High-resolution X-ray spectra from low-temperature, highly charged ions

The electron beam ion traps (EBIT) at Livermore were designed for studying the x-ray emission of highly charged ions produced and excited by a monoenergetic electron beam. The precision with which the x-ray emission can be analyzed has recently been increased markedly when it became possible to decouple the temperature of the ions from the energy of the electron beam by several orders of magnitude. By adjusting the trap parameters, ion temperatures as low as 15.8 +/- 4.4 eV for Ti20+ and 59.4 +/- 9.9 eV for Cs45+ were achieved. These temperatures were more than two orders of magnitude lower than the energy of the multi-keV electron beam used for the production and excitation of the ions. A discussion of the techniques used to produce and study low-temperature highly charged ions is presented in this progress report. The low ion temperatures enabled measurements heretofore impossible. As an example, a direct observation of the natural line width of fast electric dipole allowed x-ray transitions is described. From the observed natural line width and by making use of the time-energy relations of the uncertainty principle we mere able to determine a radiative transition rate of 1.65 fs for the 2p-3d resonance transition in neonlike Cs45+. A brief discussion of other high-precision measurements enabled by our new technique is also given.