bluuebunny/crossref_metadata_2025 huggingface dataset:
Beamline 10: A multipole wiggler beamline at SSRL (invited)
Authors: Karpenko V. , Kinney J. H. , Kulkarni S. , Neufeld K. , Poppe C. , Tirsell K. G. , Wong J. , Cerino J. , Troxel T. , Yang J. , Hoyer E. , Green M. , Humphries D. , Marks S. , Plate D.
Published: July 2002

A beamline has been constructed at Stanford Synchrotron Radiation Laboratory (SSRL) whose radiation source is a multipole permanent magnet wiggler installed in a straight section of the SPEAR 3–3.5 GeV electron storage ring. The wiggler is a hybrid design that utilizes Nd–Fe alloy magnet material combined with Vanadium Permendur poles. It is approximately 2 m long and has 15 full wiggler periods. Its field is regulated by varying its gap height. It has a peak operating field, limited by the electron beam vacuum chamber vertical aperture, of 1.4 T. The beamline consists of vacuum, safety, and optical components capable of transporting photons to one hard x-ray (3–30 keV) end station, with provisions for implementing up to two additional branch lines. The existing hard x-ray branch can be focused by a Pt-coated toroidal mirror with a cutoff energy of approximately 22 keV. The experimental end station is serviced by a Hower–Brown type double crystal monochromator. The wiggler and beamline construction was completed in the fall of 1987 and was operated for a brief period for characterization and experimental use. We present design details and results of the initial characterization studies.
Drift tubes for characterizing atmospheric ion mobility spectra using ac, ac-pulse, and pulse time-of-flight measurement techniques
Authors: Misakian M. , Anderson W. E. , Laug O. B.
Published: July 2002

Two drift tubes constructed of insulating cylinders with conductive guard rings on the inside walls are examined to determine their suitability for measuring ion mobility spectra at atmospheric pressure. One drift tube is of the pulse time-of-flight (TOF) type with adjustable drift distance, and the other is an ac-TOF drift tube similar in principle to devices reported by Tyndall and Powell [Proc. R. Soc. A 129, 162 (1930)] and Van de Graaff [Philos. Mag. 6, 210 (1928)]. The latter drift tube is evaluated using sinusoidal and alternating-polarity pulse-voltage waveforms for gating the shutters. Methods for determining the drift velocity of an ion from theoretical fits of the TOF spectrum are described for drift tubes of fixed length exhibiting ‘‘end effects.’’ Mobility values with uncertainties less than ±1% can be obtained with the pulse-TOF drift tube. Comparable results are obtained with the ac drift tube if an alternating-polarity pulse-voltage waveform is used for gating the shutter.
rf power calculations for the NRL buncher/converter microwave generator
Authors: Buschauer Robert
Published: July 2002

Simple formulas are derived for the rf power output from NRL’s novel buncher/converter microwave source. These equations emphasize the physics of the converter and explicitly demonstrate the effects of waveguide and coaxial-line loading, the positions of the tuning stubs, system dimensions, etc. Numerical examples show that capacitive loading of the coaxial line can significantly affect the level of radiated power. They also indicate that the output power is usually not limited by the radiation resistance or radiative coupling of the coaxail and rectangular sections.
A magnetic shielded room designed for magnetoencephalography
Authors: Sullivan G. W. , Lewis P. S. , George J. S. , Flynn E. R.
Published: July 2002

A magnetic shielded room has been constructed for magnetoencephalographic (MEG) measurements. The room was designed to match the noise levels of superconducting quantum interference device coupled second-order gradiometers while minimizing the overall cost of the facility. The room measures 2.6×2.6×2.6 m3 internally and consists of a single high-permeability alloy shell with an outer shell of ultrapure aluminum. The dc shielding factor at the center of the room is 200, and the ac shielding factor at 10 Hz is 2000. This is the frequency which has the maximum amplitude in a Fourier analysis of MEG results. The room is designed to operate without a door closure.
Accurate electron gun-positioning mechanism for electron beam-mapping of large cross-section magnetic surfaces
Authors: Anderson F. S. B. , Middleton F. , Colchin R. J. , Million D.
Published: July 2002

A method of accurately supporting and positioning an electron source inside a large cross-sectional area magnetic field which provides very low electron beam occlusion is reported. The application of electrical discharge machining to the fabrication of a 1-m truss support structure has provided an extremely long, rigid and mechanically strong electron gun support. Reproducible electron gun positioning to within 1 mm has been achieved at any location within a 1×0.6-m2 area. The extremely thin sections of the support truss (≤1.5 mm) have kept the electron beam occlusion to less than 3 mm. The support and drive mechanism have been designed and fabricated at the University of Wisconsin for application to the mapping of the magnetic surface structure of the Advanced Toroidal Facility torsatron1 at the Oak Ridge National Laboratory.
Resonant phase shift technique for the measurement of small changes in grounded capacitors
Authors: Miller G. L. , Wagner E. R. , Sleator T.
Published: July 2002

A simple technique has been developed for the high resolution measurement of small changes in capacitors which have one grounded electrode. The capacitor is arranged to be the tuning element in a series resonant LC tank circuit that is driven by a transistor emitter follower. Signal information is provided by observing the phase shift in the transistor collector current that results from any small change in the capacitor value. Implementation is simple, readily analyzable, provides good diagnostics, is easily multiplexed into arrays, and has potential applications in a number of areas including high resolution proximity sensing, capacitive topography, atomic force microscopy, and capacitor microphones.
Reflection high-energy electron diffraction intensity oscillation recorder for molecular-beam epitaxy systems
Authors: Sa C. J. , Wieder H. H.
Published: July 2002

A simple, comparatively inexpensive reflection high-energy electron diffraction (RHEED) intensity oscillation detection and recording system is described. The RHEED pattern obtained on the screen of a molecular-beam epitaxial reactor during growth of epitaxial layers is detected by a video camera, displayed on a video monitor, and simultaneously recorded on a videocassette recorder. A mechanically positioned optical fiber relative to the monitor screen is used to select a particular element of the RHEED pattern whose time dependent intensity oscillations are applied to a photodiode-operational amplifier whose output signal is digitized, analyzed, displayed, and recorded by a desktop computer.
Plasma fluctuation measurements in tokamaks using beam-plasma interactions
Authors: Fonck R. J. , Duperrex P. A. , Paul S. F.
Published: July 2002

High-frequency observations of light emitted from the interactions between plasma ions and injected neutral beam atoms allow the measurement of moderate-wavelength fluctuations in plasma and impurity ion densities. To detect turbulence in the local plasma ion density, the collisionally excited fluorescence from a neutral beam is measured either separately at several spatial points or with a multichannel imaging detector. Similarly, the role of impurity ion density fluctuations is measured using charge exchange recombination excited transitions emitted by the ion species of interest. This technique can access the relatively unexplored region of long-wavelength plasma turbulence with k⊥ρi≪1, and hence complements measurements from scattering experiments. Optimization of neutral beam geometry and optical sightlines can result in very good localization and resolution (Δx≤1 cm) in the hot plasma core region. The detectable fluctuation level is determined by photon statistics, atomic excitation processes, and beam stability, but can be as low as 0.2% in a 100 kHz bandwidth over the 0–1 MHz frequency range. The choices of beam species (e.g., H0, He0, etc.), observed transition (e.g., Hα, Lα, He i singlet or triplet transitions, C vi Δn=1, etc.) are dictated by experiment-specific factors such as optical access, flexibility of beam operation, plasma conditions, and detailed experimental goals. Initial tests on the PBX-M tokamak using the Hα emissions from a heating neutral beam show low-frequency turbulence in the edge plasma region.
Diagnostics of alpha particles and their effects (abstract)
Authors: Young K. M. , Strachan J. D. , Zweben S. J.
Published: July 2002

The pending approach of significant alpha particle populations in D-T plasmas in TFTR and JET and in the burning plasma devices, CIT and ITER, has led to detailed study of the measurement of the alpha particles both directly and through their potential effects on the plasma. The possible diagnostics of alpha particles, previously reviewed, for example, by Zweben [S. J. Zweben, Rev. Sci. Instrum. 57, 1723 (1986)], for use on such devices have been narrowed down to a relatively small number of possibilities. Small scintillator detectors at the wall have proven very effective in detecting the escaping T and p fusion products from the D-D reaction and hence mocking-up the relevant studies of loss required by ITER. Development of high-power pulsed microwave scattering systems for investigating the fast confined alphas is in progress for TFTR and JET. Selection of the right frequency and mode will be needed for CIT and ITER but this technique has the major advantage of being able to conform to readily available access. The use of a carbon impurity pellet to provide a suitably dense ablation target cloud so that the spectra of the emitted helium light will provide data on the energy distribution of these fast alphas is also being developed. For the slowing-down group (Eα≤500 keV), charge exchange recombination spectroscopy using a source beam of neutrals is the most probable diagnostic but it becomes limited by the penetration of the beams. But, in addition to the direct measurement of the alphas, or of the neutrons, to give information on their source profile and time behavior, they significantly heat the plasma and also, potentially, lead to new instability modes which could lead to enhanced loss of themselves or of the plasma. These instabilities have been extensively analyzed recently so that methods for identifying their presence can now be evaluated. These diagnostics, and some aspects of their implementation on TFTR, CIT, and ITER will be described. This work was supported by U.S. DOE contract No. DE-AC02-76-CHO-3073.
γ-ray and neutron calibration facility (abstract)
Authors: Coleman J. W. , Wenzel K. W. , Li C. K. , Lo D. , Petrasso R. D.
Published: July 2002

High-temperature inertial and magnetically confined plasmas are copious emitters of γ rays and neutrons. Some γ-ray and neutron reactions of interest are D+He3→Li5+γ (16.7), D+P→He3+γ (5.5 MeV), D+T→He5+γ (16.6 MeV), D+D→He4+γ (23 MeV), and D+D→He3+n (2.45 MeV). In order to test and absolutely calibrate γ-ray and neutron diagnostics for such reactions, we are investigating the feasibility of renovating a Cockcroft–Walton accelerator which resides in our laboratory. We will report on the status of this work. This work was supported by U. S. Department of Energy contract No. DE-AC02-78ET51013.
Jet time of flight neutral particle analyzer (abstract)
Authors: Betello G. , Bracco G. , Moleti A. , Tilia B. , Zanza V.
Published: July 2002

Neutral particle analyzers in large tokamaks are affected by the high neutron fluxes due to the sensitivity to neutrons of the particle detectors. The time of flight technique can be applied to a neutral particle analyzer providing at the same time the mass analysis and the random noise rejection mechanism. A time of flight neutral particle analyzer has been developed for the installation on JET providing 15 energy channels up to a maximum energy of 250 keV. The energy selection is performed by an electrostatic deflector and each energy channel consists of a time of flight detection system composed by two channeltrons, the first of which is triggered by the secondary electrons emitted by the incoming ion in a carbon foil. The analyzer has been calibrated with neutral beams of hydrogen, deuterium, and helium in the energy range (0.5, 200 keV).
Low-energy neutral particle analysis by a time-of-flight method on JFT-2M (abstract)
Authors: Miura Y. , Okano F.
Published: July 2002

A time-of-flight method is used to measure the energy spectrum of charge exchange atoms emitted from the JFT-2M plasma in the energy range below 1000 eV/amu. The neutral flux is chopped in bunches of about 0.8 μs by a slotted cylinder. The rotating cylinder is driven by a turbomolecular pump. After the flight of 1.5 m the particles are detected by a secondary particle detector. This is an electron multiplier modified from a photomultiplier which can be gated for an intense photon. The signal from the electron multiplier is digitized at a sampling time of 0.2 μs. To get good statistics of the arrival time distribution (ATD), eight or nine ATDs are averaged. Then the energy spectrum of charge exchange neutrals is measured by a 2 ms interval. The fast change (≤2–6 ms) of energy spectra at the L/H and H/L transition is also reported. The average energy defined by ∫E(dΓ/dE)dE/∫(dΓ/dE)dE increases by about 100 eV at the H transition like the increase of the ECE electron temperature at the edge. The neutral flux defined by ∫(dΓ/dE)dE decreases like the divertor Hα/Dα signal. In the energy distribution of the flux, the number of particles with energy less than about 400 eV decrease by the H transition but those greater than 500 eV do not change or increase. The flux at 200 eV in the H phase is two times lower than that in the L phase.
Observation of up-down asymmetric impurity densities in TEXT from a horizontal x-ray imaging array (abstract)
Authors: Wenzel K. W. , Petrasso R. D. , McCool S. C. , Ritz Ch. P. , Rowan W. L. , Brower D. L. , Austin M. E.
Published: July 2002

Up-down asymmetries were observed in the x-ray emission from aluminum injected into TEXT [K. W. Wenzel et al., Bull. Am. Phys. Soc. 34, 2153 (1989)]. The Z dependence of these asymmetries will be explored by injecting carbon, aluminum, titanium, chromium, and iron into similar TEXT discharges. Furthermore, the current-direction dependence will be tested. The latter experiment may clarify coupling between impurity density asymmetries and electron density fluctuation asymmetries, because the fluctuation asymmetries were found to reverse with changed current direction [D. L. Brower et al., Phys. Rev. Lett. 54, 689 (1985)]. A possible theoretical coupling between impurity density and fluctuation asymmetries comes from the effect of radiative cooling on thermally driven convection cells [D. R. Thayer and P. H. Diamond, Phys. Fluids 30, 3724 (1987)].
High mass resolution isochronous time-of-flight spectrograph for three-dimensional space plasma measurements (abstract)
Authors: Möbius E. , Bochsler P. , Ghielmetti A. G. , Hamilton D. C.
Published: July 2002

By combining a toroidal electrostatic analyzer with a novel cylindrically symmetric isochronous time-of-flight mass spectrometer, we have developed an instrument that simultaneously determines the three-dimensional distribution function of ions and differentiates species. The ion mass is determined to high resolution (M/ΔM≳50) from the time of flight within a harmonic field configuration defined by hyperboloid equipotential surfaces. A second conventional time-of-flight channel makes use of particles leaving the thin entrance foil as neutrals. An additional solid state detector in which the neutrals are stopped allows the total energy and thereby the ionic charge of the incident ions to be determined as well. Information from the neutral and the ion channels can be combined to determine the total mass of an incident molecular ion and the mass of one atomic fragment. This also removes the ambiguity between molecular ions and isotopic species of the same mass. A laboratory prototype has been used to demonstrate the feasibility of the principle of operation.
Neutron beam measurements at high-power fusion plasmas
Authors: Källne Jan
Published: July 2002

High fusion power (0.1 to above 1 GW) tokamaks now under consideration can be expected to provide collimated (Δθ≤±0.02 rad) neutron fluxes up to 1011 n/s cm2. This presents special opportunities for neutron measurements to diagnose the plasma but would also make it possible to perform neutron irradiation or cross-section studies. It is proposed that the neutron flux can be characterized with high count rate magnetic proton recoil (MPR) spectrographs. These can also be used as continuous flux monitors in the beam constituting an interesting neutron test channel. The main beam properties and the monitoring capabilities are presented and examples of how the neutron test channel can be used are given. Especially, the possibility to calibrate neutron yield activation measurements is discussed. The proposed method would reduce the error in absolute yield determinations for fusion plasmas to the 5% level.
Calibration of the JET neutron yield monitors using the delayed neutron counting technique
Authors: van Belle P. , Jarvis O. N. , Sadler G. , de Leeuw S. , D’Hondt P. , Pillon M.
Published: July 2002

The time-resolved neutron yield is routinely measured on the JET tokamak using a set of fission chambers. At present, the preferred technique is to employ activation reactions to determine the neutron fluence at a well-chosen position and to relate the measured fluence to the total neutron emission by means of neutron transport calculations. The delayed neutron counting method is a particularly convenient method of performing the activation measurement and the fission cross sections are accurately known. This paper outlines the measurement technique as used on JET.
Time-resolved mass and energy analysis by position-sensitive time-of-flight detection
Authors: Pollard J. E. , Lichtin D. A. , Janson S. W. , Cohen R. B.
Published: July 2002

We describe a method for time-resolved mass and kinetic energy analysis of ionic or neutral species (1–150 amu, 0.5–500 eV) in diagnostic measurements on spacecraft electric thrusters. Time-of-flight mass spectrometry is combined with position-sensitive detection to measure energy spectra for multiple masses at sampling rates as high as 50 kHz. A rectangular microchannel plate detector with a 96-element metal anode array is read out by fast analog-to-digital converters or by discriminators and scalers. The ion drift time varies as the square root of the mass-to-charge ratio, and the displacement along the detector varies as the square root of the energy-to-charge ratio. The energy resolution is enhanced by minimizing the field distortion near grid wires.
Ion composition measurement techniques for space plasmas (abstract)
Authors: Gloeckler George
Published: July 2002

Plasmas found in space range from the solar wind with a typical temperature of 105–106 K, ∼400 km/s bulk flow speed, and high ionization (charge states) of ions, to the hot, slowly moving plasmas in the outer magnetospheres of the giant planets, to the cold, co-rotating plasmas in inner magnetospheres. While measurements of the distribution functions of protons and electrons, which have been available for several decades of space exploration, are providing important information about the heating and acceleration mechanisms producing these plasmas, knowledge of the elemental composition and charge states of ions in these plasmas is essential for establishing their sources of origin. We review space plasma instruments and techniques, with an emphasis on hot plasma composition measurements. Starting with Faraday Cup detectors some 30 years ago, plasma instruments have evolved to the present time-of-flight systems with excellent mass resolution and three-dimensional viewing capabilities.
Use of positrons to probe magnetic versus electrostatic turbulence
Authors: Stambaugh R. D.
Published: July 2002

Kwon et al. have shown that runaway electron (positron) diffusion is produced by magnetic turbulence and unaffected by electrostatic turbulence. By measuring the diffusion coefficient of positrons at runaway energies (0.1–2 MeV) as a function of radius for two discrete positron energies, the radial correlation length W of the turbulence can be extracted. Then if the thermal electrons are in the weak turbulence regime, the thermal electron diffusion coefficient from magnetic fluctuations alone can be calculated and compared to values from other techniques. We propose to inject charged energetic positrons (100–2000 keV) in few millisecond bursts from radioactive sources by means of their curvature drift when trapped in toroidal field ripples. The energetic positrons will diffuse over 60–600 ms time scales. At any time the radial profile of the positrons can be sampled by injecting a small solid pellet. A fraction of all the positrons on a flux surface will annihilate in the pellet as it passes that flux surface. The time-dependent 0.511 MeV γ-ray signal then can be unfolded into the positron radial profile and the positron diffusion coefficient determined from the time evolution of those profiles.
ATF heavy ion beam probe: Installation and initial operation
Authors: Zielinski J. J. , Aceto S. C. , Connor K. A. , Lewis J. F. , Glowienka J. C. , Henkel G. H. , Fehling D. T. , DeVan W. R. , St. Onge K. D. , Lee D. K. , Carnevali A.
Published: July 2002

Installation of the HIBP on ATF began in the summer of 1988. All of the major hardware components have now been installed. The initial operation of the diagnostic has begun amid the final stages of testing and control system integration. The existence of significant magnetic fields and gradients outside of the main plasma volume and fully three-dimensional particle trajectories have raised several interesting issues during the design, assembly, alignment, and operation of the beamline and analyzer. The diagnostic must function in a challenging environment. It must perform satisfactorily despite electrical interference from several nearby sources, pressure excursions caused by gas puffing, and UV/plasma loading.
Portable probe system for edge turbulence and transport measurements
Authors: Ritz Ch. P. , Tsui H. Y. W. , Rhodes T. L. , Bengtson Roger D. , Lin H. , Wootton A. J.
Published: July 2002

A compact of self-contained portable system has been designed to diagnose the edge plasma of devices with a wide range of sizes and configurations. The system is capable of measuring mean and fluctuation quantities of density, temperature, potential from a standardized Langmuir probe array using a fast reciprocating probe drive, but can also be used for other fluctuation sources, e.g., magnetic probes. The signal processing software allows an immediate analysis of the turbulent characteristics. The results are stored in a database. The portable device is available for collaborative measurements with the goal of allowing cross-device comparison of edge fluctuation characteristics and transport.
Application of correlation techniques to the angular spectrum of scattered radiation from tokamak plasmas
Authors: Nazikian Raffi
Published: July 2002

In the limit of the first Born approximation for a partially coherent secondary source consisting of a spatially random plasma illuminated by a coherent plane wave, it is shown that the spectral coherence of the scattered radiation conveys information on the three-dimensional intensity distribution of the secondary source.
Equilibrium q-profile determination and stability analysis from magnetic field pitch angle measurements using motional Stark effect polarimetry
Authors: Roberts D. W. , Kaita R. , Levinton F. M.
Published: July 2002

The motional Stark effect polarimetry technique has been used to measure the magnetic pitch angle in a variety of PBX-M plasma conditions. For high aspect ratio, circular plasmas, the q profile can be obtained directly from the γp profile using the cylindrical expression q(r)=(rBT/RBp). In strongly shaped PBX-M plasmas, the magnetic pitch angle data are used as an internal constraint on the plasma equilibrium calculated by solving the Grad–Shafranov equation, subject to external flux measurements. Thus, an accurate determination of q(r) depends upon detailed knowledge of the plasma equilibrium. Discussion of uncertainties in the equilibrium determination and their effect on q(r) will be presented. The equilibrium solutions using the pitch angle data are required for MHD stability calculations, which are being used to investigate the relationship between internal kink modes and plasma shape.
Visible imaging of the diagnostic neutral beam on TFTR
Authors: Schilling G. , Medley S. S. , Zweben S. J.
Published: July 2002

An attempt was made to image the 2-D spatial patterns of the edge density turbulence of the Tokamak Fusion Test Reactor (TFTR) by using the visible light emission from an injected diagnostic neutral beam (DNB). A clear image of the 12 cm×20 cm DNB ‘‘sheet beam’’ was obtained using the Doppler-shifted line emission at 584.9±0.5 nm (2.7 nm blue shifted) from the neutral helium beam with a 2 ms exposure time. Although the signal level was too low to observe the edge density turbulence, potential improvements are described which could improve the sensitivity enough to obtain an image on the desired 10 μs timescale.
High-resolution absorption and emission spectroscopy of high Z laser-produced plasmas (abstract)
Authors: Kania D. R. , Hammel B. A. , MacGowan B. J. , Keane C. J. , Seely J. F. , Feldman U. , Brown C. M. , Reader J.
Published: July 2002

Up to 7 kJ of 0.53 μm laser light was used to irradiate solid and thin foil high Z disk targets. The 1 ns flat-topped laser pulses were focused to an intensity greater than 1016 W/cm2. The spectra were recorded on a 3 m grazing incidence spectrograph. We have extended the range of ions observed to emit lines in the O-like, F-like, Na-like, and Cu-like isoelectronic sequences. In addition, layered targets and atomic mixtures have been used to study opacity effects and VUV line emission. This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.
Thomson scattering diagnostic for the microwave tokamak experiment
Authors: Foote J. H. , Barter J. D. , Sewall N. R. , Jolly J. J. , Schlander L. F.
Published: July 2002

The Thomson scattering diagnostic system (TSS) on the microwave tokamak experiment (MTX) at LLNL routinely monitors electron temperature (Te) and density. Typical measured values at the plasma center under clean conditions are 900±70 eV and 1–2×1014 (±30%) cm−3. The TSS apparatus is compact, with all elements mounted on one sturdy, two-level optics table. Because of this, we maintain with minimum effort the alignment of both the ruby-laser input optics and the scattered-light collecting optics. Undesired background signals, e.g., plasma light as well as ruby-laser light scattered off obstacles and walls, are generally small compared with the Thomson-scattered signals we normally detect. In the MTX Te region, the TSS data are definitely fitted better when relativistic effects are included in the equations. Besides determining the temperature of the Maxwellian electron distribution, the system is designed to detect electron heating from GW-level free-electron laser (FEL) pulses by measuring large wavelength shifts of the scattered laser photons. TSS data suggest that we may indeed be able to detect these electrons, which can have energies up to 10 keV, according to computer simulation.
Development of a vibration-compensated CO2 interferometer for the RFX experiment
Authors: Innocente P. , Martini S. , Schio A. , Roca Ch. Ferrer
Published: July 2002

The accuracy of a vibration-compensated CO2 interferometer is often worse than expected in the design phase. This paper describes a laboratory study performed during the development of a multichord two-color CO2 interferometer for the RFX experiment with the aim of assessing the performance of this diagnostic. The phase demodulation system (quadrature phase comparators and AGC linear IF amplifiers) has been carefully tested and a set of optimum conditions has been found for which its overall accuracy is better than 1°. Other sources of error such as noncompensated vibrations or standing waves in the acousto-optic cells have been sought for and studied on a test bench interferometer. A scheme is proposed by which density measurements with an accuracy better than 1018 m−2 can be achieved.
Techniques for soft x-ray absorption in laser-produced plasmas
Authors: Burkhalter P. G. , Mehlman G. , Newman D. A. , Ripin B. H.
Published: July 2002

Interest in x-ray absorption derives from soft x-ray transport studies to characterize laser-solid-interaction effects. The object of this work was to determine whether x-ray absorption features were measurable in laser-produced plasmas from solid targets. X-ray emission was made using high-atomic-number microsphere targets irradiated with a focused beam of the Pharos laser while the laser-solid-interaction plasmas were generated by a second beam in Al foil targets. High-resolution, spatially resolved x-ray spectra were collected with instrumentation and geometry similar to previous tracer-dot spectroscopy measurements of plasma profile parameters. Soft x-ray absorption lines, observed at different distances from the aluminum target surface, may be related to density gradients in the laser-generated plasmas.
High-count-rate operation of a TFTR position-sensitive x-ray detector with delay-line readouts
Authors: Hsuan H. , Bitter M. , von Goeler S. , Harder J. A. , Hill K. W. , Lemunyan G.
Published: July 2002

X-ray spectra obtained with position-sensitive detectors which use delay-line readout systems are subject to distortions at count rates comparable to the inverse of the temporal length of the delay line. These distortions are due to the simultaneous existence of pulses from different photons on the delay line. High incident rates up to several MHz can be obtained on the detectors of the TFTR crystal spectrometer under certain conditions. This paper describes improvements which can be obtained by an interarrival time discriminator circuit.
Recent results from experiments on x-ray confining cavities (abstract)
Authors: Tsakiris G. D. , Sigel R. , Massen J. , Lavarenne F. , Fedosejevs R. , Meyer-ter-Vehn J. , Eidmann K. , Witkowski S. , Nishimura H. , Kato Y. , Takabe H. , Endo T. , Kondo K. , Shiraga H. , Sakabe S. , Jitsuno T. , Takagi M. , Yamanaka C. , Nakai S.
Published: July 2002

In continuation of the collaborative work between the Institute of Laser Engineering, Osaka and Max–Planck-Institut für Quantenoptik, Garching on x-ray confining cavities, we have performed a new series of experiments using the GEKKO-XII laser facility (4 kJ, 0.9 ns, λ=0.35 μm). The results from two experimental objectives will be presented. The first objective was the direct observation of the x-ray confinement effect in a cavity. A special design target allowed the simultaneous measurement of the x-ray flux emanating from a ‘‘closed’’ cavity and an ‘‘open’’ cavity. The second objective was the study of radiation transport mechanism in high- and low-Z materials. Thin foils of Au and Al were used as windows on diagnostic holes of x-ray confining cavities and their emission was compared to that of an open hole. A summary of the main results will be presented.
Construction and operation of an isothermal flow reactor system for study of SO2 removal by injected limestone sorbents
Authors: Hepola Jouko
Published: July 2002

Desulfurization capacity of Finnish limestones was studied with the aid of an isothermal flow reactor at the Laboratory of Fuel and Process Technology of the Technical Research Center of Finland over the years 1985–1989. Construction and operation of this isothermal flow reactor are presented in the article. Reaction temperature, residence time, and flue gas composition can be regulated independently of each other. The flue gas is formed by burning LPG (mixture of propane and propene). Other gases can be mixed with the flue gases to get the desired gas composition. The hot flue gas is led into a vertical reactor. To compensate heat losses the reactor tube is kept at the desired temperature with the aid of an electric resistance heater installed around the tube. Flow in the reactor is laminar. Limestone powder of 1–100 μm in particle size can be fed by a powder feeder at a rate of 0.2–5 g/min into the reactor. Reacted solid matter is collected with an axially movable, water-cooled, and nitrogen-diluted sampling probe in the reactor tube. It is very important to feed the fine powdered limestone as separate particles into the reactor and to sample the solid product so that detrimental reactions in the sampling system are minimized. The residence time of solid matter in the reactor ranges 0.1–1 s, depending on the gas amount flowing in the reactor tube, and on the position of the sampling probe in the tube. The sample is collected in a cyclone or a filter at the end of the probe. Calcium and sulfur compounds, specific surface area, and pore and particle size distributions are analyzed for the sample.
Stable system for multiple pulse, magic angle spinning and dynamic angle spinning NMR
Authors: Gerstein B. C. , Pan Hong-Jun , Pruski M.
Published: July 2002

A rotor-stator system is described that is suitable for (a) homonuclear decoupling experiments on solids, and (b) dynamic angle spinning experiments. The angle of rotation can be changed by 45° in 9 ms with no loss in rotation stability when spinning at 10 kHz.
Mounting and quality factor of a sensor for a gravitational radiation bar detector
Authors: Richard J.-P. , Pang Yi , Hamilton J. J.
Published: July 2002

A new method for the assembly of multimode gravitational radiation bar detectors is described. The method permits easy assembly and disassembly of a multiresonator system. In the test system used, a mechanical quality factor of 2.9×106 has been measured.
Simple laser setup for continuous laser spark generation
Authors: Pjatnitsky L. N. , Polonsky L. Ya. , Uvaliev M. I.
Published: July 2002

The continuous extended laser spark (CELS) is an optical breakdown in a gas arising at the axis of a ‘‘diffraction-free’’ beam at the caustic of a conical lens (axicon). It looks like a long (10–15 cm) continuous plasma string. In this article a setup for the CELS generation and investigation is described. It consists of a powerful Nd-glass laser, an axicon mounted in a discharge chamber, and diagnostic apparatus. CELSs were obtained in air, xenon, argon, helium, and carbon dioxide under pressures of 0.02 to 1 atm. It is proved that the simple laser with unstable cavity can be successfully used for CELS formation. This laser is highly reliable in operation and relatively cheap. It can be recommended for different scientific and technological applications.
Interface for the control of an optical multichannel analyzer by an IBM PC−Example: Vidicon detectors of the series PAR 1250
Authors: Chini G. , Kelbert K. , Bettermann H.
Published: July 2002

This article presents an interface device connecting an IBM PC with an optical multichannel analyzer. The processor (optional 8088 or 80286/80386) is directly integrated in the synchronization logic of the data acquisition. This is carried out by transferring strobe pulses from the controller of the multichannel analyzer to the input ‘‘TEST’’ of the processor 8088. The specific conditions of the operation modes (e.g., signal accumulation modes and target scannings stabilizing the detector target) have been taken into account by the signal processing routine.
A double pendulum vibration isolation system for a laser interferometric gravitational wave antenna
Authors: Stephens M. , Saulson P. , Kovalik J.
Published: July 2002

We have developed a nested double pendulum suspension system for the test masses of a laser interferometric gravitational wave antenna. The system consists of a mass hung as a pendulum inside a shell mass that is also hung as a pendulum. A set of two-degree-of-freedom reflective ‘‘shadow detectors’’ senses motion of the shell relative to ground. Identical sensors measure motion of the mass relative to the shell. The equations of motion were solved to find the resonances and mode shapes for all of the rigid body degrees of freedom. The predicted resonant frequencies agree well with the measured frequencies. A damping system has been implemented that damps the resonances by applying forces to the shell mass alone. The vibration transfer function along the optic axis was measured. It shows the steep f−4 decline expected of a double pendulum. We have also measured the vertical vibration transfer function and the cross coupling due to misalignment. A set of plates on the inner surface of the shell allows the application of low noise electrostatic forces directly to the test mass for high-bandwidth control such as interferometer fringe lock. We have measured the response of the system to this input, and compared it to that predicted by our model equations of motion. We have determined that there exist stable feedback loops that can maintain fringe lock. The possibilities of active isolation are discussed.
A procedure for the manufacture of EXAFS samples of concentrated materials
Authors: Marcus Matthew A. , Flood William
Published: July 2002

We describe a method of making samples of concentrated materials for use in fluorescence EXAFS (extended x-ray absorption fine structure) measurements. With this technique, one can easily make samples of a given areal density, with fine particle sizes. Both of these qualities are necessary in order to insure that self-absorption will not cause distortions in the fluorescence spectrum. These samples are also suitable for transmission measurements.
A ceramic-type diamond anvil cell for optical measurements at high pressure in pulsed high magnetic fields
Authors: Yamamoto K. , Endo S. , Yamagishi A. , Mikami H. , Hori H. , Date M.
Published: July 2002

A diamond anvil cell made of stabilized zirconia ceramic for high-pressure experiments under a pulsed high magnetic field is described. As an application, the magneto-optical spectra of ruby have been obtained at 77 K up to 7 GPa and 33 T, showing the Zeeman splitting of the fluorescent lines, R1 and R2.
Ion source metal-arc fault current protection circuit
Authors: deVries G. J. , Lietzke A. F. , van Os C. F. A. , Stearns J. W.
Published: July 2002

Ion sources can be damaged by arcs between metallic components of the source if these arcs are permitted to last. The negative-biased low-work-function converter in a surface conversion negative ion source is especially susceptible to metal-arc breakdown damage. Here an electronic circuit for minimizing the damage caused by such an arc is described. The circuit uses a transistor switch and an inductor in series with the converter bias power supply to limit the damage during the metal-arc breakdown.
Measurement of refractive indices of fibers with regular or irregular transverse sections and having a skin-core structure
Authors: Kabeel M. A.
Published: July 2002

Multiple-beam Fizeau fringes crossing fibers of different cross-sectional shapes and having a skin-core structure are studied to determine the refractive indices of the two layers. These fibers are of circular, rectangular, triangular, trilobal, elliptical, kidney, and dog-bone cross-sectional shapes. The area enclosed under the fringe shift is considered to represent the optical path difference integrated across the fiber. This method is suitable for the measurement of refractive indices of fibers of regular or irregular transverse sections. This method is applied to nylon 6 fibers.
Universal stress generating device for investigations of transmission properties of optical fibers under mechanical perturbations
Authors: Wisniewski Roland , Bock Wojtek J.
Published: July 2002

A universal apparatus is presented, designed to precisely generate a controlled state of mechanical stress upon any kind of optical fiber waveguide. With only minor procedural modifications, hydrostatic or radial pressure (up to about 300 MPa) can be generated, as well as an axial elongation up to 2000 microstrain and a twist up to about 50 full turns. A combination of any two of these types of stresses, such as twist under hydrostatic pressure, can also be generated to satisfy a specific need for a particular experiment. The apparatus provides a unique possibility to experimentally investigate several nontrivial effects associated with propagation of light through a waveguide remaining under a controlled stress environment. An example of such an application related to polarization coupling in highly birefringent fibers is also discussed.
Spatial distributions of the emitting species in a Penning surface-plasma source
Authors: Smith H. Vernon , Allison Paul , Schneider J. David , Saadatmand Kourosh
Published: July 2002

Using optical spectroscopy we study the spatial and temporal distributions of the Hα, Cs i(4555 Å), Cs ii(4604 Å), and Mo i(3903 Å) emission lines in a Penning surface-plasma source (SPS). A diagnostic slit exposes the entire SPS discharge gap either parallel or perpendicular to the magnetic field. The spatial and temporal distributions of the emitting species are recorded using a 1-m monochromator. In addition, the visible light and the Hα and Cs ii(4604 Å) spatial distributions are recorded with a video camera. The cesium atomic and ionic light, and the molybdenum atomic light, is strongly concentrated near the cathodes; the visible light and the Hα light is almost uniform in both directions. Electron-impact ionization of atoms sputtered from the cathodes and the return of the ions to the cathodes by residual plasma fields is probably the mechanism which concentrates cesium near the cathodes. The Cs0 mean free path is estimated to be 16 and 0.43 mm for 2 and 400 A discharges, respectively.
Optically pumped CdZnSe/ZnSe blue-green vertical cavity surface emitting lasers
Authors: Floyd P. D. , Merz J. L. , Luo H. , Furdyna J. K. , Yokogawa Toshiya , Yamada Yoichi
Published: July 2002

We describe the fabrication and operation of vertical cavity surface emitting layers by pulsed optical pumping. The structure consists of a vertical cavity resonator with SiO2/SiN distributed Bragg reflectors and a CdZnSe/ZnSe strained-layer superlattice active region. The emission spectra rapidly narrow to full width at half-maximum of 7 Å and the emission intensity increases by over two orders of magnitude, indicating stimulated emission. Lasing is observed at thresholds of ≊44 kW/cm2 at temperatures up to 30 K with lasing wavelength near 488 nm.
A conceptual approach for noncontact calorimetry in space
Authors: Fecht H. J. , Johnson W. L.
Published: July 2002

A concept is developed and described which allows to measure the heat capacity and the effective thermal conductivity of stable and undercooled liquid metals and alloys in an electromagnetic levitation apparatus. We propose to use an ac pulse heating method which is used nowadays as a standard technique for precision measurement of low temperature heat capacities. The ideal process parameters including the drop diameter D, temperature T, and frequency of measurement ω can be optimized when the following relations hold for the external and internal relaxation time constants τ1 and τ2, respectively: ωτ1≳10 and ωτ2<0.1. Then heat capacity data can be obtained with an accuracy of better than 1% with D about 5 to 10 mm, T between 1200 and 1800 K and ω between 0.1 and 1 Hz for typical metals and alloys.
Measurement of the cooling capacity of an RMC-Cryosystems Model LTS 4.5-025 closed-cycle helium refrigerator
Authors: de Zafra R. L. , Mallison W. H. , Emmons L. K. , Koller D.
Published: July 2002

We have measured the cooling capacity of a recently purchased RMC-Cryosystems Model LTS 4.5-025 closed-cycle He refrigerator over the range 4–35 K. We find that the nominal cooling capacity of 250 mW is only met or exceeded over a narrow temperature range around 4.3±0.5 K, and that above this range, there exists a considerable region of much lower cooling capacity, not exceeding ∼100 mW. We believe this behavior results from use of a fixed-aperture Joule–Thompson expansion valve, and might be alleviated if the J–T valve could be adjusted to compensate for changing flow within the 5–20 K temperature range. Present performance may severely limit or prevent effective use in applications where an irreducible heat inflow exists which is greater than ∼100 mW, yet substantially less than the quoted capacity at ∼4 K.
A digital temperature control system
Authors: Cofrancesco Pacifico , Ruffina Umberto , Villa Marco , Grossi Paolo , Scattolini Riccardo
Published: July 2002

The article outlines the hardware and software components of a general-purpose, PC-based temperature programming system. The multichannel thermocouple readout unit can switch, under computer control, among several modes of operation: calibration, analog cold junction compensation, differential temperature reading. The heating power is proportional to the output of a 12-bit DAC and is delivered by an efficient switching power supply. On the software side, we first introduce the development environment and the algorithms used to compute the control action. We show that an adaptive strategy outperforms the traditional proportional-integral-differential approach, and yields fast and accurate temperature responses when driving devices with widely different thermal characteristics.
High-performance pressure sensors using double silicon-on-insulator structures
Authors: Chung Gwiy-Sang , Kawahito Shoji , Ishida Makoto , Nakamura Tetsuro , Kawashima Mitsuo , Suzaki Tetsuo
Published: July 2002

A high performance pressure sensor using double silicon-on-insulator (SOI) structures, a (100) Si// (100) Al2O3// (100) Si/ SiO2/ (100) Si substrate, has been developed that is capable of very accurate operation at temperatures as high as 350 °C. A first SOI layer made by bonding two oxidized Si wafers together was employed as an etch-stop layer during KOH selective anisotropic etching and for controlling the thickness of the thin diaphragm. A double-heteroepitaxially grown second SOI layer on the first SOI layer was used as a dielectrically isolated single-element four terminal strain gauge that was placed at the center of a rectangular diaphragm. The dimensions of the diaphragm and its thickness were 360 μm ×1140 μm and 5 μm, respectively. This sensor has high sensitivity (0.04 mV/V⋅mmHg) for 700 mmHg full scale pressure range, with a nonlinearity less than +0.15% full scale. In the temperature range from −20 °C to +350 °C, the shift in sensitivity and offset voltage are less than −0.2% and +0.1%, respectively. Moreover, the implemented sensor is very useful for the miniaturization and integration of the sensor.
Mixture distributions fitted to instrument counts
Authors: Jones P. N.
Published: July 2002

A technique for fitting mixture distributions to discrete and continuous instrument count data is presented. The use of the EM algorithm for performing maximum likelihood estimation is introduced and advantages over other methods are discussed. Equations are presented for fitting mixtures of Poisson distributions and mixtures of normal distributions. Examples of the fitting of these two types of mixture distribution are given, and it is shown how standard errors of the parameter estimates can be obtained from within the framework of the fitting process.