Simulation studies of plasma waves in the electron foreshock: The generation of Langmuir waves by a gentle bump-on-tail electron distribution
The generation of Langmuir waves by a gentle bump-on-tail electron distribution is analyzed. It is shown that with appropriately designed simulation experiments, quasi-linear theory can be quantitatively verified for parameters corresponding to the electron foreshock. The distribution function developed a plateau by resonant diffusion, and changes outside this velocity range are negligible, except for the contribution of nonresonant diffusion to acceleration of bulk electrons. The dispersions relation is solved for the evolving distribution function and exhibits the dynamics of wave growth and changes in real frequency. The integral of the quasi-liner equations is also used to relate the evolution of distribution function and wave spectrum and gives agreement with the simulations. Even in extremely long simulation runs there is practically no evolution in wave energy or the distribution function once a plateau has been formed. The saturated field levels are much lower than the estimates that are generally used to assess the importance of additional weak or strong turbulence effects. These effects cannot prevent plateau formation and are only noticeable if ions are also included in the model. They then lead to a redistribution of the spectrum toward low wave numbers modes which propagate mainly opposite to the beam. This occurs long after plateau formation and play no significant role in the overall system dynamics or energy balance. One will have to live with quasi-linear theory as a key ingredient for a global model of foreshock wave phenomena.
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge, MA (USA)
- OSTI ID:
- 5931839
- Report Number(s):
- AD-A-228765/4/XAB; CNN: AFOSR-90-0085
- Resource Relation:
- Other Information: Pub. in Jnl. of Geophysical Research, Vol. 95, No. A6, 8095-8110(1 Jun 1990)
- Country of Publication:
- United States
- Language:
- English
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GENERAL PHYSICS
IONOSPHERE
PLASMA WAVES
SIMULATION
ACCELERATION
CYCLOTRON RESONANCE
DIFFUSION
DISTRIBUTION FUNCTIONS
DISTURBANCES
DYNAMICS
ELECTRONS
IONS
LANGMUIR PROBE
QUASILINEAR PROBLEMS
SATURATION
TURBULENCE
VELOCITY
CHARGED PARTICLES
EARTH ATMOSPHERE
ELECTRIC PROBES
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