SLAC MeV ultrafast electron diffraction facility upgrade plans

Mega-electronvolt ultrafast electron diffraction (MeV-UED) is a complementary tool to X-ray based instruments that has enabled ground-breaking studies in condensed matter physics and chemical science. The SLAC MeV-UED facility uses a state-of-the-art 1.6-cell RF photoinjector to deliver 3 to 4 MeV electrons for a variety of pump-probe studies in solids, liquids, and gases, with over 6600 delivered hours and >87 publications since 2021. To broaden the scientific opportunities, facility expansion and enhanced instrument performance of MeV UED have been heavily requested. We discuss near and long-term plans for upgrade and expansion of MeV-UED, with anticipated improvements in beam delivery, system performance, data acquisition, and temporal and momentum-space resolution.