Low-Pressure Helicon-Plasma Discharge Initiation via Magnetic Field Ramping

Discharge initiation at low pressures and flow rates is investigated in the Madison Helicon Experiment flowing helicon source. At low pressures (below 14-sccm flow rate), a threshold magnetic field exists for discharge initiation which depends on RF power and gas flow rate. Above the threshold magnetic field, RF discharges start only after a significant delay (approximately seconds) and sometimes will not start at all. This threshold magnetic field is interpreted using electron multipactor arguments. A technique is described for initiating discharges at low flow rates and pressures $(lambda_{{rm en}, {rm iz}} ≫ L_{rm system})$ and high magnetic fields (above the threshold value). Without a static magnetic field present, the RF power is turned on, and a lower density $(≪ 10^{11} hbox{cm}^{-3})$ unmagnetized discharge occurs. The magnetic field is then applied, and the discharge transitions to the higher density (up to $10^{13} hbox{cm}^{-3}$) regime. Using this method, magnetized discharges can be started at flow rates as low as 1 sccm ( $1.8 times 10^{-4} hbox{torr}$ at $z = -91 hbox{cm}$ , $1.7 times 10^{-5} hbox{torr}$ at $z = 105 hbox{cm}$) at 500 W in a 1.04-kG magnetic field. This technique can be used to initiate low-pressure helicon discharges for basic plasma science experiments and other applications.      

Non-equilibrium plasma production by pulsed laser ablation of gold

A gold target has been irradiated with a Q-switched Nd:Yag laser having 1064\,\hbox{nm} wavelength, 9\,\hbox{ns} pulse width, 900\,\hbox{mJ} maximum pulse energy and a maximum power density of the order of 10^{10}\,\hbox{W}/\hbox{cm}^2 . The laser-target interaction produces a strong gold etching with a production of a plasma in front of the target. The plasma contains neutrals and ions having high charge state. Time-of-flight measurements are presented for the analysis of the ion production and ion velocity. A cylindrical electrostatic deflection ion analyzer permits to measure the yield of the emitted ions, their charge state and their ion energy distribution. Measurements indicate that the ion charge state reaches 6^+ and 10^+ at a laser fluence of 100\,\rm{J/cm}^2 and 160\,\rm{J/cm}^2 , respectively. The maximum ion energy reaches about 2\,\hbox{keV} and 8\,\hbox{keV} at these low and at high laser fluence, respectively. Experimental ion energy distributions are given as a function of the ion charge state. Obtained results indicate that electrical fields, produced in the plume, along the normal to the plane of the target surface, exist in the unstable plasma. The electrical fields induce ion acceleration away from the target with a final velocity dependent on the ion charge state. The ion velocity distributions follow a "shifted Maxwellian distribution", which the authors have corrected for the Coulomb interactions occurring inside the plasma.     

Studies of ion energy and yield from argon clusters heated by intense femtosecond laser pulses

Using time-of-flight spectrometry, the interaction of intense femtosecond laser pulses with argon clusters has been studied by measuring the energy and yield of emitted ions. With two different supersonic nozzles, the dependence of average ion energy on cluster size in a large range of has been measured. The experimental results indicate that when the cluster size , the average ion energy Coulomb explosion is the dominant expansion mechanism. Beyond this size, the average ion energy gets saturated gradually, the clusters exhibit a mixed Coulomb-hydrodynamic expansion behavior. We also find that with the increasing gas backing pressure, there is a maximum ion yield, the ion yield decreases as the gas backing pressure is further increased.     

Computational Studies of Atmospheric-Pressure Methane–Hydrogen DC Micro Glow Discharges

Atmospheric-pressure methane–hydrogen micro glow discharges were computationally investigated using a 2-D hybrid model. The plasma model was solved simultaneously with a model for the external circuit. Simulations were conducted for a pin-to-plate electrode configuration with an interelectrode separation of 400 ${rm mu}hbox{m}$. The spatiotemporal evolutions of electrons, species densities, electric field, and electron and gas temperatures were studied. A total of 81 reactions were considered, which included electron–neutral, electron–ion, ion–neutral, and neutral–neutral reactions. An 84-step reaction mechanism consisting of 15 surface species and four deposited bulk species was considered. A time-stepping technique was employed to address the time scales of plasma transport (in microseconds) and neutral and fluid transport (in milliseconds) in 2-D simulations with detailed volume and surface chemistry. The simulations indicated $hbox{H}_{3}^{+}$ and $hbox{CH}_{5}^{+}$ ions to be the most prominent hydrogen and hydrocarbon ions. The gas temperature predictions suggested the discharge to be operating as a nonthermal glow discharge. The effect of discharge current on both plasma and deposition characteristics was studied. The simulations predicted a flat voltage–current characteristic, indicating the discharge to be operating in normal glow mode. The predicted voltage–current characteristic was found to be in favorable agreement with the experimental measurements. With an increase in discharge current, the deposition rate profile expanded in the lateral direction, suggesting that deposition occurred at the cathode spot.      

Singularity of the Velocity Distribution Function in Molecular Velocity Space

We study the boundary singularity of the solutions to the Boltzmann equation in the kinetic theory. The solution has a jump discontinuity in the microscopic velocity \({\zeta}\) on the boundary and a secondary singularity of logarithmic type around the velocity tangential to the boundary, \({\zeta_{n} \sim 0_{-}}\), where \({\zeta_{n}}\) is the component of molecular velocity normal to the boundary, pointing to the gas. We demonstrate this secondary singularity by obtaining an asymptotic formula for the derivative of the solution on the boundary with respect to \({\zeta_{n}}\) that diverges logarithmically when \({\zeta_{n} \sim 0_{-}}\). Our study is for the thermal transpiration problem between two plates for the hard sphere gases with sufficiently large Knudsen number and with the diffuse reflection boundary condition. The solution is constructed and its singularity is studied by an iteration procedure.     

Ion storage technique for very long living states: The decay rate of the 5D 3/2 state of Ba II

The metastable 5D _3/2 state of Ba⁺ is used to demonstrate the possibility of the ion storage technique for the measurement of extremely long lived states. The ions are confined in a r.f. quadrupole trap and excited by a strong pulsed tunable dye laser to the 6P _1/2 state which partially decays into the 5D _3/2 state. Sampling of the time development of the ground state population leads to the determination of the 5D _3/2 decay rate. Using He as a buffer gas at a pressure of about 10^?6 mbar to initially store the ions, varying the gas density and extrapolating to zero pressure, we find for the lifetime \(\tau _{D_{3/2} } = 17.5 \pm 4s\) .     

Laser Cooling and Spectroscopy of Relativistic C^{3+} Beams at the ESR

We report on the first laser cooling of a bunched beam of multiply charged ions performed at the ESR (GSI) at a beam energy of GeV. Moderate bunching provided a force counteracting the decelerating laser force of one counterpropagating laser beam. This versatile type of laser cooling lead to longitudinally space-charge dominated beams with an unprecedented momentum spread of . Concerning the beam energy and charge state of the ion, the experiment depicts an important intermediate step from the established field of laser cooling of ion beams at low energies toward the unique laser cooling scheme proposed for relativistic beams of highly charged heavy ions at SIS 300 (FAIR). Funded by the German BMBF under contract number 06ML183.     

Reciprocal Relativity of Noninertial Frames and the Quaplectic Group

The frame associated with a classical point particle is generally noninertial. The point particle may have a nonzero velocity and force with respect to an absolute inertial rest frame. In time–position–energy–momentum-space {t, q, p, e}, the group of transformations between these frames leaves invariant the symplectic metric and the classical line element ds² = d t². Special relativity transforms between inertial frames for which the rate of change of momentum is negligible and eliminates the absolute rest frame by making velocities relative but still requires the absolute inertial frame. The Lorentz group leaves invariant the symplectic metric and the line elements and . General relativity for particles under only the influence of gravity avoids the issue of noninertial frames as all particles follow geodesics and hence have locally inertial frames. For other forces, the question of the absolute inertial frame remains.) Born conjectured that the line element should be generalized to the pseudo-orthogonal metric . The group leaving this metrics and the symplectic metric invariant is the pseudo-unitary group of transformations between noninertial frames. We show that these transformations also eliminate the need for an absolute inertial frame by making forces relative and bounded by b and so embodies a relativity that is shape reciprocal in the sense of Born. The inhomogeneous version of this group is naturally the semidirect product of the pseudo-unitary group with the nonabelian Heisenberg group. This is the quaplectic group.     

Energetics and dynamics of decaying cluster ions

The recent addition of (i) a third sector field to our two sector field mass spectrometer (resulting in a BE1E2 field configuration) and of (ii) a high performance electron gun enables us now to study in detail the time dependence of the kinetic energy release distribution (KERD) over a relatively wide range of cluster ion lifetimes. Using this newly constructed device we have studied here for the first time KERDs and deduced binding energies BEs (using finite heat bath theory) of large rare gas cluster ions (an upper size limit in earlier studies arose from the fact that different naturally occurring isotopes will contribute to a chosen metastable peak when the size exceeds a certain value) and in addition of fullerene ions smaller and larger than (here again contaminating coincidences did not allow such studies earlier). Moreover, high precision KERD measurements for the decay of rare gas dimer ions in conjunction with model calculations (using recently calculated potential energy curves for the rare gas dimer ions) also enable us to obtain information on the dynamics and the mechanisms of the underlying spontaneous decay reactions . In addition, we are also reporting here a novel method (unified breakdown graph method) to determine cluster ion binding energies using a recently constructed tandem mass spectrometer BESTOF allowing us to measure fragmentation patterns arising from the unimolecular decay of molecular cluster ions induced by surface collisions. The fragmentation and reaction patterns of protonated ethanol cluster ions investigated here clearly demonstrate in contrast to some of the earlier cluster ion studies that unimolecular dissociation kinetics determines the formation of product ions in the surface-induced decomposition.     

Probing spin-orbit quenching in Cl (2P) + H2 via crossed molecular beam scattering

In our previous work we investigated electronically non-adiabatic effects in using crossed molecular beam scattering coupled with velocity mapped ion imaging. The prior experiments placed limits on the cross-section for electronically non-adiabatic spin-orbit excitation and electronically non-adiabatic spin-orbit quenching . In the present work, we investigate electronically non-adiabatic spin-orbit quenching for which is the required first step for the reaction of Cl^* to produce ground state HCl+H products. In these experiments we collide Cl (²P) with H₂ at a series of fixed collision energies using a crossed molecular beam machine with velocity mapped ion imaging detection. Through an analysis of our ion images, we determine the fraction of electronically adiabatic scattering in Cl^* +H₂, which allows us to place limits on the cross-section for electronically non-adiabatic scattering or quenching. We determine the following quenching cross-sections σ _quench(2.1 kcal/mol) = 26 ± 21 ?², σ _quench(4.0 kcal/mol) = 21 ± 49 ?², and σ _quench(5.6 kcal/mol) = 14 ± 41 ?².     

气体中心式离心喷嘴喷雾实验与三维仿真

在实验的基础上, 基于RNG k-ε模型对常压下气体中心式同轴离心(gas-centered swirl coaxial,GCSC)喷嘴喷雾形态和破碎模式进行了三维仿真研究。采用网格自适应加密(adaptive mesh refinement,AMR)技术、耦合水平集和流体体积(coupled level-set and volume of fluid, CLSVOF)方法对气液界面进行捕捉。结果表明, 液体质量流率($\dot{m}_{\mathrm{l}}$)不变, 随着气体质量流率($\dot{m}_{\mathrm{g}}$)的增加, 中心气流的引射作用增强, 液膜内外压差增大, 雾化锥角减小, 并对其流动特性进行了分析; 而$\dot{m}_{\mathrm{g}}$不变时, 液膜在喷嘴出口的径向速度与切向速度随$\dot{m}_{\mathrm{l}}$的增大而增大, 导致雾化锥角增大。同时根据气液质量流率比(gas-liquid mass flow rate,GLR), 将喷雾的破碎模式分为穿孔破碎、气泡破碎和气动破碎。      

Strange quark star with Tolman IV background

In this paper, using the optical emission spectroscopy (OES) technique, the optical characteristics of a radiofrequency (RF) plasma jet are examined. The \(\hbox {Ar}/\hbox {O}_{2}\) mixture is taken as the operational gas and, the Ar percentage in the \(\hbox {Ar}/\hbox {O}_{2}\) mixture is varied from 70% to 95%. Using the optical emission spectrum analysis of the RF plasma jet, the excitation temperature is determined based on the Boltzmann plot method. The electron density in the plasma medium of the RF plasma jet is obtained by the Stark broadening of the hydrogen Balmer \(H_{\beta }\). It is mostly seen that, the radiation intensity of Ar 4p\(\rightarrow \)4s transitions at higher argon contributions in \(\hbox {Ar}/\hbox {O}_{2}\) mixture is higher. It is found that, at higher Ar percentages, the emission intensities from atomic oxygen (O) are higher and, the line intensities from the argon atoms and ions including O atoms linearly increase. It is observed that the quenching of \(\hbox {Ar}^{*}\) with \(\hbox {O}_{2}\) results in higher O species with respect to \(\hbox {O}_{2}\) molecules. In addition, at higher percentages of Ar in the \(\hbox {Ar}/\hbox {O}_{2}\) mixture, while the excitation temperature is decreased, the electron density is increased.     

Dynamical properties and electronic structure of (LaLi)TiO3 conductors

A computer simulation by a molecular dynamics method is performed to study the properties of structure and Li ion diffusion in La_4/3???x Li (LaLi)TiO₃ ;LLTO;Li ion conductors;Superionic conductors;Perovskite;Off-site;Electronic structureA computer simulation by a molecular dynamics method is performed to study the properties of structure and Li ion diffusion in La_{4/3 − x} Li Ti₂O₆ =(LaLi)TiO₃ =LLTO, which is the perovskite-type Li ion conductor. In the low Li concentration, Li ions conduct a two-dimensional motion, while Li ions diffuse a three-dimensional motion in the high Li ion concentration. The partial distribution function for Li–Ti and the diffusion paths of Li ions suggest that Li ions stay for a long time at off-site positions, which are 2.7? away from a body-centered Ti ion. The Li ion concentration dependence to the conductivity σ is in approximate agreement with experiments. The energy band dispersion and the density of states are calculated using the linear-muffin-tin-orbital method. The energy contour map shows the stable position of Li ions is off center of the vacant La sites. Both calculations suggest that the stable position of Li ions is off center of the vacant La sites. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

The Standard Model in strong fields: electroweak radiative corrections for highly charged ions

Electroweak radiative corrections to the matrix element are calculated for highly charged hydrogen like ions. The operator represents the parity nonconserving relativistic effective atomic Hamiltonian at the tree level. The deviation of these calculations from the calculations valid for the neutral atoms demonstrates the effect of the strong field. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photodetachment cross-section of $$\hbox {H}^{-}\,\hbox {ion}$$ in a three-dimensional cubical microcavity

The photodetachment of negative ions inside a two-dimensional microcavity has been studied by many researchers. As to the photodetachment of negative ions in the three-dimensional microcavity, the research is relatively little. In this paper, we study the photodetachment cross-section of \(\hbox {H}^{-}\) ion inside a three-dimensional cubical microcavity for the first time. We have observed the classical dynamics of the photodetached electron inside the cubical microcavity and found out its closed orbits. Then we calculate the photodetachment cross-section of this system. It is shown that owing to the interference effects of the electron wave travelling along various closed orbits, oscillatory structures appear in the photodetachment cross-section. And the oscillatory structures depend on the laser polarization sensitively. Compared to the photodetachment of \(\hbox {H}^{-}\) ion inside a square microcavity, in photodetachment of \(\hbox {H}^{-}\) ion in cubical cavity the number of the closed orbits is increased and the oscillatory structure in the photodetachment cross-section becomes much more complex. Through our study, researchers can gain a deep understanding on the correspondence of the classical dynamics and the quantum mechanics. Our study may guide future experimental research in the field of the photodetachment electron dynamics inside a three-dimensional microcavity.     

Features of materials alloying under exposures to pulsed plasma streams

Surface modifications and features of materials alloying under pulsed plasma exposures are investigated in this paper. The experiments were carried out with a pulsed plasma gun, which generates plasma streams with ion energies of up to 2 keV, a plasma density of (2–, an average specific power of 10 MW/cm² and plasma energy densities in the range of (5–. Nitrogen, helium, hydrogen, oxygen and different mixtures can be used as working gases. Modification of thin (1–2 μm) PVD coatings of molybdenum coating mixed with substrate in liquid phase under the pulsed plasma processing are analyzed. After alloying of ferritic/martensitic steel EP-823 with Mo the concentration of molybdenum in the modified layer of 15–20 μm achieved 20% for single treatment cycle and 30% after two cycles. Decrease of grain sizes (from tens of μm to hundreds of nm), roughness and porosity were obtained by plasma irradiation of thick (~0.1–0.3 mm) plasma sprayed coatings of Co-32Ni-21Cr-8Al-0.5Y and Ti64. A modified layer with homogeneous structure and thickness up to 50 μm is formed as a result of plasma treatment. Mechanisms of surface modification of WC-Co under irradiation with pulsed plasma streams of different ions are discussed.     

The performance of the jet identification and reconstruction in heavy ions collisions with CMS detector

A jet reconstruction algorithm is developed for events with a high particle density in the calorimetric system. The performance of the reconstruction of hard QCD jets with initial parton energies 50–300 GeV is studied in central Pb–Pb collisions with a modified cone jet finder which includes an algorithm for event-by-event background subtraction. The heavy ion background is simulated using the HIJING Monte Carlo generator with . Results on the achieved jet reconstruction efficiency, purity, energy and spatial resolution are presented.     

Production of Capacitively Coupled Atmospheric Plasma Jet With Multiring Electrodes for the Medical Plasma Tool

An atmospheric capacitively coupled plasma jet has been developed by using multiring-electrode configurations for medical applications. It was found that the discharge conditions for plasma-jet production expanded with the increase of the number of pairs of multiring electrodes. The length of the plasma jet increased with the increase of the injected power and helium-gas flow rate. The temperature of the plasma jet, measured by a thermocouple, decreased with the increase of gas flow rate and was then attained to be around 50 $^{circ}hbox{C}$ at a helium flow rate of 30 L/min. Optical measurements of plasma-jet emission showed various optical emissions from helium atoms, nitrogen atoms, hydroxyl radicals, and metal atoms originating from the electrode material.      

Low-threshold, high SMSR tunable external cavity quantum cascade laser around 4.7\,\upmu \hbox {m}

Room-temperature pulsed and continuous-wave (cw) operation of a tunable external cavity (EC) quantum cascade laser (QCL) at an emitting wavelength of $4.7\,\upmu \hbox {m}$ 4.7 μ m was presented. The effect of different external cavity lengths and grating angles of the EC–QCL system were analyzed numerically. A wide tuning range greater than $131\,\hbox {cm}^{-1}$ 131 cm - 1 was obtained in pulsed mode at room temperature. Without the anti-reflection coating procedure, single-mode cw operation with a side-mode suppression ratio (SMSR) above 20 dB and a wide tuning range greater than $116\, \hbox {cm}^{-1}$ 116 cm - 1 were achieved. Near the center region, SMSR about 30 dB was also realized through designing the external cavity length. Strain-compensation combined with two-phonon resonance in an active region design and the high-reflection coating promised low threshold current density. A record low threshold current density of $0.901\,\hbox {kA/cm}^{2}$ 0.901 kA/cm 2 for an EC–QCL operated in cw mode was realized.     

Einfluß des Randes auf das effektive Verhalten heterogener Körper - Anwendung auf Rayleighwellen

Effective Elastic Properties of Finite Heterogeneous Media - Application to Rayleigh-waves Rayleigh waves in a heterogeneous material (multiphase mixtures, composite materials, polycrystals) are governed by integrodifferential equations derived by the aid of known methods for infinite heterogeneous media. According to this wave equation the velocity depends on the frequency, and the waves are damped. After some simplifications (isotropy, nonrandom elastic constants) the following is obtained: if the fluctuations of the mass density are restricted to the vicinity of the boundary, the frequency dependent part of the velocity behaves like \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{l^3 \omega ^3}}{{{\mathop c\limits^\circ} _t^3}} $\end{document} and the damping is proportional to \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{l^4 \omega ^5}}{{{\mathop c\limits^\circ} _t^5}} $\end{document}, whereas \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{l^2 \omega ^2}}{{{\mathop c\limits^\circ} _t^2}} $\end{document} respectively \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{l^3 \omega ^4}}{{{\mathop c\limits^\circ} _t^4}} $\end{document} is found if the fluctuations are present in the whole half-space. From this it is seen, what assumptions are necessary to describe the waves by differential equations with frequenc y-dependent mass density.