bluuebunny/crossref_metadata_2025 huggingface dataset:
Miniature bellows-free low-temperature valve
Authors: Spencer Gregory F. , Ihas Gary G.
Published: July 2002

A novel design for a low-temperature valve is presented. Designed to be used on fill-line capillaries and flow lines in low-temperature apparatus, the valve has nearly zero dead volume as well as a very small total volume. It employs no metallic bellows as in standard valve designs. Instead, a Kapton membrane is epoxied into a cylindrical form to provide a flexible diaphragm, which is activated by pressurized helium. The valve is simple to construct, having only one machining operation, and uses materials readily available. It has been tested in liquid helium to be leaktight above Tλ with a 1-bar pressure differential across the capillary containing the valve.
Large-area lanthanum hexaboride electron emitter
Authors: Goebel D. M. , Hirooka Y. , Sketchley T. A.
Published: July 2002

A large-area cathode assembly which is capable of continuous, high-current electron emission is described. The cathode utilizes an indirectly heated lanthanum hexaboride (LaB6) disk as the thermionic electron emitter. The LaB6 cathode emits over 600 A of electrons at an average of 20 A/cm2 continuously with no observable lifetime limits to date after about 400 h of operation in a plasma discharge. Proper clasping of the LaB6 disk is required to avoid impurity production from chemical reactions with the holder and to provide adequate support if the disk fractures during rapid thermal cycling. Modification of the LaB6 surface composition due to preferential sputtering of boron by hydrogen and argon ions in the plasma discharge has been observed. The surface appearance is consistent with the formation of LaB4 as a result of boron depletion. The electron emission capability of the cathode is not significantly altered by the surface change. This surface modification by preferential sputtering is not observed in hollow cathodes where the ion energy from the cathode sheath voltage is typically less than 50 V. The electron emission by the cathode has not been affected by exposure to both air and water during operation. Utilizing thick disks of this intermediate temperature cathode material results in reliable, high-current, long-lifetime electron emitter assemblies.
Nanoscale oxide patterns on Si(100) surfaces
Authors: Shen T.-C. , Wang C. , Lyding J. W. , Tucker J. R.
Published: July 2002

Ultrathin oxide patterns of a linewidth of 50 Å have been created on Si(100)-2×1 surfaces by a scanning tunneling microscope operating in ultrahigh vacuum. The oxide thickness is estimated to be 4–10 Å. The morphology and spectroscopy of the oxide region are obtained. Hydrogen passivation is used as an oxidation mask. The defects caused by oxidation in the passivated region before and after the hydrogen desorption are compared and discussed. The multistep silicon processings by an ultrahigh vacuum scanning tunneling micropscope is thus demonstrated.
Improvement of cylindrical microwave cavities using a TE01n mode
Authors: Iddings C. K.
Published: July 2002

The usual cylindrical microwave cavity for the TE011 mode has sidewalls made of a closely spaced helix of enameled magnet wire. This wirewound construction splits off the degenerate, low Q, TM111 mode and thus raises the effective cavity Q. We propose a cavity design which, in addition, surrounds the helix with a solid conducting cylinder. Our construction has higher Q, no losses from external fields, and appears to be relatively insensitive to the presence of a dielectric rod (sample tube) along the central axis.
Manufacture, observation, and test of membranes with locatable single pores
Authors: Packard R. E. , Pekola J. P. , Price P. B. , Spohr R. N. R. , Westmacott K. H. , Yu-Qun Zhu
Published: July 2002

A method for generating single pores down to 0.1 μm diameter in the center of a large circular foil is described, based on nuclear tracks. The foil is framed by a tension ring which enables one to handle the foils in a well-defined precise way. The single pore has a lateral displacement of ±0.1 mm with respect to the tension ring center. The foils used are polycarbonate of the type Makrofol and have thicknesses between 2 and 10 μm. For calibration of the single pore diameters, multiple nuclear tracks between 0.1 and 3.5 μm diameter are etched and observed by microscopy. The microscopic observations are compared with gas-flow measurements, using two alternative methods: multiple holes are tested under viscous flow conditions of N2 gas at normal temperature and pressure; single holes are tested under collisionless flow conditions of 4He gas at liquid-nitrogen temperature, using a capacitance method.
Programmable scan controller for fast access to individual elements in a self-scanned silicon photodiode array
Authors: Ricci D. , Lampugnani L. , Papoff P. , Rotunno T.
Published: July 2002

A programmable scan controller to implement a fast access readout of individual photodiodes in a self-scanned silicon photodiode array (SPDA) was assembled using transistor–transistor logic (TTL) presettable counters handled by a single-chip microcontroller. This controller makes it possible to skip groups of unwanted diodes at fast scan rate, whereas the others are read and digitized at normal scan rate. The skipping scan rate (Fs) and the reading scan rate (Fr) are switch selectable, the former in the 4 MHz–250 kHz range, the latter in the Fs/2–Fs/4095 range. Any scan pattern is software programmable. Up to 29 groups of contiguous diodes can be skipped. Integration time and number of scans are also software programmable. Programming is accomplished by the host computer issuing the scan parameters through a strobed 8-bit parallel port to the microcontroller, which provides for the controls necessary for the scan pattern generation required.
New imaging bandpass electron energy analyzer
Authors: Turner D. W. , Plummer I. R. , Porter H. Q.
Published: July 2002

An electron energy analyzer which acts as a bandpass filter while maintaining the spatial integrity of an electron image in a uniform magnetic field is described. It embodies some new electron-optical properties. Image electrons injected parallel to the magnetic field are guided, using crossed electrostatic and magnetic fields, to a low-pass electron mirror and then through a high-pass retardation filter. Nonuniform electrostatic deflection fields are used to compensate for the energy-dependent dispersion of the crossed fields. A simple computer modeling method used to design the electrostatic fields is described. A test analyzer was constructed to operate in a 0.0125-T (125 G) uniform magnetic field to investigate its properties. Bandpass filtered images of an 18-eV electron source demonstrating the removal of energy-dependent dispersion and the narrowing of the bandwidth to 100 meV are presented. Another application of the analyzer, to obtain an energy spectrum from a spatially extended electron source, is demonstrated.
Characterization of an atom beam produced with the help of a hollow-cathode discharge
Authors: Babin F. , Gagné J.-M.
Published: July 2002

A hollow-cathode type discharge is used as a refractory element vapor generator for the formation of an atomic beam. The development of the technique brings us to discuss its possibilities in spectroscopic studies of refractory elements. We focus primarily on the production of a uranium atomic beam and its characterization by laser-induced fluorescence spectroscopy. We determine, among other things, the beam divergence and the most probable velocity along its axis for specific current and pressure conditions in the discharge. We also discuss beam behavior with respect to buffer gas pressure and electric current in the discharge.
Analog technique for the analysis of pyroelectric optical-detection signals
Authors: Cornelius W. A. , Sargent R. V.
Published: July 2002

An experimental technique has been specifically developed for the determination of heating inequivalence errors in the use of electrically calibrated pyroelectric optical detectors. The technique is based upon an analog simulation of detector response. A null balance current detection method is used to eliminate preamplifier distortion errors. The technique is similar to thermal pulse methods used in the study of electret materials and may, therefore, find further application in this area. In addition, the technique may be adapted to allow investigation of thermally stimulated relaxation effects in the audiofrequency range.
In situ x-ray diffraction apparatus for metal hydride studies
Authors: Gavra Z. , Murray J. J.
Published: July 2002

An easily dismountable arrangement for in situ x-ray diffraction studies of metal/hydrogen reactions (and other gas/solid reactions) which is usable on any open type of diffractometer is described. Gas pressures to 5.0 MPa (50 atm) and sample temperatures in the range 190–575 K have been used successfully.
Measurement of multilayer mirror reflectivity and stimulated emission in the XUV spectral region
Authors: Keane C. , Nam C. H. , Meixler L. , Milchberg H. , Skinner C. H. , Suckewer S. , Voorhees D. , Barbee T.
Published: July 2002

We present measurements of multilayer mirror reflectivity and stimulated emission in the XUV spectral region. A molybdenum–silicon multilayer mirror with 12% measured reflectivity at 182 Å was found to produce a 120% enhancement of the C vi 182-Å line (3→2 transition) in a strongly recombining plasma. No such enhancement of the C v 186.7-Å line was seen, demonstrating amplification of stimulated emission at 182 Å.
Convenient and precise method of measuring both stability and homogeneity of magnetic fields
Authors: Linzhang Pan , Shanmin Zhang , Xianqan Zhang , Feng Tian , Huiping Zhang
Published: July 2002

This paper presents a method which can be used to measure both stability and homogeneity of magnetic fields in terms of nuclear side-band oscillation (NSO). By simply monitoring the changes of the NSO frequency ωm, one can calculate the changes of the magnetic field according to the simple formula Δωm=γΔH. The basic principle of NSO and the conditions for stable NSO are elucidated. The measuring accuracy depends on the removal of relaxation oscillation in NSO. The mechanism of relaxation oscillation in NSO is analyzed in detail. The results of measuring the homogeneity distribution of a laboratory magnet are given as well.
X-ray film calibration: Dynamic range modification for imaging and spectroscopy
Authors: Stone G. F. , Dittmore C. H. , Henke B. L.
Published: July 2002

The use of silver halide x-ray films for imaging and spectroscopy is limited by the range of intensities that can be recorded and densitometered. Using the manufacturers processing techniques can result in 102–3 range in intensity recorded over a 0–5.0 density range. By modifying the chemistry and processing times, ranges of 105–6 can be recorded in the same density range. We report on x-ray film calibration work and dynamic range improvements. Changes to the processing chemistry and the resulting changes in dynamic range and x-ray sensitivity will be discussed. Work performed under the auspices of the U. S. DOE by Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.
Enhanced ESR sensitivity using a dielectric resonator
Authors: Walsh W. M. , Rupp L. W.
Published: July 2002

Miniaturized TE011 resonators using cylinders of commercial high dielectric constant materials yield up to 30×ESR sensitivity improvements for small samples.
Evaluation of soft x-ray average recombination coefficient and average charge for metallic impurities in beam-heated plasmas
Authors: Sesnic S. S. , Bitter M. , Hill K. W. , Hiroe S. , Hulse R. , Shimada M. , Stratton B. , von Goeler S.
Published: July 2002

The soft x-ray continuum radiation in tokamak fusion test reactor (TFTR) low-density neutral-beam discharges can be much lower than its theoretical value obtained by assuming a corona equilibrium. This reduced continuum radiation is caused by an ionization equilibrium shift toward lower states, which strongly changes the value of the average recombination coefficient of metallic impurities γ̄, even for only slight changes in the average charge Z̄. The primary agent for this shift is the charge exchange between the highly ionized impurity ions and the neutral hydrogen, rather than impurity transport, because the central density of the neutral hydrogen is strongly enhanced at lower plasma densities with intense beam injection. In the extreme case of low-density, high neutral-beam power TFTR operation (energetic ion mode) the reduction in γ̄ can be as much as one-half to two-thirds. We calculate the parametric dependence of γ̄ and Z̄ for Ti, Cr, Fe, and Ni impurities on neutral density (equivalent to beam power), electron temperature, and electron density. These values are obtained by using either a one-dimensional impurity transport code or a zero-dimensional code with a finite particle confinement time. As an example, we show the variation of γ̄ and Z̄ in different TFTR discharges.
Optical fiducials for x-ray streak cameras at LLE
Authors: Jaanimagi P. A. , DaSilva L. , Gregory G. G. , Hestdalen C. , Kiikka C. D. , Kotmel R. , Richardson M. C.
Published: July 2002

The incorporation of an optical timing fiducial onto a time-resolved x-ray streak record permits one to precisely relate the x-ray emission to the incident laser pulse. At the Laboratory for Laser Energetics, our approach to recording fiducials is twofold. In addition to recording the x-ray emission on a bifurcated photocathode, we also streak the incident laser light at 351 nm, which is scattered from the target and an independent signal at 4ω0 (264 nm), which is derived by frequency quadrupling a tiny fraction of the OMEGA laser driver output. The signal at 4ω0 is transported through the vacuum wall to the streak camera photocathode via fiber optics. A 200-Å aluminum layer on mica is utilized for the UV sensitive photocathode. We will present examples and further details of this system.
Neutral beam interlock system on TFTR using infrared pyrometry
Authors: Medley S. S. , Kugel H. W. , Kozub T. A. , Lowrance J. L. , Mastrocola V. , Renda G. , Young K. M.
Published: July 2002

Although the region of the Tokamak Fusion Test Reactor (TFTR) vacuum vessel wall which is susceptible to damage by neutral beam strike is armored with a mosaic of TiC-clad POCO graphite tiles, at power deposition levels above 2.5 kW/cm2 the armor surface temperature exceeds 1200 °C within 250 ms, and itself becomes susceptible to damage. In order to protect the wall armor, a neutral beam interlock system based on infrared pyrometry measurement of the armor surface temperature was installed on TFTR. For each beamline, a three-fiber-optic telescope views three areas of ∼30 cm diameter centered on the armor hot spots for the three ion sources. Each signal is fiber-optic coupled to a remote 900-nm pyrometer which feeds analog signals to the neutral beam interrupt circuits. The pyrometer interlock system is designed to interrupt each of the 12 ion sources independently within 10 ms of the temperature exceeding a threshold which can be set in the range of 500–2300 °C. A description of the pyrometer interlock system and its performance will be presented.
Generation of ultrashort electrical pulses with variable pulse widths
Authors: Keil U. D. , Gerritsen H. J. , Haverkort J. E. M. , Wolter J. H.
Published: July 2002

Electrical pulses from 450 fs to 3 ps are generated using coplanar strip lines and coplanar waveguides on SI GaAs substrate. We use two optical pump beams to generate two steplike electrical transients with opposite sign and then superimpose the signals resulting in rectangular shaped pulses. By varying the delay between the two pump beams the pulse width can be adjusted.
Flat response detectors from UV to x-ray region (invited)
Authors: Kania D. R.
Published: July 2002

Photoconductive detectors can provide fast, sensitive, flat response in a simple package. We have studied 1-mm cubes of InP doped with Fe and neutron-damaged GaAs for use as detectors in the UV and x-ray region. The doping and neutron damaging are used to increase the speed of the detectors which may be as fast as a few picoseconds. These detectors are not sensitive to radiation below the band gap of the material (1.3 eV) and are limited by the stopping power of the material at high photon energies. The sensitivity of the detectors which is proportional to the energy to form an electron-hole pair in the material is constant throughout the UV and x-ray range resulting in a flat response detector. The magnitude of the sensitivity of these detectors can far exceed that of photoemissive detectors (XRDs). Lasers, synchrotrons, z pinches, and laser-produced plasmas have been used as radiation sources to calibrate the detectors’ performance: sensitivity and linearity. The results of these measurements will be reviewed and the limits of the applicability of these detectors will be described. This work was performed under the auspices of the U. S. DOE.
New diagnostic for spheromaks? What are the possibilities?
Authors: Boyd D. A.
Published: July 2002

Electron cyclotron emission from a spheromak plasma may be able to provide information about the confining magnetic field. Emission generated in the extraordinary mode with its electric vector perpendicular to the local magnetic field at sufficiently high frequency will propagate out of the plasma while retaining the orientation of the electric vector that it had at its source. Thus a measurement of the orientation of the emergent electric vector and the frequency of the emitted wave will allow one to deduce the orientation and strength of the magnetic field at the radiation source. A simple model of the Maryland spheromak is used to determine the practicality of this diagnostic possibility.
ECRH absorption and propagation studies via collective Thomson scattering
Authors: Peebles W. A. , Kim S. , Luhmann N. C. , Zimmerman P.
Published: July 2002

Electron cyclotron resonance heating (ECRH) has made rapid progress over the last few years due primarily to improved gyrotron source technology. The unique ability of ECRH to deposit energy locally offers numerous advantages, such as the ability to preionize, initiate, control, and heat fusion plasmas. However, wave propagation and absorption mechanisms are not well understood and the fusion community would clearly benefit from a nonperturbing monitor of ECRF wave activity. The use of FIR collective Thomson scattering techniques on the upcoming ECRH experiment on TEXT is described. The intention is to probe both k⊥ and k∥ ECRF wave activity as well as simultaneously monitoring microturbulence levels. The existing source frequency of 245 GHz will experience a large frequency shift (∼60 GHz) after scattering from ECRF waves. This has a number of important consequences for the accurate interpretation of scattering data. These will be described in detail as well as alternative CO2 and FIR laser scattering schemes.
137-GHz gyrotron diagnostic for instability studies in Tara
Authors: Machuzak J. S. , Woskoboinikow P. , Mulligan W. J. , Cohn D. R. , Gerver M. , Guss W. , Mauel M. , Post R. S. , Temkin R. J.
Published: July 2002

A narrow linewidth (<100 kHz), 1-kW, 137-GHz gyrotron and an efficient TE03 to TE11 cylindrical waveguide mode converter set (>97% TE11 mode output) have been built for collective Thomson scattering diagnostics. The main goal will be to study instability driven ion density fluctuations in the Tara plug such as the drift cyclotron loss cone (DCLC), the axial loss cone (ALC), harmonics of the DCLC and ALC, and the ion two-stream instability. The heterodyne receiver and signal optics have been installed on Tara. Background electron cyclotron emission (ECE) at 139±1.5 GHz after electron cyclotron resonance heating (ECRH) in the Tara plug corresponded to equivalent blackbody temperatures of 453 and 70 eV for extraordinary and ordinary emission, respectively. The well-collimated receiver field of view completely through the Tara plug has allowed for excellent polarization discrimination of the ECE. The high-power capability of this gyrotron will allow weak fluctuation levels (ñ/n<10−6) to be detected above this background during ECRH in the plugs.
High-efficiency soft x-ray emission spectrometer for use with synchrotron radiation excitation
Authors: Callcott T. A. , Tsang K. L. , Zhang C. H. , Ederer D. L. , Arakawa E. T.
Published: July 2002

A new soft x-ray spectrometer designed for use with photon excitation from synchrotron light sources is described and characterized. Special design features, including a close-spaced input slit, large toroidal gratings, and a two-dimensional charge-coupled-device array based detector system, provide exceptional measuring efficiency in a 5-m Rowland circle design. Descriptions are given of the spectrometer’s mechanical and detector design, and of calibration and alignment procedures. The beam line providing photon excitation from a synchrotron light source is described. Typical electron beam and/or photon excited emission spectra of Al, Si, and LiF are presented and compared with those produced by other instruments.
cw dye laser system for Li-beam spectroscopy in a tokamak
Authors: West W. P. , Thomas D. M.
Published: July 2002

The current-density-profile diagnostic system developed for the Texas experimental tokamak (TEXT) employs a cw dye laser system to induce fluorescence in a Li beam injected into a tokamak. This laser has spectral and polarization modulation requirements not available in commercial systems. The required spectrum is a bandwidth of approximately 5 GHz at a wavelength of 667 nm. The intensity within the bandwidth should be as uniform as possible, i.e., a quasicontinuum within the 5-GHz bandwidth. The polarization of the laser must remain linear, but the plane of polarization must be rotated at a high frequency, 50 kHz. The details of the Li atomic spectroscopy in a tokamak and the requirements of the diagnostic system that lead to these desired laser parameters will be addressed. The laser system and polarization modulator which have been developed will be discussed in detail, including both design and performance parameters.
Detection limits in the measurement of alpha particles by CO2 laser Thomson scattering
Authors: Richards R. K. , Hutchinson D. P.
Published: July 2002

It is found for plasma conditions expected during ignition studies (ne∼1014 cm−3, Te∼10 keV) that alpha-particle densities as low as 1011 cm−3 can be measured with CO2 laser Thomson scattering. This detection limit is set by the background signal from the electrons and will change with the plasma conditions, increasing for increasing electron temperature and decreasing for increasing electron density. The effect of the B field in producing a spatially concentrated alpha-particle signal does lead to an improvement in detecting the alpha particles over the electrons. However, this improvement is typically only a factor of 2 or 3. The reason for such a minimal improvement is that a large detector bandwidth (required for heterodyne detection) broadens the B-field resonance. The principal effect of the B field is to greatly reduce the area needed for detection. This research was supported by the Office of Fusion Energy, U.S. DOE, under Contract No. DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc.
Barium ion beam magnetic field and space potential diagnostic
Authors: Wickham M. , Higgins L. , Lazar N. H. , Dandl R.
Published: July 2002

Improvements have been made in the TRW barium ion beam magnetic and space potential diagnostic1 to increase the signal-to-noise ratio which have made measurements in the STM hydrogen plasma possible. These improvements include larger solid angle collection optics, higher delivered laser power, and higher ion-beam densities. The improvements have been more than sufficient to allow measurements of plasma parameters under any desired operating conditions of the STM device. Measurements of plasma diamagnetism, space potential, and potential fluctuations have been made under various ECRH plasma conditions. Diamagnetism β of 14% with stored energy of 13.4 J have been observed under ‘‘ring’’ conditions. Under ‘‘disk’’ conditions and similar stored energy diamagnetism over 80% of the plasma diameter has been observed peaking at ΔB=150 G out of 2000 G at r=0. This work was supported by U. S. DOE Contracts DE-AC03-79ET1017 and DE-AC03-85ER51089.
TMX-U computer system in evolution
Authors: Casper T. A. , Bell H. , Brown M. , Gorvad M. , Jenkins S. , Meyer W. , Moller J. , Perkins D.
Published: July 2002

Over the past three years, the total TMX-U diagnostic data base has grown to exceed 10 Mbytes from over 1300 channels; roughly triple the originally designed size. This acquisition and processing load has resulted in an experiment repetition rate exceeding 10 min per shot using the five original Hewlett–Packard HP-1000 computers with their shared disks. Our new diagnostics tend to be multichannel instruments, which, in our environment, can be more easily managed using local computers. For this purpose, we are using HP series 9000 computers for instrument control, data acquisition, and analysis. Fourteen such systems are operational with processed format output exchanged via a shared resource manager. We are presently implementing the necessary hardware and software changes to create a local area network allowing us to combine the data from these systems with our main data archive. The expansion of our diagnostic system using the parallel acquisition and processing concept allows us to increase our data base with a minimum of impact on the experimental repetition rate.
Double scatter neutron time-of-flight spectrometer as a plasma diagnostic
Authors: Walker S. E. , Preszler A. M. , Millard W. A.
Published: July 2002

The energy and flux measurement of D–D and D–T fusion neutrons provides a nonperturbing probe of plasma performance. In particular, ion temperature distribution of the plasma can be determined. This information can distinguish neutron production mechanisms, i.e., knock-on or thermonuclear in origin. To perform a fast neutron measurement, a high data rate double scatter spectrometer has been developed. This allows for a definitive measurement of the flux, energy, angle, and time distributions of neutrons from within the plasma. In addition, x-ray discrimination can be achieved from the time-of-flight information. The specific design issues and performance of the spectrometer will be described.
Fiber sensor neutron streak camera for ICF diagnostics
Authors: Kislev H. , Miley G. H.
Published: July 2002

We propose a new neutron streak camera design for ICF burn studies. It uses a fiber-optic sensor so that the camera itself can be removed from the target chamber. The sensor element is based on the decreased optical transmission (darkening) of a fiber optics doped with fissile material during neutron irradiation. The velocity spread of the neutron pulse requires positioning of any neutron sensor within 5 cm from the target in order to resolve the burn dynamics. A major advantage over other designs is that sensitive and costly components are removed from the intense radiation field. Estimates of minimum yield requirements, darkening time response, and overall temporal resolution are presented.
Frequency-resolved multiple k scattering diagnostic
Authors: Kirk R. E. , Forrest M. J. , Peacock N. J.
Published: July 2002

In conventional Thomson scattering diagnostics S(w,k) is measured with either w or k fixed; this paper describes a technique which enables the frequency spectrum to be determined along three different density fluctuation k vectors simultaneously. Such a technique is invaluable in the diagnosis of irreproducible plasmas, since the complete dynamic form factor for the scattered light S(w,k) can be measured instantaneously. Experiments on the Culham Plasma Focus, with its short-lived (10–50 ns) dense plasma phase, demonstrate the advantages of the method. Three sets of collection optics were orientated to view an identical scattering volume with scattering k’s parallel, orthogonal, and at 45° to the plasma Z axis. The scattered light from each system was relayed by optical fibers to a Czerny–Turner spectrometer with a triple input slit. A gated optical multichannel analyzer was used to record the three dispersed spectra produced by this arrangement. The results demonstrate the gross variations in the density fluctuations parallel and perpendicular to the current flow. Examples of some of the detailed analyses of the results in terms of a two-component plasma with different Te, Ti, ne, V drift, etc., are given.
All digital inelastic electron tunneling spectrometer utilizing the IEEE-488 instrument bus and an IBM PC-XT controller
Authors: Hipps K. W.
Published: July 2002

An easily assembled computer-controlled tunneling spectrometer is described. Spectral acquisition time is user selectable over a wide range. Low-resolution spectra may be taken rapidly (about 30s/scan) or very slow scans with long time exponential averaging may be chosen. Data are obtained using a two-phase lock-in in magnitude mode so that no phasing of the lock-in amplifier is required. The advantages of this system are discussed and some representative data presented.
Very high-vacuum heat treatment facility
Authors: Folkner W. M. , Moody M. V. , Richard J.-P.
Published: July 2002

We have designed and constructed a vacuum heat treatment facility, with hot zone dimensions of 12×19×19 cm, at a cost substantially below that of a commercial unit. The design incorporates efficient water cooling and a resistive heating element. A vacuum pressure of 1.5×10−8 Torr at room temperature has been obtained after baking. The temperature limit is approximately 1900 °C. This limit results from our choice of niobium as the hot zone material.
Microcomputer-controlled perturbed angular correlation spectrometer
Authors: Jaeger H. , Gardner J. A. , Su H. T. , Rasera R. L.
Published: July 2002

A four-detector time-differential perturbed angular correlation spectrometer controlled by an inexpensive microcomputer is described. The use of twin-single-channel analyzers permits each detector to identify both gamma rays in the cascade. An improved gating logic system reduces the MCA/computer deadtime and allows larger sample activity and faster data accumulation. The twin-single-channel analyzer and gating circuit additions also permit simultaneous accumulation of two statistically independent sets of four-channel spectra. The spectrometer provides on-line display of raw data and the perturbation function derived from either set of four-channel spectra.
Fast-scanning autocorrelator with 1-ns scanning range for characterization of mode-locked ion lasers
Authors: Xinan Guan , Lambsdorff M. , Kuhl J. , Biachang Wu
Published: July 2002

We describe a rapid-scanning autocorrelator interferometer, which will be extremely useful to measure and monitor laser pulses in the 100-ps regime. A scan range as wide as 1.4 ns is achieved by using a self-compensated, rotating prism system for the generation of the optical delay. Combining this interferometer with a β-BaB2O4 crystal for second-harmonic generation, a low-cost device for real-time display of the autocorrelation function of mode-locked ion lasers is obtained.
Torsional oscillator for internal friction data at 100 kHz
Authors: Cahill David G. , Van Cleve J. E.
Published: July 2002

We describe a method for measuring the internal friction of solids at low temperatures. Our design uses a composite oscillator vibrating in torsion at 100 kHz. The oscillator makes good thermal contact to the cryostat while maintaining a low background loss of Q−1≂2×10−6 at 2 K. The usefulness of the design is demonstrated by data for BaF2 and a-SiO2 from 2 to 300 K.
Current-to-frequency converter for electron multipliers
Authors: Carr R. , Yang J.
Published: July 2002

We have developed a current-to-frequency converter which is designed to be used with electron multipliers whose anodes are raised to high voltages. It has three sensitivity scales: 10 fC/Hz, 100 fC/Hz, and 1 pC/Hz, with 6.7 decades of dynamic range in each scale. We show that this technique has the high signal-to-noise ratio required for use with electron detectors such as channel plate multipliers and channel electron multipliers.
Neutron calibration techniques for comparison of tokamak results
Authors: Strachan J. D. , Adams J. M. , Barnes Cris W. , Batistoni P. , Bosch H.-S. , Brzosko J. S. , England A. C. , Fiore C. L. , Granetz R. S. , Hendel H. W. , Hoenen F. , Jarvis O. N. , Jassby D. L. , Ku L. P. , Liu P. , Martin G. , McCauley S. , Motley R. W. , Nishitani T. , Robouch B. V. , Saito T. , Sasao M. , Stav R. D. , Taylor P. L.
Published: July 2002

A workshop on 1–3 August 1989 reviewed the techniques, uncertainties, and experiences of neutron calibration on PLT, TFTR, JET, Tore Supra, JT-60, JIPPT-IIU, Alcator C-Mod, ATF, FT, ASDEX, Textor, and DIII-D. In the summary session, the workshop participants discussed possible consensus neutron calibration techniques appropriate to D-D plasmas in tokamaks. The application of such techniques would facilitate a more accurate comparison of neutron yields from different devices, and also allow new calibration techniques to relate their precision to a reference value. General agreement was reached on the suitability of two techniques: (1) a 252Cf source calibration of epithermal neutron detectors, and (2) threshold neutron activation of Ni foils placed vertically above or below the plasma. This paper will present details on detector positioning, neutron transport calculations, and interlab normalization needed to accomplish the standardized calibration using a Cf neutron source.
Resonance due to the interaction of tunneling particles with modulation quanta
Authors: Hagmann Mark J.
Published: July 2002

Numerical simulations of quantum tunneling with time-dependent barriers show that there is a resonance, with a marked increase in the transmission coefficient. For a raised cosine potential, and for low energies with square barriers, the resonance occurs when a modulation quantum can take a tunneling particle to the top of the barrier. For energies near the top of a square barrier the resonance may be understood by hypothesizing that a tunneling particle may travel from end to end of the barrier until it is ultimately either transmitted or reflected.
A continuous flow probe method for on-line introduction of liquid samples for detection by laser desorption with resonant two-photon ionization in supersonic beam mass spectrometry
Authors: Lustig David A. , Lubman David M.
Published: July 2002

A continuous flow probe is used as a direct inlet source for injection of liquid samples into a time-of-flight (TOF) mass spectrometer. The direct liquid inlet is coupled to laser desorption as a means of rapidly vaporizing the nonvolatile sample dissolved in the solvent for entrainment into a supersonic jet expansion. The target analyte is then selectively analyzed by resonance enhanced multiphoton ionization (REMPI) in the TOF device. This method demonstrates the ability to continuously inject thermally labile biological samples such as neurotransmitters and oligopeptides for detection and structural analysis by REMPI. In addition, sensitivity limits in the low ng regime are demonstrated with quantitation over 3 orders of magnitude.
A simple Stark modulator
Authors: Benedetti M. , Prado D. , Martinez N.
Published: July 2002

A simple, all solid-state, circuit is described that produces a square wave with variable amplitude from 0 to 1000 V and a frequency of 120 kHz into a capacitive load. The device is of application to Stark modulation in microwave and gas radical e.s.r. spectroscopy. It has certain advantages over previous systems, being more compact, excluding supply short circuits, providing an output that is automatically real zero based and being continuously variable over the range 0–1000 V, thus avoiding the need for capacitive division.
Optical transition probabilities for lines obtained from pulsed sources
Authors: Bertuccelli D. , Bertuccelli G. , Di Rocco H. O.
Published: July 2002

A simple and fast method for the measurements of transition probabilities for lines obtained from pulsed sources is presented. Measuring the linewidth and peak intensities transformed in an internal absolute scale, relative transition probabilities are obtained from a simple relation. The method is useful only for lines with Lorentzian or Voigt type profiles, but many transitions are of this form. For testing the method, 6s-6p Xe II transitions were selected since several works exist for comparison.
Correcting for x-ray energy calibration error caused by misalignment of a right-angle linkage monochromator
Authors: Kim K. H. , Bell M. I. , Dozier C. M. , Freitag R. K. , Bouldin C. E.
Published: July 2002

Small alignment errors of right-angle linkage monochromators typical to many x-ray absorption fine structure beamlines can cause significant errors in the energy calibrations. A 1° misalignment produces errors greater than 1 keV over the hard x-ray operating range of a typical monochromator. The energy error caused by such misalignments is analyzed and its mathematical form given. The error can be corrected by inverting the expression and the amount of misalignment determined by accurate energy measurements at a few points. The accuracy of the corrections is tested. The effects of this error on x-ray absorption fine structure data and their interpretation are also discussed.
Protection of fast and sensitive preamplifiers
Authors: Mahajan S. M. , Sudarshan T. S.
Published: July 2002

An extremely simple and inexpensive scheme for the protection of preamplifiers is reported. A protection scheme consisting of seven pairs of back-to-back diodes was used to measure low voltage level (<0.1 V), high frequency (400 MHz) signals with a relatively high gain of ∼35. The protection scheme could limit the voltage surge caused by a 100 kV breakdown in a compressed gas test gap to less than ∼3 V at the input of the preamplifier thereby providing adequate protection.
An impulse compression/tension loading technique for microscopic materials strength studies
Authors: Fishbine B. H.
Published: July 2002

In materials testing it is well known that material strengths depend on: loading rate, whether loading is compressive or tensile and, in some cases, previous loading history; a widely useful loading technique should provide adjustable loading rate and reproducible compressive or tensile loading. Further, real-time microscopic studies require localized loading in a predetermined region−the microscope field of view. Symmetrical axial loading of cylindrical specimens can provide predetermined loading localization. Symmetrical loading may also facilitate analysis by localizing loading within a region of specimen material far from interfaces with other material or fixed or free ends. We describe a symmetrical impulse loading technique for compressive or tensile microscopic response studies. The technique is based on the use of magnetically induced stress waves and is capable of microsecond pressure pulse widths, ≳10 000 psi pressure peaks and nanosecond synchronization of the symmetrical loading pulses. Our goal is to observe in real time the response of structural materials at the micron level with a scanning electron microscope.
A novel boundary layer sensor utilizing domain switching in ferroelectric liquid crystals
Authors: Parmar D. S.
Published: July 2002

A new sensor for optical detection of shear stress field induced by air or gas flow on a rigid surface is reported. The sensor uses the novel effects of shear induced optical switching in ferroelectric liquid crystals. The principle of operation of the sensor is described and a theoretical model for the optical response to shear stress is given. Director dynamics and system-free energy considerations predict a system response time ≊10 ns for an applied shear stress step of ≊700 Torr. A thin (≊1 μm) ferroelectric liquid crystal film coated on a flat glass model surface is exposed to gas flow from a micro wind tunnel attached to the polarizing microscope employed for optical measurements. Schlieren texture of the thin film consists of two stable domains separated by a domain wall. Gas or air flow on the liquid crystal surface induces director reorientation resulting in optical contrast. Transmitted and reflected light intensities from polarization microscopy provide measurement of the flow parameters. System response time τ∼150 μs has been estimated from the material viscosity and the time variation of the applied shear stress in the experiment. Optical response is linear for applied differential pressures up to ≊800 Torr beyond which it tends to saturate. Second-order nonlinear effects are observed for flow rates beyond ≊42 ℓ/min. The configuration used in the present method overcomes many of the limitations of similar measuring techniques including those using cholesteric liquid crystals. The present method offers a preferred alternative for flow visualization and skin friction measurements in wind-tunnel experiments on laminar boundary layer transition investigations.
Laptop chemistry: A fiber-optic, field-portable, near-infrared spectrometer
Authors: Lysaght Michael J. , van Zee James A. , Callis James B.
Published: July 2002

We describe a fiber-optic, field-portable spectrophotometer for measurement in the near-infrared (NIR) (680–1050 nm) region of the spectrum. This instrument, bundled with a laptop computer for data acquisition and statistical analysis, has a footprint of only 6 in.×14 in.×18 in. and weights approximately 20 pounds. The instrument uses the single beam measurement principle by employing a grating-based spectrograph for wavelength dispersion and a silicon photodiode-array (PDA) as detector. A computer-controlled, optically stabilized 5.5-W tungsten lamp is used as the light source. Sample measurements are made with a bifurcated fiber bundle for noninvasive diffuse reflectance and/or transflectance measurements. The portable spectrometer attains an RMS signal-to-noise ratio of 1.24×10−5 AU, stray light intensity levels of 0.1%, spectral resolution of 25 nm, and a dynamic range of approximately three orders of magnitude. The analysis of three-component hydrocarbon mixtures by transflectance NIR spectroscopy is demonstrated.
Rotating dynamic seal for use under high pressure
Authors: Doremus P. , Piau J. M.
Published: July 2002

The design of a sealed rotation point suitable for use under a nitrogen pressure of 8000 bars and a shaft rotation speed of 1.5 rpm is described. Several metallic and plastic materials forming the seal were tested using the same geometry. The test conditions and characteristics of the seal friction torques are described. Certain plastic materials (especially PA6 G Oil) are of particular interest as they ensure good sealing and display a low, stable average friction torque.
Three-dimensional recording and measurement of swimming paths of micro-organisms with two synchronized monochrome cameras
Authors: Baba Shoji A. , Inomata Shoko , Ooya Mayumi , Mogami Yoshihiro , Izumi-Kurotani Akemi
Published: July 2002

Instrumentation is described that permits analysis of the three-dimensional (3-D) swimming paths of micro-organisms. The signals from two monochrome cameras for the front and side views of micro-organisms are encoded into a composite signal for a video tape recorder (VTR). The signals decoded from the VTR or those directly from the cameras are processed by computer.
A sealed-off tunable boron nitride waveguide CO2 laser
Authors: Xiaoyong Hu , Fengmei Liu , Taixun Zhu , Jingshan Zhao , Shuqin Lou
Published: July 2002

This note first reports the operation and the characteristics of a completely sealed boron nitride (BN) waveguide CO2 laser with an operating time of over 400 h. Up to now it was still operating with an output power of 1.8 W. The original power output was 2.1 W.
Time-resolving electron energy spectrometer
Authors: Weidman D. J. , Rhee M. J. , Schneider R. F.
Published: July 2002

A compact, time-resolving, electron energy spectrometer, which measures the temporal energy behavior of a pulsed relativistic electron beam, is described. It is shown that typical experimental results obtained with an ∼700-keV, 100-ns electron beam are qualitatively in excellent agreement with the diode voltage waveform.
A multiple path cell, without mirrors, for far infrared spectroscopy
Authors: Marteau Ph. , Obriot J.
Published: July 2002

We describe a new type of multiple-path cell with internal reflections but without mirrors. Its principle is based upon the high reflecting power of some metals. The light beam is directly reflected on the internal walls of the cell in which it goes back and forth before partially and gradually leaving through an exit light hole. The device is particularly well adapted to far infrared spectroscopy at room temperature and even more at lower temperatures. Its main advantages are a reasonable volume and the absence of any optical adjustment. It is shown that the maximum efficiency can be reached only under peculiar geometrical conditions, so as to get a uniform intensity distribution of the light through the cross section of the cylindrical cell. The relation between the experimentally measured quantity and the true absorption coefficient is established. Some spectra obtained with the cell are also shown.
A beamline zero-degree spectrometer for measurements of projectile fragment distributions
Authors: Souliotis G. A. , Morrissey D. J. , Sherrill B. M.
Published: July 2002

A technique for using a section of a beamline as a zero-degree spectrometer is described. The beamline magnets of the K1200 cyclotron at NSCL were operated as a zero-degree medium acceptance spectrometer to measure projectile fragment distributions. Projectile fragments were produced in a fragmentation target at the exit of the cyclotron and detected at the end of the beamline with a detector array consisting of two position-sensitive detectors and a ΔE−E telescope. Energy loss, position and angle at the focal plane and time of flight were measured for the isotopes produced. A procedure was developed to calculate the reaction angle and the momentum of the isotopes from the measured quantities. Typical examples of momentum and angular distributions of projectile fragments from a 14N beam at 75 MeV/u with Al and Ta targets at and near 0° are shown.
Digital feedback control loops for scanning tunneling microscopes
Authors: Morgan B. A. , Stupian G. W.
Published: July 2002

Many circuit functions can now be realized using digital rather than analog techniques. The application of digital signal processing (DSP) technology for the implementation of the feedback control loop of a scanning tunneling microscope is discussed. A system that utilizes a commercially available PC AT-compatible plug-in card based on the Texas Instruments TMS320 series of digital processing chips to implement a loop controller of the proportional-integral-differential type is described. The advantages afforded by DSP in comparison to analog systems include greater flexibility in the choice of the signal processing algorithm and greater ease of control of loop parameters by the host computer.
Use of a silicon surface-barrier detector for measurement of high-energy end loss electrons in a tandem mirror
Authors: Saito T. , Kiwamoto Y. , Honda T. , Kasugai A. , Kurihara K. , Miyoshi S.
Published: July 2002

An apparatus for the measurement of high-energy electrons (10–500 keV) with a silicon surface-barrier detector is described. The apparatus has special features. In particular, a fast CAMAC transient digitizer is used to directly record the wave form of a pulse train from the detector and then pulse heights are analyzed with a computer instead of on a conventional pulse height analyzer. With this method the system is capable of detecting electrons with a count rate as high as ∼300–400 kilocounts/s without serious deterioration of performance. Moreover, piled up signals are reliably eliminated from analysis. The system has been applied to measure electron-cyclotron-resonance-heating-induced end loss electrons in the GAMMA 10 tandem mirror and has yielded information relating to electron heating and diffusion in velocity space.