Dielectronic recombination measurements in a single pass experiment

Abstract

Until 1983 the only experimental information on DR had come from spectroscopic observations of plasmas from which only thermally averaged rates may be inferred. In 1983-84 four groups reported DR cross section measurements. A group at the joint Institute for Laboratory Astrophysics (JILA) measured the DR cross section of Mg/sup +/ using crossed ion-electron beams and recording coincidences between recombined Mg atoms and stabilizing photons from the collision region. A similar experiment was carried out by Williams for Ca/sup +/. Two groups used merged electron-ion beam methods (i.e. similar in geometry to electron beam cooling systems). One experiment at the University of Western Ontario used a tenuous; emission limited, highly monoenergetic electron beam merged with a 450 keV C/sup +/ beam to reach the requisite collision energies of a few eV; (the signal levels here were very low). At Oak Ridge National Laboratory (ORNL) we wish to work with multiply charged ions and we have chosen to use a compressed space charge limited electron beam. We chose a merged beam approach to take advantage of our ability to produce high charge state, MeV/amu ions and a high current, high energy (1-3 keV) electron beam. The merged beam apparatus is constructed such that in the interaction region, the ion beam is coaxial with and embedded within the electron beam for a distance of 84 cm. 6 references, 8 figures