Inductance gradient (L′) is one of the important parameters on the design and evaluation of rail-type electromagnetic launcher (EML) performance. From the relation between inductance and magnetic energy, we derived the expression of L′ for rail-type EML under 2-D transient conditions. To analyze the diffusion behaviors of electromagnetic field in the rail, we built the magnetic field diffusion equation, which was combined with the finite element software Ansoft-Maxwell, and simulated the magnetic field and current density distribution. The results show that the value of L′ ,under transient conditions, ranges from Kerrisk’s high frequency L′ to Grover’s low frequency L′, when the current diffuses from the rail surface to the state when the current is uniform throughout the rail cross section. The total current decreases or electrical conductivity changes, the diffusion behaviors of electromagnetic field will change, so does the transient L′ curve. We believe that the transient L′ curve is closely related to the diffusion behaviors of electromagnetic field, which is affected by the eddy current.
KEY WORDS :inductance gradient;armature;magnetic energy;transient;diffusion;eddy current;
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