Abstract
A model for laser light absorption in electron–positron plasmas self-consistently created via QED cascades is described. The laser energy is mainly absorbed due to hard photon emission via nonlinear Compton scattering. The degree of absorption depends on the laser intensity and the pulse duration. The QED cascades are studied with multi-dimensional particle-in-cell simulations complemented by a QED module and a macro-particle merging algorithm that allows to handle the exponential growth of the number of particles. Results range from moderate-intensity regimes (∼10 PW) where the laser absorption is negligible to extreme intensities (>100 PW) where the degree of absorption reaches 80%. Our study demonstrates good agreement between the analytical model and simulations. The expected properties of the hard photon emission and the generated pair-plasma are investigated, and the experimental signatures for near-future laser facilities are discussed.
Highlights
We present a study of QED cascades in counter propagating laser pulses of 10-100 PW, leveraging on the original setup proposed by Bell & Kirk[18]
We first recall the initial development of the cascades that are characterised by a single parameter, the growth rate which depend itself on the laser intensity and polarisation
In order to address numerically this late time of the cascade where the colossal multiplicity has led to a photon-pair plasma whose kinetic energy becomes comparable with the initial energy of the pulse, we resort on the coupling of our QED-PIC framework with a particle merging algorithm which permits, despite the exponential growth of the particles, to keep the number of PIC particles approximatively constant in the simulation box
Summary
We present a study of QED cascades in counter propagating laser pulses of 10-100 PW, leveraging on the original setup proposed by Bell & Kirk[18]. We first recall the initial development of the cascades that are characterised by a single parameter, the growth rate which depend itself on the laser intensity and polarisation. In order to address numerically this late time of the cascade where the colossal multiplicity has led to a photon-pair plasma whose kinetic energy becomes comparable with the initial energy of the pulse, we resort on the coupling of our QED-PIC framework with a particle merging algorithm which permits, despite the exponential growth of the particles, to keep the number of PIC particles approximatively constant in the simulation box. Besides detailed predictions regarding the photons and pair-plasma self-consistently generated, we demonstrate the conditions required to achieve strong laser absorption regimes in upcoming laser facilities
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