Coatings for Fusion Reactors
proven in international collaborations
Functional Principle
The coatings are thin ceramic layers (up to 500 µm) engineered to absorb microwave radiation through controlled interference. Incident radiation is partially reflected at the coating surface and at the coating–substrate interface. By tuning layer thickness and material composition to the target frequency, these reflected components cancel out, and the radiation is dissipated as heat within the layer instead of being reflected back. This allows absorption rates of up to 90 %. Because the coatings are ceramics, they withstand the high temperatures and vacuum conditions found near the plasma.
Bolometers are used for radiation diagnostics in fusion experiments. Microwave-absorbing ceramic coatings provide a functional absorber surface that converts incident electromagnetic radiation into heat. The resulting thermal response can be detected by the sensor and used for the determination of the incident radiation. The absorption characteristics of the coating can be tailored to the relevant radiation conditions while maintaining the thermal and vacuum compatibility required for fusion environments.
Used in W7-X (IPP, Max-Planck-Institute of Plasma Physics)
Gyrotrons generate high-power microwave radiation for applications such as electron cyclotron heating in fusion reactors. Dummy loads are required to safely absorb microwave power during gyrotron development for calcualtion of the power output. At IKMT we were involved in the manufacturing of ceramic absorber coatings for gyrotron dummy-load components in cooperation with KIT. The coating converts incident microwave radiation into heat and provides a robust absorbing surface for operation under high microwave loads.
Used at KIT (Karlsruher Institute of Technology)
Electron Cyclotron Heating (ECH) systems use high-power microwave radiation to heat and control fusion plasmas. Monitoring this radiation is essential for the operation and protection of the surrounding systems.
Our ceramic absorber coatings can be integrated into ECH sensor concepts, where they absorb incident microwave radiation and convert it into a measurable thermal response. The coating therefore acts as the functional interface between the electromagnetic radiation and the sensor.
Used in ITER (International Thermonuclear Experimental Reactor)
Diagnostic windows provide optical or electromagnetic access to the plasma while separating sensitive diagnostic systems from the fusion environment. Microwave stray radiation reaching these windows can expose the diagnostic components to unwanted power loads. Our coated diagnostic window sensors are positioned in front of the respective diagnostic windows. The ceramic coating absorbs incident microwave stray radiation and converts it into a measurable thermal response. This enables the local microwave power reaching the diagnostic window to be monitored. The sensor therefore combines two functions: controlled absorption of stray radiation and measurement of the incident microwave power directly at the diagnostic interface.
Used in ITER (International Thermonuclear Experimental Reactor)
Cryopump cooling units contain complex copper lamellar structures providing a large surface area and high thermal conductivity. Without additional surface functionalization, the metallic copper surfaces strongly reflect incident microwave stray radiation, allowing it to propagate further through the system. By applying a ceramic microwave-absorbing coating to the lamellar structure, the cooling unit additionally acts as a defined sink for microwave stray radiation. Instead of being reflected, the incident radiation is absorbed by the coating and converted into heat. The thermally conductive copper substrate and active cooling enable the resulting thermal load to be efficiently dissipated. This approach utilizes the large existing surface area of the cooling structure to suppress unwanted microwave reflections and limit the propagation of stray radiation within the system.
Used in W7-X (IPP, Max-Planck-Institute of Plasma Physics)
High-power microwave systems can generate stray radiation that propagates outside the intended microwave path. This radiation can interfere with sensitive diagnostics and expose surrounding components to additional electromagnetic and thermal loads. Ceramic microwave-absorbing coatings can be applied to shielding surfaces and surrounding components to absorb this unwanted radiation and reduce microwave reflections. The coatings therefore contribute to the protection of diagnostics and other sensitive equipment in the fusion environment.
Used in JT-60SA
