Thomson scattering at plasma densities below 1012 cm−3

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Abstract
Major upgrades in the ruby‐laser Thomson scattering system on the microwave‐driven ELMO Bumpy Torus‐Scale plasma have enabled routine and reliable measurements of the electron temperature and density along a plasma radius. Consisting of both signal‐to‐noise enhancement techniques and refined data handling procedures, these upgrades allow density determinations down to 2×1011 cm−3. Radial profiles of bulk electron parameters are essentially flat across the core plasma. Evidence is presented for a 1011‐cm−3 density suprathermal distribution of electrons, which leads to an understanding of contradictory temperature measurements and of energy flow in the plasma.