Determination Of Plasma Parameters Research Articles

Characterization of compact bright soft X-ray source based on picosecond laser plasma

Radiation emission of silicon and aluminum plasmas produced by 40-ps laser pulses with peak intensity above 1014 W/cm2 was studied. High-resolution soft X-rayspectra of H-like and He-like ions were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the intercombination lines of He-like ions with the results of model calculations. Such comparisons gave average values of the electron number density Ne=(1-1.9)×1021 cm-3 and the electron temperature Te=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. The plasma size is about 100 μm. According to our estimations, more than 1012 photons were produced within the resonance line spectral width and in the solid angle 2π during the total decay period.

Generation and characterization of a bright X-ray source using picosecond laser

High-resolution soft X-ray spectra of H-like and He-like ions were produced from laser irradiated silicon and aluminum targets. Plasma size was about 100 μm. X-ray spectra were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the inter combination lines of He-like ions, with the results of model calculations. Such comparison gave average values of the electron density N e=(1−1.9)×1021 cm−3 and the electron temperature T e=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. According to our estimations, more than 1012 photons were produced within the resonance line spectral width and in the solid angle 2π steredian during the total decay period.

Characterization of a plasma produced by pulsed arc using an electrostatic double probe

In this work the determination of plasma parameters of a pulsed-arc discharge by using an electrostatic double probe is presented. The system to generate the plasma is composed mainly of a reaction chamber, where the electrodes of different materials (Ti, Zr, Al) were placed in order to identify the variation of the plasma parameters when the cathode material is changed. An automatic system has been implemented for acquiring data starting from the bias of a double electrostatic probe. This system allowed registering complete curves of current-voltage in relatively short times (≈30ms). The electron density ne and electron temperature Te can be extracted from the I-V characteristic curves obtained. The advantage of this technique is its facility to provide the whole quantity of “in situ” information, which can be compared with the theoretical results using numeric methods for the I-V curves simulation. By means of a suitable fit this allowed the determination of the plasma parameters. The values obtained for Te were in the order of 1eV and for ne of about 1013cm−3. A significant variation for ne was not found.

Probe Measurements: Fundamentals to Advanced Applications

This intensive course gives fundamentals of probe measurement and its advanced applications. The first part reviews the theory of the electrostatic probe used in the plasma and methods for determining plasma parameters (space potential, electron temperature, plasma density, energy distribution, etc.). Several types of conventional probes are presented. The second part presents new methods and techniques that have been developed to measure complicated cases: electronegative plasma, flowing plasma, strongly magnetized (fusion) plasma, space plasma and (high pressure) microplasma by giving some examples.

First results on the fast neutral lithium beam diagnostics probing the edge plasma of the ETE tokamak

One of the main objectives of the research program at ETE is devoted to the study of confinement properties in a low aspect ratio tokamak plasma configuration, and to attain this purpose the determination of plasma parameters of the edge region plays an essential role. A Fast Neutral Lithium Beam (FNLB) diagnostics was developed to perform the measurement of the density profile and its fluctuations at the edge of the plasma in ETE. The first light signals were collected after the filling of ETE chamber with He gas (10-4 Torr), where the optimization of this diagnostics was done, to adjust the better point for focalization of the beam and for the optical detection system setup. An extensive study of the variation of the intensity of the light signal with the variation of the gas pressure was carried out. This calibration will be used during shots in ETE to measure the rapidly varying pressure of the pulsed discharge by FNLB technique, a requirement imposed by the use of puff valves for injection of the gas. This paper will also describe the several phases of the development of this diagnostics, discuss the problems occurred and the adopted solutions and show the first measurements of the probing of the edge plasma of ETE with FNLB.

X-ray spectroscopy for high energy-density X pinch density and temperature measurements (invited)

X pinch plasmas produced from fine metal wires can reach near solid densities and temperatures of 1 keV or even more. Plasma conditions change on time scales as short as 5–10 ps as determined using an x-ray streak camera viewing a focusing crystal spectrograph or directly viewing the plasma through multiple filters on a single test. As a result, it is possible to determine plasma conditions from spectra with ∼10 ps time resolution. Experiments and theory are now coming together to give a consistent picture of the dynamics and kinetics of these high energy density plasmas with very high temporal and spatial precision. A set of diagnostic techniques used in experiments for spectrally, temporally, and spatially resolved measurements of X pinch plasmas is described. Results of plasma parameter determination from these measurements are presented. X ray backlighting of one x- pinch by another with ∼30 ps x-ray pulses enables the dynamics and kinetics to be correlated in time.

Optical emission studies of the plasma during high-pressure sputtering of Y–Ba–Cu–O targets

Quantitative determination of plasma parameters based on optical emission measurements usually requires two types of calibration. First, in order to be able to calculate the absolute values of emission intensities, the transmission of the optical system must be measured with the help of a calibrated source or detector. Second, if utilizing the ratio of atomic-to-ionic lines for determining the electron temperature Te, another quantitative method, e.g. Langmuir probes, must be applied for calibration of the absolute value of Te. However, the necessary plasma modeling must take into account the particular geometry of the system, because the Langmuir measurements are local, whilst the sampling of the optical signal involves plasma volume along the line-of-sight. Such modeling can be complex, especially in conditions of high-pressure sputtering of multielemental targets in a mixture of reactive gases. Nevertheless, appropriate data handling of relative optical emission measurements can give information about variations of deposition conditions, which have an impact on the properties of deposited films.This paper presents results of implementation of optical emission spectroscopy as a tool for detecting deviations in sputter deposition conditions, including gas composition, pressure and target cation ratio. Films deposited under varying conditions were subsequently characterized.

Electron cyclotron emission as diagnostic tool in spheromak

The potential of electron cyclotron emission (ECE) diagnostic to determine plasma parameters in spheromak experiments and spheromak reactor is examined in detail. When a linearly polarized electromagnetic wave propagates through a sheared magnetic field in dense plasma, it undergoes rotation. The amount of rotation depends on plasma parameters, magnetic field amplitude and its orientation as well as on spatial variation. We have calculated the value of the rotation angle for different anisotropy conditions. It is observed that the amount of the rotation angle is negligible for a weak anisotropy. That means the wave is propagated as if in vacuum and local information carried by the wave is preserved. We show that, by proper choice of harmonics frequency of ECE radiation, a weak anisotropy condition can be satisfied. Hence measurement of ECE radiation for those range of frequencies (for which the weak anisotropy condition is satisfied), plasma parameters and magnetic field orientation can be obtained easily. As an example, the use of this diagnostic method in existing sustained spheromak physics experiment is described. We also mention that this diagnostic can measure electron temperature with about 10 cm or less spatial resolution in a ‘two-component type spheromak reactor’ having electron temperature ⩽7 keV. The measurement aspects of ECE for a spheromak are discussed.

Simulating Thermal Noise

Thermal noise measurements by space-borne antennas are commonly used to determine plasma parameters like the electron density and the plasma temperature from the noise spectra. It would be desirable to have a controlled experiment in which noise from a plasma with known properties is sampled in space and in time and which results can then be used to reproduce the satellite measurements. Here we examine the possibility to use particle-in-cell (PIC) simulations as such an experiment. In this work we present a statistically averaged noise spectrum computed with a PIC code for a simple single-Maxwellian and unmagnetized electron plasma and we compare it to both, the thermal noise spectrum for the corresponding real plasma and the noise spectrum we would anticipate from our numerical scheme. We find that we can produce noise fields with sufficiently low amplitudes to keep the plasma in a linear regime. We show that the simulation noise at low and at large wave numbers differs not only from thermal noise of a physical plasma but also from the numerical noise we would expect from our numerical scheme. We explain the drop of the noise power at low wave numbers by our initial conditions. We find experimentally the relation that connects the theoretical noise spectrum for our simulation code with that we actually measure, provided that the phase velocity of the noise is less than the maximum velocity of the computational particles.

Numerical modelling of laser beam–target interaction near the plasma-formation threshold

Experimental investigations of laser-produced plasmas often determine plasma parameters as averaged values only and these data cannot be compared with actual conditions at a target surface. In this paper, numerical modelling of target heating with non-constant target material properties was used to estimate the temperature at the surface of the target as a function of time. Three target materials (magnesium, aluminum and silicon) and an experimentally determined laser pulse profile were used for modelling. Gray-body radiation of the target surface and thermal diffusion losses are taken into account during numerical modelling. It was assumed that radiation from the laser impacts perpendicularly onto the target surface. The results obtained by modelling are in good agreement with the experimentally observed plasma parameters and they are consistent with thermal target heating in which the laser beam is treated as a source of very intense input heat energy.

Probe measurements in anisotropic discharges

A current–voltage characteristic of one-side planar and cylindrical probes was considered for the use in the determination of plasma parameters when the electron velocity distribution functions (EVDFs) were significantly anisotropic. The EVDFs, space potential, and rates of inelastic process in pulse modulated and stratified discharges were obtained. The results obtained using the exact and simplified method were compared. It was also shown that only a simplified method gives satisfactory results in the wide range of discharge conditions. Some discrepancies between theoretically determined and measured potentials in homogeneous plasma were found. A procedure, which allows for exact determination of space potentials, was given.

Probe diagnostics of high pressure microwave discharge in helium

A method for the determination of electron temperature and plasma density in high pressure helium plasmas is established using numerical results of the continuum probe model by Cohen [Phys. Fluids 6, 1492 (1963)]. Simple algebraic functions are derived to approximate the probe characteristics of high pressure plasmas calculated by Cohen and are applied to use iterative procedures for the determination of plasma parameters. The proposed fitting technique has allowed one to obtain reasonable plasma parameters even for the probe characteristics strongly affected by large secondary electron emission currents from the probe. Fitting of the ion saturation current may possibly be used to estimate the ion temperature, provided that the electron temperature and plasma density are known. Finally high pressure helium microwave discharges have been produced by moderate microwave power of 400 W and investigated by the present method.

EUV emission from Kr and Xe capillary discharge plasmas

Kr and Xe plasmas are very intensive emitters in thespectral range of 100-150 Å, which is relevant for a numberof applications (for example microlithography). We presentinvestigations of the extreme utraviolet (EUV) emission from a slow capillary dischargewith Kr and Xe fillings. The emission of Kr ions (Kr VIII to Kr XI)within the range of 70-150 Å consists of three bands oflines of about 10 Å width with maxima at 116, 103and 86 Å. Xe emission bands of about 15 Å width havetheir maxima at 136 and 115 Å (Xe IX to Xe XII). Theradiation duration in this spectral range is ~150 ns forboth elements. At the optimum conditions, the Kr emission at103 Å is 2-3 times more intense than the Xe emission at136 Å. The measured spectral energy of Kr radiation is about0.1 J sr-1 Å-1. Experimental results arecompared with numerical modellings of the dynamics and emission ofthe capillary discharge plasma, which enables the determination ofplasma parameters and the future use of the codes as additionalinstruments for plasma diagnostics.

Исследование эффективности алгоритмов обработки характеристик симметричного двойного зонда Ленгмюра (СДЗЛ) на основе предложенного показателя качества

Исследование эффективности алгоритмов обработки характеристик симметричного двойного зонда Ленгмюра (СДЗЛ) на основе предложенного показателя качества

Contamination-free sounding rocket Langmuir probe

A technique for removing surface contaminants from a sounding rocket spherical Langmuir probe is presented. Contamination layers present on probe surfaces can skew the collected data, resulting in the incorrect determination of plasma parameters. Despite following the usual probe cleaning techniques that are used prior to a launch, the probe surface can become coated with layers of adsorbed neutral gas in less than a second when exposed to atmosphere. The laboratory tests reported here show that by heating the probe from the interior using a small halogen lamp, adsorbed neutral particles can be removed from the probe surface, allowing accurate plasma parameter measurements to be made.

Atomic spectral line free parameter deconvolution procedure.

We report an advanced numerical procedure for deconvolution of theoretical asymmetric convolution integral of a Gaussian and a plasma broadened spectral line profile j(A,R)(lambda) for spectal lines. Our method determines all broadening parameters, self-consistently and directly from the line profile with minimal assumptions or prior knowledge. This method is useful for obtaining complete information on all plasma parameters directly from the recorded shape of a single line, which is very important in case no other diagnostic methods are available. The method is also convenient for determination of plasma parameters in the case of a symmetrical profile such as Voigt one.

Time resolving diagnostic of the compensation process of pulsed ion beams at high-intensity light ion source

Time-resolved measurements of the compensation process have been performed at the (high-intensity light ion source)-low-energy beam transport test stand (CEA-Saclay) using an 92 kV; 73 mA proton beam. A residual gas ion energy analyzer was used to measure the potential distribution as a function of time. To measure the radial density profile of the ion beam a charge coupled device camera has been used to perform time-resolved measurements and to estimate the rise time of compensation. Both measurements in combination allow an investigation of the space-charge compensation process due to the residual gas ionization and the experimental study of the rise of compensation. A numerical simulation of selfconsistent equilibrium states [J. Pozimski, Il Nuovo Cimento 106, A.N.11 (1993)] of the ion beam has been used to determine plasma parameters such as the density and the temperature of the electrons from the measured data. An interpretation of the acquired data and the achieved results is given.

On energetic electrons in a multipolar magnetically confined Ar plasma

Energetic electrons in the filament vicinity of a multipolar magnetically confined Ar plasma were investigated by spherical and planar probes using the test function method. Being very sensitive to deviation of the electron energy distribution function from Maxwellian, the test function was able to emphasize the influence of primary electrons on the determination of plasma parameters. In order to avoid ambiguity in the estimation of energetic electron parameters, the energetic electrons were separated into anisotropic-primary and isotropic-hot electrons.

Spectroscopic diagnostics and modelling of silane microwave plasmas

Low-pressure silane plasmas (2-20 Pa) diluted with the noble gases helium and argon as well as hydrogen were generated by microwave excitation in order to determine plasma parameters and absolute particle number densities. Specific silane radicals (SiH, Si, , H) were measured by means of optical emission spectroscopy, whereas particle densities of silane, disilane and molecular hydrogen were measured with mass spectroscopy. Experimental results confirm model calculations, which were carried out to determine number densities of all silane radicals and of higher silanes as well as electron temperature. The electron temperature varies from 1.5 to 4 eV depending on pressure and gas mixture. The temperature of heavy particles is 450 K and the electron number density is . The rotational temperatures of SiH are between room temperature and 2000 K due to increasing dissociative excitation. In the plasma the number density of silane is reduced, whereas the number density of molecular hydrogen is close to the silane density, which is fed in. Particle densities of , disilane and atomic hydrogen are in the range of a few per cent of the silane number density. At low pressure the density is similar to and decreases with increasing pressure due to heavy particle collisions with silane producing higher silanes. Particle densities of SiH and Si are only in the range of some of the silane density decreasing with increasing collisions of heavy particles with silane and molecular hydrogen. In mixtures with argon Penning reactions increase the silane dissociation.

Diagnostics of magnetically enhanced RF discharges in methane, argon and methane - argon mixtures

The determination of plasma parameters in RF capacitive discharges enhanced by an external magnetic field using emission spectroscopy, double Langmuir probes and thermocouple methods is reported. The gas temperature, rotational temperature of CH radicals, electron temperature, and charged particle and atomic hydrogen densities as functions of the discharge parameters are determined. The system operating parameters can be adjusted in the following ranges: gas pressure in the discharge chamber 0.1 - 10 Pa; discharge power 80 - 200 W; magnetic field strength 0 - 200 G. Pure methane and pure argon, as well as mixtures of methane and argon in various proportions were used as working gases. In addition, carbon films were deposited on glass substrates and their optical properties were investigated. It is shown that the external magnetic field has a significant influence on both plasma parameters and properties of the deposited films.