Manufacture and performance test result of a 95 kA-class Nb-Ti cable-in-conduit conductor for the low field winding-package of CFETR-TF coil

The engineering design of the CFETR TF prototype coil and conductors has been completed. The wind-package (WP) of the coil is graded into three regions based on the magnetic field distribution for saving cost. High-Jc Nb3Sn strand, ITER-like Nb3Sn strand and Nb-Ti strand are applied for high-field, mid-field and low-field WP respectively. In order to verify the conductor design, full-size short samples have been manufactured for the three types of conductors. The samples are tested in the SULTAN facility at CRPP in Villigen, Switzerland. At present, the test of Nb-Ti conductor for low-field WP is finished, DC and AC tests were performed. In DC test, several current sharing temperature (Tcs) measurements were performed with 500 electromagnetic cycles and one thermal cycle. Additionally, minimum quench energy (MQE) measurement was performed for investigating the stability of the conductor. The test results and analysis are reported in this paper.</p

Analysis of Uncertainties in Protection Heater Delay Time Measurements and Simulations in Nb₃Sn High-Field Accelerator Magnets

The quench protection of superconducting high-field accelerator magnets is presently based on protection heaters, which are activated upon quench detection to accelerate the quench propagation within the winding. Estimations of the heater delay to initiate a normal zone in the coil are essential for the protection design. During the development of Nb$_{3}$Sn magnets for the LHC luminosity upgrade, protection heater delays have been measured in several experiments, and a new computational tool CoHDA (Code for Heater Delay Analysis) has been developed for heater design. Several computational quench analyses suggest that the efficiency of the present heater technology is on the borderline of protecting the magnets. Quantifying the inevitable uncertainties related to the measured and simulated delays is therefore of pivotal importance. In this paper, we analyze the uncertainties in the heater delay measurements and simulations using data from five impregnated high-field Nb$_{3}$Sn magnets with different heater geometries. The results suggest that a minimum variation of 3 ms or 20% should be accounted in the heater design for coil outer surfaces and at least 10 ms or 40% in the inner surfaces due to more uncertain heater contact. We also propose a simulation criterion that gives an upper bound enclosing 90% of the measured delays for heaters on the coil outer surface

Analysis of Uncertainties in Protection Heater Delay Time Measurements and Simulations in Nb3_{3}Sn High-Field Accelerator Magnets

The quench protection of superconducting high-field accelerator magnets is presently based on protection heaters, which are activated upon quench detection to accelerate the quench propagation within the winding. Estimations of the heater delay to initiate a normal zone in the coil are essential for the protection design. During the development of Nb$_{3}$Sn magnets for the LHC luminosity upgrade, protection heater delays have been measured in several experiments, and a new computational tool CoHDA (Code for Heater Delay Analysis) has been developed for heater design. Several computational quench analyses suggest that the efficiency of the present heater technology is on the borderline of protecting the magnets. Quantifying the inevitable uncertainties related to the measured and simulated delays is therefore of pivotal importance. In this paper, we analyze the uncertainties in the heater delay measurements and simulations using data from five impregnated high-field Nb$_{3}$Sn magnets with different heater geometries. The results suggest that a minimum variation of 3 ms or 20% should be accounted in the heater design for coil outer surfaces and at least 10 ms or 40% in the inner surfaces due to more uncertain heater contact. We also propose a simulation criterion that gives an upper bound enclosing 90% of the measured delays for heaters on the coil outer surface

Axial-Field Magnetic Quench Antenna for the Superconducting Accelerator Magnets

We have developed and tested a novel magnetic inductive antenna for detecting and localizing quenches and flux jumps in superconducting accelerator magnets during ramping and steady-state operations. The antenna principle is based upon sensing temporal variation of the axial field gradient in the magnet bore that is specific to propagating quench. Two antenna configurations were developed and built, optimized respectively for sensing disturbances of the off-axis (for the dipole magnet) and axial (for the quadrupole magnet) gradient of the axial field. The antennas were qualified during tests of LBNL's high-field dipole, HD3b, and LARP's Nb$_{3}$Sn quadrupole HQ02b. A reliable and accurate localization of quenches and flux jumps was demonstrated. Upon ramping up the magnet current, we observed peculiar dynamics of the magnetic disturbances travelling along the cable at velocities of ~800 m/s. Also, details of slow quench propagation in the HQ02 quadrupole at a small fraction of operational current were detected and recorded

Measurements and Analysis of Dynamic Effects in the LARP Model Quadrupole HQ02b During Rapid Discharge

This paper presents the analysis of some quench tests addressed to study the dynamic effects in the 1-m-long 120-mm-aperture Nb$_{3}$Sn quadrupole magnet, i.e., HQ02b, designed, fabricated, and tested by the LHC Accelerator Research Program. The magnet has a short sample gradient of 205 T/m at 1.9 K and a peak field of 14.2 T. The test campaign has been performed at CERN in April 2014. In the specific tests, which were dedicated to the measurements of the dynamic inductance of the magnet during the rapid current discharge for a quench, the protection heaters were activated only in some windings, in order to obtain the measure of the resistive and inductive voltages separately. The analysis of the results confirms a very low value of the dynamic inductance at the beginning of the discharge, which later approaches the nominal value. Indications of dynamic inductance variation were already found from the analysis of current decay during quenches in the previous magnets HQ02a and HQ02a2; however, with this dedicated test of HQ02b, a quantitative measurement and assessment has been possible. An analytical model using interfilament coupling current influence for the inductance lowering has been implemented in the quench calculation code QLASA, and the comparison with experimental data is given. The agreement of the model with the experimental results is very good and allows predicting more accurately the critical parameters in quench analysis (MIITs, hot spot temperature) for the MQXF Nb$_{3}$Sn quadrupoles, which will be installed in the High Luminosity LHC

Performance of the Cable-in-Conduit Conductors for Super-X Test Facility

Following the conceptual design, the engineering design of the dc magnet and cable-in-conduit conductor (CICC) for the Super-X test facility has been done in 2021. Totally three types of conductors with different structures were designed for the three pairs of coils in the dc magnet, respectively. High- Jc Nb 3 Sn strand (J c ∼2200 A/mm 2 at 12 T, 4.2 K) was applied to high field and middle field coils for reducing the radius of the dc magnet. In order to qualify if the designed parameters of the conductors could fulfill the performance criteria, three pairs of short samples have been manufactured and tested successfully in the SULTAN facility at SPC, Switzerland. Test results and analysis show that dc performance of the three types of conductors can meet the design criteria. The conductor qualification process including the sample preparation, test results, and analysis are presented in this article. The HFC and LFC conductors exhibit different ac loss behavior to the MFC conductor, which is discussed in the article

3-D Thermal-Electric Finite Element Model of a Nb₃Sn Coil During a Quench

High field superconducting magnets for particle accelerators often exhibit premature quenches. Once a normal zone is generated within the conductor, the quench may propagate causing temperature and resistive voltage rise along the coil. The resulting thermal gradients can potentially cause new peak stresses that might exceed the tolerable limits, degrading the conductor. The computation of the strain state in the coils during quench then becomes of paramount importance for magnet design, and requires a complete three-dimensional (3-D) analysis of quench phenomena. The objective of this paper is to present the first multiphysics modeling activities towards a new full 3-D methodology for the analysis of magnet mechanics during quench. As a first step, a 3-D thermal-electric finite element model of a Nb₃Sn superconducting coil is developed and explained here. The model uses direct coupled-field elements to solve the system of thermal and electrical equations. A solving algorithm has also been implemented in order to investigate the physics behind quench transients. The output from this model, built in ANSYS APDL, can be easily coupled in a later stage to a mechanical model in order to estimate the strain state in the coil windings. A very good agreement has been observed between the numerical results and experimental tests performed in individual superconducting cables and real superconducting magnets

Summary of the Mechanical Performances of the 1.5 m Long Models of the Nb3_{3}Sn Low-β\beta Quadrupole MQXF

The Nb3Sn quadrupole MQXF is being developed as a part of the large hadron collide (LHC) High Luminosity upgrade. The magnet design was tested on 1.5-m-long short models, sharing the same cross section with the full-length magnets. Various azimuthal and longitudinal preloads were applied, studying the impact on the magnet training and on its mechanical performances. The experiments demonstrated the possibility to control the magnet prestress. However, various factors, coil size among the others, may affect the stress variation between and within each winding. This variation could prevent the magnets from reaching the magnet performances, as for example as a result of the critical current reduction of the Nb3Sn strands. This paper analyzes the mechanical performances of the short models, studying in particular the stress variation on different coils. The measured coil size was used as input in the numerical simulations, and the results were then compared with the strain gauge measurements. Finally, the short model experience was used to evaluate the feasibility of a loading operation that does not rely on the strain measurements

Summary of the Mechanical Performances of the 1.5 m Long Models of the Nb3^3Sn Low-β\beta Quadrupole MQXF

The Nb3Sn quadrupole MQXF is being developed as a part of the LHC High Luminosity upgrade. The magnet design was tested on 1:5m long short models, sharing the same cross-section with the full-length magnets. Various azimuthal and longitudinal preloads were applied, studying the impact on the magnet training and on its mechanical performances. The experiments demonstrated the possibility to control the magnet prestress. However, various factors, coil size among the others, may affect the stress variation between and within each winding. This variation could prevent the magnet to reach the desired performances, for example as result of critical current degradation of the Nb3Sn strands. This paper analyzes the mechanical performances of the short models, studying in particular the stress variation on different coils. The measured coil size was used as input in the numerical simulations, and results were then compared with the strain gauge measurements. Finally, the short models experience was used to evaluate the feasibility of a loading operation that does not rely on the strain measurements.The Nb3Sn quadrupole MQXF is being developed as a part of the large hadron collide (LHC) High Luminosity upgrade. The magnet design was tested on 1.5-m-long short models, sharing the same cross section with the full-length magnets. Various azimuthal and longitudinal preloads were applied, studying the impact on the magnet training and on its mechanical performances. The experiments demonstrated the possibility to control the magnet prestress. However, various factors, coil size among the others, may affect the stress variation between and within each winding. This variation could prevent the magnets from reaching the magnet performances, as for example as a result of the critical current reduction of the Nb3Sn strands. This paper analyzes the mechanical performances of the short models, studying in particular the stress variation on different coils. The measured coil size was used as input in the numerical simulations, and the results were then compared with the strain gauge measurements. Finally, the short model experience was used to evaluate the feasibility of a loading operation that does not rely on the strain measurements