Green, M.I.

Marks, S.

Nelson, D.

eScholarship - University of California

Lawrence Berkeley National LaboratoryRecent WorkTitleDESIGN, FABRICATION, AND CALIBRATION OF CURVED INTEGRAL COILS FOR MEASURING TRANSFER FUNCTION, UNIFORMITY, AND EFFECTIVE LENGTH OF LBL ALS BOSSTER DIPOLE MAGNETSPermalinkhttps://escholarship.org/uc/item/3q23z11nAuthorsGreen, M.I.Nelson, D.Marks, S.Publication Date1989-03-01eScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaLBL-25965 ~·~ Lawrence Berkeley Laboratory UNIVERSITY OF CALIFORNIA Accelerator & Fusion Research Division RECEIVED LAWRENCE 8ERK~l?Vi.DROR~TORY Presented at the 1989 IEEE Panicle Accelerator Conference rl r C :1 1989 Chicago, IL, March 2G-23, 1989 1 • Design, Fabrication, and Calibration of Curved UBHARY AND DOCUMENTS SECTION Integral Coils for Measuring Transfer Function, Uniformity, and Effective Length of LBL ALS Booster Dipole Magnets M.I. Green, D. Nelson, S. Marks, B. Gee, W. Wong, and J. Meneghetti March 1989 TWO-WEEK LOAN COPY ) This is a Library Circulating Copy which may be borrowed for two weeks. Prepared for the U.S. Department of Energy under Contract Number DE-AC03-76SF00098. DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness 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 its 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 the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. "' ' i ·, \1 " j \ .. · LBL-25965 t ' .. Design, Fabrication, and Calibration of Curved Integral Coils for Measuring Transfer Function, Uniformity, and Effective Length of LBL ALS Booster Dipole Magnets Mike I. Green, Don Nelson, Steve Marks, Bruce Gee, Weyland Wong, and John Meneghetti Accelerator and Fusion Research Division Lawrence Berkeley Laboratory 1 Cyclotron Road Berkeley, California 94720 Paper presented at the 1989 Particle Accelerator Conference in Chicago, illinois, March 20 to 23, 1989 This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division of the U. S. Department of Energy under Contract No. DE-AC03-76SF00098 DESIGN, FABRICATION, AND CAUBRATION OF CURVED INTEGRAL con..s FOR MEASURING 1RANSFER FUNcriON, UNIFORMITY AND EFFECTIVE LENGTII OF LBL ALS BOOSTER DIPOLE MAGNETS• M. I. Green, D. Nelson. S. Marks, B. Gee, W. Wong, and J. Meneghetti Lawtence Berltdey Laboratory University of California Berkeley, CA 94720 USA A matched pair of curved integral coils has been designed, fabricated and calibrated at Lawrence Berkeley Laboratory for measuring Advanced Light Source (ALS) Booster Dipole Magnets. Distinctive fabrication and calibration techniques are described. The use of multifilar magnet wire in fabricating integral search coils is described. Procedures used and taults of AC and DC nasumnelliS of transfer function. effective length. and uuifmmity of the proiDtype booster dipole magnet are presented in companion pape!S. Inqpduction The ALS is a third generation. 1-2 GeV synchrotron radiation facility specifically designed to maximize the brightness of the radiation from wigglers and undulators 1. Twenty-four dipole magnets will provide the main guide field for the booster synchrotron. The synchrotron is intended to operate at 1 Hz. but the magnets are designed for 10Hz operation. The booster synchrotron dipole magnet is of the split H type with flat pancake coils. To minimize the stored energy and power requirements, the core is curved to follow the electron-beam trajectory. Table 1 gives dipole magnet design parameters2. An engineering model of this dipole magnet has been designed, fabricated, qualified through magnetic measurements, and twenty four magnets are now in production. Table L ALS l.S GeV Boosu:r Dipole Magnet [)esign Panune=s Injection Magnetic Field Desig11 Magnetic Field Test Magnetic Field Bend Angle EnttanceiExit Edge Angles Magnet Bend Radius Magnetic Length Along Orbit Magnet Vertical Aperture Good Field Aperture Width Good Field Aperture Height field Quality (excluding fringe field) Excitation Waveform @1Hz @10Hz .0416T 1.248 T 1.6 T 15 Degrees 7.5 Degm:s 4.0107 m 1.050 m 4.4cm +/- 3.0cm +1- 1.8 em +/- 1.0 xt~3 Modified sawtooth DC biased sinusoid A pair of curved integral coils featuring multifilar wire windings were designed fabricated, c:alibraled and then used to make AC and, DC magnetic measurements of the Booster Dipole Engineering model magnet. Magnetic Specification The primary objective was to make a pair of curved integral coils to measure the magnitude and uniformity of the integral. JByds. A future objective is to use the ooill to make accurate comparisons of JBvds between a reference magnet and production magnets. The coils need to follow the electron beam trajectory, requiring that the section within the magnet be curved while thc.end sections be straight. The coils need to have a sensitivity that will allow measurements of variations of 0.01% at the injection field level of 0.04 T without overloading the instrumentation at the maximum test field of 1.6 T. A single layer coil wound on a square cross section form satisfies the requirement far insensitivity to the even harmonics (i.e. quadrupole and etc), and the sextupole spatial hannonic. In reality, due to the finite number of turns, a slight correction to the square cross section is required. . For making uniformity measurements the noise due to power supply fluctuations can be minimized by placing two identical coils inside a magnet and connecting them in series opposition. A oonsttaint we had 10 consider was instrumentation noise level which is approximately 1 microvolt second for measurement dumtions in the range of one minutc. For ease of construction, we wound the coils from color coded, 12 strand ##44 multifilar magnet win:,.3 The twelve strands add up to a width of 0.0635 mm or 0.025 inches. To obtain the required sensitivity, six adjacent windings were used to obtain a total of 72 turns, with a square cross section. Mechanical Specifications Fig. 1 shows a plan view of the search coils; Fig. 2 shows a cross-sectional view of one of the coils. Each of the coils consists of 6 windings of 12 strand wire wrapped on a precision ground fonn. The forms were secured to U-shaped strong backs which provide structural support for the coils. In order to enable positioning the coils adjacent to each other the two strongbacks had cross sections which were 'mirror images' of each other. The convex coil assembly haVing the winding form attached to the strong back whose outer radius is solid, and the concave coil assembly having the coil form attached to the strong back whose inner radius is solid. The coils conform to the hypothetical beam path through the Booster Dipole, as suggested by Fig. 1; this consists of 0.4 m straight sections at either end, and a curved middle section on a 4.011 m radius of curvature. (41. 3391 ( 15.7481 \------ 1. 05m-----J < 15 7481 _......\ . 4m : . 4m !--: I !' I : : I i I \ i i, i R4.011m · \ (15790211 \ i i i i -----15"---~; r , \ i CONCAVE COIL Fig. 1 Plain view of curved inte8ral coils. The search coil assembly is equivalent to a curved beam with uniform gravitational load acting perpendicular to the plane of curvature. The coil assembly is supported at the extreme ends. Under these load conditions, a curved beam is subject to vertical deflection as well as angular roll. The calculated deflections for the coil usembly with dimensions as shown in Fig. 2 are: maximum vertical deflection = 0.016 in, angular roll = 0.11". • This wortt wuiiUppOIUid by lhe Dinlclor, Office of Energy Relarch, Offic:e of Bale Energy Scialces, Mllerials Sc:iax:ea Olvili011, of 1be U.S. D.O.B., IIIICier Conlnet No. DE·AC03-76SRI0098. 6 WINDINGS OF 12 CONDUCTOR MULTIFILAR MAGNET WIRE COIL WIRE COIL STRONG BACK Fig. 2 Cross section of a coil uscmbly. The convex coil for example, having the center of radius of curvaiUI'e to the left. Mechanical Fabrication The coils were fabricated in two separate pieces: the coil strong back. and the coil wire form Both components wcm: fabric:all:d from NEMA G-10. The components were first Blanchard ground to the specified thickness. The coil sttong back was then shaped on an NC mill to the requixed final shape. The coil form was initially sttaight; the coil was wound onto it in this configuration. After winding, the coil and coil form were bent and secured to the coilsttong back to conform 10 the required final geometry. The coil winding was done in a fixture consisting of two flat steel bars clamped to sandwich the coil Conn. The upper surfaces ~f the steel bars had been previously ground flat with a sharp corner, placed adjacent to the coil fonn. The upper surface of the steel ban provided a n:gister for the first tum of the multiple fllamcnt wire cable. This ammgcmcnt iJ shown in Fig. 3. 6 ADJACENT WINDINGS WINDING FIXTURE WITH FLAT EDGE COIL WIRE FORM .150 f Fig. 3 Cross section of winding ftxtun: wtih coil form. The multiple filament wirc cable consisted of 12 strands of #f44 gauge insulated copper wire. The cable is coated with 1 polyvinyl 2 butyral bonding agent that is activated by the application of isopropyl alcohoL The same material was used to bond the individual strands together. The original plan was to bond 10 the coil form by clamping the win: in place and activate the bonding agent with alcohol and allow it 10 cure. 1bis technique proved unsuccessful, since the application of the alcohol also released the inter-strand bond, n:sulting in delamination of the cable. After considerable experimentation a procedun: was developed where an acrylic bonding agent was activated by ethylene dichloride, which does not activate polyvinyl butyral. Mynetic Calibration and Wuing .Mdn& The A.L.S. Booster Dipole Integral Coil was wound with 12 conductor ribbon wire. In order to make the coil a single conductor coil the ends (terminations) wen: soldered with low thennal emf solder in an offset configuration, i.e., eleven wires from the start of the cable wen: soldered to eleven wires at the end of the winding. The requin:d connections Wen: made in a manner that minimized changes in the coil's sensitivity (turns area). A printed circuit board with narrow, close traces was attached near to one end of the coil form to terminate/join the individual conductor ends of the ribbon wire. A service loop (doubled back) was put into the ribbon befon: it was teiminated to facilitate repair. The ribbon ends wen: prepan:d befon: they wen: soldered to the circuit board by separating the conductors (no small task) and fanning them, then stic.lcing them to some kapton tape so that they would align with the traces of the circuit board. This made it easier to solder the almost invisible wire to the trace with minimum effort. One end of the ribbon was terminated at one ievel" on the circuit board and then at a different ievel" the other end of the ribbon was terminated. The leads were attached to a stick-on cable mount to n:licve the sttain from the circuit board connection. Resistance was measured far each individual tum and for the coil as a whole. The individual turns measured -210 Ohms and the coil as a whole measun:d - 2500 Ohms. The the tcrminal:ions were covered with a thin, flexible plastic material to. protect them Magnetic Calibration The coils wen: calibrated absolu1ely against a Nuclear Magnetic Rcsonaoc::c (NMR) MagoeiOmcter and relatively against each other, using a long bending magnet as a transfer device. For calibration the two coils wen: mounted on a ftxtun: that preserved their angular integrity, and provided a number of precision holes for positioning the NMR probe to measun: magnetic induction By(Si) (Sj is the position of the i-th hole on the imaginary line that bisected the two coil c::cntcr lines and determined the hole pattern.) After measuring By at each Si, we used numerical integration to determine /Byds over the coil's length;. Before and after the NMR measurements we measured chaDges in flux-linkage of each coil scparaldy doe to JByds by a.lnlcting the fixture from the magnet and pl.King it in a "field free" location. The sensitivity (nw) of each coil was delennincd from cq. 1 ow= o0/ JByds [tmn mcten] (1) where: {10 = the flu linkage in the magnet JByds = the inlegral deiCJmined from the NMR measurements The flux linkage was dctmnined by flu-standard calibrations imrnedialdy befon: each measurement. Variations in JByds over the fixture's width wen: determined to be negligible through sepamtc measurements of the variations in flux linkage of one coil as the ftxture was translated so that the coil covered the positions both of the hole pattern and the other coil. The "field free" location outside the magnet and normal to the earth's magnetic field and stray field from the bending magnet was established by another measurement The oct field integral at the chosen location was verified to be negligible by flipping the fvtiUI'e 180 degrees. In order to demonstrate that the sensitivities of the two coils could be matched to 1:10000, by adjusting a signal divider installed between the most sensitive coil and the integrator, we connected the two coils in series opposition and measured the change in flux-linkage when the fixture was extracted. We recorded the divider setting that nulled the resultant signal. This setting wa5 used in making DC measurements. During AC measurements, we found that a slightly different divider adjustment was ncccssaty to minimize the time dependant peak to peak signal from the two coils connected in series opposition. Munetic Measurements Measurements were made with the coils connected to analog integrators. DC BLeff was dctctmined with the following proc:edme. With an integral coil in a zero field chamber, the analog integrator was zeroed; the time and integrator voltage were computer recorded. The coil was then inserted into the magnet, the magnet mmped to the desired fields, simultaneously recording both the time and the integrator outpuL After tee:Ording data for all specified fields, the coil was rcsinscrted into the zcro field chamber in order to measure the integrator drifL All coil signals were corrected assuming linear drift of the integrator. A signal representing the magnet's effective length was aeatcd by dividing the integral signal by the magnetic induction signal from a point coil and/or Hall probe. Tbe transfer functions were produced by dividing both the integral signal and the magnetic induction signal by the current signal. DC uniformity data was acquired using null techniques. The moving integral coil was connected in series opposition to the stationary integral coil in order to cancel out power supply noise and drift. The magnet was ramped to the desired field, integrator zeroed, and then the moving coil was positioned at the various horizontal and/or vertical positions by axnputer conttolled stepping motors. All data. position, time, integrator voltage, power supply shunt voltage were recorded and processed by the computer. Quadropole and sextupole coefficients were extracted from the uniformity data. The results of some of these measurements an: reported at this conference and elsewherc.4,5,6,7,8 Magnet parameters were also measured at 2 and 10 Hz frequencies. Together with measurements at selected DC levels, the AC mcasutements demonsttated that the magnet design met specifications and qualified it for production. Ac!cnow!edmnenrs We gratefully thank Dave Van Dyke and Chinh Vu for their careful soldering of the multifilar cable under a stereo microscope. References (1] "1-2 Gev Synchrotron Radiation Source", Conceptual Design Report. LBL PUB-5172. July, 1986. [2] E. Hoyer, "Ught Source Booster Dipole Magnet Design Calculation", LBL Engineering Note MT 387, 1988. (3] MWS W"U'C Industries, 31200 Cedar Valley Drive, Westlake Village, CA 91362. [4] J. Tanabe, J. Milbum, E. Hoyer, K. Halbach, R.T. Avery, D. Humphries, S. Marks, M.L Green, D. Yee, R. Caylor, S. Hernandez, W. Low, "Fabrication and Test of Prototype Ring Magnets for the ALS", Proceedings of this Conference. (5] R. Keller, M.I. Green, Y.M. Koo, S. Marks, "Measurement of the magnetic Properties of the ALS Booster Synchrotron Prototype Magnets'", Proceedings of this Conference. [6] M.L Green, E. Hoyer, R. Keller, D.H. Nelson, "AC Magnetic Measurements of the ALS Boosrcr Dipole Engineering Model Magnet", Proceedings of this Conference. 3 [7] R. Keller, M.l. Green, E. Hoyer, Y.M. Koo, S. Marks, D.H. Nelson. "Measured Properties of the ALS Booster Synchrottm Magnet Engineering Model", LBL Internal Report LSAP-61, 1989. [8] M.l. Green, E. Hoyer, R. Keller, D.H. Nelson, "AC Magnetic Measurements of the ALS Booster Synchrotron Dipole Magnet Engineering Model". LBL Report LBL-26003,1988. ....,.;,-~--LA~NCEBERKELEYLABORATORY TECHNICAL INFORMATION DEPARTMENT 1 CYCLOTRON ROAD BERKELEY, CALIFORNIA 94720 -·-,. 

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DESIGN, FABRICATION, AND CALIBRATION OF CURVED INTEGRAL COILS FOR MEASURING TRANSFER FUNCTION, UNIFORMITY, AND EFFECTIVE LENGTH OF LBL ALS BOSSTER DIPOLE MAGNETS

DESIGN, FABRICATION, AND CALIBRATION OF CURVED INTEGRAL COILS FOR MEASURING TRANSFER FUNCTION, UNIFORMITY, AND EFFECTIVE LENGTH OF LBL ALS BOSSTER DIPOLE MAGNETS

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