Magnetic gradient drift
= Magnetic gradient drift
{title2=$\mathbf v_{\nabla B}=\mu\,\mathbf B\times\nabla B/(qB^2)$}
A slowly varying field magnitude exerts the gyroaveraged force $-\mu\nabla B$ on a particle with magnetic moment $\mu=mv_\perp^2/(2B)$. Applying the perpendicular-force <guiding-centre drift> formula gives the displayed velocity. Its direction depends on the sign of the particle charge.