A small and compact ion beam source has been developed for a heavy ion beam probe as a plasma diagnostic technique. The source consists of a thermal contact ionizer with a beam material reservoir, and an electrostatic accelerating lens system. The beam modulation is possible by means of a beam extracting electrode. An alkali or an alkali earth metal ion beam was produced at an energy up to 3 keV. The sourcefunctioned sufficiently in a magnetic field up to 2 kG. Especially, operating parameters for Cs
+ and Ba
+ ion beams were investigated in detail. A beam Current up to 10μ A and a diameter of 1 mm at a focussing point were easily obtained. A method is also presented to compensate both the beam current reduction and the beam profile distortion which were observed in the operation in a stronger magnetic field above 2 kG.
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