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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Langmuir Probe Measurements of Inductively Coupled Plasmas in CF4/Ar/O2 Mixtures

Inductively coupled plasmas of CF4:Ar:O2, which have been of importance to material processing, were studied in the GEC cell at 80:10:10, 60:20:20, and 40:30:30 mixture ratios. Radial distributions of plasma potential (V(sub p)), electron and ion number densities (n(sub e) and n(sub i), electron temperature (T(sub e)), and electron energy distribution functions (EEDFs) were measured in the mid-plane of plasma across the electrodes in the pressure range of 10-50 mTorr, and RF (radio frequency) power of 200 and 300 W. V(sub p), n(sub e) and n(sub i), which peak in the center of the plasma, increase with decrease of pressure. T(sub e) also increases with pressure but peaks toward the electrode edge. Both V(sub p) and T(sub e) remain nearly independent of RF power, whereas n(sub e) and n(sub i) increase with power. In all conditions the EEDFs exhibit non-Maxwellian shape and are more like Druyvesteyn form at higher energies. They exhibit a broad dip in the energy range 0-10 eV suggesting an electron loss mechanism, which could be due to via resonance electron attachment processes producing negative ions in this rich electronegative gas mixture. This behavior is more prominent towards the electrode edge.

Rao, M. V. V. S.↗
NASA NTRS2001

Langmuir Probe and Mass Spectroscopic Measurements in Inductively Coupled CF4 Plasmas

Abstract Electron and ion energy distribution functions and other plasma parameters such as plasma potential (V(sub p)) , electron temperature (T(sub e)), and electron and ion number densities (n (sub e) and n(sub i)) in low pressure CF4 plasmas have been measured. The experiments were conducted in a GEC cell using an inductively coupled plasma (ICP) device powered by a 13.56 MHz radio-frequency (rf) power source. The measurements were made at 300 W of input rf power at 10, 30 and 50 mTorr gas pressures. Langmuir probe measurements suggest that n(sub e), n(sub i) and V(sub p) remain constant over 60% of the central electrode area, beyond which they decrease. Within the limits of experimental error (+/- 0.25 eV), T(sub e) remains nearly constant over the electrode area. T(sub e) and V(sub p) increase with a decrease in pressure. n(sub e) and n(sub i) are not affected as significantly as T(sub e) or V(sub p) by variation in the gas pressure. The electron energy distribution function (EEDF) measurements indicate a highly non-Maxwellian plasma. CF3+ is the most dominant ion product of the plasma, followed by CF2+ and CF+. The concentrations of CF2+ and CF+ are much larger than that is possible from direct electron impact ionization of the parent gas. The cross-section data suggest that the direct electron impact ionization of fragment neutrals and negative ion production by electron attachment may be responsible for increase of the minor ions.

Rao, M. V. V. S.↗
NASA NTRS1973

The electric potential of the moon in the solar wind

Acceleration and detection of the lunar thermal ionosphere in the presence of the lunar electric field yields a value of approximately +10 V for the lunar electric potential for solar zenith angles between 20 and 45 deg and in the magnetosheath or solar wind. The ion number density of the thermal ionosphere observed is compatible with a surface neutral number density of about 100,000 atoms/cu cm.

Freeman, J. W., Jr.↗
NASA NTRS1983

Bottomside sinusoidal irregularities in the equatorial F region

By using the Ogo 6 satellite, McClure and Hanson (1973) have discovered sinusoidal irregularities in the equatorial F region ion number density. In the present investigation, a description is provided of the properties of a distinct category of sinusoidal irregularities found in equatorial data from the AE-C and AE-E satellites. The observed scale sizes vary from about 300 m to 3 km in the direction perpendicular to B, overlapping with and extending the range observed by using Ogo 6. Attention is given to low and high resolution data, a comparison with Huancayo ionograms, the confinement of 'bottomside sinusoidal' (BSS) irregularities essentially to the bottomside of the F layer, spectral characteristics, and BSS, scintillation, and ionosonde observations.

Valladares, C. E.↗
NASA NTRS1986

Scintillations associated with bottomside sinusoidal irregularities in the equatorial F region

Multisatellite scintillation observations and spaced receiver drift measurements are presented for a category of equatorial F region plasma irregularities characterized by nearly sinusoidal waveforms in the ion number density. The observations were made at Huancayo, Peru, and the measurements at Ancon, Peru, associated with irregularities observed by the Atmospheric-Explorer-E satellite on a few nights in December 1979. Utilizing ray paths to various geostationary satellites, it was found that the irregularities grow and decay almost simultaneously in long-lived patches extending at least 1000 km in the east-west direction.

Basu, S.↗
NASA NTRS1995

Structure of mass-loading shocks. 2: Comparison of theory and observation at comet Halley

The multifluid diffusive model of G. P. Zank et al. (1994), which describes the interaction of the solar wind with a cometary plasma in the outer coma, has been used to model the structure of the Halley bow shock. The theoretical results are compared to in situ observations made by Giotto. We compare the solar wind and cometary ion number densities and pressures upstream and through the quasi-perpendicular and quasi-parallel shocks (observed on the inbound and outbound legs of the encounter, respectively). In general, good agreement is found between theory and observations in terms of shock structure, strength, and location, especially for the quasi-parallel shock. The comparison between tha quasi-perpendicular shock observations and theory is complicated by the apparently nonstationary behavior of the shock, a feature which has been remarked upon by other investigators. The cometary bow shock appears to be an excellent example of an energetic-particle-mediated shock where the energetic particles comprise less than 10% of the total number density.

Zank, G. P.↗
NASA NTRS2016

Modeling an Iodine Hall Thruster Plume in the Iodine Satellite (ISAT)

An iodine-operated 200-W Hall thruster plume has been simulated using a hybrid-PIC model to predict the spacecraft surface-plume interaction for spacecraft integration purposes. For validation of the model, the plasma potential, electron temperature, ion current flux, and ion number density of xenon propellant were compared with available measurement data at the nominal operating condition. To simulate iodine plasma, various collision cross sections were found and used in the model. While time-varying atomic iodine species (i.e., I, I+, I2+) information is provided by HP Hall simulation at the discharge channel exit, the molecular iodine species (i.e., I2, I2+) are introduced as Maxwellian particles at the channel exit. Simulation results show that xenon and iodine plasma plumes appear to be very similar under the assumptions of the model. Assuming a sticking coefficient of unity, iodine deposition rate is estimated.

Iodine↗
NASA NTRS2016

Modeling an Iodine Hall Thruster Plume in the Iodine Satellite (ISAT)

An iodine-operated 200-W Hall thruster plume has been simulated using a hybrid-PIC model to predict the spacecraft surface-plume interaction for spacecraft integration purposes. For validation of the model, the plasma potential, electron temperature, ion current flux, and ion number density of xenon propellant were compared with available measurement data at the nominal operating condition. To simulate iodine plasma, various collision cross sections were found and used in the model. While time-varying atomic iodine species (i.e., I, I+, I2+) information is provided by HPHall simulation at the discharge channel exit, the molecular iodine species (i.e., I2, I2+) are introduced as Maxwellian particles at the channel exit. Simulation results show that xenon and iodine plasma plumes appear to be very similar under the assumptions of the model. Assuming a sticking coefficient of unity, iodine deposition rate is estimated.

Numerical Simulation↗
NASA NTRS1977

Factors affecting ion kinetic temperature, number density, and containment time in the NASA Lewis bumpy-torus plasma

The degree of toroidal symmetry of the plasma, the number of midplane electrode rings, the configuration of electrode rings, and the location of the diagnostic instruments with respect to the electrode rings used to generate the plasma are discussed. Impurities were deliberately introduced into the plasma, and the effects of the impurity fraction on ion kinetic temperature and electron number density were observed. It is concluded that, if necessary precautions are taken, the plasma communicates extremely well along the magnetic field lines and displays a high degree of symmetry from sector to sector for a wide range of electrode ring configurations and operating conditions. Finally, some characteristic data taken under nonoptimized conditions are presented, which include the highest electron number density and the longest particle containment time (1.9 msec) observed. Also, evidence from a paired comparison test is presented which shows that the electric field acting along the minor radius of the toroidal plasma improves the plasma density and the calculated containment time more than an order of magnitude if the electric field points inward, relative to the values observed when it points (and pushes ions) radially outward.

Roth, J. R.↗
NASA NTRS1976

Preliminary scaling laws for plasma current, ion kinetic temperature, and plasma number density in the NASA Lewis bumpy torus plasma

Parametric variation of independent variables which may affect the characteristics of bumpy torus plasma have identified those which have a significant effect on the plasma current, ion kinetic temperature, and plasma number density, and those which do not. Empirical power law correlations of the plasma current, and the ion kinetic temperature and number density were obtained as functions of potential applied to the midplane electrode rings, the background neutral gas pressure, and the magnetic field strength. Additional parameters studied included the type of gas, the polarity of the midplane electrode rings, the mode of plasma operation, and the method of measuring the plasma number density. No significant departures from the scaling laws appear to occur at the highest ion kinetic temperatures or number densities obtained to date.

Roth, J. R.↗
NASA NTRS1976

Preliminary scaling laws for plasma current, ion kinetic temperature, and plasma number density in the NASA Lewis Bumpy Torus plasma

Parametric variation of independent variables which may affect the characteristics of the NASA Lewis Bumpy Torus plasma have identified those which have a significant effect on the plasma current, ion kinetic temperature, and plasma number density, and those which do not. Empirical power-law correlations of the plasma current, and the ion kinetic temperature and number density were obtained as functions of the potential applied to the midplane electrode rings, the background neutral gas pressure, and the magnetic field strength. Additional parameters studied include the type of gas, the polarity of the midplane electrode rings (and hence the direction of the radial electric field), the mode of plasma operation, and the method of measuring the plasma number density. No significant departures from the scaling laws appear to occur at the highest ion kinetic temperatures or number densities obtained to date.

Roth, J. R.↗
NASA NTRS1999

Relationship of O(+) Field-Aligned Flows and Densities to Convection Speed in the Polar Cap at 5000 km Altitude

Measurements of thermal O(+) ion number fluxes, densities, field-aligned velocities, and convective velocities from the Thermal Ion Dynamics Experiment (TIDE) on POLAR obtained near 5000 km altitude over the Southern hemisphere are examined. We find that the O(+) parallel velocities and densities are strongly related to the convection speeds. The polar cap densities decrease rapidly with convection speed, with a linear least square fit formula to bin averaged data giving the relationship log(N(sub (sub _)O(+))) = -0.33* V(sub (sub _)conv)) + 0.07, with a linear regression coefficient of r = -0.96. The parallel bulk flow velocities are on average slightly downward (0 - 2 km/s) for V(sub (sub _)conv) < 2.5 km/s, but tend to be upward (0 - 4 km/s) for average V(sub (sub _)conv) > 2.5 km/s. We interpret these relationships in terms of the Cleft Ion Fountain paradigm [e.g., Horwitz and Lockwood, 1985]. The densities decline with convection speed owing to increased spreading and resulting dilution from the restricted cleft source over the polar cap area with convection speed. The parallel velocities tend to be downward for low convection speeds because they fall earthward after initial cleft injection at shorter distances into the polar cap for low convection speeds. At the higher convection speeds, the initially-upward flows are transported further into the polar cap and thus occupy a larger area of the polar cap.

Stevenson, B. A.↗
NASA NTRS1990

Giotto IMS measurements of the production rate of hydrogen cyanide in the coma of Comet Halley

The ion composition measurements in the ionosphere of Comet Halley by the ion mass spectrometer (IMS) experiment on the Giotto spacecraft are used to estimate the relative abundance of HCN. From a comparison of the normalized number density of ions with mass-to-charge (M/q) ratio of 28 AMU/e with steady-state photochemical models, it can be determined that the production rate of HCN directly from the central nucleus is Q(HCN) is less than about 0.0002 Q(H2O) at the time of Giotto encounter. The related photochemical- model calculations also indicate that Q(NH3)/Q(H2O) at the time of Giotto encounter. The related photo-chemical model calculations also indicate that Q(HN3)/Q(H2O) equals about 0.005, in agreement with recent determination from ground-based observations. The estimated value of Q(HCN) is lower than the relative abundance of Q(HCN)/Q(H2O) of about 0.001, as derived from radio observations of the 88.6 GHz emission of the J = 1 - 0 transition of HCN. The difference may be the result of time variations of the coma composition and dynamics, as well as other model-dependent effects.

Ip, W.-H.↗
NASA NTRS1994

Ion properties of the high-latitude middle-atmosphere

Investigations of high-latitude, middle-atmosphere ion properties have been conducted using rocket probe techniques. Electrodynamics studies have addressed: mesospheric dynamics and small-scale structure (the MAC/EPSILON Campaign during October-November 1977); ionization effects associated with highly energetic greater than or equal to 1 MeV) precipitating electrons (the MAC/REP Program during May 1990); and the characteristics of noctilucent cloud (NLC) and polar mesosphere summer echo (PMSE) regions (the NLC-91 Campaign during July-August 1991). Recent developments in Gerdien condenser probe theory, using computational fluid dynamics to model ion collection, have resulted in more accurate evaluation of the ion mobilities and number densities. Measurements of very small ion mobilities are thought to indicate an aerosol ion presence in the upper mesosphere.

Li, C.↗
NASA NTRS1996

Formation of the Electric Double Layer and its Effects on Moving Bodies in a Space Plasma Environment

In this paper we solve the self-consistent Vlasov and Poisson equations by a numerical method to determine the local distribution function of the ion and the electron, within a thin layer near the moving body, respectively. Using these ion and electron distributions, the number density for the ions and electrons are determined, such that, the electric potential is obtained within this thin layer (i.e., measured by Debye length). Numerical results are presented for temporal evolution of the electron and ion density and its corresponding electric potential within the layer which shows the formation of electric double layer and its structures. From these numerical results, we are able to determine the maximum conditions of the electric potential, it may create satellite anomaly.

Yang, Qianli↗
NASA NTRS1986

Evidence for HCS(+) and CH2SH(+) in the inner coma of Comet Halley

Number densities for ion species with masses 44, 45, and 47 amu/q were derived from ram energy spectra of the neutral gas mass spectrometer experiment on Giotto in the inner coma of comet Halley. The relative abundances of the masses suggest the presence of the ions CS(+), HCS(+), and CH2SH(+).

Krankowsky, D.↗
NASA NTRS1987

Comet P/Giacobini-Zinner electron and H2O(+) column densities from ICE and ground-based observations

An H2O(+) spatial mission profile, extracted from an optical CCD spectrogram obtained during the ICE/Giacobini-Zinner encounter, is compared to the electron-density profile that was deduced from in situ measurements by the radio experiment aboard ICE. The electron column density along a line of sight has two components, one from the spherically symmetric coma, and the second from a thin plasma sheet, whenever it is along the line of sight. The deduced electron column-density profile agrees well with the observed H2O(+) emission profile. It is concluded that the electrons and the H2O(+) ions are distributed similarly 9600 km tailward from the cometary nucleus, that the ratio of number densities of H2O(+) ions to electrons is about 1/4 at this point, and that the width of the plasma sheet is about 16,000 km.

Meyer-Vernet, N.↗