Micro-scale Plasma Research Articles

Thermal conductivity with bells and whistlers: Suppression of the magnetothermal instability in galaxy clusters

In the hot and dilute intracluster medium (ICM) in galaxy clusters, kinetic plasma instabilities that are excited at the particle gyroradius may play an important role in the transport of heat and momentum, thus affecting the large-scale evolution of these systems. In this paper, we continue our investigation of the effect of whistler suppression of thermal conductivity on the magneto-thermal instability (MTI), which may be active in the periphery of galaxy clusters and may contribute to the observed levels of turbulence. We use a subgrid closure for the heat flux inspired from kinetic simulations and show that MTI turbulence with whistler suppression exhibits a critical transition as the suppression parameter is increased: for modest suppression of the conductivity, the turbulent velocities generated by the MTI decrease accordingly, in agreement with scaling laws found in previous studies of the MTI. However, for suppression above a critical threshold, the MTI loses its ability to maintain equipartition-level magnetic fields through a small-scale dynamo (SSD), and the system enters a ``death-spiral.'' We show that analogous levels of suppression of thermal conductivity with a simple model of flat uniform suppression would not inhibit the dynamo. We propose a model to explain this critical transition, and speculate that conditions in the hot ICM are such that in substantial portions of the galaxy cluster periphery the MTI might struggle to sustain its own dynamo. We then look at spatial correlations and energy transfers in spectral space and find that, with whistler suppression, most of the heat is transported along thin bundles of strong magnetic fields (the Autobahns of electrons), while high-beta regions are brought out of thermal equilibrium. We link this behavior to the intermittent nature of magnetic fields, and we observe an overall reduction of the efficiency of MTI turbulent driving at the largest turbulent scales. Finally, we show that external turbulence interferes with the MTI and leads to reduced levels of MTI turbulence. While individually both external turbulence and whistler suppression reduce MTI turbulence, we find that they can exhibit a complex interplay when acting in conjunction, with external turbulence boosting the whistler-suppressed thermal conductivity and even reviving a ``dead'' MTI. Our study illustrates how extending magnetohydrodynamics with a simple prescription for microscale plasma physics can lead to the formation of a complicated dynamical system and demonstrates that further work is needed in order to bridge the gap between micro- and macro scales in galaxy clusters.

Humidity-enhanced microfluidic plasma separation on Chinese Xuan-papers.

The first step in blood testing necessitates blood separation to obtain an adequate volume of plasma. Traditional centrifugation is bulky, expensive and electricity-powered, which is not suitable for micro-scale blood plasma separation in point-of-care testing (POCT) cases. Microfluidic paper-based plasma separation devices present a promising alternative for plasma separation in such occasions. However, they are limited in terms of plasma yield, which hinders analyte detection. Herein, we proposed a humidity-enhanced paper-based microfluidic plasma separation method to address this issue. Specifically, paper was first treated by blood-typing antibodies, then samples of whole blood were introduced into the prepared paper. After waiting for 5 min for RBC agglutination and plasma wicking under high humidity, micro-scale plasma separation from whole blood was achieved. As a result, an extremely high plasma yield of up to 60.1% could be separated from whole blood through using Xuan-paper. Meanwhile, the purity of plasma could reach 99.99%. Finally, this innovative approach was effortlessly integrated into distance-based glucose concentration detection, enabling rapid determination of blood glucose levels through naked-eye observation. Considering the simplicity and inexpensiveness of this method, we believe that this technology could be integrated to more paper-based microfluidic analytical devices for rapid and accurate detection of plasma analytes in POCT.

Development of a novel DC micro-discharge code on dsmcFoam+ for plasma effect in DSMC flow profile simulations and its application to a micro-plasma system

Recent advances in the miniaturisation of plasma-based microelectromechanical systems have permitted their application in the space sector, such as flow control of flying vehicles and the potential usage in high precision attitude and orbit control systems for CubeSats. To determine its contribution in pressure, velocity, and temperature profiles for thrust analysis on micro-fluidic channels in space/vacuum environments, a novel DC micro-discharge code has been developed in the dsmcFoam+ solver in order to simulate the ionic effects on the gas flow during the breakdown voltage in microgaps.The rarefied gas flow was solved using the direct simulation Monte Carlo (DSMC) method, with the Fowler–Nordheim equation to calculate the ionic current density during the vacuum field emissions effect for the micro-plasma simulation.The incorporation of the Fowler–Nordheim model avoids the addition of an exponential increase in computational power requirements for a DSMC simulation. Instead of introducing new electrons and ions as equivalent particles into the system, the existing DSMC gas particles in the cells are accelerated. Through this, a computationally lightweight alternative for micro-scale plasma simulations utilising the dsmcFoam+ solver is achieved, which can be tailored to the thrust requirements of a particular mission.

Two-dimensional metamaterials as meta-foams for optimized surface-enhanced solar steam generation

We report on a new class of metamaterials, which consists of meta-foams, optimized for high performance in enhanced solar steam generation. The design of these meta-foams involves precise dimensional control of a periodic two-dimensional micro-pore array. Proof-of-concept of meta-foams efficiency is demonstrated using two fabrication technologies. The first one involves microscale plasma etching onto a nanostructured black silicon substrate. As an alternative low-cost technique, we also use 3D printing of a graphene-containing polymer material. The experimental validation shows that the best evaporation rate reaches 1.34 kg/(h·m2) under 1 sun illumination, in open-air conditions under normal temperature and relative humidity conditions of 20 °C and 58%, an unmatched value so far under similar conditions, while the theoretical limit is estimated at 1.5 kg/(h·m2). This corresponding to a 89% conversion efficiency. Experimental data concur well with the predicted performance obtained by numerical simulations. The proposed model simultaneously accounts for both heat and mass transfer, including photothermal conversion and water phase change, to guide the optimization towards the maximization of the evaporation rate, an important figure of merit in many applications, including solar heat harvesting and solar water purification.

우주날씨 관측을 위한 큐브위성 도요샛 임무

The Small Scale magNetospheric and Ionospheric Plasma Experiment (SNIPE)’s scientific goal is to observe spatial and temporal variations of the micro-scale plasma structures on the topside ionosphere. The four 6U CubeSats (~10 kg) will be launched into a polar orbit at ~500 km. The distances of each satellite will be controlled from 10 km to more than ~1,000 km by the formation flying algorithm. The SNIPE mission is equipped with identical scientific instruments, Solid-State Telescopes(SST), Magnetometers(Mag), and Langmuir Probes(LP). All the payloads have a high temporal resolution (sampling rates of about 10 Hz). Iridium communication modules provide an opportunity to upload emergency commands to change operational modes when geomagnetic storms occur. SNIPE’s observations of the dimensions, occurrence rates, amplitudes, and spatiotemporal evolution of polar cap patches, field-aligned currents (FAC), radiation belt microbursts, and equatorial and mid-latitude plasma blobs and bubbles will determine their significance to the solar wind-magnetosphere-ionosphere interaction and quantify their impact on space weather. The formation flying CubeSat constellation, the SNIPE mission, will be launched by Soyuz-2 at Baikonur Cosmodrome in 2023.

Engineered Membranes for Residual Cell Trapping on Microfluidic Blood Plasma Separation Systems: A Comparison between Porous and Nanofibrous Membranes.

Blood-based clinical diagnostics require challenging limit-of-detection for low abundance, circulating molecules in plasma. Micro-scale blood plasma separation (BPS) has achieved remarkable results in terms of plasma yield or purity, but rarely achieving both at the same time. Here, we proposed the first use of electrospun polylactic-acid (PLA) membranes as filters to remove residual cell population from continuous hydrodynamic-BPS devices. The membranes hydrophilicity was improved by adopting a wet chemistry approach via surface aminolysis as demonstrated through Fourier Transform Infrared Spectroscopy and Water Contact Angle analysis. The usability of PLA-membranes was assessed through degradation measurements at extreme pH values. Plasma purity and hemolysis were evaluated on plasma samples with residual red blood cell content (1, 3, 5% hematocrit) corresponding to output from existing hydrodynamic BPS systems. Commercially available membranes for BPS were used as benchmark. Results highlighted that the electrospun membranes are suitable for downstream residual cell removal from blood, permitting the collection of up to 2 mL of pure and low-hemolyzed plasma. Fluorometric DNA quantification revealed that electrospun membranes did not significantly affect the concentration of circulating DNA. PLA-based electrospun membranes can be combined with hydrodynamic BPS in order to achieve high volume plasma separation at over 99% plasma purity.

Evaluating MHD parameters of relativistic shock waves with particle-in-cell modeling

Relativistic plasma outflows are observed in gamma-ray burst sources, jets of active galactic nuclei, pulsar wind nebulae and supernovae explosions. Magnetohydrodynamical (MHD) shock waves inevitably result from interactions of such relativistic outflows with the ambient interstellar matter. The widely used single-fluid MHD description of relativistic shock waves is the main tool to study the global structure of such objects. However, to justify the validity of the global MHD models and to interpret the observed emission spectra of space objects with relativistic shocks, a kinetic description of electrons, positrons, and ions at microscales is needed. We model a plane relativistic shock propagating transverse to a regular magnetic field in the electron-ion plasmas with imposed turbulent fluctuations in the shock upstream. Namely we study the effect of the micro-scale plasma processes on macroscopic parameters of the mildly-relativistic shocks as the adiabatic index of the relativistic fluid in the shock downstream. The adiabatic index is a macroscopic parameter of the single-fluid MHD models commonly used for shock modeling at much longer hydrodynamical scales and it is especially important for the MHD modeling of the mildly-relativistic shocks.

Evolution and observational signatures of the cosmic ray electron spectrum in SN 1006

ABSTRACT Supernova remnants (SNRs) are believed to be the source of Galactic cosmic rays (CRs). SNR shocks accelerate CR protons and electrons which reveal key insights into the non-thermal physics by means of their synchrotron and γ-ray emission. The remnant SN 1006 is an ideal particle acceleration laboratory because it is observed across all electromagnetic wavelengths from radio to γ-rays. We perform 3D magnetohydrodynamics (MHD) simulations where we include CR protons and follow the CR electron spectrum. By matching the observed morphology and non-thermal spectrum of SN 1006 in radio, X-rays, and γ-rays, we gain new insight into CR electron acceleration and magnetic field amplification. (1) We show that a mixed leptonic–hadronic model is responsible for the γ-ray radiation: while leptonic inverse-Compton emission and hadronic pion-decay emission contribute equally at GeV energies observed by Fermi, TeV energies observed by imaging air Cherenkov telescopes are hadronically dominated. (2) We show that quasi-parallel acceleration (i.e. when the shock propagates at a narrow angle to the upstream magnetic field) is preferred for CR electrons and that the electron acceleration efficiency of radio-emitting GeV electrons at quasi-perpendicular shocks is suppressed at least by a factor ten. This precludes extrapolation of current 1D plasma particle-in-cell simulations of shock acceleration to realistic SNR conditions. (3) To match the radial emission profiles and the γ-ray spectrum, we require a volume-filling, turbulently amplified magnetic field and that the Bell-amplified magnetic field is damped in the immediate post-shock region. Our work connects microscale plasma physics simulations to the scale of SNRs.

Relativistic magnetic reconnection driven by a laser interacting with a micro-scale plasma slab

Magnetic reconnection (MR) is a fundamental plasma process associated with conversion of the magnetic field energy into kinetic plasma energy, which is invoked to explain many non-thermal signatures in astrophysical events. Here we demonstrate that ultrafast relativistic MR in a magnetically dominated regime can be triggered by a readily available (TW-mJ-class) laser interacting with a micro-scale plasma slab. Three-dimensional (3D) particle-in-cell (PIC) simulations show that when the electrons beams excited on both sides of the slab approach the end of the plasma, MR occurs and it gives rise to efficient energy dissipation that leads to the emission of relativistic electron jets with cut-off energy ~12 MeV. The proposed scenario allows for accessing an unprecedented regime of MR in the laboratory, and may lead to experimental studies that can provide insight into open questions such as reconnection rate and particle acceleration in relativistic MR.

Understanding the scaling of electron kinetics in the transition from collisional to collisionless conditions in microscale gas discharges

When gas discharge and plasma devices shrink to the microscale, the electrode distance in the device approaches the mean free path of electrons and they experience few collisions. As microscale gas discharge and plasma devices become more prevalent, the behavior of discharges at these collisionless and near-collisionless conditions need to be understood. In conditions where the characteristic length d is much greater than the mean free path λ (i.e., macroscopic conditions), electron energy distributions (EEDs) and rate coefficients scale with the reduced electric field E/p. However, when d is comparable with or much lower than λ, this E/p scaling breaks. In this work, particle-in-cell/Monte Carlo collision simulations are used to explore the behavior of the EED and subsequent reaction rate coefficients in microscale field emission-driven Townsend discharges for both an atomic (argon) and a molecular (hydrogen) gas. To understand the behavior, a pseudo-analytical model is developed for the spatially integrated EED and rate coefficients in the collisional to collisionless transition regime based on the weighted sum of a fully collisional, two-temperature Maxwellian EED and the ballistic EED. The theory helps clarify the relative contribution of ballistic electrons in these extreme conditions and can be used to more accurately predict when macroscopic E/p scaling fails at the microscale.

Incoherent Scatter Plasma Lines: Observations and Applications

Space plasmas are host to the electrostatic Langmuir waves and a rich range of processes associated with them. Many of such processes that are of interest in micro-scale plasma physics and magnetosphere-ionosphere physics are open to investigation via incoherent scatter plasma lines—i.e., a pair of resonant peaks in the incoherent scatter radar (ISR) spectrum, symmetrically displaced from the radar transmitting frequency by about the plasma frequency, as the signature of Langmuir waves in the ISR spectrum. There now exists a large body of literature devoted to the investigation of a number of topics in ionospheric physics via plasma line theory and observation. It is the goal of this work to provide a comprehensive review of this literature, from the early theoretical works on oscillations in magnetized plasma to the recent advances in plasma line measurements and applications. This review includes detailed theoretical discussions on the intensity and frequency displacement of plasma lines. It reviews the experimental observations of plasma lines enhanced by various sources of energy and discusses the implications of the observations in the context of ionospheric physics. The review also covers the practical aspects of plasma line measurements, from measurement techniques to the applications of plasma lines in estimating the bulk parameters of the ionosphere.

Micro glow plasma for localized nanostructural modification of carbon nanotube forest

This paper reports the localized selective treatment of vertically aligned carbon nanotubes, or CNT forests, for radial size modification of the nanotubes through a micro-scale glow plasma established on the material. An atmospheric-pressure DC glow plasma is shown to be stably sustained on the surface of the CNT forest in argon using micromachined tungsten electrodes with diameters down to 100 μm. Experiments reveal thinning or thickening of the nanotubes under the micro glow depending on the process conditions including discharge current and process time. These thinning and thickening effects in the treated nanotubes are measured to be up to ∼30% and ∼300% in their diameter, respectively, under the tested conditions. The elemental and Raman analyses suggest that the treated region of the CNT forest is pure carbon and maintains a degree of crystallinity. The local plasma treatment process investigated may allow modification of material characteristics in different domains for targeted regions or patterns, potentially aiding custom design of micro-electro-mechanical systems and other emerging devices enabled by the CNT forest.

Atmospheric-pressure glow plasma synthesis of plasmonic and photoluminescent zinc oxide nanocrystals

In this paper, we present a large-volume (non-micro) atmospheric pressure glow plasma capable of rapid, large-scale zinc oxide nanocrystal synthesis and deposition (up to 400 μg/min), whereas in the majority of the literature, nanoparticles are synthesized using micro-scale or filamentary plasmas. The reactor is an RF dielectric barrier discharge with a non-uniform gap spacing. This design encourages pre-ionization during the plasma breakdown, making the discharge uniform over a large volume. The produced zinc oxide nanocrystals typically have diameters ranging from 4 to 15 nm and exhibit photoluminescence at ≈550 nm and localized surface plasmon resonance at ≈1900 cm−1 due to oxygen vacancies. The particle size can be tuned to a degree by varying the gas temperature and the precursor mixing ratio.

High throughput blood plasma separation using a passive PMMA microfluidic device

Since plasma is rich in many biomarkers used in clinical diagnostic experiments, microscale blood plasma separation is a primitive step in most of microfluidic analytical chips. In this paper, a passive microfluidic device for on-chip blood plasma separation based on Zweifach---Fung effect and plasma skimming was designed and fabricated by hot embossing of microchannels on a PMMA substrate and thermal bonding process. Human blood was diluted in various times and injected into the device. The main novelty of the proposed microfluidic device is the design of diffuser-shaped daughter channels. Our results demonstrated that this design exerted a considerable positive influence on the separation efficiency of the passive separator device, and the separation efficiency of 66.6 % was achieved. The optimum purity efficiency of 70 % was achieved for 1:100 dilution times.

Microbubble generation by microplasma in water

A microscale plasma and a spherical microscale bubble were generated by the application of a single pulsed discharge in water with no pre-existing bubble. The microscale corona discharges were created at the tip of a microelectrode by applying a voltage at around −11 kV with a rise time of around 20 ns. The energy inputs for microplasma generation were controlled by varying the durations of the discharges from nanoseconds to microseconds. Two different energy inputs of 103 and 0.5 mJ were studied in detail and the differences in the microplasma-generated microbubbles, such as the maximum radii, numbers of oscillations and durations of the bubble were observed. These microbubbles were visualized using a microscope based optical system with two different high speed cameras. Images of the discharges were captured by a nanosecond gated intensified charge-coupled device (CCD) camera, and the microbubbles' dynamics were recorded by a million-frame-per-second CCD video camera. A Rayleigh–Plesset (RP) model considering both condensable (water vapour) and incondensable (H2 and O2) gases in the microbubble predicts the bubbles' dynamics accurately. Comparisons of the experimental results and the RP models allow estimation of the thermodynamic states of the microplasmas and microbubbles. The energies in the microbubbles are analysed quantitatively from the model and rough approximations for energy dissipation and the energy of the microplasma are made. The microplasma energy can be significantly less than the applied energy input. Such low initiation energy is the reason that the size of microplasmas is at the micron scale and all microplasmas are confined in a spherical microbubble. All the microbubbles reported in this paper are spherical. The low energy also provides conditions for non-equilibrium plasmas in liquid.

Metamaterials for remote generation of spatially controllable two dimensional array of microplasma.

Since the initial demonstration of negative refraction and cloaking using metamaterials, there has been enormous interest and progress in making practical devices based on metamaterials such as electrically small antennas, absorbers, modulators, detectors etc that span over a wide range of electromagnetic spectrum covering microwave, terahertz, infrared (IR) and optical wavelengths. We present metamaterial as an active substrate where each unit cell serves as an element for generation of plasma, the fourth state of matter. Sub-wavelength localization of incident electromagnetic wave energy, one of the most interesting properties of metamaterials is employed here for generating high electric field to ignite and sustain microscale plasmas. Frequency selective nature of the metamaterial unit cells make it possible to generate spatially localized microplasma in a large array using multiple resonators. A dual resonator topology is shown for the demonstration. Since microwave energy couples to the metamaterial through free space, the proposed approach is naturally wireless. Such spatially controllable microplasma arrays provide a fundamentally new material system for future investigations in novel applications, e.g. nonlinear metamaterials.

Microbubbles Enhanced Synthetic Phorbol Ester Degradation by Ozonolysis

A phorbol-12-myristate-13-acetate (TPA) is a synthetic analogue of phorbol ester (PE), a natural toxic compound of Euphorbiaceae plant. The oil extracted from plants of this family is useful source for primarily biofuel. However this oil might also be used as a foodstuff due to its significant nutrition content. The limitations for utilizing the oil as a foodstuff are mainly due to a toxicity of PE. Currently, a majority of PE detoxification processes are expensive as include multi steps alcohol extraction sequence. Ozone is considered as a strong oxidative agent. It reacts with PE by attacking the carbon-carbon double bond of PE. This modification of PE molecular structure yields a non toxic ester with high lipid content. This report presents data on development of simple and cheap PE detoxification process with water application as a buffer and ozone as reactive component. The core of this new technique is an application for a new microscale plasma unit to ozone production and the technology permits ozone injection to the water-TPA mixture in form of microbubbles. The efficacy of a heterogeneous process depends on the diffusion coefficient which can be controlled by contact time and interfacial area. The low velocity of rising microbubbles and high surface to volume ratio allow efficient mass transfer to be achieved during the process. Direct injection of ozone is the most efficient way to process with such highly reactive and short lived chemical. Data on the plasma unit behavior are presented and the influence of gas oscillation technology on the microbubble production mechanism has been discussed. Data on overall process efficacy for TPA degradation is shown.

Surface and volume effects in micro-scale plasma evolution

Micro-scale plasmas are extremely interesting due to the spectrum of applications potentially feasible for these small scale plasmas. Due to the small physical size and short temporal scales, simulations can provide complementary and insightful tools to help understand the underlying physical processes. The present paper discusses a numerical model coupling the plasma, metastable species and gas dynamics in atmospheric microcavities in helium at atmospheric pressure. The self-consistent and time-dependant model is described with emphasis on terms involved in the close coupling among species (plasma, metastable and gas) and the applied field – both electric and magnetic fields. The microplasmas are studied from an initial cloud and transients are particularly important in the evolution. Gas heating, neutral depletion initiation and electrohydrodynamic effects are observed, highlighting the interaction between neutral gas and plasma species in governing the microplasmas. The crucial effects of the applied magnetic field and secondary emission are discussed – and surface and volume effects are compared in terms of spatial and temporal evolutions of the plasma and gas dynamics in atmospheric microplasmas.

Nano and micro-scale fluid and plasma dynamics: present and future applications

In this letter, we illustrate the importance of fluid dynamics research by considering two particular areas of study: nano- and micro-scale fluid and plasma dynamics. We show how improved scientific knowledge of nano- and micro-fluid dynamics can significantly enhance our future. Application is also discussed regarding environmental aspects.

Micro-scale blood plasma separation: from acoustophoresis to egg-beaters

Plasma is a rich mine of various biomarkers including proteins, metabolites and circulating nucleic acids. The diagnostic and therapeutic potential of these analytes has been quite recently uncovered, and the number of plasma biomarkers will still be growing in the coming years. A significant part of the blood plasma preparation is still handled manually, off-chip, via centrifugation or filtration. These batch methods have variable waiting times, and are often performed under non-reproducible conditions that may impair the collection of analytes of interest, with variable degradation. The development of miniaturised modules capable of automated and reproducible blood plasma separation would aid in the translation of lab-on-a-chip devices to the clinical market. Here we propose a systematic review of major plasma analytes and target applications, alongside existing solutions for micro-scale blood plasma extraction, focusing on the approaches that have been biologically validated for specific applications.