JET enters "Restart"

For the last six months JET has been in a Shutdown state. This means that the JET vacuum vessel, which, during experiments, is pumped by turbo-molecular and cryogenic pumps, has been at ambient pressure and temperature. Furthermore, big ports at octants 5 and 1 have been opened to allow access for an articulated remote handling boom and for other purposes.

In addition to a significant number of inspections, maintenance tasks and substantial remedial work on key equipment, this Shutdown was mainly devoted to the installation of various new systems. The most extensive of these was the ITER-like antenna (see Fig. 1, below) (read more).

Another enhancement was the High Frequency Pellet Injector, which is a device capable of shooting small cubes of deuterium ice into the plasma. The motivation for this device is to have a direct fuelling method for the plasma core and to mitigate instabilities located in the plasma edge (Edge Localised Modes).

At octant 4 a second array of Toroidal Alfven Eigenmode antennas has been installed (see fig. 2). The purpose of these RF antennas is to excite Toroidal Alfven Eigenmodes (TAEs) in order to study their impact on the plasma. TAEs are a type of instability considered to pose a risk for loss of confinement in ITER.

Some other enhancements were to do with upgrading diagnostic equipment to improve measurements during experiments.

Most of the in-vessel work during this Shutdown, and especially all installations of new systems, was performed by remote handling. By mid-November 2007 the in-vessel work was complete. The extensive equipment which facilitated access for the remote handling boom and for other purposes was then removed from the Torus Hall. The phase we are entering now is known as "Restart". This involves powering up the electrical systems and pumping down the JET vessel, followed by a period of leak testing and inner-wall conditioning. Then we will be ready for the next experimental campaign to begin.

Fig. 1: The ITER like antenna during installation

Fig. 2: Toroidal Alfven Eigenmode antenna array

4th December, 2007