NBI systems are an important component of Tokamak Projects that can present challenging requirements. We present here the preliminary results of R&D work on innovative techniques to produce extraction and accelerating grids. In the framework of the DTT Project, the NBI accelerating system consists of four layers. We are working on the engineering validation phase of an innovative design and production approach, alternative to the one typically adopted for the NBI acceleration system. The proposal of realization both of the grid structure as well as the permanent magnets, by means of the additive manufacturing for metals technology (AM) is reported. We will present the challenging configuration of the integrated cooling channel topology as well as the comparison of possible material choice: Ultra Pure Copper and a suitable copper alloy (CuCrZr). The characterization of the AM processed material (density, mechanical ultimate stress, thermal conductivity, fatigue lifetime) of the two candidates will be reported, together with the fluid dynamic analysis of the cooling system to maximise its efficiency through their optimised topology. The R&D results may be applicable to other installations like the ITER NBI. The full scale prototype for both DTT and ITER (MITICA as practical example) will be reported.
Description of the activity.
Additive manufacturing (AM), widely known also as 3D printing, is a method of manufacturing parts by progressively adding thin layers of materials guided by a digital model. Various processes have been developed over the years for the processing of metals, allowing the production of complex or customized parts directly from the design without the need for expensive tooling. By virtue of this, intricate parts can be made in one-step without the limitations of conventional processing methods.
The proposal of applying this challenging technology for the realization of the accelerating grids of the NBI was issued several years ago, but at that time there was no evidence of application for printing of pure Cu, due to the peculiar behaviour of the material (high reflectance of Cu gas atomised powders at the typical wavelength of the laser adopted: >90% reflectance on bulk at 1070 nm). We developed successfully the test characterization of pure Cu at DIAM Laboratory at INFN Padova (Developments and Innovations on Additive Manufacturing), also studying peculiar Copper alloy to maximise the mechanical properties (Ultimate strength and Brinnel resistance as well as fatigue ultimate strength), in particular for the CuCrZr alloy.
We then proposed an optimised solution to produce in a single step, the grid accelerating structure, comparing different alternative solutions for the cooling ducts geometry (topological optimisation for both the geometrical transversal shape of the ducts as well as the tailored design of the path to reach the most critical regions heated by charged particles, not accessible with a standard subtractive mechanical technology).
A wide campaign of CFD simulations and test bench has been developed, offering a reliable comparison for a fine tuning of the simulations.
The full scale production of the accelerating grids has been produced, both for the DTT and ITER NBI’s, with the CuCrZr alloy, as well as a reduced shape of them adopting pure Cu. The overall rough dimensions of the accelerating grid are namely:
- NBI for the DTT plant: 430x430x(9-17) [mm];
- NBI for the ITER plant: 830x430x (9-17) [mm].
The detailed design of the parts will be presented as well as the material characterisation and the test performed with the full scale parts (tightness, cooling system flow parameters and performances, etc.).
|Country or International Organization||Italy|