On Friday, October 23rd, JET’s C27 Experimental Campaign came to a successful conclusion. As soon as the experimental team had finished, work began on the shutdown required to install the major components of the second JET Enhancement Programme in Support of ITER (EP2).

For EP2, JET’s plasma facing components, which currently consist of carbon materials, will be removed, replacing the first wall and the divertor by a combination of beryllium and tungsten components, respectively (see article on the tungsten coatings in this issue). In parallel, JET’s diagnostic and control capabilities will be enhanced and the neutral beam heating power increased from 23 to 34 megawatts.

The refurbishment, which will last 65 weeks, is a huge undertaking, exchanging a total of 4500 plasma facing components. Most of the tasks are carried out remotely, for which the equipment has been largely enhanced (see FN May 2009). The remote handling staff have been practicing manoeuvres for the past months to make sure they are operating the booms in the most efficient way. Nevertheless, the tight work plan requires remote handling to be run in two shifts, seven days a week, during the entire shutdown period. The ambitious schedule however does include contingency for the historically required allowances for equipment failures and maintenance periods for the remote handling equipment. In early 2011, JET will restart.

The critical path of the shutdown is determined by the in-vessel activities that must be carried out. As JET was not designed to be maintained entirely remotely, work will switch between remote and manual handling phases.

It will take several weeks alone to prepare JET for the work to come by attaching and commissioning access chambers for work personnel and access facilities for the remote handling booms. The divertor tile carriers are the first components to come off, so that they can be refitted with tungsten-coated tiles. This task is estimated to last about nine weeks. Next, the beams containing diagnostics to measure the magnetic field inside the vessel are dismounted from the vacuum vessel wall and the upper Inner Wall Guard Limiter tiles will be removed. Some components inside the vessel will be welded remotely and a photogrammetry survey will be carried out to measure the exact position of the ports and other important points inside the vessel, providing data for the sub sequent remote handling procedures. Thereafter, all remaining tiles will be removed and stored. The empty vessel is then cleaned and surveyed, the diagnostic beam is put back in and the infrastructure for some of the new or enhanced diagnostics is installed. Beginning about 42 weeks into shutdown, the new wall tiles will be fitted, followed by the limiters and finally the divertor. After removing all previously installed access-facilities and remote handling equipment, JET can be pumped down.

Besides installing the new wall, the neutral beam duct scrapers will be  replaced during the shutdown. The duct scrapers are located in the neutral beam ports of the vessel, protecting the ports from neutral particles in the edge of the beams that would not pass through the ports and from particles that are re-ionised as they pass through the port. Since the enhanced neutral beams will supply much higher power, the new scraper needs to be actively cooled.

During the entire shutdown period, significant attention will be devoted to the calibration and adjustment of JET diagnostics for the operation of the machine with the ITER-like wall. The main in-vessel activities on diagnostics will be the calibration of the neutron measurements and the calibration of the spectroscopic systems.

Thanks to Lorne Horton, JET, for his input

EFDA-JET’s newsletter “Shutdown Weekly” will highlight the most exciting aspects of this shutdown week by week: