Simulating the Injection of Magnetized Plasma without Electromagnetic Precursor Wave

Injecting magnetized plasma with changes in magnetization or injection rate necessitate a time variable magnetic field at the boundary of the simulation box. Naive implementation will lead to electromagnetic precursor waves that can affect the simulation results. The problem is well-known and is described e.g. in Lemebege and Dawson 1987. Since then few papers have attempted to deal with this problem and no standard solution exists. In this research note we suggest that the ad-hoc pulse shape that was used in the paper by Lemebege and Dawson 1987 can be replaces by a standard digital low pass filter. The cut off frequency of this filter should coincide with the gyro frequency in the magnetized plasma, to make use of (Doppler-broadend) resonant absorption caused by gyrating electrons. We illustrate this idea with a code example and demonstrate the efficency of this method throug sample simulations with our electromagnetic particle-in-cell code.