Excitation and ionization of ions by electron impact. Technical progress report, September 1, 1976--May 31, 1977. [Summaries of research activities at Georgia Institute of Technology

Abstract

This effort is devoted to experimental measurements of electron impact excitation and ionization cross sections of ions. The cross sections of interest are those of importance in the diagnostics of CTR plasmas. Current tasks include: the completion of absolute measurements of the electron impact double ionization cross sections for Na/sup +/, K/sup +/, Rb/sup +/, Cs/sup +/, and Tl/sup +/ ions; the development of a laboratory-size ion source of multiply-charged ions to be used in the measurement of electron impact excitation and ionization cross sections; and the completion of absolute measurements of the electron impact excitation of Li/sup +/ ions. Preliminary measurements of the electron impact double ionization cross sections of Na/sup +/, K/sup +/, Rb/sup +/, Cs/sup +/, and Tl/sup +/ ions were completed. Measurements were made over the range of electron energies from the respective threshold values to approximately 1000 eV. Peak cross sections were found to vary from 7.2 x 10/sup -19/ cm/sup 2/ for Na/sup +/ to 3.5 x 10/sup -17/ cm/sup 2/ for Cs/sup +/. The data were obtained with a crossed beam apparatus operating with modulated beams. A PIG-type source of multiply charged ions is undergoing final development. The source is of laboratory size and is compatible with existing collision apparatus. The previous problem with inadequate magnetic field has been solved. Spectroscopic techniques verified the production of ions of charge state C/sup 4 +/ when CO/sub 2/ was used as the source gas. Some difficulty has been encountered in extracting adequate ion currents. Also under investigation is the optimum technique for the production of metal ions with the PIG-type ion source. A list of publications is included.