Abstract
When charged particle trajectories are numerically calculated in discrete electro-magnetic fields obtained from computer simulations, it is necessary to interpolate spatially the field data. Usually, linear interpolation has been used for this purpose, but in this case adiabatic invariants are not conserved for the calculated particle trajectory. We hence propose an interpolation method, by which the solenoidal condition of magnetic field is exactly satisfied. The adiabatic invariants are conserved for particle trajectories calculated in the resulting continuous fields, and the use of the lowest order interpolation scheme demands cpu time only little more than the case of linear interpolation. This method is applied to two test magnetic fields of simple topology and a complicated electro-magnetic field data obtained from MHD simulation. It is argued that in order to calculate particle trajectories correctly magnetic field data should be interpolated so that the solenoidal condition is satisfied. It is also argued that this method is applicable to general plasma particle simulations.
