Measurement of electron-impact<i>–</i>excitation cross sections for very highly charged ions

Abstract

We report the first measurements of electron-impact--excitation cross sections for very highly charged ions (${\mathrm{Ba}}^{46+}$), and introduce a powerful new technique for studying these ions. Approximately 2\ifmmode\times\else\texttimes\fi{}${10}^{4}$ ${\mathrm{Ba}}^{46+}$ ions/cm were trapped inside the space charge of an \ensuremath{\simeq}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 ${\mathrm{Ba}}^{46+}$ ground state were measured relative to radiative recombination on the same ions.