THE IMPLEMENTATION OF THE DIAGNOSTIC SYSTEMS ON ITER

In order to achieve its operational and programmatic goals, ITER requi res an extensive set of plasma diagnostics. In terms of the number and type of measuring instruments, the diagnostic system will be similar to those existing on today's large tokamaks such as JET, TFTR, and JT6 0U. However, the implementation of the diagnostics is especially deman ding because of the high levels of radiation, the limited access, the stringent requirements for vacuum integrity and tritium containment, a nd the requirement for very high levels of reliability and availabilit y of the measurements. The individual diagnostic systems are being des igned by a combined effort of the ITER Joint Central Team and the Home Teams. Underpinning the design work is an extensive R&D programme whi ch thus far has concentrated on the effects the high levels of neutron and gamma radiation will have on materials used in diagnostic constru ction, but it is planned in the near future to focus on prototypes of key diagnostic components. In this paper, we outline the ITER diagnost ic system identifying the plasma measurements required for (i) machine protection and plasma control, (ii) evaluating and optimizing the pla sma performance, and (iii) understanding important physical phenomena that may limit ITER performance. In Control will require measurements of the conventional control parameters such as the plasma position and shape, current, and density, but also of parameters such as the plasm a density and total fusion power. For optimization and evaluation, mea surements not only of the profile of key parameters such as the electr on density and temperature, ion temperature, and radiation, are requir ed. Because this is the first device dependent on alpha particle heati ng, measurements of parameters such as the confined and escaping alpha particles, the helium density in the plasma core, and the long-term n eutron fluence have to be performed. We describe the integration of ty pical diagnostic systems in the equatorial and top ports and in the di vertor. A description of the magnetic diagnostics will provide insight on the in-vessel systems. These systems will illustrate the solutions adopted for the ITER environment and identify the most critical desig n areas. The X-ray crystal and VUV spectrometers will be presented as one of the most challeging systems to be integrated in ITER. Finally, we briefly describe the role plasma measurements are anticipated to pl ay in the ITER operational and physics programme.