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 fjk4@st-andrews.ac.uk 1
Mu2e experiment 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 14.08.2013 fjk4@st-andrews.ac.uk 2
Basic structure of the tracker Source: Mu2e Figure 2: Doc888 Figures 4,6,7 TL: Assembled tracker TR: 1 of the 18 stations BL: Plane consisting of 6 panels 14.08.2013 fjk4@st-andrews.ac.uk 3
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 14.08.2013 fjk4@st-andrews.ac.uk 4
General principal to test whether electronics are magnetic 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 one of the transducers approaching 14.08.2013 fjk4@st-andrews.ac.uk 5
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!!! 14.08.2013 fjk4@st-andrews.ac.uk 6
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 14.08.2013 fjk4@st-andrews.ac.uk 7
Sketch of the situation 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 14.08.2013 fjk4@st-andrews.ac.uk 8
Position of the transducers Region concerned with FEE space Figure 6: Positions of the transducers within the tracker. Note there will be two transducers positioned at each star 14.08.2013 fjk4@st-andrews.ac.uk 9
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 14.08.2013 fjk4@st-andrews.ac.uk 10
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 14.08.2013 fjk4@st-andrews.ac.uk 11
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 14.08.2013 fjk4@st-andrews.ac.uk 12
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) 14.08.2013 fjk4@st-andrews.ac.uk 13
Monitoring alignment with a 2D Hall probe 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) 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 14.08.2013 fjk4@st-andrews.ac.uk 14
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 𝜄 10,000G) 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) 14.08.2013 fjk4@st-andrews.ac.uk 15
Potential problems and solutions 𝑧 -solenoid 𝑦 -solenoid • Accuracy of Alignment of Hall sensors • Time dependence • Temperature dependence • Potential solution: Use two solenoids to measure the magnetic field Figure 11: Hall probe with 2 solenoids 14.08.2013 fjk4@st-andrews.ac.uk 16
B in x vs I using solenoid 1 250 200 y = 230,65x + 0,0004 R² = 0,9993 150 Bx[G] 100 50 0 0,00 0,20 0,40 0,60 0,80 1,00 1,20 I [A] Figure 12: 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 14.08.2013 fjk4@st-andrews.ac.uk 17
Future Challenges • 2 nd 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? 14.08.2013 fjk4@st-andrews.ac.uk 18
Backup 14.08.2013 fjk4@st-andrews.ac.uk 19
Check for Two Dipoles (moving transducer in x-direction) 12 10 Magnitude of the Magnetic Field [G] 8 6 Bt Linear (Bt) y = -17.881x 4 2 0 -0,7 -0,6 -0,5 -0,4 -0,3 -0,2 -0,1 0 Proportionality factor p1 [cm^-3] Figure 12: Check for Two Dipoles with 𝜈 0 𝑛 𝐶 𝑢 = 2𝜌 𝑞 1 ≈ −17.9 𝑞 1 14.08.2013 fjk4@st-andrews.ac.uk 20
Magnetic field distortions in panel plane positioned in the middle of the tracker Figure 14: Magnetic field distortions for a panel plane in the middle of the tracker, magnitude plot 14.08.2013 fjk4@st-andrews.ac.uk 21
Hall Effect 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 qvB qE (1) Magnetic force Force from V gradient I ev A (2) Current, where v is drift velo city d d V H E (3) From defn. of E V w I B Source: Wikipedia from (1) and (2) ρeA I B V H ρed A conveniently linear effect by which to measure the projection of the B field! 14.08.2013 fjk4@st-andrews.ac.uk 22
Calibration of the Hall probe: B vs V B vs V 250 200 y = -211,75x + 538,5 150 B[G] R² = 1 100 50 0 0 0,5 1 1,5 2 2,5 3 V [V] 14.08.2013 fjk4@st-andrews.ac.uk 23
Temperature dependence at 𝐶 ≈ 0 Vx vs T 2,581 2,580 2,580 2,579 V[V] 2,579 2,578 2,578 2,577 2,577 2,576 2,576 295 300 305 310 315 320 325 330 335 340 T[K] 14.08.2013 fjk4@st-andrews.ac.uk 24
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 25
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