bluuebunny/crossref_metadata_2025 huggingface dataset:
Wölter x-ray microscope characterization facility (abstract)
Authors: Morales R. , Remington B. A. , Schwinn T. , Hensley G.
Published: July 2002

The capability for making ongoing characterization measurements of the spatial resolution and spectral reflectance of the Wölter x-ray optics used at Nova is essential for the interpretation of data taken with these imaging diagnostics. Equally important is an assessment of the long-term performance of grazing incidence x-ray optics used in the harsh environment of an ICF target chamber. We have designed and are currently building an off-line facility for such a characterization. The facility will consist of an x-ray source with specially designed pinhole-target foil array, the Wölter optics housing, monitoring and measuring detectors, a data acquisition system, and an in situ alignment system for rapid periodical verification. Each component of this lab will be discussed, along with possible initial results. This work was performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.
An infrared vibration compensated interferometer for the MST experiment
Authors: Innocente P. , Martini S. , Roca Ch. Ferrer
Published: July 2002

The paper describes a two-color CO2/HeNe laser (10.6/3.4 μm) interferometer which has been designed and built at the IGI laboratory in Italy and installed on the MST Reversed Field Pinch (R=2 m, a=0.52 m, I=0.6 MA) at University of Wisconsin Madison. The system is very compact and is mounted on a 1.2×0.6 m wood board for a total weight of ≊60 kg. The infrared vibration compensation system allows us to use a one-window access (the beam is reflected back by a mirror mounted in the vacuum vessel) and to operate without a stiff mechanical structure embracing the machine. Several new features, such as the use of an interferometric local oscillator, the on-line calibration algorithm, and the four-passage scheme, allow a line-integral density accuracy of 1×1018 m−2.
Cluster-impact fusion, or beam-contaminant fusion? (abstract)a),b)
Authors: Lo Daniel H. , Petrasso Richard D. , Wenzel Kevin W.
Published: July 2002

Beuhler, Friedlander, and Friedman (BFF) reported anomalously huge D-D fusion rates while bombarding deuterated targets with (D2O)N+ clusters (N∼25–1000) accelerated to ≊325 keV [R. J. Beuhler et al., Phys. Rev. Lett. 63, 1292 (1989); R. J. Beuhler et al., J. Phys. Chem. 94, 7665 (1990)] [i.e., ≊0.3 keV lab energy for D in (D2O)100+]. However, from our analysis of BFF’s fusion product spectra, we conclude that their D lab energy was ∼50 keV. Therefore, no gross anomalies exist. Also, from our analysis of the BFF beam-ranging experiments through 500 μg/cm2 of Au, we conclude that light-ion-beam contaminants (e.g., D+ of order 100 keV) have not been ruled out, and are the probable cause of their fusion reactions. This work was supported by LLNL Subcontract B116798, Department of Energy (DOE) Grant No. DE-FG02-91ER54109, DOE Magnetic Fusion Energy Technology Fellowship Program (D. H. Lo), and DOE Fusion Energy Postdoctoral Research Program (Kevin W. Wenzel).
Gamma ray to charged particle branching ratios for the radiative capture of deuterons by 2H, 6Li, and 10B
Authors: Cecil F. E. , Liu H. , Yan J. S. , Medley S. S.
Published: July 2002

The gamma to charged particle branching ratios for the radiative capture reactions of deuterons by 2H, 6Li, and 10B have been measured between center of mass energies of 20 and 40 keV, 80 and 110 keV, and 150 and 170 keV, respectively. The branching ratios for these very high-energy gamma rays, having values of 23.8, 22.3, and 25.2 MeV for the targets 2H, 6Li, and 10B, respectively, constitutes the data base for the gamma ray diagnostics of the corresponding fusion plasmas. For the fusion gamma ray detector on TFTR, counting rates for these gamma rays as a function of the total fusion reaction rate will be presented.
Artificial neural networks for plasma x-ray spectroscopic analysis
Authors: Larsen J. T. , Morgan W. L. , Goldstein W. H.
Published: July 2002

Modern diagnostic instrumentation produces a vast amount of data that often requires substantial analysis efforts. New methods are needed to improve the efficiency of the analysis process. Artificial neural networks have been applied to a variety of signal processing and image recognition problems. The feed-forward, back-propagation technique is well suited for the analysis of scientific laboratory data, which is viewed as a pattern-matching problem. We summarize the concepts and algorithms as implemented on a personal computer, and illustrate the method using a nonlocal thermodynamic equilibrium theoretical atomic physics model for k-shell x-ray spectroscopy of a high density, high temperature aluminum plasma. Extensions to other types of spectroscopy data analysis are discussed.
Analysis of a proton driven, exploding pusher target on PBFA II (abstract)
Authors: Dukart R. J. , Olson R. E. , Bailey J. E. , Chandler G. A. , Derzon M. S.
Published: July 2002

During the past year we have conducted a series of PBFA II target experiments. The design of the experiments was threefold: to characterize the response of targets to ion beams, develop our experimental diagnostic capability, and benchmark our theoretical ability to design and predict the response of the experimental diagnostics to ion-beam-heated, ICF targets. We present here an analysis of spherical exploding pusher experiments. The targets were 6-mm-diam, 100-μm-thick, Cl-doped CH spheres, filled with 1.2 atm of deuterium doped with 7 Torr of H2S. The diagnostics included XRDs, x-ray pinhole, framing, and streak cameras, and a spatially resolved, x-ray crystal spectrometer. Our analysis includes comparisons between experimental results and theoretical predictions of diagnostics responses and sulfur line emission from the compressed target using one- and two-dimensional radiation/hydrodynamic code runs. This work supported by the U. S. Department of Energy under Contract No. DE-AC04-76-DP00789.
Divergence measurement of light ion beams using ultracompact ion pinhole cameras on PBFA II (abstract)
Authors: Haill T. , Johnson D. , Bailey J. , Leeper R. , Hebron D. , Stygar W.
Published: July 2002

Ion beam divergence reduction will increase the power density deliverable to an ICF target and is one step towards demonstrating a credible path to target ignition. Measurement of the divergence is made with an ultracompact ion pinhole camera (UC-IPC). The UC-IPC is mounted in the PBFA II diode near the ion source at a 10° angle to compensate for beam bending in the diode’s applied magnetic field. The beam is transported through an entrance pinhole and down an entrance tube to a gold scattering foil. The beam is scattered 90° through a second pinhole to CR39 film where the ion track count is recorded. This paper will describe the results of off-axis ion beam divergence measurements using the UC-IPC. Together with other diagnostics, the UC-IPC provides information about beam species and charge state, about particle energy and about divergence of the beam. This paper will also describe UC-IPC simulation using PICDIAG, a 2D code that models the ion transport and diagnostic response of experiments on Sandia’s PBFA II accelerator. This work supported by the U. S. Department of Energy Contract No. DE-AC04-76DP00789.
A Rayleigh light scattering facility for the investigation of free jets and plumes
Authors: Bryner Nelson , Richards Cecilia D. , Pitts William M.
Published: July 2002

A Rayleigh light scattering facility (RLSF) has been developed and successfully used to examine mixing in free jets and buoyant plumes. The RLSF couples laser diagnostics with a cylindrical clean room, test section diameter of 2.4 m and a height of 2.4 m, to monitor the real-time concentration behavior within turbulent flows. The facility has been carefully designed to minimize interferences of glare and Mie scattering by suppressing background light and removing dust particles. The relatively large working section of the RLSF allows quantitative concentration measurements via Rayleigh light scattering (RLS) in free shear flows entering quiescent surroundings. As a result, RLS measurements are now possible in momentum-driven flows for conditions which were impossible in the past and in buoyancy-driven flows for which no previous RLS investigations have been made. Initial measurements of concentration in momentum-driven jet flows of helium and Freon-13 and a transitional (momentum- to buoyancy-driven) jet of Freon-13 demonstrate the advantages of the new RLSF.
Measurement of the nonaxisymmetric heat load distribution on the first wall of TFTR due to locked modes
Authors: Janos A. C. , Fredrickson E. , McGuire K. M. , Nagayama Y. , Owens D. K.
Published: July 2002

The first wall of TFTR is covered in large part (23%) by an inner-wall bumper limiter which is the primary power handling structure in TFTR. The limiter is comprised of more than 2000 tiles, and is instrumented with a large number (≳100) of thermocouples in a two-dimensional (2D) array, primarily for protection of the wall. While only about 5% of the tiles are monitored, this thermocouple system is nevertheless capable of mapping details in the nonaxisymmetric, as well as symmetric, heat load patterns encountered under different conditions. In particular, helical heating patterns are observed in discharges which have locked modes. The helical patterns clearly match the expected trajectories based on the m/n mode numbers obtained from Mirnov coils (m/n=2/1 and 4/1), so that the thermocouple system can and was used to identify the existence and mode number of a locked mode. While TFTR discharges rarely suffer from locked modes, locked modes always alter the heating pattern. The locked modes are found to very significantly redistribute the heat load for both ohmic and NBI heated discharges. Locked modes can make what were the coldest areas into the hottest areas, and vice versa. Locked modes also can alter the heat pattern resulting from the frequent disruptions which occur as a result of a locked mode.
Abel-inversion method for interferometry data in highly noncircular plasmas with X point in TFTR (abstract)
Authors: Zhao Y. , Park H. K. , Bell M. , Budny R.
Published: July 2002

In TFTR plasmas, reliable and accurate time-dependent electron density profiles are routinely available via an Abel inversion of interferometry measurements [H. Park, Plasma Phys. Controlled Fusion 31, 2035 (1989)]. This technique does not require constancy of density on a equiflux surface and mild deviations of the flux surfaces from a circular shape are accommodated through analytic approximations. However, when the flux surfaces become extremely noncircular as the plasma β is increased significantly, the inverted profiles are not consistent with the Thomson scattering measurements. In order to obtain accurate time-dependent density profiles in high-β plasmas, detailed flux surface information from magnetic measurements must be used to invert the interferometric measurements. The basic inversion process is similar but the scrape-off layer treatment is different when an X point is introduced on the high field side. In this paper, we present a comparison between the inverted profiles obtained with the flux-surface data and with the analytic method. This work supported by U. S. Department of Energy Contract No. DE-AC02-76-CHO-3073.
Characteristics of gyrotron scattering system for α particle diagnostics in TFTR (abstract)
Authors: Park H. K. , Bretz N. , Ellis R. , Efthimion P. C. , Marsala R. , McCarthy M. , Renda G. , Young K. M. , Cohn D. R. , Machuzak J. S. , Rhee D. Y. , Woskov P.
Published: July 2002

In D-T plasmas, the understanding of the physics of confined α particles is extremely valuable for the future fusion plasma device. Among the various proposed α diagnostics, an X-mode collective Thomson scattering system employing a high-power gyrotron source (P≂200 kW, f=60 GHz, pulse length ≂0.5 s, and modulation frequency=10–25 kHz) is being designed for TFTR. The detailed description of the gyrotron source, transmission lines, optical designs, beam and viewing dump design, and receiver system will be presented in this paper. In particular, the test results of the beam and viewing dump indicate that the stray light can be reduced by 60 dB. The background emission level (∼20 eV) near 60-GHz range during high Q discharge may also be reduced with beam and viewing dump further. The optical system is designed to measure the radial profile of α particles and to orient the incident wavevector (k0) to test the electromagnetic effects of the scattered spectrum. Prior to the study of α physics in D-T plasmas, this scattering system will be used to measure not only a bulk ion temperature but also the scattered spectrum due to fast ions produced by NB and ICRF heating in TFTR. This work was supported by the U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.
TFTR microwave reflectometer (abstract)
Authors: Mazzucato E. , Nazikian R. , Bretz N. , McCarthy M. , Nagy A.
Published: July 2002

A microwave reflectometer is in operation on TFTR for the measurement of density fluctuations. The system operates in the X mode and comprises three channels with fixed frequencies of 140, 132, and 125 GHz, and one with stepped frequency of 111–123 GHz. All channels use solid state Gunn oscillators and a heterodyne detection scheme. The system is located outside of the TFTR test cell with the power conveyed to the tokamak vessel by low-loss corrugated waveguides and remotely controlled parabolic mirrors. Preliminary results indicate that the level of density fluctuations with k⊥ <1 cm−1 is very small in the central region of Ohmic plasmas (ñ/n<10−3), and that it increases monotonically with minor radius to values of ≊10−2 at r/a=0.9. This work supported by U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.
Investigation of the neutron detection properties of the fast liquid scintillator BC-505
Authors: Cecil F. E. , Scorby J. C.
Published: July 2002

The energy resolution, the absolute detection efficiency, and the pulse-shape discrimination capability for fast neutrons by the fast liquid scintillator BC-505 have been investigated. The response to fast neutrons was investigated using the proton-tagged neutrons from the d-d reaction generated by the Colorado School of Mines low-energy charged particle accelerator. Using a collimated source of gamma rays from a 60Co source, the spatial resolution of the scintillator was measured by comparing the arrival times of the scintillation signals at the PMTs at the ends of the scintillator cell. A spatial resolution of 2.7 cm was measured corresponding to a total time resolution of about 150 ps. The results of our investigation will be applied to the conceptual design of a ‘‘pin-hole’’ neutron camera which may be used to provide real-time radial distributions of fast neutron sources in fusion plasmas.
Initial operation of the TEXT-Upgrade 2-MeV heavy ion beam probe (abstract)
Authors: Ouroua A. , Crowley T. P. , Hickok R. L. , Schoch P. M. , Connor K. A. , Lewis J. F. , McLaren P. E. , Schatz J. G. , Schwelberger J. , Hoffman B.
Published: July 2002

The new heavy ion beam probe diagnostic system on TEXT is presently operational at reduced energy. Thallium and cesium ion beams with energy up to 590 keV have been obtained using a single injection beamline and an energy analyzer that can be operated with low-energy beams only (≤590 keV). At full energy (up to 2 MeV) two injection beamlines and two energy analyzers (presently under construction) will allow access to 90% of the plasma cross section. Stable 2-MeV test beams with currents up to 10 μA have been obtained but not injected into the tokamak. The capacitive liner feedback control system allowed stable operations with ripple less than 100 V. Results of initial operations and preliminary measurements of density fluctuations are presented. This work is supported by the U. S. Department of Energy.
The ATF heavy ion beam probe (invited)
Authors: Connor K. A. , Zielinski J. J. , Schwelberger J. G. , Aceto S. C. , Glowienka J. C. , Carnevali A.
Published: July 2002

A heavy ion beam probe (HIBP) has been implemented on the ATF torsatron at Oak Ridge National Laboratory with the primary goal of providing direct measurements of the plasma potential radial profile and thus of the radial electric field. The complex ATF geometry and magnetic field structure presented a diagnostic environment more challenging than that found on previous beam probe systems. Particular attention has therefore been given to in situ system alignment and control capabilities. Measurements of electric potential profiles, electron density profiles, electron density fluctuations, and electric potential fluctuations have now been made with this system. Most of the data obtained were for ECH heated discharges, but we were also able to make measurements of a few NBI heated plasmas. In addition to our calibration techniques, we were able to establish a reasonable confidence level for the data obtained since we could identify the most important potential profile characteristics predicted by theory and to corroborate our measurements with information from other diagnostics.
Focusing monochromators for high energy synchrotron radiation
Authors: Suortti P.
Published: July 2002

Bent crystals are introduced as monochromators for high energy synchrotron radiation. The reflectivity of the crystal can be calculated reliably from a model where the bent crystal is approximated by a stack of lamellas, which have a gradually changing angle of reflection. The reflectivity curves of a 4 mm thick, asymmetrically cut (χ=9.5°) Si(220) crystal are measured using 150 keV radiation and varying the bending radius from 25 to 140 m. The width of the reflectivity curve is up to 50 times the Darwin width of the reflection, and the maximum reflectivity exceeds 80%. The crystal is used as a monochromator in Compton scattering measurements. The source is on the focusing circle, so that the resolution is limited essentially by the detector/analyzer. A wide bandpass, sharply focused beam is attained when the source is outside the focusing circle in the transmission geometry. In a test experiment. 1012 photons on an area of 2 mm2 was observed. The energy band was about 4 keV centered at 40 keV. A powder diffraction pattern of a few reflections of interest was recorded by an intrinsic Ge detector, and this demonstrated that a structural transition can be followed at intervals of a few milliseconds.
Instrumental features for microcrystal diffraction (abstract)
Authors: Schulz H.
Published: July 2002

The signal/background ratio is the main problem for microcrystal diffraction experiments. Background scattering can be reduced by special mounting techniques, by reducing or avoiding air scattering, and reducing diffuse scattering from the crystal. Furthermore, the intrinsic noise of the counter system has to be made as small as possible. To avoid very long measuring time per diffraction event, area counters have to be applied in order to register several of such events at a time.
A 2600-K tantalum cavity as an interesting infrared source for absorbance measurements
Authors: Maseri F. , Philippe L. , Derycke I. , Darville J. , Vigneron J. P. , Gilles J. M.
Published: July 2002

A design is proposed for a stable infrared source suited to absorbance measurements. The source is a parallelepipedic cavity of tantalum, heated to 2600 K, with an apparent emissivity in excess of 0.7. It is observed to be three times brighter at 3000 cm−1 than the 1440-K SiC bar. A model is constructed in order to estimate the temperature distribution. For this kind of source, the temperature and emissivity are found to be quite uniform. A comparison between estimated and experimental values of temperature and emissivity is discussed.
An efficient 14-MeV neutron detector for use in mixed 2.5- and 14-MeV neutron beams
Authors: Croft S. , Bond D. S. , Hawkes N. P.
Published: July 2002

A neutron detector capable of measuring the time-dependent yield of 14-MeV neutrons from a D–D plasma producing predominantly 2.5-MeV neutrons has been developed. The detector consists of a thick polythene recoil proton radiator backed by a graphite foil attached to a large area totally depleted ion-implanted diode. Protons scattered in the forward direction by 14-MeV neutrons pass through the graphite foil and are registered in the diode. Recoil protons from 2.5-MeV neutrons, however, are prevented from reaching the diode by the foil. When operated with a 1.5-MeV energy bias, the measured neutron detection efficiency for 15-MeV neutrons is 3.2×10−3 per neutron. The corresponding figure for 3.1-MeV neutrons is a factor of 540 lower. The neutron detector and its laboratory calibration are described, as is its deployment at the Joint European Torus where it serves as a triton burn-up monitor.
A precision drive for a Michelson wavemeter
Authors: Jaffee S. M. , Yen W. M.
Published: July 2002

We have developed a high precision Michelson wavemeter using a novel drive mechanism. The moving arm of the Michelson interferometer is actively stabilized, producing a stable fringe rate that can be electronically multiplied by a factor of 100. A special gating circuit eliminates the turning points from the drive motion yielding continuous measurements. This circuitry also allows for wavelength measurements of nonstabilized continuous wave lasers. A resolution of ±20 MHz is achieved with a measurement cycle of less than 6 s.
Remote alignment and control system based on radio-controlled servos
Authors: Wittry D. B. , Chang W. Z.
Published: July 2002

A miniature remote alignment and control system based on systems that are used in radio-controlled models is described. The modified servos provide high output torque and proportional speed control for positioning alignment adjustments, spectrometer controls, accessories, or specimen stages.
High frequency capillary waves: A light scattering spectrometer
Authors: Hughes C. J. , Earnshaw J. C.
Published: July 2002

Modifications to a light scattering apparatus to permit study of liquid surface fluctuations of significantly higher wave number than hitherto are described. Various problems associated with the modified system are discussed. Typical results are presented for capillary wave propagation on the surface of two different fluids, demonstrating the satisfactory functioning of the spectrometer despite these problems.
Microliter flow cell for measurement of irreversible optical absorbance transients
Authors: Lewis James W. , Kliger David S.
Published: July 2002

Time-resolved UV-visible absorbance measurements made after laser photolysis are important for mechanistic understanding of many biological systems. Some of these systems are available in extremely small quantities and/or are destroyed by light so that averaging strategies for signal-to-noise improvement are severely restricted. An apparatus is described which measures the absorbance difference spectrum at a variable delay (10 ns resolution) after photolysis of a 1 μl sample (optical path 2 mm). After each photolysis pulse the sample is replaced using a pump which delivers 0.5 μl increments. Waste of sample is avoided by making sure that the sample’s cross section exactly matches the image of the spectrograph slit in the sample cell. Data are presented for photolysis of the bovine visual pigment rhodopsin both in transparent octyglucoside detergent suspensions and more turbid, sonicated disk membrane preparations. Rate constants obtained from a biexponential fit of difference spectra at five delay times from 40 to 640 ns agree well with those obtained previously from much larger detergent samples. Equally high quality results are obtained for the turbid membrane suspensions at longer delay times.
Manipulation of C60 molecules on a Si surface
Authors: Beton P. H. , Dunn A. W. , Moriarty P.
Published: July 2002

We have used the tip of a scanning tunneling microscope to position individual C60 molecules on a Si(111) surface. It is possible to form simple patterns of molecules at room temperature using this technique.
Accurate rotation and displacement in the millikelvin range: A new positioner design
Authors: Guthmann C. , Balibar S. , Chevalier E. , Rolley E. , Sutra-Fourcade J. C.
Published: July 2002

dc micromotors have been used to rotate helium 4 crystals in a pressurized cell (25 bars) at very low temperature (down to 30 mK). After slight modifications of the motors and optimization of bearings and transmission design, rotations of ±6° were obtained with an accuracy of ±0.01° and a dissipation of 20 μW.
Construction and performance of a low noise inductive transducer for the Louisiana State University gravitational wave detector
Authors: Solomonson N. , Hamilton W. O. , Johnson W. , Xu B.
Published: July 2002

The design, fabrication, and performance of an inductive transducer for a two-mode resonant mass gravitational radiation detector is described. The design of the transducer is based on a detailed noise model of the detector. The transducer combines a large dynamic mass, a large loaded quality factor, and transformer impedance matching to an integrated dc superconducting quantum interference device (SQUID). The transducer has been in continuous use on the Louisiana State University detector for two years. Its performance on the antenna is reported. The Q’s of the two resonant modes measure 6.7×106 and 2.3×106 at a transducer coupling coefficient of 0.74%. The electrical Q ranges from 2×105 to 9×105 and is dependent upon trapped magnetic flux in the transducer. The detector’s dominant noise source is the commercial SQUID amplifier, and not losses in the transducer. The predicted sensitivity of the detector equipped with our transducer agrees well with its measured burst strain sensitivity, h≊6×10−19. The detector’s gravitational burst strain sensitivity could be improved to 1.7×10−19 by coupling the transducer to a 200ℏ SQUID, while operating at 4 K.
A new method to attach electrical leads on a single crystal of a submillimeter size
Authors: Matsuzaki S.
Published: July 2002

A new method was developed to prepare a small single crystal sample for electrical conductivity measurement. The method was based on the use of commercially available XYZ mechanical stages as micromanipulators, and its accuracy was high enough to attach successfully four gold wires for four-probe measurement on a needlelike crystal 0.2 mm long.
A circuit and five probe resistivity method for measuring pulse I–V characteristics of superconductors
Authors: Gupta S. K. , Gadkari S. C. , Aswal D. K. , Gupta M. K.
Published: July 2002

An electronic circuit has been developed to study the pulse I–V characteristics of superconductors. A special feature of the circuit is its low rms noise voltage of less than 10 nV, which allows measurements over a broad voltage range of 50 nV to 500 mV for the first time. In order to overcome the limitations of a four probe technique at high common mode voltages, a novel five probe geometry is developed. The measurements on single crystals of the Bi2Sr2CaCu2Ox superconductor are carried out to demonstrate the circuit performance.
Simple transmission mode near-field optical microscope
Authors: Fann Wunshain
Published: July 2002

A simple transmission mode near-field optical microscope is demonstrated. A low noise, large area Si photodetector is mounted directly between the piezoelectric transducer scanning stage and the sample. This method provides a simple way to convert the commercial atomic force microscope/scanning tunneling microscope scanning stage to a near-field optical microscope.
Phase-locked noncontact scanning force microscope
Authors: Kikukawa Atsushi , Hosaka Sumio , Honda Yukio , Imura Ryo
Published: July 2002

A new tip height control system for noncontact scanning force microscope (SFM) utilizing the phase-lock technology is proposed. Its most extensive feature is that the system is unconditionally stable whereas the conventional control systems have difficulties in stability especially when the tip is at close proximity to the sample surface. In this new system, an oscillator using the cantilever as a mechanical resonator is used as a voltage controlled oscillator (VCO) in a phase-locked loop. Its output signal phase is locked to a high precision frequency source. The force gradient detected by the cantilever equivalently alters the VCO control voltage, which is detected as a compensational signal of the loop filter output. The phase-lock technique made it possible to reduce the tip height to an extent which was impossible with the conventional servo technology. Thus this new control technique is expected to be effective in improving the resolution of the noncontact SFM.
Radio frequency superconducting parametric transducer for gravitational wave antennae
Authors: Fisher M. A. , Bocko M. F. , Marchese L. E. , Zhang G. , Karim M.
Published: July 2002

We report on the design and testing of an ultrasensitive, electromechanical transducer for use on resonant mass gravitational wave antennae. The transducer is a superconducting, radio frequency resonant bridge circuit operating near 200 MHz. We have minimized several important sources of noise in this transducer system. The Johnson noise of the transducer circuit is reduced through using a superconducting niobium stripline circuit and low-loss insulating materials. At a temperature of 4.2 K we have achieved unloaded electrical quality factors of 200 000. The bridge circuit is balanced by piezoelectric actuators which control the spacing between the proof mass and capacitive segments of the stripline circuit and we have achieved a residual bridge imbalance of 3×10−7. Finally, low noise cryogenically cooled field-effect transistors are used for the first amplifier stage, enabling us to obtain an amplifier noise level which is 5400 times the quantum limit. The transducer, which has a 0.080 kg proof mass, was affixed to the end of a prototype, resonant bar, gravitational wave antenna with a mass of approximately 100 kg. The primary purpose of this small antenna was to evaluate the transducer, which is designed to be mounted on a much more massive antenna. Our theoretical analysis and measurements of the detector agree and indicate a burst noise temperature of 1.8 K using the 100 kg bar. This corresponds to a gravity wave burst sensitivity of h=1.1×10−16, in terms of relative strain amplitude. With no other improvements, if the transducer mechanically resonant frequency were tuned to and installed on a 2000 kg antenna, the antenna would reach a noise temperature of 1.3 mK, which is equivalent to a gravitational wave burst sensitivity, h≊5.7×10−19.
Extraction pulse generator for time-of-flight mass spectrometry
Authors: Loboda A. V. , Dodonov A. F.
Published: July 2002

We describe an extraction pulse generator for time-of-flight mass spectrometry. It has an improved pulse shape, flat top and bottom, and suppressed tail after switching.
Design and calibration of a scanning force microscope for friction, adhesion, and contact potential studies
Authors: Koleske D. D. , Lee G. U. , Gans B. I. , Lee K. P. , DiLella D. P. , Wahl K. J. , Barger W. R. , Whitman L. J. , Colton R. J.
Published: July 2002

We present the design and calibration of a scanning force microscope which can be used to study friction, adhesion, and contact potential differences between the cantilever tip and surface. The microscope uses a modular design where the laser, cantilever/sample holder, reflecting mirror, and detector are mounted directly on an optical table. The laser, reflecting mirror, and detector are mounted on translation and rotation stages. With this design the components can be rearranged to calibrate the Z piezo motion as a function of applied voltage. Using the detector micrometers, the detector response (voltage-to-distance relationship) can be determined after each series of measurements. The cantilever/sample holder is constructed such that the components are material matched and thermally compensated from a common reference point. This design feature minimizes thermal drift of the instrument. The instrument can be used in a contact scanning mode where both normal and lateral deflections of the cantilever are measured. In addition, the instrument can be used in frictional force studies, force curve mapping of the surface, and contact potential measurements. We present examples of each, including a detailed account of the instrument design and calibration.
Measurement of velocity fluctuations in plasmas by a conventional visible spectrometer
Authors: Ejiri Akira , Oikawa Toshihiro , Toyama Hiroshi
Published: July 2002

A conventional visible spectrometer system has been applied to velocity fluctuation measurements in plasmas. By measuring the number of photons, the effect of quantum noise is subtracted, and real velocity fluctuations are obtained. The first measurements in a reversed-field-pinch plasma show finite velocity fluctuations of about 1.7×103 m/s when the system views off-center chords. When it views the central chord, finite fluctuations are not found. These results impose an upper limit to spurious Doppler broadening, which could arise from fast and large vibrations of cold plasma. The effect of the spurious Doppler broadening is found to be small.
A new technique for dynamic annealing of amorphous alloys using Joule effect with controlled mechanical tensile stress
Authors: Houzali A. , Alves F. , Perron J. C. , Barrué R.
Published: July 2002

We present a new dynamic technique performed in air and under mechanical stress, intended to anneal amorphous metallic ribbons on their final curvature. This method is based on dc Joule heating. The ribbon is raised to high temperature for short time (a few tens of seconds) while it is subjected to a tensile stress. The maximum annealing temperature was measured by means of an infrared pyrometer which necessitates the value of total emissivity of the heated ribbon. This emissivity was determined by using a simple experimental device. To illustrate the interest of this new technique, we give, as an example, the magnetic properties obtained after dynamic annealing on Fe-based amorphous alloys with high magnetostriction (Fe78B13Si9). The experimental results show the influence of the different annealing parameters on the magnetic properties. This method has also been used successfully to anneal other amorphous alloys (e.g., Fe–Ni-based and Co-based alloys) and to obtain nanocrystalline ribbons.
A method for contact-free calibration of piezoelectrical actuators
Authors: Müller F. , Müller A.-D. , Hietschold M.
Published: July 2002

The voltage-displacement-characteristics of tube-shaped piezoscanners were determined and used for the calibration of the scanning range of a scanning probe microscope (SXM). Inside a scanning electron microscope the displacements were measured as a function of the voltage and analysed by an imaging system. The detection of non-linearities as well as the investigation of the dynamic properties are possible. The method may be useful for various applications, e.g., all SXM instrumentation as well as micropositioning devices.
A rotatable parallel glass plate periscope for effective aperture magnification in metrology
Authors: Lotem Haim , Horvitz Zvi , Avnet Zeev , Hillel Shlomo , Lando Mordechai
Published: July 2002

Optical instruments like autocollimator or interferometers have a limited aperture. Here we describe a simple device that effectively enlarges the viewing aperture, based on parallel shifting of the beam in a tilted parallel glass plate. This periscopic action is done with two additional degrees of freedom: variable radial displacement adjusted by the plate tilt angle and azimuthal movement controlled by plate rotation around an axis parallel to the optical axis of the device. For example, a 1.8 refractive index glass plate of 80 mm thickness can be tilted up to 60°, enlarging a 40 mm diameter aperture up to 130 mm effective aperture. A rotatable parallel glass plate periscope was constructed to explore the inside aperture of a ceramic tube, using a 1 mm diameter HeNe laser beam as a probe, obtaining 1 mm accuracy. To ease the plate rotation, the glass plate was chosen to have a trapezoid shape and a balancing weight was designed and constructed to evenly balance the plate weight through the operation range of the device.
Shot-noise-limited detection of absorbance changes induced by subpicojoule laser pulses in optical pump-probe experiments
Authors: Savikhin Sergei
Published: July 2002

We describe a high-frequency modulation and detection system capable of measuring absorbance changes ΔA on the order of 10−6 in optical pump-probe experiments using submilliwatt laser powers from a mode-locked ultrafast laser. For probe beam powers ≥9 μW, the system offers nearly shot-noise-limited performance.
High performance detection of biomolecules using a high magnetic field electrospray ionization source/Fourier transform ion cyclotron resonance mass spectrometer
Authors: Guan Ziqiang , Campbell Victoria L. , Drader Jared J. , Hendrickson Christopher L. , Laude David A.
Published: July 2002

An improved, high-performance version of the concentric vacuum chamber design is shown for forming ions at high pressure in a strong magnetic field and detecting them in an adjacent Fourier transform ion cyclotron resonance mass spectrometry (FTICR) trapped ion cell. Improvements in system design, including primarily the addition of a mechanical shutter to halt the flow of neutrals to the trapped ion cell during FTICR detection, allow a more than 100-fold improvement in pressure drop between the source and analyzer chamber to be realized. Within a 20 cm distance, ions formed in an electrospray ion source at atmosphere are transported across five concentric tube conductance limits to a trapped ion cell at a shuttered pressure below 2×10−9 Torr. High resolution detection of electrosprayed proteins is demonstrated and, for example, mass resolutions of 1×105 for the +14 charge state of horse heart myoglobin (at m/z 1211) and 2×105 for +5 charge state of bovine insulin (at m/z 1147) are obtained. The original advantages of the concentric tube vacuum chamber are retained. Forming the ions within the magnetic field permits a 40-fold enhancement in sensitivity to be obtained. Narrow kinetic energy distributions are achieved because magnetic field confinement eliminates the need for complex electric focusing assemblies that exhibit mass discrimination and broaden the kinetic energy distribution. Finally, the shutter is demonstrated to serve effectively as an alternative to pulsed valve assemblies for the transient introduction of a collision gas to the trapped ion cell.
Simple and efficient method of spin-polarizing a metastable helium beam by diode laser optical pumping
Authors: Granitza B. , Salvietti M. , Torello E. , Mattera L. , Sasso A.
Published: July 2002

Diode laser optical pumping to produce a highly spin-polarized metastable He beam to be used in a spin-polarized metastable atom deexcitation spectroscopy experiment on magnetized surfaces is described. Efficient pumping of the beam is performed by means of an SDL-6702 distributed Bragg reflector diode laser which yields 50 mW of output power in a single longitudinal mode at 1083 nm, the resonance wavelength for the 23 S→23 P0,1,2 (D0, D1, and D2) transitions of He*. The light is circularly polarized by a quarter-wave plate, allowing easy change of the sense of atomic polarization. The laser frequency can be locked to the atomic transition for several hours by phase-sensitive detection of the saturated absorption signal in a He discharge cell. Any of the three transitions of the triplet system can be pumped with the laser but the maximum level of atomic polarization of 98.5% is found pumping the D2 line.
The effect of a ZnTe buffer layer on the structural and optical properties of the CdTe/ZnTe/GaAs strained heterostructures grown by temperature-gradient vapor-transport deposition
Authors: Kim T. W. , Park H. L. , Lee J. Y.
Published: July 2002

Lattice-mismatched CdTe epilayers on GaAs (100) substrates with and without ZnTe buffer layers were grown by the simple method of double-well temperature gradient vapor-transport deposition. X-ray diffraction measurements were performed to investigate the structural properties of the epitaxial layers. Photoluminescence and transmission electron microscopy measurements showed that the crystallinity of the CdTe epilayers grown on the GaAs substrates was remarkably improved using the ZnTe buffer. The strain of the CdTe layer was determined from photoreflectance measurements. These results indicated that the CdTe epitaxial films grown on GaAs substrates with the ZnTe buffer can be used for applications as buffer layers for the growth of HgxCd1−xTe and CdxZn1−xTe.
A very low current scanning tunneling microscope
Authors: Dunlap David , Smith Steve , Bustamante Carlos , Tamayo Javier , García Ricardo
Published: July 2002

The applications of the scanning tunneling microscope (STM) in air are usually restricted to good conducting materials as clean metals, doped and passivated semiconductors, or to some molecular adsorbates deposited onto graphite. In order to study poor conducting materials as biological molecules, we have built a very low current STM. This instrument can routinely be operated at 0.1 pA while having a bandwidth of 7 kHz. The advantages of using very low currents are illustrated by imaging 5-nm-thick purple membranes. These membranes can only be imaged at currents smaller than 2 pA.
A freon-filled, holographic bubble chamber as a high-energy photon burst spectrometer
Authors: Dendooven Peter G. , Lerche Richard A.
Published: July 2002

A small holographic, freon-filled bubble chamber is being built to measure the energy spectrum of high-energy photons (energy above a few 100 keV) emitted in a short burst (less than about 1-μs duration). The photon energy is calculated from the scattered electron’s energy and direction in the case of Compton scattering or from the electron and positron energies in the case of pair production. Electron and positron energies are determined from the curvature of the tracks in a magnetic field. The use of freon results in a large photon interaction probability. Holography combines good spatial resolution with large depth of field. The main concern for the holographic system is the minimization of the bubble image size, so as to maximize the number of bubbles visible in one hologram. A high-energy photon burst spectrometer has several potential applications in inertial confinement fusion research.
Long exposure time schlieren photography of plasma focus discharges
Authors: Melzacki K. , Nardi V.
Published: July 2002

An effect of the oscillating acceleration of the current sheet during the compression phase in a plasma focus discharge has been observed using long (60 ns) exposure time schlieren photography. This effect had not been previously observed in experiments using exposure times of a few nanoseconds or less. A 1 J Q-switched ruby laser has been used as a source of light. The photograms are taken in dark-background schlieren with a circular stop (disk) instead of a usually used knife edge. The various acceptance ranges of refraction angle have been selected by the size of the stop and aperture in order to limit the integral of the electron density gradient along the beam within the apparatus range, which is between 3×1018 and 3×1020 cm−3. Raising the sensitivity threshold to 2×1019 cm−3 (refraction angle of 4 mrad) has helped to clear the pictures by limiting their image to high gradients of density only. Using this technique and other diagnostic methods, the dynamics of 6-kJ, 16-kV plasma focus discharges have been investigated. These discharges were made in deuterium at 5 Torr, with a 10% decrease of the magnetic insulation at the breech. The average radial velocity of the current sheet, 5×104 m/s, obtained with this effect agrees with those measured by the smear effect. The peak value of 1×105 m/s is consistent with results received with magnetic probes. The electron density gradient has been determined for several instants; its maximum value at the pinch is (1.2±0.2)×1021 cm−4.
Review of divertor diagnostics (invited) (abstract)a)
Authors: Leonard A. W.
Published: July 2002

We will review tokamak divertor diagnostics currently in use to study issues relevant to next generation divertor design. The divertor represents perhaps the greatest technological challenge in the design of reactor tokamaks such as ITER, with designs currently requiring a reduction in heat flux to plasma facing surfaces obtained through radiative and charge exchange processes (i.e., the radiative divertor). Experiments to study these new divertor regimes and concepts require 2D profile measurements of the important plasma parameters, scrape-off-layer (SOL) and divertor plasma density and temperature, radiated power, impurity concentrations, particle sources, neutral pressure, and heat flux to surfaces. Diagnostics measurements in use on ASDEX-U, Alcator C-MOD, DIII-D, JET, and JT-60U include Langmuir probes, IRTV cameras, bolometer arrays, fast neutral pressure gauges, photodiode arrays, CCD cameras, and visible and VUV spectroscopy. Each diagnostic obtains unique information, but each also presents its own challenges of access and interpretation. For the future, ITER divertor diagnostics will require innovation to adapt to the long pulse, high power, and neutron environment.
Thomson scattering diagnostic for the TdeV tokamak
Authors: Côté A. , Michaud D. , Richard N. , Neufeld R. , Legros C.
Published: July 2002

The Thomson scattering diagnostic system on the TdeV tokamak (R/a=87/27 cm, BT=1.5 T, Ip<300 kA) routinely monitors electron temperature (Te) and density (ne). The scattered light from a vertically oriented Nd:YAG laser beam (E=0.8 J, f=50 Hz, Δt=30 ns) is analyzed by six polychromators looking at different vertical positions. Each polychromator splits the light into three spectral bands by means of bandpass interference filters. Avalanche photodiode detectors are used to measure the scattered radiation. These detectors also measure the plasma radiation (including bremsstrahlung) between laser pulses. Two polychromators are optimized for edge temperature measurements (50<Te<400 eV), while the four others look at the main plasma (0.3<Te<4 keV). Sawtooth-correlated variations of Te(t) and ne(t) are measured by creating a time base locked-in on the sawtooth crash time of soft x-ray signals, so that we can remove the aliasing effect of undersampling Te. Most of the observed temperature fluctuations (20%) at the plasma center are sawtooth induced.
Design of a CO2-laser Thomson scattering ion-tail diagnostic for Alcator C-Mod
Authors: Richards R. K. , Hutchinson D. P. , Ma C. H.
Published: July 2002

A CO2-laser Thomson scattering diagnostic has been designed for the measurement of the ICRH-produced ion tail on Alcator C-Mod. The plasma parameters and port access require that the detection of scattered radiation be made at small angles, typically 1° or less. The receiver system consists of five heterodyne detectors and the source laser produces an energy of 10 J per pulse with a 1–5 μs pulse length. The scattering system is currently being installed on the Alcator C-Mod experiment. Details of the diagnostic, calculations of the expected measurements, and application of the diagnostic for ITER are presented.
Statistical methods of magnetic islands identification in T-10 Tokamak (abstract)
Authors: Melnikov A. V. , Fomin G. A. , Gorshkov A. V. , Lysenko S. E. , Mochalova L. A. , Sannikov V. V. , Tarasyan K. N.
Published: July 2002

Statistical analysis of noisy and regular components of the radial profiles of the electron temperature, measured with Thomson scattering in the T-10 tokamak have been performed. It was shown that the noise variance in the middle part of the profile is independent on the radius. That allowed to unite the homogeneous data into a large sample with a good statistic, and to show that the noise has a normal distribution. The regular component, extracted with nonlinear regression analysis, is consistent with monotonic part and magnetic islands. In the studied regime (B=1.5 T, I=135 kA, n̄e=1.9–2.7×1019 m−3) the islands (q=2) were identified with a high probability.