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                          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 [1]. 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 [2]-                         with an effective length of 2.14 m and a warm bore diameter
[6], 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 [7] 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
info@scientificmagnets.co.uk)
                                                                                  of the yoke leads to some stray field along the primary beam
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                                                                        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
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                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 [8] 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 [9]. 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 [11]. 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 [10] are expected to be the largest
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tested and all indications are that it will remain cryostable and            [2]  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                [3] 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
                                                                             [4] 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             [5] 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.
                                                                             [6] 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.
                                                                             [7] John J. LeRose, JLAB, Newport News, VA, “Optics Study of SHMS
                                                                                  using Raytrace and TOSCA fields”, private communication, January
                                                                                  2007.
                                                                             [8] “NbTi Superconducting Cable for SSC Dipole Magnets (Outer)”. SSC-
                                                                                  Mag-M-4148 Rev 6.
                                                                             [9] Study of the SHMS Q1 with 15% longer cold mass. Technical Report
                                                                                  Ref No. E165-01 SW1, Sept. 2006.
                                                                             [10] 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.
                                                                             [11] 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
[1]   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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