Plasma Absorption Research Articles

Numerical Study on the Influence of the Plasma Properties on the Keyhole Geometry in Laser Beam Welding

Keyhole laser welding is the benchmark for deep-penetration joining processes. It needs high incident laser beam power densities at the workpiece surface to take place. The gaseous phase plays a fundamental role to keep the deep and narrow keyhole cavity open during the process. The plasma created in this process is a mixture of ionized metal vapors and the environmental gas and it develops inside the keyhole (keyhole plasma) and above the workpiece surface (plasma plume). The presence of plasma implicates absorption, scattering, and refraction of laser beam rays. These phenomena alter the power density of the laser beam irradiating the workpiece surface and thus affect the resulting welding process. In this work, a mathematical and numerical model has been developed to calculate the keyhole shape taking into account the plasma absorption effects. The model considers the keyhole walls as the liquid-vapor interface and computes the keyhole geometry applying a local energy balance at this interface. In addition, the model takes into account the multiple reflections effects inside the cavity through an iterative ray-tracing technique, and calculates the absorption mechanism due to inverse Bremsstrahlung for each ray along its segmented path inside the keyhole. Results show the effect of plasma properties on the keyhole shape and depth.

Full-wave 2D modeling of helicons propagation and absorption in thespherical tokamak Globus-M2

Numerical modeling of propagation and absorption of fast waves(helicons) with frequency 200 MHz in 2D inhomogeneous plasma of thespherical tokamak Globus-M2 was carried out with 2D full-wave code. Toroidal effects, poloidal magnetic field and the actual shape of the fluxsurfaces were taken into account. The full wave electric field and RF powerabsorption profiles were computed by solving plasma wave equation withelectron Landau damping term. The modeling demonstrated a fairly highefficiency of helicons absorption in the bulk plasma within a wide range ofexperimental parameters. The waves propagate to the inner regions of theplasma column and are mainly absorbed there; less than 20% of RF energyreturns back to the plasma periphery. Keywords: high temperature plasma, nuclear fusion, tokamak, high frequency plasma waves, helicons, plasma wave equation, full-wave code.\

Full-wave 2D modeling of helicons propagation and absorption in the spherical tokamak Globus-M2

Numerical modeling of propagation and absorption of fast waves (helicons) with frequency 200MHz in 2D inhomogeneous plasma of the spherical tokamak Globus-M2 was carried out with 2D full-wave code. Toroidal effects, poloidal magnetic field and the actual shape of the flux surfaces were taken into account. The full wave electric field and RF power absorption profiles were computed by solving plasma wave equation with electron Landau damping term. The modeling demonstrated a fairly high efficiency of helicons absorption in the bulk plasma within a wide range of experimental parameters. The waves propagate to the inner regions of the plasma column and are mainly absorbed there; less than 20% of RF energy returns back to the plasma periphery. Keywords: high temperature plasma, nuclear fusion, tokamak, high frequency plasma waves, helicons, plasma wave equation, full-wave code.

Полноволновое двумерное моделирование распространения и поглощения геликонов в плазме сферического токамака Глобус-М2

Numerical modeling of propagation and absorption of fast waves (helicons) with frequency 200 MHz in 2D inhomogeneous plasma of the spherical tokamak Globus-M2 was carried out with 2D full-wave code. Toroidal effects, poloidal magnetic field and the actual shape of the flux surfaces were taken into account. The full wave electric field and RF power absorption profiles were computed by solving plasma wave equation with electron Landau damping term. The modeling demonstrated a fairly high efficiency of helicons absorption in the bulk plasma within a wide range of experimental parameters. The waves propagate to the inner regions of the plasma column and are mainly absorbed there; less than 20% of RF energy returns back to the plasma periphery.

Attosecond laser-matter interaction: A short note

The physics of Attosecond laser irradiation with material surface is different compared to femtosecond or longer duration pulses. At this time duration electronic movement takes place. The energy deposition by an attosecond pulse is so quick that the excited region can only respond after the pulse propagates through this region. It is yet to be seen the kind of morphological changes these ultrashort laser pulses can produce. It is important to understand the consequences of such interactions and their implications in the area of materials processing. This article presents a short note on the attosecond laser-matter interaction. A suitable comparison is made with the case of femtosecond and longer duration pulses. It is proposed that in attosecond regime the plasma absorption will be absent. Higher density of free carrier generation in attosecond regime should be generated by inner shell photoionization. Due to more than 10% career transition from valence band to conduction band, the career screening in conduction band should be observed very similar to femtosecond regime.

Human health risk assessment of lead, cadmium, and mercury co-exposure from agricultural soils in the Tuzla Canton (Bosnia and Herzegovina)

The aim of this study was to assess the risk of human exposure to lead (Pb), cadmium (Cd), and mercury (Hg) through agricultural soil by considering both uncertainty and variability in key exposure parameters. For this reason we collected soil samples from 29 locations in the Tuzla Canton (Bosnia and Herzegovina) and measured their metal levels with inductively coupled plasma atomic emission or absorption spectrometry (ICP-AES and ICP-AAS, respectively). The levels of Pb ranged from 13.33 to 1692.33 mg/kg, of Cd from 0.05 to 3.67 mg/kg, and of Hg from 0.02 to 2.73 mg/kg. To estimate cancer and non-cancer risks we used deterministic and semi-probabilistic methods. Lead was found to involve higher health risk than the other two heavy metals. Its hazard index (HI) decreased between population groups (children>women>men) and exposure routes (ingestion>skin contact>inhalation). Our Monte Carlo simulations indicated that Pb HIs for both adult populations had a 0.6 % probability to exceed the threshold value of 1, while in children this probability was 14.2 %. Cd and Hg showed no probability to exceed the threshold in any scenario. Our simulation results raise concern about possible adverse health effects of heavy metals from soil, especially in children. It is very important to continue monitoring environmental pollution and assess human health risk, not only with respect to soil, but also with other important environmental compartments, such as air and water.

Action spectrum of phototherapy in hyperbilirubinemic neonates.

Phototherapy with blue light matching plasma absorption spectrum of the bilirubin-albumin complex with peak at 460 nm is standard treatment of neonatal hyperbilirubinemia. To demonstrate clinically the action (efficacy) spectrum of phototherapy in hyperbilirubinemic neonates, through determination of the fraction of total serum bilirubin (TSB) decreased by phototherapy with peak emission wavelengths ≥478 nm (blue-green) compared with that of light of 459/452 nm (blue). TSB values were compiled from three earlier trials, in which hyperbilirubinemic neonates were randomized to receive 24 h of either blue-green light (478/490/497 nm) (intervention groups) or blue light (459/452/459 nm) (control groups) with equal irradiance and exposed body surface areas. Ratios (efficacy) between the decrease in TSB between intervention and control groups were calculated and graphed versus peak wavelengths, demonstrating the course of the action spectrum. Calculated efficacy ratios were 1.31, 1.18, and 1.04 for light with peak wavelengths of 478, 490, and 497 nm, respectively. The action spectrum increases from 452/459 to maximum at 478 nm, from where it decreases to 1.18 and finally to 1.04. For optimal phototherapeutic treatment, neonates need to be exposed to light with peak wavelength some 20 nm longer than is presently used. The action (efficacy) spectrum of phototherapy for hyperbilirubinemic neonates has its peak wavelength at 478 nm. The peak wavelength of this action spectrum is 20 nm longer than the wavelength presently believed to be most efficient. The peak is also different from the peak found in vitro. For optimal phototherapeutic effect, neonates need to be treated with light of wavelengths some 20 nm longer than are presently used.

Shielding effects in interaction of nanosecond laser pulses with solid target

We present experimental study of radiation absorption in copper plasma created by Nd:YAG laser fundamental (1064nm) harmonic. Absorption is recorded by monitoring attenuation of HeNe laser (633nm) illuminating plasma side on. Assuming that inverse bremsstrahlung is dominant process, absorbtion of the Nd:YAG 1064nm wavelength is evaluated relying on measurements conducted at 633nm specific for He–Ne laser and using common analytical expressions. Radial profile of the absorption, the absorption coefficient, is deduced applying inverse Abel transform. The absorption is measured for several distances from the copper target and for various delays at each position. This procedure is repeated for three different energies of 1064nm wavelength. It is shown that for high laser energies in IR domain absorption of radiation in the plasma is, within accuracy of the experiment, close to 92% while for lower energies considerable amount of the laser energy reaches the target surface. The absorption of the plasma attains its maximal value after the maximum of the laser power and remains at this value for couple of nanoseconds after the laser pulse ceases. It is also found that total energy absorbed by the plasma depends linearly on total incident energy in the investigated range of energy.

Fabrication of thrombin loaded TEMPO-oxidized cellulose nanofiber-gelatin sponges and their hemostatic behavior in rat liver hemorrhage model

Excessive blood loss due to trauma or major surgical intervention can be life threatening which necessitates rapid hemorrhage management for the prevention of such bleeding related sufferings. Broad interest in developing new hemostatic technologies have been paid for bleeding control but none of them found completely satisfactory especially in terms of rapid clotting, absorbability, porosity, cost effectiveness and safety. To address these issues, a combination of active and passive hemostatic materials from biological sources could be a wise choice. Therefore, plant-derived TEMPO-oxidized nanocellulose (TOCN)/biopolymer gelatin (G) sponge was successfully prepared in co-operation with intrinsic blood coagulation enzyme thrombin (Th) via freeze drying method and their application as rapid hemostatic dressing was investigated. Morphological and in vitro characteristics of the samples were evaluated where uniformity, porosity, swelling, degradation behavior had direct relationship with the percent gelatin incorporation. In vitro hemocompatibility and cyto-compatibility of these sponges were confirmed as well. Among the samples, TOCN 2.5G-Th sponge exhibited excellent hemostatic effect, rapid absorbability, minimum clotting time (1.37 ± 0.152 min) and reduction of blood loss was ensured through rat liver punch biopsy model. The results demonstrated that, Th enhanced blood coagulation, platelet and red blood cell aggregation following application of biopolymer TOCN 2.5G-Th sponge compared with samples devoid of Th. In short, the functional, cost effective and nontoxic sponge developed via facile preparation could potentially be used as an absorbable biomaterial to achieve immediate hemostasis. Highlights Plant-derived TEMPO-oxidized nanocellulose (TOCN) and biopolymer gelatin (G) was successfully used to prepare a hemostatic sponge in combination with intrinsic blood coagulation enzyme thrombin (Th). The TG sponge combines the advantages of TOCN and gelatin, exhibiting biocompatibility, biodegradability and superior blood-absorption performance. The TOCN 2.5G-Th sponge improves plasma absorption, red blood cell adhesion, aggregation, platelet adhesion and activation leading to enhanced hemostasis effect and shorter hemostasis time in vitro and in vivo

SRS-SBS competition and nonlinear laser energy absorption in a high temperature plasma

Stimulated Raman and Brillouin scattering of laser radiation in a plasma corona are outstanding issues for the inertial confinement fusion. Stimulated Raman scattering may produce absorption of a significant fraction of laser energy near the plasma quarter critical density associated with plasma cavitation and generation of hot electrons. By contrast, stimulated Brillouin scattering operates in a lower density plasma and prevents the laser light access to the absorption region. In the present paper, we report the results of analysis of competition of these two parametric instabilities with a series of one-dimensional kinetic simulations of laser-plasma interactions. We revised several flexible methods for controlling the SRS-SBS competition in inertial fusion plasmas. Suppression of SBS favors SRS excitation, electron acceleration and cavitation. The latter process makes an important contribution to the laser absorption by trapping the backscattered light. Consequently, by controlling the Brillouin backscattering through variation such plasma parameters as ion acoustic wave damping, divergence of the plasma expansion velocity or the laser bandwidth, we demonstrate the possibility of controlling the level of nonlinear laser absorption and scattering in a hot, weakly collisional plasma.

Experimentally constrained multidimensional simulation of laser-generated plasmas and its application to UV nanosecond ablation of Se and Te

We carry out simulations of laser plasmas generated during UV nanosecond pulsed laser ablation of the chalcogens selenium (Se) and tellurium (Te), and compare the results to experiments. We take advantage of a 2D-axisymmetric, adaptive Cartesian mesh framework that enables plume simulations out to centimeter distances over tens of microseconds. Our model and computational technique enable comparison to laser-plasma applications where the long-term behavior of the plume is of primary interest, such as pulsed laser synthesis and modification of materials. An effective plasma absorption term is introduced in the model, allowing the simulation to be constrained by experimental time-of-flight kinetic energy distributions. We show that the effective simulation qualitatively captures the key characteristics of the observed laser plasma, including the effect of laser spot size. Predictions of full-scale experimentally-constrained Se and Te plasmas for 4.0 J cm−2 laser fluence and 1.8 mm2 circular laser spot area show distinct behavior compared to more commonly studied copper (Cu) plumes. The chalcogen plumes have spatial gradients of plasma density that are steeper than those for Cu by up to three orders of magnitude. Their spatial ion distributions have central bulges, in contrast to the edge-only ionization of Cu. For the irradiation conditions explored, the range of plasma temperatures for Se and Te is predicted to be higher than for Cu by more than 0.50 eV.

Radial spatiotemporal evolution of rf magnetic field and plasma current in a very-high-frequency plasma source over a wide range of plasma density and pressure.

We present detailed spatiotemporal measurements of rf magnetic fields and plasma conduction current as well as the corresponding plasma density profiles when very-high-frequency 100-MHz waves are introduced to a parallel plate plasma. The magnetic probe, optical emission, and plasma absorption probe measurements support a model in which the interaction of high-frequency waves with the moving plasma sheath at specific phases of the very high frequencies (VHF) period leads to local reversals in the vertical rf electric field which can lead to conduction current reversals and circulations. The presence of current reversals and circulation correlate with measured plasma uniformity. In particular, measured electric field and current reversals coincide with the strongly center-peaked plasma density profiles frequently observed in VHF plasma. The magnitude of the center peak increases with the number and magnitude of the current reversal cells. The scale length of the current reversal cells is on the order of what is expected for plasma surface waves. Measurements indicate that plasma conductivity is the common scaling factor for both plasma uniformity and the circulation. The propagation of high-frequency waves and the generation of rf current reversal in one phase of the rf cycle rather than another results in the appearance of harmonics in Fourier decomposed magnetic probe wave forms. These harmonics turn out not to be actual waves or evidence of standing waves at these frequencies but rather consequences of packets of wave propagation that occur periodically.

Development of solid state terahertz interferometer for the first plasma on HL-2M tokamak.

A solid state terahertz interferometer has been developed on the recent commissioned HL-2M tokamak. It can work in a wide frequency region of 220-325GHz, and the terahertz wave is generated from a low frequency phase locked voltage controlled oscillator with the frequency multiplying technique. A phase processor based on field programmable gate array (FPGA) technology is designed for the heterodyne interferometer, and it contributes to real-time display of electron density. To extract phase information, a novel numerical algorithm related to fast Fourier transform is written on the FPGA chip and enables one to obtain phase shift without being affected by amplitude variation induced by plasma absorption or frequency modulation from the outer electromagnetic environment. The interferometer achieves minimum measurable electron density in the order of 1016m-3. With the plasma diagnosis, electron density and low frequency tearing mode have been measured during the first experimental campaign.

Electron Bernstein wave aided beat wave of Hermite-cosh-Gaussian laser beam absorption in a collisional nanocluster plasma

In this paper, we investigate the electron Bernstein wave aided beat wave of Hermite-cosh-Gaussian laser beam absorption in a collisional nanocluster plasma. The interactions of electric field profile of Hermite-cosh-Gaussian laser beams with electron clouds of nanoclusters cause the beat wave. The nonlinear ponderomotive force is generated through the beat wave of two Hermite-cosh-Gaussian laser beams. The time average power absorption per electron per unit area per unit time by electron Bernstein wave aided electric field of laser beat wave is derived. The graphical discussions were promised to achieve extreme absorption via spatial shape of Hermite-cosh-Gaussian laser beam and resonance condition of beat wave to surface plasmon frequency. The electron Bernstein waves parameters such as thermal velocity, cyclotron frequency and perpendicular component of wavenumber is also leading with beat wave for control and enhancement of absorption process in plasma embedded with nanocluster. The absorption is controlled by tuning the laser beam width, mode index, collisional frequency, clustered radius, and density.

Iron supplement for anemia developed from home industry waste of snake fruit Pondoh (Snake fruit edulis Reinw.)

Anemia due to iron deficiency in young girls and pregnant women remains a nutritional health problem in Indonesia. They take iron tablet/day to improve their iron status but it sometimes has some side effects. In Sleman Regency, snake fruits Pondoh are used to make various processed foods but some home food industries leave snake fruit seeds as industrial waste. Therefore, the aim of this study was to extract gradually seeds of snake fruits Pondoh for development of anemia iron supplement. In this explorative study, we collected seeds of snake fruits Pondoh from a home food industry in Turi district, Sleman Regency, Yogyakarta. In brief, we made simplicia of snake fruit seeds in several steps from washing, selecting, drying, cutting in small pieces, grinding to separating with 100 mesh sieve. After that, the simplicia was extracted using tetrahydrofuran, methanol, acetic acid, hexane and or ethyl acetate reagents to separate lipid, water and organic fractions, which were then dried using a vacuum evaporator. Dried fractions of snake fruit seeds (SFS) were finally measured using the inductively coupled plasma or atomic absorption spectroscopy method for iron levels and using ferric chloride for tannin content. From two different methods of making simplicial, we got 26.88 and 22.82% (weigh/weight) iron levels while ethyl acetate SFS fraction had higher iron levels (2.65% w/v) than lipid and water fractions (1.62 and 1.88% respectively). In addition, there was only the water fraction that contained tannin. In conclusion, the ethyl acetate fraction of SFS Pondoh may be useful for development of anemia iron supplement.

Simulations of the effects of laser wavelength, pulse duration, and power density on plume pressure generation using a one-dimensional simulation code for laser shock processing

We have developed a one-dimensional simulation code for laser shock processing with an atomic model code, an equation of state code, and a laser ablation peening code, in order to calculate laser-plume interactions during laser shock processing. We calculated the temporal changes of some energy ratios [e.g., the ratio (α′) of the thermal energy of a plume to an incident laser energy] and physical quantities, such as electron temperature, ion temperature, absorbed laser power density, and plume pressure under various laser parameters at the laser wavelengths of 355, 532, and 1064 nm. In the case of shorter pulse durations less than 10 ns, a peak plume pressure can be predicted by using α′ of ∼0.25 for 1064 nm and ∼0.40 for 355 and 532 nm below the power density threshold, at which plume pressures start to saturate. These values of α′ were consistent with those obtained in the previous experiments. In the case of longer pulse durations more than 10 ns, α′ for 1064 nm increased up to ∼0.45 at 15 GW/cm2 and an enhanced plume pressure would generate due to plasma absorption via inverse bremsstrahlung absorption in the partially ionized region far from the initial surface of the metal and due to heat conduction of the thermal energy of the plume near the initial surface of the metal. Thus, we showed the validity of our one-dimensional simulation code for laser shock processing and will investigate laser-plume interactions using double pulses during laser shock processing in the future.

Comparison of transient absorption of laser ablation plasma with fundamental plasma absorption relations

Nanosecond pulsed laser ablation plasmas were studied by time resolved shadowgraphy coupled with normal imaging, followed by laser probing and plasma spectroscopy in the 5-25 J/cm2 fluence regime. We describe methods for imaging and probing that allow us to determine variations in the distribution of ejecta in the plume and monitor the optical absorption using a probe laser to obtain a measure of the linear absorption coefficient of the plasma. Experimental determination of absorber distribution also corresponds well to the theoretical prediction of density increase near the emitted shockwave edge. We finally demonstrate that fundamental plasma correlations can accurately describe the absorption of light by the plasma near the ablation wavelength. We observed good agreement in peak attenuation, directly measuring 65% peak absorption and compared to a calculation of 57% using a simple model of the plasma, but a 10 ns shift in peak attenuation time. The shift in dip times is explained both by experimental error and a fundamental imprecision in the model proposed for the expansion.

Line-tied Boundary Conditions Can Cause Resonant Absorption Models to Generate Unphysically Large Boundary Layers

Abstract This paper uses linear magnetohydrodynamics to model resonant absorption in coronal plasma with a Cartesian coordinate system. We impose line-tied boundary conditions and tilt the background magnetic field to be oblique to the transition region. Halberstadt & Goedbloed, Goedbloed & Halberstadt, and Arregui et al. show that line-tied boundary conditions cause their resonant absorption models to produce steep boundary layers/evanescent fast waves. We aim to study the importance of boundary layers and assess their significance in a solar context. We calculate solutions in a model where we impose line-tied boundary conditions and compare this with a model where we include the chromosphere instead. Results are calculated analytically and then verified numerically. We show that line-tied boundary conditions can cause the model to overestimate the boundary layers’ amplitude significantly. If the fast waves can propagate in the chromosphere, then the line-tied model accurately predicts the boundary layers’ amplitude. However, if the fast waves are evanescent, then the boundary layers’ size is reduced significantly, and the line-tied model overestimates their amplitude. This leads to the counterintuitive result that length scales tangential to the transition region can play an essential role in determining line-tied boundary conditions’ validity. The results suggest that line-tied boundary conditions can cause the model to generate unphysically large boundary layers. However, researchers may wish to continue to use them in their models for their simplicity and ability to significantly reduce computation time if they understand and are aware of their flaws.

Effects of α-Casein on the Absorption of Blueberry Anthocyanins and Metabolites in Rat Plasma Based on Pharmacokinetic Analysis.

Blueberry anthocyanins are well known for their beneficial biological activities. However, the poor bioavailability of anthocyanins limits their functional capacity in vivo. Our current study aimed to detect the effects of α-casein on the absorption of blueberry anthocyanins and their metabolites in rats. Blueberry anthocyanins with and without α-casein were intragastrically administered to two groups of rats and their blood samples were collected within 24 h. Results illustrated that rapid absorption of anthocyanins was observed in the rat plasma, but their concentration was relatively low. With the complexation of α-casein, the maximum concentration (Cmax) of bioavailable anthocyanins and metabolites could increase by 1.5-10.1 times (P < 0.05 or P < 0.01). The promotional effect on the plasma absorption of malvidin-3-O-galactoside and vanillic acid was outstanding with the Cmax increasing from 0.032 to 0.323 and from 0.360 to 1.902 μg/mL, respectively (P < 0.01). Besides, the molecular docking models presented that anthocyanins could enter the structural cavity and interact with amino acid residues of α-casein, which was in accordance with the improved bioavailability of anthocyanins. Therefore, α-casein could assist more blueberry anthocyanins and their metabolites to enter blood circulation.

Highly efficient few-cycle laser wakefield electron accelerator

A significant part of the laser wakefield acceleration (LWFA) research effort focuses on studying high-energy, quasi-monoenergetic electron beams. For other applications, such as the production and application of intense betatron x-ray radiation, Bremsstrahlung γ-rays and positron beams, the beam’s spectral quality is secondary to the number of electrons produced. This work discusses 3D particle-in-cell simulations of a highly efficient LWFA acceleration process, generating a broad spectrum of electrons, driven by a 12 TW few-cycle laser on high-density gas targets. In some cases, laser absorption in plasma exceeds 80%, and up to 27% of the driving laser energy is transferred to electrons over 20 MeV leaving the plasma. We also observe a deceleration of the accelerated beam at the plasma downramp and plasma exit, which arises from transitioning from laser-driven to beam-dominated wake, and also from the induced axial electric field. This effect is similar to magnetic vortex acceleration, where the induced axial electric field, instead of accelerating plasma ions, would slow down the opposite-charged electron beam and also a strong return current and backward electron beam.