating HHs field remains when the driving frequency is increased to 2 GHz, however, it is highly reduced at higher driving frequency of 5 GHz, as oscillations at the fundamental frequency start playing a more important role.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Producing entangled photon pairs and quantum squeezed states in plasmas

Plasma is capable of mediating the conversion of two pump photons into two different photons through a relativistic four-wave mixing nonlinearity. Spontaneously created photon pairs are emitted at symmetric angles with respect to the colinear pump direction, and the emission rate is largest if they have identical frequency. Thus, two orthogonally polarized pumps can produce polarization-entangled photon pairs through a millimeter-long homogeneous plasma. Here, the noise from Raman scattering can be avoided if the pump detuning differs from twice the plasma frequency. However, pump detuning exactly equal to twice the plasma frequency can significantly enhance the interaction rate, which allows for the production of strong two-mode squeezed states. Remarkably, the amplified noise from Raman scattering are correlated and hence can be suppressed in one of the output quadratures, thereby maintaining the squeezing magnitude.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Cosmological evolution of light dark photon dark matter

Light dark photons are subject to various plasma effects, such as Debye screening and resonant oscillations, which can lead to a more complex cosmological evolution than is experienced by conventional cold dark matter candidates. Maintaining a consistent history of dark photon dark matter requires ensuring that the superthermal abundance present in the early Universe (i) does not deviate significantly after the formation of the cosmic microwave background (CMB), and (ii) does not excessively leak into the Standard Model plasma after big band nucleosynthesis (BBN). We point out that the role of nonresonant absorption, which has previously been neglected in cosmological studies of this dark matter candidate, produces strong constraints on dark photon dark matter with mass as low as 10 - 22 eV . Furthermore, we show that resonant conversion of dark photons after recombination can produce excessive heating of the intergalactic medium (IGM) which is capable of prematurely reionizing hydrogen and helium, leaving a distinct imprint on both the Ly- α forest and the integrated optical depth of the CMB. Our constraints surpass existing cosmological bounds by more than 5 orders of magnitude across a wide range of dark photon masses.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Core electron temperature turbulence and transport during sawtooth oscillations in the DIII-D tokamak

Abstract Sawteeth are one of the concerning instabilities in ITER and future burning plasma experiments. Sawtooth dynamics and its interaction with broadband plasma turbulence has been a challenge for predictive simulations of core transport in future fusion devices. This study provides new observations of core turbulence behavior during sawtooth oscillations in DIII-D hydrogen L-mode neutral beam injection heated plasmas in an inner wall limited configuration. A strong correlation of electron temperature and density turbulence levels with the sawtooth oscillation phase has been observed at locations inside the T e inversion radius and/or safety factor q = 1 magnetic surface. The T e turbulence amplitude in the core during the sawtooth ramp exhibits a critical T e gradient behavior inside but not near the T e inversion radius/ q = 1 magnetic surface. The most unstable mode calculated from the trapped gyro-landau fluid turbulence simulations reveal a change from low- k ion-type to low-k electron-type modes from pre- to post- sawtooth crash time periods.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Analytical model of plasma response to external magnetic perturbation in absence of no-slip condition

Recent simulation and experimental results suggest that the magnetic island and flow on a resonant surface often do not satisfy the “no-slip” condition in the steady state. A new theoretical model on a nonlinear plasma response to external magnetic perturbation in the absence of a no-slip condition is proposed. The model is composed of the equations for the evolution of both the width and phase of the magnetic island due to forced reconnection driven by the external magnetic perturbation, and the force-balance equation for the plasma flow. When the island width is much less than the resistive layer width, the island growth is governed by the linear Hahm–Kulsrud–Taylor solution in the presence of time-dependent plasma flow. In the other regime when the island width is much larger than the resistive layer width, the evolution of both the island width and phase can be described using the Rutherford theory. The island solution is used to construct the quasilinear electromagnetic force, which, together with the viscous one, contributes to the nonlinear variation in plasma flow. The no-slip condition assumed in the conventional error field theory is not imposed here, where the island oscillation frequency depends on but does not necessarily equal to the plasma flow frequency at the rational surface.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2023

Self-organization of photoionized plasmas via kinetic instabilities

Abstract Self-organization in an unmagnetized collisionless plasma (in this paper) refers to formation of transient coherent structures such as collective oscillations (electrostatic waves) or magnetic fields resulting from so-called kinetic effects in the plasma. This topical review provides a comprehensive analysis of the self-organization of strong-field photoionized, non-equilibrium plasmas through kinetic instabilities. The authors propose and demonstrate a novel experimental platform that enables the formation of dense plasmas with known highly anisotropic and non-thermal electron velocity distribution functions on a timescale on the order of an inverse electron plasma frequency. We then show that such plasmas are highly susceptible to a hierarchy of kinetic instabilities, including two-stream, current filamentation and Weibel, that convert a fraction of the electron kinetic energy into electric and/or magnetic energy stored in self-organized structures. The electrostatic waves so produced are measured using a collective light (Thomson) scattering technique with femtosecond resolution as the kinetic instabilities aided by collisions eventually thermalize the plasma electrons. In addition, we describe a novel experimental technique that has made it possible to map the temporal evolution of the wavenumber spectrum of the thermal Weibel instability with picosecond resolution, which leads to the formation of quasi-static coherent magnetic fields with different topologies in photoionized plasmas. Finally, the paper summarizes the important results and discusses future directions on this topic.

Zhang, Chaojie (ORCID:0000000180353014)↗

NASA NTRS1986

Nonlinear upper hybrid drift waves for a longitudinal electric field perpendicular to a uniform magnetic field in the Vlasov-Maxwell approximation

Upper hybrid drift waves are found as a special solution to a Vlasov-Maxwell plasma which has a longitudinal electric field and a perpendicular uniform magnetic field. A single-species plasma with a constant-density mobile neutralizing background supports spatially varying disturbances that oscillate at the upper hybrid frequency. The general functional dependences of the electric field, the plasma number density, and the one-particle distribution function for the special case are found from more general Vlasov-Maxwell equations invariant under a Lie group point transformation. The one-particle distribution function for the plasma is a function of the Liouville invariant, which is the energy in the generalized Bernstein-Greene-Kruskal (BGK) reference frame, and the momentum in the drift direction.

Abraham-Shrauner, B.↗

NASA NTRS1986

Continuous blood densitometry - Fluid shifts after graded hemorrhage in animals

Rapid fluid shifts in four pigs and two dogs subjected to graded hemorrhage are investigated. Arterial blood density (BD), mean arterial pressure (MAP), central venous pressure (CVP), arterial plasma density (PD), hematocrit (Hct) and erythrocyte density were measured. The apparatus and mechancial oscillator technique for measuring density are described. Fluid shifts between red blood cells and blood plasma and alterations in the whole-body-to-large vessel Hct, F(cell) are studied using two models. The bases of the model calculations are discussed. A decrease in MAP, CVP, and BP is detected at the beginning of hemorrhaging; continued bleeding results in further BD decrease correlating with volume displacement. The data reveal that at 15 ml/kg blood loss the mean PD and BD dropped by 0.99 + or - 0.15 and 2.42 + or 0.26 g/liter, respectively, and the Hct dropped by 2.40 + or 0.47 units. The data reveal that inward-shifted fluid has a higher density than normal ultrafiltrate and/or there is a rise in the F(cell) ratio. It is noted that rapid fluid replacement ranged from 5.8 + or - 0.8 to 10.6 + or - 2.0 percent of the initial plasma volume.

Hinghofer-Szalkay, H.↗

NASA NTRS1995

Radial energy transport by magnetospheric ULF waves: Effects of magnetic curvature and plasma pressure

The 'radial' transport of energy by internal ULF waves, stimulated by dayside magnetospheric boundary oscillations, is analyzed in the framework of one-fluid magnetohydrodynamics. (the term radial is used here to denote the direction orthogonal to geomagnetic flux surfaces.) The model for the inhomogeneous magnetospheric plasma and background magnetic field is axisymmetric and includes radial and parallel variations in the magnetic field, magnetic curvature, plasma density, and low but finite plasma pressure. The radial mode structure of the coupled fast and intermediate MHD waves is determined by numerical solution of the inhomogeneous wave equation; the parallel mode structure is characterized by a Wentzel-Kramer-Brillouin (WKB) approximation. Ionospheric dissipation is modeled by allowing the parallel wave number to be complex. For boudnary oscillations with frequencies in the range from 10 to 48 mHz, and using a dipole model for the background magnetic field, the combined effects of magnetic curvature and finite plasma pressure are shown to (1) enhance the amplitude of field line resonances by as much as a factor of 2 relative to values obtained in a cold plasma or box-model approximation for the dayside magnetosphere; (2) increase the energy flux delivered to a given resonance by a factor of 2-4; and (3) broaden the spectral width of the resonance by a factor of 2-3. The effects are attributed to the existence of an 'Alfven buoyancy oscillation,' which approaches the usual shear mode Alfven wave at resonance, but unlike the shear Alfven mode, it is dispersive at short perpendicular wavelengths. The form of dispersion is analogous to that of an internal atmospheric gravity wave, with the magnetic tension of the curved background field providing the restoring force and allowing radial propagation of the mode. For nominal dayside parameters, the propagation band of the Alfven buoyancy wave occurs between the location of its (field line) resonance and that of the fast mode cutoff that exists at larger radial distances.

Kouznetsov, Igor↗

DOE OSTI2020

Predictive Integrated Modeling of Heated Tokamak Plasmas (Final Technical Report)

The research carried out by the Lehigh University fusion group during this reporting period: (1) Self-consistent predictive core-pedestal ITER scenario modeling; (2) Microtearing instabilities and electron thermal transport in standard and spherical tokamak discharges; (3) Neural network model of the Multi-Mode anomalous transport module; (4) Anomalous transport in KSTAR, JET, EAST, Alcator C-Mod and DIII-D discharges; (5) Theory for transport in magnetized plasmas; (6) Control-oriented modeling of the q-profile dynamic response in preparation for advanced scenario control in KSTAR and in EAST; (7) Modeling of edge harmonic oscillation in DIII-D QH mode discharges; (8) Elucidating plasma dynamics in Hasegawa-Wakatani turbulence by information geometry; (9) Non-linear Langevin and Fractional Fokker–Planck equations for anomalous diffusion by Levy stable processes; and (10) Investigation of the plasma shaping effects on the H-mode pedestal structure.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2021

Studies of a modulated Hall thruster

A typical Hall thruster is powered from a DC power supply and operates with a constant discharge voltage. In operation, the discharge current is subject to strong low frequency oscillations (so-called breathing oscillations). Recent studies have shown that not only can these breathing oscillations be correlated with improved performance, but these oscillations can be induced and controlled by modulating the anode voltage. In this work, a systematic experimental study of the plasma flow in a modulated cylindrical Hall thruster was performed to characterize the effect of natural and modulated breathing oscillations on thruster performance. Measurements suggest that modulating the anode voltage in resonance with the natural breathing frequency does increase the thrust, but a corresponding phase alignment of discharge current and discharge voltage causes the efficiency gains to be insignificant. In addition, the outward shift of the acceleration region causes the plasma plume divergence to increase at the resonance condition and thereby, limit the thrust increase. Further, mechanisms underlying the relative phase between discharge current, ion current, and discharge voltage are investigated experimentally and corroborated with one-dimensional hybrid simulations of the thruster discharge.

modelling↗

DOE OSTI2025

The low frequency edge oscillation in alcator C-Mod and ASDEX upgrade I-mode

The low frequency edge oscillation (LFEO) is a low frequency fluctuation in many plasma quantities in the pedestal region of the I-Mode confinement regime. It is observed on Alcator C-Mod between 10–30 kHz and on ASDEX Upgrade between 5–10 kHz. On both tokamaks it has been previously identified as a geodesic acoustic mode (GAM), however the recent discovery of the edge temperature ring oscillation (ETRO) in a similar frequency and spatial location as the LFEO in I-Modes on EAST has called this identification into question. In this paper we investigate the LFEO on C-Mod and AUG using a variety of different experimental techniques including spectral analysis, magnetic mode number analysis, localization, and direct measurement of the LFEO zonal structure and propagation using a mirror Langmuir probe. This investigation has reconfirmed the identification of the LFEO as a GAM and determined that it has several key differences from the ETRO.

AUG↗

NASA NTRS1990

Toroidal standing waves excited by a storm sudden commencement - DE 1 observations

A 74-nT sudden commencement on July 13, 1982, was observed in the magnetosphere, with instruments on the Dynamics Explorer 1 satellite. Inbound, near L = 4.5, the satellite was located at 1524 magnetic local time and 20 deg magnetic latitude. The sudden commmencement established a strong, east-west oscillation, with 100-s period, which was observed in the magnetic field, the electric field, and the plasma flow velocity records. There was also a compressional component of this 100-s oscillation and a rapidly damped 300-s compressional pulsation. The compressional oscillations may be an evidence of cavity resonances, excited by the sudden commencement. The cavity waves may, in turn, couple to toroidal waves in field line resonance at the satellite location. In addition, the sudden commencement caused the onset of waves with frequencies from 0.1 up to at least 0.5 Hz. The observations are compared with similar reports from earlier pulsations related to sudden commencements.

Cahill, L. J., Jr.↗

DOE OSTI2020

Surface Josephson plasma waves in a high-temperature superconductor

Abstract Electron density oscillations with acoustic dispersions and sustained at boundaries between different media provide information about surface and interface properties of heterostructures. In ultrathin metallic films these plasmonic excitations are heavily damped. Superconductivity is predicted to reduce dissipation allowing detection of these resonances. Emerging low-loss interface Cooper-pair waves have been studied before, however, the observation of surface-confined Josephson plasmons in highly anisotropic superconductors has remained elusive. Here, we report on generation and coupling to these excitations in an ultrathin single-crystal film of high-temperature superconductor La 1.85 Sr 0.15 CuO 4 . The film becomes brighter than Au below the critical temperature when probed with sub-gap THz photons. We show that the enhanced signal in the superconducting state, which can be visualized with a spatial resolution better than λ/3000, originates from near-field coupling of light to surface Josephson plasmons. Our results open a path towards non-invasive investigation of enhanced superconductivity in artificial multilayers, buried interface states in topological heterostructures, and non-linear phenomena in Josephson devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1975

Theory of type 3b solar radio bursts

During the initial space-time evolution of an electron beam injected into the corona, the strong beam-plasma interaction occurs at the head of the beam, leading to the amplification of a quasi-monochromatic large-amplitude plasma wave that stabilizes by trapping the beam particles. Oscillation of the trapped particles in the wave troughs amplifies sideband electrostatic waves. The sidebands and the main wave subsequently decay to observable transverse electromagnetic waves through the parametric decay instability. This process gives rise to the elementary striation bursts. Owing to velocity dispersion in the beam and the density gradient of the corona, the entire process may repeat at a finite number of discrete plasma levels, producing chains of elementary bursts. All the properties of the type IIIb bursts are accounted for in the context of the theory.

Smith, R. A.↗

NASA NTRS1976

Theory of type IIIb solar radio bursts

Smith, R. A.↗