Energy Distribution Of Thermal Electrons Research Articles

Inner-shell radiation from wire array implosions on the Zebra generator

Implosions of brass wire arrays on Zebra have produced L-shell radiation as well as inner-shell Kα and Kβ transitions. The L-shell radiation comes from ionization stages around the Ne-like charge state that is largely populated by a thermal electron energy distribution function, while the K-shell photons are a result of high-energy electrons ionizing or exciting an inner-shell (1s) electron from ionization stages around Ne-like. The K- and L-shell radiations were captured using two time-gated and two axially resolved time-integrated spectrometers. The electron beam was measured using a Faraday cup. A multi-zone non-local thermodynamic equilibrium pinch model with radiation transport is used to model the x-ray emission from experiments for the purpose of obtaining plasma conditions. These plasma conditions are used to discuss some properties of the electron beam generated by runaway electrons. A simple model for runaway electrons is examined to produce the Kα radiation, but it is found to be insufficient.

Possible interaction between thermal electrons and vibrationally excited N<sub>2</sub> in the lower E-region

Abstract. As one of the tasks to find the energy source(s) of thermal electrons, which elevate(s) electron temperature higher than neutral temperature in the lower ionosphere E-region, energy distribution function of thermal electron was measured with a sounding rocket at the heights of 93–131 km by the applying second harmonic method. The energy distribution function showed a clear hump at the energy of ~0.4 eV. In order to find the reason of the hump, we conducted laboratory experiment. We studied difference of the energy distribution functions of electrons in thermal energy range, which were measured with and without EUV radiation to plasma of N2/Ar and N2/O2 gas mixture respectively. For N2/Ar gas mixture plasma, the hump is not clearly identified in the energy distribution of thermal electrons. On the other hand for N2/O2 gas mixture, which contains vibrationally excited N2, a clear hump is found when irradiated by EUV. The laboratory experiment seems to suggest that the hump is produced as a result of interaction between vibrationally excited N2 and thermal electrons, and this interaction is the most probable heating source for the electrons of thermal energy range in the lower E-region. It is also suggested that energy distribution of the electrons in high energy part may not be Maxwellian, and DC probe measures the electrons which are non Maxwellian, and therefore "electron temperature" is calculated higher.

Integral cross sections for electron impact excitation of the 1Σ+u and 1Πu electronic states in CO2

We apply the method of Kim (2007 J. Chem. Phys. 126 064305) in order to derive integral cross sections for the 1Σ+u and 1Πu states of CO2, from our corresponding earlier differential cross section measurements (Green et al 2002 J. Phys. B: At. Mol. Opt. Phys. 35 567). The energy range of this work is 20–200 eV. In addition, the BEf-scaling approach is used to calculate integral cross sections for these same states, from their respective thresholds to 5000 eV. In general, good agreement is found between the experimental integral cross sections and those calculated within the BEf-scaling paradigm, over the entire common energy range. Finally, we employ our calculated integral cross sections to determine the electron energy transfer rates for these states, for a thermal electron energy distribution. Such transfer rates are in principle important for understanding the phenomena in atmospheres where CO2 is a dominant constituent, such as on Mars and Venus.

Time-dependent spectrum of thermionic emission from hot C60

Experimental measurements of time-dependent photoelectron spectra observed in thermionic emission of hot C60 excited by multiphoton absorption are presented. Time resolved velocity-map imaging is used to record photoelectron spectra and to disentangle direct and delayed processes. The evolution of the kinetic energy distribution of thermal electrons as a function of the delay after multiphoton excitation is described within the general formalism of the detailed balance theory. Experimental spectra obtained in the near-UV are in excellent agreement with the assumption of thermal equilibrium.

Time-dependent spectrum of thermionic emission from hot clusters: Model and example ofC60

We have studied the evolution of the kinetic energy distribution of thermal electrons emitted from energy-rich clusters as a function of the delay after multiphoton excitation. In this paper we emphasize the description of thermionic emission based on the general formalism of the detailed balance theory. Our description accounts for competing decay channels and underlines the fundamental role of the observation time window. Simulations including two decay channels (namely, delayed electron emission and loss of ${\mathrm{C}}_{2}$ fragments) are compared with experimental results in the case of hot fullerenes ${\mathrm{C}}_{60}$. The most striking result of the model is the close connection between the effective temperature of the electron distribution and the time delay of observation. Our model is in very good agreement with our experimental measurements of time-dependent photoelectron spectra.

VLBA Imaging of Quiescent Radio Emission from UX Arietis

Using the Very Long Baseline Array (VLBA) and the Very Large Array (VLA), we have observed the quiescent coronal microwave emission from the active RS CVn system UX Ari. We complement the data with X-ray information obtained from the X-ray satellite ASCA. The 8.4 GHz continuum radio source is resolved on linear scales comparable to the projected separation of the binary components, indicating the existence of large magnetic structures. Circular polarization is detected, and a polarization gradient across the radio source is observed, suggesting the existence of interacting magnetic fields between the components or a large magnetic loop anchored to one component. The VLBA lower limit to the brightness temperature (~26 MK) is close to the broad temperature peak in the contemporaneous emission measure distribution seen by ASCA; we examine the possibility that the quiescent radio flux may be gyrosynchrotron emission from a thermal electron energy distribution. We find that no simple thermal model can reproduce the observed spectral index of the quiescent emission.

High altitude observations of electron temperature and a possible north–south asymmetry

Measurements of electron temperature made by the thermal electron energy distribution (TED) instrument on board the EXOS-D (Akebono) satellite have been analysed. From the data taken between 1989 and 1995, averaged daytime and nighttime temperature profiles for different geophysical conditions have been produced. These profiles represent the averaged thermal electron temperature between 1000 and 8000 km altitude for conditions of high (F10.7>150) and low (F10.7<120) solar activity. Results indicate that increased solar activity has a marked effect on the electron temperature. At 8000 km altitude, the typical low-latitude daytime electron temperature is around 8000 K. The nighttime electron temperature at 8000 km is around 4000 K. The averaged daytime difference between high and low solar activity conditions is around 1000 K at altitudes above 2500 km. Between 1000 and 2000 km altitude this situation is reversed, and the electron temperature is comparatively higher during periods of low solar activity during both day and night. Composition changes in the region are proposed as a mechanism for this reversal. In addition, there is evidence of an asymmetry in thermal electron temperature between the northern and southern hemispheres. The averaged electron temperature is found to be comparatively higher in the northern hemisphere during the daytime and comparatively higher in the southern hemisphere during the nighttime. This difference between hemispheres is particularly evident during the nighttime, and during the rapid heating and cooling periods around sunrise and sunset. Possible reasons for the asymmetry are discussed. Profiles are also presented for conditions of high (Ap>30) and low (Ap<20) magnetic activity. Analysis has confirmed that geomagnetic activity has little effect on electron temperature below L=2.2.

Investigation of lower hybrid wave damping in the PBX-M tokamak

Lower hybrid (LH) current drive experiments on the Princeton Beta Experiment-Modified (PBX-M) [Phys. Fluids B 2, 1271 (1990)] have shown that the current profile can be changed by varying the phase velocity of the waves. The radial profile of the current carrying electrons was deduced from two-dimensional hard x-ray tomography. For a certain range of phase velocities, there is a correlation between the peak of the fast electron profile and the launched wave spectrum, despite the presence of a wide spectral gap between the phase velocity and the thermal electron energy distribution. A new model is proposed to explain how first-pass wave damping is possible in such plasmas. The rf power can form a tail of energetic electrons, and subsequently waves with moderate phase velocity can damp on them. For waves with very fast phase velocity, there must be an upshift of the n∥ spectrum for any damping to occur. These hypotheses are supported by ray tracing results which are coupled to relativistic Fokker–Planck calculations of the electron distribution function.

Plasmasphere electron temperature profiles and the effects of photoelectron trapping and an equatorial high‐altitude heat source

The electron temperature Te in the Earth's plasmasphere up to 10,000 km altitude, has been measured routinely by a thermal electron energy distribution instrument on board the EXOS D satellite. The measurements made during the years 1989–1995 have been analyzed to obtain altitude (1000–8000 km) profiles of Te for magnetic latitudes 0°–40°N at different times of the day. The profiles are compared with those computed by the Sheffield University plasmasphere‐ionosphere model, modified to include nonlocal heating due to trapped photoelectrons and an equatorial high‐altitude heat source. The photoelectrons are trapped at altitudes above 600 km, and the high‐altitude heat source is applied as energy input along the magnetic field lines with apex altitude greater than 600 km between ±10° magnetic latitude. The results for 8000 km altitude show that the modeled values of Te computed without photoelectron trapping and the high‐altitude heat source are much less than the mean measured values, 3700 K compared with 6500 K. Depending upon altitude and latitude, a photoelectron trapping of up to 100% is required to raise the modeled electron temperatures to the mean measured values. However, photoelectron trapping alone cannot account for the observed latitude variation of Te, which depends on altitude. Model calculations carried out with 50% photoelectron trapping and an altitude and local time‐dependent high‐altitude heat source reproduce the measurements, including the latitude variation; the heat source required for nighttime is about one fourth of that required for daytime. An equatorial high‐altitude heat source appears to be the only mechanism that can account for the measured values of Te; values in excess of 12,000 K have been measured. There are some quantitative differences between the measured and modeled temperatures at night in the lower plasmasphere (&lt;2500 km), which could be caused, in whole or in part, by the inaccuracies of the nighttime measurements due to the low plasma densities.

SCIFER‐Cleft region thermal electron distribution functions

Differential directional ionospheric electron measurements at energies from &lt;1 to 60 eV have been obtained in the Earth's geomagnetic cleft ionosphere on NASA's Sounding of the Cleft Region Ion Fountain Energization Region (SCIFER) rocket. We introduce the electron data set, present electron temperature measurements, and show examples of phase space distributions measured near and in the cleft ionosphere. Topside electron temperatures ranged from near 0.15 eV south of the high energy electron trapping boundary to near 1 eV within precipitation regions in the auroral cleft. Field‐aligned electron bursts extend down to thermal energies and merge with the core, yielding core heating and anisotropy in the derived electron temperature. One interval is identified where enhanced electron temperature is collocated with a deep density depletion, low frequency electrostatic waves, and transverse ion heating, consistent with operation of the current‐driven ion cyclotron instability. On the downleg, in what may be polar cap, the shape of the thermal electron energy distribution was observed to be quite uniform, with temperatures near 0.25 eV.

Characteristic features of electron temperature and density variations in field‐aligned current regions

Observations by the thermal electron energy distribution (TED) instrument on board the Akebono (EXOS ‐ D) satellite show that variations in electron temperatures, at altitudes from 300 to 2300 km, are closely related to field‐aligned current (FAC) structures. At higher altitudes, electron temperatures increase in upward FAC regions and decrease in regions of downward FAC, while at the lower altitudes only temperature increases in upward FAC and adjacent regions are observed. Electron temperature variations were also found to be related to the number density of ambient electrons and the field‐aligned current density. A numerical simulation is carried out to examine energetic particle precipitation and Joule dissipation as a possible mechanism for the observed temperature variations using the electron energy equation. In the present study, we focus the simulations on the temperature increase. Thermal electrons are found to be efficiently heated by Joule dissipation at lower altitudes; however, for increasing altitudes, energetic particle precipitation becomes the major heating source. These conclusions are supported by TED observations at low altitudes (&lt;500 km); however, an additional heat source is required to explain the observed higher‐altitude (&gt;800 km) temperature increases.

Variations of thermal electron energy distribution associated with field‐aligned currents

Relationships between thermal electrons and field aligned currents (FACs) in the auroral region have been investigated using data simultaneously obtained from the Thermal Electron Detector (TED) and the fluxgate magnetometer both onboard the EXOS‐D satellite. Several features resulted from the observations are summarized as; (1) At altitudes from 300 to 1800km, electron temperature in the upward FAC region is higher than that of the neighboring no FAC region by the increment ΔT=1100∼9500K, while the temperature is lower in the downward FAC region by the decrement −ΔT=500∼1500K. (2) The electron temperature increase in the upward‐current region grows with an increase of the FAC density. (3) The thermal electrons do not have Maxwell distribution in the upward‐current region at altitudes higher than about 2000km.

Hydrodynamic equations in 16-moment approximation allowing for interactions of thermal electrons with ion-cyclotron waves in the earth's outer plasmasphere

The 16-moment approximation is used to obtain a closed set of anisotropic hydrodynamic equations to describe thermal electrons making allowance for the effects of their Cerenkov resonance interactions with the ion-cyclotron (IC) waves generated in the outer plasmasphere. The moments of quasilinear integral have been found which define the variations of the electron component parameters due to collisionless wave attenuation. The source which heats the thermal electrons is calculated for the characteristic conditions of the outer plasmasphere and for the measured parameters of IC-wave spectra. The dependences of the source on plasma concentration, temperature, and anisotropy are analysed. The heating source intensity is shown to decrease with increasing anisotropy parameter μ = T ∥ T ⊥ because the effectiveness of electron—wave interactions decreases due to a decrease in the number of resonance particles. The thermal source is found to exhibit an effect of self-control by the temperature anisotropy produced by the source. The electron temperature anisotropy produced by IC-wave absorption is calculated and its dependence on plasma parameters is studied. The effectiveness of the IC-source of the anisotropy is compared with other mechanisms resulting in an anisotropy of the thermal electron energy distribution in the examined plasmaspheric region.

Observation of the energy distribution of thermal electrons in the midlatitude ionosphere

Results of measurements of the energy distribution of thermal electrons below 1 eV in a midlatitude upper atmosphere are presented and compared with some recent measurements at other places. Measurements are based on the Druyvesteyn method using Langmuir probes. In the periods without solar light, distribution does not depart much from Maxwellian above 0.3 eV. Below 0.2 eV, depletion and sometimes double humps are seen. In the periods with solar light, bumps are sometimes observed on the high energy tail at altitudes between 100 and 160 km. Energy distribution in the F layer above 180 km fits the Maxwellian distribution rather well. The reason for the appearance of such non-thermal electrons at lower altitudes may be due to super-elastic collisions with vibrationally excited nitrogens.

Non‐Maxwellian Characteristics of the Energy Distribution of Thermal Electrons in the Upper Atmosphere

AbstractThe Result of Measurements of the energy distribution of thermal electrons in a midlatitude ionosphere is presented. A comparison is made in particular between the characteristics at sunrise and sunset periods because of the effect of vibrationally excited nitrogen molecules.At sunrise the distribution has a little‐irregularity but the middle and higher energy parts (0.2‐0.5 eV) deviate from the Maxwellian distribution only slightly at all heights. The electron temperature varies from 900 K to 1300 K between 130 km and 300 km. These values are higher than the kinetic temperature of neutral particles but comparable with the theoretical values of the vibration temperature of N2.At sunset small bumps due to non‐thermal electrons are seen on the high energy tail between 108 and 160 km, their density being from 5 × 10−3 to 1 × 10−2 of that one of the thermal electrons. Above 170 km (F‐layer) the deviation of the distribution from the Maxwellian one becomes smaller. The electron temperature varies from 500 K to 900 K between 100 km and 220 km. These values are higher than the kinetic temperature but lower than the theoretical values of the vibration temperature of N2. A mechanism of the appearance of non‐thermal electrons is considered to be due to super‐elastic collisions with vibrationally excited N2.

Energy distribution of thermal electrons at the height oflower- E-region

Energy distributions of thermal electrons (0.2 – 1 eV) were measured in the lower E region from the height of 90 Km. The distributions of the electrons started deviating from Maxwellian distributions at the height of ∼104 Km. The distortion becomes most intense at the height of 107 Km and the electron population apparently consists of two groups at different electron temperatures in addition to excess high energy tail. The distortion almost vanished at the height of ∼130 Km, again increased at ∼150 Km and finally faded out at the height of ∼210 Km. We suggest that both high electron temperature and excess high energy tail are locally generated by some ionospheric-current related mechanism.

Distortions of the energy distribution of ionospheric thermal electrons near the focus of Sq current vortex

Energy distributions of the thermal electrons in the ionospheric plasma were measured on 16 January 1974 and 16 September 1976 by two Japanese rockets, K-9M-45 and K-9M-55 respectively near the focus of S q current vortex. The main effort was to investigate the energy state of the thermal electrons in a localized hot electron layer which occurs at a height of around 105 km in winter. The results obtained on 16 January 1974 showed that the thermal electrons in the hot electron layer had not a pure Maxwell distribution. While on 16 September 1976, the energy distribution of the electrons was found to be almost Maxwellian in the dynamo region as well as the F-region.

Evidences of a distorted electron energy distribution in ionospheric plasma

The energy distribution of thermal electrons in the ionospheric plasma was measured by means of a glass-sealed Langmuir probe. Second derivatives of the v- i curves were obtained electrically by using the second harmonic method. The height of the measurement was from 103 to 360 km. Above 130 km the energy distribution of thermal electrons were Maxwellian enough to evaluate electron temperature. Below 130 km the electrons appeared to consist of two groups of electrons of different temperatures. Because of the bi-Maxwellian energy distribution, the apparent electron temperature obtained from the above method differed from that of an electron temperature probe.

Application of a glass-sealed Langmuir probe to ionosphere study

A glass-sealed Langmuir probe was developed to get accurate information on the ionospheric plasma. An electrode sealed in a glass tube is first baked in low pressure and tipped off the pumping system to keep the electrode surface clean. An essential advantage of the glass-sealed Langmuir probe is that it will not require the rapid sweeping of a probe voltage for reliable data acquisition. It is noted that the glass-sealed Langmuir probe is strongly recommended for the measurement of energy distribution of thermal electrons by the second harmonic method.

Thermal electron energy distribution measurements in the ionosphere

Results of electron spectrometer and cylindrical Langmuir probe measurements of ionospheric electron energy distribution in the range from about 0·2 eV to 4·0 eV are presented and discussed in this paper.