Separation of emission lines of multiply charged ions against background of a very noisy spectrum of femtosecond laser plasma

At high intensities of interaction of femtosecond laser pulses with various targets, numerous high-energy particles emitted from plasma in all directions lead to the appearance of parasitic peaks in the X-ray spectra of femtosecond laser plasma (FLP) during detection of these peaks with a detector based on a charge-coupled device (CCD). The algorithm proposed in this study allows identification of parasitic peaks in a series of experimental spectra, which are recorded for each pixel of the CCD detector independently of other pixels, and removal of these peaks. The algorithm is able to detect peaks in the presence of both variations in the intensities of spectral lines and very intense noise. The efficiency of the algorithm has been confirmed via testing with the use of a series of model spectra and spectra of Fe and Al ions recorded in experiments devoted to studies of the interaction of ultrahigh-intensity and ultrashort laser pulses with solid targets.     

Plasma characterization of dry ��-EDM

An attempt was made to characterize the dry microelectric discharge machining (??-EDM) plasma systematically by using optical emission spectroscopy. In order to characterize the plasma and its parameters such as plasma temperature, electron density, Debye length, and gamma parameter, the optical spectra were recorded for different energies and with different diameters of tool electrode. From the recorded spectra, using line pair method and modified Saha equation, plasma temperature and electron density, respectively were calculated. From these two, Debye length and plasma parameter were also calculated. These studies indicate that the plasma produced in dry ??-EDM is ideal. In addition to this, we found that the dry ??-EDM region is below the conventional EDM region in log electron density and log temperature plot. Morphological analysis was carried out on crater produced by different energies on the workpiece using a scanning electron microscope. The crater shape may dependent on the geometry of the tool tip, number of discharges, and energy of discharge.     

Multichannel neutral-particle analyzer system

A multichannel neutral-analyzer system developed for the analysis of charge-exchange flux from magnetically confined plasma is described. The system uses tandem magnetic-electrostatic deflection of ions produced from neutrals stripped in a gas cell to obtain the energy spectra of specific charge-to-mass-ratio species. The analyzer is collimated with a spatial resolution of 2 cm FWHM at the plasma and is movable so that radial scans of charge-exchange flux can be made. Data are recorded digitally, allowing frequency response of fluctuations in charge-exchange flux up to 50 kHz. The calibration procedure employs an auxiliary single-channel analyzer calibrated over the full energy range of the multichannel instrument with an atomic-beam setup. Typical data obtained from the 2XIIB neutral-beam-injected mirror machine are briefly presented.     

四苯基卟啉的激光等离子体质谱研究

在自制的仪器上记录了四苯基卟啉的激光等离子体质谱。在正离子质谱中不仅出现了准分子离子峰(M H)~ ,而且出现了单、双、三吡咯碎片峰,这些谱峰间每相差一个非氢原子的碎片离子的谱峰也都能观察到。各负离子则是由碎片离子和自由基进一步离子—分子反应后生成的簇团离子,具有明显结构规律。研究结果显示激光等离子体质谱不仅是一种有效的结构分析手段,还能产生与研究各种簇团离子。     

激光等离子体质谱用于岩样化学成份的分析

在自制的仪器上,记录了一系列岩样的激光等离子体质谱。通过对正负离子质谱的分析,可以确定岩样的化学组成。本文通过对仪器工作原理、实验条件和测试结果的介绍,显示出该测试手段具有分析速度快、分析结果准确可靠、所得信息较为丰富、可进行微区与深度分析等优点。文章还讨论了不足之处及改进方向。     

Calibration and analysis of spatially resolved x-ray absorption spectra from a nonuniform plasma

We report here the calibration and analysis techniques used to obtain spatially resolved density and temperature measurements of a pair of imploding aluminum wires from x-ray absorption spectra. A step wedge is used to measure backlighter fluence at the film, allowing transmission through the sample to be measured with an accuracy of ±14% or better. A genetic algorithm is used to search the allowed plasma parameter space and fit synthetic spectra with 20?μm spatial resolution to the measured spectra, taking into account that the object plasma nonuniformity must be physically reasonable. The inferred plasma conditions must be allowed to vary along the absorption path in order to obtain a fit to the spectral data. The temperature is estimated to be accurate to within ±25% and the density to within a factor of two. This information is used to construct two-dimensional maps of the density and temperature of the object plasma.     

基于高阶统计量的滚动轴承故障诊断方法

针对滚动轴承故障振动信号易受高斯噪声影响的问题,从高阶统计量的理论入手,提出了由信号的高阶谱恢复功率谱.由恢复的功率谱提取故障特征信息的高阶统计量方法,建立了通过高阶谱恢复功率谱的数学模型,并对仿真数据和实测故障数据进行了分析.结果表明,利用高阶累积量对高斯噪声不敏感的特点,可实现高斯噪声下瞬态信号频率与功率谱的正确估计.与传统方法相比,本研究方法可以有效地提取滚动轴承故障特征,同时具有更高的分辨率.     

A pulse-periodic gyroresonant plasma accelerator

A plasma electron accelerator based on the gyromagnetic autoresonance effect is described. Electrons of the initially cold internal-injection plasma (a classical ECR discharge) are accelerated in the magnetic field of a magnetic mirror trap under a one-stage effect of the resonant microwave field and an additional pulsed magnetic field. The synchronism in maintaining the resonance conditions is ensured by a smooth increase in the pulsed magnetic field in the course of a microwave pulse. At the moderate values of the input microwave power (up to 2.5 kW) and the steady-state and pulsed magnetic fields (each up to 1 kG), it is possible to obtain stable relativistic plasma bunches, in which the energy of the electron components is a few hundred keV. The measured X-ray bremsstrahlung spectra have features characteristic of the energy distribution of photons, and the high-energy tails are recorded in the region of 600–800 keV. The dependences of the bremsstrahlung characteristics on the experimental conditions—the value of the steady-state magnetic field and the amplitude of the pulsed magnetic field—are investigated. The experimental data are in good agreement in the quantitative sense with the results of the computer simulation and with the earlier studies.     

Fourier-ratio deconvolution techniques for electron energy-loss spectroscopy (EELS)

We discuss several ways of using Fourier-ratio deconvolution to process low-loss spectra. They include removal of the tail arising from the zero-loss peak, extraction of the spectrum of a particle from data recorded from the particle on a substrate, separation of the bulk and surface components in spectra recorded from samples of the same composition but different thickness, and investigation of interface energy-loss modes. We also demonstrate the use of a Bayesian-equivalent procedure based on the Richardson–Lucy algorithm.     

Spatial and spectral calibration of an acousto-optical spectrometer

The problem of determining the optical spectra at separate points of images that are recorded with an endoscopic acousto-optical spectrometer is considered. The factors that cause distortions in images and spectra are investigated. Algorithms for calibration of this type of instruments and digital data correction for the sequential elimination of distortions of various types are developed. In a model experiment, it is shown that the proposed algorithm provides a quite high quality of determining spectra at arbitrary points of the field of vision.     

Rising the signal-to-noise ratio in X-ray spectra of femtosecond laser-produced plasmas using the “mean-median” algorithm

As femtosecond laser pulses increase in intensity and decrease in duration, interaction between the focused laser radiation and a substance is followed by a sharp increase in the intensity of fast-electron, ion, and electromagnetic noise generation. In turn, the noise signals of X-ray detectors grow in amplitude and the signal-to-noise ratio in recording X-ray spectra of multiply charged ions approaches unity. A significant excess of the noise level over the useful signal is observed in plasmas generated by laser pulses with a power density of ≥10¹⁷ W/cm². The most powerful effect of the above factors is exerted on X-ray spectra recorded by such electromagnetic equipment as CCD-based detectors, photoelectron amplifiers, etc. A new “mean-median” algorithm is described, with which it is possible to considerably increase the signal-to-noise ratio of CCD detectors used to measure X-ray spectra of femtosecond laser-produced plasma.     

Two-photon excitation and emission spectra of the green fluorescent protein variants ECFP, EGFP and EYFP

Two-photon (TP) excitation (820–1150 nm) and emission (280–700 nm) spectra for the fluorescent proteins (FPs) ECFP ³ , EGFP ³ and EYFP ³ produced in human tumour cells were recorded. TP excitation spectra of pure and highly enriched samples were found to be more differentiated in comparison with their one-photon (OP) spectra. They exhibited more pronounced main and local maxima, which coincided among different purity grades within small limits. TP and OP emission spectra of pure and enriched samples were identical. However, in crude samples, excitation was slightly blue-shifted and emission red-shifted. The data indicate that both OP and TP excitation routes led to the same excited states of these molecules. The emission intensity is dependent on the pH of the environment for both types of excitation; the emission intensity maximum can be recorded in the alkaline range. Reconstitution of emission intensity after pH quenching was incomplete, albeit that the respective spectral profiles were identical to those prequenching. When emission data were averaged over the whole range of excitation, the resulting emission profile and maximum coincided with the data generated by optimal excitation. Therefore, out-of-maximum excitation, common practice in TP excitation microscopy, can be used for routine application.     

Note: Zeeman splitting measurements in a high-temperature plasma

The Zeeman effect has been used for measurement of magnetic fields in low-temperature plasma, but the diagnostic technique is difficult to implement in a high-temperature plasma. This paper describes new instrumentation and methodology for simultaneous measurement of the entire Doppler-broadened left and right circularly polarized Zeeman spectra in high-temperature plasmas. Measurements are made using spectra emitted parallel to the magnetic field by carbon impurities in high-temperature plasma. The Doppler-broadened width is much larger than the magnitude of the Zeeman splitting, thus simultaneous recording of the two circularly polarized Zeeman line profiles is key to accurate measurement of the magnetic field in the ZaP Z-pinch plasma device. Spectral data are collected along multiple chords on both sides of the symmetry axis of the plasma. This enables determination of the location of the current axis of the Z-pinch and of lower-bound estimates of the local magnetic field at specific radial locations in the plasma.     

X-ray spectroscopy of Cu impurities on NSTX and comparison with Z-pinch plasmas

X-ray spectroscopy of mid-Z metal impurities is important in the study of tokamak plasmas and may reveal potential problems if their contribution to the radiated power becomes substantial. The analysis of the data from a high-resolution x-ray and extreme ultraviolet grating spectrometer, XEUS, installed on NSTX, was performed focused on a detailed study of x-ray spectra in the range 7-18 A?. These spectra include not only commonly seen iron spectra but also copper spectra not yet employed as an NSTX plasma impurity diagnostic. In particular, the L-shell Cu spectra were modeled and predictions were made for identifying contributions from various Cu ions in different spectral bands. Also, similar spectra, but from much denser Cu plasmas produced on the UNR Z-pinch facility and collected using the convex-crystal spectrometer, were analyzed and compared with NSTX results.     

激光诱导铜产生等离子体羽辉的颜色特性

为了研究等离子体羽的辐射特性,建立了激光诱导辐射模型。通过时空分辨光谱测量技术,测定了激光烧蚀铜诱导产生等离子体羽辉在氧气环境下的发射光谱及其发射强度随时间与空间的分布;利用快速照相法,拍摄了等离子体羽的照片。结果表明:等离子体羽光谱主要由Cu的原子谱线、一价离子谱线组成;其不同区域的颜色不同,且随环境气压而变化。认为等离子体羽的不同区域诱导发光机理不同,中心区域以连续辐射为主;中间区域以原子谱线和一价离子谱线为主;外围区域以原子谱线为主。连续辐射主要来自近靶处高能电子运动而产生的韧致辐射以及电子和一价离子的复合;一价离子谱线主要来自近靶处高能电子与一价离子碰撞传能;原子谱线主要来自电子与原子的碰撞传能以及近靶处电子与一价离子的复合。     

Total quantitative recording of elemental maps and spectra with a scanning microprobe

A system of data recording and analysis has been developed by means of which simultaneously all data from a scanning instrument such as a microprobe can be quantitatively recorded and permanently stored, including spectral outputs from several detectors. Only one scanning operation is required on the specimen. Analysis is then performed on the stored data, which contain quantitative information on distributions of all elements and spectra of all regions.     

Quantitative extraction of spectral line intensities and widths from x-ray spectra recorded with gated microchannel plate detectors

Plasma spectroscopy requires determination of spectral line intensities and widths. At Sandia National Laboratories Z facility we use elliptical crystal spectrometers equipped with gated microchannel plate detectors to record time and space resolved spectra. We collect a large volume of data typically consisting of five to six snapshots in time and five to ten spectral lines with 30 spatial elements per frame, totaling to more than 900 measurements per experiment. This large volume of data requires efficiency in processing. We have addressed this challenge by using a line fitting routine to automatically fit each spectrum using assumed line profiles and taking into account photoelectron statistics to efficiently extract line intensities and widths with uncertainties. We verified that the random data noise obeys Poisson statistics. Rescale factors for converting film exposure to effective counts required for understanding the photoelectron statistics are presented. An example of the application of these results to the analysis of spectra recorded in Z experiments is presented.     

An Automatic Data-Processing Technique for the High-Pressure Xenon γ-Ray Spectrometer

We describe an algorithm for radionuclide detection and identification by the -ray spectra recorded with a high-pressure xenon -ray spectrometer. The algorithm is based on the comparison of the measured spectra with the tabulated radionuclide data. The fitting criteria were formulated. The software package, implementing the algorithm and providing the execution of a complete cycle of -ray spectrum processing, was developed. The algorithm usability and efficiency were demonstrated by testing it with actual spectra.     

Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch

Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian function associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. These measurements are used to gain a better understanding of Z-pinch equilibria.     

Mapping the ionization state of laser-irradiated Ar gas jets with multiwavelength monochromatic x-ray imaging

Two-dimensional monochromatic images of fast-electron stimulated Ar?Kα and He-α x-ray self-emission have recorded a time-integrated map of the extent of Ar(≈6+) and Ar(16+) ions, respectively, within a high density (10(20)?cm(-3) atomic density) Ar plasma. This plasma was produced by irradiating a 2 mm wide clustering Ar gas jet with an ultrahigh intensity (10(19)?W/cm(2), 50 TW) Ti:sapphire laser operating at 800 nm. Spherically bent quartz crystals in the 200 (for Kα) and 201 (for He-α) planes were used as near-normal incidence reflective x-ray optics. We see that a large (830?μm long) region of plasma emits Kα primarily along the laser axis, while the He-α emission is confined to smaller hot spot (230?μm long) region that likely corresponds to the focal volume of the f/8 laser beam. X-ray spectra from a Bragg spectrometer operating in the von Hamos geometry indicate that the centroids of the Kα and He-α emission regions are separated by approximately 330?μm along the laser axis.