The beryllium tiles used to refit JET are machined into precise shapes with a deep grid of cuts designed to prevent stresses developing as the tiles heat and cool during the reactor’s operation.
The reactor is lined with 5,000 of these tiles, which cover every part of the interior apart from a trench running around the base of the torus. Known as the diverter, this is where plasma particles are slowed down to expend their energy. At this stage the plasma is in direct contact with the lining, which is made of tungsten tiles, as the heavier metal is less likely to be displaced from the surface by light helium and hydrogen nuclei, Matthews says.
The refit of JET took around 15 months. All of the tiles from the former lining had to be stripped out and replaced with beryllium or tungsten. Because the reactor shell itself has been rendered radioactive by neutron bombardment, the bulk of the work had to be carried out by remote operation.
The work is also likely to have implications for laser-driven fusion research, according to Chris Matthews, director of the High Power Laser Energy Research (HiPER) project, a European attempt to devise a power station-like fusion reactor running on the same principle as the National Ignition Facility.
“The first wall is an area where we and magnetic fusion have a crossover of interest,” he says. “The environment is rather different, because ITER has a constant plasma loading, whereas we have to deal with a pulsed load, but we’re hoping to benefit from the research that’s going into the ITER-like wall.”