Enhanced beam transport via space charge mitigation in a multistage accelerator for fusion plasma diagnostics
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arXiv
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| Main Authors: | , , , , , , , |
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| Format: | Preprint |
| Published: |
2025
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| _version_ | 1866916958732025856 |
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| author | Nishiura, M. Nakamura, K. Ueda, K. Shimizu, A. Takubo, H. Kanda, M. Ido, T. Okamura, M. |
| author_facet | Nishiura, M. Nakamura, K. Ueda, K. Shimizu, A. Takubo, H. Kanda, M. Ido, T. Okamura, M. |
| contents | Efficient transport of high-current negative ion beams is critical for accurate plasma potential diagnostics using heavy-ion beam probe (HIBP) systems in magnetically confined fusion plasmas. However, strong space-charge effects often degrade transport efficiency, particularly for heavy ions such as Au-. In this study, we demonstrate a substantial improvement in beam transport by introducing an electrostatic lens effect through optimized voltage allocation in a multistage acceleration system. Numerical simulations using IGUN, supported by experiments with the LHD-HIBP system, show that this approach effectively suppresses space-charge-induced beam divergence and loss. Without requiring mechanical modifications to the beamline, the optimized configuration enables a 2-3 fold increase in Au-beam current injected into the tandem accelerator. Consequently, plasma potential measurements were extended to higher-density plasmas, reaching line-averaged electron densities up to $1.75\times 10^{19}$ m$^{-3}$ with improved signal-to-noise ratio. This technique offers a compact, practical, and highly effective solution for transporting high-current heavy-ion beams under space-charge-dominated conditions. Beyond its impact on plasma diagnostics, the method is broadly applicable to a wide range of accelerator systems, including those used in scientific and industrial applications where high-intensity beam transport is required. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_20948 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Enhanced beam transport via space charge mitigation in a multistage accelerator for fusion plasma diagnostics Nishiura, M. Nakamura, K. Ueda, K. Shimizu, A. Takubo, H. Kanda, M. Ido, T. Okamura, M. Plasma Physics Efficient transport of high-current negative ion beams is critical for accurate plasma potential diagnostics using heavy-ion beam probe (HIBP) systems in magnetically confined fusion plasmas. However, strong space-charge effects often degrade transport efficiency, particularly for heavy ions such as Au-. In this study, we demonstrate a substantial improvement in beam transport by introducing an electrostatic lens effect through optimized voltage allocation in a multistage acceleration system. Numerical simulations using IGUN, supported by experiments with the LHD-HIBP system, show that this approach effectively suppresses space-charge-induced beam divergence and loss. Without requiring mechanical modifications to the beamline, the optimized configuration enables a 2-3 fold increase in Au-beam current injected into the tandem accelerator. Consequently, plasma potential measurements were extended to higher-density plasmas, reaching line-averaged electron densities up to $1.75\times 10^{19}$ m$^{-3}$ with improved signal-to-noise ratio. This technique offers a compact, practical, and highly effective solution for transporting high-current heavy-ion beams under space-charge-dominated conditions. Beyond its impact on plasma diagnostics, the method is broadly applicable to a wide range of accelerator systems, including those used in scientific and industrial applications where high-intensity beam transport is required. |
| title | Enhanced beam transport via space charge mitigation in a multistage accelerator for fusion plasma diagnostics |
| topic | Plasma Physics |
| url | https://arxiv.org/abs/2507.20948 |