[PPT] - Magnetic Field Status of the Muon g-2 Experiment Rachel Osofsky PowerPoint Presentation

SLIDE 1

Rachel Osofsky New Perspectives 2018 June 19, 2018

Magnetic Field Status of the Muon g-2 Experiment

FERMILAB-SLIDES-18-108-E

This document was prepared by [Muon g-2 Collaboration] using the resources of the Fermi National Accelerator Laboratory (Fermilab), a U.S. Department of Energy, Office of Science, HEP User Facility. Fermilab is managed by Fermi Research Alliance, LLC (FRA), acting under Contract No. DE-AC02-07CH11359.

SLIDE 2

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Outline

Magnetic field requirements
Magnetic field mapping and monitoring
Trolley
Fixed Probes
Magnetic field shimming
NMR probe calibration

2

UNIVERSITY of WASHINGTON

SLIDE 3

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

g-2 Reminder

Measure the anomalous magnetic

moment of the muon

Fermilab goal: 140 parts per billion (ppb)
Measure 2 frequencies
Anomalous precession frequency of

muons in a highly uniform magnetic field

Larmor precession frequency of free

protons in the magnetic field

See previous talk by C. Schlesier

3

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SLIDE 4

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Magnetic field requirements

Total systematic error: B-field over

muon’s trajectory must be known to 70ppb

Magnetic field measurements
Trolley measurements: 30ppb
Fixed probe interpolation: 30ppb
NMR calibration
Calibration of absolute probe: 35ppb
Cross-calibration of trolley probes: 30ppb

4

Wa

Source of uncertainty Absolut calibration of standard prob Calibration of troll y prob Trolley measurements of B 0 Interpolation with fixed probes Unc rtainty from muon distribution Inflector fringe field uncertainty Tim d pendent xt rnal B fi Ids

0th rs t

Total sy t matic rror on wp_ Muon-averaged field [Hz): wp/21r

µpmµ 9e

R99

[ppb)

50 200 100 150 120 200 150 400

61 791256

m

e

ROO

[ppb)

50 150 100 100 30 100 240

2

61 791595

ROI

E989

[ppb) [ppb)

50 35 90 30 50 30 70 30 30 10

5

100 30 170 70

61 791400

UNIVERSITY of WASHINGTON

SLIDE 5

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

How do we measure the magnetic field?

Use pulsed proton nuclear magnetic

resonance (NMR) probes to measure the magnetic field

NMR probes hold a sample of protons (we

use petroleum jelly)

In a magnetic field, net magnetization aligns

with field

Apply a π/2 pulse to tilt magnetization 90°
Observe relaxation of magnetization
Relaxation produces a free induction decay

(FID) signal

Extract frequency

5

B

qg B

· 2m

9000 :8000 7000 6000

5000 4000 3000 100.00 mm End ca

Serial inductor coil

Base

iece with double crim connection

Petroleum ·ell volume I nner conductor of ca acitor Parallel inductor coil

PTFE tunin

iece with slot

0.0010

0.0004
0.0005

0.002 (l.003

UNIVERSITY of WASHINGTON

SLIDE 6

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Trolley

Circular array of 17 NMR probes
Can only be in storage region when muons aren’t present
Otherwise parked in garage at 180°, out of storage region
Pulled in one direction by signal cable, in other direction by fishing line
Run every 3-4 days

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SLIDE 7

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Trolley measurements

We do a multipole expansion of the trolley data

7

Look at azimuthally averaged measurements, as well as measurements as a

function of azimuth

4

n

B(r,8) =Bo+ L

[ an, Gos(n0) +

bn.

Sin(n0)]

n==O

Normal Quadrupole

· fi Id (ppm)

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x (em)

UNIVERSITY of WASHINGTON

SLIDE 8

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Fixed probe measurements

In between trolley measurements, need a way to monitor the field
378 NMR probes mounted on top and bottom of vacuum chambers
Interpolate evolution of storage region field
Analysis ongoing

8

I

•

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SLIDE 9

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Magnetic field shimming

Shimming: smoothing of the magnetic field and minimization of magnetic field

multipoles

Passive shimming: movement and addition of over 10,000 pieces of ferrous

and nonferrous material

9

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UNIVERSITY of WASHINGTON

SLIDE 10

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Magnetic field shimming

Shimming: smoothing of the

magnetic field and minimization

f magnetic field multipoles
Active shimming:
Power supply feedback: regulation
f main magnet power supply to

keep dipole field constant

Surface coils: 200 coils above and

below vacuum chambers to further reduce azimuthally averaged multipoles and transverse field components

10

Moment Normal (ppm) Skew (ppm) Quadrupole

0.19

0.28 Sextupole 0.05 0.27 Octupole

0.07

0.25 Decupole 0.23 0.07

e.

field (ppm)
3
2
1

1 2 3 x (om)

UNIVERSITY of WASHINGTON

SLIDE 11

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Calibration

What we really need is the precession frequency of free protons
Not what we get from our NMR probes
Need a calibration

11

Diamagnetic shielding of protons by electrons. σ=25680(2.5)x10-9 at 25C Shape dependent perturbation of magnetic susceptibility Sphere: 4π/3 Cylinder: 2π χH2O=-720(2)x10-9 Magnetization of probe materials

41r

.

(H O T)

r.

free

3 . X . 2

, .

Os . WP

UNIVERSITY of WASHINGTON

SLIDE 12

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Plunging and absolute calibration probes

Plunging probe
In the ring at Fermilab, used to calibrate trolley

probes

Cylindrical sample
Perturbations have been measured
Absolute calibration probe
Will live at Argonne National Laboratory
Spherical sample
Not yet built
Serves to calibrate the plunging probe, another

cross check with different systematics

12

Plunging Probe Absolute Calibration Probe Absolute Probe

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SLIDE 13

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Calibration Procedure

Select a trolley probe to calibrate
Impose x,y,z gradients and

measure ΔB between trolley

probes. This gives the trolley probe

position

Can calculate spatial effect of applied

gradients

Move plunging probe into volume

and measure ΔB, then can move PP and redo measurement until PP is at same location as trolley probe

Current status: Center probe

calibrated, working on rings

13

B0 x

Imposed gradient ΔBx

Trolley ~

Horizontal Gradient Vertical Gradient

Plunging Probe Calibration Volume

I

Overhead View I Muon Storage Volume Azimuthal Gradient

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SLIDE 14

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Tasks moving forward

Understand field tracking using fixed probes
Dipole, normal quadrupole are main components we’re concentrating on right now
Finish calibration of all 17 trolley probes
Apply calibration to data analysis
Install magnet insulation and understand the effects
Insulation process began last week

14

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SLIDE 15

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Backup Slides

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SLIDE 16

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Passive Shimming

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UNIVERSITY of WASHINGTON

SLIDE 17

R. Osofsky | Improving Magnetic Field Uniformity in the Muon g-2 Storage Ring

Active Shimming - Surface Coils

100 concentric current carrying coils, above and below

vacuum chambers

Current range: ±2.5A
Different current configurations (radial dependence)

target different field multipoles

17 Multipole Normal, top Normal, bottom Skew, top Skew, bottom Dipole — — 1 1 Quadrupole a a x

x

Sextupole ax ax x2-a2

x2+a2

Octupole 3ax2-a3 3ax2-a3 x3-3a2x

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UNIVERSITY of WASHINGTON

SLIDE 18

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Plunging probe perturbations

Shape dependence:
Can rotate cylinder around its long axis, try different length cylinders
Material perturbations:
Take measurement using a fixed probe
Insert the fixed probe into plunging probe shell and take another measurement
Difference is due to material perturbations (Measured to be 3.24±0.04ppb)
BNL: ~40ppb

18

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w f r e e

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Plunging probe (sample removed) vs.

lit

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Fixed probe

UNIVERSITY

f

WASHINGTON

SLIDE 19

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Muon convolution

Really need the magnetic field convolved with the muon distribution
Get muon distribution from trackers (see Cristina’s talk)

19

B-field (ppm)

1

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UNIVERSITY of WASHINGTON

SLIDE 20

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Time dependent external magnetic fields

Monitor external magnetic fields using

fluxgate magnetometers

Measure field strength along 3 axes
±10G range per axis, 1kHz bandwidth
Saturate at 10G → live outside the 5G line

20

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SLIDE 21

R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment

Fluxgate magnetometers

Small, magnetically susceptible core wrapped by 2 coils of wire (drive

and sense)

Think of it as 2 separate half cores. One core will generate field in

same direction as Bext, one opposite

AC current passed through drive coil, drives core through

alternating cycle of magnetic saturation

Constantly changing field induces a current in sense coil (this

current is monitored)

With no Bext, field generated by 2 half cores cancels (cores go into

and out of saturation at the same time) → No induced current in sense winding

With Bext, half core generating field in opposite direction comes out
f saturation sooner, and half core generating in same direction

comes out later. During this time the fields do not cancel, net flux in sense winding

Size and phase of induced spikes gives magnitude and direction of

Bext

21

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with no extert'18I field

Fig, 2c: B generated by each half core in e'Ktemal field

Fig_

2d: Voltage induced in the sense winding (bfack) Resultant voltage if the sensor is tuned (red)

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