Plasma Absorption Research Articles

Synthesis Gas Conversion over Rh-Based Catalysts Promoted by Fe and Mn

Rh/SiO2 catalysts promoted with Fe and Mn are selective for synthesis gas conversion to oxygenates and light hydrocarbons at 523 K and 580 psi. Selective anchoring of Fe and Mn species on Rh nanoparticles was achieved by controlled surface reactions and was evidenced by ultraviolet–visible absorption spectroscopy, scanning transmission electron microscopy, and inductively coupled plasma absorption emission spectroscopy. The interaction between Rh and Fe promotes the selective production of ethanol through hydrogenation of acetaldehyde and enhances the selectivity toward C2 oxygenates, which include ethanol and acetaldehyde. The interaction between Rh and Mn increases the overall reaction rate and the selectivity toward C2+ hydrocarbons. The combination of Fe and Mn on Rh/SiO2 results in trimetallic Rh-Fe-Mn catalysts that surpass the performance of their bimetallic counterparts. The highest selectivities toward ethanol (36.9%) and C2 oxygenates (39.6%) were achieved over the Rh-Fe-Mn ternary system with a...

Inverse Bremsstrahlung absorption in under-dense plasma with Kappa distributed electrons

Absorption and averaged energy absorption are studied in a plasma system comprising of Kappa distributed electrons. Electrons temperature and Kappa parameter influences on the absorption and the averaged energy absorption. The increase in the electron kappa parameters causes the absorption to increase. Results may be helpful, in understanding the absorption phenomena in laser plasma interaction in the presence of Kappa distributed electrons.

Increase in the energy absorption of pulsed plasma by the formation of tungsten nanostructure

The synergistic effects of steady-state and pulsed plasma irradiation to material have been investigated in the device NAGDIS-PG (NAGoya DIvertor Simulator with Plasma Gun). The duration of the pulsed plasma was ~0.25 ms. To investigate the pulsed plasma heat load on the materials, we developed a temperature measurement system using radiation from the sample in a high time resolution. The heat deposited in response to the transient plasma on a tungsten surface was revealed by using this system. When the nanostructures were formed by helium plasma irradiation, the temperature increase on the bulk sample was enhanced. The result suggested that the amount of absorbed energy on the surface was increased by the formation of nanostructures. The possible mechanisms causing the phenomena are discussed with the calculation of a sample temperature in response to the transient heat load.

Momentum transfer cross-section for ion scattering on dust particles

The momentum transfer cross-section for ion scattering on charged dust particles is calculated using different models of the interaction potential. The results are applied to estimate the ion drag force for typical conditions used in the experiments with complex (dusty) plasmas. The influence of two factors on the ion-dust collision cross section is discussed. The first is related to the nonlinear screening effects associated with the strong coupling between ions and dust particles. The second factor is the plasma absorption by dust particles. It is shown that the nonlinear screening effects are of importance and affect both the momentum transfer cross-section and the ion drag force. On the other hand, the absorption process affects the scattering momentum transfer cross-section only at low collision energies and thus can be neglected in estimating the ion drag force.

Attenuation of low-frequency electromagnetic wave in the thin sheath enveloping a high-speed vehicle upon re-entry

Low-frequency (LF) electromagnetic (EM) waves are suggested as potentially solving “radio blackout” caused by a plasma sheath enveloping a high-speed vehicle on re-entry. However, the traditional plasma absorption theory neglects the fact that the plasma sheath is electrically small compared to LF EM wavelengths. To understand clearly the attenuation of such waves through the plasma sheath, different attenuation mechanisms for the electric field (SE) and magnetic field (SH) were studied using the equivalent circuit approach. Analytical expressions were derived by modeling the plasma sheath as a spherical shell, and numerical simulations were performed to validate the effectiveness of the expressions. SE and SH are calculated for various plasma parameter settings; the EM wave attenuations obtained from plasma absorption theory are used for comparison. Results show that, instead of SE and SH being equal in the plasma absorption theory, SE and SH are no longer the same for electrically small sizes. Whereas |SH| is close to that from plasma absorption theory, |SE| is much higher. Further analysis shows that |SH| is a function of the ratio of electron density (ne) and collision frequency (ve) and increases with increasing ne/ve. Numerical simulations with radio-attenuation-measurement-C-like vehicle's plasma sheath parameters are performed and the results show that the magnetic field attenuation in the front part of the vehicle is much lower than in the rear. So it is suggested to place the magnetic loop antenna in the very front part of the vehicle. Finally, SH at different frequencies are calculated using plasma sheath parameter values simulating the re-entry phase of a radio-attenuation measurement-C vehicle and results show that such a vehicle might overcome radio blackout during the entire re-entry phase if systems operating below 3 MHz and above the L-band are combined with a lower-frequency system working below Earth's ionosphere and a higher-frequency system working above the Earth's ionosphere.

Stimulated Raman scattering in the relativistic regime in near-critical plasmas.

Interaction of a high-intensity short laser pulse with near-critical plasmas allows us to achieve extremely high coupling efficiency and transfer laser energy to energetic ions. One-dimensional particle-in-cell simulations are considered to detail the processes involved in the energy transfer. A confrontation of the numerical results with the theory highlights a key role played by the process of stimulated Raman scattering in the relativistic regime. The interaction of a 1 ps laser pulse (I∼6×10^{18}Wcm^{-2} with an undercritical (0.5n_{c}) homogeneous plasma leads to a very high plasma absorption reaching 68% of the laser pulse energy. This permits a homogeneous electron heating all along the plasma and an efficient ion acceleration at the plasma edges and in cavities.

Parametric Instabilities During High Power Helicon Wave Injection on DIII-D

High power helicon (whistler) waves at a frequency of 0.47 GHz are being considered for efficient off-axis current generation in high performance DIII-D plasmas and in K-Star [3]. The need for deploying helicon waves for current profile control has been noted in previous publications since penetration to the core of reactor grade plasmas is easier than with lower hybrid slow waves (LHCD) which suffer from accessibility limitations and strong electron Landau absorption in fusion grade high temperature plasmas. In this work we show that under typical experimental conditions in present day tokamaks with 1 MW of RF power coupled per antenna, the associated perpendicular electric fields of the order of 40 kV/m can drive strong parametric decay instabilities near the lower hybrid layer. The EXB and polarization drift velocities which are the dominant driver of the PDI can be comparable to the speed of sound in the outer plasma layers, a key measure of driving PDI instabilities. Here we calculate growth rates and convective thresholds for PDIs, and we find that decay waves into hot ion lower hybrid waves and ion cyclotron quasi modes dominate in the vicinity of the lower hybrid layer, possibly leading to pump depletion. Such instabilities in future reactor grade high temperature plasmas are less likely.

Alfven wave absorption in dissipative plasma

We consider nonlinear absorption of Alfven waves due to dissipative effects in plasma and relaxation of temperatures of electrons and ions. This study is based on an exact solution of the equations of two-fluid electromagnetic hydrodynamics (EMHD) of plasma. It is shown that in order to study the decay of Alfven waves, it suffices to examine the behavior of their amplitudes whose evolution is described by a system of ordinary differential equations (ODEs) obtained in this paper. On finite time intervals, the system of equations on the amplitudes is studied numerically, while asymptotic integration (the Hartman-Grobman theorem) is used to examine its large-time behavior.

Spatiotemporal distributions of plasma and optical field during the interaction between ultra-short laser pulses and water nanodroplets

The transient changes of free electron density distribution and light field intensity during the interaction between the femtosecond Gaussian laser pulses and millimeter scale water droplets are studied. Based on the nonlinear Maxwell's equations and the ionization rate equation, a transient coupled model is proposed to describe the laser plasma produced in water droplet. The changes of electron density and light field with time are obtained by the finite element method. The calculation results show that the laser induced breakdown threshold in the droplet is about 2 TW/cm2, one quarter of that in a boundaryless water medium under the same condition. We find that the region of plasma generated in the droplet will move along the laser direction at first, however, when the incident laser intensity becomes larger, it will move in the direction opposite to the laser beam propagation and the plasma shielded effect becomes more obvious. The laser beam converged by the droplet focuses outside the droplet, and its power density is five times larger than that of the incident laser. There happen the laser pulse duration compression and waveform distortion at the focus point due to the plasma absorption, and the absorption energy increases with the laser intensity increasing and reaches a saturation finally. We expect the model and calculation results to be able to be used for the study of laser pulse propagation in cloud or rain, the precision control of droplet by laser or eye surgery by laser, and other laser technology applications.

Mechanisms of micro-groove formation on single-crystal diamond by a nanosecond pulsed laser

Micro-grooves were machined onto a single-crystal diamond surface by laser irradiation with a nanosecond pulse, and the resulting damage was investigated. The causes of four different forms of damage have been identified and examined; cracking, ripple formation, groove shape deformation and debris deposition. Cracking is caused by a rapid temperature change; ripples by interference of the laser reflected from the groove walls; groove shape deformation by enhanced absorption of the laser-induced plasma; deposited ablation debris by two different ablation regimes. Cracking and shape deformation is reduced at the center of the groove, which is very smooth and ripple-free for line irradiations using a single pass. These results provide useful information for reducing the laser-induced damage in diamond and creating damage-free micro-grooved diamond cutting tools.

Transdermal Adhesive Patches Loaded with Ketoprofen Evaluated by Dynamic Detection of Percutaneous Absorption

Topical delivery has many benefits toward NSAIDs administration, and the best-selling transdermal preparation in 2015 was the NSAID patch MOHRUS®. Herein, we report a ketoprofen adhesive patch (KAP) and evaluate the penetration and absorption compared to MOHRUS®. Microdialysis sampling technique was applied to determine drug penetration in the dermis and subcutaneous tissue. Simultaneously, blood samples were withdrawn over time to obtain the drug absorption in plasma. The ketoprofen concentrations in the dermis, subcutaneous tissue, and plasma were compared with the commercially available patch (MOHRUS®). Based on the detection, pharmacokinetic parameters including Cmax, Tmax, and AUC0-8h were determined for both the formulations. No significant differences were found in the dermis, subcutaneous tissue, and plasma in rats according to the bioequivalence assessment. The KAP demonstrated multiple therapeutic advantages including the controlled drug release and the sustained drug concentration in the skin as well as in plasma. The pharmacokinetic study coupled with microdialysis sampling provided an effective strategy to evaluate transdermal delivery.

Laser ablation of a Cu–Al–Ni combinatorial thin film library: analysis of crater morphology and geometry

The conventional approach to studying laser–workpiece interaction in the ablation regime is to vary beam parameters used on a specimen of uniform chemical composition. The current work instead utilises a pulsed laser beam of constant parameters to ablate a ternary alloy thin film where the chemical composition of the sample varies continuously; this will enhance the understanding of pulsed laser ablation by means of a combinatorial approach. The analysis of the studied workpiece (a Cu–Al–Ni thin film deposited by magnetron sputtering) revealed the presence of both compositional and morphological gradients. Variation in the surface morphology was correlated with aluminium content. Single-pulse laser ablation (Nd:YAG, 1064 nm, 30 ns, 4.54 J/cm2) of the surface resulted in different crater features, geometry and volume. Two characteristic regions separated by a transition zone were identified based on the craters’ geometrical and morphological characteristics. The ablated volume increases with the atomic percentage of aluminium up to a threshold value of roughly 30 at.% after which the ablation volume slowly declines. This phenomenon may be attributed to plasma absorption and heat dissipation in the thin film.

Hybrid simulations of solenoidal radio-frequency inductively coupled hydrogen discharges at low pressures

In this article, we have described a radio-frequency (RF) inductively coupled H2 plasma using a hybrid computational model, incorporating the Maxwell equations and the linear part of the electron Boltzmann equation into global model equations. This report focuses on the effects of RF frequency, gas pressure, and coil current on the spatial profiles of the induced electric field and plasma absorption power density. The plasma parameters, i.e., plasma density, electron temperature, density of negative ion, electronegativity, densities of neutral species, and dissociation degree of H2, as a function of absorption power, are evaluated at different gas pressures. The simulation results show that the utilization efficiency of the RF source characterized by the coupling efficiency of the RF electric field and power to the plasma can be significantly improved at the low RF frequency, gas pressure, and coil current, due to a low plasma density in these cases. The densities of vibrational states of H2 first rapidly increase with increasing absorption power and then tend to saturate. This is because the rapidly increased dissociation degree of H2 with increasing absorption power somewhat suppresses the increase of the vibrational states of H2, thus inhibiting the increase of the H−. The effects of absorption power on the utilization efficiency of the RF source and the production of the vibrational states of H2 should be considered when setting a value of the coil current. To validate the model simulations, the calculated electron density and temperature are compared with experimental measurements, and a reasonable agreement is achieved.

Laser wavelength effect on nanosecond laser light reflection in ablation of metals

Reflection of nanosecond laser pulses with different wavelengths (1.06 and 0.69 µm) in ablation of titanium in air is studied experimentally. The laser wavelength effect on reflection is essential at low laser fluence values. However, it becomes negligible for laser fluence values by about an order of magnitude higher than the plasma ignition threshold. We speculate that the disappearance of the wavelength effect is explained by counter-acting processes of the laser light absorption in plasma, which increases with laser wavelength, and absorption in the surface layer, which decreases with increasing laser wavelength.

Pharmacokinetics, toxicity, and cytochrome P450 modulatory activity of plumbagin.

BackgroundThe antimalarial activity of plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone), a naturally occurring naphthoquinone widely distributed in the Plumbaginaceae family has previously been demonstrated in vitro (good activity) and in vivo (weak activity). The aim of the study was to investigate the pharmacokinetic profile following a single oral dosing to explain inconsistency of results of the in vitro and in vivo antimalarial activities. In addition, toxicity profiles and potential of modulation of cytochrome P450 enzymes (CYP1A2 and CYP3A11) were also investigated.MethodsThe pharmacokinetics and toxicity of plumbagin were investigated in rats. The propensity of plumbagin to modulate the mRNA expression and activities of the two inducible forms of hepatic drug metabolizing enzyme cytochrome P450 (CYP450), i.e., CYP1A2 and CYP3A11, was investigated using microsomes prepared from mouse livers.ResultsAcute and subacute toxicity tests indicate low toxicity of plumbagin with maximum tolerated doses of 150 (single oral dose) and 25 (daily doses for 28 days) mg/kg body weight, respectively. The pharmacokinetic profile of plumbagin following a single oral dose of 100 mg/kg body weight suggests that delayed absorption and short residence time (median values of time to maximal concentration and elimination half-life = 9.63 and 5.0 h, respectively) in plasma. Plumbagin did not modulate mRNA expression and activities of CYP1A2 and CYP3A11.ConclusionsPlumbagin was well tolerated following oral dose administration in rats. Pharmacokinetic property of this compound may be a limiting factor that explains the weak antimalarial activity of plumbagin observed in animal models. Potential metabolic interaction with co-administered drugs that are metabolized by CYP1A2 or CYP3A11 are unlikely.

Stabilization effect of Weibel modes due to inverse bremsstrahlung absorption in laser fusion plasma using Krook collisions model

In this work, the Weibel instability due to inverse bremsstrahlung absorption in laser fusion plasma has been investigated. The stabilization effect due to the coupling of the self-generated magnetic field by Weibel instability with the laser wave field is explicitly showed. The main result obtained in this work is that the inclusion of self-generated magnetic field due to Weibel instability to the inverse bremsstrahlung absorption causes a stabilizing effect of excited Weibel modes. We found a decrease in the spectral range of Weibel unstable modes. This decrease is accompanied by a reduction of two orders in the growth rate of instability or even stabilization of these modes. It has been shown that the previous analyses of the Weibel instability due to inverse bremsstrahlung have overestimated the values of the generated magnetic fields. Therefore, the generation of magnetic fields by the Weibel instability due to inverse bremsstrahlung should not affect the experiences of an inertial confinement fusion.

Salt efflorescence in historic wooden buildings

Efflorescence and subflorescence are frequent phenomena occurring in buildings of porous inorganic materials such as bricks, stone, and concrete. Since the above phenomena have detrimental effects, they were the subject of detailed physicochemical investigations. Efflorescence on wooden material was commonly observed on collection artefacts treated with preservatives such as inorganic salts or organic pesticides. Occurrence of efflorescence in historical wooden buildings was less studied although it could cause serious conservation concerns. This paper describes an examination of chemical and mineralogical composition of salt efflorescence in wooden buildings. In situ analysis by X-ray fluorescence spectrometry was followed by investigation of plain efflorescence by infrared spectrometry, X-ray diffraction, electron microscopy, and electron probe microanalysis. Quantitative analysis of purified efflorescence was performed by plasma atomic emission spectrometry, ion chromatography and absorption spectrophotometry. In addition, depth-profiling of characteristic ions in wood was performed. The objects of study were a series of log houses of the Sverresborg Trondelag Folk Museum in Trondheim, Norway. It was found that the efflorescence in these buildings includes a series of metal ions, the most abundant being Al3+, Mg2+, Zn2+, K+, Na+, and Fe2+. In addition the ammonium ion is present in a large amount. The single detected anion is sulfate. Actually, the efflorescence consists of a mixture of simple and double sulfate salts of alum and Tutton’s compound types. Identified Tutton’s compounds are mohrite ((NH4)2Fe(SO4)2·6H2O), ammonium zinc sulfate hexahydrate ((NH4)2Zn(SO4)2·6H2O)), and boussingaultite ((NH4)2Mg(SO4)2·6H2O)). Among the alums, both tschermigite (NH4Al(SO4)2·12H2O), and potassium alum (KAl(SO4)2·12H2O)) were detected. The composition of efflorescence suggests that the wooden material was treated with a blend of sulfate salts ((NH4)2SO4, Al2(SO4)3·18H2O, MgSO4·7H2O, FeSO4·7H2O, ZnSO4·7H2O, and Na2SO4·10H2O)) for protection against fire and biological degradation. The efflorescence appeared as a consequence of water leakage through the roof that led to the dissolution of the salts contained in the wood, followed by evaporation and salt crystallization at the surface in the form of double sulfate salts. Although the occurrence of efflorescence in this case was accidental, a natural and more frequent cause of efflorescence could be the deliquescence of inorganic preservatives impregnated in the wood.

Comment on "A doubly curved elliptical crystal spectrometer for the study of localized x-ray absorption in hot plasmas" [Rev. Sci. Instrum. 85, 103114 (2014)

The elliptical spectrometer described by Cahill et al. [Rev. Sci. Instrum. 85, 103114 (2014)] is designed to enable absorption X-ray spectroscopy under circumstances in which the object plasma is, itself, a relatively bright X-ray emitter. An implementation of this design was developed using a doubly curved mica crystal for X-ray dispersion. The geometry of the spectrometer was verified by ray tracing calculations assuming Bragg reflection from mica in the second order. Control of X-ray reflections from other orders was an anticipated challenge and has been attempted by means of filtering and control of the source spectrum. These efforts have been found to be insufficient to allow the spectrometer to operate as designed because of the strong fifth order reflection of source radiation by the mica crystal. Potential solutions are presented that may enable a successful implementation of this novel crystal spectrometer design.

Revealing plasma oscillation in THz spectrum from laser plasma of molecular jet.

Contribution of plasma oscillation to the broadband terahertz (THz) emission is revealed by interacting two-color (ω/2ω) laser pulses with a supersonic jet of nitrogen molecules. Temporal and spectral shifts of THz waves are observed as the plasma density varies. The former owes to the changing refractive index of the THz waves, and the latter correlates to the varying plasma frequency. Simulation of considering photocurrents, plasma oscillation and decaying plasma density explains the broadband THz spectrum and the varying THz spectrum. Plasma oscillation only contributes to THz waves at low plasma density owing to negligible plasma absorption. At the longer medium or higher density, the combining effects of plasma oscillation and absorption results in the observed low-frequency broadband THz spectra.

Role of the Cu-ZrO2 Interfacial Sites for Conversion of Ethanol to Ethyl Acetate and Synthesis of Methanol from CO2 and H2

Well-defined Cu catalysts containing different amounts of zirconia were synthesized by controlled surface reactions (CSRs) and atomic layer deposition methods and studied for the selective conversion of ethanol to ethyl acetate and for methanol synthesis. Selective deposition of ZrO2 on undercoordinated Cu sites or near Cu nanoparticles via the CSR method was evidenced by UV–vis absorption spectroscopy, scanning transmission electron microscopy, and inductively coupled plasma absorption emission spectroscopy. The concentrations of Cu and Cu-ZrO2 interfacial sites were quantified using a combination of subambient CO Fourier transform infrared spectroscopy and reactive N2O chemisorption measurements. The oxidation states of the Cu and ZrO2 species for these catalysts were determined using X-ray absorption near edge structure measurements, showing that these species were present primarily as Cu0 and Zr4+, respectively. It was found that the formation of Cu-ZrO2 interfacial sites increased the turnover freque...