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

In 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. Although efficiently transporting the electron beam from the LPA to the TGU within this acceptance range required an optimized beam transport line too. Phase-space analysis for single particles across this energy range revealed that earlier transport line designs at KIT exhibited a nonlinear dependence of beam transverse position x on energy deviation, leads to beam dynamics complication. By incorporating combined dipole-quadrupole magnets, maintaining a transport line length of 2.9 m for 300 MeV beams, a linear relationship between 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.