Extensive Analyses of Superconducting Cables 3D Geometry With Advanced Tomographic Examinations

Abstract

In the framework of activities embedding magnet design and associated R&D activities and relying on Cable in Conduit Conductors (CICC) technology, the singularity of the concept can rise some challenges versus their modelling in operation. Indeed, CICC includes thousands of superconducting strands, twisted together under a multi-staged scheme that also includes deformation by cabling and compaction during manufacture. This causes the accurate predictability of strands position in CICC extremely difficult, while it can be a key element for modelling their performances in operation. As a matter of fact the coupling losses rely on the CICC capability to establish interstrand shielding currents, driven by the inter-strand contacts mapping which are only accessible in prediction via accurate 3D strand trajectories geometry. Same applies for prediction of CICC mechanical properties (deformation of Nb3Sn strands) and hydraulic properties (helium coolant force-flowed between the strands), making those investigations of high added-value. In this context, INFLPR installed a new set-up dedicated to micro-tomography that is able to examine CICCs with high resolution, allowing to get an overall overall 3D overview regarding picture of the strands location. CEA and INFLPR further developed a post-processing method to reconstruct the strands trajectories with high accuracy. The measurement and data analysis workflow was applied to two middle-size CICCs with variable void fraction from which statistics of contacts were issued. The obtained database was exploited to reconstruct equivalent 3D resistive network, in view of interpreting coupling losses tests with help of analytic CEA model (COLISEUM) based on multi-stage representation.The above applications using CICC topology database will be discussed and tentatively compared to experimental AC losses database conducted at CEA. The outcomes will be discussed and the subsequent guidelines for future work presented.

Inputs generation for COLISEUM coupling losses model using X-ray tomography: analytic and experimental approaches

“…The higher the contact width is, the more crushed the strands are. A similar study was conducted in [10] on samples #2 and #3. Fig 3 shows the number of contacts per slice for sample #1 to #6 as a function of the contact width.…”

Analytical Modeling of Coupling Losses in CICCs, Extensive Study of the COLISEUM Model

“…The resulting image is compared with the real picture of the end extremity as shown in Fig 7 . The results show that the tomographic picture and the real end extremity picture match at 100%. Moreover, it has been shown in [3] that the identified strand stays the same from slice to slice. Therefore, no strand substitution is responsible for that result.…”

“…In the framework of a collaboration between the CEA (France) and INFLPR (Romania), CICC samples were tomographied using a 320 kV high penetration power microtomograph allowing sufficient image resolution and contrast to identify each strand in the cable. Details about the experimental setup are available in [6] and [3]. The images were used to identify and reconstruct the strand trajectories which will be used in the future to measure the associated geometrical parameters (cabling radii and the twist pitches).…”

“…The second configuration allows cable dimensions in the model closer to the reality. The second part of this paper describes the extension of the work started in [3] to determine realistic effective parameters to be used as COLISEUM inputs.…”