bluuebunny/crossref_metadata_2025 huggingface dataset:
Multimegawatt tunable infrared source up to 7.7 μm
Authors: Bierry M. , Frey R. , Pradère F.
Published: March 2003

Efficient generation of high peak radiation has been achieved in the 0.72–7.7 μm region. A dye laser and its Stokes components in hydrogen gas are used to cover the total spectral range with powers between 1000 and 9 MW. The linewidth of the dye laser is 0.07 cm−1. A successful attempt was made to reduce it to 0.02 cm−1 without any change in the output power.
Evaluation of stereoscopic trace particle records of turbulent flow fields
Authors: Elkins III Rush E. , Jackman Gary R. , Johnson Richard R. , Lindgren E. Rune , Yoo Jae K.
Published: March 2003

An experimental technique is described for the recording of instantaneous spatial functions of particles tracing the motion in liquid flow fields. Software development necessary for subsequent computerized numerical evaluation of the instantaneous, three-dimensional flow field also is described. The paper reports only the first stages of software development, in which descriptions are obtained of the detailed structure of turbulence events over whole flow regions simultaneously.
Production of sinusoidally modulated electron beams of high spectral purity
Authors: Norris C. B. , Stuart D. T.
Published: March 2003

This paper describes a system for producing sinusoidally modulated electron beams with cancelled second-harmonic content. The system consists of a predistortion synthesizer, a high-voltage coupling transformer, and a current modulator circuit for a gridded gun. Despite the nonlinear effects inherent in electron beam transport systems, second-harmonic contamination levels at the target have been suppressed to ∼100 ppm. Such beam modulation permits sensitive measurements of the linearity of the beam–target interaction.
Pitch angle measurement of an intense rotating relativistic electron beam
Authors: Roberson C. W. , Saenz G. , Tzach D.
Published: March 2003

The perpendicular and parallel velocity components of an intense rotating relativistic electron beam in a plasma is determined from the damage on Lucite rods.
Channel plate multiplier as an emissive mode detector in the SEM
Authors: Hill M. S. , Gopinath A.
Published: March 2003

A channel plate multiplier was placed between the specimen and scintillator to increase the number of secondary electrons in the emissive mode of operation of the SEM. A comparison between this system and the conventional scintillator detector shows that the presence of the plate improves the signal-to-noise ratio.
Analysis of parallel-plate retarder in electrostatic zoom lens
Authors: Draper James E. , Lee Cheng-yi
Published: March 2003

A simple preretarding lens system is analyzed which involves a parallel-plate retarder B placed between two cylindrical lens systems A and C. The exact transfer matrix elements for the retarder are developed. The system can deliver fixed-energy electrons for any input energy by providing potentials on the upstream lens element which are a fixed fraction of the desired input kinetic energy. The location of the Gaussian image plane of the system is independent of the retarding factor for mode β and nearly so for mode α. In one mode, α, the retarder is at a crossover between lenses A and C. In the other mode, β, the retarder is anywhere in the field-free region between lenses A and C, and the rays from a given point in the object are parallel to each other near B. It is shown that the magnification in mode α can be independent of the retarding factor while that in mode β can be proportional to the square root of the retarding factor. The lens effect of the holes in the two grids is analyzed and a numerical example is given. Electron trajectories are shown for a particular example of lens systems A and C.
High flux medium resolution normal incidence monochromator for sunchrotron radiation
Authors: Lavollee M. , Lopez-Delgado R.
Published: March 2003

Based on the peculiar spatio-optical properties of synchrotron radiation (SR) we have designed a wavelength dispersing system in the normal incidence spectral range, the entrance slit being the tranverse section of the electron bunch itself. The system can work only in conjunction with an SR source and at a given (optical) distance to the electron orbit tangent point. Our design employs very asymmetrical grating conjugates (r∼95 m; r′0.5 m). Tuning is accomplished by simple rotation of the grating. The angle between the monochromator arms is of the order of 4°; the astigmatic length of the image is very short (0.3 mm). In our design, light from the exit slit is refocused by a toroidal mirror to a spot 60 μm in diameter. The optical elements of the system are placed on a vertical plane with respect to the electron orbital plane, so that the already high degree of polarization of SR is increased to 95%. With a 600-grove/mm grating the measured resolving power in the 1500-Å region is of the order of 1000. The flux measured in the same spectral region is of the order of 1010 photons sec−1 Å−1, which gives a transmission factor T∼3×10−2. Some examples of utilization are given.
Transmission experiment for measuring total positron–atom collision cross sections in a curved, axial magnetic field
Authors: Kauppila W. E. , Stein T. S. , Jesion G. , Dababneh M. S. , Pol V.
Published: March 2003

We describe and analyze a transmission experiment developed for measuring total scattering cross sections for low-energy poistrons (0.3–250 eV) colliding with gases in a region containing a curved, axial magnetic field. It is determined that spiralling does not appreciably increase the beam path length through the curved, axial magnetic field in the gas scattering region. An overall test of the experimental apparatus and technique is made by measuring total cross sections for electrons colliding with helium and argon atoms in the energy range from 1.5 to 30 eV, where it is found that the present measurements are within 15% of the most reliable prior measurements.
Crossed slotted tube resonator (CSTR) —a new double resonance NMR probehead
Authors: Schneider H. -J. , Dullenkopf P.
Published: March 2003

The crossed slotted tube resonator (CSTR) is presented as an NMR detection system for induction and double resonance experiments. The intensity of the magnetic rf field and the filling factor are calculated. The construction of the CSTR comprising matching and tuning network is given in detail. A helically twisted feedline saves space in the geometric length, keeps free space for the sample tube, and simplifies the balancing. High decoupling by simple mechanical adjusting favors the well-known advantages of an induction detection system.
Hollow drop production by injection of gas bubbles into a liquid jet
Authors: Calliger R. J. , Turnbull R. J. , Hendricks C. D.
Published: March 2003

An apparatus has been constructed which produces uniform hollow shells of liquid. The techniques used are to ultrasonically excite and inject a gaseous jet into a liquid jet. The physical arrangement consists of dual capillary nozzles with the gas nozzle coaxial to and inside the liquid nozzle. The gas jet is broken up into uniform bubbles by acoustical excitation. The bubbles then break up the fluid jet into uniform spheres which contain the bubbles and therefore are hollow shells. The system was tested with Freon-113 (C2Cl3F3) as the liquid and nitrogen as the gas. This system was built as a prototype to evaluate these procedures before proceeding to construct apparatus to produce solid hydrogen shells.
Multichannel analog transient acquisition system
Authors: Jancarik J. , Kochanski T. P.
Published: March 2003

A 16-channel data acquisition system MATAS-16 capable of receiving data with a sampling frequency up to 40 MHz has been built to process the signals from measurements on the Texas Turbulent Torus experiment. To avoid the necessity of using a number of fast (and expensive) digitizers, the signals are first stored in serial analog memories. Subsequently, they are sequentially read out, digitized, and stored in digital memory. These data are then transmitted to the computer for analysis and are graphically displayed. Delayed trigger, post-trigger, pretrigger, and change of sampling frequency during the data acquisition are also provided.
Resonant optical schlieren system for plasma flow studies
Authors: Siebeneck H.-J. , Koopman David W. , Cobble James A.
Published: March 2003

A dye laser, pumped by ruby second harmonic radiation at 3471 Å, emitting ∼5-mJ, 20-nsec pulses with a bandwidth of 0.3 Å, has been developed as a light source in a schlieren optical system which utilizes enhanced refractivity to examine plasma flow phenomena. When the dye laser is tuned adjacent to the BaII ion resonance line at 4554 Å, the sensitivity of the system to density gradients in a barium plasma becomes 100–1000 times greater than can be achieved with nonresonant light sources which rely on the free electron contributions to plasma refractivity. Absorption effects also yield data on plasma flow patterns.
Method for performing gas gun experiments in two-dimensional strain
Authors: Swegle J. W. , Dick J. J. , Duvall G. E.
Published: March 2003

A method is described for performing shock wave experiments in two-dimensional strain using a light-gas gun. The experimental configuration allows the impact of a projectile on a wedge whose impact face makes an angle α with the projectile impact face. Free surface motion is detected by resistance wires stretched parallel to and offset from the wedge rear surface. The system is capable of producing data over a continuous range of shock propagation distances in a single experiment. Reproducibility is 3%–4% and measurements of free surface speed are accurate to about 5%. Experiments were done on aluminum wedges and on iron and potassium chloride wedges shocked past their transition points. Comparison with computer calculations of the problem shows reasonable agreement. The method appears to be worthy of further development.
High-voltage microsecond pulse-forming network
Authors: Riepe Kenneth B.
Published: March 2003

A large CO2 laser being developed at Los Alamos Scientific Laboratory for fusion research requires a high-voltage, high-power pumping pulse of several microseconds duration. A pulse generator has been developed which provides a flat-topped pulse of 120 kA at 300 kV into a matched impedance load, with a 2.5-μsec pulse duration. The design is based on a combination of the Guillemin and Marx circuits. Eight of these will be used to pump an eight-beam laser system. There are applications for this circuit in other fields, such as electron beams for plasma heating. Design techniques for the pulse-forming network are discussed, including physical layout and triggering techniques.
Compact high-pressure electron-beam-controlled laser system
Authors: Harris N. W. , O’Neill F. , Whitney W. T.
Published: March 2003

The design of a cold-cathode electron gun and its integration into a small high-pressure gas laser system are described. The gun, which has produced current densities up to 4 A/cm2 for pulse durations of ∼1 μsec FWHM, and the laser chamber are compact enough to mount on an optical table. This system has been used to achieve multiatmosphere operation of a number of molecular gas lasers, including CO2, N2O, CS2, CO, and C2H2.
High average power pulser design for copper halide laser systems
Authors: Pack J. L. , Liu C. S. , Feldman D. W. , Weaver L. A.
Published: March 2003

A circuit using two thyratrons is described which provides alternating polarity, high-current pulses at pulse repetition rates up to 20 kHz, suitable for operating copper halide lasers. The circuit is a modification of a Blumlein configuration in which two networks are charged in parallel and discharged in series, providing a voltage quadrupling effect when used with resonant charging. By triggering the thyratrons sequentially the current is reversed on alternate pulses, which greatly reduces axial cataphoretic effects and extends the laser tube operating lifetime. The circuit can deliver up to 5 kW average power at 15 kHz.
Correction of instrumental time response variation with wavelength in fluorescence lifetime determinations in the ultraviolet region
Authors: Rayner D.M. , McKinnon A.E. , Szabo A. G.
Published: March 2003

The successful ratio correction technique described earlier to account for and eliminate the instrumental time response variation with wavelength was limited to wavelengths in the visible region. In this paper we described a modification of the ratio correction technique which allows the extension of this technique into the ultraviolet region (<350 nm). The modified technique is shown to allow the confident determination of fluorescence decay parameters of several molecular systems which show either single- or multiexponential decay in the ultraviolet region.
Faraday cups for laser plasmas
Authors: Pearlman Jay S.
Published: March 2003

An ion accelerator has been used to evaluate three types of Faraday cups commonly used to measure plasma expansion characteristics in laser-produced plasmas. One type of cup was found to have very low secondary emission and is very suitable for absolute measurement of ion numbers and energies.
Polarization scrambling using photoelastic modulator: Application to linear dichroism measurement
Authors: Cheng J. C.
Published: March 2003

The signal-to-noise ratio in linear dichrosim measurements using the polarization modulation technique is hindered by the presence of fictitious signals originating from briefringence and polarization sensitivity in the optical components. We have shown both theoretically and experimentally that such artifacts resulting from optical elements after the sample can be removed by placing a second modulator immediately after the sample. The second modulator, which must be of a different frequency than the first, and which must be adjusted to a specific that the synchronous time average of the fictitious signal is zero. The true linear dichroism signal is unaffected. In wavelength regions where thjere are no fictitious signals. The scrambler neither introudces artifact signals nor does it affect the real signals. Fictitious signals due to imperfections in optical components before or within the sample itself cannot be nulled in the same manner.
Speer carbon resistance thermometer magnetoresistance effect
Authors: Sanchez J. , Benoit A. , Flouquet J.
Published: March 2003

Speer carbon resistors (100 Ω, grade 1002) have been calibrated in the range 5–50 mK using a 60Co Co nuclear orientation thermometer. Negative longitudinal magnetoresistance effects have been observed up to 2.5 T.
Combined UHV/flow system: Apparatus for the study of reactions of atoms with solid surfaces by electron spin resonance
Authors: Svejda P.
Published: March 2003

A flow system apparatus was built by which it was possible to study by ESR the interactions of atoms with powder surfaces. The atoms (e.g., H, O, and N atoms) were generated by microwave discharge of the corresponding molecular gases in the carrier gas argon (total pressures, 1–6×102 Pa≃1–5 Torr) and were then transported to the sample situated in the cavity for in situ ESR observations. In the same apparatus, mainly because a cylindrical ESR cavity with large access was used, it was also possible to pretreat the samples in ultrahigh vacuum usually not encountered in ESR measurements and under well-defined thermal conditions. Results on the reactions of atoms with some solid surface (e.g., MgO and zeolite-4A) are summarized. The method introduced appears to be promising for future ESR work on surfaces.
Transient CD measurements at submillisecond time resolution—application to studies of temperature-jump relaxation of equilibria of chiral biomolecules
Authors: Anson Michael , Martin Stephen R. , Bayley Peter M.
Published: March 2003

A new system for the measurement of transient circular dichroism (CD) has been developed, with improved bandwidth, optical aperture, and source ratioing electronics, and applied to the study of temperature-jump relaxation processes of chiral complexes of ligands with biological molecules. Transient changes in circular dichroism and optical transmission are measured simultaneously. The optimal CD resolution is 2×10−6 (66×10−6 degrees ellipticity) at 300 μsec time constant and optimal absorbance resolution is ±4×10−5. The noise spectrum of the light source is important in determining the resolution achievable in either channel, and broadband stabilization of the mercury arc source is necessary. The potential of low-noise laser sources has also been demonstrated. Careful optical alignment reduces spurious signals to the order of the CD resolution. A theoretical treatment of the CD resolution has been evaluated specifically as a function of sample absorbance and available light power. Resolution is determined by detector shot noise, electronic system noise, and hence, time constant (1/bandwidth). Theoretical resolution for photon-noise-limited sources is approached in experimental measurements. At high light power the CD resolution is a slowly varying function of total sample absorbance, including both dichroic and nondichroic absorbing species. This property allows relaxation times to be determined over sufficient concentration range for analysis of temperature-jump (TJ) relaxation effects. Finally we indicate the additional spectroscopic features characterizing simple equilibria which may be derived from observation of the transient circular dichroism in TJ relaxation experiments.
Discharge counter for the determination of uranium in water by the fission track method
Authors: McCorkell R. H. , Huang Y. F.
Published: March 2003

The circuit and mechanical design of a counter for electrical discharges through fission tracks etched through 10-μm Kimfol and a system for distributing uranium-containing residues from drops of water evaporated on Lexan disks which are covered with Kimfol and irradiated with neutrons are described. The resulting system is used to measure (0.1–10) ×10−9 of U in natural waters and would be able to measure at least 5×10−11 and produce 100–200 analyses per person per day.
Linear scanning circuit for a piezoelectrically controlled Fabry–Perot etalon
Authors: Lindsay S. M. , Shepherd I. W.
Published: March 2003

Linear scanning of a piezoelectrically controlled Fabry–Perot spectrometer is essential where certain schemes of signal averaging are used. The circuit described provides frequency independent ramp shaping which enables correction of nonlinearities in scan.
Simple, pulsed, electron beam gun
Authors: Brau C.A. , Raybun J. L. , Dodge J. B. , Gilman F. M.
Published: March 2003

The construction of a simple, inexpensive electron beam gun is described. The pulsed power supply consists of a homemade spiral generator, constructed with aluminum and vinyl pressure-sensitive tapes, which is switched into the electron beam gun with a spark gap. The electron beam gun itself consists of a vacuum diode with a cold carbon cathode. From an inital charge voltage of 12 kV, the apparatus produces a 10-A beam of 100-keV electrons having a pulse duration of about 7 nsec and diameter of 6 mm.
Two multipurpose EPR cavities for applications between 1.6 and 1300 K
Authors: Berlinger W. , Müller K. A.
Published: March 2003

Two modular EPR cavities are described with which a temperature range from 1.6 to 1300 K is covered. They are widely applicable and permit normal solid-state EPR experiments, as well as the application of electric field, in situ optical illumination, uniaxial stress, and ENDOR experiments.
Mass spectrometer beam system for applications in the stratosphere
Authors: Mauersberger Konrad
Published: March 2003

Mass spectrometer investigations in the stratosphere require a special gas inlet system in order to reduce the high ambient pressures to ion source operating pressures. This paper describes a system where pressure reduction is achieved by differential pumping using high-speed liquid helium pumps and small orifices. Ambient gas particles are formed into a molecular beam, with a flag mechanism allowing the separation of beam and background particles. Laboratory tests have shown that the system has the capability of identifying gases with abundances below 10−8. Many problems encountered in the gas analysis of trace constituents are reduced, such as adsorption and desorption processes of walls and memory effects of pumps.
Bent crystal spectrometer for solar x-ray spectroscopy
Authors: Rapley C. G. , Culhane J. L. , Acton L. W. , Catura R. C. , Joki E. G. , Bakke J. C.
Published: March 2003

A bent crystal Bragg spectrometer is described which provides continuous and simultaneous coverage for all x-ray wavelengths within its spectral range. This instrument provides high spectral resolution but involves no precision crystal rocking or position encoding mechanisms and therefore may be highly ruggedized. Principles of operation are discussed and its application to solar x-ray spectroscopy is described.
Wide bandwidth cross correlator
Authors: Leikind Bernard J. , DeSilva Alan
Published: March 2003

An auto- or cross-correlator based on modification of a dual-trace sampling oscilloscope plug-in has been built. The device, which operates over a broad frequency band from dc to over 2.5 GHz, generates an equivalent-time correlogram in about 100 sec. This paper contains a description of the principle of the correlator, the details of the circuit changes required in the Tektronix equipment, and two examples of applications of the correlator.
Control system for maintaining a Langmuir probe at plasma potential
Authors: Michau J. L.
Published: March 2003

A closed-loop system to maintain a Langmuir probe at plasma potential, and to follow its fluctuations up to a frequency of 1 kHz, has been developed for diagnostics of the ionospheric plasma. The modulation technique is utilized and the second harmonic component of an alternating current is detected and filtered by a lock-in amplifier, to give the second-derivative curve of the Langmuir characteristic. The zero crossing of this second-derivative curve occurs at plasma potential, and it is used to provide an error signal which is applied, together with a steady bias voltage, to the probe. The values of the fluctuating current and of its first and second derivatives at plasma potential are directly available.
Derivation and testing of a model to calculate electrical shunting and leakage errors in sheathed thermocouples
Authors: Roberts M. J. , Kollie T. G.
Published: March 2003

A three-wire transmission line model was derived to calculate temperature measurement errors caused by electrical shunting and leakage in metal sheathed, oxide insulated, compacted thermocouple assemblies. Input parameters for the model were measured and used to verify experimentally the validity of the model on a 0.5-mm-diam stainless steel sheathed, MgO insulated, Chromel/Alumel thermocouple assembly. When a 1.27-m length of the assembly was heated to 1274 K, the errors due to shunting, calculated using the model, were 6.4% and 9.4% lower than the experimentally measured errors for theromocouple measuring junction temperatures of 273.2 and 371.5 K, respectively. With the 1.27-m length heated to 1373 K, the errors due to shunting, calculated using the model, were 12.6% and 14.9% lower than the experimentally measured errors for measuring junction temperatures of 273.2 and 371.5 K, respectively. For a 1.27-m length of the thermocouple assembly at 1274 K, the measuring junction at 273.2 K, and sheath currents of 20, 40, 60, and 80 mA, the error due to leakage, calculated using the model, was within 6% of the experimentally measured error. With the 1.27-m length heated to 1373 K and all other conditions the same, the calculated error due to leakage was within 9.1% of the measured error. This paper describes the experimental apparatus and measurements, explains the method used to infer parameters from experimental measurements, presents the model, and derives the differential equations that describe the electrical phenomena. These equations are solved exactly for a uniform line. A fortran iv coded numerical solution for nonuniform lines is described. Several illustrative examples are presented to clarify the concepts involved in electrical shunting.
Use of minicomputer for measuring kinetics over many orders of magnitude in time
Authors: Sharrock M.
Published: March 2003

Procedures are described for using an on-line computer to acquire and process digital data from a kinetic experiment in such a way that final data points are evenly spaced on a logarithmic time scale and the signal-to-noise ratio can be optimized. This arrangement is particularly suited for recording processes where changes occur over many decades of time. Emphasis is on techniques that can be used with a minimum of additional expense and programming sophistication. Some general considerations regarding sampling rate and electrical filtering are discussed.
Improved microchannel plate performance with a resistive anode encoder
Authors: Wiza J. L. , Henkel P. R. , Roy R. L.
Published: March 2003

Performance of microchannel plates in the high-gain chevron configuration has been improved by the addition of an interplate voltage VB. For VB=100 V, and positive ion excitation, the output electron distribution FWHM decreased from 166% to 97%. Using a resistive anode encoder (RAE) readout, and 1216-Å uv excitation, we observed a corresponding spatial resolution improvement of 16%.
Cooled low-noise bolometer preamplifier
Authors: Knotek S. , Gush H. P.
Published: March 2003

The circuit of a germanium bolometer preamplifier which employs constant voltage operation of the bolometer is described. The input stage consists of a cooled, temperature-regulated JFET located physically near the bolometer. In addition to the ac signal, a dc output signal which is useful in monitoring the bolometer temperature is available.
Use of light-emitting diodes as temperature sensors
Authors: Griffing B. F. , Shivashankar S. A.
Published: March 2003

Gallium arsenide phosphide diode chips retrieved from ordinary red light-emitting diodes (LEDs) can be used as inexpensive, reproducible, and durable temperature sensors over the range 4–300 K. Their low thermal mass results in response times, below 25 K, of considerably less than 1 msec.
Efficient and inexpensive glass circulating pump
Authors: Sime M. E. , Caplin M. L. , Phillips D.
Published: March 2003

An efficient and inexpensive pump has been developed for the circulation of gaseous mixtures in a closed system. A continuous unidirectional flow of gas at rates of 0–40 l min−1 was produced over an operating range of 10−5–10−3 Torr.
Dual-mode microwave cavity for measurements of harmonic power
Authors: Amato J. C.
Published: March 2003

A method of studying relaxation effects in conductors by harmonic power measurements is discussed. A dual-mode microwave cavity, with resonances at 11 and 33 GHz, is described which is suitable for such measurements.
20–40-GHz broadband frequency doubler with gallium aresenide varactor
Authors: Jounet P. , Fourrier M.
Published: March 2003

A crossed waveguide type varactor frequency doubler is described here which gives a conversion efficiency of 39% and a 4-GHz bandwith (−1 dB) around 40 GHz for 100-mW input power. Gallium arsenide varactor diodes in commerical packages are used, permitting great flexibility, in particular in molecular spectroscopy experiments.
Recirculating atomic beam oven
Authors: Carter Gary M. , Pritchard David E.
Published: March 2003

We describe an atomic beam oven that reuses alkali metal in the unused portion of the beam. This is accomplished by condensing the desired vapor on a cooled jacket from which it may be drained back into the oven.
Picosecond-resolution fluorescence lifetime measuring system with a cw laser and a radio
Authors: Menzel E. Roland , Popovic Zoran D.
Published: March 2003

A procedure for measurement of fluorescence lifetimes with picosecond time resolution is described. A cw laser beam is modulated with a standing-wave acousto-optic modulator. The modulated beam is split; one part serves as a reference beam, the other part excites the fluorescent sample. The sample flourescence and the reference beam, attenuated and delayed optically to be equal in amplitude and opposite in phase to the fluorescence, are incident onto a single photomultiplier tube. The thus achieved photodetector ac null is monitored either by an AM radio, whose intermediate-frequency signal is displayed on an oscilloscope, or by a spectrum analyzer. With 30-MHz light modulation and the radio, lifetimes could be determined with resolution better than 15 ps. With the spectrum anlyzer and 170-MHz light modulation frequency we have achieved 4-ps lifetime resolution. Correction for photomultiplier transit time versus incident wavelength is made.
Sensitivity considerations for NMR in metal single crystals
Authors: Stakelon T. S. , Follstaedt D. M.
Published: March 2003

We report a study of the factors determining the sensitivity of NMR measurements using bulk metal single crystal samples. We show that, in an ideal case, the NMR signal intensity from such a sample can be characterized by a figure of merit which is a function of only the fractional radio-frequency power losses in the coil winding compared to the losses in the sample. This allows the Q factor of the NMR coil to be varied considerably with no appreciable change in the figure of merit, thus permitting the coil Q to be chosen on the basis of the noise characteristics of the spectrometer being used. Measurements indicate that the absolute signal intensity from a metal single crystal with a near-optimum coil is about 1/10 of that from a powdered sample with particle radii approximately equal to the rf skin depth.
Polycrystalline techniques for conductivity studies of organic charge transfer salts
Authors: Coleman L. B.
Published: March 2003

Polycrystalline compaction conductivity measurements are extensively used to characterize newly synthesized quasi-one-dimensional organic charge transfer salts. This technique, however, can be both quantitatively and qualitatively misleading. Studies of the polycrystalline compaction and single crystal conductivities of a variety of tetracyanoquinodimethan (TCNQ) salts allow us to define the limits of reliability of the polycrystalline compaction technique, and denote its shortcomings. A new polycrystalline technique, the voltage shorted compaction (VSC), is described. The VSC has proven to be a valuable aid in characterizing the electrical properties of new materials where single crystals are difficult to produce.
Stability of germanium resistance thermometers at 20 K
Authors: Besley L.M. , Plumb H.H.
Published: March 2003

Thirty germanium resistance thermometers have been thermally cycled 100 times between 20 and 300 K, and their stability at 20 K has been evaluated. The results reveal a wide range of stabilities, ranging from 0.1 to 20 mK. Five different modes of behavior have been provisionally classified as stable, drifting, jumping, bimodal, and irregular.
Variable temperature UHV dual-range cell for spectroscopic surface studies
Authors: Förster H. , Meyn V. , Schuldt M.
Published: March 2003

A stainless steel cell for transmission spectroscopy of surface compounds is described. This cell allows subsequent spectra recording of the sample in two spectral regions requiring different window materials. The sample temperature can be varied from 100 to 700 K, the pressure from 10−6 to 105 Pa. The mean temperatue is measured inside the wafer with a thin platinum wire as a resistance thermometer.
Conical slow wave antenna as a plasma source
Authors: Grubb D. P. , Lovell T.
Published: March 2003

A simple conical helix has been successfully employed as a slow wave structure to generate plasmas by electron cyclotron resonance heating (ECRH). The plasma is typical of plasmas created by ‘‘Lisitano coil’’ sources, n∼1010–1012 cm−3 with Te≈2–20 eV. This source, however, is much simpler to fabricate. The ease of fabrication allows the user some flexibility in designing the source to fit a specific plasma physics experiment.
Uniformity condition for a rectangular field coil with a split winding
Authors: Casselman T. N. , Fryer R. B. , Simon F. N.
Published: March 2003

A generalized Helmholtz condition for field uniformity is derived from the closed form solution of the magnetic field in a multilayer rectangular coil pair as a function of coil dimensions and pair separation. The relation among the dimensions satisfying this condition is found and plotted in parametric form for single layer coils and for a multilayer coil with a specific winding thickness. For square coils of cross section small compared to their mean radius, the gap separation approaches half the coil radius, analogous to the classical condition for circular coils. Comparison between theoretical and measured values for tolerances within ±5% of the field at the system center agree within a 6% maximum deviation. For the experimental coil, the area enclosed by the ±5% contour was 58% of the area of the full coil.
Interpretation of electrostatic energy analyzer data of a flowing plamsa
Authors: Küdyan H. M.
Published: March 2003

Extracting correct plasma parameters from the experimental data from a retarding field electrostatic energy analyzer in a flowing plasma requires proper interpretation of the effect of plasma flow on the collector current. In this paper, relationships for computing plasma parameters directly from the analyzer data are described for any type of velocity distribution of particles.
Fluorescence polarization detector for the computation of the degree of polarization P
Authors: Smith J. C. , Graham N. , Chance B.
Published: March 2003

A device has been designed and constructed which when used with a commercial fluorimeter allows the computation of the degree of polarization P on a time shared basis.
Emergency power source for an ion vacuum pump
Authors: Taylor Edward
Published: March 2003

This note describes a simple high-voltage dc generator which serves as an emergency power source for an ion vacuum pump during power interruptions, or failure of the main supply.
Compact CO2 laser for infrared heterodyne radar
Authors: Marcus S. , Caunt J. W.
Published: March 2003

A compact CO2 laser has been developed for field use as part of an infrared heterodyne radar. The laser, which contains a separate local oscillator, transmits 10.5 W cw or 7 W average in the electrooptically Q-switched mode at a repetition rate of 50 kHz. The applicability of this laser to active imaging is discussed.
Volumetric calibration of experimental apparatus by xenon gas transfer
Authors: Rutherford W. M.
Published: March 2003

The volumes of interconnected sections of large, irregular, or inaccessible apparatus can be measured by quantitative cryogenic transfer of a xenon gas fill to weighing bottles. Tests with eight containers from 75 to 10 000 cm3 using relatively simple equipment, showed that: (1) absolute volumes of 250 cm3 or larger can be measured with a reproducibility on the order of 0.02% and with an accuracy on the order of 0.05% and (2) the ratios among two or more volumes can be determined with a reproducibility of 0.01%–0.001%, depending on volume.
Pulsed electrostatic probes as a diagnostic for transient plasmas
Authors: Schoenberg Kurt F.
Published: March 2003

A pulsed, electrostatic probe data acquisition system, applicable to transient or noisy plasmas, is presented. The system digitally records a probe characteristic, and its first and second derivatives. The latter are shown to be proportional to the projected electron energy distribution function, and the isotropic electron energy distribution function, respectively. The acquisition system and its experimental accuracy are discussed. Using the Lawrence Berkeley Laboratory 10-A neutral beam ion source, several examples demonstrating the systems application to transient plasmas are given.
Intense proton beam current measurement via prompt γ rays from nuclear reactions
Authors: Golden J. , Mahaffey R. A. , Pasour J. A. , Young F. C. , Kapetanakos C. A.
Published: March 2003

The current of an intense, pulsed proton beam is experimentally determined by monitoring prompt γ rays from nuclear reactions induced in a suitable target. Relevant data are given on the reactions employed including 7Li(p,γ) 8Be, 19F(p,αγ) 16O, and 12C(p,γ) 13N so that absolute currents can be determined. This method avoids the complication of target blowoff and the need for attenuating screens when applied to high current density beams.
Automatically sweeping dual-channel boxcar integrator
Authors: Keefe Donald J. , Patterson Donald R.
Published: March 2003

An automatically sweeping dual-channel boxcar integrator has been developed to automate the search for a signal that repeatedly follows a trigger pulse by a constant or slowly varying time delay when that signal is completely hidden in random electrical noise and dc-offset drifts. The automatically sweeping dual-channel boxcar integrator improves the signal-to-noise ratio and eliminates dc-drift errors in the same way that a conventional dual-channel boxcar integrator does, but, in addition, automatically locates the hidden signal. When the signal is found, its time delay is displayed with 100-ns resolution, and its peak value is automatically measured and displayed. This relieves the operator of the tedious, time-consuming, and error-prone search for the signal whenever the time delay changes. The automatically sweeping boxcar integrator can also be used as a conventional dual-channel boxcar integrator. In either mode, it can repeatedly integrate a signal up to 990 times and thus make accurate measurements of the signal pulse height in the presence of random noise, dc offsets, and unsynchronized interfering signals.
Pulsed illumination, closed circuit television system for real-time viewing of unsteady (≳1 μs) events
Authors: Marden W. W. , Steinberger R. L. , Bracco F. V.
Published: March 2003

A pulsed illumination closed circuit television system is described whereby fast (times ≪33 ms), unsteady events can be observed in real time. A low-power helium–neon laser beam is modulated to send a short duration light pulse through the unsteady test medium. The light is refracted according to the instantaneous optical properties of the medium. The refracted light travels to a solid state television camera, known as a charge injection device (CID), in which the sensor array is charged within microseconds. The scanning of the charged array then follows, requiring the standard 33 ms for information transfer to video tape and a TV monitor. The image is thus formed during the laser pulse duration (which presently is 10 to 100 μs, but shorter duration pulses are possible with more powerful lasers), but no more than one image every 33 ms can be observed and recorded. Thus this method is particularly suited for the investigation of high frequency periodic events in which one can observe both a single image, or an ensemble average of as many as 100 images, occurring at corresponding times in different cycles. The reported applications include the recording of steady and transient propane torch flames, of the transient fuel injection process in a motored internal combustion engine, and of the propagation of a flame under firing conditions in the engine. In the shadowgraph and Schlieren modes the method is particularly suited for application to periodic combustion events such as those occurring in internal combustion engines. The method then presents the following advantages over high-speed filming (≳3000 pictures/s); real-time observation and recording of chamber events at any crankangle; real-time observation and recording of the effects of changes in the engine variables (speed, load, spark timing, injection pressure and duration, chamber swirl, etc.) on the combustion events; real-time observation and recording of ensemble averages and cycle-to-cycle variations. The technique also eliminates the delays and unknowns of film processing. Finally, the cost of this system is similar to that of a high-speed camera.
Multiple-circuit pulse generator for high repetition rate rare gas halide lasers
Authors: Wang C. P.
Published: March 2003

A multiple-circuit high pulse repetition frequency (PRF) pulse generator for the pumping of rare gas halide lasers is reported. With this multiple-circuit design, high PRF can be achieved by the use of existing low PRF thyratron switches and capacitors. A two-circuit pulse generator was constructed, and its performance is described. By means of this pulse generator and a blowdown-type fast transverse-flow system, high PRF laser action in XeF was obtained, typically, 6 mJ/pulse at 1 kHz or 6 W average power. High PRF laser action in N2 was also observed.
New circuit for a constant voltage supply using series-shunt regulation
Authors: Kumano Masafumi , Ikenoue Tsuneo
Published: March 2003

A new circuit for constant voltage supply with series-shunt regulation has been designed to improve the suppression ratio of the incoming fluctuating noise. A typical example applicable to instruments with high sensitivity is also reported.
Visual stimulator
Authors: Van Toi Vo , Grounauer P. A.
Published: March 2003

An easily portable apparatus for flicker fusion experiments is described. It uses crossed polarizers to produce modulated beams and a light guide made of optical fibers to mix these beams for producing a sinusoidally modulated stimulus of which the frequency, the modulation amplitude, the luminance, the color adaptation light, and the field size can be varied independently.
Enhancement of pneumatic nebulization efficiency through application of an electric field
Authors: Savage R. N. , Hieftje G. M.
Published: March 2003

A technique is described for reducing the size of aerosol droplets produced by a pneumatic nebulizer of the kind commonly used in flame or plasma spectrometry. The technique involves the application of an electric field to the tip of the nebulizer, resulting in an induced surface charge on the liquid being nebulized. In turn, the surface charge reduces the liquid’s surface tension and results in the generation of a finer aerosol. In this study, the effect of the electric field is quantified in terms of the spatial dispersion and size distribution of aerosol droplets formed in the presence and absence of the field. Droplet size distributions, obtained using the MgO impression technique and analyzed using log-normal and upper-limit functions, reveal a 63% decrease in the volume mean droplet diameter in the field’s presence. As a result, this system is expected to be useful in both flame and plasma spectrometry, where reduced droplet size can yield improved precision and freedom from interferences.
Producing small scale temperature fluctuations in an airstream
Authors: Schacher G. E. , Fairall C. W.
Published: March 2003

A 4.5-μm ’’hot’’ wire is used to heat a low-speed airstream at frequencies from dc to 400 Hz. For dc excitation the thermal noise spectrum produced was white to a frequency of 2 kHz. ac heating of the wire up to a frequency of 400 Hz (800 Hz thermal fluctuation of the airstream) yielded a good thermal signal as far as 2 cm from the hot wire. Calculation shows excellent heat transfer between the wire and airstream. The technique is very useful for calibrating the frequency response of temperature sensors and for investigating turbulent heat transfer for various flow configurations.
Incoherent energy and coherence time of depolarized microwaves—application in the case of atmospheric propagation
Authors: Sardos René
Published: March 2003

After having briefly summarized the principle of interferometric analyzers, the author shows that they can be utilized for the simultaneous measurement, in two orthogonal directions, of self-coherence time, of coherent energy, and of incoherent energy. In the second part, he demonstrates the interest that they can have in the case of atmospheric propagation and suggests drawing the polar diagrams of the square root of the incoherent power source (a hypothetical amplitude) and the self-coherence times.
Rapid response gas injection technique
Authors: Komar James J.
Published: March 2003

A unique gas injection technique has been developed which has rapid response and is capable of supplying gas flowrates up to 5 kg/s at pressures of 3.45×106 N/m2. Rise times to equilibrium pressure varied from 7 to 15 ms over the operating range. The reliability, excellent repeatibility, and uniform pressure have shown the system to be superior to previously utilized expansion tube gas injection techniques associated with very short duration impulse test facilities. The achievement of precise timing control of the valve opening permitted a complex electronic sequencing of facility events. An additional feature of automatic gas supply shut-off resulted in significant cost savings when rare gases were used as injectants.
Measurement of low shock pressures with piezoresistive carbon gauges
Authors: Krehl Peter
Published: March 2003

A new sensitive technique which permits the detection of small pressures in shock waves down to 5 bars with good time resolution has been developed. It consists of a pulsed double-compensated Wheatstone bridge in conjunction with piezoresistive carbon gauge transducers. It is shown that the advantages of piezoresistive gauges, such as short rise time, small dimensions, and in-material stress measurement, may be utilized for low shock pressure recording even in explosive environments, an area previously dominated by piezoelectric gauges. Comparative data for the two types of sensors are presented for shock tube side-on and head-on collision experiments and underwater explosions. This new development opens the possibility of PRG applications in classical fields of low shock pressure recording such as gas dynamics and underwater explosions.
UHV-manipulator attachment for azimuthal sample rotation with electrical readout
Authors: Larscheid J. , Kirschner J.
Published: March 2003

A nonmagnetic UHV-compatible sample manipulator is described, which allows direct electrical readout of the azimuthal rotation angle by a wire-wound potentiometer inside the vacuum. The rotation about an axis in the sample surface is completely decoupled from the azimuthal rotation about the surface normal. The sample temperature can be varied between +2000° and −70°C by resistive heating or by cooling the current leads. The sample manipulator is designed such that it can easily be attached to commerical manipulators with a flip actuator.
Gas-component analysis of laser fusion targets
Authors: Schneggenburger R. G. , Updegrove W. S. , Nolen R. L.
Published: March 2003

A gas-chromatographic method for analyzing the fuel content of laser fusion targets has been developed. It provides information on isotope ratios in the fuel gas, percent of molecular species, and total pressure of fuel gas in individual targets to a limit of 0.2 ng DT. The method can also be used to quantify other gaseous components not active in the thermonuclear process (e.g., H2, He, etc.).
High resolution calorimeter for the investigation of melting in organic and biological materials
Authors: Tanasijczuk O. S. , Oja Tõnis
Published: March 2003

A high-resolution, high-sensitivity ac calorimeter has been developed to investigate the ’’melting’’ of organic and biological materials. The heart of this system is a simple yet very versatile sample cell which can be reused. High-temperature-resolution studies of the melting of n-octadecane and tert-butyl alcohol indicate interesting premelting and prefreezing phenomena in the specific heat capacity in these substances. With pure dipalmitoyl L-α-lecithin (DPL), in water, we obtain a very sharp (FWHM=0.38°C) first-order phase transition showing no pretransition broadening or post-transition tails in the specific heat curves near the 41.2°C transition point.
Microprocessor-based, programmable laboratory equipment controller and data acquisition system
Authors: Taylor D. W.
Published: March 2003

A microprocessor-based programmable laboratory equipment controller and data acquisition system is presented. In most instances, this system can replace a minicomputer at a substantial cost reduction with no loss of performance. The system hardware and a special purpose programming language, designed to provide good interaction between this system and other equipment, are described.