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Nachrichten, Termine, Experten
Nachrichten, Termine, Experten
Nuclear fusion is a source of great hope for future energy security, with this field being explored in research reactors around the world. Accurately detecting their performance requires measurement systems that supply valid data even under extreme conditions. And the centerpiece of those systems are the bolometers from the Fraunhofer Institute for Microengineering and Microsystems IMM. Experts from the institute will be presenting their sophisticated sensors at the joint Fraunhofer booth (Hall 2, Booth B24) at this year’s Hannover Messe trade show from March 31 to April 4.
Fusion technology could be the solution to the increasing energy needs of the growing global population, but it is a highly demanding technology. The current challenge is to carry out fusion experiments that produce more energy than they consume. To accurately capture advances in this field, specialists need exceptionally sensitive measuring instruments to analyze and control the complex processes taking place inside the reactors. Determining how much power is emitted from the fusion plasma is crucial to this.
Precision under extreme conditions
The detectors used to achieve this, known as bolometers, must reliably supply valid data under extreme conditions. “We are talking about an extremely intense environment: We have high-energy neutrons at very high density, high levels of extra-hard X-rays, extreme temperatures, changing loads in terms of vacuum and ventilation — all aspects that require considerable care in choosing materials,” explains Stefan Schmitt, Head of Special Sensor Technology at Fraunhofer IMM. Schmitt and his team have succeeded in developing a suitable sensor for these requirements, even under the strict rules that apply to this research segment.
Their solution is a silicon chip about 20 by 23 millimeters in size that holds four individual sensors. Each sensor has two absorber areas measuring 1.5 by 4 millimeters. The light emitted by the plasma along a narrow sight line is captured in each case by one of these absorbers, raising the absorber’s temperature. The temperature increase is measured by meander resistors made of platinum on the side facing away from the absorber as resistance increases by an equivalent measure. In this way, the sensor directly captures the radiation power present in the plasma, from infrared to the hard X-ray end of the spectrum.
The experts can use the measurement data from the many different lines of sight aligned complementarily inside the reaction vessel to associate this power with physical points in the plasma, thereby calculating a cross-sectional profile of the fusion plasma. To achieve this, the silicon chips produced at Fraunhofer IMM are incorporated into cameras consisting of a head where the chip is located and an aperture system. The cameras make it possible to use the different measurement signals to assess how well the plasma regulation inside the reactor is going while also determining the overall energy balance.
Solutions for specific diagnostics
One challenge was the high energy levels present in a fusion reactor. This means that the radiation simply passes through most materials. To get around this issue, Schmitt’s team designed the gold or platinum absorbers to be relatively thick, at 20 micrometers, about one-third the diameter of a single strand of human hair.
The conductor, or meander resistor, is made of platinum, a material that does not undergo changes even when exposed to high levels of radiation. By using gold absorbers and special carbon coatings that absorb visible light even more effectively on the absorber surface, the scientists were able to develop bolometers that are highly stable both mechanically and electrically for any use.
An integral element of active fusion research
These bolometers are already in use at prominent fusion research facilities around the world, including ASDEX Upgrade in Garching, Wendelstein 7-X in Greifswald and EAST in China. They have also been specially modified for ITER, the world’s largest fusion experiment at the Cadarache nuclear research center in the south of France. Schmitt, the project manager, is proud of the team’s achievements: “Our bolometers are proof that we can respond excellently to the extremely specific needs and requirements of our partners. Especially in the case of fusion research, it is highly beneficial that we speak the language of science.”
Fraunhofer IMM will be presenting its innovative measurement technology at the joint Fraunhofer booth (Hall 2, Booth B24) at the Hannover Messe 2025, using the sensor chip to illustrate that even highly specific inquiries are in excellent hands with this team.
https://www.fraunhofer.de/en/press/research-news/2025/april-2025/precision-measu...
Highly stable bolometer chips like this one precisely measure the power in fusion reactors.
© Fraunhofer IMM
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Highly stable bolometer chips like this one precisely measure the power in fusion reactors.
© Fraunhofer IMM
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