Development of the plasma shape real-time visualization system in JT-60

Since plasma ellipticity and triangularity seem to partially determine the energy confinement performance of a plasma, the importance of plasma shape have been recognized in recent years. On the other hand, reproduction of the plasma full shape in real-time has been considered impossible due to the limitation of present computational capability. To solve this problem, computation of special functions and matrix inversion, that are obstacles for speed improvement in the calculation, should be removed from the real-time procedures. A method using particular coefficient vectors in tabular form has been developed and the table is stored in a large scale memory of the fast computer, where the vectors are corresponding to the in-vessel flux calculation points on the poloidal cross-section. This improvement in software was taken together with the new installation of advanced electronics devices. As a result, we succeeded to reduce the computation time extremely, and the full JT-60 plasma shape is reproduced every 60 ms in real-time. This system visualizes the time evolution of plasma shapes clearly and in detail, from the beginning to the end of a discharge pulse. This report describes the development of the system in both hardware and software, and also gives the prospect of this system in application to plasma real-time feedback control. (author)