bluuebunny/crossref_metadata_2025 huggingface dataset:
A submillimeter polychromator for plasma spectroscopy
Authors: Tudisco O. , Berton F. , Buratti P. , Grilli E. , Mantovani S.
Published: July 2002

A 12-channel grating polychromator for the measurement of electron cyclotron emission on the Frascati tokamak upgrade (FTU) has been built. Three gratings can be exchanged remotely, to allow the instrument to cover three different spectral ranges (between 200 and 600 GHz) which correspond to the second harmonic of electron cyclotron emission for tokamak magnetic fields of 4, 6, and 8 T. Three sets of low-pass filters, whose cut-off frequencies are optimized for each grating, are used to cut the high diffraction orders. In order to exchange the filters together with the grating it was necessary to integrate the groups of filters with the polychromator itself. This has been done reducing the grating sizes and assembling them all closely on a moveable structure. The exchange of gratings and filters can be performed remotely via computer in few seconds without any lost of the alignment. InSb cryogenic hot-electron bolometers are used as detectors. The cryostat hold-time is more than 30 days. Spectral resolution λ/δλ is about 40 corresponding to a spatial resolution of δR≊2.3 cm. The minimum detectable temperature is about 10 eV at 20 kHz bandwidth. The spatial structure and temporal evolution of several kinds of fast temperature perturbations (as the ones due to magnetohydrodynamic activity, temperature fall during pellet injection and plasma disruption) have been measured on FTU by means of this diagnostic system.
Beam position monitor for the SPring-8 synchrotron
Authors: Aoki T. , Yonehara H. , Suzuki H. , Tani N. , Abe H. , Fukami K. , Hayashi S. , Ueyama Y. , Kaneta T. , Okanishi K. , Ohzuchi S. , Miyaoka T. , Sato K. , Toyoda E. , Ito H. , Yokomizo Hideaki
Published: July 2002

Beam position monitors (BPMs) for the SPring-8 synchrotron have already been designed and manufactured. Each BPM pickup has four button-type electrodes, and the output signals from the electrodes are switched by fast PIN-diode and are measured by signal detection systems. Eighty BPMs and four detection systems are placed around the synchrotron. Calibration of beam position of the 80 BPMs was finished successfully. In this paper, we present the structure of the BPM pickup, the electronics of the signal detection system, and the calibration system.
Macromolecular crystallographic results obtained using a 2048×2048 CCD detector at CHESS
Authors: Thiel Daniel J. , Ealick Steven E. , Tate Mark W. , Gruner Sol M. , Eikenberry Eric F.
Published: July 2002

We present results of macromolecular crystallographic experiments performed at the Cornell High Energy Synchrotron Source (CHESS) with a new CCD-based detector. This detector, installed in January 1995, complements a 1024×1024 CCD detector that has been in continuous operation at CHESS since December 1993. The new detector is based on a 4-port, 2048×2048 pixel CCD that is directly coupled to a Gd2O2S:Tb phosphor by a 3:1 tapered fiber optic. The active area of the phosphor is a square 82 mm on an edge. The readout time is 7 seconds. In the standard mode of operation, the pixel size at the active area is 41 μm on the edge leading to the capability of resolving approximately 200 orders of diffraction across the detector face. The detector also operates in a 1024×1024 mode in which the pixel size is electronically increased by a factor of 4 in area resulting in smaller data files and faster detector readout but at the expense of spatial resolution. Most of the data that has been collected by this detector has been collected in this mode. Dozens of data sets have been collected by many experimenters using this detector at CHESS during the four month period from its installation until the start of the six-month down period of the storage ring. The capabilities of the detector will be illustrated with results from various crystallographic measurements including experiments in which the recorded diffraction patterns extend in resolution as far as 1 Å. The results demonstrate that this detector is capable of collecting data of quality at least equal to that of imaging plates but, in many circumstances, with much greater beamline efficiency.
White beam transport design for insertion device beamlines at the Advanced Photon Source
Authors: Shu Deming , Haeffner Dean , Job P.K.
Published: July 2002

To evaluate the feasibility of designing an economic beamline transport system for insertion device beamlines at the Advanced Photon Source, two sample cases have been designed and analyzed, one for an undulator source and the other for a wiggler source. The results show that it is possible to build a 70-meter-long beamline transport system for an undulator source with less than four lead/tungsten-alloy bremsstrahlung collimators. Six or fewer collimators are needed to construct a 70-meter-long white-beam transport system for a wiggler source. To prevent damage from any missteered powerful white beam, a water-cooled fixed mask is placed in front of each collimator. Ray tracing for both bremsstrahlung and synchrotron radiation have been conducted for the sample transports. Modular mask/collimator assembly designs and ray-tracing results are presented.
A software-controlled analog random pattern generator for space-borne detector simulation
Authors: Chun H. J. , Thomas P. D. , Bowles J. A.
Published: July 2002

This article describes a user-controlled detector simulator to aid development of the grazing incidence spectrometer (GIS), which forms part of the coronal diagnostic spectrometer on-board the solar and heliospheric observatory. The simulator was a vital element in carrying out full range tests of the GIS processing electronics in the absence of real detectors, including extreme conditions not easily achievable by other means. With a large degree of flexibility, the simulator provides a wide range of characteristics of output events of realistic shapes. Although the simulator was designed specifically to simulate the spiral anode as used by the GIS, the design is applicable to any three channel detector system and has since been used for the FONEMA instrument for the Russian Mars96 mission. The simulator functionality, performance parameters, software and hardware design, and the overall grounding scheme are presented. The simulator performance with some test results are also discussed.
A simple current mode preamplifier for electron multipliers with high voltage biased anode
Authors: Seo Seong-Heon , Chang Hong-Young , Kim S. K.
Published: July 2002

We developed a simple current mode preamplifier for the microchannel plate (MCP) with the anode biased to high voltage. It uses a capacitor to block dc high voltage and measures the MCP current through the capacitor. Then it compensates exactly the distortion caused by the capacitor so the amplifier can measure any length of signals without distortion. It is much less expensive and simpler than using the phosphor screen system to isolate the dc high voltage. We derived a formula for that compensation and implemented it by using an op-amp’s circuit. It gives an approximate time resolution of 10 μs which is restricted by the op-amp’s characteristics. So, it may be improved by using fast op-amp’s. This can also be used for channeltron and other electron multipliers. For the test of the preamplifier, we measured the photoelectron currents induced by the soft x rays radiated from the KT-1 tokamak of which the pulse length was 20 ms. The data revealed well, without distortion, the time evolution of the line radiation.
Computer-controlled apparatus for internal friction and Young’s modulus measurements as a function of temperature
Authors: Coluzzi B. , Biscarini A. , Mazzolai F. M.
Published: July 2002

A mechanical resonance apparatus has been developed which allows automatic recording of internal friction Q−1and dynamic Young’s modulus E as a function of temperature. The attainable accuracies ΔQ−1/Q−1 and ΔE/E are approximately equal to 3.5×10−2 and 1×10−5, respectively. The vibrating sample is kept at resonance, during heating and cooling, by continuously readjusting the frequency of the driving signal supplied by a computer-controlled frequency synthesizer. The frequency regulation is obtained by keeping either the amplitude of the response signal at its maximum level or the phase difference between the excitation and vibration signals at a fixed, selected value. In comparison with previous automatic control systems designed for similar applications, the one described here is more versatile, being able to measure internal friction from the width of the resonance curve as well as from the logarithmic decrement of freely decaying vibrations, and being able to regulate the vibration frequency by either the amplitude or the phase control method. The two automatically interchangeable measuring procedures allow recording over wide ranges of the dissipation coefficient (10−5≤Q−1≤10−2),while the two frequency regulation methods permit, according to the requirements, either higher data acquisition rates (phase control approach) or better accuracies (amplitude control approach). Tests carried out on a CuZnAl alloy show good performance of the apparatus during temperature-induced martensitic transitions, which are associated with large relative changes of frequency and energy dissipation.
Ultrafast broadband frequency-modulation reflectometer for density profile measurements in GAMMA 10
Authors: Tokuzawa T. , Mase A. , Oyama N. , Itakura A. , Tamano T.
Published: July 2002

A broadband microwave reflectometer was applied to the GAMMA 10 tandem mirror using a fast-sweep hyperabrupt varactor-tuned oscillator (HTO) that can be swept over the full band (12–18 GHz) in less than 5 μs. Clear fringes are observed during a plasma shot when the resultant frequencies from the reflectometer output are much larger than the ion cyclotron range of frequency (3–10 MHz). The density profile measurement is performed for various sweep times of HTO from 1 ms to 5 μs in which two reconstruction methods are utilized, zero-cross counting of the fringes and frequency analysis using the maximum entropy method. The reliability of the profile measurement seems to be improved when the sweep time is faster than 10–30 μs. The integrated value of many reconstructed density profiles agrees well with the profile obtained from a scanning interferometer. The fast-sweep reflectometer is also applied to the measurement of density fluctuations such as plasma movement as well as density profiles.
Bursts of electron cyclotron emission during disruptions of high beta discharges in the Tokamak Fusion Test Reactor tokamak
Authors: Janos A. , McGuire K. , Fredrickson E. , Parks W. , Zweben S. , Hastie J.
Published: July 2002

Disruptions are sudden terminations of tokamak plasma discharges. During disruptions at high beta β where β ≡ plasma pressure/magnetic pressure, short (order of μs) and intense bursts of electron cyclotron emission (ECE), an order magnitude above thermal levels, are observed in the second harmonic electron cyclotron frequency range, which corresponds to 100s of GHz in the Tokamak Fusion Test Reactor tokamak. A unique combination of two, fast, 500 kHz, 20-channel grating polychromator instruments, located at different toroidal positions, is used to measure the emission and characterize these bursts. New insights into the three-dimensional dynamics of these disruptions and the accompanying bursts of ECE have been obtained. Bursts of ECE occur at the beginning of the thermal quenches and exhibit strong toroidal asymmetries. Bursts are localized to the vicinity of the ballooning mode, a fast growing (few ms) medium toroidal mode number (n=10–20) precursor, localized toroidally, poloidally, and radially, which triggers the disruptions. Fast-particle losses occur with the explosive growth of the ballooning mode, followed by plasma/wall interaction. Bursts of ECE occur shortly afterwards, within 10s of μs of the fast particle losses. An explanation of the bursting is presented which is consistent both qualitatively and quantitatively, with observations predicting, for example, radiation enhancement factors of ≈10. Bursting can be explained not in terms of enhanced excitation of emission but rather in the reduction of absorption of thermal emission. Bursting is consistent with a modification to the electron distribution function fe due to a rapid energy or particle exchange between hot electrons and cold electrons from the edge, momentarily reducing the velocity gradient of fc in the thermal region. Large edge localized mode events also exhibit bursts of ECE due to a similar sequence of events.
Neutron source strength monitors for ITER
Authors: Barnes Cris W. , Roquemore A. L.
Published: July 2002

There are several goals for the neutron source strength monitor system for the International Thermonuclear Experimental Reactor. Desired is a stable, reliable, time-dependent neutron detection system which exhibits a wide dynamic range and broad energy response to incident neutrons while being insensitive to gamma rays and having low noise characteristics in a harsh reactor environment. This system should be able to be absolutely calibrated in situ using various neutron sources. An array of proportional counters of varying sensitivities is proposed along with the most promising possible locations. One proposed location is in the preshields of the neutron camera collimators which would allow an integrated design of neutron systems with good detector access. As part of an ongoing conceptual design for this system, the detector-specific issues of dynamic range, performance monitoring, and sensitivity will be presented. The location options of the array will be discussed and most importantly, the calibration issues associated with a heavily shielded vessel will be presented.
A compact Thomson scattering system
Authors: Dimock D. , Grek B. , Johnson D. , LaBombard B. , Lipschultz B. , McCracken G.
Published: July 2002

We have made and installed a multipulse Nd:YAG Thomson scattering system for measuring electron temperature and density profiles in the throat of the divertor of the Alcator C-Mod machine. The observing head is located in the vacuum vessel in a re-entrant chamber. It is optically fast and very compact. A system for providing feedback to maintain the laser beam alignment is a part of the observing head assembly. The head is designed to minimize eddy currents, and have a very rigid adjustable mounting to resist the forces generated by the eddy currents during plasma disruptions. A four wavelength polychromator using 25 element avalanche photodiode arrays for spatial resolution has been designed and built for this system. Two of these polychromators and a single observing head will provide 50 spatial resolution elements.
Study of laser-imploded core plasmas with an advanced Kirkpatrick–Baez x-ray microscope
Authors: Kodama R. , Shiraga H. , Miyanaga M. , Matsushita T. , Nakai M. , Azechi H. , Mima K. , Kato Y.
Published: July 2002

We developed an advanced Kirkpatrick–Baez (AKB) x-ray microscope which consisted of two hyperbolic mirrors and two elliptic mirrors. The spatial resolution of ≲3 μm was realized over ∼1 mm diam. This AKB microscope was used for x-ray imaging in laser fusion experiments. Laser absorption nonuniformity with a large wave number on a spherical solid target or a plane slab target was estimated by measurements of x-ray emission from the target surface with the microscope. The x-ray images of the imploded core plasmas were also obtained with the AKB microscope, changing the laser focus condition and the laser energy balance.
Edge density profile measurements in TdeV using amplitude modulation reflectometry
Authors: Pinsonneault D. , Quirion B. , Lachambre J.-L. , Legros C.
Published: July 2002

A single channel AM reflectometer, operating in the frequency range of 33.0⩽f⩽50.0 GHz, has been developed to provide edge electron density profiles on TdeV. The X-mode cut-off layer, covering densities ne⩽1019 m−3 for 1.5 T operation, is used to measure a portion of the plasma edge region 0.9⩽r/a⩽1.2. Briefly, our design consists in launching a microwave beam amplitude modulated at 201 MHz. The reflected wave is detected and downconverted to 1 MHz to facilitate filtering and phase detection. Finally, a linear phase detector compares the phase of the resulting signal (1 MHz) with that of the reference source. The design and construction of the reflectometer will be described and preliminary results presented.
Tapping mode capacitance microscopy
Authors: Goto Kazuya , Hane Kazuhiro
Published: July 2002

We present a new technique for microscopic capacitance measurements. Capacitance microscopy is combined with tapping mode force microscopy. The tapping motion is successfully used for the capacitance modulation and also for the tip-sample distance regulation. Furthermore, capacitive and topographic images are simultaneously obtained. The technique was applied to observations of a gratinglike electrode and of a nitride-oxide-silicon structure for a nonvolatile memory.
Photovoltaic effects in GaN structures with p-n junctions
Authors: Zhang X. , Kung P. , Walker D. , Piotrowski J. , Rogalski A. , Saxler A. , Razeghi M.
Published: July 2002

Large-area GaN photovoltaic structures with p-n junctions have been fabricated using atmospheric pressure metalorganic chemical vapor deposition. The photovoltaic devices typically exhibit selective spectral characteristics with two narrow peaks of opposite polarity. This can be related to p-n junction connected back-to-back with a Schottky barrier. The shape of the spectral characteristic is dependent on the thickness of the n- and p-type regions. The diffusion length of holes in the n-type GaN region, estimated by theoretical modeling of the spectral response shape, was about 0.1 μm.
Very high resolution soft x-ray spectrometer for an electron beam ion trap
Authors: Beiersdorfer P. , Crespo López-Urrutia J. R. , Förster E. , Mahiri J. , Widmann K.
Published: July 2002

A very high resolution vacuum flat-crystal spectrometer was constructed for analyzing soft x rays emitted by an electron beam ion trap. The spectrometer was designed to operate at large Bragg angles (θ⩽85°) in order to maximize the spectral dispersion and thus the resolving power. Using a quartz (100) crystal at a Bragg angle of 82°, a measurement of the 2p1/2, 2p3/2→1s1/2 transitions in hydrogenic Mg11+ situated near 8.42 Å was made. The nominal resolving power of the instrument was better than 30 000 allowing us to infer the ion temperature (246±20 eV) from the observed line widths. A comparison with an existing flat-crystal spectrometer demonstrates the great improvement in resolving power achieved.
X-ray imaging of targets irradiated by the Nike KrF laser
Authors: Brown C. , Seely J. , Feldman U. , Obenschain S. , Bodner S. , Pawley C. , Gerber K. , Serlin V. , Sethian J. , Aglitskiy Y. , Lehecka T. , Holland G.
Published: July 2002

Foil targets irradiated by the Naval Research Laboratory Nike KrF laser were imaged in the x-ray region with two-dimensional spatial resolution in the 2–10 μm range. The images revealed the smoothness of the emission from target and backlighter foils, the acceleration of the target foils, and the growth of Rayleigh–Taylor instabilities that were seeded by patterns on the irradiated sides of CH foils.
Ultrahigh vacuum surface analysis coupled with a high pressure system for the study of near critical and supercritical fluid processing
Authors: Bakker G. L. , Hess D. W.
Published: July 2002

A system has been constructed for ultrahigh vacuum analysis investigation of surfaces after high pressure fluid processing. The system features a cell capable of withstanding pressures up to 400 bar that opens directly into an ultrahigh vacuum (10−10 Torr) system to allow transfer of samples for analysis. Temperature control of the cell and fluid is possible to within ±1 °C up to temperatures of 400 °C. The high pressure system design allows the preparation and study of supercritical fluid mixtures as well as of pure components. X-ray photoelectron spectroscopy, Auger electron spectroscopy, sputter etching, and vacuum anneal capabilities comprise the surface analysis system. The fluids investigated include supercritical carbon dioxide, methanol, water, and their mixtures; these are applied to processes such as surface cleaning and thin film etching using high pressure fluids.
Automatic fast fitting of single Langmuir probe characteristics on RFX
Authors: Bagatin M. , Desideri D. , Martines E. , Manduchi G. , Serianni G. , Antoni V.
Published: July 2002

An array of single Langmuir probes is routinely used in the RFX reversed field pinch for time-resolved measurements of edge electron density and temperature. In order to allow an automatic analysis of the large number of current–voltage characteristics, three different methods have been developed, which consider restricted subsets of data with voltage lower than an upper cutoff value. The first one determines this limiting voltage by a neural network based technique, combined with criteria for the rejection of too noisy characteristics. In the second one a standard fitting routine is applied repeatedly to the data while varying the upper cutoff voltage. The third one consists of a numerical technique, where the best fit is obtained by minimizing a properly defined cost function. An error index is also calculated, which allows the reliability of the results to be easily estimated. The best results have been achieved using the last two methods.
Design and construction of a heat stage for investigations of samples by atomic force microscopy above ambient temperatures
Authors: Baekmark Thomas Rosleff , Bjo/rnholm Thomas , Mouritsen Ole G.
Published: July 2002

The construction from simple and cheap commercially available parts of a miniature heat stage for the direct heating of samples studied with a commercially available optical-lever-detection atomic force microscope is reported. We demonstrate that by using this heat stage, atomic resolution can be obtained on highly oriented pyrolytic graphite at 52 °C. The heat stage is of potential use for the investigation of biological material at physiological temperatures.
A feasibility study of an infrared tangential viewing polarimeter for measurement of the electron density profile in ITER (abstract)
Authors: Ma C. H. , Hutchinson D. P. , Richards R. K. , Irby J.
Published: July 2002

Preliminary results of a feasibility study of a CO2 laser tangential viewing polarimeter for measuring electron density profiles in ITER are reported. For ITER plasma parameters and a polarimeter wavelength of 10.6 μm, a Faraday rotation of up to 26° is predicted. An electro-optic polarization modulation technique has been developed at ORNL. Laboratory tests of this polarimeter demonstrated a sensitivity of ⩽0.01°. Because of the similarity in the expected Faraday rotation in ITER and Alcator C-Mod, a collaboration between ORNL and the MIT Plasma Fusion Center has been undertaken to test this polarimeter system on Alcator C-Mod. A 10.6 μm polarimeter has been constructed and integrated into the existing C-Mod multichannel two-color interferometer. Detailed analyses and the preliminary results of the C-Mod measurements will be shown.
An apparatus for the characterization of the static and dynamic wettability of complex interfaces
Authors: Aurenty Patrice , Lanet Véronique , Tessadro Ana , Gandini Alessandro
Published: July 2002

The apparatus described in this work is a novel tool which improves the capabilities of studying the static and dynamic features of wetting. It is composed, on the one hand, of an operational part which includes the mechanical setup for the precise deposition of drops and their correct viewing once they start evolving on a substrate. On the other hand, a specific vision system completes the instrument and is made up of different cameras and focusing optics, capable of acquiring images at variable rates (up to 200 Hz) and of a data-processing card designed to provide parameters such as contact angles, interfacial tensions, and spreading kinetics. Numerous examples of the use of this apparatus are provided in order to illustrate its merits within a wide range of static and dynamic situations related to the basic properties of interfaces.
A simple computer-interfaced multichannel scaler for photon counting
Authors: Ko Dong-Seob
Published: July 2002

A computer-interfaced multichannel scaler consisting of two counters and FIFO chips as an external memory has been fabricated for use in photon counting. This configuration makes it possible to get a minimum bin width of 1 μs and to continuously acquire a number of bins. The programmable interval timer is used for setting the bin width through a computer.
Miniature microwave powered steam sterilization chamber
Authors: Atwater James E. , Dahl Roger W. , Garmon Frank C. , Lunsford Teddie D. , Michalek William F. , Wheeler Richard R. , Sauer Richard L.
Published: July 2002

A small device for the rapid ultrahigh temperature sterilization of surfaces is described. Microwave power generated by a 2.45 GHz magnetron is delivered via coaxial cable to a silicon carbide block housed within the chamber. Small quantities of water or aqueous hydrogen peroxide are introduced into the chamber. Upon application of power, the liquid flashes to vapor and superheats producing temperatures to 300 °C. The hot vapor permeates the enclosed space and contacts all exposed surfaces. Complete microbial kill of >10 6 colony forming units of the spore forming thermophile, Bacillus stearothermophilus, has been demonstrated using a variety of temperatures and exposure times in both steady state and thermal pulse modes of operation.
A cylindrical reflectron time-of-flight mass spectrometer
Authors: Vialle J. L. , Baguenard B. , Bourgey A. , Cottancin E. , Lermé J. , Palpant B. , Pellarin M. , Valadier F. , Broyer M.
Published: July 2002

A new reflectron time-of-flight mass spectrometer with a cylindrical electrostatic mirror instead of the usual plane reflector is described. When it is mounted at right angles to the direction of an incoming molecular beam, this system automatically compensates for the transverse drift of the ions in the spectrometer due to their initial velocity parallel to the molecular beam direction. As a consequence, ions of any mass can be collected onto the detector, whatever their initial transverse velocity is. The mass range accessible in a single scan with our cylindrical reflectron is thus strongly increased as compared to the case of a usual plane reflectron. This article presents the general design of our cylindrical reflectron. A detailed description of the apparatus is given and its performances are illustrated on selected examples. Cluster mass spectra extending over a very wide size range are presented. A mass resolution of about 4000 is achieved in mass spectra of laser photoionized aluminum clusters. Moreover, the cylindrical geometry of the reflector gives rise to focusing properties onto the detector, which could be interesting in view of collection efficiency improvement.
Simple radio-frequency power source for ion guides and ion traps
Authors: Jones Ronald M. , Gerlich Dieter , Anderson Scott L.
Published: July 2002

A high power oscillator circuit, designed to power radio-frequency (rf) ion guides and traps, is described. The rf circuit is directly coupled to the guide/trap electrodes, and no frequency or impedance matching is required. The design provides precisely adjustable rf amplitudes from ∼50 to 600 V, either under manual or computer control. The operating frequency can be varied from <1 to ∼30 MHz to allow best trapping conditions for different ion mass ranges. Provisions are made for balancing the rf amplitude to compensate for small load asymmetries. The rf can be switched off and on under control of a transistor–transistor logic signal, and the rise and fall time for the rf amplitude can be manually controlled from a few rf cycles to milliseconds. Provisions are made for applying both direct current (dc) difference and dc float potentials to the ion guide. The design is easily constructed from readily available parts.
Spectral characteristics and effects of heat treatment on intrinsic Nd-doped fiber thermometer probes
Authors: Zhang Z. Y. , Grattan K. T. V. , Palmer A. W. , Meggitt B. T.
Published: July 2002

A detailed investigation of the practical spectroscopic features and the effect of prolonged exposure to elevated temperatures of an intrinsic Nd:doped fiber optic thermometer probe using the fluorescence decay time technique has been carried out. Results have shown the optimum length for the doped fiber and a maximum operating temperature of 750 °C, beyond which a range of high-temperature “annealing” effects are seen. These are discussed in light of the operation of the thermometers over the range from −196 to 750 °C and potentially above.
Determination of ion charge state distributions in krypton and cobalt electron cyclotron resonance plasmas by wavelength dispersive x-ray spectroscopy
Authors: Grübling P. , Küchler D. , Lehnert U. , Ullrich A. , Werner T. , Zschornack G.
Published: July 2002

Wavelength dispersive x-ray measurements on cobalt and krypton ions were presented to determine the ion charge state distribution (CSD) inside the electron cyclotron resonance (ECR) plasma of the 14.5 GHz ECR ion source of the TU Dresden. For clearly from the parent diagram lines separating x-ray satellites a comparison between calculated wavelength shifts and measured ones allows it to deduce the ion CSD of the analyzed ions. In the case of small line shifts (lower ionization states) a comparison with x-ray spectra derived from plasma modeling is done. By approximating the modeled spectra to the measured ones a most probable ion CSD was derived.
High-current negative-ion beam acceleration with a large negative-ion source for large helical device-neutral beam injection system
Authors: Takeiri Y. , Osakabe M. , Tsumori K. , Oka Y. , Kaneko O. , Asano E. , Kawamoto T. , Akiyama R.
Published: July 2002

A large hydrogen negative-ion source was constructed as a prototype one for the negative-ion-based neutral beam injection (NBI) system in large helical device. The ion source is designed to produce 180 keV-40 A of the negative ion beam with a current density of 40 mA/cm2, and is a cesium-seeded volume production source characterized by the external magnetic filter. The arc chamber of multicusp bucket is rectangular of 35 cm×145 cm in cross section and 21 cm in depth. The accelerator is a three-grid single-stage one, and the total grid area is 25 cm×125 cm, which is divided into five sections. The ion source was installed on the negative-ion-based NBI test-stand, and using one section of the grid 5.5 A of the negative-ion beam was produced at a gas pressure of 1.8 mTorr corresponding to a current density of 27.5 mA/cm2. The extracted electron current is low of 50% of the negative ion current, and the acceleration efficiency, defined as the negative ion current divided by the acceleration drain current, is more than 75%. The ion source operation with the full grid area has just started, and, so far, 21 A of the negative ion beam was obtained. The large area beam has been successfully focused by both the geometrical arrangement of five grid sections and the aperture displacement technique of the grounded grid.
Development of the Penning ionization gauge source for higher current
Authors: Mühle C. , Leible K. D. , Spädtke P.
Published: July 2002

For the first phase of the GSI high current project, an improvement of Penning ionization gauge (PIG) ion sources is necessary. Therefore, we carry out several PIG source development activities. A test bench for PIG ion sources was set up. It was equipped with the same source magnet, the same beam line, and the same computer control as at the accelerator injector. It has been partly operational since the beginning of 1997. Contrary to the UNILAC accelerator with a typical pulse width of up to 5 ms at a repetition rate of 50 Hz, the synchrotron injection requires a pulse length of about 200 μs at 0.3 Hz. Therefore, the use of lower repetition rates is possible. Thus, more power can be applied to the discharge and increased ion currents can be extracted. This mode requires higher cathode heating, which decreases the lifetime of the filament. The use of monocrystalline LaB6 cathodes drastically reduces the necessary heating power at the same electron current, which should increase the lifetime of the filament and the cathode. The yield of ions from solids was improved by the use of optimized combinations of target and sputtering gas. The use of xenon instead of argon as the sputtering gas for the uranium target yielded a current enhancement of 40%. To achieve a shift of the charge-state distribution to higher charge states, an optimized gas feeding is one option. In collaboration with JINR Dubna, we developed a pulsed gas feeding system. Two piezovalves directly mounted to the source allowed us to control the pressure in the source.
A novel distributed system for plasma immersion ion implanter control and automation
Authors: Liu A. G. , Wang X. F. , Tang B. Y. , Chu P. K. , Ko P. K. , Cheng Y. C.
Published: July 2002

The high voltage and electromagnetic field environment poses a big challenge to a control system for plasma immersion ion implantation (PIII). The automation process must be immune to electric field interference produced by the high voltage power supply, modulator, radio-frequency or microwave plasma generator, MEVVA plasma sources, and so on. We have recently designed and installed a distributed control system, PIIIDCS, to automate the operation of our PIII facility. Programmable logic controllers are used as the field control stations because of their good anti-interference ability and good real time response. A DH-485 network is used as the communication link between the field controllers and the management station in order to improve the robustness and reliability of the system. The newly developed interface is designed to work in a graphic mode in Microsoft Windows 95. Test runs have shown that the system is reliable, flexible, and easy to operate. The development of this novel control system will expedite the development of commercial PIII instrumentation.
Extending a continuous scan Fourier transform spectrometer for time-resolved Fourier transform spectroscopy with <0.5 cm−1 spectral and <10 ns time resolution in the visible region
Authors: Lindner Jörg , Stahlhut Oliver , Wilhelm Ralf , Ermisch Karsten
Published: July 2002

The extension of a continuous scan high spectral resolution (0.006 cm−1) Fourier transform spectrometer for time-resolved Fourier transform spectroscopy with a temporal resolution in the ns regime is described. The time resolution is achieved by synchronizing a laser/transient digitizer system with the interferometer. The realization of the data acquisition and the experimental setup are described. Examples of time-resolved measurements are given. Detector limited temporal resolution of <10 ns is shown by recording scattered light from a pulsed dye laser. Spectral resolution of <0.5 cm−1 is demonstrated by observing the fluorescence of electronically excited CH radicals produced in the multi photon dissociation of CHBr3. The signal-to-noise behavior of time-resolved Fourier transform apparatus is investigated as a function of spectral (0.1–4.0 cm−1 unapodized) and time resolution and of the intensity of the detected light.
Low energy solid intense ion beams extracted by electron beam evaporation ion source for material modifications
Authors: Feng Y. C. , Wong S. P.
Published: July 2002

An investigation to reduce the energy of the solid ion beam extracted from electron beam evaporation ion source for material modifications has been performed. The preliminary results have shown that the beam energy can be reduced to lower than 100 eV by a specially designed extraction system for carbon and nitrogen mixed ion beams. The beam current extracted is up to 30 mA for a small 20 mm extraction diameter ion source. It has been found that the extraction energy can be controlled by adjusting the bias voltage of the sample used for coating and the crucible potential. The extraction capability and the composition of the ion beam can also be controlled by changing the gas flow rate and the input power of the ion source. For carbon nitride films synthesized at low energy by this system, the results have shown to exhibit very high hardness values. The microhardness is over HK 6000 kg/mm2. The principle of this ion source is described. The structure of the ion source, and the experimental results are also described in this article.
Technique for measurement of the noise of a sensor in the presence of large background signals
Authors: Barzilai Aaron , VanZandt Tom , Kenny Tom
Published: July 2002

This work reports on a method to measure the instrumental noise of a sensor in the presence of large background signals, based on measuring the coherence and output of two identical sensors exposed to the same input stimulus. The technique can be applied to any sensor characterization problem where there is interest in distinguishing random noise from common-mode noise. The method is demonstrated using geophones, a single-axis seismometer that has been an important sensor for geophysical measurements for decades. Previous experimental work has not published measurements of the geophone’s instrumental noise at frequencies near the geophone’s resonance because of the presence of large background seismic signals compared to the predicted instrumental noise, which is a minimum at the geophone’s resonant frequency. With this coherence technique, measurements performed in the presence of 1 μg/Hz seismic signals showed that the minimum instrumental noise was within a factor of 2 of the predicted minimum noise of 0.6 ng/Hz.
Advances in the transient dc photocurrent technique for excited state dipole moment measurements
Authors: Smirnov Sergei N. , Braun Charles L.
Published: July 2002

Recent advances in the transient dc photocurrent technique for measuring excited state dipole moments, developed in our group, are discussed. A variety of approaches with detailed analyses of their advantages and disadvantages including cell design, circuit construction tricks, the data acquisition procedure, calibration, and the theoretical treatment of different conditions, are presented. Sensitivity, time resolution limitations, and newly developed features, such as the signal’s dependence on light polarization as well as charge separation at interfaces are outlined. Dipole moments of a few molecules (diphenylcyclopropenone, bianthryl, dimethylaminonitrostilbene, Coumarin 153, and fluoroprobe) suitable for calibration purpose are reported—some of them for the first time.
A velocity interferometer system for any reflector utilizing a short coherence length laser
Authors: Lwin M. J. , Voevodkin G. G. , Killen P. D. , Page N. W. , Bell J. M.
Published: July 2002

A velocity interferometer system for any reflector, utilizing a laser of coherence length less than the optical path difference (OPD) between the two interferometer arms, is described and tested. In this instrument the laser beam is passed through the interferometer both before and after it is reflected from the target. As a result the coherence length of the laser need only be twice the relatively small distance traveled by the target in the time taken for light to traverse the OPD. Results are presented for a nonspecular target.
A simple high pressure flow cell for on-line absorption, Raman, and time resolved laser induced fluorescence spectroscopy in supercritical fluids
Authors: Addleman R. Shane , Hills J. Ward , Wai Chien M.
Published: July 2002

A versatile spectroscopic flow cell for high pressure liquids and supercritical fluid solutions is described. The cell is capable of being coupled to either standard or fiber optic spectrometers. There are two perpendicular optical paths that are adjustable in length and aperture diameter. The cell has shown it can be used for absorption, emission, or scattering spectroscopy. The design is simple, inexpensive, serviceable, uses conventional materials, and is self aligning. With apertures of 5.7 mm the cell has been tested to pressures up to 500 atm and temperatures up to 90 °C. However, the cell would allow usage at higher temperatures and pressures if desired.
Natural crystals selection process for neutron diffraction applications
Authors: Stasiulevicius R. , Rodrigues C. , Parente C. B. R.
Published: July 2002

This work aims to show a selection process for natural crystals that considers the major characteristics and performance as gratings for neutron monochromators using the neutron diffraction technique. A total of 19 crystals have been selected and classified regarding their adequacy for use as neutron diffraction devices. Applying special criteria, method and the rocking curve technique, the measurements have been performed and the theoretically available values compared with the experimental results, obtained directly from a neutron diffractometer in operation at the IEA-R1 (5 MW) nuclear research reactor. The choice for natural crystals, expanding the operational range of the neutron diffraction instruments, is related with the purpose of getting monochromatic neutron sources suitable for the applications. The neutron has proved to be the most powerful microscopic testing particle in condensed matter studies and in many other areas of application.
Software corrected hot wire thermal lag for the constant voltage anemometer featuring a constant bandwidth at the selected compensation setting
Authors: Sarma Garimella R. , Comte-Bellot Genevieve , Faure Thierry M.
Published: July 2002

Software compensation correction for thermal lag of a hot wire in the application of a constant voltage anemometer (CVA) for turbulence measurements in the boundary layer of a supersonic wind tunnel has been demonstrated. The CVA was used with a fixed compensation setting while measuring the in situ thermal lag (time constant) of the hot wire. Using the measured time constant, corrections are applied to the fixed compensation output of the CVA in postprocessing of the data. To demonstrate the flexibility of the approach it was used for two compensation settings at a test point to obtain the same results from both settings. A unique advantage of this approach is shown to be that for a given compensation setting in the CVA the bandwidth of the measurements for the test remains constant for all of the different test conditions and yields higher productivity. The results of the turbulence levels measured with this method agree with earlier research using other anemometers. Spectral plots of the mass flux and temperature and the measured in situ time constant responses under different conditions of the hot wire have been presented.
A novel design of piezo-driven dual-dimension optical scanning mechanism
Authors: Chang S. H. , Tung Y. C.
Published: July 2002

An optical scanning mechanism capable of dual-dimension scanning is presented. The mechanism uses a piezoelectric element to drive a V-shaped reflecting mirror surface through two pairs of elastic beams. The design entails the use of various vibration modes to reflect the incident light in orthogonal directions. The design, fabrication, and mechanical, electrical, and optical performance of this scanning mechanism are presented. The scanning sensitivities of 88.8 and 19.3 μrad/V in each scanning direction are measured when operated at frequencies of 23.8 and 48.8 kHz, respectively. The capability of fine scanning sensitivity, high operating frequency, and wide scanning range is applicable for fine adjustment of the laser beam.
Microwave temperature-jump nuclear magnetic resonance system for aqueous solutions
Authors: Kawakami Masaru , Akasaka Kazuyuki
Published: July 2002

A microwave temperature-jump nuclear magnetic resonance (NMR) system suitable for aqueous solutions has been developed. A microwave pulse of a desired length is generated at a frequency of 2.46 GHz from a 1.3 kW magnetron, and is delivered through a waveguide and a coaxial cable to a coupling loop which works as an antenna to the dielectric resonator in the NMR probe. Inside the dielectric resonator, the microwave power is efficiently absorbed by the sample solution (about 100 μl) contained in a glass tube, causing a temperature jump by about 25 °C in less than 20 ms. The temperature after the jump can be maintained by applying intermittent microwave pulses of shorter length. A saddle-type radio-frequency coil is placed around the sample tube inside the hollow of the dielectric resonator to excite spins and detect NMR signals. Both the microwave pulses and the radio-frequency pulses are gated by a pulse programmer of the NMR spectrometer to form a desired temperature-jump pulse sequence. A mechanical mixing device is introduced, which significantly reduces the temperature gradient of the sample solution well within 100 ms after the jump. Application to an aqueous solution of ribonuclease A showed that the protein unfolds within 20 ms of microwave heating.
High Q tunable LC resonator operating at cryogenic temperature
Authors: Bonaldi Michele , Falferi Paolo , Dolesi Rita , Cerdonio Massimo , Vitale Stefano
Published: July 2002

We present a step-motor based cryogenic tuning device for a high Q electrical resonator. The resonator can be tuned in the 145–175 Hz frequency range. Tuning is achieved by moving a superconducting core inside the 3 H superconducting coil of the resonator. The resonator intrinsic quality factor of 1.8×106 is found to be unaffected by the superconducting core and by the drive system. The noise of the resonator has been measured to be thermal. The device has been developed to improve sensitivity and bandwidth performance of cryogenic resonant gravitational wave detectors equipped with resonant capacitance transducers.
A variable-angle electron spin polarization detection system
Authors: Getzlaff Mathias , Heidemann Bernhard , Bansmann Joachim , Westphal Carsten , Schönhense Gerd
Published: July 2002

An ultrahigh vacuum apparatus for investigations of ferromagnetic samples allowing the variation of detection angle and spin resolution of secondary and photoelectrons is described. Angle variation is facilitated by a special combination of 180° and 90° deflectors and a cylindrical sector analyzer serves as energy dispersing element. Spin analysis is carried out using a hemispherical high energy (90 keV) Mott polarimeter without retarding potentials. Its efficiency was determined as 2.4×10−4. Due to acceleration in a short spherically symmetric field, the setup is rather compact and the sensitivity to geometrical misalignment is small. The performance of the instrument is demonstrated by angle dependent measurements of thin ferromagnetic Co(0001) films, evaporated on W(110), and modifications of surface magnetic properties of a xenon adsorbate layer.