= Wind-driven magnetic braking of a solar-type star
{title2=$\dot J\simeq-\dot M_w\Omega R_A^2$}
A magnetized <stellar wind> extracts angular momentum through matter transport and <Maxwell stress tensor>. The <Alfvén radius> supplies an effective lever arm larger than the stellar radius, with geometry factors absorbed into an averaged lever arm. <Dynamo action> couples the torque to rotation by supplying the magnetic field. For a simplified radial wind of fixed speed, $R_A^2$ scales as $B_*^2R_*^4/(\mu_0\dot M_wv_w)$, so unsaturated $B_*\propto\Omega$ gives a torque proportional to $-\Omega^3$. Magnetic topology and wind thermodynamics can alter this scaling.
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