(IT/P1-25) Progress in Development of Thomson Scattering Systems for ITER

G.T. Razdobarin1), M.J. Walsh2), T. Hatae3), E.E. Mukhin1), K. Narihara4), G. Vayakis5), D. Johnson6), T. Carlstrom7), ITPA Specialists Working Group on Thomson scattering
 
1) Ioffe Physico-Technical Institute, Saint Petersburg , Russian Federation
2) EURATOM/UKAEA Association, Culham Science Centre, Abingdon UK
3) Fusion Research and Development Directorate, Naka, Ibaraki 311-0193, Japan
4) National Institute for Fusion Science, Toki 509-5292, Japan
5) ITER International Team, Garching-bei-Muenchen, Germany
6) Princeton Plasma Physics Laboratory, Princeton, USA
7) General Atomics, San Diego, USA

Abstract.  Electron temperature and density are important indicators of plasma performance as well as key components in transport analyses. The Thomson scattering system for the plasma core will be an implementation of the LIDAR technique. The central part of the burning plasma has the highest temperature (up to 40keV). In these conditions relativistic effects have a pronounced effect on the blue wing of the spectra. If suitable detectors are developed for the wavelength region 850-1060nm, all spectral measurements could be done with a single laser wavelength at 1064nm. In order to meet the demanding specification for spatial resolution in the edge (equivalent to 0.5cm at the mid-plane), a conventional Thomson scattering system is planned for the upper edge region. It is supposed that the high-resolution measurements would extend into the plasma, to r/a of 0.9. The target requirements would be met by using a specially designed Nd:YAG laser of high output energy (5J) and high repetition rate (100Hz). Te,ne measurements at the X-point region along a line-of-sight passing about 50 cm above the X-point are to be performed with use of a LIDAR system with a laser beam direction tilted to the flux surfaces in the space of a significant flux expansion. The system will provide measurements with a spatial resolution of 7cm along the beam (equivalent to 0.7cm at the mid-plane) in the specified temperature and density ranges with a lower temperature limit of 10eV. Significant effort has been focused on developing a Thomson scattering system for the outer divertor leg with a lower temperature limit of about 1eV. Resolutions of 5 cm along the leg and 0.3cm across are foreseen with time resolution of about 50ms (up to 1ms in a burst mode). The measurement lines up with the flux lines in the divertor leg. This geometry facilitates the diagnosis of proper divertor operation, especially the location of the ionization front. Many elements of the designs still have to be completed, especially the engineering details of the components, and some further R&D is required, concerning reliability and redundancy in parts of the systems. Much work is going on around the world to develop the lasers, detectors and others aspects of the Thomson scattering systems to ensure that the conceptual designs are realizable, tested and ready to be deployed to ITER.

Full paper available (PDF)