Plasma Measurements and Diagnostics
Making comprehensive measurements of plasma parameters will be crucial to attainment and control of burning plasma conditions in ITER and to the conduct of the science and technology studies - detailed elsewhere within this site - to be conducted in this regime. ITER will follow the lead of present tokamaks, where the availability of detailed plasma measurement data - provided by more than 50 separate plasma diagnostic systems that encircle the torus - allows fusion scientists to control the plasma properties to an unprecedented degree and to understand the underlying physics basis for plasma behavior at both macroscopic and microscopic levels. ITER must attain this same degree of plasma diagnostic excellence and must also address the further requirements - barely touched upon in present tokamaks - of providing detailed data on the birth, energy loss and eventual thermalization and exhaust of fusion-generated alpha-particles.

Requirements, Challenges and Solutions
Requirements for ITER plasma measurements have received extensive scrutiny by the world fusion science and plasma diagnostics communities and both measurement requirements and likely solutions have been documented in the ITER Physics Basis. There are significant challenges in meeting these requirements: in many cases the methods needed are themselves scientifically and technically difficult, and the resulting diagnostic systems can approach the size of the ITER device itself and have a significant impact on the overall ITER facility size, configuration and cost. Furthermore, in ITER, as in any burning-plasma-capable experiment, the presence of high levels of neutron and gamma radiation, the need to rigorously confine tritium to the plasma torus and the radiation-induced deterioration of optical windows - crucial to many plasma viewing systems - pose a combination of environmental and operational challenges that make realization in ITER of present tokamak diagnostic concepts difficult, and in some cases mandate the development of 'new' burning-plasma-compatible methods and diagnostic system components for the measurement of traditional plasma parameters. There are also opportunities for the development and testing in present tokamaks of innovative methods for detailed in-situ scrutiny of alpha particle birth, thermalization, transport and exhaust.