| Budget Amount *help |
¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1988: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1987: ¥900,000 (Direct Cost: ¥900,000)
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| Research Abstract |
Large amplitude Alfven waves play important roles in various heliospheric environment. We have investigated nonlinear phenomena of these large amplitude Alfven waves:
(1) Nonlinear dynamics of the Alfven waves excited by ion beams throuth the cyclotron resonant interaction:
In upstream regions of collisionless shocks, large amplitude Alfven waves are often observed. These waves are excited by the beam ions injected at the shock front. We discuss several specific topics about the nonlinear dynamics of these waves: frequency shift of the waves owing to the beam deceleration, a parametric decay process, and the formation of ion clumps (spatially bunced ions).
(2) Nonlinear phenomena in the subharmonic resonance between ions and magnetosonic waves propagating oblique/perpendicular to the background magnetic field:
It is found that subhamonic resonant interaction between ions and magnetosonic waves becomes quite efficient in accelerating ions when the wave amplitude exceeds 10% of the background field. Further, when the wave amplitude exceeds 50% of the background field, ions have stochastic orbits and are accelerated to quite high energy.
(3) Nonlinear effect on the stochastic acceleration process of particles in a turbulent Alfven waves:
From a test particle experiment, we have found that if the energy density of the turbulence is less than 10% of that of the background magnetic field, the behavior of particles are well described by the quasilinear theory. When the turbulence becomes stronger, contribution from the nonresonant wave components, which is negligible in weaker turbulence, tends to enhance the acceleration rate.
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