Quantitatively consistent computation of coherent and incoherent radiation in particle-in-cell codes—A general form factor formalism for macro-particles

Abstract

Quantitative predictions from synthetic radiation diagnostics often have to consider all accelerated particles. For particle-in-cell (PIC) codes, this not only means including all macro-particles but also taking into account the discrete electron distribution associated with them. This paper presents a general form factor formalism that allows to determine the radiation from this discrete electron distribution in order to compute the coherent and incoherent radiation self-consistently. Furthermore, we discuss a memory-efficient implementation that allows PIC simulations with billions of macro-particles. The impact on the radiation spectra is demonstrated on a large scale LWFA simulation. Particle-in-cell codes as synthetic diagnostic for laser plasma acceleratorsLaser plasma-based accelerators such as laser wakefield accelerators (LWFA) offer various advantages over conventional accelerators such as their compact size due to their orders of magnitude larger acceleration gradient [1] resulting in GeV energy gains on centimeter scales [2-4], while allowing for compact electron bunch size [5,6], low beam emittance [7] and high current [8]. Since these laser plasma accelerators operate in a highly nonlinear regime, particle-in-cell (PIC) codes are essential for understanding the plasma dynamics in these experiments [9,10]. Making quantitative predictions on the measurable outcome of these experiments is done by so-called synthetic diagnostics. An essential form of these synthetic diagnostics are predictions on the radiation emissions [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. However, most of these simulations lack quantitative predictions due to the small number of sample particles used (see [22] for details), but also due to an inconsistent treatment of the discrete nature of the electrons represented by macro-particles in PIC codes. This often renders quantitative comparisons to experiments difficult to impossible.The general form factor formalism introduced in this paper overcomes this problem.

Ionization dynamics of dense matter generated by intense ultrashort X‐ray pulses

“…The pump‐probe scheme with the SDU can, however, be an efficient tool to investigate the relaxation process and the target expansion. More advanced theoretical analysis is necessary in this context, e.g., kinetically self‐consistent simulation includes atomic and relaxation processes—a step that may lead to such a kind of simulation is already initiated—and non‐equilibrium effects on XRTS …”

Coherent subcycle optical shock from superluminal plasma wake

“…The spherical detector θ − ϕ plane is resolved as N θ × N ϕ observers, with N θ = 128 along θ, N ϕ = 32 along ϕ and θ ranging from 0 to 150 mrad, ϕ from 0 to 2π, respectively. Note that computing far-field radiation by tracing macro-particles with large weight will greatly exaggerate the amplitude of incoherent radiation, but not for the coherent radiation [38]. The detailed information on the FaTiDo simulations can be found in the Supplemental Materials [30].…”