Magnetic Fluctuations Research Articles

Estimates of the wavenumber wavelet power spectrum of magnetic fluctuations during magnetic reconnection

Fluctuation analyses of experimental observations generally lack high temporal resolution and are in frequency-space f, contrary to theoretical efforts in wavenumber-space k. This is due to the inherent limits of the Fourier transform, though it is prominent due to the ease of diagnostic implementation. Advances in wavelet-based analysis have provided relief due to its temporal resolution, but in its common use, is still hard to compare to theoretical models. By using the two-point correlation technique in conjunction with large data sets, a wavelet power spectrum in wavenumber-space can be created. Dubbed the wavenumber wavelet power spectrum, this spectrum relates wavenumber to power in time. This analysis technique more closely connects characterizations of experimentally observed fluctuations with other system parameters and theoretical predictions. In this article, we develop the wavenumber wavelet power spectrum using magnetic fluctuations caused by tearing instability driven magnetic reconnection in reproducible, high temperature laboratory plasmas. These dynamic magnetic fluctuations generated in reversed field pinch plasmas are broadband, ranging from the low frequency, 10's of kHz, up to the ion gyroradii frequencies, 100's of kHz. The dominant fluctuations have poloidal and toroidal mode numbers (m,n)=(1,6−10) and can grow to 2%–3% of the mean magnetic field. During these reconnection events, ions, and electrons are energized, magnetic fluctuation amplitudes increase, plasma flow is halted, and the toroidal magnetic flux increases, all on a semi-periodic basis. The newly developed spectrum provides better temporal resolution of spectrum characteristics to correlate with these particle energization phenomena.

Design of the Superconducting Magnet System for the New $g-2$/EDM Experiment in the J-PARC

A superconducting solenoid system has been designed for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$g$</tex-math></inline-formula> -2/EDM experiment at the J-PARC, which is used to store muon beam of 0.3 GeV/c. High homogeneous magnetic field is required to be below <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.1 ppm at 3 T within a muon storage region of 33.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 1.5 cm in radius and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {\pm }$</tex-math></inline-formula> 5 cm in height around the magnet center. The muon beam is spirally injected to the storage region from the top end of the magnet, therefore the magnetic field distribution is carefully designed in the region where the muon beam pass through. In order to achieve both requirements, NbTi superconducting coils are surrounded by an iron yoke with pole tips, which can optimize the field distribution by adjusting the shape and size. The superconducting coils are cooled by pool boiling in liquid helium, and the evaporated helium gas is re-condensed by GM cryocoolers to keep the liquid helium level for a long time. The main coils are operated in a persistent current mode to remove the magnetic field fluctuation with time caused by a power supply. This paper presents the current design of the magnet system for the experiment at the J-PARC.

Design of Uniform Field Coils Based on the Ferromagnetic Coupling Effect Inside Single-Ended Open Magnetic Shielding Cylinder

This research proposes a novel method for designing uniform field coils inside a single-ended open magnetic shielding cylinder (MSC). It solves the problems of distorted magnetic field distribution and decreased uniformity resulting from the coupling between the coils and the single-ended open MSC. The magnetic field analytical model of the uniform field coils inside the single-ended open MSC with high-permeability materials is first established. Then, minimizing the sum of relative errors of the magnetic field in the target area is taken as the objective function, and the improved particle swarm optimization algorithm is adopted to optimize the structural parameters for ensuring high uniformity of the coils. The results of the simulation indicate that comparing this work with the Lee-Whiting coil in the single-ended open MSC, the maximum relative error of the magnetic field is reduced from 6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> to 2.3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> and 6.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> . The experimental results also demonstrate the efficacy of the proposed method, and practicality for real-time compensation of magnetic field fluctuations within single-ended open MSC. The research content provides the basis for improving the performance of the magnetocardiography device.

Expected EMIC Wave Generation and Unexpected MS Wave Disruption in a Magnetic Dip

AbstractMagnetic dip plays a potentially important role in the ring‐current‐radiation‐belt‐coupling. Here, we report a proton‐driven magnetic dip event accompanied by the expected generation of electromagnetic ion cyclotron (EMIC) wave and the unexpected disruption of fast magnetosonic (MS) wave observed by the Van Allen Probe B on 03 November 2015. The effect of magnetic dip on the EMIC wave generation and MS wave propagation is analyzed. The analysis of EMIC wave instability demonstrates that EMIC waves are more easily excited in the magnetic dip. Moreover, the cold plasma density shows a highly positive correlation with the magnetic field fluctuation, and they are closely related to the disappearance of MS wave during the magnetic dip structure, which is confirmed by theoretical estimation. Our results indicate that magnetic dip may play different roles in the activities of EMIC and MS waves, which has rarely been discussed before.

Energetic ion enhancements in sheaths driven by interplanetary coronal mass ejections

We analyze here an energetic proton enhancement in a sheath ahead of a slow interplanetry coronal mass ejection (ICME) detected by Parker Solar Probe on June 30, 2021 at the heliospheric distance of 0.76 AU. The shock was likely quasi-parallel and had a high Mach number. However, the proton fluxes were not enhanced at the shock but about an hour later. The fluxes stayed elevated with a sporadic behaviour throughout the sheath. We suggest that some mechanism internal to the sheath was responsible for the energization. The observations show enhanced levels of magnetic field fluctuations in the sheath and frequent presence of highly reduced magnetic helicity structures (sigma _{m}) at various time scales, representing either small-scale flux ropes or Alfvénic fluctuations that could have contributed to the energization. The correlation between the energetic proton fluxes and normalized fluctuation amplitudes/occurrence of high sigma _{m} structures was generally weak or negligible. The most striking feature of the sheath was a strong enhancement of density (up to 50 cm−3) that implies the importance of compressive acceleration in the sheath. A statistical analysis of ion enhancements of 73 sheaths detected by ACE at {sim} 1 AU reveals that this sheath was peculiar as in ICME-driven sheaths preceded by strong shocks the ion fluxes typically peak at the shock and strongly decline through the sheath.

Topological Superconductivity in Doped Magnetic Moiré Semiconductors.

We show that topological superconductivity may emerge upon doping of transition metal dichalcogenide heterobilayers above an integer-filling magnetic state of the topmost valence moiré band. The effective attraction between charge carriers is generated by an electric p-wave Feshbach resonance arising from interlayer excitonic physics and has a tunable strength, which may be large. Together with the low moiré carrier densities reachable by gating, this robust attraction enables access to the long-sought p-wave BEC-BCS transition. The topological protection arises from an emergent time reversal symmetry occurring when the magnetic order and long wavelength magnetic fluctuations do not couple different valleys. The resulting topological superconductor features helical Majorana edge modes, leading to half-integer quantized spin-thermal Hall conductivity and to charge currents induced by circularly polarized light or other time-reversal symmetry-breaking fields.

Intermittency at Earth's bow shock: Measures of turbulence in quasi-parallel and quasi-perpendicular shocks

Turbulent plasmas such as the solar wind and magnetosheath exhibit an energy cascade that is present across a broad range of scales, from the stirring scale at which energy is injected, down to the smallest scales where energy is dissipated through processes such as reconnection and wave–particle interactions. Recent observations of Earth's bow shock reveal a disordered or turbulent transition region exhibiting features of turbulent dissipation, like reconnecting current sheets. We used observations from magnetospheric multiscale (MMS) over four separate bow shock crossings of varying shock normal angle to characterize turbulence in the shock transition region and how it evolves toward the magnetosheath. These cases studies have been chosen to ensure validity of Taylor's hypothesis, which we discuss in depth. We observe the magnetic spectrum evolving by fitting power laws over many short intervals, finding that the power-law index in the shock transition region is separable from the upstream and downstream plasma, for both quasi-perpendicular and quasi-parallel shocks. Across the shock, we see a change in the breakpoint location between inertial and ion power-law slopes. We also observe the evolution of scale-independent kurtosis of magnetic fluctuations across the shock, finding a reduction of high kurtosis intervals downstream of the shock. Finally, we adapt a method for calculating correlation length to include a high-pass filter, allowing estimates for changes in correlation length across the shock. In a quasi-perpendicular shock, we find the correlation length to be significantly smaller in the magnetosheath than in solar wind; however, the opposite can occur for quasi-parallel shocks.

Implications for Chondrule Formation Regions and Solar Nebula Magnetism from Statistical Reanalysis of Chondrule Paleomagnetism

Converging lines of evidence show that protoplanetary disks are complex environments hosting spatial and temporal variability at multiple scales. Here we reanalyze paleomagnetic estimates of solar nebula magnetic field strengths using a Bayesian framework that tests for recording bias due to chondrule motion and explicitly accounts for time-varying ambient fields. We find that LL and CO group chondrule paleointensities likely rotated during cooling (p = 0.79–0.99), validating assumptions in previous paleomagnetic studies. Chondrule rotation also suggests low gas density formation environments beyond 2 and 4 au for LL and CO chondrules, respectively. Our recomputed paleointensities for LL and CO chondrules imply either: (1) temporally constant magnetic fields of μT and μT, respectively; or (2) time-varying magnetic fields with peak amplitudes between μT and μT. Considering the known mechanisms for sustaining magnetic field gradients and high-amplitude temporal magnetic fluctuations in the solar nebula, we find that magnetic field flux concentrations in disk gaps or time-varying magnetic fields, for example due to the Hall shear instability, are most compatible with the existing data. Using this statistical framework, future paleointensity studies of chondrules can be used to directly test for the variability of magnetic fields in the solar system protoplanetary disk and to distinguish between these scenarios.

Competition of Quasiparticles and Magnetization Noise in Hybrid Ferromagnetic Transmon Qubits

The coexistence between ferromagnetic ordering and superconducting transport in tunnel ferromagnetic Josephson junctions (SFS JJs) accounts for a wide range of unconventional physical properties. The integration of both insulating ferromagnets or multi-layered insulator-ferromagnet barriers allows to combine ferromagnetic switching properties with peculiar low quasiparticle dissipation, which could enhance the capabilities of SFS JJs as active elements in quantum circuits. Here we show that split-transmon qubits based on tunnel ferromagnetic JJs realize an ideal playground to study noise fluctuations in ferromagnetic Josephson devices. By considering the transport properties of measured Al-based tunnel SFS JJs, we report on a theoretical study of the competition between intrinsic magnetization fluctuations in the barrier and quasiparticles dissipation, thus providing specific operation regimes to identify and disentangle the two noise sources, depending on the peculiar properties of the F layer and F/S interface.

Spectrum of kinetic-Alfvén-wave turbulence: intermittency or tearing mediation?

ABSTRACT We investigate the spectral properties of the electromagnetic fluctuations of sub-ion scale turbulence in weakly collisional, low-beta plasmas using a two-field isothermal gyrofluid model. The numerical results strongly support a description of the turbulence as a critically balanced Kolmogorov-like cascade of kinetic Alfvén wave fluctuations, as amended by previous studies to include intermittency effects. The measured universal index of the energy spectra from systems with different flux-unfreezing mechanisms excludes the role of tearing mediation in determining the spectra. The fluctuations remain isotropic in the plane perpendicular to the strong background magnetic fields as they cascade to smaller scales, which explains the absence of tearing mediation. The calculation of high-order, multipoint structure functions of magnetic fluctuations suggests that the intermittent structures have a quasi-2D, sheet-type morphology. These results are useful for explaining recent observations of the spectrum and structure of magnetic and density fluctuations in the solar wind at sub-proton scales, and are relevant for modelling the energy dissipation in a broad range of astrophysical systems.

The energetic storm particle events of 3 November 2021

Observations of energetic particles at interplanetary shocks are important to study acceleration mechanisms and their connection with magnetohydrodynamic turbulence. Energetic storm particle (ESP) events are increases in proton fluxes that occur locally at the passage time of interplanetary shocks. These events are more dangerous when they are superimposed on the solar energetic particles (SEPs) produced by the eruption of flares and/or CME-driven shocks propagating from the corona to the interplanetary space. We considered ESP events occurring in association with SEPs on 3 November 2021. We used proton fluxes provided by Solar Orbiter (located at 0.85 AU) in the energy range of 30 keV–82 MeV, by Wind at energies from 70 keV to 72 MeV, and ACE in the range from 40 keV to 5 MeV (both located at the Lagrangian point L1, close to 1 AU along the Sun-Earth direction). In order to broaden the range of analyzed energies (40 keV - 72 MeV), we combine these data with the proton fluxes from the SOHO spacecraft, also located at L1. We analyzed the ESP event and fitted the proton energy spectra at both locations with several distributions to shed light on the mechanisms leading to the acceleration of energetic particles. We also investigated the turbulent magnetic field fluctuations around the shock. The obtained ESP spectra, best reproduced by the so-called double power law function, the spectral differences at the two locations, and the shock features (quasi-parallel geometry, enhanced downstream turbulence) suggest that diffusive shock acceleration is responsible for acceleration of low energy particles, whereas stochastic acceleration contributes to the (re) acceleration of high energies ones.

Broadband Alfvénic excitation correlated to turbulence level in the Wendelstein 7-X stellarator plasmas

During the first operational phase (OP1) of the Wendelstein 7-X (W7-X) stellarator, poloidal magnetic field fluctuations, , were measured in several different plasma scenarios with a system of Mirnov coils. In the spectrograms, multiple frequency bands close together in frequency are observed below f = 600 kHz. Furthermore, a dominant feature is the appearance of a frequency band with the highest spectral amplitude centred between kHz. The fluctuations are observed from the beginning of most W7-X plasmas of OP1, which were often operated solely with electron cyclotron resonance heating. The fluctuations show characteristics known from Alfvén waves and possibly Alfvén eigenmodes (AEs). However, the fast particle drive from heating sources, which is generally a driver necessary for the appearance of AEs in magnetic confinement plasmas, is absent in most of the analysed experiments. A characterization of the Alfvénic fluctuations measured during OP1 plasmas is possible using a newly developed tracking algorithm. In this paper, we extensively survey the different spectral properties of the fluctuations in correlation with plasma parameters and discuss possible driving mechanisms. The correlation studies of the dynamics of the possible ellipticity induced AEs indicate that Alfvén activity in the frequency interval between kHz could be excited due to an interaction with turbulence, or profile effects also affecting the turbulence amplitude.

Electromagnetic turbulence simulation of tokamak edge plasma dynamics and divertor heat load during thermal quench

The edge plasma turbulence and transport dynamics, as well as the divertor power loads during the thermal-quench phase of tokamak disruptions, are numerically investigated with BOUT++’s flux-driven six-field electromagnetic turbulence model. Here, transient yet intense particle and energy sources are applied at the pedestal top to mimic the plasma power drive at the edge induced by a core thermal collapse, which flattens the core temperature profile. Interesting features, such as surging of divertor heat load (up to 50 times) and broadening of heat-flux width (up to four times) on the outer-divertor target plate, are observed in the simulation, in qualitative agreement with experimental observations. The dramatic changes in divertor heat load and width are due to the enhanced plasma turbulence activities inside the separatrix. Two cross-field transport mechanisms, namely, the E × B turbulent convection and the stochastic parallel advection/conduction, are identified to play important roles in this process. First, an elevated edge pressure gradient drives instabilities and subsequent turbulence in the entire pedestal region. The enhanced turbulence not only transports particles and energy radially across the separatrix via the E × B convection, which causes the initial divertor heat-load burst, but it also induces amplified magnetic fluctuation . Once themagnetic fluctuation is large enough to break the magnetic flux surface, magnetic flutter effect provides an additional radial transport channel. In the late stage of our simulation, reaches to 10−4 level that completely breaks magnetic flux surfaces such that stochastic field lines are directly connecting pedestal top plasma to the divertor target plates or first wall, further contributing to the divertor heat-flux width broadening.

Cluster spin glass in off-stoichiometric Ni2.01Mn1.58Sn0.41 alloy

The Ni2.01Mn1.58Sn0.41 alloy is a member of the Heusler material family which undergoes diffusionless structural transition from cubic austenite to orthorhombic martensite during its cooling. The transition was observed at temperature 398 K from paramagnetic austenite to martensite with complex magnetic structure. The measurement of AC magnetic susceptibility of the alloy confirmed spin-glass state at temperatures below 155 K and from the frequency dependence of the cups in AC susceptibility, a presence of clusters (11 nm3 in size) with strong interaction is deduced. The alloy shows anomalous Hall effect (AHE) of the order of 0.051 μΩ cm at 2 K in the spin-glass state of the alloy and its sign changes at around 140 K. The ordinary Hall coefficient of the metallic alloy is strikingly positive in the whole studied temperature region, and it points to complex magnetic and electronic structure of the alloy. The electrical resistance of the sample shows a flat maximum of 220 μΩ cm at spin-glass transition temperature. The magnetoresistance is of the order of 1% and is negative in the whole temperature region which points to a standard scattering of charge carriers on magnetic fluctuations. Quantum-mechanical calculations of supercells with compositions Ni32Mn25Sn7, Ni32Mn26Sn6 and Ni32Mn24Sn8 simulated different arrangement of Mn and Sn atoms. Ni32Mn25Sn7 composition is thermodynamically the most stable, although its magnetic moment is 1.67 μB/f.u., twice higher than the measured value. The combination of the latter two states, with additional Mn–Sn swaps, provides the magnetic moments matching the experimental value at a very small energy cost. Theoretical results then indicate that a scenario of local chemical variations and clustering is likely in the studied alloy.

Formation of the hot tail seeds for runaway electron generation during disruptions with lower hybrid waves in the HL-2A tokamak

The hot tail generation is expected to be the dominant mechanism for the runaway electron (RE) seed formation during disruptions, especially in large devices with high electron temperature such as international thermonuclear experimental reactor. This issue has been studied in the HL-2A tokamak by using the superthermal electrons produced by lower hybrid waves (LHWs), which can adjust the hot tail distribution. It was observed that RE generation was significantly enhanced during disruptions with LHWs. The measurements show that the multitudinous superthermal electrons with energy of 40–60 keV created by LHWs greatly transform the landscape of hot tail distribution. The tail electrons can be directly converted into REs under the acceleration of the high toroidal electric field during disruptions. Runaway current plateaus are more likely to be formed than in normal disruptions without LHWs. However, some abnormal phenomena have also been observed, that is, RE generation was not enhanced and no runaway current plateau was formed during some disruptions with LHWs. It is found that this is attributed to the complete loss of RE seeds caused by strong magnetic fluctuations, which prevents the generation of REs during disruptions. This may provide a way to avoid the generation of REs during disruptions by actively exciting magnetic fluctuations.

Quantum Sensing via Magnetic‐Noise‐Protected States in an Electronic Spin Dyad

AbstractExtending the coherence lifetime of a qubit is central to the implementation and deployment of quantum technologies, particularly in the solid state where various noise sources intrinsic to the material host play a limiting role. This study examines theoretically the coherent spin dynamics of a hetero‐spin system formed by a spin featuring a non‐zero crystal field and in proximity to a paramagnetic center . An analysis of the energy level structure of the dyad shows this system exhibits apair of levels separated by a magnetic‐field‐insensitive energy gap, which can be exploited to create long‐lived zero‐quantum coherences. It is found that these coherences are selectively sensitive to “local”—as opposed to “global”—magnetic field fluctuations, suggesting these spin dyads can serve as a nanoscale gradiometer for precision magnetometry. On the other hand, the distinct response of either spin species to electric or thermal stimuli allows one to implement alternative sensing protocols for magnetic‐noise‐free electrometry and thermometry.

Cosmic ray fluctuations and MHD waves in the solar wind

During large-scale solar wind disturbances, variations in galactic cosmic rays with periods from several minutes to 2–3 hours, which are called cosmic ray fluctuations in the scientific literature, often occur. Such fluctuations are not observed in the absence of disturbances. Since cosmic rays are charged particles, their modulation in the heliosphere occurs mainly under the influence of the interplanetary magnetic field, or rather its turbulent part — MHD waves. In order to adequately describe the relationship between their fluctuation spectra, it is necessary to be able to isolate a certain type of MHD waves from direct measurements of the interplanetary medium parameters. In this paper, we consider some methods for determining the contribution of three solar wind MHD turbulence branches, namely, Alfvén, fast, and slow magnetosonic waves corresponding to the turbulence spectrum inertial region frequencies 10⁻⁴&lt;ν&lt;10⁻¹ Hz, at which cosmic ray fluctuations are observed, to the observed power spectra of interplanetary magnetic field modulus fluctuations. To do this, we apply the methods of spectral and polarization analysis. In the absence of measurement data on SW parameters, to identify the type of MHD turbulence we use the known wave polarization properties that Alfvén and magnetosonic waves are polarized in different planes relative to the plane containing the average IMF vector and wave vector.&#x0D; Our results show that with the correct determination of the spectra of three MHD wave types, their sum, within the limits of errors, agrees well with the observed spectra of the interplanetary magnetic field modulus, and a small difference can be attributed to static inhomogeneities and oscillations frozen into plasma, as well as to various discontinuities that are always inevitably present in the solar wind.

Флуктуации космических лучей и МГД-волны в солнечном ветре

During large-scale solar wind disturbances, variations in galactic cosmic rays with periods from several minutes to 2–3 hours, which are called cosmic ray fluctuations in the scientific literature, often occur. Such fluctuations are not observed in the absence of disturbances. Since cosmic rays are charged particles, their modulation in the heliosphere occurs mainly under the influence of the interplanetary magnetic field, or rather its turbulent part — MHD waves. In order to adequately describe the relationship between their fluctuation spectra, it is necessary to be able to isolate a certain type of MHD waves from direct measurements of the interplanetary medium parameters. In this paper, we consider some methods for determining the contribution of three solar wind MHD turbulence branches, namely, Alfvén, fast, and slow magnetosonic waves corresponding to the turbulence spectrum inertial region frequencies 10⁻⁴&lt;ν&lt;10⁻¹ Hz, at which cosmic ray fluctuations are observed, to the observed power spectra of interplanetary magnetic field modulus fluctuations. To do this, we apply the methods of spectral and polarization analysis. In the absence of measurement data on SW parameters, to identify the type of MHD turbulence we use the known wave polarization properties that Alfvén and magnetosonic waves are polarized in different planes relative to the plane containing the average IMF vector and wave vector. &#x0D; Our results show that with the correct determination of the spectra of three MHD wave types, their sum, within the limits of errors, agrees well with the observed spectra of the interplanetary magnetic field modulus, and a small difference can be attributed to static inhomogeneities and oscillations frozen into plasma, as well as to various discontinuities that are always inevitably present in the solar wind.

Optimizing the design of wide magneto-mechano-electric generators to maximize their power output and lifetime in self-powered environmental monitoring systems

Magneto-mechano-electric (MME) generators are increasingly being investigated as a sustainable power source for Internet of Things (IoT) systems owing to their ability to efficiently harvest electrical energy from stray magnetic field noise. However, to be practical, this technology must achieve a longer lifespan while maintaining high-power output and withstanding magnetic field fluctuations. To address this, extensive numerical simulations and experimental verifications have been performed to amplify the magneto-mechanic vibration by increasing the magnetic proof mass volume, generate high electrical output through a larger active piezoelectric volume, and enhance lifetime by optimizing the cantilever structure in a wide-structural MME architecture. MME generators with a wide and short (WS) trapezoidal structure (WS-MME) have demonstrated excellent performance, with a high output power of 7.4 mW (equivalent power density of 0.58 mW/cm3. Oe) and an excellent lifespan of over 1012 fatigue cycles under a magnetic noise field level of 3 Oe. Moreover, a self-powered environmental IoT sensor node has been demonstrated by continuously powering the multifunctional (temperature, humidity, light, sound noise, UV index, pressure, discomfort index, and heatstroke) sensor and wireless communication systems by utilizing the stray magnetic field noise around the electrical power cables of various home appliances. In conclusion, the combination of a longer lifespan and high-power generation achieved with WS-MME generators is a significant step towards the commercialization of MME generators for powering wireless sensor technology.

Interstellar Polarization Survey. III. Relation between Optical Polarization and Reddening in the General Interstellar Medium

Optical starlight can be partially polarized while propagating through the dusty, magnetized interstellar medium (ISM). The polarization efficiency describes the polarization intensity fraction per reddening unit, P V /E(B − V), related to the interstellar dust grains and magnetic field properties. The maximum value observed, [P V /E(B − V)]max, is thus achieved under optimal polarizing conditions of the ISM. Therefore, the analysis of polarization efficiency observations across the Galaxy contributes to the study of magnetic field topology, small-scale magnetic fluctuations, grain-alignment efficiency, and composition. Infrared observations from Planck satellite have set [P V /E(B − V)]max to 13% mag−1. However, recent optical polarization observations in Planck's highly polarized regions showed polarization efficiency values between 13.6% mag−1 and 18.2% mag−1 (depending on the extinction map used), indicating that [P V /E(B − V)]max is not well constrained yet. We used V-band polarimetry of the Interstellar Polarization Survey (consisting of ∼10,500 high-quality observations distributed in 34 fields of 0.°3 × 0.°3) to accurately estimate the polarization efficiency in the ISM. We estimated the upper limit of P V /E(B − V) with the weighted 99th percentile of the field. In five regions, the polarization efficiency upper limit is above 13% mag−1. Furthermore, we found [P V /E(B − V)]% mag−1 using diffuse intermediate-latitude (∣b∣ > 7.°5) regions with apparently strong regular Galactic magnetic field in the plane-of-sky. We studied the variations of P V /E(B − V) across the sky and tested toy models of polarization efficiency with Galactic longitude that showed some correspondence with a uniform spiral magnetic field.