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| Fig. 1: Wendelstein 7-X under construction. (Source: Wikimedia Commons) |
Burning fossil or renewable resources is the most primal way of generating energy, but still today it is our predominant source of energy. Besides their limited availability, the drawback of oil, coal or gas resources is that burning them releases carbon monoxide and dioxide, which increase the greenhouse effect. Thus, we spend a lot of resources to find alternative sources of energy. However, it seems to be impossible to find a clean and efficient way to generate energy. Nuclear power plants have the drawback that we cannot find a proper permanent repository site, while we have to alter the flow of rivers or even flood whole canyons for hydropower stations. Sources of energy such as solar panels and wind turbines promise to provide us with clean energy. Unfortunately, their efficiency and stability depends strongly on the environmental conditions. Thus, a stable supply is not guaranteed unless vast majorities of land are covered. Scientists hope to find the ideal source of energy in nuclear fusion and recent experiments in Wendelstein 7-X, a stellarator type nuclear fusion reactor in Germany, show that progress has been made towards nuclear fusion.
Wendelstein 7-X is a nuclear fusion reactor based on the stellarator technology, which was built in Greifswald, Germany. It has a toroid shape and superconducting magnetic coils all around it to keep the generated plasma within the reactor, using magnetic fields of up to 3 Tesla. To maintain the superconducting properties of the coils, they are cooled down to 4 K with liquid helium. [1] Inside the reactor is a plasma vessel that is built to fit the shape of the magnetic field. Once the approach gets beyond the experimental stage, the aim is to use the heat that is generated by the nuclear fusion to generate power with conventional methods such as steam turbines.
The reactor Wendelstein 7-X was built to investigate the potential of stellarator type nuclear reactors for continuous operation. The expected plasma time is 30 minutes to reduce the maintenance and cooling costs. This is enough time for the all relevant processes of the system to find its steady state and thus to demonstrate that continuous operation is indeed possible. [2]
In July 2015 the construction (shown in Fig. 1) and first tests of the magnets were completed. The first helium plasma was generated in December 2015. [3] Soon after, in February 2016, the first hydrogen plasma followed, where the plasma reached a temperature of 80 million degrees Celsius. [3] Since March 2016 the first round of experiments is finalized and the reactor's plasma vessel gets upgraded for experiments with higher temperatures and longer pulses. The researchers hope to increase the time of the discharges to up to 30 minutes until 2020.
© Constantin Dory. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] K. Risse et al. "Fabrication of the Superconducting Coils for Wendelstein 7-X," Fusion Eng. Des. 66-68, 965 (2003).
[2] T. Kilnger et al., "Towards Assembly Completion and Preparation of Experimental Campaigns of Wendelstein 7-X in the Perspective of a Path to a Stellarator Fusion Power Plant," Fusion Eng. Des. 88, 461 (2013).
[3] T. Klinger et al., "Performance and Properties of the First Plasmas of Wendelstein 7-X," Plasma Phys. Contr. Fusion, 59, 014018 (2017).
