X-Ray Crystal Spectroscopy of a Theta-Pinch Plasma in the Region 15-25Å

A new synthetic crystal, potassium acid phthalate (KAP), has a spacing between crystal planes, $2d=26.6$ {}. The use of this crystal in a Bragg crystal spectrometer has permitted measurement of the Scylla I x-ray spectrum from 15 to 25 {}, a region inaccessible with the beryl crystal previously used. The principal features of the observed spectrum in this region are the lines of O vii and O viii arising from oxygen contamination of the discharge by material from the ceramic discharge tube. Six lines of the resonance series of O vii are observed, including both 1s²¹S₀-1s2p¹P₁ and 1s²¹S₀-1s2p³P₁. The first members of the Lyman series of O viii are also observed. Measurements of Doppler widths of the lines of O vii and O viii yield an oxygen-ion Doppler temperature of 9.3±{}2.8 keV. These measurements, when combined with those previously made on other ion species, show that the ions of the plasma are not in collisional equilibrium.