arXiv subjects

Alexey Arefiev

Publications and source records attributed to Alexey Arefiev.

25 records · Page 2Linked to original sources

arXiv2021

Emission of electromagnetic waves as a stopping mechanism for nonlinear collisionless ionization waves in a high-$β$ regime

A high energy density plasma embedded in a neutral gas is able to launch an outward-propagating nonlinear electrostatic ionization wave that traps energetic electrons. The trapping maintains a strong sheath electric field, enabling rapid and long-lasting wave propagation aided by field ionization. Using 1D3V kinetic simulations, we examine the propagation of the ionization wave in the presence of a transverse MG-level magnetic field with the objective to identify qualitative changes in a regime where the initial thermal pressure of the plasma exceeds the pressure of the magnetic field ($β>1$). Our key finding is that the magnetic field stops the propagation by causing the energetic electrons sustaining the wave to lose their energy by emitting an electromagnetic wave. The emission is accompanied by the magnetic field expulsion from the plasma and an increased electron loss from the trapping wave structure. The described effect provides a mechanism mitigating rapid plasma expansion for those applications that involve an embedded plasma, such as high-flux neutron production from laser-irradiated deuterium gas jets.

physics.plasm-ph↗

arXiv2020

Electron confinement by laser-driven azimuthal magnetic fields during direct laser acceleration

A laser-driven azimuthal plasma magnetic field is known to facilitate electron energy gain from the irradiating laser pulse. The enhancement is due to changes in the orientation between the laser electric field and electron velocity caused by magnetic field deflections. Transverse electron confinement is critical for realizing this concept experimentally. We find that the phase velocity of the laser pulse has a profound impact on the transverse size of electron trajectories. The transverse size remains constant below a threshold energy that depends on the degree of the superluminosity and it increases with the electron energy above the threshold. This increase can cause electron losses in tightly focused laser pulses. We show using 3D particle-in-cell simulations that the electron energy gain can be significantly increased by increasing laser power at fixed intensity due to the increased electron confinement. This finding makes a strong case for designing experiments at multi-PW laser facilities.

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↗

arXiv2018

Optimized setups for detection of Megatesla-level magnetic fields through Faraday rotation of XFEL beams

A solid density target irradiated by a high-intensity laser pulse can become relativistically transparent, which then allows it to sustain an extremely strong laser-driven longitudinal electron current. The current generates a filament with a slowly-varying MT-level azimuthal magnetic field that has been shown to prompt efficient emission of multi-MeV photons in the form of a collimated beam required for multiple applications. This work examines the feasibility of using an x-ray beam from the European XFEL for the detection of the magnetic field via the Faraday rotation. Post-processed 3D particle-in-cell simulations show that, even though the relativistic transparency dramatically reduces the rotation in a uniform target, the detrimental effect can be successfully reversed by employing a structured target containing a channel to achieve a rotation angle of $10^{-4}$ rad. The channel must be relativistically transparent with an electron density that is lower than the near-solid density in the bulk. The detection setup has been optimized by varying the channel radius and the focusing of the laser pulse driving the magnetic field. We predict that the Faraday rotation can produce $10^3$ photons with polarization orthogonal to the polarization of the incoming 100 fs long probe beam with $5 \times 10^{12}$ x-ray photons. Based on the calculated rotation angle, the polarization purity must be much better than $10^{-8}$ in order to detect the signal above the noise level.

physics.plasm-ph↗

arXiv2017

Leveraging extreme laser-driven magnetic fields for gamma-ray generation and pair production

The ability of an intense laser pulse to propagate in a classically over-critical plasma through the phenomenon of relativistic transparency is shown to facilitate the generation of strong plasma magnetic fields. Particle-in-cell simulations demonstrate that these fields significantly enhance the radiation rates of the laser-irradiated electrons, and furthermore they collimate the emission so that a directed and dense beam of multi-MeV gamma-rays is achievable. This capability can be exploited for electron-positron pair production via the linear Breit-Wheeler process by colliding two such dense beams. Presented simulations show that more than $10^3$ pairs can be produced in such a setup, and the directionality of the positrons can be controlled by the angle of incidence between the beams.

physics.plasm-ph↗

arXiv2016

Enhanced proton acceleration in an applied longitudinal magnetic field

Using two-dimensional particle-in-cell simulations, we examine how an externally applied strong magnetic impacts proton acceleration in laser-irradiated solid-density targets. We find that a kT-level external magnetic field can sufficiently inhibit transverse transport of hot electrons in a flat laser-irradiated target. While the electron heating by the laser remains mostly unaffected, the reduced electron transport during proton acceleration leads to an enhancement of maximum proton energies and the overall number of energetic protons. The resulting proton beam is much better collimated compared to a beam generated without applying a kT-level magnetic field. A factor of three enhancement of the laser energy conversion efficiency into multi-MeV protons is another effect of the magnetic field. The required kT magnetic fields are becoming feasible due to a significant progress that has been made in generating magnetic fields with laser-driven coils using ns-long laser pulses. The predicted improved characteristics of laser-driven proton beams would be critical for a number of applications.

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↗