The need to handle the coupling between microscopic and macroscopic
processes in plasma physics is ubiquitous.
The wide difference in mass between electrons and ions and the great
change in time and space scales between large scale magnetohydrodynamic
processes and small scale kinetic effects pose a great challenge to the
simulation of plasma physics problems.
The traditional approach has been to try to derive reduced models of the
full first principle physics model and solve them considering only the
scales of interest. The approach decouples the simulation of small
scales and large scales and uses different methods to treat both. The
classic example is anomalous resistivity that is used as a tool to
summarise in resistive MHD models the presence of kinetic
microinstabilities.
We propose an alternative approach, the use of the implicit kinetic PIC
model to resolve all scales at the kinetic level. The approach relies on
numerical methods that can effectively average the smallest scales
within a correct kinetic treatment while focusing on large-scale
structures. We remark that the approach is different from the
gyrokinetic approach that relies on a mathematical formulation of the
equations that eliminates the smallest scales. Our approach, instead, is
valid on all limits and does not eliminate the contribution of any scale.
After describing the approach, we present a specific example of its
application: the study of current sheets evolution and reconnection.