Tesis doctoral de Gonzalo Sánchez Arriaga
The generarion and nonlinear evolution of a low-frequency wavefront generated by electrodynamic tethers is analyzed. Two configurations are proposed; the first one in-volves an array of tethers earrying a time modulated current with frequency in the range of whistler waves. The second case lias a set of parallel tethers in a cylindrical configurarion and the modiilation frequency wonld be below rhe ion cyclor.Ron freqnency (mhd regime). The wavefronr wonld be excited rhrongh a parametric instability that involves pnmping by the radiare wave, with intensity and freqnency controlled. The pertnrbations in the plasma, that sarisfy certain resonance conditions within the radi-ated waves, are nnstable and they grow producing the wavefront. Characteristic valnes of growth rat.Es and other important design parameters such as the nnmber of tethers, currents, mass of the system, required power and dimensions have been determined for the ambient conditions in an experimenr at a low earth orbit. the derivative nonlinear schródinger equarion (dnls), that describes the dynamics of alfven waves propagating quasiparallel to the ambienr magnetic field, has been proposed to study the nonlinear evolution of a possible wavefront. As the parametric instability showed, some modes are strongly excited and it wonld become dominant; for a tentative study, a truncation model of the dnls may describe the dynamics of the waves in its early sr.Age. The dnls equation and two extensions, the tdnls equation with the sound wave coupled as well and the kdnls that includes kinetic effects, have been analyzed numerieally and with the previously mentioned truncation models. further on the possibility of the wavefront. Description, the truncation models have theoretical applications to plasma physics. The relationship between the modulational instability in rhe dnls and the tdnls equations and the phase space dynamics in their truncation models was investigated. When growth and dissipative terms were in-cluded. Both equations were solved numerieally and the dependence of gross dynamical ix e.T.S. Ingenieros aeronáuticos universidad politécnica de Madrid features on the dissipation strength were studied too. There are different dynami-cal regimens and, in some of them, the truncation model fit the solution properly. Very complex dynamics, such as blue sky catastrophes, chaotic attractors arising from feigenbaum sequences or intermittency have been found in both the original equations and their truncation models. the work is concluded with a topic quite far from the tether experiment. The dnls equation perturbed by a random forcing and a dissipative term due to the nonlinear landau damping (kdnls) has been proposed as a simple model for strong dispersive alfvenic turbulence. The energy transfer and the behaviour of the dnls solitons under such perturbations have been investigated numerically. The analysis has applications for both plasma turbulence and the magnetic hole formation in the solar wind. Finally, a truncation model of the kdnls equation is derived and the conservation of the helicity is discussed.
Datos académicos de la tesis doctoral «Nonlinear low-frequency wavefront generated by electrodynamic tethers«
- Título de la tesis: Nonlinear low-frequency wavefront generated by electrodynamic tethers
- Autor: Gonzalo Sánchez Arriaga
- Universidad: Politécnica de Madrid
- Fecha de lectura de la tesis: 06/07/2009
Dirección y tribunal
- Director de la tesis
- Juan Ramon Sanmartín Losada
- Tribunal
- Presidente del tribunal: Francisco javier Sanz recio
- enrico Lorenzini (vocal)
- Manuel Martínez sánchez (vocal)
- alain Hilgers (vocal)