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DOE OSTI2022

Sheath formation around a dielectric droplet in a He atmospheric pressure plasma

Interactions at the interface between atmospheric pressure plasmas and liquids are being investigated to address applications ranging from nanoparticle synthesis to decontamination and fertilizer production. Furthermore, many of these applications involve activation of droplets wherein the droplet is fully immersed in the plasma and synergistically interacts with the plasma. To better understand these interactions, two-dimensional modeling of radio frequency (RF) glow discharges at atmospheric pressure operated in He with an embedded lossy dielectric droplet (tens of microns in size) was performed. The properties of the sheath that forms around the droplet were investigated over the RF cycle. The electric field in the bulk plasma polarizes the dielectric droplet while the electron drift in the external electric field is shadowed by the droplet. The interaction between the bulk and sheath electric fields produces a maximum in E/N (electric field/gas number density) at the equator on one side of the droplet where the bulk and sheath fields are aligned in the same direction and a minimum along the opposite equator. Due to resistive heating, the electron temperature T e is maximum 45° above and below the equator of the droplet where power deposition per electron is the highest. Although the droplet is, on the average, negatively charged, the charge density on the droplet is positive on the poles and negative on the equator, as the electron motion is primarily due to diffusion at the poles but due to drift at the equator.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2023

Developing compact tuning fork thermometers for sub-mK temperatures and high magnetic fields

There is a growing demand for experiments on calorimetric and thermal transport measurements at ultra-low temperatures below 1 mK and high magnetic fields up to 16 T. Particularly, milligram-sized solid samples are of great interest. Here, we present the development of scalable thermometers based on quartz tuning fork resonators immersed in liquid 3 He and adapt hydrodynamic models to provide an improved description of temperature dependence in the high viscosity regime between 1 and 10mK. We demonstrate successful thermometer operation and discuss the feasibility of fast and compact thermal probes suitable for small samples.

47 OTHER INSTRUMENTATION↗

DOE OSTI2024

On the force exerted on a non-spherical asymmetric dust grain from homogeneous, stationary, isotropic, non-magnetized plasma

Whereas the conventional wisdom suggests that the force between non-magnetized homogeneous, stationary, isotropic plasma, and the dust grain is only possible for the case of relative plasma–grain velocity, it is shown that stationary non-spherical asymmetric dust grain immersed in stationary, non-magnetized, isotropic plasma can experience a force caused by the grain–plasma interactions. The component of the force due to scattering of plasma particles in the limit of infinite Debye length is considered analytically. Both the particle scattering and absorption force components are modeled numerically in the limits of infinite and finite Debye length using a newly developed 2D3V Aspherical Particle-in-Cell code. The code simulates interactions of dust grain of selected non-spherical asymmetric shape with plasmas using dust shape conforming coordinates. Here, the simulations confirm the existence of the force on non-spherical asymmetric grain in stationary non-magnetized plasma and show that the plasma screening effects can lead to reversal of the force direction.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Nonlinear susceptibilities for weakly turbulent magnetized plasma: Electrostatic approximation

The plasma weak turbulence theory is a perturbative nonlinear theory, which has been proven to be quite valid in a number of applications. However, the standard weak turbulence theory found in the literature is fully developed for highly idealized unmagnetized plasmas. As many plasmas found in nature and laboratory are immersed in a background static magnetic field, it is necessary to extend the existing discussions to include the effects of ambient magnetic field. Such a task is quite formidable, however, which has prevented fundamental and significant progresses in the subject matter. The central difficulty lies in the formulation of the complete nonlinear response functions for magnetized plasmas. The present paper derives the nonlinear susceptibilities for weakly turbulent magnetized plasmas up to the third order nonlinearity, but in doing so, a substantial reduction in mathematical complexity is achieved by the use of Bessel function addition theorem (or sum rule). The present paper also constructs the weak turbulence wave kinetic equation in a formal sense. For the sake of simplicity, however, the present paper assumes the electrostatic interaction among plasma particles. Fully electromagnetic generalization is a subject of a subsequent paper.

Physics↗

DOE OSTI2024

Investigation of high field plasma dynamics in a laser-produced plasma expanding into a background gas

This paper presents an overview of experimental results of a laser-produced plasma expanding into a background gas, immersed within a large range of highly uniform magnetic fields (of up to 3 T), that are transverse to the expanding plasma. We used intensified gated imaging to capture the expansion of the plasma across and along the magnetic field lines to observe the spatiotemporal expansion dynamics for different magnetic field strengths. We observe changes in the perpendicular and parallel dynamics of the laser-produced plasmas expansion at high magnetic field. In addition, our results have also indicated the presence of electron-ion hybrid instabilities at relatively high pressures (100 mTorr) and relatively high magnetic field strengths (2 T), in accordance with theoretical calculations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2025

Spherical and sessile droplet dynamics by fluctuating hydrodynamics

We simulate the mesoscopic dynamics of droplets formed by phase-separated fluids at nanometer scales where thermal fluctuations are significant. Both spherical droplets fully immersed in a second fluid and sessile droplets which are also in contact with a solid surface are studied. Our model combines a Cahn–Hilliard formulation with incompressible fluctuating hydrodynamics; for sessile droplets, the fluid–solid contact angle is specified as a boundary condition. Deterministic simulations with an applied body force are used to measure the droplets' mobility from which a diffusion coefficient is obtained using the Einstein relation. Stochastic simulations are independently used to obtain a diffusion coefficient from a linear fit of the variance of a droplet's position with time. In some scenarios, these two measurements give the same value but not in the case of a spherical droplet initialized near a slip wall or in the case of sessile droplets with large contact angles (≥90°) on both slip and no-slip surfaces.

Bell, John B↗

DOE OSTI2025

Identifying environmentally induced calibration changes in cryogenic RF axion detector systems using deep neural networks

The axion is a compelling hypothetical particle that could account for the dark matter in our universe while simultaneously solving the strong CP problem in quantum chromodynamics. The most sensitive axion detection technique demonstrated so far makes use of a high Q cavity immersed in a strong magnetic field, where axions are converted to microwave photons. This is called an axion haloscope and has primarily targeted the 1–10 GHz range. As searches scan up in axion mass, toward the parameter space favored by theoretical predictions, individual cavity sizes decrease in order to achieve higher frequencies. This shrinking cavity volume translates directly to a loss in signal-to-noise, motivating the plan to replace individual cavity detectors with arrays of cavities. When the transition from one to (N) multiple cavities occurs, haloscope searches are anticipated to become much more complicated to operate, requiring N times as many measurements but also the new requirement that N detectors operate in unison, which can be achieved by locking them to a common frequency. To offset this anticipated increase in detector complexity, we aim to develop new tools for diagnosing experiments using neural networks. Current experiments monitor scattering parameters of their receiver for periodically measuring cavity quality factor and coupling. However, off-resonant data remain relatively useless. In this paper, we ask if it is possible that off-resonant information contained in vector network analyzer scans could be used to diagnose equipment failures/anomalies and measure physical conditions (e.g., temperatures and ambient magnetic field). We demonstrate a proof-of-concept that AI techniques can help manage the complexity of an axion haloscope search for operators.

Engel, Andrew W. [Pacific Northwest National Labor↗

DOE OSTI2025

Resistive hose modes in tokamak runaway electron beams II

Resistive hose instabilities of runaway electron (RE) beams immersed in resistive background plasmas are examined with analytic and numerical calculations. The RE beam-plasma equilibria considered are characteristic of the situation observed post-thermal quench in a tokamak disruption. An analytic linear dispersion relation is presented for the case of a uniform RE current density profile with a sharp boundary in cylindrical geometry. Initial value linear calculations for a more general profile in toroidal geometry find that reducing aspect ratio increases the resistive hose mode growth rates with fixed safety factor profile. Nonlinear calculations in cylindrical and toroidal geometry find that the resistive hose instability-driven fluctuations relax the gradient of the current density profile. In toroidal geometry, changes to the magnetic topology are observed as a result of the resistive hose activity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2025

Microscopic insights into the solvation of polyethylene glycol chains in water: A machine learning potential approach

Polyethylene glycol (PEG) is a structurally simple, nontoxic, and water-soluble polymer widely utilized in medical and pharmaceutical applications. Notably, when a PEG chain is immersed in water, the surrounding water molecules play a key role in driving conformational changes of this macromolecule. In this study, we explore the solvation behavior of PEG under mechanical strain using molecular dynamics simulations, with an interatomic potential obtained from machine learning. Our focus is on the transition from the favored coil-like conformation to an extended one under external force. Through analyses of radial distribution functions, hydrogen bonding, and solvation dynamics, we uncover how mechanical stretching influences the local hydration environment. Furthermore, we disentangle the enthalpic and entropic contributions to the conformational stability of PEG in water. Surprisingly, our neural network potential model identifies dewetting of PEG C-atoms, and not water H-bonding with PEG O-atoms, as the main enthalpic driving force for the coiling of PEG in water.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Development of an ultraprecise glue-free bimorph deformable mirror with a length of 460 mm

Lead zirconate titanate (PZT) bimorph mirrors are essential for performing multiple functions, such as beam shaping, wavefront correction, and dynamic focusing with adjustable beam sizes. They typically consist of a mirror substrate with PZT electrodes bonded to the substrate using a thin epoxy film. However, glue-bonded PZT mirrors exhibit low reproducibility in measurement results. One source of this variability is water absorption by the substrate’s epoxy adhesive during wet fabrication processes, such as elastic emission machining (EEM), which leads to swelling and deformation. Additionally, longer deformable bimorph mirrors require larger PZT electrodes, further complicating their design and fabrication, particularly during bonding and ultraprecise metrology. To address these challenges, silver nanoparticles were employed to bond PZT elements to the silicon (Si) mirror, eliminating the need for epoxy glue. Here, in this study, we developed an inorganic-glue-free PZT bimorph mirror with a length of 460 mm and 28 channels. The glue-free bonding method successfully ensured the high reproducibility of measurements after water immersion. This approach resulted in a shape error of only 0.41 nm root mean square after the figure correction process using an ultraprecise EEM process. Scanning acoustic tomography and basic response function tests confirmed the success of the bonding process, showing no critical voids. Furthermore, the shape changes induced by applying voltages to the PZT electrodes closely matched predictions obtained from simulations. These results demonstrate the reliability and precision of the proposed glue-free bonding technique, paving the way for improved performance of new PZT bimorph mirrors.

Ichii, Yoshio [SLAC National Accelerator Laborator↗

DOE OSTI2020

Control of the optical properties of gum and dentin tissue of a human tooth at laser spectral lines in the range of 200 – 800 nm

A change in the optical properties of the tissue of the gums and dentin of a human tooth is experimentally investigated in vitro with the application of a 99.5 % glycerol solution. The kinetics of the total transmittance in the spectral range of 200 – 800 nm on characteristic laser lines is studied. It is shown that the effectiveness of optical clearing, expressed as a relative increase in the total transmittance, for gum tissue in the laser radiation range of 200 – 800 nm can vary significantly (by an order of magnitude). In this case, the absolute values of optical transmittance in the UV region are relatively small due to the strong absorption by the endogenous chromophores of the studied tissues, and in the visible and NIR regions, on the contrary, they are significant, which is due to the absence of strongly absorbing chromophores. The effectiveness of dentin clearing in the entire visible and NIR spectral regions is on average 25 % for 300 minutes of immersion of the sample in a 99.5 % glycerol solution. The presented results are necessary for increasing the efficiency of laser therapy and methods for optical monitoring of morphological changes in biological tissues for the purpose of early diagnosis of diseases. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2021

Chemical pumps and flexible sheets spontaneously form self-regulating oscillators in solution

The synchronization of self-oscillating systems is vital to various biological functions, from the coordinated contraction of heart muscle to the self-organization of slime molds. Through modeling, we design bioinspired materials systems that spontaneously form shape-changing self-oscillators, which communicate to synchronize both their temporal and spatial behavior. Here, catalytic reactions at the bottom of a fluid-filled chamber and on mobile, flexible sheets generate the energy to “pump” the surrounding fluid, which also transports the immersed sheets. The sheets exert a force on the fluid that modifies the flow, which in turn affects the shape and movement of the flexible sheets. This feedback enables a single coated (active) and even an uncoated (passive) sheet to undergo self-oscillation, displaying different oscillatory modes with increases in the catalytic reaction rate. Two sheets (active or passive) introduce excluded volume, steric interactions. This distinctive combination of the hydrodynamic, fluid–structure, and steric interactions causes the sheets to form coupled oscillators, whose motion is synchronized in time and space. We develop a heuristic model that rationalizes this behavior. These coupled self-oscillators exhibit rich and tunable phase dynamics, which depends on the sheets’ initial placement, coverage by catalyst and relative size. Moreover, through variations in the reactant concentration, the system can switch between the different oscillatory modes. This breadth of dynamic behavior expands the functionality of the coupled oscillators, enabling soft robots to display a variety of self-sustained, self-regulating moves.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Out-of-equilibrium interactions and collective locomotion of colloidal spheres with squirming of nematoelastic multipoles

Many living and artificial systems show similar emergent behavior and collective motions on different scales, starting from swarms of bacteria to synthetic active particles, herds of mammals, and crowds of people. What all these systems often have in common is that new collective properties like flocking emerge from interactions between individual self-propelled or driven units. Such systems are naturally out-of-equilibrium and propel at the expense of consumed energy. Mimicking nature by making self-propelled or externally driven particles and studying their individual and collective motility may allow for deeper understanding of physical underpinnings behind collective motion of large groups of interacting objects or beings. Here, in this work, using a soft matter system of colloids immersed into a liquid crystal, we show that resulting so-called nematoelastic multipoles can be set into a bidirectional locomotion by external oscillating electric fields. Out-of-equilibrium elastic interactions between such colloidal objects lead to collective flock-like behaviors emerging from time-varying elasticity-mediated interactions between externally driven propelling particles. Repulsive elastic interactions in the equilibrium state can be turned into attractive interactions in the out-of-equilibrium state under applied external electric fields. We probe this behavior at different number densities of colloidal particles and show that particles in dense dispersions collectively select the same direction of a coherent motion due to elastic interactions between near neighbors. In our experimentally implemented design, their motion is highly ordered and without clustering or jamming often present in other colloidal transport systems, which is promising for technological and fundamental-science applications, like nano-cargo transport, out-of-equilibrium assembly, and microrobotics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2025

Audible enclaves crafted by nonlinear self-bending ultrasonic beams

Delivering audible content to a targeted listener without disturbing others is paramount in audio engineering. However, achieving this goal has long been challenging due to the diffraction of low-frequency (long-wavelength) audio waves in linear acoustics. Here, we introduce an approach for creating remote audio spots, dubbed audible enclaves, by harnessing the local nonlinear interaction of two self-bending ultrasonic beams with distinct spectra. The self-bending ultrasonic beams created by acoustic metasurfaces, though inaudible, can bypass obstacles such as human heads. At their intersection behind obstacles, highly localized audible enclaves are formed due to the local nonlinear interactions. Additionally, we demonstrate the ultrabroadband capabilities of our metasurface-based implementation both numerically and experimentally, spanning from 125 Hz to 4 kHz (6 octave bands), covering the majority of the audible frequency range. The practicality of our proposed technique is underscored by its compact implementation size (0.16 m, equivalent to 0.06 wavelengths at 125 Hz), as well as its robust performance under wideband transient audio signal excitation and in a common room with reverberations. Our proposed audible enclaves hold significant potential for various applications in advanced audio engineering, including private speech communications, immersive spatial audio reproduction, and high-resolution sound/quiet zone control.

Science & Technology - Other Topics↗

DOE OSTI2021

Parametric Study of Used Nuclear Oxide Fuel Constituent Dissolution in Molten LiCl-KCl-UCl 3

Prior work identified dissolution of used nuclear oxide fuel constituents from a uranium oxide matrix into molten LiCl-KCl-UCl 3 at 500°C, prompting a subsequent series of three progressive studies (including an initial scoping study, an electrolytic dissolution study, and a chemical-seeded dissolution study) to further investigate associated parameters and mechanisms. Thermodynamic calculations were performed to identify possible reaction mechanisms and their propensities in used oxide fuel constituent dissolution. Used nuclear oxide fuels with varying preconditions from fast and thermal test reactors were separately immersed in the subject salt system to assess fuel constituent migration from the bulk fuel matrix to the salt phase in an initial scoping study. Dissolution of expected fuel constituents, including alkali, alkaline earth, lanthanide, and transuranium oxides, into the chloride salt phase varied widely, ranging from 12% to 99% in the initial study. Uranium isotope blending between the salt phase and bulk fuel matrix was also observed, which was attributed to reducing conditions in the fuel matrix. Electrolytic and chemical-seeded dissolution studies were subsequently performed to effect reducing conditions in the fuel. Other parameters, including temperature (at 500°C, 650°C, 725°C, and 800°C) and uranium trichloride concentrations (at 6, 9, and 19 wt% uranium), were investigated in the latter two studies, resulting in fuel constituent dissolution above 90%. Extents of dissolution were based on initial and final fuel constituent concentrations in the oxide fuels following operations in the salt and subsequent removal of the salt via distillation. Finally, in this series of progressive studies, oxide fuel preconditioning and in situ reducing conditions, along with elevated temperature and uranium trichloride concentrations, were the primary parameters promoting used nuclear oxide fuel constituent dissolution in accordance with identified reaction mechanisms.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2023

Multi-modal chemical characterization of highly viscous submicrometer organic particles

Distinguishing highly viscous organic particles within complex mixtures of atmospheric aerosol and accurate descriptions of their composition, size distributions, and mixing states are challenges at the forefront of aerosol measurement science and technology. Here, we present results obtained from complementary single-particle measurement techniques employed for the in-depth characterization of highly viscous particles. In this study, we demonstrate advantages and synergy of this multi-modal particle characterization approach based on the analysis of individual viscous particles formed in the air-discharged waste produced by a common sewer pipe rehabilitation technology. Using oil immersion flow microscopy, we investigate particle size distributions and morphology of colloidal components present in field-collected aqueous waste condensates. We compare these results with corresponding measurements of viscous particles formed in drying droplets of the aerosolized discharged waste. The colloidal components and viscous particles were found to be approximately 10 µm and 0.5 µm, respectively. The aerosolized viscous particles exhibited a spherical morphology, while the colloidal particles appeared noticeably fractal, resembling fragments of a cured composite material. Chemical imaging of the viscous particles collected on substrates was performed using scanning electron microscopy and soft X-ray spectro-microscopy techniques. Through these methods, comprehensive description of these particles emerged, confirming their high solid-like viscosity, wide-ranging sizes, diverse carbon speciation with high degrees of oxygenation, and high organic volume fractions. The aerosolized viscous particles were further characterized using high-throughput single particle mass spectrometry. This technique provides real-time measurements of composition, size, and morphological metrics for large numbers of individual particles, enabling the identification of their distinct mass spectrometric signatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

CFD Simulations of Molten Salts Within Plasma-Facing Components with Twisted Tape Inserts Under One-Sided–Heated Conditions

For liquid immersion blankets (LIBs), the heat removal within different plasma-facing components (PFCs) requires substantial heat removal capabilities that could benefit from the usage of heat transfer enhancements. Of consideration are twisted tape insert heat transfer enhancements that are ribbon-like metal pieces inserted within cooling channels that increase fluid mixing, resulting in higher heat transfer and pressure drop. Unlike traditional applications, PFCs such as divertor coolant tubes experience a significantly higher heat flux on one side versus the other or entirely one-sided heating. These conditions are not well studied for molten salts where the higher Prandtl numbers characteristic of the fluids are significantly higher than water, gases, and liquid metals. As an effort to study this knowledge gap, large eddy simulations were done with Prandtl numbers representative of FLiBe at proposed operating conditions. In this study, the effects of applying a surface heat flux to one side of a tube versus the entire tube with a twisted tape insert were investigated for the heat transfer coefficient and effects on the temperature profile. The findings of the study suggest that for Prandtl number fluids above unity, the Nusselt number was largely unaffected by the change in boundary condition. Both boundary conditions showed good agreement with the Manglik and Bergles Nusselt number correlation for tight-fitting twisted tapes. Finally, the outcomes of this study will be useful for future design studies of LIBs to provide fundamental guidance implementing twisted tape inserts and their performance in one-sided–heated conditions.

molten salts↗

DOE OSTI2024

Controlling the charge of dust particles in an afterglow by modulating the plasma power

Abstract A dust particle immersed in a glow-discharge plasma has long been known to have a charge that is negative , while the plasma is powered. However, in the afterglow, following the stopping of the plasma power, a large positive charge can collect on the particle, as was shown recently for particles in a cathodic sheath. While that outcome of positive charging in the afterglow may be common, an experimental discovery reported here reveals that the opposite outcome is also possible: a particle can develop a negative charge in the afterglow, if the plasma had previously been operated with a modulated power. Before stopping the plasma power off altogether, in a run with power modulated at a low duty cycle of 4.5 % , the particle’s residual charge was negative, but it was positive in a control run without modulation. This result points to a way of controlling the charge of dust particles in a decaying plasma, which can be useful for mitigating defects in semiconductor manufacturing.

Physics↗