Towards spectroscopy of Highly Ionized Atoms in a 0.29 T compact EBIT for measuring forbidden transitions and fundamental constants

We present an ongoing effort at NIST to observe the visible spectra of atomic transitions in highly charged ions produced/excited in a compact 0.29 T electron beam ion trap (EBIT). This mini-EBIT is made extremely compact using room-temperature permanent magnets, attaining sufficient current density to produce a variety of interesting charge states with ionization thresholds below 5 keV. For instance, recent theoretical studies suggest that In-like praseodymium and Sn-like neodymium exhibit highly forbidden transitions in the visible and infrared region of the E/M spectrum, making them promising candidates for high-accuracy optical frequency standards [1]. Additionally, precise measurements of the isotopic shift in the stretched-ground-state fine structures of K-like and Ca-like krypton ([Ar]3d and [Ar]3d² respectively [2]) may offer a pathway for determining fundamental constants, contingent on further theoretical developments. Experimental progress will be discussed.

[1] M. Safronova, et al., PRL 113, 030801 (2014).

[2] NIST Atomic Spectra Database (ver. 5.12), [Online].