We investigate the dynamics of electrons counterpropagating along a radially polarized optical Bessel beam (OBB). (i) It is shown that a significant fraction of the electrons can be transversally trapped by the OBB even in the case of “unmatched” injection. Moreover, (ii) these transversally trapped particles (TTPs) can be transported without loss along many thousands of wavelengths. As long as there is full longitudinal overlap between the electrons and laser pulse, this transport distance is limited only by the length of the OBB region. (iii) The unique profile of the transverse field components facilitates guiding either azimuthally symmetric pencil beams or annular beams. Space charge tends to totally suppress the annular beams, and it reduces the amount of charge trapped on axis for pencil beams. (iv) Assessment of the emittance of the TTPs alone reveals typical values of 10–50 pm. In fact, our simulations indicate if we trace the emittance of those particles that are trapped from the input to the output of the OBB, we find that this emittance is conserved. (v) We developed an analytic model whereby we average over the fast oscillation associated with the counterpropagating electrons and OBB. The resulting Hamiltonian has a Bessel potential $J_1^2(u)$, which, when operated in the linear regime near equilibrium, causes rotation of the phase space. A Kapchinskij-Vladimirskij beam-envelope equation is derived including space-charge and emittance effects. Relying on conservation of the longitudinal canonical momentum, the energy spread in the interaction region is determined in terms of the OBB intensity and the electron energy.

中文翻译：

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激光贝塞尔光束引导电子束

我们研究了沿径向偏振贝塞尔光束（OBB）反向传播的电子动力学。（i）表明，即使在“不匹配”注入的情况下，OBB仍可将很大一部分电子横向俘获。此外，（ii）这些横向捕获的粒子（TTP）可以沿着数千个波长无损失地传输。只要电子和激光脉冲之间存在完全的纵向重叠，该传输距离就仅受OBB区域长度的限制。（iii）横向场分量的独特轮廓有助于引导方位角对称的笔形光束或环形光束。空间电荷趋于完全抑制环形光束，并且减少了笔形光束在轴上捕获的电荷量。（iv）评估TTP的发射率仅显示10–50 pm的典型值。实际上，我们的模拟表明，如果我们跟踪从OBB的输入到输出被捕获的那些粒子的发射率，我们发现该发射率是守恒的。（v）我们开发了一个解析模型，可以对与反向传播的电子和OBB相关的快速振荡求平均。产生的哈密顿量具有贝塞尔势${Ĵ}_{\mathrm{1个}}^2（ü）$当在接近平衡的线性状态下运行时，会引起相空间旋转。推导了包括空间电荷和发射效应的Kapchinskij-Vladimirskij束流方程。依赖于纵向规范动量的守恒，相互作用区域中的能量扩散是根据OBB强度和电子能确定的。