Part 1 of 2 Parts
The Axially Symmetric Divertor Experiment (ASDEX) Upgrade is a divertor tokomak that went into operation at the Max Planck Institute for Plasma Physics (MPIPP) in Germany in 1991. For the last thirty years, the ASDEX Upgrade has been blazing a trail towards the creation of a nuclear fusion power plant that could generate climate-neutral energy. This experimental fusion reactor has been repeatedly expanded and improved during this time. It has provided numerous insights that have been incorporated into the design and operation of other fusion reactors. One example of this is scenarios that the ASDEX Upgrade team have provided for the operation of the JET test plant in the U.K. and the ITER test plant in France. They have also provided forecasts for a planned demonstration power plant.
The main goal of nuclear fusion research is to develop a climate-and environmental-friendly power plant for commercial use. Its purpose is to derive energy from the fusion of atomic nuclei. The fuel used in nuclear fusion reactors is an extremely thin, ionized gas called a plasma. In order to ignite the fusion reaction, the plasma must be enclosed in powerful magnetic fields and heated to over a hundred million degrees.
In order to control the interaction between the hot fuel and the surrounding walls of the donut-shaped tokamak, the team at the MPIPP have equipped the ASDEX Upgrade with a divertor which is part of its name. Through an additional magnetic field, the divertor field removes impurities from the plasma and improves its thermal insulation.
In contrast to its predecessor ASDEX, in the ASDEX Upgrade, the divertor and important properties of the plasma, especially density and load on the walls, are more closely adapted to the conditions expected in later fusion power reactors. The ASDEX Upgrade is equipped with powerful plasma heaters and sophisticated measuring equipment for observing the plasma. This means that the ASDEX Upgrade can be used to develop operating modes for a potential fusion power plant. In over thirty-eight thousand plasma discharges to date, the ASDEX Upgrade has answered important research questions for the European Joint Experiment (JET) and the International Experimental Reactor (ITER) as well as a planned demonstration plant.
The ASDEX Upgrade team took an important step towards the design and construction of future fusion power plant when they covered the walls of the plasma containment vessel with tungsten instead of carbon. Carbon does have some experimental advantages for experimental plants. However, it is not suitable for the operation of an actual commercial fusion power plant because it is too strongly eroded by the plasma and too much of the plasma binds to the carbon. Due to its high melting point, tungsten is well suited to act as a wall coating. However, the plasma cools down quickly because of even the smallest impurities in the tungsten coating that are released from the walls. Following a lot of experimentation, the ASDEX Upgrade team was able to solve this problem.
In a major rebuild, the JET received a tungsten divertor in 2011. The ITER team decided not to bother working with a carbon diverter and to go straight to a tungsten divertor.
Please read Part 2 next