Well collimated MeV electron beam generation in the plasma channel from relativistic laser-solid interaction

Abstract

Efficient direct electron acceleration in the plasma channel with injection through the breaking of plasma waves generated by parametric instabilities was demonstrated experimentally and reproduced in the 2D3V PIC simulations. The electron bunch was produced using the specific plasma profile containing arbitrary sharp, ∼0.5λ, gradient at the vicinity of 0.1-0.5 critical density and a long tail of a tenuous preplasma. Such a preplasma profile was formed by an additional nanosecond laser pulse with intensity of 5×10 12 W cm −2 . In the case of optimal preplasma parameters femtosecond laser pulse with an intensity of 5×10 18 W cm −2 and an energy of 50 mJ generates a collimated electron bunch having divergence of 50 mrad, exponential spectrum with the slope of ∼2 MeV and charge of tens of pC. The charge was confirmed measuring neutron yield from Be(g, n) photonuclear reaction with threshold of 1.7 MeV. By the contrast, a ring-like electron beam with divergency of 300 mrad and significantly lower charge is generated if the prepulse intensity drops to 5×10 11 W cm −2 . The 2D PIC simulations confirmed beamed electron's acceleration in the plasma channel (so-called direct laser acceleration). This channel is formed in a long tail of teneous preplasma by the laser pulse specularly reflected from the arbitrary sharp gradient. The ring-like electron beam was attributed to the longer gradient case enlarging divergence of the reflected laser beam, preventing channel's formation and electron acceleration by the so-called vacuum laser acceleration, or VLA. We also showed that injected electrons appeared from the wave breaking of plasma waves of hybrid SRS-TPD instability for the both gradients. Electrons received an initial momentum from this breaking to be effectively injected into the plasma channel.

Optimized laser-assisted electron injection into a quasi-linear plasma wakefield

“…In the recent paper [13], an efficient method for electron acceleration up to MeV energies via laser-solid interaction has been demonstrated experimentally and with 2d3v PIC simulations. According to [13], the fast elec- trons are generated via breaking of plasma waves excited by parametric instabilities near the laser reflection point. These electrons are further accelerated by the mechanism of direct laser acceleration [17].…”

“…Here we reproduce the experimental results of [13] using full 3d particle-in-cell simulations with the VLPL code. This is the first stage of two-step simulation.…”

“…A laser pulse synchronized with the driver hits the surface of the target at the 45 degree angle. The laser expels electrons from the solid target and accelerates them up to MeV energies in a direction close to that of the reflected laser pulse (the specular direction) [13]. Electrons that catch the appropriate phase of the wakefield can be trapped and further accelerated.…”

“…In the first part we simulate the laser interaction with the solid target. Thus, we repeat the results of [13] using full 3d PIC simulations. After the laser-solid interaction is over, we store the full phase space of the generated hot electrons.…”

Hybrid Stimulated Raman Scattering -- Two Plasmon Decay Instability and 3/2 Harmonic in Steep-Gradient Femtosecond Plasmas

“…Excitation of SRS and twoplasmon decay (TPD) instabilities by subrelativistic or relativistic femtosecond laser pulses in a long inhomogeneous plasma (L ≈ 10 − 100λ) was studied in [10][11][12][13][14][15]. Parametric instabilities are apparently responsible for formation of relativistic high-energy electron beams upon reflection of a powerful femtosecond laser pulse from a dense steep plasma [16,17].…”