ION-BEAM GENERATION FROM A THERMAL CONTACT-IONIZATION PLASMA SOURCE

The ion beams are produced by a cylindrical thermal contact-ionization plasma source with an electrostatic lens system. The source plasma is produced at the inside surface of a 5-mm-diam 20-mm-long Re foil cylinder protected with a W cylinder. The surface is heated up to 3000 K by electron bombardment. The material to be ionized is fed to the surface through a guide pipe from a reservoir. Generation of all alkaline metal ions have been tested and a beam current of hundreds of muA is obtained. The efficiency for Li+ production is 30%, while that for Cs+ is nearly 100%. Alkaline earth ion beams, except Mg, are generated. A current of Ba+ up to 200 muA is obtained, while a Tl+ beam of over 200 muA is achieved. Halogen negative ion beams, except F-, of the order of 10 muA are also obtained when alkali halides are used. Attempts to extract Li- from the source are also being made.