Presence Of High-energy Electrons Research Articles

Influence of high energy electrons on negative ion density in a hot cathode discharge

This study investigates the influence of high energy electrons on the negative ion density along with the effect of filament current, discharge voltage, pressure, and magnetic filter field strength by carrying out measurements of negative ion density in a hot cathode discharge system in the double plasma device using a Langmuir probe technique. In the volume production technique, negative ions are formed by the dissociative attachment of low energy electrons to metastable hydrogen molecules and among the negative ion loss mechanisms; the presence of high energy electrons in the plasma is one of the important factors. Although the magnetic filter could reduce the temperature of the electrons in the target region considerably, high energy electrons were still present in the diffusion region, which could reduce the negative ion density. Negative hydrogen ion density measured by using Langmuir probe in the target region is also compared with the particle balance model considering the set of reactions involved in the production and destruction of negative ions, and a reasonably good match between them has been observed.

Low‐dose liquid cell electron microscopy investigation of the complex etching mechanism of rod‐shaped silica colloids

AbstractUnderstanding the chemical structure of rod‐shaped silica colloidal particles is attainable by investigating their etching mechanism in solution. Liquid Cell (Scanning) Transmission Electron Microscopy (LC‐(S)TEM) is a promising technique through which the etching of these particles can be observed in real time, and at the single particle level, without possible deformations induced by the surface tension of dried particles. However, the presence of high energy electrons, and the different geometry in LC experiments may alter the conditions of in situ experiments compared to their ex situ counterparts. Here we present a controlled low‐dose LC‐STEM study of the basic etching process of micron‐sized silica rods that are immobilized on the SiN window of a liquid cell. The results show that using low‐dose imaging conditions, combined with a low accumulated electron dose, and optimized flow rates of solutions allow for investigation of the chemical etching mechanism of silica colloidal particles using the LC‐(S)TEM technique with negligible effects of the electron beam. A comparison of ex situ etching experiments with LC‐STEM observations show that the LC geometry can play a crucial role in LC‐STEM experiments where the diffusion of the etching particles is important, which should be considered during the interpretations of LC‐STEM results.

Nonequilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind (Invited Review)

We review the presence and signatures of the non-equilibrium processes, both non-Maxwellian distributions and non-equilibrium ionization, in the solar transition region, corona, solar wind, and flares. Basic properties of the non-Maxwellian distributions are described together with their influence on the heat flux as well as on the rates of individual collisional processes and the resulting optically thin synthetic spectra. Constraints on the presence of high-energy electrons from observations are reviewed, including positive detection of non-Maxwellian distributions in the solar corona, transition region, flares, and wind. Occurrence of non-equilibrium ionization is reviewed as well, especially in connection to hydrodynamic and generalized collisional-radiative modelling. Predicted spectroscopic signatures of non-equilibrium ionization depending on the assumed plasma conditions are summarized. Finally, we discuss the future remote-sensing instrumentation that can be used for detection of these non-equilibrium phenomena in various spectral ranges.

Electron kinetic energy and plasma emission diagnosis from femtosecond laser produced air plasmas

The characteristics of a plasma formed by a focused ultrashort laser in atmospheric-pressure air are studied with linear and circular pulses. We show that the ionization threshold for circular pulses is 1.36 times higher than for that linear pulses. Using an intensified CCD camera, we study plasma emission over seven orders of magnitude in a dynamic range. In spite of possessing a lower total ion number, plasmas produced by circular pulses are found to be brighter visible-light emitters than those produced by linear pulses of the same energy. This indicates that circular pulses produce plasmas with more electron kinetic energy than linear pulses and that kinetic energy plays a role in the optical emission intensity. The presence of high energy electrons is verified by demonstrating that a high-ionization-potential gas can be made to radiate more brightly by the addition of a low-ionization-potential gas even though the second gas lowers the achievable focal intensity.

Statistical Analysis of Reducing Biochemical Oxygen Demand (BOD) on Industrial Rubber Wastewater using Dielectric Barrier Discharge Plasma

Dielectric Barrier Discharge plasma (DBD) is one of type non-thermal plasma (non-equilibrium plasma) or can be referred to as cold plasma. In this research, DBD plasma be utilized to reduce organic compounds like Biochemichal oxygen demand in the wastewater rubber processing. In the environment field DBD plasma has been used as a treatment for reducing air pollutants such as gas COx, NOx and HC. In addition DBD plasma have been developed to processed wastewater as an alternative technology in wastewater treatment. DBD plasma appears when the electrode is given a high voltage so that, it will form electric field in the area of the electrodes which allows the ionization and the presence of high-energy electrons in the area. The presence of these electrons will ionize molecules of H2O into active species such as OH•, H• and H2O2. The active species that can oxidize into CO2 and H2O so, BOD that can be degraded. In this research for wastewater treatment used high voltage are 10kV, 11kV, 12kV and 13kV and variations of processing time for 5, 10, 15, 20, and 25 (minutes). By increasing the voltage and extend the contact time then the speed variation of electrons to ionize the greater and more active species to be formed to degrade the pollutants to the maximum. This research used quantitative analysis with statistical analysis using SPSS software.

Statistical Analysis of Reducing Biochemical Oxygen Demand (BOD) on Industrial Rubber Wastewater Using Dielectric Barrier Discharge Plasma

Dielectric Barrier Discharge plasma (DBD) is one of type non-thermal plasma (non-equilibrium plasma) or can be referred to as cold plasma. In this research, DBD plasma be utilized to reduce organic compounds like Biochemichal oxygen demand in the wastewater rubber processing. In the environment field DBD plasma has been used as a treatment for reducing air pollutants such as gas COx, NOx and HC. In addition DBD plasma have been developed to processed wastewater as an alternative technology in wastewater treatment. DBD plasma appears when the electrode is given a high voltage so that, it will form electric field in the area of the electrodes which allows the ionization and the presence of high-energy electrons in the area. The presence of these electrons will ionize molecules of H2O into active species such as OH•, H• and H2O2. The active species that can oxidize into CO2 and H2O so, BOD that can be degraded. In this research for wastewater treatment used high voltage are 10kV, 11kV, 12kV and 13kV and variations of processing time for 5, 10, 15, 20, and 25 (minutes). By increasing the voltage and extend the contact time then the speed variation of electrons to ionize the greater and more active species to be formed to degrade the pollutants to the maximum. This research used quantitative analysis with statistical analysis using SPSS software.

SEPARATION OF TWO CONTRIBUTIONS TO THE HIGH ENERGY EMISSION OF CYGNUS X-1: POLARIZATION MEASUREMENTS WITHINTEGRALSPI

Operational since 2002 on-board the INTEGRAL observatory, the SPI spectrometer can be used to perform polarization measurements in the hard X-ray/soft gamma-ray domain (~ 130 keV - 8 MeV). However, this phenomenon is complex to measure at high energy and requires high fluxes. Cyg X-1 appears as the best candidate amongst the X-ray binaries since it is one of the brightest persistent sources in this energy domain. Furthermore, a polarized component has recently been reported above 400 keV from IBIS data. We have therefore dedicated our efforts to develop the required tools to study the polarization in the INTEGRAL SPI data and have first applied them to 2.6 Ms of Cyg X-1 observations, covering 6.5 years of the INTEGRAL mission. We have found that the high energy emission of Cyg X-1 is indeed polarized, with a mean polarization fraction of 76 % +/- 15 % at a position angle estimated to 42 +/- 3 degrees, for energies above 230 keV. The polarization fraction clearly increases with energy. In the 130-230 keV band, the polarization fraction is lower than 20 %, but exceeds 75 % between 370 and 850 keV, with the (total) emission vanishing above this energy. This result strongly suggests that the emission originates from the jet structure known to emit in the radio domain. The same synchrotron process could be responsible for the emission from radio to MeV, implying the presence of high energy electrons. This illustrates why the polarization of the high energy emission in compact objects is an increasingly important observational objective.

Influence of high energy electrons on ECRH in LHD

The central bulk electron temperature of more than 20 keV is achieved in LHD as a result of increasing the injection power and the lowering the electron density near 2 10 18 m 3 . Such collision-less regime is important from the aspect of the neoclas- sical transport and also the potential structure formation. The presences of appreciable amount of high energy electrons are indicated from hard X-ray PHA, and the discrep- ancy between the stored energy and kinetic energy estimated from Thomson scattering. ECE spectrum are also sensitive to the presence of high energy electrons and discussed by solving the radiation transfer equation. The ECRH power absorption to the bulk and the high energy electrons are dramatically affected by the acceleration and the confinement of high energy electrons. The heating mechanisms and the acceleration process of high energy electrons are discussed by comparing the experimental results and the ray tracing calculation under assumed various density and mean energy of high energy electrons.

Using the ROSAT catalogue to find counterparts for unidentified objects in the first Fermi/LAT catalogue

There are a total of 1451 gamma-ray emitting objects in the Fermi Large Area Telescope First Source Catalogue. The point source location accuracy of typically a few arcminutes has allowed the counterparts for many of these sources to be found at other wavelengths, but even so there are 630 which are described as having no plausible counterpart at 80% confidence. In order to help identify the unknown objects, we have cross-correlated the positions of these sources with the Rosat All Sky Survey Bright Source Catalogue. In this way, for Fermi sources which have a possible counterpart in soft X-rays, we can use the, much smaller, Rosat error box to search for identifications. We find a strong correlation between the two samples and calculate that there are about 60 sources with a Rosat counterpart. Using the Rosat error boxes we provide tentative associations for half of them, demonstrate that the majority of these are either blazars or blazar candidates and give evidence that most belong to the BL Lac class. Given that they are X-ray selected and most are high synchrotron peaked objects, which indicates the presence of high energy electrons, these sources are also good candidates for TeV emission, and therefore good probes of the extragalactic background light.

Electron avalanches and diffused γ-mode in radio-frequency capacitively coupled atmospheric-pressure microplasmas

Space-, time- and wavelength-resolved optical emission profiles suggest that the helium emission at 706 nm can be used to indicate the presence of high energy electrons and estimate the sheath in helium rf discharges containing small concentration of air impurities. Furthermore, the experimental data supports the theoretical predictions of energetic electron avalanches transiting across the discharge gap in rf microdischarges and the absence of an α-mode. Nonetheless, microdischarges sustained between bare metal electrodes and operating in the γ-mode can produce diffuse glowlike discharges rather than the typical radially constricted plasmas observed in millimeter-size rf atmospheric-pressure γ discharges.

Neutralization mechanisms in He +–Al surface collisions

From a quantum mechanical calculation where the populations of He ground and first excited states are properly taken into account, we can identify for the first time the neutralization to the He first excited state as an operative mechanism in He +–Al surface collisions. This identification allows us to understand the presence of high energy electrons in the ion induced electron emission spectra, through the inclusion of Auger deexcitation as an electron emission source, as well as to suggest a possible cause for the disagreement still found between theory and experiments in low energy ion scattering (LEIS) for this system.

Ballistic electrons in GaAs and ZnS

Ballistic electron scattering and transport in the compound semiconductors GaAs and ZnS are simulated by a Monte Carlo program based on the electron interaction with polar-optical and acoustic phonons, intervalley and interband scattering as well as impact ionization. These scattering processes are considered for higher electron energies and proved in a multiple energy band model of the materials in crystalline fcc-zinkblende structure. The energy band structure and the related density of states are calculated by the empirical pseudopotential method. The scattering processes were considered as intra- and inter-valley transitions within and between nonparabolic bands and in terms of effective mass tensors. A first check of the scattering and transport simulation is applied to electron drift velocity and mobility calculations demonstrating the well-known Gunn effect in these materials. Then, the high electric field transport is aimed at the avalanching process as well as at vacuum emission experiments as a direct spectroscopy of ballistic electrons. MC simulations as well as experimental vacuum emission spectroscopy show the presence of high energy electrons up to 6.5 eV in ZnS supporting the excitation mechanisms in thin film electroluminescence devices.

Extreme synchrotron BL Lac objects

We performed an observational program with the X-ray satellite BeppoSAX to study objects with extreme synchrotron peak frequencies (nu_peak > 1 keV). Of the seven sources observed, four showed peak frequencies in the range 1-5 keV, while one (1ES 1426+428) displayed a flat power law spectrum (alpha= 0.92), locating its synchrotron peak at or above 100 keV. This is the third source of this type ever found, after Mkn 501 and 1ES 2344+514. Our data confirm the large nu_peak variability of this class of sources, compared with lower peaked objects. The high synchrotron peak energies, flagging the presence of high energy electrons, make the extreme BL Lacs also good candidates for TeV emission, and therefore good probes for the IR background.

A low noise FET with integrated charge restoration for radiation detectors

A novel pulsed, nonoptical, reset technique for use in charge-sensitive amplifiers and radiation detectors is described. The first-stage FET and charge restoration are integrated into one five-terminal device called the Pentafet. A pulse of minority carriers is injected directly into the channel of the FET. The technique is fast, and there are no aftereffects on the operation of the FET. Very low noise performance is achieved, even at high count rates. The high energy rate product capability of the device is demonstrated by analyzing Mn X-rays in the presence of high-energy electrons from an Sr-90 beta source and in a transmission electron microscope.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Effects of High-Energy Electrons on the Charging of Spacecraft Dielectrics

Results are presented of a laboratory investigation of discharges in spacecraft dielectrics using both a low-energy electron and a combined low- and high-energy electron environment. Comparison of the charging and discharge characteristics indicates that the presence of high-energy electrons in space will result in significantly different behavior from that predicted for low-energy electron simulations alone. For Kapton, fiberglass, and second-surface mirrors, the effect of the high-energy electrons is primarily to increase the conductivity, thus often limiting surface potentials to below discharge threshold values. Variation of the relative fluxes of low- and high-energy electrons can lead to discharge; however, the magnitude of the charge blowoff is significantly smaller (~1/20) than that observed upon exposure to low-energy electrons alone. Astroquartz, which for low-energy electron exposures exhibited no measurable charge blowoff, exhibited significant charge blowoff (Ip = 2 amp) upon exposure to a combined high- and low-energy electron environment.

Spectroscopic Study of the Negative Glow in Usual Glow and in Hollow-Cathode Discharges

The negative glow(NG) in a low pressure He and a He–Cd glow discharge was investigated by a spectroscopic method. Atomic line intensities and their excitation cross-sections were utilized to estimate the electron energy and density in the NG. In the NG, some electrons have the energies more than 100 eV and the density of low energy (30–34 eV) electrons is larger than in the positive column (PC) by two orders of magnitude. Using a plane parallel type hollow-cathode, the line distribution and intensities can be controlled by changing the inter-cathode distance. In the case of He–Cd discharge, the main component of emission spectra can be controlled between the ionic lines of Cd and the atomic lines of He by changing only the intercathode distance. The most significant property of the NG for applications regardless of the gas composition is the presence of high energy electrons.

Calculations and measurements on the maximum energy of secondary electrons in inclined-field acceleration tubes

Trajectory calculations have been carried out for secondary electrons emitted on the electrodes and in the interelectrode gaps of inclined-field acceleration tubes. It was shown that a number of trajectories originating in the neighbourhood of the prismatic field sections will be inflected in the paraxial region. Consequently, the corresponding electrons will be accelerated to considerable energies before being stopped by other electrodes. The presence of high-energy electrons in inclined-field tubes was experimentally proved by X-ray measurements around the 5 MV Van de Graaff generator in this Institute. Similar measurements performed with a homogeneous field tube enable us to compare the behaviour of tubes of different types.

Gamma Radiation from NP 0532

THE pulsar NP 0532, located in the Crab Nebula, emits pulses of light1,2 with the same period as the radio emission. The polarization2 of the light suggests an origin in the synchrotron radiation process, indicating the presence of high-energy electrons. In this article the gamma radiation resulting from various processes associated with these electrons is calculated. While gamma radiation from NP 0532 has not been observed experimentally, there are observations of gamma radiation from the Crab Nebula3–8 that give upper limits on gamma emission from NP 0532. My calculations and these upper limits lead to the conclusion that the magnetic field H near the light-emitting region of NP 0532 is 102 ≲ H ≲ 104 G.

Some observations on the scattering of β-particles by thick absorbers

Using a range of elements of differing atomic number the variation in intensity of backscattered electrons with energy of the incident β-particles has been measured with a β-spectrometer. The method also allows observations to be made about the variation in energy of backscattered electrons with atomic number. The presence of high-energy electrons in the emergent spectrum is in conflict with experiments based on absorption methods of energy differentiation. The value of energy selection in practical applications of β-backscattering is noted.

High energy electrons produced in a thunderstorm

Synopsis A number of cases has been observed in which the presence of high energy electrons of 10 9 eV is directly recorded during thunderstorms. In one instance on the 3rd of May 1952, a 4 to 6% increase above the mean value of the ionisation was found in 6 different recording instruments. In one vessel shielded by 110 cm Fe no increase was found. Three cases were noticed in 1951, and since the 3rd of May 1952 three more have been detected. No influence was discovered in vessels with 110 cm iron shelding. The energies lie below 10 10 eV. An increased ionisation was also found during heavy rainfall.