Recent advances in PIConGPU methods for modeling lasers, ionization and radiation

Abstract
We present recent simulations of laser wakefield acceleration (LWFA) and nonlinear Thomson scattering performed with the fully relativistic 3D3V particle-in-cell code PIConGPU. These cover both experimental setups currently carried out at HZDR and setups beyond state-of-the-art experiments. We discuss the recent advances in our code that allowed performing these simulations and examine their physical implications in detail.

Summary
The simulations presented require a variety of algorithmic extensions to the standard particle-in-cell cycle. These include a laser implementation which allows more freedom in modifying the simulated laser to describe the experimentally available laser to a high degree of accuracy, including setups ranging from simple chirping to TWTS-type laser pulses. These extensions also encompass a variety of ionization schemes, including BSI and ADK, for which we will discuss the physical foundation and the performance implications. Our code also provides algorithms for both classical radiation reaction effects, based on Landau and Lifshitz, and QED recoil to include radiation losses, as they occur for example during betatron oscillation. Furthermore, PIConGPU also provides in-situ synthetic radiation diagnostics: a classical radiation diagnostic, based on Liénard-Wiechert potentials, that allows predicting coherent and incoherent radiation spectra simultaneously for hundreds of observation directions and thousands of frequencies and a just recently implemented extension to include QED based photon generation and electron recoil beyond the classical scope. Encompassing these new algorithms and still being able to reach performances that allow large scale parameter scans is crucial and was only possible by strictly following an in-situ approach and efficiently using the GPU hardware, which will be discussed in detail.

The simulation presented will cover the emission expected during nonlinear Thomson scattering as experimentally performed with the DRACO laser and the ELBE accelerator at HZDR. We will further discuss the simulated plasma dynamic, electron acceleration and resulting X-ray signatures from laser wakefield acceleration for various He/N gas mixture and compare these to experiments. Furthermore we will present a radiation sky map of LWFA containing various spectral signatures to diagnose the plasma dynamic and new accelerator schemes.