Saha Ionization Equation
A thermodynamic relation expressing the ionization state of a plasma in thermal equilibrium as a function of temperature and electron density.
Governing formula
(n_i+1 n_e) / n_i = (2 g_i+1 / g_i) (2 π m_e k_B T / h²)^(3/2) e^(-E_ion / (k_B T))
SI unit
m⁻³ (Ionization Balance Density)
In depth
Formulated by Meghnad Saha in 1920. Relates neutral atom and ion densities (n_i, n_i+1) to thermal kinetic energy k_B T and ionization energy E_ion, providing the basis for stellar atmosphere spectroscopy.
Examples in the real world
Calculating the ionization fraction of hydrogen in stellar atmospheres and thermal plasma arc columns.