For Review Only

Vertical Magnetic Measurement System Commis-sioning and First Measurements of the First Full-Length Prototype

Quadrupole Magnet for the LHC Hi-Lumi Upgrade

Journal: Applied Superconductivity Conference 2018

Manuscript ID Draft

Conference Manuscript Type: Invited Manuscript

Date Submitted by the Author: n/a

Complete List of Authors: Song, Honghai; Brookhaven National Laboratory, Superconducting Magnet Department; DiMarco, Joseph; Fermilab, TD/MSDJain, Animesh; Argonne National Laboratory, Advanced Photon SourceSabbi, GianLuca; LBNL, AFRD-SMPWanderer, Peter; Brookhaven National Lab, Superconducting Magnet DivisionWang, Xiaorong; Lawrence Berkeley National Laboratory, Accelerator Technology and Applied Physics

Keywords:Accelerator magnets < Accelerator magnets: dipoles, quadrupoles, correctors < Superconducting Magnets, Nb3Sn Wire < Niobium-based wires and tapes < Conductors, Superconducting Magnets

draft

For Review Only

> 4LOr3A-02 <

1

Vertical Magnetic Measurement System Commis-sioning and First Measurements of the First Full-

Length Prototype Quadrupole Magnet for the LHC Hi-Lumi Upgrade

H. Song, Senior Member, IEEE, J. DiMarcro, A. Jain, G. Sabbi, P. Wanderer and X. Wang

(Invited)

Abstract—This paper will report the commissioning of the ver-

tical magnetic measurement system and the warm (room temper-ature) and cold (cryogenic) magnetic field measurements of the

first full-length (4.2 m) quadrupole built by the US Accelerator Upgrade Project (AUP) project (formerly the LARP collabora-tion) for the high luminosity upgrade of the Large Hadron Col-

lider at CERN. The magnet, designated MQXFAP2, is a proto-type preceding production for the AUP Accelerator Upgrade Project (AUP). AUP will provide ten 8.4 m superconducting in-

sertion region (IR) quadrupoles for the Hi-Lumi Upgrade. The 8.4 m quadrupoles will be built by assembling two 4.2 m magnets in a single cryostat. Agreement between BNL’s and LBNL’s

warm measurement data has indicated that the upgraded vertical magnetic measurement system at BNL is ready for MQXFA magnet production testing. The cold magnetic measurement has

been performed and preliminary data analysis has been conduct-ed. The measured data indicates that the MQXFAP2 magnet has good magnetic field which meets the preliminary MQXFA mag-

net acceptance criteria.

Index Terms— LARP, AUP, Hi-Lumi, LHC, Nb3Sn, super-

conducting magnets

I. INTRODUCTION

n the framework of the High-Luminosity (HL) upgrade of

the Large Hadron Collider (LHC) to achieve peak luminosi-

ty of 5∙1034 cm-2s-1 and to reach 3000 fb-1 integrated lumi-

nosity in the period of 2024-2026 [1-5], the U.S. AUP (previ-

ously LARP) collaboration and CERN have joined efforts to

develop production 150 mm aperture Nb3Sn quadrupoles for

the LHC interaction regions[6-8]. The HL LHC Accelerator

Upgrade Project (AUP) has been established to fulfill a US

contribution to HL-LHC which will deliver 12 cryostatted as-

semblies, each containing two 4.2 m long Nb3Sn high gradient

quadrupole magnets. They will be components of the triplets

Manuscript receipt and acceptance dates will be inserted here. Acknowledg-

ment of support is placed in this paragraph as well. Consult the IEEE Editorial Style Manual for examples. This work was supported by the IEEE Council on Superconductivity under contract. ABCD-123456789. (Corresponding author: Honghai Song.)

H. Song and P. Wanderer are with Brookhaven National Laboratory, Upton, NY 11973 United States (email: honsong@bnl.gov). J. DiMacro is with Fermi National Accelerator Laboratory, Batavia, Illinois, United States. A. Jain is with Argonne National Laboratory, 9700 S. Cass Avenue Lemont, IL 60439, USA. G. Sabbi and X. Wang are with Lawrence Berkeley National Laboratory, Berke-ley, CA 94720-8203 United States.

for two LHC insertion regions. To deliver these magnets

(called MQXF), a full range of training and tests on the

MQXF magnets is required to reach the normal operating cur-

rent of 16.47 kA and ultimate current of 17.89 kA, as well as

magnetic field measurement to make sure that the magnetic

field meets functional requirements and acceptance criteria [9-

15]. The vertical superconducting magnet testing facility of

the Superconducting Magnet Division (SMD) at Brookhaven

National Laboratory (BNL) has been significantly upgraded to

perform testing in superfluid He at 1.9 K and 1 bar. This paper

reports new development of the vertical magnetic field meas-

urement facility at BNL and recent magnetic measurement ac-

tivities on the MQXFAP2 magnet including room temperature

and the cold magnetic field measurement at 1.9 K, as well as

comparison with the warm measurement at LBNL and de-

tailed field analysis.

II. THE UPGRADED VERTICAL MAGNETIC MEASUREMENT SYS-

TEM

A. PCB Rotating Probe and Calibration

The magnetic measurements for the MQXFAP2 magnet will

employ Printed Circuit Board (PCB) rotating coil probes as

shown in Figure 1 and the technique has been validated

though the HQ magnetic measurement program[12, 16, 17].

The PCB board length, width and thickness are 425 mm, 95

mm and 4.57 mm respectively. The MQXFAP magnet has 150

I

Figure 1: The magnetic measurement probe with Printed Circuit Board (PCB) rotating coil. (A): the fully assembled PCB rotating coil; (B): the internal PCB board, Probe 220 on the left, and Probe 110 on the right. Note that Probe 110 is above Probe 220 in vertical testing condition

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mm aperture diameter and the reference radius for magnetic

field measurement is 50 mm. The PCB has two circuits (long

and short), 220 mm and 110 mm long (see Figure 1) so they

are called Probe 220 and 110. Their center-to-center distance

is 220 mm. Each has two layers and each layer has 5 different

tracks (one is a spare) side to side across the board. Each track

is 18.55 mm wide and has 12 loops. The loops are combined

in an analog bucking configuration via jumpers on the board

to have Un-Bucked (UB), Dipole-Bucked (DB), and Dipole-

Quadrupole-Bucked (DQB) signals. Each circuit board has

three signals, and signals 1-3 are for Probe 220 (Left in Figure

1) and signals 4-6 are for Probe 110 (Right). The wire re-

sistances for all the 6 signals have been measured as 63.2,

120.6, 235.0, 34.7, 65.0 and 125.4 ohms. Note that the PCB

rotating probe will be vertically placed inside the magnet bore

centered by the support bearings, where Probe 110 is above

Probe 220 in the vertical testing condition.

With all the geometrical information, the sensitivity matri-

ces of Probes 220 and 110 are calculated as input for the rotat-

ing coil signals process. The sensitivities for the quad term are

6.36E-2 m2 in long Probe 220, and 3.17E-2 m2 in short Probe

110. The MQXF magnet has 150 mm inner diameter and a

gradient of 143.2 T/m at the nominal current of 16470 A, re-

sulting in flux in UB signal B2*K2 = 7.16 * 6.36E-2 = 4.55

Vs in Probe 220. With the probe rotating at 1/3.5 Hz, the UB

signal is ~1.63 V. Similarly, the UB signal in Probe 110 is es-

timated at 0.817 V. Furthermore, the PCB coil was calibrated

in a calibration quadrupole at the Superconducting Magnet

Division at BNL. The calibration magnet at BNL was powered

at ~1000 A, and the field is ~0.167 T at a radius of 50 mm.

The measured UB signals in long Probe 220 and short Probe

110 are 0.039 and 0.019 V. The calibration measurement con-

firmed that both circuits measure the magnetic field accurate-

ly, and the consistency between UB and DB signal within each

coil is within +/-0.03%.

B. Vertical Transport System Development

As the MXQF AP2 magnet is ~4563 mm long and the

probes are only 220 m and 110 mm long, one of the key ef-

forts is to transport the PCB rotating probe to scan the field

along the magnet axis with a vertical linear motion transport.

Figure 2 shows the magnet vertical length, Probe 220 and 110

locations and their center-center distance, which is about 220

mm. Considering the detailed design of the PCB, the actual

magnetic length is 108.74 mm for Probe 110, and 217.88 mm

for Probe 220. With Probe 220 as a primary rotating coil and

Probe 110 recorded in parallel, the measurement increment

along the magnet axis (vertical z direction) is 108.94 mm

which is nearly the Rutherford cable twist pitch length. As the

Probe 220 is lower than Probe 110, its first measured point is

220 mm closer to the magnet return end than probe 110.

A LabVIEW based vertical transport motion system has

been developed to transport the rotating PCB probe accurately

and safely. A survey has been made to check the axial motion

accuracy. As shown in Figure 3, the motion has accuracy of

0.6 mm which satisfies the MQXFAP magnet field measure-

ment requirement. To implement the ZSCAN, a script file

which includes all the Z positions will be loaded to the pro-

gram and start the motion. Meanwhile, a HTBasic system can

take a single magnetic field measurement. A hand-shake func-

tion has been established to connect the LabVIEW and

HTBasic systems. The system will take the measurement at

the first Z, and then move to the next Z while the HTBasic

program is waiting. Once the next Z is reached and confirmed,

the next measurement will take place, and so on until the last

Z position, indicated by EOF, when the ZSCAN stops. In ad-

dition, the LabVIEW system online monitoring of three phase

AC status and a real-time watch-dog checks the system to

make sure that the electrical supplies and computer operating

system are working functionally. If any of them malfunctions,

the LabVIEW program will stop running and exit automatical-

ly. Most importantly, the E-Stop hardware is incorporated in

the motion system, so any error message or system malfunc-

tion will stop the motor instantly

4753.61 mm

[187.142 in]

Top of Magnet Shell

Bottom of Warm Bore Tube

Bottom of Magnet Shell

4563 mm

[179.646 in]

Top of Warm Bore Tube

6256.57 mm

[246.322 in]

903.86

[35.585]

Top hat to Lambda

plateRotating coil in

MAX UP Post

656

25.827

Rotating coil

~220 mm

200.8 mm

Home

4

7

3

0

m

m

190.61mm

164.99mm

331.99mm

Switch_UL

Figure 2: A schematic for the MQXFAP magnet and the rotating probe. The total magnet length is 4,563 mm and the probes are only 220 and 110 mm long. The total vertical linear stroke between HOME and the upper limit switch is 4,730 mm at the maximum. When the rotating probe is at HOME, the distance between the probe bottom and the warm bore tube (upper surface) is 355.6 mm, and the distance between the probe bottom and the bottom of magnet shell is 164.99 mm. Limit switches have been placed at the very bottom and top for motion safety.

Figure 3: The LabVIEW-based vertical transport motion for the MQXFAP Magnet. A survey has been conducted to check the motion accuracy. One set of measurements was made from HOME to the further end (1a), and another set forwards (2a) and backwards (2b).

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III. MAGNETIC MEASUREMENTS

A. Warm Measurements

The magnetic field in the aperture of the straight section of

a quadrupole magnet can be expressed in terms of field coeffi-

cients in a series expansion in the following complex function

formalism [18]:

(1)

where Bx and By are the horizontal and vertical field compo-

nents in T in Cartesian coordinates, Bn and An are the normal

and skew multipole fields at the reference radius, which is Rref

50 mm. The warm measurement was performed at LBNL in

June 2018 prior to delivery to BNL for vertical magnet testing.

In late August, the warm magnetic measurement was per-

formed at BNL before the magnet cool-down. The warm

ZSCAN measurement has 42 points starting from HOME

(lowest), with an increment of 108.94 mm. Harmonics up to n

of 15 have been measured. To eliminate the remnant field due

to the background field and iron contribution, separate meas-

urements at +/- 15 A currents have been made allowing sepa-

ration of the remnant field from the field due to magnet’s

coils. The transfer function has been measured and plotted

along the Z direction (magnet axis). The BNL and LBNL

transfer function data are plotted in Figure 4 for direct com-

parison. Both are very close to the design transfer function of

8.86 T/m/kA at room temperature. The two curves agree very

well along the magnet axis. Note that there is no BNL data at

the return end due to the limited length of the underground

Dewar.

B. Cold Measurement at 1.9 K and 4.5 K

The quench training test of the second MQXFA prototype

(MQXFAP2) is in progress at BNL Vertical Test Facility. The

magnet reached 15 kA in 9 quenches and showed detraining

Figure 5: Harmonics b3/a3, b6/a6 of the first +/-15 A warm magnetic field measurement before the magnet cooldown. Good agreement between LBL and BNL data has been confirmed.

Figure 4: The averaged +/-15 A warm magnetic field measurement prior to the magnet cooling-down. There is good agreement between LBNL and BNL warm measurements.

Figure 7: Transfer functions and b6 of currents in the stair-step loop measurements.

Figure 6: Transfer functions at 15 A (averaged, warm), 960 A, 6kA and 10 kA in cold MM in the ZSCAN.

Figure 8: Center offset found in the ZSCAN. The X direction has less offset than the Y direction. The higher the current is, the more the Y offset becomes..

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after quench 13. The quench training was interrupted to dis-

cuss magnet performance and test continuation which offered

an opportunity for the cold magnetic field measurements. The

cold measurement has ZSCAN like that in the warm meas-

urement, and ISCAN which is also called stair-step (or DC

loop) measurement. The ZSCAN was performed at currents of

Iinj (960 A) at 1.9 K, Ilim (6kA) at ~2 K, 10 kA at 4.5 K. The

temperature change was due to a temporary problem with the

cryo facility. The short MQXF magnet data has indicated that

the temperature dependence of magnetic fields is not signifi-

cant[12]. The precyle for 960 A measurement was a ramp up

to 10 kA (300 second dwell) and down to Ires (100A), and up

to Iinj (960 A, 1000 second dwell).

The transfer functions (T.F.) of all the three currents are

plotted along with comparison to that of averaged 15 A as

shown in Figure 6. The magnet has highest T.F. at Iinj (960A),

and slightly decreases as current increases due to iron satura-

tion. It agrees with the findings in the short MQXF quadru-

poles. In the ISCAN as plotted in Figure 7, both the T.F. and

the allowed coefficient b6 present considerable hysteresis

which is caused by persistent current. In analyzing the cold

measurement data, it is found that offset occurred between the

PCB probe center and the magnet center as shown in Figure 8.

The Y direction has more offset than the X direction. It has the

largest offset at the lower return end and smallest at the lead

end. Moreover, it increases as the current increases. The warm

bore tube (WBT) which contains the PCB rotating probe may

have tilted during the cool down. This may trace back to the

fact both the WBT and rotating probe are suspended from the

top. It seems more centering is necessary though detailed in-

vestigation is underway. While all the harmonics analysis in

Figure 7 are corrected for the effects of the center offset be-

tween the rotating PCB probe and the magnet, a smaller offset

is still preferred to allow accurate corrections particularly for

high order multipole coefficients.

Furthermore, the cold multipole coefficients of 960 A, 6kA

and 10 kA are plotted along the Z axis, directly compared to

the warm coefficients of 15 A in the ZSCAN as shown in Fig-

ure 9-11. Most of them agree well with each other. The slight

difference in b4 and b5 may be related to the geometric

Figure 9: Nonallowed b3 and a3 at currents of 960 A at 1.9 K, 6 kA at ~2 K, 10 kA at 4.5 K, with comparison to that of averaged 15 A at room temperature.

Figure 11: Allowed b6 and nonallowed a6 at currents of 960 A at 1.9 K, 6 kA at ~2 K, 10 kA at 4.5 K, with comparison to that of averaged 15 A at room temperature.

Figure 10: Nonallowed b5 and a5 at currents of 960 A at 1.9 K, 6 kA at ~2 K, 10 kA at 4.5 K, with comparison to that of averaged 15 A at room temperature.

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shrinkage during cooling down. The change in b6 is due to a

combination of iron saturation and persistent currents. The

measured field quality confirms the necessity of having a fine

tuning of the cross-section to increase b6 by about 4 units[19,

20]. A decision has been recently made and shall be imple-

mented for the future magnets through a change of 0.125 mm

shims in the pole and in the midplane. On the other hand, the

non-allowed harmonic that showed large values in the short

model program appear to be close to the targets.

TABLE I

Harmonics bn (n≤6) of MQXFAP2 at 10 kA and 4.5 K.

b3 b4 b5 b6

Current mean rms mean rms mean rms Mean Rms

15A -1.23 1.96 -1.12 1.25 -0.46 0.95 -5.90 1.12

960A -0.92 2.02 -0.91 1.30 -1.38 1.02 -17.03 1.28

6kA -0.67 2.07 -1.11 1.28 -1.12 1.06 -7.37 1.28

10kA -0.87 2.09 -1.25 1.33 -0.99 1.06 -4.18 1.26

TABLE II

Harmonics an (n≤6)) of MQXFAP2 at 10 kA and 4.5 K.

a3 a4 a5 a6

Current mean rms mean rms mean rms mean rms

15A 4.10 1.77 2.61 1.69 1.94 0.78 0.45 0.49

960A 4.19 1.77 3.07 1.83 1.75 0.82 0.47 0.49

6kA 2.79 1.82 2.24 1.96 1.35 0.83 0.40 0.52

10kA 3.17 1.85 2.54 1.95 1.48 0.85 0.40 0.52

The cold and warm harmonics (bn and an, n≤6) of 10 kA

and 15 A in the straight section have been averaged and plot-

ted against each other in Y and X axis as shown in Figure 12.

Most the data points are next to the 45 deg angle line, which

indicates a correlation between the cold and warm field data.

The b6 has the largest value of -5.9 units for 15 A and -4.18

units for 10 kA. The a3 has the largest value of 4.10 units for

15 A and 3.17 units for 10 kA as summarized in TABLE I and

II.

As Probe 220 is twice as long as Probe 110, the Probe 110

is expected to have better resolution with ~110 mm step. Data

of the two probes have been compared in Figure 13. Their

starting points are off by ~220 mm. For the allowed harmonic

Probe 220 Probe 110

Probe 220

Probe 110

Figure 13: Field comparison between Probe 220 and 110.

Figure 12: Cold and warm harmonics correlation for the field in the straight section (Probe 220) between -1.915 m and 1.642 m, 10 kA vs 15 A.

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b6 with 10 – 20 units, their difference is not significant. For

the nonallowed harmonics a6, b4 and a4, the data profiles of

Probe 110 at 15 A and 960 are sharper than those of Probe

220.

IV. CONCLUSIONS

The vertical magnetic measurement system which includes the

newly developed vertical motion transport system has been

commissioned for the magnetic measurement of the

MQXFAP2 magnet. The good agreement between the BNL

and LBNL data in the warm magnetic measurements of aver-

age 15 A indicates that the PCB rotating coil functions well

for the full-length MQXFA production magnets. Furthermore,

the system has been used for the cold measurement and col-

lected ZSCAN and ISCAN (stair-step) data. A preliminary

analysis of the Probe 220 data, corrected for the center offset

between the probe and the magnet, shows good agreement be-

tween the warm and cold measurements. The Probe 110 does

have better resolution than Probe 220 which will be very use-

ful for measurement of the lead end. The measurement indi-

cates that the MQXFAP2 magnet has magnetic field which

meets the preliminary MQXFA magnet acceptance criteria.

The large offset of the measuring coil at the magnet return end

is likely because both the WBT and the probe are suspended

from the top flange. Improvement to better center the rotating

probe in the vertical magnet testing facility seem necessary.

Further investigation of the offset is underway.

ACKNOWLEDGEMENT

The authors thank the magnet testing team at BNL for the

measurement setup and preparations, and general support from

FermiLab and LBNL and thank G. Ambrosio, G. Apollinari,

K. Amm, M. Anerella, S. I. Bermudez, S. Feher, P. Joshi, J.

Muratore, E. Todesco for helpful discussions and suggestions.

This work was supported in part by the U.S. Department of

Energy, Office of Science, Office of High Energy Physics,

through the U.S. LHC Accelerator Research Program, and in

part by the High Luminosity LHC project at CERN.

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> 4LOr3A-02 <

1

Vertical Magnetic Measurement System Commissioning and First Measurements of the First Full-Length Prototype Quadrupole Magnet for the

LHC Hi-Lumi UpgradeH. Song, Senior Member, IEEE, J. DiMarcro, A. Jain, G. Sabbi, P. Wanderer and X. Wang

(Invited)

Abstract—This paper will report the commissioning of the vertical magnetic measurement system and the warm (room temperature) and cold (cryogenic) magnetic field measurements of the first full-length (4.2 m) quadrupole built by the US Accelerator Upgrade Project (AUP) project (formerly the LARP collaboration) for the high luminosity upgrade of the Large Hadron Collider at CERN. The magnet, designated MQXFAP2, is a prototype preceding production for the AUP Accelerator Upgrade Project (AUP). AUP will provide ten 8.4 m superconducting insertion region (IR) quadrupoles for the Hi-Lumi Upgrade. The 8.4 m quadrupoles will be built by assembling two 4.2 m magnets in a single cryostat. Agreement between BNL’s and LBNL’s warm measurement data has indicated that the upgraded vertical magnetic measurement system at BNL is ready for MQXFA magnet production testing. The cold magnetic measurement has been performed and preliminary data analysis has been conducted. The measured data indicates that the MQXFAP2 magnet has good magnetic field which meets the preliminary MQXFA magnet acceptance criteria.

Index Terms— LARP, AUP, Hi-Lumi, LHC, Nb3Sn, superconducting magnets

I. INTRODUCTION

n the framework of the High-Luminosity (HL) upgrade of the Large Hadron Collider (LHC) to achieve peak luminosity of 5∙1034 cm-2s-1 and to reach 3000 fb-1

integrated luminosity in the period of 2024-2026 [1-5], the U.S. AUP (previously LARP) collaboration and CERN have joined efforts to develop production 150 mm aperture Nb3Sn quadrupoles for the LHC interaction regions[6-8]. The HL LHC Accelerator Upgrade Project (AUP) has been established to fulfill a US contribution to HL-LHC which will deliver 12 cryostatted assemblies, each containing two 4.2 m long Nb3Sn

Manuscript receipt and acceptance dates will be inserted here. Acknowledgment of support is placed in this paragraph as well. Consult the IEEE Editorial Style Manual for examples. This work was supported by the IEEE Council on Superconductivity under contract. ABCD-123456789. (Corresponding author: Honghai Song.)

H. Song and P. Wanderer are with Brookhaven National Laboratory, Upton, NY 11973 United States (email: honsong@bnl.gov). J. DiMacro is with Fermi National Accelerator Laboratory, Batavia, Illinois, United States. A. Jain is with Argonne National Laboratory, 9700 S. Cass Avenue Lemont, IL 60439, USA. G. Sabbi and X. Wang are with Lawrence Berkeley National Laboratory, Berkeley, CA 94720-8203 United States.

high gradient quadrupole magnets. They will be components of the triplets for two LHC insertion regions. To deliver these magnets (called MQXF), a full range of training and tests on the MQXF magnets is required to reach the normal operating current of 16.47 kA and ultimate current of 17.89 kA, as well as magnetic field measurement to make sure that the magnetic field meets functional requirements and acceptance criteria [9-15]. The vertical superconducting magnet testing facility of the Superconducting Magnet Division (SMD) at Brookhaven National Laboratory (BNL) has been significantly upgraded to perform testing in superfluid He at 1.9 K and 1 bar. This paper reports new development of the vertical magnetic field measurement facility at BNL and recent magnetic measurement activities on the MQXFAP2 magnet including room temperature and the cold magnetic field measurement at 1.9 K, as well as comparison with the warm measurement at LBNL and detailed field analysis.

II. THE UPGRADED VERTICAL MAGNETIC MEASUREMENT SYSTEM

A. PCB Rotating Probe and Calibration

The magnetic measurements for the MQXFAP2 magnet will employ Printed Circuit Board (PCB) rotating coil probes as shown in Figure 1 and the technique has been validated though the HQ magnetic measurement program[12, 16, 17]. The PCB board length, width and thickness are 425 mm, 95

I

Figure 1: The magnetic measurement probe with Printed Circuit Board (PCB) rotating coil. (A): the fully assembled PCB rotating coil; (B): the internal PCB board, Probe 220 on the left, and Probe 110 on the right. Note that Probe 110 is above Probe 220 in vertical testing condition

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mm and 4.57 mm respectively. The MQXFAP magnet has 150 mm aperture diameter and the reference radius for magnetic field measurement is 50 mm. The PCB has two circuits (long and short), 220 mm and 110 mm long (see Figure 1) so they are called Probe 220 and 110. Their center-to-center distance is 220 mm. Each has two layers and each layer has 5 different tracks (one is a spare) side to side across the board. Each track is 18.55 mm wide and has 12 loops. The loops are combined in an analog bucking configuration via jumpers on the board to have Un-Bucked (UB), Dipole-Bucked (DB), and Dipole-Quadrupole-Bucked (DQB) signals. Each circuit board has three signals, and signals 1-3 are for Probe 220 (Left in Figure 1) and signals 4-6 are for Probe 110 (Right). The wire resistances for all the 6 signals have been measured as 63.2, 120.6, 235.0, 34.7, 65.0 and 125.4 ohms. Note that the PCB rotating probe will be vertically placed inside the magnet bore centered by the support bearings, where Probe 110 is above Probe 220 in the vertical testing condition.

With all the geometrical information, the sensitivity matrices of Probes 220 and 110 are calculated as input for the rotating coil signals process. The sensitivities for the quad term are 6.36E-2 m2 in long Probe 220, and 3.17E-2 m2 in short Probe 110. The MQXF magnet has 150 mm inner diameter and a gradient of 143.2 T/m at the nominal current of 16470 A, resulting in flux in UB signal B2*K2 = 7.16 * 6.36E-2 = 4.55 Vs in Probe 220. With the probe rotating at 1/3.5 Hz, the UB signal is ~1.63 V. Similarly, the UB signal in Probe 110 is estimated at 0.817 V. Furthermore, the PCB coil was calibrated in a calibration quadrupole at the Superconducting Magnet Division at BNL. The calibration magnet at BNL was powered at ~1000 A, and the field is ~0.167 T at a radius of 50 mm. The measured UB signals in long Probe 220 and short Probe 110 are 0.039 and 0.019 V. The calibration measurement confirmed that both circuits measure the magnetic field accurately, and the consistency between UB and DB signal within each coil is within +/-0.03%.

B. Vertical Transport System DevelopmentAs the MXQF AP2 magnet is ~4563 mm long and the

probes are only 220 m and 110 mm long, one of the key efforts is to transport the PCB rotating probe to scan the field along the magnet axis with a vertical linear motion transport. Figure 2 shows the magnet vertical length, Probe 220 and 110 locations and their center-center distance, which is about 220 mm. Considering the detailed design of the PCB, the actual magnetic length is 108.74 mm for Probe 110, and 217.88 mm for Probe 220. With Probe 220 as a primary rotating coil and Probe 110 recorded in parallel, the measurement increment along the magnet axis (vertical z direction) is 108.94 mm which is nearly the Rutherford cable twist pitch length. As the Probe 220 is lower than Probe 110, its first measured point is 220 mm closer to the magnet return end than probe 110.

A LabVIEW based vertical transport motion system has been developed to transport the rotating PCB probe accurately and safely. A survey has been made to check the axial motion accuracy. As shown in Figure 3, the motion has accuracy of 0.6 mm which satisfies the MQXFAP magnet field measurement requirement. To implement the ZSCAN, a script file which includes all the Z positions will be loaded to the program and start the motion. Meanwhile, a HTBasic system can take a single magnetic field measurement. A hand-shake function has been established to connect the LabVIEW and HTBasic systems. The system will take the measurement at the first Z, and then move to the next Z while the HTBasic program is waiting. Once the next Z is reached and confirmed, the next measurement will take place, and so on until the last Z position, indicated by EOF, when the ZSCAN stops. In addition, the LabVIEW system online monitoring of three phase AC status and a real-time watch-dog checks the system to make sure that the electrical supplies and computer operating system are working functionally. If any of them malfunctions, the LabVIEW program will stop running and exit automatically. Most importantly, the E-Stop hardware is

4753.61 mm [187.142 in]

Top of Magnet Shell

Bottom of Warm Bore TubeBottom of Magnet Shell

4563 mm [179.646 in]

Top of Warm Bore Tube

6256.57 mm [246.322 in]

903.86[35.585]

Top hat to Lambda plate

Rotating coil in MAX UP Post

65625.827

Rotating coil

~220 mm

200.8 mm

Home

4730mm

190.61mm164.99mm

331.99mm

Switch_UL

Figure 2: A schematic for the MQXFAP magnet and the rotating probe. The total magnet length is 4,563 mm and the probes are only 220 and 110 mm long. The total vertical linear stroke between HOME and the upper limit switch is 4,730 mm at the maximum. When the rotating probe is at HOME, the distance between the probe bottom and the warm bore tube (upper surface) is 355.6 mm, and the distance between the probe bottom and the bottom of magnet shell is 164.99 mm. Limit switches have been placed at the very bottom and top for motion safety.

Figure 3: The LabVIEW-based vertical transport motion for the MQXFAP Magnet. A survey has been conducted to check the motion accuracy. One set of measurements was made from HOME to the further end (1a), and another set forwards (2a) and backwards (2b).

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incorporated in the motion system, so any error message or system malfunction will stop the motor instantly

III.MAGNETIC MEASUREMENTS

A. Warm MeasurementsThe magnetic field in the aperture of the straight section of

a quadrupole magnet can be expressed in terms of field coefficients in a series expansion in the following complex function formalism [18]:

(1)

where Bx and By are the horizontal and vertical field components in T in Cartesian coordinates, Bn and An are the normal and skew multipole fields at the reference radius, which is Rref 50 mm. The warm measurement was performed at LBNL in June 2018 prior to delivery to BNL for vertical magnet testing. In late August, the warm magnetic measurement was performed at BNL before the magnet cool-down. The warm ZSCAN measurement has 42 points starting from HOME (lowest), with an increment of 108.94 mm. Harmonics up to n of 15 have been measured. To eliminate the remnant field due to the background field and iron contribution, separate measurements at +/- 15 A currents have been made allowing separation of the remnant field from the

field due to magnet’s coils. The transfer function has been measured and plotted along the Z direction (magnet axis). The BNL and LBNL transfer function data are plotted in Figure 4 for direct comparison. Both are very close to the design transfer function of 8.86 T/m/kA at room temperature. The two curves agree very well along the magnet axis. Note that there is no BNL data at the return end due to the limited length of the underground Dewar.

B. Cold Measurement at 1.9 K and 4.5 K

Figure 5: Harmonics b3/a3, b6/a6 of the first +/-15 A warm magnetic field measurement before the magnet cooldown. Good agreement between LBL and BNL data has been confirmed.

Figure 4: The averaged +/-15 A warm magnetic field measurement prior to the magnet cooling-down. There is good agreement between LBNL and BNL warm measurements.

Figure 7: Transfer functions and b6 of currents in the stair-step loop measurements.

Figure 8: Center offset found in the ZSCAN. The X direction has less offset than the Y direction. The higher the current is, the more the Y offset becomes..

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The quench training test of the second MQXFA prototype (MQXFAP2) is in progress at BNL Vertical Test Facility. The magnet reached 15 kA in 9 quenches and showed detraining after quench 13. The quench training was interrupted to discuss magnet performance and test continuation which offered an opportunity for the cold magnetic field measurements. The cold measurement has ZSCAN like that in the warm measurement, and ISCAN which is also called stair-step (or DC loop) measurement. The ZSCAN was performed at currents of Iinj (960 A) at 1.9 K, Ilim (6kA) at ~2 K, 10 kA at

4.5 K. The temperature change was due to a temporary problem with the cryo facility. The short MQXF magnet data has indicated that the temperature dependence of magnetic fields is not significant[12]. The precyle for 960 A

measurement was a ramp up to 10 kA (300 second dwell) and down to Ires (100A), and up to Iinj (960 A, 1000 second dwell).

The transfer functions (T.F.) of all the three currents are plotted along with comparison to that of averaged 15 A as shown in Figure 6. The magnet has highest T.F. at Iinj (960A), and slightly decreases as current increases due to iron saturation. It agrees with the findings in the short MQXF quadrupoles. In the ISCAN as plotted in Figure 7, both the T.F. and the allowed coefficient b6 present considerable hysteresis which is caused by persistent current. In analyzing the cold measurement data, it is found that offset occurred between the PCB probe center and the magnet center as shown in Figure 8. The Y direction has more offset than the X direction. It has the largest offset at the lower return end and smallest at the lead end. Moreover, it increases as the current increases. The warm bore tube (WBT) which contains the PCB rotating probe may have tilted during the cool down. This may trace back to the fact both the WBT and rotating probe are suspended from the top. It seems more centering is necessary though detailed investigation is underway. While all the harmonics analysis in Figure 7 are corrected for the effects of the center offset between the rotating PCB probe and the magnet, a smaller offset is still preferred to allow accurate corrections particularly for high order multipole coefficients.

Figure 6: Transfer functions at 15 A (averaged, warm), 960 A, 6kA and 10 kA in cold MM in the ZSCAN.

Figure 9: Nonallowed b3 and a3 at currents of 960 A at 1.9 K, 6 kA at ~2 K, 10 kA at 4.5 K, with comparison to that of averaged 15 A at room temperature.

Figure 10: Nonallowed b5 and a5 at currents of 960 A at 1.9 K, 6 kA at ~2 K, 10 kA at 4.5 K, with comparison to that of averaged 15 A at room temperature.

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Furthermore, the cold multipole coefficients of 960 A, 6kA and 10 kA are plotted along the Z axis, directly compared to the warm coefficients of 15 A in the ZSCAN as shown in Figure 9-11. Most of them agree well with each other. The slight difference in b4 and b5 may be related to the geometric shrinkage during cooling down. The change in b6 is due to a combination of iron saturation and persistent currents. The measured field quality confirms the necessity of having a fine tuning of the cross-section to increase b6 by about 4 units[19, 20]. A decision has been recently made and shall be implemented for the future magnets through a change of 0.125 mm shims in the pole and in the midplane. On the other hand, the non-allowed harmonic that showed large values in the short model program appear to be close to the targets.

TABLE I

Harmonics bn (n≤6) of MQXFAP2 at 10 kA and 4.5 K.

b3 b4 b5 b6

Current mean rms mean rms mean rms Mean Rms

15A -1.23 1.96 -1.12 1.25 -0.46 0.95 -5.90 1.12

960A -0.92 2.02 -0.91 1.30 -1.38 1.02 -17.03 1.28

6kA -0.67 2.07 -1.11 1.28 -1.12 1.06 -7.37 1.28

10kA -0.87 2.09 -1.25 1.33 -0.99 1.06 -4.18 1.26

TABLE II

Harmonics an (n≤6)) of MQXFAP2 at 10 kA and 4.5 K.

a3 a4 a5 a6

Current mean rms mean rms mean rms mean rms

15A 4.10 1.77 2.61 1.69 1.94 0.78 0.45 0.49

960A 4.19 1.77 3.07 1.83 1.75 0.82 0.47 0.49

6kA 2.79 1.82 2.24 1.96 1.35 0.83 0.40 0.52

10kA 3.17 1.85 2.54 1.95 1.48 0.85 0.40 0.52

The cold and warm harmonics (bn and an, n≤6) of 10 kA and 15 A in the straight section have been averaged and plotted against each other in Y and X axis as shown in Figure 12. Most the data points are next to the 45 deg angle line, which indicates a correlation between the cold and warm field data. The b6 has the largest value of -5.9 units for 15 A and -4.18 units for 10 kA. The a3 has the largest value of 4.10 units for 15 A and 3.17 units for 10 kA as summarized in TABLE I and II.

As Probe 220 is twice as long as Probe 110, the Probe 110 is expected to have better resolution with ~110 mm step. Data of the two probes have been compared in Figure 13. Their starting points are off by ~220 mm. For the allowed harmonic b6 with 10 – 20 units, their difference is not significant. For the nonallowed harmonics a6, b4 and a4, the data profiles of Probe 110 at 15 A and 960 are sharper than those of Probe 220.

Figure 11: Allowed b6 and nonallowed a6 at currents of 960 A at 1.9 K, 6 kA at ~2 K, 10 kA at 4.5 K, with comparison to that of averaged 15 A at room temperature.

Probe 220 Probe 110

Probe 220

Probe 110

Figure 13: Field comparison between Probe 220 and 110.

Figure 12: Cold and warm harmonics correlation for the field in the straight section (Probe 220) between -1.915 m and 1.642 m, 10 kA vs 15 A.

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IV. CONCLUSIONS

The vertical magnetic measurement system which includes the newly developed vertical motion transport system has been commissioned for the magnetic measurement of the MQXFAP2 magnet. The good agreement between the BNL and LBNL data in the warm magnetic measurements of average 15 A indicates that the PCB rotating coil functions well for the full-length MQXFA production magnets. Furthermore, the system has been used for the cold measurement and collected ZSCAN and ISCAN (stair-step) data. A preliminary analysis of the Probe 220 data, corrected for the center offset between the probe and the magnet, shows good agreement between the warm and cold measurements. The Probe 110 does have better resolution than Probe 220 which will be very useful for measurement of the lead end. The measurement indicates that the MQXFAP2 magnet has magnetic field which meets the preliminary MQXFA magnet acceptance criteria. The large offset of the measuring coil at the magnet return end is likely because both the WBT and the probe are suspended from the top flange. Improvement to better center the rotating probe in the vertical magnet testing facility seem necessary. Further investigation of the offset is underway.

ACKNOWLEDGEMENT

The authors thank the magnet testing team at BNL for the measurement setup and preparations, and general support from FermiLab and LBNL and thank G. Ambrosio, G. Apollinari, K. Amm, M. Anerella, S. I. Bermudez, S. Feher, P. Joshi, J. Muratore, E. Todesco for helpful discussions and suggestions. This work was supported in part by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the U.S. LHC Accelerator Research Program, and in part by the High Luminosity LHC project at CERN.

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