A probe diagnostics for high-speed flows of rarefied partially dissociated plasma

A procedure of probe diagnostics of supersonic flows of rarefied partially dissociated plasma has been developed. It is shown that the use of a single cylindrical Langmuir probe and a pressure probe allows determination of the complete set of the local values of plasma parameters and the degrees of dissociation, nonisothermality, and flow ionization.     

A calorimetric probe diagnostics for neutral and charged components of a rarefied plasma flow

A procedure for diagnosing flows of nonequilibrium rarefied plasma using cylindrical and flat calorimetric probes also connected as a Langmuir probe has been developed. It is shown that this procedure can be used to determine the full set of local values of the main kinetic parameters for the neutral and charged components of a collisionless plasma flow.     

Cylindrical-probe diagnostics of plasma flows effusing from technological plasmatrons

Mathematical and numerical models have been considered for the problem of collisional plasma flow from a technological plasmatron past a cylindrical probe. A set of theoretical volt–ampere characteristics that can be used to process probe experiments has been presented. Novel probe techniques of processing natural probe experiments for collisional plasma have been described.     

Electron-beam diagnostics of impulse rarefied gas jets

An electron-beam method for studying the local density of impulse jets ejected from a supersonic nozzle into vacuum for several seconds is developed. The method is based on a linear dependence of the intensity of bremsstrahlung excited by fast electrons in a gas on the atomic concentration in the gas. The radiation intensity is evaluated as a function of the temporal resolving power. The measurement scheme and results of studying transverse density profiles in a supersonic impulse jet are presented.     

Optical diagnostics of gas-droplet flows

A gas-droplet flow generated by a pneumatic injector with internal mixing is studied by optical methods. The fractional composition and the spatial distribution of liquid droplets for different fractions are measured, as well as the mean velocity field.     

Optical Hilbert diagnostics of dynamic structures in gas flows

The possibility of visualizing the fine structure of optical inhomogeneities in gas and condensed fluids by Hilbert optics methods is discussed. Application of optical Hilbert filtering for investigating shock waves and dynamic perturbations induced by the waves in gas is described.     

Modelling and diagnostics of multiple cathodes plasma torch system for plasma spraying

Usage of a multiple-arcs system has significantly improved process stability and coating properties in air plasma spraying. However, there are still demands on understanding and controlling the physical process to determine process conditions for reproducible coating quality and homogeneity of coating microstructure. The main goal of this work is the application of numerical simulation for the prediction of the temperature profiles at the torch outlet for real process conditions. Behaviour of the gas flow and electric arcs were described in a three-dimensional numerical model. The calculated results showed the characteristic triangular temperature distribution at the torch nozzle outlet caused by three electric arcs. These results were compared with experimentally determined temperature distributions, which were obtained with specially developed computed tomography equipment for reconstructing the emissivity and temperature distribution of the plasma jet close to the torch exit. The calculated results related to temperature values and contours were verified for the most process parameters with experimental ones.     

Boundary effects of light scattering in laser diagnostics of two-phase flows

This study is motivated by the advent of methods for measuring particle sizes in two-phase flows based on the local interaction of light with the scattering particle. Localization is easily interpreted in terms of the ray optics of a particle, which, however, does not cover all interaction effects. This paper consider effects that extend beyond the traditional concept of the total effect of the mechanisms of geometrical optics and wave diffraction by a particle as an opaque disk, in particular, surface waves and complex rays.. The results of the mathematical modeling performed in this study clarifies the contributions of the effects to the scattering and the position of the localization points of the interaction with the particle.     

A microwave two-wave interferometer for plasma diagnostics

The scheme and the main elements of an interferometer simultaneously operating at frequencies of the 8-and 4-mm ranges are presented. To combin e two radiations in a common waveguide section and separate them by sending to the corresponding receivers, a special separation filter has been developed. A homo-dyne technique for transferring phase measurements to an intermediate frequency is employed in the interferometer. The range of unambiguously measured phase shifts is 1.5°—360°, and the phase-shift measurement error is within 5%.     

Broadband notch filter design for millimeter-wave plasma diagnostics

Notch filters are integrated in plasma diagnostic systems to protect millimeter-wave receivers from intensive stray radiation. Here we present a design of a notch filter with a center frequency of 140 GHz, a rejection bandwidth of ～900?MHz, and a typical insertion loss below 2 dB in the passband of ±9 GHz. The design is based on a fundamental rectangular waveguide with eight cylindrical cavities coupled by T-junction apertures formed as thin slits. Parameters that affect the notch performance such as physical lengths and conductor materials are discussed. The excited resonance mode in the cylindrical cavities is the fundamental TE(11). The performance of the constructed filter is measured using a vector network analyzer monitoring a total bandwidth of 30 GHz. We compare the measurements with numerical simulations.     

Temperature diagnostics of ECR plasma by measurement of electron bremsstrahlung

The x-ray bremsstrahlung spectrum emitted by the electron population in a 14.5 GHz ECR plasma source has been measured using a NaI(Tl) detector, and hence the electron temperature of the higher energy electron population in the plasma has been determined. The x-ray spectra for Ne and Ar gases have been systematically studied as a function of inlet gas pressure from 7 × 10(-7) mbar to 7 × 10(-5) mbar and for input microwave power ～1 W to ～300 W. At the highest input power and optimum pressure conditions, the end point bremsstrahlung energies are seen to reach ～700 keV. The estimated electron temperatures (T(e)) were found to be in the range 20 keV-80 keV. The T(e) is found to be peaking at a pressure of 1 × 10(-5) mbar for both gases. The T(e) is seen to increase with increasing input power in the intermediate power region, i.e., between 100 and 200 W, but shows different behaviour for different gases in the low and high power regions. Both gases show very weak dependence of electron temperature on inlet gas pressure, but the trends in each gas are different.     

Time resolving bent crystal spectrometer for tokamak plasma diagnostics

A high-throughput high-resolution curved crystal spectrometer for measurements in the soft X-ray range on fusion magnetic devices is described. The spectrometer uses a large useful area (8 × 5 cm²) quartz lamina bent at a curvature radius 385 cm long as the dispersing element. The detector is a one-dimensional space resolving multiwire proportional counter. The spectral resolving power is R = 18 000, permitting to obtain adequate ion temperature measurements, down to 700 eV, from the Doppler broadening of resonance lines of highly ionized metallic impurities.     

Development of neutron spectrometer toward deuterium plasma diagnostics in LHD

Neutron spectrometer based on coincident counting of associated particles has been developed for deuterium plasma diagnostics on Large Helical Device (LHD) at the National Institute for Fusion Science. Efficient detection of 2.5 MeV neutron with high energy resolution would be achievable by coincident detection of a scattered neutron and a recoiled proton associated with an elastic scattering of incident neutron in a plastic scintillator as a radiator. The calculated neutron spectra from deuterium plasma heated by neutral beam injection indicate that the energy resolution of better than 7% is required for the spectrometer to evaluate energetic deuterium confinement. By using a prototype of the proposed spectrometer, the energy resolution of 6.3% and the detection efficiency of 3.3×10(-7)?count/neutron were experimentally demonstrated for 2.5 MeV monoenergetic neutron, respectively.     

A collimator for hot plasma x-ray diagnostics in ion sources

We present a collimator configuration for measuring energy resolved x-ray plasma volume bremsstrahlung emitted, e.g., by an ECRIS. Special attention we paid to shielding the detector against interfering Compton scattered radiation and wall bremsstrahlung stemming from the collimator entrance aperture. We estimate the efficiency for shielding of Compton scattered radiation at least attainable by this arrangement.     

Doppler spectroscopy and D-alpha emission diagnostics for the C-2 FRC plasma

Two Doppler spectroscopy diagnostics with complementary capabilities are developed to measure the ion temperatures and velocities of FRC plasmas in the C-2 device. First, the multichord ion doppler diagnostic can simultaneously measure 15 chords of the plasma using an image intensified camera. Second, a single-chord fast-response ion Doppler diagnostic provides much higher faster time response by using a 16-channel photo-multiplier tube array. To study the neutral density of deuterium under different wall and plasma conditions, a highly sensitive eight-channel D-alpha diagnostic has been developed and calibrated for absolute radiance measurements. These spectroscopic diagnostics capabilities, combined with other plasma diagnostics, are helping to understand and improve the field reversed configuration plasmas in the C-2 device.     

等离子体诊断用成像型软X射线三色谱仪设计

围绕激光惯性约束聚变研究中内爆靶丸的辐射流诊断需求,设计了一种兼顾空间成像功能的三色软X射线谱仪。该谱仪的设计中心能点为210eV、680eV和800eV,能谱分辨率E/ΔE为5~10。采用X射线掠入射光学结构,实现了三个能点的一维聚焦成像,在1mm视场内空间分辨率优于10μm。采用X射线周期多层膜,获得了三个能区的能谱响应,多层膜测试结果满足设计要求。以光学设计和多层膜为基础,建立了系统的光线追迹模型,分析了可控的空间位置误差和瞄准误差对系统光谱分辨和空间分辨的影响,为装调方案及瞄准方法设计提供了精度依据。该谱仪与条纹相机结合,可用于我国强激光装置上的等离子体诊断实验。     

A microwave interferometer with increased stability for diagnostics of steady-state plasma

The schematic and results of studying an interferometer for a wavelength of 8 mm with homodyne frequency conversion for measuring the electron density of a steady-state plasma are described. The design of its waveguide system allows the drift of the indicated initial phase to be reduced to a level of ±0.1°/h. The maximum phase shift measured is 360°, the tolerable signal-power decay in plasma is 16 dB, and the maximum phase measurement error is ～5%.     

A three-channel polarointerferometer for diagnostics of magnetic fields in high-temperature plasma

A polarointerferometer designed for studying magnetic fields in high-temperature laser or electricdischarge plasma with the method of measuring the Faraday rotation of the plane of polarization of a probing laser beam is described. The instrument’s optical system allows three—shadow, polarization, and interference—images of an object to be formed in a single diagnostic channel, thereby making it possible to record plasma images using only one digital camera.     

A twin-wave quadrature interferometer for diagnostics of pulsed processes in hydrogen and erosion plasma

A two-wave interferometer is described that is based on 0.6328-and 3.3922-μm He-Ne lasers and allows separation of the contributions of free electrons and the neutral component in partially ionized plasma to the phase shift of a probing electromagnetic wave under conditions of possible vibrations of the facility’s optical elements. Using the quadrature method for forming informative signals, phase shifts were measured in a wide range of fractions of an interference fringe to several fringes with a high homogeneous differential sensitivity. The interferometer was used to measure the dynamics of the linear electron density of both an atmospheric-pressure erosion capillary discharge in air and plasma of a hydrogen target in experiments on deceleration of heavy ions in an ionized substance.     

Laser-spectroscopic methods for diagnostics of electric fields in plasma (review)

Methods for measuring electric fields in plasma based on laser spectroscopy and the Stark effect on Rydberg atomic levels and rotational levels of polar diatomic molecules are considered. These methods feature high sensitivity and allow measurements of both static and alternating electric fields in plasma with high temporal and spatial resolutions. It is shown that laser-spectroscopic techniques also allow measurements of relatively weak magnetic fields in plasmas of facilities with magnetic plasma confinement. Such measurements can be based on the use of Stark splitting of highly excited energy levels of hydrogen atoms in a Lorentzian electric field, while a decrease in the fluorescent-radiation intensity at the Balmer-α line can serve as a recorded signal.