Photoionization of Astrophysically Relevant Atomic Ions at PIPE (original) (raw)

We review recent work on the photoionization of atomic ions of astrophysical interest that has been carried out at the photon-ion merged-beams setup PIPE, a permanently installed end station at the XUV beamline P04 of the PETRA III synchrotron radiation source operated by DESY in Hamburg, Germany. Our results on single and multiple L-shell photoionization of Fe + , Fe 2+ , and Fe 3+ ions, and on single and multiple K-shell photoionization of C − , C + , C 4+ , Ne + , and Si 2+ ions are discussed in astrophysical contexts. Moreover, these experimental results bear witness of the fact that the implementation of the photon-ion merged-beams method at one of the world's brightest synchrotron light sources has led to a breakthrough for the experimental study of atomic inner-shell photoionization processes with ions. Atoms 2020, 8, 45 2 of 17 for U 91+ . Thus, photon energies from the vacuum ultraviolet (VUV) to the hard X-ray bands are needed for investigating photoionization of ions across the entire periodic table. Powerful laboratory sources for these types of radiation are hot plasmas and synchrotron light sources, which both have been used for photoabsorption and photoionization studies with atomic ions. The dual laser plasma (DLP) technique [12] uses a laser-generated hot plasma as a back-lighter for absorption measurements with ions in a second laser-generated plasma. In contrast to the broad spectral distribution of the radiation from a hot plasma, synchrotron radiation has a much narrower photon-energy bandwidth and it is freely tunable over large energy ranges. Moreover, modern third generation synchrotron light sources provide a high photon flux, which is a prime necessity for experiments with dilute targets, such as ions, whose mutual electrostatic repulsion entails low particle densities. The density of ionic targets can be increased in ion traps, where the ion cloud can be compressed by external fields and its density can be increased by applying cooling techniques. Nevertheless, the signal rates from such arrangements are usually still rather low and, therefore, photoionization of trapped atomic ions has been performed in only a few cases , so far.