Conceptual design of JT-60SA edge Thomson scattering diagnostic

• Published in: Journal of instrumentation Vol. 15; no. 1; p. C01011
• Main Authors: Pasqualotto, R., Tojo, H., Fassina, A., Giudicotti, L., Nardino, V., Oyama, N., Pelli, S., Raimondi, V., Ricciarini, S., Soare, S., Davis, S., Sozzi, C.
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.01.2020
• Subjects: Avalanche diodes; Conceptual design; Diagnostic systems; Electron density; Electron energy; Laser beams; Neodymium lasers; Nuclear power plants; Parameter identification; Photodiodes; Plasma; Semiconductor lasers; Spatial resolution; Thomson scattering; YAG lasers
• ISSN: 1748-0221; 1748-0221
• DOI: 10.1088/1748-0221/15/01/C01011

JT-60SA will complement ITER in resolving key issues to finally decide an acceptable DEMO design. Diagnostics play a key role in this mission. The electron temperature and density profiles are measured by a core and an edge Thomson scattering (TS) diagnostics with high spatial resolution, needed to identify the pedestal parameters and small profile structures. The two systems use a common tangential Nd:YAG laser beam path in the plasma equatorial plane. The collection optics for the edge system (low field side) is hosted in a lower oblique port and that for the core system in a horizontal port. The optics fit in the port plug tube and image the scattering volumes into an array of fiber bundles. They both are exposed to a high neutron dose of 1016 n/cm2 over 13 years of operation. The optics are supported by a mechanical structure decoupled from the cryostat. A set of filter polychromators with avalanche photodiode (APD) detectors spectrally analyze the scattered radiation. The development of the TS systems is carried out by a joint Japan-EU team. The conceptual design of the edge TS system is presented here. Simulations of the TS signals show acceptable accuracy down to 1×1019 m−3 electron density, sufficient to measure the edge gradient and even a small region outside the separatrix.