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MQXFAP1b Magnetic Measurement PlanDRAFT

Contents1 Magnetic measurement goals for MQXFAP1b.......................................................................1

2 Facility and rotating probe......................................................................................................2

3 Reference parameters and conditions.....................................................................................2

4 Field quality characterization.................................................................................................4

4.1 Z scan at warm................................................................................................................4

4.2 Z scan at nominal gradient..............................................................................................4

4.3 Stair-step measurement...................................................................................................5

4.4 Accelerator cycle to nominal gradient.............................................................................6

4.5 Ramp-rate dependence....................................................................................................7

4.6 Accelerator cycle to ultimate current...............................................................................8

4.7 Z scan at ultimate gradient..............................................................................................9

4.8 Effect of reset current....................................................................................................10

4.9 Reproducibility of accelerator cycle to nominal gradient..............................................11

5 Z scan during warmup and at room temperature...................................................................12

6 References............................................................................................................................ 12

7 Appendix I – Mapping of vertical magnetic Measurements into MQXFA requirements.....13

8 Appendix II – Definition of the probe home position (z=0) in relation to the magnet..........14

1 Magnetic measurement goals for MQXFAP1b

MQXFAP1b is a reassembly of MQXFAP1, the first long prototype of the MQXF design for the HL-LHC Q1 and Q3 final focus quadrupoles. A new coil (P06) was fabricated to replace coil P05 that was damaged during the MQXFAP1 test. The other three coils from MQXFAP1 (P02-P03-P04) are being reused without changes. All three are first-generation coils built to the original length specification (4 m magnetic). The new coil P06 is made to match the same length but incorporates the latest features for production, except for the pole/mid-plane shim adjustment for b6 correction. The goal of MQXFAP1b magnetic measurements is to establish, to the extent possible, whether the MQXFA design satisfies the relevant functional requirements [1] and acceptance criteria [2]. Feedback from these measurements and analysis will be used to confirm the present design and fabrication process, or apply any needed improvements in future production magnets. In addition, MQXFAP1b will provide an opportunity to further validate and optimize the new magnetic measurements system which was developed specifically for the MQXFA vertical test. The results will be compared with those of short models previously tested

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in the US and at CERN, and with the warm measurements of MQXFAP1b performed during assembly at LBNL, and with the measurements of the MQXFAP2 prototype.

In order to optimize the overall project schedule, the first thermal cycle will include: (1) a longitudinal scan at warm before cool-down; (2) a longitudinal scan at nominal current, which will be combined with the holding test; and (3) a stair-step measurement, which will be combined with the splice resistance measurement. All other magnetic measurements will be performed in the second thermal cycle.

2 Facility and rotating probe

The PCB magnetic measurement probe was designed and fabricated at Fermilab incorporating the lessons learned from previous tests of MQXFS short models. In particular, number of layers has been optimized to provide the optimal signal strength and the length has been adjusted to better match the cable twist pitch. Two identical copies were made, one to be used at Fermilab for short models and the second to be used at BNL for long prototypes. Both probes were commissioned and cross-checked at Fermilab during the MQXFS1c test.

Two circuits are included in each probe, one with a nominal 110 mm length, and the second with a nominal 220 mm length. Taking into account the detailed design of the PCB, the effective length is 108.74 mm for the 110 mm circuit, and 217.88 mm for the 220 mm circuit. These values provide the required displacements at each step of the z-scan, in order to correctly measure the field integrals. It should be noted however that due to a restriction in the length of the cryostat and warm finger, the last portion of the return end cannot be measured during the vertical test and therefore it is not possible to obtain the integrated values over the full magnetic length.

3 Reference parameters and conditions

All cold measurement to be performed at 1.9K. Nominal ramp rate is 14 A/s.

Currents and corresponding gradients for injection, nominal and ultimate level are specified in Table 1. Injection level was calculated as follows. G.inj = 132.6/7*0.45 = 8.5 T/m. Low current transfer function is 8.86 T/m/kA [4] therefore 0.96 kA for 8.5 T/m

Table 1 Reference current levels for magnetic measurements of MQXFAP1b.

Current [kA] Symbol Gradient

[T/m] Remarks

0.1 I.res 0.9 Reset level for pre-cycle

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Current [kA] Symbol Gradient

[T/m] Remarks

0.96 I.inj 8.5 Injection level6.0 I.lim 48.8 Current limit (pre-training)

16.48 I.nom 132.6 Nominal level

17.89 I.ult 143.2 Ultimate level

An optimized profile for acceleration/deceleration at the beginning and end of each ramp is used to minimize the impact on the multipole decay and to avoid current overshoot and the resulted ramp irregularity

Pre-cycle parameters for measurements up to I.nom (or higher). A pre-cycle is applied to put the magnet into a reproducible state prior to the following measurements: accelerator cycle, stair-step measurements and ramp-rate dependence measurements.

o The pre-cycle is defined as follows:

From 0 to I.nom at 14 A/s, Hold for 300 s at I.nom, Ramp down to I.res at 14 A/s Hold for 0s at I.res Ramp to I.inj at 14 A/s [Hold at I.inj is treated as part of the measurement cycle]

o The pre-cycle needs to be adapted for measurements limited to lower current (e.g. before reaching I.nom, if any). The modified pre-cycle is described in the corresponding sections.

o For measurements requiring a pre-cycle, the pre-cycle needs to be repeated in the case of a spontaneous quench, prior to completing the measurement.

The longitudinal reference (z=0) is defined as the probe position in which the center of the 220 mm circuit is located at 226.2 mm from the bottom of the warm finger (“home” position). Details and drawings of the longitudinal reference and the magnet position in relation to this reference are provided in Appendix 2 of this document.

The “central” location for performing accelerator cycles, ramp rate, stair-step and reset current measurements is defined as z = 2174.8 mm (same as for 4.2 m production magnets).

The following sections describe the schedule and procedures for individual magnetic measurements to be performed.

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4 Field quality characterization

4.1 Z scan at warm

Goals:o Verify the system operation and data qualityo Compare the results with those obtained at LBNL o Confirm the longitudinal coordinate system used in the test facility in relation to the

magnet CAD models and magnetic design calculations

Conditions:

o Magnet current ± 15 A at each longitudinal locationo Longitudinal locations (reference is defined in section 3)

From z=0 to z=598.07 in steps of 27.185 mm From z=598.07 to z=3425.31 in steps of 108.74 mm From z=3425.31 to z=4403.97 in steps of 27.185 mm

o Data is acquired in parallel for both probeso Switch point from 27.185 mm step to 108.74 mm step may be adjusted: goal is to use

the longer step in the straight section and the shorter step in the end regions, for both probes. Therefore, short step should be stopped when the 220 mm probe exits the return end, and restarted when the 110 mm probe enters the lead end. Last point is when the 220 mm probe exits the lead end.

4.2 Z scan at nominal gradient

Goals:o Measure the field integral and magnetic length at nominal gradiento Measure field quality variations along the magnet length

Conditions:

o Longitudinal locations as for the warm scan (may be adjusted based on results from the warm scan)

o Assume magnet has been trained above I.nom

Measurement cycle :

1. Perform standard pre-cycle2. Hold 1000 s at I.inj3. Ramp to I.nom at 14 A/s4. Hold 300 s at I.nom5. Z-scan at I.nom

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6. Ramp down to zero

4.3 Stair-step measurement

Goals:o Measure static field errors at various current intervals (without ramp effects)

o Measure splice resistance

Conditions: o Assume magnet has been trained above 17 kA, otherwise stop at safe current level

depending on trainingo Probe longitudinal position at z=2174.8 mm

Measurement cycle:1. Perform standard pre-cycle2. Hold 1000 s at I.inj3. Ramp in steps as defined in Table 3. Ramp rate 14 A/s4. Hold 60 s at each step5. No measurement at 17 kA6. Ramp down to I.inj in same steps7. Ramp down to zero

Fig. 1 Current steps for stair step measurement

Table 2: Current steps for stair step measurement

Step # Current (kA)1 I.inj

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2 1.53 2.04 2.55 3.06 47 58 69 710 811 912 1013 1114 1215 1316 1417 1518 1619 I.nom20 17

4.4 Accelerator cycle to nominal gradient

Goals:o Measure central field quality in conditions that approximate the machine cycle to

nominal gradiento Assess stability at I.inj and changes in harmonics at the start of rampo Assess stability of operation at I.nomo Assess reproducibility from cycle to cycle

Conditions:o Probe longitudinal position at z=2174.8 mm

Measurement cycle:1. Perform standard pre-cycle2. Hold 1000 s at I.inj3. Ramp to I.nom at 14 A/s4. Hold I.nom for 600 s5. Ramp down to I.res at 14 A/s6. Hold for 0s at I.res7. Ramp to I.inj at 14 A/s8. Repeat point 2 to 5 for two more times9. Ramp down to zero

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Figure 2: current profile for the accelerator cycle to nominal gradient.

4.5 Ramp-rate dependence

Goals:o Measure eddy current harmonics at different ramp rates

Conditions:o Probe longitudinal position z=2174.8 mm

Measurement cycle (Fig. 3):

1. Perform standard pre-cycle2. Hold 1000 s at I.inj3. Ramp to I.nom at 20 A/s4. Hold 600 s at I.nom5. Ramp to I.inj at 20 A/s6. Hold 600 s at I.inj7. Ramp to I.nom at 40 A/s8. Hold 600 s at I.nom9. Ramp to I.inj at 40 A/s10. Hold 600 s at I.inj11. Ramp to I.nom at 80 A/s12. Hold 600 s at I.nom 13. Ramp to I.inj at 80 A/s14. Hold 600 s at I.inj15. Ramp to zero

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Figure 3: current profile for the ramp-rate dependence study

4.6 Accelerator cycle to ultimate current

Goals:o Measure central field quality in conditions that approximate the machine cycle to

ultimate gradiento Confirm operation at I.ulto Assess reproducibility from cycle to cycleo Assess persistent decay time constant using a longer injection plateau (6000 s)

Conditions: o Probe longitudinal position z=2174.8 mm

Measurement cycle (Fig. 4):

1. Perform standard pre-cycle2. Hold 1000 s at I.inj3. Ramp to I.ult at 14 A/s4. Hold I.ult for 600 s5. Ramp down to I.res at 14 A/s6. Hold for 0s at I.res7. Ramp to I.inj at 14 A/s8. Hold 1000 s at I.inj9. Ramp to I.ult at 14 A/s10. Hold I.ult for 600 s11. Ramp down to I.res at 14 A/s12. Hold for 0s at I.res

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13. Ramp to I.inj at 14 A/s14. Hold 6000 s at I.inj15. Ramp to I.ult at 14 A/s16. Hold I.ult for 600 s17. Ramp down to I.res at 14 A/s18. Hold for 0s at I.res19. Ramp to I.inj at 14 A/s20. Ramp down to zero

Figure 4: current profile for accelerator cycle to ultimate gradient

4.7 Z scan at ultimate gradient

Goals:o Measure the field integral and magnetic length at ultimate gradiento Measure field quality variations along the magnet length

Conditions:

o Longitudinal locations as for the longitudinal scan at nominalo Assume magnet has been trained above I.ult

Measurement cycle :

7. Perform standard pre-cycle

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8. Hold 1000 s at I.inj9. Ramp to I.nom at 14 A/s10. Hold 300 s at I.ult11. Z-scan at I.ult12. Ramp down to zero

4.8 Effect of reset current

Goals:o Measure effect of reset current on persistent current harmonics at injection and

subsequent ramp Conditions:

o Probe position 2174.8 mm

Figure 5: current profile for reset current study

Measurement cycle:

1. Ramp from 0 to I.nom at 14 A/s,2. Hold for 300 s at I.nom,3. Ramp down to 300 A at 14 A/s4. Hold for 0s at 300 A5. Ramp to I.inj at 14 A/s6. Hold 1000s at I.inj7. Ramp to I.nom at 14 A/s8. Hold I.nom for 600 s

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9. Ramp down to 500 A at 14 A/s10. Hold for 0s at 500 A11. Ramp to I.inj at 14 A/s12. Hold 1000s at I.inj13. Ramp to I.nom at 14 A/s14. Hold I.nom for 600 s15. Ramp down to zero at 14 A/s

4.9 Reproducibility of accelerator cycle to nominal gradient

Goals:o Assess reproducibility of accelerator cycle

Conditions: o Probe position 2174.8 mm

Measurement cycle:

1. Perform standard pre-cycle2. Hold 1000 s at I.inj3. Ramp to I.nom at 14 A/s4. Hold I.nom for 600 s5. Ramp down to I.res at 14 A/s6. Hold for 0s at I.res7. Ramp to I.inj at 14 A/s8. Repeat point 2 to 5 (one time only)9. Ramp down to zero

Figure 6: current profile for one accelerator cycle to nominal gradient.

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5 Z scan during warmup and at room temperature

Goals:o Measure geometric harmonics at low current as a function of temperature

Conditions:

o Magnet current as defined in Table 2.o Longitudinal locations refer to center of circuit #1 (circuit #2 data recorded in

parallel)o Longitudinal locations: from z=-2396.68 to z=+2396.68, every 108.94 mm

Table 1 Maximum current for different temperature intervals

Temp. (K) Current (A)200 – 295 ± 15100 – 200 ± 20

< 100 ± 30

Additional notes:

1. Perform one scan soon after the magnet enters the normal state (~ 30 K) to obtain the geometric effect with maximum effect of preload from cooldown.

2. External heating to expedite the warmup process should be off before and during the measurements to help reducing temperature gradient along the magnet.

6 References

1. G. Ambrosio et al., “MQXFA Functional Requirements Specification”, US HiLumi Doc 36, July 2017

2. G. Ambrosio et al., Acceptance Criteria Part A: MQXFA Magnet”, US HiLumi Doc 1123, July 2018

3. X. Wang, J. DiMarco, G. Sabbi, “MQXFAP2 magnetic measurements during magnet assembly”, HL-LHC WP3 Meeting, July 10, 2018

4. G. Ambrosio et al., “MQXFA Final Design Report”, US HiLumi Doc 948, July 2018 5. MQXF Test plans in HiLumi DocDB:

http://us-hilumi-docdb.fnal.gov/cgi-bin/DocumentDatabase/Search keyword: TESTPLAN

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7 Appendix I – Mapping of vertical magnetic Measurements into MQXFA requirements

Requirement Description Relevant magnetic measurement

MQXFA-R-T-01 The MQXFA coil aperture at room temperature without preload is 149.5 mm. Coil bumpers (pions) shall be installed on coil poles. The minimum free coil aperture at room temperature after coil bumpers installation, magnet assembly and preload shall be 146.1 mm.

N/A

MQXFA-R-T-02 The MQXFA physical outer diameter shall not exceed 614 mm. N/AMQXFA-R-O-01 The target for the variation of the local position of magnetic center is ±0.5 mm; the target for the

variation of the local position of magnetic axis is ±2 mrad. Local positions are measured with a probe of 500 mm maximum length, and measurements are performed at steps equal to probe length.

LBNL warm measurement + survey, then at FNAL. No contribution expected from vertical test at BNL (confirm)

MQXFA-R-T-03 The MQXFA magnet must be capable of operate at steady state providing a central gradient of 143.2 T/m in superfluid helium at 1.9 K.

Dedicated measurement separate from accelerator cycle (confirm)

MQXFA-R-T-04 The MQXFA magnet must provide an integrated gradient between 554 T and 560 T when powered with current of 16.470 kA. The difference between the integrated gradient of all series magnets shall be smaller than 0.6%. The MQXFA magnetic length requirement is 4.2 m with a tolerance of ± 5 mm at 1.9 K.

Longitudinal scan at nominal gradient

MQXFA-R-O-02 The MQXFA field harmonics shall be optimized at nominal current. Table 2 provides expected values for field harmonics at a reference radius of 50 mm

Main: Longtudinal scan at nominal grandient; accelerator cycle to nominal gradient. Additional: stair step, ramp rate, reproducibility of accelerator cycle; Marginal: accelerator cycle and z-scan at ultimate, effect of reset current

MQXFA-R-O-03 The fringe field target, for the magnet installed in the cryostat, is lower than 50 mT at 10 mm from the outer surface of the cryostat

N/A (planned for horizontal test)

MQXFA-R-T-05 MQXFA magnets shall be capable of operation in pressurized static superfluid helium (HeII) bath at 1.3 bar and at a temperature of 1.9 K.

Magnetic measurements are relevant but not required to meet this requirement

MQXFA-R-T-06 The MQXFA cooling channels shall be capable of accommodating two (2) heat exchanger tubes running along the length of the magnet in the yoke cooling channels. The minimum diameter of the MQXFA yoke cooling channels that will provide an adequate gap around the heat exchanger tubes is 77 mm.

N/A

MQXFA-R-T-07 At least 40% of the coil inner surface shall be free of polyimide N/AMQXFA-R-T-08 The MQXFA shall have provisions for the following cooling passages: (1) Free passage through the

coil pole and subsequent G-11 alignment key equivalent of 8 mm diameter holes repeated every 50 mm; (2) free helium paths interconnecting the four yoke cooling channels holes; and (3) a free cross sectional area of at least 150 cm2

N/A

MQXFA-R-T-10 The MQXFA magnet shall be capable of surviving a maximum temperature gradient of 100 K, during a controlled warm-up or cool-down, and to experience the thermal dynamics following a quench without degradation in its performance

N/A

MQXFA-R-T-11 The MQXFA magnets shall be capable of operating at a ramp rate smaller than ±30 A/s Ramp rate dependence study (note: requirement should probably read "up to" 30 A/s)

MQXFA-R-T-12 The MQXFA magnet shall withstand a maximum operating voltage of 670 V to ground during quench.

N/A

MQXFA-R-T-13 MQXFA magnets must be delivered with a (+) Nb-Ti superconducting lead and a (-) Nb-Ti superconducting lead, both rated for 18 kA and stabilized for connection to the cold mass LMQXFA electrical bus.

N/A

MQXFA-R-T-14 Splices are to be soldered with CERN approved materials N/AMQXFA-R-O-04 Splice resistance target is less than 1.0 nΩ at 1.9 K Stair step measurement

contributes to splice resistance measurement

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8 Appendix II – Definition of the probe home position (z=0) in relation to the magnet

The following drawings illustrate the position of the two probes at the magnetic measurement system “home” position in relation to the magnet. The longitudinal coordinates for the longitudinal scans are provided in relation to the home position. In the home position, the center of the long (nominal 220 mm) probe is at z=0 and the center of the short (nominal 110 mm) probe is at z=220 mm.