Ion skin depth
= Ion skin depth
{title2=$d_i=c/\omega_{pi}$}
For a singly charged ion species in <Gaussian units>, $\omega_{pi}=(4\pi ne^2/m_i)^{1/2}$ is its <plasma frequency> and $d_i=c\sqrt{m_i/(4\pi ne^2)}$. The ion skin depth marks a characteristic scale below which ion and electron motion can separate in a magnetized <plasma>. Together with the <Alfvén speed>, it satisfies $v_Ad_i=cB_0/(4\pi en)$, the coefficient of guide-field propagation in <electron magnetohydrodynamics>.