Argon Emission Research Articles

Detection of Cherenkov light emission in liquid argon

Detection of Cherenkov light emission in liquid argon has been obtained with an ICARUS prototype, during a dedicated test run at the Gran Sasso Laboratory external facility. Ionizing tracks from cosmic ray muons crossing the detector active volume have been collected in coincidence with visible light signals from a photo-multiplier (PMT) immersed in liquid argon. A 3D reconstruction of the tracks has been performed exploiting the ICARUS imaging capability. The angular distributions of the tracks triggered by the PMT signals show an evident directionality. By means of a detailed Monte Carlo simulation we show that the geometrical characteristics of the events are compatible with the hypothesis of Cherenkov light emission as the main source of the PMT signals.

Characterization of BCl3/N2 plasmas

Optical emission spectroscopy, quadrupole mass spectrometry, and electron density measurements were used to study the effect of the percentage of N2 on the characteristics of BCl3/N2 plasmas and their resulting etch processes. The etch rate of GaAs increased from 80 Å/min in pure BCl3 to over 1000 Å/min in a 40:60 BCl3:N2 mixture (15 mTorr, 50 W, 20 sccm). The optical emission intensities of both molecular and atomic chlorine exhibited maxima near 30% N2, and an argon actinometer indicated a large increase in argon emission as a function of the increase in N2 percentage. Microwave measurements indicated that the average electron density increased only slightly with an increase in nitrogen percentage up to 60% N2. Mass spectrometric analysis of the plasmas showed that both the dissociation of BCl3 and the production of molecular chlorine were significantly enhanced by the addition of N2. These results suggest that an increase in the electron temperature as a result of electron attachment heating (and possibly energy transfer from N2 metastables) is responsible for the increased dissociation and enhanced production of etch species.

Spectral analytical system for measuring time-resolved spectra of materials under shock

A spectral analytical system has been developed for measuring the time-resolved spectra of a transient emission. In this system, a special optical splitter-delay generator converts the time-distribution spectra into the space-distribution spectra, and the time-dependent spectra are recorded by a two-dimensional charge coupled device, accompanied with a multichannel plate intensifier. The time resolution of 20 ns and the recording time of 120 ns have been achieved in the experiment for argon emission shocked to 12 000 K.

Stress emission of helium and argon in coal seams

Stress emission of helium and argon in coal seams

Stress emission of helium and argon in coal seams

In the Yutianbao Mine, the Nantong Coal Field, Chongqing, a lot of gas samples were measured and analyzed. It has been found in these samples that helium is sensitive to stress concentration, while argon is sensitive to stress release. Compared with the flowing out of gas it-self, the combination of helium and argon can be more suitably used as an indicator to predict gas outburst. In a mining area of this mine, both δ He > 30 and δ Ar < ?0.97 can be used critically to define the dangerous area. Also, the contour maps of δ He, δ Ar and CH4 can provide a guidance for engineering monitoring.

Temporal emission characteristics of millisecond pulsed radiofrequency and direct current glow discharges

Interpretation of optical emission spectra reveals the primary excitation mechanisms for discharge gas, argon and sputtered analyte, copper, species in glow discharge plasmas operated with millisecond pulses of radiofrequency or direct current power. There is negligible difference between the two power sources. During the applied power pulse, plasma processes include ion and atom excitation through electron excitation, asymmetric charge exchange and Penning ionization. Fast ion and atom excitation processes, characterized by monitoring argon emission at 811.5 nm, occur within 2 mm of the cathode surface. Electron excitation, for both discharge gas and sputtered species, maximizes 3 mm from the cathode surface. Asymmetric charge exchange between ground state sputtered atoms and discharge gas ions, characterized by Cu II emission at 224.7 nm, occurs at 5 mm from the cathode surface. Upon power termination, the recombination of ions with thermal electrons yields excited atoms and argon metastable species. At this time, emission monitored at 811.5 nm maximizes 6–7 mm from the cathode surface, corresponding to an increase in the metastable population and, hence, Penning ionization.

Spectroscopic water vapor sensor for rapid response measurements of humidity in the troposphere

We have developed a closed‐path water vapor sensor based on optical absorption of an atomic argon emission line that is suitable for rapid response (10 Hz bandwidth) humidity measurements in the lower and middle troposphere. The sensor uses an argon emission line at 935.4 nm that can be Zeeman‐split into two components, only one of which is strongly absorbed by a water absorption line at 10,687.36 cm−1 (∼935.6 nm). The sensor exhibits a noise figure‐of‐merit of 40 ppmv Hz−1/2 at low humidities (below 0.5%); the noise level slowly rises to 60 ppmv Hz−1/2 as water vapor mixing ratios reach 2.5%. The performance of this sensor was compared to that of a chilled mirror hygrometer and a capacitance‐based polymer sensor, all of which were installed on board a Twin Otter airplane during an atmospheric humidity measurement campaign conducted northeast of Hawaii. Over a range of water vapor volume mixing ratios of 0.1–3% (at altitudes of 50–3000 m), the sensors were shown to agree with one another within 5% of the measurement in regions of slowly changing humidity. However, in regions of large humidity gradients, the optical sensor (with the use of an appropriate inlet tube) was able to track water vapor features on the scale of tens of meters or less that neither the slow‐response chilled mirror hygrometer nor the capacitance‐based sensor could adequately reproduce. The optical sensor was also able to track humidity in the vicinity of clouds and discern fine structure within the cloud itself.

Bright hydrogen-lightsource due to a resonant energy transfer with strontium andargon ions

A plasma called a resonant transfer (rt) plasma formed with a low field(1 V cm-1), at low temperatures (e.g. ≈103 K),from atomic hydrogen generated at a tungsten filament andstrontium which was vapourized by heating the metal. Strongvacuum ultraviolet emission was observed that increased with theaddition of argon, but not when sodium, magnesium or bariumreplaced strontium or with hydrogen, argon or strontium alone. Characteristic strontium and argon emission was observed whichsupported a resonant-energy-transfer mechanism. SignificantBalmer α line broadening corresponding to an averagehydrogen atom temperature of 14, 24, and 23-45 eV was observedfor strontium and argon-strontium rt plasmas and discharges ofstrontium-hydrogen, helium-hydrogen, argon-hydrogen,strontium-helium-hydrogen and strontium-argon-hydrogen,respectively, compared to ≈3 eV for pure hydrogen,krypton-hydrogen, xenon-hydrogen and magnesium-hydrogen. To achieve that same optically measured light output power,hydrogen-sodium, hydrogen-magnesium and hydrogen-bariummixtures required 4000, 7000 and 6500 times the power of thehydrogen-strontium mixture, respectively, and the addition ofargon increased these ratios by a factor of about two. A glowdischarge plasma formed for hydrogen-strontium mixtures at anextremely low voltage of about 2 V compared to 250 V forhydrogen alone and sodium-hydrogen mixtures, and 140-150 V forhydrogen-magnesium and hydrogen-barium mixtures.

A Search for Argon and O [CSC]vi[/CSC] in Three Comets Using the [ITAL]Far Ultraviolet Spectroscopic Explorer[/ITAL

We conducted a sensitive search for the resonance lines of Ar I (λλ1048.22, 1066.66) and O VI (λλ1031.93, 1037.62) in the spectra of three long-period comets observed with the Far Ultraviolet Spectroscopic Explorer (FUSE). Argon emission was not detected from C/1999 T1 (McNaught-Hartley), C/2001 A2 (LINEAR), or C/2000 WM1 (LINEAR). Compared with the solar value, the [Ar/O] ratio is depleted in C/A2 by at least a factor of 10 and in C/WM1 by at least a factor of 13. The [Ar/O] upper limit for C/T1 is essentially the solar value, as our measurement was much less sensitive for that case. We also detected CO, which has a volatility similar to that of argon, during the FUSE observations. C/T1 was CO-rich ([CO/H2O] ≈ 13%), while both C/A2 and C/WM1 were CO-poor ([CO/H2O] ≈ 0.7% for C/A2 and ≈0.4% for C/WM1). The argon and CO depletions in C/A2 and C/WM1 suggest formation temperatures 60 K for both of these comets. The high CO abundance and upper limit on the argon abundance in C/T1 suggest that its formation temperature was in the range of ~40-50 K. No O VI emission was detected from comets C/T1 or C/A2, but the stronger line was marginally detected in C/WM1.

Energy-dependentKLdouble photoexcitation of argon

The fluorescence $\mathrm{KL}$ x-ray emission of argon induced by impact with monoenergetic photons was observed with a high-resolution reflecting-type bent crystal spectrometer. The measurements were performed at the European Synchrotron Radiation Facility in Grenoble, France. X-ray beam energies in the range $3455 \mathrm{eV}l~\ensuremath{\Elzxh}\ensuremath{\omega}l~6540 \mathrm{eV}$ were used to investigate the $K+L$ double excitation from threshold to saturation. The excitation probabilities were deduced from the satellite-to-diagram line yield ratios $\mathrm{I}(KL\ensuremath{-}{L}_{2,3}L): \mathrm{I}(K\ensuremath{-}{L}_{2,3}).$ Results were compared to predictions based on the model of Thomas and the one of Roy. From the comparison, parameters such as excitation onset energies, high-energy limit shake probabilities, and radius of the $2p$ orbital in ionic Ar were deduced. The satellite line shapes and their evolution with the excitation energy were analyzed with the aid of multiconfiguration Dirac-Fock calculations.

Sub-Doppler Spectral Resolution and Improved Sensitivity in a Cesium Resonance Fluorescence Imaging Monochromator

Improvements in spectral resolution and sensitivity of a cesium based resonance fluorescence imaging monochromator (RFIM) are described. Alignment of the two lasers used in the excitation scheme in a co-propagating geometry have resulted in a detector spectral bandpass (270 MHz) that is narrower than the Doppler broadened profile (380 MHz) of cesium vapor at room temperature. Improvements in the experimental design, namely the addition of an image intensifier and cooled charge-coupled device (CCD) camera, have resulted in increased sensitivity; we report a limit of detection of 108 photons per pixel limited by image intensifier noise. Images of the cesium D2 line emission (852.12 nm) from a cesium hollow cathode lamp were compared to an argon emission line (4Sº1/2 → 4P3/2) at 852.14 nm from a silver/argon hollow cathode lamp as a demonstration of the spectral resolution. The ability of the RFIM to discriminate between photons exciting the F = 4 vs. F = 3 ground state hyperfine level (a frequency difference of 9.2 GHz) of the cesium 62S1/2 state was also investigated to further demonstrate the spectral selectivity. The potential use of the described RFIM for chemical imaging applications is discussed.

Optical emission spectroscopy of pulsed hexalfuoropropylene oxide and tetrafluoroethylene plasmas

The optical emission spectra of tetrafluoroethylene (TFE) and hexafluoropropylene oxide (HFPO) have been examined for chemistry and electron distribution transients as a function of plasma pulsing, under depositing conditions (1 torr). The major identifiable peaks in these plasmas are attributable to CF2 and CF. Other expected species, including CF3, atomic F and atomic C are not observed. HFPO plasmas show significant emission from CO and O. Comparison of CF2 emission transients to absolute absorption measurements show that the continuum emission surrounding CF2 is not attributable to CF2+ emission, as has been previously proposed, but is likely rovibrational overlap. Argon emission in TFE shows a relatively slow transient toward steady state (∼20 ms), implying slower chemistry transients, such as attachment, control the electron transient in pulsed TFE plasmas. In HFPO plasmas, CO and O actinometry are applied. CO emission trends suggest that CO is actually produced during the plasma off times, and is here attributed to etching reactions in the film. The rotational structure of CO is also examined and fit to estimate plasma rotational temperature, giving temperature transients on the order of ∼20 ms.

Some spatial effects observed in the axially viewed filament argon microwave induced plasma with solution nebulization

Spatial profiles of analyte emission in an axially viewed argon filament microwave induced plasma sustained in the TE 101 rectangular cavity have been measured along a discharge tube cross-section for neutral atoms as well as ion lines of several elements. The filament diameter was approximately 1 mm. The analyte solution was introduced by means of an ultrasonic nebulizer without desolvation. The radial emission distribution depends on the operating parameters and is different for each of the analytes examined. Spatial distributions of excitation temperature (4000–6000 K) measured with Ar I lines by the Boltzmann plot method as well as electron temperature (6000–8000 K) by line to continuum emission ratio measurements at Ar I 430 nm and electron number density (1–1.5×10 15 cm −3) by the Stark broadening method of the H β line were determined to support the evidence of plasma processes. In the presence of excess sodium the enhancement of emission intensity and its shift to the plasma center appears to be the result of increased analyte penetration to the plasma. Changes in spatial emission profiles for Ca atoms and ions suggest that for this element ambipolar diffusion may be important as an additional interference mechanism. A possibility of minimizing spectral interferences from argon emission lines by choosing an off-axis plasma region for emission intensity measurements is indicated.

Argon auroral emissions

Argon is the third most abundant constituent of the atmosphere, but has not been previously detected by any ground-based optical remote sensing method. We report observation of argon emissions at λ840.82 and λ842.46 nm during intense aurora. These are most likely excited by direct electron impact. The maximum argon intensity observed is 270 R . Argon is the fifth elemental emission conclusively observed in geo-aurora, joining N, O, H and He.

Survey of Neon and Argon Emission Between 3800 Å and 6000 Å in the EBIT-II Electron Beam Ion Trap

Using the low-energy electron beam ion trap EBIT-II at the Lawrence Livermore National Laboratory, we surveyed neon and argon spectra throughout the wavelength range from 3800 to 6000 Å employing a prism spectrograph and a scientific-grade CCD camera. By varying the electron beam energy, spectra from singly ionized to highly ionized neon and argon ions were recorded. In total, about 130 lines were observed from ions in low charge states. About half of the lines have not been reported before. From high charge state ions, several lines of forbidden transitions were observed, among which are the prominent M1 transitions from Ar XIV at 4412 Å and Ar X at 5534 Å.

Time-resolved spectral-line-filtered velocimetry

Measurements were obtained with a velocimeter that simultaneously illuminates the particulate in a flow with argon and He–Ne lasers and the scattered light is passed through a carefully controlled iodine filter. The iodine cell absorbs the argon emission at a rate proportional to the velocity of the scattering particle, while the absorption of scattered He–Ne light is independent of velocity. A tunable acousto-optic filter is used to multiplex the argon and He–Ne signals collected from a single photodetector. The problem of detector alignment in conventional Doppler global velocimetry is thus avoided. Experimental results on a scattering disk and an axisymmetric jet are presented and compared with laser Doppler anemometry measurements.

Ion energy distributions and optical emission spectra in NF3-based process chamber cleaning plasmas

To minimize ion bombardment induced damage in NF3-based chamber cleaning plasmas, we have studied the effects of diluent gases and reactor pressure on ion energy distribution functions in NF3 plasmas. We have utilized plasma ion mass spectrometry, ion energy analysis, and optical emission spectroscopy in 25 mol % NF3 plasmas with argon, helium, and oxygen diluents. We have also compared the NF3-based plasma measurements to those of 50 mol % C2F6/O2 plasmas. We have demonstrated that diluting with helium and operating at higher pressures will reduce ion energies in NF3 plasmas while maintaining superior chamber cleaning performance. In addition, we have correlated the intensity ratio of specific argon emission lines to average ion energies at the grounded electrode. This correlation provides a practical diagnostics tool for further optimization work.

Spectroscopic Temperature Measurements in Direct Current Arc Plasma Jets Used in Thermal Spray Processing of Materials

An experimental study was conducted to determine the plasma temperature field and its parametric variation with respect to plasma operating conditions using emission spectroscopy. The focus of our study was the direct current (DC) arc plasma systems used in thermal spray processing of ceramic materials. A commercial plasma system (Metco 9M series) was operated with mixtures of argon and hydrogen in the power input range from 12 to 36 kW. Temperature measurements were based on the detection of emission line intensities from Ar-I neutral species. Spatially resolved measurements were obtained of the plasma temperatures in axisymmetric plasma jets using Abel deconvolution. The variation of plasma axial and radial temperature distributions was measured as a function of the plasma input power, the total gas flow rate, and the binary gas composition of argon and hydrogen. Time-averaged plasma gas temperatures were found to increase with increasing plasma input power, increasing hydrogen content of the plasma gas, and decreasing total gas flow rate. Plasma temperatures decrease progressively with increasing distance from the nozzle exit. The peak temperatures near the nozzle exit are in the range of 12,500 to 14,000 K. The radial temperature profiles show an approximately self-similar decay in the near field of these plasma jets. It was also determined from time resolved intensity measurements that there are significant fluctuations in the argon emission intensity with increasing hydrogen fraction in the mixture. These fluctuations with a typical frequency of 5.2 kHz are attributed to the arc root instabilities observed before. Finally, the measured plasma temperature field is empirically correlated in terms of radial and axial coordinates, plasma electrical input power, plasma efficiency, and gas composition. These temperature data can be used to validate numerical simulations as well as in choosing locations where different materials can be introduced into the plasma jets. This is particularly important for “nanostructured” materials, which loose their structure upon melting as a result of being exposed to high plasma temperatures.

A first study of the infrared emission in argon excited by ionizing particles

We report on the study of infrared emission from gaseous argon excited by MeV protons in the wavelength range 0.7–1.8 μm. The dependence of the light yield on the applied electric field has been measured at different pressures. At zero field (prompt emission) the yield does not depend on pressure. When a field is applied the light emission increases linearly with the field strength above a critical value (drift emission) and a dependence from pressure is observed. Prompt and drift emission are consistent with transitions between the lowest atomic states of neutral argon. Drift emission is generated by electrons which gain energy from the electric field and excite atoms through collisions.

Time-resolved ten-channel monochromatic imaging of inertial confinement fusion plasmas

We report on what we believe to be the first use of toroidally bent crystals to record two-dimensional, spatially resolved, monochromatic images of laser-produced fusion plasmas combined with a 34-ps fast x-ray framing camera. An array of five toroidal silicon (311) and five toroidal germanium (311) crystals was developed. The imaging properties of the geometries are checked by a ray-tracing program and are compared with experimental results. The total imaging system (crystal and detector) provides an experimentally measured spatial resolution better than 15 mum. Time histories for the hydrogenlike argon emission and the heliumlike argon emission of fusion pellets driven with the GEKKO XII glass laser system are presented.