= Magnetic flux concentration
Magnetic flux concentration redistributes existing <magnetic flux> into a smaller area. For a locally straight flux bundle with conserved flux, $B\mathcal A$ is constant, so decreasing area increases field strength. Converging convection, field-line stretching and <flux expulsion> can produce concentrations; finite <magnetic diffusivity> opposes them and <Lorentz force> feedback limits the kinematic approximation. Redistribution alone is not evidence of net <dynamo action>.
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