bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of highly strained InGaAs on GaAs
Authors: Price G. L.
Published: July 2002

The early stages of the molecular beam epitaxial growth of InxGa1−xAs on GaAs have been studied with reflection high-energy electron diffraction. Measurement of the in-plane surface lattice constant as a function of film thickness clearly showed a pseudomorphic to incoherent transition. Changes in the diffraction streaks indicated a corresponding two- to three-dimensional growth transition. The results are compared with various models of dislocation nucleation and good support is found for heterogeneous misfit accommodation by 60° dislocations.
Investigation of the critical layer thickness in elastically strained InGaAs/GaAlAs quantum wells by photoluminescence and transmission electron microscopy
Authors: Reithmaier J.-P. , Cerva H. , Lösch R.
Published: July 2002

We have studied strained InGaAs quantum wells with GaAlAs barriers, grown by molecular beam epitaxy, varying In content and well thickness. Photoluminescence measurements were made at 12 K. The appearance of a characteristic additional exciton-like photoluminescence peak indicates the transition between elastically strained and relaxed layers. This transition was also observed by the occurrence of misfit dislocations in the corresponding transmission electron microsope (TEM) images. Layer thicknesses and In content were also determined by TEM. The results give a critical layer thickness of 29±0.5 nm at an In content of 32±2%. This value lies about a factor of 3–4 above the critical layer thickness calculated by Matthews and Blakeslee [J. Cryst. Growth 27, 118 (1974)].
Time-resolved transmission of thin gold films during laser blow-off
Authors: Baseman Robert J. , Froberg Nan M.
Published: July 2002

The transmission through thin gold films on optical quartz during laser blow-off with 15 ns, 532 nm laser pulses has been measured. Dramatic changes in transmission mark the duration of the blow-off event with laser fluences above the threshold for removal. The integrated laser fluence required to blow-off the films is roughly independent of incident laser fluence, and is close to that expected to raise the temperature of the film to the boiling point at the film-support interface.
Growth of Al on GaAs(001): Observation of interfacial submonolayer structure
Authors: Donner S. K. , Blumenthal Rik , Herman J. L. , Trehan Rajender , Furman Ehud , Winograd Nicholas
Published: July 2002

Submonolayer structure has been observed using reflection high-energy electron diffraction during room-temperature deposition of Al onto (2×4) reconstructed GaAs(001) surfaces prepared by molecular beam epitaxy. This structure with a (4×1) symmetry occurs after ∼0.25 monolayer of Al deposition. It is growth-rate independent, reproducible, and stable. This result shows that there is a strong, directionally dependent adatom-adatom interaction at submonolayer coverages.
Gain switching of an AlGaAs/GaAs laser with an asymmetric double quantum well
Authors: Nomura Yoshinori , Sugimoto Hiroshi , Maruno Shigemitu , Morishita Yoshitaka , Wada Osamu , Ogama Tetsuo
Published: July 2002

We demonstrate a new gain switching mechanism in semiconductor lasers with an asymmetric double quantum well. The idea is to utilize overlap integral enhancement for coupled sublevels in the double quantum well at an applied forward voltage. Optical pulses of less than 10 ps full width at half maximum have been readily obtained with a moderate electrical excitation pulse height, 16.3 V (at a 50 Ω load) and bias current of 6% of the threshold. The advantages of the structure over a single quantum well for generating optical short pulses are shown experimentally.
Use of ultrathin oxides and thin polycrystalline silicon films for stable high-efficiency silicon solar cells
Authors: Gruenbaum P. E. , Gan J. Y. , Swanson R. M.
Published: July 2002

Initial designs of single-crystal point-contact solar cells showed a degradation in their efficiency due to photoinjected hot-electron damage. We have examined the ultraviolet stability of ultrathin oxides covered by a thin polycrystalline silicon film and a thick oxide. Optical modeling has shown that these oxide/polycrystalline silicon/oxide stacks can have extremely good antireflection properties which offset the absorption losses from the polycrystalline silicon. Experiments have determined that these stacks are stable under ultraviolet exposure and that the polycrystalline silicon is absorbing less light than predicted. Point-contact solar cells fabricated with this technique have achieved efficiencies as high as 24.4% under 36 W/cm2 of concentrated sunlight.
Growth of GaInAsP using ethyldimethylindium and tertiarybutylphosphine
Authors: Sharps P. R. , Timmons M. L. , Colpitts T. S.
Published: July 2002

The growth of GaInAsP lattice matched to GaAs by organometallic vapor phase epitaxy using ethyldimethylindium and tertiarybutylphosphine is reported for the first time. The composition of the films is approximately Ga0.87In0.13As0.75P0.25, giving a band gap of about 1.52 eV. Intrinsic films are n type. Both n- and p-type doped layers have been prepared. Photoluminescence measurements on intrinsic films give spectral half widths of about 70 meV. Capping the films with AlGaAs window layers and using n+-n, high-low junctions at the GaInAsP/GaAs interface greatly improve the photoluminescent properties. A minority-carrier lifetime of 35 ns in an intrinsic film has been measured and suggests that the quaternary is equivalent to AlGaAs with the same band gap.
Diffraction determination of the structure of metastable three-dimensional crystals of Ge grown on Si(001)
Authors: Aumann C. E. , Mo Y.-W. , Lagally M. G.
Published: July 2002

A straightforward kinematic analysis of diffraction from metastable three-dimensional crystallites of Ge grown on Si(001) is presented. Low-energy electron diffraction data from these crystallites agree with diffraction images calculated for a structure determined from scanning-tunneling microscopy data. Additionally, reflection high-energy electron diffraction images predicted for these crystals agree with existing data.
Temperature dependence of Si1−xGex epitaxial growth using very low pressure chemical vapor deposition
Authors: Jang Syun-Ming , Reif Rafael
Published: July 2002

We report measured Ge contents and growth rates for Si1−xGex films grown by very low pressure chemical vapor deposition between 570–700 °C. The ratio of Ge/Si was found to increase linearly with increasing the ratio of GeH4 flow rate to SiH4 flow rate. The nonlinear Arrhenius behavior of growth rate as a function of Ge fraction suggests that Ge enhances hydrogen desorption and modifies the activation energy for Si1−xGex growth. The growth rates of Si1−xGex show different dependencies on Ge content at different temperatures. The growth rate decreases with increasing Ge content at 700 °C, but increases monotonically with Ge at 570 °C. A peak in growth rate was observed at intermediate temperatures between 570 and 700 °C.
Change in conductance is the fundamental measure of spin-valve magnetoresistance
Authors: Dieny B. , Nozieres J. P. , Speriosu V. S. , Gurney B. A. , Wilhoit D. R.
Published: July 2002

The absolute change of sheet conductance (ΔG) of spin-valve multilayers is shown analytically and experimentally to be the macroscopic observable most directly related to the physical mechanism of giant magnetoresistance. Unlike the changes in resistance ΔR/R or ΔR, ΔG is directly connected to the changes in the Fermi spheres of the ferromagnetic layers induced by the variation in magnetic alignment. In structures comprising Si/Co 80 Å/Cu 25 Å/NiFe 50 Å/FeMn 90 Å/Ta 50 Å/Cu tCu/Ta 50 Å, in which only the thickness tCu is varied, the values and the thermal variations of ΔR/R(T) and ΔR(T) are strongly influenced by tCu through its shunting effect. In contrast ΔG is found to be independent of shunting.
Effects of drift and diffusion current flow on the high-speed performance of quantum well lasers
Authors: Taylor G. W. , Claisse P. R.
Published: July 2002

A new approach is described to incorporate the effects of drift and diffusion into the small signal transfer function of the quantum well semiconductor laser. The differential gain parameter is represented by the differential stimulated lifetime and is a constant, power-independent parameter. The nonlinear gain factor is not required in the analysis with the saturation of the resonant frequency resulting instead from the effects of diffusion current flow through the active layer. The electron and photon rate equations used are interrelated by the Fermi energy as a parametric variable.
High power, high brightness electron beam generation in a pulse-line driven pseudospark discharge
Authors: Destler W. W. , Segalov Z. , Rodgers J. , Ramaswamy K. , Reiser M.
Published: July 2002

High brightness (∼1010 A/m2 rad2), high power density (∼1010 W/cm2) electron beams have been generated by the mating of a hollow-cathode discharge device operating in the pseudospark regime to the output of a high power pulse line accelerator. Very small diameter (∼1 mm) electron beams with currents in the range 500–1000 A and energies in the range 150–300 keV have been generated with effective emittances estimated to be at or below 170 mm mrad. Such emittances are comparable to those achieved in conventional electron beam sources at current densities several orders of magnitude lower than those observed in these experiments.
Semi-insulating nature of gas source molecular beam epitaxial InGaP grown at very low temperatures
Authors: Look D. C. , He Y. , Ramdani J. , El-Masry N. , Bedair S. M.
Published: July 2002

InxGa1−xP lattice matched to GaAs (x≂0.51) has proven to be useful in many device applications. Here we show that undoped, semi-insulating InGaP is possible by growing with gas source molecular beam epitaxy at very low temperatures, 150–250 °C. The material grown at about 200 °C is n-type with a 296-K resistivity of 9×105 Ω cm, a mobility of 120 cm2/V s, and a donor activity energy of 0.48 eV. When annealed at 600 °C for 1 h, the resistivity increases to greater than 109 Ω cm and the resistivity activation energy to 0.8 eV.
Electron cyclotron resonance in silicon/silicon germanium heterostructures
Authors: Murphy S. Q. , Schlesinger Z. , Nelson S. F. , Chu J. O. , Meyerson B. S.
Published: July 2002

Far-infrared measurements of the cyclotron resonance absorption of a two-dimensional electron gas (2DEG) in a strained Si/SiGe heterostructure at low temperature (0.35–4 K) in the magnetic field range 2–14 T are reported. The effective mass was determined to be m*≂0.195±0.004 m0, and exhibited only a slight decrease (3%) at low carrier densities, in contrast to the large (40%) change observed in Si metal-oxide-semiconductor field effect transistors. In addition, the cyclotron absorption lines tend to be narrow (≲1 cm−1), and show a significant dependence on both field and carrier density that appears to be related to the filling of the quantized Landau and spin levels of the 2DEG.
CuInS2 based thin film solar cell with 10.2% efficiency
Authors: Scheer R. , Walter T. , Schock H. W. , Fearheiley M. L. , Lewerenz H. J.
Published: July 2002

Efficient solar energy conversion with CuInS2 thin films is reported. The copper-rich p-type absorber is prepared by thermal coevaporation. A copper to indium ratio between 1.0 and 1.8 can be tolerated with small (≤10%) solar-to-electrical conversion losses. Copper excess phases (CuS) are removed chemically. The cell structure glass/Mo/p-CuInS2/n-CdS/n+-ZnO/Al delivers 10.2% at simulated AM 1.5 conditions. The device properties are discussed based on its energy band diagram.
Deposition of micrometer-sized tungsten patterns by laser transfer technique
Authors: Kántor Z. , Tóth Z. , Szörényi T. , Tóth A. L.
Published: July 2002

A simple single-step technique for surface patterning is presented. It is shown that well-adhering micrometer-sized patterns of 100% coverage preserving the shape and dimensions of the ablated area can be deposited by ablating and transferring tungsten thin films in the form of single solid pieces using single pulses of peak power up to 100 mW and 100 μs–1 ms duration from a diode-pumped YAG laser.
Secondary electron emission from Si-implanted GaAs
Authors: Iwase F. , Nakamura Y. , Furuya S.
Published: July 2002

The effect of the implanted Si into GaAs on the secondary electron yield was investigated using cross-sectional scanning electron microscopy. In the case of the isothermal annealing at 800 °C for 30 min, the yield was enhanced for the samples implanted at 150 keV with higher doses than 1×1014 cm−2 above which the activation efficiency of the implanted Si went down rapidly. The annealing temperature dependence also showed the enhancement of the yield for the samples with less activation efficiency. Hence, it was suggested that the yield was increased by the defects that reduced the activation efficiency.
Low jitter single-mode pulse generation by a self-seeded, gain-switched Fabry–Pérot semiconductor laser
Authors: Schell M. , Utz W. , Huhse D. , Kässner J. , Bimberg D.
Published: July 2002

While the time jitter of gain-switched multimode Fabry–Pérot lasers is relatively low, single-mode distributed feedback (DFB) lasers suffer from an inherently larger time jitter, due to the different photon statistics. Here, we determine the time jitter of a mulitmode Fabry–Pérot (FP) laser (425 fs), a single-mode DFB laser (2.2 ps), and the FP laser switched to single-mode pulsing by self-seeding (210 fs). Thus self-seeding is superior by one order of magnitude to gain switching of DFB lasers, which is presently used for generation of single-mode pulses in the low ps range. A numerical model based on multimode rate equations including Langevin terms for the spontaneous emission shows good agreement with the experimental results.
Rise time in shock consolidation of materials
Authors: Tong W. , Ravichandran G.
Published: July 2002

The rise time of a strong shock wave propagating through a porous material is estimated by analyzing the finite deformation of an elastic/viscoplastic spherical shell under impulsive pressure loading. The analysis examines explicitly the effects of dynamic loading rate and initial temperature and explains the relatively large shock rise times observed in porous materials. Results of the analysis provide a consistent and realistic interpretation of available experimental data.
High quality wavelength tuned multiquantum well GaInAs/GaInAsP lasers fabricated using photoabsorption induced disordering
Authors: McKee A. , McLean C. J. , Bryce A. C. , De La Rue R. M. , Marsh J. H. , Button C.
Published: July 2002

Broad area oxide strip lasers have been fabricated from GaInAs/GaInAsP multiquantum well laser material which has undergone various degrees of intermixing by photoabsorption induced disordering. This process provides an effective way of altering the emission wavelength of lasers fabricated from a single epitaxial wafer, and we have demonstrated blue shifts of up to 160 nm in lasing spectra. The band gap tuned lasers are also assessed in terms of threshold current density, internal quantum efficiency, and internal loss and it is shown that good device performance is maintained.
Multistability of the current-voltage characteristics in doped GaAs-AlAs superlattices
Authors: Kastrup J. , Grahn H. T. , Ploog K. , Prengel F. , Wacker A. , Schöll E.
Published: July 2002

Electric-field domain formation in doped semiconductor superlattices leads to sharp discontinuities in the current-voltage (I-V) characteristic. The successive expansion of the high-field region with increasing bias voltage through the periodic heterostructure manifests itself in a regular sequence of stable current branches. The current shows a complex hysteretic behavior. We observe two, three, and more stable current levels for fixed bias voltages. Calculations of the I-V characteristic based on a microscopic model support the experimentally observed multistability.
Photoluminescence and passivation of silicon nanostructures
Authors: Redman D. A. , Follstaedt D. M. , Guilinger T. R. , Kelly M. J.
Published: July 2002

A new method was used to fabricate nanometer-scale structures in Si for photoluminescence studies. Helium ions were implanted to form a dense subsurface layer of small cavities (1–16 nm diameter). Implanted specimens subjected to annealing in a variety of atmospheres yielded no detectable photoluminescence. However, implantation combined with electrochemical anodization produced a substantial blueshift relative to anodization alone. This blueshift is consistent with the quantum confinement model of photoluminescence in porous silicon.
Precision interferometric dilatometer
Authors: Wolff E. G. , Savedra R. C.
Published: July 2002

An improved double Michelson laser interferometer dilatometer is described. The unit is suitable for the study of materials of arbitrary size or shape with time-dependent and near zero coefficients of thermal expansion (CTE) over the range 100 to >450 K. Direct recording of four amplified photodetector signals gives a ΔL/L resolution of 5×10−8 and an average CTE error in the 10−10–10−9 K−1 range. An inexpensive automatic digital counter–microprocessor combination permits recording of instantaneous ΔL/L and CTE values at >30-s intervals. The resolution of ΔL/L in this case is <8×10−7 while the instantaneous CTE (4 K interval) has an uncertainty of <2×10−7 K−1. The latter values are based on a counting unit of λ/2 and interpolating. Smaller counting units reduce errors proportionately to the system noise level and the limitations of the temperature measurement.
Detection of a force between a charged metal foil and a current-carrying conductor
Authors: Sansbury Ralph
Published: July 2002

An experiment is described which demonstrates a force between static charges on a metal foil and a large steady electric current in a wire. The observed force vectors cannot be readily explained in terms of diamagnetism, paramagnetism, eddy currents, thermal convection currents, or the Poynting electric field associated with a dc current outside the path of the current.
Computer-controlled high-resolution capacitance dilatometer/oven system: Design, instrumentation, and performance
Authors: Johansen T. H. , Feder J. , Jo/ssang T.
Published: July 2002

A fully automated apparatus has been designed for measurements of dilatation in solid samples under well-defined thermal conditions. The oven can be thermally stabilized to better than 0.1 mK over a temperature range of −60 to 150 °C using a two-stage control strategy. Coarse control is obtained by heat exchange with a circulating thermal fluid, whereas the fine regulation is based on a solid-state heat pump—a Peltier element, acting as heating and cooling source. The bidirectional action of the Peltier element permits the sample block to be controlled at the average temperature of the surroundings, thus making an essentially adiabatic system with a minimum of thermal gradients in the sample block. The dilatometer cell integrated in the oven assembly is of the parallel plate air capacitor type, and the apparatus has been successfully used with a sensitivity of 0.07 Å. Our system is well suited for measurements near structural phase transitions with a relative resolution of Δt=(T−Tc)/Tc=2×10−7 in temperature and ΔL/L=1×10−9 in strain.
Design and performance of a new push-button controlled high-vacuum baffle valve
Authors: Chaturvedi U. K. , Nigam A. K.
Published: July 2002

An automatic push-button controlled baffle valve useful for high-vacuum system, is designed, fabricated, and evaluated for its performance. It has several novel features like its automatic closure during power interruptions, absence of mechanical vacuum feedthrough, etc. This valve works on the principle of closed magnetic hysteresis loop formed by passing a dc current through an electromagnet which attracts a ferromagnetic bar completing the loop. A weaker current of opposite polarity is required for breaking the magnetic loop resulting in the release of the bar attached to the baffle plate. For efficient electromagnetic operation, low degassing, vacuum compatible coils have been developed. A control circuit sends the valve opening current (≂1 A, 60 V) when a push button is pressed but due to formation of the closed magnetic loop, the valve remains open even when the current in the coils decays to zero. On pressing another button, or in case of power interruptions, a precharged capacitor is discharged through these coils with opposite polarity. This weaker discharge current breaks the magnetic loop and the baffle plate falls on its seat closing the valve. All these operations are arranged by a single-pin electrical vacuum feedthrough. Observed traces of contaminants from the coils can be vanished by using hermetically sealed coils making the valve even very high vacuum (VHV)compatible.
Achromatic magnet
Authors: Shanker O.
Published: July 2002

It is shown that the field variation chosen by Enge [H. A. Enge, Rev. Sci. Instrum. 34, 385 (1963)] to construct an achromatic magnet is the only variation possible.
Magnetic surface mapping with an emissive filament technique on the Auburn torsatron
Authors: Gandy R. F. , Henderson M. A. , Hanson J. D. , Hartwell G. J. , Swanson D. G.
Published: July 2002

Torsatron and stellarator plasma confinement devices rely on magnetic surface mapping to determine the critical vacuum magnetic field structure. A recently developed method employing an emissive filament offers some advantages over the traditional technique of mapping with a directed electron beam. On the Auburn torsatron a comparative study between the emissive filament and directed electron beam techniques has been conducted. The parameters varied in the comparative study are filament geometry, emission current, bias voltage, background gas pressure, and magnetic field strength. This comparative study indicates that the emissive filament technique is reliable over a broad and easily accessible range of parameters. We have also measured the spatial distribution of electrons on a given magnetic surface. As an application of the emissive filament technique, the optimization of the magnetic surfaces on the Auburn torsatron is shown.
Comments on ‘‘Improved algorithm for the discrete Fourier transform’’ [Rev. Sci. Instrum. 5
6, 2325 (1985)]
Authors: Sorella S.
Published: July 2002

It is shown that in the paper written by M. Froeyen and L. Hellemans [Rev. Sci. Instrum. 56, 2325 (1985)], the algorithm POL2*FFT proposed by myself and S. K. Ghosh [S. Sorella and S. K. Ghosh, Rev. Sci. Instrum. 55, 1348 (1984)] is used in a incorrect way, because the original paper was not very ‘‘explicit’’ in some steps. Therefore, the new algorithm represents only a different application of our general strategy.
Scaled-up production of n-C3F7I photolytic laser ‘‘fuel’’
Authors: Herrera S. D. , Schlie L. A. , Richert S. A.
Published: July 2002

A tenfold mass production scale-up that provides an economical synthesis method for producing normal-heptafluoropropyl iodide (n-C3F7I) laser ‘‘fuel’’ sustaining stable and reliable cw atomic iodine lasing at 1.315 μ via UV photolysis is reported. Such results strongly indicate that high purity n-C3F7I is being synthesized. Over 1 kg per day production of this n-C3F7I is demonstrated. The synthesis procedure involves three steps: formation of the n-C3F7COONa salt, refluxing at 45 °C, and a packed column distillation. During the synthesis, particular attention is given to minimizing those impurities producing detrimental effects on atomic iodine lasers. Yields of 65%–75% for n-C3F7I laser ‘‘fuel’’ are achieved whenever liquid nitrogen is used to collect the synthesized product.
Linearization of scan velocity of resonant vibrating-mirror beam deflectors
Authors: Chen Shun Le , Yeung Edward S.
Published: July 2002

The sinelike behavior of the scan velocity of resonant vibrating-mirror beam deflectors can be linearized by external optics. A good approximation can be achieved by reflection off an elliptical mirror after the deflector. With a moderately large major-to-minor-axes ratio, a substantial linear region is found over the total scan range in typical deflectors. Numerical simulations are presented to show how linearization can be optimized for a given scan requirement.
Design of a submillimeter-wave alpha particle Thomson scattering diagnostic for fusion plasmas
Authors: Shefer R. E. , Watterson R. L. , Goodman D. , Klinkowstein R. E.
Published: July 2002

A collective Thomson scattering system based on a NH3 laser master oscillator and a free-electron laser (FEL) amplifier operating at a wavelength of 152 μm is described. The FEL is driven by a compact, high repetition rate induction linear accelerator developed at SRL. Operation of a prototype linac at a repetition rate of 1 kHz has been demonstrated. Simulations show that the FEL is capable of supplying the required 11 kW average (220 MW peak) radiated power for a successful Thomson scattering measurement with a measurement time of 100 ms. A detailed design of the tapered FEL wiggler and beam transport system has been completed. A high repetition rate CO2  pump laser to be used in the FIR master oscillator has also been designed. This laser will employ a compact closed flow loop to achieve 1 kW average power, narrow line operation at a 1 kHz pulse rate.
Instrument for measuring the momentum flux from atomic and charged particle jets (abstract)
Authors: Cohen S. A. , Zonca F. , Timberlake J. , Bennett T. , Cuthbertson J. , Langer W. , Motley R.
Published: July 2002

We have developed an instrument to measure the momentum flux from an intense plasma stream for which the standard techniques used for low-pressure gases (<10 Torr) at room temperature are unsuitable. This device, a plasma momentum meter, can measure forces of 10−5–103 Newtons with a response time of <50 ms onto surfaces of different materials immersed in dense plasmas (n≳1012 cm−3). Such forces are transmitted predominantly by ionic and neutral species, with 10’s of eV’s of kinetic energy, are accompanied by high heat fluxes, and are pulsed. The momentum flux onto a biasable target plate is transferred via a suspended quartz tube onto a sensitive force transducer, a capacitance-type pressure gauge. This protects the transducer from thermal damage, arcing, and sputtering. An absolute force calibration of the PMM to 1% accuracy has been made and is described. A flat carbon target has been used in measurements of the momentum flux of He, Ne, Ar, and Kr plasmas produced in a magnetized linear plasma device.
Near-field characterization of hydrogen and helium operation on the TFTR diagnostic neutral beam
Authors: Kamperschroer J. H. , Schilling G. , Roquemore A. L.
Published: July 2002

An optical multichannel analyzer has been used to measure beam divergence and composition. This measurement is usually performed near the center of the neutralizer or beyond the magnet. In the past, these locations suffered difficult beam composition analysis and low light intensity, respectively. It has been determined that the light emission is relatively independent of neutralizer line density in the near field, allowing near-field measurements to overcome both difficulties. At optimum perveance, but under conditions of high gas throughput, the helium 1/e divergence angle was measured to be 1.5°. Further investigation found that the divergence decreased with gas throughput down to 1.25°. Minimum divergences for the full-, half-, and third-energy hydrogen components were 1.1°, 1.2°, and 1.4°, respectively. Relative neutral hydrogen particle fluxes available for injection into TFTR are a function of perveance. At maximum perveance, the full-, half-, and third-energy atom fractions were 0.25±0.04, 0.5±0.04, and 0.25±0.05, respectively.
Soft x-ray tomography on the RTP tokamak
Authors: da Cruz D. F. , Donné A. J. H.
Published: July 2002

A soft x-ray tomography system is being constructed for the RTP tokamak. The main aim of this system is to measure fluctuations in the plasma emissivity with relatively high poloidal m number. Five pinhole cameras will be distributed inside the vessel in such a way that it becomes possible to reconstruct modes up to m=4, without making any assumption about the plasma rotation. The system has been designed to obtain a minimum bandwidth of 200 kHz and a temporal resolution of 1 μs. We describe the hardware that is under construction.
Proposal for measuring magnetic fluctuations in tokamaks by Thomson scattering (abstract)
Authors: Haas F. A. , Evans D. E.
Published: July 2002

Thomson scattering is proposed for the direct measurement of magnetic field fluctuations in a tokamak. The analysis is based on the electron fluid equations. The ordering λ≪λturb≪a, where λ and λturb are the incident and turbulence wavelengths, respectively, and a is the torus minor radius, is suggested by spectral information from observations on the TEXT tokamak, as well as general theoretical arguments. With this ordering, temperature effects are unimportant and an expression is derived for probe radiation-induced plasma polarization that depends upon density and magnetic fluctuations only. By choosing the incident probe beam to have its plane of polarization parallel to the local mean magnetic field B0, and observing the scattered power in the plane of polarization perpendicular to B0, it is shown that contributions from density fluctuations are automatically excluded. Faraday rotation is shown to have negligible influence on the scattered signal, which is accordingly determined by magnetic field fluctuations alone.
ATF diamagnetic system (abstract)
Authors: Wing W. R. , Neilson G. H. , Glowienka J. C. , Dyer G. R. , Shipley W. D.
Published: July 2002

The diamagnetic diagnostic on ATF consists of two systems. The first uses a single-turn diamagnetic loop in a stainless-steel reentrant tube inside the vacuum vessel. Compensation signals are derived from Rogowski coils mounted on the main helical and vertical coil buses. This arrangement provides maximum sensitivity and the fastest time response, but results in signals which are dominated by noise created by the large ATF SCR power supplies. The nonlinear nature of these supplies, and their coupling, requires the use of hybrid noise reduction processing. The analog compensation loops remove the low-frequency components and digital post-processing removes the high-frequency ones. The second diamagnetic signal is derived from a set of saddle loops which respond directly to the Pfirsch-Schlüter current in the plasma. Typical results are presented. This research was sponsored by the Office of Fusion Energy, U.S. Department of Energy, under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc.
Characterization of X-pinch plasma (abstract)
Authors: Qi N. , Hammer D. A. , Kalantar D. H. , Rondeau G. D. , Mittal K. C.
Published: July 2002

The X pinch, in which two or more crossed wires are stretched between the electrodes of the 0.5 TW LION accelerator, is being studied as a bright x-ray source for photopumping an extreme ultraviolet (XUV) laser and for microlithography. Crossed Al or Mg wires with line density from 10 to 400 μg/cm have been imploded by up to 550 kA current for 40 ns. High density and temperature bright spots have been observed at the crossing point. Diagnostics include x-ray pinhole cameras, streak and framing cameras, and XUV x-ray spectrographs. The visible streak camera provides time and radial (or axial) spatially resolved information on the pinch plasma, while the 5 ns single frame camera gives spatially resolved images. The size of the soft x-ray hot spots (less than 40 μm diameter) was estimated from the time-integrated pinhole image. An x-ray spectrograph with a curved mica crystal was used to record K-shell emission spectra. From the line intensity ratios of the K-shell radiation, plasma densities of ∼1020 cm−3 and temperatures about 400 eV were obtained. This work was supported in part by the Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375-5000, under ONR contract N00014-90-J-2002 and NSF grant 89-19960.
Frequency stabilization of LNA laser to the helium absorption lines
Authors: Heil W. , Werner M. , Meyerhoff M. , Schearer L. D.
Published: July 2002

We describe and compare three methods we have used to stabilize the frequency of an end-pumped, tunable La0.85Nd0.15MgAl11O19 (LNA) laser to the absorption lines of 4He or 3He near 1083 nm. The first two methods vary the thickness of an intracavity étalon which is used for tuning and narrow banding of the laser output. The third method varies the length of the laser cavity. All three methods yield satisfactory stabilization of the laser frequency although controlling the tilt angle of a solid étalon is the simplest and most reliable method.
Sample switching interface for Fourier transform infrared spectroscopy of electrode surfaces
Authors: Faguy Peter W. , Fawcett W. Ronald , Quach James , Rieg Ron A.
Published: July 2002

A simple electronic system that enables an FTIR spectrometer to control sample state parameters through its sample switching ability is described. Up to sixteen different logic states can be assigned through the software, automating the applied FTIR experiment. The operation of the device is demonstrated for the collection of subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) using a custom designed potentiostat. One of the most important advantages of this interface is its flexibility towards various timing/sampling schemes found for different in situ spectroelectrochemical experiments. The suitability of this device for other than electrochemical switching applications is also described.
Full color printer with a He-Cd+ white-light laser
Authors: Takashima Masatake , Okada Sadami , Nishiyama Hiromi , Matsuda Mikio , Fujii Kan-ichi
Published: July 2002

A high resolution full color printer has been developed incorporating a He-Cd+ white-light laser, acousto-optic modulators, a Galvano scanner, and a circular arc recording platen on a fine translation stage. The laser oscillates at three primary colors and is controlled to be within 1% intensity stability. The spot size of the laser beam on the recording platen is improved to be 50 μm in diameter while the positioning accuracy for both horizontal and vertical scans are achieved to be better than 25 μm. The exposing energy densities on the recording surface for red, green, and blue are measured to be 4.3, 8.4, and 8.4 erg/cm2, respectively. The energy densities exceed the required exposure energy for Polacolor ER 8×10 Land film. A ‘‘reversible coding method’’ has been applied to shorten the data process time for 153.6 Mbytes image data. As the result, a 250×200 mm2 color print can be produced in 2 min. To evaluate chromaticity of the color prints, a color estimator that consists of a colorimeter, a personal computer, and an XY plotter is developed. The purity of color is found out to be high because of color matching between the laser wavelengths and the spectral sensitivity of the film.
A new device for energy-dispersive x-ray fluorescence
Authors: Swoboda Walter , Kanngiesser Birgit , Beckhoff Burkhard , Begemann Klaus , Neuhaus Hermann , Scheer Jens
Published: July 2002

A new measuring chamber for energy-dispersive x-ray fluorescence is presented, which allows excitation of the sample by three (commonly applied) modes: secondary target excitation, Barkla scattering, and Bragg reflection. In spite of the short distances required to obtain high intensities, the transmission of the radiator through the bulk matter of the chamber wall and the collimators could be kept negligibly small. In the case of Bragg reflection, the adjustment of all degrees of freedom of the crystal is performed independently and reproducibly under vacuum conditions. The device allows the choice of excitation mode optimized for the respective analytical problem. An experimental test using an environmental specimen shows the detection limits obtainable.
Testing of an advanced ‘‘volume’’ H− source and preaccelerator
Authors: Kwan J. W. , Ackerman G. D. , Anderson O. A. , Chan C. F. , Cooper W. S. , deVries G. J. , Kunkel W. B. , Leung K. N. , Purgalis P. , Steele W. F. , Wells R. P.
Published: July 2002

In testing a cesiated volume-production negative ion source, we have obtained 75 mA of H− beam current in a 270 ms pulse length delivered downstream of the 87 keV preaccelerator. Optimum pressure in the source was less than 8 mT and the electron-to-ion ratio in the beam was less than 4. With future improvements in the electron trap, it is anticipated that higher H− current can be obtained by operating with a higher discharge power and a lower plasma electrode bias.
A 94 GHz differential radiometer for observations of diffuse sky emission
Authors: Piccirillo L.
Published: July 2002

The design and performance of a portable 94 GHz differential radiometer is discussed. The antenna system is an off-axis paraboloid-hyperboloid combination with a field of view of about 50 arcmin. All mirrors are made of carbon fiber coated with silver. Beam switching is obtained by wobbling sinusoidally the primary (parabolic) mirror. This radiometer was used in Antarctica (Italian Base, Terra Nova Bay, −74 S, +164 E) to make measurements to the diffuse sky emission at mm wavelengths. In future, we are also planning to use the antenna, together with a more sensitive detector, to make measurements of the cosmic background radiation anisotropy (CBR).
A review of the GANIL activity with the 14-GHz ECR sources
Authors: Bourgarel M. P. , Bisch M. , Bony J. , Lehérissier P. , Pacquet J. Y. , Rataud J. P. , Ricaud Ch.
Published: July 2002

In this paper, these main activities will be reviewed: (1) The GANIL ECR, developed the last year, has been placed on a 100-kV high voltage platform. (2) An identical source has been realized for the Hahn–Meitner-Institut Berlin. (3) The construction of a pulsed source mostly operating on the afterglow mode for the Lead ion accelerating facility of the CERN is undertaken.
The Legnaro ECR ion source
Authors: Cavenago Marco , Bisoffi Giovanni
Published: July 2002

The Legnaro ECRIS ‘‘Alice’’ [Nucl. Instrum. Methods A 301, 9(1991)] is a small 14.4 GHz ion source that miniaturizes several features of bigger ones (first stage, differential pumping). During mechanical construction, nearly completed by now, several challenging tolerances were met. In particular, the critically stressed hexapole binding rings were tightly locked into their position; coils centering and insulation was finally accomplished. A source test stand (including microwave, main power, and water cooling apparatus) and the necessary software for controlling Alice via an economic G-64 bus computer were developed.
Two-cavity ECR source of multicharged ions
Authors: Dougar-Jabon V. D. , Kondratov B. A. , Umnov A. M.
Published: July 2002

The plasma density in ECR sources is limited by the cutoff plasma frequency, which prevents producing multicharged ions if one uses for plasma heating such low frequency microwaves as 2.45 GHz. In order to overcome this limitation a device consisting of two cavities located symmetrically in mirror regions was investigated. The ECR heating took place in the cavities and the plasma was accumulated in the zero microwave field space between the cavities. The cavities were fed with microwave power of 2.2 kW at 2.45 GHz. At an argon pressure of 0.04 mTorr, the plasma density of 2.4×1012 cm−3 in the central region of the trap was about 30 times higher than the cutoff value. A significant improvement in performance was found in comparison with the HELIOS-12. The expression for the lifetime of ions trapped into an electrostatic pit was defined. The charge state distributions both for the plasma and the extracted ion beam was calculated.
H+ beam neutralization measurements at 870 keV beam energy
Authors: Sherman Joseph , Olivo M. , Mariani E.
Published: July 2002

A non-interceptive beam neutralization monitor is being used to measure dc H+ beam neutralization properties in the Paul Scherrer Institute’s (PSI) 870 keV pre-injector beamline. This transport line uses quadrupole magnetic lenses to transport the H+ beam from the high voltage column to the injection point of the PSI 72 MeV cyclotron. The monitor is a gridded-energy analyzer type, and both positive ion and electron energy distributions are measured. The monitor’s energy resolution is measured to be ≊0.9 eV using a 12–30 eV electron gun. Complications in the measured energy distributions−apparently arising from the contaminant H2+ and H3+ beams−are resolved by changing the beam aspect ratio. Collimator biasing and collimator beam scraping have large effects on electron currents. An 870 keV, 8.2 mA dc H+ beam is found to be 10–62% neutralized, depending on the neutralizing gas and density.
ECRIS for highly charged ions−Present status and new developments (invited)(abstract)
Authors: Antaya T.
Published: July 2002

There are now approximately 40 electron cyclotron resonance ion sources (ECRIS) for highly charged positive ions, either operating or under construction, worldwide. In recent years, the number of operating sources has been doubling about every three years. The present working level for high performance is now a compact, CW 14-GHz source with high magnetic confinement, simplified microwave injection, and a somewhat suppressed first stage. It has become clear that electron injection into the main stage plasma, from electron guns, biased cathodes, or high secondary electron emission surfaces close to the plasma, raises ion extracted currents, and several efforts are under way to understand this phenomena. Much effort has also been devoted to the production of ions from nongaseous materials, with positive ion beams from approximately half the periodic table now having been produced in ECRIS. The afterglow mode may permit intense short pulse beams of highly charged ions for injection into synchrotrons. Present development efforts are centered on understanding the performance scaling with microwave frequency and magnetic confinement, as well as continued development of intense highly charged ions in existing sources and the development of new metallic species.
An EBIS/RFQ−Injector for a cancer therapy synchrotron
Authors: Becker R. , Kleinod M. , Schempp A. , Donets E. D. , Pikin A. I.
Published: July 2002

The electron beam ion source (EBIS) is an intense source of bare nuclei of light elements (C,N,O,Ne) for short pulses. A fast extraction time of 4 μs allows advantageous single turn injection into a medically dedicated synchrotron. Since the EBIS can provide bare nuclei of all light ions, it combines favorably with a 1.8 m long radio-frequency-quadrupole accelerator (RFQ) as the only LINAC needed for an injection energy of 1 MeV/u. The required intensity of 108 ions per pulse in 1 s is easily exceeded by a factor of 10 to compensate for beam losses. The technology of an EBIS with an electron current of 165 mA at 3 keV and 50 A/cm2 is well established and has proven to be very reliable for synchrotron injection over many years in Dubna, Saclay, and Stockholm. The low duty factor (10−4) of the RFQ, where 250 kW pulses of rf power will be applied for 25 μs, eliminates the need for cooling. Therefore a four-rod structure may be put on ceramic stands, biased with a negative high voltage to avoid high voltage on the source. The combination of an EBIS with a short RFQ may be considered as the least complex and most reliable injector solution for filling a cancer therapy synchrotron with fully stripped light ions.
Charge state distribution of tantalum ions produced simultaneously by CO2 and Nd:YAG laser from a laser ion source
Authors: Henkelmann T. , Korschinek G. , Belayev G. , Dubenkov V. , Golubev A. , Latyshev S. , Sharkov B. , Shumshurov A. , Wolf B.
Published: July 2002

The influence of the combined interaction of a CO2 laser (10.6 μm) and a Nd:YAG laser (1.06 μm) with a solid tantalum target has been investigated. Changing plasma parameters as temperature and density can be traced back by measurement of the charge state distribution after extraction from the expanding plasma. Analysis of the measurements for the single lasers as well as for the combined impact show an increase in plasma temperature, strongly depending on the delay between the two laser pulses. A maximum charge state rising from 11+ to 13+ can be observed.
Performance of two helium ion diodes
Authors: Drum S. , Heidbrink W. W. , Wessel F. J.
Published: July 2002

Two magnetically insulated gas-puff diodes were tested. In one design the plasma source was a fast inductive coil; in the other a coaxial gun created the plasma. The plasma current density from both sources, as well as the accelerated beam from each, was comparable to the Child–Langmuir limit of ∼10 A/cm2.
Atomic processes, cross sections, and reaction rates necessary for modeling hydrogen negative-ion sources and identification of optimum H− current densities
Authors: Hiskes J. R.
Published: July 2002

The principal electron excitation cross sections for vibrational excitation in a hydrogen discharge are reported. In the first chamber of a two-chamber hydrogen negative-ion-source system subject to the beam-line constraint of a maximum gas pressure, the density of vibrationally excited molecules reaches an asymptote for increasing discharge current or the equivalent fast electron density. Operating near this first-chamber asymptote, there exists a spatially dependent maximum negative-ion density in the second chamber. With the extraction grid placed at this maximum the optimum performance of a hydrogen-based system is determined. This optimum performance provides a criterion for the selection of differing source types for fusion applications.
Development of oxygen ion source with microwave plasma cathode
Authors: Matsubara Yoshio , Tahara Hideaki , Takahashi Masato , Nogawa Shuichi , Ishikawa Junzo
Published: July 2002

A new type of broad-beam ion source, which is a bucket-type ion source with a microwave plasma (MP) cathode instead of conventional thermionic filaments, has been developed. Producing a high-density plasma in the MP cathode under the electron-cyclotron-resonance (ECR) condition, this cathode has a capability of a high-current electron emission and has a long lifetime (more than 100 h for an oxygen gas). The structure of this cathode is very simple and compact. Rod antennas connected to coaxial lines for introducing the microwave power (2.45 GHz) and a permanent magnet for producing the ECR condition are major components. In the bucket-type ion source with the MP cathode, the high-current ion beams of 230 mA for an argon gas and 132 mA for an oxygen gas in 115 mm diameter have been successfully obtained with excellent uniformity of the ion beam.
Beam investigations at a multicusp ion source
Authors: Volk K. , Klein H. , Leung K. N.
Published: July 2002

In cooperation with the Lawrence Berkeley Laboratory, a multicusp ion source has been investigated. The goal of these investigations is to generate a nearly pure atomic nitrogen (N+) ion beam. To achieve this, the discharge chamber is divided into two parts of different plasma parameters by means of a filter magnetic field. As beam diagnostics, a bending magnet and a faraday cup have been used. Measurements of the beam current density and the ion composition for a wide range of discharge conditions have been performed. By using a Langmuir probe, we have performed measurements of electron temperature and electron density.
Atomic nitrogen ion beam from a pulsed duoplasmatron ion source
Authors: Ludwig T. , Volk K. , Klein H. , Schempp A.
Published: July 2002

A duoplasmatron ion source fed with nitrogen usually produces a N+ fraction of approx. 60% in dc mode. In pulsed mode, the duoplasmatron ion source turns out to be a nearly perfect source for atomic nitrogen ions with a high fraction of more than 90% in the milliampere range. This is achieved by pulsing the arc discharge and not by use of any filter magnets. Parameters of operation will be given, such as the comparatively low gas inlet pressure and the arc current, which far exceeds the arc current in dc mode.