Perspectives of Atomic Physics with Trapped Highly Charged Ions

Dear Colleagues,

The spectra of highly charged ions (HCI) have fascinated scientists since Edlén and Tyrén's pioneering work in the 1930s. The recognition in the 1940s that the hitherto mysterious solar coronal lines seen during solar eclipses originated from highly charged ions of Ca and Fe revolutionized the view of the sun and its workings and founded a new understanding of astrophysics. Since the 1950s, fusion plasma experiments reached higher and higher temperatures which were indicated by the production of higher and higher ion charge states. Fast ion beams were excited by being passed through thin foils; since the 1960s this technique enabled the time-resolved observations of beam-foil spectroscopy. Eventually the charge state distributions produced in the ion–foil interaction reached up to a few-electron ions of uranium, facilitating the study the high-field effects of quantum electrodynamics. However, especially at high ion beam velocities, the control of the Doppler effect poses problems to achieving high accuracy. On the other hand, heavy-ion storage rings have since enabled a plethora of very interesting physics experiments. Laser-produced plasmas were added to the spectroscopic toolbox in the 1970s; however, these hot plasmas are of high electron density and thus are more of technological interest than suited for accurate spectroscopy. Ion trapping of low charge state ions began in earnest in the 1950s, but it thrived and included highly charged ions only when vacuum technology progressed sufficiently, and when superconducting magnets supported Penning traps, and eventually the electron beam ion trap. Since the 1980s, all charge states of all elements have become available in such traps, with negligible Doppler shifts and little Doppler broadening in the spectroscopic observation. The low particle density in electron beam ion traps furthermore mimics the conditions in various astrophysical plasmas, and this wide field on its own should be extremely fruitful. Consequently, the electron beam ion trap concept and development which began at Livermore (CA, USA) by now, with ion traps of all sizes, has spread to quite a number of countries on (so far) four continents. Yet another tool has been provided by the recent combination of X-ray lasers and ion traps. Nuclear physics employs charge breeding in electron beam ion traps; extremely accurate mass measurements have been performed on trapped HCI, and fascinating processes observed on single ions in heavy-ion storage rings. There is a lot of physics to be explored! 

It should be useful and advantageous for the community to have a concentrated depository that reflects the width and variety of research in the subfield of Atomic Physics with Trapped Highly Charged Ions. For this purpose, the call for contributions to a Special Issue is renewed. Of course, "Atoms" welcomes submissions on all aspects of atomic physics, which usually report on past achievements. For this Special Issue of Atoms, I would like to particularly encourage and invite manuscripts that serve a different purpose in the community by looking ahead. I would like to see an emphasis on the assessment of a field (with suitable examples from your own work), combined with ideas of how work in the field might or should move forward. "Where are we, where do we want to go, using or developing which tools?" In any case, each paper needs original and noteworthy content.

Prof. Dr. Elmar Träbert
Guest Editor

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