  We present PICsar -- a new Particle in Cell code geared towards efficiently
simulating the magnetosphere of the aligned rotator. PICsar is a special
relativistic, electromagnetic, charge conservative code that can be used to
simulate arbitrary electromagnetics problems in axisymmetry. It features
stretchable body-fitted coordinates that follow the surface of a sphere,
simplifying the application of boundary conditions in the case of the aligned
rotator; a radiation absorbing outer boundary, which allows a steady state to
be set up dynamically and maintained indefinitely from transient initial
conditions; and algorithms for injection of charged particles into the
simulation domain. The code is parallelized using MPI and scales well to a
large number of processors. We discuss the numerical methods used in PICsar and
present tests of the code. In particular, we show that PICsar can accurately
and efficiently simulate the magnetosphere of the aligned monopole rotator in
the force free limit. We present simulations of the aligned dipole rotator in a
forthcoming paper.
