A diamond-like carbon circular target is proposed to improve the γ-ray emission and pair production with lasers intensity of 8 × 10 22 W/cm 2 by using two-dimensional particle-in-cell simulations with quantum electrodynamics. It is found that the circular target can significantly enhance the density of γ-photons than plane target when two colliding circularly polarized lasers irradiate the target. By multi-lasers irradiate the circular target, the optical trap of lasers can prevent the high energy electrons accelerated by laser radiation pressure from escaping. Hence, high density as 5164n c γ-photons is obtained through nonlinear Compton back-scattering. Meanwhile, 2.7 × 10 11 positrons with average energy of 230 MeV is achieved via multiphoton Breit-Wheeler process. Such ultrabright γ-ray source and dense positrons source can be useful to many applications. The optimal target radius and laser mismatching deviation parameters are also discussed in detail.
A special method is proposed of a laser-induced cavity pressure acceleration scheme for collimating, accelerating and guiding protons, using a single-cone target with a beam collimator through a target normal sheath acceleration mechanism. In addition, the problems involved are studied by using two-dimensional particle-in-cell simulations. The results show that the proton beam can be collimated, accelerated and guided effectively through this type of target. Theoretically, a formula is derived for the combined electric field of accelerating protons. Compared with a proton beam without a beam collimator, the proton beam density and cut-off energy of protons in the type II are increased by 3.3 times and 10% respectively. Detailed analysis shows that the enhancement is mainly due to the compact and strong sheath electrostatic field, and that the beam collimator plays a role in focusing energy. In addition, the simulation results show that the divergence angle of the proton beam in type II is less than 1.67 times that of type I. The more prominent point is that the proton number of type II is 2.2 times higher than that of type I. This kind of target has important applications in many fields, such as fast ion ignition in inertial fusion, high energy physics and proton therapy.Keywords: single-cone target with beam collimator, target normal sheath acceleration mechanism (TNSAM), particle-in-cell (PIC), sheath static electric field (SSEF), inertial fusion, high energy physics and proton therapy, proton beam density, cut-off energy of proton
We use quantum electrodynamics particle-in-cell simulation to study the generation of dense electron–positron plasma and strong γ-ray bursts in counter-propagating laser beam interactions with two different solid targets, i.e. planar (type I) and convex (type II). We find that type II limits fast electron flow most effectively. while the photon density is increased by about an order of magnitude and energy by approx. 10%–20% compared with those in type I target. γ-photon source with an ultrahigh peak brilliance of 2 × 1025 photons/s/mm2/mrad2/0.1% BW is generated by nonlinear Compton scattering process. Furthermore, use of type II target increases the positron density and energy by 3 times and 32% respectively, compared with those in type I target. In addition, the conversion efficiencies of total laser energy to γ-rays and positrons of type II are improved by 13.2% and 9.86% compared with type I. Such improvements in conversion efficiency and positron density are envisaged to have practical applications in experimental field.
A transverse gauss shape magnetic field with wide width is proposed for collimating the fast relativistic electron beam in laser irradiating plasmas, which is highlighted by the two-dimensional particle-in-cell simulations, in particular, the effects of this magnetic field on the production and transport of fast electron beam. When the axial magnetic field is also present, it is found that the energy density of fast electrons can be enhanced greatly. For example, in the presence of 30 MG axial magnetic field, it is enhanced by 3–4 times when the amplitude of the applied transverse magnetic field lies within the optimal regime 200–300 MG comparable to that without the transverse magnetic field. Meanwhile, the divergence angle of the electron beam can be controlled and even decreased a little due to the better sandwich structure of the overall weakening magnetic field. The study implies that the proposed transverse magnetic field is helpful to obtain the high quality electron beam which is beneficial to the fast ignition in inertial confinement fusion.
The use of a novel double-cone funnel target with high density layers (HDL) to collimate and focus electrons is investigated by two-dimensional particle-in-cell simulations. The proposed scheme can guide, collimate and focus electron beams to smaller sizes. The collimation reasons are analyzed by the quasi-static magnetic fields generation inside the beam collimator with HDL. It is found that the energy conversion efficiency is increased by a factor of 2.2 in this new scheme in comparison with the that without HDL. Such a target structure has potential for design flexibility and prevents inefficiencies in important applications such as fast ignition, etc.
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