Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh21a1583t&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SH21A-1583
Physics
7815 Electrostatic Structures, 7829 Kinetic Waves And Instabilities, 7851 Shock Waves (4455), 7867 Wave/Particle Interactions (2483, 6984), 7868 Wave/Wave Interactions
Scientific paper
Mixing of hot electrons and cold electrons along the magnetic field line are commonly observed in the electron foreshock region and in the boundary layers of the Earth!|s magnetosphere. In this study, we use the ion-acoustic shock as an example to study the anomalous heating of electrons by means of electrostatic Vlasov simulations. Our simulation results indicated that a quasi-steady cross-shock potential jump is established within a few electron oscillation periods at the beginning of the shock simulation. The cross shock potential can accelerate the upstream electrons across the shock ramp and decelerate the leaked electrons coming from the downstream side. The mixing of the upstream and downstream electrons can result in electron-electron two-stream instability to generate electron-acoustic waves (EAWs) with phase speed close to the average speed of the low-density electron species. The transmitted electron beam from the upstream side can lead to short-wavelength EAWs on the downstream side. The EAWs can heat up the transmitted electron beam and result in the saturation of the EAWs. The bump-on-tail distribution on the upstream side due to the presence of leakage electrons can lead to the formation of EAWs with longer wavelength. The EAWs on the upstream side can smooth out the bump-on-tail structure and lead to the saturation of the EAWs. The leakage electrons can also lead to ion-electron two-stream instability and generate ion-acoustic waves (IAWs). In general, the growth rate of the IAWs is much lower than the EAWs, but the growth of IAWs can be greatly enhanced when the phase speed of the unstable IAWs is about the same as the phase speed of the local EAWs. The amplification of the IAWs can result in large-amplitude longer-wavelength waves. The phase-space mixing of the electrons by the large-amplitude longer- wavelength IAWs can produce new bump-on-tail structures on the electrons!| distribution function and lead to formation of the secondary EAWs. The IAWs and the secondary EAWs together can heat-up the electrons in a very efficient way. Our simulation results indicate that the strong field-aligned electron heating and temperature anisotropic can be completed within a few tens of ion oscillation periods. Electromagnetic waves that can be generated by the strong temperature anisotropic will be discussed.
Lyu L.
Tsai Tun Tao
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