Wavelength measurements of the satellite transitions to then= 2 resonance lines of helium-like argon

The wavelengths of the 1s2s2p-1s 2 2s and 1s2p 2 -1s 2 2p transitions in Ar 15+ have been measured using a crystal spectrometer and an electron beam ion trap. These spectral lines are satellites to the n = 2 resonance lines of He-like Ar 16+ and play an important diagnostic role in high-temperature plasmas directed toward fusion research. The results of these measurements are compared with a number of different theoretical results, demonstrating the relative accuracy of these theoretical approaches.