Anisotropic Electron Temperature Research Articles

Laser Thomson scattering system for anisotropic electron temperature measurement in NUMBER

A laser Thomson scattering system is developed to obtain anisotropic electron temperature in a pulse operated electron cyclotron resonance plasma device. Injecting a laser with an oblique angle to the external magnetic field and detecting scattering photon from a line of sight along another oblique angle enable us to obtain parallel and perpendicular components of electron temperature. Backward (165°) scattering spectrum corresponds to quasi perpendicular velocity distribution, while that for forward (15°) scattering; quasi parallel. Collecting lenses are set in vacuum to maximize solid angle in a limited space of port, where the laser path and collecting optics share an ICF152 flange. Rayleigh scattering intensity is measured as a function of argon gas pressure. An initial result on residual stray light intensity is equivalent to the argon Rayleigh scattering intensity under ≤ 1 kPa of filled pressure. In order to obtain Thomson scattering spectra, a notch filter type stray light rejection optics, which utilize a reflective type volume holographic grating, is evaluated. Notch width (0.2 nm) and flat transmittance (≥ 90%) outside the notch measured for a prototype show that it is an effective optics.

Electron mirror and cyclotron instabilities for solar wind plasma

ABSTRACT The solar wind plasma is characterized by unequal effective kinetic temperatures defined in perpendicular and parallel directions with respect to the ambient magnetic field. For electrons, the excessive perpendicular temperature anisotropy leads to quasi-parallel electromagnetic electron cyclotron (or whistler) instability and aperiodic electron-mirror instability with oblique wave vectors. The present paper carries out a direct side-by-side comparison of quasi-linear (QL) theory and particle-in-cell (PIC) simulation of combined mirror and cyclotron instabilities acting upon the initially anisotropic electron temperatures, and find that the QL theory satisfactorily encapsulates the non-linear aspect of the combined instability effects. However, a discrepancy between the present study and a previous PIC simulation result is also found, which points to the need for further investigation to resolve such an issue.

Quasi-static surface modes of plasma layer with anisotropic electron temperature

Quasi-static surface wave propagation in a plasma layer with anisotropic electron temperature is considered. The case is analyzed where the electron temperature in the direction normal to the plasma boundary is considered to be zero, while in the direction along the boundary, electrons are described by the Maxwellian velocity distribution. It is shown that the modes of such a layer are described by equations for bulk plasma waves with renormalization of the electron density affecting the surface wave dispersion and damping.

Electron flat-top distributions and cross-scale wave modulations observed in the current sheet of geomagnetic tail

We present new observations of electron distributions and the accompanying waves during the current sheet activities at ∼60 RE in the geomagnetic tail detected by the ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun) spacecraft. We find that electron flat-top distribution is a common feature near the neutral sheet of the tailward flowing plasmas, consistent with the electron distributions that are shaped in the reconnection region. Whistler mode waves are generated by the anisotropic electron temperature associated with the electron flat-top distributions. These whistler mode waves are modulated by low frequency ion scale waves that are possibly excited by the high-energy ions injected during the current sheet instability. The magnetic and electric fields of the ion scale waves are in phase with electron density variations, indicating that they are compressional ion cyclotron waves. Our observations present examples of the dynamical processes occurring during the current sheet activities far downstream of the geomagnetic tail.

Effect of electron temperature anisotropy on near-wall conductivity in Hall thrusters

The electron velocity distribution in Hall thrusters is anisotropic, which not only makes the sheath oscillate in time, but also causes the sheath to oscillate in space under the condition of low electron temperatures. The spatial oscillation sheath has a significant effect on near-wall transport current. In this Letter, the method of particle-in-cell (2D + 3 V) was adopted to simulate the effect of anisotropic electron temperatures on near-wall conductivity in a Hall thruster. Results show that the electron-wall collision frequency is within the same order in magnitude for both anisotropic and isotropic electron temperatures. The near-wall transport current produced by collisions between the electrons and the walls is much smaller than experimental measurements. However, under the condition of anisotropic electron temperatures, the non-collision transport current produced by slow electrons which reflected by the spatial oscillation sheath is much larger and closes to measurements.

Nonlinear mirror modes in the presence of hot electrons

A non-perturbative calculation of the gyrotropic pressures associated with large-scale mirror modes is performed, taking into account a finite, possibly anisotropic electron temperature. In the small-amplitude limit, this leads to an extension of an asymptotic model previously derived for cold electrons. A model equation for the profile of subcritical finite-amplitude large-scale structures is also presented.

Principles for local measurement of anisotropic electron temperature of plasma using incoherent Thomson scattering

Anisotropic electron temperature can be measured by utilizing two Thomson scattering spectra from different scattering angles. The ideal conditions for measurement are as follows: the sum of the two scattering angles is 180°, and the magnetic field is parallel to the bisector of the angle formed by the direction of laser propagation and the line of sight or is perpendicular to this bisector. When these conditions are satisfied, one of the spectra predominantly reflects the parallel electron temperature, and the other spectrum predominantly reflects the perpendicular electron temperature. A deviation in the direction of magnetic field of the order of approximately a few tens of degrees from the ideal direction is acceptable in terms of the deviation obtained by both rotating parallel to and tilting from the scattering plane.

Electron temperatures in Saturn’s plasma disc

We present new results concerning electron temperature ( T e ) mapping in the inner magnetosphere of Saturn (<7 R S). The data are obtained by the Langmuir Probe (LP) instrument of the Radio and Plasma Wave Science (RPWS) investigation on board Cassini. The study is based on the fourteen first orbits around Saturn, and focus is on cold (<10 eV) and dense (>5 cm −3) electron populations in the inner plasma torus (plasma disc). Apart from a general increase with distance from Saturn and away from the equatorial plane (latitude), we identify a possibly anisotropic electron temperature in the plasma disc, as well as the presence of photoelectrons from the spacecraft or E-ring dust particles. A polytropic index of γ≈+0.4 is determined from the observations, which can be used in theoretical models of the plasma disc. We also infer local variations in T e near the equatorial plane, where the E-ring of dusty plasma and enhancements of water rich neutral gas exist, and determine constraints on the energy source required to heat the electrons in the plasma disc. We suggest that Joule heating or heating by low-frequency plasma waves as well as cooling by neutral gas and E-ring dust are involved in the energy balance, together with Coulomb collision heating by co-rotating ions.

Electron heating by the magnetic field-aligned electron–cyclotron waves in plasmas

It is shown that resonant nonlinear interactions between the magnetic-field aligned right-hand circularly polarized electromagnetic (CPEM) electron–cyclotron waves and electrons can produce electron temperature anisotropy due to the stochastic electron heating by waves in magnetized plasmas. The present result can thus account for the simultaneous presence of CPEM waves and an anisotropic electron temperature distribution in laboratory and space magnetoplasmas.

Linear theory for fast collisionless magnetic reconnection in the lower-hybrid frequency range

A linear theory is presented for the interplay between the fast collisionless magnetic reconnection and the lower-hybrid waves that has been observed in recent computer simulations [J. F. Drake, M. Swisdak, C. Cattell et al., Science 299, 873 (2003)]. In plasma configurations with a strong guide field and anisotropic electron temperature, the electron dynamics is described within the framework of standard electron magnetohydrodynamic equations, accounting also for the effects of the electron polarization and ion motions in the presence of perpendicular electric fields. In the linear phase, we find two types of instabilities of a thin current sheet with steep edges, corresponding to its filamentation (or tearing) and bending. Using a surface-wave formalism for the perturbations whose wavelength is larger than the thickness of the current sheet, the corresponding growth rates are calculated as the contributions of singularities in the plasma dispersion function. These are governed by the electron inertia and the linear coupling of the reconnecting magnetic field with local plasma modes propagating in the perpendicular direction that are subject to the Buneman instability. The linear surface wave instability may be particularly important as a secondary instability, dissipating the thin current sheets that develop in the course of the fast reconnection in the shear-Alfvén and kinetic-Alfvén regimes, and providing the anomalous resistivity for the growth of magnetic islands beyond the shear-Alfvén and kinetic-Alfvén scales.

Solitary waves in the Earth's magnetosphere: Nonlinear stage of the lower‐hybrid Buneman instability

A drift‐kinetic theory for electron phase‐space vortices in magnetized space plasmas is formulated in the frequency range of lower‐hybrid waves excited by the Buneman instability in the presence of an electron beam. The nonlinear model accounts for the effects of the electron polarization, anisotropic electron temperature and ion mobility, and it provides a theoretical explanation for some of the electrostatic and weakly electromagnetic bipolar structures observed by the Cluster, Polar and FAST spacecrafts in the Earth's magnetosheath, magnetopause and in the auroral zone. Quasi‐3‐D electron holes have the form of either elongated cylinders oblique to the magnetic field, or spheroids.

Nonlinear model for electron phase‐space holes in magnetized space plasmas

We formulate a drift‐kinetic theory of electron phase‐space vortices in magnetized space plasmas. It provides the theoretical explanation for the spatial and temporal scales of the electrostatic bipolar structures that have been observed by the Geotail and FAST spacecrafts in Earth's magnetotail and in the auroral zone. Our new nonlinear model accounts for the effects of both the electron polarization and the anisotropic electron temperature. Several different types of quasi‐three‐dimensional electron holes are found in the form of either cylinders or ellipsoids. Although topologically different, they produce similar signals on the spacecraft under typical FAST and Geotail observational conditions and cannot be distinguished with the use of the existing scarce satellite observational data.

Bootstrap Current for Tokamak Plasma with Anisotropic Electron Temperature

The neoclassical bootstrap current for an anisotropic plasma has been studied in a large aspect-ratio tokamak. The enhancement factor due to the temperature anisotropy in the equilibrium electron distribution function is explicitly calculated, and is shown to reach to about 1.5 when the perpendicular temperature is twice as large as the parallel temperature. This bootstrap current is also predicted to have the component proportional to the radial electric field even in an axisymmetric magnetic field.

Anisotropic temperature relaxation of plasmas in an external magnetic field

The magnetized kinetic equation derived earlier (Hassan and Watson (1977)) is used to study the problem of relaxation of anisotropic electron and ion temperatures in a magnetized plasma. The case of anisotropic electron temperature relaxation for small anisotropies the exchange of energy within the electrons between the components parallel and perpendicular to the magnetic field direction determine the relaxation rate. For anisotropic ion temperature relaxation the essential mechanism for relaxation is provided by energy transfer between ions and electrons, and the expression for the relaxation rate perpendicular to the magnetic field contains a significant term proportional to In eta 0 ln (me/mi) (where eta 0= Omega e/kDVe perpendicular to ), in addition to the term proportional to the Coulomb logarithm.

Low-frequency instability in a plasma with anisotropic electron temperature: K S Golovanivskiy and V D Dugar-Zhabon,Zh Tekh Fiz, 42 (2), Feb 1972, 452–454 ( in Russian)

Low-frequency instability in a plasma with anisotropic electron temperature: K S Golovanivskiy and V D Dugar-Zhabon,Zh Tekh Fiz, 42 (2), Feb 1972, 452–454 ( in Russian)