Dipole Magnet Design and Innovations Ramesh Gupta
NSLS II Magnet Critical Design & Production Readiness Review
Dipole Magnet Design and Innovations Ramesh Gupta
http://www.bnl.gov/magnets/staff/gupta/ Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #0 BROOKHAVEN SCIENCE ASSOCIATES Overview
• Brief review of the magnetic designs ¾ Reference, Stangenes and Buckley • Special features/considerations/innovations: ¾ Extended pole (nose) to save space by increasing the effective magnetic length ¾ Matching between 35 mm and 90 mm aperture dipoles • Analysis of the measurements ¾ Two 35 mm dipoles have been tested (short length from Stangenes and full length from Buckley)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #1 BROOKHAVEN SCIENCE ASSOCIATES 35 mm Dipole Cross-section (reference design)
• 16 turns, 13 mm X 13 mm each With circular cooling water holes. Overall current density for 0.4 T ~ 1.8 A/mm2. • Since coils are sufficiently above midplane, asymmetric pole bumps were not required for removing quadrupole-type terms despite the yoke having a C-shape.
Specified good field quality (a few part in 104) +/-20 mm in horizontal and +/-10 mm in vertical. Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #2 BROOKHAVEN SCIENCE ASSOCIATES 35 mm Dipole Cross-section (Stangenes design)
At that time, asymmetric pole deflection due to Lorentz forces was issue and an Aluminum Model ~ as delivered plate was incorporated to minimize that (more analysis showed Al plate was not required).
Width of a pole bump (closer to the added yoke) was reduced by 1 mm to keep quad term low.
Al
Specified good field quality (a few part in 104) +/-20 mm in horizontal and +/-10 mm in vertical. Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #3 BROOKHAVEN SCIENCE ASSOCIATES 35 mm Dipole Cross-section (Buckley design)
• Pole region was modified to particular construction (coil/yoke interface). • Pole bumps are almost symmetric again. • Influence of asymmetric mechanical deflection was examined.
Specified good field quality (a few part in 104) +/-20 mm in horizontal and +/-10 mm in vertical. Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #4 BROOKHAVEN SCIENCE ASSOCIATES Unique Feature : Extended Pole (Nose)
We take advantage of the low field requirements (0.4 T)
Allows magnetic length > Mechanical length Length of the nose piece in the Buckley design is about ~10 cm on each side. Thus space made available for other uses in the machine > 10 meters.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #5 BROOKHAVEN SCIENCE ASSOCIATES Special Feature: Extended Pole (Nose) (Saves a significant amount of space in tunnel) • In most iron dominated magnets, the magnetic length is determined by the length of the yoke and mechanical length by the length of the coil. Thus the mechanical space taken by the coil ends is wasted. • The proposed “Pole Extension” or “Nose” essentially eliminates this waste. For all practical purpose, yoke length becomes the same as the coil length. This works particularly well in low field magnets. • In this proposal the coil ends are placed above an extended yoke. The surface of the pole remains an equi-potential, and the magnetic field for the beam remains almost at the full value (as long as the iron is not saturated). • The coils must be raised above (or at least lifted above at the ends) to allow space for this extension. • The nose will be consisted of one or more pieces. As an added benefit, it allows easy 3-d tuning of the fields (design and machine nose pieces after the first set of magnetic measurements). • Nose piece also allows us to choose between a sector magnet or ends with parallel face. A ~5.2 mm wedge cut in the nose piece would create a sector bend with end fields perpendicular to the trajectory.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #6 BROOKHAVEN SCIENCE ASSOCIATES Optimization of Extended Pole (Nose)
A number of studies were done to optimize axial extension and height of the the extended pole (nose).
Long Nose No Nose Good Nose (too greedy, (extended pole) note saturating nose) Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #7 BROOKHAVEN SCIENCE ASSOCIATES Variation in the Length of Nose Piece
Extended pole (good nose)
Conventional Too greedy (long nose)
Note a slight gradual drop in the field (it has been verified with the measurements).
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #8 BROOKHAVEN SCIENCE ASSOCIATES Magnetic Properties of the Iron in the Nose Piece
0.41 Iron property (B-H curve) 0.4 matters. A good magnet steel 0.39 must be used.
0.38 By(average)
By (T) By(unisil) 0.37
0.36
0.35 -400 -350 -300 -250 -200 -150 -100 Z (mm)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #9 BROOKHAVEN SCIENCE ASSOCIATES Nose Pieces in the R&D Model Magnets
Why are we paying so much attention to the details of nose pieces?
If the nose pieces are not too long and they are made of good material then the length gained won’t matter so much on the details.
However, the field measurements (and simulations) indicate that: a) Choice of magnetic material of nose piece was not good in case of short model from Stangenes b) Length of the nose piece was increased a bit too much: ~68 mm in Stangenes to ~104 mm in Buckley (the initial design was examined up to 85 mm without any problem for typical iron) c) This issues is, however, a less of a concern in fixed field magnet as long as the B-H property of nose material does not vary from nose to nose.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #10 BROOKHAVEN SCIENCE ASSOCIATES Short Model Magnet from Stangenes
Back of the magnet Front of the magnet
Design Parameters for the short model magnet: • Yoke-to-yoke length = 0.962 meter • Nose-to-nose length = 1.137 meter (2 nose pieces, 68.5 mm each) • Plate-to-plate = 1 meter (plate is non-magnetic) • Design field = 0.4 T Without nose
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #11 BROOKHAVEN SCIENCE ASSOCIATES Nose Piece that was initially delivered had to be replaced
Because: • Nose piece should have extended to the coil ends ¾ it did not ! • Mounting bolts should not have extended beyond the end of the nose ¾ they did !!
Nose
Actual measurements were done with the correct nose piece.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #12 BROOKHAVEN SCIENCE ASSOCIATES Axial Field Profile of Stangenes Dipole at 0.4 Tesla
Courtesy Magnetic Field By vs Z Ping He I=360A 0.4
0.35
0.3
0.25
0.2 Tesla 0.15
0.1
0.05
0 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 Z(mm)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #13 BROOKHAVEN SCIENCE ASSOCIATES Axial Field Profile at 0.4 Tesla with/without nose piece
Courtesy Magnetic Field By vs Z Ping He I=360A 0.4
0.35
0.3
0.25
0.2 Tesla 0.15 without nose 0.1
0.05 with nose
0 200 300 400 500 600 700 800 X(mm)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #14 BROOKHAVEN SCIENCE ASSOCIATES Magnetic Model of Stangenes 35 mm Short Dipole (1)
Model made from the CAD model (SAT file) provided by the vendor
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #15 BROOKHAVEN SCIENCE ASSOCIATES Magnetic Model of Stangenes 35 mm Short Dipole (2)
Model made by extruding the optimized OPERA-2d model
• Using vendor CAD file assures that, in principle, we are make model of the as built magnet. • However, this may not necessarily produce the best mesh for the most accurate field calculations for the same number of mesh points as more mesh points may go in less critical area. • Therefore, I generally prefer the method described here is preferred as it gives a better handle on the mesh and hence on the accuracy of field calculations. • Also sometime CAD model sent by vendor may not match the actual magnet.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #16 BROOKHAVEN SCIENCE ASSOCIATES Extension of Magnetic Field Region Due to Nose
Computer model Length of the Nose Piece = 68.5 mm Measurements
0.410 Also note: A large drop in field in 0.405 nose region (only Note: In case of nose, 0.400 in measurements). a gradual decrease in 0.4 0.395 0.35 B (T) field along the axis Is it mechanical (both calc. & meas.) 0.3 0.390 Tesla or magnetic? 0.25
0.385 0.2 By(without nose) without nose 0.15 0.380 By(with nose) 0.1 with nose 0.375 0.05
0 0.370 200 300 400 500 600 700 800 -1300 -1200 -1100 -1000 -900 -800 X(mm) Z(mm)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #17 BROOKHAVEN SCIENCE ASSOCIATES Axial Field Profile at 0.2 Tesla (half the design field)
Courtesy Magnetic Field By vs Z Ping He I=180A 0.2 0.18 0.16 0.14 0.12 0.1 Tesla 0.08 0.06 0.04 0.02 0 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 z(mm)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #18 BROOKHAVEN SCIENCE ASSOCIATES Verification of Iron Saturation in Nose
If drop in field in nose region is due to mechanical discrepancy, then the relative drop would be independent of excitation
1.05 ~0.2 T
1.00 ~0.4 T
0.95
0.90 Relative Field BNL Measurements on 0.85 Stangenes 35 mm Short Dipole
0.80 400 420 440 460 480 500 520 540 560 580 Distance from the center (mm) However, if the relative drop is due to iron saturation, then the drop would be lower at lower fields (lower saturation, as here). Conclusion: It’s magnetic NOT mechanical.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #19 BROOKHAVEN SCIENCE ASSOCIATES Field Errors in the Aperture
NSLS-II Dipole Prototype Radial Field Uniformity NSLS-II Dipole Prototype Radial Field Uniformity z = 400 z = 300 z = 200 z = 100 z = 0 z = 400 z = 300 z = 200 z = 100 z = 0 z = –100 z = –200 z = –300 z = –400 Spec. z = –100 z = –200 z = –300 z = –400 Spec. Measurements 5 5 350 A Current 4 ) 4 courtesy:
z At midplane (y = 0) 3 3 ) (0,0, Animesh Jain y z 2 B
2 ) – z
)]/ 1
z & Ping He 1 (0,10, y ,10, 0 B x ( (0,0, )]/ y y 0 -1 z B B
[ -2 -1 × ) –
4 z (0,10, -3 10 y
,0, -2 B x
( -4 350 A Current y -3 B 10 mm above midplane (y = 10) [ -5 We generally ×
-4 4 -6 10 -5 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 meet the specs. -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 Radial Position, X (mm) Radial Position, X (mm) NSLS-II Dipole Prototype Radial Field Uniformity There are z = 400 z = 300 z = 200 z = 100 z = 0 z = –100 z = –200 z = –300 z = –400 Spec. always 5 4 additional 3 errors due to )
z 2 ) –
z construction, 1 (0,–10, y ,–10,
B 0 calculations and x ( )]/ y z B -1 [ measurements. ×
4 -2 (0,–10, 10
y 350 A Current The agreement
B -3 10 mm below midplane (y = –10) -4 is reasonable.
-5 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 Radial Position, X (mm)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #20 BROOKHAVEN SCIENCE ASSOCIATES Comparison Between Calculations and Measurements
Integral Magnetic Field A reasonable agreement between Measurements 1 calculations and measurements
-1 Computed Integral Errors -3 2 -5 0 -7 -2 -9 -4 Y=-10(mm) -6
(BL-BL0)/BL0 [10^(-4)] -11 Y=0(mm) Y=0 -8 -13 Y=10(mm) Y=5 -10 Y=10 -15 10^4 * dBy/By -20-15-10-50 5 101520 -12 -14 X(mm) -16 -20 -15 -10 -5 0 5 10 15 20 As per plan, the nose will be X(mm) chamfered to minimize the 100
0 measured integrated error. -40 -30 -20 -10 0 10 20 30 40 -100 Field quality specs are -200 Also present small -300 quad and perhaps expected to be met. -400 Y=0 Y=5 -500 higher order odd terms
-600
-700
-800
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #21 BROOKHAVEN SCIENCE ASSOCIATES Axial Profile in 35 mm Stangenes Dipole
1.002 ~0.2 T 1.001 ~0.4 T
1.000
Relative Field Relative 0.999 BNL Measurements on Stangenes 35 mm Short Dipole 0.998 -200 -160 -120 -80 -40 0 40 80 120 160 200 Distance from the center (mm) A few part in 1,000 variation has been observed along the magnet length. Possible cause (mechanical or magnetic) is under investigation. Is it typical? Is it a machine performance issue?
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #22 BROOKHAVEN SCIENCE ASSOCIATES Full Length 35 mm Dipole R&D Model from Buckley
Just Arrived (Friday afternoon)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #23 BROOKHAVEN SCIENCE ASSOCIATES Nose Area in Buckley 35 mm Dipole
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #24 BROOKHAVEN SCIENCE ASSOCIATES Axial Profile 0f 35 mm Buckley Dipole (as measured in New Zealand) (normal pole : 2*1.192 m)
4000
3500
x=-20mm 3000 x=-16mm (nose-to-nose : 2*1.296 m) x=-12mm 2500 x=-8mm
x=-4mm 2000 x=0mm Field (G) Field
x=4mm 1500 (actual dimensions are being verified) x=8mm
x=12mm 1000 x=16mm
500 x=20mm
0 -1600 -1400 -1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 1200 1400 1600 Axial Position (mm)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #25 BROOKHAVEN SCIENCE ASSOCIATES Details of Measurements in End (nose) Region
4000 Nose 3500
x=-20mm 3000 x=-16mm
x=-12mm 2500 (nose extension was increased to x=-8mm
~104 mm from original 68.5 mm) x=-4mm 2000 x=0mm Field (G)
x=4mm 1500 x=8mm
x=12mm 1000 x=16mm
500 x=20mm
0 1000 1050 1100 1150 1200 1250 1300 1350 1400 Axial Position (mm)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #26 BROOKHAVEN SCIENCE ASSOCIATES Nose Area in Buckley 35 mm Dipole
There is a clear opportunity to minimize a small drop in field in nose region (insert iron, extend normal pole, etc.)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #27 BROOKHAVEN SCIENCE ASSOCIATES Drop in Field in Nose Region
4000 Nose 3500
x=-20mm 3000 x=-16mm
x=-12mm 2500 (nose extension was increased to x=-8mm
~104 mm from original 68.5 mm) x=-4mm 2000 x=0mm Field (G) Field
x=4mm 1500 x=8mm
x=12mm 1000 x=16mm
500 x=20mm
0 1000 1050 1100 1150 1200 1250 1300 1350 1400 Axial Position (mm) The magnet has just arrived (Friday). We would do more analysis to explain and fix this drop. In principle it is possible to create even a larger drop than the one measured (see one simulation on right). We would do measurements at lower field, etc. to follow-on.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #28 BROOKHAVEN SCIENCE ASSOCIATES Field Along the Magnet Axis (fine variations)
4000 3999 Original measurements at Buckley 3998 3997 (more measurements to be performed at BNL)
3996 x=-20mm 3995 x=-16mm 3994 3993 x=-12mm
3992 x=-8mm 3991 x=-4mm 3990 x=0mm Field (G) Field 3989
3988 x=4mm 3987 1 part in 1,000 is ~4 Gauss (as also seen in x=8mm 3986 Stangenes dipole in BNL measurements) x=12mm 3985 3984 x=16mm
3983 x=20mm 3982 3981 3980 -1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 1200 Axial Position (mm)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #29 BROOKHAVEN SCIENCE ASSOCIATES Field Quality in Magnet Aperture
Measurements at Buckley (original) 3992
3991.6
3991.2
3990.8
3990.4
By (G) By 3990 1 box (0.4 G) is 1 part in 10,000
3989.6
3989.2 z=-10mm 3988.8 z=-5mm (z is vertical here) z=0mm 3988.4 z=+5mm z=+10mm 3988 -20 -15 -10 -5 0 5 10 15 20 Horizontal (mm)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #30 BROOKHAVEN SCIENCE ASSOCIATES Field Quality in Magnet Aperture
Measurements at Buckley (after re-machining) 3971.8 1 box (0.4 G) is 1 part in 10,000 3971.4 Field quality seems to have improved by 3971 re-machining By (G) By
3970.6 z=-10mm z=0mm (z is vertical here) z=+10mm 3970.2 -20 -15 -10 -5 0 5 10 15 20 Horizontal (mm)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #31 BROOKHAVEN SCIENCE ASSOCIATES Field Along the Magnet Axis (fine variations)
3980 3978 Measurements at Buckley after re-machining 3976 (more measurements to be performed at BNL) 3974 3972 3970
Field (G) Field 3968 3966 1 part in 1,000 is ~4 Gauss (as also seen in 3964 Stangenes dipole in BNL measurements) 3962 3960 -1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 1200
Axial Position (mm)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #32 BROOKHAVEN SCIENCE ASSOCIATES Buckley Dipole (before and after re-machine#2) 4000 3999 3998 3992 3997 3991.6 3996 3995 3991.2 3994 x=-20mm 3993 3990.8 3992 x=-16mm x=-12mm 3990.4 3991 3990 x=-8mm
By (G) By 3990 3989 x=-4mm
3988 x=0mm 3989.6 Field (G) 3987 x=4mm 3986 3989.2 x=8mm z=-10mm 3985 x=12mm 3988.8 z=-5mm 3984 z=0mm x=16mm 3983 z=+5mm x=20mm 3988.4 3982 z=+10mm 3981 3988 3980 -20 -15 -10 -5 0 5 10 15 20 -1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 1200 Horizontal (mm) Axial Position (mm)
3971.8 3980 3978
3971.4 3976 3974 3972 3971
By (G) By 3970
Field (G) Field 3968
3970.6 3966 z=-10mm 3964 z=0mm z=+10mm 3962 3970.2 3960 -20 -15 -10 -5 0 5 10 15 20 -1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 1200 Horizontal (mm) Field quality seems to have 1 part in 1,000 Axialis Position~4 (mm)Gauss (as also seen in improved by re-machining Stangenes dipole in BNL measurements)
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #33 BROOKHAVEN SCIENCE ASSOCIATES 90 mm aperture dipole
Coils and mechanical features (such as enclosure) are shown. Yoke is hidden in side this box.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #34 BROOKHAVEN SCIENCE ASSOCIATES 90 mm Aperture Dipole built at Stangenes
Magnet arrived recently. This is being prepared for magnetic measurements. No update over last review.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #35 BROOKHAVEN SCIENCE ASSOCIATES Fine Tuning of Transfer Function Matching (between 35 mm and 90 mm aperture dipoles) Ends of 35 mm Dipole Ends of 35 mm Ends of 90 mm Dipole In addition to obtaining the desired low integral harmonics in both magnets, the integral transfer function between the two must also match ¾ Computed B at 360 A: 0.39711 T in 35 mm and 0.39706 T in 90 mm. Difference <0.02%; this is within manufacturing errors/BH curve and calculation and measurement errors ¾ Fine tuning of the integral field, if needed, may be done by adjusting the length of the nose piece of 35 mm dipole after the field measurements of both 35 mm and 90 mm dipoles ¾ Controlled saturation in nose and adjustment in packing factor can be used to better match the field profile, if needed.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #36 BROOKHAVEN SCIENCE ASSOCIATES Laminations of 35 mm and 90 mm Aperture Dipoles
Note: Width has not grown as much as the pole gap
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #37 BROOKHAVEN SCIENCE ASSOCIATES Design Parameters of 90 mm Aperture Dipole
Magnet Gap – 90 mm (minimum clearance)
Nominal Field – Bo = 0.40 T (+20%) -4 Field Homogeneity in BX & BY = 1 x 10
Good field region BX : +/- 20mm, BY : +/- 10mm Magnetic length – 2620 mm Nominal Current density in the coil cross section 2 Amps/mm2 Maximum allowable temperature rise 10 degrees C Maximum Pressure across the Magnet 60 psi. Bend Radius ~25 m
• Except for the gap, all design parameters are the same as in 35 mm dipole. • Since the relative value of good field aperture is small in this magnet, the pole width to pole gap ratio can be made smaller. • 35 mm and 90 mm dipole should run on the same power supply and therefore the transfer function of the two magnets should match.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #38 BROOKHAVEN SCIENCE ASSOCIATES Comparison of 35 mm and 90 mm Aperture Dipoles
Overall design 90 mm aperture 35 mm aperture
Note: 35 mm and 90 mm are the minimum vertical clearances. Pole gaps at the magnet center are slightly higher.
• Same conductor chosen for both dipoles (number of turns are adjusted) - 16 turns (4 X 4) in 35 mm aperture case and 42 turns (6 X 7) in 90 mm aperture case.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #39 BROOKHAVEN SCIENCE ASSOCIATES Matching of Transfer Function (current) between 35 mm and 90 mm Aperture Dipoles They should match within 0.1% (initially it was 1%) 90 mm aperture 35 mm aperture
First matching is done by carefully choosing the conductor and number of turns. Then the pole gap at the center is adjusted to obtain a more closer match. Field quality optimization needs to be carried out again as it changes the pole bumps.
Finer adjustment after magnetic measurements (as discussed later) will be carried out by fine tuning the length of the extended pole (nose) in 35 mm aperture dipole.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #40 BROOKHAVEN SCIENCE ASSOCIATES 2-d Magnetic Design of 90 mm Aperture Dipole
¾ Required minimum vertical gap (clearance) is 90 mm. Since pole bumps are used for field shaping, the conventional pole gap will be higher. ¾ Pole gap was adjusted to match (fine tune) the transfer function with 35 mm dipole. ¾ Optimized bumps are : 2.58 mm high and (a) 20.5 mm wide on left and (b) 23 mm wide on right. They are made asymmetric to compensate for the inherent asymmetry of C-shape dipole (asymmetry was not required in 35 mm as coil was high). ¾ By comparison, in 35 mm dipole, bumps were 0.5 mm high and 13 mm wide on either side (symmetric). Height was kept smaller in 35 mm but not required here. ¾ Calculation of pole overhang factor (x) for 1 part in 104 for relative field errors. Half gap h=47.58 mm, good field aperture/2=20 mm, pole overhang a=90-20=70 mm • x=a/h = 70/47.58 = ~1.47. • By comparison, overhang factor was 1.67 in case of 35 (36) mm aperture dipole. • Pole width/Pole gap is ~1.9 (by comparison it was ~2.8 in 35 (36) mm dipole).
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #41 BROOKHAVEN SCIENCE ASSOCIATES SUMMARY
• 35 mm dipole program is in advanced stage. • Field quality specs are being met in the cross-section. End region will be optimized by chamfering the nose piece (as planned). • The nose piece has extended the magnetic length of the dipole. • It is important to use good steel in the nose region. This can saturate appreciably particularly since the length of it is significantly increased (68.5 mm to ~104 mm). We would further look to mitigate the saturation. • 90 mm dipole has been delivered. Field quality measurements will be carried out soon. • Integral transfer function and integral field harmonics of 35 mm aperture and 90 mm aperture dipoles will be matched with the help of nose piece, etc.
Dipole Magnet Design and Innovations, Ramesh Gupta, February 23, 2009 Slide #42 BROOKHAVEN SCIENCE ASSOCIATES