bluuebunny/crossref_metadata_2025 huggingface dataset:
ICF laser beam focal uniformity and diagnostics (abstract)
Authors: Kessler T. J.
Published: July 2002

Laser fusion requirements for ignition of thermonuclear fuel include high levels of irradiation uniformity on target. The quality of each beam’s focal spot is a major source of the dominant modes of nonuniformity. The problem is proportionately more difficult at the shorter wavelengths required for high energy-to-target coupling efficiency. Phase conversion is a focusing strategy that incorporates several wave-front modulation techniques which, when operating together, cause a reduction in the spatial coherence of the laser and thus an increase in focal uniformity. Phase masks are central to phase conversion by providing a reproducible source of multibeamlet superposition. A second type of wave-front modulation involves the addition of time-dependent phase to the laser beam, thus producing a time-dependent spectrum. Further manipulation of the beam with a diffraction grating creates color cycling over the elements of the phase mask. Another technique of interest utilizes a static, spatially distributed differential phase. This effectively doubles the number of incoherent beams that are available to overlap and better averages the various intensity nonuniformities. These three techniques have been implemented on the OMEGA laser system producing the highest quality short wavelength ICF laser. Various diagnostics are required to ensure that spatial coherence is rapidly reduced. Focal plane measurements of the spatially integrated spectrum, the spatially resolved irradiation pattern and of the one-dimensional, spatially resolved pulse shape are successfully used to understand the time resolved and time integrated uniformity levels for the OMEGA laser. This work was supported by the U.S. Department of Energy Office of Inertial Fusion under agreement No. DE-FC03-85DP40200 and by the Sponsors of the Laser Fusion Feasibility Project at the Laboratory for Laser Energetics.
Data analysis for the Rutherford magnetic spectrograph on PBFA-II
Authors: Kensek R. P. , Lee J. R. , Leeper R. J. , Johnson D. J. , Lockner T. R. , Maenchen J. , Mix L. P. , Stygar W. A. , Hebron D. E. , Wenger D. F.
Published: July 2002

A magnetic spectrograph employing a gold Rutherford scattering foil has been constructed and fielded on Sandia National Laboratories’ PBFA-II accelerator to diagnose intense ion beams. The instrument simultaneously records time-integrated data on nuclear track recording film, CR-39, and time-resolved data on a set of p-i-n diodes. The details of the analysis of these data to provide time-resolved power density, ion current density, ion energy spectra (including mean ion energy), and ion species identification will be presented.
Millimeter and submillimeter wave technology developments for the next generation of fusion devices
Authors: Hwu R. J. , Sjogren L. , Luhmann N. C. , Popovic Z. , Weikel R. W. , Kim M. , Rutledge D. B.
Published: July 2002

There is increasing demand for compact watt-level coherent sources in the millimeter and submillimeter wave region. The approach that we have taken to satisfy this need is to fabricate two-dimensional grids loaded with oscillators, electronic beam steerers, and frequency multipliers for quasioptical coherent spatial combining of the outputs of a large number of low-power devices.
Plasma fluctuation measurements in tokamaks using beam-plasma interactions (abstract)
Authors: Fonck R. J. , Duperrex P. A. , Paul S. F.
Published: July 2002

High-frequency observations of light emitted from the interactions between plasma ions and injected neutral beam atoms allow the measurement of moderate-wavelength fluctuations in plasma and impurity ion densities. To detect turbulence in the local plasma ion density, the collisionally excited fluorescence from a neutral beam is measured either separately at several spatial points or with a multichannel imaging detector. Similarly, the role of impurity ion density fluctuations is measured using charge exchange recombination excited transitions emitted by the ion species of interest. This technique can access the relatively unexplored region of long-wavelength plasma turbulence with k⊥ρi≪1, and hence complements measurements from scattering experiments. Optimization of neutral beam geometry and optical sightlines can result in very good localization and resolution (Δx≤1 cm) in the hot plasma core region. The detectable fluctuation level is determined by photon statistics, atomic excitation processes, and beam stability, but can be as low as 0.2% in a 100 kHz bandwidth over the 0–1 MHz frequency range. The choices of beam species (e.g., H0, He0, etc.), observed transition (e.g., Hα, Lα, He i singlet or triplet transitions, C vi Δn=1, etc.) are dictated by experiment-specific factors such as optical access, flexibility of beam operation, plasma conditions, and detailed experimental goals. Initial tests on the PBX-M tokamak using the Hα emissions from a heating neutral beam show low-frequency turbulence in the edge plasma region.
Development and operation of a backward wave oscillator based FIR scattering system for DIII-D
Authors: Rettig C. L. , Burns S. , Philipona R. , Peebles W. A. , Luhmann N. C.
Published: July 2002

The laser-based far-infrared scattering system (λ=1.22 mm) on DIII-D is to be upgraded by the addition of a backward wave oscillator or carcinotron. By supplying up to 300 mW at λ=1.06 mm, the carcinotron is expected to increase the scattered power and signal-to-noise ratio by more than ten times. In addition, the laser has suffered from significant frequency pulling during high density discharges which has necessitated using undesirable geometry to obtain accuracy in the low-frequency part of the fluctuation spectrum. However, the carcinotron-based system will use an IF tracking system to simultaneously remove the excessive phase noise, frequency drift typical of high-frequency tubes, and the effects of frequency pulling. This should allow more reliable measurements of low-frequency asymmetric spectra under all discharge conditions. The local oscillator will be provided by a frequency doubled and locked klystron, to enable heterodyne detection of the scattered signal. Results of extensive laboratory tests of the carcinotron-based scattering apparatus are to be presented.
Spatial resolution of microwave/millimeter-wave reflectometry
Authors: Baang S. , Domier C. W. , Luhmann N. C. , Peebles W. A. , Rhodes T. L.
Published: July 2002

Reflectometry is currently being used to investigate density fluctuations and turbulence in tokamak plasmas. However, there are unresolved questions about the spatial resolution and wave number sensitivity of this diagnostic method which impact the interpretation of the data. These questions are currently being addressed in a cylindrical, pulsed filament discharge plasma where ion acoustic waves (10–100 kHz) are launched toward the incident microwaves. Preliminary data supporting the spatially localized nature of reflectometry are presented. A computational model is also being developed to provide quantitative comparisons with experiment.
Electric field studies of a 2 MeV electrostatic energy analyzer
Authors: McLaren P. E. , Connor K. A. , Lewis J. F. , Hickok R. L. , Crowley T. P. , Schatz J. G. , Vilardi G. H.
Published: July 2002

An energy analyzer based on the Proca and Green parallel-plate design is being developed for use with the 2 MeV heavy ion beam probe on TEXT. In a departure from the conventional configuration, guard ring electrodes will not be used. Instead, a shaped top plate will provide for comparable, or improved, uniformity of the analyzer electric field region. To quantify this effect, and to characterize the electrostatic field, numerical solution methods have been utilized. Simulations have included effects of top plate shape, wire screens, vacuum chamber design, and dielectric support structures. The modeling has permitted us to design an analyzer electrode structure that is an integral part of a uniquely shaped vacuum vessel. The design electric field is 20 kV/cm with less than 1% error in uniformity within the parallel plate region. To examine the electric field structure experimentally, a quarter-scale prototype analyzer has been constructed and tested. The electric field characteristics are examined by varying the path of a heavy ion beam through the analyzer and examining the resulting analyzer performance. A simulated vacuum wall can be positioned to examine the effects of different vessel configurations and to determine the sensitivity of the analyzer to this boundary condition. The experimental results show excellent agreement with the numerically predicted fields and confirm the validity of the shaped top plate electrode concept.
A multilaser system for a fast sampling Thomson scattering diagnostic
Authors: Trost P. K. , Carlstrom T. N. , DeBoo J. C. , Greenfield C. M. , Hsieh C. L. , Snider R. T.
Published: July 2002

A multilaser system is being developed for the DIII-D Thomson scattering diagnostic. This system combines the beams from up to 8 Nd:YAG lasers onto a common beamline in which the beams are nearly parallel and are all focused into a small, common area within the desired scattering volume. Each laser can be fired at a constant rate (20 Hz per laser) for a high average repetition rate, or together in a ‘‘burst,’’ which will give very high sampling rates (10–20 kHz) for short periods. The burst mode will be triggerable by plasma events, which will allow for study of transient phenomena, but will require nonperiodic firing of the lasers. Beamline diagnostics include position sensitive detectors for computer controlled feedback alignment of the 35 m beamline, an image position detection system for monitoring the alignment of the collection lens to the scattering volume, and a 1-D reticon camera for divergence monitoring. The effects of the nonperiodic firing of the lasers will be monitored with the reticon camera.
Nonlinear absorption in polydiacetylene waveguides
Authors: Pender William A. , Boyle Adrian J. , Lambkin Paul , Blau Werner J. , Mazaheri Kourosh , Westland Duncan J. , Skarda Vladimir , Sparpaglione Massimo
Published: July 2002

We have observed nonlinear absorption in spin-coated poly(4,6-decadiyne-1, 10-diolbis {[(n-butoxycarbonyl)methyl]urethane}) [poly(3BCMU)] polydiacetylene channel waveguides at different wavelengths in the near-infrared. Intensity dependent absorption coefficients, α2 and α3, have been determined by measurements of the intensity dependent transmission. The implications of nonlinear absorption for all-optical device applications in this material are discussed.
A simplified expression for the Radon transform of Bessel basis functions in tomography
Authors: Wang Ling , Granetz Robert S.
Published: July 2002

A simplified formula for the Radon transformation of Bessel basis functions in the method of series expansion in 2-D tomography has been derived. The result is p1 Jm (xmlr) Tm(p/r)r dr√r2−p2<frx =−J′m(xml) 0 cos−1 p dθ cos(mθ) sin[xml( cos θ−p)]. A numerical comparison demonstrates at least an order of magnitude CPU time reduction using the simplified version because the integrand is written in terms of simple sinusoidal functions with no singularities.
Photometric calibration of soft x-ray and p-terphenyl coated visible photodiodes in the 180–1500 eV range for fusion plasma spectroscopy
Authors: Stutman D. , Kovnovich S. , Finkenthal M. , Zwicker A. , Moos H. W.
Published: July 2002

The efficiencies of x-ray ultraviolet silicon, and p-terphenyl coated visible photodiodes have been measured in the 180–1500 eV range using a K radiation-Manson source. It is found that the quantum efficiency (electrons/photon) of the silicon diode varies between 25 and 400 in the above-mentioned range; the p-terphenyl coated diode is by two orders of magnitude less performing at the high-energy end of the range considered, but approaches the efficiency of the silicon diode at 100 Å. Such diodes with built-in amplifiers, coated with scintillator and thin layers of metal films, can be efficiently used in spectroscopic diagnostics of magnetically confined plasmas.
Nonlinear electrical transmission line as a burst generator
Authors: Kuusela T. , Hietarinta J.
Published: July 2002

In this article we describe how nonlinear electrical transmission lines can be used to produce bursts of very short-time voltage pulses (solitons). The relevant parameters and relations for designing suitable transmission lines are given. The number of solitons and their amplitudes are given in a diagram as functions of the (normalized) amplitude and the width of the rectangular input pulse. Several examples of constructed transmission lines (including some very fast structures) are described and solitons produced by them are shown.
A simple substitute for Knudsen cells using an existing pendant-drop type electron beam evaporator
Authors: Araya-Pochet J. , Mulhollan G. A. , Erskine J. L.
Published: July 2002

A simple and elegant technique is outlined in which a specially designed crucible may be used for noble metal evaporation in a pendant-drop type electron beam evaporator with virtually no modifications.
On a new class of field integral constraints for asymmetric adjustable-phase insertion devices
Authors: Tatchyn Roman
Published: July 2002

Some alternative methods of tuning variable-field transverse insertion devices that longitudinally displace the jaws of otherwise ordinary undulator structures have been recently proposed. In this article we discuss some of the off-axis characteristics of such schemes that could limit their range of tunability and affect their possible modes of implementation on conventional storage rings. Based on the corresponding analysis, a new set of field integral constraints for facilitating the operation of such devices is derived.
High power N2 laser with a modified gas flow system and discharge geometry
Authors: Baby Thomas , Ramachandran T. , Sathianandan K. , Nampoori V. P. N. , Vallabhan C. P. G.
Published: July 2002

A high power N2 laser of the double-Blumlein type having a modified gas flow system, electrode configuration, and discharge geometry with minimum inductance is described. By incorporating a triggered-pressurized spark gap switch, arc-free operation was achieved for a wide E/P range. The device gives a peak power in excess of 700 kW with a FWHM of 3 ns and an efficiency of 0.51%, which is remarkably high for a pulsed nitrogen laser system. The dependence of output power on parameters such as operating pressure, voltage, and repetition rate are discussed.
Analysis of slit function errors in single-shot coherent anti-Stokes Raman spectroscopy (CARS) in practical combustors
Authors: Heneghan Shawn P. , Vangsness Marlin D.
Published: July 2002

The temperature determined by a single-shot coherent anti-Stokes Raman spectroscopy (CARS) system is directly related to the half width at half maximum of the instrument slit function. Therefore, an accurate knowledge of the instrument slit function is necessary to determine temperature with CARS. However, in turbulent systems, the input slits of the spectrometer may be removed in order to guarantee signal throughput and establish the necessary dynamic range. In this case, the physical input slits of the spectrometer are replaced with apparent slits created by focussing the input beams near the entrance plane of the spectrometer. The slit function will then depend on the physical relationship among all of the optical components, the probe volume, and the dispersive performance of the spectrometer and detector, as well as the optical path through density and temperature gradients which may not be invariant in a turbulent system. The presence of high temperatures and turbulence levels can effect the size of the CARS signal origin and the optical path, and as a result, the slit function is not invariant. Ignoring these changes can result in large root mean square temperatures (decreased precision) as well as mean temperature errors. The variability of the slit width can be accounted for on a shot-to-shot basis by using a two parameter (HWHM of the slit function and temperature) fitting routine. For temperatures greater than 1200 K there is convergence on a best curve implying both a temperature and a slit width. This method can be used alone or in concert with various weighting schemes to improve the precision. There are two major advantages gained by allowing the slit function to vary in a CARS system: (a) it allows an increase in the precision; (b) it allows temperatures to be calculated without the assumption that the slit function does not change with temperature or turbulence or position within the flame. In fact, it allows the temperature to be determined with almost no previous knowledge of the slit function except the general shape. These two advantages combine to significantly simplify the study of turbulent combusting systems with CARS and to improve the precision, both point-to-point and shot-to-shot, of CARS.
Inverse photoelectron spectrometer with magnetically focused electron gun
Authors: Krainsky Isay L.
Published: July 2002

This article describes an inverse photoelectron spectrometer based on the novel design of a magnetically focused low energy electron gun. The article discusses results of the ray tracing procedure conducted for this gun and some of the advantages of the magnetic focusing.
X-ray calibration of Kodak SB film in the 1.5–2.2-keV region
Authors: Dumont H. , Troussel P.
Published: July 2002

The relative response of Kodak SB film has been measured with a pulsed-laser Al plasma x-ray source in the energy region delimited by the absorption edges of Br (1599 eV) and of Ag (3351 eV) in the photographic emulsion. The data of optical density versus exposure were obtained by recording spectra at different exposures which were controlled by placing stepped Be filters. A significant variation has been observed with earlier results obtained with continuous x-ray sources at high optical densities. The data may be fit with a simple expression of exposure L determined with an arbitrary constant L0 as a function of optical density D with only two parameters, Dsat and k: L = L0/(Dsat/D − 1)1/k. It is found that Dsat=3.45 and k=0.92 over the entire energy range.
Twin-probe scanning tunneling microscope
Authors: Tsukamoto Shigemi , Siu Byron , Nakagiri Nobuyuki
Published: July 2002

Probes having two mechanically fixed, electrically independent tips were proposed (‘‘twin probes’’). A control system and mechanism for STM with a twin probe has been designed and fabricated. Two types of twin probes are fabricated. The first had Pt-Ir tips with 1.5 mm distance between the tips. The other had tungsten tips with 0.1 μm distance. Since the lengths of the two tips are not equal, the system controls not only the distance between the probe and the sample surface but also the angle between the probes and the sample to allow detection of tunneling currents with both tips of the probe at the same time. The sum of the tunneling currents is used to control the height of the probe and the difference between currents is used to control the angle of the sample. Using this system with the Pt-Ir probe, two independent images of graphite atoms from one sample were simultaneously obtained.
A simple digital system for ac magnetic measurements on superconductors
Authors: Fabbricatore P. , Gambardella U. , Gömöry F. , Musenich R. , Occhetto M. , Parodi R. , Pompa P.
Published: July 2002

This article describes a simple apparatus to perform ac inductive measurements on superconductors. The ac susceptibility, the penetrated and trapped magnetic flux and the magnetization of a sample placed in an ac magnetic field are measured by processing the signal induced in a pick-up coil that surrounds the sample. The complex harmonic analysis of the signal is also performed. The setup consists of an amplifier, a three-channel recorder, and a standard desktop computer. The main advantages of the apparatus are its simple design and low cost. Its main drawback is the noise affecting the signals. Tests were performed on a high Tc superconductor.
A multichamber system for in situ lithography and epitaxial growth of GaAs
Authors: Sugimoto Y. , Akita K. , Taneya M. , Kawanishi H. , Aihara R. , Watahiki T.
Published: July 2002

A novel multichamber system for beam-assisted etching, in situ lithography, and molecular-beam epitaxy (MBE) has been constructed and proved to be usable with full functions. This system comprises seven ultrahigh-vacuum (UHV) chambers connected by UHV tunnels. A specially designed gun column, which can be used for a focused-ion-beam (FIB) gun or an electron-beam gun, and an introduction system of Cl2 gas have been installed in a UHV chamber for beam-assisted Cl2 gas etching. In order to evaluate the induced damage by ion irradiation, the FIB gun with a novel retarding system was installed. An in situ Auger electron spectroscopy apparatus and an in situ photoluminescence unit were attached to the analysis chamber in order to evaluate the surface composition and the induced damage, respectively. Examples of GaAs/AlGaAs heterostructure grown on in situ patterned substrates showed good surface morphology, indicating the usefulness of this technique for microfabrication.
Direct digital frequency modulation in NMR spectrometers
Authors: van Os J. W. M. , Steeg G. J. W. , Veeman W. S.
Published: July 2002

An instrument is described that allows fast phase-continuous frequency switching and modulation. The instrument is designed to switch to a new frequency for a period of time or to a series of frequencies, and then switch back to the original frequency with the phase of the original output signal as if no frequency switching occurred (phase-coherent switching). The described device is implemented in Bruker NMR spectrometers.
An underwater shock wave research device
Authors: Prieto Fernando E. , Loske Achim M. , Yarger Frederick L.
Published: July 2002

It is the purpose of this article to describe the design, construction, and operation of a highly versatile, low cost experimental facility to produce, by electrical breakdown of water, weak underwater shock waves in the 50 to 2000 bar range. The device as a whole is described and then the electrical circuit used to generate the shock waves is explained in some detail. The semi-ellipsoidal or parabolic focusing mirrors, used to improve the efficiency in the transfer to the energy generated in an underwater shock wave, are also discussed. The measurement and control systems for operation of the device are described. Finally, a discussion of some of the experimental results is presented. As far as we know, this is the only apparatus of its kind with such a wide capability.
Direct production of H− from LiH
Authors: Siefken H. , Stein C. , Copeland R.
Published: July 2002

Experiments have been performed which indicate that by directly heating lithium hydride in a vacuum, up to 18 μA/cm2 of negative hydrogen can be obtained from the crystal lattice. Sample temperatures reached a maximum of about 800 °C. The amount of ion current extracted and analyzed is closely related to the temperature of the sample and to the rate at which the temperature is changed. The ion current appears to be emission limited and saturates with extraction voltage. For a fixed extraction voltage, the ion current could be maximized by placing a grid between the sample surface and the extraction electrode. Electrons accompanying the negative ions were removed by a magnetic trap. A Wien velocity filter was designed and built to provide definitive mass analysis of the extracted ion species.
Measurement of energy transfer in a five-mode gravitational wave bar detector
Authors: Pang Yi , Richard J.-P.
Published: July 2002

A 1400-kg five-mode bar detector has been constructed and tested at room temperature. Detailed calculations and computer simulations have been performed to optimize the design and study the dynamics of the system. The tests have confirmed the analytical prediction that a large fraction (67% in this experiment) of the energy deposited into the bar is transferred to the last resonator. The rise time of the energy at the last resonator is short (≂2 ms), and corresponds to an effective detector bandwidth of ≂500 Hz.
Experimental characterization of a compact ECR ion source
Authors: Srivastava A. K. , Dahimene M. , Grotjohn T. , Asmussen J.
Published: July 2002

A small ECR plasma source is experimentally evaluated. The compact, coaxial cavity source has an outer diameter of about 5.8 cm and is less than 15 cm in length, and can therefore be fitted on vacuum ports on existing MBE machines. Double- and single-Langmuir probes and an energy analyzer are used to measure ion density, electron temperature, plasma potential, and energy distributions at various downstream and cross-sectional positions in the plasma beam. The measurements are made for a variety of flow rates (2–30 sccm) and the corresponding pressures (from about 10−5 to 10−4 Torr), incident powers ranging from 80 to 164 W, and various gas types including argon and oxygen. The experimental measurements show that the ion source provides ion density of about 1011/cm3 at relatively low powers of 123 W and at sub-mTorr pressures. The ions created follow typical ambipolar diffusion out of the discharge creation region. Ions impinging downstream on a grounded substrate in an argon discharge show a narrow, peaked energy distribution that varies with pressure and power. Low-energy ion beams with energies less than 35 eV can easily be produced by varying the pressure and input power.
Photoluminescence of ytterbium-doped porous silicon
Authors: Kimura T. , Yokoi A. , Nishida Y. , Saito R. , Yugo S. , Ikoma T.
Published: July 2002

Yb3+-related photoluminescence is observed at room temperature from Yb-doped porous silicon layers prepared by the electro-chemical method developed by our group for Er doping of porous silicon layers. After rapid thermal annealing in a pure argon atmosphere at high temperatures (above ∼ 900 °C), samples show a sharp photoluminescence band at around 1.0 μm which is assigned to the intrashell 4f-4f transitions 2F5/2 → 2F7/2 of Yb3+. The enlarged energy bandgap of silicon as a result of anodization makes possible the excitation of Yb3+ 4f-electrons with the recombination energy of photocarriers generated in the host porous silicon layers.
Design and manufacture of a 6-T wiggler magnet for the Daresbury SRS
Authors: Ross John , Smith Kevin
Published: July 2002

The 6-T wiggler is an iron-cored, warm bore, superconducting dipole magnet destined for the SERC Daresbury Laboratory’s 2-GeV Synchrotron Radiation Source to enhance the available radiation spectrum. The new wiggler will be inserted in the ring in addition to an existing 5-T wiggler, both of which will use the existing, although upgraded, refrigerator. The magnet is designed to provide a peak field of 6 T on the beam line. The design and manufacturing contract for this magnet was started in September 1989 and was preceded by a feasibility study, presented by Oxford Instruments in mid 1988. The major features of the magnet, along with a discussion of the early stages of manufacture, are described in the article.
Beijing Synchrotron Radiation Facility (BSRF) status
Authors: Tang Esheng , Xian Dingchang
Published: July 2002

The history and the status of the Beijing Synchrotron Radiation Facility (BSRF) is presented. The plan for the second phase construction of BSRF in the next five years is reported.
Simple, constant length Rowland circle monochromators for undulator radiation
Authors: Senf F. , Eggenstein F. , Peatman W.
Published: July 2002

Three new designs of spherical grating monochromators with constant length for the soft x-ray energy range for an undulator beamline are proposed. The principle and the optimization are described, as well as the fact why these monochromator types can still be considered as Rowland circle monochromators. Depending on the design a maximum resolving power between 13 000 and 40 000 is achievable. The calculations are in good agreement with ray trace results. The ray tracing was performed including source size and depth, slope errors as well as finite element analysis results for the preoptics.
Soft x-ray spectroscopy beam line on the NSLS X1 undulator: Optical design and first performance tests
Authors: Randall K. J. , Feldhaus J. , Erlebach W. , Bradshaw A. M. , Eberhardt W. , Xu Z. , Ma Y. , Johnson P. D.
Published: July 2002

The layout and first data on the performance of the soft x-ray undulator beam line on the x-ray ring at Brookhaven are described. The undulator (X1) has 35 periods of 8 cm, resulting in a tuning range for the fundamental of about 200–700 eV at the nominal ring energy of 2.5 GeV. The monochromator is based on the Dragon concept with spherical grating, movable exit slit but with water-cooled optical elements in order to deal with the maximum flux of ca. 400 W. This system represents one of the next generation of soft x-ray undulator beam lines which will figure prominently at new synchrotron radiation facilities such as ALS, ELETTRA and BESSY II. During the first performance tests absorption spectra of simple molecules at the C, N, and O K edges have been recorded with resolution and flux so far unattained in the soft x-ray region.
Thermal stability and superlattice formation of sputtered platinum/alumina multilayers
Authors: Morawe Ch. , Zabel H.
Published: July 2002

By high-frequency sputtering techniques we prepared high-quality platinum/alumina artificial multilayers (Pt/Al2O3) with interface roughnesses below 0.2 nm and x-ray reflectivities close to 100% at the first satellite reflection using a wavelength of 0.1542 nm. The multilayer structure remains stable up to at least 700 °C without loss in reflectivity. Further annealing causes a structural phase transition with the formation of a coherent superlattice structure, which is finally destroyed at 1000 °C.
Construction of the general purpose diffraction beam line 4W1C at the Institute of High Energy Physics
Authors: Jing Y. , Xia S. , Zhang Q. , Zhang Y. , Liu C. , Xian D.
Published: July 2002

The design and test of the focused x-ray beam line 4W1C for general purpose diffraction study at the Synchrotron Radiation Laboratory of the Institute of High Energy Physics is reported.
Application of molecular beam mass spectrometry to chemical vapor deposition studies
Authors: Hsu W. L. , Tung D. M.
Published: July 2002

A molecular beam mass spectrometer system has been designed and constructed for the specific purpose of measuring the gaseous composition of the vapor environment during chemical vapor deposition of diamond. By the intrinsic nature of mass analysis, this type of design is adaptable to a broad range of other applications that rely either on thermal- or plasma-induced chemical kinetics. When gas is sampled at a relatively high process pressure (∼2700 Pa for our case), supersonic gas expansion at the sampling orifice can cause the detected signals to have a complicated dependence on the operating conditions. A comprehensive discussion is given on the effect of gas expansion on mass discrimination and signal scaling with sampling pressure and temperature, and how these obstacles can be overcome. This paper demonstrates that radical species can be detected with a sensitivity better than 10 ppm by the use of threshold ionization. A detailed procedure is described whereby one can achieve quantitative analysis of the detected species with an accuracy of ±20%. This paper ends with an example on the detection of H, H2, CH3, CH4, and C2H2 during diamond growth.
An inexpensive synchronous detector and its application to differential capacitance sensors
Authors: Peters Randall D. , Seibt Peter J.
Published: July 2002

A synchronous detector electronics package with self-contained oscillator is described. It uses only three integrated circuits, all of which contain operational amplifiers. The performance of the detector was evaluated with a capacitance sensor. Linearity and stability were found to compare favorably with general purpose commercial systems costing hundreds to thousands of dollars. Although the noise performance was less impressive, the dynamic range was still in excess of 90 db, permitting better than 100 μrad resolution over a range of nearly 3 rad. As presently configured, the detector is compatible only with high impedance sensors such as the capacitance type; however, coupling the oscillator output through a power amplifier would permit its use with LVDTs.
Fast 8 kV metal–oxide semiconductor field-effect transistor switch
Authors: Continetti R. E. , Cyr D. R. , Neumark D. M.
Published: July 2002

A fast high voltage switch based on ten transformer-isolated power metal–oxide semiconductor field-effect transistors in series is described. This circuit can switch 8 kV to ground with a fall time of ≊230 ns, and has proven to be useful for beam potential re-referencing in pulsed ion beam experiments.
Reliable spark gap switch for laser triggering
Authors: Golnabi Hossein
Published: July 2002

The design of a low inductance spark gap suitable for triggering lasers, using circuit boards as transmission lines, is presented. This spark gap is highly reliable for repetitive switching, and it is capable of delivering high voltage and current in the triggering operation. The switch performance has been studied in a nitrogen laser driven by a Blumlein circuit, and the preliminary results are reported. When operated at a rate of 10 pps the switch provided reproducible pulse waveforms without maintenance for a total of 108 laser shots.
Shielded cylindrical space-charge-limited diode ionization detector
Authors: Tsai Chin-Chun , Bahns John T. , Stwalley William C.
Published: July 2002

A shielded cylindrical space-charge-limited diode ionization detector with high sensitivity and high resolution has been constructed to detect ionization in metal vapors, e.g., multiphoton ionization in the sodium atom and collisional associative ionization in the Rydberg states of the sodium dimer. The diode design and construction and measurements of its characteristics are described. Using this diode detector, a wide variety of high resolution spectroscopy can be obtained using techniques such as two-photon excitation, optical–optical double resonance, perturbation-facilitated optical–optical double resonance, and all-optical triple resonance.
Normally on photomultiplier gating circuit with reduced post-gate artifacts for use in transient luminescence measurements
Authors: Herman James R. , Londo Thomas R. , Rahman Noorul A. , Barisas B. George
Published: July 2002

A normally on gating circuit with reduced gate-associated artifacts and improved extinction has been developed for focusing electrode-equipped photomultiplier tubes (PMTs) such as the Thorn EMI, Inc. model 9816. Unlike previous gating methods where the focusing electrode is pulsed negative with respect to the photocathode (PC) to gate the tube off, this method holds the focusing electrode at a constant potential of +80 V with respect to the PC and pulses the first dynode from +80 to −246 V. This technique effectively eliminates post-gate signals induced by PC irradiation during the gating period, though at the cost of lower extinction efficiencies. By also pulsing the fifth dynode capacitatively with −326 V, attenuation is restored to greater than 107:1. The circuit assembly is compact enough to fit within a standard PMT housing and operates from the PMT dynode current. Turn-off and turn-on times of 55 and 40 ns, respectively, are obtained. The gate is thus suitable for exciting light pulse rejection in low level, submicrosecond time-resolved fluorescence, and phosphorescence measurements.
A ring coded-aperture microscope for high-resolution imaging of high-energy x rays
Authors: Ress D. , Ciarlo D. R. , Stewart J. E. , Bell P. M. , Kania D. R.
Published: July 2002

We use annular apertures to produce coded images of inertial-confinement fusion targets. The images are formed with 4–9-keV x rays; they are unfolded to obtain high-quality estimates of the source spatial distribution. Excellent time-integrated images have been obtained using x-ray film as a detector, and we are working to obtain time-resolved images using a gated microchannel-plate x-ray detector. Preliminary resolution-grid experiments show that the spatial resolution is ≤5 μm, and further experiments are planned to confirm a predicted resolution of ≤3 μm. We discuss the apertures, x-ray detectors, and image-processing software that forms this novel x-ray microscope.
Construction of a scanning two-dimensional Thomson scattering system for Alcator C-Mod
Authors: Casey J. A. , Watterson R. , Tambini F. , Rollins E. , Chin B.
Published: July 2002

A novel Thomson scattering diagnostic for the Alcator C-Mod tokamak is nearing operation. A vertically oriented 1-J Nd:YAG laser beam will be viewed along eleven (initially six) quasihorizontal chords simultaneously for one-dimensional profiles every laser pulse. Each chord is viewed by a Wadsworth grating spectrometer. Laser operation at 50 pps gives a coarse time axis. A counterrotating prism arrangement steps the laser position by up to 2 cm between pulses, allowing full two-dimensional profiles to be obtained over 160 ms (within the 14-cm accessible plasma region) during a single shot. Design details, calibration results, and control system and alignment details are presented.
Simple, variable-temperature, scanning tunneling microscope
Authors: Dubson M. A. , Hwang Jeeseong
Published: July 2002

We describe a simple scanning tunneling microscope (STM) which works well from room temperature to 4 K. It is relatively easy to build, repair, or modify, and works very reliably. An unusual feature of our STM is that it is assembled without glues or solders. A list of suppliers of the components used in our STM is included in the references.
Improved performance of an optically pumped FIR laser using metallic waveguide
Authors: Jiang Y. , Jing C. , Peebles W. A. , Brower D. L. , Doane J. L.
Published: July 2002

In order to improve the overall output characteristics of far-infrared (FIR) lasers, recent development at UCLA has concentrated on the use of a metallic overmoded waveguide (smooth bore and corrugated) instead of a conventional smooth-bore dielectric waveguide. The metallic waveguide has substantially lower propagation losses, especially at frequencies below 500 GHz, and also supports the desired HE11 mode. Laboratory results show a substantial increase in output power using a corrugated metallic waveguide, with 37 mW being obtained at 1.22 mm using 13CH3F (isotopic methyl fluoride) while maintaining the same mode quality and polarization. This represents an improvement of 100% over a smooth-bore dielectric waveguide. Comparison of far-infrared output using the three types of waveguide will be made.
Shaped electrode system for high voltage parallel plate analyzer
Authors: Hamada Y. , Kawasumi Y. , Masai K. , Iguchi H. , Fujisawa A. , Abe Y.
Published: July 2002

A new modification on the parallel plate analyzer for 500 keV heavy ions to eliminate the effect of the intense UV and visible radiation, is successfully implemented. Its design principle and results of numerical optimization are presented. In addition, the analyzer characteristics experimentally obtained in a high temperature plasma device, are discussed.
Measurement of DT neutron emission from TFTR with helium-4 proportional recoil counters
Authors: McCauley J. Scott , Strachan J. D.
Published: July 2002

The DT neutron emission from Triton Burnup has been measured with four helium-4 proportional counters in TFTR’s Multichannel Neutron Collimator. The operating characteristics of an ‘‘alpha’’ recoil proportional counter are presented. The theoretical response function of these detectors, which is complicated by the strong anisotropy of the (n,α) reaction, is compared with the measured response of these detectors from TFTR. A computer simulation predicts wall and end effects. The frequency responses of the detector and electronics have also been tested. A model predicts the saturation effects seen during high-power plasmas. The calibration techniques for this detector array will be discussed. The detectors have been used to measure the radial profile of the 1 MeV tritons produced by the d(d,p)t fusion reaction. The burnup produces 14 MeV neutrons in the d(t,n)α fusion reaction.
A neutron camera for burning plasmas
Authors: Källne J. , Gorini G.
Published: July 2002

Profile diagnosis of tokamak plasmas with neutron cameras is discussed, especially with regard to neutron detection limitations and possibilities in burning DT plasmas. A new detection method based on the magnetic proton recoil spectrometer technique is presented.
The role of excess arsenic in interface mixing in low-temperature-grown AlAs/GaAs superlattices
Authors: Lahiri I. , Nolte D. D. , Chang J. C. P. , Woodall J. M. , Melloch M. R.
Published: July 2002

Undoped low-temperature-grown AlAs/GaAs superlattices experience pronounced interface intermixing with increasing anneal temperatures up to 900 °C. Quantum confinement shifts caused by intermixing of low-temperature-grown and standard-temperature-grown superlattices were studied using electromodulation spectroscopy. The effective activation energy for intermixing in the low-temperature-grown superlattices during 30 s isochronal postgrowth anneals was found to be (0.32±0.04) eV, anomalously smaller than for standard-temperature-grown superlattices. Roughening of the interfaces caused by arsenic precipitates accompanies the intermixing. Qualitative features of the intermixing have been confirmed using high resolution transmission electron microscopy and studies on x-ray rocking curves.
Experimental studies of line shapes from a Balle–Flygare spectrometer
Authors: Campbell Edward J. , Lovas Frank J.
Published: July 2002

The line shape problem for the Balle–Flygare-type microwave spectrometer is reexamined experimentally using the method of sine and cosine Fourier transforms with a phase correction. Two previous studies [E. J. Campbell, L. W. Buxton, T. J. Balle, M. R. Keenan, and W. H. Flygare, J. Chem. Phys. 74, 829 (1981), and F. J. Lovas and R. D. Suenram, J. Chem. Phys. 87, 2010 (1987)] are reviewed. Those results are combined with new experimental data to obtain a general description of line shapes obtained from this device. Our emphasis here will be on using specific examples to clarify the relationship between the frequency domain representations of experimentally measured time-domain signals and the originating active species distributions.
Techniques for attainment, control, and calibration of cryogenic temperatures at small single-crystal samples under ultrahigh vacuum
Authors: Schlichting H. , Menzel D.
Published: July 2002

On the basis of detailed considerations of the relevant effects and parameters, we describe techniques which have been developed to accurately set, maintain, and measure the temperature of a small sample (typically a single-crystal disk of about 1 cm in diameter and 1 mm thick) in a strongly nonisothermal surrounding in ultrahigh vacuum, such as required by surface science experiments, in the temperature range from at least 6.5 K up. The resettability and resolution are 30–70 mK and the absolute error is estimated as about 0.7 K at 10 K and about 1.5 K at 100 K. Controlled linear heating with rates from 10−2 to 50 K/s and high constancy (deviations below 0.1 K up to 5 K/s and below 0.5 K up to 50 K/s), and stepwise heating (≳100 K/s) without measurable overshoot can be carried out in this whole cryogenic range.
A broadband nuclear magnetic resonance spectrometer: Digital phase shifting and flexible pulse programmer
Authors: Wu Xiao , Patterson Donald A. , Butler Leslie G. , Miller Joel B.
Published: July 2002

A simple, low-cost pulse nuclear magnetic resonance (NMR) spectrometer is described. There are two key features of the instrument: (1) all radio frequency phase shifting is done digitally with a new-generation frequency synthesizer and (2) the pulse programmer is based on a high-speed 32-bit parallel interface card in a desktop computer. The spectrometer is well suited for single-frequency channel experiments such as nuclear quadrupole resonance and deuterium quadrupole echo NMR experiments. Because the rf phase shifting is done digitally, the spectrometer operates easily over a wide frequency range, here 10–300 MHz. The pulse programmer and other software functions are written in LabView, a graphical programming language.
Fully automated apparatus for thermal diffusivity measurements on HTSC in high magnetic field
Authors: Calzona V. , Cimberle M. R. , Ferdeghini C. , Putti M. , Siri A. S.
Published: July 2002

This paper describes an apparatus to measure the thermal diffusivity of high temperature superconductors in an extended range of temperature (10–300 K) and magnetic field (up to 8 T). Heat losses are taken into account by adopting an ac technique. Effects introduced by power dissipated on the heater and thermal contacts between thermocouples and sample are considered. In fact the presence of a thermocouple relaxation time not negligible in respect to the sample relaxation time causes an error in the thermal diffusivity evaluation (up to 13% in a sample with poor thermal contact). We have estimated that, also at the higher temperatures, frequencies over 0.03 Hz keep the thermal losses low enough; in this case the poor thermal contact of the thermocouples can be a major problem. All of the experiment is computer controlled. The accuracy of the measurement, mainly determined by evaluation of the sample length, is 10%, while the sensitivity to the relative variations is much higher (0.1%).
New Scholte wave emitter: Application to nondestructive evaluation
Authors: Tinel A. , Duclos J.
Published: July 2002

We briefly present the properties of a liquid/elastic solid interface wave called ‘‘Scholte–Stoneley wave.’’ This wave is generated when a bulk wave meets the edge of the elastic solid in a perpendicular plane. This study leads to an original device for generating the Scholte wave. Using this simple setup, we show that the Scholte wave is diffracted by a default in the depth of the solid surface. In the same manner the commune extremity of two different solids stuck together is detected by this wave.
Spectral resolution of diffuse luminescence by imaging with a position-sensitive detector through a variable wavelength interference filter
Authors: Mendenhall G. David , Fleming Ronald H.
Published: July 2002

The combination of a variable wavelength interference filter and a position-sensitive photon-counting detector provide spectra of low-intensity luminescence. This method has been demonstrated on two luminescent materials, europium (II)-doped barium fluorobromide [BaFBr/Eu(II)] and uranyl nitrate [UO2(NO3)2⋅6H2O]. Pixel-by-pixel division of a luminescence image taken through the filter by an image without the filter corrects for variations in image intensity. The intensity along the long axis of the filter after correction for detector sensitivity constitutes a luminescence emission spectrum. BaFBr/Eu(II) gave delayed emission with a maximum intensity at 395 nm, in reasonable agreement with the measured Eu 5d→4f fluorescence maximum that occurs at 389 nm. The same technique applied to UO2(NO3)2⋅6H2O gave peaks at 511, 539, 567, and ∼600 nm. These did not correspond to experimental fluorescence maxima due to differing self-absorption effects.
Optical design considerations and performance of a spectro-streak apparatus for time-resolved fluorescence spectroscopy
Authors: Wiessner A. , Staerk H.
Published: July 2002

A time-resolved spectral photometer, i.e., an instrument for simultaneously measuring intensity, time, and wavelength (I-t-λ) is described. The ‘‘spectro-streak’’ apparatus comprises a grating objective coupled to a commercial streak camera with 2-ps resolution, a channel plate amplifier, a CCD camera, and a computer for data processing. The necessary calibration and correction procedures are discussed in detail; these are sweep nonlinearity correction, shading correction, geometric distortion correction, wavelength calibration, spectral intensity correction, and dispersion correction. The performance of the instrument is demonstrated with an example of current interest, the measurement of the solvatochromic dynamic Stokes shift of fluorescence from a charge-transfer system in solution.