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

FERMILAB-SLIDES-18-108-E Magnetic Field Status of the Muon g-2 Experiment Rachel Osofsky This document was prepared by [Muon g-2 Collaboration] using the resources of the Fermi New Perspectives 2018 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 June 19, 2018 Contract No. DE-AC02-07CH11359.

Outline • Magnetic field requirements • Magnetic field mapping and monitoring - Trolley - Fixed Probes • Magnetic field shimming • NMR probe calibration R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 2 UNIVERSITY of WASHINGTON

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 R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 3 UNIVERSITY of WASHINGTON

Magnetic field requirements • Total systematic error: B-field over muon’s trajectory must be known to µpmµ 9e Wa 70ppb 2 m e • Magnetic field measurements - Trolley measurements: 30ppb R99 ROO ROI E989 Source of uncertainty [ppb) [ppb) [ppb) [ppb) - Fixed probe interpolation: 30ppb 50 50 50 35 Absolut calibration of standard prob 200 150 90 30 Calibration of troll y prob • NMR calibration 100 100 50 30 Trolley measurements of B 0 150 100 70 30 Interpolation with fixed probes 120 30 30 10 Unc rtainty from muon distr i bution - Calibration of absolute probe: 35ppb 200 Inflector fringe fie ld uncertainty 5 Tim d pendent xt rnal B fi Ids - Cross-calibration of trolley probes: 30ppb 0th rs t 150 100 100 30 400 240 170 70 Total sy t matic rror on wp_ Muon -averaged field [Hz): wp/21r 61 791256 61 791595 61 791400 R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 4 UNIVERSITY of WASHINGTON

How do we measure the magnetic field? • Use pulsed proton nuclear magnetic 100 . 00 mm Base i ece with doub le crim connecti on resonance (NMR) probes to measure Serial inductor coil End ca the magnetic field Petrol eum · ell volume I nner conductor of ca acitor Parallel inductor co il PTFE t un in i ece wi th slot - NMR probes hold a sample of protons (we use petroleum jelly) 0.0010 B - In a magnetic field, net magnetization aligns with field -0 .0004 - 0.0 00 5 - Apply a π/2 pulse to tilt magnetization 90° - Observe relaxation of magnetization 9000 - Relaxation produces a free induction decay :8000 7000 (FID) signal 6000 5000 • Extract frequency 4000 qg B 3000 0 0. 002 (l. 003 · 2m R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 5 UNIVERSITY of WASHINGTON

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 R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 6 UNIVERSITY of WASHINGTON

Trolley measurements • We do a multipole expansion of the trolley data • Look at azimuthally averaged measurements, as well as measurements as a 4 n B(r,8) =Bo+ L Gos(n0) + [ an , bn . Sin(n0)] function of azimuth n==O · fi Id (ppm) No rmal Quadrupole 1 1 EJ 3 E .£. >- 2 0.5 1 0 'E <.) 0 ..__, _ , -0 .5 - 2 - 1 - 3 -3 - 2 - 1 0 1 2 3 x (em) R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 7 UNIVERSITY of WASHINGTON

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 I • • R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 8 UNIVERSITY of WASHINGTON

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 2 .1 1 2 1 al .0 • • • • ' • • • • • • • • • • "' Cl. • • • • • • • • • .. • "' • • • • • • • • • • • Op m • • ' • . • 1 • • • ' • • • • 1 • • • • • • • • • • • • Iii • • ..._.. • • • • • • • • -1 2, 0 . • • • • • • • • • • • • • • • • • • • 50 150 200 250 300 350 h R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 9 UNIVERSITY of WASHINGTON

Magnetic field shimming • Shimming: smoothing of the magnetic field and minimization of magnetic field multipoles Normal Moment Skew (ppm) e. -field (ppm) (ppm) • Active shimming: Quadrupole -0.19 0.28 - Power supply feedback: regulation of main magnet power supply to Sextupole 0.05 0.27 keep dipole field constant - Surface coils: 200 coils above and Octupole -0.07 0.25 below vacuum chambers to further - 3 - 2 -1 0 1 2 3 reduce azimuthally averaged x (om) Decupole 0.23 0.07 multipoles and transverse field components R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 10 UNIVERSITY of WASHINGTON

Calibration • What we really need is the precession frequency of free protons - Not what we get from our NMR probes - Need a calibration 41r . (H O T) free r. 3 . X . 2 , . Os . WP Diamagnetic Magnetization of Shape dependent shielding of protons probe materials perturbation of by electrons. magnetic σ=25680(2.5)x10 -9 susceptibility at 25C Sphere: 4π/3 Cylinder: 2π χ H2O =-720(2)x10 -9 R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 11 UNIVERSITY of WASHINGTON

Plunging and absolute calibration probes • Plunging probe - In the ring at Fermilab, used to calibrate trolley probes - Cylindrical sample - Perturbations have been measured Plunging Probe • Absolute calibration probe - Will live at Argonne National Laboratory - Spherical sample - Not yet built Absolute Calibration Probe Absolute Probe - Serves to calibrate the plunging probe, another cross check with different systematics R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 12 UNIVERSITY of WASHINGTON

Calibration Procedure • Select a trolley probe to calibrate Plunging Probe Calibration Volume • Impose x,y,z gradients and I Overhead View I measure ΔB between trolley Muon Storage Volume probes. This gives the trolley probe Trolley ~ position - Can calculate spatial effect of applied gradients Horizontal Gradient Vertical Gradient Azimuthal Gradient • Move plunging probe into volume Imposed gradient and measure ΔB, then can move ΔB x PP and redo measurement until PP is at same location as trolley probe • Current status: Center probe B 0 calibrated, working on rings x R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 13 UNIVERSITY of WASHINGTON

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 R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 14 UNIVERSITY of WASHINGTON

Backup Slides R. Osofsky | Magnetic Field Status of the Muon g-2 Experiment 15 UNIVERSITY of WASHINGTON

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