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Formation of He 2+ shell‐like distributions downstream of the Earth's bow shock
Author(s) -
Lu Q. M.,
Wang S.
Publication year - 2005
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2004gl021508
Subject(s) - physics , bow shock (aerodynamics) , bow wave , solar wind , atomic physics , shock wave , plasma , ion , distribution function , cyclotron , beam (structure) , shock (circulatory) , computational physics , optics , nuclear physics , mechanics , medicine , quantum mechanics
When the incident solar wind He 2+ and H + distributions cross the electrostatic potential at the shock, they are decelerated differentially due to their different charge‐ to‐mass ratios. This differential slowing will produce a He 2+ ring‐beam distribution immediately downstream from a quasi‐perpendicular shock. In this letter, we perform one‐dimensional (1D) hybrid simulations and investigate the evolution of the He 2+ ring‐beam distribution in magnetized plasma. The plasma is composed of three components: H + , He 2+ and electrons, where H + has a velocity distribution with large perpendicular temperature anisotropy. It is shown that both the He 2+ ring‐beam distribution and H + distribution with large perpendicular temperature anisotropy can excite ion cyclotron waves with propagation direction parallel to the ambient magnetic field, and then the waves pitch‐angle scatter the He 2+ ions. However, only the ion cyclotron waves excited by the He 2+ ring‐beam distribution can transform He 2+ into shell‐like distribution. The results can explain the He 2+ shell‐like distributions downstream of the Earth's bow shock, which have already been observed with the AMPTE/CCE and ISEE spacecraft.