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Flow of charged particles near the plasma grid in negative ion sources affects the extraction efficiency of negative hydrogen / deuterium (H- / D-) ion beams [1][2]. In our previous research, the flow of the charged particles was measured with a four-pin directional Langmuir probe by rotating the tips around the center axis of the tips [3]. In the case of the four-pin probe, spatial resolution is determined by the distance between the probe tips, while plasma state changes with the direction and strength of Electron Deflection Magnetic (EDM) field. Furthermore, the field direction becomes opposite within the distance of the probe tips at some position close to the plasma grid. To resolve the problem of spatial resolution, a single-pin directional Langmuir probe equipped rotatable flap co-axially to shield charged-particle flow around the tip was newly developed and installed to the NIFS R&D Negative Ion Source (NIFS-RNIS). The probe is available to apply for a usual photodetachment Langmuir probe as well as usual electrostatic one. The first data obtained with the directional photodetachment Langmuir probe with the rotatable flap are going to be introduced.
[1] M. Kisaki et al., Rev. Sci. Instrum. 85, 02B131 (2014).
[2] H. Nakano et al., AIP Conf. Proc. 1515, 237 (2013).
[3] S. Geng et al., Rev. Sci. Instrum. 87, 02B103 (2016).
