Download MT-20-4M06 SHMS Q23-v2 - Hall C

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The Cosine Two Theta Quadrupole Magnets
for the Jefferson Lab Super High Momentum
Spectrometer.
Paul D. Brindza, Steven R. Lassiter and Michael J. Fowler

Abstract— The Jefferson Lab 12 Gev/c upgrade involves
building a new 12 Gev/c spectrometer for JLAB Hall C called the
SHMS. This device achieves 4.5 mStr acceptance at bend angles
for 5.5 degrees to 40 degrees by using five magnetic elements in a
dQQQD configuration. The Q1 SC quad is described elsewhere
in this Conference and is an evolution of a cold iron magnet used
previously for the existing JLAB 7.5 Gev/c HMS spectrometer.
The pair of identical Cosine Two Theta quads are an entirely new
design with a large 60 cm warm bore and 13 Tesla/meter
gradient. These 5 Tesla Quads provides focusing for particles
from 1 to 12 Gev/c and have an integral gradient strength of 23.5
(T/M) M. The magnetic design including multipole strengths will
be presented. The quadrupole cold mass uses a Stainless Steel
shrink fit force collar, Titanium keys and a Copper stabilized
super conductor consisting of a 36 strand surplus SSC outer
cable wave soldered to a copper extruded substrate. This
combination provides for a very conservative magnet that can be
assemble with little or no tooling and a high degree of stability.
The force collar mechanical analysis will be presented as well as
details of the magnet cryostat.
Index Terms—Superconducting Magnets, Detector Magnets,
Quadrupole Magnets
I. INTRODUCTION
T
HOMAS Jefferson National Accelerator Facility is
currently upgrading the CEBAF accelerator from its
original design energy of 6 Gev/c to 12 Gev/c. The Upgrade
Project is in the Project Engineering and Design (PED) phase.
Construction is expected to begin in FY10 and the 12 Gev/c
Nuclear Physics program is expected to begin in FY14. The
Upgrade involves adding 10 additional cryo modules to the
CEBAF accelerator to double the energy, new experimental
equipment in JLAB Experimental Hall’s A, B, C, and an
entirely new Experimental Hall, Hall D. Super Conducting
(SC) magnets feature prominently in the Experimental
Equipment of the 12 Gev/c upgrade as they did in the original
CEBAF construction at JLAB. The plan for JLAB Hall C
Manuscript received August 28, 2007. Notice: Authored by Jefferson
Science Associates, LLC under U.S. DOE Contract No. DE-AC0506OR23177. The U.S. Government retains a non-exclusive, paid-up,
irrevocable, world-wide license to publish or reproduce this manuscript for
U.S. Government purposes.
P.D. Brindza, S. Lassiter and M. Fowler are with the Thomas Jefferson
national Accelerator Facility, Newport New, Virginia (phone: 757-269-7588;
fax: 757-269-6273; e-mail: [email protected]).
.
Fig. 1. SHMS Q2 Quadrupole General Arrangement. The Q3 magnet is
identical except for the slotted yoke.
requires a new SC spectrometer, the Super High Momentum
Spectrometer (SHMS) [1] as a 12 Gev/c companion to the
existing High Momentum Spectrometer (HMS) [2] operating
at 7.5 Gev/c. The SHMS requires five new SC magnets, a
small initial Horizontal Bend Dipole (HB), three quadrupoles
(Q1,Q2,Q3 ) of which the subject of this paper are the Q2, Q3
magnets (collectively identified as Q23), with 13 Tesla/meter
gradient and 60 cm warm bore cosine (2theta) type SC Quads.
Fig. 1 shows Q2 with the notch in the warm return yoke to
allow for the primary beam line. The SHMS achieves a
momentum resolution of 1 x10^-3 and has a solid angle
acceptance of 4.5 mStr. This spectrometer has excellent
optical properties and is largely immune to the most common
field aberrations of the SHMS magnets. This results in simple
SC magnets with relatively large construction tolerances (1
mm). The final construction tolerances will be set entirely by
the requirements for magnet assembly and construction rather
than field errors. The SHMS Q23 Quadrupoles and the SHMS
Dipole share many similar design and construction details
including the same composite stabilized super conductor, the
same cryostat cross section, nearly the same operating current
and the same force collar design and method of coil preload.
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The Q23 Quadrupoles use a stainless steel force collar that is a
shrink fit over the coil which uses Titanium “keys” to insure
coil preload after cool down to 4.4 Kelvin. This type of cold
mass assembly does not rely on large, complex and expensive
tooling used only once. The main properties of the SHMS Q23
Quadrupoles are listed in Table I and Table II.
TABLE I Q23 QUADRUPOLE PARAMETERS
Parameter
Quantity
Warm Bore
0.600 m
Cryostat Length
2.33 m
Yoke Length
1.90 m
Current Density
5050 A.T/cm2
Mega Amp Turns
6.50 M. A.T
Turns
1288
Operating Current
5050 A
Stored Energy
9.78 MJ
Inductance
0.77 H
Magnet Weight
60 tons
TABLE II Q23 MAGNETIC RESULTS
Parameter
Quantity
Gradient
13.1 T/m
Effective Field Length
1.79 m
Peak Yoke Field
2.72 T
Peak Coil Field
Integral Gradient
Momentum Range
Integral Harmonic N=3
% of N=1
5.87 T
23.5 (T /m)m
1 to 12 Gev/c
-0.15 %
Integral Harmonic N=5
% of N=1
-0.60 %
Integral Harmonic N=9 %
of N=1
-0.10 %
TABLE III Q23 CONDUCTOR PARAMETERS
Parameter
Quantity
Conductor Size
2.00 cm x 0.50 cm
Copper size
1.89 cm x 0.44 cm
SC Cable
36 strand SSC outer
Stability Alpha
0.93
Energy Margin
0.480 Joules
Field Margin
It is the intention of JLAB to acquire all five of the SHMS
magnets from commercial or institutional sources thru the
competitive award of fixed price best value type contracts. All
five SHMS magnets will feature significant materials (GFM)
and equipment (GFE) to be furnished by JLAB. It is the
intention of JLAB to supply the tested processed
superconductor, the cryogenic control reservoir, the DC power
system including energy dump, the instrumentation and
control system including software, the warm iron yoke and
support services for the on site acceptance test at JLAB [3].
This is a significant departure from past practices at JLAB
where in general turn-key magnet systems were procured by
fixed price performance contracts. The main reasons for this
approach is to enforce standardization of external components
such as DC power , cryogenic control reservoir and Instrument
and Control systems and to help control the overall cost by
sharing in a significant way the overall technical responsibility
and project risk. The overall magnet project delivery schedule
is also expected to be shorter and more predictable as many
major systems can be provided earlier especially the
composite superconductor.
II. MAGNETIC DESIGN OF THE SHMS Q23 QUADRUPOLES
The Q23 magnets are designed as a two current sector
cosine two theta coil. The coil configuration that is being
modeled consists of standard Tosca generated constant
perimeter coils, with 8 winding layers arranged as double
cylindrical pancake windings. Return flux is contained by the
warm iron yoke. The BH curve used in the models came from
1006 iron. A notch is required in Q2’s yoke to accommodate
the primary beamline at small forward angles. The notch is
symmetrical placed on either side of the magnet to minimize
harmonics and forces. Table II shows the result for the Q3
magnet. A Fourier fit is performed on the field along the warm
bore diameter to extract the field harmonics. These harmonics
are then integrated along the axis of the magnet and compared
to the main quadrupole field. The N used follows the TOSCA
convention so the pole count is 2*(N+1).
Coil placement studies were performed and the magnetic
design was found to be very forgiving of coil misalignments.
Acceptable field quality is maintained for +/- 1 conductor turn
width per layer changes. This corresponds to a tolerance of 0.8
degrees in the angles defining the current blocks. Studies
showed that coil displacements as large as 2mm, both
symmetric and asymmetric, produced magnetic field errors
that are within acceptable range.
Magnetic studies conclude that the fields and field integrals
are very linear over the full excitation, with the effective field
length (EFL) falling off by only ~1 cm. The multipoles are
stable with only a small saturation effect on the Octupole
component. Inductance of Q23 is nearly constant up to
currents of 3000A and dropping to 0.77H at 5000 amps.
1.43 T
Critical Current Margin
1217 A
III. Q23 QUADRUPOLE SUPERCONDUCTOR AND STABILITY
Temperature Margin
2.18 K
Kapton Thickness
0.1 mm
B-stage Epoxy Thickness
0.2 mm
The SHMS Q23 Quadrupole uses 7.7Km of surplus SSC
outer conductor Rutherford cable per magnet. The Rutherford
cable will be wave soldered to a copper substrate. The
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Conductor critical current and load lines
25000
fit @ 4.4 K
SHMS quad
fit at 6.623 K
Tested Average
Current Amps
20000
15000
10000
5000
0
0
2
4
6
8
10
12
Peak field Tesla
Fig. 2. SHMS Q23 Quadrupole Short Sample and load line
IV. SHMS QUADRUPOLE MECHANICAL DESIGN
The SHMS Q23 Quadrupole cold mass design uses an
innovative coil preloading system which includes a shrink fit
stainless steel force collar and Titanium keys [6]. The FEA
analysis of the SHMS Q23 Quadrupole Force Collar is
ongoing at Accel [7] under contract from JLAB. They are
analyzing the SHMS quadrupole magnets force collars and
coil clamping mechanism in a parallel effort with JLAB. Final
results are expected soon but already there is evidence that the
general technique is sound. A somewhat related technique
now being used by a team at CEA/Saclay to design the R3BGlad Dipole [8] was the inspiration for the selection of this
cold mass clamping technique.
The cryostats for the SHMS Q23 Quadrupoles are
straightforward cylindrical assemblies. Many of the design
features of the High Momentum Spectrometer (HMS) Q2/Q3
of Hall C are incorporated into this design. The stainless steel
Helium containment vessel and insulating vacuum vessel are
based upon the Q2/Q3 design of the HMS. The new design
uses inflated stainless steel panels as the LN2 shields. The
cryogenic control reservoir for all the SHMS magnets will be
based on a standard JLAB design. The reservoir has the
capability of providing several hours of Helium and Nitrogen
cooling to the magnet in the event of cryogen feed disruption.
It also contains the “burnout proof” current leads, JLAB
standard cryogenic control valves, bayonets, and some of the
magnet instrumentation.
V. SHMS Q23 “NO BURNOUT” CURRENT LEADS
The SHMS magnets will all be equipped with nominal 5000
Amp vapor cooled current leads that are a “no burnout”
design. A pair of these current leads was designed, built and
tested at American Magnetics Inc. under contract from JLAB
[9]. These tests were conducted by Gregory J. Laughon of
AMI and Paul D. Brindza. These vapor cooled current leads
are similar in construction to standard super conducting
magnet optimized vapor cooled leads but they have a longer
effective length and a larger conducting cross section. The
extra current lead mass permits a much longer thermal
runaway time in the absence of cooling. The output of DC
power supplies available for testing was limited to 4900
Amps. The vapor cooled current leads were tested at this
current with no cooling. The time to reach the maximum safe
temperature and corresponding voltage was measured. The
current leads were also slow discharged at different rates and
again the temperature and voltage profiles were measured. The
main conclusions from these tests are that the leads can remain
at a constant current of 4900 Amps for 11.3 minutes before
reaching 200 milli Volts and 325 Kelvin maximum
temperature. The current leads exhibit a stable temperature
profile that is everywhere safe at currents up to 3400 Amps,
the maximum no cooling DC current. The leads are capable of
very slow ramp downs of 2.5 Amps/sec or 2000 seconds
discharge time. When the current reaches the no cooling
maximum DC current limit, 3400 A, the temperature and
voltage begins to decrease during the slow discharge. The time
and temperature performance of these “no burnout” vapor
cooled current leads are shown in Fig. 3 and Fig. 4. The no
burnout vapor cooled current leads are cryogenically reoptimized and they require cooling that is only 9 % higher
than conventional vapor cooled leads. It is this author’s
opinion that this is a very small cost to bear in exchange for
the safety and reliability. It is the plan of Jefferson Lab to
equip all five of the SHMS magnets with a pair of these “no
burnout” current leads as GFE.
100
90
Voltage Drop (mVolts)
properties of the Q23 Conductor are listed in Table III. This
superconductor exhibits classic Stekly stability in the SHMS
Q23 Quadrupole magnets, with an alpha of 0.93. Short sample
testing of the Rutherford cable to be used in Q23 was
performed at Brookhaven National Laboratory under the
supervision of Arup Ghosh [5]. The average results of these
tests for the spools to be used for Q23 are shown in Fig. 2
along with a nominal short sample curve and the load line for
Q23.
Each turn of the copper stabilized conductor is insulated
with half lapped Kapton tape and over wrapped with B-stage
glass epoxy tape. A 1mm thick sheet of G10 will be inserted
between the layers and used as ground insulation. The use of
B-stage tape requires that the coil assembly be cured on the
winding table. This rigid coil package allows for handling of
the coil assembly and installation of the force collar.
Lead 1
80
Lead 2
70
60
50
40
30
20
10
0
0
500
1000
1500
2000
2500
Time (seconds)
Fig. 3. Voltage profile during two discharges without cooling at 5 Amp/sec
and 2.5 Amp/sec.
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(USDOE/OHEP), Dr. Ron Scanlon (LBNL) and Dr. Dan
Dietderich (LBNL) in acquiring the surplus SSC cable for
Jefferson Lab. We would also like to acknowledge the
excellent work of Dr. Arup Ghosh whose superb test facility
provided the cable test data that will allow Jefferson Lab to
use the cable in these magnets with confidence.
300
200
150
100
REFERENCES
Sensor 1
Sensor 2
Sensor 3
Sensor 4
Sensor 5
(K)
Temperature (K)
250
[1]
[2]
50
0
0
500
1000
1500
2000
2500
3000
Time (seconds)
Fig. 4. Temperature profile during two discharges without cooling at 5
Amp/sec and 2.5 Amp/sec
[3]
[4]
[5]
VI. CONCLUSIONS
The super conducting SHMS Q23 Quadrupoles and the similar
SHMS Dipole design form the heart of the SHMS
spectrometer. The large 60 cm warm bore aperture of the Q23
magnets is essential to achieving the relatively high 4.5 mStr.
solid angle acceptance of the SHMS. The nominal 13
Tesla/meter gradients are essential to achieve focusing and
good resolution at momentum up to 12 GeV/c. Jefferson Lab
expects to award the fixed price best value contract for the
construction of the Q23 Quadrupoles in the second quarter of
FY 10 with nominal SHMS commissioning planned for FY14
and the start of the era of 12GeV Nuclear Physics at JLAB.
ACKNOWLEDGMENT
The authors would like to acknowledge the support of the
United States Department of Energy Office of High Energy
Physics and the technical support of Dr. Bruce Strauss
[6]
[7]
[8]
[9]
The Science and Experimental Equipment for the 12 Gev/c Upgrade of
CEBAF, Jan. 2005, http://www.jlab.org/12GeV/development.html.
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.
12 Gev/c Upgrade Project Conceptual Design and Safety Review of
Superconducting Magnets, Sep. 2006, http://www.jlab.org/~brindza/SC
Mag Rev -final/
John J. LeRose private communication, JLAB, January 2007, “Optics
Study of SHMS using Raytrace and TOSCA fields”
Arup Ghosh, Private communication, BNL, Report. August 2007 “Short
Sample tests of SSC Cables for JLAB”.
P.B. Brindza et al, “A Super Conducting 60 cm Warm Bore Cosine
Theta Dipole Magnet for the Jefferson Lab Super High Momentum
Spectrometer (SHMS)”, IEEE Magnetic Technology, submitted for
publication.
Bernhard Fischer and A. Hobl, private communication, Accel Inc.
August 2007
C.Mayri et al, R3B-GLAD Technical Report CEA/Saclay reference I008406 ver.1, June 29,2006.
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