arXiv subjects

Kavin Tangtartharakul

Publications and source records attributed to Kavin Tangtartharakul.

6 recordsLinked to original sources

arXiv2025

Complete reflection of nonlinear electromagnetic waves in underdense pair plasmas enabled by dynamically formed Bragg-like structures

In contrast to relativistically induced transparency in electron--ion plasmas, where nonlinear electromagnetic waves render initially opaque plasmas transparent, we show using kinetic simulations that such waves can instead make initially transparent pair plasmas fully reflective. The difference is mass symmetry, which eliminates charge-separation electric fields. As the wave compresses the pair plasma, weak reflection seeds density spikes that form a moving Bragg-like grating. Enhanced reflection enables a transition to a regime where the plasma--vacuum interface sustains complete reflection.

physics.plasm-ph↗

arXiv2025

Enhanced energy gain through higher-order resonances during direct laser acceleration with superluminal phase velocity

Ultra-high intensity laser-plasma interactions can produce ultra-relativistic electrons via direct laser acceleration, assisted by quasi-static plasma magnetic and electric fields. These fields transversely confine electron motion and induce betatron oscillations. The net energy gain is strongly influenced by the interplay between two frequencies: the betatron frequency and the frequency of laser field oscillations experienced by the electron. Prior work has shown that energy gain is enabled by a resonance between the betatron oscillations and the oscillations of the laser field. In particular, higher-order resonances occur when the laser field completes multiple cycles during one betatron oscillation, allowing additional regimes of energy transfer beyond the fundamental (betatron) resonance. In this work, we demonstrate that such resonances become particularly effective when the laser's phase velocity is superluminal. Although the two frequencies generally evolve differently with increasing electron energy, which leads to detuning, a superluminal phase velocity introduces a non-monotonic frequency ratio with a global minimum. This minimum allows sustained frequency matching over a broad energy range, thereby enabling enhanced energy gain. As the phase velocity increases, the betatron resonance becomes ineffective due to premature frequency detuning. At the same time, higher-order resonances become increasingly effective, emerging as the dominant mechanisms for enhanced energy gain in this regime of direct laser acceleration.

physics.plasm-ph↗

arXiv2024

Collimated $\gamma$-ray emission enabled by efficient direct laser acceleration

We investigate the mechanisms responsible for single-lobed versus double-lobed angular distributions of emitted $\gamma$-rays in laser-irradiated plasmas, focusing on how direct laser acceleration (DLA) shapes the emission profile. Using test-particle calculations, we show that the efficiency of DLA plays a central role. In the inefficient DLA regime, electrons rapidly gain and lose energy within a single laser cycle, resulting in a double-lobed emission profile heavily influenced by laser fields. In contrast, in the efficient DLA regime, electrons steadily accumulate energy over multiple laser cycles, achieving much higher energies and emitting orders of magnitude more energy. This emission is intensely collimated and results in single-lobed profiles dominated by quasi-static azimuthal magnetic fields in the plasma. Particle-in-cell simulations demonstrate that lower-density targets create favorable conditions for some electrons to enter the efficient DLA regime. These electrons can dominate the emission, transforming the overall profile from double-lobed to single-lobed, even though inefficient DLA electrons remain present. These findings provide valuable insights for optimizing laser-driven $\gamma$-ray sources for applications requiring high-intensity, well-collimated beams.

physics.plasm-ph↗

arXiv2024

Efficient backward x-ray emission in a finite-length plasma irradiated by a laser pulse of ps duration

Motivated by experiments employing ps-long, kilojoule laser pulses, we examined x-ray emission in a finite-length underdense plasma irradiated by such a pulse using two dimensional particle-in-cell simulations. We found that, in addition to the expected forward emission, the plasma also efficiently emits in the backward direction. Our simulations reveal that the backward emission occurs when the laser exits the plasma. The longitudinal plasma electric field generated by the laser at the density down-ramp turns around some of the laser-accelerated electrons and re-accelerates them in the backward direction. As the electrons collide with the laser, they emit hard x-rays. The energy conversion efficiency is comparable to that for the forward emission, but the effective source size is smaller. We show that the ps laser duration is required for achieving a spatial overlap between the laser and the backward energetic electrons. At peak laser intensity of $1.4\times 10^{20}~\rm{W/cm^2}$, backward emitted photons (energies above 100~keV and $10^{\circ}$ divergence angle) account for $2 \times 10^{-5}$ of the incident laser energy. This conversion efficiency is three times higher than that for similarly selected forward emitted photons. The source size of the backward photons ($5~\rm{μm}$) is three times smaller than the source size of the forward photons.

physics.plasm-ph↗

arXiv2021

Particle integrator for particle-in-cell simulations of ultra-high intensity laser-plasma interactions

Particle-in-cell codes are the most widely used simulation tools for kinetic studies of ultra-intense laser-plasma interactions. Using the motion of a single electron in a plane electromagnetic wave as a benchmark problem, we show surprising deterioration of the numerical accuracy of the PIC algorithm with increasing normalized wave amplitude for typical time-step and grid sizes. Two significant sources of errors are identified: strong acceleration near stopping points and the temporal field interpolation. We propose adaptive electron sub-cycling coupled with a third order temporal interpolation of the magnetic field and electric field as an efficient remedy that dramatically improves the accuracy of the particle integrator.

physics.plasm-ph↗

arXiv2019

Extreme Nonlinear Dynamics in Vacuum Laser Acceleration with a Crossed Beam Configuration

A relatively simple model problem where a single electron moves in two relativistically-strong obliquely intersecting plane wave-packets is studied using a number of different numerical solvers. It is shown that, in general, even the most advanced solvers are unable to obtain converged solutions for more than about 100 fs in contrast to the single plane-wave problem, and that some basic metrics of the orbit show enormous sensitivity to the initial conditions. At a bare minimum this indicates an unusual degree of non-linearity, and may well indicate that the dynamics of this system are chaotic.

physics.plasm-ph↗