Design challenges and analysis of the ITER core LIDAR Thomson scattering system

Abstract

The maximum temperature expected in ITER is in the region of 40keV and the minimum average density of approximately 3×1019m−3 is also expected. The proven capability, convenience, and port occupancy of the LIDAR Thomson scattering approach, demonstrated on JET, makes it an excellent candidate for ITER. Nonetheless, there are formidable design challenges in realizing such a diagnostic system. The expected high temperature presents its own problem of a very large relativistic blueshift of the scattered spectrum (e.g., λ∕λ0∼0.35 for Te=40keV), impacting on the laser choice and spectrometer/detector system. The combination of coupling high power lasers to the plasma and broadband wavelength detection has been examined in terms of minimizing the operational risk to the overall system, while optimizing the diagnostic performance. Part of the exercise has also included identifying the present critical components, and reducing their impact, e.g., on diagnostic reliability and performance, and attempt to make the design compatible with possible long term developments and operational requirement. Issues such as redundancy of key operational components, e.g., lasers are explored.