磁化非线性等离子体尾场用于正电子加速：机制与运行极限
Magnetizing nonlinear plasma wakefields for positron acceleration: mechanism and operating limits
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- National Taiwan University（国立台湾大学）
- Stanford University（斯坦福大学）
- SLAC National Accelerator Laboratory（SLAC国家加速器实验室）
- Heinrich Heine University（杜塞尔多夫大学）
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中文总结 AI 辅助
本文研究轴向磁场重组非线性等离子体尾场中的电子返回，以扩展正电子加速区间，通过粒子模拟验证了定位定律，在35 T磁场下将可用区间扩大四倍以上，实现92%捕获率和99-150 MeV能量增益，为单级正电子加速提供新途径。
中文摘要 AI 辅助
正电子加速在线性等离子体尾场中是可行的，但非线性电子驱动空泡机制将同时加速和聚焦限制在返回等离子体电子的狭窄区域内。本文研究了轴向磁场如何重组这种非线性返回，从而在均匀等离子体中开辟一个可持续正电子加速的运行窗口。利用准三维和全三维粒子网格模拟，我们将有限半径电子柱（即陀螺图像）的形成与见证束输运及其运行极限联系起来。图像间距由准静态不变量控制，而正则角动量限制了返回半径。经轨道采样尾场势修正后，该机制产生了一个定位定律，能在广泛的磁场强度范围内准确预测密度峰值。在等离子体密度为$10^{16} cm^{-3}$和35 T轴向磁场下，重组结构将可用加速和聚焦区间相比未磁化情况扩大了四倍以上。放置在该能带稳定相位的正电子见证束在60 mm阶段实现了92%的捕获率，归一化发射度饱和于83 mm mrad。独立代码确认了持续输运，能量增益在99至150 MeV之间，但精确能量增益的数值收敛仍是一个开放挑战。结合束负载、对准和驱动能量缩放测试，这些结果确立了非线性电子返回的磁控制作为单级正电子加速的途径。束流质量保持、形成瞬态控制和螺线管集成定义了必要的后续开发步骤。
英文摘要
Positron acceleration is possible in linear plasma wakes, but the nonlinear electron-driven blowout regime confines simultaneous acceleration and focusing to narrow regions of returning plasma electrons. Here we investigate how an axial magnetic field reorganizes this nonlinear return to open an operating regime for sustained positron acceleration in a uniform plasma. Using quasi-3D and full-3D particle-in-cell simulations, we connect the formation of finite-radius electron columns, or gyro images, to witness transport and its operating limits. The image spacing is governed by the quasi-static invariant, while canonical angular momentum limits the return radius. Modified by the orbit-sampled wake potential, this mechanism yields a positioning law that accurately predicts the density peaks across a wide range of magnetic field strengths. At a plasma density of $10^{16} cm^-3$ and a 35 T axial field, the reorganized structure expands the usable accelerating and focusing interval by more than a factor of four compared to the unmagnetized case. A positron witness bunch placed at the settled phase of this band achieves 92% capture over a 60 mm stage, with the normalized emittance saturating at 83 mm mrad. Independent codes confirm sustained transport, yielding energy gains between 99 and 150 MeV, though numerical convergence on the exact energy gain remains an open challenge. Together with beam loading, alignment, and driver-energy scaling tests, these results establish magnetic control of the nonlinear electron return as a route to single-stage positron acceleration. Beam quality preservation, formation-transient control, and solenoid integration define the necessary next development steps.
