construction and testing of superconducting magnets for the bepc-ii interaction region animesh jain...

Construction and Testing of Superconducting Magnets for the

BEPC-II Interaction Region

Animesh Jainon behalf of

Superconducting Magnet DivisionBrookhaven National Laboratory, Upton, NY 11973, USA

4th BEPC-II IMAC Meeting, Beijing, April 26-28, 2006

4th BEPC-II IMAC Meeting, April 26-28, 2006 Animesh Jain: BNL2

Introduction• Brookhaven National Laboratory has designed, built

and tested two superconducting magnets for theBEPC-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.


Nominal Design Parameters

Not listed here: Anti-Solenoids (AS1, AS2 and AS3)

CoilInner

Diameter(mm)

MagneticLength

(m)

IntegralTransferFunction

Normal Quadrupole(SCQ)

190 0.400 1.57 10–2 T/A

Normal Dipole*(SCB)

217 0.400 4.37 10–4 T·m/A

Skew Dipole(VDC)

226 0.381 8.28 10–4 T·m/A

Skew Quadrupole(SKQ)

228.5 0.400 7.72 10–3 T/A

* Normal dipole may also be used in a horizontal corrector (HDC) mode.


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.


No. of Layers and TurnsCoil

Total No.of Layers

TotalNumber of

TurnsConductor

Normal Quadrupole(SCQ)

8317

per pole1 mm dia.; 6-around-1 cable

Cu:SC = 1.8:1

Normal Dipole(SCB)

2178

per pole1 mm dia.; 6-around-1 cable

Cu:SC = 1.8:1

Skew Dipole(VDC)

2364

per pole0.33 mm dia.; single wire

Cu:SC = 1.8:1

Skew Quadrupole(SKQ)

2200

per pole0.33 mm dia.; single wire

Cu:SC = 1.8:1

Anti-Solenoid 1(AS1)

6 7322.4 mm 1.5 mm MRI wire

Cu:SC = 6.9:1Anti-Solenoid 2

(AS2)2 260

2.4 mm 1.5 mm MRI wireCu:SC = 6.9:1

Anti-Solenoid 3(AS3)

6 2802.4 mm 1.5 mm MRI wire

Cu:SC = 6.9:1


Winding Different Conductor Types

AS2

VDC

SCQ


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.


Coil Section at the Magnet CenterBEPC2 Coil Cross Section

0

10

20

30

40

50

60

70

80

90

100

110

120

0 10 20 30 40 50 60 70 80 90 100 110 120X-Position (mm)

Y-P

osit

ion

(m

m)

SCQSCB/HDCVDCSKQ


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.


Magnet 1 Magnet 2 Magnet 1 Magnet 2 Magnet 1 Magnet 2 Magnet 1 Magnet 2

Int. Trans. Func. 15.73 15.77 0.451 0.452 0.855 0.860 7.70 7.80

Field angle (mr) --- --- -2.16 11.04 7.2 8.1 8.4 8.5b 1 (unit) --- --- 10000 10000 --- --- --- ---b 2 (unit) 10000 10000 6.17 6.37 4.05 -3.34 --- ---b 3 (unit) 0.35 1.80 2.11 3.28 1.00 -0.77 5.36 0.79b 4 (unit) -0.47 0.06 -0.59 -0.17 0.02 0.41 0.84 -2.93b 5 (unit) 0.04 -0.06 -0.22 0.06 -0.22 -1.36 0.05 0.53b 6 (unit) 0.37 0.42 0.11 0.01 -0.08 0.11 0.09 -0.37b 7 (unit) 0.13 0.45 -0.02 -0.03 0.01 -0.10 -0.09 -0.08b 8 (unit) -0.13 -0.13 -0.01 0.00 0.01 -0.01 -0.03 0.08b 9 (unit) -0.04 -0.04 0.00 0.00 -0.01 0.06 -0.01 0.00b 10 (unit) -0.01 0.02 0.00 0.00 0.00 0.00 -0.03 0.02b 11 (unit) -0.02 -0.07 0.00 0.00 0.00 0.01 -0.01 -0.02a 1 (unit) --- --- --- --- 10000 10000 --- ---a 2 (unit) --- --- -4.92 -4.80 -0.63 3.32 10000 10000a 3 (unit) -1.28 -1.63 -2.68 -3.45 -1.01 2.70 -2.30 -0.68a 4 (unit) -1.26 -0.53 -0.25 0.43 0.09 0.42 1.38 -2.28a 5 (unit) 0.05 0.05 0.52 0.98 -0.04 1.01 0.25 0.19a 6 (unit) 0.04 -0.09 -0.02 0.00 0.01 0.05 0.39 0.21a 7 (unit) -0.18 -0.34 -0.03 -0.09 -0.18 -0.19 0.06 0.14a 8 (unit) -0.08 -0.11 0.01 0.00 0.05 0.02 0.02 -0.08a 9 (unit) 0.05 0.06 0.00 -0.01 0.19 0.17 0.04 0.02a 10 (unit) 0.05 0.04 0.00 0.00 -0.01 0.00 -0.04 -0.02a 11 (unit) 0.03 0.06 0.00 0.00 0.24 0.26 0.00 0.01

Summary of Warm Measurements in BEPC-II IR Magnets Built by BNLIntegral 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.

QuantitySCQ at 50 mm SCB at 38 mm VDC at 50 mm SKQ at 50 mm


AS2 Solenoid Axial Field Profiles

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

-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 1.2Axial Distance from Non Lead End (m)

Axi

al F

ield

(T

/kA

)

Magnet#1

Magnet #2


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 withS-glass to provide the prestress, and then cured.


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.

CoilNominal

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




Spot Heater Quench Results

0

100

200

300

400

500

600

100 200 300 400 500 600Current (A)

Hot

Sp

ot T

emp

erat

ure

(K

)

Magnet #1

Magnet #2

With Energy Extraction(Resistor = 0.5 Ohm)

Reduced Quench Detection Threshold used for Magnet #2


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.


Some Assembly Components

Outer Heat Shield

Inner Heat Shield

Helium Containment

Complete Magnet

This manifold is no longer in the design.


Cold Mass Angle Alignment

Precision Level

AngleAdjustment


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.


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.


Continued Support from BNL• BNL continues to provide support after shipping:

– Andrew Marone and John Escallier from BNLvisited IHEP in January, 2006 to provide supportfor 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.


Understanding the Unexpected Sextupole in the

Cold SCQ Magnets


Magnet 1 Magnet 2 Magnet 1 Magnet 2(QHG202) (QHG203) (QHG202) (QHG203)

Run 31 Run 24 Run 31 Run 24

ITF (T/kA) 15. 73 15. 77 --- ---

b 3 0. 35 1. 80 a 3 - 1. 28 - 1. 63

b 4 - 0. 47 0. 06 a 4 - 1. 26 - 0. 53

b 5 0. 04 - 0. 06 a 5 0. 05 0. 05

b 6 0. 37 0. 42 a 6 0. 04 - 0. 09

b 7 0. 13 0. 45 a 7 - 0. 18 - 0. 34

b 8 - 0. 13 - 0. 13 a 8 - 0. 08 - 0. 11

b 9 - 0. 04 - 0. 04 a 9 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

Summary of Warm Field Quality in BEPC QuadsWarm measurements at ±1A after completing the skew layers

Harmonics are in "units" of 10–4 at 50 mm radius

Note: (b n , a n ) are the normal and skew 2n -pole terms in the harmonic expansion

Low Sextupole Content

Warm Measurements

had shown good field

quality in the SCQ


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 at50 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.


DC Loop Data (20A-550A) in QHG202 Quadrupole (Runs 88-89)

-3.0E-04

-2.5E-04

-2.0E-04

-1.5E-04

-1.0E-04

-5.0E-05

0.0E+00

-550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0Current (A)

B3

(T.m

@ 5

0 m

m)

Up Ramp: 4.2323E-04 T.m/kA Dn Ramp: 4.2136E-04 T.m/kA

-2.0E-04

-1.5E-04

-1.0E-04

-5.0E-05

0.0E+00

5.0E-05

-550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0

Quadrupole Slope is 0.7935 T.m/kA

Magnet #1



-3.0E-04

-2.5E-04

-2.0E-04

-1.5E-04

-1.0E-04

-5.0E-05

0.0E+00

-550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0-2.0E-04

-1.5E-04

-1.0E-04

-5.0E-05

0.0E+00

5.0E-05

-550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0Current (A)

A3

(T.m

@ 5

0 m

m)



Magnet #1



-7.0E-05

-6.0E-05

-5.0E-05

-4.0E-05

-3.0E-05

-2.0E-05

-1.0E-05

0.0E+00

-550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0Current (A)

B3

(T.m

@ 5

0 m

m)


-5.0E-05

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

-550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0


Magnet #2


-5.0E-05

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

-550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0Current (A)

A3

(T.m

@ 5

0 m

m)

Up Ramp: -4.3381E-04 T.m/kA Dn Ramp: -4.3213E-04 T.m/kA



Magnet #2


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 aroundthe dewar, .....


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.


-8.00E-05

-6.00E-05

-4.00E-05

-2.00E-05

0.00E+00

2.00E-05

4.00E-05

6.00E-05

8.00E-05

0 100 200 300 400 500 600Current (A)

B4

(T.m

@ 4

5 m

m)

Example of Persistent CurrentsOctupole Term in the BNL-built HERA Quad

No hysteresis in unallowed terms is seen in BEPC quadrupoles.


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.


Computed Axial Scan in BEPC Quad

-100

-80

-60

-40

-20

0

20

40

60

80

100

-250 -150 -50 50 150 250 350 450 550 650 750

Axial Position (mm)

Har

mon

ic N

orm

. to

B2(

0)

b4 (unit)

a4 (unit)

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.

in “

Uni

ts”

at 5

0 m

m


Computed Axial Scan in BEPC Quad

-5

0

5

10

15

20

-250 -150 -50 50 150 250 350 450 550 650 750

Axial Position (mm)

Har

mon

ic N

orm

. to

B2(

0)

b3 (unit)

a3 (unit)

Sextupole term with no tilt.

Integral ~ 0 unit


Computed TILTED Axial Scan in BEPC Quad

-20

-15

-10

-5

0

5

10

15

20

25

30

-250 -150 -50 50 150 250 350 450 550 650 750

Axial Position (mm)

Har

mon

ic N

orm

. to

B2(

0)

b3 (unit)

a3 (unit)

(2,–3,–200) to (–2,3,720)

Sextupole with tilt:Integ. b3 = 3 unitInteg. a3 = 1.7 unit

Axis used for computations:


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 inmagnet #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.


Cold Warm Warm Warm Cold Warm Warm Warm(Geometric) (in Dewar) (Horizontal) (Mole Tilted) (Geometric) (in Dewar) (Horizontal) (Mole Tilted)Runs 88/89 Run 181 Run 188 Run 192 Runs 88/89 Run 181 Run 188 Run 192

ITF (T/kA) 15. 87 15. 78 15. 75 15. 75 --- --- --- ---

b 3 5. 32 1. 94 0. 20 - 2. 58 a 3 4. 52 - 0. 48 - 0. 69 - 1. 58

b 4 0. 21 - 0. 68 - 0. 54 - 0. 47 a 4 0. 51 - 1. 25 - 1. 26 - 1. 07

b 5 - 0. 17 0. 00 0. 02 0. 03 a 5 - 0. 27 0. 00 0. 04 0. 14

b 6 - 0. 10 0. 52 0. 50 0. 51 a 6 - 0. 26 0. 00 0. 04 0. 06

b 7 0. 44 0. 54 - 0. 01 - 0. 79 a 7 0. 09 0. 07 - 0. 03 - 0. 35

b 8 - 0. 06 - 0. 13 - 0. 13 - 0. 13 a 8 - 0. 08 - 0. 07 - 0. 09 - 0. 10

b 9 - 0. 05 - 0. 04 - 0. 04 - 0. 04 a 9 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

b 15 0. 00 0. 00 0. 00 0. 00 a 15 0. 00 0. 00 0. 00 0. 00

Note: Cold geometric values are from slopes of straight line fits, and averages of Up and Dn ramp data.

Summary of Field Quality in BEPC Quad #1Warm (±1 A) and Cold (20 A to 550 A) measurements in the Finished Magnet




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.


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.


Warm Cold ±1A Cold ±1A Cold 4.5K Warm Cold ±1A Cold ±1A Cold 4.5KDewar,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

ITF (T/kA) 15. 80 15. 86 15. 86 15. 89 --- --- --- ---

b 3 2. 09 1. 87 1. 96 1. 51 a 3 - 1. 85 - 2. 55 - 2. 73 - 5. 46

b 4 0. 06 - 0. 17 - 0. 10 - 1. 08 a 4 - 0. 77 - 0. 63 - 0. 72 - 0. 23

b 5 - 0. 07 - 0. 07 - 0. 07 - 0. 10 a 5 0. 06 0. 05 0. 09 0. 15

b 6 0. 45 0. 87 0. 86 - 0. 46 a 6 - 0. 08 - 0. 05 - 0. 06 0. 12

b 7 0. 54 0. 49 0. 50 0. 55 a 7 - 0. 39 - 0. 46 - 0. 46 - 0. 53

b 8 - 0. 13 - 0. 12 - 0. 12 - 0. 07 a 8 - 0. 10 - 0. 10 - 0. 10 - 0. 05

b 9 - 0. 04 - 0. 04 - 0. 04 - 0. 05 a 9 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

b 15 0. 00 0. 00 0. 00 0. 00 a 15 0. 00 0. 00 0. 00 0. 00

Note: Cold geometric values are from slopes of straight line fits, and averages of Up and Dn ramp data.

Summary of Field Quality in BEPC Quad #2Warm/Cold (±1 A) and Cold (4.5 K, 20 A to 550 A) measurements in the Finished Magnet




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 ~ 0.3)

• These ferrite numbers are quite large, and represent significant azimuthal asymmetry in the magnetic properties, affecting mostly the low field measurements.


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.


Low Field Sextupole in Magnet #2

-1.0E-05

-5.0E-06

0.0E+00

5.0E-06

1.0E-05

1.5E-05

2.0E-05

2.5E-05

3.0E-05

-80 -70 -60 -50 -40 -30 -20 -10 0Current (A)

A3

(T.m

@ 5

0 m

m)

Up Ramp: -1.8161E-04 T.m/kA Dn Ramp: -4.3213E-04 T.m/kA

Low Field slope:

a3 = –2.3 unit

High Field slope:

a3 = –5.4 unit

Additional cold data taken inmagnet #2 in 5 A to 40A range


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.

construction and testing of superconducting magnets for the bepc-ii interaction region animesh jain...

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