Curvature drift
= Curvature drift
{title2=$\mathbf v_c=mv_\parallel^2\,\mathbf b\times\boldsymbol\kappa/(qB)$}
For a curved field direction $\mathbf b=\mathbf B/B$, define the curvature vector $\boldsymbol\kappa=(\mathbf b\cdot\nabla)\mathbf b$. Motion along curved field lines produces a gyroaveraged drift perpendicular to both field and curvature. In a purely toroidal field this and <magnetic gradient drift> cause opposite vertical drifts for opposite charge signs.