Quasi‐linear ion cyclotron heating in the near‐Earth magnetotail

Abstract

Quasi‐linear studies in the near‐Earth (XGSE>‐25 RE) central plasma sheet and plasma sheet boundary layer indicate that the ion cyclotron proton anisotropy instability may lead to significant ion heating in these regions. Saturation of the anisotropy instability can yield both narrow and broadband magnetic spectra below the proton gyrofrequency with amplitudes of the order of 1 nT. These waves then heat thermal and suprathermal He+ and O+ ions via resonant and nonresonant processes to energies above 1 keV for He+ ions and up to 100 eV for O+ ions. He++ ions also experience significant heating to temperatures that may exceed that of the unstable proton component. These results are consistent with in situ observations of magnetic noise and heavy ion distributions in the near‐Earth magnetotail.