Algorithms for accurate relativistic particle injection

In particle-in-cell plasma codes, the second-order leap-frog method is used to push the velocity and position of each particle in the main loop. Once a velocity distribution has been inverted for injection, time-centering of the position and velocity is necessary to maintain second-order accuracy. We have set up non-relativistic time-centering algorithms for particle injection in our PIC code. We further developed relativistic time-centering methods for injection and we added methods to calculate higher order accurate position. Also, the algorithms are expanded to find the position and velocity at any specific time from those at the initial discrete time, which can be used not only in the leap-frog method but also any other algorithms.