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It's team time

31 Mar 2008 - Gary Johnson, ITER Deputy Director-General, Tokamak Division

In the last few months, we have come a long way to resolve critical issues in order to generate the 26 Procurement Arrangements (PAs) that are scheduled for this year. This big job is made even more challenging by the fact that several recommendations made by the Science and Technology Advisory Committee (STAC) will likely impact at least a few of these PAs. The three main STAC recommendations relate to ELM mitigation and vertical stability, increased asymmetric loads on the Vacuum Vessel (VV), and plasma shaping.

The mitigation of ELMs is certainly the most challenging in regards to design, cost, and schedule. The current concept which has the coils mounted on the inner wall of the vacuum vessel (which can also address vertical stability deficiencies) will see high electromagnetic loads as well as thermal loads, and must accommodate significant thermal expansion. Assuring high reliability for 20 years of operation, plus accommodating remote handling replacement (if needed) are critical requirements.

The complexity of this effort is even increased due to space constraints between the vacuum vessel and the blanket. Because the Vessel PA is planned to be issued in June this year and this is a critical path activity, every effort is being made to reduce the schedule impact. Therefore, strategies have been developed together with the Domestic Agencies involved to more fully define the design and assess impacts. This extensive effort is to be done by late May.

Increased asymmetric loads on the vacuum vessel are another design challenge that requires some reinforcement along the top of the nine divertor ports. The VV supports are located on the bottom side of these ports. Currently, every effort is being made to accommodate these loads without adding additional supports. At this time a solution with the current nine supports looks feasible.

Even without the potential changes associated with the STAC issues mentioned above, the completion of the VV design and finalizing the related Procurement Arrangements by June 2008 remains a challenge. Nevertheless, good progress is being made to finalize the interfaces, and to complete the analysis documentation and the technical specifications.

Last but not least, the STAC recommended changes to the Poloidal Field (PF) coil to address deficiencies in plasma shaping, flux and Li-control (a measure of how peaked the plasma current profile is). The current plan is to subcool PF6, move it closer to the plasma, and add an extra double pancake. Second, to add 10% more turns on PF2, and - third - to modify the conductor for PF2 to PF5 to allow enhanced current capability. Impacts on the PA issue schedule are expected to be relatively small.

Summarizing, it will take a concerted team effort within the IO to finish the related designs and keep the issue dates for the 26 Procurement Arrangements on schedule. This is starting to happen and I'm optimistic that 2008 will be not only be a pivotal but a successful year for the ITER project.

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