Beam steering characteristics of ferromagnetic electrode

In hydrogen negative ion sources, co-extracted electrons are dumped on extraction grid (EG) with electron deflection magnets (EDMs). The negative ion beam trajectory is slightly perturbed by the EDM field, and the aperture displacement technique has been applied in negative ion sources for fusion in order to compensate the beam deflection [1]. Recently, it was proposed that the beam deflection can be intrinsically cancelled by the asymmetric EDM field [2]. In this concept, the asymmetric field is formed by the combination of the conventional EDMs and additional set of permanent magnets. In this study, a ferromagnetic steering grid (SG) was used as an alternative way to realize the asymmetric EDM field. The beam acceleration experiments were carried out in the NIFS R&D negative ion source (NIFS-RNIS), and the beam footprint was measured with a beamlet monitor system consisting of an infrared camera and 1D carbon fiber composite (CFC) tiles at various operational conditions. Analysis of the beam trajectory is being carried out with OPERA-3d code. In the presentation, we will discuss the beam steering characteristics of the ferromagnetic SG.