Change In Electron Temperature Research Articles

유체 모델을 이용한 유전체 장벽 방전 플라즈마와 전자기파 간의 시간 의존적 상호 작용 분석

Abstract In determining interaction between plasma and electromagnetic wave, plasma frequency and collision frequency are two key para-meters. They are derived from electron density and temperature, which vary in an extremely wide range, depending on a plasma gene-rator. Because the parameters are usually unknown, traditional researches have utilized simplified electron density model and constant electron temperature approximation. Introduction of plasma fluid model to electromagnetics is suggested to utilize relatively precise time dependent variables for given generator. Dielectric barrier discharge(DBD) generator is selected due to its simple geometry which allows us to use one dimensional analysis. Time dependent property is analyzed when microwave is launched toward parallel plate DBD plasma. Afterwards, attenuation tendency with the change of electron density and temperature is demonstrated.Key words: Plasma Fluid Model, Dispersion Relation, DBD Plasma, Atmospheric Pressure Plasma, Microwave Attenuation {O<=_|w}~€_<=‚Lƒj€_„ ƒW‚†:G<=‡%w} ˆ‰[#M3Š‹Œ*. <ŽcF(Department of Electric and Electronic Engineering, Yonsei University) *€_<=‚(Agency for Defence Development) Manuscript received April 28, 2014 ; Revised June 17, 2014 ; Accepted July 30, 2014. (ID No. 20140428-040)Corresponding Author: Jong-Gwan Yook (e-mail: jgyook@yonsei.ac.kr)

Density and Temperature Correlations in the SOL; Implications for Gas Puff Imaging of Turbulence

AbstractUsing a two‐dimensional turbulence model, a strong linear correlation is found between density and electron temperature within scrape‐off layer fluctuations. This has important implications for gas puff image interpretation for two commonly used lines, Dα and HeI (587.6 nm). Dα emission responds approximately linearly to proportional changes in the underlying plasma density and electron temperature, making image interpretation relatively straightforward. However, above ∼25 eV, HeI (587.6 nm) emission is approximately constant with proportional changes in density and electron temperature, so underlying plasma perturbations may go unseen. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Observation of the bifurcation of tearing modes due to supersonic gas injected into the J-TEXT plasmas

Abstract The influence on the magnetohydrodynamic (MHD) behaviors due to the gas injected by Super-sonic Molecular Beam Injection (SMBI) has been observed on J-TEXT tokamak. The change of local electron temperature and density due to the injected supersonic gas triggers relaxation instability, and then the relaxation could bifurcate into two different types of tearing modes' behaviors. One is tearing mode with single m / n = 2 / 1 helicity, another is tearing modes with different helicities ( m / n = 2 / 1 , 3/2). The mechanism which is responsible for the bifurcation is closely related to changes of the pressure due to gas injection.

Distributions of Electron Density and Electron Temperature in Magnetized DC Discharge

The distribution of electron temperature Te and density Ne in a dc glow discharge that is created by a pair of circular parallel electrodes is studied using double probes. The measurement are carried out for the following two modes: in the presence and in the absence of the magnetic field. In the absence of the magnetic field, for the radial distribution, temperatures have same values with small variation, in the same discharge region [cathode fall or negative glow or positive column region], except at the edge. For the axial distribution, the distribution profiles of Te shows that Te is decreased, and Ne continues to increase toward the anode. In the presence of the magnetic field, the radial distribution of the electron density has its highest value at the edge where the magnetic field is maximum. The electron temperature changes very little. The density begins to increases also from the cathode fall region, at the edge, to the negative glow region and then it decreases sharply at the positive column region. The plasma is very intense in the cathode fall region (very thin bright ring) and very brighter and sharp in the negative glow region (extends several mm from the cathode fall region). But in the positive column, the density begins to decrease.

Effects of discharge chamber length on the negative ion generation in volume-produced negative hydrogen ion source

In a volume-produced negative hydrogen ion source, control of electron temperature is essential due to its close correlation with the generation of highly vibrationally excited hydrogen molecules in the heating region as well as the generation of negative hydrogen ions by dissociative attachment in the extraction region. In this study, geometric effects of the cylindrical discharge chamber on negative ion generation via electron temperature changes are investigated in two discharge chambers with different lengths of 7.5 cm and 11 cm. Measurements with a radio-frequency-compensated Langmuir probe show that the electron temperature in the heating region is significantly increased by reducing the length of the discharge chamber due to the reduced effective plasma size. A particle balance model which is modified to consider the effects of discharge chamber configuration on the plasma parameters explains the variation of the electron temperature with the chamber geometry and gas pressure quite well. Accordingly, H(-) ion density measurement with laser photo-detachment in the short chamber shows a few times increase compared to the longer one at the same heating power depending on gas pressure. However, the increase drops significantly as operating gas pressure decreases, indicating increased electron temperatures in the extraction region degrade dissociative attachment significantly especially in the low pressure regime. It is concluded that the increase of electron temperature by adjusting the discharge chamber geometry is efficient to increase H(-) ion production as long as low electron temperatures are maintained in the extraction region in volume-produced negative hydrogen ion sources.

Mackenzie's Demon with instabilities

MacKenzie's Maxwell Demon, consisting of positively biased thin wires, heats plasma electrons without significantly affecting the plasma potential. Experiments were performed on the Maxwell Demon in a multi-dipole confined filament discharge. It is shown that given adequate bias, the Demon reduces a bi-Maxwellian electron distribution function to a single Maxwellian electron distribution function. It is shown that a small planar electrode can perform identical heating as the Demon, provided that the electrode has the area of approximately three times the Demon's conductive surface area. The instability that limits the Demon's operation is investigated. Time-resolved measurements of changes in global electron temperature, plasma density and plasma potential within a cycle of the instability are considered. It is found that the Demon's instability is a repeating pulsed anode spot. Density measurements indicate that the frequency of the instability is dependent on plasma production and loss rates. The neutral pressure dependence of the anode spot instability is measured and modeled for the first time.

Numerical simulations of ion and electron temperatures in the ionosphere of Mars: Multiple ions and diurnal variations

This study shows how ion and electron temperatures in the ionosphere of Mars, which affect plasma densities, vary with altitude and time of day. These new results can be used to support the interpretation of existing and anticipated measurements of ionospheric conditions. Here, a one-dimensional fluid model of the martian ionosphere has been coupled to a kinetic supra-thermal electron transport model in order to self-consistently calculate ion and electron densities and temperatures. The models include diurnal variations, revealing hundreds of degrees Kelvin changes in dayside electron and ion temperatures at fixed altitude. The models treat each ion species separately, revealing hundreds of degrees Kelvin differences between H+ and O2+ temperatures. The coupled models also include an adiabatic expansion term into the heating equation, which contribute significantly to temperatures of lighter ions. Consistent with previous studies using single-ion plasma, solar EUV heating alone is insufficient to heat the thermal electrons and ion species to observed temperatures, indicating the presence of additional heating sources. Best agreement with measurements is found when additional topside heating fluxes of 15×109 and 2×107eVcm−2s−1 produce topside heating rates that are 35 and 100 times higher than the nominal solar heating rate for electrons and ions, respectively.

Effect of process parameters on properties of argon–nitrogen plasma for titanium nitride film deposition

In this study, the effect of working pressure and input power on the physical properties and sputtering efficiencies of argon–nitrogen (Ar/N2) plasma in direct current magnetron discharge is investigated. The discharge in Ar/N2 is used to deposit TiN films on high speed steel substrate. The physical plasma parameters are determined by using Langmuir probe and optical emission spectroscopy. On the basis of the different reactions in the gas phase, the variation of plasma parameters and sputtering rate are explained. A prominent change of electron temperature, electron density, ion density, and degree of ionization of Ar is found as a function of working pressure and input power. The results also show that increasing working pressure exerts a negative effect on film deposition rate while increasing input power has a positive impact on the same. To confirm the observed physical properties and evaluate the texture growth as a function of deposition parameters, x-ray diffraction study of deposited TiN films is also done.

Structure of conducting channel of lightning

The spatial distribution of the plasma density in a lightning channel is studied theoretically. It is shown that the electric-field double layer is formed at the channel boundary. In this case, the electron temperature changes abruptly and ions are accelerated by the electric field of the double layer. The ion momentum flux density is close to the surrounding gas pressure. Cleaning of the channel from heavy particles occurs in particle-exchange processes between the plasma channel and the surrounding air. Hydrogen ions are accumulated inside the expanding channel from the surrounding air, which is enriched by hydrogen-contained molecules. In this case, the plasma channel is unstable and splits to a chain of equidistant bunches of plasma. The hydrogen-enrich bunches burn diffusely after recombination exhibiting the bead lightning behavior.

Characteristics of SiO2 etching by using pulse-time modulation in 60 MHz/2 MHz dual-frequency capacitive coupled plasma

60 MHz pulsed radio frequency (rf) source power and 2 MHz continuous wave rf bias power, were used for SiO2 etching masked with an amorphous carbon layer (ACL) in an Ar/C4F8/O2 gas mixture, and the effects of the frequency and duty ratio of the 60 MHz pulse rf power on the SiO2 etch characteristics were investigated. With decreasing duty ratio of the 60 MHz pulse rf power, not only the etch rate of SiO2 but also the etch rate of ACL was decreased, however, the etch selectivity of SiO2 over ACL was improved with decreasing the duty ratio. On the other hand, when the pulse frequency was varied at a constant duty ratio, no significant change in the etch rate and etch selectivity of both materials could be observed. The variation of the etch characteristics was believed to be related to the change in the gas dissociation characteristics caused by the change in the average electron temperature for different pulsing conditions. The improvement in the etch selectivity with the decrease of duty ratio, therefore, was related to the decreased gas dissociation of C4F8 by the decrease of average electron temperature and, which resulted in a change in composition of the fluorocarbon polymer on the etched materials surface from C–C rich to CF2 rich. With decreasing the duty ratio, not only the etch selectivity but also the improvement in the SiO2 etch profile could be observed.

Influence of electron evaporative cooling on ultracold plasma expansion

The expansion of ultracold neutral plasmas (UCP) is driven primarily by the thermal pressure of the electron component and is therefore sensitive to the electron temperature. For typical UCP spatial extents, evaporative cooling has a significant influence on the UCP expansion rate at lower densities (less than 108/cm3). We studied the effect of electron evaporation in this density range. Owing to the low density, the effects of three-body recombination were negligible. We modeled the expansion by taking into account the change in electron temperature owing to evaporation as well as adiabatic expansion and found good agreement with our data. We also developed a simple model for initial evaporation over a range of ultracold plasma densities, sizes, and electron temperatures to determine over what parameter range electron evaporation is expected to have a significant effect. We also report on a signal calibration technique, which relates the signal at our detector to the total number of ions and electrons in the ultracold plasma.

The polar cliff in the morning sector of the ionosphere

Abstract. By "polar cliff" we mean the steep increase in the ionization density observed in the morning sector of the polar ionosphere. Here the properties of this remarkable feature are investigated. The data set consists of electron density and temperature measurements obtained by the Dynamics Explorer 2 satellite. Only data recorded in the Northern Hemisphere winter are considered (solar zenith angle ≥ 90°). We find that for moderately disturbed conditions, the foot of the polar cliff is located below 60° invariant latitude. Here, within about 4°, the density increases by a factor of 4, on average. The actual location of the polar cliff depends primarily on the level of geomagnetic activity, its associated density increase on geographic longitude and altitude. As to the longitudinal variations, they are attributed to asymmetries in the background ionization density at middle latitudes. Using a superposed epoch type of averaging procedure, mean latitudinal profiles of the polar cliff and the associated electron temperature changes are derived. Since these differ significantly from those derived for the afternoon/evening sector, we conclude that the subauroral ionospheric trough does not extend into the morning sector. As to the origin of the polar cliff in the morning sector, local auroral particle precipitation should play only a secondary role.

In-situ monitoring and control of hydrogenated amorphous silicon–germanium band-gap profiling during plasma deposition process

In-situ germanium content monitoring and its characteristics in SiH4/GeH4/H2 plasmas was studied during hydrogenated amorphous silicon–germanium (a-SiGe:H) film depositions. Since an appropriate band-gap profiling in a-SiGe:H deposition is very important to achieve high efficiency solar cell, the accurate monitoring and control of Ge contents are required. In this work, we found the spectral intensity ratio of silicon atom (288.2 nm) and germanium atom (303.9 nm) emission has strong relation with Ge content in plasmas. In typical, band-gap energy of films was decreased with the increasing of gas flow ratio GeH4/SiH4. However, at different total flow rate of GeH4, the band-gap was different for same gas flow ratio cases because the Ge content in plasmas was changed due to the changes of electron temperature by hydrogen dilution. On the other hand, the emission intensity ratio Ge/Si detected the band-gap variation. Using this method, therefore, we measured and control Ge/Si to make a U-shape band-gap profile which was proved by an ellipsometer and Auger electron spectroscopy depth profile analysis.

Electrodynamics of the high‐latitude trough: Its relationship with convection flows and field‐aligned currents

AbstractWe present a detailed case study of the electrodynamics of a high‐latitude trough observed at ~ 12 UT (~1 MLT) on 8 March 2008 using multiple instruments, including incoherent scattering radar (ISR), GPS total electron content (TEC), magnetometers, and auroral imager. The electron density within the trough dropped as much as 80% within 6 minutes. This trough was collocated with a counterclockwise convection flow vortex, indicating divergent horizontal electric fields and currents. Together with a collocated dark area shown in auroral images, the observations provide strong evidence for an existence of downward field‐aligned currents (FACs) collocated with the high‐latitude trough. This is further supported by assimilative mapping of ionospheric electrodynamics results. In addition, the downward FACs formed at about the same time as a substorm onset and east of the Harang reversal, suggesting it is part of the substorm current wedge. It has long been a puzzle why this type of high‐latitude trough predominantly occurs just east of the Harang reversal in the postmidnight sector. We suggest that the high‐latitude trough is associated with the formation of downward FACs of the substorm current system, which usually occur just east of the Harang reversal. In addition, we find that the ionospheric electron temperature within the high latitude trough decreases in the F region while increasing in the E region. We discuss possible mechanisms responsible for the complex change in electron temperature, such as ion composition change and/or presence of downward FACs.

Changes in the Earth's magnetic field over the past century: Effects on the ionosphere‐thermosphere system and solar quiet (Sq) magnetic variation

We investigated the contribution of changes in the Earth's magnetic field to long‐term trends in the ionosphere, thermosphere, and solar quiet (Sq) magnetic variation using the Coupled Magnetosphere‐Ionosphere‐Thermosphere (CMIT) model. Simulations with the magnetic fields of 1908, 1958, and 2008 were done. The strongest differences occurred between ~40°S–40°N and ~100°W–50°E, which we refer to as the Atlantic region. The height and critical frequency of the F2 layer peak, hmF2 and foF2, changed due to changes in the vertical E × B drift and the vertical components of diffusion and transport by neutral winds along the magnetic field. Changes in electron density resulted in changes in electron temperature of the opposite sign, which in turn produced small corresponding changes in ion temperature. Changes in neutral temperature were not statistically significant. Strong changes in the daily amplitude of the Sq variation occurred at low magnetic latitudes due to the northward movement of the magnetic equator and the westward drift of the magnetic field. The simulated changes in hmF2, foF2, and Sq amplitude translate into typical trends of ±1 km/decade (night) to ±3 km/decade (day), −0.1 to +0.05 MHz/decade, and ±5 to ±10 nT/century, respectively. These are mostly comparable in magnitude to observed trends in the Atlantic region. The simulated Atlantic region trends in hmF2 and foF2 are ~2.5 times larger than the estimated effect of enhanced greenhouse gases on hmF2 and foF2. The secular variation of the Earth's magnetic field may therefore be the dominant cause of trends in the Atlantic region ionosphere.

Modelling of radiative divertor operation towards detachment in experimental advanced superconducting tokamak

In order to actively control power load on the divertor target plates and study the effect of radiative divertor on plasma parameters in divertor plasmas and heat fluxes to the targets, dedicated experiments with Ar impurity seeding have been performed on experimental advanced superconducting tokamak in typical L-mode discharge with single null divertor configuration, ohmic heating power of 0.5 MW, and lower hybrid wave heating power of 1.0 MW. Ar is puffed into the divertor plasma at the outer target plate near the separatrix strike point with the puffing rate 1.26×1020 s−1. The radiative divertor is formed during the Ar puffing. The SOL/divertor plasma in the L-mode discharge with radiative divertor has been modelled by using SOLPS5.2 code package [V. Rozhansky et al., Nucl. Fusion 49, 025007 (2009)]. The modelling shows the cooling of the divertor plasma due to Ar seeding and is compared with the experimental measurement. The changes of peak electron temperature and heat fluxes at the targets with the shot time from the modelling results are similar to the experimental measurement before and during the Ar impurity seeding, but there is a major difference in time scales when Ar affects the plasma in between experiment and modelling.

Multiple-tracer TESPEL injection for studying impurity behaviour in a magnetically confined plasma

A new diagnostic method with tracer-encapsulated solid pellet (TESPEL) injection with multiple tracers is developed to study impurity behaviour in a magnetically confined plasma. If a pellet contains multiple tracers, it becomes possible to compare the behaviour of different impurities simultaneously under the same plasma conditions. We injected a TESPEL into the Large Helical Device mainly with triple tracers: vanadium (V), manganese (Mn) and cobalt (Co). The Li-like lines in the vacuum ultraviolet range and the Kα lines in the soft x-ray range from these tracers are simultaneously observed with a time resolution of 50 ms. As the charges of the nuclei of intrinsic impurities, chromium (Cr) and iron (Fe), are in between those of the tracers, the behaviour of Cr and Fe can be studied quantitatively by knowing the number of tracer particles and also by comparing the emission intensity change due to the electron temperature change. It is observed that the tracer impurities remain in the plasma core region when the plasma density is higher than 5 × 1019 m−3. It is also observed that the intrinsic impurities cannot enter the core region when the plasma density is higher than the same level, although the two phenomena appear to be independent.

Laboratory Investigation of Vapor Shielding for Lithium-Coated Molybdenum in Devex

To investigate the effect of lithium on a molybdenum target, a triple Langmuir probe diagnostics and target temperature measurements are carried out. Several experimental scenarios are tested to optimize the device for the vapor shielding experiment. A lithium sputtering system is used to deposit lithium on a molybdenum target. A triple Langmuir probe is placed near the target at various pressures to estimate change of plasma density and electron temperature and their effects on vapor shielding. Temperature increase at the target is measured by a thermocouple and its relationship with plasma parameters and lithium is discussed in detail.

Study on ultra fast nonequilibrium heat transfers in nano metal films by femtosecond laser pump and probe method

The reduction in size and the increase in speed of microelectronic device make the probability of nonequilibrium electron-phonon phenomena become greater, leading to the increase of thermal resistance in the device. The measurement of electron-phonon coupling factor in material resistance increasingly becomes important for accurate thermal treatment. The femtosecond laser pump and probe method is used for studing the nonequilibrium heat transfer in nano metal films with different thicknesses. Exploring parabolic two-step model (PTS) to fit the experimental data. During the fitting process, we considered the proportional relationship between the changes of electron temperature and phonon temperature, which affects the reflectivity. By studying the different thicknesses of Ni and Al films electron-phonon coupling factors, we find that the electron-phonon coupling factor does not change with film thickness. In addition, the experimental result verifies that the reflectivity of probe laser is affected by electron temperature and phonon temperature at the same time. Through the data analysis, we also get the influence coefficients of electron temperature and phonon temperature on reflectivity.

Plasma response to externally applied resonant magnetic perturbations

Based on recent finding that applied resonant magnetic perturbation (RMP) can either increase or decrease the local electron density gradient around the resonant surface (Yu and Günter 2009 Nucl. Fusion 49 062001), the plasma response to the RMP of a single helicity is studied numerically by further taking into account the electron energy transport. It is found that the changes in the local electron density and temperature by RMPs are coupled. If the local parallel heat diffusivity and/or the island width are sufficiently large, the local electron temperature profile flattens, which enhances the change in the local electron density gradient. Depending on the plasma parameters, either the plasma rotation frequency or the electron diamagnetic frequency (electron pressure gradient) can be significantly changed by RMPs, and these two changes affect each other. With a reduced set of equations that does not include the electron energy transport equation, the particle transport in stochastic magnetic fields is found to be similar to that across a single magnetic island.