A diamond-like carbon circular target is proposed to improve γ-ray emission and pair production with a laser intensity of 8×1022 W cm-2by using 2D particle-in-cell simulations with quantum electrodynamics.It is found that the circular target can enhance the density of γ-photons significantly more than a plane target, when two colliding circularly polarized lasers irradiate the target.By multi-laser irradiating the circular target, the optical trap of lasers can prevent the high energy electrons accelerated by laser radiation pressure from escaping.Hence, γ-photons with a high density of beyond 5000 ncare obtained through nonlinear Compton backscattering.Meanwhile, 2.7×1011 positrons with an average energy of 230 MeV are achieved via the multiphoton Breit-Wheeler process.Such an ultrabright γ-ray source and dense positron source can be useful in many applications.The optimal target radius and laser mismatching deviation parameters are also discussed in detail.
The electronic transverse transport of Lorentz plasma with collision and magnetic field effects is studied by solving the Boltzmann equation for different electron density distributions. For the Maxwellian distribution, it is shown that transport coefficients decrease as ? increases, ? is the ratio of an electron’s magneto-cyclotron frequency to plasma collision frequency. It means that the electrons are possible to be highly collimated by a strong magnetic field. For the quasimonoenergetic distribution with different widths, it is found that the transport coefficients decrease greatly as εˉ decreases.In particular when the width approaches to zero the transverse transport coefficients are hardly affected by the magnetic field and the minimal one is obtained. Results imply that the strong magnetic field and quasi-monoenergetic distribution are both beneficial to reduce the electronic transverse transport. This study is also helpful to understand the relevant problems of plasma transport in the background of the inertial confinement fusion.
