Robustness optimization for compact free-electron laser driven by laser wakefield accelerators

Despite the successful demonstration of compact free-electron lasers (FELs) driven by laser wakefield accelerators (LWFAs), the inherent shot-to-shot fluctuations in LWFAs, including both laser and plasma instabilities, remain a primary obstacle to realizing LWFA-driven FELs with robust operation. Here, we present a conceptual design for LWFA-driven FELs with sufficient tolerance against shot-to-shot fluctuations using the covariance matrix adaptation evolution strategy. Start-to-end simulations demonstrated that this systematic optimization resulted in a significant improvement in the robustness of FELs. With the optimized configurations, the radiation energy can be maintained above <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mn>1</a:mn> <a:mspace width="0.16em"/> <a:mi>µ</a:mi> <a:mi mathvariant="normal">J</a:mi> </a:mrow> </a:math> at a wavelength of approximately 25 nm, even when accounting for twice the root-mean-square ranges of these instabilities. This proposed scheme represents a substantial advancement in the development of compact LWFA-driven FEL systems, enabling robust operation and paving the way for the realization of reliable and widely accessible sources.