Abstract
In recent years, the prospects of performing fundamental and applied studies at the next-generation high-intensity laser facilities have greatly stimulated the interest in performing large-scale simulations of laser interaction with matter with the account for quantum electrodynamics (QED) processes such as emission of high energy photons and decay of such photons into electron-positron pairs. These processes can be modelled via probabilistic routines that include frequent computation of synchrotron functions and can constitute significant computational demands within accordingly extended Particle-in-Cell (QED-PIC) algorithms. In this regard, the optimization of these routines is of great interest. In this paper, we propose and describe two modifications. First, we derive a more accurate upper-bound estimate for the rate of QED events and use it to arrange local sub-stepping of the global time step in a significantly more efficient way than done previously. Second, we present a new high-performance implementation of synchrotron functions. Our optimizations made it possible to speed up the computations by a factor of up to 13.7 depending on the problem. Our implementation is integrated into the PICADOR and Hi-Chi codes, the latter of which is distributed publicly (https://github.com/hi-chi/pyHiChi).
Highlights
The numerical simulation of laser plasma with the Particle-in-Cell (PIC) method is an area of immediate interest in computational physics
Our analysis showed that in quantum electrodynamics (QED)-PIC simulations, the calculation of synchrotron functions using the GNU Scientific Library (GSL) library takes more than 20% of the total computation time
This paper describes our approach to speed up QED-PIC simulations by a few times
Summary
The numerical simulation of laser plasma with the Particle-in-Cell (PIC) method is an area of immediate interest in computational physics. Certain types of problems are still challenging for large-scale simulation due to distinctive algorithmic and numerical features These include extended PIC simulations with account for the effects of strong field quantum electrodynamics (QED), the so-called QED-PIC simulations [12,13,14,15,16,17,18]. Papers [21, 26] detail QED-PIC schemes with explicit formulas for the probabilities of these processes in terms of synchrotron functions These schemes impose restrictions on the time step, depending on the intensity of the electromagnetic field.
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