A measurement of deuterium neutrals by the Balmer-series in the STP-2 high beta screw pinch tokamak

The neutral particle density of a deuterium plasma in the STP-2 screw pinch tokamak has been determined spectroscopically. The particle density for the ground state of deuterium is calculated from the rate equations for population density of the excited levels with principal quantum numbers 3 and 4; both of the population densities were obtained from intensities of the Balmer alpha and beta lines, and the rate coefficients for electronic collision were estimated from the electron density (10 to the 14th per cu cm) and temperature (10 eV) measured by laser scattering. It is found that the neutral density is approx. 2 x 10 to the 12th per cu cm at the center of the plasma and 2 x 10 to the 14th per cu cm on the periphery. The time history of the neutral deuterium density is consistent with the observed increase in plasma density.