4M07 1 Q1 for JLAB‟s 12 Gev/c Super High Momentum Spectrometer Steven R. Lassiter, Paul D. Brindza, Michael J. Fowler, Steve R. Milward, Peter Penfold, and Russell Locke chosen as the basis for the SHMS‟s Q1 design. Much of the Abstract— The reference design for the first Quadrupole design and tooling can be reused in the manufacture of the magnet of TJNAF’s Super High Momentum Spectrometer magnet, leading to significant cost savings. Larger field (SHMS), Q1, is presented. The SHMS is a DQQQD design that gradients and availability of materials lead to a few changes to will be capable of resolving particles up to 11 Gev/c in the original design that include: the length of the magnet momentum. Q1 follows the successful design of the High Momentum Spectrometer’s (HMS) Q1, that of an elliptically increasing by 15%, using surplus Rutherford cable instead of shaped super ferric yoke, conformal mapped window frame coil, the original copper stabilized superconducting cable, the and helium bath cooled coil design. The primary differences elimination of the correction coils and slight increase in the between the two designs is in the choice of superconducting cable thickness of the return yoke without increasing the overall and an overall longer magnet length. A single stack of surplus magnet width. The magneto-static solver, TOSCA®, was used SSC Rutherford NbTi cable replaces the original four stack to model the magnetic performance as well as the forces and copper stabilized conductor used in the HMS’s Q1. The SHMS Q1 will have a warm bore diameter of 400 mm and produce field store energy calculations. gradients up to 9.1 T/m with an effective length of 2.14 m. Test coil windings progress will be given as well as reports on forces, conductor stability and energy margins. Dipole Index Terms— Superconductor Magnets, Detector Magnets, Cold Iron Magnets, Quadrupole Magnets Bender Q2 Q3 SHMS Q1 I. INTRODUCTION T HE planned upgrade of the Thomas Jefferson National Accelerator Facility (TJNAF) to 12 Gev/c calls for a Super High Momentum Spectrometer (SHMS) to be located HMS within the experimental area of Hall C . The SHMS is a DQQQD design using all superconducting magnets. The maximum momentum to be delivered to Hall C will be 11 Gev/c. The angle range of the SHMS is from 5.5° to 40° with a solid angle of >4.5 msr. The addition of a small bender magnet and a narrow width design for the first quadrupole, Fig. 1. SHMS and HMS at their most forward angles of 5.5° and 12.5° „Q1‟, was required to facilitate the SHMS reaching small respectively. angles in tandem with the existing High Momentum Spectrometer (HMS) at its smallest angle. Fig. 1 is a top view II. Q1 OPTICS AND SPATIAL REQUIREMENTS of the two spectrometers at their minimum angle. Optical and spatial requirements require a 9.1 T/m gradient The successful performance of the HMS‟s Q1 magnet - with an effective length of 2.14 m and a warm bore diameter , an elliptical shaped super ferric quadrupole magnet based of 0.4 m for the Q1 magnet. Resolution requirements require upon the conformal mapping of a window frame dipole, was well understood and highly reproducible magnetic characteristics. Integral field harmonics up to 2.1% of the Manuscript received August 30, 2007. quadrupole field can be tolerated and still provide an Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. acceptable resolution for the SHMS  without the need for DE-AC05-06OR23177. The U.S. Government retains a non-exclusive, paid- up, irrevocable, world-wide license to publish or reproduce this manuscript for any correction coils. U.S. Government purposes. Q1‟s cryostat cutout for the exit beamline will be increased Steven R. Lassiter, Paul D. Brindza and Mike Fowler are with Jefferson to accommodate the small forward angle requirement and its Science, Newport News, VA. 23606 USA (phone: 757-269-7129; fax: 757- 269-5520; e-mail: Lassiter@jlab.gov). longer length. The elliptical shape of Q1‟s iron provides a Steve R. Milward, Peter Penfold and Russell Locke are with Scientific return path for most of the field in the upper and lower Magnetics, Abingdon, OX14 3DB, UK (phone: +44 (0) 1865 409200; e-mail: portions. Saturation of the iron within the narrow “leg” region firstname.lastname@example.org) of the yoke leads to some stray field along the primary beam 4M07 2 at the center of the magnet. The gradient is taken at the warm bore radius of 0.20 m. The integral multipole harmonic is given in Fig. 4, over the whole momentum range of the SHMS. The position of the single stack of conductor relative to the yoke was used to optimize the harmonic content towards the higher momentum settings. TABLE II MAGNET RESULTS Parameter Quantity Gradient Max 9.105 T/m Effective Field Length 2.136 m Peak Yoke Field 4.61 T Peak Coil Field 2.78 T Fig. 2. The elliptical shaped SHMS Q1 magnet showing the notch in the Field at Pole (R=0.25 m) 2.276 T cryostat for the exit beamline and the cryogenic service can on top. Momentum Range 2 to 11 Gev/c Integral Harmonic N=4 line. This stray field must be corrected by means of corrector -.04 to -1.02 % % of N=2 magnets to ensure that the primary electron beam enters the Integral Harmonic N=6 downstream beam dump. Table I list the relevant parameters % of N=2 -2.21 to 0.21% for the Q1 quadrupole magnet. Integral Harmonic N=10 % of N=2 -0.32 to -.10 % TABLE I MAGNET PARAMETERS Parameter Quantity 16 Cryostat Pole Radius 0.250 m 14 EFL = 213.98 cm Yoke Length: 202.75 cm Warm Bore 0.402 m 12 Yoke Cryostat Length: 272.10 cm Integral Gradient = 19.48 (T/m).m Coil Axial Cryostat Length 2.72 m 10 Gradient T/m Yoke Length 2.03 m T/m 8 Current Density 18,100 A.T/cm 2 6 Kilo Amp Turns /Pole 255 A.T 4 Turns / pole 80 2 Operating Current 3188 A 0 Stored Energy 0.629 MJ 0 20 40 60 80 100 Z [m] 120 140 160 180 200 Inductance 123.7 mH Fig. 3. Field Gradient of SHMS Q1 at maximum current. Plot starts at the Magnet Weight 18 tons center of the magnet and extends out beyond cryostat. Cryostat, yoke and coil lengths are shown at the top to give perspective. III. Q1 MAGNETO-STATIC DESIGN 1.50 n=4 The yoke steel is 1006. Table II gives the magneto-static 1.00 n=6 n=8 results. The large integral field gradient requirement was met n=10 Percentage of Quadrupole Term n=14 by increasing both the overall length of the magnet and raising 0.50 the central gradient by means of increased current. The cross 0.00 sectional area of iron in the magnetic was essential unchanged. Term Only the width of the narrow “leg” was increased, utilizing -0.50 residual space from the change in the choice of conductor. -1.00 Saturation of the iron was in the range of 2.3 T within the body of the magnet. The highest field saturation occurs at the -1.50 pole edges and along the end chamfering, with fields reaching -2.00 up to 4.61 T. The largest field within the coil, 2.78 T, occurs along the inner radius of the end turns. Iron saturation leads to -2.50 0 500 1000 1500 2000 2500 3000 3500 no uniform properties, but with field maps generated with Current [A] Tosca and used in the program Snake it was verified that the optical requirements would be satisfied and understood. Fig. 3 Fig. 4. Integral Field Harmonics at warm aperture over the momentum range of 2 Gev/c to +11 Gev/c. 2xn= multipole. is a plot of the field gradient at the maximum current, starting 4M07 3 IV. CONDUCTOR AND STABILITY single source of heat for the magnet at 9 W at full current. The Surplus high current Superconducting Super Collider (SSC) heat load to 4 K helium is estimated to be less than 20 W and outer 36 strands Rutherford cable  replaces the original low the load to the LN2 shields to be less than 30 W. The report current copper stabilized conductor used in the HMS‟s also found no difficulties with the manufacturing aspects due quadrupole magnets. The SSC cable was originally key stone to lengthening of the cold mass. to an angle of 1.01°. The cable has been successfully re- flattened to within 80% of its width. Post flattened short 25000 sample test showed no signs of degradation. Table III gives the conductor characteristics. The conductor is stacked into a Tosca Fitted single layer coil consisting of 80 turns per pole. Each turn is 20000 4.42 K wrapped with a 50% overlapped Kapton film followed by B- 8.3 K Measured stage epoxy-glass tape to bond the turns together. The coil is 15000 wound unto its own support structure, providing a fully Ic [A] clamped system that also provides passages for bath cooling of 10000 liquid helium. The coil ends were wound using a near constant perimeter configuration, with the conductor being allowed to deform as it will around a cylindrical shape at the ends. Trail 5000 winding of the coil has been contracted to Scientific Magnets and the results have been successful with 2 trail coils 0 assembled to date. The cryostable design has an operational 0 1 2 3 4 5 6 7 8 9 overhead for the conductor of 3.89 K, 6784 A and 2.91 T. The Field [T] Stekly parameter has been calculated to be 0.57. The load line for Q1 is given in Fig. 5. Fig. 5. Load Line data for the SHMS Q1. BI curve is nonlinear due to saturation of iron. Measured data is from the flattened SSC cable. TABLE III CONDUCTOR PARAMETERS Electromagnetic forces were also calculated independently Parameter Quantity at JLAB using Tosca and then loaded into a two dimensional FEA model. Stress and deflection results are shown in Fig. 6. Conductor Dimensions 11.688 x 1.093 mm Stresses within the yoke were below 53 MPa. Maximum SC Cable 36 strand SSC outer deflections were less then 4x10-5 m. Strand Diameter 0.64 mm Cu:Nb:Ti Ratio 1.8 : 0.5 : 0.5 Ic (4.42K and 5.69T) 9972 Ic / Io (4.42K and 5.69T) 3.13 Kilo Amp Turns /Pole 255 A.T Critical Current Margin 6784 A Temperature Margin 3.89 K Kapton Thickness 0.10 mm B-stage Epoxy Thickness 0.05 mm V. MECHANICAL Mechanical design implications from increasing the cold mass length of the magnet by 15% have been studied by Scientific Magnetics . Their analysis included assessing the Fig. 6. Stress and deflection on one quadrant of the iron yoke due to magnetic effect of the increased cold mass on: the cold mass supports, forces. Note that the stress bar is Log scale. implications for yoke build up, yoke packing density and yoke pre-load, magnet sag issues, radiation shield support, and VI. CONCLUSION increase in cryogenic heat loads as well as manufacturing and The first quadrupole magnet of the SHMS, Q1, has cost implications. Their study concluded that sufficient undergone and passed several in house and DOE technical margins were found to exist with the original design to safely reviews . The reference design has been shown to meet the handle the expected mechanical loads. Their report also required field gradient of 9.1 T/m with an effective length of concluded that the cryogen safety relief devices need to be 2.14 m. The design meets both the spatial requirements and scaled or be capable to accommodate a pressure 15% higher optical requirements over the whole momentum range, from 2 than original design in the HMS magnet. The 5 KA “No to 11 GeV/c. The de-keystoned Rutherford cable has been Burnout” current leads  are expected to be the largest 4M07 4 tested and all indications are that it will remain cryostable and  L. H. Harwood et al, “A Superconducting Iron-dominated Quadrupole for CEBAF”, IEEE Transaction on Magnetics, vol. 25, Mar 1989, p. that training is unlikely provided that adequate mechanical 1910. support is provided. Coil forces are larger than the original  S. R. Lassiter et al, “Large Aperture Superconducting Cryostable HMS but still manageable. Trail windings using the flattened Quadrupoles for CEBAF‟s High Momentum Spectrometer”, IEEE Transaction on Magnetics, vol. 27, Mar 1991, p. 118. Rutherford cable are ongoing at Scientific Magnetics as shown  S. R. Lassiter et al, “Final Design and Construction Progress for in Fig. 7 and Fig 8. Two successful trail windings, a ten turn CEBAF‟s Cold Iron Quadrupoles”, IEEE Transaction on Applied test winding and a 80 turn winding, have been completed to Superconductivity, vol. 3, Mar 1993, p. 118. date. Winding trails will continue after an analysis of the test  S. R. Lassiter et al, “Magnetic Measurements of Large Aperture Superconducting Magnets for TJNAF‟s High Momentum trials have been completed and improvements incorporated. Spectrometer”, IEEE Transaction on Applied Superconductivity, vol. 7, June 1997, p. 614.  P. D. Brindza et al, “Commissioning the Superconducting Magnets for the High Momentum Spectrometer (HMS) at TJNAF”, IEEE Transaction on Applied Superconductivity, vol. 7, June 1997, p. 755.  John J. LeRose, JLAB, Newport News, VA, “Optics Study of SHMS using Raytrace and TOSCA fields”, private communication, January 2007.  “NbTi Superconducting Cable for SSC Dipole Magnets (Outer)”. SSC- Mag-M-4148 Rev 6.  Study of the SHMS Q1 with 15% longer cold mass. Technical Report Ref No. E165-01 SW1, Sept. 2006.  Gregory J. Laughon, private communication, American Magnetics Inc. Test Report AMI 5000 Amp Vapor Cooled Current Leads Operated at Full Power Without Cooling Flow. American Magnetics, Inc. March, 2005.  12 GeV Upgrade Project Conceptual Design and Safety Review of Superconducting Magnets, JLAB, Newport News, VA, Sep. 2006. Fig. 7. Trail winding setup. Picture courtesy of Scientific Magnetics. Fig. 8. End turn geometry, showing a ten turn trail winding layup. Picture courtesy of Scientific Magnetics. ACKNOWLEDGMENT The authors gratefully acknowledge the assistance of Dr. Bruce Strauss (USDOE/OHEP), Dr. Ron Scanlan (LBNL) and Dr. Dan Dietderich (LBNL) for providing the superconductor from the USDOE/Office of High Energy Physics equipment surplus. REFERENCES  The Science and Experimental Equipment for the 12 GeV Upgrade of CEBAF, Jan. 2005, http://www.jlab.org/12GeV/development.html.
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