共查询到20条相似文献,搜索用时 15 毫秒
1.
B. A. Demidov V. P. Efremov M. V. Ivkin I. A. Ivonin V. A. Petrov V. E. Fortov 《Technical Physics》1999,44(12):1413-1419
The propagation of pressure jumps excited by a high-current pulsed electron beam in SiO2 aerogels with density ranging from 0.025 to 0.25 g/cm3 is investigated using a laser differential interferometer and optical methods. Spallation on the back side of the aerogel
targets is observed and the velocity of the spallation fragments is measured. The expansion velocity of the aerogel in the
direction of the electron beam is determined. The parameters of the shock adiabat are established in a wide range of aerogel
porosities. The depth of the energy-deposition zone of the electron beam is determined experimentally as a function of the
aerogel density in the range from 0.015 to 0.25 g/cm3. A model describing highly porous materials which reflects the fractal properties of highly porous aerogels is developed
on the basis of the experimental data. Numerical calculations of the observed phenomena are performed.
Zh. Tekh. Fiz. 69, 18–25 (December 1999) 相似文献
2.
B. A. Demidov V. P. Efremov M. V. Ivkin I. A. Ivonin V. A. Petrov V. E. Fortov 《Technical Physics》2000,45(7):870-877
The evolution of the glow of the energy-release zone in porous transparent aerogel, with a density of 0.03–0.25 g/cm3, which is irradiated by a high-power pulse electron beam, is studied experimentally. In addition to a fast (τ≤τbeam) and a luminescent (τ≈10−6 s) glow components, a slow glow component (τ≈2×10−5 s) has been revealed. The appearance of this slow component is associated with an aerogel rarefaction wave and its destruction (cracking) arising after its isochoric bulk heating by electron radiation, which may occur due to an electrostatic field induced under irradiation. The discovered glow is utilized to visually determine the current position of the rarefaction wave front. The sound velocity measured as a function of the density of SiO2 aerogels with porosities of 10–100 allowed us to experimentally determine the percolation parameter of the aerogel equation of state. 相似文献
3.
Results are presented from the first stage of studies on the passage of an electron beam with energy 100–500 eV in a magnetic
field of 300–700 Oe through the curvilinear solenoid of the KRéL unit, the latter being a prototype of the closing segment
of the Drakon stellarator system, in the plasma-beam discharge regime. The ion density at the end of the curvilinear part
of the chamber, n
i
≈8×108–1010 cm−3, the electron temperature T
e
≈4–15 eV, and the positions at which the beam hits the target for different distances from it to the electron source are determined
experimentally. The motion of the electron beam is computationally modeled with allowance for the space charge created by
the beam and the secondary plasma. From a comparison of the experimentally measured trajectories and trajectories calculated
for different values of the space charge, we have obtained an estimate for the unneutralized ion density of the order of 5×107 cm−3.
Zh. Tekh. Fiz. 69, 22–26 (February 1999) 相似文献
4.
Sharad D. Bhagat 《Applied Surface Science》2006,252(12):4289-4297
The present paper describes the comparative studies on the hydrophobic and physical properties of the tetraethoxysilane (TEOS) based silica aerogels prepared by two step sol-gel process followed by supercritical drying. Silica alcogels were prepared by keeping the molar ratio of TEOS:methanol (MeOH):H2O (acidic):H2O (basic) constant at 1:33:3.5:3.5 with oxalic acid and ammonium hydroxide concentrations fixed at 0.001 and 1 M, respectively. In all, nine different co-precursors (CP) of the type RnSiX4 − n, have been used. The aerogels have been characterized by density, porosity, percentage of volume shrinkage, optical transmission, contact angle and thermal conductivity measurements. The surface chemical modification of silica aerogels was confirmed by the presence of CH and SiC peaks at 2900, 1450 and 840 cm−1, respectively, from the Fourier transform-infrared spectroscopy (FT-IR). The microstructure of the aerogels was studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques. In addition to these studies, the stability of the hydrophobic aerogels against an organic impurity (methanol, in the present studies) in water has also been studied. 相似文献
5.
The system TiO2–photo sensitive dye of a dye-sensitized TiO2 solar cell is numerically simulated. The steady-state numerical model used is based on the continuity and transport equations
for all charge species involved in the system, in connection to Poisson’s equation. The dependence of both electron diffusion
coefficient and light absorbance upon TiO2 porosity is taken into consideration. The resulting electron density after illumination is also set as a function of the
illuminating beam characteristics and material properties. Furthermore, an effective dielectric constant dependent upon the
porosity of TiO2 is used in the model. Results for different values of pore size and thickness of the TiO2 electrode are found in accordance with results reported in the literature.
Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.
An erratum to this article can be found at 相似文献
6.
An essential feature of the ambient pressure dried aerogel manufacturing process is the end-capping of the reactive silanol groups in the silica wet gel. In this report, we have presented the effect of two different trimethyl silylating agents viz. trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) on the hydrophobic and physical properties of ambient pressure dried silica aerogels. The hydrogels were prepared by sol-gel processing of sodium silicate precursor (Na2SiO3) in the presence of acetic acid catalyst followed by vapour passing treatment and different solvent exchanging steps. The silylating agent in hexane was used for end-capping of the silanols present on the silica surface of the gel. To study silylation behavior silylating agent/Na2SiO3 molar ratio was varied from 2.4 to 5.6. The aerogels have been characterized by density, % of volume shrinkage, porosity, % of optical transmission, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermo-gravimetric and Differential Thermal Analysis (TG-DTA) and contact angle measurements. 相似文献
7.
8.
The fluorescence of CO2 clusters excited by an electron beam in a molecular beam formed from a free jet expansion of carbon dioxide is investigated.
Data on the fluorescence of the clusters are obtained by comparing the electron-beam-induced fluorescence with the signal
appearing in an electronic-fluorescence detector as a result of reflection of the cluster beam from an obstacle placed after
the electron beam, as well as with the intensity of the cluster beam. It is established that, unlike a jet expansion, for
CO2 clusters in a molecular beam the fluorescence yield from a cluster decreases significantly with increasing cluster size and
is very small for clusters of large size. It is concluded on the basis of the results from an investigation of the fluorescence
of CO2 clusters that the electron-beam-induced fluorescence technique can be used for measurements in molecular beams with CO2 clusters.
Zh. Tekh. Fiz. 67, 63–71 (July 1997) 相似文献
9.
ABSTRACT The wide range of applications of the plasma-based electron beam generator make it necessary to diagnose the device with a noninterfering method. The results of experimental and modeling studies of neutral helium and hydrogen beta spectral lines emitted from the double discharge pulsed electron beam generator are presented in this paper. Neutral helium lines emitted from the plasma in the pressure range 0.1–0.4 torr are studied and compared with results of the collisional radiative model. The duration of the electron beam is shorter than 100 ns, and the peak current intensity is of order amperes. The full width at half maximum of the H β spectral line is used for the determination of the plasma electron density, found as 3.16 × 1021 m?3 at 0.3 torr, and good agreement is obtained by comparing with the full computer simulation method. 相似文献
10.
V. M. Orlovskii É. A. Sosnin V. F. Tarasenko A. G. Ponomarenko Yu. I. Khapov 《Technical Physics》1999,44(1):69-73
Results are presented from a study of HF lasers pumped by non-chain chemical reactions initiated by a radially convergent
and by a planar electron beam. The main channels of formation of vibrationally excited HF molecules are analyzed. The distribution
of the energy density of the radiation in the output beam of a wide-aperture laser is measured. In 30 liters of a mixture
of SF6:H2=8:1 at a pressure of 1.1 atm an output energy of ∼200 J is obtained at an ∼11% efficiency with respect to the energy deposition.
It is shown that the admixture of a buffer gas of neon or argon improves the uniformity of the radiation energy distribution
in the output beam of an HF laser pumped by a non-chain chemical reaction and initiated by an electron beam, and it also increases
the output energy.
Zh. Tekh. Fiz. 69, 76–81 (January 1999) 相似文献
11.
In measurements in jets of condensing gases, problems arise in interpreting the results obtained with the use of electron-beam
fluorescence diagnostics, in particular due to the possible contribution of clusters to the radiation from the jet. Data on
the fluorescence are obtained by comparing the optical and x-ray emission excited by an electron beam with calculations of
the amount of condensate. Studies are made on the fluorescence of CO2 clusters excited by an electron beam in a free jet of the condensing carbon dioxide gas. It is found that the clusters radiate
at wavelengths of the monomers extremely effectively per molecule, almost as much as the free molecules, and the dependence
on size is quite weak. It is shown that with electron-impact excitation the emission of the clusters comes about as the result
of the ejection of excited molecules from the cluster as the latter fragments. The results of this investigation of the fluorescence
of CO2 clusters lead to conclusions regarding the use of electron beam fluorescence diagnostics for measurements in free jets with
CO2 clusters.
Zh. Tekh. Fiz. 67, 43–52 (March 1997) 相似文献
12.
Abstract The effects of temperature are discussed when the ZnS:Cu,Al,Au (P22G) phosphor powder is bombarded by a 2 keV electron beam with a current density of 88 mA/cm2 at an oxygen pressure of 2 × 10?6 Torr at temperatures between 25 and 300°C. The rate of surface reaction decreases at higher temperatures due to the reduction in the mean stay time of the O2 on the surface which is vital for the reactions according to an electron stimulated surface chemical reaction model. A direct correlation between the temperature and the initial cathodoluminescence (CL) brightness which depicts thermal quenching of the CL was observed. 相似文献
13.
Organic modification of TEOS based silica aerogels using hexadecyltrimethoxysilane as a hydrophobic reagent 总被引:2,自引:0,他引:2
Nagaraja D. Hegde 《Applied Surface Science》2006,253(3):1566-1572
The experimental results on the synthesis and characterization of tetraethoxysilane (TEOS) based hydrophobic silica aerogels using hexadecyltrimethoxysilane (HDTMS) as a hydrophobic reagent by two step sol-gel process, are described. The molar ratio of tetraethoxysilane (TEOS), methanol (MeOH), acidic water (0.001 M, oxalic acid) and basic water (10 M, NH4OH) was kept constant at 1:55:3.25:1.25 and the molar ratio of HDTMS/TEOS (M) was varied from 0 to 28.5 × 10−2. The organic modification was confirmed by infrared spectroscopic studies, and the hydrophobicity of the aerogels was tested by the contact angle measurements. The maximum contact angle of 152° was obtained for M = 22.8 × 10−2. The aerogels retained the hydrophobicity up to a temperature of 240 °C and above this temperature the aerogels became hydrophilic. The aerogels were characterized by the thermal conductivity, density, contact angle measurements, optical transmission and scanning electron micrographs. 相似文献
14.
Y. C. Du H. Wang D. C. Sun F. M. Li 《Applied Physics A: Materials Science & Processing》1988,45(2):165-168
Dry etching using a novel large-area electron beam has been obtained on polysilicon over SiO2/Si samples in the pressure range 0.1–0.4 Torr. The dependence of etching rate upon electron-beam power density, total pressure
of the CF4/He mixture, and the ratio of CF4/He pressure has been determined. An etching rate of 150 nm/min without any addition of O2 has been achieved with a low-energy density electron beam for poly-Si dry etching. 相似文献
15.
Density and impurity profile behaviours in HL-2A tokamak with different gas fuelling methods
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The electron density profile peaking and the impurity accumulation
in the HL-2A tokamak plasma are observed when three kinds of
fuelling methods are separately used at different fuelling particle
locations. The density profile becomes more peaked when the
line-averaged electron density approaches the Greenwald density limit
nG and, consequently, impurity accumulation is often
observed. A linear increase regime in the density range ne<
0.6nG and a saturation regime in ne > 0.6nG
are obtained. There is no significant difference in achieved density
peaking factor fne between the supersonic molecular beam
injection (SMBI) and gas puffing into the plasma main chamber.
However, the achieved fne is relatively low, in particular,
in the case of density below 0.7nG, when the working
gas is puffed into the divertor chamber. A discharge with a
density as high as 1.2nG, i.e. ne = 1.2nG,
can be achieved by SMBI just after siliconization as a wall
conditioning. The metallic impurities, such as iron and chromium,
also increase remarkably when the impurity accumulation happens. The
mechanism behind the density peaking and impurity accumulation is
studied by investigating both the density peaking factor versus the
effective collisionality and the radiation peaking versus density
peaking. 相似文献
16.
A numerical simulation is made of the processes occurring in a plasma lens under conditions when the focusing of a relativistic
electron beam is strongly affected by the ionization of the residual gas in the lens region by the beam itself. The paraxial,
azimuthally symmetric, 1.5-dimensional, electrostatic kinetic model, taking account of plasma production, expansion of the
plasma electrons away from the beam region, and contraction of the ions toward the axis of the beam, was used for the calculation.
The dynamics of the formation of a focal spot is studied, and the size and position of the spot are determined as functions
of time for different values of the gas pressure, initial plasma density, and energy of the beam electrons.
Zh. Tekh. Fiz. 67, 90–94 (October 1997) 相似文献
17.
H.-C. Wu J. Meyer-ter-Vehn 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(2):443-449
The coherent reflectivity of a dense, relativistic,
ultra-thin electron layer is derived analytically for an obliquely
incident probe beam. Results are obtained by two-fold Lorentz
transformation. For the analytical treatment, a plane uniform
electron layer is considered. All electrons move with uniform
velocity under an angle to the normal direction of the plane; such
electron motion corresponds to laser acceleration by direct action
of the laser fields, as it is described in a companion paper [Eur. Phys. J. D 55, 433 (2009)]. Electron density is chosen high enough to ensure that many
electrons reside in a volume λR
3, where λR is the
wavelength of the reflected light in the rest frame of the layer.
Under these conditions, the probe light is back-scattered coherently
and is directed close to the layer normal rather than the direction
of electron velocity. An important consequence is that the Doppler
shift is governed by γx=(1-(Vx/c)2)-1/2 derived from
the electron velocity component Vx in normal direction rather
than the full γ-factor of the layer electrons. 相似文献
18.
The possibility of using a plasma electron source (PES) with a discharge in crossed E × H field for compensating the ion beam from an end-Hall ion source (EHIS) is analyzed. The PES used as a neutralizer is mounted
in the immediate vicinity of the EHIS ion generation and acceleration region at 90° to the source axis. The behavior of the
discharge and emission parameters of the EHIS is determined for operation with a filament neutralizer and a plasma electron
source. It is found that the maximal discharge current from the ion source attains a value of 3.8 A for operation with a PES
and 4 A for operation with a filament compensator. It is established that the maximal discharge current for the ion source
strongly depends on the working gas flow rate for low flow rates (up to 10 ml/min) in the EHIS; for higher flow rates, the
maximum discharge current in the EHIS depends only on the emissivity of the PES. Analysis of the emission parameters of EHISs
with filament and plasma neutralizers shows that the ion beam current and the ion current density distribution profile are
independent of the type of the electron source and the ion current density can be as high as 0.2 mA/cm2 at a distance of 25 cm from the EHIS anode. The balance of currents in the ion source-electron source system is considered
on the basis of analysis of operation of EHISs with various sources of electrons. It is concluded that the neutralization
current required for operation of an ion source in the discharge compensation mode must be equal to or larger than the discharge
current of the ion source. The use of PES for compensating the ion beam from an end-Hall ion source proved to be effective
in processes of ion-assisted deposition of thin films using reactive gases like O2 or N2. The application of the PES technique makes it possible to increase the lifetime of the ion-assisted deposition system by
an order of magnitude (the lifetime with a Ti cathode is at least 60 h and is limited by the replacement life of the deposited
cathode insertion). 相似文献
19.
The orientational dependence for different groups of secondary electrons — quasi-elastically scattered, inelastically reflected
with excitation of a plasmon and with ionization of the core level M
4.5, and the Auger electrons M
4.5
VV — are measured in the primary electron energy range 0.6–1.5 keV. The data are obtained for a Nb (100) single crystal by varying
the azimuthal angle of incidence of the primary beam, with complete collection of secondaries. A relationship is established
between the processes of focusing and defocusing of the electrons that have penetrated into the crystal in the 〈110〉 and 〈133〉
directions, which differ substantially in the atomic packing density. Specific details of the Auger orientation effect, due
to the focusinginduced variation of the flux density of the reflected electrons, are identified and explained. The contributions,
both of anisotropy of ionization of the core level and of variation of the backscattering intensity, to the angular dependence
of Auger emission and reflection with ionization loss are estimated. The possibilities of using such orientational dependences
for an element-sensitive analysis of the local atomic structure of surfaces are assessed.
Zh. Tekh. Fiz. 67, 117–123 (August 1997) 相似文献
20.
Auger and secondary electron spectroscopy become a more and more routine technique in surface characterization. Even with primary electron beam current density as low as 10?2 or 10?3 A cm?2 beam damage were reported in both Auger and LEED experiments. So we developed and compared counting method, brightness modulation and Harris' modulation techniques in terms of signal to noise ratio. The two first methods offer the advantage of a primary beam current density decreasing about 104 times. So various mechanisms of beam damage were identified as thermal, chemical and electrical. The advantage of the method is shown with hydrocarbons adsorption layer; the beam cracking of the organic chain produces a chemical shift of the CKLL maximum Auger line about 5 eV. This progressive shift is observed with current densities of 10?5 A cm?2 order of magnitude. The reproducibility of this low current density Auger spectroscopy allowed the study of the background and the true secondary electron yield modifications when adsorbed layers are built up. 相似文献