Acceleration of Picked-up Interstellar Helium Ions at the Earth's Bow Shock: GEOTAIL Observation

Details Acceleration of Picked-up Interstellar Helium Ions at the Earth's Bow Shock: GEOTAIL Observation Acceleration of Picked-up Interstellar Helium Ions at the Earth's Bow Shock: GEOTAIL Observation

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsh41b0761o&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #SH41B-0761

Physics

2144 Interstellar Gas, 2152 Pickup Ions, 2154 Planetary Bow Shocks, 2164 Solar Wind Plasma, 2451 Particle Acceleration

Scientific paper

After ionization in the solar wind, He+ ions of the interstellar origin are expected to be accelerated at heliospheric shock (the termination shock, CIR shocks, and planetary shocks). Although there are some observational evidence of the pickup ion acceleration at CIR shocks, there have been no direct observations at the earth's bow shock. In this report, we present the first identification of the acceleration process of pickup He+ at the bow shock. The observation was provided by the Low Energy Particle experiments (LEP) onboard GEOTAIL. It was a high Mach number shock (Ma>10) with a large shock angle ( ~76[deg]). Such a quasi-perpendicular shock is known to form an overshoot and magnetically deflects the incoming ions. With a help of test particle simulation, we confirmed that the pickup He+ are magnetically reflected and reaches far upstream owing to their large gyro-radius. The infered fraction of the reflection ( ~24%) was higher than that of the general solar wind component ( ~11%) because a significant numbers of pickup ions which have a broad pitch angle distribution are outside of the loss cone in the de Hoffman-Teller frame. The drift accelerated pickup heliums are found to be energized to the maximum energy ~1.7 times their initial energy.

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