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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. [ABSTRACT FROM AUTHOR]

We propose a compact scheme for high-density and high-energy positron generation. In the scheme, the generation, compression and acceleration of positrons are encompassed in a plasma channel irradiated by an ultra intense laser. In about 20 μm, positrons are accelerated with their energy beyond 20 GeV, and are compressed with a maximal density of 4.1nc. The obtained positron beam with a wave-like density profile is accelerated via the direct laser acceleration. [ABSTRACT FROM AUTHOR]

By using three-dimensional particle-in-cell simulations, we investigate the dynamics of ultraintense Laguerre–Gaussian (LG) laser pulses interacting with a wire target. When a relativistic LG-mode laser pulse sweeps a wire target, annular electron bunches with attosecond duration are periodically dragged out of the left tip of the wire. Due to the radial laser electric field force exerted on the electrons, the annular bunches are tightly constrained near the target surface and steadily propagate along the wire. A strong return current is thus induced to satisfy the plasma neutralization condition. Once leaving from the right tip of the target, the electron emission angle gradually decreases and each hollow electron bunch is converged into an electron disc. Under the action of the longitudinal electric field, electrons are continuously accelerated to 100s MeV. At the same time, the laser angular momentum is transferred efficiently to the beam angular momentum (BAM) of the bunches. The structure of the dense short electron bunches is stable and keeps intact for more than 300 fs. We can manipulate the quality of the bunches by changing the laser and target parameters, such as the laser handedness and intensity, beam waist radius, wire length and radius. The scheme paves the way for the generation of high-quality attosecond electron bunches with low divergence, high beam charge and large BAM, which will have wide-range applications in various domains. [ABSTRACT FROM AUTHOR]

High-energy-density electron–positron pairs play an increasingly important role in many potential applications. Here, we propose a scheme for enhanced positron production by an ultra intense laser irradiating a gas-Al compound target via the multi-photon Breit–Wheeler (BW) process. The laser pulse first ionizes the gas and interacts with a near-critical-density plasma, forming an electron bubble behind the laser pulse. A great deal of electrons are trapped and accelerated in the bubble, while the laser front hole-bores the Al target and deforms its front surface. A part of the laser wave is thus reflected by the inner curved target surface and collides with the accelerated electron bunch. Finally, a large number of γ photons are emitted in the forward direction via the Compton back-scattering process and the BW process is initiated. Dense electron–positron pairs are produced with a maximum density of m−3. Simulation results show that the positron generation is greatly enhanced in the compound target, where the positron yield is two orders of magnitude greater than that in only the solid slab case. The influences of the laser intensity, gas density and length on the positron beam quality are also discussed, which demonstrates the feasibility of the scheme in practice. [ABSTRACT FROM AUTHOR]