Dissipation of Alfven Waves via Generation of High-Frequency Electrostatic Waves and Transverse Ion Acceleration

Details Dissipation of Alfven Waves via Generation of High-Frequency Electrostatic Waves and Transverse Ion Acceleration Dissipation of Alfven Waves via Generation of High-Frequency Electrostatic Waves and Transverse Ion Acceleration

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsh11a0362m&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SH11A-0362

Physics

2407 Auroral Ionosphere (2704), 2471 Plasma Waves And Instabilities (2772), 2483 Wave/Particle Interactions (7867), 6984 Waves In Plasma (7867), 7846 Plasma Energization

Scientific paper

Satellite observations in the auroral plasma have revealed that extremely low frequency (ELF) waves play a dominant role in the acceleration of electrons and ions in the auroral plasma. The electromagnetic components of the ELF (EMELF) waves are the electromagnetic ion cyclotron (EMIC) waves below the cyclotron frequency of the lightest ion species in a multi-ion plasma. Shear Alfvén waves (SAWs) constitute the lowest frequency components of the ELF waves below the ion cyclotron frequency of the heaviest ion. The mechanism for the transfer of energy from such EMELF waves to ions affecting transverse ion heating still remains a matter of debate. A very ubiquitous feature of ELF waves now observed in several rocket and satellite experiments is that they occur in conjunction with high-frequency electrostatic waves. The frequency spectrum of the composite wave turbulence extends from the low frequency of the Alfvénic waves to the high frequency of proton plasma frequency and/or the lower hybrid frequency. The spectrum does not show any feature organized by the ion cyclotron frequencies and their harmonics. Such broadband waves consisting of both the EM and ES waves are now popularly referred as BBELF waves. We present results here from 2.5-D particle-in- cell simulations showing that the ES components are directly generated by cross-field plasma instabilities driven by the drifts of the ions and electrons in the EM component of the BBELF waves. We also demonstrate that the ES wave generation is directly involved in the transverse acceleration of ions (TAI) as commonly measured with the BBELF wave events. In the simulation we drive the plasma by the transverse electric field, Ey, of the EM waves; the frequency of Ey is varied from a frequency below the heavy ion cyclotron frequency to below the light ion cyclotron frequency. We have also performed simulations for Ey having a continuous spectrum given by a power law with different spectral indexes. The driving electric field generates polarization and ExB drifts of the ions and electrons. When the interspecies relative drifts are sufficiently large, they drive electrostatic waves, which cause perpendicular heating of both light and heavy ions. The heavy ions are preferentially heated.

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