in february, the last components for the installation of the Jet iter-likewall were delivered. with these components, the extensive upgrade referred to as enhancement pro – gramme 2 is coming to an end. the machine is scheduled for pump down in early May and the first experimental campaigns are to begin in early august 2011.

The last component to be delivered for the installation of the ITER-Like-Wall (see Fusion News December 2009) was the high vacuum feed-through. This device feeds the cables of the JET in-vessel installations through a vacuum port to the external control systems. Now, more than 80 percent of the tile assemblies have been installed in the machine and the final push is underway.

Surprises in the wall

After removing the old, carbon wall in August 2010, the inside of the machine was surveyed in detail (Fusion News September 2010). Many of these areas were last seen in the early 1990s when the JET Mark II divertor was installed. The survey revealed many ‘anomalies’ or discrepancies between the actual measured geometry of the machine and the configuration as shown in the CAD model of JET. Since the design of new ITER-Like- Wall components was based on the CAD information, they needed to be modified to make them fit-for purpose. Consequently, the shutdown critical path, which had always been defined by the time required to install the ITER-Like-Wall, had to be lengthened to include the design, procurement and assembly work associated with resolving the anomalies. These modifications are now almost complete so that the critical path is once again set by the installation activities and with the pump down scheduled for the beginning of may.

Upgraded heating

The second major enhancement to JET’s capabilities is the upgrade of the neutral beam heating system which increases its maximum power by more than 50 percent. The system heats the plasma by injecting a beam of high-speed neutral atoms. Since the higher power beams dissipate more heat, several components along the beam have been upgraded. In particular, two new, actively-cooled liners have been installed in the vacuum vessel ports through which the beams are injected into the plasma.

New diagnostics

The final pillar of the enhancement is a suite of new and upgraded diagnostics, which serve two purposes: The interaction of the new wall with the more energetic high performance plasmas as produced by the upgraded machine must be diagnosed carefully to prevent damage to the wall. The systems also increase JET’s capabilities for diagnosing deuterium-tritium plasmas. These will ultimately be employed to fully exploit the new wall. Several systems were already
available before the shutdown and the remainder have now either been set up or will be installed before the experiments start.

The next experiments

In parallel to the completion of the shutdown, extensive planning is underway to define the first experimental campaigns with the new wall. A detailed restart plan and experimental timeline have been prepared, covering the period from the end of the shutdown up until February 2012. A formal Call has been sent to the EU Fusion Associates asking for their participation in the project.

Lorne Horton, Head of JET-Department, EFDA