X-ray microanalysis of polyvinyltrimethylsilane surface after impact of accelerated oxygen plasma flow

The elemental composition and surface structure of polyvinyltrimethylsilane exposed in oxygen plasma flow accelerated to an energy of 20–30 eV are studied by scanning electron microscopy and X-ray microanalysis. A microrelief is developed on the surface of the material reflecting its fibrillar supramolecular structure: the oxygen concentration increases, but the carbon concentration decreases. The surface is contaminated with Cu and F atoms as a result of their emission to the plasma due to the wear of the accelerator components.     

Decay of plasma cluster accelerated by coaxial gun

In this paper the decay of air cluster accelerated into the vacual tube is studied. The time dependence of electron density and electron temperature is introduced and the influence of various recombination processes is discussed. The observed plasma decay shows an exponential law, and is for various gun regimes independent and may be explained by ambipolar diffusion to the tube walls.     

Interaction of a plasma source with an ambient plasma

Summary Plasma sources are used to control spacecraft potential and, in general, to improve the electrical contact between a charged body and the space plasma. In the present paper we address the problem of the interaction of a plasma source with the ambient plasma. The source is supposed to be positively charged with respect to the ambient. A self-consistent collisionless one-dimensional fluid model is sketched and some of the results obtained are then presented and discussed. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

A multiple-cathode arc-discharge plasma source

A plasma source for obtaining a 1-cm length of high-fractional ionized plasmas with electron densities in the range of 10¹⁵-10¹⁷ cm^-3 is described. The source consists of a capacitive discharge between a metal anode and an array of small metal cathodes embedded in epoxy, each with a current-limiting resistor. The effect is to have an array of sources which merge into each other, producing the plasma as a whole. The design and performance of the plasma source are presented. The entire system consists of the main electrode and shielding structures, the preionization circuit, and the main discharge circuit. Each of these components is described and the operating parameters and results are given     

Pulsed plasma source of refractory metals

A pulsed plasma source of metal vapors is proposed, including refractory metals. The potentials of this source are illustrated on atomic rhenium, for example. A spectroscopic investigation of the spatial and temporal characteristics of the radiation arid the plasma parameters is conducted for a Re-He mixture. It is shown that the source permits one to realize a plasma over a wide range of parameters. In the spatial zone above the electrodes, the temporal evolution of the concentration distribution of Re atoms in the ground state is measured. A maximum value of 5·10⁺¹⁴ cm^–3 is achieved.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 48–52, April, 1988.     

XUV lines emitted from plasma accelerated during magnetic reconnection

Summary We compute the intensity of the emission in the O VI, Mg X, Si XII, Fe XIII, Fe XVI transitions and the profiles of these spectral lines for a plasma flowing out of reconnecting current sheets that originate in the active region corona either during transient brightenings or in preflare conditions. The characteristic of these lines is a significant non-thermal broadening consistent with plasma non-thermal velocities of the order of 300 km s⁻¹. Hence, it is possible to infer the occurrence of magnetic reconnection in the solar corona by investigating the broadening of transition region and coronal lines in the sites where reconnection is presumed to take place.     

匀加速运动声源的声场建模及其数值算法研究

针对匀加速运动点声源的声场特性与其运动状态密切相关这一问题,提出匀加速直线运动状态下点声源的声场计算方法。利用此方法建立了匀加速直线运动时点声源的声压模型,对模型中的关键参数声矢量R进行数值解析,并对声压进行数值分析仿真,得出匀加速直线运动时固定接收点的声压数值计算方法。用此方法对固定接收点位置的匀加速点声源声压进行声场建模,结果表明:在声源接近接收者一定距离以后,声压明显增大;在此距离之外,距离对声压的影响不大。     

高频离子源等离子体的光谱诊断

采用发射光谱法研究了高频离子源的等离子体性质。该离子源应用于ZF-200keV中子发生器中,是一种电感耦合型无极环形放电高频离子源。实验采用绝对定标后的光学多道分析系统测定了离子源等离子体在不同阶段氢原子巴耳末谱线系中前三条谱线的强度,并采用部分局部热力学平衡状态的理论,计算出了相应阶段高频离子源等离子体的电子温度、氢原子浓度、氢离子浓度等参数,并进行了简要分析。     

Rayleigh flow of one-fluid plasma

The unsteady hydromagnetic flow of a one-fluid plasma confined between two infinitely large and infinitely separated magnetic pole-pieces in investigated. The resistive and ion-cyclotron terms are retained in the governing equations. The time-dependent motion is set up by the impulsive change in velocity of one of the pole-pieces. By means of Laplace transform technique, a solution is obtained which provides the smooth transition from zero to infinite conductivity of the plasma in addition to the effects of viscosity and the Hall current. The resulting two-dimensional flow is found to be permeated by hydromagnetic waves generated by the interaction of the skin-effect, Alfvén propagation and ion-cyclotron gyration. At the stages of motion the shearing stress at the pole-piece is found to be oscillatory.     

Chromatic monitoring of downstream microwave plasma source

The application of the chromatic sensing for monitoring of a microwave plasma source is described. The emitted radiation from the plasma excited in the argon, oxygen and CF₄ mixture was measured with three PIN-diodes with integrated optical filters. The response of the chromatic signals on variation of power and gas composition was investigated. Whereas a good sensitivity of the integrated optical signal to the power was confirmed, only a limited sensitivity to the working gas mixture was found.     

高频离子源等离子体的光谱诊断

 采用发射光谱法研究了高频离子源的等离子体性质。该离子源应用于ZF-200keV中子发生器中，是一种电感耦合型无极环形放电高频离子源。实验采用绝对定标后的光学多道分析系统测定了离子源等离子体在不同阶段氢原子巴耳末谱线系中前三条谱线的强度，并采用部分局部热力学平衡状态的理论，计算出了相应阶段高频离子源等离子体的电子温度、氢原子浓度、氢离子浓度等参数，并进行了简要分析。     

Evaluation of intracranial stenoses and aneurysms with accelerated 4D flow

The aim of this study was to evaluate intracranial arterial stenoses and aneurysms with accelerated time-resolved three-dimensional (3D) phase-contrast MRI or 4D flow. The 4D flow technique was utilized to image four normal volunteers, two patients with intracranial stenoses and two patients with intracranial aneurysms. In order to reduce scan time, parallel imaging was combined with an acquisition strategy that eliminates the corners of k-space. In the two patients with intracranial stenoses, 4D flow velocity measurements showed that one patient had normal velocity profiles in agreement with a previous magnetic resonance angiogram (MRA), while the second showed increased velocities that indicated a less significant narrowing than suspected on a previous MRA, as confirmed by catheter angiography. This result may have prevented an invasive angiogram. In the two patients with 4-mm intracranial aneurysm, one had a stable helical flow pattern with a large jet, while the other had a temporally unstable flow pattern with a more focal jet possibly indicating that the second aneurysm may have a higher likelihood of rupture. Accelerated 4D flow provides time-resolved 3D velocity data in an 8- to 10-min scan. In the stenosis patients, the addition of 4D flow to a traditional MRA adds the velocity data provided from transcranial Doppler ultrasound (TCD) possibly allowing for more accurate grading of stenoses. In the aneurysm patients, visualization of flow patterns may help to provide prognostic information about future risk of rupture.     

Photo-ionized lithium source for plasma accelerator applications

A photo-ionized lithium source is developed for plasma acceleration applications. A homogeneous column of lithium neutral vapor with a density of 2×10^15-3 is confined by helium gas in a heat-pipe oven. A UV laser pulse ionizes the vapor. In this device, the length of the neutral vapor and plasma column is 25 cm. The plasma density was measured by laser interferometry in the visible on the lithium neutrals and by CO₂ laser interferometry on the plasma electrons. The maximum measured plasma density was 2.9×10 ¹⁴ cm^-3, limited by the available UV fluence (≈83 mJ/cm²), corresponding to a 15% ionization fraction. After ionization, the plasma density decreases by a factor of two in about 12 μs. These results show that such a plasma source is scaleable to lengths of the order of 1 m and should satisfy all the requirements for demonstrating the acceleration of electrons by 1 GeV in a 1-GeV/m amplitude plasma wake     

On “Fermi accelerated” ions from an expanding plasma sheath

Ions with a velocity equal to twice the expansion velocity of a sheath are observed. The acceleration mechanism is interpreted in terms of “Fermi acceleration”.     

Cable guns as a plasma source in a plasma opening switch

The characteristics of a plasma generated by cable plasma guns have been studied by a laser interferometer. Cable plasma guns are frequently used as a plasma source in plasma opening switches. In our experiments, the plasma source consists of eight coaxial cable guns mounted on the outer electrode of concentric coaxial electrodes. The reproducibility of the gun in subsequent shots is found to be better than 10%, and the gun-to-gun difference is less than 15%. Assuming a symmetry of eight guns, the contour maps of the electron plasma density are plotted as functions of time. The plasma density becomes maximum near the gun nozzle and near the inner coaxial electrode. The plasma density is low in the area between the coaxial electrodes during the early time of the discharge. At a later time, the plasma fills the space between the two guns more uniformly. Still photographs of the plasma luminosity show a good correspondence with the plasma density plots which were taken 10 μs after the discharge initiation. The plasma gun system is designed for use in a 400-kA inductive voltage adder with the inductive energy storage system     

Observation of synchrotron radiation from electrons accelerated in a petawatt-laser-generated plasma cavity

The dynamics of plasma electrons in the focus of a petawatt laser beam are studied via measurements of their x-ray synchrotron radiation. With increasing laser intensity, a forward directed beam of x rays extending to 50 keV is observed. The measured x rays are well described in the synchrotron asymptotic limit of electrons oscillating in a plasma channel. The critical energy of the measured synchrotron spectrum is found to scale as the Maxwellian temperature of the simultaneously measured electron spectra. At low laser intensity transverse oscillations are negligible as the electrons are predominantly accelerated axially by the laser generated wakefield. At high laser intensity, electrons are directly accelerated by the laser and enter a highly radiative regime with up to 5% of their energy converted into x rays.