Spectral modeling of Fe XVII pumped by a free-electron x-ray laser

Abstract

ABSTRACTThe atomic structure and x-ray pumping of neonlike Fe xvii have been calculated and modeled under free-electron laser excitation conditions using the Flexible Atomic Code. Speci“cally, pumping of the (2p 3 / 2 3s 1 / 2 ) 2 ,1 ,(2p 1 / 2 3s 1 / 2 ) 1 , (2p 3 / 2 3d 5 / 2 ) 1 , and (2p 1 / 2 3d 3 / 2 ) 1 levels that connect with the ground state (2s 2 2p 6 ) 0 by the so-called M2, 3G, 3F, 3D, and 3C transitions have been studied. In addition, the spectrum of sodiumlike Fe xvihas been modeled to account for possible line coincidences with the neonlike spectrum. The calculations includeoscillator strengths, radiative lifetimes, autoionization rates, non-resonant photoionization cross sections, andline emissivities.Keywords: atomic spectra, x-ray pumping, laboratory astrophysics, free-electron laser1. INTRODUCTIONThe combination of electron beam ion traps (EBITs) with accelerator-based light sources is a novel laser-spectroscopic technique for the study of x-ray transitions in highly charged ions. The x-ray emission from asynchrotron or free-electron laser (FEL) is guided into an EBIT, where ions of a certain charge state are createdand con“ned in an electromagnetic trap. The laser radiation can then pump speci“c atomic resonances of thenearly stationary highly charged ions and populate energy levels otherwise not readily excited in a low-densitycollisional plasma. The technique allows for new regimes of atomic physics to be explored, such as line-formationprocesses in photoionized plasmas. The EBIT accelerator arrangement has been tested at laboratories such asthe BESSY- iielectron storage ring