In order to produce high-brilliance hard X-ray photon beams, permanent magnet short-period undulators are applied in many synchrotron facilities worldwide. Superconducting undulators (SCUs) have the potential to further increase the spectral range and brilliance. At the ANKA (˚ANgstrom source KArlsruhe) synchrotron radiation facility, we thus pursue an SCUfocused research and development program in a collaboration between the Karlsruhe Institute of Technology (KIT) and Babcock Noell GmbH (BNG), the status of which is reported in this contribution. The effort to develop instruments and tools for quality assessment of the magnetic field of SCUs and to enhance the understanding of beam heat load mechanisms in a cold bore is also described

Baumbach, T.

Boffo, C.

Casalbuoni, S.

De Jauregui, D.S.

Gerstl, S.

Grau, A.

Hagelstein, M.

Heske, C.

Holubek, T.

Walter, W.

Journal of Physics Conference Series

S Casalbuoni

T Baumbach

S Gerstl

A Grau

M Hagelstein

C Heske

T Holubek

D Saez de Jauregui

C Boffo

W Walter

Crossref

Status of the development of superconducting undulators at ANKA

De Jauregui, D. S.

KITopen

Journal of Physics: Conference SeriesStatus of the development of superconductingundulators at ANKATo cite this article: S Casalbuoni et al 2013 J. Phys.: Conf. Ser. 425 032008 View the article online for updates and enhancements.Related contentShort Period Undulators for Storage Ringsand Free Electron LasersJ Bahrdt and Y Ivanyushenkov-Development of a superconductingundulator for the APSY Ivanyushenkov, M Abliz, C Doose et al.-Beam heat load due to geometrical andresistive wall impedance in COLDDIAGS Casalbuoni, M Migliorati, A Mostacci etal.-Recent citationsA novel concept of high temperaturesuperconducting undulatorT Holubek et al-This content was downloaded from IP address 129.13.72.197 on 18/04/2018 at 11:48Status of the development of superconductingundulators at ANKAS Casalbuoni1, T. Baumbach1, S. Gerstl1, A. Grau1, M. Hagelstein1,C. Heske1, T. Holubek1, D. Saez de Jauregui1, C. Boo2, W. Walter21 Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1,76344 Eggenstein-Leopoldshafen, Germany2Babcock Noell GmbH, Alfred Nobel Str. 20, 97080 Wurzburg, GermanyE-mail: sara.casalbuoni@kit.eduAbstract. In order to produce high-brilliance hard X-ray photon beams, permanent magnetshort-period undulators are applied in many synchrotron facilities worldwide. Superconductingundulators (SCUs) have the potential to further increase the spectral range and brilliance. Atthe ANKA (ANgstrom source KArlsruhe) synchrotron radiation facility, we thus pursue an SCU-focused research and development program in a collaboration between the Karlsruhe Instituteof Technology (KIT) and Babcock Noell GmbH (BNG), the status of which is reported in thiscontribution. The eort to develop instruments and tools for quality assessment of the magneticeld of SCUs and to enhance the understanding of beam heat load mechanisms in a cold boreis also described.1. IntroductionFor the production of synchrotron radiation with highest brilliance, third generation synchrotronsources make use of insertion devices (IDs). The state-of-the-art available for IDs today isbased on permanent magnet technology, with magnet blocks placed inside the vacuum of thestorage ring. Following an initial proposal at SPring-8 [1], the concept of Cryogenic PermanentMagnet Undulators (CPMU) evolved from in-vacuum undulators is presently considered forseveral synchrotron light sources. Superconducting undulators (SCUs) can reach, for the samegap and period length, higher elds even with respect to CPMU devices, allowing to increasethe spectral range and brilliance [2].At the ANKA (ANgstrom source KArlsruhe) synchrotron radiation facility, we pursue aresearch and development program for such superconducting IDs. The collaboration betweenANKA and BNG (Babcock Noell GmbH) foresees the development of two planar devices, oneof them with switchable period length.2. A new superconducting undulator demonstrator for ANKAA new SCU demonstrator to be tested at ANKA is currently under development [3]. Thesystem is cooled by 4 cryocoolers that provide a total refrigerating power of 5 W at 4 K. TheSCU demonstrator coils have a period length of 15 mm, with a total of 100.5 full periodsplus an additional matching period at each end. The coils are fabricated using a commerciallyavailable NbTi superconductor. The operating magnetic gap is 8 mm, with a beam-stay-clear11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012) IOP PublishingJournal of Physics: Conference Series 425 (2013) 032008 doi:10.1088/1742-6596/425/3/032008Published under licence by IOP Publishing Ltd 1(vacuum gap) of 7 mm. The beam vacuum chamber is quite challenging since, together withthe requirements for a UHV radiation hard environment and the necessity to keep the resistivelosses as low as possible [4], it needs to open to 16 mm during electron beam injection andenergy ramping in the ANKA storage ring.The eld calculated from the Radia [5] simulations, using the pole height (25m) and thehalf period length deviations (5m) measured for the two coils at room temperature [3], hasan r.m.s phase error of 5:6 over 186 poles [6]. Local eld measurements of the 1.5 m longcoils were performed in a liquid helium bath cryostat at CERN. The 1.5 m long coils reached855 A/mm2 [6] allowing to reach a peak eld on axis at 8 mm magnetic gap of 0.69 T. Themeasured eld shows, after mechanical shimming, an r.m.s. phase error of 7:4 on 106 poles, overa length of 0.795 m [6]. The expected ux at ANKA, calculated with B2E [7] from the measuredshimmed eld is higher than the one of an ideal CPMU, e.g., as designed for the Diamond LightSource (DLS) [8, 9]. The use of mechanical shims to reduce the bimetallic eect, applicable toxed gap undulators, together with further adjustment to keep the gap uniform to within 40m, would make it possible to reach an r.m.s phase error of  3:5 without additional correctioncoils. For the installation of the SCU demonstrator at ANKA, where the gap is movable, BNGwill prebend the coils at room temperature to try to compensate the bending measured at 4 K.Because of the lack of a shimming technique for SCUs easily applicable to long devices (> 1 m)it is of course important to evaluate the real requirements on the r.m.s. phase errors for presentand future applications. The ux calculated with B2E [7] by the eld simulated with Radiataking into account the mechanical tolerances measured at room temperature and with an r.m.sphase error of 5:6 is reduced not more than 10% at the harmonics with respect to the oneproduced by the ideal eld. This is demonstrated up to the 15th harmonic in the upper plot ofFig. 1. We can conclude that an r.m.s. phase error of  6 is sucient (ux reduction < 25%)for the existing and planned storage rings up to the 15th harmonic [9].1 3 5 7 9 11 13 150.50.60.70.80.91.0ANKAslit 4mmx0.9mmslit 40 mx9 mDLSslit 1.2mmx0.6mmslit 12 mx6 mMAXIVslit 0.68mmx0.64mmslit 6.8 mx6.4 m  Relative intensityHarmonic numberFigure 1. Ratio of the ux produced by the eld simulated with Radia taking into account themechanical tolerances measured at room temperature and with an r.m.s phase error of 5:6, tothe one from an ideal eld at the dierent harmonics for ANKA, the DLS, and MAXIV [9].3. Superconducting undulator wigglerSwitching between an 18 mm period undulator and a 54 mm period length wiggler is foreseen forthe source of the planned IMAGE beamline at ANKA. At CASPERI (Characterisation Setupfor Phase Error Reduction, see Sect. 5.1) [11] we demonstrated the feasibility of period lengthswitching using a 9 pole mock-up designed and manufactured by BNG and showed that thereis no need to train the magnet again after each switch [10].In order to use only one power supply instead of two for the two circuits, thus reducingthe thermal input to the device, work is ongoing at ANKA to develop a conduction-cooled superconducting switch (SCS). Conduction-cooled cryogen-free IDs as the ones under11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012) IOP PublishingJournal of Physics: Conference Series 425 (2013) 032008 doi:10.1088/1742-6596/425/3/0320082development at ANKA make use of cryocoolers, which typically have a cooling power of 1-1.5 Watts at 4 K. For this reason, our application requires an SCS which must not dissipate morethan a fraction of a Watt. A rst successful test in an ad hoc conduction-cooled environmentat CASPERI has been performed, demonstrating a minimum power dissipation of 200 mW perheater [12]. We believe that this value can be further reduced: additional tests are foreseen inthe cryogen free environment in the facility CASPERII (see Sect. 5.1) [13].4. New materialsThe \work horse"wire material for superconducting magnets are multilament NbTi wires, whichtoday are also used for superconducting IDs. Even higher magnetic elds can be reached by usinga conductor with enhanced critical current density, such as a NbTi wire with articial pinningcenters (APC), developed by SupraMagnetics, Inc. [14] and not yet commercially available. Aracetrack coil has been built and measured to study the possible use of NbTi APC wire inSCUs [15].Promising for future applications in SCUs are HTS (High Temperature Superconductor)tapes. Their engineering current density is rapidly increasing and they can be operated at highertemperatures than NbTi, allowing to sustain higher beam heat loads. HTS tapes can be usedfor planar SCUs in geometries similar to the ones used for NbTi wire. A short mock-up has beendesigned and manufactured by BNG [16] and tested in the facility CASPERI at ANKA/KIT,at 4 K reaching similar results as obtained with the new SCU demonstrator. Together with thegroup of W. Goldacker (Institute of Technical Physics, KIT) we follow at ANKA the proposal ofS. Prestemon et al. [17] of an HTS tape stacked undulator for free electron lasers applications.The concept is particularly promising for narrow-gap, short period (< 10 mm) regimes. Stillopen issues in both the above described applications of HTS tape to SCUs are the quenchdetection and protection, radiation damage, engineering current density as a function of themagnetic eld, stress and geometry, test eld accuracy and the joint resistance of 50   100nano-Ohm cm2 [18]. This last point could be solved for a planar HTS SCU by using a windingscheme with no joints.5. Tools and instruments for R&D5.1. Magnetic eld characterizationCASPER I is an operating vertical cryostat in which coils with maximum dimensions of 35 cmlength and 30 cm diameter can be immersed in liquid helium for testing [11]. The magnetic eldalong the beam axis is measured by Hall probes xed to a sledge and moved by a linear stage.The eld and position precision are B < 1 mT and z < 3m. With CASPER I, we cantest new winding schemes, new superconducting materials and wires, and new eld-correctiontechniques.CASPER II is a horizontal cryogen-free test stand that will be used to perform qualitycertication (max. length 1500 mm, max. diameter 500 mm) of new superconducting IDs.It will also serve to test small prototype coils in a cryogen free environment. CASPER II iscurrently under construction. Quench tests performed with a 10-plate mock-up successfullyconrmed its functionality, already demonstrated in the nal acceptance test of the device [13].In CASPER II, the magnetic eld along the beam axis is measured by Hall probes xed to asledge and moved by a linear stage. The precisions are B < 1 mT and z < 1m. Fieldintegral measurements will be performed using the stretched wire technique.5.2. Cold vacuum chamber for diagnosticsWith the aim of measuring the beam heat load on a cold bore, needed to specify the cooling powerfor the cryogenic design of superconducting IDs, and in order to gain a deeper understandingin the beam heat load mechanisms, a cold vacuum chamber for diagnostics (COLDDIAG)was built [19]. We are oering its installation in dierent synchrotron light sources with11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012) IOP PublishingJournal of Physics: Conference Series 425 (2013) 032008 doi:10.1088/1742-6596/425/3/0320083dierent energies and beam characteristics. COLDDIAG was installed in the storage ring at theDiamond Light Source in November 2011. With the equipped instrumentation, which includestemperature sensors, pressure gauges, mass spectrometers, as well as retarding eld analyzers,it is possible to measure the beam heat load, total pressure, gas content, as well as the ux ofelectrons and/or ions hitting the chamber walls. Preliminary results show a superposition oflinear and quadratic behavior of the beam heat load as a function of the average beam current.The measured beam heat load of 8.2 W at 250 mA is almost two orders of magnitude largerthan the predicted value from resistive wall heating calculations (0.1-0.2 W, depending on thepurity of the copper coating of the liner). The small, but visible eect of the solenoid on thetemperature distribution points to electron bombardment as at least one component of the beamheat load observed. Currently, the design of the liner thermal transition is being optimized forfurther installation in a third-generation synchrotron facility [20].AcknowledgmentsSC would like to thank J. Chavanne (ESRF) for useful advice on the program B2E and R.Walker (DLS) for detailed discussions on the eects of phase errors on the ux.References[1] Hara T, Tanaka T, Kitamura H, Bizen B, Marchal X, Seike T, Kohda T and Matsuura Y 2004 Phys. Rev.ST Accel. Beams 7, 050702[2] Casalbuoni S, Baumbach T, Gerstl S, Grau A, Hagelstein M, Heske C, Holubek T, Saez de Jauregui D, BooC and Walter W 2012 Proc. ICFA Workshop on Future Light Sources (Newport News, VA)[3] Boo C, Walter W, Baumbach T, Casalbuoni S, Gerstl S, Grau A, Hagelstein M, Saez de Jauregui D 2011IEEE Trans. on Appl. Supercond. 21-3,1756-1759[4] Saez de Jauregui D, Baumbach T, Casalbuoni S, Grau A, Gerstl S, Hagelstein M, Heske C, Holubek T,Krause B, Seiler A, Stankov S, Weinhardt L, Boo C, Antoine C and Boudigou Y 2012 Proc. Int. Part.Acc. Conf. (New Orleans, LA)[5] Chubar O, Elleaume P and Chavanne J 1998 J. Synchrotron Rad. 5, 481[6] Casalbuoni S, Baumbach T, Gerstl S, Grau A, Hagelstein M, Saez de Jauregui D, Boo C, Steinmann J andWalter W 2011 IEEE Trans. on Appl. Supercond. 21-3,1760-1763[7] Elleaume P and Marechal X 1991 Report ESRF-R/ID-9154[8] Ostenfeld C W and Pedersen M 2010 Proc. Int. Part. Acc. Conf. (Kyoto, Japan)[9] Casalbuoni S, Baumbach T, Gerstl S, Grau A, Hagelstein M, Heske C, Holubek T, Saez de Jauregui D, BooC and Walter W 2012 Proc. Int. Part. Acc. Conf. (New Orleans, LA)[10] Grau A, Baumbach T, Casalbuoni S, Gerstl S, Hagelstein M, Saez de Jauregui D, Boo C and Walter W2011 IEEE Trans. on Appl. Supercond. 21-3, 1596-1599[11] Mashkina E, Grau A, Schneider Th, Bernhard A, Casalbuoni S, Hagelstein M, Kostka B, Rossmanith R,Steens E, Wollmann D and T. Baumbach 2008 Journal of Physics: Conf. Series 97 012020[12] Holubek T, Baumbach T, Casalbuoni S, Gerstl S, Grau A, Hagelstein M, Saez de Jauregui D, Boo C andWalter W 2012 Proc. Int. Part. Acc. Conf. (New Orleans, LA)[13] Grau A, Baumbach T, Casalbuoni S, Gerstl S, Hagelstein M, Holubek T and Saez de Jauregui D 2012accepted for publication in IEEE Trans. on Appl. Supercond.; Grau A, Baumbach T, Casalbuoni S, GerstlS, Hagelstein M, Holubek T and Saez de Jauregui D 2012 Proc. Int. Part. Acc. Conf. (New Orleans, LA)[14] http://www.supramagnetics.com/[15] Holubek T, Casalbuoni S, Gerstl S, Grau A, Saez de Jauregui D, Klaser M, Schneider Th, Motowidlo L 2012accepted for publication in Physics Procedia.[16] Boo C, http://www.maxlab.lu.se/usermeeting/2010/sessions/IDmax2010/[17] Prestemon S, Arbelaez D, Davies S, Dietderich D R, Lee D, Minervini F and Schlueter R D 2011 IEEETrans. on Appl. Supercond. 21-3, 1880-1883[18] Selvamanickam V, http://www.itep.kit.edu/hts4fusion2011[19] Casalbuoni S, Baumbach T, Gerstl S, Grau A, Hagelstein M, Saez de Jauregui D, Boo C, Sikler G, BaglinV, Cimino R, Commisso M, Spataro B, Mostacci A, Cox M, Schouten J, Wallen E, Weigel R, Clarke J,Scott D, Bradshaw T, Shinton I and Jones R 2011 IEEE Trans. on Appl. Supercond. 21-3, 2300-2303[20] Gerstl S, Baumbach T, Casalbuoni S, Grau A, Hagelstein M, Saez de Jauregui D, T. Holubek, Bartolini R,Cox M, Schouten J, Walker R, Migliorati M, Spataro B and Shinton I 2012 Proc. Int. Part. Acc. Conf.(New Orleans, LA)11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012) IOP PublishingJournal of Physics: Conference Series 425 (2013) 032008 doi:10.1088/1742-6596/425/3/0320084

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Status of the development of superconducting undulators at ANKA

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