Balduin Katzer

Bio: Balduin Katzer is an academic researcher from CERN. The author has contributed to research in topics: Physics & Dislocation. The author has an hindex of 1, co-authored 2 publications receiving 5 citations.

Effect of Applied Compressive Stress and Impregnation Material on Internal Strain and Stress State in Nb 3 Sn Rutherford Cable Stacks

Abstract: The Nb3Sn superconductor in accelerator magnets must resist high mechanical stresses. In order to better understand the effect of the coil impregnation system on the stresses exerted on the strain-sensitive Nb3Sn superconductor, we have measured the elastic strain evolution in the conductor constituents under externally applied loads. For this purpose, a dedicated load frame that enables rotation of the sample load axis with respect to the neutron scattering geometry was installed in the Stress-Spec beamline at the neutron source Heinz Maier-Leibnitz FRM II. The Nb3Sn- and Cu-loading strains were measured in situ by neutron diffraction under monotonic and cyclic compressive loading. So-called ten-stack samples composed of Nb3Sn Rutherford type cables with different impregnation and coil blocks extracted from an 11 T dipole short model coil were investigated.

Texture in Superconducting Magnet Constituent Materials and Its Effect on Elastic Anisotropy

Abstract: The materials used in superconducting magnet coils and in the structural magnet constituents are textured to various extents. This causes an angular dependence of the Young's moduli that needs to be taken into account when predicting the stress and strain distribution in the magnets. We have measured by neutron diffraction the texture in metallic materials typically used in superconducting magnets. Based on the neutron diffraction data the elastic anisotropy of the different materials has been calculated. Among the materials studied, the extruded Al oxide dispersion strengthened Cu coil wedges exhibit the strongest elastic anisotropy of 37%. The Young's moduli calculated from single crystal elastic constants and grain orientation distributions are compared with highly accurate Young's moduli derived experimentally from resonance tests.

Identification of dislocation reaction kinetics in complex dislocation networks for continuum modeling using data-driven methods

Abstract: Plastic deformation of metals involves the complex evolution of dislocations forming strongly connected dislocation networks. These dislocation networks are based on dislocation reactions, which can form junctions during the interactions of different slip systems. Extracting the fundamentals of the network behaviour during plastic deformation by adequate physically based theories is essential for crystal plasticity models. In this work, we demonstrate how knowledge from discrete dislocation dynamics simulations to continuum-based formulations can be transferred by applying a physically based dislocation network evolution theory. By using data-driven methods, we validate a slip system dependent rate formulation of network evolution. We analyse different discrete dislocation dynamics simulation data sets of face-centred cubic single-crystals in high symmetric and non-high symmetric orientations under uniaxial tensile loading. Here, we focus on the reaction evolution during stage II plastic deformation. Our physically based model for network evolution depends on the plastic shear rate and the dislocation travel distance described by the dislocation density. We reveal a dependence of the reaction kinetics on the crystal orientation and the activity of the interacting slip systems, which can be described by the Schmid factor. It has been found, that the generation of new reaction density is mainly driven by active slip systems. However, the deposition of generated reaction density is not necessarily dependent on the slip system activity of the considered slip system, i.e. we observe a deposition of reaction density on inactive slip systems especially for glissile and coplanar reactions.

The 16 T Dipole Development Program for FCC and HE-LHC

Abstract: A future circular collider (FCC) with a center-of-mass energy of 100 TeV and a circumference of around 100 km, or an energy upgrade of the LHC (HE-LHC) to 27 TeV require bending magnets providing 16 T in a 50-mm aperture. Several development programs for these magnets, based on Nb3Sn technology, are being pursued in Europe and in the U.S. In these programs, cos–theta, block-type, common-coil, and canted–cos–theta magnets are explored; first model magnets are under manufacture; limits on conductor stress levels are studied; and a conductor with enhanced characteristics is developed. This paper summarizes and discusses the status, plans, and preliminary results of these programs.

Effect of Epoxy Volume Fraction on the Stiffness of Nb 3 Sn Rutherford Cable Stacks

Abstract: For the optimization of Nb3Sn superconducting accelerator magnet design and assembly parameters the stress-strain behavior of the coils needs to be known. We have measured the stiffness of Nb3Sn Rutherford cable stacks with different epoxy volume fraction. The cable stack stiffness is strongly dependent on the load direction. The highest stiffness of about 95 GPa is measured in axial direction, as predicted by the rule of mixtures. In transverse load direction the stiffness is stress dependent, and about half of the axial stiffness. As expected the stiffness of the cable stacks increases with decreasing epoxy volume fraction. The stiffness of a conductor block extracted from an already cold tested 11 T dipole coil is comparable to that of a ten-stack sample with similar epoxy volume fraction.

Effect of the fabrication route on the phase and volume changes during the reaction heat treatment of Nb 3 Sn superconducting wires

Abstract: Accelerator magnets that can reach magnetic fields well beyond the Nb-Ti performance limits are presently built and developed using Nb3Sn superconductors. This technology requires a reaction heat treatment of the magnet coils, during which Nb3Sn is formed from its ductile precursor materials (wind and react approach). The Nb3Sn microstructure and microchemistry are strongly influenced by the conductor fabrication route, and by the phase changes during the reaction heat treatment. By combining in situ differential scanning calorimetry, high energy synchrotron X-ray diffraction and micro-tomography experiments, we have acquired a unique data set that describes in great detail the phase and microstructure changes during the processing of Restacked Rod Process (RRP), Powder-in-Tube (PIT) and Internal Tin (IT) Nb3Sn wires. At temperatures below 450 °C the phase evolution in the three wire types is similar, with respectively solid state interdiffusion of Cu and Sn, Cu6Sn5 formation, and Cu6Sn5 peritectic transformation. Strong differences in phase evolutions in the different wires are found when temperatures exceed 450 °C. The volume changes of the conductor during Reaction Heat Treatment (RHT) are a main challenge in the production of Nb3Sn accelerator magnets. We compare the wire diameter changes measured in situ by dilatometry with the phase and void volume evolution of the three different Nb3Sn wire types. Unlike the Nb3Sn wire length changes, the wire diameter evolution is characteristic for each Nb3Sn wire type. The strongest volume increase of about 5% is observed in the RRP wire, where the main diameter increase occurs above 600 °C upon Nb3Sn formation.

Texture in Superconducting Magnet Constituent Materials and Its Effect on Elastic Anisotropy

Abstract: The materials used in superconducting magnet coils and in the structural magnet constituents are textured to various extents. This causes an angular dependence of the Young's moduli that needs to be taken into account when predicting the stress and strain distribution in the magnets. We have measured by neutron diffraction the texture in metallic materials typically used in superconducting magnets. Based on the neutron diffraction data the elastic anisotropy of the different materials has been calculated. Among the materials studied, the extruded Al oxide dispersion strengthened Cu coil wedges exhibit the strongest elastic anisotropy of 37%. The Young's moduli calculated from single crystal elastic constants and grain orientation distributions are compared with highly accurate Young's moduli derived experimentally from resonance tests.