An upgrade to the normal conducting miniature transport line for laser plasma accelerator-driven FELs

n this contribution, we present advancements in upgrading the employed normal-conducting electron beam transport line at the JETI laser facility, University of Jena. To address spectral broadening caused by the large energy spread in laser-plasma accelerators (LPAs), a transverse gradient undulator (TGU) with an energy acceptance of Δ𝐸/𝐸0 = ±10 % has been developed. Efficiently transporting the electron beam from the LPA to the TGU within this acceptance range required an optimized beam transport line as well. Phase-space analysis for single particles across this energy range revealed that earlier transport line designs at KIT exhibited a nonlinear dependence of the transverse beam position 𝑥 on energy deviation, which led to complications in beam dynamics. By incorporating combined dipole-quadrupole magnets and maintaining a transport line length of approximately 3 m for 300 MeV beams, a linear
relationship between the transverse position 𝑥 and energy deviations was achieved, with minimal variation in the phase 𝑥′ (less than 2.4 × 10$^{−4}$). This redesigned transport line meets the TGU’s dispersion requirements, enabling more precise beam alignment and transport.