Whitepaper #270 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: space weather applications; basic research. Additional topics: solar physics; other space weather; user-need-driven basic space weather research.
CMEs have been well observed in the low/high corona + interplanetary space; but they mostly accelerate in the middle corona (1.5-6 Rs). We have numerous models to explain how they are triggered and accelerated, but insufficient observational constraints. New tech is now available to remedy that. We should prioritize acquisition of these observations from multiple lines-of-sight.