arXiv subjects

C. M. Swank

Publications and source records attributed to C. M. Swank.

13 recordsLinked to original sources

arXiv2025

Superconducting properties of commercially available solders for low-field applications

Solders with superconducting properties around $4\,{\rm K}$ are useful in low magnetic field environments for AC current leads or in electrical and mechanical bonds. Accurate knowledge of these properties are needed in high precision experiments. We have measured the electrical resistance of five commercially-available solders: 50\%Sn-50\%Pb, 60\%Sn-40\%Pb, 60\%Sn-40\%Pb-0.3\%Sb, 52\%In-48\%Sn, and 96.5\%Sn-3.5\%Ag, down to $2.3\,{\rm K}$ and in applied magnetic fields from 0 to 0.1$\,{\rm T}$. Their critical temperatures $T_c$ and critical fields $B_c$ were extracted in our analysis, taking into account the observed 90\%-to-10\% transition widths. Our best candidate for low-loss AC current leads in low fields is 50\%Sn-50\%Pb, which had zero-field $T_{c,0} = (7.1 \pm 0.3)\,{\rm K}$, and remained high to $T_c(B=0.1\,{\rm T}) = (6.9 \pm 0.3) \,{\rm K}$. We report $T_c$ and $B_c$ of 60\%Sn-40\%Pb-0.3\%Sb and $B_{c,0}$ of 96.5\%Sn-3.5\%Ag for the first time. Our $T_{c,0}= (3.31 \pm 0.04)\,{\rm K}$ for 96.5\%Sn-3.5\%Ag disagrees with a widely adopted value.

cond-mat.supr-con↗

arXiv2019

A New Cryogenic Apparatus to Search for the Neutron Electric Dipole Moment

A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). It uses superfluid $^4$He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experiment, to be operated at the Spallation Neutron Source at Oak Ridge National Laboratory, uses polarized $^3$He from an Atomic Beam Source injected into the superfluid $^4$He and transported to the measurement cells as a co-magnetometer. The superfluid $^4$He is also used as an insulating medium allowing significantly higher electric fields, compared to previous experiments, to be maintained across the measurement cells. These features provide an ultimate statistical uncertainty for the EDM of $2-3\times 10^{-28}$ e-cm, with anticipated systematic uncertainties below this level.

physics.ins-det↗

arXiv2019

The neutron electric dipole moment experiment at the Spallation Neutron Source

Novel experimental techniques are required to make the next big leap in neutron electric dipole moment experimental sensitivity, both in terms of statistics and systematic error control. The nEDM experiment at the Spallation Neutron Source (nEDM@SNS) will implement the scheme of Golub & Lamoreaux [Phys. Rep., 237, 1 (1994)]. The unique properties of combining polarized ultracold neutrons, polarized $^3$He, and superfluid $^4$He will be exploited to provide a sensitivity to $\sim 10^{-28}\,e{\rm \,\cdot\, cm}$. Our cryogenic apparatus will deploy two small ($3\,{\rm L}$) measurement cells with a high density of ultracold neutrons produced and spin analyzed in situ. The electric field strength, precession time, magnetic shielding, and detected UCN number will all be enhanced compared to previous room temperature Ramsey measurements. Our $^3$He co-magnetometer offers unique control of systematic effects, in particular the Bloch-Siegert induced false EDM. Furthermore, there will be two distinct measurement modes: free precession and dressed spin. This will provide an important self-check of our results. Following five years of "critical component demonstration," our collaboration transitioned to a "large scale integration" phase in 2018. An overview of our measurement techniques, experimental design, and brief updates are described in these proceedings.

nucl-ex↗

arXiv2018

Spin Dressed Relaxation and Frequency Shifts from Field Imperfections

Critical dressing, the simultaneous dressing of two spin species to the same effective Larmor frequency, is a technique that can, in principle, improve the sensitivity to small frequency shifts. The benefits of spin dressing and thus critical dressing are achieved at the expense of generating a large (relative to the holding field $B_{0}$,) homogeneous oscillating field. Due to inevitable imperfections of the fields generated, the benefits of spin dressing may be lost from the additional relaxation and noise generated by the dressing field imperfections. In this analysis the subject of relaxation and frequency shifts are approached with simulations and theory. Analytical predictions are made from a new quasi-quantum model that includes gradients in the holding field $B_{0}=ω_{0}/γ$ and dressing field $B_{1}=ω_{1}/γ$ where $B_{1}$ is oscillating at frequency $ω$. The results are compared with a Monte Carlo simulation coupled with a 5$^{\text{th}}$ order Runge-Kutta integrator. Comparisons of the two methods are presented as well as a set of optimized parameters that produce stable critical dressing at a range for oscillating frequencies $ω,$ as well as pulsed frequency modulation parameters for maximum sensitivity.

physics.atom-ph↗

arXiv2017

Cryogenic magnetic coil and superconducting magnetic shield for neutron electric dipole moment searches

A magnetic coil operated at cryogenic temperatures is used to produce spatial, relative field gradients below 6 ppm/cm, stable for several hours. The apparatus is a prototype of the magnetic components for a neutron electric dipole moment (nEDM) search, which will take place at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory using ultra-cold neutrons (UCN). That search requires a uniform magnetic field to mitigate systematic effects and obtain long polarization lifetimes for neutron spin precession measurements. This paper details upgrades to a previously described apparatus, particularly the introduction of super-conducting magnetic shielding and the associated cryogenic apparatus. The magnetic gradients observed are sufficiently low for the nEDM search at SNS.

physics.ins-det↗

arXiv2015

High-Sensitivity Measurement of 3He-4He Isotopic Ratios for Ultracold Neutron Experiments

Research efforts ranging from studies of solid helium to searches for a neutron electric dipole moment require isotopically purified helium with a ratio of 3He to 4He at levels below that which can be measured using traditional mass spectroscopy techniques. We demonstrate an approach to such a measurement using accelerator mass spectroscopy, reaching the 10e-14 level of sensitivity, several orders of magnitude more sensitive than other techniques. Measurements of 3He/4He in samples relevant to the measurement of the neutron lifetime indicate the need for substantial corrections. We also argue that there is a clear path forward to sensitivity increases of at least another order of magnitude.

physics.ins-det↗

arXiv2011

Comment on "Pressure dependence of wall relaxation in polarized He^3 gaseous cells." by W. Zheng, H. Gao, Q. Ye, and Y.Zhang

The authors have demonstrated a strong linear pressure dependence of the longitudinal relaxation time for He^3 at room and cryogenic temperatures in a given experimental setup. They offer a theoretical explanation of the effect based on diffusion theory in the bulk and an unusual boundary condition. We question the physical basis of the boundary condition and suggest some alternate explanations of the observations.

physics.atom-ph↗

arXiv2011

Search for the Neutron Electric Dipole Moment: Contributions from the Triangle Universities Nuclear Laboratory

A significant fraction of the research effort at the Triangle Universities Nuclear Laboratory (TUNL) focuses on weak interaction studies and searches for physics beyond the Standard Model. One major effort is the development of a new experimental technique to search for the neutron electric dipole moment (nEDM) that offers the potential for a factor of 100 increase in sensitivity over existing measurements. The search for this moment has the potential to reveal new sources of time reversal (T) and charge-conjugation-and-parity (CP) violation and to challenge calculations that propose extensions to the Standard Model. We provide a brief overview of the experiment as a whole and discuss the work underway at TUNL as part of this effort.

physics.ins-det↗

arXiv2011

Spectral properties of correlation functions of fields with arbitrary position dependence in restricted geometries from the ballistic to the diffusive regimes

The transition between ballistic and diffusive motion poses difficult problems in several fields of physics. In this work we show how to calculate the spectra of the correlation functions between fields of arbitrary spatial dependence as seen by particles moving through the fields in regions bounded by specularly reflecting walls valid for diffusive and ballistic motion as well as the transition region in between for motion in 2 and 3 dimensions. Applications to relaxation in nmr are discussed.

physics.data-an↗

arXiv2010

Relaxation, frequency shifts and other phenomena at the transition between diffusion and ballistic motion

There are many fields where the transition from diffusive to ballistic motion is important. Here we deal with relaxation processes in nmr in gases. Correlation functions for trajectory variables (position and velocity) valid across this transition are known for several geometries in the case of specular wall reflections. In this work we show that the conditional probability density p(r,t|r_0,t_0) for a random walk satisfies the telegrapher's equation and present an analytic solution for this function. We will use it for calculating the relaxation due to an axion mediated force and a magnetic dipole impurity.

cond-mat.stat-mech↗

arXiv2010

Relaxation of spins due to a magnetic field gradient, revisited; Identity of the Redfield and Torrey theories

There is an extensive literature on magnetic gradient induced spin relaxation. Cates, Schaefer and Happer (CSH) in a seminal paper, have solved the problem in the regime where diffusion theory (the Torrey equation is applicable using an expansion of the density matrix in diffusion equation eigenfunctions and angular momentum tensors. McGregor has solved the problem in the same regime using a slightly more general formulation using Redfield theory formulated in terms of the auto-correlation function of the fluctuating field seen by the spins and calculating the correlation functions using the diffusion theory Green's function. The results of both calculations were shown to agree for a special case. In the present work we show that the eigenfunction expansion of the Torrey equation yields the expansion of the Green's function for the diffusion equation thus showing the identity of this approach with that of Redfield theory. The general solution can also be obtained directly from the Torrey equation for the density matrix. Thus the physical content of the Redfield and Torrey approaches are identical. We then introduce a more general expression for the position autocorrelation function of particles moving in a closed cell, extending the range of applicability of the theory.

physics.atom-ph↗

arXiv2009

Electric dipole moment searches: Effect of linear electric field frequency shifts induced in confined gases, II

The next generation of particle edm searches will be at such a high sensitivity that it will be possible for the results to be contaminated by a systematic error resulting from the interaction of the motional (E x v/c) magnetic field with stray field gradients. In this paper we extend previous work to present an analytic form for the frequency shift in the case of a rectangular storage vessel and discuss the implications of the result for the neutron edm experiment which will be installed at the SNS (Spallation Neutron Source) by the LANL collaboration

nucl-ex↗

arXiv2009

Measuring the Neutron Lifetime Using Magnetically Trapped Neutrons

The neutron beta-decay lifetime plays an important role both in understanding weak interactions within the framework of the Standard Model and in theoretical predictions of the primordial abundance of 4He in Big Bang Nucleosynthesis. In previous work, we successfully demonstrated the trapping of ultracold neutrons (UCN) in a conservative potential magnetic trap. A major upgrade of the apparatus is nearing completion at the National Institute of Standards and Technology Center for Neutron Research (NCNR). In our approach, a beam of 0.89 nm neutrons is incident on a superfluid 4He target within the minimum field region of an Ioffe-type magnetic trap. A fraction of the neutrons is downscattered in the helium to energies <200 neV, and those in the appropriate spin state become trapped. The inverse process is suppressed by the low phonon density of helium at temperatures less than 200 mK, allowing the neutron to travel undisturbed. When the neutron decays the energetic electron ionizes the helium, producing scintillation light that is detected using photomultiplier tubes. Statistical limitations of the previous apparatus will be alleviated by significant increases in field strength and trap volume resulting in twenty times more trapped neutrons.

nucl-ex↗