Bastian, Y.

Bernhard, A.

Bonura, M.

Bordini, B.

Bortot, L.

Favre, M.

Lindstrom, B.

Mentink, M.

Monteuuis, A.

Mueller, A.-S.

Oslandsbotn, A.

Schmidt, R.

Senatore, C.

Siemko, A.

Stachon, K.

Usoskin, A.

Vaananen, M.

Verweij, A.

Will, A.

Wollmann, D.

KITopen

BEAM IMPACT EXPERIMENT OF 440GeV/p PROTONS ONSUPERCONDUCTING WIRES AND TAPES IN A CRYOGENICENVIRONMENT∗A. Will†1,2, Y. Bastian 1, A. Bernhard2, M. Bonura3, B. Bordini1, L. Bortot1, M. Favre1, B. Lindstrom1,M. Mentink1, A. Monteuuis1, A.-S. Mueller2, A. Oslandsbotn1, R. Schmidt1, C. Senatore3,A. Siemko1, K. Stachon1, A. Usoskin4, M. Vaananen1, A. Verweij1, D. Wollmann1,1 CERN, Geneva, Switzerland, 2 Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany3 University of Geneva, Switzerland, 4 BRUKER HTS GmbH, GermanyAbstractThe superconducting magnets used in high energy parti-cle accelerators such as CERN’s LHC can be impacted bythe circulating beam in case of speciﬁc failure cases. Thisleads to interaction of the beam particles with the magnetcomponents, like the superconducting coils, directly or viasecondary particle showers. The interaction leads to energydeposition in the timescale of microseconds and induceslarge thermal gradients within the superconductors in theorder of 100 K/mm. To investigate the eﬀect on the super-conductors, an experiment at CERN’s HiRadMat facilitywas designed and executed, exposing short samples of Nb-Tiand Nb3Sn strands as well as YBCO tape in a cryogenicenvironment to microsecond 440 GeV/p proton beams. Theirradiated samples were extracted and are being analyzed fortheir superconducting properties, such as the critical trans-port current. This paper describes the experimental setupas well as the ﬁrst results of the visual inspection of thesamples.INTRODUCTIONIn order to understand the damage limits of supercon-ducting accelerator magnets due to direct beam impact, anexperimental road-map was set up, as described in [1, 2].Within this road-map several experiments, with and withoutbeam, have been launched to study the degradation of Nb-Tiand Nb3Sn based superconducting strands due to ultra shortand localized energy deposition. This paper describes theﬁrst direct beam impact experiment in cryogenic environ-ment on Nb-Ti, Nb3Sn and YBCO superconductors.The low temperature superconductors (LTS) used in themagnets of CERN’s LHC and its upgrade, the HL-LHC, arebased on Nb-Ti and Nb3Sn. Therefore, in the beam exper-iment 50mm long samples of the LHC dipole type Nb-Tistrands with a diameter of 0.825mm [3] and the HL-LHCtype RRP® Nb3Sn strand with a diameter of 0.85mm [4]were used. The Nb3Sn short strand samples were reacted inquartz glass tubes, to guarantee perfect strand straightnessand ease the alignment in the sample holder. The cross sec-tion of both strand types are shown in Fig. 1. The coppermatrix and the ﬁlaments are clearly visible. Furthermore,∗ Supported by the HL-LHC project and the Wolfgang Gentner Programmeof the German Federal Ministry of Education and Research† andreas.will@cern.chFigure 1: Nb3Sn∗ (top left) and Nb-Ti strand∗ (top right) aswell as short sample of YBCO-tape (bottom), used in theexperiment. ∗Image Courtesy M. Meyer, CERN.Figure 2: Side view of the assembled LTS tape sample holder.The setup from diﬀerent blocks of copper is clearly visible.The blue arrow indicates the proton beam direction.60mm long samples of high temperature superconductor(HTS) tape based on YBCO were used. This tape was pro-vided by BRUKER and one sample is shown in Fig. 1.EXPERIMENTAL SETUPSample HoldersThe two sample holders consist of blocks of copper, allow-ing easy sample mounting. The blocks of the ﬁrst sampleholder have slits adapted to the geometry of the HTS tapes.10th Int. Particle Accelerator Conf. IPAC2019, Melbourne, Australia JACoW PublishingISBN: 978-3-95450-208-0 doi:10.18429/JACoW-IPAC2019-THPTS066THPTS0664264ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2019).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOIMC7: Accelerator TechnologyT10 Superconducting MagnetsFigure 3: Energy deposition in the sample holders alongthe beam axis, calculated with FLUKA [5, 6]. The corre-sponding peak temperatures reached in copper are indicatedon the right axis. The red dots indicate the position of theNb-Ti and Nb3Sn strand samples, the blue bars indicate theposition of the YBCO tapes.The blocks of the second sample holder have grooves de-signed to ﬁx the Nb-Ti and Nb3Sn strands. Figure 2 showsthe fully assembled sample holder for the LTS strands. TheLTS sample holder houses 50 short strand samples, splitinto ﬁve batches (B1-5 in Fig. 2) of 10 samples each. Intotal, three batches of Nb3Sn strands and two batches ofNb-Ti strands were mounted in the LTS-sample holder. Foreach batch, the samples are installed along the beam axis.Therefore, they are impacted simultaneously by one beampulse. The HTS sample holder houses six batches of sevenHTS-tape samples, i.e. a total of 42.The energy deposition in the sample holders and sampleswas calculated using FLUKA [5,6] and is shown along thebeam axis for one beam pulse in Fig. 3. The equivalentpeak temperatures reached in the copper varied between300K and 1200K with a spacing of about 100K betweenthe samples. This peak temperatures are calculated underthe assumption of instantaneous energy deposition as thebeam impact happens within 600 ns.CryostatFigure 4 shows the open experimental cryostat withoutthermal shields and vacuum vessel. It is a cryogen-freesystem, based on a two-stage cryo-cooler with a large copperinterface plate on the second stage, which can be cooled to4K. The two sample holders are bolted to this interface plateto ensure good thermalization. The ﬁrst stage is used to coola thermal shield that fully surrounds the second stage. Thesystem is compact with a height of about 0.9m, includingthe cold head, and a diameter of about 0.6m. As the vacuumvessel consists of Aluminum, leading to a suﬃciently lowenergy deposition of the 440 GeV proton beam into thevessel, beam windows are not required.BEAM TIMEThe experiment was carried out in HiRadMat [7], a facilityat CERN, providing proton beam pulses of up to 288 buncheswith 25 ns bunch spacing and an energy of 440GeV/p to-Figure 4: Open experimental cryo-cooler based cryostatwithout thermal shields. The sample holders are bolted tothe second stage interface to ensure good thermalization.wards ﬁxed targets. The beam size at the sample positionwas chosen with a standard deviation of σ = 1.1 mm. Forthe experiment 11 beam pulses of 24 bunches with an inten-sity of ∼ 3.1×1012 protons per pulse were used, resulting inthe energy deposition to the samples as shown in Fig. 3. Thecryostat was moved horizontally and vertically to change theimpacted batch between the pulses. After each pulse a pauseof 45 mins was required to allow the setup to cool down tothe initial temperature of ∼ 4 K.The beam size and position in the facility as well as thebeam intensity were reproducible during the ∼ 9 hours ofthe experiment. The beam parameters and the temperaturesof the sample holders were monitored and recorded duringthe experiment.SAMPLE EXTRACTION AND FIRSTVISUAL INSPECTIONThe impact positions of the beam were determined byvisual inspection of the impact marks on various pieces ofthe sample holder, using a digital optical microscope andmeasuring the distance to the edges of the blocks. A system-atic vertical oﬀset of about one millimeter was observed forthe LTS samples. The vertical beam oﬀset from the expectedimpact positions for the HTS samples was observed to bearound 0.5mm for batches one to three. For batches fourto six of the HTS samples, the beam oﬀset was up to 2mmdue to an operator error in the vertical positioning duringthe experiment.10th Int. Particle Accelerator Conf. IPAC2019, Melbourne, Australia JACoW PublishingISBN: 978-3-95450-208-0 doi:10.18429/JACoW-IPAC2019-THPTS066MC7: Accelerator TechnologyT10 Superconducting MagnetsTHPTS0664265ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2019).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOIFigure 5: Calculated maximum temperature proﬁles per-pendicular to the LTS strands, with the measured verticalbeam oﬀset taken into account, for a pulse with 3.1 × 1012protons. The strands outline with respect to the beam centeris indicated with a solid line, the center of the strand with adashed line.Temperature ProﬁlesAccording to the evaluated oﬀsets and using the mea-sured beam properties, reﬁned FLUKA simulations wereperformed and the energy deposition for all samples andeach shot individually was calculated. The reached peaktemperature intervals are summarized in the Table 1 below.The simulated temperature proﬁles transverse to the strandsare shown in Fig. 5.Table 1: Lowest and highest peak temperatures reached inthe strands and tapesSuperconductor Min. Temp Max Temp.Nb-Ti 300K 1190KNb3Sn 290K 1200KYBCO 240K 1357KNb-Ti and Nb3SnBeing a ductile material, the Nb-Ti strands showed no vi-sual degradation. The Nb3Sn based strands however showedclear deformations starting from the ﬁfth sample in the sam-ple holder with a peak temperature of about 700K. Thedeformation is prominent in the form of a central bendingof the strands around the beam position of few degrees ascan be seen in Fig. 6. This bending results from the oﬀsetof the beam impact in vertical (y-) direction which results ina transverse temperature gradient of up to 300K. This largeimbalance in thermal expansion then results in a bendingand permanent deformation, when the stresses in the mate-rial become too large. Furthermore, the copper matrix ofseveral samples showed partial cracks. For these samples,permanent degradation in the critical transport current isexpected.YBCOSome of the YBCO-tapes have been welded to the sampleholder by the beam impact, which complicated the removalFigure 6: One of the samples at position S8 of the Nb3Snstrands after beam impact. Clear deformation in form ofa bending of the strand around the beam impact center isvisible. The radial lines indicate the energy deposition.Figure 7: HTS tape which had seen a peak temperature of∼ 1200 K after removal from the sample holders. The redlines indicate the tape position according to the simulationwith measured beam parameters and oﬀsets. The circlesindicate the temperature at diﬀerent parts of the tape. Adamage of the top copper layer is clearly visible.of the samples after the experiment. Four HTS samples couldnot be removed from the sample holder and two sampleswere damaged during the removal. The welding occurred forsamples in position S5 and higher (see Fig. 3), reaching peaktemperatures of around 700K and above. Figure 7 shows asan example the last sample of one of the batches, overlayedwith the calculated peak temperatures, taking into accountthe measured beam parameters and oﬀset. A damage of thetop copper layer is clearly visible.SUMMARY AND OUTLOOKFor the ﬁrst time a damage experiment has been performedwith superconducting Nb-Ti and Nb3Sn strands, as well asYBCO tapes at 4.2 K using 440 GeV protons. In total 92short samples were impacted by shots of 3.1 × 1012 protons.A visual inspection revealed clear mechanical deformationof Nb3Sn samples, which experienced peak temperaturesof ∼ 700 K and above. At comparable peak temperaturesalso HTS tapes showed visual damage. No visual damagewas observed in Nb-Ti samples. The measurement of thecritical current density of the irradiated samples is currentlyongoing in collaboration with the University of Geneva. Inaddition, thermo-mechanical transient stresses present in theNb3Sn strands during the experiment are currently studiedwith coupled simulations of FLUKA and FEM codes fortransient structural analysis.REFERENCES[1] V. Raginel et al., “Change of Critical Current Density in Nb-Ti and Nb3Sn Strands After Millisecond Heating”, in Proc.8th Int. Particle Accelerator Conf. (IPAC’17), Copenhagen,Denmark10th Int. Particle Accelerator Conf. IPAC2019, Melbourne, Australia JACoW PublishingISBN: 978-3-95450-208-0 doi:10.18429/JACoW-IPAC2019-THPTS066THPTS0664266ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2019).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOIMC7: Accelerator TechnologyT10 Superconducting Magnets[2] V. Raginel et al., “First Experimental Results on Damage Lim-its of Superconducting Accelerator Magnet Components Dueto Instantaneous Beam Impact”, in IEEE Transactions on Ap-plied Superconductivity, 2018, vol. 28-4[3] T. Boutboul, S. Le Naour, D. Leroy, L. Oberli and V. Previtali,“Critical Current Density in Superconducting Nb-Ti Strands inthe 100 mT to 11 T Applied Field Range”in IEEE Transactionson Applied Superconductivity, 2006, vol. 16-2[4] P. Ferracin et al., “Magnet Design of the 150 mm ApertureLow-β Quadrupoles for the High Luminosity LHC”, in IEEETransactions on Applied Superconductivity, 2014, vol. 24-3[5] T.T. Böhlen, F. Cerutti, M.P.W. Chin, A. Fasso, A. Ferrari, P.G.Ortega, A. Mairani, P.R. Sala, G. Smirnov and V. Vlachoudis,“The FLUKA Code: Developments and Challenges for HighEnergy and Medical Applications”, in Nuclear Data Sheets120, 211-214 (2014), URL: http://www.fluka.org[6] A. Ferrari, P.R. Sala, A. Fasso, and J. Ranft, “FLUKA:a multi-particle transport code”, in CERN-2005-10 (2005),INFN/TC_05/11, SLAC-R-773[7] I. Efthymiopoulos et al., “HiRadMat: A New Irradiation Fa-cility for Material Testing at CERN”, in Proceedings of IPAC2011, San Sebastien, Spain, paper TUPS05810th Int. Particle Accelerator Conf. IPAC2019, Melbourne, Australia JACoW PublishingISBN: 978-3-95450-208-0 doi:10.18429/JACoW-IPAC2019-THPTS066MC7: Accelerator TechnologyT10 Superconducting MagnetsTHPTS0664267ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2019).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI

Beam Impact Experiment of 440GeV/p Protons on Superconducting Wires and Tapes in a Cryogenic Environment

https://publikationen.bibliothek.kit.edu/1000099081/44346641

Beam Impact Experiment of 440GeV/p Protons on Superconducting Wires and Tapes in a Cryogenic Environment

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