bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave detecting diode rise-time measurements
Authors: Ballard W. P. , Earley L. M.
Published: July 2002

Investigators of high-power microwave sources have recently become interested in measuring the rise times of their detecting diodes. It has become important to know these limits because pulses as short as 5 ns are produced by some devices. A simple method to test diodes requiring only an oscillator, a mixer, and a high-bandwidth oscilloscope is described. A number of diodes have been tested and their properties are reported.
Experimental performance of a microwave cavity plasma disk ion source
Authors: Root Joseph , Asmussen Jes
Published: July 2002

The detailed description and performance characteristics of a microwave ion source are presented. This ion source utilizes an internally tuned, single-mode (or selective multimode) cylindrical cavity applicator to focus and match microwave energy into a disk-shaped discharge zone. The combination of mode focus control and variable, internal cavity matching allows the efficient operation and beam extraction over a wide range of pressures, powers and gaseous inputs. Experimental measurements of ion beam current versus accelerating voltage and input microwave power in xenon and oxygen gas are presented. Ion source specific energy and mass utilization versus experimental variables are also determined. The experimental performance demonstrates the ability of this ion source to extract an ion beam with a well matched, stable, and continuous operation over a wide range of input gases, low pressures, and over input gas flow rates in excess of 100 to a few sccm. Double Langmuir probe measurements in xenon gas indicate high degrees of ionization, and electron and ion concentrations in excess of 100 critical densities in the microwave discharge zone. This ion source has many potential uses such as spacecraft electric propulsion, material ion beam processing, and neutral beam ion sources.
Beam isolated Michelson interferometer for Fourier transform infrared spectroscopy
Authors: Man C. K. , Tardy D. C.
Published: July 2002

An enhanced Michelson-type interferometer using two beam splitters and corner cubes has been constructed from readily available components. The interferometer is controlled by a microprocessor which also performs the Fourier transform. This instrument can be used in continuous or stepwise scan modes with signal averaging and can be configured for single or double beam (source) operation.
Fiber optics for low-temperature spectroscopy: Applications to photoluminescence from (Cd, Mn)Te
Authors: Heiman D.
Published: July 2002

A simple fiber-optic system for optical spectroscopy is demonstrated. It allows experiments to be performed at low temperatures without an optical Dewar. This low-cost apparatus is useful for a variety of optical experiments such as photoluminescence, reflectivity, and absorption, in addition to polarization measurements such as Faraday rotation. The main feature is an all-glass system made from commercially available fiber-optic cables and glass rods, and contains no focusing optics. Small diameter (<1 cm) sample holders are constructed that fit conveniently into storage Dewars or small diameter Dewars for high-field magnets. Large diameter (few mm) flexible fiber bundles permit efficient coupling to inexpensive light emitting diode (LED) sources and to fiber-optic illuminators. Fiber-optic measurements of photoluminescence in Cd1-xMnxTe, x=0.1, at high magnetic fields is illustrated.
Active-wall device for the generation of small traveling surface waves
Authors: Park Joel T. , Silvus H. Stanley , Cerwin Steve A.
Published: July 2002

An all solid-state electromechanical device has been developed which produces short-wavelength traveling surface waves. The active wall was nominally designed for the cancellation of Tollmien–Schlichting waves in a laminar boundary layer in water. The primary purpose of the device was determination of traveling surface wave characteristics which are important for drag reduction with compliant coatings. Wave form, wave speed, frequency, and amplitude are independently selectable. Sinusoidal wall motion, measured in air with an electro-optical displacement sensor, ranged from 0.6–13 μm over a frequency span of 10–150 Hz. Roll-off frequency at the −3 dB point was 120 Hz, while the maximum phase speed was 166 cm/s. The electronic subsystem is a hybrid analog/digital device, and the active wall employs piezoelectric ceramic elements to produce surface motion.
Collimated ZnS (Ag)-detector array for Tokamak Fusion Test Reactor neutron source strength radial profile measurements
Authors: Hendel H. W. , Ku L. P. , Long D. C. , Nieschmidt E. B. , Strachan J. D.
Published: July 2002

Time-resolved radial profile measurements of neutron source strength and Ti are required to determine ion energy balance especially during sawtooth oscillations and adiabatic compression. We describe the Tokamak Fusion Test Reactor (TFTR) vertical multichannel (10) collimator, two channels of which are now being completed. ZnS detectors will be used (Bicron 720) to reject γ rays and scattered neutrons, and operated in both count rate and current modes. The frequency response is limited by counting statistics and sampling times, but resolves compression times ≂15–30 ms and Ti collapse times during sawtooth ≂2–3 ms. The collimator consists of the 6-ft test cell floor plus ∼2-ft detector shield. Detector cross talk is calculated to be negligible. The dynamic range of the detectors is ≳106, covering the range from ohmically heated deuterium (2.5 MeV neutron emissions of ≳1013 s−1) to deuterium-beam heated tritium plasmas (14 MeV, ≲1019 s−1).
3He gas scintillation spectrometer for fusion neutron measurements
Authors: Derzon M. S. , Slaughter D. R. , Prussin S. G.
Published: July 2002

A high-efficiency, good resolution neutron spectrometer can obtain time-resolved fusion rates and mean ion energies from yield and Doppler width measurements of the 2.5 -MeV neutron peak. Gas scintillation spectrometers are capable of operating at high data rates. In order to obtain adequate energy resolution large light yields and uniform light collection over the active detector volume are required. We have measured the absolute light yield from He–Xe gas mixtures. With a high light collection efficiency the detected photon yield from the 3He(n, p)t reaction due to D–D neutrons will give adequate statistics for resolutions of a few percent. Calculations have been performed to model the detector optics in an effort to optimize the light yield and the uniformity of response. Measurements of detector resolution and time response have been made.
Scaling of heavy ion beam probes for reactor-size devices
Authors: Hickok R. L. , Jennings W. C. , Connor K. A. , Schoch P. M.
Published: July 2002

Heavy ion beam probes for reactor-size plasma devices will require beam energies of approximately 10 MeV. Although accelerator technology appears to be available, beam deflection systems and parallel plate energy analyzers present severe difficulties if existing technology is scaled in a straightforward manner. We propose a different operating mode which will use a fixed beam trajectory and multiple cylindrical energy analyzers. Development effort will still be necessary, but we believe the basic technology is available.
Ultrahigh-vacuum double-axis goniometer for angle-resolved spectroscopies
Authors: Martini K. M.
Published: July 2002

Described here is a double-axis goniometer currently used in angle-resolved neutral atom beam scattering. A special feature is the decoupling of the two rotation axes. An additional design concept is flexibility; the device can be adapted to almost all existing UHV systems, independent of port position and size, and of chamber diameter.
Instrument to measure the polarization state of waves
Authors: Olson John V. , Domke R.
Published: July 2002

We report here on the design and implementation of analog circuitry which allows the processing of the components of vector waveforms to obtain polarization information. The waveforms are the voltages derived from orthogonal sensors such as magnetometers or seismometers which provide information on the time variation of vector processes. The circuits take the voltages from the individual sensors and process them to produce estimates of the spectral matrix at a particular frequency. From the components of the spectral matrix one may determine the wave polarization parameters including the signal power, ellipticity, handedness, and orientation of the polarization ellipse. In cases where the information of interest to the investigator depends upon the relatively slow modulations of a carrier and not upon the frequency of the carrier itself, the preprocessing of the spectral information as described here allows the investigator to sample the data at a much reduced rate, or with a narrower bandwidth, without loss of information. We have implemented the circuits described in our investigation of electromagnetic waves in the ULF (3 mHz–3 Hz) frequency band and have achieved a reduced demand for storage and processing capacities in the project.
Simplified theory of variable impedance stripline under pulse excitation
Authors: McWright Glen M.
Published: July 2002

This paper describes a simple method to predict the transient response of variable impedance stripline to pulse excitation. The technique uses a finite-difference-based quasi-static impedance formulation to calculate the reflection coefficient at each point along the direction of pulse propagation. Excellent correlation between predictions and results obtained via time-domain reflectometry was noted.
Very simple torque magnetometer for measuring magnetic thin films
Authors: Tejedor M. , Fernandez A. , Hernando B. , Carrizo J.
Published: July 2002

A new torque magnetometer has been developed and built in order to measure magnetization saturation and perpendicular anisotropy of magnetic thin films. Its main characteristic is that it employs for counteraction the torque exerted on the sample in the same field used for exciting it. This gives rise to a great simplicity and sensitivity of the measuring system.
Cryogenic photoemissive electron source
Authors: Wilen L. A. , Giannetta R. W.
Published: July 2002

A compact, low-energy electron source for use at cryogenic temperatures is described. The device uses quartz optical fibers and a discharge lamp to excite photoelectrons from a cold zinc emitter. Picoampere currents are obtained with low heating. The source has been used in studies of surface-state electrons on liquid helium.
Comparison of continuous moisture monitors in the range 1 to 15 ppm
Authors: Mehrhoff T. K.
Published: July 2002

Electrolytic, chilled mirror, and aluminum oxide dielectric hygrometers were evaluated by exposing them to known moisture levels in gaseous argon. The experiments were performed over a period of several months to determine the long-term hysteresis effects which may occur under continuous operation in the range of 1 to 15 ppm (parts per million). Air exposure effects were also examined. The results indicated hysteresis and drift problems in the case of the aluminum oxide dielectric hygrometers. The electrolytic hygrometer required a ‘‘recovery’’ period following exposure to high moisture levels. The chilled mirror hygrometer (with certain specified modifications) proved to be the most accurate and responsive in the 1- to 15-ppm test range.
Energy dispersive x-ray diffraction in the diamond anvil, high-pressure apparatus: Comparison of synchrotron and conventional x-ray sources
Authors: Spain Ian L. , Black David R.
Published: July 2002

An analysis is given of the rate at which photons are incident on a sample in a diamond anvil high-pressure cell, from a conventional, fixed-anode source, and a synchrotron source. Comparison is then made of the rate at which photons can be detected for an energy-dispersive diffraction experiment. The rate at which photons are detected in synchrotron experiments is limited by detector electronics, so that the relative photon detection rate is considerably lower than theoretically possible.
Evolution of low-density Thomson scattering on ELMO Bumpy Torus
Authors: Cobble J. A.
Published: July 2002

The ELMO Bumpy Torus (EBT) confines a low-density, steady-state, microwave-driven plasma. On the basis of favorable initial diagnostic results, major machine upgrades—increases in microwave power and magnetic field—were initiated, and the feasibility of Thomson scattering was considered. From the time of the first laser measurements, in which a two-point spectrum was integrated during 30 or more Q-switched pulses, the Thomson scattering system has evolved into a reliable diagnostic tool that is able to obtain scans along 20 cm of the plasma diameter and to determine the central electron temperature at densities as low as 2×1011 cm−3. Based on a 25-J ruby laser and a seven-channel polychrometer, the present system (1) reveals a bulk plasma with Te=20–100 eV and ne=5–10×1011 cm−3 and (2) indicates a suprathermal tail consistent with x-ray measurements. With up to 200 kW of microwave power inside the machine, major problems to overcome were radiation damage to optical materials (≤3000 R/h) and plasma coating of windows and dumps.
Experimental verification of the grid effects in a velocity analyzer with variable geometry
Authors: Donoso Guillermo , Martin Pablo , Puerta Julio
Published: July 2002

A velocity analyzer with adjustable interelectrodic distances is described here. Several experiments have been performed in a double plasma machine with this analyzer of variable geometry in order to investigate the effects of the discontinuous structure of the grids. The measured displacements of the characteristic curve for different interelectrodic distances show excellent agreement with the theoretical predictions due to the depletion of the discriminating potential in the holes of the grid, as is shown in our recent theoretical analysis using a Schwarz–Christoffel transformation. The influence of the grid structure on the temperature determined from the characteristic curve is also investigated and the correlation experiment theory is qualitatively correct.
Powerful 160-keV neutral deuterium beam injector for application in fusion research
Authors: Fumelli M. , Bayetti P. , Becherer R. , Bottiglioni F. , Desmons M. , Jequier F. , Pamela J. , Raimbault P. , Valckx F. P. G.
Published: July 2002

A 160-keV neutral deuterium beam injector has been developed for plasma heating in JET (Joint European Torus) fusion experiment. This injector has been reliably operated at 5.9-MW extracted deuterium ion beam power (37-A, 160-keV ion beam) and 5-s pulse duration. The neutral beam power was 1.75 MW corresponding to an overall neutral injector power efficiency of 30%. The beam divergence was 0.6°. The ion beam was accelerated with a three-grid multiaperture system (aperture diameter φ=11 mm). The accelerating gap length was 24 mm. The extracted deuterium ion current density amounted to 150 mA/cm2. Grid and source body power loadings were acceptable for quasi-steady-state operation.
Flash x-ray source of intense nanosecond pulses produced at high repetition rates
Authors: Collins C. B. , Davanloo F. , Bowen T. S.
Published: July 2002

Described here is a repetitively pulsed, flash x-ray source capable of emitting 35-mW average power in 6-ns pulses of radiation near 1.5 A. From this device a significant fraction of the output is represented by the K lines of copper, so that in less than 1 min of experimental time a peak spectral density is radiated that exceeds 2×1017 keV/keV. For some applications this device can offer a laboratory alternative to laser plasma x rays or synchrotron radiation.
Short-length large-bore metal vapor cell
Authors: Ueda K. , Hill W. T. , Ginter M. L.
Published: July 2002

Stainless-steel cells with a small cooled length (window to hot zone) to tube diameter ratio designed for use at electron storage rings have been constructed and tested using barium metal. Under optimum conditions of barium sample size and helium buffer gas pressure the cell and oven system can be operated for at least 8 h with constant (within experimental errors) line-of-sight number densities, Nl, of ∼1016 cm−2. When Nl values begin to fall toward the end of their initially constant period or the light path becomes blocked by barium condensed at the edge of the hot zone, the original cell conditions can be regenerated within 15 min. These regeneration procedures provide essentially unlimited (though segmented) operation of the system with constant Nl values.
Rapid scanning autocorrelator for measurements of ultrafast laser pulses
Authors: Myslinski Piotr
Published: July 2002

A rapid scanning autocorrelation interferometer for measurements of ultrafast laser pulses is described. The optical system is based on a new type of beam splitter allowing one to send all of the input beam power to the SHG crystal making the SHG signal four times greater than in the standard designs. Autocorrelation measurements of transform limited picosecond pulses from a synchronously pumped mode-locked dye laser are presented.
Use of ‘‘Five-Minute Epoxy’’ as a cryogenic leak sealant
Authors: Martin Douglas L.
Published: July 2002

‘‘Five-Minute Epoxy’’ has been used successfully to mend small leaks in a liquid-helium cryostat; it is an alternative to more specialized epoxies for this purpose.
Multichannel dynamic light-scattering system for measuring bacterial motility
Authors: Kobayasi Syoyu , Imae Yasuo
Published: July 2002

In aiming to reduce the duration of measurement, a four-channel dynamic light-scattering system was developed. The four independent lights scattered at a fixed angle from a sample were detected in homodyne mode by a four-channel photon counter. The accumulation and analysis of the data were carried out with a microcomputer. By this four-channel system, swimming speed of bacteria was measured within 15 s with a statistical error of a few percent.
Electrical contact to semiconducting samples for use in the diamond-anvil cell
Authors: Patel Dinesh , Spain Ian L.
Published: July 2002

Techniques are described for preparing electrical contacts to samples for measurements in the diamond-anvil high-pressure cell. Typical dimensions are 150×150×30 μm. Bulk, epitaxial, and multiple-quantum well (MQW) structures on GaAs and InP wafers have been successfully contacted. The techniques are also suitable for other experiments than those at high pressure, where miniaturization is important.
On the spatial and temporal resolution of ion temperature measurements based on neutral beam scattering: Comment on ‘‘Design of an ion temperature diagnostic based on neutral beam scattering’’ [Rev. Sci. Instrum. 5
7, 1792 (1986)]
Authors: Donné A. J. H. , Barbian E. P.
Published: July 2002

Small-angle neutral beam scattering is a promising technique to measure the local ion temperature in a hot plasma. We will show that in general a 10% accuracy in the temperature measurement can be obtained with a temporal resolution in the order of 1 ms and a spatial resolution of 10 cm. These values are less favorable than previous claims by Van Heesch et al.
Effects of electrode design on null point motion of spheres suspended in the electrodynamic balance
Authors: Eversole J. D. , Lin H.-B.
Published: July 2002

Three similar but geometrically distinct electrode designs for an electrodynamic balance or quadrupole particle levitation cell have been compared in terms of the minimum periodic motion, or ‘‘null point’’ motion of single, suspended glass spheres of either 30 or 11 μm in diameter. The three electrode surface designs included the ideal hyperbolic shape, similar but spherical surfaces, and spherical surfaces in which the center ring electrode was split. The motion of the glass spheres was determined by forming an interferometer from scattered laser light and a reference beam using a single frequency He–Ne laser. A heterodyne signal was generated by shifting the frequency of the reference beam an arbitrary but known amount. No significant distinctions in terms of small amplitude motion were observed among the different cell designs. All three cells were able to suspend and stabilize a 30-μm sphere to an rms amplitude of motion of less than 0.14 μm. For each of these designs, dependence of the particle motion on the dc balancing voltage was measured, and the effect of other operating parameters determined. Also, previously unreported sensitivity with regard to the vertical tilt of the cell axis was observed.
Broadband calibration for magnetic probes for use in the Maryland spheromak
Authors: Shaw R. S. , Booske J. H. , McCarrick M. J.
Published: July 2002

Magnetic probes are commonly used in plasma experiments to measure the magnetic and plasma properties of the configuration. Probes consisting of coils of copper wire encased in one or more layers of stainless-steel tubing are used both inside and outside the plasma to measure the magnetic field in the Maryland spheromak. A technique has been developed to calibrate the probes over a large frequency bandwidth using digital computer signal processing. The frequency-dependent effects of the stainless-steel tubing and the self-inductance of the coils on the recorded signal are taken into account over the entire bandwidth. This technique may also be used to take into account the eddy currents present in the metal vessel walls.
Signal processing circuit for a mass flow rate digital meter design
Authors: Abdul-Hameed Kamal Hilal , Abdul-Karim Majid A. H.
Published: July 2002

This paper introduces the design of a signal processing circuit which can be used in conjunction with additional arrangement for measuring gas mass flow rate. Measurement is based on Bernoulli’s equation for subsonic flow. Voltages representing gas static pressure, static temperature, and difference pressure generated across an orifice plate are supposed to be taken from appropriate transducers. These voltages are processed with this circuit in such a way as to produce a digital number representing the mass flow rate value. The circuit shows a good accuracy result with uncertainty of about ±0.1%.
UHV deposition system for quench condensation and i
n s
i
t
u study of amorphous transition metal alloy films
Authors: Naugle D. G. , Bandyopadhyay B. , Bo Yin , Nicoli V. M. , Wang F.-C. , Rathnayaka D.
Published: July 2002

An UHV deposition system for the production of amorphous transition metal alloy films by quench condensation from the vapor phase onto substrates held at liquid-helium temperature is described. The system can be operated with either of two helium cryostats which are designed for different in situ experiments. One of the cryostats incorporates a superconducting solenoid for superconducting critical field, Hall effect, and magnetoresistance measurements from 1.4 to 300 K in fields to 7 T. The other, which provides a larger working space, can be used for a variety of in situ experiments (a rapid survey of the properties of amorphous alloys as a function of concentration, thin-film heat capacity measurements, or superconducting tunneling experiments) between 1.4 and 300 K. Critical field and Hall coefficient measurements for amorphous Ti–V alloys and tunneling results for amorphous gallium films are presented to illustrate the system capabilities.
Capacitance dilatometer for i
n s
i
t
u measurement of radiation-induced dimensional changes of solids
Authors: Tanimura Katsumi , Itoh Noriaki , Arima Kazuaki , Imaike Hiroshi , Heikkinen Dale W.
Published: July 2002

We describe a new capacitance dilatometer for measuring radiation-induced volume change of solids having high stability and capability of measuring a fractional length change of 10−6.
Diagnosing high-reliability, low-jitter Marx generators
Authors: Lockwood G. J. , Schneider L. X. , Neyer B. T. , Ruggles L. E.
Published: July 2002

We have made photonic measurements to assess the performance of a bipolar Marx generator. Measurements of the switch-closing sequence were made with a high-speed multichannel data recorder using fiber optics to monitor the light produced by each switch closure. Experience gained during this research coupled with computer simulations has led to a fundamental understanding of the operation of these multistage devices. As a result of this research, significant improvement in erection time jitter has been realized. Erection time jitter has been measured as low as 2.6 ns for a 3.2-MV, 16-stage PBFA-I Marx generator. Photonic data are presented from this research program, along with a discussion on the use of computer simulations and photonic measurements in designing low-jitter Marx generators.
Noise properties of analog correlators with exponentially weighted average
Authors: Dmowski K. , Pióro Z.
Published: July 2002

Detailed calculations of the root-mean-square value of the output noise of correlators with an exponentially weighted average and an arbitrarily chosen weighting function for three commonly used mathematical models of white noise are derived. A comparative analysis has been made of noise properties of correlators with exponentially weighted average and true average based on two figures of merits: the output signal-to-noise ratio and the signal-to-noise improvement ratio. An analysis of noise properties of a boxcar averager for any gate width is performed. Expressions for the output signal-to-noise ratio and the signal-to-noise improvement ratio of a boxcar averager are derived.
Electron-impact ionization time-of-flight mass spectrometer for molecular beams
Authors: Pollard J. E. , Cohen R. B.
Published: July 2002

A method is described for performing electron-impact ionization time-of-flight mass spectrometry in a molecular beam apparatus. It provides a convenient means for optimizing the performance of pulsed or continuous nozzle sources and can be used in conjunction with laser excitation. Mass spectra are produced either as analog waveforms or in a high repetition rate ion counting mode. The device can also be operated as a fast ionization gauge for time-resolved detection of pulsed beams.
Kratky block-collimation small-angle x-ray diffractometer for synchrotron radiation
Authors: Chu Benjamin , Wu D.-Q. , Wu C.
Published: July 2002

A block slit collimation system of the Kratky design concept has been modified and adapted for synchrotron radiation. The building block small-angle x-ray diffractometer (SAXD) not only retains the essential advantages of the Kratky camera, i.e., accessibility at small values of q[=(4π/λ)sin(θ/2) with λ and θ being the x-ray wavelength and the scattering angle, respectively] and ease of alignment, but also provides portability and low construction cost. With our SAXD operating at the SUNY X21A beamline of the National Synchrotron Light Source, we were able to reach θ∼1 mrad corresponding to q∼0.04 nm−1 (or a Bragg spacing of 150 nm) using an incident slit width (d) of 0.5 mm and λ=0.15 nm. At d=0.5 mm, ∼10% of the monochromatic synchrotron x-ray radiation passed through the block collimation system and a parasitic intensity to main beam intensity ratio of ∼10−5 at θ=1 mrad was achieved. With d∼0.1 mm, it is anticipated that q ∼0.01 nm−1 can be accessible. By changing the vacuum tube length between the sample chamber and the beam stop from ∼1400 to ∼200 mm, we could reach an intermediate q range of ∼0.04≲q≲10 nm−1 using a 5-cm-long linear position-sensitive detector with a resolution of ∼100 μm/channel. A description of the SAXD and its operation is presented.
Theoretical modeling and experimental testing of a multimode optical system and energy analyzer for electron spectroscopy
Authors: Chou Y. C. , Robrecht M. J. , Tonner B. P.
Published: July 2002

An electron-optical system and hemispherical electrostatic energy dispersing element for quantitative electron spectroscopy over a wide range of kinetic energies is described. The electron optics were modeled using several calculational techniques, in order to determine the theoretical conditions under which a fixed linear magnification could be obtained. By designing an optical system with a plane of reflection symmetry, fixed magnification focus was possible over a calculated range of retard ratios from 1/40 to 40/1. The optics can be run in two different modes, one with and one without a retarding field grid to achieve the energy retardation. Comparisons between the predictions made using the various computational methods are reported, as well as experimental verification of the actual performance of the electron optics and energy analyzer. A method is described by which the angular acceptance of the electron optics can be varied by changing the excitation potentials on the lenses. The completed system allows for the simple installation of single-channel, multichannel, and spin-polarization detectors without modification of the analyzer.
Time-resolved visible spectroscopy of laser-produced lithium plasmas
Authors: Bailey J. , Tisone G. C. , Hurst M. J. , Morrison R. L. , Bieg K. W.
Published: July 2002

We have measured time-resolved visible spectra emitted from a plasma formed when the output from a dye laser irradiates solid lithium. Such a plasma has potential as a source of lithium ions for ion-driven inertial confinement fusion, and it also provides a useful source for developing diagnostics. The laser delivered 0.5 J onto a 2–7-mm-diam spot, with a 900-ns pulse length. Experiments were performed with the wavelength tuned to the Li i 2s–2p resonance line at 6708 Å and off resonance at 6728 Å. The target was a 500–1000-Å-thick Li film, vacuum evaporated in situ onto a substrate. The light from the plasma was coupled into the entrance slit of a 1-m Czerny–Turner spectrograph, and the output from the spectrograph was focused onto the input slit of a streak camera. The electron density was obtained from Stark-broadened widths of Li i 2p–4d, 2p–5d, and 2p–4s, and H i 2p–4d. An irradiance of 2×106 W/cm2 at 6708 Å resulted in a peak electron density of 3.9×1017 cm−3. The density decreased at lower irradiance, with an intensity threshold of 5×105 W/cm2 for producing an ionized plasma. The threshold for producing a plasma was higher with the laser tuned off resonance, although high-density lithium plasmas could still be formed at relatively low laser irradiance.
Microdetector for rapid changes of oxygen partial pressure ( pO2) during the respiratory cycle in small laboratory animals
Authors: Barnikol W. K. R. , Gaertner Th. , Weiler N. , Burkhard O.
Published: July 2002

An oxygen microdetector suitable for respiratory experiments with small laboratory animals is described. Its principle structure is an O2-sensitive dye layer. To measure pO2 the capability of O2 to quench the fluorescence of dyes is used. The instrumental dead space of the detector amounts to 0.1 ml only. The detector indicates 90% of a concentration jump from 20 to 15 vol. % O2 in less than 20 ms without any dead time. Neither O2 nor sample volume are consumed. The special setup of the dye layer prevents CO2, N2O, and the humidity of the gas from affecting the fluorescence quenching of oxygen. The mean standard deviation is 0.95% of the relative fluorescence signal between 9.99 and 59.62 kPa pO2. The detector is suitable to measure rapid changes of pO2 in inspired and expired gases and may be enlarged for use in man.
Programmable instrumentation for high repetition rate experiments providing control in real time and acquisition of a train of pulses
Authors: Kraus R. , Treanor M. , Sarjeant W. J. , Dollinger R.
Published: July 2002

An automated, low-cost programmable instrumentation system which solves many of the problems associated with the data acquisition and control of high repetition rate experiments is described. The system can monitor and control experiments on a pulse-by-pulse basis while digitally storing consecutive pulses which occur in the train. The system compares well with manual test equipment and commercial transient diagnostic systems which cannot provide the high-speed control and data acquisition available here. The oscilloscope used to store the train of pulses can digitize at a maximum rate of 100 MHz, and has 32 kbytes of acquisition memory that can be subdivided into a sequence of as many as 250 separate segments. In order to reduce the system software reinitialization time to acquire each successive sequence within the total train, a novel IEEE-488 compatible microprocessor system is used in conjunction with a host personal computer. The microprocessor controls triggering of the experimental equipment based on digitally acquired waveform information. This information is also used to coordinate the reinitialization of the oscilloscope by the host computer. The system can acquire each and every pulse at repetition rates up to 40 Hz. Above this rate, the probability of acquiring a particular pulse in the train falls slightly below unity due to the finite time required to reinitialize the oscilloscope. The maximum synchronously controllable pulse repetition rate of the microprocessor is 20 000 Hz. Minimum performance specifications are provided which are significantly better than other approaches. The system is employed in high-voltage, dielectric breakdown experiments. For the example given, there are 62 segments in the acquired sequence, with a 100-MHz digitizing rate during the 5-μs acquisition time for each segment. The breakdown pulse in the train and as many as 61 pulses preceding it are obtained.
Superior free-standing meshes for use as infrared Fabry–Perot elements made with a new photolithographic technique
Authors: Taylor C. Jackson , Smith Howard A. , Fischer Jacqueline
Published: July 2002

A photolithographic technique for fabrication of very smooth and highly uniform metallic, free-standing, inductive meshes, is described. The fabrication process was developed in order to produce highly reflective, low-loss Fabry–Perot étalon elements for use in the infrared spectral region. The measured rms smoothness of the grids is typically ≤30 Å. Because of their nickel core, the mechanical strength of the grids is such that they can be easily stretched flat on stainless-steel rings.
Position and velocity sensing laser interferometer–fringe counter
Authors: Martin F. , Gauthier J. , Gulick S. , Laroche F.
Published: July 2002

A CO2 laser interferometer and fringe counter, made of commercially available equipment, which can resolve displacements of 5 μm and accurately track velocities of up to 50 m/s in either a positive or negative sense, is described. Coupled to a heterodyne interferometer, this simple fringe-counting circuit does not require exact quadrature to determine the direction of motion, is wideband and capable of high count rates (dc—10 MHz) and will not introduce false fringe counts at phase reversal or due to dithering of the target. A prototype has been built and employed to characterize the operation of a pulsed gas valve.
Dynamic control of flowing gases using a microcomputer
Authors: Gleixner R. A.
Published: July 2002

Equilibrium decomposition pressures of many inorganic substances are difficult to determine using static equilibration methods, particularly at low temperatures where the equilibration time may be excessively long. Additionally, in static experiments metastable conditions can develop so that true equilibrium is not reached. To overcome these problems, the author has previously used a cyclic thermogravimetric technique to study the decomposition of several carbonates. This dynamic method involved cycling the furnace temperature while a gas stream with a fixed partial pressure of CO2 flowed over the sample. This procedure allowed equilibrium to be established rapidly; thus, reliable data were obtained in a much shorter period of time than had been required previously. An alternative cyclic technique for carbonates has now been developed, where the CO2 partial pressure of the flowing gas stream is cycled at a fixed temperature. The cyclic CO2 pressure method has several advantages over other techniques. The decomposition pressure of calcium carbonate as a function of temperature, which is well known, has been measured to test the viability of the cyclic CO2 pressure technique. The results agree well with the previous thermal cycling data and with currently accepted literature values. A detailed description of the cyclic control of the flowing gas stream using a Rockwell AIM-65 microprocessor appears in this article.
Compact, high-stability, ‘‘thimble-size’’ scanning tunneling microscope
Authors: Besenbacher F. , Laegsgaard E. , Mortensen K. , Nielsen U. , Stensgaard I.
Published: July 2002

A new high-stability scanning tunneling microscope (STM) has been developed. Its key design feature is the application of two, concentrically aligned, piezoelectric ceramic tubes, allowing x–y–z motion of the tungsten tip as well as sample mounting to be cast into a single compact unit. The construction is small, very rigid, and temperature compensated, yielding reduced sensitivity to mechanical and acoustic vibrations and temperature variations. Other advantages of this ‘‘thimble-size’’ STM include easy sample mounting and, at a later stage, operation under UHV conditions with access to other surface-analysis (UHV) tools. At present, the microscope is operated in air, and its performance is tested by imaging a highly oriented pyrolytic graphite surface and a Si(111) surface on which a 100-Å-thick Au layer has been deposited.
Aspects of negative-ion generation and extraction from a refocus geometry cesium sputter negative-ion source. II
Authors: Alton G. D.
Published: July 2002

The basic parameters of the refocus geometry cesium sputter ion source for the production of negative ions from a low-sputtering material (carbon) and a high-sputtering material (copper) have been measured. The question of the influence of sample temperature on the negative-ion generation process has been addressed. Negative-ion yields from carbon samples are found to be weakly dependent on temperature over a range from 26° to 400 °C, while those from copper samples are found to be essentially independent of temperature over a range of 26° to 200 °C. The results of these investigations indicate that (1) sample temperature does not strongly influence negative formation in these sources, and (2) the maximum negative-ion yields for a given sample are dependent on both cesium-ion energy and positive-ion current. In addition to these data, the negative-ion extraction optics of the source are briefly discussed and cursory estimates of the probabilities for negative-ion formation presented.
The constricted glow discharge: A stationary source of vacuum–UV rare-gas excimer continua
Authors: Lindau D. , Döbele H. F.
Published: July 2002

The construction and operation of a filamentary discharge in noble gases are described. The power and spectral properties of the observed continuous vacuum–UV excimer radiation are measured and compared with values found with standard VUV sources.
Spin sensitivity of a channel electron multiplier
Authors: Scholten R. E. , McClelland J. J. , Kelley M. H. , Celotta R. J.
Published: July 2002

We report direct measurements of the sensitivity of a channel electron multiplier to electrons with different spin orientations. Four regions of the multiplier cone were examined using polarized electrons at 100-eV incident energy. Pulse counting and analog modes of operation were both investigated and in each case the observed spin effects were less than 0.5%.
Diamond anvil cell and loading system for liquid CO2
Authors: Baggen Michael , Manuputy Ron , Scheltema Ruud , Lagendijk Ad
Published: July 2002

A diamond anvil cell designed for optical experiments at low temperatures is described. The design is focused on alignment stability and accurate pressure adjustment. To fill the cell with liquid CO2 a special technique is employed, combining features from high-pressure and cryogenic-loading procedures. The method has a short cycle time and does not require the use of gas compressors.
An electrostatically and a magnetically confined electron gun lens system
Authors: Bernius Mark T. , Man Kin F. , Chutjian Ara
Published: July 2002

Focal properties, electron trajectory calculations, and geometries are given for two electron ‘‘gun’’ lens systems that have a variety of applications in, for example, electron-neutral and electron-ion scattering experiments. One nine-lens system utilizes only electrostatic confinement and is capable of focusing electrons onto a fixed target with extremely small divergence angles, over a range of final energies 1–790 eV. The second gun lens system is a simpler three-lens system suitable for use in a uniform, solenoidal magnetic field. While the focusing properties of such a magnetically confined lens system are simpler to deal with, the system does illustrate features of electron extraction and Brillouin flow that have not been suitably emphasized in the literature.
Computer-controlled vibrating capacitor technique for determining work function
Authors: Baczyński J.
Published: July 2002

Another technical variation of the Kelvin method and a computer circuit are described for the measurements of the work function or its changes by the vibrator capacitor. The measuring technique of the contact potential difference is based on the detection of the signal phase shift from the vibrating capacitor by a time analyzer. The present technique allows one to obtain precise results and simultaneously to use the capacitor which does not meet high constructional requirements. The described circuit is incorporated into an autonomous CAMAC system which is joined with the Amstrad/Schneider 6128 microcomputer.
Greater voltage gain for Tesla-transformer accelerators
Authors: Reed Jay L.
Published: July 2002

The governing equation of secondary potential is reformatted and analytically optimized. A circuit adjustment is predicted that yields an 18% increase in voltage gain.
Development testing of the U.S. common long pulse source at 120 kV
Authors: Vella M. C. , Cooper W. S. , Pincosy P. A. , Pyle R. V. , Weber P. D. , Wells R. P.
Published: July 2002

The U. S. magnetic fusion energy program has developed a single design, long-pulse neutral beam source for TFTR, MFTF-B, and DIII-D. The arc is a very compact axial magnetic line cusp. The accelerator is an actively cooled tetrode with water-cooled grid tubes of shaped molybdenum forming ‘‘slot’’ beamlets. DIII-D and MFTF-B configurations have an 80-kV accelerator gap, with a 12×18 cm aperture, and a 10-m ‘‘module’’ focus. TFTR modules are unfocused, with a 120-kV gap and 12×43-cm mask. The first CLPS was tested in the TFTR configuration, at 120 kV, 2s. Optimum current was 73 A, or 1.76 μpervs (deuterium), with 80%–85% atomic fraction. Optimum divergence of ions plus neutrals was 0.4° parallel to the slots, and 0.7° perpendicular to the slots (1/e half-angle). The combination of an axial cusp magnetic bucket and slot accelerator apertures gives the common long pulse source about twice the beam power per unit cross section of other long pulse sources, plus lower divergence in the direction parallel to the slots.
Subsurface damage profiling system for semiconductors materials
Authors: Ives N. A. , Leung M. S.
Published: July 2002

Subsurface damage in polished GaAs wafers has been identified by electron microscopy and other surface analytical techniques. The presence of subsurface damage can adversely affect the performance and reliability of a device fabricated on such substrates. In this article, we introduce a method for determining the degree of subsurface damage as a function of depth. Interferometry is used to measure the rate at which substrate material is being etched from the sample. Measuring the etch rate as a function of depth reveals the profile of subsurface damage in the sample. We describe the methodology and present our findings on GaAs wafers that have been subjected to surface damage. Samples obtained from different wafer manufacturers were investigated.
Simulation and interpretation of ion beam diagnostics on PBFA-II
Authors: Mehlhorn T. A. , Nelson W. E. , Maenchen J. E. , Stygar W. A. , Ruiz C. L. , Lockner T. R. , Johnson D. J.
Published: July 2002

Ion diode and beam focusing experiments are in progress on PBFA-II working toward an ultimate goal of significant burn of an ICF pellet. Beam diagnostics on these experiments include a Thomson parabola, Kα x-ray pinhole cameras, filtered ion pinhole cameras, and a magnetic spectrometer. We are developing two new computer programs to simulate and interpret the data obtained from these diagnostics. vida is a VAX-based program that manipulates and unfolds data from digitized particle and x-ray diagnostic images. vida operations include: image display, background subtraction, relative-to-absolute coordinate transformations, and image projection into the beam reference frame. picdiag allows us to study the effects of time-dependent ion focusing on the performance of ion beam diagnostics.
The use of a multigigahertz digital oscilloscope as a full-wave microwave detector for subnanosecond time-resolved microwave conductivity measurements
Authors: de Haas Matthijs P. , Warman John M. , Ron van Ewijk C. , Varma Cyril A. G. O.
Published: July 2002

A ‘‘6-GHz’’ transient digitizing oscilloscope (Tektronix 7250) has been used as a nonrectifying detector of microwaves in the X-band region (8.2–12.4 GHz) to observe subnanosecond transient changes in microwave power level transmitted by a crystal of cadmium sulfide when subjected to flash photolysis (25 ps, 532 nm) or pulse-radiolysis (300 ps, 3-MeV electrons). The response time for monitoring the change in microwave power level following the pulse was found to be approximately 200 ps.
W-band six-port network analyzer for two-port characterization of millimeter wave transistors
Authors: Moeller Karl J. , Schaffner James H. , Fetterman Harold R.
Published: July 2002

A W-band (75–100 GHz) six-port network analyzer was constructed from discrete WR-10 waveguide components for the two-port S-parameter characterization of state-of-the-art submicron gate length high electron mobility transistors. The six-port was capable of measuring the phase of a circuit’s reflection or transmission coefficient to within a 6° and the magnitude to within 1.5% for large reflections and to within 10% for small reflections (return loss of 20 dB). A comparison between the six-port and a down-converter-type frequency extender for a conventional network analyzer revealed the superior performance of the six-port. To demonstrate the applicability of the six-port network analyzer to device characterization, the S-parameters of 0.1-μm gate length HEMTs were measured and then used to calculate the maximum available gain achievable with these transistors at W-band frequencies. These measurements indicate the important role the six-port network analyzer will play in the future development of millimeter wave transistors.
A high-temperature pulsed solenoid valve for supersonic jet introduction up to 550 °C
Authors: Li Liang , Lubman David M.
Published: July 2002

A pulsed solenoid valve which can operate up to 550 °C has been designed for supersonic jet introduction. This valve uses a novel design where the nozzle head, which serves as the hot oven, and the solenoid operator are separated and the latter is maintained at a relatively low temperature using water cooling. A long steel plunger forms a metal-to-metal seal at the orifice which is broken when the magnetic field generated by the solenoid pulls back the plunger. Thus, although the oven operates at the high temperatures required for nonvolatile materials, the solenoid operator and electrical parts remain relatively cool.