Polarization measurement of dielectronic recombination transitions in highly charged krypton ions

TL;DR

This study measures the linear polarization of x rays from dielectronic recombination in highly charged krypton ions, confirming theoretical predictions and highlighting sensitivity to relativistic effects, with applications in plasma diagnostics.

Contribution

It provides the first polarization measurements of dielectronic recombination x rays in krypton ions, validating relativistic calculations and demonstrating sensitivity to Breit interaction effects.

Findings

Measured polarization degrees agree with relativistic calculations.

High polarization sensitivity to Breit interaction observed.

Results useful for plasma polarization diagnostics.

Abstract

We report linear polarization measurements of x rays emitted due to dielectronic recombination into highly charged krypton ions. The ions in the He-like through O-like charge states were populated in an electron beam ion trap with the electron beam energy adjusted to recombination resonances in order to produce $K\alpha$ x rays. The x rays were detected with a newly developed Compton polarimeter using a beryllium scattering target and 12 silicon x-ray detector diodes sampling the azimuthal distribution of the scattered x rays. The extracted degrees of linear polarization of several dielectronic recombination transitions agree with results of relativistic distorted--wave calculations. We also demonstrate a high sensitivity of the polarization to the Breit interaction, which is remarkable for a medium-$Z$ element like krypton. The experimental results can be used for polarization diagnostics of hot astrophysical and laboratory fusion plasmas.