The most advanced ‘stellarator’ type nuclear fusion reactor on the planet is ready. This is now its purpose

The Wendelstein 7-X experimental nuclear fusion reactor is a marvel. The path to fusion energy through magnetic confinement is not only being taken by nuclear reactors. tokamak. ITER is the most ambitious experiment of its kind, but in Europe we have a fusion reactor of type stellarator The Wendelstein 7-X is an extremely promising satellite. It is located in one of the buildings of the Max Planck Institute for Plasma Physics in Greifswald, Germany, and was completed in 2015.

Its purpose is to contribute to the development of technologies involved in the development of nuclear fusion reactors using magnetic confinement, but its formula is different from that proposed by ITER and JET. The most obvious difference between tokamak and stellarator reactors lies in their geometry. The former are shaped like a toroid (or doughnut), and the latter have a more complex geometry that resembles a doughnut twisted on itself.

However, the fundamental difference between these two designs is that the reactors tokamak require that the magnetic fields confining the plasma be generated by coils and induced by the plasma itself, while in reactors stellarator Everything is done with coils. There is no current inside the plasma. This ultimately means that the latter are more complex and difficult to build. Fortunately, the Wendelstein 7-X experiment is making steady progress.

A campaign of experiments begins with a refurbished Wendelstein 7-X

The first tests carried out on this fusion reactor between 2015 and 2018 went as planned, so in November of this year an important moment in its itinerary arrived: it was necessary to modify it to install a water cooling system capable of more efficiently evacuating the residual thermal energy from the walls of the vacuum chamber, as well as a system that would allow the plasma to reach a higher temperature. The work requiring these modifications was successfully completed in August 2022.

When scientists make such major modifications to such a complex experiment, they are forced to obsessively check everything before restarting the machine to make sure everything will go as planned. Fortunately, everything went well and in February 2023 the Wendelstein 7-X reactor reached an important milestone: it managed to confine and stabilize the plasma. for 8 uninterrupted minutes The reactor delivered a total energy output of 1.3 gigajoules. But that was not enough. The machine was now due for a new phase of maintenance and renovation in order to go even further.

One year later, the reactor is once again ready to carry out new experiments, and it now has significant improvements. The technicians who have been working on it for the past few months have optimized the control and data acquisition systems, improved the plasma heating system and implemented nearly 50 additional diagnostic tests.

Of all these improvements, the most relevant is the heating system, which is now capable of generating more than 1 megawatt of power in the plasma thanks to the application of microwaves. This technology is known as the microwave heating system. electron cyclotron resonance heating (ECRH or Electron Cyclotron Resonance Heating in English).

In any case, the most interesting thing is to find out what experiments the scientists operating the Wendelstein 7-X reactor have planned for the new campaign that has just begun (it started on September 10). Its main purpose is to gradually increase the temperature of the plasma. “We are gradually approaching higher heating powers,” Professor Thomas Klinger sayswho is the director of the Max Planck Institute for Plasma Physics.

“On the one hand, we want to thoroughly test the thermal loading limits on the carbon walls of W7-X. On the other hand, we also want to better understand the turbulence-controlled transport processes that occur in the plasma, as well as the mechanisms of heat depletion,” explains Klinger. It sounds exciting. I hope you achieve your goalsThe next phase of maintenance and renovation will run from June 2025 to August 2026, so that the next experiment campaign will start in August 2026 and will run almost uninterrupted until May 2027.

Image | MPI for Plasma Physics, Jan Hosan

rmation | EUROfusion

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