First assessment of microwave diagnostics for DEMO
Résumé
Microwave diagnostics like reflectometry and ECE with their need for reduced access, front-end robustness, space coverage and spatial resolution are strong candidates to provide DEMO with measurements of electron density and temperature profiles and their associated fluctuations. To evaluate the microwave accessibility to the plasma, two DEMO1 scenarios were analyzed. O-mode reflectometry can cover the plasma from edge to core, both from high and low field sides, with a set of frequencies ranging from 15 to 110 GHz. A low gradient at the plasma core can be a problem, which can be magnified due to relativistic effects (T-e >2 key). For plasma position and shape control several poloidal views should be used with O-mode reflectometers probing the scrape-off layer. X-mode upper cut-off can be used to probe from the edge to core with frequencies ranging from 140 to 250 GHz. Due to relativistic effects, profile reconstruction depends on the knowledge of local Te. There can also be conditions where large plasma regions are not accessible due to hollow or no gradient profile induced by peaked Te profiles. A first evaluation of the LFS plasma position reflectometer (PPR) behaviour was done using a 2D full-wave Maxwell FDTD code REFMUL. For ECE some 40 channels ranging from 130 to 250 GHz using O-mode electron cyclotron first harmonic will give electron temperature profiles from edge to core with a spatial resolution of about 6 cm, very similar to what it is foreseen for ITER. (C) 2015 Elsevier B.V. All rights reserved.