Metrology

Controlling the geometry of the machine during the assembly process is a very demanding activity that can only be achieved by managing variation at each stage. Accurate dimensional control ensures that the exacting tolerances required for machine operation are achieved, and by the end of the machine assembly process metrologists will have recorded the exact as-built geometry of the machine—an invaluable source of information for future maintenance, modifications or revision.

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 computed uncertainty.

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 are added within the buildings themselves. The accuracy requirements for each network vary according to the alignment tasks for which they are designed.

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.

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 against this.

During the assembly phase and beyond, metrology processes ensure that the machine and its supporting systems are dimensionally compliant. This is critical for the successful operation of the ITER machine.

Gallery

Setting up where the action is

2025-11-24

And it's off for a day of preparation, calibration, and precision verification for these metrologists from Metromecánica. Sector module #5 will be the third (of nine) to be installed in the tokamak pit.

From the top of the tower

2025-11-24

Reflective targets installed on the module play a key role in guiding the operation. Metrologists constantly monitor the module's position relative to the reference frame in the tokamak pit.

It takes a team

2025-11-24

The metrology team for vacuum vessel sector module #5 installation gathers around a computer screen.

Metrology "nests"

2025-10-01

Fiducial target nests, in red, can be seen in various locations inside the vacuum vessel sector. These nests are used to receive spherically mounted reflectors (SMRs), which are surveyed with laser trackers to establish their coordinate values and confirm their compliance with the simulation.

Metrology is finalized on sector #8

2025-07-21

Metrology confirms that sector #8 is ready to be transferred to assembly tooling. Bevel joint repair has been completed successfully and all attachments (bosses, sensors) have been installed.

A team meeting precedes the lift of sector module #6

2025-06-17

Three shifts are necessary to complete the transfer operation of sector module #6 into the pit. Before each shift the teams, including metrology, meet together.

All in a day's work

2025-06-15

These metrologists are set up in the Assembly Hall near the sector module assembly stations. Exact measurements at every stage are important for component assembly; they also create a valuable "as-built" record.

The importance of measurements

2025-05-19

Yes, it takes big hooks (and complex rigging) to lift and transfer components from the Assembly Hall to the tokamak assembly pit. But another of the key factors in successfully assembling, handling and positioning components that can weigh up to 1,350 tonnes is the precision of every measurement, explains assembly metrology engineer Lionel Poncet to this group of visitors.

Keeping the instruments accurate

2025-01-09

Preparing laser trackers for a field survey. Records are kept of calibration so that each instrument is maintained at optimal performance.

The importance of calibrating instruments

2025-01-09

ITER relies on properly calibrated metrology instruments to provide accurate measurements. Pictured: as part of the calibration process, a laser tracker is being compensated using a reference sphere—a sphere manufactured with an extreme level of accuracy against which coordinate measuring machines can be calibrated.

Metrology after repair

2024-12-26

Support thermal shield panel #17 is surveyed by a metrologist after repair and before installation in the tokamak pit.

An essential role

2024-07-15

Metrology is playing an essential role in the repair of ITER vacuum vessel sectors, including in the positioning, with micrometric precision, of the milling machines responsible for shaving off excess material.

Measuring precisely

2024-02-23

In order to precisely identify the bevel regions that need to be rectified, metrologists from the SIMANN (SIMIC-Ansaldo) consortium are performing ultra-precise measurements on both sides of vacuum vessel sector #7.

Vacuum vessel metrology

2024-02-08

In the ITER Assembly Hall, metrologists from the SIMANN (SIMIC-Ansaldo) consortium are performing ultra-precise measurements on the bevel joint region of vacuum vessel sector #7.

Assessing structural changes caused by repair

2024-01-26

Metrologists are being called on to assess the structural changes resulting that may result from repairs—but in order to do so, they have to quantify several sources of variation such as support structure pressure and temperature. Here, a metrologist performs a shell scan using ATS600.

Supporting ITER units for all metrology needs

2024-01-26

Metrology is involved in every step of ITER machine assembly, including the repair works underway on critical components. The size of thermal shield segments, measuring around 15 metres by 10 metres in area, is one of the challenges for metrologists, obliging them to take laser observations from multiple instrument locations. (See more at /newsline/-/3992)

Scanning before thermal shield repair

2024-01-26

A vacuum vessel thermal shield outboard segment is surveyed before repairs. Capturing flange features (hole cylinders) helps to define the as-built reference model.

Recording as-built dimensions

2023-08-30

This segment of thermal shield must be dismantled into four individual panels. Before that takes place, teams of metrologists record all of its as-built dimensions.

Disassembling sector #7

2023-08-29

To prepare for the repair of the bevel region of vacuum vessel sector #7, the two toroidal field magnets have been removed from the sector into the wings of the tool.

Back in tooling

2023-07-05

In order to carry out this reverse operation—sector module #6 from the Tokamak pit and re-placing it in tooling in the Assembly Hall—metrologists were part of the preparation and execution teams.

Investigating repair strategies

2022-12-19

Under a plastic tent set up in the Cryostat Workshop teams, including metrologists, are investigating repair solutions for the ITER Tokamak's thermal shield panels. See more at: /newsline/-/3830

Toroidal field coil alignment

2022-12-15

The assembly tolerances required to align a pair of toroidal field coils in the Tokamak pit are shown in this image. The measurement of deviations from ideal "as-designed" parts on a computer screen to "as-built" coils ready for installation at ITER is a vital part of the assembly strategy. See more at: /newsline/-/3826

Preparing sector #7

2022-10-06

Measurements are taken before, during and after the activities to assemble sector #7 with panels of thermal shielding (pink) and, later, two toroidal field coils.

Final alignment

2022-09-15

Sector module #6, following alignment in the Tokamak pit, which was achieved in September by the assembly and metrology teams.

Repelling down the module

2022-06-09

The first section of the ITER vacuum vessel has been in place in the assembly pit since 11 May. This "rope access technician" is positioning fiducial targets on the surfaces of the component to be used in laser metrology.

Adjusting a correction coil

2022-01-05

Workers from the CNPE Consortium are seen here carrying out metrology measurements at the bottom of the Tokamak pit, adjusting a kidney-shaped bottom correction coil on its yellow temporary supports. Final positioning will be possible only when all vacuum vessel modules are in place.

Focused

2022-01-03

A metrology instrument has been fixed to a port cell (right), with its camera trained on the centre of the assembly pit. During the assembly phase and beyond, metrology processes ensure that the machine and its supporting systems are dimensionally compliant.

First correction coil lowered

2021-10-21

The lowering of the BCC/4 coil onto its temporary supports goes smoothly in October, thanks to detailed preparation that included metrology, reverse engineering and accurate positioning. In the final machine geometry, the correction coils will be attached to the toroidal field coil superstructure.

Major alignment achievement

2021-10-04

The four major components of the first building block of the ITER plasma chamber have been precisely aligned (here, a view of the vacuum vessel taken from inside the sub-assembly). This major achievement smooths the way for the similar assembly of eight other sub-assemblies in the months and years ahead.

Precision is vital

2021-10-04

Precision in assembling and positioning the vacuum vessel sub-assembly components is paramount; any deviation from required tolerances in any component would result in knock-on issues in the sub-assembly and the finalized torus.

Ring coil PF5 installed successfully

2021-09-16

The coil slowly descends into the assembly pit on 16 September 2021. It will make a long pause for final metrology before being delicately deposited on its temporary supports.

Planarity checks

2021-09-16

Lifting and positioning huge components, like this 17-metre-in-diameter poloidal field coil (PF5) demands a perfect balancing of the lifting hooks and a constant check for planarity. The metrology teams are essential.

Metrology underway

2021-06-29

Metrology is a constant presence in the Tokamak Complex, whether for construction or assembly tasks. © Les Nouveaux Médias/SNC ENGAGE

Real-time photogrammetry

2021-06-17

Two cameras at the bottom of the lifting frame collect data every 5 seconds during the two-hour lift operation of toroidal field coil #12. This real-time photogrammetry permits operators to verify that the deformation of component as it is raised to vertical does not exceed limits.

In the Tokamak pit

2021-06-04

Metrology is an essential tool for installing components to within tight tolerances, controlling the interfaces berween the different elements, and keeping the right distances between surfaces in order to avoid clashes.

Verifying component shape

2021-05-27

Photogrammetry is one of the techniques used to inspect and validate the shape of components. The bright points in the picture are photogrammetry targets placed on the outer shell of a vacuum vessel segment before final machining. Mangiarotti, Italy, May 2021.

Measurements at every step

2020-11-06

As the silver-coated panels of the lower cryostat thermal shield are assembled, metrologists are constantly at hand to verify alignment.

The eye in the pit

2020-10-30

At the centre of the pit, a rotating "eye" blinks red and green atop a tall structure. The eye is the central piece of a metrology system that monitors a component's potential deformations by computing data acquired from several dozen targets.

Camera in place

2020-10-27

The first panel of the lower cryostat thermal shield is in place and metrologists verify that assembly can continue.

Counting on metrology

2020-09-09

The cryostat lower cylinder is now positioned in the Tokamak pit above the cryostat base and the remaining gap is less than 6 millimetres. Before welding activities begin, the exact position of the lower cylinder is recorded through metrology.

2020-05-04

Because rotating the heavy cryostat base during installation would be difficult, metrologists were on hand as the base entered the Assembly Hall to make sure the transporter positioned the component exactly as it must be lifted by the overhead cranes. The team managed to achieve a rotational tolerance of +/- 5 mm.

Clear lines of sight

2020-05-04

The team anticipated the arrival of the cryostat base in the Assembly Hall by installing one instrument station high up on the nearest sector sub-assembly tool (you can see the instrument if you look closely) for a clear line of sight.

5-degree increments

2020-03-02

In the Assembly Hall, the steel upending tool is lifted by increments of 5 degrees. A photogrammetric survey is performed between lifts in order to acquire baseline measurements and to monitor deformations.

Pre-assembly preparations

2020-02-24

The upending tool is lifted off the floor so that metrologists can measure the planarity of its support pads.

Aligning loads vertical to gravity

2020-02-14

When two 340-tonne test loads were positioned on one of the sector sub-assembly tools in the Assembly Hall, the metrology team was there to help the operators align the loads vertical to gravity and within one millimetre. The team has established the Tokamak Complex Global Coordinate network for the alignment of components, as well as a local coordinate system in the Assembly Hall for vacuum vessel sector sub-assembly.

Measuring the cryostat during assembly

2019-05-06

ITER's Lionel Poncet (right) and Giacomo Calchi of the European Domestic Agency Fusion for Energy (F4E) perform a surface scan of a port opening inside the cryostat's lower cylinder. The ITER Organization and F4E enjoy an efficient resource-sharing collaboration in the area of metrology.

For the alignment of machine components and plant systems

2018-11-12

A vast network of fiducial target nests installed on the concrete surfaces of the bioshield, port cells and galleries will enable installation contractors to align components to sub-millimetre accuracy. Advanced software was used to lay out the positions of each instrument station and simulate clear lines of sight to the fiducial nests. This simulated measurement geometry was used to predict the measurement uncertainty to be expected, which was subsequently qualified with real measurement data. (Pictured: one level of the Tokamak Complex)

Fiducial target nests

2018-10-15

2,000 of these small fiducial tests will be placed by European building contractors in accessible areas of the Tokamak Complex. The nests are used to receive spherically mounted reflectors (SMRs), which are surveyed with laser trackers to establish their coordinate values and confirm their compliance with the simulation used during the network design process. Photo: F4E

Helping to erect of the giant tools

2018-02-12

Before and after each component of the sector sub-assembly tool (SSAT) is preassembled and put into place, metrology engineers carry out a variety of measurements and computational analysis to verify that every component is assembled and positioned in accordance with its design requirements.

Several metrology tools necessary

2018-01-25

Due to the size of the vacuum vessel sector sub-assembly tool (SSAT), several metrology instrument positions are needed to achieve the best precision measurements. A network of target nests embedded in the ground of the Assembly Building helps position the instruments around the SSAT. Photo: PES Metrology

Providing the "as-built" data

2017-01-16

One of the optical metrology tools used to take measurements on the ITER site. As the buildings rise, metrology teams carry out the measurements that provide the "as built" footprint to ITER teams.

Metrology on the construction site

2014-09-29

Surveyors from the metrology consortium G2Métric & Arkadia use laser measurement equipment to verify the position and elevation of the 80 embedded steel plates used to anchor the drain tanks.

Aligning the blanket

2013-10-07

Central to identifying the variances—and defining customization requirements—are sophisticated optical metrology techniques. Alignment of the ITER blanket will be achieved by customizing approximately 4,000 interfacing components.

9000 measurement targets to simulate in-vessel survey

2011-10-26

Once assembly is complete, a survey will be carried out to determine the as-built position of the interfaces for in-vessel components. Using software tools developed specifically for ITER, a survey simulation was carried out to determine achievable accuracy. 9,000 measurement targets were simulated using the CAD file as a template, to represent targeting the complete vacuum vessel.

In-vessel photogrammetry survey simulation

2011-10-26

In this illustration, the field of view for each camera is modelled and used to identify measurable targets. This array of cameras is repeated 18 times toroidially around the ITER vacuum vessel.

Virtual assembly of vacuum vessel triplet

2011-10-26

The vacuum vessel sectors shall be aligned and welded as pairs and then triplets. The 3 triplets will then be aligned and simultaneously welded together. The as-built geometry of the various sectors shall be dimensionally controlled throughout this process to ensure that the required tolerances are maintained. This image, produced through a virtual assembly process, indicates how manufacturing and assembly variation can be visually represented as compared with the CAD model.

Metrology measurements in October 2011

2011-10-26

Metrology contractors (GDV) take GPS measurements as part of the primary survey network qualification survey. Photo: F4E

Photogrammetry simulation

2011-10-26

Measurement geometry for the survey of the interface components of an inboard blanket shield module. Photogrammetry simulation is used to predict the measurement uncertainty.

The ITER pit survey network

2011-10-26

The ITER pit survey network will consist of approximately 220 target nests mounted to the bioshield wall at the port cell openings. Metrology instruments mounted on dedicated stands, within the port cells, will extend through the cryostat ports into the pit to measure and align tokamak components with respect to this network. Lines of sight have been carefully studied to ensure that the network remains available throughout construction of the principle tokamak components.

Vacuum vessel sector survey

2011-10-26

Alignment of the vacuum vessel sectors will require a survey from multiple instruments to measure their large volume and to minimize measurement uncertainty. This image shows measurements from five laser tracker stations with lines of sight indicated to both in-vessel and ex-vessel fiducial target points.

Eleven monuments in the ITER Primary Survey Network

2011-10-26

Eleven survey monuments were positioned around the ITER site in 2010 as part of the ITER Primary Survey Network. Two additional temporary monuments were used during the surveys to shorten the measurement distance to improve the accuracy. On top of the monument is a Leica GPS Receiver. Photo: ITER Organization (Pictured: contractors from GDV Systems GmbH, Germany)

Accuracy of approximately 1 mm

2011-10-26

The first survey of the ITER Primary Survey Network, as well as subsequent monitoring surveys, was carried out using a combination of terrestrial measurements (pictured here with a Leica Total station) combined with differential GPS and levelling measurements. An accuracy of approximately 1 mm was achieved for these surveys.

1-3 mm

assembly tolerances

2000

fiducial nests in the Tokamak Complex

0.2-0.4 mm

network uncertainty range

11

geodetic pillars on site

Reference coordinates

PRIMARY SURVEY NETWORK

The primary survey network for the ITER site provides a global coordinate system for civil engineering works and the positioning of the buildings. It is based on 11 geodetic pillars that have been measured in relation to one another and to a wider GPS system, and which now provide a fixed reference base (or datum) from which more localized measurements can be made and calculated.

TOKAMAK GLOBAL COORDINATE SYSTEM

Inside of the Tokamak Complex a vast matrix of reference "targets," or fixed points, provides the physical manifestation of the global coordinate system. Metrologists can access the overall coordinate system from any location by measuring a small number of local reference points. The accuracy of the network has been measured within a global uncertainty range of 0.2 to 0.4 mm, allowing installation contractors to align components to sub-millimetre accuracy.

TOKAMAK PIT NETWORK

Inside of the concrete bioshield, target nests covering the full height of the walls are used to derive the vertical datum axis for machine assembly. As the pit becomes more crowded and lower pit wall targets are progressively hidden from view, targets in the port cell galleries will maintain lines of sight and play an important role in measurement tasks.

ASSEMBLY DATUMS

As machine assembly progresses, the as-built geometry of core components serves as a reference for further alignment activities. The cryostat base is aligned using the target nests of the Tokamak Pit Network; the toroidal field coils and cryostat lower cylinder are aligned in relation to the as-built position of the cryostat base; and the coordinate frame of the 18 toroidal field coils serves as reference for the final alignment of the vacuum vessel, the remaining magnet systems and the in-vessel components.

ALL ASSEMBLY PHASES

Metrology will continue to play an important role after the assembly of the core machine, as in-vessel components are installed in large numbers. Manufactured in plants around the world and shipped to ITER, several thousand components must be customized during assembly to achieve the demanding tolerances allocated to in-vessel systems. As a single example, the assembly of the blanket modules inside the vessel requires a survey of approximately 4,400 components; each one needs to be individually customized to deliver the required alignment.