Superconducting Magnet Test Facility Research Articles

Building the Runway: A New Superconducting Magnet Test Facility Made for the SPARC Toroidal Field Model Coil

Building the Runway: A New Superconducting Magnet Test Facility Made for the SPARC Toroidal Field Model Coil

Test Results of the First Pre-Series Quadrupole Magnets for the LHC Hi-Lumi Upgrade

The future high luminosity (Hi-Lumi) upgrade of the Large Hadron Collider (LHC) at CERN will include eight (plus two spares) 10.2 m-long Cryo-assemblies which will be components of the triplets for two LHC insertion regions. Each cold mass in the Cryo-assemblies will consist of two 4.2 m-long Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn high gradient quadrupole magnets, designated MQXFA, with aperture 150 mm and operating gradient 132.2 T/m, for a total of twenty magnets. Before assembling and testing the final cold masses at Fermilab, the component quadrupoles are being tested first at the vertical superconducting magnet test facility of the Superconducting Magnet Division (SMD) at Brookhaven National Laboratory (BNL), in superfluid He at 1.9 K and up to 18.0 kA, in accordance with operational requirements of the LHC. The tests of the first two full-length prototype quadrupole magnets MQXFAP1 and MQXFAP2 at BNL have been reported previously. The first two pre-series magnets, the first two that will be used in the LHC, have also now been tested. This paper reports on the quench test and training results of these two magnets. The test results of these magnets will be important for validating the final MQXFA design for operational magnets.

Test Results of the First Two Full-Length Prototype Quadrupole Magnets for the LHC Hi-Lumi Upgrade

The future high luminosity (Hi-Lumi) upgrade of the Large Hadron Collider (LHC) at CERN will include eight (plus two spares) 8.4 m-long cryostatted cold masses which will be components of the triplets for two LHC insertion regions. Each cold mass will consist of two 4.2 m long Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn high gradient quadrupole magnets, designated MQXFA, with aperture 150 mm and operating gradient 132.6 T/m, for a total of twenty magnets. Before assembling and testing the final cold masses at Fermilab, the twenty component quadrupoles will be tested first at the vertical superconducting magnet test facility of the Superconducting Magnet Division at Brookhaven National Laboratory (BNL), in superfluid He at 1.9 K and to 18.0 kA, to meet LHC operational requirements. The first two full-length prototype quadrupole magnets, MQXFAP1 and MQXFAP2, have been tested at BNL. This paper reports on the quench test and training results of these magnets, and also the retest of the first prototype, rebuilt and designated as MQXFAP1b. The test results of these magnets will be important for validating the MQXFA design.

Development of a Digital Quench Detection System for Nb3Sn Magnets and First Measurements on Prototype Magnets

The High Luminosity upgrade for the Large Hadron Collider LHC (HL-LHC) requires new Nb3Sn superconducting magnets and it triggers a development of novel hardware for the quench detection system (QDS) based on a field programmable gate array (FPGA) digital platform and a number of individually isolated analogue front-ends. Galvanic insulation has been implemented downstream the analogue to digital convertors to eliminate a usage of analogue isolation amplifiers. This concept was already successfully implemented in the current LHC QDS system, however the mitigation of new phenomena inside Nb3Sn materials required development of a new generation of QDS. The newly developed universal QDS offers flexibility of firmware defined architecture. Adopted prototype driven strategy includes thorough characterization of the analogue front-ends in the laboratory and prototype unit measurements performed on HL-LHC magnet prototypes at CERN's superconducting magnet test facility SM18. The tests also reveal the characteristics of the magnets as well as the measurement electronics at an early stage. The test results are used to optimize the analogue input stages as well as the digital signal processing within the FPGA. The preliminary test results are presented and focus is given to the measurement and studies of the so-called “flux jumps” to mitigate the effects of these voltage perturbations in the QDS.

Quench Propagation Velocity and Hot Spot Temperature Models in Nb3Sn Racetrack Coils

Since 2010 to present, several subsize magnet assemblies, designed as test beds for the validation of impregnated Nb 3Sn-based coil technology, have been tested at the Superconducting Magnet Test Facility (SM18) at CERN. These short model coils and racetrack model coils have been used to study two types of Rutherford cables foreseen for the coils of the Nb3Sn magnets in the framework of the HL-LHC upgrade and High Field Magnet program of CERN. During several test campaigns, the Rod Restack Process and the Powder-In-Tube conductors have been characterized in terms of performance and quench propagation velocity (QPV). Moreover, hot spot temperature (HST) increase during quenches has been estimated from the analysis of the registered voltage and current signals. In this paper, the multiphysics problem of quench propagation in Nb3Sn cables is addressed under adiabatic conditions by means of a set of analytical formulae and several finite element models with different level of complexity in ANSYS APDL, COMSOL Multiphysics, and MATLAB. These models are aimed at describing the conductor behavior in terms of HST and QPV observed during the training of racetrack coils at SM18.

Design and Fabrication of the 1.9 K Magnet Test Facility at BNL, and Test of the First 4-m-Long MQXF Coil

The future high luminosity upgrade of the Large Hadron Collider (LHC) at CERN will include 20 4.2-m-long Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn high gradient quadrupole magnets, which will be components of the triplets for two LHC insertion regions. In order to test these and four preproduction models, the vertical superconducting magnet test facility of the Superconducting Magnet Division (SMD) at Brookhaven National Laboratory (BNL) has been upgraded to perform testing in superfluid He at 1.9 K and 1 bar, the operational condition at the LHC. This has involved extensive modification of the 4.5 K cryogenics plant, including piping, compressors, and other upgraded components; a new vertical test cryostat, which can accept larger diameter magnets; a modernized power supply system upgraded with IGBT switches and fast shutoff capability, and that can supply 24 kA to test high field Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn magnets; and completely new data acquisition, signal analysis, and control software and hardware, allowing for fast, high precision, large volume data collection. This paper reports on the design, assembly, and commissioning of this upgraded test facility, and presents results of the first magnet test performed.

Upgrade of the CERN Superconducting Magnet Test Facility

The superconducting magnet test facility at CERN has hosted the series test of the majority of the LHC magnets. The facility has evolved, and is presently divided in two main areas: a vertical test facility, equipped with three vertical cryostats, and a horizontal test facility, with ten feedboxes for test of cryostated magnets in horizontal position. The test demands from construction projects, such as the high-luminosity LHC, or design studies, such as the future circular collider, are calling for a further upgrade. The new accelerator magnet technology based on Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and HTS superconductors, and the demand for higher bore field, result in high current (up to 30 kA), large cold mass dimensions (up to 1 m diameter), and increased stored energy (up to 1.5 MJ/m). To meet the new demands, two new vertical cryostats with their associated ancillary equipment are being built, and one horizontal test stand is being upgraded for operation at higher current. In addition, an upgrade of the cryogenic plant and services is planned to absorb the additional test needs. The paper gives the input parameters for the upgrade of the magnet test stations and the main characteristics of the new equipment.

New Analysis Framework Software for the CERN Superconducting Magnet Test Facility

Since 2013, the existing but aging analysis tools that were routinely used for the large hadron collider (LHC) magnet series production measurement campaigns conducted at the CERN superconducting Magnet Test Facility (SM18) are being replaced by a novel open-data and user-driven analysis environment. This effort is running in parallel to the current development of magnet prototypes in the framework of the High Luminosity Upgrade of the CERN LHC (HL-LHC project). This R&D phase requires new features in the quench analysis software to cope with the dedicated or specific magnet tests (splice resistance, inductance, ac loss, Quench Heater efficiency, Hot Spot Temperature assessment, etc…), as well as a more open access to the mathematical routines and to the output results. The new data handling and analysis tools framework that is currently deployed is based on two pillars. First, the availability of the legacy proprietary raw data in an open and widely accessible format. Second, the new possibility for the user to process with the data through dedicated numerical tools and algorithms recently developed for data viewing, analysis, and formatted test result reports. In this paper, the initial analysis framework is described in terms of the acquisition system that produces data, the conversion tool that standardizes the file format, the new analysis tool that replaces the existing quench analysis software, and the database tool that archives the summary of every test. Finally, some statistics of the current situation are presented, based on facts and results of one year of analysis working within the superconducting magnet test facility.

Commissioning Test Results of Variable-Temperature Helium Refrigerator/Liquefier for NIFS Superconducting Magnet Test Facility

The superconducting magnet test facility in the National Institute for Fusion Science has been upgraded for excitation tests at a wide temperature range and a higher magnetic field of 13 T. As part of the upgrade, the helium refrigerator/liquefier that operated for 24 years was replaced with a variable-temperature helium refrigerator/liquefier. The required liquefaction rate is 250 L/h, and the required refrigeration capacity is 600 W at 4.5 K, same as the previous one. In addition, it has a new feature that can supply helium gas of a wide temperature range. The typical design cooling capacity is 1 kW under the condition of 20-K supply/30-K return and 1.5 kW under the condition of 40-K supply/50-K return. After the replacement, a series of commissioning tests were performed under the various operational conditions. From the results, the satisfactory thermodynamic performance was confirmed. In the future, it is expected that the substantial progress will be made in the development of large-scale superconducting magnets with advanced superconductors such as high-temperature superconductors and MgB2. The design of the variable-temperature helium refrigerator/liquefier and the results of the commissioning tests are reported in detail.

Upgrade Plan on NIFS Superconducting Magnet Test Facility

Upgrade Plan on NIFS Superconducting Magnet Test Facility

Axial and transverse stress–strain characterization of the EU dipole high current densityNb3Sn strand

We have measured the critical current(Ic) of a highcurrent density Nb3Sn strand subjected to spatial periodic bending, periodic contact stress and uniaxial strain.The strand is destined for the cable-in-conduit conductors (CICC) of the European dipole(EDIPO) 12.5 T superconducting magnet test facility. The spatial periodic bending wasapplied on the strand, using the bending wavelengths from 5 to 10 mm with a peakbending strain of 1.5%, a periodic contact stress with a periodicity of 4.7 mm anda stress level exceeding 250 MPa. For the uniaxial strain characterization, thevoltage–current characteristics were measured with an applied axial strain from−0.9% to+0.3%, with a magnetic field from 6 to 14 T, temperature from 4.2 to 10 K and currents up toalmost 900 A. In addition the axial stiffness was determined by a tensile axial stress–straintest. The characterization of the strand is essential for understanding the behaviour of thestrand under mainly axial thermal stress variation during cool down and transverseelectromagnetic forces during charging, which is essential for the design of the CICC for thedipole magnet.The strand appears to be fully reversible in the compressive regime during the axialstrain testing, while in the tensile regime, the behaviour is already irreversiblydegraded when reaching the maximum in the critical current versus straincharacteristic. The degradation is accentuated by an immediate decrease of then value by a factor of 2. The parameters for the improved deviatoric strain description are derived fromthe Ic data, giving the accuracy of the scaling with a standard deviation of 4 A, which is by farwithin the expected deviation for the large scale strand production of such a highJc strand.The Ic versus the applied bending strain follows the low resistivity limit, indicative of fullinterfilament current transfer, while a strong decrease is observed at a peak bending strain of∼0.5%. For the periodic contact stress it appears that beyond 60 MPa, theIc becomes noticeablyirreversible. The n value, being a better indicator for the irreversible behaviour than theIc, seems to indicate a somewhat lower level of the transverse stress irreversibility. Since thestrand appears to be quite sensitive to the tensile strain, for the EDIPO CICC design,the tensile intrinsic axial strain in the filamentary region should stay well belowzero (only compressive) and the contact stress sufficiently below 50 MPa. Theserequirements are feasible, in particular for a CICC design with steel conduit which wouldprovide sufficient thermal compression, a sufficiently low void fraction and a cablingpattern that limits the peak bending strain during transverse load to about 0.3%.

Influence of fast magnetic pulses on the superconducting magnet test facility TOSKA

An overview is given about the influence of fast magnetic field pulses (up to 40 T/s) on components of the TOSKA magnet test facility at KfK, Karlsruhe. Such fast magnetic field changes occur during the operation of poloidal field coils and accidental plasma disruptions in a Tokamak and also during safety discharges of superconducting magnets. Induced eddy currents in surrounding conductive components can cause some detrimental damage. FEM calculations were performed in order to study the influence on critical components of TOSKA and to identify necessary modifications of the facility. The paper presents the results of these calculations. >

A VME-based quench detection and logging system for superconducting magnets

Quench detection is one of the crucial parts in the superconducting magnet test facility, specially related to the safety issue of the measurement environment. Consequently, those old systems, mainly relying on analog/TTL gate technologies, tend to be carefully adopted with minimum modification even for a new measurement facility, to maintain the working functionality. For a new measurement environment, readjustment of the system is necessary to control the different noise environment, and to incorporate the new measurement system configuration. For this purpose, an understanding of the physics of the quench-induced signals and noises is recommended to customize a new system. We have recently developed a prototype of the new fully digital quench detection system for the Magnet Test Lab. (MTL), Superconducting Super Collider (SSC) Laboratory, based on five out-of-shelf VME cards supported by a real-time O/S VxWorks. The new digital system not only provides improved signal processing and additional logging functions, but also supports user-friendly interfacing of parameter control and status display. One demonstration shows the modularity, simplicity, versatility, and compatibility of the new with the existing systems. This paper describes the overall system design, with the development and test environment. >

The IEA Large Coil Task test results in IFSMTF

The Large Coil Task (LCT) is an international collaboration under the auspices of the International Energy Agency (IEA) among the United States, EURATOM, Japan, and Switzerland to develop large superconducting toroidal field magnets for tokamak fusion reactors. Six 2.5-m*3.5-m bore coils capable of producing 8 T were fabricated, three by the US and one each by the other participants, and assembled in a toroidal array in the International Fusion Superconducting Magnet Test Facility (IFSMTF) at the Oak Ridge National Laboratory (ORNL). The coils were widely different in design with three cooled by pool-boiling helium at atmospheric pressure and three cooled for forced-flow helium at supercritical pressure (1.5 MPa). An overview is given of the various single-coil and six-coil array tests, to design point and beyond, and also the symmetric torus tests that were performed. All six coils exceeded the design goals, both as single coils and in six-coil toroidal tests. In the symmetric torus set, a maximum field of 9 T was reached in all coils simultaneously. Only brief summary is given of the specific thermal and mechanical experiments that were also conducted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Stability tests of the Westinghouse coil in the International Fusion Superconducting Magnet Test Facility

The Westinghouse coil is one of three forced-flow coils in the six-coil toroidal array of the International Fusion Superconducting Magnet Test Facility. A discussion is presented of results taken when the coil was tested both individually and in the six-coil array. The tests covered charging to full design current and field, when measuring the current-sharing threshold temperature using resistive heaters (installed to simulate nuclear heating), and when measuring the stability margin using pulsed inductive heaters (used to facilitate stability testing). It was found that at least one section of the conductor exhibits a very broad resistive transition (resistive transition index=4). The broad transition, though causing the appearance of voltage at relatively low temperatures, does not compromise the stability margin of the coil, which was greater than 1.1 J/cm/sup 3/ of strands. In another, nonresistive location, the stability margin was between 1.7 and 1.9 J/cm/sup 3/ of strands. This is from six to ten times larger than the value obtained by analyzing the current-sharing threshold. The cause of this discrepancy has been traced to failure of the conductor to obey the ideal critical-state theory.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Testing of the Euratom LCT coil in the toroidal arrangement of the International Fusion Superconducting Magnet Test Facility without external pulsed fields (standard-I) and with them (standard II) and an extended single-coil test

In this test, the coil reached (in stable operation) a field of 9 T at 140% of rated current. It reached the short-sample values of the strands used in the cable. The coil was operated up to 8 T with and without poloidal field transients in a toroidal configuration. The mass flow rate was reduced by a factor of 5 compared with the design value without any visible impact on stability. Averaged AC losses (winding, 14 W; case, 7 W) were measured under Large Coil Task (LCT)-specified poloidal field pulses, and the findings agreed with those of the short-sample measurements. The coils mechanical properties, which behaved as theoretically predicted, are also reported. All results obtained are thought to demonstrate that the applied technology has achieved reliable engineering standards.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Test results of the US-LCT pool-boiling coils in the International Fusion Superconducting Magnet Test Facility (IFSMTF)

The international Large Coil Task (LCT) designed, built, and successfully tested six different toroidal-field coils. Included in the torus are two pool-boiling coils designed and fabricated by US firms, General Dynamics/Convair Division (GD) and General Electric/Oak Ridge National Laboratory (GE). Both coils were instrumented for studies of electromagnetic, mechanical and thermodynamic properties and performed well and met design specifications. The authors summarize the complete test results, including the extended-condition test in which both coils demonstrated capability for operation beyond design points. The highlights of all major experiments since April 1987 that involved the GD or GE coils are presented in tabular form. In the extended-condition tests, both coils operated stably at 100% design current and above 9 T, even with bath temperature higher than 4.3 K. The mechanical behavior of both coils was generally in good agreement with calculations. Both coils were also safely discharged several times in the extended-condition tests. All results indicate that the technology developed for these two pool-boiling LCT coils can be directly applied for future large-scale applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Experimental results on the Japanese LCT coil in the IFSMTF: pulsed field tests and extended-condition tests

Selected experimental test results and evaluations are presented for the Japanese Large Coil Task (LCT) test coil used in the International Fusion Superconducting Magnet Test Facility (IFSMTF). Pulsed-field tests, and extended-condition tests in which the coil was operated above the design point (10220 A and 8 T) were performed at the bath temperature of 4.3-4.4 K. In the pulsed field tests, the coil demonstrated a stable operation in the pulsed field of 0.14 T/s and an accompanied overturning force. The AC losses of the coil were measured to be 15 W at the design point, and good agreement was obtained between measurement and calculation. In extended-condition tests, the coil was charged singly to 14 kA (138% of the design current) and obtained 8.8 T, where the coil had a quench. In the full torus, the coil demonstrated a stable operation at 11 kA (107%) and 9.0 T, and in a final operation, the coil reached 9.1 T at 10.8 kA (106%) without a quench.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Testing of the Euratom LCT-coil, a forced-flow cooled NbTi coil, in the international fusion superconducting magnet test facility (IFSMTF)

The Euratom-LCT-coil was tested as a single coil in the TOSKA facility at KfK Karlsruhe and in IFSMTF at ORNL Oak Ridge. Different mechanical boundary conditions and other operation parameters (mass flow, current) in the IFSMTF led to new set of results which broaden the knowledge about the coil. During cooldown the coil showed excellent heat transfer properties. The design current 11.4 kA with a max. field of 6.63 T could be reached with a ramp rate of 4 A/S without visible instabilities and thermal losses. The coil had at rated current a Stekly parameter α = 2.3 and could safely operated outside the cryogenic stability regime. The coil was 7 times dumped from currents higher than 4 kA with a peak voltage of 2.5 kV. Pressure increase was investigated under different boundary conditions and remained moderate. Dump losses measured were about 2 % of the stored energy. The coil was two times quenched during investigation of the operation limits. The quench detection system specially developed for this coil could be successfully tested with a level setting of 50 mV. For the first time the operation limits of such a coil were determined by current sharing measurement with heated helium slugs. The results are in fair agreement with those extrapolated from single strand measurements.

Testing of the pool-boiling cooled Japanese LCT coil in the international fusion superconducting magnet test facility

The Japanese LCT coil has successfully achieved the design field of 8 T in the toroidal array of the six LCT coils. In March, 1986, tests of the LCT coils were started following the cooldown of the whole facility. In the single-coil test and design-point test, in which the maximum field was 6.4 T and 8.1 T, respectively, the coil was charged, discharged, and dumped under different conditions. A recovery test and a simulated nuclear heating test were performed to investigate the stability of the coil. Measurements of displacement under the several conditions of electromagnetic load were analyzed to explain the mechanical behavior of the coil. Results obtained in the tests are reported in this paper.