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The numerical noise inherent to particle-in-cell simulation of 3D highintensity bunched beams is studied with the TRACEWIN code and compared with ananalytical model by Struckmeier. The latter assumes that entropy growth can berelated to Markov type stochastic processes due to temperature anisotropy andthe artificial collisions caused by using macro-particles and calculating thespace charge effect. The resulting noise can lead to growth of thesix-dimensional rms emittance and a suitably defined rms entropy. We confirmthe dependence of this growth on the bunch temperature anisotropy as predictedby Struckmeier. However,we also find an apparently modified mechanism of noisegeneration by the non-Liouvillean effect of the Poisson solver grid, whichexists in periodic focusing systems even in the complete absence of temperatureanisotropy. Our findings are applicable in particular to high current linacsimulation, where they can provide guidance to estimate noise effects and helpfinding an effective balance between the number of simulation particles and thegrid resolution.

Grid induced noise and entropy growth in 3d particle-in-cell simulation of high intensity beams