Ar+ and Xe+ velocities near the presheath-sheath boundary in an Ar/Xe discharge

The velocities of Ar+ and Xe+ ions near the presheath-sheath boundary in an Ar/Xe discharge are studied by particle-in-cell Monte Carlo simulation. For a pure argon discharge the argon ion has almost the same velocity profile as it does in the mixture of argon and xenon. Similarly, for a xenon discharge the xenon ion has almost the same velocity profile as it does in the mixture of argon and xenon. The ion speed at the sheath-presheath boundary is the same for an ion in a pure argon or xenon discharge and for the same ion in a mixture of argon and xenon. We conclude that, in our simulation, each ion reaches its own Bohm speed at the presheath-sheath interface.     

High-intensity femtosecond laser absorption by rare-gas clusters

The energy absorption efficiency of high-intensity (～10^{16}W/cm^2) femtosecond laser pulses in a dense jet of large rare-gas clusters has been measured. Experimental results show that the energy absorption efficiency is strongly dependent on the cluster size and can be higher than 90%. The measurement of the ion energy indicates that the average ion energies of argon and xenon can be as high as 90 and 100keV, respectively. The dependence of the average energy of the ions on the cluster size is also measured. At comparatively low gas backing pressure, the average ion energies of argon and xenon increase with increasing gas backing pressure. The average ion energy of argon becomes saturated gradually with further increase of the gas backing pressure. For xenon, the average ion energy drops a little after the gas backing pressure exceeds 9 bar (3.2×10^5 atoms/cluster). The result showing the existence of a maximum average ion energy has been interpreted within the framework of the microplasma sphere model.     

Sputter yields of Mo,Ti, W,Al, Ag under xenon ion incidence

The sputter yield is an important material parameter not only for various surface treatment techniques, but also for electric spacecraft propulsion. Many satellite or thruster components might be subject of erosion due to energetic and/or related secondary ions. In order to estimate the lifetime of these components the sputter yield under xenon ion incidence has to be known in dependence on ion energy and incidence angle, mainly in the low energy region (i.e. below 1500 eV). However, for many materials related to electric propulsion the supply of sputter yield data in literature is quite poor. Therefore, in this study the sputter yields of molybdenum, titanium, tungsten, silver and aluminium was investigated under xenon ion incidence.     

Low-energy ion emission from a xenon gas-puff laser-plasma X-ray source

We have measured low-energy ion emission from a gas-puff laser-plasma X-ray source. The ions may cause the degradation of the condenser mirror of the extreme ultra-violet projection lithography system. A 0.7 J in 8 ns Nd:YAG laser at 1.06 μm was focused onto the xenon gas-puff target with an intensity of ∼10¹² W/cm². The silicon (111) plates, placed at a distance of 32 mm from the laser-interaction region, were exposed with the xenon ions. The average ion energy was measured to be less than 50 eV with a Faraday-cup detector placed close to the silicon plates. The xenon deposition occurred in the silicon plates with a depth of less than 40 nm. The deposition density was measured with a quadrupole secondary ion mass spectrometer to be 10²¹ /cm³ after 1500 laser shots. The energy-conversion efficiency from the laser energy into the ions is ∼0.1%/4 π sr/shot. For the lithography system, if we can remove such ion bombardment completely using novel techniques such as electro-magnetic devices or gas flow curtain techniques, the lifetime of the condenser mirror will be extended significantly. Received: 20 November 2000 / Published online: 9 February 2001     

Dose dependence of the substitutional fraction of Xe implanted in Fe

By means of the nuclear orientation technique a systematic study of the behaviour of xenon implanted in iron has been done. Strong evidence for the dose dependence of the substitutional fraction is shown. Radiation damage during implantation is obviously the cause of this phenomenon. By means of a general mathematical model one can describe what happens during implantation. A physical two-site model derived from the general one enabled us to explain the dose dependence of the substitutional fraction. At the same time, the dependence of the substitutional fraction on other parameters as temperature and ion flux appears in the equations.     

Electron production by metastable rare gas atom impact on a molybdenum (110) surface

Electron production by impact of thermal energy metastable helium, argon, and xenon atoms on a molybdenum (110) surface was studied. The electron yield was always highest for a clean surface and decreased considerably when the surface was exposed to either oxygen or carbon monoxide. The change in electronic yield with gas coverage of the surface was most drastic for xenon and smallest for helium metastables. The similarity of the present results to earlier measurements of electron production by low energy noble gas ion impact led us to believe that metastable deexcitation proceeded via resonance ionization followed by Auger neutralization in the present cases.     

L x‐ray transitions in F‐like to Na‐like xenon ions determined at a room temperature electron beam ion trap

Fluorine‐like to sodium‐like xenon ions were investigated by wavelength‐dispersive x‐ray spectrometry at the Dresden Electron Beam Ion Trap (EBIT) working at room temperature. In addition to the precise measurement of the L x‐ray transition energies following ionization, excitation and recombination processes in the highly charged xenon ions, the spectra were analyzed for different gas pressures in the trap. Multiconfiguration Dirac‐Fock calculations are introduced that were applied to the energies, transition probabilities and excitation cross‐sections. The production of neon‐like xenon ions was demonstrated even at very high gas pressures. Copyright © 2005 John Wiley & Sons, Ltd.     

Observation of a transition in the dynamics of strong-field double ionization

The double ionization of argon and xenon in an intense laser field has been studied in detail using an electron-ion coincidence technique. The observed double ionization electron spectra in xenon show resonancelike structures here resolved for the first time. In argon, the featureless spectra are consistent with rescattering. This represents a clear transition in the dynamics of strong-field double ionization, analogous to the well-known transition between the tunneling and multiphoton regimes in single ionization.     

New Applications of Langmuir Probes

In this work, two new possibilities for standard probe diagnostics are described. The first one can be used to study isotropic, collisionless low-pressure plasma in which the electron energy distribution function is close to a Maxwellian one. In such plasmas, the Boltzmann law, Bohm effect, and 3/2 power law are valid. Use of corresponding system of equations for cylindrical Langmuir probes allowed for measurements of probe sheath thicknesses and the mean ion mass. The solution of this task was provided by accurate probe diagnostics of inductive xenon plasma at pressure p = 2 mTorr that resulted in the determination of the Bohm coefficient C_BCyl = 1.22. The second possibility of probe diagnostics includes a method and device for evaluation of ion current density to a wall under a floating potential using a radially movable plane wall Langmuir probe simulator. This measurement in the same xenon plasma served as the basis for development of an ion source in which the given wall was represented by an ion extracting electrode of the ion extraction grid system.     

Xenon prevents cellular damage in differentiated PC-12 cells exposed to hypoxia

Background  

The neuroprotective effect of xenon has been demonstrated for glutamatergic neurons. In the present study it is investigated if dopaminergic neurons, i.e. nerve-growth-factor differentiated PC-12 cells, are protected as well against hypoxia-induced cell damage in the presence of xenon.     

Laser-induced fluorescence measurements of velocity within a Hall discharge

The results of a study of laser-induced fluorescence velocimetry of neutral and singly ionized xenon in the plume and interior portions of the acceleration channel of a Hall thruster plasma discharge operating at powers ranging from 250 to 725 W are described. Axial ion and neutral velocity profiles for four discharge voltage conditions (100 V, 160 V, 200 V, 250 V) are measured as are radial ion velocity profiles in the near-field plume. Ion velocity measurements of axial velocity both inside and outside the thruster as well as radial velocity measurements outside the thruster are performed using laser-induced fluorescence with nonresonant signal detection on the xenon ion 5d[4]_7/2–6p[3]_5/2 excitation transition while monitoring the signal from the 6s[2]_3/2–6p[3]_5/2transition. Neutral axial velocity measurements are similarly performed in the interior of the Hall thruster using the 6s[3/2]⁰ ₂–6p[3/2]₂transition with resonance fluorescence collection. Optical access to the interior of the Hall thruster is provided by a 1-mm-wide axial slot in the insulator outer wall. While the majority of the ion velocity measurements used partially saturated fluorescence to improve the signal-to-noise ratio, one radial trace of the ion transition was taken in the linear fluorescence region and yields a xenon ion translational temperature between 400 and 800 K at a location 13 mm into the plume. Received: 27 September 2000 / Revised version: 2 March 2001 / Published online: 9 May 2001     

The influence of implanted xenon on the sputtering yield of silicon

Following implantation labeling with either 200 or 270 keV Xe⁺ the sputtering yield of silicon bombarded with 20 keV Xe⁺ has been determined in situ by means of the backscattering technique (Y = 3.0 ± 0.3 (atoms/ion)). Yield enhancement by up to 60% was observed in cases where the implantation-induced xenon concentrations exceeded the saturation concentration during sputtering. The effect is attributed to (i) an increase in energy deposition at the surface introduced by pronounced xenon loading of the target and (ii) lowering of the surface binding energy. As a consequence the energy dependence of the xenon sputtering yield of silicon is expected to be strongly affected by the energy dependence of the xenon saturation concentration in silicon. Available experimental data support this idea.     

Xenon induced changes of plasma drop and electron temperature of a thermionic converter

The I–V curves of a thermionic converter were measured for several cesium pressures and various electrode distances, and partial pressures of added xenon as well. The minimum internal voltage drop across the electrode gap was determined and correlated with cesium pressure, spacing and xenon pressure. Without xenon added this voltage drop shows the well-known minimum at an optimum pressure-spacing product ofp _Cs d=5·10⁻²cm·Torr. Only for smaller values of the pressure-spacing product the internal voltage drop can be reduced by the addition of xenon. An interpretation is achieved by a comparatively simple model assuming a uniform electron temperature in the electrode gap. Using this model, the electron temperatures were calculated for various spacings and xenon pressures. Comparing the experimental data of the internal voltage drop and the correspondingly calculated electron temperatures it turns out that, within the framework of the model used, the internal voltage drop is represented by the electron temperature. The electron temperature itself is determined by the ion balance. Presented at the 10th Intersociety Energy Conversion Engineering Conference, Newark, Delaware, USA (1975).     

First results from the Freiburg electron beam ion trap FreEBIT

Initial tests from the Freiburg electron beam ion trap are reported. Highly charged ions of xenon, barium, tungsten and krypton have been observed with charge states up to 60+ by means of X-ray spectroscopy. The current status, upgrade and future experiments are outlined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Atomistic Simulation of the Fission-Fragment-Induced Formation of Defects in a Uranium–Molybdenum Alloy

Journal of Experimental and Theoretical Physics - The formation of defects in a uranium–molybdenum alloy induced by xenon and zirconium ion irradiation with energies typical of fission...     

Laser probing of ions in a storage ring: A method for selective determination of lifetimes of metastable states

A collinear laser probing technique is introduced for use in ion storage rings. This method can be used for high resolution studies of the decay properties of metastable states in ions. An experiment on singly charged xenon utilizing this technique is presented. By selective excitation of individual hyperfine states a drastic hyperfine induced quenching was observed. Systematic effects from ion beam neutralization in the rest gas and mixing effects occurring in the bending magnets are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Energy spectra and temperature distributions of clusters produced during ion-beam sputtering of metals

A method for evaluating the energy spectra and temperature dependences of the yield of neutral and charged clusters that consist of N≥5 atoms and are produced by ion bombardment of metals is proposed. The results are presented in the form of simple formulas. Theoretical energy spectra of clusters emitted as a result of bombarding niobium, tantalum, and iron targets by atomic ions of gold or xenon and temperature dependences of the yield of silver clusters produced by bombarding the targets with xenon ions are compared with experimental data.

     

XeI and XeII radiative lifetimes and transition probabilities

The lifetimes of ten levels of the xenon atom and two levels of the ion were measured. The probabilities for several transitions are calculated. The effective decay cross section is calculated for collisions for the 2p₈ level of the xenon atom.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp.24–29, March, 1971.The authors thank V. S. Mel'chenko for assistance in this study.     

Production of multiply charged xenon ions

A multiply charged ion source based on E.C.R. heating is described and abundances for xenon ions up to Xe¹³⁺ are given.     

大功率脉冲氙灯的放电研究

利用转镜式高速摄影机分幅摄影技术,对脉冲氙灯放电中的沟道扩展和熄灭过程进行了摄影和分析.放电时沟道扩展速度很快,呈树枝状,沟道熄灭过程长于扩展过程,且呈斑状.同时研究了预电离放电对沟道扩展和熄灭过程的影响,当预电离存在时,脉冲氙灯放电的沟道扩展的时间要长.结果表明,预电离有利于放电沟道的形成,提高氙灯的发光效率,且有助于减小主放电能量对管壁材料的冲击.