Velocity scaling regimes for blob-like filaments in the Alcator C-Mod scrape-off layer

Abstract Blob sizes and velocities in the scrape-off layer of the Alcator C-Mod tokamak are analysed using gas puff imaging diagnostics for a series of Ohmically heated, lower single-null diverted plasmas with varying core plasma densities. Results reveal that both average blob size and radial velocity increase gradually with core plasma density, transitioning from sheath-connected to resistive velocity scaling regimes as the empirical discharge density limit is approached. The normalized blob sizes and velocities are comparable to those reported from other devices but the regime transitions differs. The findings presented here provide new insights into the role of collisionality in scrape-off layer transport and its implications for plasma–surface interactions. Predictions for blob parameters in the SPARC tokamak suggest similar scaling regimes, emphasizing the relevance of these results for next-generation fusion devices.