2D PIC Simulations Research Articles

Ion motion in strongly magnetized cluster laser plasma

Abstract This paper investigates the interaction of high intensity, circularly polarized, short laser pulses with heavy cluster plasma through analytical modelling and numerical simulations. The optimal parameters were found for the generation of several GigaGs, quasi-stationary magnetic field by using the upgraded analytical model and detailed 3D PIC simulations. It was confirmed that a field of such strength slows down the thermal expansion of the cluster core in the direction transverse to the laser beam axis, which can be used in nuclear physics. The generated inward shocks produce ion core compression, which is relevant to nuclear fusion. The electrostatic interaction between the rotating laser field, electrons and ions leads to ion spiral density distribution in the cluster’s transversal plane, which is absent in a cluster irradiated by linearly polarized pulses with the same parameters.

Electron Dynamics in a Relativistic Central Field Approach Associated with Laser Acceleration of Electrons

We perform 2D PIC simulations and observe different scenarios of electron trajectories trapped inside the bubble formed during the laser wakefield acceleration process (LWFA). The trajectories can close on the inside or on the outside of the bubble. The evolution of maximum energy of the injected electrons in both cases is evaluated. We propose an analytic approach based on a relativistic central field model for describing the attraction of electrons near the bubble edge and compare it with the simulations.

Self-compression of laser pulses induced by asymmetric self-phase modulation aided by backward Raman scattering in periodic density-modulated plasma.

Here a mechanism for self-compression of laser pulses is presented, based on period density-modulated plasma. In this setup, two pump beams intersect at a small angle within the plasma. This interaction is facilitated by the ponderomotive ion mechanism, which causes a modulation in the density of plasma with long wavelengths and low amplitude. This modulation enhances the backward Raman scattering of the probe pulse. The trailing edge of the probe experiences greater energy loss, resulting in a steeper intensity gradient. This, in turn, induces an asymmetric self-phase modulation, which elevates the instantaneous frequency. It is notable that the laser in plasma exhibits opposite group velocity dispersion compared to traditional solid-state media. This unique property allows laser pulses to undergo dispersion compensation while broadening the spectrum, ultimately leading to self-compression. The 2D-PIC simulations demonstrate these phenomena, highlighting how period density-modulated plasma contributes to an asymmetric spectral distribution. The intricate interplay among self-phase modulation, group velocity, and backward Raman scattering results in the self-compressing of the laser pulse. Specifically, the pulses are compressed from their Fourier transform limit duration of 50 fs to a significantly reduced duration of 8 fs at plasma densities below 1/4 critical density, without the transverse self-focusing effects.

Generation of ultra-intense vortex laser from a binary phase square spiral zone plate.

With the development of ultra-intense laser technology, the manipulation of relativistic laser pulses has become progressively challenging due to the limitations of damage thresholds for traditional optical devices. In recent years, the generation and manipulation of ultra-intense vortex laser pulses by plasma has attracted a great deal of attention. Here, we propose a new scheme to produce a relativistic vortex laser. This is achieved by using a relativistic Gaussian drive laser to irradiate a plasma binary phase square spiral zone plate (BPSSZP). Based on three-dimensional particle-in-cell (3D-PIC) simulations, we find that the drive laser has a phase difference of π after passing through the BPSSZP, ultimately generating the vortex laser with unique square symmetry. Quantitatively, by employing a drive laser pulse with intensity of 1.3 × 1018~W/cm2, a vortex laser with intensity up to 1.8 × 1019~W/cm2, and energy conversion efficiency of 18.61% can be obtained. The vortex lasers generated using the BPSSZP follow the modulo-4 transmutation rule when varying the topological charge of BPSSZP. Furthermore, the plasma-based BPSSZP has exhibited robustness and the ability to withstand multiple ultra-intense laser pulses. As the vortex laser generated via the BPSSZP has high intensity and large energy conversion efficiency, our scheme may hold potential applications in the community of laser-plasma, such as particles acceleration, intense high-order vortex harmonic generation, and vortex X/γ-ray sources.

On the impact of short laser pulses on cold diluted plasmas

We analytically study the impact of a (possibly, very intense) short laser pulse onto an inhomogeneous cold diluted plasma at rest, in particular: the duration of the hydrodynamic regime; the formation and the features of plasma waves (PWs); their wave-breakings (WBs); the motion of test electrons injected in the PWs.If the pulse is a plane wave travelling in the z-direction, and the initial plasma density (IPD) depends only on z, then suitable matched bounds on the maximum and relative variations of the IPD, as well as the intensity and duration of the pulse, ensure a strictly hydrodynamic evolution of the electron fluid during its whole interaction with the pulse, while ions can be regarded as immobile. This evolution is ruled by a family (parametrized by Z≥0) of decoupled systems of non-autonomous Hamilton equations with 1 degree of freedom, which determine how electrons initially located in the layer Z≤z<Z+dZ move; ξ=ct−z replaces time t as the independent variable. This family of ODEs is obtained by reduction from the Lorentz–Maxwell and continuity PDEs for the electrons’ fluid within the spacetime region where the change of the pulse is negligible. After the laser–plasma interaction the Jacobian of the map from Lagrangian to Eulerian coordinates is linear-quasi-periodic in ξ. We determine spacetime locations and features of the first wave-breakings of the wakefield PWs, the motion of test electrons (self-)injected in the PWs. The energy of those trapped in a single PW trough grows linearly with the distance gone, where the IPD is constant.If the pulse has cylindrical symmetry and a not too small radius, the same conclusions hold for the part of the plasma enclosed within the causal cone swept by it.This computationally light approach may help in a preliminary study of extreme acceleration mechanisms of electrons (LWFA, etc.), before 2D or 3D PIC simulations.

Computationally studying H- extraction and beamlet formation: the impact of the plasma model

The ITER NBI requires H-/D- beamlets with a low divergence, to maximize the transmitted power through the beamline. Ion extraction and beamlet formation are typically studied with gun-type codes such as IBSimu, which do not treat the plasma explicitly. These codes neglect many physical processes, such as the surface production of negative ions, particle drifts in the plasma as a result of magnetic fields, and sheath formation at surfaces. 3D PIC simulations show that the Debye sheath, which forms between the plasma and the plasma grid, has an impact on the optics of negative ions extracted from the plasma. In this paper, a repelling potential around the plasma grid is implemented ad-hoc in the IBSimu plasma model. The impact of the sheath is investigated for the BUG-MLE grid system for negative ions that come from the plasma. An electron repelling sheath increases the H- extraction probability since fewer particles are lost on the plasma grid, however the extracted current density at the edge of the aperture is reduced. The sheath increases the perpendicular energy distribution of the extracted H-, because particles are reflected towards the extraction region. In the underperveant regime, the sheath decreases the divergence, since it prevents H- from being extracted at the edge of the aperture, and these particles are highly divergent in the underperveant regime. The divergence optimum is shifted towards lower extracted current density with the sheath. The sheath leads to a higher minimum divergence due to the increased perpendicular energy distribution in the extraction region and the changed current density distribution.

Probing bulk electron temperature via x-ray emission in a solid density plasma

Bulk electron temperatures are calculated for thin Cu targets irradiated by the petawatt class Vulcan laser, from the Kα yield obtained using highly oriented pyrolytic graphite crystals. Cu-Kα emission studies have been used to probe the bulk electron temperature. A 30–80 eV core temperature extends homogeneously over distances up to ten times the laser focal spot size. Energy shifting has been observed due to different ionization states produced for different temperatures in the plasma. Polarization dependencies of plasma temperature are observed through the production of x-rays in different targets. 2D PIC simulations were performed to measure the polarization dependency of bulk electron temperature, which supports our experimental results. This paper could be of importance in understanding the different behavior of laser coupling at different polarizations and their role in x-ray production.

3D PIC Simulations for relativistic jets with a toroidal magnetic field

ABSTRACT We have investigated how kinetic instabilities such as the Weibel instability (WI), the mushroom instability (MI), and the kinetic Kelvin–Helmholtz instability (kKHI) are excited in jets without and with a toroidal magnetic field, and how such instabilities contribute to particle acceleration. In this work, we use a new jet injection scheme, where an electric current is self-consistently generated at the jet orifice by the jet particles, which produce the toroidal magnetic field. We perform five different simulations for a sufficiently long time to examine the non-linear effects of the jet evolution. We inject unmagnetized e± and e−– p+ (mp/me = 1836), as well as magnetized e± and e−– i+ (mi/me = 4) jets with a top-hat jet density profile into an unmagnetized ambient plasmas of the same species. We show that WI, MI, and kKHI excited at the linear stage, generate a non-oscillatory x-component of the electric field accelerating, and decelerating electrons. We find that the two different jet compositions (e± and e−– i+) display different instability modes, respectively. Moreover, the magnetic field in the non-linear stage generated by different instabilities is dissipated and reorganized into new topologies. A 3D magnetic field topology depiction indicates possible reconnection sites in the non-linear stage, where the particles are significantly accelerated by the dissipation of the magnetic field associated to a possible reconnection event.

High brilliance γ-ray generation from the laser interaction in a carbon plasma channel

The generation of collimated, high brilliance γ-ray beams from a structured plasma channel target is studied by means of 2D PIC simulations. Simulation results reveal an optimum laser pulse duration of 20 fs for generating photon beams of brilliances up to 1020 s−1mm−1mrad−2 (0.1 %BW)−1 with photon energies well above 200 MeV in the interaction of an ultra-intense laser (incident laser power PL ≥ 5 PW) with a high-Z carbon structured plasma target. These results are aimed at employing the upcoming laser facilities with multi-petawatt (PW) laser powers to study the laser-driven nonlinear quantum electrodynamics processes in an all-optical laboratory setup.

Stabilized Radiation Pressure Acceleration and Neutron Generation in Ultrathin Deuterated Foils.

Premature relativistic transparency of ultrathin, laser-irradiated targets is recognized as an obstacle to achieving a stable radiation pressure acceleration in the "light sail" (LS) mode. Experimental data, corroborated by 2D PIC simulations, show that a few-nm thick overcoat surface layer of high Z material significantly improves ion bunching at high energies during the acceleration. This is diagnosed by simultaneous ion and neutron spectroscopy following irradiation of deuterated plastic targets. In particular, copious and directional neutron production (significantly larger than for other in-target schemes) arises, under optimal parameters, as a signature of plasma layer integrity during the acceleration.

3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field

3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field

Vacuum breakdown in magnetic dipole wave by 10-PW class lasers.

The vacuum breakdown by 10-PW-class lasers is studied in the optimal configuration of laser beams in the form of an m-dipole wave, which maximizes the magnetic field. Using 3D PIC simulations we calculated the threshold of vacuum breakdown, which is about 10PW. We examined in detail the dynamics of particles and identified particle trajectories which contribute the most to vacuum breakdown in such highly inhomogeneous fields. We analyzed the dynamics of the electron-positron plasma distribution on the avalanche stage. It is shown that the forming plasma structures represent concentric toroidal layers and the interplay between particle ensembles from different spatial regions favors vacuum breakdown. Based on the angular distribution of charged particles and gamma photons a way to experimentally identify the process of vacuum breakdown is proposed.

Mixing the Solar Wind Proton and Electron Scales. Theory and 2D-PIC Simulations of Firehose Instability

Firehose-like instabilities (FIs) are cited in multiple astrophysical applications. Of particular interest are the kinetic manifestations in weakly collisional or even collisionless plasmas, where these instabilities are expected to contribute to the evolution of macroscopic parameters. Relatively recent studies have initiated a realistic description of FIs, as induced by the interplay of both species, electrons and protons, dominant in the solar wind plasma. This work complements the current knowledge with new insights from linear theory and the first disclosures from 2D-PIC simulations, identifying the fastest growing modes near the instability thresholds and their long-run consequences on the anisotropic distributions. Thus, unlike previous setups, these conditions are favorable to those aperiodic branches that propagate obliquely to the uniform magnetic field, with (maximum) growth rates higher than periodic, quasi-parallel modes. Theoretical predictions are, in general, confirmed by the simulations. The aperiodic electron FI (a-EFI) remains unaffected by the proton anisotropy, and saturates rapidly at low-level fluctuations. Regarding the FI at proton scales, we see a stronger competition between the periodic and aperiodic branches. For the parameters chosen in our analysis, the aperiodic proton FI (a-PFI) is excited before than the periodic proton FI (p-PFI), with the latter reaching a significantly higher fluctuation power. However, both branches are significantly enhanced by the presence of anisotropic electrons. The interplay between EFIs and PFIs also produces a more pronounced proton isotropization.

3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field

AbstractParticle-in-Cell simulations can provide a possible answer to an important key issue for astrophysical plasma jets; namely on how a toroidal magnetic field affects the evolution of pair and electron-ion jets. We show that Weibel, mushroom, and kinetic Kelvin-Helmhotz instabilities excited at the linear stage, generate a quasi-steady x-component of the electric field which accelerates and decelerates electrons. We observe significant differences in the structure of the strong electromagnetic fields that are driven by the kinetic instabilities with the pair jet. We find that the two different jet compositions (e± and e– - i+) generate different instability modes respectively. Moreover, the magnetic field in the non-linear stage generated by different instabilities is dissipated and reorganized into new topologies. A 3D magnetic field topology depiction indicates possible reconnection sites in the non-linear stage where the particles are significantly accelerated by the dissipation of the magnetic field associated to a possible reconnection manifestation.

Proton Beam Generated in PW Laser Interaction With Nano-Structure Array for Proton Therapy

In comparison with large and expensive conventional linear and circular accelerator, miniaturized laser-driven proton accelerator provides the potential to reduce the overall costs. This could allow a widespread use of the superior properties of protons and ions in radiation therapy. However, the key to success is to improve the particle energy which is not high enough to meet the requirement for the treatment. With the development of high-repetition-rate petawatt class laser technology matures gradually, different acceleration mechanisms have been able to raise the energy of protons to close to 100MeV.To confirm the feasibility of proton beam generated in petawatt-laser irradiating nano-array target, three-dimensional particle-in-cell (3D-PIC) simulations were performed with the QED-PIC code EPOCH. The simulation box has a size of 30 μm(x) × 20 μm (y) × 20 μm (z), which is sampled by cells of 1500 × 400 × 400 with 125 pseudo-electrons, eight pseudo-carbons, and four protons in each cell. The Gaussian laser pulse propagates along the x-direction with y-direction polarization, a wavelength λ0 of 1μm, a peak power of 50 PW, and a duration of 30 fs in full width at half maximum (FWHM). With an initial focal spot radius σ = 3μm. In order to reduce the computational requirements. The array wires have an initial density of ne = 300nc (where nc = 1.1 × 1021 cm-3 is the critical plasma density) and are attached to a 4-μm-thick CH foil. In these simulations, periodic boundary conditions were employed for the laser field in the transverse directions and absorbing boundary conditions for the particles.Three-dimensional particle-in-cell simulation show that the laser-driven proton beam keep quite different characteristics compared with other accelerators proton beam, such as ultra-short beam duration (ns), high strength (107 / cm2 / pulse), large divergence angle (2°) and poly real-energetic spectrum. Meanwhile, we show that under optimal interaction conditions protons can be accelerated up to relativistic energies of 300 MeV by a petawatt laser field. The proton acceleration is due to the dragging Coulomb force arising from charge separation induced by the ponderomotive pressure ∼light pressure! of high-intensity laser.We investigate the impact of nano-structure array on the proton spectrum for different laser-plasma conditions. Our simulated data show that the nanostructures lead to a significant enhancement of absorption over the entire range of laser plasma conditions investigated. At conditions that do not allow for efficient laser absorption by plane targets, nano-structure array is found to significantly enhance the proton cut-off energy and conversion efficiency.S. Wu: None. Z. Wang: None. X. Sun: None. W. Wang: None. F. Xiao: None. L. Zhao: None.

3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field

3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field

3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field

3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field

3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field

3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field

Conditions of rogue-wave generation in gyrotrons

Based on a single mode distributed non-stationary model of the gyrotron, we investigate the influence of the non-uniformity of the guiding magnetic field on the processes of rogue-wave generation. We estimate the allowable level of non-uniformity at which the statistical properties of the system are retained. 3D PIC simulations of a Ka-band gyrotron fully verify the theoretical predictions.

3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field

3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field