Inferring electron temperature in warm hydrogen plasmas from Balmer series spectral line ratios using a collisional radiative model *

The electron temperature of warm (10-400 eV), moderate density (1e11-1e13/cc) hydrogen plasmas has been investigated using a collisional radiative model (CRM) updated from earlier work [1]. Time-resolved H Balmer series spectral line radiation from pulsed hydrogen plasmas in the PFRC-2 device were measured with two spectrometers, both calibrated with an absolute-intensity standard source.  The electron temperatures were derived by comparing the measured line ratios to a CRM. In conjunction, the electron density was independently measured by an interferometer and assumptions about the plasma diameter.  The CRM-inferred electron temperature was shown to strongly depend on the method for determining the strength of the emitted light, the estimated ratio of atomic to molecular hydrogen densities, and the assumed profile of the electron density.  The causes of these dependences and methods to reduce the uncertainty in this technique are described.  The potential applicability of this CRM to other plasma physics experiments are discussed.

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