Generation of energetic barium atomic beam for fusion plasma diagnostics

A Ba+ beam is generated in a thermal contact-ionization plasma source made of a rhenium-foil cylinder 5 mm In diameter inserted into a tungsten cylinder for protection. The source can be heated up to about 3000 K. The maximum current of Ba+ already attained is 200 mu A. The beam can be accelerated to 40 keV. The Ba+ beam is passed through a Li-vapor cell and neutralized by a charge-exchange reaction with Li atoms. A 100 mu A/e Ba beam has already been obtained. The next subject is to measure the increase of energy spread of the beam passing through the Li cell by collisions with vapor atoms. An optical system has been developed for measuring it by the Doppler broadening of spectral lines emitted by Ba and Ba+ beam particles. Results of optical measurement are presented. The production of slow energy components has been observed. They are attributable to the head-on collision of Ba beam particles with a Na atom and with a K atom as impurities in the Li vapor cell. Because of the head-on collision, the energy spread of the main Ba beam is not changed in passing through the cell. (C) 1996 American Institute of Physics.