On the Boris solver in particle-in-cell simulation

A simple form of the Boris solver in particle-in-cell (PIC) simulation is proposed. It employs an exact solution of the Lorentz-force part, and it is equivalent to the Boris solver with a gyrophase correction. As a favorable property for stable schemes, this form preserves a volume in the phase space. Numerical tests of the Boris solvers are conducted by test-particle simulations and by PIC simulations. The proposed form provides better accuracy than the popular form, while it only requires few additional computation time.