Excitation of Balmer lines in low-current discharges of hydrogen and deuterium

Measurements have been made of electron-impact ionization and excitation of Balmer lines in low-current, steady-state discharges of hydrogen and deuterium. Results were obtained from spatial scans of ${\mathrm{H}}_{\mathrm{\alpha }}$ lines for E/N ranging from 250 Td to 10 kTd. Here E is the electric field, N is the gas density, and 1 Td=${10}^{\mathrm{-}21}$ V ${\mathrm{m}}^2$. Ionization and excitation coefficients versus E/N are presented for E/N between 250 and 1800 Td, and Nd (where d denotes the gap length) between 2.3×${10}^{22}$ and 1.7×${10}^{21}$ ${\mathrm{m}}^{\mathrm{-}2}$. Excitation coefficients obtained for ${\mathrm{H}}_{\mathrm{\alpha }}$ and ${\mathrm{D}}_{\mathrm{\alpha }}$ are placed on an absolute scale using a standard tungsten lamp calibrated against the blackbody radiation standard. The ionization coefficients are compared with previous experimental and theoretical data, while the excitation coefficients are compared with the calculated values.