Theory of wave activity occurring in the AMPTE artificial comet

Abstract

One of the main experiments of the Active Magnetospheric Particle Tracer Explorers (AMPTE) [J. Geophys. Res. 91, 10013 (1986)] satellite mission was the release of neutral barium atoms in the solar wind. The barium atoms ionized by photoionization extremely rapidly forming a dense, expanding, plasma cloud that interrupted the solar wind flow creating diamagnetic cavities. On the upstream side of the cavity a region of compressed plasma and enhanced magnetic field was created as the result of being produced by the slowing down and deflection of the solar wind, and magnetic field line draping. Intense electrostatic and magnetic turbulence was observed by both the IRM [J. Geophys. Res. 91, 10 013 (1986)] and UKS [J. Geophys. Res. 91, 1320 (1986)] satellites at the boundary of the diamagnetic cavity, with the most intense waves being detected near the outer boundary of the compressed region. This paper examines how the newly created expanding plasma couples to the solar wind by means of plasma–beam and current-driven instabilities. In particular, it is shown how lower-hybrid and lower-hybrid drift waves are generated by cross-field proton–barium streaming instabilities and cross-field electron currents. The saturation mechanism for these waves is considered to be the modulational instability, this instability can also lead to filamentation and coupling to magnetosonic modes, which are also observed. As the result of modulational instability the k∥ component increases, which allows the heating and acceleration of electrons that is consistent with the observations.

Charged dust and shock phenomena in the Solar System

“…The situation is similar to those which occur in the process of the AMPTE barium release (Bingham et al, 1991;Popel et al, 1995) and interaction of the solar wind with the coma of the comet Hyakutake (Dawson et al, 1997).…”

“…The width of this turbulent region is estimated to be of the order of 10-100 km. In the turbulent region which corresponds to the compression region of the collisionless shock wave (Bingham et al, 1991;Popel et al, 1995) one can expect the increase of the magnetic field while inside the vapor jet the magnetic field is decreased and the formation of the diamagnetic cavity is possible. The development of the plasma turbulence results in the electron heating.…”

“…The detection of fast electron formation and x-ray flux at the head of the comet Hyakutake (Dawson et al, 1997) and plasma oscillations at the boundary of diamagnetic cavity of the artificial comet AMPTE caused by barium release (Bingham et al, 1991;Popel et al, 1995) are the basis for our hypothesis of the plasma turbulence in large regions of the solar wind above the lunar surface.…”

dHybrid: A massively parallel code for hybrid simulations of space plasmas

“…The AMPTE experiments consisted of several gas (Lithium and Barium) releases in the upstream solar wind by a spacecraft orbiting the earth [27][28][29]. After the release, the expanding cloud of atoms is photoionized by the solar ultraviolet radiation, thus producing an expanding plasma and forming an obstacle to the flowing solar wind.…”

Particle acceleration in tangential discontinuities by lower hybrid waves

“…To estimate the nonthermal energies of the electrons and their fluxes, we follow a standard approach used by previous authors (Lampe and Papadopoulos, 1977;Spicer et al, 1981;Bingham et al, 1991 , (18) where C 2 s = k B T e /m i is the ion acoustic speed and V Ae is the electron Alfvén velocity = c ce /ω pe . Using the set of parameters that we previously employed and those computed, we find E e = 280eV .…”