HIGH-RESOLUTION MEASUREMENT, LINE IDENTIFICATION, AND SPECTRAL MODELING OF THE K-BETA SPECTRUM OF HELIUM-LIKE AR16+

High-resolution crystal spectrometer measurements of the K beta spectr um of heliumlike Ar16+ covering the wavelength region from 3.34 to 3.5 0 Angstrom are presented and compared with detailed theoretical analys es. The measurements were made on the Princeton Large Torus tokamak an d test the theoretical atomic data in the low-density limit at an elec tron density n(e) less than or equal to 2X10(13) cm(-3) and temperatur e T-e= 2.3 keV. Satellite transitions of the type 1s(2)2l-1s2l3l' and 1s(2)3l-1s3l3l' from lithiumlike Ar15+ and 1s(2)l2l'-1s2l2l'2l '' are identified that are produced by either dielectronic recombination or e lectron-impact excitation. Good overall agreement between the predicte d and measured intensities of the strong dielectronic satellites is fo und. The agreement demonstrates the utility of K beta spectra as a dia gnostic of the electron temperature of low-density plasmas, such as th ose found in the Sun or magnetic fusion facilities. Poorer agreement i s found for the weaker dielectronic satellite transitions, including t he 1s3l3l' satellites that play an important role in the analysis of h igh-density plasma produced in laser fusion. Their intensity is undere stimated by the calculations by about 50%. Moreover, it is shown that direct electron-impact excitation rates underestimate the relative int ensity of the 1s(21)S(O)-1s2p P-3(1) transition in heliumlike Ar16+ by a factor of 2, indicating the need for including additional excitatio n processes and possible blends with high-lying dielectronic satellite s of the type 1s(2)nl'-1s(2)nl'-ls31nl' with n greater than or equal t o 4 in the theoretical models.