Superconducting Undulators (SCUs) can produce higher photon flux and cover a wider photon energy range compared to permanent magnet undulators (PMUs) with the same vacuum gap and period length. To build the know-how to implement superconducting undulators for future upgrades of the European XFEL facility, two magnetic measurement test stands named SUNDAE 1 and 2 (Superconducting UNDulAtor Experiment) are being developed. SUNDAE1 will facilitate research and development on magnet design thanks to the possibility of training new SCU coils and characterizing their magnetic field. The experimental setup will allow the characterization of magnets up to 2m in length. These magnets will be immersed in a Helium bath at 2K or 4K temperature. In this article, we describe the experimental setup and highlight its expected performances

Abeghyan, S.

Baader, J. E.

Barbanotti, S.

Casalbuoni, S.

Civita, D. La

Eckoldt, H.-J.

Englisch, U.

Felice, M. Di

Grattoni, V.

Grau, A. W.

Hauberg, A.

Jensch, K.

Lederer, S.

Lilje, L.

Marchetti, B.

Ramalingam, R.

Schnautz, T.

Vannoni, M.

Yakopov, M.

Zimmermann, R.

Ziolkowski, P.

English

KITopen

SUNDAE1: A LIQUID HELIUM VERTICAL TEST-STANDFOR 2m LONG SUPERCONDUCTING UNDULATOR COILSB. Marchetti∗, S. Abeghyan, J. Baader, S. Casalbuoni, M. Di Felice, U. Englisch,V. Grattoni, D. La Civita, M. Vannoni, M. Yakopov, P. ZiolkowskiEuropean XFEL GmbH, Schenefeld, GermanyS. Barbanotti, H.-J. Eckoldt, A. Hauberg, K. Jensch, S. Lederer,L. Lilje, R. Ramalingam, T. Schnautz, R. ZimmermannDeutsches Elektronen-Synchrotron, Hamburg, GermanyA. GrauKarlsruher Institut fuer Technologie, Karlsruhe, GermanyAbstractSuperconducting Undulators (SCUs) can produce higherphoton flux and cover a wider photon energy range comparedto permanent magnet undulators (PMUs) with the same vac-uum gap and period length. To build the know-how to im-plement superconducting undulators for future upgrades ofthe European XFEL facility, two magnetic measurementtest-stands named SUNDAE 1 and 2 (Superconducting UN-DulAtor Experiment) are being developed. SUNDAE1 willfacilitate research and development on magnet design thanksto the possibility of training new SCU coils and characteriz-ing their magnetic field. The experimental setup will allowthe characterization of superconducting coils up to 2m inlength. These magnets will be immersed in a Helium bathat 2K or 4K temperature. In this article, we describe theexperimental setup and highlight its expected performances.INTRODUCTIONThe advancement of SCU technology has a strategic im-portance for the future development of the European XFELfacility. In the recent years, SCUs have been succesfully em-ployed in synchrotron radiation sources [1, 2]. In a similarway of what happened with their application to synchrotrons,SCUs can potentially improve the performance and flexibil-ity of advanced Free Electron Lasers (FELs). In particular byworking at short undulator periods, superconducting magnettechnology would allow reaching higher photon energieswhile keeping a wide range of tunability of the setpoint.The extension of the energy range of the radiation towardshigher values at European XFEL would fully exploit the highelectron energy beam capability of the accelerator [3]. More-over, this development can be considered complementary tothe study on the upgrade of the XFEL linac for continuouswave (CW) operation [4]. CW operation at European XFELis considered possible only with reduced electron beam en-ergy. Specifically the electron beam energy will be limited toabout 7 GeV, while the present maximum value is 17.5 GeV.The replacement of the existing PMUs beamline with SCUshaving shorter undulator periods would enable the 7 GeVlinac to cover the same photon energy range as the presentaccelerator.∗ barbara.marchetti@xfel.euFor all those reasons, a project for the realization of aSCU afterburner for the SASE2 line is being set-up. Themain parameters and specifications for a pre-series proto-type module (S-PRESSO) of such afterburner have beenpresented in [5].The availability of equipment for the characterization ofthe magnetic coils of the undulator is a critical point to mon-itor the performances of the undulators that have been pro-duced prior to the installation. For this reason two test-stands,SUNDAE1 and SUNDAE2 (Superconducting UNDulAtorExperiment 1 and 2) for the diagnostics of the novel SCUsare under realization in the DESY campus.The test-stand SUNDAE1 will be dedicated to the training,tuning and characterization of new SCU coils by means ofmagnetic field measurements [6]. The cryostat of SUNDAE1will have a vertical configuration and will be constitutedby a liquid Helium bath in which the coils are immersed.SUNDAE2 will be used for the characterization of the finalafterburner cryomodules [7]. This cryostat will have anhorizontal configuration and the coils will be tested in theirfinal cryostat. In this second test-stand the characterizationof the module using the pulse-wire technique will also beforeseen [8, 9].OVERVIEW OF SUNDAE1Figure 1 shows the schematic drawing of SUNDAE1. Thecoils of the SCUs will be immersed in a liquid or superfluidHelium bath, at 4K or 2K respectively. Two Hall probes willbe installed on a sledge driven by a Linear Motion System(LMS). The sledge will be able to move between the twocoils constituting a SCU. The system will be able to char-acterize coils having a magnetic gap down to 5 mm. Thecoils are supported by a structure anchored on a plate of thelid. Several thermal shields guarantee a low heat load fromthe surroundings to the cryogenic vessel. The magnet isconnected to the power supply outside the cryostat throughcurrent leads. Several feedthroughs at the lid allow the con-nection of diagnostics sensors (temperature sensors, voltagetaps, Hall probes etc.) to the outside of the cryostat.As illustrated in Fig. 1, the orientation of the Hall-probesallows the characterization of the y-component of the mag-netic field of the coils, 𝐵𝑦. The resolution of the measure-13th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-THPOPT031THPOPT031ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI2646MC7: Accelerator TechnologyT10: Superconducting MagnetsFigure 1: Scheme of SUNDAE1.ment of the magnetic field is of the order of a few T but itsaccuracy is limited by the error on the calibration of the Hallprobe, which is of the order of 0.1 mT.The LMS will be equipped with a single axis verticaltranslator with 2400 mm of travel-range.Besides its application for the final magnetic character-ization of the SCUs, SUNDAE1 will also be used for thetraining of coils. Quench events happening when the coil isinitially brought into operation have to be managed in a safeway. In order not to damage the superconducting coil, thepower supply of the coil has to be switched off immediatelyafter the detection of a quench event. For this reason, thepower supply is connected to a quench detection system.For the detection of the quench event, the three voltagetaps marked with crosses in Fig. 2 are used. The voltagedifference between points 1 and 2 (Δ𝑉12) and the one be-tween points 2 and 3 (Δ𝑉23) are monitored and the referencevalue Δ𝑉𝑟𝑒𝑓 = Δ𝑉12 − Δ𝑉23 is calculated. A quench eventis detected if the signal Δ𝑉𝑟𝑒𝑓 exceeds e.g. 100 mV within10 ms [10, 11].When a quench-event occurs, the power-supply of theundulator is switched off and the fraction of stored magneticenergy, that has not yet been dissipated in the cryostat, issent to a dump resistor.At SUNDAE1, the maximum allowed voltage of the powersupply during the discharge is 1 kV. Three different dumpresistors having resistance 2.5 Ω, 1.25 Ω and 0.66 Ω will beavailable in order to minimize the decay time for differentnominal current and inductance values of the coils.During the magnet training procedure, the input currentof the coil is increased slowly and quench events due toimperfections of the physical setup are triggered. In absenceFigure 2: Simplified scheme of the distribution of the volt-age taps. The voltage taps marked with crosses are usedby the quench detection system, the other ones are used toidentify the “hot-regions”.of errors in the design of the magnet and in the experimentalsetup for the test, after a quench event the system ends up in amore stable state, thus allowing to increase further the inputcurrent. At the end of the training procedure, the magnethas reached its nominal current value [10].During the training process, it is useful to dispose ofdiagnostics able to detect the hot-regions in the coil. The”hot-regions” are the regions of the magnet where the quenchevent has originated and, therefore, the temperature hasreached higher values.Hot-regions can be detected by monitoring voltagesignals along the coil. For this reason, voltage taps aredistributed along the SCU coil and the voltage differencebetween different portions of the magnet during a quench13th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-THPOPT031MC7: Accelerator TechnologyT10: Superconducting MagnetsTHPOPT0312647ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOIis monitored [11]. Spikes in the voltage readout identifythe hot-regions. At SUNDAE1, 40 voltage taps will beavailable for hot-region diagnostics (see Fig. 2). For a2m-long magnet with 18 mm period length, this roughlycorresponds to one voltage tap every six periods. Thevoltage taps will be connected to IMC CRONOSflex unitswith 40 simultaneously readable channels and a samplingrate per channel of roughly 50 kS/s.CONCLUSION AND OUTLOOKThe advancement of SCU technology has a strategic im-portance for the future development of the European XFELfacility. In particular, the realization of an afterburner for theSASE2 line of the facility has been foreseen. The character-ization of the magnetic field of the novel SCUs is a key stepto understand and evaluate the technology prior to the instal-lation in the beamline. The test-stand SUNDAE1 will allowthe training and characterization of one stand alone coil ina liquid or superfluid Helium bath. In this contribution, wehave presented an overview of the test-stand. The setup ispresently undergoing its procurement phase, while the com-missioning of the cryogenics and diagnostics is foreseen tostart next year. For the commissioning of the test-stand thecharacterization of coils produced within the SCU researchand development program is foreseen.REFERENCES[1] S. Casalbuoni et al., “Superconducting Undulators: FromDevelopment towards a Commercial Product”, in SynchrotronRadiation News, vol. 31, pp. 24–28, 2018. doi:10.1080/08940886.2018.1460171[2] Y. Ivanyushenkov and E. Gluskin, “Development of Supercon-ducting Undulators at the Advanced Photon Source”, ICFABeam Dynamics Newsletter, vol. 78, pp. 8–26, 2019.[3] W. Decking et al., “A MHz-repetition-rate hard X-ray free-electron laser driven by a superconducting linear accelera-tor”, Nature Photonics, vol. 14, pp. 391–397, 2020. doi:10.1038/s41566-020-0607-z[4] R. Brinkmann et al., “Prospects for CW Operation of theEuropean XFEL in Hard X-ray Regime”, in Proc. FEL’14,Basel, Switzerland, Aug. 2014, paper MOP067, pp. 210–214.[5] S. Casalbuoni et al., “A pre-series prototype for the super-conducting undulator afterburner for the European XFEL”,in Proceedings of SRI 2021 to appear in Journal of Physics:Conference Series.[6] B. Marchetti et al., “Liquid Helium vertical test-stand for 2mlong superconducting undulator coils”, in Proceedings of SRI2021 to appear in Journal of Physics: Conference Series.[7] J. E. Baader et al., “SUNDAE2 at EuXFEL: A Test Stand toCharacterize the Magnetic Field of Superconducting Undu-lators”, presented at the IPAC’22, Bangkok, Thailand, Jun.2022, paper THPOPT032, this conference.[8] J. E. Baader et al., “Requirements and limitations of thepulsed wire technique for measuring short-period long undu-lators’ magnetic field”, in Proceedings of SRI 2021 to appearin Journal of Physics: Conference Series.[9] J. E. Baader and S. Casalbuoni, “Magnetic field reconstruc-tion using the pulsed wire method: An accuracy analysis”, inMeasurement, vol. 193, p. 110873, 2020. doi:10.1016/j.measurement.2022.110873[10] A. Grau et al., “Full-scale conduction-cooled superconduct-ing undulator coils - training, stability and thermal behavior”,IEEE Transactions on Applied Superconductivity, vol. 28,no. 3, pp. 1–4, 2018. doi:10.1109/TASC.2018.2791927[11] A. Grau et al., “Characterization of a 30-cm-Long super-conducting undulator coils with the magnetic measurementsystem CASPER II”, IEEE Transactions on Applied Super-conductivity, vol. 26, no. 4, pp. 1–4, 2016. doi:10.1109/TASC.2016.252380613th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-THPOPT031THPOPT031ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI2648MC7: Accelerator TechnologyT10: Superconducting Magnets

SUNDAE1: A Liquid Helium Vertical Test-Stand for 2m Long Superconducting Undulator Coils

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SUNDAE1: A Liquid Helium Vertical Test-Stand for 2m Long Superconducting Undulator Coils

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