How to test and verify radiation diagnostics simulations within particle-in-cell frameworks

The particle-in-cell code PIConGPU provides the feature of calculating angular resolved radiation spectra in the far field based on Liénard–Wiechert potentials for all macroparticles of a plasma simulation. In order to verify the physics of our code we present a series of physics test scenarios, which compare numerical results to analytic solutions of nonlinear Thomson scattering at relativistic electrons. These scenarios range from single particle and electron bunch tests to full-scale laser-plasma simulations that include the collective effects of a plasma, as well as coherent and incoherent superposition of radiation of many particles. For the calculated test cases good agreement to the theoretical results with respect to absolute spectral intensities was found in all observation directions. In an electron density scan of a laser-plasma scenario, we reproduce a second-harmonic intensity scaling also observed in experiment.