Nonlinear wave packet evolution in a dispersive plasma: Application to rotational discontinuities

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:7041617

Vasquez, B J

This dissertation examines low frequency ([approx lt] ion gyrofrequency) wave packets and rotational discontinuities (RDs) in a dispersive two-fluid plasma. A 1-D numerical hybrid code with ion simulation particles and a massless electron fluid is used. The evolution, speed, and structure of strongly modulated wave packets, which propagate parallel to an external magnetic field, are investigated as a function of helicity, amplitude, [beta]([identical to]8[pi]P/B[sup 2]), and [beta][sub i]/[beta][sub e](=T[sub i]/T[sub c]). Gradients of the wave envelope have a substantial influence on wave speeds and other properties. Weakly nonlinear packets show wave coupling with structuring that qualitatively resembles wave solutions of the derivative nonlinear Schrodinger (DNLS) equation for all [beta] and [beta][sub i]/[beta][sub e]. Nonlinearity has its greatest impact on evolution when the initial packet speed and the linear sound speed of the plasma are equal. Strongly nonlinear Alfven wave packets do not undergo wave collapse, but do steepen for [beta] [approx lt] 1 and form substantial fast wave regions on their leading sides. An extensive parameter variation on the evolution of RDs is carried out. The RD structure has features in common with the evolution of both strongly modulated, nonlinear wave packets and linear dispersive wave propagation in oblique magnetic fields. For moderate [theta][sub B]([approx lt]45[degrees]), nonlinearity is important and strong coupling to a compressional component can occur in the main current layer. When [beta][sub i] = 0, there is a critical value of [beta][sub e] when the intermediate wavetrain moves from the downstream side of the RD to the upstream. As [beta][sub i]/[beta][sub e] increases, the spreading rate of the current layer increases for moderate [theta][sub B]. For large [theta][sub B], RDs with electron (ion) sense of rotation show increased (decreased) spreading with increasing [beta][sub i]/[beta][sub e].

• Research Organization: Maryland Univ., College Park, MD (United States)
• OSTI ID: 7041617
• Country of Publication: United States
• Language: English

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