Application to argon ions of a new technique to measure the two-electron contribution to the ground state energy of helium-like ions

We have measured the two-electron contribution of the ground state energy o f helium-like argon ions using an electron beam ion trap (EBIT). A two-dime nsional map was measured showing the intensity of x-rays from the trap pass ing through a krypton-filled absorption cell. The independent axes of this map were electron beam energy and x-ray energy. From this map, we deduced t he two-electron contribution of the ground state of helium-like argon. This experimentally determined Value (312.4 +/- 9.5 eV) was found to be in good agreement with our calculated values (about 303.35 eV) and previous calcul ations of the same quantity. Based on these measurements, we have shown tha t a ten-day absorption spectroscopy run with a super-EBIT should be suffici ent to provide a new benchmark value for the two-electron contribution to t he ground state of helium-like krypton. Such a measurement would then const itute a test of quantum electrodynamics to second order.