Studies of magnetic dipole transitions in highly charged argon and barium using an electron beam ion trap

Using the Oxford electron beam ion trap (EBIT), we have studied a number of magnetic-dipole fine-structure transitions in highly charged argon and barium, which lie in the visible and near-UV region of the spectrum. Our wavelength measurements, with uncertainties of between 7 and 20 ppm, are the most accurate yet reported using an EBIT as a spectroscopic source of ions, and provide a useful test of atomic structure calculations for many-electron systems. The argon transitions studied are also of astrophysical interest. Finally, we present the first studies of the polarization of a visible transition from a highly charged ion trapped in an EBIT.