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Comparison of the standard differencing with the exponential differencing for the FDTD method in lossy media
摘要： This paper compares the standard and exponential differencing's on time used with the FDTD method in such lossy media as conducting media and plasma media. It is shown that the performances of the two differencing's are quite close, concerning both the accuracy of the computed results and the domain of validity of the FDTD method in lossy media. There is no particular advantage nor drawback in using one differencing in place of the other, they can be used indifferently in FDTD calculations.
关键词： plasmas,conducting materials,FDTD methods
更新于2025-09-23 15:22:29
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Frequency variations of solar radio zebras and their power-law spectra
摘要： Context. During solar ?ares several types of radio bursts are observed. The ?ne striped structures of the type IV solar radio bursts are called zebras. Analyzing them provides important information about the plasma parameters of their radio sources. We present a new analysis of zebras. Aims. Power spectra of the frequency variations of zebras are computed to estimate the spectra of the plasma density variations in radio zebra sources. Methods. Frequency variations of zebra lines and the high-frequency boundary of the whole radio burst were determined with and without the frequency ?tting. The computed time dependencies of these variations were analyzed with the Fourier method. Results. First, we computed the variation spectrum of the high-frequency boundary of the whole radio burst, which is composed of several zebra patterns. This power spectrum has a power-law form with a power-law index –1.65. Then, we selected three well-de?ned zebra-lines in three di?erent zebra patterns and computed the spectra of their frequency variations. The power-law indices in these cases are found to be in the interval between –1.61 and –1.75. Finally, assuming that the zebra-line frequency is generated on the upper-hybrid frequency and that the plasma frequency ωpe is much higher than the electron-cyclotron frequency ωce, the Fourier power spectra are interpreted to be those of the electron plasma density in zebra radio sources.
关键词： plasmas,Sun: radio radiation,turbulence
更新于2025-09-23 15:22:29
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Photophoretic force measurement on microparticles in binary complex plasmas
摘要： This article presents a method to measure the photophoretic force on microparticles in complex plasmas. A laser heating setup is used to increase the kinetic temperatures of binary mixtures composed of melamine-formaldehyde (MF) and silica (SiO2) particles. The temperature gain of both particle species due to the additional thermal reservoir is compared to a laser force model. Contributions of radiation pressure and photophoretic forces are determined through a variation of neutral gas pressure and application of Lorenz-Mie theory. The photophoretic force is found to be significant for MF particles at typical conditions in complex plasma experiments.
关键词： photophoretic force,microparticles,radiation pressure,complex plasmas,Lorenz-Mie theory,binary mixtures,laser heating
更新于2025-09-23 15:22:29
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Flexible electrochromic tungsten/iron mixed oxide films synthesized by an atmospheric pressure plasma jet
摘要： Flexible electrochromic organo-tungsten- iron oxide (WFexOyCz) films are rapidly deposited onto flexible (60 Ω/□ polyethylene terephthalate/indium tin oxide; PET/ITO) substrates by a low temperature-atmospheric pressure-plasma polymerization method with an atmospheric pressure plasma jet (APPJ) for a short exposed duration of 48 s. The precursor vapors of tungsten hexacarbonyl [W(CO)6] and biscyclopentadienyl iron [ferrocene; Fe(C5H5)2] are mixed with O2 gases at various gas flow rates, injected into air plasma jet and sprayed onto PET/ITO substrates at room temperature (~23oC) and at atmospheric pressure (1.013 × 105 Pa). Flexible electrochromic WFexOyCz films are synthesized with a specific addition of oxygen gases with superior lithium electrochromic properties as demonstrated by a potential sweep alternating between -1 V and 2 V at a scan rate of 40 mV/s in a 1 M LiClO4-propylene carbonate electrolyte. With amorphous WFexOyCz films produced with an APPJ by adding oxygen gases at a specific flow rate of 0.5 sccm, a high value in oxygen deficiency up to 0.189 allows more Li+ ions to intercalate into and deintercalate out of the film. Significant coloration and bleaching are proven by the high values in optical transmittance modulation (ΔT) of up to 70.3%, optical density (ΔOD) up to 0.77 and color efficiency (η) up to 61.3 cm2/C, at a wavelength of 800 nm, respectively.
关键词： Electrochromic materials,Iron oxide,Tungsten oxide,Flexible electrochromic film,Atmospheric pressure plasmas,Plasma polymerization
更新于2025-09-23 15:21:21
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Noise mitigation methods for ion detectors operating with a direct view of high temperature plasmas
摘要： We have developed an ion current measurement instrument with a direct view of a plasma that reduces the particle and radiation-induced noise current it detects by over three orders of magnitude, from tens of microamps to tens of nanoamps. This is accomplished using electric ?elds, magnetic ?elds, and physical shielding that limit the ?ux of particles and radiation into the instrument and suppress the secondary electrons produced within it by particle and radiation impact. Operation of this detector in various con?gurations, without an ion beam, has allowed identi?cation of the sources of noise current. In our experimental setup, the largest noise contributors were found to be plasma ions and photoelectric emission due to UV radiation.
关键词： high temperature plasmas,magnetic fields,electric fields,ion detectors,physical shielding,noise mitigation
更新于2025-09-23 15:21:21
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Treatment of graphene films in the early and late afterglows of N2 plasmas: comparison of the defect generation and N-incorporation dynamics
摘要： Graphene films grown on copper substrate by chemical vapor deposition were exposed to the flowing afterglow of a reduced-pressure N2 plasma sustained by microwave electromagnetic fields (surface-wave plasma). Two set of conditions were examined by controlling the gas flow rate: the late afterglow (LA) characterized by high number densities of reactive N atoms and the early afterglow (EA) in which significant populations of metastable N2(A) states and positive ions (N2+ and N4+) coexist with plasma-generated N atoms. LA treatments of graphene films show monotonous and steady incorporation of nitrogen atoms along with very low damage. However, given the very mild LA treatment conditions, a large part of the N atoms remains weakly bonded to the graphene surface; a feature ascribed to the plasma-induced functionalization of airborne hydrocarbon contaminants. In such conditions, graphitic inclusion of plasma-generated N atoms is limited to native defect sites. On the other hand, the presence of highly energetic species in the EA induces significant damage combined with much higher N-incorporation. Detailed Raman analysis of EA-treated samples further reveals a transition from vacancy-type defects to much larger multi-vacancies with increasing treatment time. This complete set of data indicates that, through a judicious control of the populations of reactive N atoms, metastable N2(A) states, and positive ions (N2+ and N4+), the flowing afterglow of microwave N2 plasmas represents a highly promising tool for precise, post-growth tuning of the defect generation and N-incorporation dynamics in graphene films.
关键词： Microwave plasmas,Plasma-graphene interactions,Flowing afterglows,Plasma-induced modification of materials and nanomaterials
更新于2025-09-23 15:21:21
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In-fiber Dispersion Compensated Polarizer and Mode-locked Fiber Laser Application
摘要： Microplasma jets propagating in a helium flow surrounded by open air at ambient temperature have attracted the attention of many researchers for their putative ability to deliver high fluxes of reactive oxygen and nitrogen species to a target situated some centimeters away. This is of particular interest in biomedical applications. In this paper, we use Schlieren images to show that ignition of the plasma jet causes a reduction in the length of the laminar zone of the helium flow.
关键词： Atmospheric-pressure plasmas,hydrodynamics
更新于2025-09-23 15:21:01
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Analysis of alloy and solar cells with double-pulse calibration-free laser-induced breakdown spectroscopy
摘要： We applied variant of calibration free laser induced Breakdown Spectroscopy (CF-LIBS) approach for the compositional analysis of standard Gd/Ge/Si alloy and solar cells. The double pulse laser induced plasma was produced on the sample surface and the emission spectra were recorded at optimized interpulse delay and energy ratio. The Plasma temperature, determined using Boltzmann plot, was used to determine the concentration of all species present in a sample. The results are compared with reference values as well as conventional CF-LIBS results, which show that conventional and variant CF-LIBS results are similar and in close agreement to reference values. It is worth mention that the variant CF-LIBS results, but the approach is simpler and faster. Therefore, this approach was applied to three unknown polycrystalline silicon solar cells, which yield Al, C, Ca, Fe, In, Ti, Sb and Sn in the parts per million (ppm). This approach can potentially be applied for real-time trace monitoring in manufacturing processes of photovoltaic devices where conversion e?ciency depends strongly on impurities’ concentration.
关键词： Alloy and solar cells,Double pulse LIBS,Laser induced plasmas,Quantitative elemental analysis,Calibration free LIBS,Plasma parameters
更新于2025-09-23 15:21:01
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Laser-produced plasmas as drivers of laboratory collisionless quasi-parallel shocks
摘要： The creation of a repeatable collisionless quasi-parallel shock in the laboratory would provide a valuable platform for experimental studies of space and astrophysical shocks. However, conducting such an experiment presents substantial challenges. Scaling the results of hybrid simulations of quasi-parallel shock formation to the laboratory highlights the experimentally demanding combination of dense, fast, and magnetized background and driver plasmas required. One possible driver for such experiments is high-energy laser-produced plasmas (LPPs). Preliminary experiments at the University of California, Los Angeles, have explored LPPs as drivers of quasi-parallel shocks by combining the Phoenix Laser Laboratory [Niemann et al., J. Instrum. 7, P03010 (2012)] with a large plasma device [Gekelman et al., Rev. Sci. Instrum. 87, 025105 (2016)]. Beam instabilities and waves characteristic of the early stages of shock formation are observed, but spatial dispersion of the laser-produced plasma prematurely terminates the process. This result is illustrated by experimental measurements and Monte Carlo calculations of LPP density dispersion. The experimentally validated Monte Carlo model is then applied to evaluate several possible approaches to mitigating LPP dispersion in future experiments.
关键词： beam instabilities,collisionless quasi-parallel shocks,plasma dispersion,laser-produced plasmas,Monte Carlo calculations
更新于2025-09-23 15:21:01
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Absolute stimulated Raman side scatter in direct-drive laser-produced plasmas
摘要： Production of suprathermal electrons by stimulated Raman scattering (SRS) is a principal concern for contemporary direct-drive inertial confinement fusion experiments at the National Ignition Facility and similar systems since such electrons penetrate and preheat the target core, preventing efficient implosion. The higher temperatures and longer scale lengths in these experiments favor SRS over two-plasmon decay, which predominated in earlier experiments. In particular, current experiments are expected to exceed the threshold for absolute Raman side scatter, which would then dominate the interaction since it grows temporally until saturated by nonlinear mechanisms such as hot-electron production. Until recently, analyses of SRS side scatter have treated the case of a single laser beam incident on a plasma, but the direct-drive approach to laser fusion employs a multitude of beams to drive the implosion. Here, we present an analysis that can be applied to an arbitrary number of beams with varied angles of incidence and polarizations. In the case of a single beam, it allows a physically motivated derivation and verification of an analytic threshold formula. In the general case of multiple beams and arbitrary orientation and polarizations, the threshold is found by numerical integration of a set of first-order linear partial differential equations.
关键词： direct-drive,stimulated Raman scattering,inertial confinement fusion,laser-produced plasmas,suprathermal electrons
更新于2025-09-23 15:21:01