Average Electron Number Density Research Articles

Investigating star-formation activity towards the southern H ii region RCW 42

ABSTRACT The star-forming activity in the H ii region RCW 42 is investigated using multiple wavebands, from near-infrared to radio wavelengths. Located at a distance of 5.8 kpc, this southern region has a bolometric luminosity of 1.8 × 106 L⊙. The ionized gas emission has been imaged at low radio frequencies of 610 and 1280 MHz using the Giant Metrewave Radio Telescope, India, and shows a large expanse of the H ii region, spanning 20 × 15 pc2. The average electron number density in the region is estimated to be ∼70 cm−3, which suggests an average ionization fraction of the cloud to be 11 % . An extended green object EGO G274.0649-01.1460 and several young stellar objects have been identified in the region using data from the 2MASS and Spitzer surveys. The dust emission from the associated molecular cloud is probed using Herschel Space Telescope, which reveals the presence of five clumps, C1-C5, in this region. Two millimetre emission cores of masses 380 and 390 M⊙ towards the radio emission peak have been identified towards C1 from the ALMA map at 1.4 mm. The clumps are investigated for their evolutionary stages based on association with various star-formation tracers, and we find that all the clumps are in active/evolved stage.

Study of the Streamer Current Sheet with White-Light and UV Observations

Current sheets (CSs) are the main region where magnetic reconnections can convert magnetic energy into plasma thermal and kinetic energies. We have studied a CS in the streamer occurred on 3 January 2003 by combining the White-Light (WL) images observed by the Large Angle and Spectrometric Coronagraph (LASCO) and the EUV spectra detected by the Ultraviolet Coronagraph Spectrometer (UVCS). LASCO C2 WL data show that the speed of a blob in the CS increased from 60km·s−1 to 340km·s−1 with an acceleration of 60m·s−2 in its Field-of-View (FOV). By assuming the Light-of-Sight (LOS) depth of 0.3–1.5R⊙, the average electron number density of the CS is (1.52–7.60)×107cm−3 at the height of the UVCS slit. We investigate intensity distributions of the [Fexviii]974Å and Lyα lines along the UVCS slit. It is shown that the intensity of the [Fexviii] line at the CS is significantly higher than those of the surroundings, and the deduced electron temperature range of the CS is (2.94–4.04)×106K during the studied period. However, the intensity of the Lyα line at the CS does not change much when compared with those of the surroundings, and within the CS the intensity on both sides are slightly higher than that in the center. It is possible that the plasma move faster in the center resulting in stronger Doppler dimming effect. Using the observed intensity ratio of the Lyα and [Fexviii] lines provided by the UVCS and the calculated electron temperature as constraints, we find that the theoretically calculated emissivity ratio of the Lyα and [Fexviii] lines is close to their observed intensity ratio when the plasma speed range is 237–254km·s−1 at the position of the CS. The collisional component of the Lyα line is about 42%−57% of the radiative component in the CS within the speed range above. The streamer CS we studied has a higher plasma temperature and a faster blob speed than typical values in normal situations. The possible reason is that these two CMEs at the southern side enhanced the magnetic reconnection process in the CS, and more magnetic energy is released to heat and accelerate plasma. Our results on the CS can be regarded as pre-studies of the data analyses for the future mission of the Advanced Space-based Solar Observatory (ASO-S).

An improved method for fast evaluating arc quenching performance of a gas based on 1D arc decaying model

The evaluation of an arc quenching medium in circuit breakers usually requires the experimental investigation or the 2D or 3D magnetohydrodynamics simulation of switching arcs, which are expensive and time-consuming. In this work, a fast method is proposed for evaluating the arc quenching performance of gases. In this method, the arc decaying process is divided into three stages based on the results of 1D arc decaying modeling, including the thermal recovery stage, the predielectric recovery stage, and the postdielectric recovery stage. Compared to the previous method, the present method is improved mainly in the three aspects: the thermal recovery stage is featured by the average radial temperature instead of the axial temperature; the criterion of dividing the dielectric recovery stage into the pre- and postdielectric recovery stages is validated by the average electron number density instead of choosing arbitrarily; and the postdielectric recovery stage is characterized by the critical electric field strength Ecr instead of the reduced critical electric field strength (E/N)cr. The case study of SF6, CO2, CF4, and air arcs indicates that the present method yields the same descending order of the thermal recovery rate and the predielectric recovery rate for the four gases as the previous method. Moreover, the present method can avoid negative postdielectric recovery rates, which means that it is more reasonable than the previous method.

Optical emission of graphite plasma generated in ambient air using low-irradiance carbon dioxide laser pulses

Optical emission studies of graphite plasma induced by infrared (IR) Transversely Excited Atmospheric carbon dioxide (TEA CO2) laser pulses in ambient air at atmospheric pressure are reported. The plasma was induced at relatively low-irradiance, up to 40 MW cm−2, and the plasma emission was recorded using time-integrated LIBS measurements. The time profile of the 160 mJ laser pulse is composed of a short, 100 ns long initial spike, and a long 2 μs tail. About 60 mJ is contained in the initial pulse, and the 100-mJ tail contribution is favorable for extended plasma absorption that promotes creation of long-lasting highly-excited plasma. With laser pulse focused behind the target surface, recorded spectra consisted of intensive, sharp atomic and single charged ionic spectral lines of carbon, and trace elements, e.g. Ca, Cu, V, Si, and Ti. Good signal to background ratios obtained indicate potential application in the analysis of impurities in graphite, and also elemental analysis of other materials with high carbon content. The average electron number density was determined from Stark-broadened emission profile of C I 247.9 nm line, and the line intensity ratio of CII 250.9 nm/C I 247.9 nm line pair was used for estimation of ionization temperature. Depending on the applied fluence, electron density was in the range 2.6–4.8 × 1017 cm−3, and ionization temperature between 19,000 and 22,000 K. Beside line spectra, intensive and well-developed band spectra of diatomic molecules C2 (Swan system), and CN (violet system) were obtained. Pulse energy threshold for observation of molecular emission was 50 mJ. From the spectroscopic studies of the emission bands, the rotational and vibrational temperatures were estimated by comparing the experimental and simulated emission spectra. Vibrational and rotational temperatures deduced from Δν = 0 sequences of the Swan system of C2 were 3100 K and 3850 K, respectively. The most intense band of the CN violet system showed strong self-absorption and led to overestimated temperature values, Tvib = Trot = 4900 K.

Regimes of an atmospheric pressure nanosecond repetitively pulsed discharge for methane partial oxidation

The operation of a nanosecond repetitively pulsed discharge for partial oxidation of CH4 is characterized at atmospheric pressure and room temperature. Two regimes are observed: diffuse and filamentary. The first is a low power regime, characterized by low rotational temperatures around 400 K. The second is much more energetic with rotational temperatures close to 600 K. Both have vibrational temperatures of at least 10 times their rotational temperatures. The average electron number density was determined to be and cm−3, respectively, showing an increase in the ionization fraction in the more powerful filamentary regime. Results of CH4 conversion to H2, CO, CO2 and C2H6 are presented for the filamentary regime, while the diffuse regime shows no measurable conversion ability. As expected, oxidative mixtures show higher conversion ability than pure CH4. A maximum conversion efficiency of 26.3% and a maximum energy efficiency of 19.7% were reached for the oxidative mixtures.

Characterization of a dielectric barrier discharge in contact with liquid and producing a plasma activated water

In this work a low-temperature plasma source for the generation of plasma activated water (PAW) is developed and characterized. The plasma reactor was operated by means of an atmospheric-pressure air dielectric barrier discharge (DBD). The plasma generated is in contact with the water surface and is able to chemically activate the liquid medium. Electrodes were supplied by both sinusoidal and nanosecond-pulsed voltage waveforms. Treatment times were varied from 2 to 12 min to increase the energy dose released to the water by the DBD plasma. The physics of the discharge was studied by means of electrical, spectroscopic and imaging diagnostics. The interaction between the plasma and the liquid was investigated as well. Temperature and composition of the treated water were detected. Images of the discharges showed a filamentary behaviour in the sinusoidal case and a more homogeneous behaviour in the nanosecond-pulsed one. The images and the electrical measurements allowed to evaluate an average electron number density of about 4 × 1019 and 6 × 1017 m−3 for the sinusoidal and nanosecond-pulsed discharges respectively. Electron temperatures in the range of 2.1÷2.6 eV were measured by using spectroscopic diagnostics. Rotational temperatures in the range of 318–475 K were estimated by fitting synthetic spectra with the measured ones. Water temperature and pH level did not change significantly after the exposure to the DBD plasma. The production of ozone and hydrogen peroxide within the water was enhanced by increasing the plasma treatment time and the energy dose. Numerical simulations of the nanosecond-pulsed discharge were performed by using a self-consistent coupling of state-to-state kinetics of the air mixture with the Boltzmann equation of free electron kinetics. Temporal evolution of the electron energy distribution function shows departure from the Maxwellian distribution especially during the afterglow phase of the discharge. When limited deviations from Maxwellian distribution were observed, calculated electron temperature is in good agreement with the one measured by means of spectroscopic diagnostics. Computed temporal evolution of the energy delivered to the discharge is comparable with the one obtained from electrical measurements. The electrical discharges supplied by both voltage waveforms produce plasma activated water with negligible thermal effects and pH variations.

ON THE MAGNETIC AND ENERGY CHARACTERISTICS OF RECURRENT HOMOLOGOUS JETS FROM AN EMERGING FLUX

ABSTRACT In this paper, we present the detailed analysis of recurrent homologous jets originating from an emerging negative magnetic flux at the edge of an active region. The observed jets show multithermal features. Their evolution shows high consistence with the characteristic parameters of the emerging flux, suggesting that with more free magnetic energy, the eruptions tend to be more violent, frequent, and blowout-like. The average temperature, average electron number density, and axial speed are found to be similar for different jets, indicating that they should have been formed by plasmas from similar origins. Statistical analysis of the jets and their footpoint region conditions reveals a strong positive relationship between the footpoint region total 131 Å intensity enhancement and jets’ length/width. Stronger linearly positive relationships also exist between the total intensity enhancement/thermal energy of the footpoint regions and jets’ mass/kinetic/thermal energy, with higher cross-correlation coefficients. All the above results together confirm the direct relationship between the magnetic reconnection and the jets and validate the important role of magnetic reconnection in transporting large amounts of free magnetic energy into jets. It is also suggested that there should be more free energy released during the magnetic reconnection of blowout than of standard jet events.

Zakharov simulations of beam‐induced turbulence in the auroral ionosphere

AbstractRecent detections of strong incoherent scatter radar echoes from the auroral F region, which have been explained as the signature of naturally produced Langmuir turbulence, have motivated us to revisit the topic of beam‐generated Langmuir turbulence via simulation. Results from one‐dimensional Zakharov simulations are used to study the interaction of ionospheric electron beams with the background plasma at the F region peak. A broad range of beam parameters extending by more than 2 orders of magnitude in average energy and electron number density is considered. A range of wave interaction processes, from a single parametric decay, to a cascade of parametric decays, to formation of stationary density cavities in the condensate region, and to direct collapse at the initial stages of turbulence, is observed as we increase the input energy to the system. The effect of suprathermal electrons, produced by collisional interactions of auroral electrons with the neutral atmosphere, on the dynamics of Langmuir turbulence is also investigated. It is seen that the enhanced Landau damping introduced by the suprathermal electrons significantly weakens the turbulence and truncates the cascade of parametric decays.

A Relationship between Dispersion Measure and Redshift Derived in Terms of New Tired Light

New data from FRB’s have provided an exciting new window on the cosmos. For the first time we have both Dispersion Measure (DM) from distant sources and their red-shift. This gives us the opportunity to determine the average electron number density in intergalactic space and thus test New Tired Light predictions. Here, in an alternative cosmology, the universe is static and redshifts are produced by an interaction between photons and the electrons in the intergalactic medium. In a paper published in summer 2006 New Tired Light (NTL) predicted an average electron number density of n = 0.5 m-3. In 2016 a paper was published reporting that for the first time the DM of a FRB and the redshift of the host galaxy had been found. Using standard physics this confirmed the electron number density as n = 0.5 m-3. The prediction NTL made ten years earlier was proved to be correct. Using this measured electron number density enabled a definitive value of the Hubble constant to be made by New Tired Light and the value is 63 km/s per Mpc which compares well with currently accepted values. Importantly, since in NTL the redshift and dispersion are both due to the electrons in IG space, a relationship between DM’s and redshift can be predicted. NTL predicts that DM and LN(1 + z) will be directly proportional and related by the formula DM = mec/2hre(3.086 × 1022) where me, re are the rest mass and classical radius of the electron, c is the speed of light in a vacuum and h is the plank constant. The numerical term is to change units from pccm-3 to m-2. This reduces to DM = 2380LN(1 + z). Using data from five FRB’s this is tested and a linear relation is seen of the form DM = 1830LN(1 + z). The gradient of the plot from the observed data is within 23% of that predicted by NTL. Recently the Tolman Surface Brightness test has been applied to the HUDF and the results support a static universe whilst the possibility of two differing types of SN Ia whose distribution changes with distances means that tired light models can no longer be ruled out. Using SDF we know the distance to the Atlia galaxy cluster as 1.26 × 1024 m. With the average electron number density of n = 0.5 m-3 found from the Dispersion Measures of the FRB’s, from first principles, New Tired Light gives a calculated predicted redshift of 0.0086. This compares well with the value found spectroscopically of 0.0087—a difference of approximately 1%. It is shown that if the energy transferred to a recoiling electron when a UV photon of wavelength λ = 5 × 10-8 m interacts with it is emitted as a secondary photon that photon will have a wavelength of 2.2 mm— the wavelength at which the CMB curve peaks.

Experimental Results in DBD Plasma Actuators for Air Flow Control

In this paper, several planar dielectric barrier discharge fluid-dynamics actuators have been experimentally investigated. The actuator is made by an electrode pair separated by a dielectric. It is characterized by a planar geometry, and it induces a volume force on the gas above it which modifies the fluid dynamics within the aerodynamic boundary layer. Several actuator geometries, dielectric materials, ac supply voltages, and supply frequencies have been used. Rotational and vibrational temperatures have been determined by means of spectroscopic measurements. Vibrational temperatures have been found to be one order of magnitude higher than the rotational ones, confirming the nonthermal behavior of the discharge. The translational temperature has been evaluated by thermographic observations of the dielectric surface heated by the plasma. The values of the translational temperature are in a very good agreement with those of the rotational temperature. Electric measurements have been carried out to determine the average power delivered to the discharge and to estimate the average electron number density. In the plasma induced by the discharge above the actuator, an average electron density of has been determined. The gas speed of the induced wall jet has been measured with a Pitot tube. The average power delivered to the electrodes increases with a power law of the applied voltage and linearly with the supply frequency. The induced speed increases with the increase of the average power until a plateau is reached. The efficiencies of the different actuators have been compared by evaluating the relation between average power and induced gas speed.

Quantitative Microplasma Electron Number Density Measurement by Coherent Microwave Rayleigh Scattering

In this paper, a method for quantitative measurement of electron number density in a microplasma by coherent microwave Rayleigh scattering is described. Coherent microwave Rayleigh scattering reaches its maximum when the microwave frequency is at its resonance frequency. The resonance frequency depends on the electron number density in the microplasma and the electron-neutral and Coulomb collisional frequencies. When a subnanosecond microwave pulse illuminates the microplasma, the average electron number density can be measured from the frequency analysis of microwave scattering. The technique will be able to quantitatively measure subnanosecond-resolved electron number density evolution in the microplasma.

A graphical summary of solar wind electron content observations by Pioneer 6, 8, and 9

Between 1965 and 1972, solar wind density measurements were obtained by Mariner 5 and Pioneer 6, 7, 8, and 9 using a radio science method called the ‘dual‐frequency experiment.’ The measurements and data processing are now terminated. We present here a graphical summary of the best of the resulting data, showing the average electron number density of the solar wind across radio paths that vary in length up to 1.8 AU and that lie broadside to the flow direction. These graphs summarize 3.4 years of observations with a time resolution of 1 hour; the measurements provided 1‐min resolution and spanned 7 years. Because the orientation and length of the paths change continually and have a major influence on the interpretation of these data, we provide a spacecraft trajectory chart and a plot of the corotation interval.

Corotating Regions in the Solar Wind, Evident in Number Density Measured by a Radio‐Propagation Technique

Coherent phase‐modulated signals at 50 and 423 MHz are transmitted from Stanford University to specially equipped spacecraft orbiting the sun. Differential group delay and phase advance are measured; each of these parameters is approximately proportional to the average electron number density along the signal path. The experimental method enables us to discriminate between temporal and spatial variations of the solar wind by virtue of inherent spatial averaging. During the past 4.5 years, 10,000 hours of these data have been obtained from Pioneers 6, 7, 8, and 9 and Mariner 5. At times, measurements have been taken for two periods each day, by the use of first one spacecraft ahead of earth and then one behind. With such a technique, corotating flow patterns are clearly visible. Hourly samples are presented of the best data that were obtained by Pioneers 8 and 9 during the two‐year period ending in February 1970. The density patterns reveal corotating regions in each of which a recognizable character is maintained during several rotations but for less than a year. This result is in contrast to results of other observers, who have seen corotating features lasting up to 1.5 years. The short duration observed here may be due to noisiness in these data or it may be typical of the active sun, whereas a longer duration is typical of quiet times. The observed density patterns are not consistent with the concept of steady corotating flows because large transients occur too fast and because identifiable features recur with nearly (but not exactly) the same period on successive rotations of the sun. These patterns could be a result of the corotation of thin steady streams that fluctuate both north‐south and east‐west by distances well in excess of the cross‐sectional extent of the streams. It is also possible (and more likely) that the data indicate some corotating regions in which the solar wind is featureless and of low density and other regions characterized by high density and the prevalence of outward traveling plasma disturbances.

Electron Density and Temperature Decay in Mercury Afterglows

Abstract : Average electron number density and electron-temperature measurements are presented for the mercury vapor afterglow in a hot-cathode cylindrical discharge tube at a pressure range where ambipolar diffusion predominates. The average electron number density is measured using cylindrical microwave cavities in the TM010 and dipole resonance modes. The electron temperature is measured by means of a time-resolving 3.0-GHz radiometer. Three pressure regions are identified. The initially rapid electron-temperature decay occurring during the first 0.5 msec of the afterglow is pressure independent and is well explained by electron-ion elastic collisions. The slow electron temperature decay after 0.5 msec which occurs in the second pressure region is pressure dependent and is explained by a balance between energy gain from collisions of the second kind in the reaction e + triplet P(2) to triplet P(1) +e and losses due to electron-ion elastic collisions. A complete discussion of these processes is given and the neglect of other mechanisms justified. (Author)

Faraday Rotation, Dispersion in Pulsar Signals, and the Turbulent Structure of the Galaxy

view Abstract Citations (99) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Faraday Rotation, Dispersion in Pulsar Signals, and the Turbulent Structure of the Galaxy Jokipii, J. R. ; Lerche, I. Abstract We compute the mean and the variance about the mean of the Faraday rotation and signal dispersion for electromagnetic waves propagating in a turbulent medium such as the Galaxy. With regard to the e'ectron number density and the magnetic field as homogeneous random functions (with nonzero mean), we present the results in terms of the mean values and two-point correlation functions of these quantities. Application to a simple, statistically homogeneous, disk model of the Galaxy and its turbulence is then considered. The predictions of the model for the means and variances are consistent with the observed Faraday rotations and the dispersions in pulsar signals, although the observations are not yet sufficient to provide a definitive test of the theory. The mean values are much as those discussed by previous au- thors who did not consider the fluctuations. The variances of the Faraday rotations and the dispersions in pulsar signals are used to estimate statistical parameters such as the correlation length and rms fluctuations associated with turbulence in the Galaxy. We find that the correlation length L is approxi~ mately equal to the 250-pc thickness of the galactic disk. The average magnetic field is `-~3 X 1O~ gauss, and its rms fluctuation is `-~-` 1.5 X 1O~ gauss. The average electron number density is -~-`4 X 1O~2 cm~, and its rms fluctuation is `-~-3 X 1O~ cm3 Publication: The Astrophysical Journal Pub Date: September 1969 DOI: 10.1086/150142 Bibcode: 1969ApJ...157.1137J full text sources ADS |

Free-Fall Decay of a Mercury Vapor Plasma in the Early Afterglow

A free-fall theory is developed for the decay of the average electron number density and of the electron temperature in a pulsed cylindrical mercury vapor discharge plasma using moment equations for the ions with a collision term for momentum loss, and assuming Maxwellian electrons. The plasma assumption was used. Good agreement is obtained with experimental results on four tubes of varying diameter.

The effects of end holes and the glass tube on average electron number density measurements in a TM010 cavity

The importance of end holes and the glass tube in TM010 mode measurements of the average electron number density in cylindrical plasmas is evaluated.

Parameters of the Plasma Affecting the Radiation of Pulsar 1

Analysis of the relation between time delay and frequency for pulses from Pulsar 1 shows that the dispersive region of the ray path must exceed 300 astronomical units and have an average electron number density less than 8000 per cubic centimeter and average magnetic field strength less than 2 x 10(-3) gauss. These requirements almost guarantee that the observed dispersion takes place in the interstellar medium.

FREE-FALL DIFFUSION IN A DISCHARGE AFTERGLOW

The afterglow decay of the number density and electron temperature of a plasma in which collisions between electrons and molecules are rare is studied both theoretically and experimentally. The theoretical approach, using the first three moment equations solved in a one-dimensional geometry, predicts non-exponential decay profiles in time for both density and temperature. Experimental results are obtained using a cylindrical mercury vapor discharge tube at pressures where the mean free path of the electrons is much larger than the transverse dimensions of the tube. The average electron number density is measured by a surface-wave cavity method and the electron temperature by means of Langmuir probes. The theoretical and experimental results are in good agreement, especially for the density decay.

The interplanetary electron number density from preliminary analysis of the Pioneer 6 Radio Propagation Experiment

This is a preliminary report on one aspect of the radio propagation experiment on Pioneer 6. From an analysis of a small fraction of the differential group-path data from Pioneer and simultaneous ionospheric measurements using signals from two Beacon satellites, it has been determined that the average interplanetary electron number density near the earth's orbit was between 8 and 9 cm-3 in the time interval from February 20 to April 9, 1966. This is a spatial as well as a temporal average, since the measurements are of columnar electron content between the earth and spacecraft, corrected for near-earth (ionospheric and magnetospheric) electrons. During the indicated time interval, the spacecraft was between 10 and 31 million km from the earth and between about 0.93 and 0.86 AU from the sun. Temporal variations of the spatial-average number density caused an rms deviation from the mean of about 4.4 cm−3.