Polarization-dependent spectra of x-ray dielectronic satellite lines of Be-like Fe

Abstract

We have studied the polarization properties of dielectronic satellite lines in Be-like Fe ions excited through resonant electron capture by an electron beam. Using the photon density-matrix formalism, we have calculated the degree of polarization and polarization-dependent spectra of dielectronic satellite lines, i.e., the spectral intensity distribution of lines associated with a given polarization state. Theoretical results have been compared with experiments performed at the Lawrence Livermore National Laboratory electron-beam ion trap where dielectronic satellite line emission from Fe ions produced at different energies of the electron beam was simultaneously recorded with two crystal spectrometers. These spectrometers had different polarization sensitivities. The experimental spectra recorded by the two spectrometers are reproduced by the theory. This ability to model the polarization dependence of x-ray line spectra is important for the diagnosis of electron beams in plasmas.

Cascade effects on the polarization of He-like Fe1s2l−1s2x-ray line emission

“…Even for this line, however, we reproduce the two limiting values of -1 and -3/7 depending on which LS-term is taken as dominant, also in accordance with Ref. [20]. Also, polarization degree results for the He-like Si satellites of the Ly-a agree with those of Ref.…”

“…Next, magnetic sublevel populations and polarization degrees were computed according to the model discussed in the theory section. Our results agree with the B-and Be-like Fe measurements at EBIT, and also with results from independent calculations based on the photon density matrix [20,22]. The only exception is line #9 in Table I D and therefore our single-channel assumptions about its electron capture rates do not apply.…”

“…In this section we discuss the results of our calculations for the polarization degrees of dielectronic satellite lines in Fe ions, and compared them with measurements at the Livermore EBIT as well as independent calculations [20][21][22]. In particular, we consider 1s 2l 2l' 2l'' AE 1s ) we can assume that each autoionizing state is populated solely by electron capture from the ground state of the next higher ionization stage, and depopulated by autoionization and spontaneous radiative decays.…”

“…This approximation allows us to calculate sublevel rates from J-level rates (which we assume to be known) using the Clebsch-Gordan coefficients instead of calculating them "from scratch." Ultimately, this leads to the fact that the polarization degrees of the studied dielectronic satellite lines are rational numbers [20,22].…”

The importance of EBIT data for Z-pinch plasma diagnostics

“…EBIT is very important for the study of polarization because it is capable o f producing x-ray lines by the beam of non-Maxwellian electrons a t well-contro lled experimental conditions, which includes, for exa mple, selection of the atomic process, ionization stage, and value of the electron beam. Our previous w ork on x-ray line polarization at L LNL EBIT included the study of polarization-dependent spectra of x-ray diel ectronic satellites of Li-and Be-like [14][15] and B-like Fe ions [16]. In the pres ent paper we analyze polarization-dependent Ti K-shell spectr a gen erated by a quasi-Max wellian e lectron beam at the LLNL EBIT and compare this analysis with K-sh ell spectra from Ti X-pinches obtained at UNR.…”