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In order to understand the H" extraction mechanism and investigate the effect of the extraction voltage applied by the puller-electrode on the H- extraction in the Linac4 negative ion source, we are developing a 2D3V-PIC (two dimensions in the real space and three dimensions in the velocity space, Particle in Cell) model with volume produced H" ions. It is shown that how to take the magnetic filter field direction is important for the 2D modeling to take into account the important 3D effect of electron ExB drift. It is also shown that the meniscus formation is not symmetric due to the electron ExB drift in the extraction region and the divergence of the H" beam is asymmetric. In order to make more quantitative comparison of the extracted H- and electron currents with the experiments and 3D modeling, further improvements, especially the electron loss along the magnetic filter field line will be needed. [ABSTRACT FROM AUTHOR]

In order to make the predictive simulation tools for the extracted beam current and emittance in the Linac4 H- ion source, we have launched the development of the integrated model for the H- ion beam formation and extraction process. More specifically, our 3D KEIO-Beam Formation and eXtraction (3D KEIO-BFX) is coupled with the NINJA, IBSIMU and TRAVEL. The extracted H- ion beam current and co-extracted electron current obtained by the integrated model have shown reasonable agreement with the experiments. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the extraction mechanisms of the H- ions in the Linac4 negative ion source by using an improved two-dimensional in real space and three-dimensional in velocity space Particle in Cell (2D3V-PIC) model, In this model, the following collision processes of the surface produced H-(H-sp) ions have been introduced and the effects of the collisions on H-extraction have been analyzed: elastic (H-sp - H2) and charge exchange (H-sp - H). It is shown that the extracted Hs-sp current increases due to the flow reversal of the H-sp ions caused by these collisions. [ABSTRACT FROM AUTHOR]

The negative ion beam optics is studied quantitatively from the viewpoints of the heat loads due to the beam halo in the accelerator and the emittance of the negative ion beam by using the 3D3V PIC model combined with a Monte Carlo calculation, in which negative ion beam from plasma meniscus formation to the beam acceleration is modeled. As for the heat loads of the A2G and the GRG, the simulation result almost agrees with the experimental result. The simulation result indicates that the secondary electrons from the extractor also contribute to the heat load of the A1G. Moreover, the normalized rms emittance of the negative ion beam after the exit of the GRG are estimated to be around 0.25π mm mrad, which are compatible with the typical values of the negative ion sources. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the electron confinement time on the plasma meniscus and the fraction of the beam halo is investigated by 3D3V-PIC (three dimension in real space and three dimension in velocity space) (Particle in Cell) simulation in the extraction region of negative ion source. The electron confinement time depends on the characteristic time of electron escape along the magnetic field as well as the characteristic time of diffusion across the magnetic field. Our 3D3V-PIC results support the previous result by 2D3V-PIC results i.e., it is confirmed that the penetration of the plasma meniscus becomes deep into the source plasma region when the effective confinement time is short. [ABSTRACT FROM AUTHOR]

A meniscus of plasma-beam boundary in H- ion sources largely affects the extracted H- ion beam optics. Recently it is shown that the beam halo is mainly caused by the meniscus, i.e. ion emissive surface, close to the plasma grid (PG) where its curvature is large. The purpose of this study is to clarify the effect of H- surface production rate on plasma meniscus and beam halo formation with PIC (particle-in-cell) modeling. It is shown that the plasma meniscus and beam halo formation is strongly dependent on the amount of surface produced H- ions. [ABSTRACT FROM AUTHOR]