UV and soft x-ray emission from gaseous and solid targets employing SiC detectors

A ns Nd:YAG pulsed laser has been employed to produce plasma from the interaction with a dense target, generating continuum and UV and soft x-ray emission depending on the laser parameters and target properties. The laser hits solid and gaseous targets producing plasma in high vacuum, which was investigated by employing a silicon carbide detector. The two different interaction mechanisms were studied, as well as their dependence on the atomic number. The photon emission from laser-generated plasma produced by solid targets, such as boron nitride(BN) and other elements(Al, Cu, Sn and Ta) and compounds such as polyethylene, has been compared with that coming from plasma produced by irradiating different gas-puff targets based on N_2 and other gases(Ar, Xe, Kr, SF_6). The experimental results demonstrated that the yields are comparable and, in both cases, increase proportionally to the target atomic number. The obtained results, focusing the attention on the advantages and drawbacks of the employed targets, are presented and discussed.     

Characteristics of a kHz helium atmospheric pressure plasma jet interacting with two kinds of targets

This study investigates the influence of two types of target,skin tissue and cell culture medium,with different permittivities on a k Hz helium atmospheric pressure plasma jet (APPJ) during its application for wound healing.The basic optical–electrical characteristics,the initiation and propagation and the emission spectra of the He APPJ under different working conditions are explored.The experimental results show that,compared with a jet freely expanding in air,the diameter and intensity of the plasma plume outside the nozzle increase when it interacts with the pigskin and cell culture medium targets,and the mean velocity of the plasma bullet from the tube nozzle to a distance of 15 mm is also significantly increased.There are also multiple increases in the relative intensity of OH (A~2Σ?→?X~2Π) and O (3p~5S–3s~5S) at a position 15 mm away from nozzle when the He APPJ interacts with cell culture medium compared with the air and pigskin targets.Taking the surface charging of the low permittivity material capacitance and the strengthened electric field intensity into account,they make the various characteristics of He APPJ interacting with two different targets together.     

Characteristics of a kHz helium atmospheric pressure plasma jet interacting with two kinds of target

Abstract This study investigates the influence of two types of target, skin tissue and cell culture medium, with different permittivities on a kHz helium atmospheric pressure plasma jet (APPJ) during its application for wound healing. The basic optical–electrical characteristics, the initiation and propagation and the emission spectra of the He APPJ under different working conditions are explored. The experimental results show that, compared with a jet freely expanding in air, the diameter and intensity of the plasma plume outside the nozzle increase when it interacts with the pigskin and cell culture medium targets, and the mean velocity of the plasma bullet from the tube nozzle to a distance of 15 mm is also significantly increased. There are also multiple increases in the relative intensity of OH (A² Σ → X² Π) and O (3p⁵ S–3s⁵ S) at a position 15 mm away from nozzle when the He APPJ interacts with cell culture medium compared with the air and pigskin targets. Taking the surface charging of the low permittivity material capacitance and the strengthened electric field intensity into account, they make the various characteristics of He APPJ interacting with two different targets together.     

Spectroscopic measurements in Fe-plasma produced by pulsed laser ablation

A Nd:Yag laser is employed to irradiate thick Fe targets placed in vacuum. The obtained non-equilibrium Fe-plasma is investigated with various analytical techniques. An electrostatic ion energy analyzer (IEA) and a ring ion collector (ICR) are employed, in time-of-flight configuration, to monitor in situ the ejected ions from the plasma along the normal direction to the target surface and to determine the plasma core temperature and the ion energy distributions.The visible plasma emission, detected with an optical spectrometer, permitted to evaluate the electronic temperature and density and the fluence threshold of the visible light emission. The spectroscopy measurements of ions and photons and the fast CCD plasma images are employed to evaluate the temperature gradients in the laser-generated plasma plume.     

低速重离子在热等离子体中电子能量损失的Z1振荡效应

关于离子束和等离子体相互作用的实验和理论结果现已有大量报道【’一幻。这些研究的最重要的结果就是重离子在热等离子体中的能量损失较之在冷物质中有显著增强，而且离子的有效电荷也较在冷物质中大大增加。关于在冷物质中低速重离子电子阻止本领的电荷ZI振荡在实验上和理论上都有明确的结论＊司，而在等离子体中，低速重离子阻止本领随着＆的变化还没有得到较透彻的研究。我们应用量子散射理论具体计算了热等离子体靶对低速重离子的电子阻止本领。应用散射理论，带有电荷为ZI，速度为［）的重离子贯穿热等离子体时的电子阻止本领为（dE…     

Two-Dimensional Modeling of Ideal Merging Plasma Jets

Idealized merging argon plasma jets are simulated in 2D using both gas dynamic and MHD models. Results indicate that peak pressures of several hundred kilobar can be achieved for high Mach number jets. Including a simple optically thin bremsstrahlung radiation model and plasma targets shows that extremely high densities and magnetic fields can be achieved during jet merging on the order of ~1,000 times the initial density/field. Further investigations should include detailed ionization processes and more accurate radiation modeling to properly capture the radiation transport and subsequent target compression.     

Simulation of Targets Feeding Pipe Rupture in Wendelstein 7-X Facility Using RELAP5 and COCOSYS Codes

Wendelstein nuclear fusion device W7-X is a stellarator type experimental device, developed by Max Planck Institute of plasma physics. Rupture of one of the 40?mm inner diameter coolant pipes providing water for the divertor targets during the “baking” regime of the facility operation is considered to be the most severe accident in terms of the plasma vessel pressurization. “Baking” regime is the regime of the facility operation during which plasma vessel structures are heated to the temperature acceptable for the plasma ignition in the vessel. This paper presents the model of W7-X cooling system (pumps, valves, pipes, hydro-accumulators, and heat exchangers), developed using thermal–hydraulic state-of-the-art RELAP5 Mod3.3 code, and model of plasma vessel, developed by employing the lumped-parameter code COCOSYS. Using both models the numerical simulation of processes in W7-X cooling system and plasma vessel has been performed. The results of simulation showed, that the automatic valve closure time 1?s is the most acceptable (no water hammer effect occurs) and selected area of the burst disk is sufficient to prevent pressure in the plasma vessel.     

Machine learning application to predict the electron temperature on the J-TEXT tokamak

The reliability of diagnostic systems in tokamak plasma is of great significance for physics researches or fusion reactor. When some diagnostics fail to detect information about the plasma status, such as electron temperature, they can also be obtained by another method: fitted by other diagnostic signals through machine learning. The paper herein is based on a machine learning method to predict electron temperature, in case the diagnostic systems fail to detect plasma temperature. The fully-connected neural network, utilizing back propagation with two hidden layers, is utilized to estimate plasma electron temperature approximately on the J-TEXT. The input parameters consist of soft x-ray emission intensity, electron density, plasma current, loop voltage, and toroidal magnetic field, while the targets are signals of electron temperature from electron cyclotron emission and x-ray imaging crystal spectrometer. Therefore, the temperature profile is reconstructed by other diagnostic signals, and the average errors are within 5%. In addition, generalized regression neural network can also achieve this function to estimate the temperature profile with similar accuracy. Predicting electron temperature by neural network reveals that machine learning can be used as backup means for plasma information so as to enhance the reliability of diagnostics.     

Thermo-mechanical analysis of the Wendelstein 7-X divertor

The stellarator Wendelstein 7-X (W7-X) has a divertor consisting of 10 units installed inside the plasma vessel (PV). It was decided not to install the long pulse high-heat flux (HHF) divertor targets at the first two years stage of W7-X operation and to start with an adiabatically cooled test divertor unit (TDU) and shorter plasma pulses operation. This allows to accumulate operation experience with much simpler components, and as a result to adjust accurately the actively cooled HHF divertor which replaces the TDU for the stationary operation. Finite element (FE) analyses have been performed for better understanding of thermo-mechanical problems of divertor targets, and to guide the design of the TDU and HHF divertors. This paper presents the detailed results of the temperature response, the deformation and thermal stress of the divertor components.     

Improvement of atmospheric jet-array plasma uniformity assisted by artificial neural networks

Atmospheric pressure plasma jet(APPJ) arrays have shown a potential in a wide range of applications ranging from material processing to biomedicine. In these applications, targets with complex three-dimensional structures often easily affect plasma uniformity. However, the uniformity is usually crucially important in application areas such as biomedicine, etc. In this work, the flow and electric field collaborative modulations are used to improve the uniformity of the plasma downstream. Taking a...     

The target for the new plasma/wall experiment Magnum-PSI

The construction of Magnum-PSI is in its final stage. The aim is to provide a controlled and highly accessible linear plasma device to perform the basic plasma-surface interaction research needed for the design of the plasma facing components of future fusion devices. This contribution will focus on the thermal challenges imposed by those extreme conditions on the design of the target holder of Magnum-PSI.The target holder is designed to allow the exposure of large size targets with variable inclination angles with respect to the magnetic field. A test set up was made to test different interlayers (grafoil^®, soft metal sheets) and improve the thermal contact between the target and the heat sink. In addition, a modular target holder for sequential exposure of smaller size targets has been designed. Finite element modeling using the ANSYS code was used to optimize the cooling geometry and to predict the temperature profiles due to the heat load of the plasma. Experiments were done on the Pilot-PSI linear device to validate the thermal calculations. Calorimetry and infrared thermography were used to experimentally measure the temperature profile on the target and the heat deposition.     

Coating of Titanium Nitride on Stainless Steel Targets by a 4?kJ Plasma Focus Device

Titanium nitride thin films were deposited on stainless steel (SS316L) targets by using a 4?kJ plasma focus device. The corresponding energy flux delivered to SS316L surface is estimated to be 2.69?×?10¹³?kev?cm^?3?ns^?1. X-ray diffraction analysis reveals the formation of a nanocrystalline titanium nitride coating on the surface of targets. Thickness of the elements found on the surface of treated samples which are obtained by Rutherford backscattering spectrometry analysis (RBS) were (×10¹⁵ at/cm²) .45% Ti, 50% N and 5% Fe. Scanning electron microscopy was used to indicate changes in surface morphology. Existence of grains in different size confirms the formation of TiN crystals on the surface of targets.     

Radar scattering width effects by coating 90Sr/90Y layers on cylindrical targets

In this paper,the ~(90)Sr/~(90)Y coating effects on scattering width(SW) of cylindrical conductor targets are investigated.The electron density distribution of plasma around cylindrical targets of different radiuses is simulated under different radioactivities in normal or oblique incidence.In normal incidence,the SWs are examined as functions of frequency and scattering angle;while in oblique incidence,the SW is inspected as a function of incident angle at the frequency of 1.5 GHz.The results obtained are compared with those from an ideal perfect electric conductor(PEC) cylinder.It is demonstrated that the SW decreases over a wide frequency range in the back scattering region by coating a ~(90)Sr/~(90)Y layer on the cylindrical target.Moreover,the reduction in bi-static SW amplitude can reach 3-20 dB,when the incident angle is smaller than 30° at 1.5 GHz.It is a significant improvement in the stealth effect.     

Theoretical studies of macroscopic erosion mechanisms of melt layers developed on plasma facing components

During plasma instabilities in tokamak devices, metallic plasma facing components (PFC) undergo surface vaporization and melting. Macroscopic losses of melt layers are of a serious concern to the lifetime of PFC, the damage of nearby components, and potential core plasma contamination. A normal or inclined plasma stream flowing at the melt layer surface of PFC at very high velocities (∼10⁵ m/s) can induce Kelvin-Helmholtz (K-H) instabilities. We present an extensive linear stability theory and capillary droplet ejection model adapted to the problem of melt layer erosion and splashing. Based on this linear analysis, the stability criterion is established accounting the influence of the thicknesses of both plasma stream and melt layer. The growth rate of the most unstable wave is investigated with respect to different parameters such as plasma density and velocity, material properties, and melt layer thickness. A capillary droplet ejection model is then developed and used to analytically estimate the erosion rate of the melt layer for tungsten and aluminum targets. The present work brings a detailed understanding of the onset of K-H instabilities developed in melt layers due to plasma stream impact and builds a theoretical basis to estimate a macroscopic erosion rate, material losses and lifetime for PFC.     

Investigation of Plasma Facing Components in Plasma Focus Operation

Both aspects of the plasma–wall interactions, counter effect of plasma and materials, have been considered in our experiments. The AEOI plasma focus, Dena, has Filippov-type electrodes. The experimental results verify that neutron production increases using tungsten as an anode insert material, compared to the copper one. The experiments show decrement of the hardness of Aluminum targets outward the sides, from 135 to 78 in Vickers scale. The sputtering yield is about 0.0065 for deuteron energy of 50 keV.     

Determination of ion fraction and energy analysis of sputtered particles from deuterium bombarded surfaces

Ion energy distributions and sputtering yields have been measured in the presence of various background gases for deuterium, helium and argon ions in the 1–40 keV energy range. Alteration of the surface chemistry of hydride forming metals such as Ti, Y and V by exposure to hydrogen has a significant effect on the charge state of the sputtered particles. Under conditions likely to prevail in plasma devices and possible reactors, the ion/neutral fraction may be drastically increased, reaching ~41% for Ti. Such large ion fractions for metal targets have been previously observed only by sputtering with oxygen ions and present the possibility of improved impurity control in plasma devices. Both gas adsorption and recoil implantation are involved in the mechanism determining the ion fraction of sputtered products.     

Neutronic design analyses for a dual-coolant blanket concept: Optimization for a fusion reactor DEMO

The generation of design specifications for a DEMO reactor, including breeding blanket (BB), vacuum vessel (VV) and magnetic field coils (MFC), requires a consistent neutronic optimization of structures between plasma and MFC. This work targets iteratively to generate these neutronic specifications for a Dual-Coolant He/Pb15.7Li breeding blanket design. The iteration process focuses on the optimization of allowable space between plasma scrapped-off-layer and VV in order to generate a MFC/VV/BB/plasma sustainable configuration with minimum global system volumes. Two VV designs have been considered: (1) a double-walled option with light-weight stiffeners and (2) a thick massive one. The optimization process also involves VV materials, looking to warrant radiation impact operational limits on the MFC. The resulting nuclear responses: peak nuclear heating in toroidal field (TF) coil, tritium breeding ratio (TBR), power amplification factor and helium production in the structural material are provided.     

Time-of-flight and UV spectroscopy characterization of laser-generated plasma

A study of laser ablation of different targets (Al, Ti, Mo, Au and polyethylene), in vacuum, by using 3 ns Nd:YAG laser radiation, at 1064 nm wavelength, is reported. The ion emission from the plasma was monitored through time-of-flight (TOF) measurements, performed by using an ion collector placed along the normal to the target surface. The deconvolution of the IC experimental spectra with a Coulomb-Boltzmann-shifted function permitted to evaluate the equivalent ion temperature and the acceleration voltage developed inside the non-equilibrium plasma.The UV plasma emission, detected with an optical spectroscope, permitted to estimate the electronic temperature and density, to evaluate the Debye length and the temperature gradient in the laser-generated plasma plume.     

Influence of high flux hydrogen-plasma exposure on the thermal shock induced crack formation in tungsten

The influence of high flux hydrogen-plasma on the thermal shock behaviour of tungsten was investigated in a combined experiment using the linear plasma device Pilot-PSI and the electron beam facility JUDITH 1. Tungsten targets were exposed to high flux hydrogen plasma, cyclic thermal shock tests and a combination of both loading conditions. The induced thermal shock crack networks and surface modifications were investigated and characterised using scanning electron microscopy (SEM), optical microscopy and laser profilometry. Comparisons of the results showed that the combination of hydrogen plasma and thermal shock loading has a significant influence on the crack pattern in terms of crack distance, width and depth. Furthermore the sequence of the different loading types is of importance. Due to the prior loading with hydrogen plasma the thermal shock cracks were not limited to the electron beam loaded area but propagated through the just plasma loaded area and even through the unexposed area at the edges of the tungsten target.