  This paper concerns development of a high-performance implementation of the
Particle-in-Cell method for plasma simulation on Intel Xeon Phi coprocessors.
We discuss suitability of the method for Xeon Phi architecture and present our
experience of porting and optimization of the existing parallel
Particle-in-Cell code PICADOR. Direct porting with no code modification gives
performance on Xeon Phi close to 8-core CPU on a benchmark problem with 50
particles per cell. We demonstrate step-by-step application of optimization
techniques such as improving data locality, enhancing parallelization
efficiency and vectorization that leads to 3.75 x speedup on CPU and 7.5 x on
Xeon Phi. The optimized version achieves 18.8 ns per particle update on Intel
Xeon E5-2660 CPU and 9.3 ns per particle update on Intel Xeon Phi 5110P. On a
real problem of laser ion acceleration in targets with surface grating that
requires a large number of macroparticles per cell the speedup of Xeon Phi
compared to CPU is 1.6 x.
