Gyrophase-restricted 100 keV-2 MeV ion beams near the foreshock boundary - art. no. 2049

摘要

1] We report on gyrophase-restricted ion beams with energies extending from similar to 100 keV up to similar to 2 MeV, observed by Wind in the Earth's distant (similar to 65 R-E) foreshock. The ion gyrophases seen were nearly constant during periods when the distance to the shock contact point could be expected to vary by several RE, when there was no significant wave activity. At times the distributions had two peaks similar to 180degrees apart in gyrophase. These were consistent with a remotely-sensed energetic ion foreshock region having a thickness < 2 gyroradii (&SIM; 1.5 R-E for 0.5 MeV protons with pitch-angle α = 30&DEG;). In this picture, gaps in phase space would correspond to particles with guiding centers outside of the energetic foreshock region. Similar observations over a decade of energies ( 100 keV - 2 MeV) suggest that the region thickness scales with gyroradius. According to this interpretation, we have determined a rough range of geometries for which energetic particle production is favored. (Eg., θ(Bn) &SIM; 70 - 80&DEG; for 500 keV ions with α = 30&DEG;.) [References: 15