Emanuela Barzi

The critical current of superconductors is commonly measured by testing unloaded wires under an external magnetic field. While stressed by intense Lorentz forces, the existing HTS/LTS superconductors are prone to a reduction in critical current before reaching their structural mechanical limit. In this work, the magnetic and mechanical analysis of the FNAL 4-layer Bi-2212/Nb$_{3}$Sn hybrid dipole magnet is reported, aimed at predicting the critical current degradation for both the superconductors during powering at 16T. All the Rutherford cables in the coils of the hybrid magnet were modeled at the strand level in Ansys APDL with the heterogeneous cable model. Utilizing this detailed geometry, it was possible to evaluate the effects of strain on the critical current degradation for both the Nb$_{3}$Sn and Bi-2212 superconductors under the intense Lorentz forces. The analysis presented in this paper integrates strain-dependent critical current laws, with parameters derived from experimental data, to simulate the hybrid magnet's performance for all possible current-powering configurations. The proposed methodology enables a detailed assessment of conductor integrity and I$_{C}(\varepsilon$) reduction in existing hybrid magnet designs, providing a versatile and rigorous framework for optimizing future high-field hybrid magnets.

A new measurement of the magnetic anomaly a μ of the positive muon is presented based on data taken from 2020 to 2023 by the Muon g − 2 Experiment at Fermi National Accelerator Laboratory (FNAL). This dataset contains over 2.5 times the total statistics of our previous results. From the ratio of the precession frequencies for muons and protons in our storage ring magnetic field, together with precisely known ratios of fundamental constants, we determine a μ = 1 165 920 710 ( 162 ) × 10 − 12 (139 ppb) for the new datasets, and a μ = 1 165 920 705 ( 148 ) × 10 − 12 (127 ppb) when combined with our previous results. The new experimental world average, dominated by the measurements at FNAL, is a μ ( exp ) = 1 165 920 715 ( 145 ) × 10 − 12 (124 ppb). The measurements at FNAL have improved the precision on the world average by over a factor of 4.

The joint expertise of ANL and FNAL has led to the production of $\text{Nb}_{3}\text{Sn}$ undulator magnets in operation in the ANL Advanced Photon Source (APS). These magnets showed performance reproducibility close to the short sample limit, and a design field increase of 20% at 820 A. However, the long training did not allow obtaining the expected 50% increase of the on-axis magnetic field with respect to the ∼1 T produced at 450 A current in the ANL NbTi undulator. To address this, 10-pole long undulator prototypes were fabricated, and CTD-101K was replaced as impregnation material with TELENE, an organic olefin-based thermosetting dicyclopentadiene resin produced by RIMTEC Corporation, Japan. Training and magnet retraining after a thermal cycle were nearly eliminated, with only a couple of quenches needed before reaching short sample limit at over 1,100 A. TELENE will enable operation of $\text{Nb}_{3}\text{Sn}$ undulators much closer to their short sample limit, expanding the energy range and brightness intensity of light sources. TELENE is Co-60 gamma radiation resistant up to 7–8 MGy, and therefore already applicable to impregnate planar, helical and universal devices operating in lower radiation environments than high energy colliders.

The U.S. Magnet Development Program (US-MDP) explores high-field accelerator magnets compatible with operational conditions beyond the limits of Nb ₃ Sn technology. The ongoing R&D High-Temperature Superconductors (HTS) suggests using Bi ₂ Sr ₂ CaCu ₂ O 8 − x   (Bi-2212) as superconducting element. Bi-2212 Rutherford cables maintain a high critical current ( I C ) when exposed to a large external magnetic field. However, Bi-2212 exhibits an oversensitive stress–strain response when subject to large Lorentz forces. This paper reports on the magnetic and mechanical analysis of the Bi-2212 cosine-theta insert being developed at Fermilab for a hybrid magnet composed of two external layers of Nb ₃ Sn and two internal layers of Bi-2212. We performed a FEM analysis of the insert to estimate the HTS stress state in the coil’s strands under magnetic and mechanical loads.

A 123-mm-aperture Nb₃Sn cos-theta (CT) dipole coil with stress management (SM) has been developed at Fermilab to demonstrate and test the SM concept, including coil design, fabrication technology, and performance. The first SMCT1 coil has been fabricated and assembled together with a 60-mm-aperture Nb₃Sn coil inside a dipole mirror structure and tested separately and in series with the inner coil. This article summarizes the design, parameters, and quench performance of the SMCT1 coil in a dipole mirror configuration.

The Lawrence Berkeley National Laboratory (LBNL) and the National High Magnetic Field Laboratory (NHMFL) have published results on Bi-2212 superconductive magnets realized and tested in the canted cosine-theta and solenoid designs, respectively. Fermilab is now preparing for the assembly of the first Bi-2212 stress-managed cosine-theta insert magnet. The insert will be part of the first hybrid cosine-theta magnet made of Nb$_{\text{3}}$Sn outer layers within the US-MDP effort to reach a 20 T bore field. This paper presents the analytical analysis of the cosine-theta Nb$_{\text{3}}$ Sn/Bi-2212 hybrid magnet. We report the parameters, logic, and implementation method of the 2D electromagnetic and mechanical FEM analysis of the LTS/HTS hybrid magnet. Results from a detailed heterogeneous model are compared to the homogeneous model implemented in the past. A Python code has been developed to simulate the current degradation due to stresses in the detail-modeled conductor areas. The current degradation has been introduced in the simulation dynamics for the HTS conductor as an iteration process, updating the input load of Lorentz forces of the energization at each step. The magnetic and mechanical analysis results of the 2D cosine-theta LTS/HTS dipole magnet have been described and analyzed.

A major remaining challenge for Nb₃Sn high field magnets is their training due to random temperature variations in the coils. The main objective of our research is to reduce or eliminate it by finding novel impregnation materials in replacement of the epoxies currently used. An organic olefin-based thermosetting dicyclopentadiene resin, C₁₀H₁₂, commercially available in Japan as TELENE^® by RIMTEC, was used to impregnate a short Nb₃Sn undulator coil developed by ANL and FNAL. This magnet reached short sample limit after only two quenches, compared with ∼100 when CTD-101K^® was used. Ductility, i.e. the ability to accept large strains, and toughness were identified as key properties to achieve these results. In addition, we have been investigating whether mixing TELENE with high heat capacity ceramic powders such as Gd₂O₃, Gd₂O₂S, and HoCu₂, increases the specific heat (C_p ) of impregnated Nb₃Sn superconducting magnets. The viscosity, heat capacity, thermal conductivity, and other physical properties of TELENE with high-C_p powder fillers were measured in this study as a function of temperature and magnetic field. The TELENE-87 wt%Gd₂O₂S had a peak in C_p between 4.3 K and 5.3 K at fields between 0 and 8 T. We have also investigated the effect on the mechanical properties of pure and mixed TELENE under 10 MGy of gamma ray irradiation at the Takasaki Advanced Radiation Research Institute in Takasaki, Japan. TELENE-87 wt%Gd₂O₂S exhibited exceptional radiation resistance. Impregnating an undulator coil with TELENE mixed with Gd₂O₂S powder will verify whether the coils’ thermal stability further improves, or whether its low diffusivity will require engineering the material with high-thermal conductivity components. Short magnet training will lead to better magnet reliability, lower magnet margins, lower risk and substantial saving in accelerators’ commissioning costs. Part of this study is supported by the U.S.-Japan Science and Technology Cooperation Program in high energy physics operated by MEXT in Japan and DOE in the U.S.

The existing research on why people fail to act ethically identifies a range of motivations, with character traits and peer pressure being the top two causes. Other factors include gain, fear of loss, relationships, competition, opportunity, and cultural factors. In addition to the ethics component, studies have identified also individual and institutional ones. For instance, narcissism plays a significant role in misconduct. The effect of institutional actions, from neglecting punishment in many cases of misconduct up to letting researchers succeed through unethical behavior, was also studied. The only way for an organization to have every member perceive that ethical conduct will enhance their standing and reputation is to display leadership by example. However, despite leaders in academia being nowadays much more educated than twenty years ago about equity, diversity, inclusion and ethical behavior, the occurrence of misconduct has not decreased. Because of the power t hat this demographic holds in enacting reform, as opposed to minority groups who are already encumbered enough, it would be helpful to target the former for equity education. Education and intervention in identifying patterns of thought and action that prevent ethical progress, in deflecting peer pressure, in assuming accountability for their departments, etc. can help.more » Once again, all roads lead to Rome: an educated and inspired leadership is the most effective tool for change. « less

A novel Nb ₃ Sn-based superconducting undulator (SCU) was developed and integrated into the Advanced Photon Source (APS) at Argonne National Laboratory. The SCU achieved user operation within an accelerator environment. Compared to its Nb-Ti counterpart, the Nb ₃ Sn SCU operates at substantially higher currents. Thus, a detailed experimental evaluation of the SCU magnets’ performance was necessary under both “wet” and indirectly cooled conditions to ensure its reliability during operation. Our study indicated that the cooling method has a noticeable influence on the magnet's behavior. Specifically, energy dissipation in the magnets during quenches was observed to be greater under indirect cooling than with “wet” cooling. This investigation provided insights into the safe operational limits. Guided by these insights the more challenging high-current tests were successfully carried out at the end of the user phase. The SCU achieved the design undulator field of 1.17 T at 820 A and 4.2 K, with a magnetic gap of 9.5 mm and a period of 18 mm. Actual performance exceeded the specifications, reaching 850 A.