Acceleration Of Thermal Electrons Research Articles

Macroscopic electric fields driven by lower-hybrid turbulence and acceleration of thermal electrons in the foot of quasi-perpendicular shocks

A new mechanism is suggested that draws non-resonant thermal electrons into a higher-velocity range, where they can be effectively accelerated by waves. We argue that the acceleration of a small number of pre-existing resonant particles influences the dynamics of the bulk plasma and results in a macroscopic electric field. The solution for the spatial dependence of this electric field is obtained, and it appears to be a new type of electrostatic shock, which forms only in the presence of background turbulence. This field enriches the region of resonant particles with thermal electrons, which leads to a build-up of an excess of accelerated particles. The number of accelerated particles is calculated. This mechanism appears as a good candidate to explain electron acceleration in the foot of quasi-perpendicular shocks.

Volume ignition of laser driven fusion pellets and double layer effects

The realization of an ideal volume compression of laser-irradiated fusion pellets (by C. Yamanaka) opens the possibility for an alternative to spark ignition proposed for many years for inertial confinement fusion. A re-evaluation of the difficulties of the central spark ignition of laser driven pellets is given. The alternative volume compression theory, together with volume burn and volume ignition (discovered in 1977), have received less attention and are re-evaluated in view of the experimental verification by Yamanaka, generalized fusion gain formulas, and the variation of optimum temperatures derived at self-ignition. Reactor-level DT fusion with MJ-laser pulses and volume compression to 50 times the solid-state density are estimated. Dynamic electric fields and double layers at the surface and in the interior of plasmas result in new phenomena for the acceleration of thermal electrons to suprathermal electrons. Double layers also cause a surface tension which stabilizes against surface wave effects and Rayleigh–Taylor instabilities.

Acceleration of thermal electrons by ICW's propagating in a multicomponent magnetospheric plasma

Norris et al. [1983] have recently shown that thermal (∼1 eV) electrons are accelerated along field lines (up to tens of electron volts) when intense ion cyclotron waves (ICW's) are simultaneously present in the equatorial magnetosphere. In the present paper a mechanism that explains these observations is proposed. It is shown that, owing to the small but finite parallel electric field developed by ICW's in a multicomponent plasma (e.g., containing minor He+ ions), electrons having parallel velocities close to the Alfven velocity (at the equator) can be trapped in the potential troughs of this ICW. Then, taking into account the inhomogeneity along geomagnetic field lines, it is shown that the increase of the parallel phase velocity of the ICW as it leaves the equator implies a parallel acceleration of these trapped electrons. The maximum parallel energy that is reached (a few tens of electron volts) is in agreement with observations; it is obtained by matching the trapping force (proportional to E⫽) to the detrapping force due to the inhomogeneity along field lines.

Electron pitch angle scattering and the impulsive phase microwave and hard X-ray emission from solar flares

Observations and theoretical considerations have led to a model for impulsive phase flare emission involving the heating and acceleration of thermal electrons in the coronal part of a magnetic loop. The bulk of the heated gas is confined between conduction fronts, but particles with velocities a few times greater than the thermal velocity can escape into the lower part of the loop. It is shown that, when the electron gyrofrequency exceeds the plasma frequency, the escaping electrons are unstable to the generation of electrostatic plasma waves which scatter the particles in pitch angle to a nearly isotropic distribution. It is also shown that this scattering can (1) enhance the microwave emission from the upper part of the loop, and (2) due to the Landau damping of both low and high phase velocity waves, can lead to one or two breaks in the impulsive-phase hard X-ray spectrum.

Polar cap electron acceleration regions

The characteristics of polar cap electron acceleration regions and the relationship of their occurrence to the interplanetary magnetic field (IMF) have been investigated by using data from Atmosphere Explorer D and Imp J. It was found that electron energy spectra and angular distributions within the acceleration regions are generally consistent with models of acceleration of auroral primaries and reflection of atmospheric secondaries by field‐aligned electrostatic potential differences. However, localized strongly field‐aligned fluxes are also observed at energies below the spectral peak. It is suggested that these transient beams of field‐aligned low‐energy electrons result from the acceleration of thermal electrons from within the acceleration regions and that this thermal electron population may be partially replenished by small pitch angle atmospheric secondaries. The occurrence of the polar cap acceleration regions in the northern hemisphere is strongly correlated with IMF vectors which project into the (−X, +Z) sector of the solar magnetospheric X‐Z plane; that is, with northward ‘away’ IMF polarities.