Abstract Plasma spraying as a coating method has the ability to coat large areas as well as repair the damaged regions in-situ, without removing the whole component from the machine. Boron carbide is a possible layer material for the components of a fusion reactor that are directly exposed to the plasma. The low atomic number and the high melting point are two of the important properties of this material. On the other hand, these properties make thermal spraying difficult. Boron carbide was originally processed using VPS or LVPS syringes. In this paper, water-stabilized plasma spraying is used, which allows the coating of large areas. Boron carbide is coated by varying various parameters, and the properties of the coatings are characterized. The layer composites are then optimized with regard to the requirements of the application. Paper includes a German-language abstract.

Abstract The Laser Megajoule (LMJ) is designed to produce, in laboratory, fusion energy with a significant gain. Such an energy could be achieved by imploding a small capsule filled with a DT mixture. Fusion experiments produce a large emission of neutrons, x-rays, laser scattered light and debris which impose a first wall protection for the laser target chamber made of a low Z and refractory material. As boron carbide appeared to be a good candidate, among others, it was decided to evaluate the potentiality of plasma sprayed B4C coatings for this application. This paper deals with the optimization of plasma spraying conditions to build up coatings that satisfy specifications required for the first wall. Coating general properties are presented as well as outgassing performances. Specific x-ray and laser tests were performed to evaluate coating behavior close to real LMJ working conditions.

Abstract The development of nuclear fusion reactors is presently considered to be the only possible answer to the world's increasing demand for energy, while respecting the environment. Nuclear fusion devices may be broadly divided into two main groups with distinctively different characteristics: magnetic confinement fusion (MCF) and inertial confinement fusion (ICF) reactors. Although the two nuclear fusion technologies show similarities in energy levels (as high as 3 J/cm2) and type of environment (high temperature plasmas) to be contained, the materials of choice for the protective shields (first wall in the ICF and deflectors in the MCF) differ significantly. In ICF reactors, multiple laser beams are used to ignite the fuel in single pulses. This process exposes the first wall to microshrapnel, unconverted light, x-rays, and neutrons. B4C is a low Z material that offers high depth x-ray absorption to minimize surface heating, is not activated by neutrons (will not become radioactive), and offers high hardness and vapour temperature. The long term operation envisioned within MCF reactors, where a continuous nuclear fusion of the fuel is sustained within the confinement of a magnetic field, favours the use of high Z materials, such as W, to protect the plasma exposed deflectors. The reason is a lower erosion rate and a shorter ionization distance in the plasma, which favours the redeposition of the sputtered atoms, both resulting in a lower contamination of the plasma. The production of the first wall and the deflector shields using solid B4C and W materials respectively, is obviously unthinkable. However, ProTeC has developed high density coatings for both ICF and MCF nuclear fusion reactors. W coatings with less than 2% porosity have been produced for both, the Tokamac MCF reactor and its Toroid Fueler. The toroid fueler is a plasma generating device designed to accelerate particles and inject them into the centre of the operating fusion reactor in order to refuel. For the application in an ICF reactor, B4C coatings exhibiting porosity levels below 3% with a hardness above 2500 HV have been deposited directly onto Al substrate. Properties such as outgassing, resistance to erosion and shrapnel, and the influence of x-rays have been studied and showed exceptional results.

Abstract Thermally-sprayed low-Z coatings of boron carbide (B4C) on aluminum substrates were investigated as candidate materials for first-wall reactor protective surfaces. Comparisons were made to thermally-sprayed coatings of boron, MgAl204, Al2O3, and composites. Graded bond layers were applied to mitigate coefficient of thermal expansion mismatch. Microstructures, thermal diffusivity before and after thermal shock loading, steel ball impact resistance, CO2 pellet cleaning and erosion tolerance, phase content, stoichiometry by Rutherford backscattering spectroscopy (RBS), and relative tensile strengths were measured.