Study of SGEMP Field-Coupling Inside and Outside Reentrant Cavity

This article studies system-generated electromagnetic pulse (EMP) and coupling in a reentrant cavity—a simplified spacecraft model with the annular slit and internal shaft, numerically by using the three-dimensional conformal particle-in-cell method. The results indicate that when the electromagnetic fields arrive at the annular slit, obvious field-coupling will be induced that EMP may enter or escape from the slit without many restrictions at the low-irradiation fluence. In this case, the total field can be acquired by linearly summing the EMPs derived from the moving electrons released separately by the external and internal emitting surfaces. The reentrant cavity is to form a repetitive-oscillating capacitor model, while the electromagnetic waves of damped oscillation with comparatively large amplitude are found near the annular slit and the internal shaft. The frequency of the damped oscillation is mainly influenced by the cavity geometrical factor and is going to converge to the natural frequency of the reentrant cavity. Furthermore, the reason accounting for the change of both the frequencies is revealed.