From a strict industrial point of view, repairing the dimensional non-conformities that affect the ITER vacuum vessel sectors is not an insurmountable task. What needs to be done can be formulated quite simply: filling the 'valleys' or shaving the 'hills' along the bevel joint region in order to restore geometry to nominal and recover the ability to weld the sectors together. Sectors, however, are not ordinary chunks of steel; their geometry is complex and their weight (~440 tonnes) is comparable to that of a jumbo airliner. Once assembled and welded to form the fusion reaction chamber they will act as the installation's first nuclear safety barrier and, as such, are subject to very stringent regulations. Whereas two of the three sectors present on site are already positioned in the sub-assembly tools where they will be repaired (#6 and #7), the handling and positioning of the third (#8) requires adapting and manufacturing heavy bespoke tooling. Before repair operations can begin in earnest, the different procedures to be implemented need to be validated. In Italy, the repair contract beneficiary SIMANN, a SIMIC-Ansaldo Nucleare consortium, is manufacturing 1.4-metre-long mockups of the same steel grade and profile as the vacuum vessel sector bevels. Just like the actual component, these 'representative coupons' will undergo metal build-up, machining and welding, prior to being tested for mechanical properties through a series of traction and flexion trials. Eventually, the coupons will be shared with ENSA, the Spanish company entrusted with the final assembly and welding of the nine sectors. Operations will begin in parallel on sectors #6 and #7 by the end of February/beginning of March when all tests and qualification procedures are complete. The first operation will consist of grinding the bevel joint regions, followed by manual metal build-up and final machining to restore the bevels' nominal dimensions. As machining is simpler and does not alter mechanical properties, build-up will be minimized as much as possible. Optimizations are still under assessment, but it is estimated that sectors #6 and #7 will each require approximately 24 kgs of metal to fill the 'valleys' in the bevels. Grinding, metal build-up and machining will be performed under local protections in order to avoid altering the Assembly Hall's controlled environment. Sectors #6 and #7 will remain in the giant sector sub-assembly tools for the duration of the repair operations. Things will be different for Sector #8. Delivered in April 2022, the component had not yet gone through the full equipment and pre-assembly operations. After spending just about one year in vertical tooling, it was returned to a horizontal orientation and eventually moved from the Assembly Hall to the now-vacated Cryostat Workshop in December 2023. Of the three sectors delivered, Sector #8 is the one most affected by dimensional non-conformities—approximately 400 kgs of metal filler will be needed to recover its bevel geometry. Due to the quantity, the build-up process on sector #8 will be partly automated. The major difficulty, however, will not be in the repair operation—it will be in the handling of this exceptionally massive component. As both sub-assembly tools are mobilized for the repairs of sectors #6 and #7, there is no other option than to repair sector #8 in a horizontal position, which restricts access to only one side of the component at a time. Once repairs are complete on the top side, how can it be flipped to be able to continue on the bottom side? Of all the bespoke tools designed to handle ITER's heavy components, not one was designed for such a manœuvre. Using an extra upending tool could solve the problem. With two such frames, the sector could be lifted from one, flipped and placed horizontally inside the second thus making the other side of the sector's bevel accessible for repair. The decision to manufacture a second frame was recently taken and a call for tender was launched a few weeks ago, but there is no absolute guarantee that the tool will be delivered by the time it is needed. If the second upending tool is not available in time, the only remaining solution consists in transferring sector #8 to the assembly pit to 'park' it there while the existing upending tool is modified to accommodate the sector in its flipped position. This of course would be a much heavier and longer operation but there might be no other choice. As the same welding techniques were used in the manufacturing of all nine vacuum vessel sectors (four procured by Korea, five by Europe) all are affected to some degree by deviations from nominal and are undergoing repair procedures at manufacturing sites in Korea and Italy. Once all sectors are repaired and their bevel profile restored as near as possible to nominal, the module assembly process, interrupted in September 2022, will resume. One by one the nine modules will be positioned in the Tokamak pit, prior to being welded together according to a sequence that is yet to be determined.  Thermal shield repair is also moving forward. We will report on progress in an upcoming issue of the ITER Newsline.

Metrologists are required to assess the structural changes resulting from repairs—but in order to do so, they have to quantify several sources of variation. In late 2022, the ITER metrology group was asked to support the thermal shield team by providing deformation data during specific repair steps such as clamping parts or removing, welding and buffing pipes. Because each of these tasks results in deformations of the highly flexible components, metrologists were called in to predict the nature and size of the deformations before each investigatory step and then measure the change after the work was done. "We supported several test trials, including vacuum vessel thermal shield trials at both the segment and panel level, as well as testing on part of the cryostat thermal shield—namely the support thermal shield," says Lionel Poncet, assembly metrology engineer. Thermal shield segments are made of assembled panels. At the segment level, tests included different sequences of pipe removal and buffing to assess deformation that would be induced by certain operations. Panel-level tests took place on the four to six panels that make up a segment, removing them from the segment to analyze separately. Because the segments are so large, measuring around 15 metres by 10 metres in area, one of the challenges was that, due to obstructed lines of sight, not everything could be measured from the same instrument position, obliging the metrology team to take laser observations from multiple instrument locations. With the help of advanced metrology tools that use Monte Carlo equations to resolve measurement uncertainties, several observations were taken of each point in a network and then optimized. Different sources of variation had to be quantified to determine the effects of repairs. One source is the pressure caused by supporting structures, which can change the shape of the relatively thin thermal shield panels. "Deformations can come either from the support or from the pipe removal," explains Poncet, "but what we really want to know is what comes from the pipe removal—so we need to separate the two. That's why the supporting conditions have to be monitored and controlled throughout the activity. We take reference measurements both with and without the support structures to evaluate the difference." Variation also results when changes in temperature affect laser distance measurements. A subsystem in the laser instrument compensates for this effect with software that makes immediate adjustments based on live temperature readings together with pressure and humidity values. Temperature fluctuations also affect the size of components—the warmer the ambient environment, the more the parts expand. Given the large size of the thermal shield components, even a small change in temperature can result in significant thermal distortion. That is why metrology was performed on the thermal shield segments and panels in a temperature-controlled building—the poloidal field coil facility on site. "The ITER metrology team is accustomed to supporting the ITER units in all of their metrology needs," says Poncet. "So, when we received this request for the thermal shield in 2022, we geared up to do it by determining the as-built shape of the different components to be measured in order to set up references that could be monitored throughout the investigatory process. The trials performed through mid-2023 helped to contribute to the repair strategy that was defined that year, and which got underway after the selection of repair contractors."

European researchers at the Joint European Torus (JET) facility have announced that a new fusion energy record was achieved during the device's final campaign in late 2023. In its final deuterium-tritium experimental campaign, called DTE3, JET tested operating scenarios extrapolated from small- and medium-sized European devices to pave the way for ITER and fusion power plants to follow. JET's unique capability to work with deuterium-tritium fuel allowed it to demonstrate relevant plasma scenarios and offer critical insights into key aspects such as heat exhaust, managing fuel retention, and the effect of fusion neutrons on cooling systems and electronics. Using advanced scenarios to structure and control the plasma, researchers set a new fusion energy record of 69.26 megajoules of heat released during a single pulse in JET. This surpasses the record of 59 megajoules achieved during a five-second pulse in December 2021 as part of the previous (DTE2) campaign.  The ITER Director-General celebrated the accomplishment: 'Throughout its lifecycle, JET has been remarkably helpful as a precursor to ITER: in the testing of new materials, in the development of innovative new components, and nowhere more than in the generation of scientific data from deuterium-tritium fusion. The results obtained here will directly and positively impact ITER, validating the way forward and enabling us to progress faster toward our performance goals once operation begins. On a personal note, it has been for me a great privilege having myself been at JET for a few years. There, I had the opportunity to learn from many exceptional people.'  ITER's Deputy Construction Project Leader Tim Luce, who participated in the JET press conference on 8 February 2024, added, "The ITER project rests on the foundation of the world's community of science and technology research and especially on JET, because JET is at the cutting edge. It has unique capabilities and it has performed unique experiments. [...] This result is inspiring to us. It is one of the key operating scenarios we intend to explore on ITER and so having this result provides us confidence going forward. [...] I am extremely confident that the results here as they're become known and analyzed will have a profound effect on the ITER Research Plan.' JET ceased plasma operations at the end of 2023 after 105,842 pulses. The findings of JET's research have critical implications not only for ITER but also for the UK's STEP prototype powerplant, Europe's demonstration powerplant, DEMO, and other global fusion projects. Read the full press release on the EUROfusion website here.See the record pulse, #104522, on YouTube here.

Fusion Power Associates is calling out for nominations for two awards: * The 2024 Leadership and Distinguished Career Awards (nominations are sought by 1 June). No supporting material is required for these nominations, although supporting statements are appreciated. * The 2024 Excellence in Fusion Engineering Awards (Nominations are sought by 15 June). The purpose is to recognize individuals in the early part of their careers (maximum age 42) with both technical accomplishment and demonstrated leadership qualities. Nominating material should include the candidate's bio and letters of recommendation, including at least one letter from outside the nominee's home institution.  Nominations and nominating material should preferably be sent electronically but may also be faxed to 1-301-975-9869 or mailed to Fusion Power Associates, 2 Professional Drive, Suite 249, Gaithersburg, MD 20879, USA. The purpose, criteria and list of previous recipients for all awards are posted at http://fusionpower.org and click on Awards. For questions contact: fusionpwrassoc@aol.com