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We suggest that pairing of bouncing medium-energy electrons in the auroral upward current region close to the mirror points may play a role in driving the electron cyclotron maser instability to generate an escaping narrow band fine structure in the auroral kilometric radiation. We treat this mechanism in the gyrotron approximation, for simplicity using the extreme case of a weakly relativistic Dirac distribution instead the more realistic anisotropic Juttner distribution. Promising estimates of bandwidth, frequency drift and spatial location are given.
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The mirror mode evolving in collisionless magnetised high-temperature thermally anisotropic plasmas is shown to develop an interesting macro-state. Starting as a classical zero frequency ion fluid instability it saturates quasi-linearly at very low magnetic level, while forming elongated magnetic bubbles which trap the electron component to perform an adiabatic bounce motion along the magnetic field. {Further evolution of the mirror mode towards a stationary state is determined by the bouncing trapped electrons which interact with the thermal level of ion sound waves, generate attractive wake potentials which give rise to formation of electron pairs in the lowest-energy singlet state of two combined electrons. Pairing takes preferentially place near the bounce-mirror points where the pairs become spatially locked with all their energy in the gyration. The resulting large anisotropy of pairs enters the mirror growth rate in the quasi-linearly stable mirror mode. It breaks the quasilinear stability and causes further growth. Pressure balance is either restored by dissipation of the pairs and their anisotropy or inflow of plasma from the environment. In the first case new pairs will continuously form until equilibrium is reached. In the final state the fraction of pairs can be estimated. This process is open to experimental verification. To our knowledge it is the only process where in high temperature plasma pairing may occur and has an important observable macroscopic effect: breaking the quasilinear limit and generation of localised diamagnetism.}
Analysis of 15314 electron velocity distribution functions (VDFs) within $pm$2 hours of 52 interplanetary (IP) shocks observed by the emph{Wind} spacecraft near 1 AU are introduced. The electron VDFs are fit to the sum of three model functions for the cold dense core, hot tenuous halo, and field-aligned beam/strahl component. The best results were found by modeling the core as either a bi-kappa or a symmetric (or asymmetric) bi-self-similar velocity distribution function, while both the halo and beam/strahl components were best fit to bi-kappa velocity distribution function. This is the first statistical study to show that the core electron distribution is better fit to a self-similar velocity distribution function than a bi-Maxwellian under all conditions. The self-similar distribution deviation from a Maxwellian is a measure of inelasticity in particle scattering from waves and/or turbulence. The range of values defined by the lower and upper quartiles for the kappa exponents are $kappa{scriptstyle_{ec}}$ $sim$ 5.40--10.2 for the core, $kappa{scriptstyle_{eh}}$ $sim$ 3.58--5.34 for the halo, and $kappa{scriptstyle_{eb}}$ $sim$ 3.40--5.16 for the beam/strahl. The lower-to-upper quartile range of symmetric bi-self-similar core exponents are $s{scriptstyle_{ec}}$ $sim$ 2.00--2.04, and asymmetric bi-self-similar core exponents are $p{scriptstyle_{ec}}$ $sim$ 2.20--4.00 for the parallel exponent, and $q{scriptstyle_{ec}}$ $sim$ 2.00--2.46 for the perpendicular exponent. The nuanced details of the fit procedure and description of resulting data product are also presented. The statistics and detailed analysis of the results are presented in Paper II and Paper III of this three-part study.
The analysis of the wave content inside a perpendicular bow shock indicates that heating of ions is related to the Lower-Hybrid-Drift (LHD) instability, and heating of electrons to the Electron-Cyclotron-Drift (ECD) instability. Both processes represent stochastic acceleration caused by the electric field gradients on the electron gyroradius scales, produced by the two instabilities. Stochastic heating is a single particle mechanism where large gradients break adiabatic invariants and expose particles to direct acceleration by the DC- and wave-fields. The acceleration is controlled by function $chi = m_iq_i^{-1} B^{-2}$div($mathbf{E}$), which represents a general diagnostic tool for processes of energy transfer between electromagnetic fields and particles, and the measure of the local charge non-neutrality. The identification was made with multipoint measurements obtained from the Magnetospheric Multiscale spacecraft (MMS). The source for the LHD instability is the diamagnetic drift of ions, and for the ECD instability the source is ExB drift of electrons. The conclusions are supported by laboratory diagnostics of the ECD instability in Hall ion thrusters.
Continuous plasma coherent emission is maintained by repetitive Langmuir collapse driven by the nonlinear evolution of a strong electron two-stream instability. The Langmuir waves are modulated by solitary waves in the linear stage, and by electrostatic whistler waves in the nonlinear stage. Modulational instability leads to Langmuir collapse and electron heating that fills in cavitons. The high pressure is released via excitation of a short wavelength ion acoustic mode that is damped by electrons and that re-excites small-scale Langmuir waves---this process closes a feedback loop that maintains the continuous coherent emission.
A statistical analysis of 15,210 electron velocity distribution function (VDF) fits, observed within $pm$2 hours of 52 interplanetary (IP) shocks by the $Wind$ spacecraft near 1 AU, is presented. This is the second in a three-part series on electron VDFs near IP shocks. The electron velocity moment statistics for the dense, low energy core, tenuous, hot halo, and field-aligned beam/strahl are a statistically significant list of values illustrated with both histograms and tabular lists for reference and baselines in future work. The beam/strahl fit results in the upstream are currently the closest thing to a proper parameterization of the beam/strahl electron velocity moments in the ambient solar wind. This work will also serve as a 1 AU baseline and reference for missions like $Parker Solar Probe$ and $Solar Orbiter$. The median density, temperature, beta, and temperature anisotropy values for the core(halo)[beam/strahl] components, with subscripts $ec$($eh$)[$eb$], of all fit results respectively are $n{scriptstyle_{ec(h)[b]}}$ $sim$ 11.3(0.36)[0.17] $cm^{-3}$, $T{scriptstyle_{ec(h)[b], tot}}$ $sim$ 14.6(48.4)[40.2] $eV$, $beta{scriptstyle_{ec(h)[b], tot}}$ $sim$ 0.93(0.11)[0.05], and $mathcal{A}{scriptstyle_{ec(h)[b]}}$ $sim$ 0.98(1.03)[0.93]. The nuanced details of the fitting method and data product description were published in Paper I and the detailed analysis of the results will be shown in Paper III.
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