Average Electron Temperature Research Articles

Study of the current-sheath formation during the implosion of multishell gas puffs

Results are presented from experimental studies of the dynamics of large-diameter multishell gas puffs imploded by microsecond megampere current pulses. The experiments were conducted on the GIT-12 generator in the regime of microsecond implosion (timp = 1.1–1.2 μs, I0 = 3.4–3.7 MA). The influence of the load configuration on the dynamics of current losses and gas-puff radiative characteristics was studied. The correlation between the radial compression ratio (the ratio between the initial and final Z-pinch radii) and the magnitude of the current flowing at the plasma periphery was investigated. The experiments show that, in a multishell gas puff, large-scale instabilities insignificantly affect the gas-puff implosion even over microsecond time intervals and that a compact dense pinch with a relatively high average electron temperature (400–600 eV) forms at the Z-pinch axis. The diameter of the plasma column radiating in the K-shell lines of neon is about 3–4 mm, the K-shell radiation yield being 5–11 kJ/cm. In the final stage of implosion, only a small portion of the current flows through the high-temperature central region of the pinch plasma, whereas the major part of the generator current flows through the residual peripheral plasma.

Diurnal, seasonal, latitudinal and solar cycle variation of electron temperature in the topside F-region of the Indian zone ionosphere

Abstract. Electron temperature Te observed by the SROSS C2 satellite at equatorial and low latitudes during the low to high solar activity period of 1995–2001 at the height of ~500 km is investigated in terms of local time, season, latitude, solar sunspot number Rz and F10.7 cm solar flux. The satellite covered the latitude belt of 31° S–34° N and the longitude range of 40°–100° E. The average nighttime (20:00–04:00 LT) Te varies between 750–1200 K and then rises sharply in the sunrise period (04:00–06:00 LT) to the morning high from 07:00 to 10:00 LT and attains a daytime (10:00–14:00 LT) average of 1100–2300 K. The morning enhancement is more pronounced in the equinoxes. A secondary maximum in Te is also observed around 16:00–18:00 LT in the June solstice and in the equinoxes. Daytime electron temperature was found to be higher in autumn compared to that in spring in all latitudes. Between the solstices, the amplitude of the morning enhancement is higher in winter compared to that in summer. Both day and nighttime Te observed by the SROSS C2 satellite bears a positive correlation with solar activity when averaged on a shorter time scale, i.e. over the period of a month. But on a longer time scale, i.e. averaged over a year, the daytime electron temperature gradually decreases from 1995 till it reaches the minimum value in 1997, after which Te again continues to rise till 2001. The variations are distinctly seen in summer and in the equinoxes. The sunspot activity during solar cycle 23 was minimum in 1996 and maximum in 2000. Annual average electron temperature, therefore, appears to follow the variation of solar activity with a time lag of about one year, both at the bottom and top of solar cycle 23, indicating an inherent inertia of the ionosphere thermosphere regime to variations in solar flux.

TheSpitzerIRS Infrared Spectrum and Abundances of the Planetary Nebula IC 2448

We present the mid-infrared spectrum of the planetary nebula IC 2448. In order to determine the chemical composition of the nebula, we use the infrared line fluxes from the Spitzer spectrum along with optical line fluxes from the literature and ultraviolet line fluxes from archival IUE spectra. We determine an extinction of C(H-beta) = 0.27 from hydrogen recombination lines and the radio to H-beta ratio. Forbidden line ratios give an electron density of 1860 cm-3 and an average electron temperature of 12700 K. The use of infrared lines allows us to determine more accurate abundances than previously possible because abundances derived from infrared lines do not vary greatly with the adopted electron temperature and extinction, and additional ionization stages are observed. Elements left mostly unchanged by stellar evolution (Ar, Ne, S, and O) all have subsolar values in IC 2448, indicating that the progenitor star formed out of moderately metal deficient material. Evidence from the Spitzer spectrum of IC 2448 supports previous claims that IC 2448 is an old nebula formed from a low mass progenitor star.

X-ray emission from T Tauri stars and the role of accretion: inferences from the XMM-Newton extended survey of the Taurus molecular cloud

Context. T Tau stars display di erent X-ray properties depending on whether they are accreting (classical T Tau stars; CTTS) or not (weak-line T Tau stars; WTTS). X-ray properties may provide insight into the accretion process between disk and stellar surface. Aims. We use data from the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST) to study di erences in X-ray properties between CTTS and WTTS. Methods. XEST data are used to perform correlation and regression analysis between X-ray parameters and stellar properties. Results. We confirm the existence of a X-ray luminosity (LX) vs. mass (M) relation, LX/ M 1:69 0:11 , but this relation is a consequence of X-ray saturation and a mass vs. bolometric luminosity (L ) relation for the TTS with an average age of 2.4 Myr. X-ray saturation indicates LX= constL , although the constant is di erent for the two subsamples: const= 10 3:73 0:05 for CTTS and const= 10 3:39 0:06 for WTTS. Given a similar L distribution of both samples, the X-ray luminosity function also reflects a real X-ray deficiency in CTTS, by a factor of 2 compared to WTTS. The average electron temperatures Tav are correlated with LX in WTTS but not in CTTS; CTTS sources are on average hotter than WTTS sources. At best marginal dependencies are found between X-ray properties and mass accretion rates or age. Conclusions. The most fundamental properties are the two saturation laws, indicating suppressed LX for CTTS. We speculate that some of the accreting material in CTTS is cooling active regions to temperatures that may not significantly emit in the X-ray band, and if they do, high-resolution spectroscopy may be required to identify lines formed in such plasma, while CCD cameras do not detect these components. The similarity of the LX vs. Tav dependencies in WTTS and main-sequence stars as well as their similar X-ray saturation laws suggests similar physical processes for the hot plasma, i.e., heating and radiation of a magnetic corona.

Baseline high‐latitude ionospheric parameters and field‐aligned ion motion

Establishing baseline values for ionospheric parameters allows for the identification of special events and comparison of events that occur at different magnetic local times, seasons, or solar cycle phases. Variations in average electron densities, ion and electron temperatures, and ion velocities between 100 and 800 km altitude are determined from Svalbard and Sondrestrom radar data. Despite their similar geomagnetic latitudes, Svalbard and Sondrestrom are found to measure significantly different populations. The average ion flux and ion, electron and plasma pressures can be calculated from the measured quantities. The primary location for upward moving ions is the dayside noon region, where the cusp can be expected. The role of plasma pressure is discussed.

Electron Heating of LHCD Plasma in HT-7 Tokamak

Electron heating via lower hybrid current drive (LHCD) has been investigated in HT-7 superconducting tokamak. Experiments show that the central electron temperature Te0, the volume averaged electron temperature <Te> and the peaking factor of the electron temperature QTe = Te0/<Te> increase with the lower hybrid wave (LHW) power. Simultaneously the electron heating efficiency and the electron temperature as the function of the central line-averaged electron density (ne) and the plasma current (Ip) have also been investigated. The experimental results are in a good agreement with those of the classical collision theory and the LHW power deposition theory.

Influence of doping density on electron dynamics in GaAs∕AlGaAs quantum cascade lasers

A detailed theoretical and experimental study of the influence of injector doping on the output characteristics and electron heating in midinfrared GaAs∕AlGaAs quantum cascade lasers is presented. The employed theoretical model of electron transport was based on a fully nonequilibrium self-consistent Schrödinger-Poisson analysis of the scattering rate and energy balance equations. Three different devices with injector sheet doping densities in the range of (4–6.5)×1011cm–2 have been grown and experimentally characterized. Optimized arsenic fluxes were used for the growth, resulting in high-quality layers with smooth surfaces and low defect densities. A quasilinear increase of the threshold current with sheet injector doping has been observed both theoretically and experimentally. The experimental and calculated current-voltage characteristics are in a very good agreement. A decrease of the calculated coupling constant of average electron temperature versus the pumping current with doping level was found.

Hard X-ray generation from solids driven by relativistic intensity in the lambda-cubed regime

Interaction of relativistic intensity laser pulses encompassed at focus by a volume of a few wavelengths cubed with solids is examined. Spectroscopy of hard X-rays of several metallic targets, including Cu, Ge, Mo, Ag, and Sn, irradiated in this regime at a high repetition rate (0.4 kHz), has been experimentally studied. The Kα and Kβ peaks of all targets were obtained. Averaged electron temperatures of several tens of keV and total X-ray conversion efficiencies up to 0.02% are calculated. The X-ray source size is measured to be ∼10 micron with varying elliptical shape.

Spectral study of the object HH12

Spectral studies of one of the brightest Herbig-Haro objects, HH12, using a multiaperture (multi-pupil) spectrograph are reported. We identify nine knots (densification nodes) in intensity diagrams. Hα emission mainly predominates in this object, except in two of the knots (C and M) which have a lower excitation level, given their high [SII] line intensity. The average electron temperature across the object is 6700 K. It is shown that the radial velocity of the object as a whole is low, i.e., its motion is mostly in the celestial plane. The excitation source for HH12 is also discussed.

Plasma diagnostics of active-region evolution and implications for coronal heating

A detailed study is presented of the decaying solar active region NOAA 10103 observed with the Coronal Diagnostic Spectrometer (CDS), the Michelson Doppler Imager (MDI) and the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). Electron density maps formed using Si X (356.03A/347.41A) show that the density varies from ~10^10 cm^-3 in the active region core, to ~7x10^8 cm^-3 at the region boundaries. Over the five days of observations, the average electron density fell by ~30%. Temperature maps formed using Fe XVI(335.41A)/Fe XIV(334.18A) show electron temperatures of \~2.34x10^6 K in the active region core, and ~2.10x10^6 K at the region boundaries. Similarly to the electron density, there was a small decrease in the average electron temperature over the five day period. The radiative, conductive, and mass flow losses were calculated and used to determine the resultant heating rate (P_H). Radiative losses were found to dominate the active region cooling process. As the region decayed, the heating rate decreased by almost a factor of five between the first and last day of observations. The heating rate was then compared to the total unsigned magnetic flux (Phi_tot), yielding a power-law of the form P_H ~ Phi_tot^(0.81 +/- 0.32). This result suggests that waves rather than nanoflares may be the dominant heating mechanism in this active region.

Formation of micromodifications in a KDP crystal irradiated by tightly focused femtosecond visible laser pulses

The formation of micromodifications in the bulk of a KDP crystal irradiated by tightly focused 600-nm, 100-fs and 200-fs, 0.02–10 μJ femtosecond laser pulses is studied. A theoretical model describing the initial stage of formation of a plasma channel taking into account field ionisation and heating of the electron component of the plasma is proposed. The laser pulse intensity (1013 W cm-2), the electron concentration (1020 cm-3) and the average electron temperature (5 eV) in the plasma channel are estimated.

Experimental Characterization of a Strongly Coupled Solid Density Plasma Generated in a Short‐pulse Laser Target Interaction

AbstractWe have measured high resolution copper Kα spectra from a picosecond high intensity laser produced plasma. By fitting the shape of the experimental spectra with a self‐consistent‐field model which includes all the relevant line shifts from multiply ionized atoms, we are able to infer time and spatially averaged electron temperatures (Te) and ionization state (Z) in the foil. Our results show increasing values for Te and Z when the overall mass of the target is reduced. In particular, we measure temperatures in excess of 200 eV with Z ∼ 13‐14. For these conditions the ion‐ion coupling constant is Γii ∼ 8‐9, thus suggesting the achievement of a strongly coupled plasma regime. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A physical model of quantum cascade lasers: Application to GaAs, GaN and SiGe devices

AbstractThe philosophy behind this work has been to build a predictive “bottom up” physical model of quantum cascade lasers (QCLs) for use as a design tool, to interpret experimental results and hence improve understanding of the physical processes occurring inside working devices and as a simulator for developing new material systems. The standard model uses the envelope function and effective mass approximations to solve two complete periods of the QCL under an applied bias. Other models, such as k·p and empirical pseudopotential, have been employed in p‐type systems where the more complex band structure requires it. The resulting wave functions are then used to evaluate all relevant carrier–phonon, carrier–carrier and alloy scattering rates from each quantised state to all others within the same and the neighbouring period. This information is then used to construct a rate equation for the equilibrium carrier density in each subband and this set of coupled rate equations are solved self‐consistently to obtain the carrier density in each eigenstate. The latter is a fundamental description of the device and can be used to calculate the current density and gain as a function of the applied bias and temperature, which in turn yields the threshold current and expected temperature dependence of the device characteristics. A recent extension which includes a further iteration of an energy balance equation also yields the average electron (or hole) temperature over the subbands. This paper will review the method and describe its application to mid‐infrared and terahertz, GaAs, GaN, SiGe cascade laser designs. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Characterization of SiCl4 / N 2 Plasmas

Optical emission spectroscopy, quadrupole mass spectrometry, and microwave phase measurements of electron density were used to study the characteristics of plasmas and their resulting etch processes. The addition of to plasmas enhanced the etch rate of GaAs from 1000 Å/min in pure to 2300 Å/min in a 40:60 mixture (15 mTorr, 10 sccm). The optical emission intensities of atomic and molecular chlorine remained nearly constant with increasing percentage (up to 20% but an argon actinometer exhibited a large increase in optical emission intensity with addition, indicating a shift in the electron density distribution function. Electron density measurements showed negligible difference between the average electron densities of pure and 60% in plasmas except at high power. Mass spectrometric results showed an increase in dissociation and a subsequent increase in production with the addition of nitrogen, accounting for the increase in etch rate. The enhanced dissociation is believed to be due in part to an increase in the average electron temperature. © 2005 The Electrochemical Society. All rights reserved.

Enhancement in electron and ion temperatures due to solar flares as measured by SROSS-C2 satellite

Abstract. The observations on the ionospheric electron and ion temperatures (Te and Ti) measured by the RPA payload aboard the SROSS-C2 satellite have been used to study the effect of solar flares on ionospheric heating. The data on solar flare has been obtained from the National Geophysical Data Center (NGDC) Boulder, Colorado (USA). It has been found that the electron and ion temperatures have a consistent enhancement during the solar flares on the dayside Earth's ionosphere. The estimated enhancement for the average electron temperature is from 1.3 to 1.9 times whereas for ion temperature it is from 1.2 to 1.4 times to the normal days average temperature. The enhancement of ionospheric temperatures due to solar flares is correlated with the diurnal variation of normal days' ionospheric temperatures. The solar flare does not have any significant effect on the nightside ionosphere. A comparison with the temperature obtained from the IRI-95 model also shows a similar enhancement.

Plasmasphere electron temperature model based on Akebono data

Average electron temperature ( T e) distribution in altitude range 1000–10,000 km and in geomagnetic latitude range ± 70° are used to construct a simple analytical model of T e. T e distribution is considered constant during daytime (9–16 h) and nighttime (22–04 h) local time sectors. Transition between the constant thermal states is described by cubic splines. The vertical T e profiles at fixed geomagnetic latitudes are approximated by second order polynomials and then the three constants of these polynomials are approximated by another set of analytical expressions, being explicit functions of altitude, geomagnetic latitude and local time. No seasonal variation or hemispheric asymmetry is considered in the model. The average T e distributions at L shells greater than three were reconstructed, in order to avoid the unrealistically high temperatures measured in the regions with low plasma density. For this purpose, T e distributions above 3000 km along the L shells were calculated, taking the gradients obtained at L=2 (0.3 K/km during the day and 0.1 K/km during the night), reduced with latitudes as 1/( L−1). The accuracy and limitations of the model are discussed.

The electron temperature and density in interstellar medium by using carbon radio recombination line observations

The intensities of carbon radio recombination lines (RRL’s) are definedallowing for the effect of dielectronic-like recombination. The rate ofdielectronic-like recombination is calculated as functions of line number,electron density and temperature accurate to 0.05. Following from the balanceequation solutions for populations, the RRL intensities are analytically foundby the method of successive approximations to an accuracy of 0.15. Theobservations of carbon RRL’s are analyzed toward Cassiopeia A. The averageelectron temperature, density, expanded CII region lengths and inaccuraciesare found with the experimental values of RRL widths and intensities.

Implosion compression characteristic of direct-driven ablation target with 1.06μm laser

This paper describes the diagnostic techniques and experimental methods used for investigating the properties of implosion compression in direct drive . Several diagnostic techniques with fine time, space and spectrum resolution are employed to obtain the information concerning implosion, such as radiation un iformity on the capsule, compression symmetry, volume compression ratio, implosi on time, implosion velocity and average electron temperature of the capsule shell. Some of the typical results measured in the experiments are presented and as imple discussion is also given.

Enhancement in ionospheric temperatures during thunderstorms

It has been realized in recent years that the ionospheric temperatures and ion densities are influenced by the lightning activity. The ionospheric temperature (electron and ion temperature) were measured by the retarded potential analyzer payload aboard the Indian SROSS-C2 satellite. The data at low latitudes falling in the Indian subcontinent in the height range of 425– 625 km for the period 1995–1998 were used for this study. The data on thunderstorm activity for the same period were obtained from India Meteorological Department. To see the effect of active thunderstorm the ionospheric electron and ion temperatures have been compared to the values on normal days. It has been found that the average electron temperature is enhanced during thunderstorm activity by 1.2–1.7 times over the normal days. A similar enhancement has been found in ion temperature by 1.1–1.5 times. It is suspected that the ULF to VLF radiations generated during lightning and sprites from thunderstorm (Geophys. Res. Lett. 18 (1991) 705; 23 (1996) 1067) may cause of the enhancement in electron and ion temperatures.

Active control of instabilities for plasma processing with electronegative gases

Feedback stabilization of instabilities was demonstrated in inductively coupled electronegative plasmas by modulating the radio frequency power in response to a feedback control signal. Two modes were observed and stabilized: a fast bursting mode (designated ‘B’ mode) and a slower oscillatory mode (designated ‘O’ mode). ‘B’ mode is a low duty-cycle non-linear phenomenon characterized by short (<1 µs) spikes on optical signals, at a pulse repetition rate of 10–40 kHz. ‘O’ mode is characterized by continuous oscillations in ion saturation current at lower frequency (200 Hz–1 kHz). Some parameter ranges exhibit both modes. Fluctuations in similar processing plasmas and having similar characteristics have previously been observed and identified with instability due to electron attachment to the electronegative neutral gas species.Because ‘O’ mode exhibits fluctuations in ion density, it may be of more concern than ‘B’ mode for repeatable plasma processing. Stabilization of ‘O’ mode may be accomplished using the ion saturation current signal collected by a Langmuir probe as a measure of the plasma density. The floating potential obtained from the capacitively coupled plasma bias electrode is similar in shape to the ion saturation current, and can also be used as the feedback control signal.The bandwidth required for stabilizing the ‘O’ mode is in the kHz range, whereas the bandwidth required to stabilize ‘B’ mode may be closer to a MHz. In practice, it is far easier to stabilize the ‘O’ mode than the ‘B’ mode, but both may be effectively suppressed. However, since a purely ‘B’ mode does not seem to measurably modulate the ion density, and unless it dramatically changes the average electron temperature it may not be necessary to stabilize it in order to achieve repeatable plasma processing.