ASDEX Upgrade fusion device in operation again
Eight-month conversion finished / experimentation under ITER conditions
With production of the first plasma, experimentation on Garching’s ASDEX Upgrade fusion device has now been resumed after an eight-month conversion. This involved primarily reinforcing the wall cladding of the plasma vessel at particularly stressed places. Along with other technological improvements, this allows IPP scientists to experiment with ASDEX Upgrade under conditions that will prevail in the ITER international test reactor. This large-scale device is now being built at Cadarache, France, as a world-wide cooperation project.
ITER is to demonstrate that it is possible to derive energy from fusion of atomic nuclei, as happens in the sun. The fuel, a hydrogen plasma, is confined in a magnetic field cage and heated to temperatures of 100 million degrees. It is important here to achieve tolerable interaction between the plasma vessel and the hot plasma hovering in it. ASDEX Upgrade is the only fusion experiment in the world where the plasma vessel is completely shielded inside with tungsten, the metal with the highest melting point. Because of good results tungsten is meanwhile envisaged also as material for special wall sections of ITER.
To allow investigation at ASDEX Upgrade of the mutual influence of the plasma and wall under ITER conditions, the particularly stressed parts were converted: carbon tiles, hitherto clad with a thin tungsten coating, were replaced with massive water-cooled tungsten plates. This applies primarily to parts of the divertor, i.e. a section on the floor of the vessel where the wall is in direct contact with the plasma. The robust new tiles now allow cases of overloading to be investigated. This happens when the plasma suddenly ejects heat and particles onto the floor plates due to instabilities.
A newly installed rail system, viz. the divertor manipulator, also helps to replace divertor plates without eliminating the vacuum in the plasma chamber, which hitherto entailed experimentation interruptions lasting several weeks. As a result, tiles can be fitted with different probes according to the experiment. Above all, it is now also possible to test prototype tiles for ITER or Wendelstein 7-X under realistic plasma conditions.