Angular dependence of the ion energy,charge, and mass distributions in surface discharge plasma

Previously, the ion energy, charge, and mass distributions in vacuum discharge plasma at the surface of polymeric insulators were studied using an analyzer oriented perpendicularly to the surface, and both multiply charged and high-energy ions were found in the plasma. This Letter presents the first experimental results on the dependence of the ion energy, charge, and mass distributions in the plasma on the particle take-off angle relative to the insulator surface.     

Energy and charge distributions in nanosecond vacuum spark plasma flux

The characteristics of vacuum sparks formed under the action of a 4-ns high-voltage pulse with an amplitude of 150 kV have been studied. Ions of a cathode material (copper or graphite) with energies of up to 150 keV were found in the flux of plasma from the cathode region. In the case of a graphite cathode, only singly charged carbon ions with a dome-shaped energy distribution were observed. For a copper cathode, differently charges ions (+1, +2, +3) were detected and their energy distribution exhibited several maxima. The characteristic ion energies depended on the interelectrode distance.     

An investigation of surface energy input to gas during initiation of a nanosecond distributed surface discharge

The fraction of energy, directly introduced into gas during the initiation of a distributed pulsed surface discharge of the plasma sheet type, is analyzed using the results of investigation of the dynamics of resultant shock waves. Results are given of numerical calculation of development of flow within the model of thermal energy input. It is demonstrated that the experimentally obtained values of the velocity of motion of perturbations agree well with the calculation results assuming that 40 ± 10% of the energy of surface electric discharge of nanosecond duration changes to thermal energy in the stage of energy input, i.e., during the time which is much shorter than 1 μs.     

Periodic plasma structures in nanosecond discharge with a slit cathode

The spatial structure of optical emission from a transverse nanosecond pulsed electric discharge with a hollow (slit) cathode has been experimentally studied. A regular periodic plasma structure has been observed during nanosecond pulsed discharge in helium at medium pressures. Conditions of the plasma structure formation with respect to the discharge voltage and current are determined. It is shown that the observed plasma structure differs from the known types of striations.     

Corona discharge in charge reduction electrospray mass spectrometry

Corona discharge is applied to charge reduction electrospray mass spectrometry for the analysis of complex mixtures of biological molecules. Recent work has described a method of charge reduction (reducing the charge states of analyte ions generated by the electrospray process) employing the radioactive isotope 210Po to produce neutralizing species. A variation to this approach is presented, in which charge neutralization is mediated by ions produced in a corona discharge. Varying the corona discharge voltage controls the current and the degree of charge reduction, providing predominantly singly charged ions that are detected by a commercial electrospray time-of-flight mass spectrometer. This technique provides charge reduction for the simplification of ESI spectra, without need for any radioactive material.     

Ion energy distributions in a special glow-discharge ion source

The ion energy distributions for a special glow-discharge source were obtained by two means: theoretical and experimental. The experimental energy distributions, determined by mass spectrometry, differ significantly from the theoretical energy distributions calculated according to the Davis model in which the charge transfer process plays an important part. Space potential distributions necessary in the Davis theory, were determined with an electrostatic probe. The differences between the distributions, calculated and measured, can be caused by some inaccuracy of the ‘simple’ Davis model.     

Ion energy cost in a combined inductive-capacitive rf discharge

Experimental measurements were made of the ion energy cost η as a function of the parameters of a combined rf inductive-capacitive discharge at low pressures (p<10⁻² Torr). It was established that η does not depend on the power supplied, it has a minimum as a function of pressure, and also decreases when an rf potential is applied to the electrodes. The results can be used to find the optimum parameters in terms of energy efficiency of ion formation and may be useful for refining the theoretical models of a combined rf inductive-capacitive discharge. Pis’ma Zh. Tekh. Fiz. 24, 33–39 (November 26, 1998)     

Energy deposition in boundary gas layer during initiation of nanosecond sliding surface discharge

The process of rapid gas heating in the region of distributed pulsed sliding surface gas discharge (plasma sheet) of nanosecond duration has been studied. The fraction of electric energy converted into heat during the passage of discharge current has been estimated from a detailed analysis of the dynamics of shock wave fields arising upon the initiation of discharge. Experiments are performed in quiescent gases (air, nitrogen, helium) and in supersonic airflows behind a plane shock wave in a shock tube at gas densities within 0.04–0.45 kg/m³ and flow velocities up to 1600 m/s.     

The surface energy deposited into gas during initiation of a pulsed plasma sheet discharge

Gasdynamic perturbations arising during the initiation of a pulsed surface (plasma sheet) discharge have been experimentally studied in a shock tube. The evolution of flow was also numerically simulated within the framework of a thermal energy deposition model. Experimental values of the velocity of perturbations well agree with the results of calculations obtained assuming that about 50% of the energy deposited in the surface layer is converted into heat in the stage of energy supply.     

Ion sputtering of cathode surface in a hollow cathode discharge

In this paper, ion sputtering of cathode material in a specific type of glow discharge—hollow cathode discharge (HCD)—is analyzed. To estimate both real sputtering yield and screening effect of the buffer gas, two different methods—combination of experimental and analytical approach (applicable for Ar buffer gas only) and use of Monte Carlo simulations—are used. The latter, which is introduced for the first time here, can be used for any buffer gas. Real sputtering yield S_k is estimated by Monte Carlo simulations for several commercial HCD lamps with Ne buffer gas: Ne-Li (0.046), Ne-As (0.862), Ne-Ca (0.337) and Ne-Cd (1.069).     

Study on plasma discharge parameters in double-glow plasma surface alloying furnace

Double Langmuir probe technique was used for plasma diagnostics of discharge process in double-glow plasma alloying furnace. Investigated that the effect of changes of voltage of the source pole and air pressure on plasma parameters. Results show that plasma density increases, electron temperature decreases and potential of the probe decreases, with the rise of voltage of the source pole under condition of fixed cathode potential and fixed air pressure. During increasing of air pressure in furnace, electron temperature decreases and probe potential increases. The change of probe potential is smart at start of the measuring and probe potential goes to stabilization only when degas process goes to finishing.     

Ion energy distribution of an inductively coupled radiofrequency discharge in argon and oxygen

We report an experimental investigation of the ion energy distribution in an inductively coupled electron cyclotron wave resonance (ECWR) discharge with a superimposed static magnetic field. The inductively coupled discharge is sustained by applying a 13.56 MHz radiofrequency (RF) power to an aluminium single-turn coil located inside the vacuum chamber. The source region was separated by a grid from the diffusion region. Ion energy distribution (IEDF) measurements employing an energy-dispersive mass spectrometer or plasma process monitor (PPM) whose entrance opening was 15 cm away from the grid were performed in the diffusion region. The IEDF is composed of two peaks; a low-energy peak due thermalized ions and a high-energy peak due to ions coming directly from the source region without undergoing thermalization. The energetic difference between the groups thus reflects the plasma potential difference between the source region and the diffusion region. The pronounced intensity variation of the high-energy peak with increasing pressure is caused by charge-changing collisions yielding a depletion of the high-energy ions with increasing effective path length.     

Studying surface glow discharge for application in plasma aerodynamics

Surface glow discharge in nitrogen between two infinite planar electrodes occurring on the same plane has been studied in the framework of a diffusion-drift model. Based on the results of numerical simulations, the plasma structure of this discharge is analyzed and the possibility of using it in plasma aerodynamics is considered.     

Control of the energy of ion flow affecting electrically insulated surface in plasma processing reactor based on a beam plasma discharge

We compare two ways to control the distribution function of ions on the isolated structure which is treated in a plasma reactor based on beam plasma discharge. In the first case, the periodic pulse voltage is applied to the substrate holder. The calculation of currents and voltages on the surface in contact with the plasma in a simple empirical model has been performed; the comparison of results of calculation and experiment is presented. In the latter case, the pulsed voltage is applied to the discharge collector, thus modulating the plasma potential. The comparison shows that the second method provides more efficient control of the distribution function of ions, acting on the treated substrate.     

Comparison of ultraviolet femtosecond and nanosecond laser ablation inductively coupled plasma mass spectrometry analysis in glass, monazite, and zircon

We compared the analytical performance of ultraviolet femtosecond and nanosecond laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). The benefit of ultrafast lasers was evaluated regarding thermal-induced chemical fractionation, that is otherwise well known to limit LA-ICPMS. Both lasers had a Gaussian beam energy profile and were tested using the same ablation system and ICPMS analyzer. Resulting crater morphologies and analytical signals showed more straightforward femtosecond laser ablation processes, with minimal thermal effects. Despite a less stable energy output, the ultrafast laser yielded elemental (Pb/U, Pb/Th) and Pb isotopic ratios that were more precise, repeatable, and accurate, even when compared to the best analytical conditions for the nanosecond laser. Measurements on NIST glasses, monazites, and zircon also showed that femtosecond LA-ICPMS calibration was less matrix-matched dependent and therefore more versatile.     

Ion energy distribution at a negatively biased electrode in a sputtering discharge

An energy electrostatic analyser was used to study the energy distributions of ions impinging on the negatively biased substrate table of a dc diode sputtering system. The imfluence of the negative bias voltage (−50 to −200 V) was specifically examined in argon and argon-nitrogen discharges. The energy distributions were characterized by an important peak at the maximum energy and a tail with sometimes a secondary peak at lower energies. The tail and the secondary peak arose from charge exchange collisions in the sheath. When the argon pressure was increased, the secondary peak increased too. The secondary peak disappeared in an argon-nitrogen discharge and the tail was reduced.     

Shock-wave structure formation by nanosecond discharge in helium

We have experimentally studied and numerically simulated the shock-wave flow that arises as a result of the development of a system of microchannels of pulsed sliding surface discharge in helium at low pressure. Using numerical simulations based on a solution of the system of regularized Grad equations (R13) and Navier-Stokes equations, results obtained for various Knudsen numbers are compared and it is shown that the influence of rarefaction on the discharge-plasma-induced shock-wave flow is manifested in a transient regime at Kn = 10^?1.     

Ion transport diagnostics in a microsecond pulsed Grimm-type glow discharge time-of-flight mass spectrometer

A Grimm-type glow discharge ion source, operated in the microsecond pulsed mode, has been interfaced to a commercial time-of-flight mass spectrometer. Ion transport from the source to the mass spectrometer, an inherent limitation of a Grimm source and mass spectrometer combination, was evaluated. The primary discharge operating conditions found to influence transport efficiency were gas flow rate and source pressure. The configuration of the Grimm-type source also influenced ion transport, including use of a gas-directing sleeve device. The effect of transport efficiency was separated into two components: (1) total ion signal and (2) temporal resolution. The latter is an advantage afforded by use of a pulsed glow discharge source and time-of-flight spectrometer, which allows discrimination against interfering gaseous background ions by appropriate ion sampling time. Shown as an example is the identification of trace magnesium from potential background interference using an optimized source configuration based on this temporal resolution method.     

Investigation of the processes of periodic plasma structure formation in transverse nanosecond discharge with a slotted cathode

A periodic standing-like plasmic striation in inert gases has been observed and investigated under transversal nanosecond electric discharges. The pressure limits relevant for formation of a periodic plasma structure have been established, and the critical values for the voltage amplitude and discharge current have been found corresponding to the upper boundary of the range in which the plasma structure is formed. The external magnetic field effect on the parameters of the periodic plasma structure has been studied. It is stated that the plasma structure is formed at the stage of steady-state discharge and that the lifetime of the periodic structure considerably increases when the transversal magnetic field is applied.