Papers on FAST
Papers are located on the Geophysical Research Letters server.
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FAST observations of preferentially accelerated He+ in association with auroral electromagnetic ion cyclotron waves
- GEOPHYSICAL RESEARCH LETTERS, VOL. 25, NO. 12, JUNE 15, 1998
- The TEAMS instrument on the FAST satellite has detected events in which He+ ions are resonantly accelerated perpendicular to the magnetic field to energies of several keV. The events occur in association with electromagnetic ion cyclotron (EMIC) waves and conic distributions of up to a few hundred eV in H+ and a few keV in O+. Concentrations of He+ can be significantly elevated during the events. Our interpretation is that the He+ ions are accelerated through a cyclotron resonance with the waves. This acceleration is similar to a proposed mechanism for selective ion acceleration in impulsive solar flares.
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Species dependent energies in upward directed ion beams over auroral arcs as observed with FAST TEAMS
- GEOPHYSICAL RESEARCH LETTERS, VOL. 25, NO. 12, JUNE 15, 1998
- Beams of energetic ions with energies ranging from several hundred eV to several keV flowing upward along magnetic field lines over auroral arcs are known as an integral part of the aurora and as a source of ions for the magnetosphere. The presence of the fast 3-dimentional ion mass spectrograph TEAMS on the FAST satellite allows detailed measurements of ions beams with unprecedented temporal and spatial resolution, including their compositional signatures. We have performed a statistical study on a sample of approximately 80 ion beams from the auroral campaign in early 1997. All observed ion beams contain substantial amounts of H+, He+ and O+. A clear ordering of the total energies of the ion species according to their mass is found, with H+ having the lowest energy and O+ the highest energy. Higher energies for O+ have been observed in statistical studies of beams during solar minimum conditions by various groups. The difference in energy between the species changes from beam to beam, but in none of the cases so far have the energies of all singly charged species been the same, as would be expected for pure electrostatic accelerations along the field line. The composition varies significantly from beam to beam, with O+/H+ ratios varying from 0.1 to 10 during the observation period. However, no variation of the energy ratio between species is observed as a function of relative abundance in the beams.
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FAST/TEAMS Observations of Charge Exchange Signatures in Ions Mirroring at Low Altitudes
- GEOPHYSICAL RESEARCH LETTERS, VOL. 25, NO. 12, JUNE 15, 1998
- Using the TEAMS instrument on FAST, we have observed a case in which signatures of the inner edge of the plasma sheet are clearly observed in the energy spectra of ions mirroring at the FAST altitude. That inner edge is dominated by He+. We show that this is the natural expected from charge exchange as the ions drift in from the plasma sheet.
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