Quasi-monoenergetic Electron Beams Research Articles

Quasi-monoenergetic electron beam from LWFA: analytical approach

Analytical dependence of the energy spread of electron beam on time and injection duration has been obtained with the 1D model of the quasi-linear laser wakefield electron acceleration, presented as phase portraits of electron energy relative to the plasma wave phase. The method for producing electron beams with variable energy and a lower energy spread compared to a standard bubble-like approach by transferring to a deaccelerating part with another phase trajectory (by reducing the plasma amplitude of a wave) has been developed. The analytically obtained results successfully describe key features of the previously obtained in Tsymbalov et al (2024 arXiv:2403.19828) experimental and numerical (PIC) data.

Ultrarelativistic electron beams accelerated by terawatt scalable kHz laser

We show the laser-driven acceleration of unprecedented, collimated (2 mrad divergence), and quasi-monoenergetic (25% energy spread) electron beams with energy up to 50 MeV at 1 kHz repetition rate. The laser driver is a multi-cycle (15 fs) 1 kHz optical parametric chirped pulse amplification system, operating at 26 mJ (1.7 TW). The scalability of the driver laser technology and the electron beams reported in this work pave the way toward developing high-brilliance x-ray sources for medical imaging and innovative devices for brain cancer treatment and represent a step toward the realization of a kHz GeV electron beamline.

Modular supersonic nozzle for the stable laser-driven electron acceleration.

The sharp density down-ramp injection (shock injection) mechanism produces the quasi-monoenergetic electron beam with a bunch duration of tens of femtoseconds via laser wakefield acceleration. The stability of the accelerated electron beam strongly depends on the stability of the laser beam and the shock structure produced by the supersonic gas nozzle. In this paper, we report the study of a newly designed modular supersonic nozzle with a flexible stilling chamber and a converging-diverging structure. The performance of the nozzle is studied both numerically and experimentally with the computational fluid dynamics simulation and the Mach-Zehnder interferometry method. The simulation results and the experimental measurements are well consistent, and both prove the effectiveness of the stilling chamber in stabilizing the gas flow.

Spin-polarized electron beam generation in the colliding-pulse injection scheme

Employing colliding-pulse injection has been shown to enable the generation of high-quality electron beams from laser–plasma accelerators. Here, by using test particle simulations, Hamiltonian analysis, and multidimensional particle-in-cell simulations, we lay the theoretical framework for spin-polarized electron beam generation in the colliding-pulse injection scheme. Furthermore, we show that this scheme enables the production of quasi-monoenergetic electron beams in excess of 80% polarization and tens of pC charge with commercial 10-TW-class laser systems.

Laser-accelerated electron beams at 1 GeV using optically-induced shock injection

In recent years, significant progress has been made in laser wakefield acceleration (LWFA), both regarding the increase in electron energy, charge and stability as well as the reduction of bandwidth of electron bunches. Simultaneous optimization of these parameters is, however, still the subject of an ongoing effort in the community to reach sufficient beam quality for next generation’s compact accelerators. In this report, we show the design of slit-shaped gas nozzles providing centimeter-long supersonic gas jets that can be used as targets for the acceleration of electrons to the GeV regime. In LWFA experiments at the Centre for Advanced Laser Applications, we show that electron bunches are accelerated to {1}text {GeV} using these nozzles. The electron bunches were injected into the laser wakefield via a laser-machined density down-ramp using hydrodynamic optical-field-ionization and subsequent plasma expansion on a ns-timescale. This injection method provides highly controllable quasi-monoenergetic electron beams with high charge around {100}text {pC}, low divergence of {0.5}text {mrad}, and a relatively small energy spread of around {10}% at {1}text {GeV}. In contrast to capillaries and gas cells, the scheme allows full plasma access for injection, probing or guiding in order to further improve the energy and quality of LWFA beams.

Laser-driven low energy electron beams for single-shot ultra-fast probing of meso-scale materials and warm dense matter

Laser wakefield acceleration has proven to be an excellent source of electrons and X-rays suitable for ultra-fast probing of matter. These novel beams have demonstrated unprecedented spatial and temporal resolution allowing for new discoveries in material science and plasma physics. In particular, the study of dynamic processes such as non-thermal melt and lattice changes on femtosecond time-scales have paved a way to completely new scientific horizons. Here, we demonstrate the first single-shot electron radiography measurement using an femtosecond electron source based on the downramp-density gradient laser-wakefield-acceleration with the use of a compact Ti:sapphire laser. A quasi-monoenergetic electron beam with mean energy of 1.9 ± 0.4 MeV and charge 77 ± 47 pC per shot was generated by the laser incident onto a gas target and collimated using a two ring-magnet beam path. High quality electron radiography of solid objects with spatial resolution better than 150 upmum was demonstrated. Further developments of this scheme have the potential to obtain single-shot ultrafast electron diffraction from dynamic lattices. This scheme poses a great promise for smaller scale university laboratories and facilities for efficient single-shot probing of warm dense matter, medical imaging and the study of dynamic processes in matter with broad application to inertial confinement fusion and meso-scale materials (mg g/cm^2).

Observation of Monoenergetic Electrons from Two-Pulse Ionization Injection in Quasilinear Laser Wakefields

The generation of low emittance electron beams from laser-driven wakefields is crucial for the development of compact x-ray sources. Here, we show new results for the injection and acceleration of quasimonoenergetic electron beams in low amplitude wakefields experimentally and using simulations. This is achieved by using two laser pulses decoupling the wakefield generation from the electron trapping via ionization injection. The injection duration, which affects the beam charge and energy spread, is found to be tunable by adjusting the relative pulse delay. By changing the polarization of the injector pulse, reducing the ionization volume, the electron spectra of the accelerated electron bunches are improved.

Direct laser acceleration of electrons from a plasma mirror by an intense few-cycle Laguerre–Gaussian laser and its dependence on the carrier-envelope phase

A direct acceleration scheme to generate high-energy, high-charge electron beams with an intense few-cycle Laguerre–Gaussian (LG) laser pulse was investigated using three-dimensional particle-in-cell simulations. In this scheme, an intense LG laser pulse was irradiated onto a solid density plasma slab. When the laser pulse is reflected, electrons on the target front surface are injected into the longitudinal electric field of the laser and accelerated further. We found that the carrier-envelope phase (CEP) of the few-cycle laser pulse plays a key role in the electron injection and acceleration process. Using a three-cycle LG laser pulse with and an appropriate CEP, an about 60 pC electron beam could be obtained at a maximum energy of 16 MeV. In comparison, when a laser pulse with mismatched CEP was used, a total of 4 pC electron beam with a maximum energy of 3.5 MeV was obtained. Linear scaling of electron energy to the laser strength was shown up to at which a quasi-monoenergetic electron beam of 850 MeV energy with a charge equal to 600 pC could be obtained. These results demonstrate that high-energy electron beams can be stably generated through direct laser acceleration using a CEP-controlled intense few-cycle LG laser pulse.

Optimization of the beam quality in ionization injection by a tailoring gas profile* *Project supported by the National Natural Science Foundation of China (Grant Nos. 12005297, 11975308, and 11775305), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA25050200), the Fund of Science Challenge Project (Grant No. TZ2018001), Natural Science Foundation of Hunan Province, China (Grant No.

A new scheme is proposed to improve the electron beam quality of ionization-induced injection by tailoring gas profile in laser wakefield acceleration. Two-dimensional particle-in-cell simulations show that the ionization-induced injection mainly occurs in high-density stage and automatically truncates in low-density stage due to the decrease of the wakefield potential difference. The beam loading can be compensated by the elongated beam resulting from the density transition stage. The beam quality can be improved by shorter injection distance and beam loading effect. A quasi-monoenergetic electron beam with a central energy of 258 MeV and an energy spread of 5.1% is obtained under certain laser–plasma conditions.

Highly efficient few-cycle laser wakefield electron accelerator

A significant part of the laser wakefield acceleration (LWFA) research effort focuses on studying high-energy, quasi-monoenergetic electron beams. For other applications, such as the production and application of intense betatron x-ray radiation, Bremsstrahlung γ-rays and positron beams, the beam’s spectral quality is secondary to the number of electrons produced. This work discusses 3D particle-in-cell simulations of a highly efficient LWFA acceleration process, generating a broad spectrum of electrons, driven by a 12 TW few-cycle laser on high-density gas targets. In some cases, laser absorption in plasma exceeds 80%, and up to 27% of the driving laser energy is transferred to electrons over 20 MeV leaving the plasma. We also observe a deceleration of the accelerated beam at the plasma downramp and plasma exit, which arises from transitioning from laser-driven to beam-dominated wake, and also from the induced axial electric field. This effect is similar to magnetic vortex acceleration, where the induced axial electric field, instead of accelerating plasma ions, would slow down the opposite-charged electron beam and also a strong return current and backward electron beam.

Physics of High-Charge Electron Beams in Laser-Plasma Wakefields

Laser wakefield acceleration (LWFA) and its particle-driven counterpart, plasma wakefield acceleration (PWFA), are commonly treated as separate, though related branches of high-gradient plasma-based acceleration. However, novel proposed schemes are increasingly residing at the interface of both concepts where the understanding of their interplay becomes crucial. Here, we report on experiments covering a wide range of parameters by using nanocoulomb-class quasi-monoenergetic electron beams from LWFA with a 100-TW-class laser. Based on a controlled electron injection, these beams reach record-level performance in terms of laser-to-beam energy transfer efficiency (up to 10%), spectral charge density (regularly exceeding 10 pC/MeV) and divergence (1 mrad full width at half maximum divergence). The impact of charge fluctuations on the energy spectra of electron bunches is assessed for different laser parameters, including a few-cycle laser, followed by a presentation of results on beam loading in LWFA with two electron bunches. This scenario is particularly promising to provide high-quality electron beams by using one of the bunches to either tailor the laser wakefield via beam loading or to drive its own, beam-dominated wakefield. We present experimental evidence for the latter, showing a varying acceleration of a low-energy witness beam with respect to the charge of a high-energy drive beam in a spatially separate gas target. With the increasing availability of petawatt-class lasers the access to this new regime of laser-plasma wakefield acceleration will be further facilitated, thus providing new paths towards low-emittance beam generation for future plasma-based colliders or light sources.

Plasma bubble evolution in laser wakefield acceleration in a petawatt regime

The bubble regime of the laser wakefield acceleration is one of the most recent and promising mechanisms for generating quasi-monoenergetic electron beams. In this work, we propose to study the dynamics of bubble (a wake structure devoid of electrons created in underdense plasma by a highly-intense ultrashort laser pulse) in a petawatt regime. The dependence of the electron beam energy and the quality of the electron beam on the shape of the bubble is the main motivation behind this work. The bubble length as well as bubble shape have been investigated using two-dimensional particle-in-cell simulations. The evolution of the bubble with time, and the correlation of bubble length (longitudinal and transverse radius) with the intensity of laser pulse have been revealed in this study. The change of bubble dimensions can be estimated by various determining factors such as the laser pulse focusing, the beam loading, the residual electrons, and the bubble velocity. It has also been confirmed that the shape of the bubble cannot be predicted using fixed shape models as spherical or elliptical. Simulations unveil that as the bubble traverses in plasma, it evolves from spherical shape to the highly elliptical shape. And, as it approaches the dephasing length, the eccentricity decreases further. Consequently, the self-injection of plasma electrons in the bubble is seriously affected by the bubble evolution. Comparison of the electron energy gain at different intensities of laser pulse has also been provided. Various scaling laws for electron beam energy estimations are predicted in this investigation. High quality electron beam can be obtained by controlling the bubble evolution, which may have significant applications in future coherent light sources, biomedical, condensed matter physics, and x-ray generation by table-top FEL.

Effect of laser polarization and target location on acceleration of electrons generated during ionization of gases by a laser pulse

We investigate the effect of the target position, laser polarization, and focusing on the energy spread and the angle of emittance for the acceleration of electrons generated during the ionization of rarefied gases, neon ions Ne8+, krypton ions Kr32+, and argon ions Ar16+ by a laser pulse. The electrons generated from the ions at the position after laser focus interact with the laser pulse for a longer duration and gain more energy than those electrons generated from the ions at the position before laser focus. There are two peaks in the energy spectrum for linear polarization and only one peak for circular polarization. The energy spectrum peak is sharper for circular polarization than that for linear polarization. The energy gained by the electrons increases with the laser spot size due to the increase in the laser energy. The spectrum of the angle of emittance for electrons shows the sharpest peak at the lowest angle for linear polarization for ions at the position after laser focus. The circular polarization is good to obtain quasi-monoenergetic electron beams and linearly polarized laser pulse is good to generate collimated electron beams. The required laser intensity to ionize electrons from the ions Ne8+, Kr32+, and Ar16+ increases and the electron energy peaks are at higher energies and scattering angles are at lower values for these gases, in their respective orders.

Direct laser acceleration of electrons in a high-Z gas target and the effect of threshold plasma density on electron beam generation

An experimental study of laser driven electron acceleration in N2 and N2-He mixed gas-jet targets using laser pulses with durations of ∼60–70 fs is presented. Generation of relativistic electron beams with quasi-thermal spectra was observed at a threshold plasma density of ∼1.6 × 1018 cm−3 in the case of pure N2. The threshold density was found to increase with increasing doping concentrations of He. At an optimum fraction of 50% of He in N2, generation of quasi-monoenergetic electron beams was observed at a comparatively higher threshold density of ∼2 × 1018 cm−3, with an average peak energy of ∼168 MeV, average energy spread of ∼21%, and average total beam charge of ∼220 pC. The electron acceleration could be attributed to direct laser acceleration as well as the hybrid mechanism. The observation of an optimum fraction of He in N2 (in turn threshold plasma density) for comparatively better quality electron beam generation can be understood in terms of the plasma density dependent variation in the dephasing rate of electrons with respect to the transverse oscillating laser field. Results are also supported by 2D particle-in-cell simulations performed using the code EPOCH.

Beam quality improvement of ionization injected electrons by using chirped pulse in wakefield acceleration

Ionization-induced electron injection in a chirped laser pulse driven wakefield acceleration is investigated through particle-in-cell simulations. We find that negative (positive) chirp can longitudinally stretch (compress) laser pulse, and the wakefield amplitude can be enhanced regardless of the chirp sign. On the other hand, the rapid compression of a positively chirped pulse leads to the decrease of the wakefield potential difference, which breaks the ionization injection condition and consequent injection truncation occurs. The effective injection only lasts for a few hundred micrometers and the detailed injection length is determined by the chirp parameter. As a result, a highly tunable quasi-monoenergetic electron beam with narrow energy spread, hundreds of MeV central energy and tens of pC charge can be stably produced by this scheme.

High-resolution X-ray spectroscopy of highly charged tungsten EBIT plasma

Abstract Highly charged tungsten transitions can be used as a diagnostic tool for investigating performance of the fusion device. Systematic spectroscopic investigations of the radiative decay channels of the tungsten charge states allow for extending the fundamental understanding of highly charged ions and can serve as a diagnostic tool to improve applied plasma research. Electron beam ion traps (EBIT) offer the ability to generate emission from highly charged tungsten ions because of their charge state and excitation selectivity due to their quasi-monoenergetic electron beam. In this work, we report the current experimental capabilities of the EBIT at the National Institute of Standards and Technology (NIST). High-resolution measurements of EUV and x-ray transitions from tungsten charge states are shown, demonstrating our ability to produce and identify the spectral features of highly charged tungsten plasma. While the experimental results were limited by the lack of an absolute calibration of the spectrometer, we present approximate transition energies of two strong transitions from the Ti-like W52+ and Sc-like W53+ charge states. Our estimates agree quite well with the results of FAC simulations, where these strongest transitions were identified to originate from 3d-4f transitions. This decay channel has been shown to be the strongest transition for surrounding charge states.

Betatron resonance electron acceleration and generation of relativistic electron beams using 200 fs Ti:sapphire laser pulses

The generation of relativistic electron beams with quasi-thermal energy distribution (maximum energy: 30 MeV) by the interaction of a Ti:sapphire laser pulse of 200 fs duration, focussed to an intensity of ∼2.1 × 1018 W cm−2, with an underdense (electron density ∼3.6 × 1019 to ∼1.1 × 1020 cm−3) He gas-jet plasma was observed. We observed two stages of self-focusing of the laser pulse in the plasma. Two groups of accelerated electrons associated with these two stages of laser channeling were also observed, and are attributed to the betatron resonance acceleration mechanism. This is supported by 2D PIC simulations performed using the EPOCH code and a detailed theoretical analysis. Further, the generation of quasi-monoenergetic (ΔE/E ∼ 10%–20%) electron beams with a peak energy of ∼17–22 MeV was also observed, even with such long laser pulses, although with a low probability of occurrence.

Laser wakefield acceleration in Kr–He plasmas and its application to positron beam generation

We present the generation of quasi-monoenergetic electron beams via ionization injection in a laser wakefield acceleration by using a krypton–helium plasma. We obtained higher-energy electron beams of low divergence as compared with beams from the nitrogen–helium plasma at low plasma densities. This is attributed to an immediate ionization, trapping and acceleration of many electrons from several inner shells of the krypton atoms. On the other hand, there are very high ionization potentials of the K-shell nitrogen electrons which require the pulse (in our laser-plasma parameters) to experience a self-focusing (after 1.6 mm of propagation) at first before any ionization injection and acceleration of those two electrons per atom can occur. Based on those high-quality electron beams from the Kr–He plasmas, we generated ultra-relativistic positron beams with energies up to 100 MeV by placing a lead slab converter with a thickness of the order of its radiation length in the electron beam path after the gas jet. Experimental and Mont-Carlo simulated energy spectra of the positron beams are compared for the energy range of 30 MeV ≤ Ee+ ≤ 100 MeV along with the positron yields. In addition, various parameters of the positrons are investigated against the primary electron beam parameters. Such electron–positron cascading experiment could be helpful in future development for the composition of an all-optical electron–positron collider.

Control of quasi-monoenergetic electron beams from laser-plasma accelerators with adjustable shock density profile

The injection physics in a shock-induced density down-ramp injector was characterized, demonstrating precise control of a laser-plasma accelerator (LPA). Using a jet-blade assembly, experiments systematically varied the shock injector profile, including shock angle, shock position, up-ramp width, and acceleration length. Our work demonstrates that beam energy, energy spread, and pointing can be controlled by adjusting these parameters. As a result, an electron beam that was highly tunable from 25 to 300 MeV with 8% energy spread (ΔEFWHM/E), 1.5 mrad divergence, and 0.35 mrad pointing fluctuation was produced. Particle-in-cell simulation characterized how variation in the shock angle and up-ramp width impacted the injection process. This highly controllable LPA represents a suitable, compact electron beam source for LPA applications such as Thomson sources and free-electron lasers.

A system for the measurement of electron stopping powers: proof of principle using a pure β-emitting source

The accuracy of the electron stopping powers of elements and compounds is of great importance to medical dosimetry, radiation therapy, and radiation transport simulations. This paper summarises the commissioning of a new high purity Germanium (HPGe) detector and presents a feasibility study confirming the suitability of a method to determine electron stopping power data.A high-efficiency, HPGe detector was commissioned and found to match the manufacturer's performance specifications. A simple experiment was designed to obtain spectra acquired from a Sr-90/Y-90 radioactive check source with varying thicknesses of absorber (Al and Cu foils) placed between the source and the detector. The entire experimental arrangement was simulated using the EGSnrc radiation transport system. The Monte Carlo model of the detector accurately replicated the detector response to electrons and a quantitative analysis showed that the difference between the simulated and measured spectra was less than 1.5%, using the standard tabulated ICRU 37 stopping power data for the simulations.Based on the experiment with the low-energy Sr-90/Y-90 source, it is anticipated that this method can be used with a well-characterized quasi-monoenergetic electron beam, as available from a research linear accelerated to yield accurate measurements to validate current tabulated stopping power data.