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Estimation of the Persistent Oxygen Impurity Density in a Theta Pinch Plasma by VUV Absolute Intensity Measurements

An order of magnitude estimation of the oxygen density is carried out in a helium plasma produced by a small linear theta pinch from the absolute intensity measurements in a VUV (vacuum ultraviolet) wavelength region using a grazing incidence spectrometer absolutely calibrated by the branching ratio method. The corona model is used for the analysis, and its applicability is discussed to this plasma in terms of the electron temperature and density which are estimated from the measurements in the VUV wavelength region. The ratio of total oxygen density to the electron density is about 0.02% in a discharge of helium gas of 99.9% purity. The origin of the oxygen atoms is discussed.