Excitation of wakefield in a rectangular waveguide: Comparative study with different microwave pulses (original) (raw)
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Numerical studies on wakefield excited by Gaussian-like microwave pulse in a plasma filled waveguide
Optics Communications, 2009
Based on a differential equation derived analytically in terms of wakefield potential / MW in a plasma filled rectangular waveguide, we investigate the wakefield (E MW) generated with the help of Gaussianlike microwave pulse under the effect of microwave frequency (f), pulse duration (s), waveguide width (b), equilibrium plasma density (n 0) and microwave intensity (I). The study conducted for three cases of s > 1/f p , s = 1/f p and s < 1/f p , where f p is the plasma frequency, reveals that the amplitude of the wakefield is increased for the large pulse duration and higher microwave intensity but is decreased with the waveguide width and microwave frequency for all these cases. The wakefield shows stronger dependence on the microwave frequency when the microwave with larger intensity is used. The wakefield decreases at a faster rate with the waveguide width for the case of s > 1/f p .
Wakefield generation in a plasma filled rectangular waveguide
Open Plasma Phys. J, 2008
We study the wakefield in a plasma filled rectangular waveguide based on a differential equation derived in terms of the wake potential , when the pulse duration matches with inverse of the plasma frequency f p 1. This equation is solved using fourth-order Runge-Kutta method for the Gaussian-like profile of the microwave pulse. The effects of microwave frequency f , waveguide width b and microwave intensity I are investigated on the wakefield E W. The amplitude of the wakefield is found to increase with microwave pulse duration and its intensity, but it gets decreased with microwave frequency and waveguide width. By optimizing various parameters, we can achieve wakefield of appreciable strength for the purpose of particle acceleration.
Microwave and plasma interaction in a rectangular waveguide: Effect of ponderomotive force
Journal of Applied Physics, 2010
Studies on the propagation of high power microwave and its interaction with a plasma in a metallic waveguide are carried out. For this we consider the fundamental TE 10 mode that propagates in an evacuated rectangular waveguide and encounters a plasma which is filled in another waveguide of the same size. Using Maxwell's equations we evaluate the field components of the mode in the evacuated waveguide and then obtain coupled differential equations for the field components of the mode in the plasma filled waveguide, where the plasma effect enters in terms of its dielectric constant. These equations are solved numerically using the fourth-order Runge-Kutta method for the electric field amplitude of the microwave and its wavelength under the effect of plasma density, waveguide width, and microwave frequency. All the investigations are carried out for different initial plasma density profiles, namely homogeneous density, linear density with gradient in the propagation direction and the density with Gaussian profile along the waveguide width. The structure of the perturbed density due to the ponderomotive force exerted by the mode is also investigated under the effect of microwave parameters and waveguide width. Numerical studies are conducted for the isothermal plasma in the waveguide.
Electron acceleration in a rectangular waveguide filled with unmagnetized inhomogeneous cold plasma
Laser and Particle Beams, 2008
This paper deals with the study of propagation of electromagnetic wave in a rectangular waveguide filled with an inhomogeneous plasma in which electron density varies linearly in a transverse direction to the mode propagation. A transcendental equation in ω (microwave frequency) is obtained that governs the mode propagation. In addition, an attempt is made to examine the effect of density inhomogeneity on the energy gain acquired by the electron (electron bunch) when it is injected in the waveguide along the direction of the mode propagation. On the basis of angle of deflection of the electron motion we optimize the microwave parameters so that the electron does not strike with the waveguide walls. Conditions have been discussed for achieving larger energy gain. The plasma density inhomogeneity is found to play a crucial role on the cutoff frequency, fields and dispersion relation of the TE10 mode as well as on the acceleration gradient in the waveguide.
Acta Physica Academiae Scientiarum Hungaricae, 1980
Expressions for power reflection (R), transmission (T) and absorption (A) coefficients for TE modes for a homogeneous and collisional plasma slab (with sharp boundaries and thicknessd 0) which is moving with a constnat velocity (v) inside an infinitely long rectangular waveguide are investigated. The effects of slab velocity (β=v/c) and electron density (ωp /ω)2 on reflection, transmission and absorption coefficients are discussed numerically. It is observed that at low plasma density (ωp /ω)2=0.5,T andA are minimum, whereasR is maximum atβ=0. In case of high plasma density (ωp /ω)2=1.5, for high collision frequency,R andA; and for low collision frequency,R andT are more than unity in the limit −0.5 β
Generation of electron cyclotron resonance plasma in a rectangular waveguide by high power microwave
APS, 2002
The dispersion relation for plasma oscillations in a thin layered film is calculated in the SCF approximation for a model in which the electron motion along the film thickness is described like a tunnelling process between adjacent planes. For a semi-infinite medium the linear term in the dispersion relation of the surface plasmon is obtained. This is done using an appropriate expansion technique and in the limit of a 'greate' separation between adjacent planes.
Wakefield generation and GeV acceleration in tapered plasma channels
Physical Review E, 2001
To achieve multi-GeV electron energies in the laser wakefield accelerator ͑LWFA͒, it is necessary to propagate an intense laser pulse long distances in a plasma without disruption. One of the purposes of this paper is to evaluate the stability properties of intense laser pulses propagating extended distances ͑many tens of Rayleigh ranges͒ in plasma channels. A three-dimensional envelope equation for the laser field is derived that includes nonparaxial effects such as group velocity dispersion, as well as wakefield and relativistic nonlinearities. It is shown that in the broad beam, short pulse limit the nonlinear terms in the wave equation that lead to Raman and modulation instabilities cancel. This cancellation can result in pulse propagation over extended distances, limited only by dispersion. Since relativistic focusing is not effective for short pulses, the plasma channel provides the guiding necessary for long distance propagation. Long pulses ͑greater than several plasma wavelengths͒, on the other hand, experience substantial modification due to Raman and modulation instabilities. For both short and long pulses the seed for instability growth is inherently determined by the pulse shape and not by background noise. These results would indicate that the self-modulated LWFA is not the optimal configuration for achieving high energies. The standard LWFA, although having smaller accelerating fields, can provide acceleration for longer distances. It is shown that by increasing the plasma density as a function of distance, the phase velocity of the accelerating field behind the laser pulse can be made equal to the speed of light. Thus electron dephasing in the accelerating wakefield can be avoided and energy gain increased by spatially tapering the plasma channel. Depending on the tapering gradient, this luminous wakefield phase velocity is obtained several plasma wavelengths behind the laser pulse. Simulations of laser pulses propagating in a tapered plasma channel are presented. Experimental techniques for generating a tapered density in a capillary discharge are described and an example of a GeV channel guided standard LWFA is presented.
In this paper, we examine changes of the electric field distributions in waveguide-based axial-type microwave plasma source (MPS) during tuning procedure. The distributions strongly depend on position of the movable short, so does the wave reflection coefficient of the incident wave. A method of determining tuning characteristics of the MPS consisting in treating the MPS as a two-port network, finding its scattering matrix coefficients and then calculating the reflection coefficient from analytical expressions is proposed. The results of calculations show that the tuning characteristics depend on plasma parameters such as the electron density and on MPS dimensions such as the height of the reduced-height waveguide section. It is possible to find such a position of the movable short for which the reflected wave power is less than 10% of the incident wave power.
Electric and magnetic wakefields in a plasma channel
Physical Review Special Topics-accelerators and Beams, 2005
A detailed analytical study of plasma wakefield generation in a wide parabolic plasma channel is reported. A perturbative technique involving orders of the incident laser beam and the effects of inhomogeneity of the plasma density is used to obtain explicit electric as well as magnetic wakefields. The axial and transverse forces acting on a test electron due to the wakefields have been evaluated.