Plasma Ball Research Articles

Ion Coulomb explosion of clusters by a Gaussian laser beam

A collisionless model of ion Coulomb explosion of clusters, due to an intense short pulse laser with Gaussian radial intensity distribution, is developed. The laser quickly converts the clusters into plasma balls via tunnel ionization. The free electrons of a cluster execute oscillatory motion with large excursion Δ and partially move out of the cluster. The unbalanced positive charge within the cluster leads to ion Coulomb explosion. The ion energy distribution function due to a single cluster rises monotonically with energy ε up to a cutoff energy εm and vanishes beyond it. εm depends on electron excursion, hence decreases with r. The cumulative ion energy distribution due to all the clusters of the laser channel turns out to be a decreasing function of energy as observed in recent experiments. The ions so produced can generate neutrons with reasonably high yields. The scheme may also find application in tokamak fusion.

Fabrication of inorganic molybdenum disulfide fullerenes by arc in water

Closed caged fullerene-like molybdenum disulfide (MoS 2) nano-particles were obtained via an arc discharge between a graphite cathode and a molybdenum anode filled with microscopic MoS 2 powder submerged in de-ionized water. A statistical study of over 150 polyhedral fullerene-like MoS 2 nano-particles in plan view transmission electron microscopy revealed that the majority consisted of 2–3 layers with diameters of 5–15 nm. We show that the nano-particles are formed by seamless folding of MoS 2 sheets. A model based on the agglomeration of MoS 2 fragments over an extreme temperature gradient around a plasma ball in water is proposed to explain the formation of nano-particles.

Multi-spacecraft tracing of turbulent boundary layer

Multi-spacecraft tracing of the high latitude magnetopause (MP) and boundary layers and Interball-1 statistics indicate that: 1. (a) The turbulent boundary layer (TBL) is a persistent feature in the region of the cusp and ‘sash’, a noticeable part of the disturbances weakly depends on the interplanetary magnetic field By component; TBL is a major site for magnetosheath (MSH) plasma penetration inside the magnetosphere through percolation and local reconnection. 2. (b) The TBL disturbances are mainly inherent with the characteristic kinked double-slope spectra and, most probably, 3-wave cascading. The bi-spectral phase coupling indicates self-organization of the TBL as the entire region with features of the non-equilibrium multi-scale and multi-phase system in the near-critical state. 3. (c) We've found the different outer cusp topologies in summer/winter periods: the summer cusp throat is open for the decelerated MSH flows, the winter one is closed by the distant MP with a large-scale (∼several Re) diamagnetic ‘plasma ball’ inside the MP; the ‘ball’ is filled from MSH through patchy merging rather than large-scale reconnection. 4. (d) A mechanism for the energy release and mass inflow is the local TBL reconnection, which operates at the larger scales for the average anti-parallel fields and at the smaller scales for the nonlinear fluctuating fields; the latter is operative throughout the TBL. The remote from TBL anti-parallel reconnection seems to happen independently.

Studies of the plume accompanying pulsed ultraviolet laser ablation of zinc oxide

The plume of ejected material accompanying pulsed laser ablation of a ZnO target at 193 nm in vacuum has been investigated using wavelength and spatially resolved optical emission spectroscopy and Langmuir probes. All lines in the observed optical emission spectra are assignable to electronically excited Zn+* cations, and Zn* and O* neutrals, all of which emitting species we attribute to the result of electron–ion recombination processes in the gas phase following material ejection, laser–plume interactions, ionization, and thus, plasma formation. Various contributory components can be identified within the plume. Included among these are: a fast distribution of Zn2+ ions (observed via emission from highly excited states of Zn+*) together with an accompanying subset of fast electrons—the relative importance of which increases with increasing incident fluence on the target; a more abundant slower component involving both Zn+ and O+ ions, which expand in association with the main body of the electron distribution; and a slow moving component of Zn* emitters, which we suggest should be associated with material that has been backscattered from the expanding plasma ball towards the target surface and then rebounded or desorbed into the gas phase. The observation that the postablated target surface is substantially enriched in Zn provides additional support for the importance of material backscattering from within the dense plasma ball, accommodation, and in this case, recondensation on the target. The deduction that the target surface in the vicinity of the irradiated area is Zn rich after just a few laser shots provides an explanation for the oft-reported observation that ZnO films deposited by pulsed laser ablation of ZnO in vacuum are nonstoichiometric, with a Zn:O ratio greater than unity. Such backscattering from the plasma volume and selective recondensation of the less volatile component or components within the plume prior to the next ablation pulse being incident on the target surface appear to account for virtually all reported instances of nonstoichiometric film growth by pulsed laser deposition (PLD) in vacuum. Indeed, given the deduced area of the target surface affected by such redeposition and the target translation speeds typically employed in PLD studies, it would appear that nonstoichiometric film growth is likely to be the norm whenever PLD is carried out in vacuum and at wavelengths and fluences that lead to formation of a sufficiently dense plasma to cause material redeposition on the target.

Can Devices Facilitate a Hypnotic Induction?

Historically, many devices were believed to have the ability to facilitate a hypnotic induction, but in time such devices proved to have no inherent facilitating properties other than a general placebo effect. To test the efficacy of a device called a “plasma ball” that may facilitate an induction by combining two sensory modalities simultaneously (visual and auditory), 42 college students who scored 6 and below on the Harvard Group Scale of Hypnotic Susceptibility, Form A (HGSHS: A) and completed a scale rating the realness of items, were selected for a second session. Participants were matched on hypnotizability scores and randomly assigned to experimental or standard eye fixation induction control condition. Although hypnotizability scores and realness ratings increased significantly from the initial session, use of the device did not produce higher hypnotizability scores or realness ratings in the experimental compared with the control condition. Results indicate that there is still no evidence that one fixation device works better as a target than any other.

Diagnostics of plasma ball formed in high pressure microwave plasma for diamond film synthesis

A high pressure hydrogen microwave plasma for diamond film deposition has been experimentally studied. Spatial distributions of plasma parameters and electric field intensity inside the plasma reactor were investigated in detail to understand the mechanism of plasma ball formation under the discharge conditions; a filling pressure is typically 10–50 torr and an input microwave power is 1.3 kW. In order to study the spatial distributions of the high-energetic electrons, we carried out the measurements using the optical emission measurements with the periscope technique, together with the electron saturation current profile measurements with the electrostatic probe. Numerical analysis using the finite difference time domain (FDTD) method shows a fairly good agreement with the experimental results of the electric field distributions and power dissipation inside the plasma ball.

Functionalization of multiwall carbon nanotubes: Properties of nanotubes-epoxy composites

Multiwall nanotubes were functionalized using plasma treatments, chemical oxidation, ball milling and thermal treatments. In optimized conditions, plasmas modify nanotubes surface chemistry with a great selectivity. Vickers microindentation and tension tests performed on epoxy resin loaded with multiwall nanotubes allow comparison of the influence of nanotubes surface chemistry and microtexture on loaded resin mechanical properties.

Diagnostic of a pulsed CH 4–H 2 plasma to improve microwave plasma assisted chemical vapour deposition process for diamond synthesis

A microwave plasma assisted chemical vapour deposition (MWPACVD) process used for diamond growth was studied under continuous wave (CW) and pulsed mode. Depending on the plasma conditions, it is shown that the discharge exhibits two different regimes. One is characteristic of a resonant cavity and allows a stationary wave to be created in the centre part of the reactor. Thus the discharge can be placed in the middle of the tubular reactor, just above the treated substrate. Within the second regime, the microwave power is absorbed as soon as it enters the reactor, thus implying a displacement of the plasma ball on the side wall of the reactor. These two regimes are explained by considering the wave propagation according to the plasma parameters, especially the electron density and the collisions through the gas pressure. It is pointed out that the pulsed mode allows the input peak power to be higher than in CW operation and consequently to increase the H-atom density in the close vicinity of the substrate. Experiments with specific conditions have shed light on contradictory results dealing with pulsed MWPACVD processes.

Cluster mechanism of the energy accumulation in a ball electric discharge

1. OBSERVATIONAL RESULTSExperiments on a man-made initiation of a ball-lightning discharge attract attention in the context ofemploying this phenomenon in technological applica-tions [1]. There are well-known hypotheses that treatthis form of discharge as matter with a condensedexcited phase (E. Manykin, M. Ozhovan), as a systempossessing magnetic self-organization (B. Kadomtsev),as a result of the electromagnetic-field capture into aplasma waveguide (V. Kunin, V. Pleshivtsev, L. Furov),as a consequence of electromagnetic-wave interfer-ence, etc. There are also rather exotic hypotheses likeV. Korshunov’s model, which invokes Dirac magneticmonopoles for the explanation of plasma-ball “pump-ing” or the “polymer” model (V. Bychkov et al. ). Thesehypotheses were reviewed in [2], as well as in mono-graphs [3, 4]. Undeniably, any of the scenarios pro-posed corresponds to usual atmospheric conditions andis unavoidably accompanied by physicochemical pro-cesses in gas, ionization being the most importantamong them. Ionization necessarily causes ion hydra-tion at sufficiently low temperatures.The lack of a generally recognized ball-lightningtheory is an essential gap in the general gas-dischargetheory. The key problem is the energy-accumulationmechanism. Estimates of the energy released in the dis-charge for its lifetime show that the mechanism cannotbe reduced to simple gas heating. At high temperatures,a plasma ball would be of a low density, would beentrained vertically upwards by the Archimedean buoy-ancy force, and would disintegrate in the presence ofturbulent flows caused by its own motion. As observa-tions reveal, the plasma bunch (plasmoid) has a densityof the same, or slightly higher, order of magnitude asthat of ambient air and the stable spherical shape is aconsequence of the positive surface tension at the plas-moid boundary. An excess specific weight of a ball,even in the moderate-heating state, testifies to an ele-vated average molecular weight of its material. This isindirect evidence of intense clustering. A short but pow-erful electric-field pulse is undoubtedly required forball-lightning initiation. Such conditions occur in a lin-ear electric discharge of lightning.The relatively rare occurrence of ball lightning inthe course of a thunderstorm suggests that the coinci-dence of several conditions is necessary for ball-dis-charge formation. As a consequence of the requirementof a high degree of ionization in combination with amoderate gas temperature, spontaneous ball-lightningformation is a relatively rare phenomenon. The mostfavorable prerequisites for ball-discharge initiation are,apparently, realized at the periphery of a powerful lin-ear discharge. A shock acoustic wave is capable ofcausing fast adiabatic gas expansion and its local cool-ing. The optimum geometry of a linear-discharge cur-rent-conducting channel might be responsible for thelocal interference amplification of an electromagneticwave. Apparently, a combination of antinodes for astanding electromagnetic wave and a standing shockacoustic wave composes an origin in which the genera-tion of a ball plasma bunch is most likely to beexpected.Independent measurements of the hydrated-ion con-tent in the atmosphere indicate that the concentration ofcharged clusters is moderate and does not exceed10

Investigations of the plume accompanying pulsed ultraviolet laser ablation of graphite in vacuum

The plume accompanying 193 nm pulsed laser ablation of graphite in vacuum has been studied using wavelength, time and spatially resolved optical emission spectroscopy and by complementary Faraday cup measurements of the positively charged ions. The temporal and spatial extent of the optical emissions are taken as evidence that the emitting species result from electron–ion recombination processes, and subsequent radiative cascade from the high n,l Rydberg states that result. The distribution of C neutral emission is symmetric about the surface normal, while the observed C+ emission appears localized in the solid angle between the laser propagation axis and the surface normal. However, Faraday cup measurements of the ion yield and velocity distributions, taken as a function of scattering angle and incident pulse energy, indicate that the total ion flux distribution is peaked along the surface normal. The derived ion velocity distributions are used as input for a two-dimensional model which explains the observed anisotropy of the C+ emission in terms of preferential multiphoton excitation and ionization of C species in the leading part of the expanding plasma ball that are exposed to the greatest incident 193 nm photon flux, prior to electron–ion recombination and subsequent radiative decay.

Electron density in moderate pressure diamond deposition discharges

The electron density is measured in a microwave plasma-assisted chemical vapor deposition diamond reactor at moderate pressures (5–60 Torr) using a millimeter-wave open resonator technique. The discharge plasma is generated using a resonant cavity excited at the frequency 2.45 GHz. The absorbed input power of 400 W generates a microwave discharge above a substrate holder located in a quartz dome. The discharge, shaped as a plasma ball or hemisphere, is positioned in the resonant path of the millimeter-wave open resonator operating at the frequency 32.2 GHz. The millimeter-wave open resonator operates with a quality factor of approximately 3500. The shift in the resonant frequency of the resonator when the discharge plasma is present allows the determination of the electron density. The electron densities measured were in the range of (1–6)×10 11 cm −3 for the pressure range of 5–60 Torr. Electron density measurements for various reactor parameter settings are presented for both pure hydrogen and hydrogen–methane mixture discharges.

Temperature and electron density gradient in Xe laser produced plasmas, by spectral analysis

We have performed a spectroscopic analysis on laser produced plasmas in Xe at intermediates pressures (less than 1 atm), resolved both spectrally and temporally, also discriminating different regions of the plasma. This is produced by tightly focusing the radiation of a Q-switched Nd : YAG laser on a cell equipped with an observation window at right angles with respect to the laser. Our results confirm that there is a gradient in electron density in the plasma ball formed by the laser. This gradient almost defines at least two regions, an outer layer of higher electron number density, and an inner core of lower electron number density. The electron temperature gradient has the same sign. These conclusions are supported by evidence taken using the spectral results mentioned above.

Spatially resolved optical emission spectroscopy of the secondary glow observed during biasing of a microwave plasma

A secondary glow region is commonly observed between the main plasma ball and the substrate during biased enhanced nucleation (BEN) of diamond films grown using the process of microwave plasma-enhanced chemical vapour deposition. Under conditions of very careful optimisation BEN can allow (1 0 0) oriented polycrystalline diamond films to be grown on (1 0 0) silicon substrate; such films are industrial important. Recently it has been suggested that this secondary plasma plays a key role in nucleation density enhancement and orientation effects of the BEN process. However to-date this region of the plasma has received little study. We have used spatially resolved optical emission spectroscopy (OES), optical photography and electrical measurements as diagnostics to qualitatively investigate this region. The measurements show that the appearance of the secondary glow exhibits threshold behaviour which correlates with the I– V measurements carried out during BEN. OES measurements show that the glow region is located about 2 mm above the substrate surface and suggest that it can act as a strong source of atomic hydrogen supporting its role as a region below which strong etching occurs as suggested in recent models of the BEN process.

An exact solution of three-dimensional dynamo-effect problem in expanding plasma ball, based on using the generalized spherical functions

Consideration of the dynamo effect in the expanding ball with strongly anisotropic conductivity is of importance in modelling the experiments on artificial plasma injection into the Earth's ionosphere and magnetosphere. Previously used approaches for solving the respective equations were based either on (i) reduction to a quasi-two-dimensional form by the assumption of infinite longitudinal conductivity or (ii) the use of numerical methods for the case of a realistic three-dimensional geometry. We put forward an analytic method that can give exact solutions for the case of three-dimensional spatial configuration and arbitrary values of plasma conductivities. This approach is based on using the generalized spherical functions, whose theory was developed in our study. Despite a quite sophisticated form, these functions possess, in fact, exactly the same properties as well-known Legendre polynomials and can be applied to solving the dynamo-effect equations with the same efficiency as ordinary spherical functions are used to solve Laplace equation.

Studies of the ablation plume arising in 193 nm laser irradiation of graphite in vacuum

Abstract Pulsed ArF ( λ =193 nm) laser ablation of graphite in vacuum has been investigated using wavelength, spatially and temporally resolved measurements of the plume emission. Electronically excited neutral carbon atoms, along with singly and doubly charged atomic carbon ions are identified amongst the ablated material. Plume expansion velocities are estimated from time gated CCD imaging of specific emissions, by measuring the time dependence of selected emissions through localised regions of space, and via complementary Langmuir probe measurements of the charged material within the plume. The relative merits and limitations of each measurement type are considered. Neutral C atoms are observed to expand with a velocity distribution which is symmetrical about the surface normal. In contrast, the emission from C + ions expanding in vacuum is found to maximise in the solid angle between the laser propagation axis and the surface normal. Such behaviour is rationalised in terms of excitation, and subsequent multiphoton ionisation, of C atoms in the leading edge of the expanding plasma ball whilst the 193 nm laser pulse is incident.

Effects of bias voltage on microwave plasma used for diamond growth

A tungsten-needle substrate was perpendicularly set onto a substrate holder. Diamond films were grown on the substrate by varying the length of the needle inserted into plasma. The results demonstrated that when the bias voltage was −50 V and the methane concentration was 5%, a diamond thin film grew for a needle length of 0.5 mm, and granular diamond grew for a needle length of 1 mm. Plasma potentials were measured while the bias voltage was varied. The plasma potential became negative at bias voltage of 0 V, and it changed to positive as the negative bias voltage increased. These results revealed that diamonds were grown near the boundary between the transition region surrounding the plasma ball and the ion sheath. In addition, the results also indicated that the bias voltage can control the density and energy of ions, electrons and radicals near the plasma, and therefore plays a role in providing optimal conditions for diamond growth.

Peeling back the Sun

Observations show that the Sun is not simply a ball of hot plasma but contains several discrete layers: the interior where the energy is generated is covered by the photosphere, the chromosphere and finally the corona. This article describes a photon's journey to the outside and links features such as prominences and sunspots to the regions in which they occur.

Initial phase of laser-induced air optical breakdown: a new picture

Optical breakdown has been generated by focusing YAG laser radiation in the air. The laser radiation itself was scattered due to laser-induced air optical breakdown. Angular distributions of scattered radiation at 1064, 532, and 355 nm were measured. Analysis of the distributions has been performed in terms of Mie scattering. It has been assumed that scattering of laser radiation is due mainly to highly ionized plasma balls in the initial phase of air optical breakdown. The wavelength-dependent angular distribution has been analyzed with two parameters. The mean radius and the plasma frequency of the plasma balls have been determined by a least-squares fit procedure. Observed wavelength-dependent angular distributions are in good agreement with ones calculated by Mie theory.

Stoichiometry of the diamond/silicon interface and its influence on the silicon content of diamond films

Thin films of diamond were grown by microwave plasma chemical vapor deposition at growth pressures of 10, 20, 40, and 60 Torr keeping the substrate temperature constant at 975 °C. Increase in the growth pressure reduced the size of the plasma ball resulting in an increase in the microwave power density (MPD). The films were characterized by scanning electron microscopy, micro-Raman, and photoluminescence (PL) spectroscopy. A systematic variation was observed in surface morphology and quality of the films. The intensity of the peak at 1.68 eV in the PL spectra of the films, which is assigned to Si impurities was also observed to increase consistently with the MPD. The stoichiometry of the diamond/silicon interface was studied by x-ray photoelectron spectroscopy (XPS) and found to be a sensitive function of the MPD. XPS results showed the formation of nonstoichiometric SiC along with other carbon phases in the initial stages of the growth. A correlation was observed between the composition of the interface and the intensity of the 1.68 eV peak. The above results are explained in terms of the increase in the impingement flux density of atomic hydrogen with the MPD.

A simplified fluid model of the metallic plasma and neutral gas interaction in a multicathode spot vacuum arc

A stationary fluid model with spherical symmetry is presented to describe the interaction between metallic plasma ions with neutral gas in the outer region of a multicathode spot vacuum are operated with a neutral background gas. It is found that the neutrals penetrate into the metallic plasma with density values smaller than the initial gas density values, but higher than the metallic ion densities. The neutrals are also strongly heated during the transient expansion stage of the metallic plasma. As a consequence, the ion kinetic energy is gradually delivered to the neutral gas so that the mean free path for ion-neutral elastic collisions is larger than the visible plasma ball radius which surrounds the arc.