Translational Temperature Of Gas Research Articles

Argon metastable density and temperature of a 94 GHz microplasma

Laser diode absorption spectroscopy is used to experimentally measure Ar(1s5) metastable density and translational gas temperature within a 94 GHz microplasma. A square two-dimensional photonic crystal (PhC) at this resonance frequency serves to ignite and sustain the plasma from 20 to 200 Torr (2.7 × 103–2.7 × 104 Pa) by using millimeter wave power from 300 to 1000 mW. Metastable density within the plasma is estimated from the absorption line shape of the laser traversing the PhC. The metastable density reaches an order of 1019 m−3 at lower pressure and decreases as pressure increases. From the Lorentzian line shape of the absorption profile at 811.53 nm, the gas temperature is extracted and found to increase from 500 K at 20 Torr to 1300 K at 200 Torr. These data are analyzed and compared with a zero-dimensional plasma model and with previous experimental plasma results at 43 GHz.

Argon metastable density and temperature of a 43 GHz microplasma

Argon (1s5) metastable density and translational gas temperature are experimentally measured using laser diode absorption spectroscopy within a 43 GHz microplasma. The plasma is initiated and sustained within a photonic crystal constructed from a rectangular array of alumina rods, each 1 mm in diameter. This configuration generates stable microplasma from 10 to 600 Torr using millimeter wave power from 100 to 1200 mW. The metastable density is in the order of 1018 m−3 at low pressure. However, Ar(1s5) density decreases to undetectable levels with increasing pressure and wave power. The gas temperature is extracted from the Lorentzian line shape of the absorption profile at 811.53 nm. The gas temperature increases from approximately 400 K at low pressure to 2000 K at 320 Torr (427 mbar, 4.27 × 104 Pa). These data are compared with previous results and suggest that the microplasma has a dense core of electrons that depletes the metastable density at high gas pressure and wave power.

Analysis of applicability of triplet-state emission of molecular hydrogen for spectral diagnostics of a DC discharge

The applicability of emission of the N 3Λσ triplet states of molecular hydrogen for spectral diagnostics of the positive column of a dc glow discharge in hydrogen at translational gas temperatures of 360–600 K, specific absorbed powers of 0.8–4.25 W/cm, gas pressures of p = 0.3–15.0 Torr, reduced fields of E/N = 30–130 Td, and electron densities of n e = 4.0 × 109–6.5 × 1010 cm–3 is analyzed by using an advanced level-based semi-empirical collisional−radiative model. It is found that secondary processes make the main contribution to the population and decay of the N 3Λσ = a 3Σ+ g , c 3Π u , g 3Σ+ g , h 3Σ+ g , and i 3Π g triplet states. The dipole-allowed transitions e 3Σ+ g → a 3Σ+ g , f 3Σ+ g → a 3Σ+ g , g 3Σ+ g and k 3Π u → a 3Σ+ g can be used for spectral diagnostics of a dc discharge within a simplified coronal model.

Absolute CF2 density and gas temperature measurements by absorption spectroscopy in dual-frequency capacitively coupled CF4/Ar plasmas

Broadband ultraviolet absorption spectroscopy has been used to determine the CF2 radical density in dual-frequency capacitively coupled CF4/Ar plasmas, using the CF2 Ã1B1←X̃1A1 system of absorption spectrum. The rotational temperature of ground state CF2 and excited state CF was also estimated by using Ã1B1←X̃1A1 system and B2Δ−X2Π system, respectively. The translational gas temperature was deduced from the Doppler width of the Ar*(3P2) and Ar*(3P0) metastable atoms absorption line by using the tunable diode laser absorption spectroscopy. The rotational temperatures of the excited state CF are about 100 K higher than those of ground state CF2, and about 200 K higher than the translational gas temperatures. The dependences of the radical CF2 density, electron density, electron temperature, rotational temperature, and gas temperature on the high frequency power and pressure have been analyzed. Furthermore, the production and loss mechanisms of CF2 radical and the gas heating mechanisms have also been discussed.

Coherent Rayleigh-Brillouin scattering measurement of atmospheric atomic and molecular gas temperature.

Broadband coherent Rayleigh-Brillouin scattering (CRBS) was used to measure translational gas temperatures for nitrogen, argon, and methane at the ambient pressure of 0.8 atm. Temperatures derived from spectral analysis were compared with experimentally-measured temperatures, with a maximum 5.2% difference for all gases at all temperatures; and with nitrogen, argon, and methane exhibiting average differences over the temperature range tested of 0.8%, 1.4% and -0.5%, respectively. These values are consistent with the 2% estimated, experimental error of the experiment. Improving upon the efficiency of previous line shape acquisition methods, CRBS data were spectrally de-convolved using a cost effective, purpose-designed, Fabry-Perot etalon spectrometer. The resulting line shapes were compared to models obtained from approximations to the 1D Boltzmann equation. Although this study employed broadband CRBS for explicit gas temperature measurement, similar line shape acquisition techniques could be used with broadband coherent Rayleigh scattering (CRS) to experimentally-measure gas temperatures, pressures and other transport properties in both the kinetic (CRBS) and rarefied (CRS) regimes.

Absorption spectroscopy in BCl3 inductively coupled plasmas: determination of density, rotational, translational and vibrational temperatures of BCl molecule

Broadband absorption spectroscopy experiments have been carried out in low pressure (<120 mTorr) inductive plasmas of pure BCl3 to study the A 1Π–X 1Σ+ system of BCl radicals formed in these discharges. We have detailed the simulation code of the absorption spectrum of the transition, which is essential for the correct analysis of the recorded absorption profiles when the absorbing medium is optically thick. A comparison between recorded and simulated spectra provides the absolute line-averaged density of BCl molecules, together with population distributions in rotational and vibrational levels of the BCl (X 1Σ+) ground state. In pure BCl3 plasmas, the BCl density increases with the discharge power and pressure from 4 × 1017 m−3 to 2 × 1019 m−3 at the maximum, its mole fractions staying always lower than 5%. Rotational and vibrational distributions are found to be close to Boltzmann distributions, with vibrational temperatures ranging from 700 to 2000 K, while rotational temperatures vary between 550 and 1800 K. Using the diode laser absorption technique, the translational gas temperature was also measured from the Doppler width of the 811.5 nm line absorbed by Ar*(3P2) metastable atoms, with argon added as a trace gas to BCl3. Our results show that in low pressure conditions (<50 mTorr), vibrational and rotational temperatures of BCl in both excited A 1Π and ground X 1Σ+ states are not in equilibrium with the gas temperature. It is concluded that rotationally and vibrationally hot BCl radicals are produced mainly by dissociative excitation in the gas phase of heavier BCl2 and BCl3 radicals and that they are rapidly lost by diffusion and sticking, with a high probability, on the reactor walls. All these characteristics suggest a very high reactivity of BCl radicals on the surfaces exposed to the plasma.

Gas temperature measurements in a microwave plasma by optical emission spectroscopy under single-wall carbon nanotube growth conditions

Plasma gas temperatures were measured via in situ optical emission spectroscopy in a microwave CH4–H2 plasma under carbon nanotube (CNT) growth conditions. Gas temperature is an important parameter in controlling and optimizing CNT growth. The temperature has a significant impact on chemical kinetic rates, species concentrations and CNT growth rates on the substrate. H2 rotational temperatures were determined from the Q-branch spectrum of the (0) transition. N2 rotational and vibrational temperatures were measured by fitting rovibrational bands from the N2 emission spectrum of the C 3Πu → B 3Πg transition. The N2 rotational temperature, which is assumed to be approximately equal to the translational gas temperature, increases with an increase in input microwave plasma power and substrate temperature. The measured H2 rotational temperatures were not in agreement with the measured N2 rotational temperatures under the CNT growth conditions in this study. The measured N2 rotational temperatures compared with the H2 rotational temperatures suggest the partial equilibration of upper excited state due to higher, 10 Torr, operating pressure. Methane addition in the hydrogen plasma increases the gas temperature slightly for methane concentrations higher than 10% in the feed gas.

Gas heating in the neutralizer of the ITER neutral beam injection systems

Indirect heating of the neutralizer gas by the beam has been shown to be responsible for the reduced neutralization efficiency observed in positive ion neutral beam systems. The translational gas temperature can be predicted from the neutralizer plasma density and electron temperature and, in general, a higher gas temperature implies a lower neutralization target. A simple one-dimensional model, originally developed for the JET positive ion neutral injection system, has been adapted for ITER relevant negative ion systems. The results imply that gas heating for the ITER heating and diagnostic beams is unlikely to be severe and hence the neutralization target might be expected to be close to the design value.

Ionized physical vapor deposition of titanium nitride: Plasma and film characterization

The ionized physical vapor deposition of titanium nitride is experimentally investigated in terms of both plasma characteristics and TiN material properties. The vibrational and translational gas temperatures of N2 molecules are determined using optical emission spectroscopy by fitting the intensities of vibrational transitions to the nonequilibrium Treanor distribution. The gas temperature is typically 720 K at 15 mTorr. The dissociation of nitrogen is determined using mass spectrometry and found to increase with plasma power from 10% to 30% as the power is increased from 750 to 1500 W. From this data, it is calculated that the density of atomic nitrogen in the inductively coupled plasma source is the order of 1012 cm−3. Langmuir probe measurements indicate that the electron temperature is 1.6–2.0 eV and the ion density is (2–6)×1011 cm−3. Rutherford backscattering spectroscopy (RBS) shows that the TiNx films have increasing nitrogen composition (0.26&amp;lt;x&amp;lt;1.5) as the nitrogen content increases from 2% to 9% in the Ar/N2 plasma. The flux of nitrogen atoms from the plasma, as determined from the measured gas temperature and dissociation, is compared with the flux of nitrogen that is incorporated in the film according to RBS. The ratio of these two fluxes gives an upper-bound for the sticking coefficient of atomic N on TiNx, which is ∼0.1 for titanium-rich films and ∼0.003 for nitrogen-rich films.

Measurement of the gas temperature in fluorocarbon radio frequency discharges using infrared absorption spectroscopy

The translational gas temperature was measured in 13.56 MHz radio-frequency (rf) discharges in CF4 and CHF3. Infrared absorption spectra of CF4 and CF2 were recorded using a tunable diode laser and the gas temperature was deduced from the linewidths of the absorption lines of these molecules. It is shown that linewidth measurements yield a simple and direct method to determine the gas temperature, with an accuracy up to ∼10 K. The results obtained in CF4 and CHF3 plasmas indicate that the translational temperatures of all particles investigated in these plasmas are, at most, 50 K above the room temperature. The temperature increases with increasing gas pressure and rf power, but it is independent of the flow rate. This is attributed to an increased heating rate of the gas. Moreover, it was found that the temperature rise is significantly smaller in CHF3 than in CF4, under the same plasma conditions. This can be attributed to a higher power dissipation by chemical conversion of the parent gas in a CHF3 discharge, as compared with a CF4 plasma.

The Temperature Dependence of Spectral Broadening in the Hg (61S0-63P1) Multiplet At High Optical Densities.

A new method has been developed for determining rapidly changing translational temperatures in a gas that has been heated by such transient phenomena as the passage of a shock wave or the absorption of sub-microsecond pulses of radiation from an infrared laser. The method depends upon the use of trace amounts of Hg vapor and its absorption of radiation in the neighborhood of the 253.7 nm isotopic and hyperfine multiplet. As the Hg atoms sense changes in the translational temperature of the host gas, the absorption of 253.7 nm radiation also changes by virtue of the Doppler and Lorentz broadening of the multiplet lines. Emission spectra of a Hg discharge light source in the neighborhood of 253.7 nm were shown to be readily simulated by a two zone computer model even at large optical densities. The same lamp parameters that were used in these calculations could also be used to simulate the experimental pressure and temperature dependence of the total integrated absorption. This provided a means for obtaining the temperature calibration curves needed to monitor the changing translational temperature of a gas undergoing rapid heating or cooling.

Vibrational Relaxation of Anharmonic Oscillators in Expansion Nozzles

The problem of the vibrational relaxation of anharmonic oscillators in expansion nozzles has been analysed numerically. It is concluded: (1) Effects of anharmonicity increase with increasing p r r * /tan θ and/or T r , where p r and T r are the reservoir pressure and temperature, and r * and θ are the throat radius and expansion angle of the nozzle respectively. (2) Anharmonicity has the effect of somewhat lowering the translational temperature of gas. This effect being taken into account, the relaxation rate of the vibrational energy gets an increase of less than a factor 1.3 due to anharmonicity. Contrary to the Boltzmann distribution of the harmonic oscillators, however, the vibrational distribution function of the anharmonic oscillators undergoes a considerable distortion in the expanding flow.

Radiative Transitions and Temperature Time Dependences in Pulse Excited Microwave Discharges – (N2, Ar + N2)

AbstractQuantitative spectral and microwave measurements of vibrational temperatures and electron densities were performed for 2400 MHz non‐isothermic pulse excited discharges in flowing nitrogen and argon at pressures (60–2700) Pa. A detailed analysis of the N2 vibrational states population for the N2 C3Πu, X1Σg+ electronic states has been carried out. The basic difficulties encountered when comparing the spectroscopically determined values of vibrational temperatures with corresponding quantities of the ground electronics state are mentioned and the time resolved dependences of the translational gas temperature in N2 during the microwave pulse is evaluated. The steady state in the nitrogen pulse excited microwave plasma is reached within 3 · 10−4 s, but generally, this time depends on the gas pressure in the discharge tube. In the Ar + N2 mixtures the excitation conditions are complicated by the metastable argon atoms (3P2,0) creating the nonequilibrium populations of electronic, vibrational and rotational N2 states.