It is demonstrated that the inherent structure of Boris pusher may result in the accumulation of errors in numerical integration when estimating the works of electric fields on particles. This, in turn, leads to an incorrect estimations of particle acceleration mechanisms. A method of error correction, reducing error to the acceptable levels of < 10%, is implemented. Numerical integration error in question is most pronounced in scenarios where substantial number of electrons are injected into the accelerating structure through wave breaking of plasma waves i.e. in near-critical density plasma.
KEYWORDS: Plasma, Electrons, Pulsed laser operation, Particles, Fusion energy, Electron beams, Wave propagation, Uranium, Target detection, Simulation of CCA and DLA aggregates
Efficient forward electron acceleration by the direct laser acceleration (DLA) in the plasma channel was experimentally demonstrated using a 16 µm thick tape target. An electron beam with ∼0.05 rad divergence, 50-100 pC charge (for E<1.7 MeV), and temperature ∼ several MeV was observed on 1 TW laser system utilizing an additional controlled nanosecond prepulse. Using this beam, several near-threshold photonuclear reactions were studied and neutron flux of ∼ 105 − 106 s-1 J-1 was achieved. We also used neutron flux measurements to estimate electron beam charge, calculating conversion coefficients from GEANT4 simulations. Terahertz radiation emission from this type of interaction was also studied, exhibiting a two-maxima structure with the change of delay between main pulse and nanosecond prepulse.
In this work, we will show that electrons can be accelerated in the plasma channel, which is formed by a laser pulse reflected from a dense plasma. Preplasma, on the one hand, mast have a sufficient length in the low (<0.1nc) density region to create a channel inside it, and on the other hand, does not lead to strong absorption and destruction of the laser pulse and provides injection of the maximum number of electrons into the channel. It is shown that in order to fulfill the latter conditions, the optimum slope of the plasma gradient near the critical density should be ~ 0.5λ. In this case, the injection of electrons, which received an initial acceleration after the breaking of plasma waves excited by parametric instabilities, effectively occurs in the plasma channel.
In this paper we present experimental research on the possibility of electron bunch generation at intensity around 1018 W/cm2. It is shown that by optimizing preplasma profile one can obtain collimated (~0.05 rad) electron beam with relatively high charge (30 pC) and temperature around 1.5 MeV. This beam can be used to study low-energy nuclear physics and to create secondary particle sources (neutrons, positrons, etc.) on lasers. We also demonstrate the possibility to reversely study the beam parameters, such as charge, based on yield measurements in photonuclear experiments and GEANT4 simulations.
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