Acceleration grids of the Neutral Beam Injector in nuclear fusion reactors must be extremely accurate and satisfy specific geometrical requirements to work properly. The implementation of the additive manufacturing technology was proposed since 2017 starting the characterization of pure copper up to the recent excellent results in terms of density, process reliability and repeatability. To assure the required performance and maximize the beam optics and the overall system efficiency, an intense study of the geometry of these components was performed, adopting a spherical aspect of planes. The material selection was also an important step of the work. An integrated cooling system, peculiar of the AM technology, was optimized, ensuring a relevant reduction of temperature peaks. Pure copper and CuCrZr alloy were investigated for reaching the best material properties: parameters optimization was executed using different machines and laser beams, and several post processes were assessed, such as surface treatments to smooth the cooling ducts. After the material characterization, which was focused on the evaluation of density, thermal conductivity and mechanical strength of the AMed parts. Lastly, several prototypes were produced and power tests were carried out.

Niobium is particularly appreciated for its superconductive properties. One of the main applications of this metal in Nuclear Physics is the production of superconducting radiofrequency (SRF) cavities for particle accelerators. Additive Manufacturing (AM) gives the chance to fabricate objects with very complex shapes; also, high melting temperature and hard-to-machine materials can be easily processed. However, AM is not free from challenges, and the creation of devices such as the SRF cavities is not trivial. In this work, the characterization of pure niobium produced by Laser Powder Bed Fusion (LPBF) and a fine-tuning of the printing parameters have been carried out. Much emphasis was put on the development of innovative contactless supporting structures for improving the quality of downward-facing surfaces with very small inclination angles. A relative density higher than 99.8% was achieved and the efficiency of such innovative supports was demonstrated, as they made the fabrication of seamless SRF cavities possible. Smoothing surface treatments and performance tests on AMed cavities were also performed.

Recently, Metal Additive Manufacturing technology enables the possibility to realize cooling systems in accelerator components during the manufacturing process phase, obtaining extremely high density, high thermal, and mechanical properties in metals. In the Neutral Beam Injection for the Divertor Tokamak Test facility, the beam acceleration components are submitted to extremely high-power loads. A tailored cooling channel shape for the acceleration grids is proposed and tested. However, the roughness issue in MAM manufacturing is a problem that can strongly affect the pressure drop in long and small-section channels. CFD is a valid tool that, if properly calibrated, predicts the pressure drop and efficiency of the cooling system. In this work, different single-channel samples have been manufactured via MAM and they have been tested to characterize the pressure drop behaviour. The single-channel samples have been internally smoothed via a chemical process to reduce the pressure drop and tested again. CFD models, using Ansys Fluent software, have been calibrated to properly predict the pressure drop of the single-channel samples. The CFD models have been implemented to optimize the channel design of the Extraction Grid cooling system. The optimized shape of the EG channels has been adopted to produce different scaled AM prototypes and tested with a thermal power map, which is similar to the nominal one.

Traditionally produced SRF cavities are characterized by many limiting drawbacks, such as welding lines and poor reproducibility of their properties. Additive Manufacturing, and in particular Laser Powder Bed Fusion (LPBF), may overcome these issues: with this technology, it is possible to create seamless components with reproducible characteristics. But 6 GHz cavities cannot see internal supports because they would not be easily removable. On the other hand, the down-skin self-supporting surfaces are extremely rough and unsuitable for the intended application. Indeed, very smooth surfaces are required since copper cavities are internally coated with superconducting materials (like Nb or Nb alloys): several surface treatments have been performed and studied; tests like tightness, resonant frequency and internal inspections have also been carried out before and after the post-printing smoothening and coating stages. Results are very promising and they will be shown in this work.

Copper and copper alloys are widely used in the Nuclear Fusion field for their outstanding characteristics, especially in terms of thermal and electrical conductivities. CuCrZr is peculiarly suitable and well-known in High Energy applications because it combines good conductivity and good mechanical properties. Moreover, the material properties can be tuned with thermal treatments to fit the application requirements even more. Additive manufacturing is then a revolutionizing process that permits the creation of geometrically optimized components. This near-net-shape process allows to produce seamless parts reducing material waste and saving time. We investigate the application of the Laser Powder Bed Fusion technology to produce the acceleration grids of a Neutral Beam Injector. In this work, the authors analyzed different CuCrZr powders and investigated the material properties obtained after the printing parameters optimization, in as-built conditions and after several heat treatments. The high density and high mechanical and thermal properties allowed us to proceed with the creation of the first prototypes of the acceleration components.

The Laser Powder Bed Fusion (LPBF) is an AM technology suitable to produce almost free-form metallic components. At Legnaro National Laboratories of the Italian National Institute for Nuclear Physics, the LPBF process was recently used to produce parts of the Forced Electron Beam Induced Arc Discharge (FEBIAD) ion source for the SPES Isotope Separation On-Line (ISOL) facility. Such device is a critical component for the ISOL process, as its correct functioning is fundamental to ensure the availability of the radioactive ion beam to the experimental users. One of the main parts of the ion source is the tantalum cathode, a component that is electrically heated up to 2200°C and is subjected to thermal stresses. Currently, the cathode is produced by subtractive manufacturing processes and TIG welding, which are not trivial in the case of Tantalum. Therefore, the cathode lacks dimensional/geometrical precision, affecting the performance repeatability and reliability of the ion source. The LPBF technology allows to perform a morphological/topological optimization of the cathode aiming to overcome the intrinsic assembly limits of the present design and making more repeatable and reliable the ion source performance. In this work, the production of the prototypical cathodes via AM, the results of dimensional–geometrical measurements, and the endurance high-temperature test are presented.