PIC simulation of short scale‐length phenomena

The characteristics of a beam propagating in a channel of large aperture quadrupole magnets, and an anisotropy driven instability which transfers thermal energy from the transverse to longitudinal directions, are presented as two examples of phenomena requiring fine numerical resolution to be adequately described. In the first case, adequate resolution of the thin beam‐edge sheath is found necessary to accurately simulate the particles whose orbits are driven unstable by the focusing nonlinearity. In the latter case, the tendency of the unstable mode to occur at longitudinal wavelengths comparable to beam diameter, requires adequate longitudinal resolution for the instability to be observed.