Search NASA⌕ Search

SEARCH · Search NASA

Results for “nitrogen”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Nitrogen ion clusters in Triton's atmosphere

The nitrogen ion chemistry that controls Triton's ionospheric composition and may be responsible for the hazes detected by the Voyager spacecraft are discussed. In particular, it is shown that nitrogen cluster ion formation should readily occur in Triton's thin cold atmosphere. The very low temperatures of Triton's atmosphere imply that these clustered ions can nucleate into solid nitrogen particles, creating the extended visible hazes. A model based on the chemical kinetics of nitrogen ions predicts a dense ionosphere at 200-400 km, as detected by Voyager radio occultation measurements.

Delitsky, Mona L.↗
NASA NTRS1991

Experimental thermal conductivity, thermal diffusivity, and specific heat values for mixtures of nitrogen, oxygen, and argon

Experimental measurements of thermal conductivity and thermal diffusivity obtained with a transient hot-wire apparatus are reported for three mixtures of nitrogen, oxygen, and argon. Values of the specific heat, Cp, are calculated from these measured values and the density calculated with an equation of state. The measurements were made at temperatures between 65 and 303 K with pressures between 0.1 and 70 MPa. The data cover the vapor, liquid, and supercritical gas phases for the three mixtures. The total reported points are 1066 for the air mixture (78.11 percent nitrogen, 20.97 percent oxygen, and 0.92 percent argon), 1058 for the 50 percent nitrogen, 50 percent oxygen mixture, and 864 for the 25 percent nitrogen, 75 oxygen mixture. Empirical thermal conductivity correlations are provided for the three mixtures.

Perkins, R. A.↗
NASA NTRS1990

Single- and double-photoionization cross sections of atomic nitrogen from threshold to 31 A

The relative photoionization cross section of atomic nitrogen for the production of singly and doubly charged ions has been measured from 44.3 to 275 A and from 520 to 852 A. The results have been made absolute by normalization to one-half of the molecular nitrogen cross section at short wavelengths. The smoothed atomic nitrogen cross sections sigma can be accurately represented, at short wavelengths, by the equation sigma(Mb) = 36,700 x (E exp-2.3) as a function of the photon energy E (eV), thereby allowing the cross sections to be extrapolated to the nitrogen K edge at 31 A.

Samson, James A. R.↗
NASA NTRS1992

The production and escape of nitrogen atoms on Mars

The lack of agreement between our previously computed values and those measured by Viking of the N-15:N-14 isotope enhancement ratio has led us to reevaluate our model of the Martian ionosphere. In previous models, we were unable to reproduce the ion profiles measured by the RPA on Viking using electron temperatures that were higher that the ion temperatures. When we increased the electron temperatures to 2500-3000 K and with a zero flux upper boundary condition, the ion densities at high altitudes exceeded the measured values by a large factor. We found that we can better fit the observed profiles if we impose a loss process at the upper boundary of our model. If the horizontal fluxes of ions do not constitute a net loss of ions, then the escape of N due to dissociative recombination is also inhibited and better agreement with the measured isotope ratio is found. The production of escaping nitrogen atoms is closely related to the production of thermospheric odd nitrogen; therefore, the densities of NO measured by Viking provide a convenient check on our nitrogen escape model. Our standard model NO densities are less that the measured values by a factor of 2-3, as are those of previous models. We find that reasonable agreement can be obtained by assuming that the rate coefficient for loss of odd nitrogen in the reaction of N with NO is smaller at temperatures that prevail in the lower Martian thermosphere than the standard value, which applies to temperatures of 200-400 K. Other aspects of this investigation are presented.

Fox, J. L.↗
NASA NTRS1992

On the isotopic signature of recent solar-wind nitrogen

One of the most intriguing discoveries yielded by the Apollo samples was evidence pointing towards a significant long-term change in the composition of the sun. Such a change, of the size inferred from the lunar sample data, is inconsistent with present theories of solar evolution. Consequently, there is much interest in exploring this phenomenon as closely as possible, to determine exactly what compositional changes have taken place and whether those changes really did take place in the sun, or whether the cause lies elsewhere. The reason why we can use the moon to analyze the elements in the sun is that the sun emits a stream of ions, known as the solar wind, whose composition, on average, is believed to be the same as that in the surface regions of the sun. When the solar-wind ions hit the surface of the moon, many of them penetrate a short distance into the dust grains lying on the lunar surface. Thus, after a grain has sat on the lunar surface for a while, it has a rim of material that is partly lunar and partly solar in composition. For most chemical elements, the difference between lunar and solar composition is so sufficiently small that the solar elements cannot be detected, but for a handful of elements that are missing from the moon, their solar 'signature' can be observed in samples of lunar soil brought back by the astronauts. Among those elements is nitrogen, the most common element in the air we breathe, but very rare indeed on the moon. Our analytical techniques are not sophisticated enough yet to enable us to analyze individual lunar soil grains for nitrogen, much less to zero in on just the nitrogen in the surface of such a grain. Consequently we are forced to analyze samples consisting of many different grains, each of which could have experienced its own individual history. This makes it difficult to identify the nitrogen implanted in grain surfaces, and also to define the age of a sample.

Kim, Y.↗
NASA NTRS1992

Relationship of peroxyacetyl nitrate to active and total odd nitrogen at northern high latitudes - Influence of reservoir species on NO(x) and O3

The partitioning of relative nitrogen in the Arctic and the sub-Arctic troposphere based on measurements conducted during the 1988 Arctic Boundary Layer Expedition (ABLE 3A) is described. The first set of comprehensive odd nitrogen and O3 measurements from the Arctic/sub-Arctic free troposphere shows that a highly aged air mass that has persisted under very cold conditions is present. A large fraction of the odd nitrogen appears to be present in the form of reservoir species such as PAN. Significant quantities of as yet unknown reactive nitrogen species, such as complex alkyl nitrates and pernitrates, are expected to be present. Together with PAN, these nitrate and pernitrate reservoir species could control the entire NO(x) availability of the high-latitude troposphere and in turn influence the O3 photochemistry of the region. The role of PAN in influencing the O3 reservoir is shown to be important and may be responsible for the increasing O3 temporal trend observed at high latitudes.

Singh, H. B.↗
NASA NTRS1992

Soil nitrogen cycling and nitrous oxide flux in a Rocky Mountain Douglas-fir forest - Effects of fertilization, irrigation and carbon addition

Nitrous oxide fluxes and soil nitrogen transformations were measured in experimentally-treated high elevation Douglas-fir forests in northwestern New Mexico, USA. On an annual basis, forests that were fertilized with 200 kg N/ha emitted an average of 0.66 kg/ha of N2O-N, with highest fluxes occurring in July and August when soils were both warm and wet. Control, irrigated, and woodchip treated plots did not differ, and annual average fluxes ranged from 0.03 to 0.23 kg/ha. Annual net nitrogen mineralization and nitrate production were estimated in soil and forest floor using in situ incubations; fertilized soil mineralized 277 kg/ha/y in contrast to 18 kg/ha/y in control plots. Relative recovery of 15NH4-N applied to soil in laboratory incubations was principally in the form of NO3-N in the fertilized soils, while recovery was mostly in microbial biomass-N in the other treatments. Fertilization apparently added nitrogen that exceeded the heterotrophic microbial demand, resulting in higher rates of nitrate production and higher nitrous oxide fluxes. Despite the elevated nitrous oxide emission resulting from fertilization, we estimate that global inputs of nitrogen into forests are not currently contributing significantly to the increasing concentrations of nitrous oxide in the atmosphere.

Matson, Pamela A.↗
NASA NTRS1985

Pathways of nitrogen loss following land clearing in a humid tropical forest

Tropical deforestation generally leads to large losses of carbon and nitrogen. The Premontane Wet Forest Life Zone is subject to the highest rate of deforestation in Central America, and carbon and nutrient losses in from these fertile soils is very rapid and extreme. Losses of 2000 to 3000 kgN/ha have been reported. Losses of this magnitude could be extremely significant on a regional or global scale if even a small proportion of this nitrogen is lost as nitrous oxide to the atmosphere or through leaching of nitrate to rivers. This study seeks to measure the rates and regulation of nitrogen transformations, and the pathways of nitrogen losses following land clearing and burning at a site in the Premontane Wet Forest Life Zone near Turrialba, Costa Rica.

Matson, Pamela↗
NASA NTRS1993

Fingerprints of carbon, nitrogen, and silicon isotopes in small interstellar SiC grains from the Murchison meteorite

We report ion microprobe determinations of the carbon, nitrogen, and silicon isotopic compositions of small SiC grains from the Murchison CM2 chondrite. Analyses were made on samples containing variable numbers of grains and on 14 individual grains. In some cases the multiple-grain sample compositions were probably dominated by only one or two grains. Total ranges observed are given. Only a few grains show values near the range limits. Both the total ranges of carbon and nitrogen isotopic compositions, and even the narrower ranges typical for the majority of the grains, are similar to those observed for larger SiC grains. Two rare components appear to be present in the smaller-size fraction, one characterized by C-12/C-13 about 12-16 and the other by very heavy nitrogen. The carbon and nitrogen isotopic compositions qualitatively may reflect hydrostatic H-burning via the CNO cycle and He-burning in red giants, as well as explosive H-burning in novae. The silicon isotopic compositions of most grains qualitatively show what is the signature of He-burning. The silicon isotopic composition of one grain, however, suggests a different process.

Hoppe, Peter↗
NASA NTRS1994

Ozone and nitrogen dioxide above the northern Tien Shan

The results of systematic perennial measurements of the total ozone (since 1979) and nitrogen dioxide column (since 1983) in the atmosphere in the European-Asian continent center above the mountainmass of the Tien Shan are given. This region is distinguished by a great number of sunny days during a year. The observation station is at the Northern shore of Issyk Kul Lake (42.56 N 77.04 E 1650 m above the sea level). The measurement results are presented as the monthly averaged atmospheric total ozone and NO2 stratospheric column abundances (morning and evening). The peculiarities of seasonal variations of ozone and nitrogen dioxide atmospheric contents, their regular variances with a quasi-biennial cycles and trends have been noticed. Irregular variances of ozone and nitrogen dioxide atmospheric contents, i.e. their positive and negative anomalies in the monthly averaged contents relative to the perennial averaged monthly means, have been analyzed. The synchronous and opposite in phase anomalies in variations of ozone and nitrogen dioxide atmospheric contents were explained by the transport and zonal circulation in the stratosphere (Kamenogradsky et al., 1990).

Arefev, Vladimir N.↗
NASA NTRS1996

Development of airborne eddy-correlation flux measurement capabilities for reactive oxides of nitrogen

This research is aimed at producing a fundamental new research tool for characterizing the source strength of the most important compound controlling the hemispheric and global scale distribution of tropospheric ozone. Specifically, this effort seeks to demonstrate the proof-of-concept of a new general purpose laser-induced fluorescence based spectrometer for making airborne eddy-correlation flux measurements of nitric oxide (NO) and other reactive nitrogen compounds. The new all solid-state laser technology being used in this advanced sensor will produce a forerunner of the type of sensor technology that should eventually result in highly compact operational systems. The proof-of-concept sensor being developed will have over two orders-of-magnitude greater sensitivity than present-day instruments. In addition, this sensor will offer the possibility of eventual extension to airborne eddy-correlation flux measurements of nitrogen dioxide (NO2) and possibly other compounds, such as ammonia (NH3), peroxyradicals (HO2), nitrateradicals (NO3) and several iodine compounds (e.g., I and IO). Demonstration of the new sensor's ability to measure NO fluxes will occur through a series of laboratory and field tests. This proof-of-concept demonstration will show that not only can airborne fluxes of important ultra-trace compounds be made at the few parts-per-trillion level, but that the high accuracy/precision measurements currently needed for predictive models can also. These measurement capabilities will greatly enhance our current ability to quantify the fluxes of reactive nitrogen into the troposphere and significantly impact upon the accuracy of predictive capabilities to model O3's distribution within the remote troposphere. This development effort also offers a timely approach for producing the reactive nitrogen flux measurement capabilities that will be needed by future research programs such as NASA's planned 1999 Amazon Biogeochemistry and Atmospheric Chemistry Experimental portion of LBA.

Bradshaw, John↗
NASA NTRS1998

Nitrogen Species in the Post-Pinatubo Stratosphere: Model Analysis Utilizing UARS Measurements

We present an analysis of the impact of heterogeneous chemistry on the partitioning of nitrogen species measured by the Upper Atmosphere Research Satellite (UARS) instruments. The UARS measurements utilized include: N2O, HNO3 and ClONO2 (Cryogen Limb Array Etalon Spectrometer (CLAES), version 7), temperature, methane, ozone, H2O, HCl, NO and NO2 (HALogen Occultation Experiment (HALOE), version 18). The analysis is carried out for the data from January 1992 to September 1994 in the 100-1 mbar (approx.17-47 km) altitude range and over 10 degree latitude bins from 70degS to 70degN. Temporal-spatial evolution of aerosol surface area density (SAD) is adopted according to the Stratospheric Aerosol and Gas Experiment (SAGE) 11 data. A diurnal steady-state photochemical box model, constrained by the temperature, ozone, H2O, CH4, aerosol SAD and columns of O2 and O3 above the point of interest, has been used as the main tool to analyze these data. Total inorganic nitrogen (NO(y)) is obtained by three different methods: (1) as a sum of the UARS measured NO, NO2, HNO3, and ClONO2; (2) from the N2O-NO(y) correlation, and (3) from the CH4-NO(y) correlation. To validate our current understanding of stratospheric heterogeneous chemistry for post-Pinatubo conditions, the model-calculated NO(x)/NO(y) ratios and the NO, NO2, and HNO3 profiles are compared to the UARS-derived data. In general, the UARS-constrained box model captures the main features of nitrogen species partitioning in the post-Pinatubo years. However, the model underestimates the NO2 content, particularly, in the 30-7 mbar (approx. 23-32 km) range. Comparisons of the calculated temporal behavior of the partial columns of NO2 and HNO3 and ground based measurements at 45degS and 45degN are also presented. Our analysis indicates that ground-based and HALOE v. 18 measurements of the NO2 vertical columns are consistent within the range of their uncertainties and are systematically higher (up to 50%) than the model results at mid-latitudes in both hemispheres. Reasonable agreement is obtained for HNO3 columns at 45degS suggesting some problems with nitrogen species partitioning in the model. Outstanding uncertainties are discussed.

Danilin, M. Y.↗
NASA NTRS1998

Nitrogen Species in the Post-Pinatubo Stratosphere: Model Analysis Utilizing UARS Measurements

We present an analysis of the impact of heterogeneous chemistry on the partitioning of nitrogen species measured by the Upper Atmosphere Research Satellite (UARS) instruments. The UARS measurements utilized include: N2O, HNO3 and ClONO2 (Cryogen Limb Array Etalon Spectrometer (CLAES), version 7), temperature, methane, ozone, H2O, HCI, NO and NO2 (HALogen Occultation Experiment (HALOE), version 18). The analysis is carried out for the data from January 1992 to September 1994 in the 100-1 mbar (approximately 17-47 km) altitude range and over 10 degree latitude bins from 70 deg S to 70 deg N. Temporal-spatial evolution of aerosol surface area density (SAD) is adopted according to the Stratospheric Aerosol and Gas Experiment (SAGE) II data. A diurnal steady-state photochemical box model, constrained by the temperature, ozone, H2O, CH4, aerosol SAD and columns of O2 and O3 above the point of interest, has been used as the main tool to analyze these data. Total inorganic nitrogen (NOy) is obtained by three different methods: (1) as a sum of the UARS measured NO, NO2, HNO3, and CIONO2; (2) from the N2O-NOy correlation, (3) from the CH4-NOy correlation. To validate our current understanding of stratospheric heterogeneous chemistry for post-Pinatubo conditions, the model-calculated NOx/NOy ratios and the NO, NO2, and HNO3 profiles are compared to the UARS-derived data. In general, the UARS-constrained box model captures the main features of nitrogen species partitioning in the post-Pinatubo years. However, the model underestimates the NO2 content, particularly, in the 30-7 mbar (approximately 23-32 km) range. Comparisons of the calculated temporal behavior of the partial columns of NO2 and HNO3 and ground based measurements at 45 deg S and 45 deg N are also presented. Our analysis indicates that ground-based and HALOE v.18 measurements of the NO2 vertical columns are consistent within the range of their uncertainties and are systematically higher (up to 50%) than the model results at mid-latitudes in both hemispheres. Reasonable agreement is obtained for HNO3 columns at 45 deg S suggesting some problems with nitrogen species partitioning in the model. Outstanding uncertainties are discussed.

Danilin, M. Y.↗
NASA NTRS1999

Measurements of Nitric Acid and Aerosol Species Aboard the NASA DC-8 Aircraft During the SASS Ozone and Nitrogen Oxide Experiment (SONEX)

The SASS Ozone and Nitrogen Oxides Experiment (SONEX) over the North Atlantic during October/November 1997 offered an excellent opportunity to examine the budget of total reactive nitrogen (NO(sub y)) in the upper troposphere (8 - 12 km altitude). The median measured NO(sub y) mixing ratio was 425 parts per trillion by volume (pptv). Two different methods were used to measure HNO3: (1) the mist chamber technique and, (2) chemical ionization mass spectrometry. Two merged data sets using these HNO3 measurements were used to calculate NO(sub y) by summing the reactive nitrogen species (a combination of measured plus modeled results) and comparing the resultant values to measured NO(sub y) (gold catalytic reduction method). Both comparisons showed good agreement in the two quantities (slope > 0.9 and r(exp 2) > 0.9). Thus, the total reactive nitrogen budget in the upper troposphere over the North Atlantic can be explained in a general manner as a simple mixture of NO(sub x). (NO + NO2), HNO3, and PAN. Median values of NO(sub x)/NO(sub y) were approximately equal to 0.25, HNO3/NO(sub y) were approximately equal to 0.35 and Peroxyacetyl Nitrate (PAN)/NO(sub y) were approximately equal to 0. 17. Particulate NO3 and alkyl nitrates together composed <10 % of NO(sub y), while model estimated HNO4 averaged 12%.

Talbot, Robert W.↗
NASA NTRS1999

Measurements of Nitric Acid and Aerosol Species Aboard the NASA DC-8 Aircraft During the SASS OZone and Nitrogen Oxide Experiment (SONEX)

The SASS Ozone and Nitrogen Oxides Experiment (SONEX) over the north Atlantic during October/November 1997 offered an excellent opportunity to examine the budget of total reactive nitrogen (NO(y)) in the upper troposphere (8 - 12 km altitude). The median measured NO(y) mixing ratio was 425 parts per trillion by volume (pptv). Two different methods were used to measure HNO3: (1) the mist chamber technique and, (2) chemical ionization mass spectrometry. Two merged data sets using these HNO3 measurements were used to calculate NO(y) by summing the reactive nitrogen species (a combination of measured plus modeled results) and comparing the resultant values to measured NO(y) (gold catalytic reduction method). Both comparisons showed good agreement in the two quantities (slope greater than 0.9 and r(sup 2) greater than 0.9). Thus, the total reactive nitrogen budget in the upper troposphere over the North Atlantic can be explained in a general manner as a simple mixture of NO(x). (NO + NO2), HNO3, and PAN. Median values of NO(x)/NO(y) were approx. = 0.25, HNO3/NO(y) approx. = 0.35 and PAN/NO(y) approx. = 0.17. Particulate NO3 and alkyl nitrates together composed less than 10% of NO(y), while model estimated HNO4 averaged 12%.

Talbot, Robert W.↗
NASA NTRS1999

Nitrogen Species in the Post-Pinatubo Stratosphere: Model Analysis Utilizing UARS Measurements

We present an analysis of the impact of heterogeneous chemistry on the partitioning of nitrogen species measured by the Upper Atmosphere Research Satellite (UARS) instruments. The UARS measurements utilized include N2O, HNO3, and ClONO2 from the cryogenic limb array etalon spectrometer (CLAES), version 7 (v.7), and temperature, methane, ozone, H2O, HCl, NO and NO2 from the halogen occultation experiment (HALOE), version 18. The analysis is carried out for the UARS data obtained between January 1992 and September 1994 in the 100- to 1-mbar (approx. 17-47 km) altitude range and over 10 deg latitude bins from 70 deg S to 70 deg N. The spatiotemporal evolution of aerosol surface area density (SAD) is adopted from analysis of the Stratospheric Aerosol and Gas Experiment (SAGE) II data. A diurnal steady state photochemical box model, constrained by the temperature, ozone, H2O, CH4, aerosol SAD, and columns of O2 and O3 above the point of interest, has been used as the main tool to analyze these data. Total inorganic nitrogen (NOY) is obtained by three different methods: (1) as a sum of the UARS-measured NO, NO2, HNO3, and ClONO2; (2) from the N2O-NOY correlation; and (3) from the CH4-NOY correlation. To validate our current understanding of stratospheric heterogeneous chemistry for post-Pinatubo conditions, the model-calculated monthly averaged NO(x)/NO(y) ratios and the NO, NO2, and HNO3 profiles are compared with the UARS-derived data. In general, the UARS-constrained box model captures the main features of nitrogen species partitioning in the post-Pinatubo years, such as recovery of NO(x) after the eruption, their seasonal variability and vertical profiles. However, the model underestimates the NO2 content, particularly in the 30- to 7-mbar (approx. 23-32 km) range. Comparisons of the calculated temporal behavior of the partial columns of NO2 and HNO3 and ground-based measurements at 45 deg S and 45 deg N are also presented. Our analysis indicates that ground-based and HALOE v.18 measurements of the NO2 vertical columns are consistent within the range of their uncertainties and are systematically higher (up to 50%) than the model results at midlatitudes in both hemispheres. Reasonable agreement is obtained for HNO3 columns at 45 deg S, suggesting some problems with nitrogen species partitioning in the model. Outstanding uncertainties are discussed.

Danilin, Michael Y.↗
NASA NTRS1999

Nitrogen Species in the Post-Pinatubo Stratosphere: Model Analysis Utilizing UARS Measurements

We present an analysis of the impact of heterogeneous chemistry on the partitioning of nitrogen species measured by the Upper Atmosphere Research Satellite (UARS) instruments. The UARS measurements utilized include N2O, HNO3, and ClONO2 from the cryogenic limb array etalon spectrometer (CLAES), version 7 (v.7), and temperature, methane, ozone, H2O, HCl, NO and NO2 from the halogen occultation experiment (HALOE), version 18. The analysis is carried out for the UARS data obtained between January 1992 and September 1994 in the 100-to 1-mbar (approx. 17-47 km) altitude range and over 10 degrees latitude bins from 70 S to 70 N. The spatiotemporal evolution of aerosol surface area density (SAD) is adopted from analysis of the Stratospheric Aerosol and Gas Experiment (SAGE) II data. A diurnal steady state photochemical box model, constrained by the temperature, ozone, H2O, CH4, aerosol SAD, and columns of O2 and O3 above the point of interest, has been used as the main tool to analyze these data. Total inorganic nitrogen (NOy) is obtained by three different methods: (1) as a sum of the UARS-measured NO, NO2, HNO3, and ClONO2; (2) from the N2O-NOy correlation, and (3) from the CH4-NOy correlation. To validate our current understanding of stratospheric heterogeneous chemistry for post-Pinatubo conditions, the model-calculated monthly averaged NOx/NOy ratios and the NO, NO2, and HNO3 profiles are compared with the UARS-derived data. In general, the UARS-constrained box model captures the main features of nitrogen species partitioning in the post-Pinatubo years, such as recovery of NOx after the eruption, their seasonal variability and vertical profiles. However, the model underestimates the NO2 content, particularly in the 30- to 7-mbar (approx.23-32 km) range. Comparisons of the calculated temporal behavior of the partial columns of NO2 and HNO3 and ground-based measurements at 45 S and 45 N are also presented. Our analysis indicates that ground-based and HALOE v.18 measurements of the NO2 vertical columns are consistent within the range of their uncertainties and are systematically higher (up to 50%) than the model results at midlatitudes in both hemispheres. Reasonable agreement is obtained for HNO3 columns at 45 S, suggesting some problems with nitrogen species partitioning in the model. Outstanding uncertainties are discussed.

Danilin, Michael Y.↗
NASA NTRS1998

Flow Characteristics of UHV Nitrogen Arcjet

Flow characteristics in the nozzle of a nitrogen arcjet have been simulated by a model. Electrons, ions, and neutral atoms and molecules are represented as separate species. Dissociation, ionization, and recombination are treated as separate reactions. Thermal non-equilibrium is represented by a two-temperature model. Energy input to plasma from the arc is modeled as a source determined by local current and electrical conductivity. Momentum and energy losses and recombinations at the nozzle wall are included as source/sink determined by fluxes to the wall. The results show essentially frozen gas-phase reactions and thermal nonequilibrium due to Joule heating of electrons and in the expansion part of the nozzle. Wall interactions have strong effects on the results, indicating that they play important roles in the flow due to very high surface area relative to the volume of the plasma. For example, plasma velocity decreases from 6000 m per s without wall interactions to 3000 m per s with modest amount of wall interactions. These results also show reasonable agreement with optical emission measurements, which confirms that the arcjet plasma is far from LTE. The spectra suggest nitrogen dissociation levels of 0.3% - 9%, depending on nitrogen flow rate and arc plasma current, which also determine the relative amounts of excited atomic and molecular nitrogen. Langmuir probe studies of the source show that electron and ion fluxes increase with increasing power, and that the ion energy distribution shifts to lower energies. Typical ion fluxes were on the order of 4E-9 A/cm**2 with a maximum ion kinetic energy of 3.5eV. The median electron energy was 1eV, with a maximum of less than 4eV.

Chang, C. H.↗