bluuebunny/crossref_metadata_2025 huggingface dataset:
Signal-to-noise ratio in lock-in amplifier synchronous detection: A generalized communications systems approach with applications to frequency, time, and hybrid (rate window) photothermal measurements
Authors: Mandelis Andreas
Published: July 2002

Detailed analytical models of signal-to-noise ratios (SNR) of the conventional frequency domain (FD) and time domain (TD) photothermal measurement methodologies are developed and compared to the rate-window photothermal method, both theoretically and experimentally. The conclusions of this study demonstrate that the lock-in amplifier (LIA) rate-window measurement mode in general, and the digital LIA mode, in particular, exhibits superior SNR to both the conventional frequency-scanned LIA FD method and to the transient, time-averaged TD method. Between the pulse-duration-scanned and pulse-repetition-period scanned rate-window methodologies, the former clearly exhibits superior SNR. The theoretical conclusions are in agreement with experimental SNRs using the implementation of the foregoing measurement methodologies with simple infrared photothermal radiometric setups.
Scanning nearfield optical microscope using microfabricated probes
Authors: Radmacher M. , Hillner P. E. , Hansma P. K.
Published: July 2002

Microfabricated tips, usually used for atomic force microscopy (AFM), can be modified and used in a scanning nearfield optical microscope. Initial images show a resolution of about 80 nm (λ/8) demonstrating the quality and usefulness of these tips. They are mechanically stable, potentially commercially available, and have high light transmissibility. Furthermore, they can be easily combined with an atomic force microscope to give simultaneous nearfield optical and AFM images.
A VUV filter spectrometer with spatial resolution and its plasma diagnostic capabilities
Authors: Zurro B. , García-Castañer B.
Published: July 2002

The performance of an original VUV filter spectrometer with spatial resolution is illustrated with typical applications as a plasma diagnostic. The spectrum of the total radiated power obtained in the TJ-I tokamak, the observation of flattenings on radiation profiles associated with magnetic islands, and the determination of particle confinement times in laser blow-off impurity injection experiments are highlighted.
A fully computerized technique to measure conductivity in liquid mixtures
Authors: Junquera Elena , Aicart Emilio
Published: July 2002

An experimental technique for the accurate measurement of the conductivity in liquid mixtures at a constant temperture is described. The equipment is fully computerized, the conductimeter and the burette being controlled through the IEEE-488 and the RS-232C interfaces, respectively. The automatic procedure provides the measurement of the experimental parameters for each concentration as a statistical average of 2400 data. It permits an increase in the accuracy of the results, optimizing the time and avoiding human mistakes along the set of measurements.
Symmetrical magnet magnetron sputtering method for improving target utilization
Authors: Chen Xiao-hong , Fan Qi-hua , Chen Hong-you , Zhang Ying
Published: July 2002

A symmetrical magnet magnetron sputtering method, with one inner annular magnet and two outer annular magnets facing each other, has been developed. This magnetron cannot only deposit films at high rate but also greatly improves target utilization. The maximum deposition rate of Cu films was about 11 000 Å/min. The target utilization efficiencies in the volume of the whole target body and in the area of the target plane were about 64% and 97.5%, respectively.
Investigation of MEVVA ion source for metal ion injection into accelerators at GSI
Authors: Wolf B. H. , Emig H. , Rück D. , Spädtke P.
Published: July 2002

High current metal ion production is a challenging task for ion source designers. The MEVVA ion source has proven to be a useful tool for accelerator injection and for ion implantation. We have investigated the MEVVA ion source in connection with the GSI heavy ion accelerators. At the Unilac accelerator as injector for the heavy ion Synchrotron SIS (1 Hz and 100 μs pulse length) the MEVVA can deliver mA beams of multiply charged ions up to 3+ (or mass to charge ratio of ≤24 accepted by Unilac). At the 300 kV ion implantation facility the MEVVA is used to inject metal ions into the RFQ accelerator with duty cycles above 1%. Here we discuss the ion beam currents and charge state distributions for various ion species and beam formation and transport at the accelerators. Space-charge effects and ion beam instabilities are discussed in detail. At the Unilac injector results with titanium and nickel from the MEVVA ion source are compared with those of neon from a CHORDIS gas ion source.
Characterization of wear and profile of diamond drill bit by optical profilometry
Authors: Pelletier Sylvain , Dufour Marc
Published: July 2002

A new technique to measure wear and profile of impregnated diamond drill bit for mineral exploration is presented. A three-dimensional surface mapping of worn diamond drill bit surface is obtained by the laser triangulation method. With adequate algorithms all relevant data can be obtained. Consequently, the volume loss between two distances cored can easily be measured with a great precision. Moreover, computerized cross sections of the worn surface give relevant information about the profile resulting from the drilling process.
Beetle-like scanning tunneling microscope for ultrahigh vacuum and low-temperature applications
Authors: Schulz R. R. , Rossel C.
Published: July 2002

A new beetle-like scanning tunneling microscope is presented that operates under ultrahigh vacuum conditions and at temperatures down to 7 K. Magnetic fields up to 8 Tesla can be applied using a movable superconducting magnet. The entire setup is described in detail and test measurements are presented.
Camera for imaging hard x rays from suprathermal electrons during lower hybrid current drive on PBX-M
Authors: von Goeler S. , Jones S. , Kaita R. , Bernabei S. , Davis W. , Fishman H. , Gettelfinger G. , Ignat D. , Paoletti F. , Petravich G. , Rimini F. , Roney P. , Stevens J. , Stodiek W.
Published: July 2002

During lower hybrid current drive on tokamaks, suprathermal electrons are generated that emit hard x-ray bremsstrahlung. A pinhole camera has been installed on the PBX-M tokamak that records 128×128 pixel images of the hard x-ray plasma bremsstrahlung emitted in the 30–200 keV photon energy range. The camera has a temporal resolution of 3 ms and a spatial resolution of 3–4 cm in the plasma. The detector is a 230-mm-diam hard x-ray image intensifier. This instrument has identified hollow radiation profiles on PBX-M, indicating off-axis current drive. A detailed account of the construction of the hard x-ray camera, its operation, and its performance is given.
Characteristics of Hall effect plasma accelerator for industrial application
Authors: Kim Woong Chae , Chung Kie Hyung , Choi Byung Ho
Published: July 2002

For thin film fabrication and surface modification, ion sources with high current, low energy, and broad beam are required. The source should be simple and reliable to operate, mechanically rugged, and highly productive for commercial use. To meet these requirements, a Hall effect plasma accelerator has been manufactured and tested. A beam energy of 200–300 eV and a beam current density of up to 10 mA/cm2 have been obtained with the source. Operational characteristics and possibility for industrial application are presented.
Laser and spectroscopic diagnostics of H− ion source plasmas
Authors: Young A. T. , Chen P. , Leung K. N. , Pan L. , Ponce D. , Stutzin G. C.
Published: July 2002

This paper reviews the results obtained in this laboratory in experimental studies of volume H− ion sources. Two techniques are discussed, emission spectroscopy and vacuum ultraviolet laser absorption spectroscopy. Time-resolved detection of Balmer-alpha emission has been used to study the excited-state hydrogen atom population. Vacuum ultraviolet laser absorption spectroscopy has been used to measure the ground electronic state atomic and molecular hydrogen populations. The Balmer-alpha emission exhibits a modulation in the intensity at a frequency of twice the exciting rf radiation. On the other hand, the laser absorption measurements show that the density of ground-state hydrogen atoms does not vary significantly with the phase of the exciting rf. Measurements of the vibrational population summed over all rotational states give a vibrational temperature of 6200 K. However, there is no evidence of the ‘‘plateau’’ predicted in the distribution for v≥5.
Optimization of intermediate charge state output from electron beam ion source devices
Authors: Hershcovitch Ady
Published: July 2002

A few methods for optimizing output of intermediate charge state ions from electron beam ion source devices are examined. The schemes are based on reducing the charge state of the highest charge state ions into the intermediate states, thus enhancing the relative abundance of these states. Only the most elementary considerations are invoked. Although a thorough analysis may not be feasible due to lack of good data, the schemes are easy to try experimentally.
Noncontact thermoacoustic method to measure the magnetocaloric effect
Authors: Gopal B. R. , Chahine R. , Földeàki M. , Bose T. K.
Published: July 2002

We report here the measurement of the magnetocaloric effect in a magnetic material with the use of noncontact type detection. The technique is based on the thermoacoustic principle. A sample with a periodically changing surface temperature induces exponentially decaying pressure waves which can be detected by a sensitive microphone. A magnetic material placed within a gas-tight cell at an appropriate dc magnetic field and temperature will exhibit a periodically changing surface temperature due to the magnetocaloric effect when subjected to a small ac field superimposed over the dc field. The microphone response, detected via a lock-in amplifier can be correlated to the magnitude of the temperature changes after suitable calibration. The knowledge of the magnetic equation of state allows the determination of the total magnetocaloric effect ΔT for an arbitrary field step from zero to the final value, using the magnetization data of the sample as well. Gadolinium has been used for calibration, and new results are presented for a gadolinium-dysprosium and a gadolinium-erbium alloy.
Small cavity nonresonant tunable microwave-frequency alternating current scanning tunneling microscope
Authors: Bumm L. A. , Weiss P. S.
Published: July 2002

We have developed a broadly tunable microwave-frequency alternating current scanning tunneling microscope which employs a cavity with no resonances in the frequency range used. This results in a low, flat background for spectroscopic measurements with this instrument.
A dual-cable noise reduction method for Langmuir probes
Authors: Yang T. F. , Zu Q. X. , Liu Ping
Published: July 2002

To obtain fast time response plasma properties, electron density and electron temperature, with a Langmuir probe, the applied probe voltage has to be swept at high frequency. Due to the RC characteristics of coaxial cables, an induced noise of a square-wave form will appear when a sawtooth voltage is applied to the probe. Such a noise is very annoying and difficult to remove, particularly when the probe signal is weak. This paper discusses a noise reduction method using a dual-cable circuit. One of the cables is active and the other is a dummy. Both of them are of equal length and are laid parallel to each other. The active cable carries the applied probe voltage and the probe current signal. The dummy one is not connected to the probe. After being carefully tuned, the induced noises from both cables are nearly identical and therefore can be effectively eliminated with the use of a differential amplifier. A clean I–V characteristic curve can thus be obtained. This greatly improves the accuracy and the time resolution of the values of ne and Te.
A four-point probe to measure the electrical resistivity of alloys under UHV conditions
Authors: Morton S. A. , Turton J. , Greig D.
Published: July 2002

A method based on standard four-point probe geometry is described for measuring the resistivity and temperature coefficient of resistivity of conducting samples under UHV conditions. The device has been designed to be combined with in situ sample preparation and synchrotron induced photoemission, and as such it is fully compatible with a wide range of surface science experiments. The equipment has been used to measure the electrical properties of the reactive alloys CaAl and CaMg over a temperature range of −70 °C to room temperature and has been tested over a range of −100–600 °C. The results have shown that it can be used to provide immediate characterization of the amorphicity of samples for photoemission studies. The observed resistivity ranges of 14–400 μΩ cm for CaAl and 9–30 μΩ cm for CaMg are entirely comparable with previous measurements.
Simple technique for scattering experiments of submillimeter droplets
Authors: Taniguchi Hiroshi , Yanagida Yasuhiro
Published: July 2002

A simple technique is presented of allowing the generation of submillimeter-sized single droplets for scattering experiments. Multiorder Raman spectra (including Stokes, anti-Stokes, and combination emission) from a liquid CCl4 spherical droplet formed by a hollow glass fiber is also obtained by this technique, with a frequency-doubled Nd:YAG pulsed pumping (532 nm).
High accuracy digital temperature control for a laser diode
Authors: Barone Fabrizio , Calloni Enrico , Grado Aniello , De Rosa Rosario , Di Fiore Luciano , Milano Leopoldo , Russo Guido
Published: July 2002

A digital servo-loop was implemented to control the temperature of a laser diode. By using a conditionally stable loop we obtained a temperature stability of about ±20 μK over periods of hours.
Laser-driven flow reactor as a cluster beam source
Authors: Ehbrecht M. , Ferkel H. , Smirnov V. V. , Stelmakh O. M. , Zhang W. , Huisken F.
Published: July 2002

A novel technique for the production of expansion-cooled cluster beams from materials with low vapor pressure is presented. The clusters are produced in a flow reactor from gas phase reactants by aggregation of CO2-laser-induced decomposition products. By introducing a conical nozzle into the reaction zone, they are extracted into a molecular beam apparatus and analyzed with a time-of-flight mass spectrometer. Depending on the type of CO2-laser employed, the source can be operated in the pulsed or continuous mode. The generation of carbon and silicon clusters is demonstrated by decomposing gaseous C2H2 and SiH4, respectively. The laser-driven cluster course is also employed to generate fullerenes and nanosized silicon particles.
On-line dynamic gas pyrometry using two-thermocouple probe
Authors: Warshawsky I.
Published: July 2002

Real-time observation of the fluctuations in the temperature of a flowing gas may be obtained with a probe containing two geometrically similar thermocouples differing only in size, and an electronic analog circuit using commercially available integrated circuits. The thermocouple lag time constants may vary as gas flow rate varies, and need not be known. Only the thermocouple time-constant ratio, a substantially invariant function of geometry, needs to be known. Under favorable circumstances, even this ratio need not be known in advance and can be determined in situ. The improvement in frequency response depends on the magnitude of the temperature fluctuation and is limited by the quality of the electronics. The system is useful when the thermocouple time constants vary appreciably during the course of the temperature fluctuations because of correlative fluctuations in gas flow rate. A thermocouple simulator is used to adjust the analog circuit and to test its efficacy.
Ion-implanted charge collection contacts for high purity silicon detectors operated at 20 mK
Authors: Young B. A. , Yu K. M.
Published: July 2002

We have developed a technique for fabricating high resolution, ohmic contacts for cryogenic silicon detectors operated at temperatures well below 1 K. In this paper, we give a detailed description of the techniques used to fabricate these boron-implanted contacts, and present characterization data obtained on 24 test samples studied during the design phase of our program. We then describe the fabrication and operation of a 23 g prototype silicon hybrid detector which simultaneously senses both the phonons and ionization produced by a single event, and which incorporates these new contacts into its design. Finally, we present data obtained using a radioactive source of 241Am and this detector operated at 20 mK, and conclude that the contacts are fully sufficient for applications in particle astrophysics as well as in many other areas of physics.
Tracking and dynamic control of the angular alignment position in a photolithographic mask aligner by the moiré interference technique
Authors: Singh Brahm Pal , Goto Toshio , Sharma Rina , Kanjilal A. K. , Narain Ram , Chitnis V. T. , Liu J. , Uchida Yoshiyuki
Published: July 2002

An automatic tracking of the angular alignment position of mask with respect to the wafer in a photolithographic mask aligner is reported. It is demonstrated that automatic dynamic control with very high accuracy and stability of the angular alignment position is practically possible. The moiré interference fringe method is employed for the present experiments. The alignment marks are used in the form of 25 μm pitch Ronchi ruling gratings. The best angular alignment accuracy obtained with the present experimental conditions is of the order of 2×10−7 rad. An alignment accuracy up to ±3×10−7 rad is reported for more than 30 min which enables the present technique to be used for the real photolithographic mask aligner.
Initial operation of insertion devices in ELETTRAa)
Authors: Walker R. P. , Diviacco B.
Published: July 2002

The initial operation of the first three insertion devices in ELETTRA is described, including the effects on the electron beam and analysis of the first spectral measurements. Some details are also given about compensation of the ID effects, and operation of the ID control system and vacuum chamber protection system.
Computer-controlled high-speed peak detector for use with pulsed lasers
Authors: Vetrivel L. , Sivaram B. M.
Published: July 2002

A simple, computer-controlled high-speed peak detector for monitoring relative energies in experiments that involve pulsed lasers, is described. In many experiments the laser pulse energy is monitored by feeding the output from a photomultiplier to the 1 MΩ input of an oscilloscope having a bandwidth of about 100 MHz. The computer-controlled peak detector described in this paper can effectively replace the oscilloscope in such cases. There is, further, an additional advantage that the data can be processed shot by shot. High speed and long hold time are achieved by using two peak detectors in tandem. The first peak detector is capable of tracking fast pulses, but has a low hold time. The second peak detector is slower than the first but has a long hold time. The peak value is held for several minutes without appreciable decay, so that several channels can also be monitored one by one manually with an ordinary volt meter. Its versatility in measuring shot-to-shot energy variation of laser pulses, and in real-time pulse selection are demonstrated. Saturation characteristics of a nitrogen laser pumped dye laser has also been studied with two such peak detectors operated simultaneously.
Detection probe-tip configuration optimization for photopyroelectric thermal-wave imaging instrument using finite-element-method analysis
Authors: Yarai Atsushi , Yokoyama Yasuhiro , Nakanishi Takuji
Published: July 2002

This paper describes detection probe-tip configuration optimization for a photopyroelectric thermal-wave imaging instrument. In order to obtain reconstructed thermal-wave tomographic images with high fidelity, it is necessary to obtain the optimum conditions of the detection probe-tip configuration. These conditions were obtained by analyzing the electric fields around a capacitive-coupled detection probe-tip using finite-element-method (FEM) analysis. Experimental results are also shown, verifying the FEM analysis results. It was also confirmed that the equivalent probe-tip diameter determined from our previous experimental work agreed almost perfectly with that obtained using FEM analysis. As a result, high-fidelity thermal-wave tomographic images were obtained.
Second-order focusing property of 210° cylindrical energy analyzer
Authors: Fujisawa A. , Iguchi H. , Sasao M. , Hamada Y.
Published: July 2002

It was confirmed experimentally that a 210° cylindrical energy analyzer with drift spaces has second-order focusing. The properties of the analyzer are strongly dependent on the fringing field around the entrance and exit of the cylinders.
New detector calibration facility for the wavelength range 35–400 nm based on an electrical substitution radiometer
Authors: Lau-Främbs A. , Kroth U. , Rabus H. , Tegeler E. , Ulm G.
Published: July 2002

In the radiometry laboratory of the Physikalisch-Technische Bundesanstalt at the Berlin electron storage ring BESSY a new instrumentation has been set up for the calibration of transfer detectors in the wavelength range from 35 to 400 nm with an aspired uncertainty of <1%. The spectral responsivity of a detector is determined by comparison with the known responsivity of an electrical substitution radiometer operated at liquid helium temperature as the primary detector standard. A first calibration of silicon photodiodes was performed in the spectral range above 250 nm. The spectral responsivity determined with 3% uncertainty was found to agree with previous calibrations conducted with lasers as sources.
Modification of the coherence of undulator radiation
Authors: White D. L. , Wood O. R. , Bjorkholm J. E. , Spector S. , MacDowell A. A. , LaFontaine B.
Published: July 2002

The spatial coherence of undulator radiation has been modified in a quantitative way, such that when imaging with undulator light of λ=14 nm, the resultant images do not have the usual coherent artifacts of ringing and speckle. To achieve this, we made a soft-x-ray scatter plate which, when inserted into the beam, produces the required amount of divergence and phase shifting to fill the pupil of a 20:1 Schwarzschild camera operating at λ=14 nm. Details of this soft-x-ray scatter plate and its effect on imaging will be presented.
Performance of the extreme ultraviolet high resolution undulator beamline BW3 at Hasylab: First results and time-of-flight spectroscopy
Authors: Björneholm O. , Federmann F. , Larsson C. , Hahn U. , Rieck A. , Kakar S. , Möller T. , Beutler A. , Fössing F.
Published: July 2002

The extreme ultraviolet beamline BW3 at Hasylab is a state of the art beamline for the energy range 15–2000 eV consisting of a triple undulator equipped with a modified high-flux SX-700 plane grating monochromator. The first three optical elements of the beamline are made of graphite coated with SiC to withstand the high heat load at the 4.5 GeV storage ring Doris III. Excellent spectral resolution of the order of 104 at the nitrogen K edge at 400 eV is obtained by replacing the elliptical focusing mirror of the original SX-700 design by a spherical mirror with very small tangent errors and with a large focal length in order to suppress spherical aberrations. In the energy range 50–1700 eV a photon flux of 1011–1013/s is obtained in a bandpass of 0.1%. Photoionization and photoemission measurements on atoms, molecules, and clusters making use of time-of-flight techniques demonstrate the excellent performance of the beamline.
Luminescence and transmission measurements on fibers exposed to high neutron fluxes
Authors: Adler H. G. , Hill K. W. , Ramsey A. T. , Tighe W.
Published: July 2002

Fiber-based diagnostic systems suffer from induced luminescence and transmission losses due to neutron and γ radiation from high-power D-D and D-T discharges. Whereas the luminescence follows the neutron rate, the transmission loss increases monotonically during a shot and decays slowly after the discharge. To study these effects we are using dedicated fiber coils (increasing the exposed length) which are positioned close to the discharge vessel (increasing the neutron flux) and close to neutron detectors. The fibers studied are typical for diagnostics on TFTR. One fiber is of the same type used for the JET/TFTR heated fiber study. We measure spectrally selected luminescence and transmission with a light emitting diode based, modulated three-phase exciter system. We have measured substantial transmission losses during D-T shots which reduce the test signals and the radioluminescence. The transmission losses recover only partially; we will show first long-term measurements of the loss recovery. A simple model is presented which allows the derivation of values for luminescence source strength per length unit and neutron flux even if the luminescence is reduced by the induced transmission loss.
Analysis of nuclear-radiation-induced noise in spectroscopic and x-ray diagnostics during high power deuterium–tritium experiments on the tokamak fusion test reactor
Authors: Hill K. W. , Adler H. , Bitter M. , Fredrickson E. , von Goeler S. , Hsuan H. , Janos A. , Johnson D. , Ramsey A. T. , Renda G.
Published: July 2002

Intense fluxes of 14-MeV neutrons from deuterium–tritium (DT) fusion reaction in TFTR resulted in significantly enhanced background noise levels and reduced quality of data from the shielded UV (SPRED) and visible (VIPS) grating spectrometers and the x-ray imaging system (XIS) camera. Both enhanced background levels, attributed to gamma rays and small angle neutron scattering, and large spikes, attributed to nuclear reactions in the silicon detectors, were observed. Both the enhanced background and the frequency of spikes were higher, on a per neutron basis, and the spike amplitudes were higher for DT than for DD operation. The VIPS shield reduced noise by 1/100 for DD radiation; the noise per DT neutron was 4 times higher than per DD neutron. The SPRED detector shield reduction factor was 1/12 in DD; extension of the shield around the vacuum chamber resulted in another factor of 1/5.5 reduction for DT plasmas. Spikes with amplitude up to 10 MeV were observed in the XIS detectors. The shielding effectiveness agrees with predictions. The spike heights are consistent with (n,p) and (n,α) reactions in the silicon detectors.
Alpha-particle kinetic effects in the neutron emission of burning DT plasmas
Authors: Gorini G. , Ballabio L. , Källne J.
Published: July 2002

Fast α-particle kinetic effects on the fuel ions are discussed in the perspective that they can give rise to minority populations of super thermal fuel ions. The resulting modifications of the neutron emission spectrum are computed for a plasma in the state of thermonuclear burning such as envisaged for the planned ITER tokamak. Comparison is made with estimated the instrumental capabilities available for their observation. The findings represent the first evidence that neutron spectrometry is a potential α-particle diagnostic for burning fusion plasmas.
An x-ray technique for precision laser beam synchronization
Authors: Landen O. L. , Lerche R. A. , Hay R. G. , Hammel B. A. , Kalantar D. , Cable M. D.
Published: July 2002

A new x-ray technique for recording the relative arrival times of multiple laser beams at a common target with better than ±10-ps accuracy has been implemented at the Nova laser facility. 80-ps, 3ω Nova beams are focused to separate locations on a gold ribbon target viewed from the side. The measurement consists of using well-characterized reentrant x-ray streak cameras for one-dimensional streaked imaging of the ≳3-keV x rays emanating from these isolated laser plasmas. After making the necessary corrections for the differential laser, x-ray and electron transit times involved, timing offsets as low as ±7 ps are resolved, and on subsequent shots, corrected for, verified, and independently checked. This level of synchronization proved critical in meeting the power balance requirements for indirectly driven pulse-shaped Nova implosions.
Sheath physics study using the divertor materials evaluation system (DIMES) on DIII-D
Authors: Buchenauer D. , Cuthbertson J. W. , Whaley J. A. , Miller J. D. , Watkins J. G. , Junge R. , West W. P. , Hill D. N.
Published: July 2002

A set of 19 dome-shaped divertor Langmuir probes similar in design to probes used in JET and JT-60 has been used successfully in DIII-D to measure the divertor electron temperature, particle flux, and floating potential. A comparison of the power flux using IR cameras with the particle flux and electron temperature from the probes using collisionless sheath theory has indicated that the particle flux to the divertor surface may be strongly modified by collisions within the magnetic sheath. In order to study this effect, a set of probes have been designed that can be inserted into the divertor plasma using DIMES. Two dome-shaped probes compare fluxes intercepted both above and within the magnetic sheath of the divertor surface. In addition, a third probe oriented normal to the magnetic field is used to verify the projected area of the probe surface. The probe design accommodates parallel power fluxes up to 50 MW/m2 for 30 ms, allowing for the study of beam-heated plasmas in DIII-D.
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measurements in open- and closed-geometry long-scale-length laser plasmas via isoelectronic x-ray spectral line ratios
Authors: Shepard T. D. , Back C. A. , Kalantar D. H. , Kauffman R. L. , Keane C. J. , Klem D. E. , Lasinski B. F. , MacGowan B. J. , Powers L. V. , Suter L. J. , Turner R. E. , Failor B. H. , Hsing W. W.
Published: July 2002

We have successfully employed isoelectronic line ratios to measure the electron temperature in gas-filled hohlraums and ‘‘gas bags’’ shot with the Nova laser. Isoelectronic line ratios are well suited to this measurement because they are relatively insensitive to radiation field effects (in hohlraums), opacity, transients, and variations in electron density compared to conventional line ratios. Targets were designed to produce plasma parameters Te∼3 keV and Ne∼1021 cm−3 over a scale length of ∼2 mm. Collisional-radiative, transient K-shell atomic kinetics calculations including line transfer were performed by post-processing the Lasnex results. By comparing these calculations with experimental data, we infer electron temperatures of at least 3 keV for both types of targets.
Target imaging and backlighting diagnosis
Authors: Yaakobi B. , Shvarts D. , Marshall F. J. , Epstein R. , Su Q.
Published: July 2002

The expected backlighting and self-emission images of a particular CH target to be imploded on the Omega Upgrade are calculated for a variety of experimental parameters. It is shown that to overcome the problem of target self-emission, the image has to be monochromatized with a diffracting crystal. For the target studied, the two image components are then comparable in intensity and both provide useful information on target behavior. A particularly interesting feature is the appearance in the self-emission of a circular spike which closely delineates the fuel-shell interface, but requires high spatial resolution to be observed.
An apparatus for the study of the kinetics and mechanism of hydrothermal reactions by in situ energy dispersive x-ray diffraction
Authors: Evans J. S. O. , Francis R. J. , O’Hare D. , Price S. J. , Clark S. M. , Flaherty J. , Gordon J. , Nield A. , Tang C. C.
Published: July 2002

The design and implementation of a pressure cell for the study of hydrothermal reactions by in situ energy dispersive x-ray diffraction is described. The cell permits the study of both the kinetics and mechanism of formation of a wide range of important solid-state compounds such as zeolites and other microporous solids. Reactions can be studied over a wide range of temperature (5–230 °C) and autogenous pressure [0–400 psi (gauge)] conditions. The use of this apparatus is illustrated by a study on the synthesis of a microporous tin chalcogenide phase performed on Station 9.7 of the UK Synchrotron Radiation Source.
W16.1: A new fixed wavelength diffraction station at the SRS Daresbury
Authors: Bliss N. , Bordas J. , Fell B. D. , Harris N. W. , Helsby W. I. , Mant G. R. , Smith W. , Towns-Andrews E.
Published: July 2002

Station W16.1 is a fixed wavelength (1.4 Å) x-ray diffraction station recently constructed and commissioned at the SRS. It has been designed specifically for time-resolved studies of noncrystalline and fibrous materials and optimized for low angle measurements. Wide angle diffraction will also be available with simultaneous small and wide angle scattering/diffraction a future facility. In order to perform dynamic (∼1 ms) low angle measurements on weakly scattering systems, the station design has had to incorporate several novel features so as to achieve the predicted 1×1013 photon/s at the specimen.
Light emitting diode-based nanosecond ultraviolet light source for fluorescence lifetime measurements
Authors: Araki Tsutomu , Misawa Hiroaki
Published: July 2002

A compact pulsed-light source is devised from an InGaN/AlGaN double heterostructure light-emitting diode (LED). The LED emits a 450-nm (blue) light under conventional dc operation below 30 mA. When a current larger than 50 mA is applied, the intensity of the 450-nm light saturates, but that of the 380-nm light due to the InGaN component continues to increase. This phenomenon is utilized to realize a nanosecond ultraviolet (UV) light source. Under repetitive, large current pulsing (frequency=10 kHz, pulse width=4 ns, peak current=2 A), the peak LED emission shifts from 450 to 380 nm. Intense light pulses (peak value=40 mW) of 4-ns duration were generated. To evaluate the potential of the pulsed LED as an excitation source, the fluorescence lifetime of a quinine-sulfate solution was measured. The observed lifetime characteristics agreed well with the generally accepted behavior.
Simulations of neutron focusing with curved mirrors
Authors: Copley J. R. D.
Published: July 2002

We have developed a ray-tracing program to calculate the imaging properties of ellipsoidal and toroidal mirrors in glancing angle configurations. It has been proposed that such mirrors be used in small angle neutron scattering instruments, in order to achieve increased count rates without sacrificing angular resolution. We describe the method of calculation, including effects due to gravity, and we present a number of instructive examples of calculations for both types of mirrors. We also illustrate a practical method of reducing image degradation associated with gravitational effects.
A new wideband (1 mHz to 100 Hz) seismic spectrometer
Authors: Cherry Randall H. , Spetzler Hartmut A. , Paffenholz Josef
Published: July 2002

A new instrument has been developed to measure the compressional attenuation and Young’s modulus of rocks in the seismic-frequency range. This instrument has been calibrated over a frequency range from 1 mHz to 100 Hz at a strain of about 2.5×10−6. The attenuation of the sample is calculated from a relative phase measurement between a low-attenuation reference material and the sample. The Young’s modulus of the sample is calculated from the displacement amplitude of the sample relative to the displacement amplitude of the reference material. Use of this instrument has allowed the investigation of the dependence of a rock’s attenuation and Young’s modulus on its fluid content.
Calculating method for confinement time and charge distribution of ions in electron cyclotron resonance sources
Authors: Dougar-Jabon V. D. , Umnov A. M. , Kutner V. B.
Published: July 2002

It is common knowledge that the electrostatic pit in a core plasma of electron cyclotron resonance sources exerts strict control over generation of ions in high charge states. This work is aimed at finding a dependence of the lifetime of ions on their charge states in the core region and to elaborate a numerical model of ion charge dispersion not only for the core plasmas but for extracted beams as well. The calculated data are in good agreement with the experimental results on charge distributions and magnitudes for currents of beams extracted from the 14 GHz DECRIS source.
Negative hydrogen ion emission from heated metal hydride powder
Authors: Kawano Hiroyuki , Nagayasu Hiroshi , Serizawa Naoshi , Ohta Hideto , Takeda Makiko , Wada Motoi , Sasao Mamiko
Published: July 2002

A small ion source (∼2 cm2) of the self-surface negative ionization (SSNI) type was developed to generate H− from a powdery sample (∼10 mg) deposited on a molybdenum ribbon (∼0.1 cm2). For example, CaH2 heated up to ∼900 K emitted ∼0.1 nA of H− together with ∼1 mA of thermal electrons. The work function of CaH2 was ∼6 to 5 eV, depending upon the history of its thermal processing. The introduction of H2 up to ∼10−4 Torr did not increase H−, indicating that the efficiency of producing H− by electron impact of H2 is much poorer than that by SSNI of CaH2. Emission of H− was also observed with LiH but not with NaH and ZrH2.
Simulations of the response function of a plasma ion beam spectrometer for the Cassini mission to Saturn
Authors: Vilppola J. H. , Tanskanen P. J. , Huomo H. , Barraclough B. L.
Published: July 2002

To obtain very high (∼1%) energy resolution with spherical-section electrostatic analyzers requires high precision in both fabrication and in the alignment process. In order to aid in the calibration of the instrument and to help minimize fabrication costs, we have applied simulation models to the ion beam spectrometer for the NASA/ESA Cassini mission to Saturn. In our previous article we studied the effects of misalignment and simple irregularities of the hemispherical surfaces on the performance of an electrostatic analyzer. We have considered a hemispherical electrostatic analyzer equipped with an aperture plate to collimate the stray electric field at the entrance apertures. The influence of a curved entrance aperture has also been added to the simulation model, and its effects have been studied in detail. A cylindrical three-dimensional simultaneous overrelaxation algorithm has been introduced to solve for the stray electric field. The maximum loss of transmitted particles with respect to the transmission of an ideal instrument has been set at 10%. We demonstrate that the deviation in the distributions of the energies is less than 0.2% and that the deviation in the distributions of entrance angles of transmitted particles is less than 0.1°. It has been found that the energy resolution of an electrostatic analyzer can be improved from ΔE/E=(1.6±0.2)% to ΔE/E=(1.3±0.2)% by the introduction of front aperture plates. Through the introduction of curved entrance slits, the azimuthal angle resolution has changed from β=(1.4±0.1)° for the simplified geometry simulation results of our previous article to β=(2.3±0.1)°. We have confirmed that an accuracy of 25 μm in the alignment of the two hemispherical surfaces is sufficient to give the instrument the desired resolutions.
High sensitivity, inductively coupled miniature magnetic probe array for detailed measurement of time varying magnetic field profiles in plasma flows
Authors: Black D. C. , Mayo R. M.
Published: July 2002

A modified Ḃ circuit design has been implemented as part of a miniature magnetic probe array for the Coaxial Plasma Source experiment [R. M. Mayo et al., Plasma Sources Sci. Technol. 4, 47 (1995)] at the North Carolina State University. This facility is currently being used for the generation of energetic plasma flows to allow laboratory study of magnetogasdynamics with particular emphasis on the importance of the Hall effect [D. C. Black et al., Phys. Plasma 1, 3115 (1994)] and plasma microinstabilities [R. M. Mayo et al., Phys. Plasma 2, 337 (1995)] to plasma transport in coaxial plasma sources. The miniature magnetic probe array consists of ten spatially separated coils wound on an Acetal form of dimensions 2.38 cm by 0.32 cm by 0.32 cm. At five positions, with roughly 0.32 cm separation, two mutually perpendicular coils are wound to measure the magnetic field in the θ̂ and ẑ directions. The modification to the signal processing circuitry consists of the use of a step-up transformer to boost the probe signal prior to filtering and acquiring the signal at the data acquisition system. This additional means of amplifying the signal allows for reduction in the size of the probe, and thus helps minimize the perturbing effect of the magnetic probe on the plasma. An additional advantage of using a signal transformer is that it provides electrical isolation between the experiment and the data acquisition system.
Sputtering-assisted production of multicharged boron ions from solid material in a 2.45 GHz electron cyclotron resonance source
Authors: Kato Yushi , Ishii Shigeyuki
Published: July 2002

Multiply charged boron ions have been successfully produced and extracted from 2.45 GHz electron cyclotron resonance (ECR) ion source without gaseous feedstocks. A target material, solid-state boride, is immersed in an ECR plasma and dc bias voltages are applied to it. Argon is chosen for operating gas. The extracted boron ion current increases as the target approaches the ECR zone. The increase of boron atomic flux into the ECR zone enhances production of the boron ions. The enhancement is deduced from the dependence of boron ion current on solid angle subtended by the target at the ECR zone. The total boron ion current is equal to about 10% of the total argon one. The B2+ current is equal to 10%–20% of B+ one. The B3+ current can be detected at low microwave powers (∼150 W). The isotopes of boron are closely separated in natural abundance ratio.
The electron spectroscopy for chemical analysis microscopy beamline data acquisition system at ELETTRA
Authors: Gariazzo C. , Krempaska R. , Morrison G. R.
Published: July 2002

The electron spectroscopy for chemical analysis (ESCA) microscopy data acquisition system enables the user to control the imaging and spectroscopy modes of operation of the beamline ESCA microscopy at ELETTRA. It allows the user to integrate all experiment, beamline and machine operations in one single environment. The system also provides simple data analysis for both spectra and images data to guide further data acquisition.
Simple and low cost experimental arrangement for continuous tunable narrow-band dye laser
Authors: Skowronek S. , Gonzalez Ureña A.
Published: July 2002

The conversion of a commercial dye laser into a narrow-linewidth laser system, tunable over a large frequency range, is described. Its experimental details as well as its application to high resolution laser spectroscopy in molecular beams are reported. The laser linewidth in different configurations was determined. The major advantages of the system described include its low cost and simplicity in construction and performance.
Design considerations and performance of a spectro-streak apparatus applying a planar LIGA microspectrometer for time-resolved ultrafast fluorescence spectroscopy
Authors: Staerk H. , Wiessner A. , Müller C. , Mohr J.
Published: July 2002

Results of a pilot study with a spectro-streak apparatus applying a grating microspectrometer with a self-focusing reflection grating are reported. The microspectrometer chip (dimensions: 17×6.4 mm2; 125 μm effective thickness of the three-layer x-ray resist system), fabricated with the versatile LIGA technique, has been adapted to a picosecond streak camera. Performance tests have been carried out with a fluorescent probe exhibiting a dynamic Stokes shift of the exciplex fluorescence band due to solvation of the charge transfer dipole within about 400 ps. The use of a LIGA microspectrometer in ultrafast spectroscopy proved to be of advantage in time-resolved studies of complex luminescence spectra where a moderate spectral resolution is required and a large spectral range must be covered.
A new intensity modulation based fiber optic probe for bubble shape detection, velocity, and diameter measurements
Authors: Rossi G. L.
Published: July 2002

In this article a new noncontact fiber optic probe, previously developed for bubble velocity measurements, is described. The sensing element is based on the optical interaction between the bubble and two focused laser beams. Not only the reflected but also the refracted beams are detected by the probe to perform bubble parameter measurements. The measurement principle is based on a transit-time technique, used, for example, in laser dual focus velocimetry or cross-correlation based measuring systems. The measurement system makes use of optical fiber components. The probe is designed for measurements on two-phase bubble flows without contact between the bubble and the probe tip and with minimal disturbance to the flow in the measurement region. The probe tip diameter is only 4 mm. No optical access to the flow is necessary because the probe can be installed inside the flow. Performances of the probe are theoretically and experimentally analyzed. Bubble-laser beam interaction has been analyzed by developing a special purpose simulation software. The probe was then tested in a hydraulic test rig circulated by a vertical air–water bubble flow at velocities up to 2 m/s and bubble diameter from 1 to 4 mm. The developed probe was calibrated by a laser Doppler velocimeter and classical photographic techniques. First results have shown uncertainty values of about 2% (one standard deviation) for velocity measurements.
Passive vibration damping of the APS machine components
Authors: Mangra D. , Sharma S. , Jendrzejczyk J.
Published: July 2002

The accelerator and beamline components of the Advanced Photon Source have stringent vibration criteria in order to meet the beam stability requirements. For instance, the vibration amplitude of the storage ring quadrupoles is restricted to 0.11 μm (rms) over a frequency range of 4–50 Hz. Damping pads, consisting of thin viscoelastic films sandwiched between stainless steel plates, have been designed for passive vibration damping. Results presented in this paper show that the damping pads under the storage ring girder-magnet assemblies reduced the vibration amplification factor Q from over 100 to 8. The broad band rms motion of the magnets was reduced by a factor of 2.5 to 3. Preliminary results for a monochromator housing show a potential use of such damping pads for vibration control of beamline components. Radiation and creep effects on the damping pads’ performance are considered.
Measurement of position and orientation of optical elements in interferometric gravity wave detectors
Authors: Heitmann Henrich , Drezen Christine
Published: July 2002

Interferometric gravitational wave detectors like VIRGO or LIGO will use mirrors suspended as pendulums, forming systems of optical cavities; this requires precise control of alignment and of the mirror pendular motions. We describe a system for the measurement of position and orientation of a mass with respect to a local reference frame. We use a single computer read out charge coupled device camera to determine all six degrees of freedom by observing reference marks on the mass, and, in the case of small mass misalignment, reflections of two auxiliary laser beams. The derived information is available in a shared memory segment on an industrial standard bus system (VME) crate for further digital processing, which will be necessary for alignment and damping of the pendular movements. The mass coordinates can be calculated at the camera frame rate of 60 Hz. In a table top experiment with fixed test mass, the short term rms measurement errors for the translational degrees of freedom were measured to be better than 0.5 μm; for two rotational degrees of freedom, the errors were better than 0.5 μrad, and for the third one about 15 μrad. The long term stability over several days is about an order of magnitude less; it is limited by drifts, to a large extent of thermal origin.