= Magnetic-history constant in an undamped plasma
{title2=$\partial_t(\nabla\times\mathbf j+\epsilon_0\omega_p^2\mathbf B)=0$}
The linear carrier acceleration equation $\dot{\mathbf j}=\epsilon_0\omega_p^2\mathbf E$ and <Faraday's law> imply this conserved local quantity. Setting its initial value to zero gives the second <London equation> and <London screening>. An undamped response alone does not select that initial value, so it must not be used to infer expulsion of a pre-existing <magnetic field> for every magnetic history.<The electromagnetic equations of the supraconductor by Fritz London and Heinz London>[pp. 71–74: acceleration theory and the additional superconducting relation]{ref}
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