Metrology activities will contribute significantly to the success of the assembly operations for the ITER Tokamak. Accurate dimensional control will be applied from component manufacture right through the supply chain to final assembly at the ITER site.
Measurement geometry for the Primary Survey Network monuments. Image credit: ITER Organization
All measurement tasks require a fixed reference base (or datum) from which measurements can be made and calculated. For large-volume metrology applications, the reference base typically takes the form of a survey network that consists of a collection of target "nests" and/or instrument stations that have known geometry and uncertainty. The survey networks for ITER will cover the whole of the site, providing a global coordinate matrix for alignment and dimensional control. The accuracy requirements for each network vary according to the alignment tasks for which they are designed.
The primary survey network for ITER was installed and measured in 2010, and now provides a precise and accurate datum reference for construction of the ITER buildings and subsequent survey networks that will be added within the buildings themselves.
During machine assembly, the environment within the various constructions sites will become increasingly congested. This constraint, together with the exacting alignment requirements for the majority of the major ITER systems, means that the metrology processes need to be carefully considered and qualified.
A wide range of metrology systems will be used during the assembly of the ITER machine such as laser trackers, total stations and photogrammetry, which will interface with dedicated software packages and measurement plans specific to the ITER requirements.
The amount of measurement data generated during machine assembly will be immense. As a single example, the assembly of the blanket modules inside the vessel will require a survey of approximately 4,400 components; each one will need to be individually customized to deliver the required alignment.
Optimization algorithms will be used to achieve the best possible configuration for machine operation by analyzing "as-built" geometry at each stage of the assembly and by modifying the alignment criteria to suit. This is especially important when defining the as-built magnetic axis of the machine and the subsequent alignment of components aligned to it.
During the assembly phase and beyond, metrology processes will ensure that the machine and its supporting systems are dimensionally compliant for the successful operation of the ITER machine.