Turbulent Electric Fields Research Articles

Transport of ions in presence of induced electric field and electrostatic turbulence: Source of ions injected into ring current

The transport of ions from the polar ionosphere to the inner magnetosphere during stormtime conditions has been computed using a Monte Carlo diffusion code. The effect of the electrostatic turbulence assumed to be present during the substorm expansion phase was simulated by a process that accelerated the ions stochastically perpendicular to the magnetic field with a diffusion coefficient proportional to the energization rate of the ions by the induced electric field. This diffusion process was continued as the ions were convected from the plasma sheet boundary layer to the double-spiral injection boundary. Inward of the injection boundary, the ions were convected adiabatically. By using as input an O + flux of 2.8 × 10 8 cm −2 s −1 (w > 10 eV) and an H + flux of 5.5 × 10 8 cm −2 s −1 (w > .63 eV), the computed distribution functions of the ions in the ring current were found to be in good agreement, over a wide range in L (4 to 8), with measurements made with the ISEE-1 satellite during a storm. This O + flux and a large part of the H + flux are consistent with the DE satellite measurements of the polar ionospheric outflow during disturbed times.

Scaling Property of the Relative Diffusion of Charged Particles in Turbulent Electric Fields. I

Modele de champs electriques turbulents correles decrivant la diffusion relative de 2 particules-tests chargees

Particle simulations of ion-cyclotron turbulence in a mirror plasma

Particle–fluid hybrid simulations of electrostatic ion-cyclotron instabilities in a mirror plasma have been extended to include axial ion bouncing in a nonuniform magnetic field. This model admits unstable ion-bounce modes as well as drift-cyclotron and drift-cyclotron-loss-cone modes. Linear theory showed that ion-bounce modes were as difficult to stabilize as drift-cyclotron-loss-cone modes, but the ion-bounce modes saturated at very low levels in simulations. Simulations have also followed the self-consistent interaction of a mirror plasma with turbulent electric fields in the presence of warm plasma stream, ion drag on electrons, injection of energetic neutral beams, and transit losses. Driven by velocity diffusion due to the drift-cyclotron-loss-cone instability, the plasma evolved to a stable configuration. The wave turbulence was moderated by streaming plasma and axial electron dissipation, was insensitive to the energy width of the neutral beam, and decayed when the neutral beam was removed. The simulation results confirmed many of the predictions of quasilinear theory and theories of orbital stochasticity, and were in qualitative agreement with many (but not all) of the observations in the Lawrence Livermore National Laboratory 2XIIB experiment.

Particle acceleration during the explosive phase of a solar flare

Starting with the quasi-linear equation of the distribution function of particles in a regular electric field, a combined diffusion coefficient in the momentum space conbining the effects of the regular field and a turbulent field is obtained and a combined mechanism of acceleration by the regular and turbulent fields in the neutral sheet of solar proton flares is proposed. It is shown by calculation that conditions in solar proton flares are such that the charged particles can be effectively accelerated to tens of MeV, even ~1 GeV. It is shown that the combined acceleration by a regular electric field and ion-acoustic turbulence pumps the protons and other heavy ions into ranges of energy where they can be accelerated by Langmuir turbulence. By considering the combined acceleration by Langmuir turbulence and the regular electric field, the observed spectrum of energetic protons and the power-law spectrum of energetic electrons can be reproduced.

Electric fields measured by ISEE‐1 within and near the neutral sheet during quiet and active times

A statistical survey of electric fields observed at 146 neutral sheet crossing events of the ISEE‐1 satellite during 1980 has been made. The observations can be divided into two classes — quiet or turbulent — according to the magnitude of the standard deviation in the 3 second spin period sine wave least‐squares fit to the electric field data. Events classified as turbulent are also turbulent in the magnetic field. During quiet crossings, the dawn‐dusk component of the electric field, Ey, is usually constant to ≲ 1/2 mV/m, with larger variations sometimes occurring over 2‐10 minute time scales. During turbulent crossings, Ey fluctuates rapidly with 3‐second‐average peak‐to‐peak amplitudes of 2‐16 mV/m, and instantaneous field magnitudes up to ∼ 30 mV/m. Turbulent crossings correlate with high levels of ground magnetic activity as indicated by AE and ground magnetograms, and with southward interplanetary magnetic field, while quiet crossings occur primarily during periods of low magnetic activity and northward or mixed interplanetary magnetic field.

On the color of the 26 February 1981 white light flare

We describe visual observations of a white light flare which displayed a pink color in a part of the flare which covered a sunspot umbra. We then show that visible pink tint, if attributable to strong Hα emission, requires a minimum equivalent emission line width of approximately 140 A, or three times larger than in any flare previously measured. Such extreme line broadening might be interpreted to result from flare penetration to unusually high chromospheric densities (≳ 1014 cm−3), or from anomalous Stark broadening due to turbulent electric fields in an unstable plasma (Spicer and Davis, 1975) at lower density.

Turbulent electric fields in the nightside magnetosphere

Electric field measurements from the long‐wire double‐probe instrument (baseline of 179 m) on ISEE 1 have shown the magnetospheric electric field on auroral L shells to be extremely turbulent during periods of magnetic activity. During intense activity these turbulent electric fields can penetrate to very low L values. The variational component of the electric field is typically larger than the DC value. Measurements are presented at frequencies up to 14 Hz. Magnitudes of over 40 mV/m (zero to peak) have been observed with spectral power levels in the 1–10 Hz range greater than 10 mV²/m² Hz. The spectral shape of the most intense events was generally flatter than that predicted by two‐dimensional hydromagnetic cascading of energy, which argues that the source of this turbulence must be driving the plasma near these frequencies. This in turn suggests that the instability is in the low‐energy plasma.

On relative spatial diffusion in plasma and fluid turbulences: clumps, Richardson's law and intrinsic stochasticity

The relative diffusion of charged particles in turbulent electric fields exhibits different behaviours according to the time regime: t3, for short times (representing a reduction of diffusion due to trajectory correlations); exp (t), for intermediate times (due to trajectory renormalisation); t3 again, asymptotically, for long times (representing independent particle diffusion). The second regime corresponds to an exponential separation of neighbouring trajectories and a strong dependence on initial conditions, with non-zero Lyapunov exponent. However, this behaviour is due to an extrinsic stochasticity. Analogous regimes exist in problems of Brownian motion and neutral fluid turbulence. The appearance of an exponential behaviour is due to a failure of the quasilinear approximation for neighbouring particles. A similar situation exists in other classical problems of plasma kinetic theory.

The structure of Titan's wake from plasma wave observations

During the Voyager 1 flyby of Saturn's moon Titan, the plasma wave instrument detected several types of plasma wave emissions. On the inbound leg a broad region of intense low‐frequency noise was detected on the side of Titan facing away from Saturn. This noise has characteristics similar to the electric field turbulence observed in the magnetosheath at the earth and the ionosheath at Venus and is believed to be generated by newly created ions that are being accelerated in the vicinity of Titan by the corotational electric field. During the pass through the induced magnetic tail of Titan, a series of upper hybrid resonance emissions were observed. The electron density profile inferred from these emissions shows three distinct peaks with densities of ∼40 cm−3, the first peak corresponding to the entry into the magnetic tail, the second peak corresponding to the neutral sheet crossing from the northern to the southern tail lobe, and the third, somewhat smaller, peak corresponding to the outbound exit from the tail. Large depressions in the magnetic field strength are observed coincident with each of the density peaks. These effects indicate that a dense plume of plasma is being carried downstream of Titan by the interaction with the rapidly rotating magnetosphere of Saturn. By equating the magnetic field pressure in the tail lobe to the plasma pressure in the neutral sheet, the temperature of the plasma is estimated to be about 8600°K. This low temperature suggests that the plasma originates from the ionosphere of Titan, probably forming a plume of plasma with a θ or H cross section extending downstream from Titan. Within the tail lobes, a second type of low‐frequency electric field noise was observed, with characteristics very similar to a type of noise called broadband electrostatic noise, which is found in the earth's magnetic tail. As in the case of the earth, this noise is most intense near the outer boundary of the plasma sheet and is almost completely absent in the high‐density region near the neutral sheet.

Impact of the Vibrationally Excited States on the Macroscopic Behaviour of the Band‐like Electron Beam Discharge Plasma in H/H2‐Mixture

AbstractThe investigation of the impact of the vibrationally excited molecules in the electronic ground state was performed by simultaneously solving a balance equation system for the main charge carriers, the H atoms, the metastable H atoms, the H2 molecules in the different vibrational states and for the power transfer of the electrons in the beam discharge mixture plasma. The balance equations for the vibrational states include in particular one‐quantum step excitation and deexcitation, electronic excitation, dissociation and ionization from each vibrational level in electron collisions as well as the finite life time of these states because of the gas transfer through the band‐like plasma. A main finding is that due to the additional impact of vibrationally excited molecules there is a marked enhancement of the resulting dissociation and ionization degree in the beam discharge plasma at medium power input from the turbulent electric field. For discharge parameters of practical interest the ionization and dissociation budget, the population of the vibrational states, the different energy dissipation processes and the energy pumping into the ladder of the vibrational states were calculated and discussed in detail.

The Impact of Direct Ionization by Beam Electrons on the Electron Kinetics of the Beam Discharge Plasma in Molecular Hydrogen

AbstractIn a recent paper the stationary beam plasma discharge in partially dissociated hydrogen was investigated where the electron component was described by the Boltzmann equation for a mixture of atomic and molecular hydrogen and the main heavy charged and neutral particles by balance equations. It was assumed that, via the quasilinear beam plasma interaction, the electron beam produces only the turbulent electric field whilst an additional production of plasma electrons due to direct ionization by the beam and thus a direct influence on the balances of charge carriers were neglected. Now the additional production of plasma electrons due to direct ionization by the beam is studied on the basis of a generalized Boltzmann equation but for the simpler model of a purely molecular hydrogen plasma. For experimentally obtainable values of the turbulence energy density, beam energy, beam ionization degree and electron life time the calculation of the electron energy distribution function and of the direct beam contribution to the electron particle balance shows a marked influence of the direct beam ionization with increasing degree of beam ionization.

Auto-correlation time of turbulent electric fields in a magnetized positive column

In strong magnetic fields the plasma of a positive column is in a turbulent state. The auto-correlation time τ 0 of the fluctuating electric fields is experimentally studied. It is found that τ 0 is governed by the ion saturation current i ps, and decreases exponentially as i ps increases.

Observations of nonlinear turbulence in the upstream solar wind

Plasma, electric-field and magnetic-field data from several experiments on board the spacecraft ISEE 1 and 2 have been analysed in the interaction region upstream of the Earth's bow shock. Upstream waves which are known to be associated with diffuse distributions of backstreaming protons are shown to correlate also with variability in the distribution of the incoming solar-wind protons. Both phenomena are also clearly connected with the presence of enhanced electric-field turbulence. On the basis of these relations, a preliminary discussion can be given of the complex nonlinear plasma processes occurring in the foreshock region.

Plasma wave turbulence at the magnetopause: Observations from ISEE 1 and 2

In this paper we investigate plasma wave electric and magnetic fields in the vicinity of the magnetopause by using recent measurements from the ISEE 1 and 2 spacecraft. Strong electric and magnetic field turbulence is often observed at the magnetopause. The electric field spectrum of this turbulence typically extends over an extremely large frequency range, from less than a few hertz to above 100 kHz, and the magnetic field turbulence typically extends from a few hertz to about 1 kHz. The maximum intensities usually occur in the magnetopause current layer and plasma boundary layer. Somewhat similar turbulence spectra are also sometimes observed in association with flux transfer events and possible ‘inclusions’ of boundary layer plasma in the magnetosphere. In addition to the broad‐band electric and magnetic field turbulence, narrow‐band electrostatic emissions are occasionally observed near the electron plasma frequency in the vicinity of the magnetopause. Two possible plasma instabilities, the electrostatic ion‐cyclotron instability and the lower‐hybrid‐drift instability, are considered the primary candidates for explaining the broad‐band electric field turbulence. The narrow‐band electrostatic emissions near the local electron plasma frequency are believed to be either plasma oscillations or electrostatic waves near the upper‐hybrid‐resonance frequency.

Plasma Wave Observations Near Jupiter: Initial Results from Voyager 2

This report provides an initial survey of results from the plasma wave instrument on the Voyager 2 spacecraft, which flew by Jupiter on 9 July 1979. Measurements made during the approach to the planet show that low-frequency radio emissions from Jupiter have a strong latitudinal dependence, with a sharply defined shadow zone near the equatorial plane. At the magnetopause a new type of broadband electric field turbulence was detected, and strong electrostatic emissions near the upper hybrid resonance frequency were discovered near the low-frequency cutoff of the continuum radiation. Strong whistler-mode turbulence was again detected in the inner magnetosphere, although in this case extending out to substantially larger radial distances than for Voyager 1. In the predawn tail region, continuum radiation was observed extending down to extremely low frequencies, approximately 30 hertz, an indication that the spacecraft was entering a region of very low density, approximately 1.0 x 10(-5) per cubic centimeter, possibly similar to the lobes of Earth's magnetotail.

A diagnostic for electron beams in solar flares

Whether energetic beam particles or a thermal wave carries the energy from corona to chromosphere in the flash phase of the solar flare is one of the major unresolved questions of the flare phenomenon. We study some effects of a charged-particle beam on the chromosphere, namely, turbulent electric field induced in the plasma which will broaden lines and induce the satellite lines of the forbidden transitions. The technique employed to measure these properties has been used in laboratory plasma experiments. An appropriate choice of spectral lins and the timing of the observations may make this technique applicable to solar flares.

Polarization of high latitude ionospheric turbulence as determined by analysis of data from the OV1‐17 satellite

A reanalysis of OV1‐17 data shows that high latitude ionospheric electric field turbulence is polarized with an electric field perpendicular to the magnetic field.

Plasma wave turbulence associated with an interplanetary shock

In this paper we give a brief summary of the interplanetary shocks detected and analyzed to date from the Helios 1 and 2 spacecraft and present a detailed analysis of the plasma wave turbulence associated with one particular shock, on March 30, 1976. This event was selected because a very clearly defined burst of plasma wave turbulence occurs at the shock with otherwise quiet conditions in the solar wind upstream and downstream of the shock. The shock is an oblique shock and the upstream parameters are characterized by a low Mach number, a low beta, and an unusually large electron to ion temperature ratio. Three types of plasma waves are detected in association with this shock: (1) electron plasma oscillations, (2) electrostatic ion‐acoustic or Buneman mode turbulence from about 1 to 30 kHz, and (3) whistler‐mode magnetic noise. Because of the high velocity of the shock and the quiet conditions in the solar wind this event provides a particularly good determination of the scale size and characteristics of the precursor waves upstream of the shock and the electric and magnetic field turbulence in the wake behind the shock. The primary burst of electric and magnetic field noise at the shock occurs a few seconds after the jump in the magnetic field, with a broad maximum in the electric field intensities at about 3 kHz and a monotonically decreasing magnetic field spectrum below about 1 kHz. Many of the characteristics of this shock are found to be closely similar to, and are compared with, previous observations of plasma wave turbulence associated with the earth's bow shock.

Suppression of an instability by the introduction of external turbulence

The problem of suppression of a plasma instability by the introduction of an externally controlled spectrum of turbulent electric fields is considered. The theory of strong turbulence is extended to include external fields, and is applied to the half-cyclotron frequency instability occurring in counterstreaming, magnetically confined electron beams. Experimental results from such an electron beam system are presented which confirm that the suppression of the instability is due to resonance broadening.

Direct interaction approximation and plasma turbulence theory

The authors show that a generalization of the Kraichnan Direct Interaction Approximation for fluid turbulence to the Vlasov or Klimontovich equations for plasmas contains most previously proposed 'strong' turbulence theories with the addition of further ad hoc approximations. This comparison depends on an exact factorization of the DIA into screened and unscreened quantities. The usual perturbed orbit or renormalized weak turbulence corrections to the unscreened Green's function are shown to inadequately account for the self-consistent nature of the turbulent electric fields. A direct prescription for the calculation of the unscreened correlation function which determines the Fokker-Planck friction coefficient is carried through in an approximation which neglects mode coupling effects. No enhanced noise due to phase-space clumps is found; in the discrete particle theory a turbulence renormalized (broadened) expression for the discrete particle noise is obtained.