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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Study of the Heater-Coil Electrical Insulation for the HL-LHC Low Beta Quadrupoles

In the framework of the HL-LHC project, the present LHC low-β superconducting quadrupoles will be substituted with higher performance Nb 3 Sn magnets (MQXF) with 11.4 T coil peak field. MQXF coils are impregnated with epoxy resin to reduce risk of stress concentration on the brittle conductor. The magnet quench protection is provided by CLIQ and quench heaters to ensure a redundant system. Quench heaters are impregnated with the coils in order to have suitable thermal contact with them, and to prevent the hot spot temperature from exceeding 350K during normal operation in case of a quench. Quench heaters are insulated from the coil by S-2 Glass and polyimide. Here, the test of the first MQXF prototype (4 m long) MQXFAP1 was stopped by a coil-to-ground short circuit triggered by a heater-to-coil short. This issue triggered a root analysis of the causes of this short. Here we prove that the use of a non-conforming cloth in coil impregnation, further weakened by non-conforming high voltage test, has triggered the shorts. Moreover, we present an analysis of the heater-to-coil insulation strength, showing the role of blistering phenomena and how they are triggered by a combination of magnet powering and heater firing.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Development and Understanding of Nb 3 Sn films for radiofrequency applications through a sample-host 9-cell cavity

Nb 3 Sn is a promising advanced material under development for superconducting radiofrequency cavities. Past efforts have been focused primarily on small development-scale cavities, but large, often multi-celled cavities, are needed for particle accelerator applications. In this work, we report on successful Nb 3 Sn coatings on Nb in a 1 m-long 9-cell Nb sample-host cavity at Fermilab. The geometry of the first coating with only one Sn source made it possible to study the influence of Sn flux on the microstructure. Based on these results, we postulate a connection between recently observed anomalously large thin grains and uncovered niobium spots observed in the past by other authors (Trenikhina et al 2018 Supercond. Sci. Technol. 32 015004). A phenomenological model to explain how these anomalously large grains could form is proposed. Overall, this model is invoked to provide possible explanations for literature results from several groups and to guide key process parameters to achieve uniform vapor-diffusion coatings, when applied to complex structures as the multi-cell cavity under study.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

A new ductile, tougher resin for impregnation of superconducting magnets

A major remaining challenge for Nb 3 Sn 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, C 10 H 12 , commercially available in Japan as TELENE® by RIMTEC, was used to impregnate a short Nb 3 Sn 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 Gd 2 O 3 , Gd 2 O 2 S, and HoCu 2 , 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%Gd 2 O 2 S 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%Gd 2 O 2 S exhibited exceptional radiation resistance. Impregnating an undulator coil with TELENE mixed with Gd 2 O 2 S 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.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2026

Microstructural Characterization of Nb$_3$Sn Thin Films Using FIB Tomography

The accelerating gradient of N b3Sn superconducting radiofrequency (SRF) cavities is currently limited, and the underlying cause remains an open question in the field. One leading hypothesis attributes this limitation to the presence of tin-deficient regions within the N b3Sn coating, which can suppress the superheating field. Due to the relatively large coherence length of N b3Sn, defects near the surface may significantly interact with the RF field. However, these subsurface defects have proven difficult to characterize. This research aims to investigate the structure and distribution of subsurface Sn deficient regions to better understand their influence on cavity performance. We employ focused ion beam (FIB) tomography to analyze the subsurface microstructure of N b3Sn thin films. This technique enables threedimensional reconstruction of both the tin distribution and the grain structure within the film. By correlating Sn content with grain structure, we find that Sn deficient regions are more prevalent that previously thought. However, the Sn deficient regions are consistently located below the surface of the film where RF fields are strongly attenuated by supercurrent screening and are likely not a limiting factor for cavity performance

Viklund, Eric [Fermilab]↗
DOE OSTI2023

Development of a Bi2212 Dipole Insert at Fermilab

A goal of the U.S. Magnet Development Program (US-MDP) is high-field magnets for accelerators with magnetic fields larger than 15 T, i.e., above the limits of Nb 3 Sn accelerator magnets. Composite round wires and Rutherford cables made of high temperature superconductor Bi2212 may achieve this goal. Bi2212 is sensitive to transverse stresses and strains, and this requires stress management in the coil design. A stress management approach was developed at Fermilab for high-field large-aperture Nb 3 Sn accelerator magnets. Now it is being applied to high-field dipole insert coils based on Bi2212 Rutherford cable. Here this paper describes the insert coil design and main parameters, including the superconducting wire and cable. The coil will be installed inside a 60-mm bore Nb 3 Sn dipole outsert coil and cold iron yoke. The Bi2212 coil will be tested individually and in series with the Nb 3 Sn outsert coil. The expected Bi2212 insert test parameters are reported and discussed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

Analysis of vapor diffusion Nb$^{3}$Sn coating at Fermilab: Minimizing impurities using TOF-SIMS

Nb₃Sn demonstrates steady advancements nowadays offering reduced power cost in superconducting radio-frequency cavities due to its high critical temperature, quality factor, and achieved accelerating gradient. However, theoretical estimates of its radio-frequency parameters have not been achieved due to several potentially limiting mechanisms: tin spots, patchy regions, defects, thermal impedance, and impurities. While some of these limitations have been intensively studied, impurity analysis in Nb$_3$Sn coatings have received less attention. We report an investigation of impurities in several vapor-diffused Nb₃Sn coated samples using time-of-flight secondary ion mass spectroscopy (TOF-SIMS) and show allowable impurity levels in view of superconducting cavity performance. Challenges and lessons learned in maintaining clean Nb$_3$Sn coatings are also discussed.

Tagdulang, Nikki [Fermilab]↗
DOE OSTI2021

Development and characterization of Nb3Sn/Al2O3 superconducting multilayers for particle accelerators

Abstract Superconducting radio-frequency (SRF) resonator cavities provide extremely high quality factors > 10 10 at 1–2 GHz and 2 K in large linear accelerators of high-energy particles. The maximum accelerating field of SRF cavities is limited by penetration of vortices into the superconductor. Present state-of-the-art Nb cavities can withstand up to 50 MV/m accelerating gradients and magnetic fields of 200–240 mT which destroy the low-dissipative Meissner state. Achieving higher accelerating gradients requires superconductors with higher thermodynamic critical fields, of which Nb 3 Sn has emerged as a leading material for the next generation accelerators. To overcome the problem of low vortex penetration field in Nb 3 Sn, it has been proposed to coat Nb cavities with thin film Nb 3 Sn multilayers with dielectric interlayers. Here, we report the growth and multi-technique characterization of stoichiometric Nb 3 Sn/Al 2 O 3 multilayers with good superconducting and RF properties. We developed an adsorption-controlled growth process by co-sputtering Nb and Sn at high temperatures with a high overpressure of Sn. The cross-sectional scanning electron transmission microscope images show no interdiffusion between Al 2 O 3 and Nb 3 Sn. Low-field RF measurements suggest that our multilayers have quality factor comparable with cavity-grade Nb at 4.2 K. These results provide a materials platform for the development and optimization of high-performance SIS multilayers which could overcome the intrinsic limits of the Nb cavity technology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Optimizing the use of pressurized bladders for the assembly of HL-LHC MQXFB magnets

The use of pressurized bladders for stress control of superconducting magnets was firstly proposed at Lawrence Berkeley National Laboratory in the early 2000s. Since then, the so-called ‘bladders and keys’ procedure has become one of the reference techniques for the assembly of high-field accelerator magnets and demonstrators. Exploiting the advantages of this method is today of critical importance for Nb$_{3}$Sn-based accelerator magnets, whose production requires the preservation of tight stress targets in the superconducting coils to limit the effects of the strain sensitivity and brittleness of the conductor. The present manuscript reports on the results of an experimental campaign focused on the optimization of the ‘bladders and keys’ assembly process in the MQXFB quadrupoles. These 7.2 m long magnets shall be among the first Nb$_{3}$Sn cryomagnets to be installed in a particle accelerator as a part of the High Luminosity upgrade of the LHC. One of the main practical implications of the bladders technique, especially important when applied to long magnets like MQXFB, is that to insert the loading keys, the opening of a certain clearance in the support structure is required. The procedure used so far for MQXF magnets involved an overstress in the coils during bladder inflation. The work presented here shows that such an overshoot can be eliminated thanks to additional bladders properly positioned in the structure. This optimized method was validated in a short model magnet and in a full-length mechanical model, becoming the new baseline for the series production at CERN. Furthermore, the results are supported by numerical predictions using finite element models.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Nb$^{3}$Sn Technology for Low-beta linacs

Nb3Sn is the most advanced potential successor for niobium in superconducting RF accelerator cavities. Nb3Sn has a significantly higher critical temperature (18.3 K) compared to that of niobium (9.2 K). This has a large effect on the BCS surface resistance, and therefore, on the dynamic RF losses at 4.5 K. The higher critical temperature allows two important changes for cavity and cryomodule design. First, the lower BCS losses allow the designer to use a higher frequency, translating to physically smaller cavities and cryomodules. Second, the low dynamic losses allow the use of stand-alone cryocoolers instead of complex helium refrigerators and distribution systems. Fabrication of a prototype 218 MHz cavity, test results, and continuing challenges are discussed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Investigations Towards Ultra-Low Cost Nb 3 Sn SRF Fabrication via Melt Casted Bronze Route Processing

Here, a novel approach to fabricating Nb 3 Sn SRF cavities and other RF components using an ultra-low-cost melt casting fabrication process has been investigated. This simple, low cost melt casting technique has the potential to be used to fabricate nearly any superconducting Nb3Sn structure using either the Bronze Route (BR), Internal Tin (IT), External Tin (ET) processes as well as normal conducting pure copper (Cu) cavities. Most of the heat treated samples that were examined using SEM/EDX seemed to show a reasonable correlation of T c onset and transition width (ΔT c ) of the ingots initial/starting Sn content to the desired stoichiometric Nb 3 Sn phase, where the lower starting Sn content coupons resulted in lower T c 's with broader transition widths and the higher starting Sn coupons resulted in higher T c 's with narrower ΔT c ’s. The best samples had T c onsets ~17-18 K and ΔT c 's < 2 K. Two samples were further tested for RF surface resistance (R s ) and Quality Factor (Q) at JLAB. Here, these RF measurements were performed at 7.4 GHz using a calorimetric technique and showed two transitions, one at ~ 8 K and another at ~ 14 K; values of R s were at least two orders of magnitude higher than similar high quality Nb 3 Sn films directly deposited substrates by JLAB and with another superconducting transition close to the superconducting transition temperature of niobium. Substantial improvements in the processing variables ranging from higher quality of the initial ingots with higher Sn content, to better electropolishing and reaction heat treatment regimens will be necessary to realize improved RF performance metrics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Magnetic and Mechanical Analysis of Bi-2212 Rutherford Cable in a Cos-Theta Sub-Scale Dipole Coil

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.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Origin of the enhanced Nb3Sn performance by combined Hf and Ta doping

Abstract In recent years there has been an increasing effort in improving the performance of Nb 3 Sn for high-field applications, in particular for the fabrication of conductors suitable for the realization of the Future Circular Collider (FCC) at CERN. This challenging task has led to the investigation of new routes to advance the high-field pinning properties, the irreversibility and the upper critical fields ( H Irr and H c2 , respectively). The effect of hafnium addition to the standard Nb-4Ta alloy has been recently demonstrated to be particularly promising and, in this paper, we investigate the origins of the observed improvements of the superconducting properties. Electron microscopy, Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) and Atom Probe Tomography (APT) characterization clearly show that, in presence of oxygen, both fine Nb 3 Sn grains and HfO 2 nanoparticles form. Although EXAFS is unable to detect significant amounts of Hf in the A15 structure, APT does indeed reveal some residual intragrain metallic Hf. To investigate the layer properties in more detail, we created a microbridge from a thin lamella extracted by Focused Ion Beam (FIB) and measured the transport properties of Ta-Hf-doped Nb 3 Sn. H c2 (0) is enhanced to 30.8 T by the introduction of Hf, ~ 1 T higher than those of only Ta-doped Nb 3 Sn, and, even more importantly the position of the pinning force maximum exceeds 6 T, against the typical ~ 4.5–4.7 T of the only Ta-doped material. These results show that the improvements generated by Hf addition can significantly enhance the high-field performance, bringing Nb 3 Sn closer to the requirements necessary for FCC realization.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Conceptual Structural Design and Analysis of a 20 T Hybrid Cos Dipole for Future Particle Colliders

Here, to reach high collision energy for future high-energy particle colliders, like the Future Circular Collider (FCC) or the Muon Collider, it is required to achieve high field strength of the bending dipoles. Currently, the practical limit for Nb$_{\text{3}}$ Sn technology is around 16 T and, in order to further increase the magnetic field, the superconducting magnet community is considering High Temperature Superconductors (HTS), in particular Bi-2212 and REBCO conductors. However, their relevant higher cost has led the community to consider a hybrid approach where HTS materials are used in the high field region of the coils with so-called insert coils, and Low Temperature Superconductors are involved in the lower field part ($< $ 16 T) with so-called outsert coils. This paper describes the conceptual mechanical design of a 20 T hybrid cos$\theta$ dipole configuration. The high stress levels that the structure is facing due to the high magnetic field are discussed. Moreover, it presents the results of the optimization analysis of the shell-based support structure based on the key-and-bladder technology that provides the azimuthal pre-stress during room temperature assembly and cooldown to cryogenic temperatures. The aim of this work is to present a feasible design that satisfies the stress requirements.

D'Addazio, Marika [Politecnico di Torino (Italy); ↗
DOE OSTI2025

Comparison of Nb 3 Sn Insulation Systems With as Received and De-Sized Glass

Epoxy cracking has been the main suspected contributor to training in Nb 3 Sn magnets for some time, as it leads to energy release and magnet quenching. Cracking in a superconducting composite can occur from several modes, and the likelihood of these modes is not well understood. Failure has been observed between insulation systems and the superconducting cable itself rather than within the cable or insulation. To target the behavior at the interface, samples have been fabricated and tested for Mode I fracture toughness in an adapted version of ASTM D5528. This work seeks to better characterize the fracture toughness of this interface to better understand how to model and design insulation systems.

Krave, Steven T. [Fermilab] (ORCID:000000021752145↗
DOE OSTI2021

Test of Superconducting Wires and Rutherford Cables With High Specific Heat

High-field accelerator magnets made of state-of-the-art Nb 3 Sn Rutherford cables demonstrate relatively long trainings due to sudden heat depositions originated by thermo-mechanical perturbations in the magnet coils. Coil sensitivity to these perturbations can be reduced by increasing the specific heat, Cp, of major coil components - strands, or whole cable, or epoxy. The R&D on all these three approaches is in progress. This paper studies feasibility of increasing the Cp of Rutherford-type cables by using a thin composite Cu/Gd 2 O 3 tape. The tape can be either wrapped around the cable, placed on the cable wide faces under the insulation, and/or inserted as a core. In this work, Cu/Gd 2 O 3 ribbons with ~30% of Gd 2 O 3 powder and two different thicknesses were produced by Hyper Tech Research, Inc. Wire and cable samples outfitted with these high-Cp ribbons, or tapes, were prepared and tested at FNAL for the Minimum Quench Energy (MQE). At 80%Ic, the MQE gain average over the tested magnetic field range of the NbTi cable with high-Cp tape on both sides was ~1.3. The MQE gain average of the NbTi wire wrapped with the high-Cp ribbon was 3.1.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Wall plug efficiency analysis of a compact SRF industrial accelerator [Poster]

Superconducting radiofrequency cavities offer extremely high (>90%) RF-to-beam energy conversion efficiency. Recent breakthroughs in the Nb 3 Sn SRF cavity technology, successful demonstration of the conduction cooling technique, and the availability of high cooling capacity cryocoolers has made possible the use of SRF for industrial particle accelerators. However, the overall wall plug-to-beam efficiency of such an SRF accelerator can be limited by the wall plug-to-RF power efficiency of the RF source powering this accelerator. The present study quantifies the wall plug-to-beam efficiency of a conduction-cooled SRF accelerator considering several different choices of the RF power source. The study concludes that the wall plug efficiency of the accelerator is indeed limited by that of the power source.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Wall plug efficiency analysis of a compact SRF industrial accelerator [Poster]

Superconducting radiofrequency cavities offer extremely high (>90%) RF-to-beam energy conversion efficiency. Recent breakthroughs in the Nb 3 Sn SRF cavity technology, successful demonstration of the conduction cooling technique, and the availability of high cooling capacity cryocoolers has made possible the use of SRF for industrial particle accelerators. However, the overall wall plug-to-beam efficiency of such an SRF accelerator can be limited by the wall plug-to-RF power efficiency of the RF source powering this accelerator. The present study quantifies the wall plug-to-beam efficiency of a conduction-cooled SRF accelerator considering several different choices of the RF power source. The study concludes that the wall plug efficiency of the accelerator is indeed limited by that of the power source.

43 PARTICLE ACCELERATORS↗