Gyrotrons are microwave oscillators generating a temperature of up to 150 million degrees Celsius in the reactor, similar to a very big microwave. This high temperature makes the tritium fuel reach the plasma state required for fusion. To guide microwave radiation from the gyrotrons into the plasma and in order to maintain a vacuum and keep the radioactive tritium inside the reactor, a team around Dr. Dirk Strauss and Professor Theo Scherer of KIT's Institute for Applied Materials (IAM) designs appropriate window units.

The Diamond disks guide radiation of more than one megawatt power into the ITER research reactor, numerous diamond windows have been designed by IAM and produced in cooperation with industry partners. Meanwhile, scientists are also working on window units for ITER's successor called DEMO, in which power will be produced from 2050 onwards. As a consequence of planned multi-frequency operation of the microwave heating system in DEMO, however, new types of gyrotrons will be required.