Loading and injection of Maxwellian distributions in particle simulations

Existing and new particle loading and injection algorithms for particle sim ulations are analyzed to determine numerical accuracy and computational eff iciency. Emphasis has been placed on loading and emission of Maxwellian, dr ifting Maxwellian, and cutoff Maxwellian velocity distributions. Once a vel ocity distribution has been inverted for loading or injection, time-centeri ng of the position and velocity is necessary in order to maintain second-or der accuracy. Here, the accuracy of these methods is determined and compare d to three analytic test cases with spatially varying, time-dependent, and time-independent electric fields in a homogeneous magnetic field and a self -consistent crossed-field diode. The initial push is shown to be important in calculating the correct electric field at the boundary where particles a re injected, in relaxing constraints on the time step, and in providing rel iable field fluctuations due to particle statistics. (C) 2000 Academic Pres s.