Method for modifying the structure and elemental composition of the solid surface during a high-voltage vacuum discharge

A new method for modifying the surface of a solid, which makes it possible to change effectively the structure and elemental composition of the surface with a high precision, is developed and tested experimentally. The method is based on the action of the plasma of a pulsed high-voltage vacuum discharge, the ion beam from the plasma, and the electron beam on a solid target. The emission and plasma parameters are observed in a pulsed electric field produced in the diode system to which a pulsed voltage with an amplitude of ～10³–10⁵ V and a duration from 10^?9 to 10^?5 s is applied.     

A numerical model for lithium plasma process in a hybrid microwave ion source

Lithium ions are widely used in many scientific fields; in order to get these ions, it is necessary to study lithium plasma process thoroughly. Recently, a hybrid ⁷Li³⁺ ion source has been designed and tested at Peking University (PKU). To understand the lithium plasma behaviour inside the plasma chamber and to provide some guidelines for ion source optimization to generate ⁷Li³⁺, a numerical model based on the plasma equilibrium equations is developed in this work, which is helpful not only for our ion source, but also for understanding the physical process of lithium plasma from ECR ion sources with different frequencies. This model can describe the density and fraction of lithium ions in various system parameters. The dependences of the Li⁺, Li²⁺, and Li³⁺ ion density and fraction on electron temperature, gas pressure, microwave power, surface ionizer, and the magnetic field are investigated systematically.     

惰性物质等离子体物态方程研究

对高温高压下惰性等离子体的电离度和物态方程，给出了一种基于Thomas-Feimi(TF)统计模型的简化计算新方法，即首先对TF模型电离势的数值结果进行函数逼近，得出近似计算电离势的简单解析函数；在局部热动平衡情况下，假定离子数密度n(Z^*)为Z^*的连续函数，再由Debye-Hückel修正的 Saha 方程，得出了一个便于数值求解的电离度的近似计算公式，从而建立了一种惰性等离子体物态方程的简化模型，并对氦、氖、氩三种惰性物质等离子体进行了计算.计算结果与其他文献计算结果和实验值均符合很好.所提出的简单模型也适用于计算混合物物态方程，在高温高密度强电离等离子体领域将有更为广阔的应用前景.     

Breath water-based doubly labelled water method for the noninvasive determination of CO2 production and energy expenditure in mice

ABSTRACT

We explored a novel doubly labelled water (DLW) method based on breath water (BW-DLW) in mice to determine whole body CO₂ production and energy expenditure noninvasively. The BW-DLW method was compared to the DLW based on blood plasma. Mice (n?=?11, 43.5?±?4.6?g body mass (BM)) were administered orally a single bolus of doubly labelled water (1.2?g H₂¹⁸O kg BM^?1 and 0.4?g ²H₂O kg BM^?1, 99 atom% (AP) ¹⁸O or ²H). To sample breath water, the mice were placed into a respiration vessel. The exhaled water vapour was condensed in a cold-trap. The isotope enrichments of breath water were compared with plasma samples. The ²H/¹H and ¹⁸O/¹⁶O isotope ratios were measured by means of isotope ratio mass spectrometry. The CO₂ production (RCO₂) was calculated from the ²H and ¹⁸O enrichments in breath water and plasma over 5 days. The isotope enrichments of breath water vs. plasma were correlated (R²?=?0.89 for ²H and 0.95 for ¹⁸O) linearly. The RCO₂ determined based on breath water and plasma was not different (113.2?±?12.7 vs. 111.4?±?11.0?mmol?d^–1), respectively. In conclusion, the novel BW-DLW method is appropriate to obtain reliable estimates of RCO₂ avoiding blood sampling.     

Femtosecond Fourier interferometry of a nonideal plasma

Experimental diagnostic methods based on the measurement of the reflectance of a plasma are considered. The application of Fourier interferometry for measuring the dynamics of variation of the amplitude and phase of the complex reflectance of the Au plasma for various delay times in intervals shorter than 1 ps relative to the pumping laser pulse with a femtosecond time resolution is described in detail in the intensity range ∼10¹³–10¹⁴ W/cm². The variation of the complex refractive index of the heated Au target for a pump pulse intensity of ∼10¹²–10¹³ W/cm² is analyzed on the basis of experimental data using the Fresnel formulas.     

Generation of a dense electron beam in a thin film using an ultraintense femtosecond laser pulse

Electron dynamics in a thin target irradiated with femtosecond laser pulses at an intensity of 10²⁰ W/cm² is studied in the framework of the kinetic theory of laser plasma based on the construction of propagators (in classical limit) for electron and ion distribution functions in plasma. The calculations are performed for real densities and charges of plasma ions. Electrons are partly ejected from the target. The laser pulse energy is predominantly absorbed by electrons, and the electrons are accelerated to relatively high energies.     

Experiments on two-step heating of a dense plasma in the GOL-3 facility

This paper presents the results of experiments on two-stage heating of a dense plasma by a relativistic electron beam in the GOL-3 facility. A dense plasma with a length of about a meter and a hydrogen density up to 10¹⁷ cm⁻³ was created in the main plasma, whose density was 10¹⁵ cm⁻³. In the process of interacting with the plasma, the electron beam (1 MeV, 40 kA, 4 μs) imparts its energy to the electrons of the main plasma through collective effects. The heated electrons, as they disperse along the magnetic field lines, in turn reach the region of dense plasma and impart their energy to it by pairwise collisions. Estimates based on experimental data are given for the parameters of the flux of hot plasma electrons, the energy released in the dense plasma, and the energy balance of the beam-plasma system. The paper discusses the dynamics of the plasma, which is inhomogeneous in density and temperature, including the appearance of pressure waves. Zh. éksp. Teor. Fiz. 113, 897–917 (March 1998)     

A Source for Fuel Supply to a Fusion Reactor Core

We present the results of studies of the plasma source based on the coaxial accelerator with the slothole channel geometry for plasma acceleration and working gas inlet into the accelerator via the electrodynamic valve. The plasma parameters at the output of the accelerator are measured. The slot-hole channel of the accelerator created higher jet pressure, as compared to the coaxial channel, especially at large distances from the source. The jet pressure reached 10⁶ N/m² at a distance of 0.7 m. The source created moderately pure plasma for a current below 80 kA. The density was (2.5–5) × 10²² m^–3, which was higher than the density obtained with the coaxial gun.     

磁化等离子体的纵向电阻率

从动力论方程出发,推导并讨论了磁化与非磁化等离子体的纵向电阻率。结果是:(1)各向同性磁化等离子体的电阻率约为非磁化者的1.5倍;(2)对各向异性的等离子体而言,磁化后的电阻率约与T_e⊥T_e‖^-5/2成正比,但非磁化时的电阻率则与T_e⊥^-1T_e‖^-1/2成正比。以上的差异主要是来自外磁场对电子运动轨迹的作用。同时本文亦论述了在讨论经典电阻率时,静态屏蔽作用是主要的,而动力屏蔽对电阻率的影响是可以忽略不计的。 关键词：     

纳秒激光诱导紫铜黄铜等离子体特征参数的对比研究

基于1064 nm Nd:YAG激光器,对比研究了紫铜和黄铜等离子的特征参数。洛仑兹函数拟合Cu I 324.75 nm得到紫铜和黄铜等离子体的电子密度分别是3.61017 cm-3和3.31017 cm-3。为了减小谱线自发辐射跃迁几率不确定性和测量误差带来的计算误差,采用改进型迭代玻耳兹曼算法精确求解紫铜等离子体和黄铜等离子体的电子温度分别是6316 K和6051 K,分析表明,两种等离子体特征参数的差异主要是由于黄铜中的锌元素的电离能（9.39 eV）大于铜元素的电离能（7.72 eV）而造成的。实验数据证实激光诱导的紫铜和黄铜等离子体满足局部热力学平衡模型和光学薄模型。     

Electron temperature (T e) measurements by Thomson scattering system

Thomson scattering technique based on high power laser has already proved its superoirity in measuring the electron temperature (T _e and density (n _e) in fusion plasma devices like tokamaks. The method is a direct and unambiguous one, widely used for the localised and simultaneous measurements of the above parameters. In Thomson scattering experiment, the light scattered by the plasma electrons is used for the measurements. The plasma electron temperature is measured from the Doppler shifted scattered spectrum and density from the total scattered intensity. A single point Thomson scattering system involving a Q-switched ruby laser and PMTs as the detector is deployed in ADITYA tokamak to give the plasma electron parameters. The system is capable of providing the parameters T _e from 30 eV to 1 keV and n _e from 5 × 10¹²cm⁻³−5 × 10¹³cm⁻³. The system is also able to give the parameter profile from the plasma center (Z=0 cm) to a vertical position of Z=+22 cm to Z=−14 cm, with a spatial resolution of 1 cm on shot to shot basis. This paper discusses the initial measurements of the plasma temperature from ADITYA.     

Analysis of plasma photonic crystal with a tunable band gap using parallel method

This paper presents a parallel frequency-dependent finite-difference time-domain ((FD)²TD) method for plasma in the dispersive media. Results obtained with parallel and serial algorithms verify that parallel (FD)²TD has the same precision as the serial (FD)²TD, while the parallel approach could reduce the CPU time efficiently. A tunable filter is analyzed based on a one-dimensional photonic crystal containing a plasma defect by this method. The tunability of the photonic crystal filter can be achieved by adjusting the defect layer parameters instead of changing the dimension of photonic crystal.     

Rates and channels of water ionization by a high-current high-voltage pulsed discharge

The experimentally observed growth of the plasma density in a high-current high-voltage pulsed discharge in a liquid medium is compared with the results of calculations based on the effective cross sections for electron-impact ionization and other elementary processes. It is found that, in the initial stage of the discharge, the plasma density grows linearly with time, whereas at densities above 3 × 10¹⁰ cm^?3, the growth becomes exponential due to the collective acceleration of plasma electrons. The gas-vapor fraction of the water medium is ionized by two groups of electrons: low-energy electrons, with energies about several tens of electronvolts, and high-energy ones, with energies in the kiloelectronvolt range. The energy spent on water ionization is estimated and is found to be several times higher than the energy required to ionize a rarefied gas.     

Preliminary results of the study of the d(d,n)3He reaction in the astrophysical energy range with the use of a Hall plasma accelerator

The possibility of using a plasma accelerator based on a pulsed Hall ion source to study the characteristics of pd, dd, d³He, ³He, and⁴He reactions in the astrophysical energy range (2–12 keV) has been considered. The preliminary experimental data on measurement of the astrophysical S factor for the dd reaction (dd → ³He + n (2.5 MeV)) at average deuteron collision energies E _col = 4.5 and 4.95 keV and the deuteron beam energy spread FWHM = 18% are reported. The found value of the S factor is in agreement with the results of the experiments carried out by us previously using linear plasma in the inverse Z-pinch configuration.     

Non-contact acoustic tests based on nanosecond laser ablation: Generation of a pulse sound source with a small amplitude

A method to generate a pulse sound source for acoustic tests based on nanosecond laser ablation with a plasma plume is discussed. Irradiating a solid surface with a laser beam expands a high-temperature plasma plume composed of free electrons, ionized atoms, etc. at a high velocity throughout ambient air. The shockwave generated by the plasma plume becomes the pulse sound source. A laser ablation sound source has two features. Because laser ablation is induced when the laser fluence reaches 10¹²–10¹⁴ W/m², which is less than that for laser-induced breakdown (10¹⁵ W/m²), laser ablation can generate a lower sound pressure, and the sound source has a hemispherical radiation pattern on the surface where laser ablation is generated. Additionally, another feature is that laser-induced breakdown sound sources can fluctuate, whereas laser ablation sound sources do not because laser ablation is produced at a laser beam–irradiation point. We validate this laser ablation method for acoustic tests by comparing the measured and theoretical resonant frequencies of an impedance tube.     

NOx generation in laser-produced plasma in air as a function of dissipated energy

An experimental study on the production of NO_x as a function of dissipated energy in laser-produced plasma in air is presented. A plasma was produced by focusing a (60–180) mJ, 5 ns, 532 nm pulse from a Q-switched Nd:YAG laser. The results show that for laser energy in the range of 13–99 mJ the laser plasma generates 6.7×10¹⁶ NO_x molecules per joule and 4.6×10¹⁶ NO molecules per joule. An order of magnitude estimate of the NO and NO_x production per unit volume of heated gas based on a simple model show that the NO_x and NO production efficiency in air are about 3×10²² and 2×10²² molecules J⁻¹ m⁻³.     

HL-2A托卡马克中性束辐射光谱的数值模拟

采用数值模拟的方法研究中性束辐射光谱(BES)对开展与中性束相关的光谱诊断与实验有重要的指导意义.本文在HL-2A托卡马克装置上利用ADAS数据库（Atomic Data and Analysis Structure,1998）计算有效束辐射系数和有效束衰减系数,分析了束辐射光谱强度与等离子体运行参数和中性束参数的关系,并在不同的中性束注入能量、等离子体密度分布和等离子体温度分布的情况下,获得了束辐射光谱强度的空间分布.在n_e=2×10¹³ cm< 关键词： 中性束 束辐射光谱 束衰减     

Effect of strongly coupled plasma on the doubly excited states of heliumlike ions

The effect of strongly coupled plasma occurring in astrophysical context has been studied for the first time to estimate the energy levels of the autoionizing states of highly stripped astrophysically important ions Al¹¹⁺, Si¹²⁺, P¹³⁺, S¹⁴⁺ and Cl¹⁵⁺ and also C⁴⁺ isoelectronic to helium. The transition energies corresponding to 1s ²:¹S^e → 2s ²:¹S^e, 2p ²:¹D^e, 2s2p:¹P^o, 2s3d:¹D^e and 2p3d:¹F^o are analyzed with respect to different plasma densities using the ion sphere (IS) model of strongly coupled plasma. Transition energies are obtained from the position of the poles of a variational functional based on frequency dependent perturbation calculation probing the collective oscillation modes of the plasma embedded two electron ions. For the free ions corresponding to zero plasma coupling our calculated data agree well with those obtained from spectroscopic data while for the plasma embedded ions the data are new but follow systematic trend. The work has been performed in the domain of linear response theory. The analytical wave function of the doubly excited states have been obtained and may be useful for calculating various transition properties of the plasma embedded ions and also for estimating the rate coefficients for dielectronic recombination processes which play a major role in maintaining equilibrium in high temperature astrophysical or laser produced plasmas.     

Anomalous slowdown of relaxation in an ultracold plasma

Recent experiments by T.C. Killian et al. [Phys. Rev. Lett. 83, 4776 (1999)], in which an ultracold plasma (N _e～2×10⁹ cm^?3, T _e～0.1K, and T _i～10 μK) with anomalously long lifetime of ～100 μs was obtained, are explained based on a previously developed theory. The results of computer simulations of the plasma transition into a metastable state and initial heating of electrons up to several K are presented. An expression earlier obtained for the rate of the metastable plasma recombination agrees with the measured anomalously long lifetime. A conclusion is drawn that the previously predicted new physical object—a metastable overcooled plasma—is realized experimentally.     

“碰撞-辐射”模型在Z箍缩等离子体K壳层线辐射谱分析中的应用

介绍了由K壳层谱线强度比估算等离子体状态参数的"碰撞-辐射"模型的基本原理.详细描述了自行研制的基于该模型的Z箍缩等离子体K壳层线辐射谱分析程序——ZSPEC的基本情况.给出了氖等离子体的计算结果,包括不同电离态离子的相对含量随电子温度的变化曲线和K壳层谱线强度比在"电子密度-电子温度"平面内的等高线分布图.该程序已在"阳"加速器Z箍缩实验结果分析中得到应用,将椭圆晶体谱仪测得的氖等离子体K壳层谱线强度比与ZSPEC程序计算结果相比较,得出在该发实验 关键词： 碰撞-辐射模型 K壳层线辐射谱')" href="#">K壳层线辐射谱 氖气喷气Z箍缩 阳加速器