Design of a compact focusing lens system with short acceleration tube at 300 kV

Ishii, Yasuyuki; Okubo, Takeru; Kojima, Takuji; Kamiya, Tomihiro

A high-demagnification acceleration lens system is developed for a compact apparatus forming gaseous ion nanobeam with an energy ranging from several hundred keV to MeV in Japan Atomic Energy Agency (JAEA). For gaseous ion nanobeam formation, it is necessary to use a plasma-type ion source. The diameter of the anode through-hole, which is an object in the lens system, in the ion source is several hundred micrometers to extract sufficient ion beams from ion source plasma. Therefore the lens system with the higher demagnification of over 1000 was required to form the nanobeam. In this study, the compact high-energy acceleration lens system up to several hundred keV was designed by combining the double acceleration-lens system already developed in JAEA to form several tens keV gaseous ion nanobeams and an acceleration tube newly designed in this study to boost up its beam energy. Especially since the acceleration tube plays roles of not only the ion beam acceleration but also a final focusing lens, the lens effect of its tube was studied in detail in the design. In the conference, the design of the new lens system based on the ion optical calculation and the specification of the whole system with a duoplasmatron-type ion source will be presented.