Magnetic stretching moment growth
= Magnetic stretching moment growth
{title2=$\partial_t\langle B^q\rangle=Dq(q+3)\langle B^q\rangle$}
Twice integrating the <radial magnetic-field Fokker-Planck equation> by parts gives the displayed law when moments and endpoint terms are controlled. In particular $\langle B^2\rangle$ grows at rate $10D=2\gamma$, with $\gamma=5\kappa_2/4$. The corresponding <magnetic energy> density is $\langle B^2\rangle/(8\pi)$ in <Gaussian units>.