Neon Pressure Research Articles

Effect of insulator sleeve length on soft x-ray emission from a neon-filled plasma focus device

Insulator sleeves of different lengths were used at the closed end of the coaxial electrode assembly of the 3.3 kJ United Nation University-International Centre for Theoretical Physics (UNU-ICTP) plasma focus device to investigate soft x-ray (SXR) (900–1550 eV) yield for different filling gas pressures of neon. The time and space resolved SXR emission characteristics were investigated using a multi-channel diode x-ray spectrometer and a CCD based pinhole imaging camera. At pressures below 6 mbar, the average SXR yield was also found to increase with increasing sleeve length from 19 to 22 mm. A further increase in insulator sleeve length to 25 mm, however, decreased the SXR yield. At pressures above 6 mbar, the SXR yields were almost the same for insulator sleeves of different lengths. The UNU-ICTP plasma focus device is found to be best optimized for neon SXR production with a 22 mm insulator sleeve at 4 mbar filling gas pressure, with the highest average yield of 8.2 J per shot, for which the conversion efficiency is about 0.25%. For this sleeve length, even the average yield at 2 or 6 mbar pressure was comparable with the maximum yield of a 25 mm sleeve.

Gas scattering effects and microstructural evaluation of electron beam evaporated titanium coatings in neon and argon at different gas pressures

Titanium coatings were deposited on stainless steel and glass substrates by electron beam evaporation in vacuum (4×10 −4 Pa) and at different neon and argon gas pressures (from 0.33 to 2.00 Pa). The effect of background gas pressure and type on film microstructure was evaluated by scanning electron microscopy (SEM). Since it was not feasible to maintain a constant evaporation rate for all runs, the ‘deposition efficacy’, a parameter defined as the ratio between coating thickness and mass of material evaporated, was statistically modelled using non-linear regression analysis to determine the effects of gas scattering. The results revealed that neon and argon promote similar scattering of the titanium vapour and this may point to a lower likelihood of gas-phase metal cluster formation in neon. The coating microstructure was found to change from a tapered grain structure, obtained under vacuum conditions, to a faceted one at low gas pressure (0.33 Pa), becoming more porous as gas pressure increased. For a given gas pressure, no significant differences could be observed in coating microstructure between the use of argon or neon. These findings may be significant when considering the use of neon as an alternative gas to argon, for improving reactive gas ionisation (through Penning mechanisms) in Plasma-Assisted Physical Vapour Deposition.

Emission from a transverse volume discharge in neon with small admixtures of water vapor and air

Emission from the plasma of a pulsed discharge in neon with small admixtures of water vapor and air in the wavelength range 210–620 nm is investigated. A transverse volume discharge with spark UV preionization is ignited in neon at a pressure of 100–200 kPa and charging voltage of Uch≤20 kV. It is shown that the discharge acts as a source of pulsed UV radiation on OH(A-X) (λ=308–314 nm) and NO(B-X) (247.8 nm) transitions, which is of interest for the use in an ecologically safe lamp based on the mixtures of neon with water vapor and air. In the visible spectral region, plasma emission consists of the NeI (3s, 3s′-3p, 3p′) band and Hβ 486.1-nm spectral line. On the short-wavelength side of the spectrum, a broadband emission (the third continuum of neon) is observed, whose intensity increases with increasing neon pressure and decreasing emission wavelength.

Effect of matching of a power supply with a laser tube and of pumping conditions on the relaxation of metastable states and the frequency — energy parameters of a copper vapour laser

The relation between the lasing efficiency of a copper vapour laser and relaxation of the metastable states is studied at high average pump powers. The prepulse concentration Nms0 of metastable states in tubes of diameter 2 cm in lasers with a high efficiency (above 1%) is shown to be negligible up to linear output powers of ~50 W m-1 and has no effect on the output power. At a lower lasing efficiency caused by the mismatch between a power supply and the laser tube, the population of metastable states strongly increases during afterglow and can become a main factor restricting the output power in a repetitively pulsed regime. As the neon pressure is increased or hydrogen is added, the matching is facilitated and the effect of Nms0 on the lasing parameters of a high-power copper laser decreases.

Compression of Fe 3 C to 30 GPa at room temperature

Polycrystalline Fe3C (cementite) was compressed in a neon pressure medium to 30.5 GPa at 300 K using diamond-anvil cell techniques. Angular dispersive X-ray diffraction of Fe3C was measured using monochromatic synchrotron radiation and imaging plates. No phase transition was observed up to the highest pressure studied. The pressure–volume data were fitted to a third-order Birch–Murnaghan equation of state. With V 0 constrained to a measured value of 155.28 A3, the best fit yielded a 300-K isothermal bulk modulus K 0 = 174 ± 6 GPa, and its pressure derivative at constant temperature K 0 ′ =(K 0 /P) T = 4.8±0.8.

Experimental Investigations of x-ray Emission in a New Filippov-Type Plasma Focus

We present an experimental study of the soft and hard x-ray performance characteristics of neon and neon-krypton mixture (Pkr up to 0.2 torr) plasma produced by a new Filippov-type plasma focus device named “Dena”, with 90 kJ (25 kV, 288 µF) operating at pressures in the range 0.3–1.5 torr. In this investigation, the soft and hard x-ray intensities are measured using a filtered PIN diode, a pinhole camera with a Be filter (10 µm thickness), a plastic and NaI scintillators. Using pure neon as the filling gas, and a charging voltage of 16 kV with 37 kJ stored energy, the maximum intensities of the soft and hard x-rays were found to be about 5 V/shot and 2.2 V/shot, respectively. These measurements were obtained at an optimum operating pressure in the range of 0.5–0.9 torr (for the soft x-ray) and about 0.8 torr (for the hard x-ray). The relationships between the optimum neon pressure range and the time of spike appearances on the discharge current signal were experimentally studied. The results indicate that, the x-ray emission is more sensitive to the time of spike appearances than the neon filling gas pressure. By using a krypton admixture to the neon filling gas (PNe = 1 torr), the most pronounced effect is observed for the hard x-ray yield (up to eight times of the initial value) at the optimum krypton pressure of about 0.1 torr. The measurements of maximum x-ray intensity, performed with krypton admixture, show that as the pressure of krypton admixture increases, the optimum discharge voltages fall to a value depending on the quantity of krypton admixtures used. This effect was generally an intensity decreasing matter for the soft x-ray.

New plasma Hall effect magnetic sensors: macrosensors versus microsensors

This paper is the first attempt to use the plasma Hall effect for magnetic field detection. The plasma Hall sensor measures the Hall voltage induced by ac electrons plasma in the magnetic field. In a theoretical analysis, we develop an analytical model of the plasma Hall sensor in order to express the plasma Hall voltage as a function of electrode geometry, magnetic field, plasma discharge field, and fluid pressure. On these bases, we have designed, fabricated, and characterized the neon plasma Hall sensors in the macroscale as well as those in the microscale. The plasma Hall macrosensor, using steel wire electrodes in a low-pressure chamber, shows a magnetic field sensitivity of 136.7±10.1 mV/G with 8.43% nonlinearity at a neon pressure of 80±5 Torr for a circuit gain of 15.56. The macrosensor, however, shows long-term instability due to the neon pressure instability in the vacuum chamber, which motivates the research on the plasma Hall microsensor. The plasma Hall microsensors using the electroplated copper electrodes in on-chip vacuum package show a magnetic field sensitivity of 8.87±0.18 mV/G with 4.48% nonlinearity at a neon pressure of 7±1 Torr for a circuit gain of 5.5. The microsensor shows good stability for 12 h. Fundamental characteristics of the macrosensors and microsensors are compared and discussed, thus verifying the feasibility of the plasma Hall sensor for a new class of magnetic microsensor.

Investigationof the neon 2p collisional excitation transfer processes via CWlaser collisionally induced fluorescence

We present a method for determining the 2p (in Paschen notation)collisional excitation transfer coefficients in noble gasesusing continuous-wave laser collisionally induced fluorescence(CW LCIF, i.e. fluorescence from an upper level which is notthat of the laser transition). The technique requires isolationof the specific 2p coupling process under examination, wherebythat process provides an important and quantifiable contributionto the LCIF. This is achieved by selecting appropriate laserexcitation and LCIF transitions. For a neon discharge operatingat pressures ranging from 1.5 to 8.0 Torr and currents from 1 to 10 mA,2p coupling is by ground-state atom collisions and thelargest coupling exists between adjacent states. We show thatin certain cases excitation transfer plays an important role inthe excited-state kinetics.

Path-integral Monte Carlo simulations of solid neon at room temperature

The kinetic and potential energies and the pressure of solid neon at room temperature have been calculated by means of path-integral Monte Carlo simulations using the HFD-C2 pair potential. At these high densities, the quantum corrections to the kinetic energy are appreciable, but for the potential energy and pressure classical simulations (even with a nearest-neighbor model) are generally within $1%$ of the quantum-mechanical values. The present results for the pressure are significantly higher than the experimental equation of state in the 10--100-GPa range. It is shown that inclusion of many-body short-range interactions might bring the simulations in agreement with experiment.

Experimental study of speed-dependent collisional effects of He and Ne on the 687.1 nm argon line

Using a pressure-scanned Fabry-Perot interferometer precise measurements of the profiles of the 687.1 nm argon line perturbed by helium and neon pressures between 0.5 and 44 torr have been performed. Careful analysis of line shapes showed that for Ar-He the speed-dependent effects do not play any essential role. Contrary to that, for Ar-Ne these effects can give rise to noticeable decrease of the Doppler width determined using the Voigt profile. It was shown that for Ar-Ne the inclusion of speed-dependent effects can reduce the apparent dependence of the Doppler width on the neon density and cause the Doppler temperatures determined from the profiles to be consistent with the source temperature. The role of the Dicke narrowing is also discussed.

VUV Radiation of Afterglow Generated by Pulsed Discharge of Xenon.

The characteristics of xenon-neon discharge fluorescent lamps with inner electrodes and of xenon discharge lamps with external electrodes are described in this paper. All these lamps were operated at pulsed discharge. In the case of inner electrode type, when the partial pressure of neon is high, the ignition voltage is low because of the Penning effect. Then, the high mixing ratio of neon is desirable for the lower ignition voltage. However, the luminance of phosphor increases as the mixing ratio of xenon increases. Therefore, in order to obtain high luminance, xenon should be filled at high mixing ratio. In both cases, that is, inner electrode type and external electrode type, as the pressure of xenon increases, the afterglow peak of phosphor emission increases. These increases seem to be caused by the VUV radiation of xenon excimers. The emission of light from phosphor shows that xenon excimers are generated effectively by pulsed discharge of high pressure xenon, because they are generated by three-body collision at the low electron temperature Te during the non-discharge period.

A simple extended cavity diode laser for spectroscopy around 640 nm

We report on an extended cavity diode laser for operation near 640 nm. The laser is continuously tunable in 10 GHz ranges with a maximum output power of 3 mW. The laser system has been constructed using off-the-shelf optoelectronic components and easily machinable mechanical parts. The constructed system has been used to study the saturated absorption of the closed 1s 5–2p 9 neon transition in a radio-frequency discharge that can be maintained at neon pressures down to 10 −2 Pa.

Fundamental Research on Mercuryless Fluorescent Lamps I – Inner Electrode Operation with Pulsed Discharge –

The characteristics of xenon-neon discharge fluorescent lamps with inner electrodes are described in this paper. All lamps were operated by pulsed discharge. When the partial pressure of neon is high, the ignition voltage and operation voltage are low because of the Penning effect. Thus, a higher mixing ratio of neon is desirable for lower ignition and operation voltages. However, the luminance of phosphor increases as the mixing ratio of xenon increases. As the pressure of xenon increases, the second peak of phosphor emission in afterglow increases. These increases seem to be caused by the VUV light of xenon excimers. Therefore, though there is the problem of ion bombardment of the cathode under a high operation voltage, the pulsed discharge of the xenon-neon mixture at a high xenon mixing ratio is desirable in mercuryless fluorescent lamps because a strong radiation of xenon excimer is obtained.

Static compression of the hydrous magnesium silicate phase D to 30 GPa at room temperature

Phase D is a dense hydrous magnesium silicate (ideal formula MgSi2H2O6) which contains silicon cations exclusively in octahedral coordination. Measurements of the unit cell parameters of phase D were made to pressures of 30 GPa using a diamond anvil cell and employing synchrotron X-ray diffraction. A neon pressure medium was used. Using a third order Birch-Murnaghan equation of state the isothermal bulk modulus of phase D was determined as 166(±3) GPa with K′ equal to 4.1(±0.3). The compression of phase D is anisotropic with the c-axis twice as compressible as the a-axis. Above 20 GPa, however, the c/a ratio becomes pressure independent.

Characterization of afterglow kinetics at atmospheric pressures by emission spectroscopy. I: reactions of neon ions with

The afterglow of a 1 kA, 10 ns duration discharge in neon at 1-4 bar pressure containing up to 10 mbar of reactant admixture was studied by time-resolved emission spectroscopy. Destruction rates of neon ions have been experimentally determined from the selectively excited fluorescence of emitted as the result of charge transfer. Reasonable agreement with previously reported results was obtained over the smaller range of nitrogen pressures (below 0.8 mbar) used in those studies. Data obtained at reactant pressures higher than about 1.2 mbar were consistent with a kinetic model in which vibrationally excited ions play an important role. The slow collisional relaxation of these ions (rate coefficient ) would limit the rate of to conversion at neon pressures higher than about 0.2 bar.

Minimum Alveolar Concentrations of Noble Gases, Nitrogen, and Sulfur Hexafluoride in Rats

We assessed the anesthetic properties of helium and neon at hyperbaric pressures by testing their capacity to decrease anesthetic requirement for desflurane using electrical stimulation of the tail as the anesthetic endpoint (i.e., the minimum alveolar anesthetic concentration [MAC]) in rats. Partial pressures of helium or neon near those predicted to produce anesthesia by the Meyer-Overton hypothesis (approximately 80-90 atm), tended to increase desflurane MAC, and these partial pressures of helium and neon produced convulsions when administered alone. In contrast, the noble gases argon, krypton, and xenon were anesthetic with mean MAC values of (+/- SD) of 27.0 +/- 2.6, 7.31 +/- 0.54, and 1.61 +/- 0.17 atm, respectively. Because the lethal partial pressures of nitrogen and sulfur hexafluoride overlapped their anesthetic partial pressures, MAC values were determined for these gases by additivity studies with desflurane. Nitrogen and sulfur hexafluoride MAC values were estimated to be 110 and 14.6 atm, respectively. Of the gases with anesthetic properties, nitrogen deviated the most from the Meyer-Overton hypothesis. Implications: It has been thought that the high pressures of helium and neon that might be needed to produce anesthesia antagonize their anesthetic properties (pressure reversal of anesthesia). We propose an alternative explanation: like other compounds with a low affinity to water, helium and neon are intrinsically without anesthetic effect. (Anesth Analg 1998;87:419-24)

Minimum alveolar concentrations of noble gases, nitrogen, and sulfur hexafluoride in rats: helium and neon as nonimmobilizers (nonanesthetics)

We assessed the anesthetic properties of helium and neon at hyperbaric pressures by testing their capacity to decrease anesthetic requirement for desflurane using electrical stimulation of the tail as the anesthetic endpoint (i.e., the minimum alveolar anesthetic concentration [MAC]) in rats. Partial pressures of helium or neon near those predicted to produce anesthesia by the Meyer-Overton hypothesis (approximately 80-90 atm), tended to increase desflurane MAC, and these partial pressures of helium and neon produced convulsions when administered alone. In contrast, the noble gases argon, krypton, and xenon were anesthetic with mean MAC values of (+/- SD) of 27.0 +/- 2.6, 7.31 +/- 0.54, and 1.61 +/- 0.17 atm, respectively. Because the lethal partial pressures of nitrogen and sulfur hexafluoride overlapped their anesthetic partial pressures, MAC values were determined for these gases by additivity studies with desflurane. Nitrogen and sulfur hexafluoride MAC values were estimated to be 110 and 14.6 atm, respectively. Of the gases with anesthetic properties, nitrogen deviated the most from the Meyer-Overton hypothesis. It has been thought that the high pressures of helium and neon that might be needed to produce anesthesia antagonize their anesthetic properties (pressure reversal of anesthesia). We propose an alternative explanation: like other compounds with a low affinity to water, helium and neon are intrinsically without anesthetic effect.

Diffusive gas losses from silica glass ampoules at elevated temperatures

Changes in the pressure of hydrogen, helium and neon due to diffusion through the wall of silica crystal growth ampoules at elevated temperatures were determined experimentally. We show that, while both He- and Ne-losses closely follow the conventional model of diffusive gas permeation through the wall, hydrogen losses, particularly at low fill pressures, can be much larger. This is interpreted in terms of the high solubility of hydrogen in silica glasses.

Application of a species-selective Penning gauge to the measurement of neon and hydrogen-isotope partial pressures in the plasma boundary

A species-selective Penning gauge, previously applied to He partial pressures, is now applied to the detection of small concentrations of Ne in a D2 gas. This is important for the study of Ne in the boundary region of magnetic fusion devices, where this impurity is deliberately injected to enhance the radiated power in that region. The application of the technique to the detection of the partial pressure of a minority hydrogen isotope is also examined. In this latter application, the detection system and the data analysis are more complex, because of the proximity of the spectral lines of the isotopes. In both applications, it is found that use of a proper detection scheme permits reliable measurements of concentrations as low as 0.5% of the minority neutral species, without requiring changes to the standard commercial Penning gauge setup.

Interaction of a Ne-H2 SOL-like plasma with graphite

Neon was recently introduced in tokamak plasmas to enhance the radiative properties of the scrape off layer (SOL). We have studied on SPISA (Surface Plasma Interaction Simulation Apparatus) the interaction of a Nez.sbnd;H2 mixed plasma (electronic density ∼ 5 × 1018m−3, Te ≈ 20 eV) with a graphite 5890PT sample. The subsequent thermodesorption of the sample shows that the total amount of implanted neon depends on the ratio of partial pressures of neon and hydrogen more than on ionic densities, bombarding energies or total fluences. The thermodesorption spectra are shown to be in good agreement with a diffusion model with an activation energy of 0.35 ± 0.07 eV and a pre-exponential factor D0 = 3 × 10−17m2s−1. These results are in agreement with Tore Supra results on neon desorption from the walls after plasma shots.