Emission-Line Intensity Ratios in F[CLC]e[/CLC] [CSC]xvii[/CSC] Observed with a Microcalorimeter on an Electron Beam Ion Trap

Abstract

We report new observations of emission line intensity ratios of Fe xvii under controlled experimental conditions, using the National Institute of Standards and Technology electron beam ion trap (EBIT) with a microcalorimeter detector. We compare our observations with collisional-radiative models using atomic data computed in distorted wave and R-matrix approximations, which follow the transfer of the polarization of level populations through radiative cascades. Our results for the intensity ratio of the 2p6 1S –2p53d 1P 15.014 A ̊ line to the 2p6 1S – 53 ̊010 2 p 3d D1 15.265 A line are 2.94 0.18 and 2.50 0.13 at beam energies of 900 and 1250 eV, respectively. These results are not consistent with collisional-radiative models and support conclusions from earlier EBIT work at the Lawrence Livermore National Laboratory that the degree of resonance scattering in the solar 15.014 A ̊ line has been overestimated in previous analyses. Further observations assess the intensity ratio of the three lines between the 2p6–2p5 3s configurations to the three lines between the 2p6–2p5 3d configurations. Both R-matrix and distorted wave approximations agree with each other and our experimental results much better than most solar and stellar observations, suggesting that other processes not present in our experiment must play a role in forming the Fe xvii spectrum in solar and astrophysical plasmas.