Hybrid Simulations of Global Magnetospheric Alfven-Ballooning Eigenmodes

A two-dimensional (2D) gyrokinetic-magnetohydrodynamic (MHD) hybrid simulation code has been developed to investigate radially global Alfven-Ballooning modes kinetically excited in the Earth's magnetosphere. The theoretical model is based on the gyrokinetic formulation for two-component (core and energetic) plasmas [Chen and Hasegawa, 1991]. The Alfvenic modes, supported by the core-component ideal MHD fluid, are destabilized by the energetic ions via drift-bounce resonances and are possible candidates for the observed Pc 4-5 geomagnetic pulsations. Two types of global Alfven-Ballooning modes are found to be radially localized in the strong kinetic drive region. One is the global energetic-particle mode in the low pressure case, where there exists no MHD potential well and the energetic ions provide both the instability drive and the radial localization of the bounded eigenstates. The other is the global MHD eigenmode in the high pressure case, where MHD potential wells exist [c.f.,Vetoulis and Chen, 1996] and energetic ions provide the instability drive. Detailed simualtion results and global stability features for both types will be discussed.