KWD.acceleration_exponent
The acceleration_exponent sets the length scale over which the accleration to \(v_\infty\) is accomplished. This value is the \(\beta\) exponent from the Caster & Lamers equation of a stellar wind,
\[v(r) = v_0 + (v_\infty-v_0) * (1 - R_s/r)^{\beta}.\]