72 research outputs found
Investigation of the Chaotic Dynamics of an Electron Beam with a Virtual Cathode in an External Magnetic Field
The effect of the strength of the focusing magnetic field on chaotic dynamic
processes occurring inan electron beam with a virtual cathode, as well as on
the processes whereby the structures form in the beamand interact with each
other, is studied by means of two-dimensional numerical simulations based on
solving a self-consistent set of Vlasov-Maxwell equations. It is shown that, as
the focusing magnetic field is decreased,the dynamics of an electron beam with
a virtual cathode becomes more complicated due to the formation andinteraction
of spatio-temporal longitudinal and transverse structures in the interaction
region of a vircator. The optimum efficiency of the interaction of an electron
beam with the electromagnetic field of the vircator isachieved at a
comparatively weak external magnetic field and is determined by the
fundamentally two-dimensional nature of the motion of the beam electrons near
the virtual cathode.Comment: 12 pages, 8 figure
Analysis and optimization of a free-electron laser with an irregular waveguide
Using a time-dependent approach the analysis and optimization of a planar
FEL-amplifier with an axial magnetic field and an irregular waveguide is
performed. By applying methods of nonlinear dynamics three-dimensional
equations of motion and the excitation equation are partly integrated in an
analytical way. As a result, a self-consistent reduced model of the FEL is
built in special phase space. The reduced model is the generalization of the
Colson-Bonifacio model and takes into account the intricate dynamics of
electrons in the pump magnetic field and the intramode scattering in the
irregular waveguide. The reduced model and concepts of evolutionary computation
are used to find optimal waveguide profiles. The numerical simulation of the
original non-simplified model is performed to check the effectiveness of found
optimal profiles. The FEL parameters are chosen to be close to the parameters
of the experiment (S. Cheng et al. IEEE Trans. Plasma Sci. 1996, vol. 24, p.
750), in which a sheet electron beam with the moderate thickness interacts with
the TE01 mode of a rectangular waveguide. The results strongly indicate that
one can improve the efficiency by a factor of five or six if the FEL operates
in the magnetoresonance regime and if the irregular waveguide with the
optimized profile is used
Experimental Study of the Effect of External Signal on Microwave Oscillations in a Nonrelativistic Electron Beam with Virtual Cathode
The effect of an external harmonic signal on the characteristics of microwave
generation in a nonrelativistic electron beam with virtual cathode (VC) formed
in a static retarding electric field (low-voltage vircator system) has been
experimentally studied. A significant increase in the vircator generation power
is observed when the frequency of the external signal is close to the frequency
of VC oscillations. At large detunings, a broadband chaotic generation is
observed.Comment: 3 pages, 2 figure
Experimental and Theoretical Investigation into the Effect of the Electron Velocity Distribution on Chaotic Oscillations in an Electron Beam under Virtual Cathode Formation Conditions
The effect of the electron transverse and longitudinal velocity spread at the
entrance to the interaction space on wide-band chaotic oscillations in intense
multiple-velocity beams is studied theoretically and numerically under the
conditions of formation of a virtual cathode. It is found that an increase in
the electron velocity spread causes chaotization of virtual cathode
oscillations. An insight into physical processes taking place in a virtual
cathode multiple velocity beam is gained by numerical simulation. The
chaotization of the oscillations is shown to be associated with additional
electron structures, which were separated out by constructing charged particle
distribution functions.Comment: 9 pages, 8 figure
Synchronisation schemes for two dimensional discrete systems
In this work we consider two models of two dimensional discrete systems
subjected to three different types of coupling and analyse systematically the
performance of each in realising synchronised states.We find that linear
coupling effectively introduce control of chaos along with
synchronisation,while synchronised chaotic states are possible with an additive
parametric coupling scheme both being equally relevant for specific
applications.The basin leading to synchronisationin the initial value plane and
the choice of parameter values for synchronisation in the parameter plane are
isolatedin each case.Comment: 17 pages 8 figures. submitted to physica script
Generalized Chaotic Synchronizationin Coupled Ginzburg-Landau Equations
Generalized synchronization is analyzed in unidirectionally coupled
oscillatory systems exhibiting spatiotemporal chaotic behavior described by
Ginzburg-Landau equations. Several types of coupling betweenthe systems are
analyzed. The largest spatial Lyapunov exponent is proposed as a new
characteristic of the state of a distributed system, and its calculation is
described for a distributed oscillatory system. Partial generalized
synchronization is introduced as a new type of chaotic synchronization in
spatially nonuniform distributed systems. The physical mechanisms responsible
for the onset of generalized chaotic synchronization in spatially distributed
oscillatory systems are elucidated. It is shown that the onset of generalized
chaotic synchronization is described by a modified Ginzburg-Landau equation
with additional dissipation irrespective of the type of coupling. The effect of
noise on the onset of a generalized synchronization regime in coupled
distributed systems is analyzed.Comment: 12 page
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