bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation-based technique for automated tunable diode laser scan stabilization
Authors: May Randy D.
Published: July 2002

A software-based method for real-time, active stabilization of tunable diode laser spectral scans is described. The procedure is suitable for use with field and laboratory instrumentation where automated, unattended spectrometer operation is required. An autocorrelation of two high-resolution reference gas infrared spectra is computed at regular intervals, and the location of the maximum value of the autocorrelation provides the relative abscissa shift between the spectra. Small adjustments to the laser scan parameters are thereby made to ensure that drifts in the laser output frequency are tracked and compensated. Calculations required for stabilization of a 512-point spectrum can be completed in under 25 ms using an inexpensive, moderate-speed, array processor installed in a PC.
Laser-slaved piezo-controlled Fabry–Perot interferometer
Authors: Zuccheretti E. , Fua D. , Fiocco G.
Published: July 2002

A high-resolution Fabry–Perot interferometer was inserted in a feedback loop which, by monitoring elements of the fringe pattern, keeps the position of the transmitting window fixed with respect to a given line, taking into account the instability of the radiation source which would produce a wander of the line itself and the noise affecting the tuning of the receiving interferometer. The system, in this preliminary form, is able to lock itself and maintain its position indefinitely for slow and moderately fast varying disturbances.
Ion sources for dry etching: Aspects of reactive ion beam etching for Si technology (invited)a)
Authors: Scheer H. -C.
Published: July 2002

Aspects of ion beam sources are treated which emerge from their use for reactive ion beam etching (RIBE) in silicon VLSI technology. As a basis for this treatment, the requirements for dry etching for VLSI are elaborated, as well as the consequences of these requirements for ion beam sources to be used for such technology. Practical experience with two types of ion beam sources for this application are highlighted, a classical Kaufman source and a first-generation ECR source. Aspects relevant for microfabrication related to grid optics, and the use of reactive gases, are discussed. Most important in this context are the internal microdivergence of an ion beam and the fragmentation of molecular gases taking place in the source and the ion beam as well. The consequence for potential application of RIBE for micropatterning must be to characterize sources by measuring their energy- and angle-resolved particle fluxes to the wafer.
Ion beam diagnostics by Doppler shifted light emissionsa)
Authors: Heinrich F. , Stoll H.-P. , Hoffmann P. , Scheer H.-C.
Published: July 2002

Broad ion beams in the energy range of 0.2 to 1.5 keV originating from a filament source with argon as feed gas have been analyzed by high-resolution emission spectroscopy. The Doppler structure of Ar+ emissions reveals the existence of different velocity classes. Besides slow ions and ions possessing the main beam energy, electronically excited Ar+ ions with twice the main beam energy are detected which are attributed to a single-electron capture process in Ar++/Ar collisions. As a preliminary result from a reactive beam extracted from a microwave CF4 source plasma fast F atoms are detected which are attributed to charge exchange and dissociative collisions in the process chamber.
Chromaticity correction for the VUV and soft x-ray ring at the Photon Factorya)
Authors: Kobayashi Yukinori , Kamiya Yukihide
Published: July 2002

We will present a method of chromaticity correction for a high brilliant SR ring. This method has been successfully applied to a low emittance ring, the VUV and soft x-ray ring, which is one of the future plans of the Photon Factory. As a result, we have obtained a sufficiently wide dynamic aperture, more than 40 mm in both transverse directions.
A time-resolved light-scattering photometer
Authors: Chu Benjamin , Zhou Zukang , Moser H. O.
Published: July 2002

A time-resolved light-scattering photometer based on a combination of a fiber optic device (an optical transformer) with an intensified photodiode array detector is described. The key feature includes a baffle arrangement which defines the angular apertures of the scattering angles as viewed by the array detector and limits the background stray light as viewed by the fiber bundles. The instrument, which is a modified version of a previous report [Moser et al., J. Phys. Chem. 92, 6723 (1988)], can be used for time-resolved measurements of angular distribution of scattered intensity from weak to very strong scattering systems.
Nanosecond rise-time laser-produced stress pulses with no asymptotic decay
Authors: Gupta Vijay , Yuan Jun , Pronin Alexander
Published: July 2002

Stress pulses with rise times of 1.14 ns and amplitudes in excess of 3 GPa are produced using an Nd:YAG laser. In contrast to pulse profile assuming an asymptotic tail at about 5% to 10% of the peak stress, the pulses reported here show much sharper, post-peak decays resulting in a zero stress at about 17 ns. Use of such stress pulses in the determination of the tensile strength of planar interfaces between thin coatings of 0.1-μm thickness and substrates is also discussed.
Determination of thermal conductivity and specific heat by a combined 3ω/decay technique
Authors: Frank R. , Drach V. , Fricke J.
Published: July 2002

A technique is presented that allows measurement of both the thermal effusivity and diffusivity of the specimen. It employs the thermal excitation of a sample with a plane-surface heater at frequency ω and the observation of the 3ω thermal response of this metal element. In addition the temperature decay of the surface is observed, after the periodic heating current is switched off. Using this technique, the temperature dependence of the thermal conductivity and the specific heat of fused silica have been determined over a wide temperature range. For measurements on electrically conducting solids a technique for preparation of a dielectric insulating magnesiumoxide (MgO) film has been developed. A theoretical model is discussed, that allows to investigate not only bulk materials, but layered structures, also. Applying this model, the thermal effusivity of the upper polymethylmetacrylate (PMMA) layer of a PMMA-aluminum system and the effusivity of the substrate in a MgO stainless-steel system has been measured.
Measurement of the Seebeck coefficient by an ac technique: Application to high-temperature superconductors
Authors: Aubin M. , Ghamlouch H. , Fournier P.
Published: July 2002

We report on a sensitive and reliable ac technique to measure the Seebeck coefficient S of materials, in particular of high Tc superconductors. The small temperature difference between the ends of the sample allows structure in the S(T) curve to be observed. This technique avoids the creation of a component proportional to dS/dT in the measured signal. Such a component has in the past led to erroneous conclusions regarding the high-temperature superconductor YBCO. A mathematical analysis shows the origin of this component and how it can be avoided. These predictions are confirmed by experiments on a YBCO single crystal.
Condensed matter electron momentum spectrometer with parallel detection in energy and momentum
Authors: Storer P. , Caprari R. S. , Clark S. A. C. , Vos M. , Weigold E.
Published: July 2002

An electron momentum spectrometer has been constructed which measures electron binding energies and momenta by fully determining the kinematics of the incident, scattered, and ejected electrons resulting from (e,2e) ionizing collisions in a thin solid foil. The spectrometer operates with incident beam energies of 20–30 keV in an asymmetric, non-coplanar scattering geometry. Bethe ridge kinematics are used which for 20 keV incident energy has scattered electron energies of 18.8 keV at a polar angle of θs=14°and azimuthal angles φs in the range from −18° to +18° and ejected electrons of 1.2 keV and θe=76°with φe=π±6°. The technique uses transmission through the target foil, but it is most sensitive to the surface from which the 1.2 keV electrons emerge, to a depth of about 2 nm. Scattered and ejected electron energies and azimuthal angles are detected in parallel using position sensitive detection, yielding true coincidence count rates of 6 Hz from a 5.5 nm thick evaporated carbon target and an incident beam current of around 100 nA. The energy resolution is approximately 1.3 eV and momentum resolution approximately 0.15 a0−1. The energy resolution could readily be improved by monochromating the incident electron beam.
Active ripple filter of a synchrotron magnet power supply
Authors: Ozaki Toshiyuki
Published: July 2002

The design and testing of a new active ripple filter for synchrotron magnet power supplies are described. The conventional active filter suppresses not only ripple, but also any rapid change in dc current; thus a well-controlled current cannot be obtained when using a high-speed ramping operation. This restriction could be relaxed by using the proposed active filter.
Photoacoustic methods for real-time measurement of laser beam diameter and position, and for laser cavity alignment
Authors: Villagrán-Muniz M. , García-Segundo C. , Ranea-Sandoval H. F. , Bilmes G. M.
Published: July 2002

Photoacoustic signals generated in absorbing media can be used for real-time alignment of laser cavity components, for measurements of positions and diameters of pulsed laser beams, and for control of the degree of overlap of two or more, focused and unfocused pulsed laser beams. The developed techniques require an absorbing medium and a piezoelectric detector. Measurements and control can be performed by real-time inspection of the acoustic signals in an oscilloscope. These methods are convenient for experiments in nonlinear optics in which the power requirements lead to focusing and superposition of the beams, and for alignment of laser cavities in the liquid phase as well as gas and solid state infrared lasers.
Radiometric calibration of a video fluorescence microscope for the quantitative imaging of resonance energy transfer
Authors: Niles Walter D. , Cohen Fredric S.
Published: July 2002

A video microscope for radiometric imaging of resonance energy transfer (RET) between donor and acceptor fluorophores is described and calibrated. The donor is excited by epi-illumination with monochromatic light. Light emitted by donor and acceptor fluorophores in the specimen is filtered into separate emission images, which are viewed with a pair of multichannel plate image intensifiers in tandem with charge-coupled device (CCD) cameras. The RET rate constant is calculated at each location in the specimen from the ratio of the donor and acceptor emission intensities. These intensities are computed from the video brightnesses after transformation to irradiances using an experimentally obtained calibration, which accounts for the spectral transmission of the optical pathways and the spectral response of the detectors to determine the energies emitted by the probes in the specimen. We describe procedures for measuring the input irradiance–output brightness relations of the intensifier-CCD cameras. With these calibrations, the RET ratio image enables measurement of molecular-scale (nanometer) distances between probes within membranes of biological and biophysical interest.
X-ray imaging of polycrystalline materialsa)
Authors: Wroblewski T. , Geier S. , Hessmer R. , Schreck M. , Rauschenbach B.
Published: July 2002

A novel method yielding simultaneous information about location and orientation of the crystallites in a polycrystalline specimen has been developed and succesfully applied to the investigation of thin diamond films deposited on silicon. The experiment uses the parallel beam from a synchrotron radiation source and a microchannel plate as collimator in front of an image plate detector. Exposure times of only a few minutes could be realized. The spatial resolution was 0.375 mm but can easily be improved.
64 channel fiber optic spectrometer for a dual wavelength interferometric pressure sensor array
Authors: Castracane J. , Clow L. P. , Wegener S. , Seidler G.
Published: July 2002

As part of a fiber optic, interferometric pressure sensing array system for hypersonic wind tunnel studies, a 64 channel spectrometer has been developed to separate the return signals by both position and wavelength. The spectrometer is designed to optically separate the quadrature signals from the interferometer. A ribbon of single-mode fibers carrying the dual wavelengths (811.7 and 813.3 nm) from the sensing surface array forms the entrance slit to the spectrometer. This spectrometer uses a unique optical layout consisting of a 32 element microlens array, narrow passband interference filter and concave mirror to separate and focus the optical signals onto the photosensitive surface of a 1×64 photodiode array. The microlens array collimates the emerging beams from the single-mode fibers to minimize cross talk between channels. The detector array and its control electronics are an integral part of the spectrometer and are mounted on the same baseplate as the other optical components. Fast scanning and digitizing electronics produce an effective data rate of 160 kHz for 64 channels. Details of the construction and results of the calibration are presented.
On the dynamic behaviors of a strain gauge pressure transducer
Authors: Huang Wei , Zou Yida , Wang Changmin
Published: July 2002

In this paper, the dynamic behavior of a strain gauge pressure transducer is analyzed with the one-dimensional elastic wave theory. An infinite series type formulation for the output strain of the transducer is put forward and proved to be correct by comparing the analytic results with those from experiments. Analysis on a real pressure transducer suggests that the transducer will be unreliable as the rise time of a pressure pulse is too short (e.g., less than 500 μs), and the maximum pressure readings will be either much too high or much too low, depending on the rise time and the base length of the strain gauge, etc. The results presented will be helpful for practical dynamic pressure measurements.
End station for polarization and excitation energy selective soft x-ray fluorescence spectroscopy
Authors: Guo J.-H. , Wassdahl N. , Skytt P. , Butorin S. M. , Duda L.-C. , Englund C. J. , Nordgren J.
Published: July 2002

An end station for soft x-ray fluorescence spectroscopy has been constructed, which includes an experiment chamber, rotatable 90° under ultrahigh vacuum conditions around the incoming synchrotron radiation beam, which is provided with a high-resolution soft x-ray spectrometer. A manipulator allowing three axes of rotation, three directions of translation, as well as LN2 cooling and resistive heating is mounted to the chamber and serves as the sample holder. Samples can be transferred under vacuum between the experiment chamber and two other chambers, one for sample preparation and another for introducing new samples and for sample storage. The end station has been used at two different synchrotron radiation laboratories (beamline BW3) at HASYLAB in Hamburg and at ALS (beamline 7.0) in Berkeley. Polarization-dependent and angular resolved, selectively excited x-ray emission studies have been made on ordered as well as nonordered systems, e.g., high-Tc superconducting systems, diamond, fullerenes, and molecular ices. The experimental system will be presented along with some recent scientific results.
Observations of Alcator C-Mod plasmas from a five chord high energy resolution x-ray spectrometer array
Authors: Rice J. E. , Bombarda F. , Graf M. A. , Marmar E. S. , Wang Y.
Published: July 2002

X-ray spectra from Alcator C-Mod plasmas have been collected using a high wavelength resolution, five spectrometer array during a wide range of operating conditions, providing a large variety of diagnostic information. Each independently scannable von Hamos type spectrometer has a wavelength range of 2.8–4.0 Å, and the complete Rydberg series of helium- and hydrogenlike argon have been observed. Spectra of Δn=1 ground state transitions and satellites taken along different chords have been simulated using the results from a collisional-radiative model and the mist transport code. Line ratios are very sensitive to the electron temperature and deduced profiles are in good agreement with ECE profiles. Line intensities have been utilized to obtain absolute argon densities. The widths of the strongest lines have been used to deduce ion temperature profiles. Transitions from around n=9 to the ground state are populated by charge exchange in the outer regions of the plasma and these line intensities have been used to determine the neutral hydrogen density profile. Spectra from heliumlike scandium have been obtained during injection experiments and time histories and line intensities have been utilized to determine impurity transport coefficients.
Metallic ion production with electron cyclotron resonance ion source Caprice
Authors: Barué C. , Bossler J. , Schennach S. , Schulte H. , Wolf B. H.
Published: July 2002

In cooperation with CEN-Grenoble we developed a high temperature oven for the production of beams from rare and expensive nickel isotopes (62Ni and 64Ni) with an electron cyclotron resonance (ECR) ion source Caprice-14 GHz. For the first time, nickel has been produced in this way. For an experiment at the Unilac we have provided a stable Ni9+ beam for 40 days with a mean intensity of 25 eμA. The nickel consumption was a few mg per hour and ten ovens have been used for that period. Surprising and promising results were obtained with this oven for the production of uranium beams by using UO2 samples. These results are compared with the ‘‘plasma heating’’ method. Complementary investigations about the already studied ‘‘sputtering’’ method are also presented.
Ion sources for radioactive beams and related problems (Review) (invited)
Authors: Kirchner R.
Published: July 2002

Ion sources for radioactive beam facilities are integrated systems of production target and ionizer which have to convert the limited number of particles produced in nuclear reactions efficiently and selectively into an ion beam. The figures of merit for such a system are thus its efficiency for a desired isotope and its discrimination against the unwanted elements. The efficiency is the product of release efficiency (a characteristic of the integrated system) and ionization efficiency, the latter characterizing the ionizing mechanism. The ionizers described include both the ones routinely used in isotope separation on-line as well as promising new developments; they are classified according to their ionizing medium, utilizing electrons, heat, or photons, respectively.
Large range subgap absorption measurements in thin semiconducting films
Authors: Zammit U. , Marinelli M. , Mercuri F.
Published: July 2002

A detailed description of an experimental configuration based on photothermal deflection spectroscopy (PDS) and transmittance techniques that enables high sensitivity room temperature absorption measurements over a spectral region extending between 300 nm and 3.4 μm is reported. It is shown that the simultaneously determined PDS and transmittance spectra can be processed to eliminate completely the interference induced oscillations in the spectra which are observed when the film refractive index differs substantially from the one of the substrate. A configuration based on the photopyroelectric and transmittance techniques, though less sensitive than the previous one, is shown to be suitable for the same kind of measurements at cryogenic temperatures. Absorption bands in implanted Si between 2.8 and 3.4 μm have thus been detected and tentatively associated with multiphonon defect assisted absorption bands.
Phase-shift generation and monitoring by a simple circuit
Authors: Golnabi H. , Ashrafi A.
Published: July 2002

A simple circuit for generating phase shifts along with a monitoring scheme is described. The circuit reported here produces a squarewave signal with fixed phase shift relative to the incoming signal. The amount of this phase shift can be monitored by the input voltage of a voltage-controlled oscillator. By varying the free-running frequency of the voltage-controlled oscillator the phase shift of the output signal can be varied for a range of 0°–180° corresponding to a voltage change of −1.2 to 1.2 V. The produced phase shift is a linear function of the voltage setting that can be controlled with a high accuracy. The reported circuit can be used in phase sensitive detection systems operating based on a shifted squarewave reference signal.
Friction free active-element bulk-modulus high-pressure transducer
Authors: Wisniewski R. , Molinar G. F.
Published: July 2002

The described bulk-modulus high-pressure transducer having a friction free active element can be used for pressure measurements up to 2.0 GPa with an estimated uncertainty better than 0.2% and 0.1 MPa sensitivity. An electronic length-measuring gauge of 0.1 μm uncertainty has been used as a detector of active-element deformation.
New high-pressure hot stage for optical microscopy
Authors: Maeda Yoji , Koizumi Mitsuo
Published: July 2002

A new high-pressure optical hot-stage system combined with polarizing optical microscope has been constructed for in situ observation of optical texture of liquid crystals as well as polymers during the mode of either temperature or pressure scanning. It operated well in a temperature region between room temperature and 250 °C under hydrostatic pressures up to 300 MPa. The texture of a pressure-induced crystal polymorph of a dimesogenic liquid crystal was successfully observed.
A specialized torsion balance designed to measure the absolute flux density of hyperthermal molecular beams containing reactive species
Authors: Cook Steven R. , Hoffbauer Mark A. , Cross Jon B. , Wellenstein Hermann , Fink Manfred
Published: July 2002

A torsion balance is described that has been used to measure the absolute flux density of seeded hyperthermal molecular beams containing reactive and/or condensable species with uncertainties of approximately ±5%. The balance is ultrahigh-vacuum compatible and can be used in corrosive environments. A specially designed beam stop mounted on the torsion balance lever arm, traps the incoming beam and allows only completely thermalized molecules to exit. The thermalized molecules exit the beam stop in equal numbers per unit time in opposite directions, ensuring that the force exerted on the beam stop by the exiting molecules is zero. The balance was suspended from a 25-μm-diam gold-coated tungsten wire that had a torsion constant of 6.04×10−8 N m/rad and a period of slightly larger than 400 s. Absolute molecular beam flux density measurements were made using both the torsion balance and the effusive method for a variety of pure and seeded molecular beams. The beams were composed of gases that could easily be measured by the effusive method. Measured fluxes ranged from 2.41×1015 mol/s cm2 for a beam of CO seeded in H2 to 1.25×1017 mol/s cm2 for a beam of pure H2. A comparison of the two methods establishes the ability of the torsion balance to accurately measure the flux of molecular beams.
Momentum rate probe for use with two-phase flows
Authors: Bush S. G. , Bennett J. B. , Sojka P. E. , Panchagnula M. V. , Plesniak M. W.
Published: July 2002

An instrument for measuring the momentum rate of two-phase flows is described, and design and construction details are provided. The device utilizes a conelike body to turn the flow from the axial to the radial direction. The force resulting from the change in momentum rate of the turning flow is measured using a strain-gage-instrumented cantilevered beam. The instrument is applicable to a wide range of flows including nuclear reactor coolant streams, refrigerants in heating-ventilating air-conditioning equipment, impingement cooling of small scale electronic hardware (computer chips are one example), supercritical fuel injection (in Diesel engines, for instance), and consumer product sprays (such as hair-care product sprays produced using effervescent atomizers). The latter application is discussed here. Features of the instrument include sensitivity to a wide range of forces and the ability to damp oscillations of the deflection cone. Instrument sensitivity allows measurement of momentum rates considerably lower (below 0.01 N) than those that could be obtained using previous devices. This feature is a direct result of our use of precision strain gages, capable of sensing strains below 20 μm/m, and the damping of oscillations which can overwhelm the force measurements. Oscillation damping results from a viscous fluid damper whose resistance is easily varied by changing fluids. Data used to calibrate the instrument are presented to demonstrate the effectiveness of the technique. As an example of the instrument’s utility, momentum rate data obtained using it will be valuable in efforts to explain entrainment of surrounding air into effervescent atomizer-produced sprays and also to model the effervescent atomization process.
An easy-to-use non-optical shear-force distance control for near-field optical microscopes
Authors: Barenz J. , Hollricher O. , Marti O.
Published: July 2002

We present an easy-to-use non-optical shear-force detection system for tip–sample distance control in scanning near-field optical microscopes. The fibre tip is fixed in a four-segmented piezo-tube by a polymer, Polyisobutylene, which couples the tip stiffly to the piezo at frequencies of 10 kHz or more at room temperature. One segment of the piezo-tube excites the fibre tip in resonance, while the other three segments detect the tip vibration in the manner of a piezo-microphone. When the tip is damped by shear forces the induced voltage at the three segments changes and can easily be detected with a lock-in amplifier. Further our method allows a fast and reproducible tip exchange with minor adjustments of mechanical or electrical components. We demonstrate the performance of our distance control on a holographically fabricated line pattern with 417 nm lattice spacing and 10 nm height. A height resolution of better than 1 nm is demonstrated.
Seismic vibrations mechanical filters for the gravitational waves detector VIRGO
Authors: Braccini S. , Bradaschia C. , Del Fabbro R. , Di Virgilio A. , Ferrante I. , Fidecaro F. , Flaminio R. , Gennai A. , Giassi A. , Giazotto A. , Gorini G. , Losurdo G. , Palla F. , Pasqualetti A. , Passuello D. , Poggiani R. , Torelli G. , Zhang Z.
Published: July 2002

VIRGO is a detector of gravitational waves based on a laser interferometer with 3 km long arms, now under construction. In order to detect gravitational waves down to 10 Hz, the seismic noise has to be reduced by several orders of magnitude. New mechanical filters using cantilever springs as elastic elements have been developed for the VIRGO seismic isolation system. The spring total stiffness is reduced by more than one order of magnitude using magnetic antispring. A control system allows one to keep the spring length constant. The new filters provide an attenuation ≥40 dB each for frequencies above 10 Hz and, compared to the previously adopted solution (gas springs), are much less sensitive to temperature changes.
A study of a microwave cavity tuned oscillator
Authors: Chen W. M. , Li L. Y. , Zhang B. P. , Wu F. M. , Yu Z. , Jin X.
Published: July 2002

By using a microwave cavity tuned oscillator (MCTO), the relative dielectric constant ε of nonpolar dielectric fluid was measured with high accuracy. The theory of this technique was studied in detail. A new formula for evaluating the uncertainty of the measured ε was derived. From the formula, we have found that MCTO has a locking characteristic and therefore only operates in certain discrete regions. We have also found that a higher resonant frequency f of the MCTO, a longer delay time of the delay line, and a higher quality factor of the cavity Q lead to a higher accuracy of the measurement. When the values of the above parameters are taken properly, the uncertainty measured ε by the MCTO may become as small as an order of 10−5. The ε of saturated liquid nitrogen was measured by this approach and the experimental results agree very well with the values calculated by our formula.
A liquid-He automatic cooling system for a balloon-borne infrared telescope
Authors: Morigi G. , Ventura G. , Mandolesi N. , Cortiglioni S. , Attolini M. R.
Published: July 2002

A cooled telescope for astronomical infrared observations at balloon altitudes in the range 2–5 μm was successfully flown on June 12–13, 1995 from the NASA/NSBF base at Palestine, Texas. A cylindrical cryostat (42 cm in diameter, 120 cm high), housing the optics and the detector, was cooled by using liquid He as the refrigerating fluid. During the 11 h flight, the temperatures of the detector, optics, and internal telescope subparts were regulated between 45 and 80 K with very good stability. The cryogenics were controlled by a pressure control equipment designed to operate at both ground level and at 40 km altitude. Further thermal stabilization of the focal plane detector array was provided by a dedicated servocontrol to obtain a stability of ±0.02 K over time scales of a few minutes. The main features of the telescope, as well as on-ground and in-flight performances of the cryogenic system are described.
The determination of the interference fringe order in the split-beam liquid crystal display cell gap meter
Authors: Ye Yutang , Liu Yongzhi , Liu Xu
Published: July 2002

In the split-beam method, accurate measurement of the liquid crystal display cell gap requires determining the interference fringe order correctly. One method to determine the orders is the so-called intensity method in which the brightest fringe is determined to be the zeroth order. Using this method, the measurement accuracy may be affected by random noise. The color method in which the order of the fringes is determined according to their colors is presented. It is easy to get much better measurement accuracy by using the new method.
Infrared–far-infrared stabilized laser system with adjustable frequency offset for spectroscopic measurements
Authors: Sárközi J. , Bakos J. S. , Djotyan G. P. , Sörlei Zsuzsa
Published: July 2002

A double resonance infrared–far-infrared spectroscopic system is described. The variation of the 118.8 μm wavelength gain line shape of the methanol far-infrared laser on the diameter of the pump CO2 laser beam due to the induced nonlinear waveguiding effect has been measured. The high-frequency stability and continuous tunability of the pump CO2 lasers necessary for such measurement were achieved by frequency offset locking them to a molecular line center stabilized reference laser. The long term frequency stability achieved for the offset locked lasers is 24 kHz.
Possible application of silicon microstrip detectors in solid state physics
Authors: Brovetto P. , Maxia V. , Salis M.
Published: July 2002

The possibility of utilizing silicon microstrip detectors for analyzing the angular correlations of positron annihilation γ rays is examined in some detail. It is found that suitable experimental arrangements, which allow exploitation of the high spatial resolution of these detectors, can be devised.
Pressure applied to epoxy-potted samples by thermal contraction of the epoxy matrix
Authors: Lukefahr H. G. , Collins J. K. , Camacho E. , Yeager C. , MacLaughlin D. E. , Myers A. , Bernal O. O.
Published: July 2002

Using a cuprous oxide manometer developed by Reyes et al. [Rev. Sci. Instrum. 63, 3120 (1992)] we have measured the pressure applied to powdered cuprous oxide due to thermal contraction of an epoxy matrix commonly used for cryogenic nuclear magnetic resonance experiments. The measured pressure is approximately 1 kbar at low temperatures, which is significant for certain materials.
A femtosecond absorption spectrometer tunable from 50 000 to 800 cm−1: Nonlinear optics and pump/probe geometries
Authors: Akhremitchev Boris , Wang Chengfei , Walker Gilbert C.
Published: July 2002

Solid state Ti:sapphire lasers were constructed and combined with nonlinear optics to produce a 100 fs resolution absorption spectrometer with tunability from 50 000 to 800 cm−1 and <1 m o.d./s sensitivity. Tunable light generation and array detection technology are presented, including a discussion of the suitability of different infrared nonlinear optical materials. A systematic approach to stable infrared pulse generation is provided. Critical parameters of the pump/probe beam geometry are enumerated, revealing detrimental nonlinear contributions to the observed pump-induced change in probe absorbance. These effects include pump-induced probe phase modulation and pump-induced refractive index lenses. Measurements and simulations of the unwanted features in various system geometries reveal their systematic control and elimination.
Investigation of two negative hydrogen and deuterium ion sources: Effect of the volume
Authors: Bruneteau A. M. , Courteille C. , Leroy R. , Bacal M.
Published: July 2002

We have investigated by probes and by photodetachment the plasma properties of two negative ion sources of different volume. We compared the data relevant to these two sources and identify the effects induced by the change in volume and the isotope effects. The observed scaling law for the electron temperature is in each case Te∼I0.27d. Positive ions are predominantly lost to the walls, but due to the increasing influence of their loss by dissociative recombination when the source volume is increased, the scaling laws are ne∼I0.7d, for the small source, and ne∼I0.59d, for the large source. Atoms limit the production of negative ions and destroy them. Thus we see an isotope effect, with higher negative ion density in hydrogen than in deuterium, and the effect of the source volume, with the negative ion density larger in the small source than in the large one.
Exoemissive noise activity of different metallic materials
Authors: Bichevin V. , Käämbre H. , Sammelselg V. , Kelle H. , Asari E. , Saks O.
Published: July 2002

A method is proposed for testing the exoemission activity of different metals, used as materials in high sensitivity electrometry (attoammetry). The presented test results allow us to select materials with weaker exoelectron spurious currents.
Sensitivities of two free vibration torsion pendulums
Authors: Zhu Xianfang , Shui Jiapeng
Published: July 2002

In this article, for the necessity of measuring the damping of new materials, a detailed comparison was made between two important free vibration torsion pendulums, that is, the inverted torsion pendulum and the Collette pendulum. Special attention was paid to the strong effect of the torsionally weak suspension in both pendulums on the difference between measured damping of the overall system and the real damping exclusively contributed by the investigated specimen. This difference was successfully quantitatively characterized by a parameter: the sensitivity of the pendulum only via which the accurate damping for the specimen can be determined for each case. The comparison showed that the sensitivities of the two systems obviously behave differently. Although it produces smaller performing strain amplitude on the specimen and has a narrower preset vibration frequency range, the sensitivity of the Collette pendulum is always lower than that of the inverted torsion pendulum.
Development of a visible framing camera diagnostic for the study of current initiation in z-pinch plasmas
Authors: Muron D. J. , Hurst M. J. , Derzon M. S.
Published: July 2002

We assembled and tested a visible framing camera system to take 5 ns FWHM images of the early time emission from a z-pinch plasma. This diagnostic was used in conjunction with a visible streak camera allowing early time emissions measurements to diagnose current initiation. Individual frames from gated image intensifiers were proximity coupled to charge injection device cameras and read out at video rate and 8-bit resolution. A mirror was used to view the pinch from a 90° angle. We observed the destruction of the mirror surface, due to the high surface heating, and the subsequent reduction in signal reflected from the mirror. Images were obtained that showed early time ejecta and a non-uniform emission from the target. This initial test of the equipment highlighted problems with this measurement. We observed nonuniformities in early time emission. This is believed to be due to either spatially varying current density or heating of the foam. Images were obtained that showed early time ejecta from the target. The results and suggestions for improvement are discussed in the text.
Thermal and nonthermal electron cyclotron emission by high-temperature tokamak plasmas
Authors: Airoldi A. , Ramponi G.
Published: July 2002

An analysis of the electron cyclotron emission (ECE) spectra emitted by a high-temperature tokamak plasma in the frequency range of the second and third harmonic of the electron cyclotron frequency is made, both in purely Maxwellian and in non-Maxwellian cases (i.e., in the presence of a current-carrying superthermal tail). The work is motivated mainly by the experimental observations made in the supershot plasmas of the Tokamak Fusion Test Reactor (TFTR), where a systematic disagreement is found between the Te measurements by second-harmonic ECE and Thomson scattering. We show that, by properly taking into account the overlap of superthermals-emitted third harmonic with second-harmonic bulk emission, the radiation temperature observed about the central frequency of the second harmonic may be enhanced up to 30%–40% compared to the corresponding thermal value. Moreover we show that, for parameters relevant to the International Thermonuclear Experimental Reactor (ITER) with Te(0)>7 keV, the overlap between the second and the downshifted third harmonic seriously affects the central plasma region, so that the X-mode emission at the second harmonic becomes unsuitable for local Te measurements.
Neutron spectrometry for plasma rotation
Authors: Gorini G. , Källne J. , Ballabio L.
Published: July 2002

The principles of neutron spectrometry for determination of the toroidal rotation velocity (Vt) of the plasma in tokamaks are discussed. Comparison is made with photon spectroscopy which shows that neutron spectroscopy can be used as a rotation diagnostic and that its applicability depends on the availability of high neutron fluxes and the development of methods to measure the neutron energy with very high precision. It is found that neutron spectroscopy could be a feasible rotation diagnostic for burning fusion plasmas to be produced in the next generation tokamaks such as ITER. It is proposed that Vt should be derived from the difference spectrum obtained from the simultaneous measurement of neutrons emitted tangentially in two opposite directions. The problems connected with the calibration and stability requirements on the neutron spectrometer system for Vt measurements are illustrated and possible technical solutions discussed.
Feasibility of neutron spectrometry diagnostic for the fuel ion density in DT tokamak plasmas
Authors: Källne J. , Gorini G. , Ballabio L.
Published: July 2002

The neutron wall emission (WE) background is a crucial element of neutron spectrometry as a fuel density diagnostic for burning deuterium-tritium fusion plasmas in tokamaks. WE spectra have been studied based on MCNP neutron transport calculations applied to the conditions of the ITER vessel according to the preliminary EDA design taking into account the multiple nuclide composition of the plasma facing wall multilayered structure. The results of calculated signal and background intensities suggest that neutron spectrometry is a feasible density diagnostic on ITER for burning plasmas for aim set at the 10% accuracy level (random and systematic).
Charged-coupled devices for charged-particle spectroscopy on OMEGA and NOVA
Authors: Li C. K. , Hicks D. G. , Petrasso R. D. , Seguin F. H. , Cable M. D. , Phillips T. W. , Sangster T. C. , Knauer J. P. , Cremer S. , Kremens R. L.
Published: July 2002

Charge-coupled devices (CCDs) are to be utilized as charged-particle detectors for ρR and implosion symmetry diagnostics on OMEGA and NOVA. Using a large range of MeV charged particles, comprehensive studies have been performed on several back-illuminated CCDs in order to establish their utility for determining particle energy and identity (e.g., H, D, or T). Issues of signal and noise (i.e., especially from neutrons and gammas interacting with the CCDs) are also being investigated.
Burn history measurements in laser based fusion
Authors: Caldwell S. E. , Han S. S. , Joseph J. R. , Petersen T. L. , Young C. S.
Published: July 2002

Gamma-ray measurements from fast burning deuterium/tritium capsules used in the laser based fusion program inherently carry more high bandwidth information than neutron measurements because they are not subject to Doppler induced time-of-flight broadening. GaAs photoconducting detectors are used to record both the gamma-ray and neutron pulses temporally separated by the time-of-flight difference. The technique has been successfully demonstrated to produce gamma-ray burn history measurements for capsules yielding more than 1012 neutrons.
Neutron-induced noise in National Ignition Facility-class diagnostic instruments
Authors: Lerche R. A.
Published: July 2002

Neutron yields from deuterium–tritium-filled inertial-confinement-fusion targets have reached 1014. Above 1013, a significant neutron-induced background appears in images recorded with nearby streak cameras. Since camera components (streak tube, image-intensifier tube, and charge coupled device arrays) are similar to components that will be used in many National Ignition Facility (NIF) instruments, streak camera images provide information about neutron-induced backgrounds that will be encountered in the NIF environment. At a fluence of 107 neutrons/cm2, the background consists of two distinct components: a uniform component equal to nearly 20% of the camera’s linear range and sharp, intense spikes each localized to just a couple of image pixels. About 80% of the uniform background is caused by interactions with the streak tube and image-intensifier tube. Nearly all the sharp spikes are caused by interactions with pixels of the charged-coupled device array. The spikes make the most significant contribution to image noise.
Imaging backscattered and near to backscattered light in ignition scale plasmas (invited)
Authors: Kirkwood R. K. , Back C. A. , Blain M. A. , Desenne D. E. , Dulieu A. G. , Glenzer S. H. , MacGowan B. J. , Montgomery D. S. , Moody J. D.
Published: July 2002

Diagnostics have been developed and fielded at the Nova laser facility that, for the first time, image nearly all the light scattered within 20° of the laser axis, including the light collected by the laser focusing lens as well as that just outside the lens. Absolute calibration of optical components exposed to the target debris have been achieved by a combination of routine in situ calibration and maintenance. Measurements from plasmas relevant to ignition experiments indicate that scattering is peaked in the direction of backscatter with significant energy scattered both into the lens and just outside the lens. The scattering outside the lens is found to be dominant when the f number is large (f/8).
One-dimensional time resolved soft x-ray imaging of colliding plasmas in a laser heated cavity
Authors: Eagleton R. T. , Foster J. M. , Rosen P. A. , Graham P.
Published: July 2002

We describe x-ray streak camera measurements of wall motion and plasma filling in hohlraum targets heated by the AWE HELEN laser. An x-ray streak camera using a transmission mode photocathode on a thin plastic substrate (1000 Å Parylene-N) was coupled to a 15° incidence gold mirror to define a spectral channel response of width 45 eV full width at half-maximum centered around 120 eV. A 20 μm diam pinhole was used to image the hohlraum interior onto the photocathode slit of the streak camera, via the gold reflector. Plasma expansion from the laser hot spots, and the indirectly heated wall, was recorded. The experimental data are compared with simulations using the AWE Lagrangian hydrocode NYM.
First results from the phase contrast imaging system on TEXT-U
Authors: Chatterjee R. , Hallock G. A.
Published: July 2002

A phase contrast imaging (PCI) diagnostic with a vertical beam covering the central third of the plasma was successfully operated to study density fluctuations in the TEXT-U tokamak. The diagnostic had a wave number range of 0.5–12 cm−1, a bandwidth of 500 kHz and a sensitivity of about 1010 cm−3. We present the optical design of the system and discuss three calibration techniques. We compare density fluctuation spectra obtained with spectra from Langmuir probes at the edge and the heavy ion beam probe diagnostic in the core of the plasma. This provides evidence that the PCI diagnostic is sensitive to both edge and core turbulence.
Optimization of the extracted current density from the high energy diagnostic neutral beam injector of TdeV
Authors: Sarkissian A. H. , Charette E. , Condrea I. , Gregory B. C.
Published: July 2002

Development of a high energy (40 kV, 1 A) neutral beam injector for diagnostic applications on TdeV is in progress. The injector operates with its source at ground potential and the neutralizer canal at ⩽−40 kV. The electrons in the neutralizer canal are retained by an electrostatic trap. The residual ions are collected near ground potential. Several diagnostics, including calorimetry, spectroscopy and a scanning multipin open probe array, are used to study the beam characteristics on its test stand. Hall probes and voltage dividers coupled with fiber optic links are used to optimize the efficiency of the extraction system, the electron trap, and the residual ion collection units. In its first stage of development, the injector has been optimized for operation with a single hydrogen beamlet. A beamlet divergence of less than 0.5 degrees was obtained. Up to 75 mA of ion current at 35 kV was extracted. The addition of another six extraction holes boosted the total extracted current to more than 600 mA at 36 kV.
Colliding plasma neutron production at Trident
Authors: Obst A. W. , Chrien R. E. , Wilke M. D.
Published: July 2002

Trident is a two-beam Nd:glass laser producing typically 100 J at 2ω in 2 ns pulses. Diffraction unlimited f/6 optics reduce the 20-cm-diam beams down to 100 μm diameter. The laser is capable of producing neutrons from D-D and D-T plasmas, and has demonstrated yields of >106 D-D neutrons from colliding plasma geometries. We have combined a previously existing neutron activation technique with two large photomultiplier tubes (PMTs) coupled to scintillators to produce a neutron measuring capability on Trident. In addition, we have coupled a time-of-flight compensated scintillator to a fast microchannel plate PMT to provide neutron energy resolution and hence the potential to measure ion temperatures through time-of-flight spread. The activation technique is sensitive to >105 neutrons per count in its present configuration. The PMT/scintillators have comparable sensitivities. The MCP/PMT/scintillator combination has 220 ps rise time with an order of magnitude less sensitivity. We will describe these detectors and the methods used to calibrate the individual detector sensitivities.