Measurement of electron-impact–excitation cross sections for very highly charged ions

We report the first measurements of electron-impact--excitation cross sections for very highly charged ions (Ba⁴⁶⁺), and introduce a powerful new technique for studying these ions. Approximately 2×{}10⁴ Ba⁴⁶⁺ ions/cm were trapped inside the space charge of an {}120-mA electron beam and their x-ray emission spectra observed with Si(Li) and Bragg-crystal--diffraction spectrometers. Cross sections for several N=3 levels excited from the neonlike Ba⁴⁶⁺ ground state were measured relative to radiative recombination on the same ions.