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A. G. Khachatryan

Publications and source records attributed to A. G. Khachatryan.

12 recordsLinked to original sources
arXiv2009

Generation of stable ultra-relativistic attosecond electron bunches via the laser wakefield acceleration mechanism

In recent experiments ultra-relativistic femtosecond electron bunches were generated by a Laser Wakefield Accelerator (LWFA) in different regimes. Here we predict that even attosecond bunches can be generated by an LWFA due to the fast betatron phase mixing within a femtosecond electron bunch. The attosecond bunches are stable outside the LWFA and can propagate in vacuum many tens of centimeter without significant change in their duration. Our calculations show that evidence for the formation of attosecond bunches can be found in the spectrum of coherent betatron radiation from LWFA's.

physics.acc-ph↗
arXiv2008

Electron bunch injection at an angle into a laser wakefield

External injection of electron bunches longer than the plasma wavelength in a laser wakefield accelerator can lead to the generation of femtosecond ultrarelativistic bunches with a couple of percent energy spread. Extensive study has been done on external electron bunch (e.g. one generated by a photo-cathode rf linac) injection in a laser wakefield for different configurations. In this paper we investigate a new way of external injection where the electron bunch is injected at a small angle into the wakefield. This way one can avoid the ponderomotive scattering as well as the vacuum-plasma transition region, which tend to destroy the injected bunch. In our simulations, the effect of the laser pulse dynamics is also taken into account. It is shown that injection at an angle can provide compressed and accelerated electron bunches with less than 2% energy spread. Another advantage of this scheme is that it has less stringent requirements in terms of the size of the injected bunch and there is the potential to trap more charge.

physics.plasm-ph↗
arXiv2008

Electromagnetic radiation from a laser wakefield accelerator

Coherent and incoherent electromagnetic radiation emitted from a laser wakefield accelerator is calculated based on Lienard-Wiechert potentials. It is found that at wavelengths longer than the bunch length, the radiation is coherent. The coherent radiation, which typically lies in the infrared range, shows features that reveal details of the acceleration process and properties of the electron bunch, such as its duration, charge, energy, and offset with respect to the wakefield axis. The incoherent range of the spectrum, which extends to the X-ray frequency range, consists of rather broad peaks, which are caused by the acceleration.

physics.acc-ph↗
arXiv2007

Dynamics of Femtosecond Electron Bunches

In the laser wakefield accelerator (LWFA) a short intense laser pulse, with a duration of the order of a plasma wave period, excites an unusually strong plasma wake wave (laser wakefield). Recent experiments on laser wakefield acceleration [Nature (London) 431, p.535, p.538, p.541 (2004)] demonstrated generation of ultra-short (with a duration of a few femtoseconds) relativistic electron bunches with relatively low energy spread of the order of a few percent. We have studied the dynamics of such bunches in vacuum and in laser wakefield. The results show strong bunch dynamics already on a few millimeters propagation distance in both cases. In vacuum, the bunch radius and emittance quickly grow. The latter worsens the focusability of the bunch. We found that when a femtosecond bunch is accelerated in a channel-guided laser wakefield, for realistic bunch lengths, the bunch length is approximately conserved. However, the spread in betatron frequencies leads to fast betatron phase mixing in the bunch envelope for on-axis injection. When bunch is injected in a laser wakefield off-axis, the bunch decoherence results in considerable increase in the normalized bunch emittance, and, in some cases, in increase in the energy spread, after acceleration. We also discuss a possible two-stage laser wakefield accelerator.

physics.plasm-ph↗
arXiv2006

Ponderomotive scattering of an electron-bunch before injection into a laser wakefield

For the purpose of laser wakefield acceleration, it turned out that also the injection of electron bunches longer than a plasma wavelength can generate accelerated femtosecond bunches with relatively low energy spread. This is of high interest because such injecting bunches can be provided, e.g., by state-of-the-art photo cathode RF guns. Here we point out that when an e-bunch is injected in the wakefield it is important to take into account the ponderomotive scattering of the injecting bunch by the laser pulse in the vacuum region located in front of the plasma. At low energies of the injected bunch this scattering results in a significant drop of the collection efficiency. Larger collection efficiency can by reached with lower intensity laser pulses and relatively high injection energies. We also estimate the minimum trapping energy for the injected electrons and the length of the trapped bunch.

physics.plasm-ph↗
arXiv2000

Magnetic Field of Relativistic Nonlinear Plasma Wave

Longitudinal and transverse behavior of magnetic field of relativistic nonlinear three-dimensional plasma wave is investigated. It is shown that the magnetic field of the wave is different from zero and performs higher frequency oscillations compared to the plasma electron frequency. An increase in the nonlinearity leads to strengthening of magnetic field. The oscillations of magnetic field in transverse direction arise, that caused by the phase front curving of nonlinear plasma wave. The numerical results well conform with predictions of the analytical consideration of weakly-nonlinear case.

physics.plasm-ph↗
arXiv2000

Method of laser-radiation guiding in plasma

The diffraction broadening of the intense laser radiation restricts its efficient use in many applications. Proposed in the present work is a method for laser radiation guiding in a density channel formed in plasma by a relativistic electron beam. The conditions and parameters of the relativistic beam ensuring the guiding by means of the proposed method have been examined.

physics.plasm-ph↗
arXiv1999

Two-Dimensional Nonlinear Regime in the Plasma Wakefield Accelerator

The effect of nonlinearity on plasma wake wave excited by a relativistic cylindrical charged bunch is investigated. It is shown that owing to the nonlinearity the amplitude of wake wave gets modulated in the longitudinal direction. The nonlinear wavelength in the excited field changes in the transverse direction with the result that the phase front is distored and a turbulence developed. The nonlinear phase front distortion may be compensated by radial change of unperturbed plasma density.

physics.acc-ph↗
arXiv1998

An Explicit Solution for Nonlinear Plasma Waves of Arbitrary Amplitude

Based on the known implicit solution for nonlinear plasma waves, an explicit solution was obtained in the form of decomposition into harmonics. The solution obtained exhibits a mechanism for steepening of nonlinear plasma wave as a result of increasing contribution of harmonics and may be used in theoretical studies of processes involving nonlinear plasma waves.

physics.plasm-ph↗
arXiv1998

Three-dimensional wake fields, generated in plasma by cylindrical electron bunch

The expressions for wake fields, generated in plasma (in the plasma waveguide or unlimited plasma) by relativistic electron bunch, was received and analyzed for the cases of the presence and absence of strong external longitudinal magnetic field. For the both cases the comparative analysis of the dependence of field amplitudes on the parameters of the electron bunch was done.

physics.acc-ph↗
arXiv1997

One Dimensional Nonlinear Wake-fields Excited in a Cold Plasma by Charged Bunches

One dimensional nonlinear plasma wake-fields excited by a single bunch and by series of bunches are considered. Essential differences are brought to light between negatively charged bunch case and positively one. The bunches with nonuniform distributions of density are investigated. The obtained results show dependence of excited potential electric fields on bunches parameters and allows to choose these parameters optimal.

physics.acc-ph↗