Ion acceleration by parallel propagating nonlinear Alfvén wave packets in a radially expanding plasma
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Nariyuki, Y.
;
Umeda, T.
;
Suzuki, T. K.
;
Hada, T.
(2014)
The numerical simulation of the nonlinear evolution of the parallel
propagating Alfvén waves in a radially expanding plasma is performed by
using a kinetic-fluid model (the Vlasov–MHD model). In our study, both the
nonlinear evolution of the Alfvén waves and the radial evolution of the
velocity distribution function (VDF) are treated simultaneously. On the other
hand, important ion kinetic effects such as ion cyclotron damping and
instabilities driven by the non-equilibrium ion velocity distributions are
not included in the present model. The results indicate that the steepened
Alfvén wave packets outwardly accelerate ions, which can be observed as the
beam components in the interplanetary space. The energy of imposed Alfvén
waves is converted into the longitudinal fluctuations by the nonlinear
steepening and the nonlinear Landau damping. The wave shoaling due to the
inhomogeneity of the phase velocity is also observed.