Engineering topics
Publications and source records attributed to Buti, B..
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The Ulysses mission goes to the polar regions of the heliosphere and therefore is an ideal mission to study Alfven waves and discontinuities.
Nonlinear dynamics, of large-amplitude circularly polarized Alfvenic wave packets, is investigated using a one-dimensional hybrid model.
Spatio-temporal evolution, of large-amplitude Alfven waves, is investigated by means of their characteristic evolution equations as well as by MHD simulations.
Nonlinear evolution equation for Alfven waves, propagating in streaming plasmas with nonuniform densities and inhomogeneous magnetic fields, is obtained by using the reductive perturbation technique.
A nonlinear wave, in general, is equivalent to a nonlinear dynamical system, which exhibits the phenomena of chaos.
We report four different types of plasma waves detected in the near the dayside polar cap boundary layer (PCBL) region at high altitudes (>6 R***sub E***).
We report the first finding of a pair of forward and reverse slow-mode shocks in the distant heliosphere using plasma and magnetic field data from the Ulysses spacecraft located at 5.3 AU and 9 degrees South heliolatitude.
Alfven waves are a ubiquitous feature of the solar wind. One approach to studying the evolution of such waves has been to study exact solutions to approximate evolution equations. Here we compare soliton solutions of the Derivative Nonlinear Schrodinger evolution equation (DNLS) to solutions of the compressible MHD equations.
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Nonlinear evolution equation for Alfven waves, propagating in streaming plasmas with nonuniform densities and inhomogeneous magnetic fields, is obtained by using reductive perturbation technique.
The chaos in a one-dimensional system, which would be nonlinear stationary Alfven waves in the absence of an external driver, is characterized. The evolution equations are numerically integrated for the transverse wave magnetic field amplitude and phase using the derivative nonlinear Schroedinger equation (DNLS), including resistive wave damping and a long-wavelength monochromatic, circularly polarized driver. A Poincare map analysis shows that, for the nondissipative (Hamiltonian) case, the solutions near the phase space (soliton) separatrices of this system become chaotic as the driver amplitude increases, and 'strong' chaos appears when the driver amplitude is large. The dissipative system exhibits a wealth of dynamical behavior, including quasiperiodic orbits, period-doubling bifurcations leading to chaos, sudden transitions to chaos, and several types of strange attractors.
Some features of steepened magnetosonic waves are discussed with reference to the Giacobini-Zinner data set. In particular, attention is given to the discovery of discrete intervals of both phase rotation and lack of phase rotation within a single wavelength and also to the presence of intervals of 'backward' rotations (right-hand polarized in the spacecraft frame) within the magnetosonic wave. Possible explanations of these features are reviewed, and it is suggested that these features are nonlinear manifestations of the wave steepening process.
In a weakly inhomogeneous plasma, the large-amplitude Alfven waves propagating parallel to the ambient magnetic field are shown to evolve into accelerated Alfven solitons. Nonlinear interaction of the accelerated Alfven solitons with the Langmuir waves results in the emission of coherent radiations. Analytical expression for the power radiated per unit solid angle from a soliton is derived for two inhomogeneity profiles, namely the linear profile and the parabolic profile. For the case of uniform plasmas, the emission occurs via a decay-type process or resonant modes. In the presence of inhomogeneity, nonresonant modes provide a new channel for the emission of radiation. The power radiated per unit solid angle is computed for the parameters relevant to Comet Halley's plasma environment. For the nonresonant modes it is found to be several orders of magnitude higher than that for the case of resonant modes.
Results are presented of a study designed to confirm the suspected relation between Alfven solitons (steepened Afven waves) and rotational discontinuities (RDs) in the solar wind. The ISEE 3 data were used to search for the predicted correlations between the beta value of plasma, the sense of polarization of the discontinuity, and changes of the magnetic field strength and plasma density across the discontinuity. No statistically significant evidence was found for the evolution of RDs from Alfven solitons. A possibility is suggested that the observations made could have been far from the regions in which the RDs were formed.
Observational as well as semitheoretical magnetic field profiles have been used to derive self-consistently the plasma conductivity profiles for the ionosphere of Comet Halley. The characteristic diffusion length for the field, according to the present model, is about 28 km; this is in very good agreement with the Giotto spacecraft observations. It is shown that ideal MHD as well as constant conductivity models are not appropriate for the study of dynamical structure of the Halley's ionosphere.
Magnetic pulses with durations near the local proton cyclotron period (in the spacecraft frame) have been detected during the ICE encounter with Comet Giacobini-Zinner. The pulses typically last only a single cycle (solitary wave), are transverse, noncompressional oscillations, and have peak-to-peak transverse amplitudes of 2-3 nT. Occasional large pulses with amplitudes of 5-7 nT have been detected. The waves typically propagate at angles 2-15 deg relative to B(O) and are highly ellipticlly (linearly) polarized. The pulses have been detected when alpha, the angle between the ambient magnetic field and the solar wind velocity, is 90 + or - 30 deg and when ICE was 350,000-700,000 km from the comet. At the present time it is uncertain whether such pulses are generated exclusively under large alpha conditions or whether the presence of large-amplitude heavy ion cyclotron waves during more moderate alpha conditions masks their presence. It is also unclear whether these pulses are superposed on top of cometary turbulence or simply a part of it. The above observations will be compared to recent theoretical predictions of cometary waves generated during large alpha conditions.