arXiv 2601.013672026-01-06physics.plasm-phphysics.acc-ph

通过多级加速透镜系统克服低能重离子束的空间电荷困境

Overcoming the space-charge dilemma in low-energy heavy ion beams via a multistage acceleration lens system

National Institute for Fusion Science（国立研究开发法人核融合科学研究所）；Graduate School of Frontier Sciences, The University of Tokyo（东京大学前沿科学研究生院）；Department of Advanced Energy Engineering, Kyushu University（九州大学先进能源工学系）；Collider-Accelerator Department, Brookhaven National Laboratory（布鲁克海文国家实验室对撞机加速器部）

M. Nishiura, T. Ido, M. Okamura, K. Ueda, A. Shimizu, H. Takubo

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AI总结：

本研究通过多级加速透镜系统克服低能重离子束空间电荷限制，实现高束流稳定传输，适用于等离子体诊断等应用。

摘要：

低能重离子束本质上受到严重的空间电荷发散限制，这限制了传统静电加速器可传输的束流至微安级别。这一限制对高质量离子尤其关键，因为它们的广义渗透性由于速度低而迅速增加。在这里，我们证明通过调整现有多级加速器的静电电势配置，可以克服这种显而易见的空间电荷限制，从而将加速柱本身转变为结合加速和聚焦的柱。通过优化各级电压配置，强静电透镜效应被叠加在加速场上以对抗由空间电荷驱动的膨胀。我们提出了一个通用的设计框架，定量地将传输'设计窗口'映射到束流、离子质量和加速电压上。对于64 keV的金离子，这种方法使束流超过100微安的稳定传输成为可能，比传统限制高一个数量级。数值相空间分析显示，这一改进是通过优先考虑包络控制而非维持振荡度来实现的，这是空间电荷主导区域固有的权衡。我们的结果建立了一个通用且实用的高电流重离子束传输指南，适用于等离子体诊断、离子植入和大质量分子离子应用。

英文摘要：

Low-energy heavy-ion beams are fundamentally limited by severe space-charge divergence, which constrains the transportable beam current to a few microamperes in conventional electrostatic accelerators. This limitation is particularly critical for high-mass ions, where the generalized perveance increases rapidly because of their low velocity. Here, we demonstrate that this apparent space-charge limit can be overcome by shaping the electrostatic potential configuration of an existing multistage accelerator, thereby transforming the acceleration column itself into a combined acceleration-focusing column. By optimizing the interstage voltage configuration, a strong electrostatic lens effect is superimposed on the accelerating field to counteract space-charge-driven expansion. We formulate a generalized design framework that quantitatively maps the transport 'design window' in terms of beam current, ion mass, and acceleration voltage. For gold ions at 64 keV, this approach enables stable transport of beam currents exceeding 100 microA, more than an order of magnitude higher than the conventional limit. Numerical phase-space analysis shows that this improvement is achieved by prioritizing envelope control over emittance preservation, a trade-off intrinsic to space-charge-dominated regimes. Our results establish a universal and practical guideline for high-current heavy-ion beam transport, relevant to fusion plasma diagnostics, ion implantation, and massive molecular ion applications.

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