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1. A method for controlling the magnetic field near a superconducting boundary in the ARIADNE axion experiment

   https://doi.org/10.1088/2058-9565/abf1cc  

   Fosbinder-Elkins, H. ; Kim, Y. ; Dargert, J. ; Harkness, M. ; Geraci, A. A. ; Levenson-Falk, E. ; Mumford, S. ; Fang, A. ; Kapitulnik, A. ; Matlashov, A. ; et al ( January 2022 , Quantum Science and Technology)

   The QCD axion is a particle postulated to exist since the 1970s to explain the strong-CP problem in particle physics. It could also account for all of the observed dark matter in the Universe. The axion resonant interaction detection experiment (ARIADNE) intends to detect the QCD axion by sensing the fictitious ‘magnetic field’ created by its coupling to spin. Short-range axion-mediated interactions can occur between a sample of laser-polarized³He nuclear spins and an unpolarized source-mass sprocket. The experiment must be sensitive to magnetic fields below the 10⁻¹⁹T level to achieve its design sensitivity, necessitating tight control of the experiment’s magnetic environment. We describe a method for controlling three aspects of that environment which would otherwise limit the experimental sensitivity. Firstly, a system of superconducting magnetic shielding is described to screen ordinary magnetic noise from the sample volume at the 10⁸level, which should be sufficient to reduce the contribution of Johnson noise in the sprocket-shaped source mass, expected to be at the 10⁻¹²T$/\sqrt{\mathrm{H}\mathrm{z}}$level, to below the threshold for signal detection. Secondly, a method for reducing magnetic field gradients within the sample up to 10²times is described, using a simple and cost-effective design geometry. Thirdly, a novel coil design is introduced which allows the generation of fields similar to those produced by Helmholtz coils in regions directly abutting superconducting boundaries. This method allows the nuclear Larmor frequency of the sample to be tuned to match the axion field modulation frequency set by the sprocket rotation. Finally, we experimentally investigate the magnetic shielding factor of sputtered thin-film superconducting niobium on quartz substrates for various geometries and film thicknesses relevant for the ARIADNE axion experiment using SQUID magnetometry. The methods may be generally useful for magnetic field control near superconducting boundaries in other experiments where similar considerations apply.

    

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2. Detection and Bulk Properties of the HR 8799 Planets with High-resolution Spectroscopy

   https://doi.org/10.3847/1538-3881/ac1349  

   Wang 王, Jason J. 劲飞 ; Ruffio, Jean-Baptiste ; Morris, Evan ; Delorme, Jacques-Robert ; Jovanovic, Nemanja ; Pezzato, Jacklyn ; Echeverri, Daniel ; Finnerty, Luke ; Hood, Callie ; Zanazzi, J. J. ; et al ( September 2021 , The Astronomical Journal)

   Using the Keck Planet Imager and Characterizer, we obtained high-resolution (R∼ 35,000)K-band spectra of the four planets orbiting HR 8799. We clearly detected H₂O and CO in the atmospheres of HR 8799 c, d, and e, and tentatively detected a combination of CO and H₂O in b. These are the most challenging directly imaged exoplanets that have been observed at high spectral resolution to date when considering both their angular separations and flux ratios. We developed a forward-modeling framework that allows us to jointly fit the spectra of the planets and the diffracted starlight simultaneously in a likelihood-based approach and obtained posterior probabilities on their effective temperatures, surface gravities, radial velocities, and spins. We measured$v\sin (i)$values of${10.1}_{-2.7}^{+2.8}\mathrm{km}{\mathrm{s}}^{-1}$for HR 8799 d and${15.0}_{-2.6}^{+2.3}\mathrm{km}{\mathrm{s}}^{-1}$for HR 8799 e, and placed an upper limit of <14 km s⁻¹of HR 8799 c. Under two different assumptions of their obliquities, we found tentative evidence that rotation velocity is anticorrelated with companion mass, which could indicate that magnetic braking with a circumplanetary disk at early times is less efficient at spinning down lower-mass planets.

    

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3. A Comprehensive Radiative Magnetohydrodynamics Simulation of Active Region Scale Flux Emergence from the Convection Zone to the Corona

   https://doi.org/10.3847/1538-4357/ac8f95  

   Chen, Feng ; Rempel, Matthias ; Fan, Yuhong ( October 2022 , The Astrophysical Journal)

   We present a comprehensive radiative magnetohydrodynamic simulation of the quiet Sun and large solar active regions. The 197 Mm wide simulation domain spans from 18(10) Mm beneath the photosphere to 113 Mm in the solar corona. Radiative transfer assuming local thermal equilibrium, optically thin radiative losses, and anisotropic conduction transport provide the necessary realism for synthesizing observables to compare with remote-sensing observations of the photosphere and corona. This model self-consistently reproduces observed features of the quiet Sun, emerging and developed active regions, and solar flares up to M class. Here, we report an overview of the first results. The surface magneto-convection yields an upward Poynting flux that is dissipated in the corona and heats the plasma to over 1 MK. The quiescent corona also presents ubiquitous propagating waves, jets, and bright points with sizes down to 2 Mm. Magnetic flux bundles emerge into the photosphere and give rise to strong and complex active regions with over 10²³Mx magnetic flux. The coronal free magnetic energy, which is approximately 18% of the total magnetic energy, accumulates to approximately 10³³erg. The coronal magnetic field is clearly non-force-free, as the Lorentz force needs to balance the pressure force and viscous stress as well as drive magnetic field evolution. The emission measure from${\log }_{10}T=4.5$to${\log }_{10}T>7$provides a comprehensive view of the active region corona, such as coronal loops of various lengths and temperatures, mass circulation by evaporation and condensation, and eruptions from jets to large-scale mass ejections.

    

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4. Optomechanical lasers for inertial sensing

   https://doi.org/10.1364/JOSAA.396774  

   Wisniewski, Hayden ; Richardson, Logan ; Hines, Adam ; Laurain, Alexandre ; Guzmán, Felipe ( August 2020 , Journal of the Optical Society of America A)

   We have developed an inertially sensitive optomechanical laser by combining a vertical-external-cavity surface-emitting laser (VECSEL) with a monolithic fused silica resonator. By placing the external cavity mirror of the VECSEL onto the optomechanical resonator test mass, we create a sensor where external accelerations are directly transcribed onto the lasing frequency. We developed a proof-of-principle laboratory prototype and observe test mass oscillations at the resonance frequency of the sensor through the VECSEL lasing frequency,$4.18\pm <\#comment/>0.03\mathrm{H}\mathrm{z}$. In addition, we set up an ancillary heterodyne interferometer to track the motion of the mechanical oscillator’s test mass, observing a resonance of$4.194\pm <\#comment/>0.004\mathrm{H}\mathrm{z}$. The interferometer measurements validate the VECSEL results, confirming the feasibility of using optomechanical lasers for inertial sensing.

    

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5. Kinetic-scale Current Sheets in the Solar Wind at 1 au: Scale-dependent Properties and Critical Current Density

   https://doi.org/10.3847/2041-8213/ac4fc4  

   Vasko, I. Y. ; Alimov, K. ; Phan, T. ; Bale, S. D. ; Mozer, F. S. ; Artemyev, A. V. ( February 2022 , The Astrophysical Journal Letters)

   We present analysis of 17,043 proton kinetic-scale current sheets (CSs) collected over 124 days of Wind spacecraft measurements in the solar wind at 11 samples s⁻¹magnetic field resolution. The CSs have thickness,λ,from a few tens to one thousand kilometers with typical values around 100 km, or within about 0.1–10λ_pin terms of local proton inertial length,λ_p. We found that the current density is larger for smaller-scale CSs,J₀≈ 6 nAm⁻²· (λ/100 km)^−0.56, but does not statistically exceed a critical value,J_A,corresponding to the drift between ions and electrons of local Alvén speed. The observed trend holds in normalized units:$J_0/J_A\approx 0.17·{(\lambda /{\lambda }_p)}^{-0.51}$. The CSs are statistically force-free with magnetic shear angle correlated with CS spatial scale:$\mathrm{\Delta }\theta \approx 19°·{(\lambda /{\lambda }_p)}^{0.5}$. The observed correlations are consistent with local turbulence being the source of proton kinetic-scale CSs in the solar wind, while the mechanisms limiting the current density remain to be understood.

    

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