Effect of gaunt factor correction in soft x-ray plasma diagnostics

The effect of Gaunt factor correction on temperature estimation over a range 100 to 1500 eV had been studied. Greene’s analytical expression for the quantum mechanical Gaunt factor averaged over Maxwellian distribution is used. Transmission ratios are calculated with and without Gaunt factor for various combinations of beryllium foils, taking into account x-ray emission due to free-free transitions. A significant difference (≳ 15%) is observed between the temperatures estimated from classical and quantum mechanical curves, above 600 eV. Selection of foil combinations useful for estimating higher temperatures is also discussed.     

Stark broadening of neutral helium lines and spectroscopic diagnostics of pulsed helium plasma

Stark broadening parameters (widths and shifts) of two He I isolated spectral lines are measured in a plasma of a low-pressure pulsed arc. Plasma electron densities, determined by spectroscopic method based on previously calibrated He I lines, ranges from 1 x 10¹⁶ cm^-3 to 6 x 10¹⁶ cm^-3. The plasma electron temperature acquired by a Boltzmann plot of several He I lines, lies in the interval 8 000-30 000 K. Results of this work are compared with theoretical predictions and with other experimental data.Received: 30 April 2003, Published online: 29 July 2003PACS: 52.70.-m Plasma diagnostic techniques and instrumentation - 52.70.Kz Optical (ultraviolet, visible, infrared) measurements - 32.70.Jz Line shapes, widths, and shiftsR. Santamarta: Present address: DESY/ZEUS Hamburg, Germany.     

End-on x-ray backlighting experiments for axial diagnostics of wire-array Z-pinch plasma on PPG-1

An X-pinch axial backlighting system has been designed to quantitatively measure the density distribution of wirearray Z-pinch plasmas. End-on backlighting experiments were carried out on a 200 kA, 100 ns pulsed-power generator(PPG-1) at the Tsinghua University. Compared with side-on backlighting, end-on measurements provide an axial view of the evolution of Z-pinch plasmas. Early stages of 2-, 4-, and 8-wire Z-pinch plasmas were observed via point-projection backlighting radiography with a relatively high success rate. The density distribution of Z-pinch plasma on the r–θ plane was obtained directly from the images with the help of step wedges, and the inward radial velocity was calculated. The ablation rates obtained by X-pinch backlighting experiments are compared in detail with those calculated by the rocket model and the results show consistency.     

表面波型微波感偶低气压氦等离子体空间分辨光谱诊断

用光学多道分析仪考察了低气压表面波型微波感氦偶等离子体的发射光谱.经过阿贝尔(Abel)反演变换后,得到了在各种气压和微波功率下此等离子体光谱辐射光强和激发温度的空间分布及其变化规律.讨论了此等离子体的激发机理.推算了其中亚稳态原子的空间分布情况.     

Spatiotemporal spectroscopic diagnostics of a pulse-periodic strontium vapor laser

Results of spectroscopic investigations into plasma of a pulse-periodic strontium vapor laser operating in the superradiance mode on the infrared transition at λ = 6.45 μm are presented. The method of determining the electron temperature and concentration as well as the gas temperature – T _e , n _e , and T _g – based on measuring the absolute intensities of some SrI and SrII and buffer gas (helium or neon) spectral lines is used. Time dependences of the line intensities during a current pulse (τ = 150 ns) and near afterglow (up to 3 μs) are obtained under conditions of non-equilibrium plasma ionization and recombination. The optical system collects radiation from the entire length of the plasma column by means of separating radial volume zones, includingthe central zone and the zone closer to the walls, with the monochromator slit. The results obtained allow us not only to calculate T _e , n _e , and T _g values, but also to trace the spatiotemporal plasma evolution.     

Evaluation of hot spots parameters by simple soft x-ray diagnostics

Properties of the hot spots in Ar and Ne plasma of a gas-puff z-pinch were investigated. Pinhole cameras with entrance diameter 13–250 m, XRD, semiconductor detectors and flat crystal spectrographs with Si and KAP crystals were used for spatially, temporally and spectrally resolved soft x-ray diagnostics. The diameters of Ar (25–30 m) and Ne (40 um) hot spots were found and K-shell x-ray spectra were registered. Temporal evolution of x-rays within 600 ns was observed; the upper estimate of hot spots lifetime did not exceed 50 ns. The described processing and curve fitting of He-like Ar XVII lines provided the values the of electron temperature and density in Ar hot spotsT _e=1·0–1·1 keV,n _e=(1·8–4·0)×10²⁷ m^–3, which support the idea of the Bennett equilibrium validity for the spots.Reprinted with permission of American Institute of Physics from Dense Z-pinches, AIP Conf. Proc. 195 (Eds. N. R. Pereira, J. Davis, N. Rostoker), AIP, New York, 1989.     

Single-order soft x-ray spectra with spectroscopic photon sieve

A single-order diffraction transmission grating named spectroscopic photon sieve(SPS) for soft x-ray region is proposed and demonstrated in this paper. The SPS consists of many circular pinholes located randomly, and can realize both free-standing diffractions and the suppression of higher-order differations. In this paper, the basic concept, numerical simulations, and calibration results of a 1000-lines/mm SPS for soft x-ray synchrotron radiation are presented. As predicted by theoretical calculations, the calibration results of a 1000-lines/mm SPS verify that the higher-order diffractions can be significantly suppressed along the symmetry axis. With the current nanofabrication technique, the SPS can potentially have a higher line density, and can be widely used in synchrotron radiation, laser-induced plasma diagnostics, and astrophysics.     

Infrared plasma diagnostics with lasers

Infrared lasers have rendered possible measurements of plasma parameters in a range not accessible using either optical or microwave techniques. Diagnostic methods based on the refraction and scattering of radiation by free electrons are discussed.     

Plasma characterization on carbon fiber cathode by spectroscopic diagnostics

This paper mainly investigates plasma characterization on carbon fiber cathodes with and without cesium iodide (CsI) coating powered by a ～300~ns, ～ 200~kV accelerating pulse. It was found that the CsI layers can not only improve the diode voltage, but also maintain a stable perveance. This indicates a slowly changed diode gap or a low cathode plasma expansion velocity. By spectroscopic diagnostics, in the vicinity of the cathode surface the average plasma density and temperature were found to be ～ 3× 10¹⁴~cm^-3 and ～ 5~eV, respectively, for an electron current density of ～ 40~A/cm². Furthermore, there exists a multicomponent plasma expansion toward the anode. The plasma expansion velocity, corresponding to the carbon and hydrogen ions, is estimated to be ～ 1.5~cm/μ s. Most notably, Cs spectroscopic line was obtained only at the distance ≤ 0.5~mm from the cathode surface. Carbon and hydrogen ions are obtained up to the distance of 2.5~mm from the cathode surface. Cs ions almost remain at the vicinity of the cathode surface. These results show that the addition of CsI enables a slow cathode plasma expansion toward the anode, providing a positive prospect for developing long-pulse electron beam sources.     

Optical diagnostics of dispersing He plasma

An experimental study has been made of the characteristics of radiation from a dispersing helium plasma. From measurements of the space-time dependence of the line intensities of the helium 2³P — n³D series we obtained the distribution of the populations of the n³D levels for n=3–10. The study has shown that over a wide range of conditions the high-lying levels (n=5–10) are in equilibrium with electrons while a substantial deviation from equilibrium is observed for levels n=3, 4. From the energy distribution of the populations of the upper levels we determined the space-time dependence of the electron temperature, which reflects the process of effective electron cooling during dispersal of the plasma. The gas temperature was estimated from the populations of helium singlet and triplet levels with n=5. The time distribution of the electron density in the plasma was found from the Stark broadening of the spectral lines.Deceased.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 15–19, November, 1992.     

Microwave diagnostics of ultracold neutral plasma

The microwave method is suggested to diagnose the ultracold neutral plasma. Based on the calculations of the dipole radiation, we derive the microwave scattering cross section of the ultracold neutral plasma, and microwave power scattered by the ultracold plasma is calculated as a function of time. The scattering cross section is nearly ¹⁰−11 m².     

电子束离子阱对中性气体电荷交换的光谱诊断

在实验室天体物理研究中,电子束离子阱(EBIT)是极端紫外(EUV)和X射线波段能谱分析的重要实验平台,其中EBIT中心残余的中性气体对离子产生存在显著影响。研究了阱区中心残余中性气体对电荷态分布的影响,发现阱区中心残余中性气体和高电荷态离子之间的电荷/能量交换过程不仅影响离子的电荷分布, 而且对激发函数(离子分布比例随电子能量关系曲线)有着极大的影响。利用电离平衡分析方法成功诊断出阱区中心区域残留的中性气体分子数密度,以及内腔室的真空度。     

X射线激光在稠密等离子体诊断中的应用

X射线波段的相干辐射——X射线激光,由于其短波长、高强度、强相干等独特的优点,已经成为诊断稠密等离子体状态的一种工具.文章结合相应的应用演示实验对此进行了简要的描述,介绍了诊断的原理、X射线激光的获得,以及偏折法和干涉法诊断的实验及其结果.     

X射线激光在稠密等离子体诊断中的应用

X射线波段的相干辐射——X射线激光，由于其短波长、高强度、强相干等独特的优点，已经成为诊断稠密等离子体状态的一种工具．文章结合相应的应用演示实验对此进行了简要的描述，介绍了诊断的原理、X射线激光的获得，以及偏折法和干涉法诊断的实验及其结果．     

Polarization diagnostics of plasma in an electric field

A polarization diagnostics method for Stark states is presented, and it is applied to determining the electric field in a plasma. The theoretical basis of the method is given and the latter is compared with other spectroscopic methods. An apparatus is described for measuring the polarization characteristics of plasma radiation from pulsed discharges. Measurements were made in a beam-type plasma of the relative intensities of the =3964 and 4911 Å allowed and forbidden helium lines and of their degree of linear polarization. The results of the measurements were used to calculate the electric field distribution in the accelerating gap.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 26–33, January, 1995.     

Transient calorimetric diagnostics for plasma processing

We present a detailed study of the Gaussian laser propagation through a dielectric system composed by two right angle prisms. We investigate the transition between the spatial coherence limit, which exhibits wave-like properties and for which the resonance phenomenon can be seen, and the decoherence limit, which exhibits particle-like properties and for which the multiple diffusion occurs. We also analyze the tunneling at critical angles. In our numerical analysis, we shall use BK7 and Fused Silica prisms and a Gaussian He-Ne laser with a wavelength of 632.8 nm and beam waists of 2 mm and 200 μm.