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Magnetic Field Distortions due to Electronics in the Mu2e Tracker Potential use of 2D Hall Probes to measure the Alignment of a Magnetic Field Felix Johannes Kress University of St Andrews Mentor: Aseet Mukherjee 14.08.2013

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Potential use of 2D Hall Probes to measure the Alignment of a Magnetic Field

14.08.2013 1

Felix Johannes Kress University of St Andrews Mentor: Aseet Mukherjee

Magnetic Field Distortions due to Electronics in the Mu2e Tracker

fjk4@st-andrews.ac.uk

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SLIDE 2

Mu2e experiment

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Figure 1: RHS: -The most common 𝜈 −decay LHS: -Decay being tested with Mu2e experiment; If seen it would push the boundaries of the Standard Model and if not, rule out other possibilities

fjk4@st-andrews.ac.uk

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SLIDE 3

Basic structure of the tracker

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Figure 2: TL: Assembled tracker TR: 1 of the 18 stations BL: Plane consisting of 6 panels

fjk4@st-andrews.ac.uk

Source: Mu2e Doc888 Figures 4,6,7

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SLIDE 4

Sketch of the situation

Figure 3: Sketch of the situation illustrating the position of the FEE (Front end electronics) space in relation to the magnetic field concerned

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SLIDE 5

General principal to test whether electronics are magnetic

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  • 1. Fix electronic component to metal rod
  • 2. Apply field of 1T
  • 3. Set readings of Hall probes to 0
  • 4. Slide component into the field

(1cm from the Hall probes)

  • 5. Read off distortion: Should be less than 1G

Figure 4: The 3D Hall probe in-between the two poles of the magnet and

  • ne of the transducers approaching
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SLIDE 6

Results

  • Distortions for most components seemed very

small ⇒ I decided it is safe enough to enter them by hand and see whether there is a change in Magnetic field

  • There wasn’t apart from one case:

The Transducer!!!

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SLIDE 7

The Transducer

  • Changed the field at 1cm distance by up

to 15G

  • Only changed the field by 0.7G at already

4 cm, but we have more than one transducer!

  • Therefore we had to find a model

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SLIDE 8

Sketch of the situation

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Figure 5: Sketch of the measurement situation with the y - axis going into the page. The magnetic field applied shows into the z – direction. We tested whether the two packaging's for the photo elements could act as dipoles

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SLIDE 9

Position of the transducers

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Figure 6: Positions of the transducers within the tracker. Note there will be two transducers positioned at each star

FEE space

Region concerned with

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SLIDE 10

Do we have to worry?

  • Model in Mathematica:
  • Maximum Magnitude of the field in the region

concerned: 0.086G

  • This is under our specification of 1G

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SLIDE 11

Conclusion

  • Most of the components do not seem to

distort the field at all (upper limit of distortion is 0.05G at 1 cm distance)

  • The distortions from the transducers are an

exception: They will distort the field by a considerate amount if not placed at the outer part of the FEE space

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SLIDE 12

Importance of Alignment with the Magnetic Field

Figure 7: Muon (green) converting to an electron (red) (source: Mu2e CDRv14 Figure 9.19)

  • Charged particles follow helical trajectories; radius determines

the momentum

  • Misalignment of panels ⇒ ‘smeared’ observed particle position

⇒ lower overall observed efficiency of event production

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SLIDE 13

Figure 8: # of Events vs Momentum, Blue - normal muon decay, green - all other backgrounds, red - the expected signal (source: mu2e-docdb document 2936-v3,slide 31)

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SLIDE 14

Monitoring alignment with a 2D Hall probe

As long as the field is aligned with the Hall sensor, the reading won’t change with the strength of the field ⇒ can detect misalignment

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Figure 9: Sketch of a 2D Hall sensor measuring the 𝑦- and 𝑧-direction (black thick arrows), while there is a B field in 𝑢ℎ𝑓 𝑨-direction (blue arrow)

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A suitable candidate

Figure 10: Sentron Angle Sensor, 2SA-10G probe Dimensions: 5mm*6mm Cost: 6.40$ Measurements up to 800G Accuracy of about 1mV ≈ 0.21G Field of the tracker is 1T ⇒can detect changes of 1.2 mDegrees (0.21G = sin 𝜄10,000G) Has been tested before in a very similar set up

(I.B. Vasserman et al, „Magnetic Measurements and Tuning of Undulators for the aps fel project”, published in the proceedings of the 1990 particle accelerator conference, New York, 1999)

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Potential problems and solutions

  • Accuracy of Alignment of

Hall sensors

  • Time dependence
  • Temperature

dependence

  • Potential solution:

Use two solenoids to measure the magnetic field

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Figure 11: Hall probe with 2 solenoids

𝑦-solenoid 𝑧-solenoid

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SLIDE 17

Figure 12: B in x vs I using solenoid 1

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y = 230,65x + 0,0004 R² = 0,9993

50 100 150 200 250 0,00 0,20 0,40 0,60 0,80 1,00 1,20

Bx[G] I [A]

B in x vs I using solenoid 1

Note: The solenoid wasn’t perfectly aligned therefore a small field was measured in the y-direction

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Future Challenges

  • 2nd solenoid creates a smaller magnetic field
  • The coils heat up and therefore change the

reading (even at a 0 field)

  • Methods to align the probe (calibration)
  • Want to make set up smaller
  • Check for radiation damages
  • What about magnetic field distortions?

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SLIDE 19

Backup

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SLIDE 20

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y = -17.881x

2 4 6 8 10 12

  • 0,7
  • 0,6
  • 0,5
  • 0,4
  • 0,3
  • 0,2
  • 0,1

Magnitude of the Magnetic Field [G] Proportionality factor p1 [cm^-3]

Check for Two Dipoles (moving transducer in x-direction)

Bt Linear (Bt)

Figure 12: Check for Two Dipoles with 𝐶𝑢 =

𝜈0𝑛 2𝜌 𝑞1 ≈ −17.9 𝑞1

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SLIDE 21

Magnetic field distortions in panel plane positioned in the middle of the tracker

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Figure 14: Magnetic field distortions for a panel plane in the middle of the tracker, magnitude plot

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Hall Effect

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How it works:

  • Current flows in direction perpendicular to magnetic

field, forcing electrons to one side of the wire

  • This forms a potential difference which varies with the

field strength and can be read into a DAQ

Source: Wikipedia

ρed B I ρeA B I A ev I qE qvB

d

          

H H d

V (2) and (1) from V E

  • f

defn. From (3) w V E city drift velo is v where Current, (2) gradient V from Force force Magnetic (1) 

A conveniently linear effect by which to measure the projection of the B field!

fjk4@st-andrews.ac.uk

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Calibration of the Hall probe: B vs V

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y = -211,75x + 538,5 R² = 1

50 100 150 200 250 0,5 1 1,5 2 2,5 3

B[G] V [V]

B vs V

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SLIDE 24

Temperature dependence at 𝐶 ≈ 0

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2,576 2,576 2,577 2,577 2,578 2,578 2,579 2,579 2,580 2,580 2,581 295 300 305 310 315 320 325 330 335 340

V[V]

T[K]

Vx vs T

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SLIDE 25

25

New physics

also see Flavour physics of leptons and dipole moments, arXiv:0801.1826 and Marciano, Mori, and Roney, Ann. Rev. Nucl. Sci. 58, doi:10.1146/annurev.nucl.58.110707.171126