A New High Efficiency Multiwave Cerenkov Generator Operating at Low Magnetic Field

With a resonant cavity inserted between the second slow-wave-structure section and the tapered wavegulde, a new structure of the multlwave Cerenkov generator (MWCG) operating at low guiding magnetic field is proposed to produce high efficiency and high power microwave. Some features and potential advantages of the proposed device are analysed. The 2.5-dimensional partlcle-in-cell simulation is employed to verify the initial expectation.The results show that, with the use of an electron beam of 640keV and 8.4kA guided by the magnetic lield of 0.6 T, a stable and monochromatic X-band microwave output of 4 GW in peak power is achieved, and the average efficiency is over 30%.     

Excitation Mechanisms of Copper Ionic and Atomic Lines Emitted from a Low‐Pressure Argon Laser‐Induced Plasma

Abstract

Low‐pressure laser‐induced plasmas generated with a pulsed Nd∶YAG laser have complicated structures both temporally and spatially. The emission characteristics of the plasma are investigated for optimizing the experimental parameters in atomic emission spectrometry. The emission intensities of copper emission lines, measured in a time‐resolved as well as a time‐integrated mode, are strongly dependent on the kind of copper lines, ionic or atomic line, and the excitation energy. Also, the pressure of argon gas is the most important parameter for determining the behavior of these emission lines, including argon lines. Generally, copper ionic lines are dominantly emitted from the initial breakdown zone, because the copper ions are produced mainly in the hot breakdown zone. However, the Cu II 229.44‐nm line is emitted also from the expansion zone of the plasma. It results from an additional excitation process through the charge‐transfer collision particularly effective for the corresponding excited level. In this work, the excitation mechanisms for Cu I, Ar I, and Ar II lines are also discussed. The excitations occurring in the laser‐induced plasma can be well understood by taking the temporal and spatial variations in their intensities into consideration.     

Radiative Properties of an SHF Discharge Formed by a Ring‐Type Waveguide‐Slot Radiator

The actual spatial distribution of the intensity of SHF discharge glow in oxygen at different distances from the zone of input of SHF power has been investigated by the method of optical emission spectroscopy with subsequent abelization of the experimentally obtained integral characteristics of the intensity of radiation emitted by the OI ( = 777.7 nm) line. The investigations were carried out in a plasmatron on the basis of a ringtype waveguideslot radiator. The experimental results obtained indicate that the best uniformity of optical radiation over the discharge length is attained in the mode of pressureoptimum gas breakdown. Radial distributions of the radiation intensity are complicated in nature, which can be attributed to the differently pronounced skin effect exerted by a plasma on an electromagnetic wave under different discharge conditions. The results of the present work make it possible to interpret the previously obtained data of technological experiments and can be employed in developing technological processes of SHF plasma processing of materials and in designing SHF plasmatrons.     

Autoadhesion of High‐Molecular‐Weight Monodisperse Glassy Polystyrene at Unexpectedly Low Temperatures

Abstract

Healing of symmetric interfaces of amorphous anionically polymerized high‐ and ultrahigh‐molecular weight (HMW and UHMW, respectively) polystyrene (PS) in a range of the weight‐average molecular weight M _w from 102.5 (M _w/M _n = 1.05) to 1110 kg/mol (M _w/M _n = 1.15) was followed at a constant healing temperature, T _h, well below the glass transition temperature of the polymer bulk [T _g‐bulk = 105–106°C as measured by differential scanning calorimeter (DSC)]. The bonded interfaces were shear fractured in tension on an Instron tester at ambient temperature. Autoadhesion at symmetric HMW PS–HMW PS and UHMW PS–UHMW PS interfaces was detected mechanically after healing at T _h = 38°C for 107 hr, and even at 24°C (for longer healing times). The occurrence of autoadhesion between the surfaces of the UHMW PS with M _w = 1110 kg/mol at 24°C implies that the glass transition temperature at the interface, T _{g‐interface}, of this polymer was a least lower: by 82°C than its DSC T _g‐bulk, by 30–40°C than the Vogel temperature, T _∞—the lowest theoretical value of a kinetic T _g‐bulk at infinite long time—and by 20°C than T ₂ (a “true” thermodynamic T _g‐bulk corresponding to a second‐order phase transition temperature). To our knowledge, this is the first observation of such nature, which gives further evidence of the lowering of the T _g at polymeric surfaces and the persistence of this effect at early stages of healing of polymer–polymer interfaces.     

Structural Stability of CaCuMn6O12 under High Pressure and Low Temperature

In situ high pressure energy-dispersive x-ray synchrotron radiation diffraction and resistance experiments are carried out on CaCuMn6O12. Its crystal structure is stable in the measured pressure range. The equation of state of CaCuMn6O12 is obtained from the V/Vo - P relationship （V and Vo are the volumes at pressure P and at atmosphere）. The bulk modulus Bo is calculated based on the Birch-Murnaghan equation. Low temperature x-ray diffraction shows no phase transition occurring down to 160K.     

500W Rotating Switch Excimer Laser

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Fluorometric Characteristics of a Wave‐Guide Cell with Low Refractive Index

Recently, Teflon AF2400 (AF 1600, and AF 1601) was commercialized (DuPont Fluoroproducts, Wilmington, DE, U.S.A), that has a refractive index (1.29) lower than water (1.33), and which means that the wave‐guiding of light is possible in water. In this study, we used Teflon AF 2400 as a waveguide capillary longpath cell for fluorometry. He‐Cd and Ar⁺ lasers were used as the excitation source, at 325 nm and 514.5 nm respectively. The length of the capillary wave‐guide cell was 18.70 cm. The was wound twice on a flat surface (loop diameters: 2 cm and 3 cm). The excitation was executed through the wave‐guide cell and the fluorescence from the wound capillary cell wall was collected in a perpendicular direction to the loop. With excitation at 325 nm, the fluorescence intensity at 450 nm emitted from the cell wall decreased along with the increase in the refractive index of the solvent. This can be caused by attenuation of the source light due to absorption by the solvent. In our experiment, the solvent of higher refractive index has the higher absorption at 325 nm. On the other hand, the fluorescence intensity at 590 nm, with excitation at 514.5 nm, increases with increased refractive index of the solvent. This result shows that an increase in the refractive index of the solvent is preferable for maintaining the wave‐guiding of the source light. Here, the characteristics of fluorescence spectrometry are discussed in terms of the collection of fluorescence from the wave‐guide capillary cell wall.     

Electron Field Emission of CNx Thin Films Prepared by Low Pressure Plasma Enhanced Chemical Vapour Deposition

CNx thin films were prepared using low pressure plasma enhanced chemical vapour deposition,and then bombarded by low-energy N2^ .The compositions before and after N2^ bombardment were compared using x-ray photoelectron spectroscopy.The electron field emission characteristics of CNx thin films before and after N2^ bombardment were studied under the pressure of 10^-6pa.For the samples,the turn-on emission field decreased from 2.5V/μm to 1.2V/μm while the stable current density increased from 0.5mA/cm^2 to a value larger than 1mA/cm^2 before and after the bombardment.Our results illustrate that the field emission characteristics were improved after the bombardment of N2^ .     

Excimer Laser Pumped Tunable Picosecond Dye Lasers

研究了可调谐淬灭式染料激光器的染料浓度和泵浦能量对淬灭效果的影响，并且研究了它的调谐范围。对于308 nm XeCl准分子激光泵浦淬灭式香豆素498染料激光器，得到了一些具体的参数。     

Low‐temperature and high-pressure apparatus developed at ISSP,University of Tokyo

A high-pressure apparatus with cubic-anvil device has been successfully working for more than 10 years at low temperatures down to 2?K under quasi-hydrostatic pressure up to 10?GPa in study of solid-state physics. Main parts of it are composed of a set of compact cubic-anvils, a top-loading high-pressure cryostat and a 250?ton press. All the particulars of the cubic-anvil apparatus are given, including pressure calibrations at low temperature.     

An Overview of the High‐Pressure Vibrational Spectra of Clays and Related Minerals

Abstract

An overview of the effect of high external pressures on clays and related minerals is presented. The results show that this is an area that will welcome further investigation in the future, especially in view of the importance of clay minerals in the Earths's mantle and, possibly, even in prebiotic chemistry in the formation of amino acids and the mineralogy of the Martian surface.     

Growth of a Novel Periodic Structure of SiC/AIN Multilayers by Low Pressure Chemical Vapour Deposition

A novel lO-period SiC/A1N multilayered structure with a SiC cap layer is prepared by low pressure chemical vapour deposition （LPCVD）. The structure with total film thickness of about 1.45~m is deposited on a Si （111） substrate and shows good surface morphology with a smaller rms surface roughness of f.3 nm. According to the secondary ion mass spectroscopy results, good interface of the 10 period SiC/A1N structure and periodic changes of depth profiles of C, Si, A1, N components are obtained by controlling the growth procedure. The structure exhibits the peak reflectivity close to 30% near the wavelength of 322 nm. To the best of our knowledge, this is the first report of growth of the SiC/AIN periodic structure using the home-made LPCVD system.     

An ARC Facility for Studying Carbon Plasma and Obtaining Low‐Dimensional Carbon Structures

An experimental DUF2000 facility for spectroscopic investigations of a reducedpressure carbon arc and also for production of lowdimensional carbon structures (fullerenes, nanotubes, etc.) is described.     

Multiwave electric-discharge radiator for the 175–258-nm region

The radiation spectra of plasma in the region of 130–350 nm and the intensities of the 175-nm ArCl, 193-nm ArF, and 258-nm Cl₂ bands produced in the transverse volume discharge on a mixture of Ar/CF₂Cl₂ = (1–15)/(0.008–0.150) kPa are investigated. The discharge is shown to be a multiwave source of UV-VUV radiation on transitions of ArCl, ArF, and Cl₂ molecules. The optimum content of Freon-12 molecules is 0.008–0.010 kPa and that of argon atoms 10–15 kPa. The ratio of the intensities of the ArCl (B-X) and ArF (B-X) bands is 10, which is approximately equal to the ratio of concentrations of [Cl⁻] and [F⁻] ions, which are formed in the reaction of dissociative electron attachment to CF₂Cl₂ molecules. The service life of a radiator with λ = 175 nm of ArCl on one mixture in a gas-static mode is not greater than 5·10³ pulses. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 407–408, May–June, 2000.     

Effects of Shock Pressure on Transition Pressure in Zr

Measurements of free surface velocity profiles of high-purity Zr samples under shock-wave loading are performed to study the dynamic strength and phase transition parameters. The peak pressure of the compression waves is within the range from 9 to 14 GPa, and the Hugoniot elastic limit is 0.5 GPa. An anomalous structure of shock waves is observed due to the α - ω phase transition in Zr. Shock pressure has effects on transition pressure which increases with increasing compression strength, and the stronger shocks have a lower transit time.     

A Quenched Dye Laser Pumped by a KrF Excimer Laser

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Electroluminescence and Spectral Properties of N9‐Isobutyl‐2‐Oxo‐3‐Phenyl‐3N‐Benzo[F]Chromene‐9‐Sulfonamide

Experimental data on the synthesis and spectral properties (UV, IRFourier, xray photoelectronic, and luminescence spectra) of the sulfonamide derivative of benzocoumarin in an isopropanol solution and in a film applied by thermal vacuum deposition (TVD film) are reported. The use of TVD films of the investigated substance as electroluminophors is shown to be promising.     

Pressure Shifts and Pressure Broadening of the B and γ Bands of Oxygen

Measurements of pressure shift and pressure broadening in molecular oxygen have been made for rotational transitions in the B (1←0) and γ (2←0) vibrational bands of the b¹Σ⁺_g←X³Σ⁻_g visible electronic transition. The absorption features were measured simultaneously in two cells by photoacoustic spectroscopy using a scanning dye laser. The measurements were made with background gases of both pure oxygen and air at room temperature. The pressure shifts were all negative. The measurements show the magnitude of the pressure shift increasing with vibrational quantum number when compared with existing data for the A (0←0) band. The shifts also increase with rotational number within each vibrational band. The shifts in air are larger than in oxygen although the difference gets smaller with vibrational number. The average shifts in air for the A, B, and γ bands were 36, 11, and 0.2% higher, respectively, than in pure oxygen. The pressure broadening of the rotational lines does not change significantly with vibrational number and in general decreases with rotational number within a band. The pressure shift measurements were used by the high-resolution Doppler imager (on the Upper Atmospheric Research Satellite) to correct the Doppler wind measurements.     

Pressure dissociation of dense hydrogen

The self-consistent fluid variational model （SFVM） has been used to describe the pressure dissociation of dense hydrogen at high temperatures. This paper focuses on a mixture of hydrogen atoms and molecules and is devoted to the study of the phenomenon of pressure dissociation at finite temperatures. The equation of state and dissociation degree have been calculated from the free energy functions in the range of temperature 2000-10,000K and density 0.02-1.0g/cm^3, which can be compared with other approaches and experiments. The pressure dissociation is found to occur in higher density range, while temperature dissociation is a more gradual effect.