bluuebunny/crossref_metadata_2025 huggingface dataset:
Helical antenna for exciting azimuthally asymmetric Alfvén waves
Authors: Knox S. O. , Paoloni F. J. , Kristiansen M.
Published: February 2003

A new coupler for exciting azimuthally asymmetric Alfvén waves has been experimentally investigated. The coupler, which consists of four symmetrical helical straps wound around the vacuum vessel, is driven by a four-phase rf source. Waves excited by the coupler vary azimuthally as exp(jmϑ), where m can be chosen to be either +1 or −1. The coupler exhibits a strong propagation directionality and is capable of launching waves whose wavelengths differ considerably from its own. Loading measurements indicate an equivalent coil impedance, with a plasma load, of 1.2–3.9 Ω, which depends on the excitation frequency and the sign of m. The m=−1 wave was observed to propagate above and below ωci and was identified as the fast wave. The m=+1 wave was observed only below ωci as the slow wave. No m=+1 fast wave or m=−1 slow wave was observed.
A simple model for high-current arcs stabilized by forced convection
Authors: Lowke J. J. , Ludwig H. C.
Published: February 2003

Using a one-dimensional analysis investigations are made of properties of arcs stabilized by forced convection in a nozzle. For the current regime where arc diameters are large enough so that conduction and turbulence losses can be neglected at the arc center, yet small enough so that axial pressure and velocity distributions are determined by the nozzle shape, a simple model yields the following analytic properties: (i) Electric field E (z) and temperature distributions T (z) are independent of current, I; (ii) arc area is proportional to arc current and is given approximately by a simple formula; (iii) T (z) is approximately independent of p0, but E (z) ∝p01/2 and arc area ∝1/p01/2, where p0 is the tank pressure; and (iv) the Cassie equation for the time variation of arc conductance is valid. It is assumed that the effective radiation-emission coefficient U (T) is independent of arc radius. We have made measurments of arc area as a function of current in sulfur hexafluoride. These results, together with similar measurements of other investigators using also air and nitrogen, are in good agreement with the theoretical predictions.
Prediction of properties of arcs stabilized by forced convection
Authors: Tuma D. T. , Lowke J. J.
Published: February 2003

A one-dimensional arc model has been used to calculate the central temperature, arc radius, and electric field as a function of axial position for steady-state arcs in forced convection in nozzles. Calculations indicate that the axial distributions of pressure, plasma velocity, and gas velocity are sensitive to the degree of gas heating by the arc of the surrounding gas, significant differences being obtained between assumptions of the gas being isothermal or expanding adiabatically. Despite the fact that turbulence effects are omitted in the model, good agreement is obtained with experimental results of arc temperature, radius, and electric field for a 2000-A arc in nitrogen. Calculations as a function of current indicate regimes of low, intermediate, and high current where arc voltage respectively decreases, is constant, and increases with increase of current. In the latter regime, the increase in voltage is caused by the arc ’’clogging’’ or restricting the gas flow in the nozzle.
Mechanism of rf reactive sputtering
Authors: Shinoki F. , Itoh A.
Published: February 2003

The reactive mechanism of rf reactive sputtering has been investigated by mass spectrometry in an rf diode sputtering system. The result indicates that the gettering action of the sputtered active atom deposits influences the progress of reactive sputtering in addition to the target reaction. A model, taking the gettering action into consideration, is presented for the reactive sputtering of a metal. This model shows that an abrupt steplike decrease in the sputtering rate may occur at a definite partial pressure of a reactive gas p* in the plasma. The pressure p* is determined from the gettering rate of the sputtered deposits relative to the throughput of the reactive gas. The value of the pressure p* calculated on this model is in good agreement with the experimental results.
Recoil contribution to ion-implantation energy-deposition distributions
Authors: Brice David K.
Published: February 2003

A previous method for directly calculating the spatial distribution of energy deposition into damage or ionization for ions implanted into solid targets is extended to account for energy transport by recoiling target atoms. The new calculations extend the applicability of the method to lower incident ion energies. In addition, an intermediate step in the calculations provides information on the spectrum of target recoil atoms. Good agreement is obtained between experiment and theory using the improved procedure. Calculated damage energy distributions are presented for 10-keV–1-MeV B, P, As, and Sb ions incident on silicon.
Stress dependence of elastic-wave attenuation in LiF
Authors: Gupta Y. M.
Published: February 2003

Shock-wave propagation studies along the 〈100〉 direction in LiF single crystals are presented for three elastic impact stresses, namely, 39, 29, and 15 kbar. Present results demonstrate a stress threshold for a large increase in plastic strain rate and establish stress relaxation as a bulk property. Analysis of the data reveals a one-to-one correspondence between plastic strain rate and stress at the elastic-shock front. This is in agreement with the constitutive relation generally used for stress-relaxing solids under plate-impact loading.
Auger analysis of silicon thin films deposited on carbon at high temperatures
Authors: Chang Chin-An , Siekhaus Wigbert J.
Published: February 2003

Silicon films (2000–3000 Å thick) were vacuum deposited onto pyrolytic graphite, extruded graphite, and glassy carbon at 1150–1200 °C to test the possibility of using carbon as a substrate in thin-film silicon solar cells. The distribution of silicon and carbon in the carbon-silicon interface was studied using Auger spectroscopic depth profiling. The results showed that, for all substrates, carbon diffused deeply into silicon films, and for all substrates except glassy carbon, silicon also diffused deeply into carbon. In both cases, silicon carbide is formed. Several methods to build diffusion barriers were tested. A diffusion mechanism is proposed according to which silicon atoms first form a carbide layer with the surface carbon atoms, whereafter cracking of the carbon lattice and diffusion of silicon through the carbide layers into the carbon substrates follow. This mechanism is shown to explain very well the dependence of the measured silicon and carbon contents on the structure of the carbon substrates used for depositions.
Evidence of charge exchange pumping in calcium−xenon system
Authors: Chubb Donald L.
Published: February 2003

A flowing xenon plasma seeded with calcium was used to investigate the population mechanism for the 5s and 4d levels of Ca+. From the dependence of certain line intensity ratios on electron temperature it was concluded that charge exchange between Xe+ and Ca is the predominate mechanism for populating the 5s and 4d levels. Comparison with intensity ratios obtained in Ca−Ar and Ca−Kr imply the same conclusion.
Uniaxial anisotropy in MgFe2−yAlyO4
Authors: Borrelli N. F.
Published: February 2003

Single crystals of MgFe2−yAlyO4 (y=0−0.9) grown from PbO flux exhibit stripe−serpentine domains in (100) sections indicating an induced uniaxial anisotropy similar in behavior to that existing in rare−earth garnets. The anisotropy field was found to be less than 4πMs. The magnetization was found to be a complex function of temperature and aluminum content due to the variable tetrahedral occupation of the Mg2+ ion. This latter fact is proposed to account for the uniaxial anisotropy. Other low−moment spinel single crystals were grown with no observation of stripe domains.
Electric field induced deformation of ruby
Authors: Yamaguchi S.
Published: February 2003

An extremely strong electrostatic field of 2×104 kV/cm was produced at the surface of a ruby crystal by charging it with electrons. The ruby under electrostriction showed a superlattice structure along the 110 axis whose long period was about 80 Å. The deformed ruby emitted a red light whose wavelength was approximately 6000 Å, while being irradiated with an electron beam.
Role of Ca++ impurities in the evaporation kinetics of NaCl and KCl crystals
Authors: Yacamán M. José
Published: February 2003

The vacuum evaporation of NaCl and KCl crystals doped with 300 ppm calcium impurities is studied. The gold decoration technique is used to develop monotomic steps on the evaporating surfaces. It is found that impurities tend to diffuse from the voluem to the crystal surface forming a second phase on ti. The impurity nuclei interact with ledges producing several step reactions. The ratio of the perpendicular components of step reactions. The ratio of the perpendicular components of step velocities in 〈100〉 and 〈100〉 surface directions has been measured as a function of the heating period. The calcium impurities tend to reduce this ratio from 1.0 to a limiting value of 0.72. It is concluded that divalent impurities play a dominant role on the topography of the evaporating surface.
Index of refraction of barium oxide
Authors: Anderson C. J. , Hensley E. B.
Published: February 2003

Values of the index of refraction of barium oxide are reported for the wavelength range from 435 to 629 nm. Measurements were made on prisms formed from single crystals.
Carrier concentration ratio and Hall mobility of semi−insulating GaAs upon photoexcitation and electron bombardment
Authors: Euthymiou P. C. , Nomicos C. D. , Theodorou D. E.
Published: February 2003

The electron−hole concentration ratio (c) and the Hall mobility (μH) of Cr−doped semi−insulating p−type GaAs crystals were investigated as a function of illumination intensity (I), before and after bombardment with 90Sr−90Y β− particles. The quantities c and μH were determined by using photomagnetoresistance and photo−Hall measurements at room temperature. The ratio c as a function of I shows a minimum due to the action of traps. Bombardment with β− particles introduces new trapping levels resulting in a marked change of the ordinate of the minimum.
Ohmic contacts for moderately resistive p−type InP
Authors: Schiavone L. M. , Pritchard A. A.
Published: February 2003

A low−resistance (0.1 Ω/mm2) Ohmic contact to moderately resistive (1−10 Ω cm) p−type InP has been developed using Au/Zn/Au metalization.
Anisotropy in the laser performance of NdP5O14
Authors: Huber G. , Krühler W. W. , Bludau W. , Danielmeyer H. G.
Published: February 2003

We report, for the first time in a biaxial laser material, on the distribution of fluorescence cross sections in the index ellipsoid. The largest effective fluorescence cross section of pure NdP5O14 at room temperature (2.0±0.1) ×10−19 cm2 for light at 1.0512 μ wavelength polarized parallel to the 2 axis which coincides with the crystallographic b axis. We predict from the cross sections the cw thresholds and polarizations of the four highest-gain laser transitions and verify the results quantitatively by operating one crystal in all major polarizations. We measured the major phase and group refractive indices and the thermal expansion coefficient of the optical lengths near 1.05 μ wavelength. We also discuss the twin domains which have different orientations of the crystallographic and optic axes. In imperfect crystals they can easily be created by thermal stresses which can drastically increase the laser threshold.
Refractive-index behavior of ternary chalcopyrite semiconductors
Authors: Wemple S. H. , Gabbe J. D. , Boyd G. D.
Published: February 2003

Refractive-index dispersion data for 11 I-III-VI2 and II-IV-V2 chalcopyrite semiconductors are analyzed with a view towards obtaining a good representation of the data, values of physically meaningful parameters, and estimates of errors. Using a moment decomposition analysis, it is found that (i) only four parameters (three electronic and one lattice) are required to fit each dispersion curve, (ii) all differences between chalocopyrites and their zinc-blende binary analogs can be viewed as simple band-gap-shift effects, (iii) in contrast to cuprous halides, oscillator strength contributions from d-electron valence states in Cu and Ag chalcopyrites appear to be negligible, (iv) energy downshifts in chalcopyrites involve the entire ε2 spectrum, and (v) there is no clear quantitative correlation between structural distortions in chalcopyrites and anisotropies in optical parameters related to the birefringence. Finally, a brief discussion of the applicability of model ε2 spectra to descriptions of refractive-index dispersion and related optical effects is presented.
Quadrupole splitting of 57Fe in the dichalcogenides of pyrite and marcasite structure
Authors: Ward J. B. , Howard D. G.
Published: February 2003

Measurements of the quadrupole splitting in the pyrite-structure compounds FeS2, Fe0.01Co0.99S2, and Fe0.01Ni0.99S2 are reported. These splittings, and those of the similar compounds FeS2, FeSe2, and FeTe2 of the marcasite structure, are shown to correlate well with the electric field gradient at the Fe site, calculated on the point-charge model. Deviations of the calculated quadrupole splitting from that observed in these compounds are in the directions to be expected from covalent effects and from distortion of the local environment of the Fe atoms.
Theory of the photoacoustic effect with solids
Authors: Rosencwaig Allan , Gersho Allen
Published: February 2003

When chopped light impinges on a solid in an enclosed cell, an acoustic signal is produced within the cell. This effect is the basis of a new spectroscopic technique for the study of solid and semisolid matter. A quantitative derivation is presented for the acoustic signal in a photoacoustic cell in terms of the optical, thermal, and geometric parameters of the system. The theory predicts the dependence of the signal on the absorption coefficient of the solid, thereby giving a theoretical foundation for the technique of photoacoustic spectroscopy. In particular, the theory accounts for the experimental observation that with this technique optical absorption spectra can be obtained for materials that are optically opaque.
A high-yield ion source for producing beams of H+, H+3, He+, Ne+, Ar+, Li+, K+, Na+, and Cd+
Authors: Newton G. , Unsworth P. J.
Published: February 2003

A high-yield radio-frequency ion source is described in which the ionization efficiency has been considerably enhanced by arranging for the radio-frequency oscillator to excite the lowest-order (m=0) helicon wave in the plasma. It has been used to produce intense beams of H+, H+3, He+, Ne+, Ar+, Li+, K+, Na+, and Cd+. A proton beam of up to 10 mA H+ is attainable, with a proton fraction in excess of 96%, using only 300 W of excitation power.
A major advance in high-power electron-beam welding in air
Authors: Lowry J. F. , Fink J. H. , Schumacher B. W.
Published: February 2003

A major extension of the capabilities of nonvacuum electron-beam welding follows from the development of a machine with higher beam power. Tests with a new atmospheric electron gun operating at 60 kW have shown that the advantages of nonvacuum electron-beam welding must be reevaluated. Gas heating produced by the beam itself becomes very pronounced, so that electron scattering is reduced causing the high-power density of the beam to be retained over larger working distances. Single-pass butt welds with a depth-to-width ratio of 4 : 1 can be made in 3.8-cm-thick steel at a speed of 0.77 cm/sec, while the ultimate welding depth exceeds 5 cm. Medium thick material, e.g., 1.3-cm steel, can be welded at a 5-cm work distance, with a depth-to-width ratio of 3 : 1. The large work distance permits access to more complex structures and interior corners such at T sections, which can now be fabricated from a plate, 1.3 cm thick, at a speed of 2–3 cm/sec, making a full through weld from one side. Also, seam welds of two 3-mm-thick hot-rolled steel sheets can be produced at speeds of up to 15 cm/sec. High-power machines need not be significantly larger or costlier than low-power guns, and the present 60 kW does not represent any technical limit. Welding efficiency improves with higher power; when welding steel of 2 cm thickness or more the energy efficiency of the process at 60 kW is better than 50%, while at 40 kW it is merely 30%. In addition, the high power permits greater welding speed. These developments translate directly into improved cost justification for electron-beam welding and a broad expansion of its possible applications.
Structure and properties of bubble domains in cholesteric-nematic mixtures
Authors: Bhide V. G. , Chandra S. , Jain S. C. , Medhekar R. K.
Published: February 2003

Textural laser diffraction and light-scattering studies on homeotropically aligned nematic material (MBBA) doped with cholesteryl nonanoate (CN) has been carried out with and without an applied ac (50 Hz) electric field. In the narrow range of the ratio of the pitch p to the thickness l of the cell, 1.2<p/l<2, one observes uniformly densely packed bubble domains which grow in size on application of an electric field. In the range p/l≳2, the bubble domains become visible only at certain applied electric fields which increase with a decrease in the CN concentration. These bubble domains constitute a cholesteric phase with the spiral axis perpendicular to the substrate in a matrix of homeotropically aligned nematic material. The increase in the bubble domain size on application of electric field constitutes a nematic → cholesteric transformation. Light-scattering experiments indicate an optimum doping in relation to the threshold potential, contrast ratio, etc.
Composition profiles and Schottky barrier heights of silicides formed in NiPt alloy films
Authors: Thomas Simon , Terry Lewis E.
Published: February 2003

Metal silicides such as PtSi and NiSi have important applications in silicon integrated circuit technology as rectifying or Ohmic contacts. With a view to obtaining contacts with Schottky barrier heights adjustable between those of NiSi and PtSi, silicides were formed in NiPt alloy films with varying concentrations of Ni and Pt. The metal films were sputter deposited sequentially from Ni and Pt targets and also from a single alloy target containing 15 wt% Pt. Silicides were formed by sintering at 475 °C for 20 min. The depth-compositional profiles of these films were obtained by Auger electron spectroscopy (AES) coupled with Ar+ ion sputtering. The effects of the sintering and the presence of oxygen impurity on the composition profiles are discussed. The chemical effects observed in the Auger spectra from the silicides are presented. The Schottky barrier height (φB) of the silicide film on n-type silicon increases from that of NiSi-nSi to PtSi-nSi with increasing amount of Pt in the NiPt films. The variation of φB cannot be adequately explained by the interfacial composition obtained from the Auger data.
Obtaining densities of states from tunneling between two superconductors
Authors: Vopat F. E. , Lee Hyung Joon , Tomasch W. J.
Published: February 2003

We consider tunneling between two superconductors, SA and SB, in the approximation that SA is a BCS superconductor and that thermal excitations are unimportant. Inversion formulas are developed which permit numerical evaluation of the tunneling density of states for SB when the ac conductance, or its voltage derivative, is known as a function of bias voltage. The method is applied to finely spaced (∼30 μV) conductance structure produced by quasiparticle interference phenomena in a thick (∼30 μm) In film at 0.3 K (so-called Tomasch effect).
Zigzag band and bubblelike domains in Co-P amorphous thick films
Authors: Puchalska I. B. , Sadoc J. F.
Published: February 2003

Zigzag bands and bubblelike domains have been observed in Co-P amorphous films deposited on Cu and glass/Cr+Au substrates in a rotating magnetic field. The observations were carried out by the Bitter technique. Zigzag domains on the top and bottom surfaces in the virgin state and two kinds of bubblelike domains in the perpendicular and in-plane applied fields were observed. The domain’s alignment on the surfaces and in cross sections is due to perpendicular easy axis and to in-plane anisotropy induced by rotating fields during deposition. These domains are very similar to those reported in single-crystal YIG films.
Determinations of oxide thicknesses on tritided erbium films using beta-induced x-ray fluorescence
Authors: Musket R. G. , Bauer W.
Published: February 2003

For a tritided erbium film, tritium-decay betas induce characteristic x-ray emission from the film, the Er2O3 oxide layer, and the substrate. Measurement of the beta-induced x-ray spectrum for x rays with energies between ∼0.3 and 8 keV using a windowless Si(Li) detector permitted evaluation of the O(Kα)/Er(Lα) intensity ratio. This ratio was correlated with the total oxygen surface density as determined using proton-induced x rays from the same films, and the results have beeen compared to a theoretical model by Haggmark. A strong dependence of the O(Kα)/Er(Lα) ratio on Er2O3 areal density has been demonstrated for oxide thicknesses less than ∼300 Å.
Beta-induced x rays from oxides on metal tritide films: A simple theoretical model
Authors: Haggmark L. G.
Published: February 2003

A simple theoretical model has been developed to determine the intensity of the metal x rays emitted from metal tritides and also the intensity of the oxygen x rays from oxides that form on the surface of these tritides. This model includes the transport of the beta-decay electrons, the details of the x-ray production mechanisms, and the transport of the x rays out of the tritide films. It was found that for small surface oxide densities the ratio of the intensities of oxygen-to-metal x rays is a sensitive indication of the amount of surface oxide present. Reasonable comparisons were made with measured O(Kα)/Er(Lα) intensity ratios from Er(D,T).
Recent investigations on the stationarity of 1/f noise
Authors: Stoisiek M. , Wolf D.
Published: February 2003

The fluctuations of the variance of stationary Gaussian random noise with an imposed 1/f power spectrum is treated theoretically, and experiments under well-defined conditions of 1/f noise in carbon resistors and bipolar transistors are reported. The close agreement between theoretical and experimental results demonstrates that the statistical properties of 1/f noise in physical sources are fully consistent with the assumption of stationarity.
Preparation and some magnetic properties of amorphous GdxFe1−x alloy thin films
Authors: Mimura Y. , Imamura N. , Kobayashi T.
Published: February 2003

Amorphous GdxFe1−x (0⩽x⩽0.35) thin films were prepared by rf cosputtering using the iron target covered partially with small gadolinium pieces. The composition dependences of the saturation magnetization, M-H loops, and domain structures were studied. The coercive force was obtained as a function of the composition and temperature. Such magnetic properties of GdFe sputtered films were very similar those of amorphous GdCo films.
Radiofrequency echoes from piezoelectric powder
Authors: Kupca S. , Searle C. W.
Published: February 2003

Echoes of mechanical origin following a two or more pulse excitation, analogous to those observed from normal metals or ferromagnetic powders, were observed from powder of Rochelle salt. Echoes were excited by rf pulses of electric field intensity (e1,e2) ≳ 800 V/cm and varied approximately as e1e22. The echo amplitude was strongest in the ferroelectric region and the relaxation time of the echo gradually decreased with temperature.
Study of atomic disorder produced by fast neutrons in silicon using infrared spectroscopy
Authors: Rolle M. E. , Corelli J. C.
Published: February 2003

A study has been made of the absorption bands of silicon, irradiated with high doses of fast neutrons (E≳1 MeV), by infrared spectroscopy in the region between 200 and 4000 cm−1 (50–2.5 μ). The relationship between several effects [band tailing (0.2–0.5. eV), divacancy-associated band (3.45 μm), higher-order bands (700–1400 cm−1), and single-phonon bands (observed at 488, 410, and 332 cm−1)] and different irradiation doses up to 1019 fast neutrons/cm2 has been investigated. From the results of the absorption due to band tailing it can be assumed that the crystal is not amorphous. However, the observed vanishing of the higher-order bands at the highest doses indicates an important change in the damaged lattice. The annealing behavior up to 600 °C, at the measuring temperatures of 78 and 300 °K, showed a slower annealing out of the single-phonon bands for the high dose. From the stressing experiments, performed for single-phonon bands, a constant dichroic ratio of 1.12 was measured. From this an estimation of the radiation-induced strain within the lattice was made and found to be ?2×10−2. A new electronic band was found after a long-term annealing at the wave number 312 cm−1.
Infrared reflection and Raman scattering of ion-implanted nitrogen in gallium phosphide
Authors: Kachare A. H. , Cherlow J. M. , Yang T. T. , Spitzer W. G. , Euler F. K.
Published: February 2003

Infrared reflection and Raman scattering measurements were performed on a set of GaP samples implanted at room temperature with 14N+ and 15N+ ions with an energy of 3 MeV and fluences in the range of 5×1013–2×1017 ions/cm2. The reflection data for all but the most heavily implanted samples were fitted with a classical dispersion layer model. Some of the parameters used in this model were obtained from the Raman data. An increased in the damping constant γ is the largest implantation-induced change in the dispersion parameters. Annealing studies were performed on several samples implanted with 2×1017 ions/cm2. Raman and x-ray measurements indicated that samples annealed at 773 °K recrystallized in a polycrystalline fashion but those annealed at 573 °K became single crystals. After both types of annealing procedure, structure resulting from the nitrogen localized vibrational mode was seen in the reflection spectra. This mode exhibited the expected isotope shift, appearing at ∼495 cm−1 for samples implanted with 14N+ and ∼480 cm−1 for samples implanted with 15N+. That the mode was observable only after annealing indicated that there was some reduction of the short-range order in the unannealed samples. The results are discussed in terms of prevalent models for lattice disorder introduced by ion implantation.
Use of dynamic theory to describe experimental results from volume holography
Authors: Magnusson R. , Gaylord T. K.
Published: February 2003

The general applicability of dynamic theory to the description of the recording and readout characteristics of volume (thick) hologram gratings is indicated. In dynamic theory (as opposed to static theory), the volume nature of the thick holographic grating allows the interference of an incident light beam with its own diffracted beam inside the recording medium. This effect causes the continuous recording of another grating that alters the initial one, producing a resultant grating that is not uniform through the thickness of the recording material and a grating whose writing and reading characteristics may vary dramatically depending on the recording material and the experimental conditions. A large number of diverse types of writing, reading, and angular selectivity behavior have been reported in the published literature. The dynamic theory of thick hologram writing and reading is shown to predict qualitatively all of these various types of experimental behavior.
Internal bias effects on pyroelectric measurements near the Curie temperature in triglycine sulphate
Authors: Shaulov A. , Simhony M.
Published: February 2003

Simultaneous measurements of the pyroelectric (PE) coefficient λ and permittivity ε from the PE voltage responses to step ir radiation signals in triglycine sulphate (TGS) are reported as functions of temperature in both the ferroelectric and paraelectric phases. It is shown that the observed lowering and widening of the peaks of λ and ε, the appearance of a PE effect in the parelectric phase, and the shift of the ε peak to temperatures above Tc can be explained by the existence of an internal bias field Eb. The values of Eb calculated to fit the experimental results vary in different TGS samples from 30 to 150 V/cm.
Use of plasma instabilities in laser isotope separation
Authors: Book David L.
Published: February 2003

A design is sketched for a continuously operating device which separates one laser-excited isotopic species of a given element from a mixture. The essential innovation is the use of collisionless plasma instabilities to slow down ions of the desired species from two counterstreaming initially neutral beams.
Time development of the state multipoles of excited sodium atoms, pumped with dye lasers
Authors: Hertel I. V. , Stoll W.
Published: February 2003

Rate equations for optical pumping sodium atoms to the 32P3/2 (F=3) state are solved. Although the total upper-state population reaches its equilibrium value after approximately the natural lifetime τ, the magnetic sublevel population (expressed in terms of state multipole moments) becomes stationary only after over 15–30τ even in the high-intensity limit.
Frequency stability of a cw HF chemical laser
Authors: Wang C. P.
Published: February 2003

A new scheme for measuring the frequency stability of a cw HF chemical laser is described. It is based on the measurement of the beat-frequency spectrum of longitudinal modes and the mode-pulling effect in a high-gain medium. The mode-pulling effect can also be used to actively stabilize the laser frequency. Experimental measurements on the mode pulling and the stability of a free-running cw HF chemical laser agree with theory and other experimental measurements.
Shape and stability dependence of passively mode-locked pulses on absorber relaxation time
Authors: Hagelstein Peter L. , Ausschnitt Christopher P.
Published: February 2003

The dependence of the saturable absorber mode-locked pulse shape upon the relaxation time of the absorber is determined when the laser gain is assumed constant. The pulses are found to be asymmetric with a slowly rising edge and a more rapidly decaying edge. The mode-locked pulse width is a weak function of absorber relaxation time TA, becoming broader with increasing TA. Furthermore, the pulses are found to experience a delay in traversing the absorber which lengthens the cavity transit time. The growth of perturbations introduced into the steady state is shown to be bounded, indicating that stable mode-locked operation is possible even in cases where TA is comparable to or greater than the width of the steady-state pulse.
Unconventional behavior of edge dislocations in a plane shock-stress field
Authors: Ma Ching H.
Published: February 2003

Because of the existence of the factors causing shock-associated damping effect on edge dislocations, an edge dislocation in a plane shock-stress field may slip under special circumstances in a direction without an apparent shear component of the shock-stress wave. In this paper the mechanism and the factors involved in this unconventional behavior of edge dislocations will be evaluated.
dc electrical conduction in thin Ta2O5 films. I. Bulk-limited conduction
Authors: Young Peter L.
Published: February 2003

Experimental measurements on the electrical conduction characteristic of thin Ta2O5 films are reported. The measured slope of the log (I) -E1/2 plot corresponds well with the calculated Schottky slope for very thin films. However, by two independent tests it is shown that the conduction process cannot be electrode limited, even if interface states or other interface irregularities are postulated to exist. From measurements on heat-treated samples, transition from a modified Poole-Frenkel slope to a Poole-Frenkel slope is observed, thus providing direct evidence that conduction in Ta2O5 films is bulk limited. It is further shown that the presence of water in the film is a necessary ingredient for the occurrence of the modified Poole-Frenkel slope.
Correlation between nonequilibrium thermodynamic theory and V-I curves of a thermionic converter
Authors: Robinson L. B. , Shimada K.
Published: February 2003

The methods of irreversible thermodynamics have been used as a basis for developing a transport theory applicable to thermionic cesium diodes. This theory was applied in describing certain aspects of experimental voltage-current (V-I) characteristic curves of a thermionic diode. Emphasis, in obtaining the description, is placed on the open-circuit voltage and short-circuit current of the V-I curves, obtained at the Jet Propulsion Laboratory. Experimental results show that the open-circuit voltage is essentially independent of the interelectrode spacing, whereas the short-circuit current varies inversely with the interelectrode separation. The inverse dependence is in agreement with the results of this present analysis and also with results expected from diffusion theory, which has been used in other analyses. In fact, the theory used in this present investigation reduces to diffusion theory under special assumptions. Deviations from diffusion theory, which were found in experimental results, can be accounted for using the theory developed in this paper.
Theory and analyses of the ac characteristics of defect thin-film insulators
Authors: Nadkarni G. S. , Simmons J. G.
Published: February 2003

In the past, ac properties obtained from thin-film metal-insulator-metal (MIM) samples have often been analyzed qualitatively in terms of the Debye relaxation process. Here we point out several anomalies and discrepancies associated with these analyses. We then go on to develop the theory of ac electrical properties in MIM systems in which Schottky barriers are assumed to exist at the metal-insulator interface. The resulting capacitance and conductance vs frequency, temperature, and voltage bias are shown to exhibit all the salient features of the observed data, suggesting that such a model is more applicable than the Debye model, at least in the case of the materials reviewed.
Pressure dependence of helium and neon solubility in vitreous silica
Authors: Shelby J. E.
Published: February 2003

The pressure dependence of helium (at 25 °C) and neon (at 150 °C) solubility in vitreous silica has been measured at pressures up to 1400 atm. Results appear to be readily explained by a simple statistical thermodynamical model based on the Langmuir adsorption model. Values for the accessible free volume of the glass network equal to 2.3×1021 atoms/cm3 for helium and 1.3×1021 atoms/cm3 for neon were obtained from these results.
Rapid determination of metal whiskers growth axes
Authors: Siegel H. M. , Self W. B. , Johnson R. M. , Wiseman C. D.
Published: February 2003

An x-ray diffraction technique for rapidly determining the crystallographic orientation of the growth axis of metal whiskers is described. The technique utilizes the x-ray short-wavelength limit to restrict the crystallographic planes capable of diffraction to those of low Miller indices.
Loss of shear strength in polycrystalline tungsten under shock compression
Authors: Dandekar Dattatraya P.
Published: February 2003

A reexamination of existing data on shock compression of polycrystalline tungsten at room temperature indicates that tungsten may be an exception to the common belief that metals do not behave like elastic-isotropic solids under shock compression.
The effect of oxygen adsorption on the thermionic emission properties of BaB6
Authors: Yamamoto Shigehiko , Honda Yukio , Okano Hiroshi
Published: February 2003

A new model of oxygen reaction at the BaB6 surface is proposed based on the thermionic emission data. The following reaction holds when there is oxygen present as ambient, 2BaB6+9O2→6B2O3+2Ba↑. The energy of oxygen adsorption on surface boron atoms was found to be about 3.6 eV.
Superconducting T
c′s in the Nb3Al-Nb3Ge-Nb3Ga system
Authors: Somasundaram R. , Toth L. E. , Spitzer H.
Published: February 2003

Superconducting Tc′s have been measured in bulk samples in the NB3AL-Nb3Ge-Nb3Ga alloy system. A broad composition region exists in which the onset of Tc exceeds 20 K; this region is more extensive than anticipated from the Tc behavior in the pseudobinary systems.
Application of optical fibers to the transmission of solar radiation
Authors: Kato Daisuke , Nakamura Takashi
Published: February 2003

The application of optical fibers to the transmission of solar radiation is discussed. Attenuations of the extraterrestrial solar radiation spectrum in optical fiber materials, fused-silica and soda-lime-silicate glass, are calculated based on intrinsic attenuation mechanisms. It is shown that fused-silica-core optical fibers transmit solar radiation effectively over distances of about 40 m. Possible areas of application of optical fibers to the solar energy utilization systems are suggested.
Time delay in pulsed operation of a CO2 laser with foreign gas additives
Authors: Kitazima Iwao
Published: February 2003

The time delay of the laser pulse behind the current pulse decreased to approach a constant value with increasing current pulse height. The foreign gas effects on the time delay were also observed. The addition of Xe or He to a CO2 gas discharge made the time delay shorter, but that of N2 made it longer. The current dependence of the time delay was well explained by the equation of the time-dependent population difference between the upper and lower laser levels. The foreign gas effects are also sufficiently explained by this equation.
Analytic modeling of gain-switched lasers. II. Laser amplifiers
Authors: Casperson Lee W.
Published: February 2003

The pulse transfer characteristics of gain-switched laser amplifiers are investigated analytically. New closed-form solutions have been obtained including arbitrary space- and time-dependent pump distributions. The general results are specialzied to the important cases of uniform and traveling-wave excitation. Input-pulse shapes considered include step functions, practial oscillator output pulses, and also the inherent spontaneous-emission noise. The results lead to improved models for pulse amplifiers and mirrorless traveling-wave lasers. By proper choice of pump characteristics arbitrary output-pulse waveforms can be synthesized.
AES depth profile measurements of niobium for superconducting cavities
Authors: Hahn H. , Halama H. J.
Published: February 2003

The paper reports on AES measurements taken on eight niobium samples which were treated according to typical procedures used in the preparation of superconducting cavities such as ultrahigh vacuum degassing, chemical polishing, electropolishing, and anodic oxidizing. The main objective of the present investigation was the determination of the oxygen depth profile of niobium surfaces. It was concluded that the surface treatments typically applied to superconducting rf cavities result in surfaces covered by layers of lower oxides on the order of 100 Å thick. In anodized niobium, the thickness of the pentoxide-metal transition is of the same order. The presence of a layer of a two-phase mixture NbO+NbO2, up to 50 Å thick, as well as a layer of two-phase NbO+Nb, about 50 Å thick, can be inferred. It is suggested that the performance of superconducting cavities could be limited by these low-Tc layers.
Josephson-like behavior in double Dayem bridge structures
Authors: Carelli Pasquale , Modena Ivo
Published: February 2003

The behavior of a pair of aluminum ’’Dayem’’ bridges in a magnetic field is reported. The quantum interference properties of the supercurrents are found biasing the links with an ac current and measuring its mean square voltage as a function of an external magnetic field. The shape of the so-obtained curve remains the same in a relatively large range of temperature: 6×10−3< (Tc−T)/Tc<5×10−2.
Solution of potential problems in systems which include magnetic material
Authors: Caldwell J.
Published: February 2003

harmonic analysis is used in the calculatoins of the forces arising when a sphere is placed in a nonuniform magnetic field produced by a superconducting winding. The rotational forces acting on a toroidal conductor of rectangular cross section due to an asymmetrically placed sphere of magnetic materialk are also investigated.
Mean strain in crystals containing dislocation loops
Authors: Howard C. J. , Brown L. M.
Published: February 2003

For a crystal containing prismatic dislocation loops there are, even within linear elastic theory, two conceivable definitions for the mean strain. The strains defined are distinguished as the mean ’’elastic’’ strain and the mean’’total’’ strain. It is emphasized that every component of the mean elastic strain is zero, while the mean total strain has components which are nonzero and correspond precisely to those changes in the macroscopic dimensions of the crystal which result when loops are introduced. The fact that two definitions of mean strain are possible may account in part for a current controversy concerning the x-ray lattice parameter. However, as the details of the x-ray diffraction from a crystal containing loops are undoubtedly complex, it seems unlikely that the lattice parameter would in general be simply related to the mean strain of either definition.
Effect of surface stress on wave propagation in solids
Authors: Gurtin Morton E. , Murdoch A. Ian
Published: February 2003

In this paper we consider an elastic half-space whose free surface is an elastic surface capable of supporting its own stress field. This surface stress is a function of surface strain and is related to the stress in the interior of the body by a nonclassical boundary condition. We here study, within the framework of the appropriate linearized theory, the reflection of plane harmonic waves by the free surface. We show that at very high frequencies the presence of surface stress results in a marked departure from the classical theory.
Lichtenberg figures of corona discharge at low frequencies
Authors: Wei Ling Y.
Published: February 2003

Corona discharge from metal teeth has been studied at frequencies up to 40 kHz. From the Lichtenberg figures, the length and the density of streamers are shown to decrease with increasing frequency. At the low-frequency end, the cathode streamers are more intense than the anode streamers, while at the high-frequency end, the reverse is true. For the same total discharge time, shorter pulses produce stronger streamers than the longer ones. In all cases tested, glass spacer was found to enhance the streamer intensity more than other media. The implications of the above results in Kirlian photography, plasma panel display, and laser excitation are discussed.
Minimum background plasma density for plasma-grounded e-beam targets
Authors: Mendel C. W.
Published: February 2003

A density criterion is derived for background plasmas intended to carry return current from an e-beam heated target. The criterion arises due to the depletion of the ions near the target and resultant potential change of the target. It is concluded that plasma densities near the target need to be about 1020 cm−3 for breakeven fusion systems.
Space-charge wave propagation on rippled electron beams
Authors: Mahaffey R. A. , Batchelor D. B. , Trivelpiece A. W.
Published: February 2003

A measurement of the phase characteristics of space-charge waves propagating on a rippled magnetically confined electron beam reveals a shift in the average value of the wave number from that expected for an unrippled beam. An analysis of space-charge wave propagation for such a beam can be done by assuming a small-amplitude sinusoidal variation of the beam radius about its average. This analysis shows that there is a periodic variation in the space-charge wave number as a function of distance along the beam. The average value of the wave number taken over one ripple period is shifted by an amount that agrees with experimental observations. This periodic variation of wave numbers results in sidebands similar to those associated with the frequency modulation of radio waves.
Energy distributions of electrons in electron-beam-produced nitrogen plasmas
Authors: Suhre D. R. , Verdeyen J. T.
Published: February 2003

A theory was developed which predicts the equilibrium electron energy distributions resulting from the injection of an electron beam into molecular nitrogen. The results were highly non-Maxwellian with a minimum existing near 2.5 eV. Using these distributions, fractional power transfers to various excitation processes were calculated. The theory was examined experimentally by using a Langmuir probe to measure the distributions produced by a beam of electrons in low-pressure nitrogen. The distributions were measured in absolute units and compared with theory. All of the major features of the theory were found to be present in the measurements.
Surface enrichment of copper due to keV Xe sputtering of an Al-Cu mixture
Authors: Chu W. K. , Howard J. K. , Lever R. F.
Published: February 2003

A surface enrichment of Cu due to keV Xe sputtering of Al-Cu mixtures has been observed by high-energy He ion backscattering and by Auger electron spectroscopy. The complementary nature of these two methods provides information on the total Cu enrichment (4.5×1015/cm2) and depth of the altered layer (∼300 Å).
Traveling-wave corona excitation of high-power uv nitrogen lasers operating at gas pressures ranging from 0 to 3 bar
Authors: von Bergmann H. M. , Hasson V. , Brink J.
Published: February 2003

The authors use a novel 60-cm traveling-wave pulsing system to investigate the properties of corona-excited uv nitrogen lasers operating at pressures ranging from 0 to 3 bar. The device will provide subnanosecond pulses at megawatt power levels. The lasing output at 337 nm can be enhanced by the addition of sulphur hexafluoride at total pressures of ≲1.5 bar.
Soft x-ray population inversion by resonant photoexcitation in multicomponent laser plasmas
Authors: Bhagavatula V. A.
Published: February 2003

A scheme for population inversion in the soft x-ray (≳100 Å) region, where the upper laser level is photoexcited by resonant line radiation from an identical or different ion species, is proposed. Ion pairs that may be used in this scheme are presented. Applying the results obtained for a general case to the Mg XII ions pumped by C VI ions, it is shown that gains in excess of 100 cm−1 are possible for the 4→3 transition at ∼130 Å in typical laser-produced plasmas.
Electron temperature measurements in a copper chloride laser utilizing a microwave radiometer
Authors: Sovero Emilio , Chen Che Jen , Culick F. E. C.
Published: February 2003

The electron temperature as a function of laser tube temperature of a copper vapor laser utilizing copper chloride as a lasant has been obtained by measuring the microwave incoherent radiation from the plasma in the laser tube. An unexpected increase of electron temperature at higher laser tube temperature may be due mainly to Penning ionization of the Cu atom by the metastable state of He or Ne buffer gases. The results obtained in this work provide part of the basis for understanding the behavior of the laser output as a function of tube temperature.