First adiabatic invariant
= First adiabatic invariant
{title2=$\mu=v_\perp^2/(2B)$}
The magnetic-moment invariant of rapid <cyclotron motion> in slowly varying fields. Here the per-unit-<mass> convention is used: the physical magnetic moment is $m\mu$. In <drift kinetics>, using $(\mu,v_\parallel)$ as coordinates removes the leading perpendicular acceleration and leaves a <velocity-space measure> proportional to the exact <magnetic field> strength.