Transcript Sextupole Terms in the BEPC Quads #1 & #2

Construction and Testing of
Superconducting Magnets for the
BEPC-II Interaction Region
Animesh Jain
on behalf of
Superconducting Magnet Division
Brookhaven National Laboratory, Upton, NY 11973, USA
4th BEPC-II IMAC Meeting, Beijing, April 26-28, 2006
Introduction
• Brookhaven National Laboratory has designed, built
and tested two superconducting magnets for the
BEPC-II interaction region.
• Each of these magnets contains several coils to produce
normal and skew quadrupole, normal and skew dipole,
and solenoidal fields.
• All coils in both the magnets have performed
satisfactorily with ample margin.
• This talk briefly describes the construction and testing
of these magnets, with particular emphasis on field
quality.
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Nominal Design Parameters
Coil
Inner
Diameter
(mm)
Magnetic
Length
(m)
Integral
Transfer
Function
Normal Quadrupole
(SCQ)
190
0.400
Normal Dipole*
(SCB)
217
0.400
4.37  10
–4
Skew Dipole
(VDC)
226
0.381
8.28  10
–4
Skew Quadrupole
(SKQ)
228.5
0.400
1.57  10
7.72  10
–2
T/A
T·m/A
T·m/A
–3
T/A
* Normal dipole may also be used in a horizontal corrector (HDC) mode.
Not listed here: Anti-Solenoids (AS1, AS2 and AS3)
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
BEPC-II Coil Design
• All coils consist of one or more double-layers of a
“Serpentine” winding pattern.
• This type of winding pattern was recently developed at
BNL, and has several advantages over conventional
“Spiral wound” coils.
(B. Parker and J. Escallier, Proc. PAC’05, pp.737-9.)
• The patterns are wound directly on a cylindrical surface
using an automatic winding machine.
• Except for a “Serpentine” pattern, all other construction
features of the BEPC-II coils were similar to magnets
built by BNL in the past for the HERA upgrade.
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
No. of Layers and Turns
Coil
Total No.
of Layers
Total
Number of
Turns
Conductor
Normal Quadrupole
(SCQ)
8
317
per pole
1 mm dia.; 6-around-1 cable
Cu:SC = 1.8:1
Normal Dipole
(SCB)
2
178
per pole
1 mm dia.; 6-around-1 cable
Cu:SC = 1.8:1
Skew Dipole
(VDC)
2
364
per pole
0.33 mm dia.; single wire
Cu:SC = 1.8:1
Skew Quadrupole
(SKQ)
2
200
per pole
Anti-Solenoid 1
(AS1)
6
732
Anti-Solenoid 2
(AS2)
2
260
Anti-Solenoid 3
(AS3)
6
280
0.33 mm dia.; single wire
Cu:SC = 1.8:1
2.4 mm  1.5 mm MRI wire
Cu:SC = 6.9:1
2.4 mm  1.5 mm MRI wire
Cu:SC = 6.9:1
2.4 mm  1.5 mm MRI wire
Cu:SC = 6.9:1
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Winding Different Conductor Types
SCQ
VDC
AS2
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Ensuring Good Field Quality
• For a short length magnet, the ends contribute
significantly to both the allowed and the unallowed
harmonics.
• The harmonics from the ends were compensated in the
design by modulating the angular positions of the
conductor in the entire pattern.
• Warm field quality was measured after each double
layer was wound.
• In the case of the main quadrupole (SCQ), the results of
the warm measurements were used to modulate the
subsequent double-layers to progressively improve the
field quality.
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Coil Section at the Magnet Center
BEPC2 Coil Cross Section
120
SCQ
SCB/HDC
VDC
SKQ
110
100
Y-Position (mm)
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
90
100
110
120
X-Position (mm)
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Warm and Cold Tests of Coils
• Warm measurements were carried out after each double
layer was wound using a 0.92 m long, 68.5 mm radius
rotating coil system.
• The completed coil assemblies were cold tested in a vertical
dewar for satisfactory performance beyond the nominal
operating currents.
• Field quality measurements were also made in the
superconducting state using the same rotating coil system
that was used for the warm measurements.
• Field quality was measured in all the coils individually, and
also in the SKQ, VDC and HDC (SCB) coils with the SCQ
powered in the background at 477A.
• The solenoids were measured warm using a Hall probe.
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Summary of Warm Measurements in BEPC-II IR Magnets Built by BNL
Integral Transfer Functions are in T/kA for the quadrupoles and in T.m/kA for the dipoles.
Field angles are with respect to the SCQ, and are from the final warm measurements.
Quantity
Int. Trans. Func.
Field angle (mr)
b 1 (unit)
b 2 (unit)
b 3 (unit)
b 4 (unit)
b 5 (unit)
b 6 (unit)
b 7 (unit)
b 8 (unit)
b 9 (unit)
b 10 (unit)
b 11 (unit)
a 1 (unit)
a 2 (unit)
a 3 (unit)
a 4 (unit)
a 5 (unit)
a 6 (unit)
a 7 (unit)
a 8 (unit)
a 9 (unit)
a 10 (unit)
a 11 (unit)
SCQ at 50 mm
SCB at 38 mm
VDC at 50 mm
SKQ at 50 mm
Magnet 1 Magnet 2 Magnet 1 Magnet 2 Magnet 1 Magnet 2 Magnet 1 Magnet 2
15.73
----10000
0.35
-0.47
0.04
0.37
0.13
-0.13
-0.04
-0.01
-0.02
-----1.28
-1.26
0.05
0.04
-0.18
-0.08
0.05
0.05
0.03
15.77
----10000
1.80
0.06
-0.06
0.42
0.45
-0.13
-0.04
0.02
-0.07
-----1.63
-0.53
0.05
-0.09
-0.34
-0.11
0.06
0.04
0.06
4th BEPC-II IMAC Meeting, April 26-28, 2006
0.451
-2.16
10000
6.17
2.11
-0.59
-0.22
0.11
-0.02
-0.01
0.00
0.00
0.00
---4.92
-2.68
-0.25
0.52
-0.02
-0.03
0.01
0.00
0.00
0.00
0.452
11.04
10000
6.37
3.28
-0.17
0.06
0.01
-0.03
0.00
0.00
0.00
0.00
---4.80
-3.45
0.43
0.98
0.00
-0.09
0.00
-0.01
0.00
0.00
9
0.855
7.2
--4.05
1.00
0.02
-0.22
-0.08
0.01
0.01
-0.01
0.00
0.00
10000
-0.63
-1.01
0.09
-0.04
0.01
-0.18
0.05
0.19
-0.01
0.24
0.860
8.1
---3.34
-0.77
0.41
-1.36
0.11
-0.10
-0.01
0.06
0.00
0.01
10000
3.32
2.70
0.42
1.01
0.05
-0.19
0.02
0.17
0.00
0.26
7.70
8.4
----5.36
0.84
0.05
0.09
-0.09
-0.03
-0.01
-0.03
-0.01
--10000
-2.30
1.38
0.25
0.39
0.06
0.02
0.04
-0.04
0.00
7.80
8.5
----0.79
-2.93
0.53
-0.37
-0.08
0.08
0.00
0.02
-0.02
--10000
-0.68
-2.28
0.19
0.21
0.14
-0.08
0.02
-0.02
0.01
Animesh Jain: BNL
AS2 Field Profiles
in BEPC
MagnetsProfiles
#1 & #2
AS2 Solenoid
Axial
Field
Axial Field (T/kA)
0.9
0.8
Magnet#1
0.7
Magnet #2
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
Axial Distance from Non Lead End (m)
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Ensuring Good Quench Performance
• All coils are designed to have ample margin above the
nominal operating current.
• It is necessary to have enough precompression in the
coils to prevent any conductor motion due to Lorentz
forces, which could cause a quench.
• Large gaps in the pattern (e.g., at the poles) were filled
with G-10 spacers (Nomex for VDC and SKQ).
• All gaps were filled with expansion-matched epoxy.
• Each double-layer was compression wrapped with
S-glass to provide the prestress, and then cured.
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Quench Tests of Various Coils
• All coils were ramped to a maximum test limit, at first
individually, and then in combination (SR & Collider modes).
• Only the AS1 in #1 and AS3 in #2 had one training quench.
All other coils were ramped without any quench.
• All coils were forced to quench using spot heaters at 50% and
100% of the operating current.
Coil
Nominal
Operating Current (A)
Maximum
Test Current (A)
Normal Quadrupole (SCQ)
477
550 (65 in SR mode)
Normal Dipole (SCB/HDC)
496
600 (±65 as HDC)
Skew Dipole (VDC)
27
±65
Skew Quadrupole (SKQ)
47
±65
Anti-Solenoid 1 (AS1)
1078
1300
Anti-Solenoid 2 (AS2)
1078
1300
Anti-Solenoid 3 (AS3)
1078
1300
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Spot Heater Quench Results
HOT SPOT TEMPERATURE
600
Hot Spot Temperature (K)
Magnet #1
500
Magnet #2
With Energy Extraction
(Resistor = 0.5 Ohm)
400
300
200
Reduced Quench
Detection Threshold
used for Magnet #2
100
0
100
200
300
400
500
600
Current (A)
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Magnet Work after Cold Test
• Coil assembly is inserted into a double-walled helium
containment vessel to form the cold mass.
• The cold mass is covered with superinsulation and is
surrounded by an inner and an outer heat shield.
• The cold mass is inserted into the cryostat.
• The cold mass orientation is aligned to the level
surfaces on the cryostat by doing warm magnetic
measurements in the main quadrupole (SCQ). The
orientation is maintained by welding in place.
• Electrical and mechanical work in the lead end.
• Final warm measurements with survey of fiducials.
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Some Assembly Components
Helium Containment
Outer Heat Shield
This manifold is no
longer in the design.
Inner Heat Shield
4th BEPC-II IMAC Meeting, April 26-28, 2006
Complete Magnet
15
Animesh Jain: BNL
Cold Mass Angle Alignment
Precision Level
Angle
Adjustment
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Status as of IMAC in May, 2005
• Magnet #1 cold tests were completed and the first set of
cold field quality data were available.
• Magnet #2 coil winding was completed and was waiting
to be cold tested.
• As per the Committee report:
– The quench test results were quite satisfactory.
– There were concerns about the delay in delivery.
– There were concerns about unexplained sextupole in the
quadrupole (SCQ) cold measurements.
– It was suggested that the possibility of eddy currents in
the idle coils should be excluded based on measurements.
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Present Status
• Both magnets have now been delivered to IHEP:
– Magnet #1 was shipped from BNL in October, 2005.
– Magnet #2 was shipped from BNL in December 2005.
– There was a long delay in the completion of the first
magnet assembly due to leaks in the heat shield assembly
that were very difficult to locate.
– The aluminum tubes originally used in the heat shield
were eventually replaced by stainless steel tubes.
• Extensive measurements were carried out in magnet #2
to pinpoint the source of the unexpected field harmonics
seen during the cold test of magnet #1.
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Continued Support from BNL
• BNL continues to provide support after shipping:
– Andrew Marone and John Escallier from BNL
visited IHEP in January, 2006 to provide support
for valve box assembly and magnet installation.
– George Ganetis and Wing Louie from BNL are
scheduled to visit IHEP to help with the initial
powering of the magnets after cool down, and set up
quench detection and other electrical systems.
(will need at least one month’s notice for travel)
– There will be provisions in the system for remote
monitoring, which could be used when necessary.
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Understanding the Unexpected
Sextupole in the
Cold SCQ Magnets
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Summary of Warm Field Quality in BEPC Quads
Warm measurements at ±1A after completing the skew layers
Harmonics are in "units" of 10–4 at 50 mm radius
Magnet 1 Magnet 2
(QHG202) (QHG203)
(QHG202) (QHG203)
Run 31
Run 24
Run 31
Run 24
15.73
15.77
---
---
b3
0.35
1.80
a3
-1.28
-1.63
b4
-0.47
0.06
a4
-1.26
-0.53
b5
0.04
-0.06
a5
0.05
0.05
b6
0.37
0.42
a6
0.04
-0.09
b7
0.13
0.45
a7
-0.18
-0.34
b8
-0.13
-0.13
a8
-0.08
-0.11
b9
-0.04
-0.04
a9
0.05
0.06
b 10
-0.01
0.02
a 10
0.05
0.04
b 11
-0.02
-0.07
a 11
0.03
0.06
b 12
0.00
0.00
a 12
0.00
0.01
b 13
0.00
0.00
a 13
0.00
0.00
b 14
-0.03
-0.03
a 14
0.00
0.00
b 15
0.00
0.00
a 15
0.00
0.00
ITF (T/kA)
Warm
Measurements
had shown
good field
quality in the
SCQ
Magnet 1 Magnet 2
Low
Sextupole
Content
Note: (b n , a n ) are the normal and skew 2n -pole terms in the harmonic expansion
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Cold Field Quality Measurements
• Cold field quality measurements were carried out in
a vertical dewar.
• The quadrupoles (SCQ) were measured at currents
ranging from 20 A to 550 A.
• The variation of sextupole terms (in Tesla.m at
50 mm) was linear with current, as expected.
• The “geometric” sextupole terms were derived from
the slope of a straight line fit.
• Sextupole in “units” is calculated by comparing this
slope with a similar slope for the quadrupole term.
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
DC Loop Data (20A-550A) in QHG202 Quadrupole (Runs 88-89)
Up Ramp: 4.2323E-04 T.m/kA
Dn Ramp: 4.2136E-04 T.m/kA
0.0E+00
B3 (T.m @ 50 mm)
Quadrupole Slope is 0.7935 T.m/kA
-5.0E-05
-1.0E-04
-1.5E-04
-2.0E-04
Magnet #1
-2.5E-04
-3.0E-04
-550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50
0
Current (A)
Up Ramp: 3.5847E-04 T.m/kA
23
4th BEPC-II IMAC Meeting, April 26-28, 2006
5.0E-05
Dn Ramp: 3.5897E-04Animesh
T.m/kA
Jain: BNL
DC Loop Data (20A-550A) in QHG202 Quadrupole (Runs 88-89)
0.0E+00
5.0E-05
UpUp
Ramp:
4.2323E-04
T.m/kA
Ramp:
3.5847E-04
T.m/kA
Dn
DnRamp:
Ramp:4.2136E-04
3.5897E-04T.m/kA
T.m/kA
Quadrupole Slope is 0.7935 T.m/kA
B3 (T.m @ 50 mm)
A3 (T.m @ 50 mm)
-5.0E-05
0.0E+00
-1.0E-04
-5.0E-05
-1.5E-04
-1.0E-04
-2.0E-04
-1.5E-04
-2.5E-04
Magnet #1
-3.0E-04
-2.0E-04
-550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50
-550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50
Current
Current(A)
(A)
Up Ramp: 3.5847E-04 T.m/kA
24
4th BEPC-II IMAC Meeting, April 26-28, 2006
5.0E-05
0
0
Dn Ramp: 3.5897E-04Animesh
T.m/kA
Jain: BNL
DC Loop Data (20A-550A) in QHG203 Quadrupole (Runs 80-81)
Up Ramp: 1.2039E-04 T.m/kA
Dn Ramp: 1.2030E-04 T.m/kA
0.0E+00
Quadrupole Slope is 0.7945 T.m/kA
B3 (T.m @ 50 mm)
-1.0E-05
-2.0E-05
-3.0E-05
-4.0E-05
-5.0E-05
Magnet #2
-6.0E-05
-7.0E-05
-550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50
0
Current (A)
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Up Ramp: -4.3381E-04 T.m/kA
Animesh Jain: BNL
Dn Ramp: -4.3213E-04 T.m/kA
DC Loop Data (20A-550A) in QHG203 Quadrupole (Runs 80-81)
Ramp:
1.2030E-04
T.m/kA
DnDn
Ramp:
-4.3213E-04
T.m/kA
Quadrupole Slope is 0.7945 T.m/kA
-1.0E-05
2.0E-04
A3 (T.m @ 50 mm)
B3 (T.m @ 50 mm)
Ramp:
1.2039E-04
T.m/kA
UpUp
Ramp:
-4.3381E-04
T.m/kA
0.0E+00
2.5E-04
-2.0E-05
1.5E-04
-3.0E-05
1.0E-04
-4.0E-05
5.0E-05
-5.0E-05
0.0E+00
-6.0E-05
Magnet #2
-5.0E-05
-7.0E-05
-550-500
-500-450
-450 -400
-400 -350
-350 -300
-300 -250
-550
-250 -200
-200 -150
-150-100
-100-50-50 0 0
Current (A)
Current
(A)
4th BEPC-II IMAC Meeting, April 26-28, 2006
Up Ramp: -4.3381E-04 T.m/kA26
Jain: BNL
Dn Ramp: -4.3213E-04Animesh
T.m/kA
Warm to Cold Discrepancy
• The geometric values of sextupole derived from the
cold data were much larger than the warm values
measured before cold test. (For comparison, such changes in
the BNL-built HERA magnets were below 1 unit.)
Magnet #1: b3 = 5.3 units cold (was 0.35 warm)
a3 = 4.5 units cold (was –1.28 warm)
Magnet #2: b3 = 1.5 units cold (was 1.80 warm)
a3 = –5.5 units cold (was –1.63 warm)
• Possible sources: Distortion under cool down;
persistent current effects from other layers;
measurement errors due to a tilt of the measuring coil
with respect to the magnet axis, iron in and around
the dewar, .....
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Warm to Cold Discrepancy
• Out of the possible sources, distortion under cool down,
persistent current effects, and iron around the dewar
seemed to be very unlikely causes.
Distortion: Unlikely that only one harmonic will be
affected. Also, no such effects were seen in earlier
magnet productions. (Distortions also ruled out by
measurements at 35 K in magnet #2: to be discussed later)
Persistent Currents: Should produce a hysteresis (Up
Ramp to Down Ramp difference), which is not seen.
Iron around the Dewar: Should affect both magnets in a
similar way, since they were tested in the same dewar, and
were mounted similarly.
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Example of Persistent Currents
Octupole Term in the BNL-built HERA Quad
8.00E-05
No hysteresis in
unallowed terms
is seen in BEPC
quadrupoles.
B4 (T.m @ 45 mm)
6.00E-05
4.00E-05
2.00E-05
0.00E+00
-2.00E-05
-4.00E-05
-6.00E-05
-8.00E-05
0
100
4th BEPC-II IMAC Meeting, April 26-28, 2006
200
300
Current (A)
29
400
500
600
Animesh Jain: BNL
Warm-Cold Difference: Tilt of Coil
• For long magnets, and magnets with negligible end
harmonics, a tilt of the measuring coil with respect to
the magnet axis does not affect the measurement of
harmonics in a dipole or a quadrupole magnet.
• The BEPC magnets are short, with serpentine coil
design, and have large end harmonics.
• The skew octupole harmonic is large, and of opposite
sign, in the lead end and non-lead end of the magnet.
• A tilt of the measuring coil will cause a sextupole term
by feed down, and the contributions from the two ends
will add up.
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Computed Axial Scan in BEPC Quad
80
b4 (unit)
a4 (unit)
60
in “Units” at 50 mm
Harmonic Norm. to B2(0)
100
40
20
0
-20
-40
-60
-80
A tilt of the measuring coil implies
offsets of opposite sign at the two ends.
This, coupled with the opposite signs of
the skew octupole, will cause a spurious
sextupole due to feed down.
-100
-250
-150
-50
50
150
250
350
450
550
650
750
Axial Position (mm)
4th BEPC-II IMAC Meeting, April 26-28, 2006
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Animesh Jain: BNL
Computed Axial Scan in BEPC Quad
Harmonic Norm. to B2(0)
20
b3 (unit)
a3 (unit)
15
Sextupole term with no tilt.
10
Integral ~ 0 unit
5
0
-5
-250
-150
-50
50
150
250
350
450
550
650
750
Axial Position (mm)
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Animesh Jain: BNL
Computed TILTED Axial Scan in BEPC Quad
Harmonic Norm. to B2(0)
30
Sextupole with tilt:
Integ. b3 = 3 unit
Integ. a3 = 1.7 unit
25
20
b3 (unit)
a3 (unit)
15
10
5
0
-5
-10
Axis used for computations:
-15
(2,–3,–200) to (–2,3,720)
-20
-250
-150
-50
50
150
250
350
450
550
650
750
Axial Position (mm)
4th BEPC-II IMAC Meeting, April 26-28, 2006
33
Animesh Jain: BNL
Is Tilt Really the Cause?
• If the measured warm to cold difference is indeed a result of the
tilt of the measuring coil, then even a warm measurement in the
vertical dewar should show similarly large sextupole.
• Measurements were carried out in the vertical dewar in
magnet #1 after the cold tests were completed.
• Warm sextupole in dewar was much smaller than the cold value,
although not as low as the initial warm measurements.
• Magnet #1 was also warm measured horizontally after the cold
test, and was found to have low sextupole, matching the initial
warm values before cold test.
• An estimate of maximum effect from tilt was also obtained by
measuring with the coil deliberately tilted.
• A comparison of final warm measurements horizontally and
vertically gives an estimate of the actual effect of tilt.
4th BEPC-II IMAC Meeting, April 26-28, 2006
34
Animesh Jain: BNL
Summary of Field Quality in BEPC Quad #1
Warm (±1 A) and Cold (20 A to 550 A) measurements in the Finished Magnet
Harmonics are in "units" of 10–4 at 50 mm radius
Cold
Warm
Warm
Warm
Cold
(Geometric) (in Dewar) (Horizontal) (Mole Tilted)
Warm
Warm
Warm
(Geometric) (in Dewar) (Horizontal) (Mole Tilted)
Runs 88/89
Run 181
Run 188
Run 192
Runs 88/89
Run 181
Run 188
Run 192
15.87
15.78
15.75
15.75
---
---
---
---
b3
5.32
1.94
0.20
-2.58
a3
4.52
-0.48
-0.69
-1.58
b4
0.21
-0.68
-0.54
-0.47
a4
0.51
-1.25
-1.26
-1.07
b5
-0.17
0.00
0.02
0.03
a5
-0.27
0.00
0.04
0.14
b6
-0.10
0.52
0.50
0.51
a6
-0.26
0.00
0.04
0.06
b7
0.44
0.54
-0.01
-0.79
a7
0.09
0.07
-0.03
-0.35
b8
-0.06
-0.13
-0.13
-0.13
a8
-0.08
-0.07
-0.09
-0.10
b9
-0.05
-0.04
-0.04
-0.04
a9
0.04
0.05
0.05
0.04
b 10
-0.01
-0.01
-0.01
-0.01
a 10
0.05
0.06
0.05
0.05
b 11
-0.08
-0.09
0.00
0.13
a 11
-0.02
-0.01
0.00
0.05
b 12
0.00
0.00
0.00
0.00
a 12
0.00
0.00
0.00
0.00
b 13
0.00
0.00
0.00
0.00
a 13
0.00
0.00
0.00
0.00
b 14
-0.03
-0.03
-0.03
-0.03
a 14
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
ITF (T/kA)
0.00
0.00
0.00
0.00
a 15
Note: (b n , a n ) are the normal and skew 2n -pole terms in the harmonic expansion
Note: Cold geometric values are from slopes of straight line fits, and averages of Up and Dn ramp data.
4th BEPC-II IMAC Meeting, April 26-28, 2006
35
Animesh Jain: BNL
b 15
Estimates of Tilt-Corrected Sextupole (Cold)
• A tilt of the measuring coil perhaps contributed to about
+1.74 unit of b3 and about +0.2 unit of a3 in magnet #1
(see the table in the previous slide).
• Subtracting this contribution from the cold values, the
best estimates of cold sextupole harmonics in the
magnet #1 are: b3 = +3.6 unit, and a3 = +4.3 unit.
• A similar exercise for magnet #2 gives estimates of
cold sextupole harmonics as:
b3 = 1.2 unit, and a3 = –5.2 unit.
• Although the tilt correction improves sextupole a little,
it is still mostly larger than the nominal 3 unit limit.
4th BEPC-II IMAC Meeting, April 26-28, 2006
36
Animesh Jain: BNL
Distortions due to Cool Down?
• In view of the surprising results in magnet #1, we carried
out extensive studies during cool down of magnet #2 to
investigate any effect of cool down itself.
• Measurements were carried out at ±1 A in the vertical
dewar before cool down, and then at various stages of
cool down at 35 K and 80 K.
• The temperatures were chosen to be high enough such
that no superconductor magnetization effects are present,
but low enough that nearly all the mechanical contraction
had already taken place.
• No significant differences between the warm and the
cold harmonics (at ±1A) were seen, thus ruling out any
distortions as a possible cause of the sextupole change.
4th BEPC-II IMAC Meeting, April 26-28, 2006
37
Animesh Jain: BNL
Summary of Field Quality in BEPC Quad #2
Warm/Cold (±1 A) and Cold (4.5 K, 20 A to 550 A) measurements in the Finished Magnet
Harmonics are in "units" of 10–4 at 50 mm radius
Warm
Cold ±1A Cold ±1A Cold 4.5K
Warm
Cold ±1A Cold ±1A Cold 4.5K
Dewar,300K Dewar,35K Dewar,80K (Geometric)
Dewar,300K Dewar,35K Dewar,80K (Geometric)
Run 35
Run 40
Run 62
Runs 80/81
Run 35
Run 40
Run 62
Runs 80/81
15.80
15.86
15.86
15.89
---
---
---
---
b3
2.09
1.87
1.96
1.51
a3
-1.85
-2.55
-2.73
-5.46
b4
0.06
-0.17
-0.10
-1.08
a4
-0.77
-0.63
-0.72
-0.23
b5
-0.07
-0.07
-0.07
-0.10
a5
0.06
0.05
0.09
0.15
b6
0.45
0.87
0.86
-0.46
a6
-0.08
-0.05
-0.06
0.12
b7
0.54
0.49
0.50
0.55
a7
-0.39
-0.46
-0.46
-0.53
b8
-0.13
-0.12
-0.12
-0.07
a8
-0.10
-0.10
-0.10
-0.05
b9
-0.04
-0.04
-0.04
-0.05
a9
0.06
0.06
0.06
0.03
b 10
0.02
0.03
0.03
0.02
a 10
0.04
0.04
0.04
0.07
b 11
-0.08
-0.07
-0.08
-0.08
a 11
0.07
0.08
0.08
0.08
b 12
0.00
0.00
0.00
0.00
a 12
0.01
0.00
0.00
0.00
b 13
0.00
0.00
0.00
0.00
a 13
0.00
0.00
0.00
0.00
b 14
-0.03
-0.03
-0.03
-0.03
a 14
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
ITF (T/kA)
0.00
0.00
0.00
0.00
a 15
Note: (b n , a n ) are the normal and skew 2n -pole terms in the harmonic expansion
Note: Cold geometric values are from slopes of straight line fits, and averages of Up and Dn ramp data.
b 15
4th BEPC-II IMAC Meeting, April 26-28, 2006
38
Animesh Jain: BNL
Effect of Support Tube Magnetic Properties?
• The support tube material was chosen to be stainless
steel 316L, and is certified to be seamless by the vendor.
• We measured the ferrite content around the
circumference of the support tube in magnet #2 before it
was cooled down.
• The ferrite number varied azimuthally from 0.02 to
0.9 near the non-lead end, and from 0.05 to 0.6 at the
lead end. (A ferrite no. of 1 is m-1 ~ 0.3)
• These ferrite numbers are quite large, and represent
significant azimuthal asymmetry in the magnetic
properties, affecting mostly the low field measurements.
4th BEPC-II IMAC Meeting, April 26-28, 2006
39
Animesh Jain: BNL
A Closer Look at the Cold Data
• It is expected that the ferrite content in the support
tube will affect mostly the low field measurements.
• At higher fields, the small ferrite particles saturate,
and the permeability becomes essentially ~1.
• If this is true, significant non-linearity should be
seen at the low field region of the cold data.
• A departure from the high field slope was indeed
found for currents below ~25 A in both the magnets.
• The very low field slopes match very well with
the warm measurements.
4th BEPC-II IMAC Meeting, April 26-28, 2006
40
Animesh Jain: BNL
Low Field Sextupole in Magnet #2
A3 (T.m @ 50 mm)
Up Ramp: -1.8161E-04 T.m/kA
3.0E-05
Dn Ramp: -4.3213E-04 T.m/kA
2.5E-05
High Field slope:
2.0E-05
a3 = –5.4 unit
1.5E-05
1.0E-05
5.0E-06
Low Field slope:
0.0E+00
a3 = –2.3 unit
Additional cold data taken in
magnet #2 in 5 A to 40A range
-5.0E-06
-1.0E-05
-80
-70
-60
-50
-40
-30
-20
-10
0
Current (A)
4th BEPC-II IMAC Meeting, April 26-28, 2006
41
Animesh Jain: BNL
Summary
• The superconducting IR magnets for BEPC-II are some of
the most complex magnets that we have built.
• Considerable care was exercised to obtain good field quality
in the SCQ quadrupoles, resulting in very good warm field
quality.
• All magnet coils performed well above operating current
without any quench, except for one training quench in AS1.
• Assembly delays were caused by vacuum leaks that were
difficult to detect, eventually leading to rework of the heat
shield using stainless steel tubes.
• Large sextupole in the cold data was thoroughly
investigated, and is most likely caused by magnetic
properties of the stainless steel coil support tube which may
have affected the warm measurements.
4th BEPC-II IMAC Meeting, April 26-28, 2006
42
Animesh Jain: BNL