ASDEX Upgrade
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The ASDEX Upgrade divertor tokamak (Axially Symmetric Divertor EXperiment) went into operation at the Max-Planck-Institut für Plasmaphysik, Garching in 1991. At present, it is Germany's largest fusion device.
To make experiments under reactor-like conditions possible, essential plasma properties, particularly the plasma density and pressure and the wall load, have been adapted in ASDEX Upgrade to the conditions that will be present in a future fusion power plant.
ASDEX Upgrade is, compared to other international tokamaks, a midsize tokamak experiment. It began operation in 1991 and it succeeds the ASDEX experiment, which was in operation from 1980 until 1990.
One innovative feature of the ASDEX Upgrade experiment is its all-tungsten first wall; tungsten is a good choice for the first wall of a tokamak because of its very high melting point (over 3000 degrees Celsius) which enables it to stand up to the very high heat fluxes emanating from the hot plasma at the heart of the tokamak; however there are also problems associated with a tungsten first wall, such as tungsten's tendency to ionise at high temperatures, "polluting" the plasma and diluting the deuterium-tritium fuel mix. Furthermore, as a high Z material, radiation from fully ionized tungsten in the plasma is several orders of magnitude higher than that of other propesed first wall components such as carbon fibre composites (CFCs) or beryllium. This result allows for far less tungsten to "contaminate" a proposed break-even plasma. ASDEX-U will examine ways to overcome this problem, in preparation for the construction of ITER's first wall.
The experiment has an overall radius of 5 metres, a gross weight of 800 tonnes, a maximum magnetic field strength of 3.9 tesla, a maximum plasma current of 2 mega-amps and maximum heating power of up to 27 megawatts. Plasma heating and current drive in the ASDEX-U is derived from several sources, namely 1MW of ohmic heating, 20MW of neutral beam injection, 6MW via ion cyclotron resonance heating (ICRH) at frequencies between 30 and 120 megahertz, and 2 x 2MW of electron cyclotron resonance heating (ECRH) at 140 gigahertz. It has 16 toroidal field coils and 12 poloidal field coils.
