Design and demonstration of a motional narrowing method to measure a low temperature 3He diffusion coefficient for a superfluid neutron electric dipole moment experiment

Erickson, Cameron Blake

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https://hdl.handle.net/2142/129841 Copy

Description

Title

Design and demonstration of a motional narrowing method to measure a low temperature 3He diffusion coefficient for a superfluid neutron electric dipole moment experiment

Author(s)

Erickson, Cameron Blake

Issue Date

2025-07-09

Director of Research (if dissertation) or Advisor (if thesis)

Beck, Douglas H

Doctoral Committee Chair(s)

Sickles, Anne M

Committee Member(s)

• Liu, Chen-Yu
• Noronha, Jorge

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Motional Narrowing
• Diffusion
• Diffusion Coefficient
• Gaseous Diffusion
• NMR
• Nuclear Magnetic Resonance
• FID
• Free Induction Decay
• Helium 3
• Helium 4
• Superfluid
• nEDM
• Neutron Electric Dipole Moment
• Magnetic Field Design
• Cryogenics
• MEOP
• Spin Polarization

Abstract

Measurements of the neutron electric dipole moment (nEDM) are cosmologically motivated by a search for CP symmetry violations in particle physics. Despite over six decades of effort, physicists have yet to attain the precision necessary to detect a nonzero nEDM. An experiment technique first proposed in \cite{GolubLamoreaux}, is expected to be capable of achieving a precision 2 orders of magnitude smaller than the current leading bound \cite{SNSnEDM}. The key distinction of this technique is that the neutrons are measured in a superfluid 4He bath through spin dependent interactions with 3He – warranting the "superfluid nEDM experiment" label. Important to the design of a superfluid nEDM experiment is a knowledge of the transport properties of 3He in the superfluid 4He. This information is partially encoded by a "3He-phonon" diffusion coefficient denoted by $D_{3,ph}$ which describes the diffusion of 3He against the superfluid 4He phonon excitations in the liquid. All previous measurements of $D_{3,ph}$ used local 3He density dependences on temperature gradients to extract $D_{3,ph}$. The most recent measurement by Rao \cite{Rao} obtained a result that disagrees with theory \cite{BBBVeryDilute},\cite{BBBDilute} by a factor of 3. This thesis proposes, designs, and demonstrates a different method to measure $D_{3,ph}$ that does not use temperature gradients, but instead centers around use of the "motional narrowing limit" of nuclear magnetic resonance free induction decays. To the author's knowledge, this motional narrowing technique has been used only once before to determine unknown diffusion constants by \cite{Himbert}. An important difference of the work here from \cite{Himbert} is that the 3He is spin polarized at room temperature and then injected into cryogenic measurement cell as opposed to being polarized directly in a cryogenic measurement cell. Part of the contribution of this thesis is a discussion of the design of such an experiment to measure $D_{3,ph}$. It is argued that accessing the experimental parameter space required by the narrowing method is not obvious. This motivates measurements at about 45 Kelvin using only 3He gas to demonstrate 3 key attainable design elements: the "injection efficiency", minimum background magnetic gradients, and statistical precision of the diffusion coefficient extraction The injection efficiency corresponds to the fraction of remaining spin polarization after transport between room temperature to 45 K. The measurements in this thesis demonstrate an injection efficiency of up to $60\%$. Minimal background magnetic gradients are achieved with a 5 coil shimming system (the "pentacoils") and demonstrated to be equivalent to $3\times 10^{-5} \leq |G_0| \leq 1\times 10^{-4}$ Gauss/cm over the span of a few centimeters. Diffusion coefficients measurements span from 46 to 372 cm$^2$/sec are determined with a statistical precision as low as $0.2\%$ for applied gradients equivalent to $|G_{app}| \leq 3 |G_0|$. The systematic uncertainties are much larger, but these could be significantly reduced by future works.

Graduation Semester

2025-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129841

Copyright and License Information

Copyright 2025 Cameron Erickson

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