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Emanuela Barzi, Daniele Turrioni, Ibrahim Kesgin, Masaki Takeuchi, Wang Xudong, Tatsushi Nakamoto, [Akihiro Kikuchi](https://orcid.org/0000-0002-5044-7156)

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[A new ductile, tougher resin for impregnation of superconducting magnets](https://mdr.nims.go.jp/datasets/ad84376d-e664-4604-8148-91a530d18da0)

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A new ductile, tougher resin for impregnation of superconducting magnetsSuperconductor Science andTechnology     PAPER • OPEN ACCESSA new ductile, tougher resin for impregnation ofsuperconducting magnetsTo cite this article: Emanuela Barzi et al 2024 Supercond. Sci. Technol. 37 045008 View the article online for updates and enhancements.You may also likeA 24 HR GLOBAL CAMPAIGN TOASSESS PRECISION TIMING OF THEMILLISECOND PULSAR J1713+0747T. Dolch, M. T. Lam, J. Cordes et al.-COMPARISON OF SPACE TELESCOPEAND 4-METER GROUND-BASEDTELESCOPE : FAINT GALAXYDETECTION AND PHOTOMETRY.J. A. Tyson-THE MULTI-TELESCOPE TELESCOPE:A COST-EFFECTIVE APPROACH TOFIBER-FED SPECTROSCOPYWilliam G. Bagnuolo, Ingemar K. Furenlid,Douglas R. Gies et al.-This content was downloaded from IP address 144.213.253.16 on 07/08/2024 at 11:24https://doi.org/10.1088/1361-6668/ad2c25/article/10.1088/0004-637X/794/1/21/article/10.1088/0004-637X/794/1/21/article/10.1088/0004-637X/794/1/21/article/10.1086/131382/article/10.1086/131382/article/10.1086/131382/article/10.1086/131382/article/10.1086/132677/article/10.1086/132677/article/10.1086/132677Superconductor Science and TechnologySupercond. Sci. Technol. 37 (2024) 045008 (10pp) https://doi.org/10.1088/1361-6668/ad2c25A new ductile, tougher resin forimpregnation of superconductingmagnetsEmanuela Barzi1,6,∗, Daniele Turrioni1, Ibrahim Kesgin2, Masaki Takeuchi3,Wang Xudong4, Tatsushi Nakamoto4 and Akihiro Kikuchi51 Fermi National Accelerator Laboratory, Batavia, IL 60510, United States of America2 Argonne National Laboratory, Lemont, IL 60439, United States of America3 RIMTEC Corporation, Kurashiki-shi, Okayama 711-0934, Japan4 High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan5 National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan6 Ohio State University, Columbus, OH 43210, United States of AmericaE-mail: barzi@fnal.govReceived 6 November 2023, revised 15 January 2024Accepted for publication 22 February 2024Published 7 March 2024AbstractA major remaining challenge for Nb3Sn high field magnets is their training due to randomtemperature variations in the coils. The main objective of our research is to reduce or eliminateit by finding novel impregnation materials in replacement of the epoxies currently used. Anorganic olefin-based thermosetting dicyclopentadiene resin, C10H12, commercially available inJapan as TELENE® by RIMTEC, was used to impregnate a short Nb3Sn undulator coildeveloped 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 largestrains, and toughness were identified as key properties to achieve these results. In addition, wehave been investigating whether mixing TELENE with high heat capacity ceramic powderssuch as Gd2O3, Gd2O2S, and HoCu2, increases the specific heat (Cp) of impregnated Nb3Snsuperconducting magnets. The viscosity, heat capacity, thermal conductivity, and other physicalproperties of TELENE with high-Cp powder fillers were measured in this study as a function oftemperature and magnetic field. The TELENE-87 wt%Gd2O2S had a peak in Cp between 4.3 Kand 5.3 K at fields between 0 and 8 T. We have also investigated the effect on the mechanicalproperties of pure and mixed TELENE under 10 MGy of gamma ray irradiation at the TakasakiAdvanced Radiation Research Institute in Takasaki, Japan. TELENE-87 wt%Gd2O2S exhibitedexceptional radiation resistance. Impregnating an undulator coil with TELENE mixed withGd2O2S powder will verify whether the coils’ thermal stability further improves, or whether itslow diffusivity will require engineering the material with high-thermal conductivitycomponents. 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∗Author to whom any correspondence should be addressed.Original content from this workmay be used under the termsof the Creative Commons Attribution 4.0 licence. Any fur-ther distribution of this work must maintain attribution to the author(s) and thetitle of the work, journal citation and DOI.1 © 2024 The Author(s). Published by IOP Publishing Ltdhttps://doi.org/10.1088/1361-6668/ad2c25https://orcid.org/0000-0001-5829-2147https://orcid.org/0000-0002-5044-7156mailto:barzi@fnal.govhttp://crossmark.crossref.org/dialog/?doi=10.1088/1361-6668/ad2c25&domain=pdf&date_stamp=2024-3-7https://creativecommons.org/licenses/by/4.0/Supercond. Sci. Technol. 37 (2024) 045008 E Barzi et alsupported by the U.S.-Japan Science and Technology Cooperation Program in high energyphysics operated by MEXT in Japan and DOE in the U.S.Keywords: superconducting magnet, training, dicyclopentadiene, resin impregnation,specific heat1. IntroductionOne of the main challenges of Nb3Sn high field acceler-ator magnets for high energy physics is their training [1].Superconducting (SC) magnets go back to being resistivefrom their SC state, i.e. ‘quench’, when their temperatureincreases above the current sharing temperature of the com-posite superconductor over a large enough volume. The tem-perature increase ∆T is proportional to Q/Cp, where Q is thedissipated heat, and Cp is the volumetric heat capacity. Energydeposition that initiates quenches can emanate from a vari-ety of both mechanical and electromagnetic sources (mag-netic flux jumps, conductor motion, epoxy cracking, etc).Other sources of magnet training are material interfaces, suchas between conductor, insulation, impregnating material, andneighboring structural materials. All these sources contributeto a resulting ‘disturbance spectrum’.Long training has been a feature of any Nb3Sn impreg-nated magnet for decades, since the start of the developmentof this technology. Any attempt made so far to reduce mag-net training with materials and methods applicable to acceler-ator magnets failed. We show here almost total training elim-ination when using as coil impregnation material for a Nb3Snmagnet C10H12, an organic olefin-based thermosetting dicyc-lopentadiene (DCP) resin, in replacement of the CTD-101K®epoxy currently used for this purpose. This resin is commer-cially available as TELENE® byRIMTECCorporation, Japan,and its molecular structure and molecular formula are shownin figure 1. It was used to impregnate an ANL Nb3Sn shortundulator model, which at every training cycle reached shortsample limit (SSL) after only two quenches, compared with∼100 when CTD-101K was used on a number of identicalundulator coils [2]. TELENE’s pot life of up to 3.5 h at 5 ◦Calso ensures scalability to impregnate larger coil volumes. Theundulator magnet with nine racetrack coils between 10 poleswas wound at ANL. After the winding was complete, the mag-net was assembled into its reaction tooling to be heat treatedin argon at FNAL using well established treatment cycles [3].It was then vacuum impregnated with pure TELENE at ANL,and later tested at FNAL in the SC R&D lab [4].To further improve thermal stability and training in accel-erator magnets, the idea of increasing superconductor’s sta-bility, usually based on its minimum quench energy (MQE),by inserting high specific heat (high-Cp) elements in SC wiresdates back to the 1960s [5]. Then in the mid-2000s, a con-siderable improvement in stability to pulsed disturbances wasobtained for NbTi windings, when distributing large heatcapacity substances on the conductor during winding [6, 7].The MQEs of the brushed coils were several times higher,and thermal efficiency was greatest for temperature diffusiontimes much smaller than the disturbance pulse duration. Afew years ago, Hypertech and Bruker-OST have attemptedto introduce high-Cp elements in their wire design [8]. Morerecently, Hypertech fabricated samples of a thin compos-ite Cu/Gd2O3 tape, which can be inserted in Rutherford-type cables to increase the conductor Cp [9]. At NIMS andRIMTEC, TELENEwasmixedwith high-Cp ceramic powderssuch as Gd2O3, Gd2O2S and HoCu2 [10]. The Cp temperaturedependence was measured for TELENE mixed with HoCu2,and the Cp temperature dependence as function of magneticfield was measured for TELENE mixed with Gd2O3, andGd2O2S. NbTi SC wire samples impregnated with these resinswere characterized and studied at FNAL by performing MQEmeasurements.The radiation strength of insulating materials used in SCaccelerator magnets is another key specification. The commonlimit of the Hi-Lumi LHC type magnets is 25 MGy of pro-ton radiation for CTD-101K epoxy. In 2016 the resistance toCobalt-60 gamma radiation was studied for DCP and epoxyresin bisphenol-A up to a dose of 3.3 MGy with a dose rate of2 kGy h−1 [11]. By measuring and analyzing optical absorp-tion, electrical conduction, dielectric and thermal properties, itwas shown that the organic DCP resin had a superior gammaray resistance with respect to the epoxy. For nonorganic mater-ials, there is a dependence of material response on the type ofbeam irradiation. However, such a dependence is quite modestfor organic materials, and the absorbed dose can be adequatelyused to qualify their radiation resistance. Therefore, resist-ance to gamma irradiation is a promising indicator to radiationstrength and a Cobalt-60 gamma ray irradiation experiment isbeing run at an average dose rate of 8 kGy h−1 at the TakasakiAdvanced Radiation Research Institute [12], which is part ofthe National Institutes for Quantum Science and Technologyin Takasaki. Here we present results of mechanical propertiesof pure and mixed TELENE before and during irradiation upto about 10 MGy.2. Experiment descriptionIn this section, we will describe the experimental setups usedfor mixing the TELENE with high-Cp ceramic powders atNIMS (section 2.1); for measuring the resins’ physical andmechanical properties at NIMS and KEK (section 2.2); formeasuring the MQE of NbTi wire samples impregnated withthe resins at FNAL (section 2.3); for fabricating and testingNb3Sn undulator short models impregnated with TELENE atANL and FNAL (section 2.4); and for the Cobalt-60 gammaray irradiation experiment at the Takasaki Advanced RadiationResearch Institute (section 2.5).2Supercond. Sci. Technol. 37 (2024) 045008 E Barzi et alFigure 1. Molecular structure (left) and molecular formula (right)of TELENE®, i.e. C10H12.Figure 2. Micrograph of the HoCu2 particles produced by astandard melt and casting process.2.1. Fabrication of high-Cp resins and optimization of theircompositionThe high heat capacity resins are fabricated by combining aceramics powder filler with TELENE using a planetary mixer.The TELENE is then mixed with a hardener or polymeriza-tion catalyst, which is a ruthenium complex, in 2/100 partsby wt. The curing time is controlled by the amount of phos-phine derivatives as retardant. The viscosity of the resins iscontrolled by the volume fraction and average size of thepowder filler. Therefore, the chemical composition, averagepowder size and volume fraction can be optimized. Usinga Gd2O3 powder size of 0.7–1.2 µm, TELENE was mixedusing three different concentrations, i.e. 45 wt%, 61 wt%, and82 wt%. Using a Gd2O2S powder size of 10 µm, TELENEwasmixed using seven different concentrations between 22 wt% to87 wt%.Because of its high-Cp and also smaller mass attenuationcoefficient than Gd for thermal neutrons, in 2021 NIMS fab-ricated the first HoCu2 powder by gas atomization, obtaininga particle size of 80 µm. A particle size of less than 30 µmwas eventually achieved using a standard melt and castingprocess followed by a first stage grinding with a jaw crushermachine, and a second stage finer grinding with a planetarymill machine. The produced powder (figure 2) was used as afiller for TELENE with an 83 wt% concentration.2.2. Measurements of physical and mechanical properties ofeach resinPhysical properties of the resins, such as viscosity, thermalconductivity, and specific heat Cp were measured atappropriate temperatures.Figure 3. Picture (top) and schematic (bottom) of three-pointbending test.The viscosity was measured with a Brookfield-type vis-cometer, specifically an Eiko DV2T. Using a spindle speed of60 rpm, a spindle of type LV-02 was used to measure viscosityvalues larger than 1 Pas, and one of type LV-04 to measure vis-cosity values lower than 1 Pas. The vscosity of TELENE wasmeasured at 5 ◦C, 15 ◦C and 25 ◦C, and that of CTD-101K at60 ◦C.The Cp and thermal conductivity were measured witha DynaCool® physical property measurement system byQuantum Design. The Cp temperature dependence was meas-ured for TELENE mixed with HoCu2, and the Cp temperaturedependence as function of magnetic field was measured forpure TELENE and TELENEmixed with Gd2O3, and Gd2O2S.The mechanical properties that were measured for the res-ins include flexural modulus and flexural strength at room tem-perature. They were obtained through a three-point bendingtest, of which a picture and schematic are shown in figure 3.These tests follow ISO 178:2010-A1:2013. Sample size is80 mm in length, 8 mm in width and 4 mm in thickness.The flexural tests were performed at room temperature withan Autograph AG-5000C tensile machine manufactured byShimadzu. The flexural strength is the maximum stress in thestress vs. strain curve. The flexural modulus was obtained fromthe stress vs. strain curve between 0.05% strain and 0.25%strain.2.3. Stability measurements of SC wire samplesimpregnated with high-Cp resinsTwo sets of six 0.8 mm NbTi wire samples were prepared atFNAL and sent to NIMS for impregnation with TELENE only,3Supercond. Sci. Technol. 37 (2024) 045008 E Barzi et alFigure 4. Picture of NbTi wire samples instrumented with twoheaters each, and with the voltage taps (VT) attached beforeimpregnation.TELENE-82 wt%Gd2O3, and TELENE-87 wt%Gd2O2S res-ins. TheMQE of impregnated wires is measured on ITER-typebarrels. Two strain gauges of 4 mm and 1.5 mm length andwidth are used as 350Ω heaters and glued to each sample usingSTYCAST 2850FT. The instrumentation wires are solderedbefore sample and strain gauges receive resin impregnation.Figure 4 shows a picture of NbTi wire samples instrumentedwith two heaters each, and with the voltage taps attachedbefore impregnation.A 200 W power supply provides the excitation voltage tothe strain gauges. Using a LabView DAQ program, a pulseoutput is generated from the power supply and the voltageacross the strain gauge is measured. With the Ic of the samplefirst measured, a constant bias current below Ic is applied tothe sample and heat pulses are fired using the strain gauge.A separate quench protection system monitors the voltageacross the sample and shuts down the power supply if thequench threshold is reached. By gradually increasing the pulseenergy, the minimum energy that induces a quench is definedas the MQE of the sample [9]. In order to determine the mostappropriate pulse duration range for each resin, the charac-teristic time, or thermal time constant τ , was calculated asτ = 4 a2/(π2 D), where D = k/(ρ Cp) is the thermal dif-fusivity, k the thermal conductivity, ρ the material’s density,and 2a the material’s thickness. The thermal properties shownin table 1 were obtained by using a = 1 mm, ρ(STYCAST2850 FT) = 2290 kg m−3, ρ(TELENE) = 1030 kg m−3,ρ(TELENE-82 wt%Gd2O3)= 3504 kg m−3, and ρ(TELENE-87 wt%Gd2O2S) = 4110 kg m−3. Based on the results for τ ,theMQEwasmeasured for heater pulse durations from 200msto 1.5 s.2.4. Fabrication and test of Nb3Sn undulator short modelIn collaboration with FNAL and other labs, ANL developeda Nb3Sn undulator to be installed in the Advanced PhotonSource (APS) storage ring. Performance reproducibility closeto 100% SSL was obtained by using several Nb3Sn short mod-els during the R&D phase. They were vacuum impregnatedwith CTD-101K, which is the same epoxy used for Nb3Snhigh field accelerator magnets. The same performance andreproducibility were later achieved on longer models. Thetraining behavior of the undulator models was very similar tothat of HEP accelerator magnets, requiring ∼100 quenches toapproach SSL [2].The design parameters of the undulator short model aredetailed in table 2. These Nb3Sn undulators with 18mmperiodoperate at a maximum magnetic field of about 5 T and max-imum equivalent stress on the conductor below 100 MPa. Toaddress instabilities at this field, a Restacked Rod Processedwire of 0.6 mm in diameter and with 144 SC subelements over169 total subelements was used. Its equivalent subelement dia-meter is ∼35 µm, and the critical current density Jc (4.2 K,12 T) is about 2500 A mm−2. Each Nb3Sn undulator shortmodel has nine racetrack coils wound in a groove between10 poles. There are 46 turns in each groove, and each periodincludes two grooves and two poles. The S2-glass braidedNb3Sn wire is continuously wound turn-by-turn between thepoles. A picture of a short undulator model is shown beforeimpregnation in figure 5.After winding, the magnet was assembled into an existingreaction tooling. The magnet model was heat treated at FNALin argon atmosphere in a three-zone controlled tube furnace,using well-established treatment cycles [3]. Table 3 shows thenominal temperature values compared with the measured oventemperature. The temperature was averaged between two K-type calibrated and ungrounded thermocouples. Several wit-ness samples of the same Nb3Sn wire used in the coil wereincluded in the furnace. Their critical current Ic was determ-ined from measuring the V–I curve using an electrical fieldcriterion of 0.1 µV cm−1. The calculation of the expected coilSSL is obtained by intersecting the average Ic of these samplesas function of the magnetic field with the magnet load line.After winding and heat treatment, the magnet was vacuumimpregnated with pure TELENE at ANL. The undulator wasthen tested at FNAL at 4.2 K in liquid helium at atmosphericpressure, in a cryostat of the SC R&D lab, by using an insertequipped with 2000 A DC leads. Figure 6 shows the TELENEimpregnated magnet attached to the test insert. Two pairs ofvoltage taps, each covering half of the magnet, were used. Thevoltage tap wires were connected to an NI-9239 card of a com-pact RIO DAQ system. The NI card has four channels with anacquisition frequency of 50 kHz and 24 bits per channel. Thethreshold for the quench protection systemwas 100mV for thedifferential voltage.When a quench is detected, the power sup-ply is stopped, an insulated gate bipolar transistor switch opensand the current flows into a 0.125 Ω dump resistor, where thecoil energy gets dissipated.2.5. Gamma ray irradiation experimentGamma ray irradiation is being performed at the TakasakiAdvanced Radiation Research Institute using a Cobalt-60gamma irradiation facility. 40 samples (of 80 mm in length,8 mm in width and 4 mm in thickness) each of pure TELENE,TELENE mixed with 82 wt%Gd2O3, with 87 wt%Gd2O2S,and with 83 wt%HoCu2 are being irradiated in air atmosphereat an average absorbed dose rate of 8 kGy h−1. Samples ofCTD-101K epoxy were also included to verify the accuracy ofthe results. Each sample was 80 mm in length, 8 mm in widthand 4mm in thickness. Figure 7 shows the samples in their alu-minum crate. The final goal for the entire irradiation campaignis to achieve 25 MGy+. Every month from start of irradiation4Supercond. Sci. Technol. 37 (2024) 045008 E Barzi et alTable 1. Thermal properties of TELENE resins.@4.2 K ρ kg m−3 kW (mK)−1 Cp J (kg K)−1 D m2 s−1 τ sSTYCAST 2850FT 2290 0.05 0.44 500.0 · 10−7 0.008TELENE 1030 0.04 3.5 111.0 · 10−7 0.037TELENE 82%Gd2O3 3504 0.02 20 2.9 · 10−7 1.420TELENE 87%Gd2O2S 4110 0.09 60 3.7 · 10−7 1.111Table 2. Undulator short model design parameters.Design parameter ValueNo. periods 4.5Groove width 5.5 mmGroove depth 4.9 mmPeriod length 18 mmNo. turns/groove 46Nb3Sn conductor Ti-doped RRPConductor architecture 144/169Conductor diameter 0.6 mmInsulation material S2-glassInsulation thickness 65 µmFinal HT step 40 h at 650 ◦CFigure 5. Picture of Nb3Sn undulator short model after windingand reaction, and before impregnation.Table 3. Nominal vs. obtained heat treatment cycle for undulatorshort model impregnated with TELENE.Nominal ObtainedTime, h T, ◦C Time, h TAve, ◦C48 210 48 207104 370 104 36550 650 50 647(i.e. every 2–3 MGy of absorbed dose), three samples of eachresin were extracted from their aluminum rack and a htree-point bending test was performed at room temperature. Herewe present results of mechanical properties of pure and mixedTELENE before and during irradiation up to about 10 MGy.Figure 6. Picture of the first TELENE impregnated Nb3Sn smallundulator attached to its test insert.Figure 7. Picture of aluminum crate containing the resins to begamma ray irradiated in air atmosphere.For nonorganic materials, there is a dependence of mater-ial response on the type of beam irradiation. However,such a dependence is modest for organic materials, and theabsorbed dose can be used to qualify their radiation resist-ance. At a later stage, this could be confirmed with pro-ton beam irradiation experiments at the BLIP facility atBNL.5Supercond. Sci. Technol. 37 (2024) 045008 E Barzi et alFigure 8. Comparison of flexural stress vs. strain curve betweenCTD-101K epoxy and TELENE resin at room temperature.3. Results and discussionTELENE has close to 100% DCP composition. It was chosenfor these studies because of the following main reasons: 1. Itsductility, i.e. the ability to accept large strains; 2. Its tough-ness, i.e. the amount of energy per unit volume that the mater-ial can absorb before rupturing, or the area underneath thestress vs. strain curve; 3. Its potential for radiation resistance.Figure 8 shows how much more ductile and tougher is pureTELENE with respect to CTD-101K epoxy at room temper-ature. TELENE preserves its ductility also at 77K [13]. Foradhesiveness to metals, inorganic materials and carbon fibers,polar functional groups were used in the TELENE curingagent.The potential of improving TELENE’s thermal propertiesby mixing it with high-Cp ceramic powders such as Gd2O3,Gd2O2S, and HoCu2 was another component of this research.In this section, we will present and discuss the resultsobtained for the resins’ physical and mechanical proper-ties (sections 3.1.1 and 3.1.2); for the MQE of NbTi wiresamples impregnated with the resins (sections 3.2); for theTELENE impregnation and test of the first Nb3Sn undulatorshort model, which includes impregnation process scalabil-ity (sections 3.3.1), magnet SSLs (sections 3.3.2), and magnettest results (sections 3.3.3); and for the Cobalt-60 gamma rayirradiation experiment up to 10MGy at the Takasaki AdvancedRadiation Research Institute (sections 3.4).3.1. Measurements of physical and mechanical properties ofeach resin3.1.1 Physical properties. Figures 9 and 10 show respect-ively the thermal conductivity k and specific heat Cp as func-tion of temperature for CTD-101K epoxy, and for pure andmixed TELENE resins in absence of an external magneticfield. The specific heat as function of temperature at vari-ous external magnetic fields is shown in figure 11 for pureTELENE, in figure 12 for TELENE-45 wt%Gd2O3, and infigure 13 for TELENE-87 wt%Gd2O2S. The latter mixed resinFigure 9. Thermal conductivity vs. temperature for CTD-101Kepoxy, and for pure and mixed TELENE resins in absence ofexternal magnetic field.Figure 10. Specific heat vs. temperature for CTD-101K epoxy, andfor pure and mixed TELENE resins in absence of external magneticfield.has the largest thermal conductivity over the whole temperat-ure range and a peak in Cp between 4.3 K and 5.3 K at fieldsbetween 0 and 8 T. Pure TELENE has a Cp which increasesmonotonically with temperature. Beyond 6 K, the Cp of pureTELENE is larger than that of TELENE mixed with Gd2O3 atany magnetic field.3.1.2 Mechanical properties. The flexural stress vs. straincurves for pure and mixed TELENE resins are shown at roomtemperature in figure 14. After mixing the TELENE with hardceramic particles, the material becomes stronger, i.e. largerflexuralmodulus, and less ductile. On the other hand, as seen insection 3.1.1, some of the TELENEmixed resins feature largerthermal conductivity and specific heat than pure TELENE. Itis reasonable to speculate that TELENE’s capability to absorblarge strains and large energies be key to the undulator train-ing performance as detailed in section 3.3. In the close future,these mechanical properties will be measured at 77 K in liquid6Supercond. Sci. Technol. 37 (2024) 045008 E Barzi et alFigure 11. Specific heat Cp vs. temperature at various externalmagnetic fields for pure TELENE resin.Figure 12. Specific heat Cp vs. temperature at various externalmagnetic fields for TELENE-45 wt%Gd2O3 mixed resin.nitrogen. In a second part of this study, the impact on trainingbehavior of the low diffusivity of the mixed resins with high-Cp has to be checked.3.2. MQE measurements of NbTi wire samples impregnatedwith high-Cp resinsBased on the low diffusivity values obtained for the mixedTELENE resins shown in table 1, with a maximum time con-stant of 1.42 s for TELENE-82 wt%Gd2O3, the MQE of theimpregnated 0.8 mm NbTi wire samples was measured forheater pulse durations from 200 ms to 1.5 s, with Ic% of upto 90% and magnetic fields between 6 and 9 T. At 9 T, theIc (4.2 K) was 140 A. An example of results obtained at 9 Tand at 80% of Ic is in figure 15. For pulse durations compar-able to their time constant, both TELENE-82 wt%Gd2O3 andTELENE-87 wt%Gd2OsS show larger increases in MQE thanpure TELENE.Figure 13. Specific heat Cp vs. temperature at various externalmagnetic fields for TELENE-87 wt%Gd2O2S mixed resin.Figure 14. Flexural stress vs. strain curves for pure and mixedTELENE resins.3.3. Impregnation with TELENE and test of first Nb3Snundulator short modelAfter winding and heat treatment, the magnet was placed ina leak-tight impregnation mold for vacuum impregnation atANL. The two-part resin, i.e. TELENE resin plus the poly-merization catalyst, was mixed by weight. After injecting theresin, the assembly was cured at 120 ◦C for one hour. Due tothe exothermic polymerization reaction, the internal temperat-ure is higher by about 50 ◦C–100 ◦C, depending on the amountof resin.As can be seen from figure 16, at room temperature the potlife of TELENE is 20 min. However, the viscosity of TELENEis much lower than that of epoxy, i.e. its consistency is likewater.3.3.1. Impregnation process scalability. As shown infigure 16, TELENE’s pot life can be increased by loweringthe temperature during the impregnation process, which is the7Supercond. Sci. Technol. 37 (2024) 045008 E Barzi et alFigure 15. Minimum quench energy vs. heater pulse duration at80% of the critical current Ic at 9 T for NbTi wire samplesimpregnated with pure and mixed TELENE.Figure 16. Viscosity as function of time for TELENE at differenttemperatures.Table 4. Pot life vs. temperature for pure TELENE.Pot life, min Temperature,◦ C20 2575 15210 5opposite of what is done for CTD-101K, for which the tem-perature is instead increased. The dependence of TELENE’spot life with temperature is shown also in table 4.Scalability to larger impregnation volumes can be achievedby performing the impregnation process between 5 and 15 ◦C.Indeed, by using one epoxy inlet into tooling equipped withmultiple vents and an inlet pressure of 2 bar, fill times withepoxy are less than 1.5 h for the HL-LHC IR quadrupoles thatare 7.3 m long [14]. This includes about 45 min to inject CTD-101K in the coil’s mold and fill it, and about 40 min for fillingthe outflow tank.Figure 17. Viscosity as function of wt%Gd2O2S in TELENE at25 ◦C compared with that at 60 ◦C of CTD-101K mixed withGd2O3.Figure 18. Short sample limit calculation of TELENE impregnatedundulator model based on witness sample critical current test results.The viscosity of mixed TELENE resins is of the sameorder of magnitude as that of pure TELENE up to highfillers concentrations, as shown for instance at 25 ◦C forTELENE mixed with Gd2O2S in figure 17. On the otherhand, the viscosity of CTD-101K is much more sensitiveto the amount of high-Cp fillers, as shown for instance infigure 17 at 60 ◦C when mixed with Gd2O3. However,some particle sedimentation is expected to occur in TELENEmixed with high-Cp ceramic powders, due to the signific-ant density difference. This factor will have to be accountedfor when optimizing for the most effective mixed TELENEcomposition.3.3.2. Magnet SSLs. The SSL for the first undulator shortmodel was calculated based on the test results at 4.2 K of threeNb3Sn witness samples that were included in the furnace withthe coil. Figure 18 shows that the Ic vs. magnetic field curvefor these samples intersects the maximum field load line of theundulator magnet at 1143 A and 5.07 T.8Supercond. Sci. Technol. 37 (2024) 045008 E Barzi et alFigure 19. Quench history of TELENE impregnated shortundulator model as compared with that of nearly identical undulatorshort models impregnated with CTD-101K. Data for Small MagnetModel 4, i.e. SMM4, are not shown because it was damaged.Figure 20. Quench history, including two thermal cycles, forTELENE impregnated short undulator model. Actual quenches atthe standard ramp rate of 1 A s−1 are indicated with closed circles.The maximum achieved current was 1140 A, or 99.7% SSL.3.3.3. Magnet test results. The quench data for the firstTELENE impregnated short undulator model as comparedwith identical undulator short models impregnated with CTD-101K are shown in figure 19. Data for Small Magnet Model 4,i.e. SMM4, are not shown because it was damaged. Figure 20shows in more detail the quench history of this first undu-lator model, including two thermal cycles. Actual quenchesobtained at the standard ramp rate of 1 A s−1 are indicatedwith closed circles. Closed triangles indicate quenches pro-duced during ramp rate studies, which were performed up toramp rates of 50 A s−1. Open circles represent faulty trips dueto overflow of the DAQ buffer’s memory that spuriously activ-ated the quench protection feature, and stopped the data tak-ing. This problem was subsequently fixed before proceedingwith the second and third runs, where no faulty trips appearedanymore.As can be seen, the first quench at 1043 A occurred at about91% of SSL, which was 1143 A. It took only two quenchesbefore achieving SSL, compared to ∼100 quenches needed toreach a plateau for the nearly identical undulator coils impreg-nated with CTD-101K [2].The quench results during the first and second thermalcycles, i.e. second and third test sequences performed afterFigure 21. Flexural strength as function of Co-60 Gamma ray dosefor pure and mixed TELENE compared with CTD-101K.Figure 22. Flexural modulus as function of Co-60 Gamma ray dosefor pure and mixed TELENE compared with CTD-101K.warming up the magnet to room temperature and cooling itdown again, are also shown in figure 20. In this second andthird runs, the SSL was reached once again in no more thantwo quenches. However, these sequences also showed a num-ber of current drops, down to 92%–97% of SSL. The analysisof the voltage tap signals did not provide any insight on thenature of these quenches, and additional instrumentation willbe needed to investigate this phenomenon.3.4. Cobalt-60 gamma ray irradiation experiment up to10 MGyFigures 21 and 22 show the flexural strength and the flexuralmodulus respectively as function of Gamma ray dose for pureand mixed TELENE compared with CTD-101K. The flex-ural modulus monotonically increased by about 40% for pureTELENE, more than 60% for TELENE-82 wt%Gd2O3 and9Supercond. Sci. Technol. 37 (2024) 045008 E Barzi et alTELENE-87wt%Gd2O2S, andmore than 450% for TELENE-83 wt%HoCu2. The flexural strength monotonically increasedfor TELENE-82 wt%Gd2O3 and TELENE-87 wt%Gd2O2S.4. ConclusionsBy replacing CTD-101K with TELENE to impregnate a shortANL Nb3Sn undulator coil, training and magnet retrainingwere nearly eliminated before reaching SSL at over 1100 A,which is much larger than the 450 A nominal current of theNbTi undulators operating in the ANL APS. TELENE willenable operation of Nb3Sn undulators much closer to theirSSL, expanding the energy range and brightness intensityof light sources. Pure TELENE is Co-60 gamma radiationresistant up to 7–8 MGy, and therefore already applicablefor impregnation of insertion devices for synchrotron lightsources, operating in lower radiation environments than highenergy colliders.TELENE-82 wt%Gd2O3 and TELENE-87 wt%Gd2O2Shave proven to be exceptionally radiation resistant to Co-60gamma irradiation. When combined with the ductility andtoughness properties of TELENE, these resins are expec-ted to show superior training performance with respect toCTD-101K. Impregnating an undulator coil with TELENEmixed with Gd2O2S powder will verify whether the coil sta-bility further improves, or whether its low diffusivity willrequire engineering the material with high-thermal conduct-ivity components.TELENE was successful to prevent training in the Nb3SnANL undulator, which produces a maximummagnetic field ofabout 5 T and maximum equivalent stress on the conductor ofless than 100MPa. The next necessary step is to check whetherthe developed resins can lead also to a reduction in training instress managed magnets, which is the current core design inthe US Magnet Development Program.By successfully reducing coil training, and based on thecurrent radiation resistance results, TELENE impregnationtechnology is expected to have direct application to highfield Nb3Sn dipole and quadrupole magnets for high radiationenvironments. Short magnet training will lead to better magnetreliability, lower magnet margins, lower risk and substantialsaving in accelerators’ commissioning costs.Data availability statementAll data that support the findings of this study are includedwithin the article (and any supplementary files).ORCID iDsEmanuela Barzi https://orcid.org/0000-0001-5829-2147Akihiro Kikuchi https://orcid.org/0000-0002-5044-7156References[1] U.S. Department of Energy, Office of Science 2020 The 2020Updated Roadmaps for the U.S. Magnet DevelopmentProgram (arXiv:2011.09539)[2] Kesgin I et al 2019 Development of short-period Nb3Snsuperconducting planar undulator IEEE Trans. Appl.Supercond. 29 4100504[3] Barzi E, Turrioni D, Ivanyushenkov Y, Kasa M, Kesgin I andZlobin I A V 2020 Heat treatment studies of Nb3Sn RRPwires for superconducting planar undulators IEEE Trans.Appl. Supercond. 30 6001005[4] Barzi E, Andreev N, Apollinari G, Bucciarelli F, Lombardo V,Nobrega F, Turrioni D, Yamada R and Zlobin A V 2013Superconducting strand and cable development for the LHCupgrades and beyond IEEE Trans. Appl. Supercond.23 6001112[5] Hancox R 1968 Enthalpy stabilized superconducting magnetsIEEE Trans. Magn. 4 486–8[6] Alekseev P, Boev A, Keilin V, Kovalev I, Kruglov S,Lazukov V and Sadikov I 2004 Experimental evidence ofconsiderable stability increase in superconducting windingswith extremely high specific heat substances Cryogenics44 763–6[7] Alekseev P, Boev A, Keilin V, Kovalev I, Kozub S, Kostrov E,Kruglov S, Lazukov V, Sadikov I and Shutova D 2006Influence of high heat capacity substances doping onquench currents of fast amped superconducting ovalwindings Cryogenics 46 252–5[8] Xu X, Li P, Zlobin A V and Peng X 2018 Improvement ofstability of Nb3Sn superconductors by introducing highspecific heat substances Supercond. Sci. Technol.31 03LT02[9] Barzi E, Novitsky I, Rusy A, Turrioni D, Zlobin A V, Peng Xand Tomsic M 2021 Test of superconducting wires andrutherford cables with high specific heat IEEE Trans. Appl.Supercond. 31 9404812[10] Kikuchi A and Takeychi M Patent pending[11] Miyamoto M, Tomite N and Ohki Y 2016 Comparison ofgamma-ray resistance between dicyclopentadiene resinand epoxy resin IEEE Trans. Dielectr. Electr. Insul.23 2270[12] Musso A, Nakamoto T, Grande B D, Borderas C L, daSousa D F, Sugano M, Ogitsu T and Tavares S S 2022Characterization of the raidation resistance of glass fiberreinforced plastics for superconducting magnets IEEETrans. Appl. Supercond. 32 7700405[13] RIMTEC corporation (available at: www.rimtec.co.jp/en/technology/behavior.html)[14] Axensalva J and Nobrega F 2023 private communication10https://orcid.org/0000-0001-5829-2147https://orcid.org/0000-0001-5829-2147https://orcid.org/0000-0002-5044-7156https://orcid.org/0000-0002-5044-7156https://arxiv.org/abs/2011.09539https://doi.org/10.1109/TASC.2019.2897645https://doi.org/10.1109/TASC.2019.2897645https://doi.org/10.1109/TASC.2020.2974706https://doi.org/10.1109/TASC.2020.2974706https://doi.org/10.1109/TASC.2013.2240038https://doi.org/10.1109/TASC.2013.2240038https://doi.org/10.1109/tmag.1968.1066271https://doi.org/10.1109/tmag.1968.1066271https://doi.org/10.1016/j.cryogenics.2004.03.004https://doi.org/10.1016/j.cryogenics.2004.03.004https://doi.org/10.1016/j.cryogenics.2005.07.005https://doi.org/10.1016/j.cryogenics.2005.07.005https://doi.org/10.1088/1361-6668/aaa5dehttps://doi.org/10.1088/1361-6668/aaa5dehttps://doi.org/10.1109/TASC.2021.3069047https://doi.org/10.1109/TASC.2021.3069047https://doi.org/10.1109/TDEI.2016.7556503https://doi.org/10.1109/TDEI.2016.7556503https://doi.org/10.1109/TASC.2022.3157255https://doi.org/10.1109/TASC.2022.3157255www.rimtec.co.jp/en/technology/behavior.htmlwww.rimtec.co.jp/en/technology/behavior.html A new ductile, tougher resin for impregnation of superconducting magnets 1. Introduction 2. Experiment description 2.1. Fabrication of high-Cp resins and optimization of their composition 2.2. Measurements of physical and mechanical properties of each resin 2.3. Stability measurements of SC wire samples impregnated with high-Cp resins 2.4. Fabrication and test of Nb3Sn undulator short model 2.5. Gamma ray irradiation experiment 3. Results and discussion 3.1. Measurements of physical and mechanical properties of each resin 3.1.1 Physical properties. 3.1.2 Mechanical properties. 3.2. MQE measurements of NbTi wire samples impregnated with high-Cp resins 3.3. Impregnation with TELENE and test of first Nb3Sn undulator short model 3.3.1. Impregnation process scalability. 3.3.2. Magnet SSLs. 3.3.3. Magnet test results. 3.4. Cobalt-60 gamma ray irradiation experiment up to 10 MGy 4. Conclusions References