In this paper we present a novel approach to free electron laser (FEL) simulations based on the decomposition of the electromagnetic field in a finite number of radiation modes. The evolution of each mode amplitude is simply determined by energy conservation. The code is developed as an expansion of the general particle tracer framework and adds important capabilities to the suite of well-established numerical simulations already available to the FEL community. The approach is not based on the period average approximation and can handle long-wavelength waveguide FELs as it is possible to include the dispersion effects of the boundaries. Furthermore, it correctly simulates lower charge systems where both transverse and longitudinal space charge forces play a significant role in the dynamics. For free-space FEL interactions, a source dependent expansion approximation can be used to limit the number of transverse modes required to model the field profile and speed up the calculation of the system’s evolution. Three examples are studied in detail including a single pass FEL amplifier, the high efficiency TESSA266 scenario, and a THz waveguide FEL operating in the zero-slippage regime.

中文翻译：

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自洽数值方法跟踪自由电子激光与电磁场模式相互作用中的粒子

在本文中，我们基于有限数量的辐射模式中电磁场的分解，提出了一种新颖的自由电子激光（FEL）模拟方法。每个模式幅度的演变仅通过节能来确定。该代码是作为通用粒子跟踪器框架的扩展而开发的，并为FEL社区已提供的一套完善的数值模拟添加了重要功能。该方法不基于周期平均近似，并且可以处理长波长波导FEL，因为它可能包括边界的色散效应。此外，它可以正确地模拟低电荷系统，在该系统中，横向和纵向空间电荷在动力学中起着重要作用。对于自由空间的FEL交互，依赖于源的扩展近似值可用于限制对场分布进行建模所需的横向模式数量，并加快系统演化的计算速度。详细研究了三个示例，包括单通FEL放大器，高效TESSA266方案以及在零滑移状态下工作的THz波导FEL。