Equipartition magnetic field
= Equipartition magnetic field
{title2=$B_{\rm eq}=\sqrt{\mu_0\rho}\,U$}
Equating magnetic energy density $B^2/(2\mu_0)$ to kinetic energy density $\rho U^2/2$ defines this order-of-magnitude field. It marks when a weak-field kinematic treatment of a given flow can fail, not a universal upper bound on concentrated fields. Gas-pressure confinement, compression, partial evacuation and dynamic pressure can allow stronger local fields.