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, the test stand SUNDAE1 for the characterization of SCU is being developed. The purpose of SUNDAE1 is the training, tuning and development of new SCU coils by means of precise magnetic field measurements. The experimental setup will allow the characterization of magnets up to 2m in length. These magnets will be immersed in a Helium bath at 4K or 2K temperature. In this article, we describe the experimental setup and highlight its expected performances

Abeghyan, S.

Baader, J.

Barbanotti, S.

Casalbuoni, S.

Di Felice, M.

Eckoldt, H.-J.

Englisch, U.

Grattoni, V.

Grau, A.

Hauberg, A.

Jensch, K.

La Civita, D.

Lederer, S.

Lilje, L.

Marchetti, B.

Ramalingam, R.

Schnautz, T.

Vannoni, M.

Yakopov, M.

Zimmermann, R.

Ziolkowski, P.

English

KITopen

Journal of Physics: Conference SeriesPAPER • OPEN ACCESSConceptual Design of a Liquid Helium VerticalTest-Stand for 2m long SuperconductingUndulator CoilsTo cite this article: B. Marchetti et al 2022 J. Phys.: Conf. Ser. 2380 012027 View the article online for updates and enhancements.You may also likeFeasibility and electromagnetic analysis ofa REBCO superconducting undulatorIbrahim Kesgin, Matthew Kasa, CharlesDoose et al.-A review of magnetic field measurementsof full scale conduction cooledsuperconducting undulator coilsSara Casalbuoni-Current status and future perspectives ofaccelerator-based x-ray light sourcesTakashi Tanaka-This content was downloaded from IP address 141.52.248.4 on 16/02/2023 at 12:24Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing Ltd14th International Conference on Synchrotron Radiation Instrumentation (SRI 2021)Journal of Physics: Conference Series 2380 (2022) 012027IOP Publishingdoi:10.1088/1742-6596/2380/1/0120271Conceptual Design of a Liquid Helium VerticalTest-Stand for 2m long Superconducting UndulatorCoilsB. Marchetti1, S. Abeghyan1, J. Baader1, S. Barbanotti2, S.Casalbuoni1, M. Di Felice1, H.-J. Eckoldt2, U. Englisch1, V.Grattoni1, A. Grau3, A. Hauberg2, K. Jensch2, D. La Civita1, S.Lederer2, L. Lilje2, R. Ramalingam2, T. Schnautz2, M. Vannoni1, M.Yakopov1, R. Zimmermann2, P. Ziolkowski11 European XFEL GmbH, 22869 Schenefeld, Germany2 Deutsches Elektronen-Synchrotron, 22607 Hamburg, Germany3 Karlsruher Institut fuer Technologie, D-76021 Karlsruhe, GermanyE-mail: barbara.marchetti@xfel.euAbstract. Superconducting Undulators (SCUs) can produce higher photon flux and cover awider photon energy range compared to permanent magnet undulators (PMUs) with the samevacuum gap and period length.To build the know-how to implement superconducting undulators for future upgrades of theEuropean XFEL facility, the test stand SUNDAE1 for the characterization of SCU is beingdeveloped. The purpose of SUNDAE1 is the training, tuning and development of new SCUcoils by means of precise magnetic field measurements.The experimental setup will allow the characterization of magnets up to 2m in length. Thesemagnets will be immersed in a Helium bath at 4K or 2K temperature.In this article, we describe the experimental setup and highlight its expected performances.1. IntroductionSuperconducting undulator technology enables achieving stronger magnetic peak fields thanpermanent magnet technology, considering the same period length and vacuum gap in theundulator [1, 2].In the recent years, SCUs have been succesfully employed in synchrotron radiation sources [3, 4].Similarly to what has been demonstrated for synchrotrons, the use of SCUs can potentiallyimprove the performance and flexibility of advanced FELs. In particular by working at shortundulator periods superconducting magnet technology would allow reaching higher photonenergies while keeping a wide range of tunability of the setpoint. That is why the implementationof SCUs is being considered by several FEL projects world-wide [5, 6].The advancement of SCU technology has a strategic importance also for the future developmentof the European XFEL facility. The extension of the energy range of the radiation towardshigher values would fully exploit the high electron energy beam capability of the accelerator [7].Moreover, this development can be considered complementary to the study on the upgrade ofthe XFEL linac for continuous wave (CW) operation [8]. CW operation at European XFEL14th International Conference on Synchrotron Radiation Instrumentation (SRI 2021)Journal of Physics: Conference Series 2380 (2022) 012027IOP Publishingdoi:10.1088/1742-6596/2380/1/0120272is considered possible only with reduced electron beam energy. Specifically the electron beamenergy will be limited to about 7 GeV, while the present maximum value is 17.5 GeV. Thereplacement of the existing PMUs beamline with SCUs having shorter undulator periods wouldenable the 7 GeV linac to cover the same photon energy range as the present accelerator.For all those reasons, a project for the realization of a SCU afterburner for the SASE2 line isbeing set-up. The main parameters and specifications for a pre-series prototype module (S-PRESSO) of such afterburner have been presented in [9].Numerical simulations [10, 11] show that ensuring high precision manufacturing of the coils andtheir relative alignment are important aspects for the development of the prototype module.An early and fast characterization of the stand alone coil, before installation in the final cryostat,would allow a prompt evaluation of the magnet properties, as routinely pursued in other facilitiesworld-wide [12, 13]. Magnetic correction procedures, such as shimming [14] or discard of the coilcould possibly be applied early enough to guarantee proper performances of the final cryomodule.Consequently the test stand SUNDAE1 (Superconducting UNDulAtor Experiment 1) for thecharacterization of SCU has been proposed. Such test-stand will be located in the DESYcampus. The purpose of SUNDAE1 is the training, tuning and characterization of new SCUcoils by means of magnetic field measurements.A second test-stand, named SUNDAE2, for the characterization of the final afterburnercryomodules, is also under construction in the same experimental area. In this second test-stand the characterization of the module using the pulse-wire technique is also foreseen [15, 16].In this article we will describe the present design concept of SUNDAE1 and comment on theexpected performances in terms of magnetic field characterization.2. Conceptual Design of SUNDAE1Figure 1 shows the schematic drawing of SUNDAE1. The coils of the SCUs will be immersedin a liquid or superfluid Helium bath. Two Hall probes will be installed on a sledge driven by aLinear Motion System (LMS). The sledge will be able to move between the two coils constitutinga SCU. Its thickness is 4 mm, thus allowing the characterization of coils having a magnetic gapdown to 6 mm. The range of the scan of the sledge is 2.3 m. Coils having maximum length of 2m and 15 cm field tails on each side of them can be therefore characterized by the Hall probes.2.1. Magnetic Field CharacterizationIn [9] the design-parameters of the coils of S-PRESSO have been presented. The measurementof variations of the magnetic field profile ∆B/B ≪ 10−3 requires a resolution of the absolutevalue of the magnetic field better than 1.8 mT. Moreover, in order to be able to resolve errorson the manufacturing of the poole/groove width of the coil of the order of 10 µm, a resolutionof the Hall-probe position of roughly 1 µm is wished.The orientation of the Hall-probes shown in Fig. 1 allows the characterization of the y-componentof the magnetic field of the coils, By. The resolution of the measurement of the magnetic field isof the order of few µT but its accuracy is limited by the error on the calibration of the Hall probe.The cryogenic Hall-probes that will be used in SUNDAE1 have been calibrated in a physicalproperties measurement system of the Institute at KIT. The Hall-probe read-out voltage, HV,versus the magnetic field, By, was recorded under fixed temperatures (4.2 K, 30 K, and 77 K) inthe range from -5 T to +5 T. The measured data have been divided in regions. For each regiona polynomial fit of the data By versus HV has been performed. Such measurements allowed theestimation of the calibration error, which is in the order of 0.1 mT.Fulfilling the requirement on the precision of the positioning of the Hall-probe is not trivial due toa number of systematic effects acting on the system both inside and outside the cryostat. Outsidethe cryostat, environmental temperature variations of few degrees and background vibrationsare expected. Inside the cryostat, a systematic variation of the length of the rod while scanning14th International Conference on Synchrotron Radiation Instrumentation (SRI 2021)Journal of Physics: Conference Series 2380 (2022) 012027IOP Publishingdoi:10.1088/1742-6596/2380/1/0120273Figure 1. Scheme of SUNDAE1. The SCUs are immersed in a liquid or superfluid Heliumbath. Two Hall probes will be installed on a sledge placed at the edge of a rod connected to aLinear Motion System (LMS). The movement of the sledge is constrained by two rails parallel tothe longitudinal axis of the SCU. The coils are supported by a structure anchored on a plate ofthe Lid. Several thermal shields guarantee low heat load from the surroundings to the cryogenicvessel. The magnet is connected to the power supply outside the cryostat through current leads.Several feedthroughs at the Lid allow the connection of diagnostics sensors (temperature sensors,voltage taps, Hall probes etc.) to the outside of the cryostat.the magnetic field will be present. The rod supporting the sledge and Hall-probe is indeedpartially immersed in liquid Helium. The fraction of the rod that is immersed in liquid Heliumdepends on the z location of the Hall-probe. The elongation or contraction of the rod by fewmm during the scan due to the different temperature gradient influences the z position of theHall-probe with respect to the SCU.The LMS will be equipped with a single axis vertical translator with 2400 mm of travel-range.The system is presently under development by the company Hositrad and has been specified tohave resolution, accuracy and repeatability better or equal to 1 µm. The encoder of the LMS isbeeing designed to account for temperature fluctuations and vibrations outside the cryostat.The systematic error caused by the contraction/elongation of the rod inside the cryostat is morecomplex to be managed. Initially we foresee to correct the data analysis of the measured data bymaking use of the signal read by two Hall probes and by modeling the effect of the contractionof the rod analytically. More details on the data analysis will be included in future publications.Later on we plan to implement the direct measurement of the position of the sledge by using aninterferometer. This solution requires an upgrade of the experimental setup and will thereforebe implemented in the mid term future.The installation of an interferometer is the most reliable method to measure with high resolutionof the position of the Hall-probe. In this concept (illustrated in Fig. 2), the rod holding thesledge is replaced by two hollow tubes containing independent in-vacuum interferometers. The14th International Conference on Synchrotron Radiation Instrumentation (SRI 2021)Journal of Physics: Conference Series 2380 (2022) 012027IOP Publishingdoi:10.1088/1742-6596/2380/1/0120274interferometers are constituted by optical fibers, sensor heads and retro-reflectors. The sensorheads are interfaced with a pico-scale interferometer. The setup allows the simultaneous onlinemonitoring of the length of the first and second hollow tubes and therefore online measurementof the position of the sledge. This solution presents many technical challenges, such as the factthat the space for the retroreflectors is quite limited and guaranteeing the mechanical stabilityof the setup is not trivial. The technical design is presently under study.Figure 2. Sketch of the concept for the interferometric measurement of the sledge position. Therods holding the sledge are replaced by two hollow tubes containing independent interferometers.Figure 3. Simplified scheme of the distribution of the voltage taps. The voltage taps markedwith crosses are used by the quench detection system, the other ones are used to identify the”hot-regions”.2.2. Quench Events and Magnet TrainingBeside its application for the final magnetic characterization of the SCUs, SUNDAE1 will alsobe used for the training of coils. Quench events happening when the coil is initially brought intooperation have to be managed in a safe way. We define quench event as the transition from thesuperconducting to the normal conducting state of a superconducting magnet [18].A quench event leads to the appearance of voltage, temperature increase, differential thermalexpansion and electro-magnetic forces, as well as cryogen pressure increase and expulsion within14th International Conference on Synchrotron Radiation Instrumentation (SRI 2021)Journal of Physics: Conference Series 2380 (2022) 012027IOP Publishingdoi:10.1088/1742-6596/2380/1/0120275the cryostat. During a quench event, the magnetic energy stored in the magnet, and the powerprovided by the power supply, are converted into heat in a percentage that can go from a smallfraction to its totality.In order not to damage the superconducting coil, the power supply of the coil has to be switchedoff immediately after the detection of a quench event. For this reason, the power supply isconnected to quench detection system.For the detection of the quench event, the three voltage taps marked with crosses in Fig. 3 areused. The voltage difference between points 1 and 2 (∆V12) and the one between points 2 and3 (∆V23) are monitored and the reference value ∆Vref = ∆V12 −∆V23 is calculated. A quenchevent is detected if the signal ∆Vref exceeds a given threshold within a specific time-interval,e.g. 100 mV within 10 ms. We have chosen to use power supplies and quench detection systemproduced by the company JEMA. The system can detect voltage thresholds as low as 1 mV in1 ms.When a quench-event occurs, the power-supply of the undulator is switched off and the storedmagnetic energy is sent to a dump resistor.At SUNDAE1, the maximum allowed voltage of the power supply during the discharge is 1 kV.Three different dump resistors having resistance 2.5 Ω, 1.25 Ω and 0.66 Ω will be available inorder to minimize the decay time for different nominal current and inductance values of the coils(see Table 1).During the magnet training procedure, the input current of the coil is increased slowly andTable 1. Decay time of the current after a quench for a coil having inductance L = 1 H, differentnominal current and corresponding optimized dump resistors. The following symbols are used:I is nominal current of the coil, L is the inductance of the coil, R is the resistance of the dumpresistor, τ = L/R is the decay time to half the nominal current value and 5τ is the current decaytime to less than 1 % nominal current value.I[A] R[Ω] τ [s] 5τ [s]400 2.5 0.4 2800 1.25 0.8 41500 0.660 1.5 7.5quench events due to imperfections of the physical setup are triggered. In absence of errors inthe design of the magnet and in the experimental setup for the test, after a quench event thesystem ends up in a more stable state, thus allowing to increase further the input current. Atthe end of the training procedure, the magnet has reached its nominal current value [19].During the training process, it is useful to dispose of diagnostics able to detect the hot-regions inthe coil. The ”hot-regions” are the regions of the magnet where the quench event has originatedand, therefore, the temperature has reached higher values.Hot-regions can be detected by monitoring voltage signals along the coil. For this reason, voltagetaps are distributed along the SCU coil and the voltage difference between different portionsof the magnet during a quench is monitored [20]. Spikes in the voltage readout identify thehot-regions. At SUNDAE1, 40 voltage taps will be available for hot-region diagnostics (see Fig.3). For a 2m-long magnet with 18 mm period length, this roughly corresponds to one voltagetap every six periods. The voltage taps will be connected to imc CRONOSflex units with 40simultaneously readable channels and a sampling rate per channel of roughly 50 kS/s.14th International Conference on Synchrotron Radiation Instrumentation (SRI 2021)Journal of Physics: Conference Series 2380 (2022) 012027IOP Publishingdoi:10.1088/1742-6596/2380/1/01202763. Conclusion and OutlookThe advancement of SCU technology has a strategic importance for the future development ofthe European XFEL facility. In particular, the realization of an afterburner for the SASE2 lineof the facility has been foreseen. The characterization of the magnetic field of the novel SCUs isa key step to understand and evaluate the technology prior to the installation in the beamline.The test-stand SUNDAE1 will allow the training and characterization of one stand alone coilin a liquid or superfluid Helium bath. In this contribution, we have shown the conceptualdesign of the test-stand and we have described the specifications of the main parameters. Thesetup is presently undergoing its technical design and procurement phase. The commissioningof cryogenics and diagnostics is foreseen to start in 2023.References[1] P. Elleaume, J. Chavanne, and B. Faatz. Design considerations for a 1 angstrom sase undulator. NuclearInst. and Methods in Physics Research A, 455:503–523, 2000.[2] J. Bahrdt and E. Gluskin. Cryogenic permanent magnet and superconducting undulators. Nuclear Inst.and Methods in Physics Research A, 907:149–168, 2018.[3] S. Casalbuoni, N. Glamann, A. Grau, T. Holubek, D. Saez de Jauregui, S. Bauer, C. Boffo, T. Gerhard,M. Turenne, and W. Walter. Superconducting undulators: From development towards a commercialproduct. Synchrotron Radiation News, 31(3):24–28, 2018.[4] Y. Ivanyushenkov and E. Gluskin. Development of superconducting undulators at the advanced photonsource. ICFA Beam Dynamics Newsletter, 78:8–26, 2019.[5] Lcls strategic facility development plan. SLAC National Accelerator Laboratory, 2020.[6] Qisheng Tang, Qiaogen Zhou, Jingmin Zhang, Yi Ding, Yongmei Wen, Maofei Qian, and Jidong Zhang.Cooling design for the magnetic structure of shine superconducting undulator. IEEE Transactions onApplied Superconductivity, 30(4):1–4, 2020.[7] W. Decking et al. A mhz-repetition-rate hard x-ray free-electron laser driven by a superconducting linearaccelerator. Nature Photonics, 14:391–397, 2020.[8] R. Brinkmann et al. Prospects for cw operation of the european xfel in hard x-ray regime. In Proceedingsof FEL 2014. 2014.[9] S. Casalbuoni et al. A pre-series prototype for the superconducting undulator afterburner for the europeanxfel. In This conference proceedings. 2022.[10] B. Marchetti et al. Study of the tolerances for superconducting undulators at the european xfel. thisconference proceedings.[11] V. Grattoni et al. An analytical study to determine the mechanical tolerances for the afterburnersuperconducting undulators at eu-xfel. In This conference proceedings. 2022.[12] E. Mashking et al. Magnetic field test facility for superconductive undulator coils. IEEE Trans. Appl.Supercond., 18 (2), 2008.[13] D. Harder et al. 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Conceptual Design of a Liquid Helium Vertical Test-Stand for 2m long Superconducting Undulator Coils

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Conceptual Design of a Liquid Helium Vertical Test-Stand for 2m long Superconducting Undulator Coils

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