Open AccessElectromagnetic proton cyclotron instability: heating of cool magnetospheric helium ions
Author(s) -
S. Peter Gary,
L. Yin,
D. Winske
Publication year - 1996
Publication title -
annales geophysicae
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.522
H-Index - 93
eISSN - 1432-0576
pISSN - 0992-7689
DOI - 10.1007/s00585-996-0001-2
Subject(s) - proton , magnetosphere , atomic physics , instability , physics , helium , cyclotron , anisotropy , plasma , ion , isotropy , nuclear physics , mechanics , optics , quantum mechanics
The electromagnetic proton cyclotronanisotropy instability is excited if the hot proton temperature anisotropy, T\u22a5h/Tmidmidh, is sufficiently large compared to unity, where the subscript hdenotes the hot protons and the perpendicular and parallel symbols denotedirections relative to the background magnetic field. This instability isimportant in the outer magnetosphere because it has been shown to lead to anupper bound on T\u22a5h/Tmidmidh and to cool iron heating. Here one-dimensional initial-valuehybrid simulations with spatial variations in the direction of the backgroundmagnetic field are used to study this instability in a homogeneous plasma modelwhich represents three ionic constituents of the outer magnetosphere: hotanisotropic protons, cool, initially isotropic protons, and cool, initiallyisotropic singly ionized helium. These simulations show that the presence of atenuous helium component does not significantly change the scalings of eitherthe hot proton anisotropy upper bound or the heating of the cool protons. Thesimulations also show that the helium ion heating rate increases withβmidmidh in contrast to the coolproton energization which decreases with this parameter. The prediction of thishomogeneous plasma model, therefore, for cool ions subject to heating by theproton cyclotron instability is that the observed ratio of cool heliumtemperature to cool proton temperature should increase as βmidmidhincreases