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12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - W E P 0 1 4MEASURING ELECTROMAGNET POLARITY
USING MAGNETIC REMANENCE∗K. P. Wootton† , Argonne National Laboratory, Lemont, IL, USA
METHOD

Abstract
Large accelerator systems typically include many individually powered electromagnets. An important activity prior
to commissioning with beam is verifying that the polarityof the installed magnets matches the design lattice. In thepresent work, we motivate the measurement of magnet polarity in a manner that is electrically safe, by measuring themagnetic remanence of iron yokes of normal conducting
electromagnets. This has been used to confirm the polarities
of iron-dominated dipole and quadrupole electromagnets atthe Linac Extension Area at the Advanced Photon Source.

We tested this procedure using the bending magnets ofthe booster bypass vertical ramp and the Linac Extension
Area (LEA). The steps in the procedure are outlined below.

INTRODUCTION

4. Lock-Out-Tag-Out (LOTO) accelerator magnets, andverify zero energy state by Zero Voltage Verification(ZVV). At this point, all LOTO requirements should becomplete to enable authorised access to the accelerator
enclosure.

During installation and commissioning of accelerator systems, a common quality assurance task associated with theinstallation is ensuring that magnets are connected to power
supplies with the correct polarity [1–4]. Magnetic polarity
checkout has typically been performed in under administrative controls with magnets energised [5]. We consider
that procedures which require workers to approach energised magnets potentially presents an unacceptable electricalsafety hazard.
In the present work, we summarise a technique for performing magnet polarity checks using the remnant magnetic
field from prior excitation using the connected power supply.
Measuring the remnant field with the power supply off obviates the principal safety concern of needing to work adjacent
to energised electrical conductors.

BACKGROUND
In many accelerators, the main magnets are powered byunipolar power supplies. Hence, a quality assurance task
associated with the installation of a magnet and power supply system is to confirm that the installed magnet polarities
match the design polarities of the lattice [6–9]. When powered, electromagnets have the opportunity to present bothelectrical and magnetic hazards to personnel approachingthem [10]. There are different ways of mitigating these hazards, for instance by implementing electrically insulating
shielding or shielding that restricts personnel from approaching the magnetic field that the magnet generates. Anotherway is to switch off the magnet power supply, and Lock-OutTag-Out (LOTO) the source of hazardous energy.
∗ Work supported by the U.S. Department of Energy, Office of Sci-ence, Office of Basic Energy Sciences, under Contract No. DE-AC0206CH11357.
† kwootton@anl.gov

1. Accelerator enclosure secured.
2. Accelerator magnets energised at its nominal current
setpoint for 10 minutes using its connected power supply. This puts the magnet on its hysteresis curve.
3. Accelerator magnets de-energised, leaving only theremnant field in the magnet.

5. Lower the accelerator access control system level toauthorised access.
6. Enter the accelerator enclosure and approach the unpowered electromagnet.
7. Measure the polarity of the remnant field (without anyelectrical hazard) using a permanent magnet probe.

RESULTS
Initial Measurement
On the 22nd of August, 2022, Kent Wootton performed
magnet polarity checks on booster bypass and LEA magnets.
A magnet polarity checker Magnaprobe MKII was used. The
north pole of the bar magnet on the magnet probe is coloured
red, and the south pole of the magnet is coloured blue. The
polarity checker is illustrated in Fig. 1.
The polarity of quadrupoles and vertical bending magnets (skew dipoles) along the booster bypass transport line
was measured. We measured the ‘top-left’ most pole ofquadrupoles, and the ‘left’ pole of skew dipoles. This pole
convention is illustrated in Fig. 2.
The probe was held near the poles of the magnets. Photographs illustrating polarity measurements are given inFig. 3 and Fig. 4. One can see that the experimenter’s handis quite close to the magnet while performing the measurement.
Results of polarity measurements are summarised in Table 1. Magnet polarity measured from remnant field on
the 22nd of August, 2022. Magnet types 𝑄1 correspond toupright quadrupole, and 𝐵2 to skew dipole (vertically deflecting). We deliberately included a couple of quadrupoles fromWEP014
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07 Machine Parameter Measurements

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Figure 1: Polarity checker.

Figure 4: PTB:Q8. The polarity of the top-left pole is denoted ‘blue’. The beam direction in this photograph is fromright to left.

Figure 2: Pole used for measurements, and convention used
to express measurement results. (a) Skew dipole, beam direction into the page. The colour of the polarity checker
directed towards the left pole is indicated. (b) Normal (upright) quadrupole, beam direction into the page. The colourof the polarity checker directed towards the top-left pole isindicated.

the PTB line, so that we could associate a known focussing
or defocussing polarity with the existing, operational latticeof the accelerator beamline.
We see from the results of polarity measurements in Table 1 that the magnets which had previously been operated in
the booster bypass (designations BB and LA) had the correct
polarity, while newly installed magnets in the LEA beamline(designation LEA) did not all have the correct polarity. We
used this information to correct the polarity of magnets in
the LEA beamline.

16th of March, 2023
After correcting the magnet power supply lead polarities
of LEA quadrupole magnets, the magnets were re-energised
to reverse the remnant field of the magnets. The polarityof a subset of the above magnets (LEA magnets) was remeasured on the 16th of March, 2023. The results are summarised in Table 2. This shows that the polarity of all thequadrupoles has been corrected to match the design lattice.

DISCUSSION

Figure 3: BBBD1. The polarity of the left pole is denoted‘red’. The beam direction in this photograph is from right toleft.

From the perspective of electrical safety, we think thismight be the safest way to perform a magnet polarity test.
The time required to perform each test was minimal: a few
seconds at most per magnet. It took longer to record theresult of the measurement than perform the test.
We had expected that remnant field of the magnet may
be relatively short-lived. Instead, we found that the remnant
magnetisation is comparatively long-lived.
We demonstrated this procedure using magnets as partof the Linac Extension Area beamline. The procedure wasWEP014

07 Machine Parameter Measurements

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12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - W E P 0 1 4

Table 1: Initial Magnet Polarity Measurement August 2022
MagnetMagnet type

PTB:Q8PTB:Q9
BB:QE1
BB:QE2
BB:Q1
BB:BM:1-1
BB:BM:1-2
BB:BM:1-3
BB:BD:1
BD:Q1
BB:Q2
BB:Q3
BB:Q4
BB:BM:2-1
BB:BM:2-2
BB:BM:2-3
BB:Q5
BB:Q6
LA:Q1LA:Q2
LEA:Q1
LEA:Q2
LEA:Q3
LEA:Q4
LEA:Q5
LEA:Q6
LEA:Q7
LEA:BD

𝑄1
𝑄1
𝑄1
𝑄1
𝑄1
𝐵2
𝐵2
𝐵2𝐵2
𝑄1
𝑄1
𝑄1
𝑄1
𝐵2𝐵2𝐵2𝑄1
𝑄1
𝑄1
𝑄1
𝑄1
𝑄1
𝑄1
𝑄1
𝑄1
𝑄1
𝑄1
𝐵2

Polarity
Measured Correct?
Blue
Red
Blue
Red
Blue
Blue
Blue
Blue
Red
Red
Red
Blue
Red
Red
Red
Red
Blue
Red
Blue
Red
Blue
Red
Red
Red
Blue
Red
Red
Red

Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
NoNo
No
Yes
Yes

Table 2: Subsequent Magnet Polarity Measurement March
2023
MagnetMagnet type

LEA:Q1
LEA:Q2
LEA:Q3
LEA:Q4
LEA:Q5
LEA:Q6
LEA:Q7
LEA:BD

𝑄1
𝑄1
𝑄1
𝑄1
𝑄1
𝑄1
𝑄1
𝐵2

Polarity
Measured Correct?
BlueRedBlue
Blue
RedBlue
RedRed

Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes

useful in identifying magnets with incorrect power supply
polarity, which was corrected.
Alternative schemes such as connecting a small laboratory
power supply that is capable of providing current and voltage
output so low as to be considered electrically safe was also
considered as a different technique. However we consider
that such an approach has the potential to introduce newmeasurement errors, because the supply has to be connectedwith the correct polarity.
We have tested this method using magnets powered bysingle unipolar magnet power supplies. Future work could include testing this technique for magnets wound with multiple
power supplies (for instance, a quadrupole with additional
horizontal and vertical corrector trims). Whether corrector
power supplies are able to generate sufficient field to cancel the remnant magnetisation of the main magnetic circuitis probably a detail that depends on the implementation ofindividual magnet designs.

SUMMARY
We present a step-by-step procedure to test the polarity ofmagnets installed with their associated power supply off. By
exciting the magnet briefly, we propose putting the magnet
on its hysteresis curve, and observing the polarity of theexcitation using the remnant magnetic field. This procedureallows someone to approach and measure a magnet without
electrical hazards.

ACKNOWLEDGEMENTS
The submitted manuscript has been created by UChicago
Argonne, LLC, Operator of Argonne National Laboratory(“Argonne”). Argonne, a U.S. Department of Energy Office of Science Laboratory, is operated under Contract No.
DE-AC02-06CH11357. The U.S. Government retains foritself, and others acting on its behalf, a paid-up nonexclusive,
irrevocable worldwide license in said article to reproduce,
prepare derivative works, distribute copies to the public, andperform publicly and display publicly, by or on behalf ofthe Government. The Department of Energy will provide
public access to these results of federally sponsored researchin accordance with the DOE Public Access Plan. http://energy.gov/downloads/doe-public-access-plan

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ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3