Influence of a current jump on vacuum arc parameters

Based on time of flight method, influence of short time vacuum arc current jump on arc plasma parameters were investigated. Superposition of the current pulse of a vacuum arc with a high operating voltage results in the appearance of ions of higher charge state in the discharge plasma and in an increase in the mean ion charge state for most of the cathode materials used in the experiment. The method of a “short-time current jump” can be also used to investigate the parameters of a vacuum arc, in particular to estimate the ion direct velocities in vacuum arc plasmas. Our estimates show that in the presence of a current step the ion velocities are almost identical for all differently charged ions and depend only on the peak current and the ion mass     

Residence time and charge state of silver and zinc ions generatedfrom microsecond vacuum arcs

One mm vacuum gaps with silver or zinc needle-cathode were fired by a 13 μs duration sinusoidal arc or a 9 μs duration exponentially decaying arc. Time-of-flight (TOF) ion measurements were made at variable ion extraction times after the arc ignition to measure the charge state and residence time of the ions. Ag⁺, Ag⁺⁺ and Ag⁺⁺⁺ ions were generated from silver cathode and Zn⁺ and Zn⁺⁺ were generated from zinc cathode. Residual gas atom ions were generated together with the metal ions. Residence times of silver and zinc ions at the acceleration space, which was 15-25 mm apart from the needle cathode, were 5 μs and 17 μs, respectively, regardless the waveform of the arc current. Charge state fractions of silver and zinc ions were determined from the TOF ion currents and were compared with the results by other researchers     

Investigation of the Directional Velocities of Ions in a Vacuum Arc Discharge by Emission Methods

This paper is devoted to an investigation of the directional velocities of the ions generated in cathode spots of vacuum arc discharges. By using emission methods of studying the processes in a vacuum arc discharge, which involve the determination of the parameters and characteristics of the discharge plasma by analyzing the ion current extracted from the plasma and the ion charge states, the velocities of ions have been determined for the majority of cathode materials available in the periodic table. Is has been shown that at a low pressure of the residual gas in the discharge gap the directional velocities of the ions do not depend on the ion charge state. Comparison of the data obtained with calculated values allows the conclusion that the acceleration of ions in a vacuum arc occurs by the magnetohydrodynamic mechanism.     

含氢电极脉冲放电等离子体特性诊断

利用飞行时间质谱法诊断了含氢电极脉冲真空弧离子源放电等离子体成分、离子电荷状态及离子扩散速度等特性.实验结果表明,含氢电极脉冲真空弧离子源放电等离子体的离子成分主要由H+,Ti+,Ti2+和Ti3+组成,其中Ti2+占主要部分.当放电电流为40～80 A时,Ti离子的平均电荷数在1.95～2.13之间,随着放电电流的增...     

Residence time of metal ions generated from microsecond vacuum arcs

Vacuum gaps of 1 mm with lead or copper cathode are fired by a 13 μs duration sinusoidal arc or a 10 μs duration exponentially-decaying arc, and time-of-flight (TOF) ion measurements are made at variable times after the arc ignition. At the lead cathode, Pb⁺ and Pb⁺⁺ ions are generated and the upper limit on the times for Pb⁺ ion detection are 48 μs and 46 μs from the arc ignition for the sinusoidal and exponential arcs, respectively. At the copper cathode, Cu⁺, Cu⁺⁺, and Cu⁺⁺⁺ ions are generated and detected within 15 μs and 13 μs from the arc ignition for the sinusoidal and exponential arcs, respectively. The residence time of the Pb⁺ ions in the ion acceleration region is approximately 35 μs, regardless of the waveform of the arc current. The residence time of the copper ions, described by the time constant of the time-of-flight ion current delay characteristics, is 3 μs     

Study of directed ion velocities in a vacuum arc by an emission method

Directed ion velocities in a vacuum arc discharge plasma are measured on the basis of a study of the ion emission current response to a rapid change of arc current. It is shown that these velocities are about 10⁶ cm/s, are determined by the cathode material, and are almost independent of the ion charge number. Applying a magnetic field results in an increase in the directed ion velocity. As the gas pressure increases, the directed ion velocity decreases; this is the only case where the directed velocities are observed to depend on the ion charge number.     

Charge state and residence time of metal ions generated from amicrosecond vacuum arc

Metal ions generated from a microsecond vacuum arc were measured using a time-of-flight (TOF) method. A point-plane vacuum gap was fired by an impulse voltage to generate metal ions. The risetime and time constant for the decay of the arc current were 0.1 and 4.5 μs, respectively. TOF ion currents were measured for variable ion extraction times after the arc ignition. At a lead cathode, Pb⁺ and Pb ⁺⁺ ions were detected for ion extraction times less than 45 μs. The average charge-state fractions of the Pb⁺ and Pb ⁺⁺ ions were 91 and 9%, respectively. At a copper cathode, Cu ⁺, Cu⁺⁺, and Cu⁺⁺⁺ ions were detected for ion-extraction times less than 12.5 μs, and the average charge-state fractions were 42, 41, and 17%, respectively. The residence times of the generated lead and copper ions were also discussed     

Observation of atomic spin precessions of isolated fluorine ions on recoil through weak transverse magnetic fields

A new experimental method for studying the hyperfine interactions of multi-electron configurations in isolated ions is illustrated for fluorine using the long-lived 197 keV¹⁹F(5/2⁺) state as probe. The observed atomic precessions were found to vary linearly with the applied weak magnetic field integrated over the flight path of the recoiling ions. The data are well accounted for, assuming configurations from the coupling of 2s and 2p electrons in the relevant ionic charge states.     

Average charge state dependence in atomic spin precessions of fluorine ions emerging from iron and copper

The technique of perturbedγ-angular correlation has been applied to measure atomic spin precessions of nuclear excited fluorine ions on recoil through vacuum in a weak transverse magnetic field. The ions were allowed to emerge from thin iron or copper backed targets and were stopped after flight through vacuum in a Ag foil. The differing precessions observed are attributed to different average charge states of the ions on emergence from the two target backings.     

Study of the effect of varying core diameter,shell thickness and strain velocity on the tensile properties of single crystals of Cu–Ag core–shell nanowire using molecular dynamics simulations

Core–shell type nanostructures show exceptional properties due to their unique structure having a central solid core of one type and an outer thin shell of another type which draw immense attention among researchers. In this study, molecular dynamics simulations are carried out on single crystals of copper–silver core–shell nanowires having wire diameter ranging from 9 to 30 nm with varying core diameter, shell thickness, and strain velocity. The tensile properties like yield strength, ultimate tensile strength, and Young’s modulus are studied and correlated by varying one parameter at a time and keeping the other two parameters constant. The results obtained for a fixed wire size and different strain velocities were extrapolated to calculate the tensile properties like yield strength and Young’s modulus at standard strain rate of 1 mm/min. The results show ultra-high tensile properties of copper–silver core–shell nanowires, several times than that of bulk copper and silver. These copper–silver core–shell nanowires can be used as a reinforcing agent in bulk metal matrix for developing ultra-high strength nanocomposites.     

Method for calculating the nonequilibrium characteristics of light ions passing through thin organic films

A method is proposed for calculating the charge fractions, mean charges, and dispersion of the charge distribution in ion beams passing through thin organic films under nonequilibrium conditions. Calculations are performed for N ions travelling at different velocities (from 8 × 10⁸ to 12 × 10⁸ cm/s) in celluloid. The energy loss is estimated depending on the initial charge states and velocities of the incident ions.     

Features of the pre-equilibrium charge states of light ions passing through thin celluloid films

A semi-empirical method for establishing of the average charge of ions passing through thin celluloid films is proposed. Calculations for helium (He) and nitrogen (N) ions with different initial velocities (12?18.7 × 10⁸ cm/s for He and 4?12 × 10⁸ cm/s for N) are presented. The equilibrium thickness of a celluloid target in dependence on the initial charge states of incident ions is evaluated.     

Mechanism of ion flow generation in vacuum arcs

The ecton model of the cathode spot is used to analyze the main parameters of ion flow in vacuum arcs (ion erosion, mean charge, and velocity). It is shown that the arc plasma is formed as a result of microexplosions at the cathode surface, induced by the Joule heating by the high-density current of explosive electron emission. Ionization processes are localized in a narrow region of the order of a micrometer near the cathode and the ionization composition of the plasma subsequently remains unchanged. Under the action of the electron pressure gradient, ions acquire directional velocities of the order of 10⁶ cm/s even over small distances of the order of several micrometers.     

The Ecton Mechanism for the Generation of Ion Flows in a Vacuum Arc

The principal characteristics of the process of generation of the cathode plasma in a vacuum arc (ion erosion, mean charge of ions) are considered in terms of the ecton model of the cathode spot of a vacuum arc. The estimates of the parameters of ions obtained for a unit cell of a cathode spot – an ecton – are in good qualitative and quantitative agreement with experimental data. The following mechanism for the generation of the cathode plasma of a vacuum arc is proposed. When a region of the cathode is destroyed in an explosive manner due to Joule heating, the material of the cathode sequentially goes over a series of states: the condensed state and the states of imperfect and ideal plasma. During this transition the charge state of the plasma is formed and the ions are accelerated under the action of the pressure gradient in the plasma whose density decreases by several orders of magnitude over distances of 10 m from the cathode surface. The increase in current results in an increase in number of cells, and the principal parameters of the ions are formed as a result of the operation of a unit cell of the spot.     

Registration of accelerated multiply charged ions from the cathode jet of a vacuum discharge

The parameters of Cuⁿ⁺ and Taⁿ⁺ ions from the plasma of a vacuum spark with a voltage up to 2.5 kV and a current rise rate up to 2 × 10¹⁰ A/s are studied using the time-of-flight method. At the initial stage of the discharge, bursts of beams of accelerated multiply charged ions from the cathode flame have been detected. It is established that the charge state distribution and energy of a beam are controlled by the initial voltage U ₀ of the capacitor. Upon an increase in this voltage, the average charge of copper ions attains the value +9, and the average charge of tantalum ions can be as high as +20, while the energy attains values of 150 and 350 keV, respectively. It is found that the average energy of ions with charge Z increases in proportion to the charge and is close to the energy eZU ₀ which would have been acquired by ions accelerated in the electric field of the discharge gap.     

Continuous synthesis of colloidal silver nanoparticles by electrochemical discharge in aqueous solutions

This article presents an electrochemical discharge (ECD) method that consists of a combination of chemical methods and electric arc discharges. In the method, 140 V is applied to an Ag electrode from a DC power supply. The arc-discharge between the electrodes produces metallic silver nanoparticles and silver ions in the aqueous solution. Compared with the original arc discharge, this ECD method creates smaller nanoparticles, prevents clumping of the nanoparticles, and shortens the production time. The citrate ions also reduce the silver ions to silver nanoparticles. In addition, the citrate ions cap the surface of the produced silver nanoparticles and the zeta potential increases. In this article, the weight loss of the electrodes and the reduction of silver ions to silver nanoparticles as a function of citrate concentration and electric conductivity of the medium are discussed. Furthermore, the properties of the colloidal silver prepared with ECD are analyzed by UV–Vis spectroscopy, dynamic light scattering, electrophoresis light scattering, and scanning electron microscopy. Finally, a continuous production apparatus is presented for the continuous production of colloidal silver.     

Comparative analysis of light-ion ranges in gaseous,liquid, and solid media

Ranges of ions from He to Ne in gaseous (hydrogen and argon), liquid (water), and solid (carbon) media are analyzed. This analysis demonstrates the different dependences of ranges on the velocities, the charges, and the masses of ions in different velocity region. In the case of small ion velocities, the ranges are directly proportional to their velocities and masses and are inversely proportional to the nuclear charge. In the intermediate velocity region corresponding to an ion energy of Е = 0.1–1 MeV/nucleon, in which processes of ion charge exchange play an important role and the average ion charge differs from the nuclear charge, the ranges become proportional to the squared ion velocities and masses and are inversely proportional to the nuclear charge. To establish the relation between the ion ranges in the regions of small and average velocities, it is convenient to use the universal function f(Z, M) = RZ/M, successfully describing the reduced ranges of ions with given velocities in gaseous, liquid, and solid media. In the case of large velocities where ions upon passing through the media lose all electrons, the ranges are directly proportional to the squared ion energies and masses and are inversely proportional to the squared nuclear charge.     

Measurement of the transverse kinetic energies of argon recoil ions produced in 120 MeV -Ar collisions

Measurements were carried out to deduce the transverse kinetic energies of highly charged argon recoil ions produced in single collisions of 120 MeV ions with argon atoms in which the post collision charge states of the projectiles were not determined. A time of flight spectrometer was designed and fabricated to detect the charge states of recoils. Experimental procedures for optimizing the spectrometer for extraction, transmission and detection of recoils are described. A simple approach for determining the transverse kinetic energy of the recoil ions from FWHM of the peaks is reported. This method is shown to be independent of the choice of collision partners and requires only the knowledge of the physical values of “optimized parameters” of time-of-flight spectrometer used in the experiment. The transverse kinetic energy of the recoil ions determined from the present approach is found to vary from 0.03 eV for to 4.02 eV for Ar¹⁰⁺. These values are compared with the results reported by earlier workers and are shown to follow a q²-behaviour up to a charge state q =8+ of the recoil ions. Received: 5 February 1998 / Revised: 8 June 1998 / Accepted: 11 June 1998     

Generation of High Charge State Metal Ions in an Arc Plasma

Russian Physics Journal - Generation of high charge state metal ions in arc plasma is investigated and methods of elevation of the average ion charge state are analyzed. To realize multiple...     

Formation of silver thin films and nanoparticles inside and on the surface of silver-containing glasses by electron irradiation

It is shown experimentally that irradiation of silver-ion-containing glasses by 5–7-keV electrons with doses of 20–50 mC/cm² results in the formation of a silver thin film and nanoparticles on the surface. If the concentration of silver ions in the glass is high, a subsurface film arises as well. These effects are due to a negative space charge region forming under the surface. As a result, silver ions migrate in the resulting field from the volume of the glass toward the negative space charge region and the surface and thermalized electrons reduce the ions to neutral atoms.