Formation of a plane layer of plasma under irradiation by a soft X-ray source

We investigate theoretically the formation of a plasma in a plane layer of polymer foam (density ρ = 0.002 g/cm³ and thickness 800 μm) under the action of an external source of soft X-ray radiation under the conditions of PHELIX experiments. The incident flux is assumed to have a Planck’s distribution over the spectrum with T _rad = 20–40 eV. In numerical calculations, the flux of incident X-ray radiation and the spectral constants of the target substance are varied. The action of an external X-ray radiation source on a low-density foam substance with a density of 2 mg/cm³ causes a plasma to be formed with relatively homogeneous profiles of density and temperature T = 15–35 eV. Absorption of externalradiation energy is distributed in the volume. The plasma temperature increases with increase in the external energy, and the energy passed through the plasma also increases. The results prove to be sensitive to the values of optical constants used in numeral simulation. The spectral flux of external radiation passed through the plasma is chosen as a criterion of correctness of the optical constants used in the calculations. In future experiments using the PHELIX facility, we plan to investigate the slowing-down of an ion beam in a plasma formed as a result of indirect heating of low-density polymer triacetate cellulose (TAC) foam with densities ρ = 0.001–0.01 g/cm³ under the action of a pulse of X-ray radiation, into which the laser radiation is preliminarily transformed.     

Diagnostics of High-Temperature,High-Density Plasma by Radiation Analysis

This article will be restricted to the diagnostics of laboratory plasmas having an average particle energy of higher than 30 eV per particle and a density of greater than 10¹⁹ particles per cm³. Common features of such plasmas related to applied spectroscopy are their complete ionization, the high excitation and ionization levels the particles, the large emission coefficients for continuum radiation over a wide spectral range from the X-ray region up to the infrared, their small size, high temperature and density gradients to the environment, and their transient nature.     

Maximum material thickness for extreme ultra-violet and X-ray backlighter probing of dense plasma

Extreme ultra-violet (EUV) lasers, X-ray lasers and other backlighter sources can be used to probe high-energy density materials if their brightness can overcome self-emission from the material. We investigate the maximum plasma thickness of aluminum, silicon and iron that can be probed with EUV or X-ray photons of energy 89–1243 eV before self-emission from the plasma overwhelms the backlighter output. For a uniform plasma, backlighter transmission decreases exponentially with increasing thickness of the material following Beer's law at a rate dependent on the plasma opacity. We evaluate the plasma opacity with the Los Alamos TOPS opacity data. The self-emission is assumed to be either that of a black body to arise from a plasma in LTE or to only consist of free–free and free–bound emission. It is shown that at higher plasma temperature (?40 eV), EUV radiation (e.g. photon energy=89 eV) can probe a greater thickness of plasma than X-ray radiation (e.g. photon energy=1243 eV).     

Radiation cooling rates of a selenium plasma

The development of a scalable hydrogenic ionization model is described. The model utilizes correct energy and level structure data for each ionization stage and can be coupled self-consistently to a radiation transport calculation of the full nonhydrogenic X-ray spectrum. Thus it can be used to calculate accurately the effects of opacity on radiation emission rates that are of relevance to plasmas designed to produce recombination pumped population inversions due to rapid plasma cooling. The model is applied to a selenium plasma. It is found that, at ion densities where X-ray lasing has been observed, line emission from Δn≠0 transitions is a more important contributor to selenium's cooling rate than line emission from the Δn=0 transitions. Plasma opacity can also play an important role     

X-ray emission from betatron motion in a plasma wiggler

The successful utilization of an ion channel in a plasma to wiggle a 28.5-GeV electron beam to obtain broadband x-ray radiation is reported. The ion channel is induced by the electron bunch as it propagates through an underdense 1.4-meter-long lithium plasma. The quadratic density dependence of the spontaneously emitted betatron x-ray radiation and the divergence angle of approximately (1-3)x10(-4) radian of the forward-emitted x-rays as a consequence of betatron motion in the ion channel are in good agreement with theory. The absolute photon yield and the peak spectral brightness at 14.2-keV photon energy are estimated.     

Formation of a plasma with the determining role of radiative processes in thin foils irradiated by a pulse of the PEARL subpetawatt laser

A superbright X-ray source with a radiation temperature of ~1.2 keV making it possible to create a solid-state plasma whose kinetics is determined by the radiative processes has been implemented under the impact of a 170-TW pulse of the PEARL femtosecond laser facility on an aluminum target with submicron thickness. The diagnostics of the created plasma is performed by X-ray spectral methods using spectral transitions in hollow multicharged ions.     

Ultra'soft X-ray diagnostics of short-living plasmas

Ultrasoft X-ray plasma diagnostics in IPP is realized by using X-ray diodes with Al photocathodes and submicrometer nitrocellulose filters. The X-ray detections system is suitable for measurements in a relatively broad range of radiation intensities in the spectral interval of (10–1000) eV with the time resolution of (1–10) ns under various plasma conditions. Construction, calibration and characteristic properties of the measuring apparatus are described. To illustrate its use, some results of the diagnostics of REB-heated plasma are presented.We would like to acknowledge Dr. P. unka for many helpful discussions and Dr. J. Ullschmied for cooperation in REB-heated plasma diagnostics interpretation.     

渡越辐射在强流电子束诊断中的应用

文中描述了渡越辐射用于束流诊断的理论依据,介绍了利用渡越辐射对18MeV,2.7kA的强流脉冲电子束进行诊断的实验方案,介绍了在强流束测量中遇到的困难和解决方法.实验中获得了渡越辐射的特征图案,并对特征图案进行了分析,得到了测量时应该使用偏振片的结论.据此,利用渡越辐射测量了强流脉冲束的剖面、能量、发散角.并采用渡越辐射与切伦科夫辐射相结合的方法，用切伦科夫辐射测量束剖面,用渡越辐射测量能量和发散角,在同一次实验中获得了强流脉冲束的归一化发射度.     

基于发射率模型约束的多光谱辐射真温反演法

温度测量是工业生产或科学实验中保证产品质量、降低生产成本和确保实验安全的重要因素之一。目前非接触的测温方法以辐射测温法为主,二次测量法是多光谱辐射测温中一种常用的方法。但是,二次测量法不适用于实时数据处理。针对此问题,基于多光谱亮度温度数学模型引入了发射率模型约束条件,提出了一种多光谱辐射真温快速反演法。对于非黑体,根据不同波长下的亮度温度的关系,得出当亮度温度在一个区间内是增函数或者常数函数时,发射率在该区间内是增函数;当亮度温度在一个区间内是减函数时,则发射率在该区间内满足一个关于发射率和波长的不等式。该发射率模型约束条件根据亮度温度的信息,将发射率假设值的构建由多类减少到一类,避免了不必要的发射率的构建。实验分别采用实际发射率随波长单调下降、单调上升、先下降再上升、先上升再下降和随机变化的具有代表性的五个被测目标,针对两个被测温度点进行了仿真对比分析。结果表明,与二次测量法相比,对于同一个被测目标,在相同的温度初值和相同的发射率搜索范围下,新算法在保证精度的情况下,不仅所得结果相同,而且处理速度提升了19.16%～43.45%。     

Time-Resolved Transmission Measurements of Warm Dense Iron Plasma

Transmission measurements of warm dense iron plasma are reported over the photon energy range of 400-1200 eV,including the strong 2p-3d structures.One-dimensional hydrodynamic simulation is performed to estimate the plasma conditions:temperatures of several eVand densities of about 0.1g/cm~3.By using the simulated temperature and density,the calculations of the transmission spectra are performed and compared with the time-resolved experimental results.     

Calculation of radiative heat transfer in argon arc plasmas

Radiation emission and absorption in arc plasmas are important energy transfer processes. Exact calculations, though possible in principle, are usually impossible in practice because of the need to treat a large number of spectral lines and also the continuum radiation in the whole spectrum range. Recently, we have used an approximate method of partial characteristics to evaluate the radiation intensities, radiation fluxes and the divergence of radiation fluxes for SF₆ arc plasma with cylindrical symmetry. In this paper, we have extended our calculations toargon arc plasmas for the plasma pressures of 0.1, 0.5 and 1.0 MPa. We have calculated the coefficients of absorption for Ar plasmas at temperatures from 300 to 35 000 K, and have used these coefficients to calculate the partial characteristics. Both the continuum and the line spectra have been included in calculations. We have taken into account the radiative photo-recombination and bremsstrahlung for the continuous spectrum, and over 500 spectral lines for the discrete spectra.The method of partial characteristics has been applied to three-dimensional calculations of radiative heat transfer — i.e. radiation intensity, radiation flux and its divergence — in simplified temperature profiles. Conclusions have been made concerning validity and utilization of the method of partial characteristics in general gas dynamics problems.     

同步辐射的相干模式

在分析了光源相干相体积的基础上，重点研讨了第三代同步辐射中波荡器（ｕｎｄｕｌａｔｏｒ）辐射的相干模式，能谱亮度，相干光子通量等，这对提高光束线相干能量的传输效率和软Ｘ光相干学束线的设计具有重要意义。     

Interpretation of excitation temperature measurements in a cesium plasma

Electron densities and temperatures have been measured by using a Langmuir probe, as well as spectroscopic observations of continuum radiation and of spectral lines, in a cesium plasma. It is shown that the excitation temperatures determined from relative intensities of spectral lines do not always agree with electron temperature determinations. An interpretation of this discrepancy is proposed and discussed.     

部分电离稠密氦等离子体物态方程的自洽变分计算

稠密氦在高温高压下将会发生电离, 电离能会因为原子、离子以及电子之间的相互作用而降低. 考虑He，He⁺，He²⁺，e之间的相互作用, 通过粒子化学势平衡得到非理想的电离平衡方程，用自洽流体变分过程对方程求解, 进而对自由能求导获得体系的热力学状态参量. 模型计算结果与已有的实验和理论计算相一致. 用此模型预测密度10^-3—10^0.3 g/cm³和温度4—7 eV范围的物态方程, 获得了压力在500　GPa以内的理论数据. 计算表明粒子间的非理想相互作用引起的电离能降低是出现压致电离现象的主要原因，在高温高密度物态方程的计算中必须考虑粒子间非理想相互作用对电离能修正的影响. 关键词： 氦 物态方程 部分电离等离子体 自洽变分     

Measurements and modelling of high pressure pure CO2 spectra from 750 to 8500 cm. I—central and wing regions of the allowed vibrational bands

Precise modelling of infrared absorption by carbon dioxide is of primary importance for radiative transfer calculations in CO₂-rich atmospheres like those of Venus and Mars. Despite various measurements and theoretical models dedicated to this subject, accurate data at different temperatures and pressures are still lacking in numerous spectral regions. In this work, using two Fourier Transform Spectrometers, we have measured spectra of pure CO₂ in a large spectral region range, from 750 to 8500 cm⁻¹ at various densities (3-57 amagat) and temperatures (230-473 K). Comparisons between measured dipolar absorption bands and spectra calculated with the widely used Lorentz line shape show very large discrepancies. This result is expected since the Lorentz approach neglects line-coupling effects due to intermolecular collisions which transfer absorption from the wings to the band center. In order to account for this effect, a theoretical approach based on the impact and Energy Corrected Sudden approximations has been developed. Comparisons of this model with numerous laboratory spectra in a wide range of pressure, temperature and spectral domain show satisfactory agreements for band centers and near wing regions where the impact approximation is valid. However, as expected, due to the breakdown of the impact approximation, the model fails when considering far wing regions. In the absence of precise models accounting for line-mixing and finite collision duration (non impact) effects, empirical approximations are proposed in order to model the far wings.     

Ab initio calculations of thermal conductivity of metals with hot electrons

Warm dense matter (WDM) is a state of a substance with a solid-state density and temperature from 1 to 100 eV. Researchers believe that such a state exists in the cores of giant planets. Investigation of WDM is important for some applications, such as surface treatment on the nanometer scale, laser ablation, and the formation of the plasma sources of the X-ray radiation into the inertial synthesis. In this study, the conductivity and the thermal conductivity are calculated based on density functional theory and the Kubo-Greenwood theory. This approach was already used to simulate the transport properties in a broad range of densities and temperatures, and its efficiency has been demonstrated. The conductivity and the thermal conductivity of aluminum and gold are investigated. Both the isothermal state, when the electron temperature equals the ion temperature, and the two-temperature state, when the electron temperature exceeds the ion temperature, are considered. The calculations were performed for a solid body and liquid in the range of electron temperatures from 0 to 6 eV.     

Calculation of radiative heat transfer in SF6 arcplasmas

Radiation transport in SF₆ are plasmas have been treated for pressures of 0.101, 0.5, and 1.0 MPa. We have investigated the use of an approximate method of partial characteristics. We have calculated spectral absorptivities for SF₆ plasmas for temperatures from 300 to 35 000 K, and have used these absorptivities to calculate the two functions designated ΔI and ΔSim. These functions are integrals over all radiation frequencies for given line segments with a linear variation of temperature along the line. The ΔI and ΔSim values are functions of the end temperatures and the length of the line, and are used to evaluate radiation transfer from line segments in the plasma where the temperature variation for each line segment is approximated as being linear. The validity of this method of partial characteristics has been demonstrated by comparing exact calculations with the approximate calculations to evaluate radiation intensities, radiation fluxes, and divergence of radiation fluxes for specified temperature profiles. The method of partial characteristics has been applied to one- and three-dimensional calculations of radiative heat transfer in simplified temperature profiles. Agreement up to 10% is obtained with exact calculations, but with a large reduction of computation time     

Continuous radiation from a dense,weakly non-ideal,argon plasma

Continuum radiation from the argon plasma generated by a cascade arc has been investigated over the pressure range 1–10 atm and the temperature range 12?16×10³⁰K in the visible, near i.r. and u.v. spectral regions. Plasma temperatures were found from absolute intensities of the argon atom and ion lines; the concentrations of charged particles were determined from the ion-line half-widths.The results obtained on the continuum radiation intensity are compared with theoretical and experimental data obtained by other authors. At elevated pressures, the experimental data have been found to exceed theoretical values in the spectral region under investigation. The dependence of the recombination-threshold-shift in the plasma on azimuthal quantum number appears to be worthy of special attention. Possible reasons for excess radiation are discussed.     

Investigation of X-ray Emission from Plasmas Created by NIXE 6-nsec Nd: Glass Laser System

This paper reports details on the design of the Nd: glass laser facility NIXE at the Central Institute of Optics and Spectroscopy, including the target chamber and the x-ray diagnostics, spatial and temporal behaviour of the 1.06 μm radiation generated are given. Plane, massive targets of aluminium and silicon have been irradiated with 6-nsec FWHM laser pulses. Investigations of laser produced Al- and Si-plasmas have been performed with spectral and spatial high resolution diagnostics, consisting of a 3 channel crystal-spectrometer, 2 crystal-microscopes, and 2 pinhole cameras and the results are presented. Line spectra have been interpreted within the hypothesis of a steady state coronal equilibrium. He-like lines of the Al-plasma indicate temperatures up to 400 eV and densities up to 2 · 10²⁰ cm^?3. Total x-ray photon flux in the He-like resonance line has been calculated giving 10¹³ phot/ster.     

基于光谱发射率函数基形式不变的辐射测温技术

近年来,随着国防、工业、科技等领域飞速发展,无论是对于军用动力发射系统还是对于民用钢铁冶炼以及高科技新兴产业,辐射温度测量都具有重要意义。尤其在温度极高且伴随着瞬态测温(小于1 μs)需求的场合,多光谱辐射测温法被广泛运用。多光谱辐射测温法是通过选取被测目标多个特征波长,测量特征波长的辐射信息,再假设发射率与波长相关的数学模型,最终求解得到辐射温度。目前,利用该方法实际测温时,光谱发射率都采用固定的假设数学模型,而针对目标在不同温度状态下,该固定模型则无法进行自适应变化。同样,在不同温度下,如何解算最终的发射率和辐射温度也没有普适性的方法。基于普朗克黑体辐射定律,提出一种被测目标在不同温度下光谱发射率函数基形式不变的思想,简称发射率函数基形式不变法。通过该方法,发射率模型可以根据物体在不同温度状态下,函数系数动态改变来进行自适应变化。同时对于如何解算最终的发射率和辐射温度也相应提出了普适性的方法。通过大量仿真验证以及实际测量光谱辐射照度标准灯和溴钨灯温度实验,证明本文提出的方法比现有的光谱发射率处理方法更加简单实用并且能够有效地提高光谱发射率的计算精度,从而提高辐射温度测量精度。同时具有实用性好、应用广泛等特点。