The US-LHC Accelerator Research Program is developing and testing a high-gradient quadrupole (HQ) magnet, aiming at demonstrating the feasibility of Nb{sub 3}Sn technologies for the LHC luminosity upgrade. The 1 m long HQ magnet has a 120 mm bore with a conductor-limited gradient of 219 T/m at 1.9 K and a peak field of 15 T. HQ includes accelerator features such as alignment and field quality. Here we present the magnetic measurement results obtained at LBNL with a constant current of 30 A. A 100 mm long circuit-board rotating coil developed by FNAL was used and the induced voltage and flux increment were acquired. The measured b{sub 6} ranges from 0.3 to 0.5 units in the magnet straight section at a reference radius of 21.55 mm. The data reduced from the numerical integration of the raw voltage agree with those from the fast digital integrators

Ambrosio, G.

Bossert, R.

Caspi, S.

Cheng, D.

Chlachidze, G.

Deitderich, D.

DiMarco, J.

Felice, H.

Ferracin, P.

Hafalia, R.

Joseph, J.

Kashikhin, V.

Lizarazo, J.

Martchevskii, M.

Nash, C.

Sabbi, G. L.

Schmalzle, J.

Vu, C.

UNT Digital Library

    BNL-95140-2011-CP    Warm Magnetic Field Measurements of LARP HQ Magnet   X. Wang, S. Caspi, D. Cheng, D. Dietderich, H. Felice, P. Ferracin, R. Hafalia, J. Joseph, J. Lizarazo, M. Martchevskii, C. Nash, G.L. Sabbi, C. Vu, LBNL Berkeley, CA  94720, U.S.A.  J. Schmalzle, P. Wanderer, BNL, Upton, NY  11973, U.S.A.   G. Ambrosio, R. Bossert, G. Chlachidze, J. DiMarco, V. Kashikhin, FNAL, Batavia, IL  60510, U.S.A.   Presented at the Particle Accelerator Conference (PAC11) New York City, NY March 28 – April 1, 2011   May 2011    Superconducting Magnet Division  Brookhaven National Laboratory   U.S. Department of Energy DOE Office of Science    Notice: This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.  This preprint is intended for publication in a journal or proceedings.  Since changes may be made before publication, it may not be cited or reproduced without the author’s permission.     DISCLAIMER  This report was prepared as an account of work sponsored by an agency of the United States Government.  Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party’s use or the results of such use of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof or its contractors or subcontractors.  The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.                                   WARM MAGNETIC FIELD MEASUREMENTS OF LARP HQ MAGNET∗X. Wang† , S. Caspi, D. Cheng, D. Dietderich, H. Felice, P. Ferracin, R. Hafalia, J. Joseph,J. Lizarazo, M. Martchevskii, C. Nash, G.L. Sabbi, C. Vu, LBNL, Berkeley, CA 94720, U.S.A.J. Schmalzle, P. Wanderer, BNL, Upton, NY 11973, U.S.A.G. Ambrosio, R. Bossert, G. Chlachidze, J. DiMarco, V. Kashikhin, FNAL, Batavia, IL 60510, U.S.A.AbstractThe US-LHC Accelerator Research Program is develop-ing and testing a high-gradient quadrupole (HQ) magnet,aiming at demonstrating the feasibility of Nb3Sn technolo-gies for the LHC luminosity upgrade. The 1 m long HQmagnet has a 120 mm bore with a conductor-limited gra-dient of 219 T/m at 1.9 K and a peak field of 15 T. HQincludes accelerator features such as alignment and fieldquality. Here we present the magnetic measurement resultsobtained at LBNL with a constant current of 30 A. A 100mm long circuit-board rotating coil developed by FNALwas used and the induced voltage and flux increment wereacquired. The measured b6 ranges from 0.3 to 0.5 units inthe magnet straight section at a reference radius of 21.55mm. The data reduced from the numerical integration ofthe raw voltage agree with those from the fast digital inte-grators.INTRODUCTIONAs part of the US-LHC Accelerator Research Program(LARP), Fermilab (FNAL), Brookhaven National Labo-ratory (BNL), and Lawrence Berkeley National Labora-tory (LBNL) collaborate on developing Nb3Sn supercon-ducting quadrupole magnets for the LHC luminosity up-grade. Following the technology quadrupole (TQ) andlong quadrupole (LQ) programs [1, 2], the high-gradientquadruple (HQ) magnets represent another step towardsthis goal. With a bore size of 120 mm, the 1 m long HQ hasa maximum gradient of 199 T/m with short-sample currentof 17.7 kA at 4.4 K [3]. HQ magnets include acceleratormagnet features such as alignment and field quality [3, 4].Here we report the observations during the warm measure-ment of HQ01d at LBNL. Experimental setup is presented,followed by the measurement results and discussion.EXPERIMENTAL DETAILSSetupThe magnet was positioned vertically in the test cryostatwith the lead side on the top. Inside the magnet bore wasan anti-cryostat housing the rotating probe developed byFNAL (Fig. 1). The nominal bore size of the anticryostat is49 mm and the length is 2.3 m. Two coils, one 100 mm long∗This work was supported by the U.S. Department of Energy throughthe US LHC Accelerator Research Program.† xrwang@lbl.govand the other 250 mm long, were installed in the probe. Thedistance between the center of the two coils is ∼ 250 mm.Figure 1: The circuit-board probe used in the measurement.The 100 mm coil is close to the left end.Unlike the conventional rotating coil based on windingswound on a cylindrical mandrel, the coil used here con-sists of traces on a circuit board. More details about thisnovel design can be found in [5]. The radius of the out-ermost trace is ∼ 21.55 mm. Each coil has three volt-age outputs, i.e., unbucked (UB), dipole-bucked (DB) anddipole-quadrupole-bucked (DQB) signals, which were am-plified by an onboard amplifier inside the probe during themeasurement. The probe rotated at a speed of ∼ 0.5 Hz.In every revolution, a chain of 4096 quadrature pulses andone index pulse were generated by an incremental encodermounted at the end of the probe. The probe movementalong the bore direction (z) was controlled by a step mo-tor with a resolution of ∼ 2 µm [6].Data was acquired by a hybrid system composed of a dy-namic signal acquisition card (National Instruments DSA4472B), two fast digital integrators (Metrolab FDI 2056),and other auxiliary cards. All three probe voltage signalsand the encoder signals were simultaneously acquired bythe DSA card. Only the UB and DQB signals were ac-quired by the FDI cards. The DSA and FDI cards haveamplifiers at their input end. The nominal gains used ateach amplifier stage are listed in Table 1.Table 1: Nominal gains for the voltage signals.Amplifier UB DB DQBProbe 10 10 1000DSA 1 1 1FDI 100 - 50The sampling of the DSA card was driven by its internalclock at a frequency of 102.4 kHz. The quadrature sig-nal from the encoder triggered the FDI cards. The mag-net current and probe temperature were measured by anNI 6221 card. The PXI-based data acquisition system wascontrolled by a LabWindows/CVI program.                                                                                                                                     BNL-95140-2011-CP Submitted at the Particle Accelerator Conference (PAC11), New York City, NY - March 28-Apri1, 2011Measurement ProtocolThe measurements were performed at∼ 70 K during thewarmup of the magnet from 4.5 K. A constant current of 30A was applied. Once the current was stabilized, the probetook measurements at different locations along the magnetlength. Typical step size ranged from 10 mm close to thecoil end to 50 mm in the straight section. Five measure-ments (rotations) were taken at each location. The aver-aged harmonics are reported with the error bars indicatingthe maximum and minimum values of the five measure-ments. The measured results are compared to the calcula-tion given by an Opera 3D model of the magnet where thecoil and structural components were considered. A typicalone-way scan of 35 z locations took ∼ 45 minutes. Themagnet terminal voltage and the strain gage readings weremonitored to ensure minimal temperature rise.RESULTS AND DISCUSSIONData reductionThe 2D complex bore field is expanded asBy + i Bx =∞∑n=1~Cn(x + i yRref)n−1, (1)where ~Cn is complex multipole coefficients defined at thereference radius Rref. The normalized coefficients ~cn re-ported here is defined as ~cn = bn + i an = 104 ~Cn/B2,where B2 is the main field of the quadrupole magnet withzero main skew component (A2 = 0). Here we useRref = 21.55 mm, 35% of the bore radius. The flux dataas a function of angular position used to generate the ~Cnis a running sum of the flux increments over angular stepsof the probe indicated by the encoder quadrature signal [7].For the DSA voltage data, the flux increment is obtained bynumerically integrating the recorded voltage over the timeinterval defined by two consecutive quadrature signals fromthe encoder with the same polarity. For the FDI cards, theflux increments are readily available as the instrument out-put. Before the normalization, flux drift is removed dueto the stable magnet current [7]. The probe centering cor-rection is done based on the first 10 orders of harmoniccoefficients, assuming the dipole components shown in therecorded UB signal were only due to the probe offset in aquadrupole field.Transfer FunctionThe measured main-field transfer function along the boreare compared to the calculation (Fig. 2). The measurementwas done with the 100 mm coil. The UB signal is used inthis case as DB signal was not recorded for the FDI card.The theoretical value was calculated with I = 50 A.Magnetic center is located at z = 0 in Fig. 2. Lead sideof the magnet is at right (z > 0) and the return side atleft. Limited by the length of the anti-cryostat, the mea-surements did not cover the return side. Between −200-202468101214-800 -600 -400 -200 0 200 400 600 800Transfer function (T/m/kA)z (mm)theoryDSAFDIFigure 2: Axial dependence of main field (B2) transferfunction measured at ∼ 70 K with I = 30 A using the100 mm coil.mm and 200 mm, the transfer function reaches a plateau∼ 12 T/m/kA. The discrepency between the measurementand calculation becomes evident for z > 460 mm, whereless than half of the 100 mm rotating coil is within the mag-net coil. The residual value is ∼ 0.4 T/m/kA for z > 600mm, corresponding to ∼ 250 µT at the reference radius of21.55 mm. The five measurements taken at each locationwere close to each other, leading to the invisible error barsin Fig. 2. Typical variation of the measurements at eachlocation is less than 0.03%. The measured data from DSAand FDI agree well. Typical difference is less than 0.1%for z < 400 mm and less than 0.3% for z > 400 mm.Allowed harmonicsFigure 3 compares the axial dependence of b6 normal-ized to B2(z = 0). The data was reduced from the DQBsignal of the 100 mm coil.-6-4-20246-800 -600 -400 -200 0 200 400 600 800Averaged b6 (units)z (mm)theoryDSAFDIFigure 3: Axial dependence of b6 measured at∼ 70 K withI = 30 A using the 100 mm coil. Results normalized to thecentral B2. Rref = 21.55 mm.The measured data generally agrees with the calculationwith a few exceptions. First, based on the measured b6,                                                                                                                                     BNL-95140-2011-CP Submitted at the Particle Accelerator Conference (PAC11), New York City, NY - March 28-Apri1, 2011one sees that actual straight section of the magnet rangesbetween ∼ −200 mm and 100 mm. The increasing of themeasured b6 between 100 mm and 300 mm may be due tothe transition turn from the inner layer to the outer layer ofthe coil that is not considered in the present calculation andwill be addressed in future models. Second, the deviationof the measurements from the calculation is noticed for z >460 mm, which can be related to the residual B2 at the samelocation as shown in Fig. 2. This could be due to the factthat the 2D bore field assumption is not true at the coil end.b6 ranges from 0.3 to 0.5 units in the straight section(−200 < z < 100 mm) at Rref = 21.55 mm. The errorbar length is ∼ 0.5 units. Given the 2D field in the straightsection, the scaling based on Eq. (1) gives a b6 ranging from1.5 to 2.5 units at Rref = 30 mm, 50% of the magnet boreradius.Figure 4 shows the axial dependence of b10 normalizedto B2(z = 0). Due to the limited signal/noise ratio, themeasured data spread around the calculated values. Never-theless, the measured results are within ±0.2 units with astable variation within ±0.4 units.-0.8-0.6-0.4-0.200.20.40.60.8-800 -600 -400 -200 0 200 400 600 800Averaged b10 (units)z (mm)theoryDSAFDIFigure 4: Axial dependence of b10 measured at ∼ 70 Kwith a current of 30 A using the 100 mm coil. Resultsnormalized to the central B2. Rref = 21.55 mm.Comparison between DSA and FDIThe hybrid system allows the comparison between thetwo methods to acquire the angular flux data for field qual-ity analysis as mentioned previously. From Figs. 2 to 4,one sees that the data reduced from two methods are inexcellent agreement in terms of both averaged values andtheir variation. This indicates that for the measurementscenario reported here, i.e., a probe rotation speed of 0.5Hz vs. a DSA sampling rate of 102.4 kHz (a factor of2×105), the numerical integration based on the trapezoidalrule with linear interpolation between the recorded voltagedata achieves a performance comparable to the fast digitalintegrator. With the raw voltage recorded by the DSA, itis possible to postprocess the raw voltage, e.g., digital fil-tering, to reach potentially higher signal/noise ratio for theanalysis. Since the FDI cards used their front-end ampli-fier in addition to the onboard amplifier inside the probe(Table 1), the agreement between the DSA and FDI resultssuggests that the FDI gains were accurate.SUMMARYWarm magnetic measurements of HQ01d, a high-gradient Nb3Sn quadrupole, were performed at LBNL witha constant current of 30 A and a temperature of 70 K. Themeasured data given by the rotating circuit-board coil de-veloped at FNAL are in good agreement with the calcula-tion. A transfer function of ∼ 12 T/m/kA is measured atthe straight section of the magnet. At a reference radiusof 21.55 mm, the measured b6 ranges between 0.3 to 0.5units in the straight section. This scales to 1.5 to 2.5 unitsat a reference radius of 30 mm, 50% of the magnet boreradius. The measurement also compares the performanceof the flux data construction based on the numerical inte-gration of the recorded voltage and the fast digital integra-tor. The agreement between the two methods indicates thatthe setup and the associated integration technique is effec-tive for the measurement involving DC measurement withslowly rotating probes.ACKNOWLEDGMENTSWe thank the technical staff of the program for their ex-pertise and dedicated support. We also thank B. Richter ofGMW Associates and P. Keller of Metrolab for the loan oftwo fast digital integrators and their help during the systemsetup.REFERENCES[1] H. Felice et al., “Test results of TQS03: A LARP shell-based Nb3Sn quadrupole using 108/127 conductor.” Journalof Physics: Conference Series, 234(3):032010, 2010.[2] G. Ambrosio et al., “Test results of the first 3.7 m long Nb3Snquadrupole by LARP and future plans.” IEEE Trans. Appl.Supercond., 2011. In press.[3] S. Caspi et al., “Design of a 120 mm bore 15 T quadrupole forthe LHC upgrade phase II.” IEEE Trans. Appl. Supercond.,20(3):144 –147, 2010.[4] H. Felice et al., “Magnetic and mechanical analysis of theHQ model quadrupole designs for LARP.” IEEE Trans. Appl.Supercond., 18(2):281–284, 2008.[5] J. DiMarco, “Rotating circuit board probes for mag-netic measurements.” The 15th Internal MagneticMeasurement Workshop, Fermilab, August 2007,http://tdserver1.fnal.gov/immw15/.[6] J. Joseph et al., “Magnetic measurement DAQ system specifi-cation.” Document # 40Y570, Superconducting Magnet Pro-gram, LBNL, December 2008.[7] L. Bottura, “Standard analysis procedures for field qualitymeasurement of the LHC magnets — part I: harmonics.”Technical Report LHC-MTA-IN-97-007, LHC/MTA, 2001.                                                                                                                                     BNL-95140-2011-CP Submitted at the Particle Accelerator Conference (PAC11), New York City, NY - March 28-Apri1, 2011

Warm Magnetic Field Measurements of LARP HQ Magnet

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Warm Magnetic Field Measurements of LARP HQ Magnet

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