中性粒子在交变梯度波导中的非线性动力学
Nonlinear dynamics in an alternating gradient guide for neutral particles
摘要：
中性粒子可以使用电场梯度来引导和聚焦，所述电场梯度在一个横向方向上聚焦并且在另一个横向方向上散焦，在两个方向之间交替。这种导向器适合于输送被强电场吸引的颗粒，而不能使用静电场来引导该颗粒。只有当粒子的初始位置和横向速度位于波导的相空间接受范围内时，粒子才被传输。非线性力总是存在于导轨中，并且会严重降低这种可接受性。我们考虑两个最重要的非线性力的影响，一个是离轴位移的三次方的力项，另一个是将两个横向运动耦合在一起的非线性项。我们使用近似分析技术，以及数值方法，计算这些非线性力的粒子轨迹和相空间接受的影响。立方项改变聚焦和散焦能力，导致接受度的增加或减少取决于其符号。我们找到了一个近似的分析结果相空间接受，包括这个立方项。使用微扰方法，我们展示了如何耦合项导致横向振荡的振幅缓慢的变化。这个术语在降低聚焦能力时降低接受度，但在增加聚焦能力时几乎没有影响。不可能同时消除两个非线性项，但可以以牺牲另一项为代价来减小一项。我们展示了如何选择的指导参数，使接受优化。
英文摘要：
Neutral particles can be guided and focussed using electric field gradients that focus in one transverse direction and defocus in the other, alternating between the two directions. Such a guide is suitable for transporting particles that are attracted to strong electric fields, which cannot be guided using static fields. Particles are only transmitted if their initial positions and transverse speeds lie within the guide's phase space acceptance. Nonlinear forces are always present in the guide and can severely reduce this acceptance. We consider the effects of the two most important nonlinear forces, a term in the force that is cubic in the off-axis displacement, and a nonlinear term which couples together the two transverse motions. We use approximate analytical techniques, along with numerical methods, to calculate the influence of these nonlinear forces on the particle trajectories and on the phase space acceptance. The cubic term alters the focussing and defocussing powers, leading either to an increase or a decrease of the acceptance depending on its sign. We find an approximate analytical result for the phase space acceptance including this cubic term. Using a perturbation method we show how the coupling term leads to slow changes in the amplitudes of the transverse oscillations. This term reduces the acceptance when it reduces the focussing power, but has little influence when it increases that power. It is not possible to eliminate both nonlinear terms, but one can be made small at the expense of the other. We show how to choose the guide parameters so that the acceptance is optimized.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
