Characterization of the Tokamak Fusion Test Reactor plasma edge by Langmuir–calorimeter probes

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Abstract
Two combination Langmuir–calorimeter probes were operated on the Tokamak Fusion Test Reactor (TFTR) midplane to measure plasma properties of the scrape-off layer. Two different calorimeter elements were used: 0.5×3×8 mm Ta plates or 6.4 mm diameter graphite rods fitted with thermocouples. Separate graphite rods served as Langmuir elements. This paper presents Langmuir probe measurements of the radial profiles of edge density and electron temperature, and calorimeter measurements of heat flux. The variation of these quantities in certain operational regimes are presented, including dependence on Ohmic and neutral beam heating, compression and free expansion, plasma major and minor radii, plasma current, and line integral density with and without Cr gettering.