Synthetic Diamond Windows developed by Element Six help fuel the World's Fusion Energy Projects
Harnessing the process that provides the sun's energy, has been a scientific ambition since the 1940s when the potential of nuclear fusion as power source was realised. Ongoing international collaboration into fusion research is leading to a new generation of fusion research machines that will move the dream of energy from fusion closer to commercialisation. Synthetic diamond windows are a key component of the research aimed at producing energy by fusion.
In 2008, construction of ITER, the world's most ambitious fusion project so far, will begin. ITER's main aim is to demonstrate prolonged fusion power production from a deuterium-tritium plasma. It will include most of the necessary technology of a future commercial design, but will operate at about one-sixth of the output power. This project is funded by a number of companies (China, the European Union, India, Japan, the Republic of Korea, the Russian Federation and the United States of America) and will be built in Cadarache, France.
The heart of ITER is its torus-shaped fusion chamber where a magnetic field will confine the extremely hot deuterium-tritium gas mixture. To heat the gas mixture to the temperature needed to cause fusion (about 100,000,000 Kelvin), intense beams of microwaves will be admitted into the chamber through windows in the chamber's outer wall. Each window must be capable of transmitting about 1 MW of microwave power through an aperture less than 10 cm in diameter without going into thermal runaway, an extremely challenging requirement, as well as preventing the deuterium-tritium mixture from escaping from the fusion chamber.
Diamond synthesised by chemical vapour deposition, CVD, can exhibit very low level of microwave absorption combined with high thermal conductivity, both essential for avoiding thermal runaway, making it the main contender for the windows. Another advantage of CVD diamond is that its low dielectric constant means that damaging back reflection of the microwaves into the gyrotron used as the microwave source is also avoided.
Working with leading fusion research laboratories around the world, scientists at Element Six's CVD facility at Ascot have developed microwave transmission windows that meet the requirements of the fusion application. Element Six windows have transmitted 2 MW microwave beams at room temperature without difficulty. Competing materials are more difficult to fabricate and need to operate at cryogenic temperatures, requiring complex and expensive cooling systems, and even then can only transmit a fraction of the power.
Microwave windows are another example of the extreme properties of CVD diamond delivering a cost effective solution to an extreme engineering challenge.