arXiv subjects

Vladimir Khudik

Publications and source records attributed to Vladimir Khudik.

13 recordsLinked to original sources

arXiv2022

Polarization control of electron injection and acceleration in the plasma by a self steepening laser pulse

We describe an interplay between two injection mechanism of background electrons into an evolving plasma bubble behind an intense laser pulse: one due to the overall bubble expansion, and another due to its periodic undulation. The two mechanisms occur simultaneously when an intense laser pulse propagating inside a plasma forms a shock like steepened front. Periodic undulations of the plasma bubble along the laser propagation path can either inhibit or conspire with electron injection due to bubble expansion. We show that Carrier Envelope Phase (CEP) controlled plasma bubble undulation induced by the self steepening laser pulse produces a unique electron injector: Expanding Phase controlled Undulating Bubble (EPUB). The longitudinal structure of the electron bunch injected by the EPUB can be controlled by laser polarization and power, resulting in high-charge (multiple nano Coulombs) high-current (tens of kilo Amperes) electron beams with ultra short (femtosecond scale) temporal structure. Generation of high energy betatron radiation with polarization and CEP controlled energy spectrum and angular distribution is analyzed as a promising application of EPUB produced beams.

physics.acc-ph↗

arXiv2022

WAND-PIC: an accelerated three-dimensional quasi-static particle-in-cell code

We introduce a quasi-static particle-in-cell (PIC) code -- WAND-PIC -- which does not suffer from some of the common limitations of many quasi-static PICs, such as the need for a predictor-corrector method in solving electromagnetic fields. We derive the field equations under quasi-static (QS) approximation and find the explicit form of the "time" derivative of the transverse plasma current. After that, equations for the magnetic fields can be solved exactly without using the predictor-corrector method. Algorithm design and code structure are thus greatly simplified. With the help of explicit quasi-static equations and our adaptive step size, plasma bubbles driven by the large beam charges can be simulated efficiently without suffering from the numerical instabilities associated with the predictor-corrector method. In addition, WAND-PIC is able to simulate the sophisticated interactions between high-frequency laser fields and beam particles through the method of sub-cycling. Comparisons between the WAND-PIC and a first-principle full PIC code (VLPL) are presented. WAND-PIC is open-source, fully three-dimensional, and parallelized with the in-house multigrid solver. Scalability, time complexity, and parallelization efficiency up to thousands of cores are also discussed in this work.

physics.plasm-ph↗

arXiv2021

Positron Acceleration in an Elongated Bubble Regime

A new concept is proposed for accelerating positrons in a nonlinear plasma wakefield accelerator. By loading the wakefield (back of the plasma bubble) with a short electron bunch, an extended area of excessive plasma electron accumulation is created after the first bubble, resulting in a favorable region with simultaneous focusing and accelerating fields for positrons. Scaling laws for optimized loading parameters are obtained through extensive parameters scans. Owing to the good quality of the focusing field, positron acceleration with emittance preservation can be achieved in this new regime and it has been demonstrated in the three-dimensional particle-in-cell simulations.

physics.plasm-ph↗

arXiv2021

Fermi acceleration in relativistic collisionless plasma shocks correlates with anisotropic energy gains

Collisionless shocks generated by two colliding relativistic electron-positron plasma shells are studied using particle-in-cell (PIC) simulations. Shocks are mediated by the Weibel instability (WI), and the kinetic energy of the fastest accelerated particles is found to be anisotropically modified by WI-induced electric fields. Specifically, we show that all particles interacting with the shock bifurcate into two groups based on their final relativistic Lorentz factor $γ$: slow ($γ< γ_{bf}$) and fast ($γ> γ_{bf}$), where $γ_{bf}$ is the bifurcation Lorentz factor that was found to be approximately twice the initial (upstream) Lorentz factor $γ_0$. We have found that the energies of the slow particles are equally affected by the longitudinal and transverse components of the shock electric field, whereas the fast particles are primarily accelerated by the transverse field component.

physics.plasm-ph↗

arXiv2021

Sub-femtosecond wakefield injector and accelerator based on an undulating plasma bubble controlled by a laser phase

We demonstrate that a long-propagating plasma bubble executing undulatory motion can be produced in the wake of two co-propagating laser pulses: a near-single-cycle injector and a multi-cycle driver. When the undulation amplitude exceeds the analytically derived threshold, highly-localized injections of plasma electrons into the bubble are followed by their long-distance acceleration. While the locations of the injection regions are controlled by the carrier-envelope phase (CEP) of the injector pulse, the mono-energetic spectrum of the accelerated sub-femtosecond high-charge electron bunches is shown to be nearly CEP-independent

physics.plasm-ph↗

arXiv2020

Laser-Ion Lens and Accelerator

Generation of highly collimated monoenergetic relativistic ion beams is one of the most challenging and promising areas in ultra-intense laser-matter interactions because of the numerous scientific and technological applications that require such beams. We address this challenge by introducing the concept of laser-ion lensing and acceleration (LILA). Using a simple analogy with a gradient-index lens, we demonstrate that simultaneous focusing and acceleration of ions is accomplished by illuminating a shaped solid-density target by an intense laser pulse at ~10^22 W/cm^2 intensity, and using radiation pressure of the laser to deform/focus the target into a cubic micron spot. We show that the LILA process can be approximated using a simple deformable mirror model, and then validate it using three-dimensional particle-in-cell simulations of a two-species plasma target comprised of electrons and ions. Extensive scans of the laser and target parameters identify the stable propagation regime where the Rayleigh-Taylor (RT)-like instability is suppressed. Stable focusing are found at different laser powers (from few- to multi-petawatt). Focused ion beams with the focused density of order 10^23 cm^-3, energies in access of 750MeV, and energy density up to 2*10^13 J/cm^3 at the focal point are predicted for future multi-petawatt laser systems.

physics.plasm-ph↗

arXiv2020

Laser-Pulse and Electron-Bunch Plasma Wakefield Accelerator

Propagation distances of intense laser pulses and high-charge electron beams through the plasma are, respectively, limited by diffraction and self-deceleration. This imposes severe constraints on the performance of the two major advanced accelerator concepts: laser and plasma wakefield accelerators. Using numerical simulations, we demonstrate that when the two beams co-propagate in the plasma, they can interact synergistically and extend each other's travel distances. The key interactions responsible for the synergy are found to be laser channeling by the electron bunch, and direct laser acceleration of the bunch electrons by the laser pulse. Remarkably, the amount of energy transferred from the laser pulse to the plasma can be increased by several times by the guiding electron bunch despite its small energy content. Implications of such synergistic interactions for the high-gradient acceleration of externally injected witness charges are discussed, and a new concept of a Laser-pulse and Electron-bunch Plasma Accelerator (LEPA) is formulated.

physics.plasm-ph↗

arXiv2020

Electron energization in upstream of collisionless electron/ion shocks produced by interpenetrating plasmas

We discuss the mechanism of electron energization in the upstream region of relativistic e/i shock. By using particle-in-cell simulations, we demonstrate the electrons interacting with enhanced electric and magnetic fields of the magnetic vortices (MVs) can gain a significant amount of energy during interaction. MVs are self generated in the upstream region of relativistic electron-ion shock.

physics.plasm-ph↗

arXiv2018

Direct laser acceleration of electrons by tightly focused laser pulses

We present an analytical theory that reveals the importance of the longitudinal laser electric field in the resonant acceleration of relativistic electrons by the tightly confined laser beam. It is shown that this field always counterworks to the laser transverse component and effectively decreases the final energy gain of electrons through direct laser acceleration mechanism. This effect is demonstrated by carrying out the particle-in-cell simulations in the setup where the wakefield in the plasma bubble is compensated by the longitudinal laser electric field experienced by the accelerated electrons. The derived scalings and estimates are in good agreement with numerical simulations.

physics.plasm-ph↗

arXiv2017

Nonlinear plasma waves driven by short ultrarelativistic electron bunches

We advance a theory of quasistatic approximation and investigate the excitation of nonlinear plasma waves by the driving beam of ultrarelativistic electrons using novel electrostatic-like particle- in-cell code. Assuming that the beam occupies an infinitesimally small volume, we find the radius and length of the plasma bubble formed in the wake of the driver for varying values of the beam charge. The mechanism of the bubble formation is explained by developing simple models of the bubble at large charges. Plasma electrons expelled by the driver charge excite secondary plasma waves which complicate the plasma electron flow near the bubble boundary.

physics.plasm-ph↗

arXiv2016

Far-field constant-gradient laser accelerator of electrons in an ion channel

We predict that electrons in an ion channel can gain ultra-relativistic energies by simultaneously interacting with a laser pulse and, counter-intuitively, with a decelerating electric field. The crucial role of the decelerating field is to maintain high-amplitude betatron oscillations, thereby enabling constant rate energy flow to the electrons via the direct laser acceleration mechanism. Multiple harmonics of the betatron motion can be employed. Injecting electrons into a decelerating phase of a laser wakefield accelerator is one practical implementation of the scheme.

physics.plasm-ph↗

arXiv2016

Universal scalings for laser acceleration of electrons in ion channels

Direct laser acceleration of electrons in ion channels is investigated in a general case when the laser phase velocity is greater than (or equal to) the speed of light. Using the similarity of the equations of motion for ultra-relativistic electrons, we develop a universal scaling theory that gives the maximum possible energy that can be attained by an electron for given laser and plasma parameters. The theory predicts appearance of forbidden zones in the phase space of the particle, which manifests itself as an energy gain threshold. We apply the developed theory to find the conditions needed for an energy enhancement via a resonant interaction between the third harmonic of betatron oscillations and the laser wave. The theory is also used to analyze electron dynamics in a circularly polarized laser.

physics.plasm-ph↗

arXiv2011

Collisionless filamentation, filament merger and heating of low-density relativistic electron beam propagating through a background plasma

A cold electron beam propagating through a background plasma is subject to filamentation process due to theWeibel instability. If the initial beam radius is large compared with the electron skin depth and the beam density is much smaller than the background plasma density, multiple filaments merge many times. Because of this non-adiabatic process, the beam perpendicular energy of initially cold beam grows until all filaments coalesce into one pinched beam with the beam radius much smaller than initial radius and smaller than the electron skin depth. It was shown through particle-in-cell simulations that a significant fraction of the beam is not pinched by the magnetic forces of the pinched beam and fills most of the plasma region. The resulting electron beam energy distribution in the perpendicular direction is close to a Maxwellian for the bulk electrons. However, there are significant departures from a Maxwellian for low and high perpendicular energy (deeply trapped and untrapped electrons). An analytical model is developed describing the density profile of the resulting pinched beam and large low-density halo around it. Based on this analytical model, a calculation of the energy transfer from the beam longitudinal kinetic energy to the transverse beam kinetic energy, the self-magnetic field, and the plasma electrons is performed. Results of analytical theory agree well with the particle-in-cell simulations results.

physics.plasm-ph↗