Laser Acceleration Of Electrons Research Articles

Experimental signatures of direct-laser-acceleration-assisted laser wakefield acceleration

The direct laser acceleration (DLA) of electrons in a laser wakefield accelerator (LWFA) operating in the forced or quasi-blowout regimes has been investigated through experiment and simulation. When there is a significant overlap between the trapped electrons and the drive laser in a LWFA cavity, the resulting electrons can gain energy from both the LWFA and the DLA mechanisms. Experimental work investigates the properties of the electron beams produced in a LWFA with ionization injection by dispersing those beams in the direction perpendicular to the laser polarization. These electron beams show certain spectral features that are characteristic of DLA. These characteristic features are reproduced using particle-in-cell simulations, where particle tracking was used to elucidate the roles of LWFA and DLA to the energy gain of the electrons in this experimental regime and to demonstrate that such spectral features are definitive signatures of the presence of DLA in LWFA.

Multidimensional effects on proton acceleration using high-power intense laser pulses

Dimensional effects in particle-in-cell (PIC) simulation of target normal sheath acceleration (TNSA) of protons are considered. As the spatial divergence of the laser-accelerated hot sheath electrons and the resulting space-charge electric field on the target backside depend on the spatial dimension, the maximum energy of the accelerated protons obtained from three-dimensional (3D) simulations is usually much less than that from two-dimensional (2D) simulations. By closely examining the TNSA of protons in 2D and 3D PIC simulations, we deduce an empirical ratio between the maximum proton energies obtained from the 2D and 3D simulations. This ratio may be useful for estimating the maximum proton energy in realistic (3D) TNSA from the results of the corresponding 2D simulation. It is also shown that the scaling law also applies to TNSA from structured targets.

Extremely intense laser-based electron acceleration in a plasma channel

Laser pulses of extreme intensities () are about to become available in the laboratory. The prepulse of such a laser can induce a plasma expansion that generates a low-density channel in near-critical gas jets. We present a study of channel formation and subsequent direct laser acceleration of electrons within the pre-formed channel. Radiation reaction affects the acceleration in several ways. It first interferes with the motion of the return current on the channel walls. In addition, it reduces the radial expelling efficiency of the transverse ponderomotive force, leading to the radiative trapping of particles near the channel axis. These particles then interact with the peak laser intensity and can attain multi-GeV energies.

Resonant enhancement of accelerating gradient with silicon dual-grating structure for dielectric laser acceleration of subrelativistic electrons

We show that the accelerating gradient of a dual-grating structure for dielectric laser acceleration of subrelativistic electrons can be enhanced by resonating with the zeroth diffraction order inside the channel. We analyze diffraction of light at a subwavelength grating (SWG) to illustrate the principle of the resonant enhancement. We present examples of dual-grating resonators for 50 keV electrons with different channel widths. The dependence of reflectivity and phase on the SWG dimensions provides flexibility in controlling the enhancement factor and filling time, thus enabling high-gradient acceleration driven by ultrashort low-power laser pulses.

Aneutronic pB-Reaction in Magnetized Inertial Confined Plasma of Laser-Accelerated Particles

A brief review on studies aimed at initiating a neutronless nuclear reaction between protons and boron nuclei is presented. The least energy-cost of a currently known approach to ignition of pB reaction is proposed using a petawatt laser for producing a magnetized plasma of laser-accelerated ions and electrons as well as using a terawatt laser for inertial confinement of such a plasma.

A novel approach to electron data background treatment in an online wide-angle spectrometer for laser-accelerated ion and electron bunches.

Laser-based ion acceleration is driven by electrical fields emerging when target electrons absorb laser energy and consecutively leave the target material. A direct correlation between these electrons and the accelerated ions is thus to be expected and predicted by theoretical models. We report on a modified wide-angle spectrometer, allowing the simultaneous characterization of angularly resolved energy distributions of both ions and electrons. Equipped with online pixel detectors, the RadEye1 detectors, the investigation of this correlation gets attainable on a single shot basis. In addition to first insights, we present a novel approach for reliably extracting the primary electron energy distribution from the interfering secondary radiation background. This proves vitally important for quantitative extraction of average electron energies (temperatures) and emitted total charge.

Strongly Mismatched Regime of Nonlinear Laser–Plasma Acceleration: Optimization of Laser-to-Energetic Particle Efficiency

Laser electron accelerators utilize a bubble regime of nonlinear plasma waves driven as laser wakefields that, from theoretical considerations, require a matched laser spot size incident on plasma. A strongly mismatched regime of nonlinear laser–plasma acceleration in the bubble regime, favored by experiments, is introduced and modeled for optimization of laser-to-particle energy efficiency with application to the recently proposed laser positron accelerator. Strong mismatch, in contrast with the matched condition, arises from the incident laser spot size being much larger than that needed for equilibration of the laser ponderomotive and electron-ion charge-separation forces in the nonlinearly driven density structure of a plasma bubble. This is shown to be favorable for optimization of large self-injected electron charge and ultralow transverse emittance without precluding beam spectral shaping. It is shown that there are prominent signatures of the mismatched regime, strong optical-shock excitation, and bubble elongation, which are validated using multidimensional particle-in-cell simulations. This paper thus uncovers a generalized regime that apart from being used in many laser–plasma acceleration experiments also opens a novel pathway for a wide range of future applications.

Ultrafast multi-MeV gamma-ray beam produced by laser-accelerated electrons

Ultrafast multi-MeV high-flux gamma-ray beams have been experimentally produced via bremsstrahlung radiation of laser-accelerated energetic electrons through millimeter-thick copper targets. By optimizing the electron bunches to the charge of 10 nC in a clustering argon gas target, the obtained gamma-ray beam significantly increases to 1010 photons per shot. The gamma-ray beam spectrum has been measured using a differential filtering detector and has a broad spectrum up to 15 MeV, which is approximately consistent with the Geant4 simulation. The generated high-flux high-energy gamma-ray beams are promising sources for photonuclear reaction, non-destructive inspection and clinical applications.

Stable multi-GeV electron accelerator driven by waveform-controlled PW laser pulses

The achievable energy and the stability of accelerated electron beams have been the most critical issues in laser wakefield acceleration. As laser propagation, plasma wave formation and electron acceleration are highly nonlinear processes, the laser wakefield acceleration (LWFA) is extremely sensitive to initial experimental conditions. We propose a simple and elegant waveform control method for the LWFA process to enhance the performance of a laser electron accelerator by applying a fully optical and programmable technique to control the chirp of PW laser pulses. We found sensitive dependence of energy and stability of electron beams on the spectral phase of laser pulses and obtained stable 2-GeV electron beams from a 1-cm gas cell of helium. The waveform control technique for LWFA would prompt practical applications of centimeter-scale GeV-electron accelerators to a compact radiation sources in the x-ray and γ-ray regions.

Laser Acceleration of Electrons in Magnetized Collisionless Plasma

Laser Acceleration of Electrons in Magnetized Collisionless Plasma

Two-color monochromatic x-ray imaging with a single short-pulse laser.

Simultaneous monochromatic crystal imaging at 4.5 and 8.0 keV with x-rays produced by a single short-pulse laser is presented. A layered target consisting of thin foils of titanium and copper glued together is irradiated by the 50 TW Leopard short-pulse laser housed at the Nevada Terawatt Facility. Laser-accelerated MeV fast electrons transmitting through the target induce Kα fluorescence from both foils. Two energy-selective curved crystals in the imaging diagnostic form separate monochromatic images on a single imaging detector. The experiment demonstrates simultaneous two-color monochromatic imaging of the foils on a single detector as well as Kα x-ray production at two different photon energies with a single laser beam. Application of the diagnostic technique to x-ray radiography of a high density plasma is also presented.

Relativistic laser hosing instability suppression and electron acceleration in a preformed plasma channel

The hosing processes of a relativistic laser pulse, electron acceleration, and betatron radiation in a parabolic plasma channel are investigated in the direct laser acceleration regime. It is shown that the laser hosing instability would result in the generation of a randomly directed off-axis electron beam and radiation source with a large divergence angle. While employing a preformed parabolic plasma channel, the restoring force provided by the plasma channel would correct the perturbed laser wave front and thus suppress the hosing instability. As a result, the accelerated electron beam and the emitted photons are well guided and concentrated along the channel axis. The employment of a proper plasma density channel can stably guide the relativistically intense laser pulse and greatly improve the properties of the electron beam and radiation source. This scheme is of great interest for the generation of high quality electron beams and radiation sources.

DOSIMETRIC EVALUATION OF LASER-DRIVEN X-RAY AND NEUTRON SOURCES UTILIZING XG-III PS LASER WITH PEAK POWER OF 300 TERAWATT.

Current short-pulse high-intensity lasers can accelerate electrons and proton/ions to energies of giga-electron volts. For certain advanced applications, laser-accelerated electrons and protons are optimised for high-energy X-ray and neutron generation at the XG-III picosecond (ps) laser beamline. These energetic X-ray and neutron beams can significantly affect radiation safety at the facility; therefore, proper evaluation of the radiological hazards induced by laser-driven X-ray and neutron sources is required. This study presents a dosimetric evaluation of laser-driven X-ray and neutron sources at the XG-III ps laser beamline. The 'source terms' of the laser-accelerated electrons and protons are characterised utilising the particle-in-cell method and an analytical model, respectively. The Monte Carlo code FLUKA is used to calculate prompt and residual dose yields due to all radiation field components and the number of residual activated nuclei. Our results can provide a reference for radiation hazard analysis at short-pulse high-intensity laser facilities worldwide.

Improvement of hot-electron and gamma-ray yields by selecting preplasma thickness for a target irradiated by a short laser pulse

The dependences of the temperature and the number of hot electrons on the size of the plasma corona of a thin foil target irradiated by a short relativistically intense laser pulse are investigated by three-dimensional numerical simulations. For a 30-fs long laser pulse with an energy of 300 mJ we have determined the optimal preplasma size which maximises the yield of forward-accelerated electrons capable of generating gamma-ray photons several MeV in energy. A study is made of gamma-ray generation by such laser-accelerated electrons in the bombardment of a converter target placed behind the laser target; the brightness of this gamma-ray source is shown to range up to 1015 photons s−1 mrad−2 mm−2 × (0.1 % BW)−1.

Role of Direct Laser Acceleration of Electrons in a Laser Wakefield Accelerator with Ionization Injection.

We show the first experimental demonstration that electrons being accelerated in a laser wakefield accelerator operating in the forced or blowout regimes gain significant energy from both the direct laser acceleration (DLA) and the laser wakefield acceleration mechanisms. Supporting full-scale 3D particle-in-cell simulations elucidate the role of the DLA of electrons in a laser wakefield accelerator when ionization injection of electrons is employed. An explanation is given for how electrons can maintain the DLA resonance condition in a laser wakefield accelerator despite the evolving properties of both the drive laser and the electrons. The produced electron beams exhibit characteristic features that are indicative of DLA as an additional acceleration mechanism.

Breaking of dynamical adiabaticity in direct laser acceleration of electrons

The interaction of an electron oscillating in an ion channel and irradiated by a plane electromagnetic wave is considered. It is shown that the interaction qualitatively changes with the increase of electron energy, as the oscillations across the channel become relativistic. The “square-wave-like” profile of the transverse velocity in the relativistic case enables breaking of the adiabaticity that precludes electron energy retention in the non-relativistic case. For an electron with a relativistic factor γ0, the adiabaticity breaks if ωL/ωp0≪γ0. Under these conditions, the kinetic energy acquired by the electron is retained once the interaction with the laser field ceases. This mechanism notably enables electron heating in regimes that do not require a resonant interaction between the initially oscillating electron and the laser electric field.

Terahertz generation from laser-driven ultrafast current propagation along a wire target.

Generation of intense coherent THz radiation by obliquely incidenting an intense laser pulse on a wire target is studied using particle-in-cell simulation. The laser-accelerated fast electrons are confined and guided along the surface of the wire, which then acts like a current-carrying line antenna and under appropriate conditions can emit electromagnetic radiation in the THz regime. For a driving laser intensity ∼3×10^{18}W/cm^{2} and pulse duration ∼10 fs, a transient current above 10 KA is produced on the wire surface. The emission-cone angle of the resulting ∼0.15 mJ (∼58 GV/m peak electric field) THz radiation is ∼30^{∘}. The conversion efficiency of laser-to-THz energy is ∼0.75%. A simple analytical model that well reproduces the simulated result is presented.

Optimized Silicon Asymmetric Dual-Pillar Grating for Dielectric Laser Acceleration of Subrelativistic Electrons with Enhanced Accelerating Gradient

Optimized Silicon Asymmetric Dual-Pillar Grating for Dielectric Laser Acceleration of Subrelativistic Electrons with Enhanced Accelerating Gradient

Dosimetric properties of plasma density effects on laser-accelerated VHEE beams using a sharp density-transition scheme

In this paper, the effects of the plasma density on laser-accelerated electron beams for radiation therapy with a sharp density transition are investigated. In the sharp density-transition scheme for electron injection, the crucial issue is finding the optimum density conditions under which electrons injected only during the first period of the laser wake wave are accelerated further. In this paper, we report particle-in-cell simulation results for the effects of both the scale length and the densitytransition ratio on the generation of a quasi-mono-energetic electron bunch. The effects of both the transverse parabolic channel and the plasma length on the electron-beam’s quality are investigated. Also, we show the experimental results for the feasibility of a sharp density-transition structure. The dosimetric properties of these very high-energy electron beams are calculated using Monte Carlo simulations.

Preface to Special Issue on Development of Laser Electron-Accelerator for XFEL (X-Ray Free Electron Laser)

Preface to Special Issue on Development of Laser Electron-Accelerator for XFEL (X-Ray Free Electron Laser)