Electric Field Spectral Densities Research Articles

Inferring Jovian Electron Densities Using Plasma Wave Spectra Obtained by the Juno/Waves Instrument

AbstractThe Waves instrument onboard the Juno spacecraft has plasma wave‐measuring capabilities using a single electric dipole antenna and a uniaxial magnetic search coil. Together, these simultaneously measure electric and magnetic field spectral densities in the frequency range 50 Hz–20 kHz, above which only electric field spectral densities are measured up to 41 MHz. A major objective of the Juno mission is to explore Jupiter's high‐latitude magnetosphere and ionosphere. One of the key contributions of the Waves instrument is the determination of electron densities from plasma wave spectra. Given the very high magnetic field strengths near Juno's perijove passes, established techniques cannot be utilized to infer electron densities since such highly magnetized space plasma conditions have not previously been met in planetary missions. By revisiting theoretical treatments of plasma waves, we describe a novel method to determine electron densities from plasma wave spectra that is unique to the near‐Jupiter region. In the absence of the commonly observed upper hybrid resonance frequency in high‐density space plasmas (e.g., the vicinities of Io, Ganymede, Enceladus, and the near‐Earth environment), we achieve this by identifying emission cutoffs at the lower hybrid frequency and electron plasma frequency. Further, we discuss the development of the process and tools for identifying and digitizing appropriate resonance and cutoff frequencies.

Plasma waves in Jupiter's high‐latitude regions: Observations from the Juno spacecraft

AbstractThe Juno Waves instrument detected a new broadband plasma wave emission (~50 Hz to 40 kHz) on 27 August 2016 as the spacecraft passed over the low‐altitude polar regions of Jupiter. We investigated the characteristics of this emission and found similarities to whistler mode auroral hiss observed at Earth, including a funnel‐shaped frequency‐time feature. The electron cyclotron frequency is much higher than both the emission frequency and local plasma frequency, which is assumed to be ~20–40 kHz. The E/cB ratio was about three near the start of the event and then decreased to one for the rest of the period. A correlation of the electric field spectral density with the flux of an upgoing 20 to 800 keV electron beam was found, with a correlation coefficient of 0.59. We conclude that the emission is propagating in the whistler mode and is driven by the energetic upgoing electron beam.

Hot and cold ion outflow: Observations and implications for numerical models

AbstractCluster observations of oxygen ion outflow and low‐frequency waves at high altitude above the polar cap and cold ion outflow in the lobes are used to determine ion heating rates and low‐altitude boundary conditions suitable for use in numerical models of ion outflow. Using our results, it is possible to simultaneously reproduce observations of high‐energy O+ ions in the high‐altitude cusp and mantle and cold H+ ions in the magnetotail lobes. To put the Cluster data in a broader context, we first compare the average observed oxygen temperatures and parallel velocities in the high‐altitude polar cap with the idealized cases of auroral (cusp) and polar wind (polar cap) ion outflow obtained from a model based on other data sets. A cyclotron resonance model using average observed electric field spectral densities as input fairly well reproduces the observed velocities and perpendicular temperatures of both hot O+ and cold H+, if we allow the fraction of the observed waves, which is efficient in heating the ions to increase with altitude and decrease toward the nightside. Suitable values for this fraction are discussed based on the results of the cyclotron resonance model. Low‐altitude boundary conditions, ion heating rates, and centrifugal acceleration are presented in a format suitable as input for models aiming to reproduce the observations.

Oxygen ion energization by waves in the high altitude cusp and mantle

Abstract. We present a comparative study of low frequency electric field spectral densities and temperatures observed by the Cluster spacecraft in the high altitude cusp/mantle region. We compare the relation between the O+ temperature and wave intensity at the oxygen gyrofrequency at each measurement point and find a clear correlation. The trend of the correlation agrees with the predictions by both an asymptotic mean-particle theory and a test-particle approach. The perpendicular to parallel temperature ratio is also consistent with the predictions of the asymptotic mean-particle theory. At times the perpendicular temperature is significantly higher than predicted by the models. A simple study of the evolution of the particle distributions (conics) at these altitudes indicates that enhanced perpendicular temperatures would be observed over many RE after heating ceases. Therefore, sporadic intense heating is the likely explanation for cases with high temperature and comparably low wave activity. We observe waves of sufficient amplitude to explain the highest observed temperatures, while the theory in general overestimates the temperature associated with the highest observed wave activity, indicating that such high wave activity is very sporadic.

A comparison study between observations and simulation results of Barghouthi model for O<sup>+</sup> and H<sup>+</sup> outflows in the polar wind

Abstract. To advance our understanding of the effect of wave-particle interactions on ion outflows in the polar wind region and the resulting ion heating and escape from low altitudes to higher altitudes, we carried out a comparison between polar wind simulations obtained using Barghouthi model with corresponding observations obtained from different satellites. The Barghouthi model describes O+ and H+ outflows in the polar wind region in the range 1.7 RE to 13.7 RE, including the effects of gravity, polarization electrostatic field, diverging geomagnetic field lines, and wave-particle interactions. Wave-particle interactions were included into the model by using a particle diffusion equation, which depends on diffusion coefficients determined from estimates of the typical electric field spectral density at relevant altitudes and frequencies. We provide a formula for the velocity diffusion coefficient that depends on altitude and velocity, in which the velocity part depends on the perpendicular wavelength of the electromagnetic turbulence λ⊥. Because of the shortage of information about λ⊥, it was included into the model as a parameter. We produce different simulations (i.e. ion velocity distributions, ions density, ion drift velocity, ion parallel and perpendicular temperatures) for O+ and H+ ions, and for different λ⊥. We discuss the simulations in terms of wave-particle interactions, perpendicular adiabatic cooling, parallel adiabatic cooling, mirror force, and ion potential energy. The main findings of the simulations are as follows: (1) O+ ions are highly energized at all altitudes in the simulation tube due to wave-particle interactions that heat the ions in the perpendicular direction, and part of this gained energy transfer to the parallel direction by mirror force, resulting in accelerating O+ ions along geomagnetic field lines from lower altitudes to higher altitudes. (2) The effect of wave-particle interactions is negligible for H+ ions at altitudes below ~7 RE, while it is important for altitudes above 7 RE. For O+ wave particle interaction is very significant at all altitudes. (3) For certain λ⊥ and at points, altitudes, where the ion gyroradius is equal to or less than λ⊥, the effect of wave-particle interactions is independent of the velocity and it depends only on the altitude part of the velocity diffusion coefficient; however, the effect of wave-particle interactions reduce above that point, called saturation point, and the heating process turns to be self-limiting heating. (4) The most interesting result is the appearance of O+ conics and toroids at low altitudes and continue to appear at high altitudes; however, they appear at very high altitudes for H+ ions. We compare quantitatively and qualitatively between the simulation results and the corresponding observations. As a result of many comparisons, we find that the best agreement occurs when λ⊥ equals to 8 km. The quantitative comparisons show that many characteristics of the observations are very close to the simulation results, and the qualitative comparisons between the simulation results for ion outflows and the observations produce very similar behaviors. To our knowledge, most of the comparisons between observations (ion velocity distribution, density, drift velocity, parallel and perpendicular temperatures, anisotropy, etc.) and simulations obtained from different models produce few agreements and fail to explain many observations (see Yau et al., 2007; Lemaire et al., 2007; Tam et al., 2007; Su et al., 1998; Engwall et al., 2009). This paper presents many close agreements between observations and simulations obtained by Barghouthi model, for O+ and H+ ions at different altitudes i.e. from 1.7 RE to 13.7 RE.

Statistical evidence for O<sup>+</sup> energization and outflow caused by wave-particle interaction in the high altitude cusp and mantle

Abstract. We present a statistical study of the low (<1 Hz) frequency electric and magnetic field spectral densities observed by Cluster spacecraft in the high altitude cusp and mantle region. At the O+ gyrofrequency (0.02–0.5 Hz) for this region the electric field spectral density is on average 0.2–2.2 (mV m−1)2 Hz−1, implying that resonant heating at the gyrofrequency can be intense enough to explain the observed O+ energies of 20–1400 eV. The relation between the electric and magnetic field spectral densities results in a large span of phase velocities, from a few hundred km s−1 up to a few thousand km s−1. In spite of the large span of phase velocity, the ratio between the calculated local Alfvén velocity and the estimated phase velocity is close to unity. We provide average values of a coefficient describing diffusion in ion velocity space at different altitudes, which can be used in studies of ion energization and outflow. The observed average waves can explain the average O+ energies measured in the high altitude (8–15 RE) cusp/mantle region of the terrestrial magnetosphere according to our test particle calculations.

Scalable arrays of rf Paul traps in degenerate Si

We report techniques for the fabrication of multizone linear radio frequency Paul traps that exploit the machinability and electrical conductivity of degenerate silicon. The approach was tested by trapping and laser cooling M24g+ ions in the two following trap geometries: a single-zone two-layer trap and a multizone surface-electrode trap. From the measured ion motional heating rate we determine an electric field spectral density at the ion’s position of approximately 1×10−10 (V/m)2⋅Hz−1 at ωz/2π=1.125 MHz when the ion lies 40 μm above the trap surface. One application of these devices is controlled manipulation of atomic ion qubits, the basis of one form of quantum information processing.

Formula representation of auroral ionospheric O+ outflows based on systematic simulations with effects of soft electron precipitation and transverse ion heating

Systematic Dynamic Fluid Kinetic (DyFK) model simulations are conducted to obtain a simulation‐based formula representation of the O+ outflow flux level versus the energy flux of soft electron precipitation, and wave spectral density of transverse wave heating in the high‐latitude auroral region. Based on results of 140 DyFK simulations of auroral outflows, we depict the O+ outflows at the ends of these two hour simulation runs in spectrogram form versus these parameters. We also approximate the results by the formula representation: = 8.8(3.0 × 105 + 2fe1.4 × 107)(tanh (8Dwave) + 0.2Dwave0.6), where is the O+ number flux in cm−2/s at 3 RE mapped to 1000 km altitude, fe is the electron precipitation energy flux in ergs cm−2/s, and Dwave is the wave electric field spectral density at O+ gyrofrequency at 1 RE in (mV)2 m−2 Hz−1. This formula representation provides a convenient way to set the boundary conditions of the ionosphere in global magnetosphere simulation since the ionosphere is the important plasma source of the magnetosphere.

An example of resonances, coherent structures and topological phase transitions - the origin of the low frequency broadband spectrum in the auroral zone

Abstract. We consider the phenomena of intermittent turbulence in magnetized space plasmas from the point of view of topological phase transitions involving the merging and interactions of anisotropic coherent structures. The stochastic behaviour of these coherent plasma structures can undergo complex changes as the dynamic system evolves, similar to those commonly observed in (first and second order) equilibrium phase transitions. When conditions are favourable, such topological entities can evolve into a state of forced and/or self-organized criticality (FSOC). As an example, we apply these ideas to the understanding of the origin of the commonly observed broadband power-law low frequency electric field spectral densities and the characteristic filamentary current structures in the auroral zone. The broadband turbulence can provide efficient resonant energization of the ionospheric oxygen ions.

Colloid-like behavior and topological phase transitions in space plasmas: intermittent low frequency turbulence in the auroral zone

We describe a theory of topological phase transitions for dynamical space plasma systems far from equilibrium. The theory is based on the concepts of resonances and coherent structures. When conditions are favorable, the coherent structures may merge, interact and evolve into forced and/or self-organized critical topological states [FSOC]. First and second order phase changes may set in as the dynamical system evolves from one critical state to another, or from a critical state to a non-critical state, or when dynamical instabilities develop. The phenomenon resembles that of the behavior of stirred colloidal suspensions. These ideas are applied to the explanation of the development of broad-band power-law electric field spectral densities of the intermittent low-frequency fluctuations commonly observed in the auroral zone.

Impacts of dust particles m > 10 −9 g in Halley's coma as seen in the electric field waveforms of Vega 2

In this paper we draw some inferences on the response of the APV-N antenna of Vega 2 to plasma clouds induced by dust particles. We show that: (1) electric impulses were mostly generated by impacts of particles bigger than ∼10 −9 g on the whole spacecraft, (2) in the case of large particle impacts the impulse amplitude was weakly dependent on the particle mass, (3) the antenna response to the impact plasma depends on the ambient plasma parameters, and (4) the sensitivity to impacts decreases when the impact rate becomes quasicontinuous. The conclusions are based on an analysis of the wide impulses in the outbound pass of Vega 2 through the outer coma and on a comparison of the electric field spectral densities with the count rates of dust particles in various mass channels. The lower limit, down to which the amplitude vs mass dependence is weak, has been defined as the “least effective mass”; its value has been deduced to be ∼3 × 10 −9 g in the outer coma, and ∼10 −7 g in the inner coma, while near the point of closest approach to the comet it was determined to be more than ∼10 −6 g due to the continuous impact of small particles. The spectral density of impact-generated impulses should be roughly proportional to the integral flux of particles bigger than the least effective mass. Some new peculiarities of the large particle distribution in the coma are derived. The interpretation of the impulse generation involves the response of the antenna to a negative pulse of the spacecraft potential and to electric fields associated with the electron density gradients in the expanding plasma cloud. The correlation between the count rates of the light ( m < 10 −14 g) particles and of the impulses (found in a previous investigation) is reinterpreted in terms of the hypothesis that the light particles were originated by disintegration of the big ones.

Spectral density of bulk two-phonon polaritons

A linear response function is derived for a system of photons interacting with two-phonon states. This function determines the electric field spectral density of the corresponding mixed states: two-phonon polaritons. Computations of the spectral density for different values of the anharmonicity and the photon-two-phonon coupling constant are carried out.