What’s New

During the operation of a fusion machine, it is important to know the surface composition of the plasma-facing components, which can evolve over time (erosion, oxidation...) and modify plasma interaction conditions.

The team at the WEST tokamak in France is testing a new kind of diagnostic, called the fibered LIBS (for Laser-Induced Breakdown Spectroscopy), to characterize internal surfaces of WEST and later ITER. 

In LIBS, a high-intensity pulsed laser beam is focused on the surface to be analyzed. The laser/matter interaction leads to the ablation of the material and the creation of a plasma plume. The spectral analysis of the plasma emission gives access to the elemental composition of the ablated material and thus the composition of the material under study.

Installed on an inspection robot equipped with an articulated arm, the LIBS tool consists of an optical fibre carrying the incident laser light and the light emitted during the interaction of the laser beam with the material under study. The diagnostic can not only characterize all internal surfaces of the machine and follow their evolution, but also (in ITER) monitor tritium concentration in the first wall and detect eventual helium bubbles in plasma-facing components coming from the interaction of fusion neutrons with the materials.

The first tests were carried out in December 2021. Read the original article in English or in French.

There are presently two approaches to realizing hydrogen fusion. One, implemented in tokamaks and stellarators, consists in heating a very tenuous plasma to temperatures in the 100 million degrees Celsius range and to confine it in a magnetic cage—this is magnetic fusion. Another, called inertial fusion, is implemented in installations such as the American National Ignition Facility (NIF) or the French Laser Mégajoule. In inertial fusion an array of hundreds of powerful lasers, precisely focused, is used to compress to extreme density (and hence very high temperature) tiny hydrogen-filled capsules inside which fusion reactions can occur.

Now, a third approach is being considered and experimented at NASA's Glenn Research Center, in Cleveland, Ohio. Called "lattice confinement fusion," it could one day provide enough power to operate small space probes or rovers for planetary exploration.

In lattice confinement fusion (LCF), a beam of gamma rays is directed at a sample of erbium or titanium saturated with deuterium nuclei (deuteron). Occasionally, gamma rays of sufficient energy will break apart a deuteron in the metal lattice into its constituent proton and neutron. The energetic neutron has a chance of colliding with another deuteron in the lattice, imparting it with some of its energy. And sometimes that energy is enough for deuterons to fuse into a helium-3 nucleus (helion) and give off useful energy. A leftover neutron could provide the push for another energetic deuteron elsewhere in the lattice.

"Our work represents just the first step toward realizing that goal," say the scientists involved in this endeavour. "If the reaction rates can be significantly boosted, LCF may open an entirely new door for generating clean nuclear energy, both for space missions and for the many people who could use it here on Earth."

 Read more about lattice confinement fusion on the IEEE Spectrum here.

The global manufacturing intelligence firm Hexagon AB is providing metrology support to ITER for the precise assembly of components during the machine assembly phase. In this promotional video you can watch how the huge components of ITER's first vacuum vessel sub-assembly are brought together with assembly tolerances of just 1 mm.

See the video here.