Differential permeability of ferrite cores at high magnetization rates

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Since the ferrite cores are the kernel part for both the saturable transformer and the magnetic switch in a MPC system, it is necessary to evaluate the magnetic performance of the magnetic core. At higher magnetization rates, surface eddy currents partially shield the interior core causing performance of magnetic cores degraded. And the drastic drop of differential permeability in magnetic core is one of the most direct behaviors for the degradation characteristic of magnetic core. Two magnetic pulse compressor test stands were designed and built to evaluate the differential permeability of two different ferrite cores. The test stands are able to generate ‘1-cosine’ waveforms and operate at modest repetition rates. The magnetization rates achieved in the experiments extend from 0.8 to 2.5 T/μs, corresponding to saturation times from 400 to 1000 ns. The current through the core is calculated by voltage across the resistive load, and the loop voltage is picked up with a single wire loop and integrated by software. B-H curves are derived from the measured voltage and current waveforms. The differential permeability can be calculated from the slope of the B-H curve. Two materials evaluated in the experiments include a Mn-Zn ferrite magnetic core and a Ni-Zn ferrite magnetic core. The result shows that Ni-Zn ferrite magnetic core has the largest value of max differential permeability and the steepest descending segment of magnetic conductivity curve under both μs and sub-μs level pulse excitation. Furthermore, its loss under sub-μs level pulse excitation is the lowest. The above advantages allow Ni-Zn ferrite magnetic core to be properly used in the final stage magnetic pulse compression system.