Measurement of 3s - 3p lines in sodium- and magnesium-like tungsten ions

Tungsten is currently gaining popularity as a plasma facing material in magnetic confinement fusion (MCF) plasma experiments. With tungsten as a divertor and first wall material, the high heat loads on the surfaces will sputter off ions and introduce them into the plasmas. The abundances expected of highly charged tungsten ions in future MCF plasmas emphasize the need for reliable atomic data in order to accurately diagnose the experiments. Here we present a measurement of the 3s_1/2-3p_3/2 resonance transitions in sodium-like (W⁶³⁺) and magnesium-like (W⁶²⁺) tungsten ions. The wavelengths of the two lines have been measured at the electron beam ion trap facility at Lawrence Livermore National Laboratory relative to well known reference lines from oxygen and nitrogen ions. Using the high- energy SuperEBIT electron beam ion trap and a 44.3 m grazing-incidence soft X-ray spectrometer, the lines were observed with a cryogenic Princeton CCD camera. The wavelength data are compared with theoretical predictions for ions along the isoelectronic sequences. Charge balance calculations indicate that the sodium-like and magnesium-like tungsten ions have a charge state fraction of greater than 10% at electron temperatures between 10 and 25 keV. Consequently, the two emission lines could be used to diagnose the inner half of ITER plasmas.