Secondary Instabilities of Electromagnetic Ion Cyclotron Waves Associated with Cold Plasma Populations

Electromagnetic ion cyclotron (EMIC) waves are common in the Earth's inner magnetosphere, in particular during geomagnetic storms following injections of anisotropic ring current ions. These waves as well as the resulting particle scattering can strongly affect the radiation belts, and have been studied extensively. An aspect that has received comparatively much less attention is that these waves can couple very efficiently with the cold (<100 eV) particle populations of the magnetosphere. One way to do so is through secondary instabilities driven by the fact that EMIC waves induce a relative drift velocity between different plasma species which can act as a source of free energy. The properties of these instabilities (including growth rate, nonlinear saturation and energy partition) are sensitive to details of the plasma composition such as the presence of a small fraction of heavier ions, such as helium or oxygen. We will present linear theory and nonlinear simulations to show the precense and effects these secondary instabilities.