arXiv subjects

Sudip Sengupta

Publications and source records attributed to Sudip Sengupta.

28 records · Page 2Linked to original sources

arXiv2018

2-D fluid simulation of a rigid relativistic electron beam driven wakefield in a cold plasma

Fluid simulations, which are considerably simpler and faster, have been employed to study the behavior of the wakefield driven by a relativistic rigid beam in a 2-D cold plasma. When the transverse dimensions of the beam are chosen to be much larger than its longitudinal extent, a good agreement with our previous 1-D results [\textcolor{red}{\it Physics of Plasmas 22, 073109 (2015)}] are observed for both under-dense and over-dense beams. When the beam is overdense and its transverse extent is smaller or close to the longitudinal extension, the 2-D blow-out structure, observed in PIC simulations and analytically modeled by Lu et al. [\textcolor{red}{\it Phys. Rev. Lett., 96, 165002 (2006)}] are recovered. For quantitative assessment of particle acceleration in such a wake potential structure test electrons are employed. It is shown that the maximum energy gained by the test electrons placed at the back of the driver beam of energy $\sim 28.5$ GeV, reaches up to $2.6$ GeV in a 10 cm long plasma. These observations are consistent with the experimental results presented in ref. [\textcolor{red}{\it Phys. Rev. Lett. 95, 054802 (2005)}]. It is also demonstrated that the energy gained by the test electrons get doubled ($\sim 5.2$ GeV) when the test particles are placed near the axis at the end of the first blowout structure.

physics.plasm-ph↗

arXiv2018

Breaking of Large Amplitude Relativistically Intense Electron Plasma Waves in a Warm Plasma

In this paper, the effect of finite electron temperature on the space-time evolution and breaking of a large amplitude relativistically intense electron plasma wave has been studied, using a 1-D relativistic Particle-in-Cell (PIC) code. We have found that for phase velocities for which $γ_ϕ\ll 1 + \frac{k_BT_e}{mc^2}$, the wave damps within a few plasma period and essentially follows the relativistic Landau Damping rate predicted by Buti. In the opposite regime (i.e. for $γ_ϕ\gg 1 + \frac{k_BT_e}{mc^2}$) we have observed that waves propagate through the system for a long period of time and in small amplitude limit follow the relativistic warm plasma dispersion relation. Further we have demonstrated that in the same regime (i.e. for $γ_ϕ\gg 1 + \frac{k_BT_e}{mc^2}$), for the phase velocities less than the velocity of light $c$, like the cold plasma Akhiezer - Polovin wave, in a warm plasma also, relativistically intense waves break via phase mixing when perturbed by an arbitrarily small amplitude longitudinal perturbation. Using the simulation results, we have also shown that the phase mixing time scale in a warm plasma can be interpreted using Dawson's formula for phase mixing time for a non-relativistic cold inhomogeneous plasma, which is based on out of phase motion of neighbouring oscillators constituting the wave.

physics.plasm-ph↗

arXiv2017

Breaking of Large Amplitude Electron Plasma Wave in a Maxwellian Plasma

The determination of maximum possible amplitude of a coherent longitudinal plasma oscillation/wave is a topic of fundamental importance in non-linear plasma physics. The amplitudes of these large amplitude plasma waves is limited by a phenomena called wave breaking which may be induced by several non-linear processes. It was shown by Coffey [T. P. Coffey, Phys. Fluids 14, 1402 (1971)] using a "water-bag" distribution for electrons that, in a warm plasma the maximum electric field amplitude and density amplitude implicitly depend on the electron temperature, known as Coffey's limit. In this paper, the breaking of large amplitude freely running electron plasma wave in a homogeneous warm plasma where electron's velocity distribution is Maxwellian has been studied numerically using 1D Particle in Cell (PIC) simulation method. It is found that Coffey's propagating wave solutions, which was derived using a "water-bag" distribution for electrons, also represent propagating waves in a Maxwellian plasma. Coffey's wave breaking limit is also verified by loading Maxwellian velocity distributions of different initial temperatures. A clear correspondence between wave breaking and particle trapping is presented. Our simulation results are also compared with the experimental results of B. S. Bauer, A. Y. Wong, V. K. Decyk and G. Resenthal [Phys. Rev. Lett. 68, 3706 (1992)].

physics.plasm-ph↗

arXiv2017

Particle-in-cell simulation of Buneman instability beyond quasilinear saturation

Spatio-temporal evolution of Buneman instability has been followed numerically till its quasilinear quenching and beyond, using an in-house developed electrostatic 1D particle-in-cell simulation code. For different initial drift velocities $k_{L}v_{0}/ω_{pe} \approx 0.1 \, - \, 1$ and for a wide range of electron to ion mass ratios (m/M), growth rate obtained from simulation agrees well with the numerical solution of the fourth order dispersion relation. Quasi-linear saturation of Buneman instability occurs when ratio of electrostatic field energy density ($\sum\limits_{k} |E_{k}|^{2}/8π$) to initial electron drift kinetic energy density ($W_{0} = \frac{1}{2} n_{0}m v^{2}_{0}$) reaches up to a constant value, which as predicted by Hirose [Plasma Physics 20, 481(1978)], is independent of initial electron drift velocity but depends on electron to ion mass ratio m/M as $\sum\limits_{k} |E_{k}|^{2}/16πW_{0} \approx (m/M)^{1/3}$. This result stands verified in our simulations. Growth of the instability beyond the first saturation (quasilinear saturation ) till its final saturation [Ishihara et. al., PRL 44, 1404(1980)] follows an algebraic scaling with time. In contrast to the quasilinear saturation, the ratio of final saturated electrostatic field energy density to initial kinetic energy density, is relatively independent of electron to ion mass ratio and is found to depend only on the initial drift velocity. Beyond the final saturation, electron phase space holes coupled to large amplitude ion solitary waves, a state known as coupled hole-soliton , are seen in our simulations. The propagation characteristics ( amplitude - speed relation ) of these coherent modes is found to be consistent with the theory of Saeki et. al. [PRL 80, 1224(1998)].

physics.plasm-ph↗

arXiv2016

One dimensional PIC simulation of relativistic Buneman instability

Spatio-temporal evolution of the relativistic Buneman instability has been investigated in one dimension using an in-house developed particle-in-cell simulation code. Starting from the excitation of the instability, its evolution has been followed numerically till its quenching and beyond. As compared to the well understood non-relativistic case, it is found that the maximum growth rate ($γ_{max}$) reduces due to relativistic effects and varies with $γ_{e0}$ and m/M as $γ_{max} \sim \frac{\sqrt{3}}{2\sqrt{γ_{e0}}}\biglb(\frac{m}{2M}\bigrb)^{1/3}$, where $γ_{e0}$ is Lorentz factor associated with the initial electron drift velocity ($v_{0}$) and (m/M) is the electron to ion mass ratio. Further it is observed that in contrast to the non-relativistic results[Hirose,Plasma Phys. 20, 481(1978)] at the saturation point, ratio of electrostatic field energy density ($\sum\limits_{k} |E_{k}|^{2}/8π$) to initial drift kinetic energy density ($W_{0}$) scales with $γ_{e0}$ as $\sim 1/γ^{2}_{e0}$. These simulation results are found to be in good agreement with that derived using fluid theory.

physics.plasm-ph↗

arXiv2016

Phase Mixing of Relativistically Intense Longitudinal Wave Packets in a Cold Plasma

The spatio-temporal evolution and breaking of relativistically intense wave packets in a cold homogeneous unmagnetized plasma has been studied analytically and numerically. A general expression for phase mixing time scale as a function of amplitude of the wave packet and width of the spectrum has been derived. Results have been compared with the existing formulae in literature. It is shown that phase mixing time scale crucially depends on the relative magnitude of the amplitude and dimensionless spectral width of the wave packet. Finally we have verified our results with respect to both the amplitude of the wave packet and width of the spectral using numerical simulations based on Dawson Sheet Model.

physics.plasm-ph↗

arXiv2016

Relativistic electron beam driven longitudinal wake-wave breaking in a cold plasma

Space-time evolution of relativistic electron beam driven wake-field in a cold, homogeneous plasma, is studied using 1D-fluid simulation techniques. It is observed that the wake wave gradu- ally evolves and eventually breaks, exhibiting sharp spikes in the density profile and sawtooth like features in the electric field profile [1]. It is shown here that the excited wakefield is a longitudi- nal Akhiezer-Polovin mode [2] and its steepening (breaking) can be understood in terms of phase mixing of this mode, which arises because of relativistic mass variation effects. Further the phase mixing time (breaking time) is studied as a function of beam density and beam velocity and is found to follow the well known scaling presented in ref.[3].

physics.plasm-ph↗

arXiv2015

Radiation Reaction Effect on Laser Driven Auto-Resonant Particle Acceleration

The effects of radiation reaction force on laser driven auto-resonant particle acceleration scheme are studied using Landau-Lifshitz equation of motion. These studies are carried out for both linear as well as circularly polarized laser fields in the presence of static axial magnetic field. From the parametric study, a radiation reaction dominated region has been identified in which the particle dynamics is greatly effected by this force. In the radiation reaction dominated region the two significant effects on particle dynamics are seen viz., (1) saturation in energy gain by the initially resonant particle, (2) net energy gain by a initially non-resonant particle which is caused due to resonance broadening. It has been further shown that with the optimum choice of parameters this scheme can be efficiently used to produce electrons with energies in the range of hundreds of TeV. The quantum corrections to the Landu-Lifshitz equation of motion have also been taken into account. The difference in the energy gain estimates of the particle by the quantum corrected and classical Landu-Lifshitz equation are found to be insignificant for the present day as well as upcoming laser facilities.

physics.plasm-ph↗

arXiv2014

Analytical Estimate of Phase Mixing Time of Longitudinal Akhiezer - Polovin Wave

Phase mixing and eventual breaking of longitudinal Akhiezer - Polovin wave subjected to a small amplitude longitudinal perturbation is studied analytically. It is well known that longitudinal Akhiezer - Polovin wave breaks via the process of phase mixing at an amplitude well below its breaking amplitude, when subjected to arbitrarily small longitudinal perturbation[Phys. Rev. Lett.108, 125005 (2012)]. Here we analytically show that the phase mixing time (breaking time) has a linear dependence with phase velocity of the wave, inverse square dependence with the maximum fluid velocity and it is inversely proportional to the amplitude of perturbation. This analytical dependence of phase mixing time on the above three parameters is further verified using numerical simulations based on Dawson Sheet Model.

physics.plasm-ph↗

arXiv2008

Stability of nonlinear one-dimensional laser pulse solitons in a plasma

In a recent one-dimensional numerical fluid simulation study [Saxena et al., Phys. Plasmas 13,032309 (2006)], it was found that an instability is associated with a special class of one-dimensional nonlinear solutions for modulated light pulses coupled to electron plasma waves in a relativistic cold plasma model. It is shown here that the instability can be understood on the basis of the stimulated Raman scattering phenomenon and the occurrence of density bursts in the trailing edge of the modulated structures are a manifestation of an explosive instability arising from a nonlinear phase mixing mechanism.

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