Vacuum ultraviolet measurements on hydrogen resonance lines in the Maryland Centrifugal Experiment

Extended spectroscopic measurements of hydrogen emission into the vacuum ultraviolet region on the Maryland Centrifugal Experiment [R. F. Ellis, A. B. Hassam, S. Messer, and B. R. Osborn, Phys. Plasmas 8, 2057 (2001)] indicate, from opacity on the Lyman series, ∼6% atomic hydrogen coexisting with protons, electrons, and carbon-impurity ions in a plasma region where the temperature is ∼15eV. An explanation is offered, based upon charge exchange of entering cold hydrogen atoms with plasma protons, followed by collisional excitation and radiative decay.