Abstract
In the interaction of fast ions with dense matter, the collision frequency is high enough to facilitate the simultaneous excitation of several electrons. Such multiply-excited few-electron systems have been exploited variously for plasma diagnostics. Beam-foil spectroscopic techniques, benefiting from the inherent time-resolution offered by the geometry of typical experiments, have proven particularly fruitful for the study of emission patterns and level lifetimes of specific multiply-excited levels, especially those of maximum spin and total angular momentum. Typical cases are recalled to illustrate some general principles. Among many others, earlier beam-foil measurements have targeted the core-excited 2p53s3p 4D7/2 – 2p5 3s3d 4F9/2 transition in several Na-like spectra ranging from S VI to Cu XIX. Data on the six intermediate elements missing at that time are now added. The interest in such atomic systems with multiple excitations and high total angular momentum values is discussed with a variety of examples.
Highlights
In his 1964 Handbook of Physics article on atomic spectra [1], B
The simultaneous excitation of several electrons can happen. While this is rare in conventional light sources, it happens frequently by collisions in dense plasmas, including the interaction of a fast ion beam with solid targets, in high-power laser produced plasmas, or by inner-shell ionization processes as can be affected by photons in astrophysical plasmas or by X-ray lasers in the laboratory
The high total angular momentum (J) levels of such ions usually live much longer than their nearby relatives, and they offer a different access to the measurement of atomic properties
Summary
In his 1964 Handbook of Physics article on atomic spectra [1], B. Out of the vast multitude of atomic cases to study, I am selecting a small group to discuss some developments that I have witnessed or participated in. These are levels with a high value of the total angular momentum J, which have a somewhat limited number of decay channels, each of which may be more prominent and better detectable than the many weak decay channels of other levels. The same general feature is, found in singly excited atomic systems of which the structure is often simpler The inclusion of such high-J levels in computations requires the inclusion of all lower n- and J-levels, which in earlier days might have amounted to a major challenge. It may be useful to keep such measurement situations in mind so that the databases can be augmented and specific analyses can be improved
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