Measure Variation of Magnetic Field Waveforms Above Rails of a Railgun During Launching Period

To analyze the variation of magnetic field waveforms above rails of the railgun during the launching period, the magnetic fields are measured by loop probes. According to the armature's different moving statements and measurement positions, magnetic waveforms are distinguished with each other. The experiment results show that magnetic field waveforms above the rails change at different positions, and the output voltages of probes become larger with the higher velocities. The truncated waveforms expand the spectrum of signals around the rails. The waveforms at different positions are compared with each other, which can inflect the magnetic field distribution along the rails during the launching period. The results are useful in analyzing the interference of the transient environment for the rail launcher and the electromagnetic interference design of railgun systems.

I. Introduction

A railgun has two rails with an armature sliding along the rails. The magnetic field around the rails is determined by the rail current and the state of armature. According to the moving armature's position, the waveform of transient magnetic field is changed. In this paper, the transient magnetic field is measured by the loop probes [1], [2], and the rail currents are measured by the calibrated ROGOWSKI current probes. The commercial near field loop probes are used to measure the transient field [3], [4], which own the shield shell to reject the electrical field [5]–[7]. Because the spectrum of the signal is , the loop probe is used for the low frequency situation. References [8] and [9] discussed the probe factor calculation and other calibration problems. According to these analysis methods, the loops are used to measure the pulsed power supply's transient fields around the switches, and the results are used to analyze the electromagnetic interference (EMI) problem for the pulsed power supply [11]. The following measurements are all based on the above method. Although the use of ROGOWSKI coils for magnetic field measurements in railguns is well-known, the experiment results show that the velocity effect of the armature causes much higher inductive voltages and expands the spectrum period of the signal, which is useful for the EMI shield and fields measurement.