X-ray observations of Ca^{19 +}, Ca^{18 +}and satellites from Alcator C-Mod tokamak plasmas

Abstract

X-ray spectra of n = 2 to 1 transitions in hydrogen-like Ca19 +, helium-like Ca18 + and nearby satellites have been obtained from Alcator C-Mod tokamak plasmas using a spatially imaging high resolution x-ray spectrometer system. For Ca19 +, the intensity ratio of Lyα2 (1s 1S1/2–2p 2P1/2) to Lyα1 (1s 1S1/2–2p 2P3/2) was found to be ∼0.531 ± 0.005 over a range of plasma parameters, which is somewhat greater than the ratio of the statistical weights of the upper n = 2 levels, 1/2. This difference is mainly due to interaction with the 2S1/2 fine structure sub-level. Experimental results are compared to calculations from COLRAD, a collisional-radiative modelling code, and good agreement is shown. For Ca18 +, the intensity ratio of the dielectronic satellite k (1s22p 2P1/2–1s2p2 2D3/2) to the resonance line w (1s2 1S0–1s2p 1P1) is sensitive only to the electron temperature. The observed brightness ratio scaling with Te is in good agreement with the calculated ratio of the respective dielectronic recombination to the collisional excitation rates.

Electron impact excitation for He-like ions withZ= 20–42

“…Emission lines from the spectra of helium-like ions are often observed in the spectra of solar, stellar, and other astrophysical plasmas (Seely & Feldman 1985;Feldman et al 2000;Dere et al 2001;Ness et al 2003;Paerels & Kahn 2003;Phillips 2004;Landi & Phillips 2005;Güdel & Nazé 2009;. Spectral lines of helium-like ions are also prominent features in the X-ray spectra of tokamak and laser-produced plasmas (Hsuan et al 1987;Rice et al 1987Rice et al , 1999Rice et al , 2014Rice et al , 2015Beiersdorfer et al 1995). An analysis of spectral lines provides information on the temperature, density, and chemical composition of the plasma.…”

Energy levels and transition rates for helium-like ions withZ = 10–36

“…Spectral lines of helium-like ions are also prominent features in the X-ray spectra of tokamak plasmas and laser-produced plasmas. These features arise from impurity elements (e.g., Hsuan et al 1987;Bombarda et al 1988;Beiersdorfer et al 1995;Elton et al 2000;Rosmej et al 2002;Rice et al 1987Rice et al , 1999Rice et al , 2000Rice et al , 2014Rice et al , 2015. The relative intensities Full Tables 1 and 2 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A141 of spectral lines from the n = 2 shell to the ground state have been widely used in temperature and density diagnostics for solar plasma (e.g., McKenzie et al 1979;Wolfson et al 1983;Keenan et al 1984;Doyle & Keenan 1986) and tokamak plasmas (e.g., Källne et al 1983;Keenan et al 1989).…”

X-ray observations of medium Z H- and He-like ions with satellites from C-Mod tokamak plasmas

“…Regardless of the electron temperature, the total composite satellite contribution to the Ly α doublet line ratio is roughly in the same ratio as the Ly α doublet itself, so has a negligible effect on the inferred ratio. A similar exercise has been performed for the Ly α doublet of Ca 19+ , a measured spectrum of which [1,5,15] is shown in Fig.3, obtained is 0.529±0.003. The synthetic spectrum, which is in excellent agreement, utilized CR modelling for the doublet from COLRAD, for the n = 2 and n = 3 satellites from [57] and for higher n satellites from [54].…”

“…A direct comparison of the ratio as a function of atomic number is shown in Fig.6 for plasmas the curve which is in excellent agreement with the measured points. This ratio difference for different elements is due to a strong Z-dependence of the magnetic dipole transition probability for 2S 1/2 -1S 1/2 [73,43,15].…”

“…Improvements in high resolution x-ray spectrometers have allowed the detailed study of spectra from medium Z hydrogen-like [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15] and helium-like [16,17,18,19,20,4,21,22,23,24,7,25,26,27,28,29,30,31,32,33,34,35,36,37,38,14,39,15] ions in high temperature plasmas. This is made possible by corresponding advances in atomic structure codes, which enables individual line identifications to be made.…”