How to improve the diagnosis of kinetic energy in δf PIC codes

This paper propose to analyse the effect of the shape factor that is used in plasma PIC δ f codes to make interpolations between the grid and the particles positions. In δ f codes, the total density fluctuates, even when it should be conserved. We show that, in some cases, the computed non-physical part of the particle kinetic energy fluctuations is dependent on those of the total density. We deduce a method that can reduce drastically the statistical fluctuations in the diagnostics of the kinetic energy.