Study of dynamical plasma processes in stellar winds.

In this thesis the dynamical processes in stellar winds are investigated. Varioustypes of stellar objects are considered. In the first partof the thesis the processesin the winds of rapidly rotating, magnetized astrophysical objects are studied.Particularly, in the first chapter the charged particle acceleration due to therotating magnetic field, which is frozen in central object is studied. In the firstsection of the second chapter the motion of test particles along rotating curvedtrajectories is considered. The problem is studied both in the laboratory andthe rotating frames of reference. It is assumed that the system rotates withconstant angular velocity. The solutions are found and analyzed for the casewhen the form of the trajectory is given by an Archimedean spiral. It is foundthat particles can reach infinity while they move along these trajectories and thephysical interpretation of their behavior is given. The analogy of this idealizedstudy with the motion of particles along the curved rotating magnetic field linesin the pulsar magnetosphere is pointed out. An accelerated, charged, particle radiates and due to this emission itloses its kinetic energy. In other word, due to the emission the particleis affected by Radiation Reaction forces ( RR force ). In the second sectionof the second chapter we study the influence of Radiation Reaction forces, on thedynamics of centrifugally accelerated particles. It is assumed that the particlesmove along magnetic fieldlines anchored in the rotating central object. Thecommon bead-on-the-wire approximation is used. The solutions are found andanalyzed for cases when the form of the prescribed trajectory (rigidly rotating fieldline) is approximated by: (a) straight line, and (b) Archimedeanspiral. Dynamicsof particles not influenced by radiation reaction and the particles affected by RRforce are compared with the emphasizeon the role of RR forces in the latter case.It is shown that for charged particles there exist locations of stable equilibrium. Itis demonstrated that for particular initial conditions RR forces cause centripetalmotion of the particles: their falling on thecentral rotating object. It is foundthat in the case of Archimedeanspiral in both cases, when RR force is takeninto account and neglected, particles can reach infinity where their motion hasasymptotically force-free character. The possible importance of these processesfor the acceleration of relativistic, charged particles by rotating magnetospheresin the context of the generation of nonthermal, high-energy emission of pulsars isdiscussed. In the third chapter a process of generation of a toroidal component of largescale magnetic field, leading to the reconstruction of the pulsar magnetospheres ispresented. In order to understand twisting of magnetic field lines, we investigatethe kinematics of a plasma stream co-rotating in the pulsar magnetosphere.Studying an exact set of equations describing the behavior of relativistic plasmaflows, the incrementof the curvature drift instability is derived, and estimated for1-second pulsars. It is shown that a new parametric process is very efficient andit can explain rotation energy pumping in the pulsar magnetospheres.In the second section of the thesis, we focus on the dynamicalprocesses in thesolar wind. The evolution of magnetic clouds (MC) and their interaction withambient solar wind is investigated. In the fourth chapter we present an analyticalstudy of the dynamics of the MCs. In the first section of the fourth chapter wemodel and study the plasma parameters in the vicinity of interplanetary MCs.To this end we present a model in which the MCs are immersed in a magnetisedplasma flow with a homogeneous magnetic field. We first calculate the resultingdistortion of the external magnetic field and then determine the plasma velocity byemploying the frozen-in condition. Subsequently,the plasma density and pressureare expressed as functions of the magnetic field and the velocity field. The plasmaflow parameters are determined by solving MHD equations for both the stationaryregime andfor the case of an expanding cylindrical magnetic cloud, thus extendingprevious results that appeared in the literature. In the second section of the fourth chapter in order to study the evolution ofthe magnetic clouds the self-similar approach method is used. It isshown thatthe electromagnetic and the forces caused by gradient of the thermalpressure are balanced in the considered self-similarly evolving, cylindricallysymmetric magnetic structures. Explicit analytical expressions for magnetic field,plasma velocity, density and pressure within MCs are derived.In the fifth chapter we study the dynamics of the magnetic clouds using numericalcodes. In the first section of the fifth chapter we investigate the dynamics ofself-similarly evolving MCs by means of the numerical code Graale . The MCsare characterized by a density lower than in ambient solar wind andby a plasma β smaller than that in solar wind, therefore we study theirexpansion in a medium with higher density and higher plasma β . It is shown thatthe physical parameters of the MCs, such as density, pressure, magnetic andvelocity fields, maintain their self-similar character throughouttheir evolution. In the second section of the fifth chapter the 3-D numerical code (which is one ofthe versions of code CRONOS ) is used in order to investigate the dynamicsof the MCs. It is shown that initially, the analytical models represent someobservationalfeatures of the MCs. However, these characteristics are maintainedonly in those structures which move with a velocity close to the velocityof thebackground flow. In this case MC s evolution can quite accurately be describedby an analytic, self-similar approach. The dynamicsof the magnetic structureswhich move with a velocity much above or below that of the velocity of solar wind,is investigated in some detail. The case when an MC rotates around its axis isalso considered and the influence of rotation on the MC dynamics is studied. Acomparison of the numerical results with observational data indicates reasonableagreement especially for the intermediate case, in which two velocities (MC s bulkvelocity and velocity of background flow) are equal. In the particular case ofanalytical solutions obtained on the basis of the self-similar approach, describethe MC s evolution quite accurately. In general, however, numerical simulationruns are beneficial to investigate the evolution of these magnetic structures for thevarious sets of initial parameters.status: publishe