Demonstration of reliable laser-plasma accelerator driven free electron laser in the SASE regime

X-ray free electron lasers (XFELs) are fourth-generation light sources that deliver ultra-bright, coherent X-ray pulses that serve a diverse scientific user community. XFELs require high-brightness, multi-GeV electrons that generally require km-scale conventional accelerators at billion-dollar facilities. Laser-plasma accelerators (LPAs) provide a promising alternative to conventional accelerator infrastructure due to their orders-of-magnitude higher accelerating gradients (10-100 GV/m), enabling the production of high-brightness, relativistic electron beams in cm-scale distances. While critical work remains to push the stability and quality of LPA electron beams towards their conventionally accelerated counterparts, major milestones in LPA-based FEL development have been demonstrated in recent years. We present recent progress at the BELLA Center's Hundred Terawatt Undulator beamline demonstrating reliable FEL operation in the self-amplified spontaneous emission (SASE) regime.