bluuebunny/crossref_metadata_2025 huggingface dataset:
On the design of capillary and effusive gas dosers for surface science
Authors: Kuhl D. E. , Tobin R. G.
Published: July 2002

We present a theoretical analysis of flux distributions and enhancement factors for dosers of two types: capillary arrays and arrays of effusive sources. Our analysis introduces an important distinction between the flux per solid angle and the flux per unit area of the sample, and encompasses array diameters both smaller and larger than the sample. We find, contrary to earlier assertions, that a single effusive source gives unacceptably large flux gradients unless it is located so far from the sample that its enhancement factor is negligible. Arrays of a small number of effusive sources located near the sample edge, however, are competitive with capillary arrays for doser-to-sample distances comparable to the sample radius, and are readily adapted to large or unusually shaped samples. Capillary arrays outperform effusive arrays at all doser-to-sample distances, and are particularly effective when placed very close to the sample. If flux uniformity is a concern, a capillary doser should generally be at least 20% larger than the sample. Additional effects due to trapping by cold surfaces in the chamber and multiple collisions of the emitted molecules are discussed qualitatively.
The LCLS: A fourth generation light source using the SLAC linac
Authors: Arthur J. , Materlik G. , Tatchyn R. , Winick H.
Published: July 2002

Recent technological developments make it possible to consider use of the Stanford linear accelerator to drive a linac coherent light source (LCLS)—a laser operating at hard x-ray wavelengths. In the LCLS, stimulated emission of radiation would be achieved in a single pass of a high-energy, extremely bright electron beam through an undulator, without the optical cavity resonator normally used in storage ring-based free-electron lasers. The x-ray laser beam would be nearly diffraction limited with very high transverse coherence, and would exhibit unprecedented peak intensity and peak brightness, and sub-picosecond pulse length. Such an x-ray source offers unique capabilities for a large number of scientific applications.
A new technique for time-resolved x-ray diffraction measurements in the single-bunch operation applied to laser annealing
Authors: Kojima S. , Kudo Y. , Kawado S. , Ishikawa T. , Matsushita T.
Published: July 2002

We propose a new technique that is applicable to the time-resolved measurement of deformation on silicon surface during pulsed laser annealing in the single-bunch operation of the Photon Factory. There is a distribution of delay times between the activation of external trigger and the laser firing (the jitters) in the external trigger operation of laser equipment. This time distribution clearly makes the time-resolved measurement inaccurate. To overcome this disadvantage, a time-resolved measurement system that utilizes this time distribution has been developed. This system was composed of two TACs. The time distribution of the bunch (event number) and the time distribution of the intensity of the x rays diffracted from the silicon surface were measured. The respective signals were then accumulated in MCA1 and MCA2. The time course of the diffraction intensity before and after the laser irradiation was obtained by normalizing the time distribution of the intensity of the diffracted x rays with the time distribution of the event number.
Total photoelectron imaging of submicron stripe patterns using soft x-ray microbeams formed by Wolter-type mirrors
Authors: Hasegawa Masaki , Ninomiya Ken
Published: July 2002

Line scans of micro- to submicron-width stripe patterns with soft x-ray (150 eV) microbeams formed by Wolter-type mirrors were performed by detecting total photoelectron intensity. The samples were aluminum stripes delineated on a SiO2 wafer with identical width and spacing of either 0.7, 1, or 4 μm. The modulation of an image of the 4-μm-linewidth stripe pattern, which was obtained by scanning a 2.1 μm focused beam, was 0.33. The modulations of images for the 1-μm-linewidth stripe pattern and for the 0.7-μm-linewidth stripe pattern, both of which images were obtained by scanning a 1.8 μm focused beam, were, respectively, 0.12 and 0.08. We achieved the highest lateral resolution in one-dimensional photoelectron imaging performed by grazing incidence mirrors.
Feasibility of photoexcitation imaging in soft x-ray microscopy using the transition to π* orbits in biological molecules
Authors: Iketaki Yoshinori , Watanabe Tsutomu
Published: July 2002

In the so-called water-window wavelength region, the photoexcitation cross section is found to be larger by two orders of magnitude than those for the photoionizations of atoms. Making use of these physical phenomena, a new imaging method for microscopy was studied. We have concluded that this method is useful for the measuring the molecules in DNA or RNA of wet biological cells. A sufficient contrast for microscopy measurements can be obtained by using the photoexcitation of the 1s-orbital electron to π* orbits.
A voltage-controlled resistor for the remote control of monostable multivibrators
Authors: Chudobiak Michael J.
Published: July 2002

A new method is introduced for generating a precise large-signal voltage-controlled resistance for the purpose of remotely controlling monostable multivibrators (one-shots). The circuit presented offers linear control of the resistance with ten to one resistance variation and infinite resolution, and a usable resistance range of approximately 100 Ω–500 kΩ. The full-scale resistance can be arbitrarily set within this range. The circuit has a bandwidth of 10 MHz, and the voltage across the resistance can be as large as ±12 V. The voltage-controlled resistance is generated by using an analog voltage-controlled current source.
A new method for studying debris from laser-induced spall in metals
Authors: Arad B. , Eliezer S. , Henis Z. , Horovitz Y. , Kolka E. , Ludmirsky A. , Moshe E. , Werdiger M.
Published: July 2002

A new method of measuring the free-surface velocity via soft x-ray shadowgraphy is presented. Using that method, the shock-wave pressure was deduced. In addition, a new method of measuring the Mie scattering of the debris from laser-induced spall in aluminum is also presented. The data have yielded the distribution of the debris radii in the range of 1–7 μm. Furthermore, it was shown that the smaller particles are the faster ones.
Aqueous-electrolyte resistors for pulsed power applications
Authors: Beverly R. E. , Campbell R. N.
Published: July 2002

Aqueous-electrolyte resistors were developed for use as dummy loads in pulsed power systems. These resistors are simple, robust, low-inductance devices capable of operation at high voltage and high current, and may be used to dissipate large pulse energies without catastrophic failure. The resistivity and temperature coefficient of resistivity were measured for several candidate electrolytes, including aqueous solutions of copper sulfate, potassium and aluminum sulfate, potassium dichromate, silver nitrate, sodium dichromate, and sodium thiosulfate. The resistivity of potassium dichromate solution is expressed by the power law ρ(Ω cm)=1640 C−1.0942 for electrolyte concentrations in the range C=0.025–25 g/ℓ. The temperature coefficient of resistivity is in the range (1/ρ)(∂ρ/∂Ts)=−(0.01–0.03)/°C for typical aqueous metal–salt electrolytes and is dependent on the solution temperature Ts and, to a lesser extent, on the electrolyte concentration. Aqueous solutions of potassium dichromate are compatible with brass, copper, and stainless-steel electrodes and polycarbonate and polymethylmethacrylate insulators, even at high concentration and elevated temperature. Such resistors give long shelf and operational lifetimes. If the maximum allowable resistance change (decrease) during the pulse is 10%, then the energy deposition per unit volume of electrolyte solution is limited to approximately 20 J/cm3 for resistors initially at room temperature.
Improved confinement in the cold region of a Uramoto-type ion source for negative hydrogen ion production
Authors: Jimbo Kouichi , Iima Masashi
Published: July 2002

It has been reported that plasma confinement in the cold region of a Uramoto-type sheet plasma ion source is very important for negative hydrogen ion production [Rev. Sci. Instrum. 66, 1035 (1995)]. In the present experiments, the stainless chamber was biased as low as 100 V relative to the anode potential in a 150 V–15 A discharge. The negative hydrogen ion current density (5 mA/cm2) was found to be larger than the positive hydrogen ion current density under the same experimental conditions. These experimental results suggest that the negative hydrogen ions are formed directly from atomic hydrogen.
One-dimensional position-sensitive superheated-liquid-droplet in-phantom neutron dosimeter
Authors: Lim W. , Wang C. K.
Published: July 2002

The one-dimensional (1D) position-sensitive superheated-liquid-droplet in-phantom neutron dosimeter incorporating a sensitive volume emulsion has been fabricated, prepared, and tested. The 1D position-sensitive superheated-liquid-droplet dosimeter (SLDD) is fabricated from a 3/8-in.-o.d., 1/4-in.-i.d., 20-cm-long, PlexiglasTM-walled tube filled with a mixture of superheated-liquid FreonTM droplets and host medium glycerol solution. Washer-shaped piezoelectric acoustic transducers are positioned at both ends of the tube; they determine the number and positions of the acoustic events when the superheated-liquid droplets evaporate upon neutron irradiation. The SLDD is sensitive to a wide range of neutron energy, from thermal (0.0253 eV) up to 10 MeV and higher. The SLDD is irradiated with the 137Cs and 60Co γ sources, as well as a 252Cf neutron source to test for its radiation response and spatial resolution. The SLDD based on the Freon-134a superheated-liquid droplets operating at 20 °C and 1 atm is found to be ideal for measuring neutron depth dose and relative biological effectiveness dose. This study also proves that the position of the radiation-induced nucleation acoustic events can be linearly determined from the differences in the transmission times received by the acoustic transducers on the 1D SLDD. The spatial resolution of the neutron depth dose is 1 mm due to the finite response time (1 μs) of the piezoelectric acoustic transducers.
Improved circular polarizer for far-infrared lightpipe systems
Authors: Wu S. , Kaplan S. G. , Quijada M. , Sengupta K. , Drew H. D.
Published: July 2002

We present an improved design for far-infrared (FIR) circular polarizers used in a lightpipe transmission system for magneto-optical experiments. A peak efficiency of nearly 100% is achieved for FIR laser radiation by reducing the multiple reflections within the polarizer system, as well as scattering from the walls of the lightpipe. Broadband low-resolution measurements are less susceptible to errors due to multiple reflections, but incorporation of these improvements is still found to reduce systematic errors due to the reflection from the sample. Also, we have measured the low temperature index of refraction of quartz and find significant disagreement with published values for frequencies below 100 cm−1.
Noncontact sheet resistance measurement technique for wafer inspection
Authors: Kempa Krzysztof , Rommel J. Martin , Litovsky Roman , Becla Peter , Lojek Bohumil , Bryson Frank , Blake Julian
Published: July 2002

A new technique, MICROTHERM, has been developed for noncontact sheet resistance measurements of semiconductor wafers. It is based on the application of microwave energy to the wafer, and simultaneous detection of the infrared radiation resulting from ohmic heating. The pattern of the emitted radiation corresponds to the sheet resistance distribution across the wafer. This method is nondestructive, noncontact, and allows for measurements of very small areas (several square microns) of the wafer.
First results of a high-current electron cyclotron resonance proton source
Authors: Farchi A. , Delaunay M. , Melin G. , Gobin R. , Leroy P.-A. , Faure J. , Delferrière O. , Lagniel J.-M.
Published: July 2002

A 2.45 GHz electron cyclotron resonance (ECR) ion source for producing a 100 mA H+ beam is under study. The microwave power is coupled through a quartz window and a water-cooled 90° waveguide bend in order to avoid the heating of the electrons backstreaming from the source. The ECR condition is obtained with dc magnetic coils. Preliminary results reported here show that a beam current density of 75 mA/cm2 can be extracted at 10 kV from a 3-mm-diam aperture, with 1.2 kW of microwave power at 1×10−3 mbar of hydrogen pressure. The proton fraction is 75% with an alumina-coated plasma electrode and 85% with a nitride coating.
Investigations in the Joint Institute for Nuclear Research on the improvement of highly charged ion production in ion sources
Authors: Shirkov G. D.
Published: July 2002

The main statements of the new Joint Institute for Nuclear Research (JINR) research and development (R&D) project ‘‘Investigations on the Physics of Multicharged Ion Sources for JINR and CERN Hadron Accelerators’’ are presented in this report. The project will be performed with the purpose of improving the source efficiency for the JINR and CERN accelerator complexes. The project will include the theoretical and experimental investigations as well as x-ray spectroscopy of highly charged ion plasma in the sources.
High-current plasma lens: New results and applications
Authors: Goncharov A. A. , Dobrovolsky A. N. , Litovko I. V. , Protsenko I. M. , Zadorodzny V. F.
Published: July 2002

Influence of spherical and momentum aberrations of the electrostatic plasma lens (PL) on the intense ion beam focusing and maximal compression is investigated experimentally and theoretically. It is shown that when spherical aberrations are absent unavoidable momentum aberrations affect the radial profile of multicharged ion beams. This profile appeared to be steplike. PL electric potential radial profile providing transformation of unhomogeneous (Gauss) profile of a beam at the PL entrance to homogeneous one on the target on the given distance from PL is obtained analytically. High-current PL efficiency for compensated ion beam setting on the quasi-Brillouin orbit is demonstrated to be experimentally and theoretically substantiated.
Ion optical system for transport and deceleration of highly charged ions
Authors: Henke D. , Tyrroff H.
Published: July 2002

An ion optical system which transports the highly charged ions of an ECR ion source to a RBS end station of a 2 MV Van de Graaff beam line is described. The highly charged ions are focused and decelerated in a four-electrode lens to a spot size of about 5 mm on the grounded target. The system transports ion currents of 0.1–50 μA with 90% transmission to final kinetic energies of q*(10–10 000) eV (q being the charge state of the ion).
A slab-shaped electron cyclotron resonance ion beam source for in-line running target treatments
Authors: Roy V. , Wartski L. , Boukari F. , Momy A. , Schwebel C. , Coste Ph. , Aubert J.
Published: July 2002

The possibility of industrial surface treatments of broad metallic rolls by appropriate ion beams has motivated our study of an immersed electron cyclotron resonance slab-shaped ion source composed of a number of elementary microwave modules fed in parallel through a linear power divider. We describe the performances of a single module implemented by a 45-mm-height ionization chamber of 80×15 mm cross section surrounded by a set of permanent magnets in a multipole configuration. A current density of 5 mA/cm2, uniform to within 10% over a 60 mm width, has been obtained for argon as well as for oxygen and nitrogen under a 500 W input power and a gas pressure of 5–8×10−3 mbar in the ionization chamber. Moreover, we have investigated the case of the non-normal incidence of the ion beam onto the running target. For 30° and 60° incidence angles with respect to the normal, the current density loss is 15% and 25%, respectively.
A 16 cm broad-beam ion source for ion-beam etching of quartz wafers
Authors: Rao Yusheng , Li Ming , Qi Bo , Li Fei
Published: July 2002

A broad-beam ion source is developed for ion-beam etching of quartz wafers, which are used in resonators with a high basic frequency of the order of magnitude of 1 GHz. The improvement of uniformity of the extracted ion beam is investigated. The double-grid multiple-aperture ion optics is adopted, in which perveance is matched by varying both the aperture diameters and spaces between grids. The configuration of the magnetic field is optimized. Measured at the target of 12 cm from the grids, the area of uniform region (nonuniformity <5%) is approximately equal to the area of the bored region of the grids (12 cm diam) and 1/1.78 of the cross-section area of the anode (16 cm diam). A broad beam of 100–1000 eV and 0.1–2.0 mA/cm2 is extracted from the source to fulfill the requirement of the etching process. Without any cooling system, the ion source is installed in vacuum chamber.
A method for producing highly uniform field characteristic with line currents
Authors: Crow James T.
Published: July 2002

Symmetries in basic equations for dipole fields of line currents allow the use of a relatively small number of conductors to produce highly uniform transverse (dipole) magnetic fields over a large fraction of the interior of the cylinder on which the wires are located. For example, a simple 12-wire array has better than 1 ppm field uniformity for radii up to 1/3 of the cylinder radius, and better than 0.1% uniformity over more than 1/3 of the cylinder area, and a 50-wire array would have approximately 0.001 ppm uniformity over half the cylinder area if sufficient construction accuracy could be maintained. The configurations are simply transformed to quadrupoles, sextupoles, and higher multipoles that have highly uniform appropriate radial field derivatives. Shielded systems are also described.
General review of recent developments for electron cyclotron resonance ion sources (invited)
Authors: Sortais P.
Published: July 2002

In this article we will recall the main characteristics of electron cyclotron resonance (ECR) discharges for the production of multicharged ions and we will show basic limitations of ECRIS performances using the elementary zero dimension ionization equilibrium model. Then we will present main domains where the ion source characteristics are the limiting factor for the applications. The improvement of the technology of compact ECR ion sources dedicated to applications in special environments like on line isotopic separators or high-voltage platforms will be discussed. Finally, we will describe advanced ion sources projects for future production of very highly charged ions generally connected to superconducting devices.
A simple digital multilevel streak image of combustion
Authors: Hajossy R. , Morva I. , Pavlík J. , Sůra P.
Published: July 2002

A method of a digital streak photography of combustion or a detonation process is described. The streak image is reconstructed from binary words produced by an ordered set of sensors which monitor the process. The temporal and spatial resolution of the process is increased by a quick periodic changing of threshold levels used for the analog–digital conversion of the sensor signals. The multilevel digitization gives a measure of signal intensity with time. The proposed streak-photograph-like projection of the flame position has been used to visualize the condition of the burning fuel in long pipes.
Absolute calibration of nuclear activation diagnostics for intense pulsed ion beams
Authors: Young F. C. , Boller J. R. , Stephanakis S. J.
Published: July 2002

Absolute calibration of an annihilation-radiation NaI coincidence detection system for short-lived ion-induced radioactivity is described. Calibration with a 22Na radioactive source is compared with an independent calibration using the 12C(p,γ)13N(β+) reaction with 1 MeV protons from a Van de Graaff accelerator. These calibrations are consistent, provided correction for summing of the 0.51 and 1.27 MeV gamma rays from the 22Na source in the NaI detectors is included. This summing correction depends on the total efficiency for detecting 1.27 MeV gamma rays and can alter the calibration by as much as a factor of 2, depending on the size and separation of the detectors. A procedure to determine this correction using 60Co and 22Na radioactive sources is described. These two calibrations give a thick-target yield for the 12C(p,γ)13N reaction at 1 MeV of (8.0±0.4)×10−10 reactions/proton. Intense pulsed proton fluences of 0.08 to 3.7 cal/cm2, determined by coincidence counting β+ annihilation radiation produced by the 12C(p,γ)13N(β+) reaction, are in agreement with ion-beam fluences measured independently with carbon calorimeters on the same carbon sample.
High-pressure, capillary x-ray absorption fine structure cell for studies of liquid and supercritical fluid solutions
Authors: Wallen Scott L. , Pfund David M. , Fulton John L. , Yonker Clement R. , Newville Matthew , Ma Yanjun
Published: July 2002

A method is described to acquire x-ray absorption fine structure (XAFS) spectra of high-pressure liquid and supercritical fluid solutions. The technique employs a short length of fused-silica capillary tubing that has an inner diameter of 250 μm and an outer diameter of 360 μm. A hairpin bend is formed near the center of the capillary and the bend is then placed end-on directly in the focused x-ray beam. Fluorescence spectra were acquired in a 90° geometry using a 13 element Ge detector. Demonstration XAFS spectra are reported for a Mn organometallic complex dissolved in subcritical and supercritical CO2. Although the maximum pressure of these studies was 160 bar, with slight modification, the method will be applicable to studies requiring pressures as high as 4 kbar.
Midinfrared cw difference-frequency generation using a synchronous scanning technique for continuous tuning of the full spectral region from 4.7 to 6.5 μm
Authors: Chen W. , Burie J. , Boucher D.
Published: July 2002

We report in this article an experiment of laser-based continuous-wave (cw) midinfrared difference-frequency generation using a synchronous scanning technique for continuous tuning of the complete spectral region from 4.7 to 6.5 μm (1550 to 2200 cm−1). A wavelength-tuned, noncritically phase-matched AgGaS2 crystal was used as the nonlinear optical mixing medium. Midinfrared output power of ∼10 μW was obtained by mixing two tunable lasers with ∼430 mW total pump power. The pump lasers were synchronously scanned during infrared wavelength tuning. The infrared frequency was deduced from the difference between the two laser frequencies which were simultaneously measured by wavemeters with an absolute accuracy of better than 0.007 cm−1. No reference cell was needed for frequency calibration. High-resolution spectra of carbonyl sulfide (OCS) were recorded for an evaluation of the frequency calibration and high-resolution spectroscopic characteristics.
Time evolution of charge states in an electron cyclotron resonance ion source (abstract)a)
Authors: Pardo R. C. , Harkewicz R. , Billquist P. J.
Published: July 2002

The production of high charge-state ions in an electron cyclotron resonance ion source has been studied as a function of time using a pulsed Nd:YAG laser to ablate heavy metal (bismuth) ions into the plasma. The time required to produce a charge state has been measured by observing the arrival time of the ions at a Faraday cup after the source analyzing magnet. The results of these measurements have been compared to a simple sequential ionization model and are found to be in good agreement with the data. The data can be used to characterize the plasma electron density, electron temperature, and neutral atom density, since these are the only three adjustable parameters in the model and are sufficient to achieve good agreement for the time evolution of all observed charge states.
Projecting two-axis nanometer scale displacement of microscopic beads onto a quadrant photodetector with a laser beam
Authors: Li Daqun , Schnapp Bruce J.
Published: July 2002

A quadrant photodetector has been added onto a custom differential interference contrast microscope to measure two-axis displacement of silica beads with a noise ⩽0.1 nm/√Hz below 150 Hz. A diode-pumped solid-state laser is incorporated to function not only as a light source for displacement detection but also as an optical trap for motility studies of protein motors. This system is designed for studies in which the motility needs to be simultaneously monitored along both axes at nm accuracy.
Demountable epoxy joints
Authors: Feldman Martin
Published: July 2002

We have been using epoxy adhesive to bond components in a way which has significant advantages over both conventional adhesive and screw joints. The joints are demountable, and can often be used where conventional techniques would be impractical.
Intermodulation measurement of nonlinearities in piezoceramic resonators
Authors: Albareda A. , Pérez R. , Villar J. L. , Minguella E. , Gorri J. A.
Published: July 2002

A method for measuring the nonlinear coefficients of piezoceramic resonators with low signal excitation is presented. It consists of the intermodulation produced by two signals with variable amplitude and closely spaced in frequency at the neighborhood of the resonance, performing the measurement of the intermodulation distortion signals at frequencies near excitation. This method is highly sensitive and allows nonlinear measurements to be taken at relatively low levels, avoiding thermal effects. The module and argument of the nonlinear increase in the impedance can be determined by the analysis of these measurements. This method is compared with other previously used methods, and the advantages of the proposed method are analyzed. The described nonlinear coefficient allows us to understand and foresee the nonlinear behavior near the resonance: amplitude-frequency shift effect, decrease of mechanical quality factor Q, and the jump phenomenon observed in frequency sweeps.
Longitudinal detection of pulsed low-frequency, low-temperature nuclear magnetic resonance using a dc SQUID
Authors: Wurm Martin , Brison Jean-Pascal , Flouquet Jacques
Published: July 2002

We present our new setup of longitudinal nuclear magnetic resonance detected by a superconducting quantum interference device. It was built specifically for the study of metallic single crystals at low frequency. We report the main difficulties encountered with such measurements, mainly thermal effects which are usually barely discussed in the literature although they put the true limit of such measurements. We also illustrate in detail the actual performances of our experiment on different test samples up to the first measurement of a metallic single crystal with such a technique.
Prototype negative-ion sources for radioactive ion-beam generation
Authors: Alton G. D. , Welton R. F. , Williams C. , Cui B. , Murray S. N.
Published: July 2002

Radioactive ion beams (RIBs) of F17 and F18 are of interest for investigation of astrophysical phenomena such as the “hot” CNO cycle and the rp stellar nuclear synthesis processes. In order to generate useful beam intensities of atomic F−, the species must be efficiently and expediently released from the target material, thermally dissociated from fluoride release products during transport to the ionization chamber of the ion source, and efficiently ionized in the source upon arrival. We have conceived and evaluated two prototype negative-ion sources for potential use for RIB generation: (1) a direct extraction source and (2) a kinetic-ejection source. Both sources utilize Cs vapor to enhance F− formation. The mechanical design features, operational parameters, ionization efficiencies for forming atomic F−, and delay times for transport of F and fluoride compounds for the respective sources are presented. The efficiency η for formation and extraction of F− for the direct extraction negative-ion source is found to be η∼1.0% while the characteristic delay time τ for transport of F and fluorides through the source is, typically, η∼120 s; the analogous efficiencies and delay times for the kinetic ejection negative-ion source are, respectively: η=∼3.2% and τ=∼70 s.
High-pressure cell for neutron scattering under cryogenic temperature and high magnetic field: The Osaka–Kyoto cell
Authors: Amita Fujitsugu , Onodera Akifumi
Published: July 2002

A high-pressure cell has been developed which can be accommodated with neutron-scattering systems for triple extreme conditions of high pressure, low temperature, and high magnetic field. The design of this cell, the Osaka–Kyoto cell, is basically a piston-cylinder type carrying a compound cylinder that consists of segmented inner and autofrettaged outer parts. The pistons are made of sintered diamond while the cylindrical parts are composed of hot-pressed alumina and nonferrous alloys. A 4-mm-diam, 15-mm-long sample can be studied under pressures exceeding 1.6 GPa.
Operation of an 8 m suspended Michelson interferometer
Authors: Zhao C. , Notcutt M. , Ju L. , Blair D.
Published: July 2002

In this article we report the successful locking and operation of an 8 m Michelson interferometer which uses multistage cantilever spring vibration isolators. The control system for normal mode damping is described. The performance and dominant noise sources of this interferometer are discussed.
The motional Stark effect diagnostic on TEXTOR-94: First measurements
Authors: Soetens T. , Jaspers R. , Desoppere E.
Published: July 2002

We have developed a diagnostic to measure the motional Stark effect (MSE) on TEXTOR-94. This diagnostic allows us to measure locally the strength and direction of the magnetic field. Furthermore, the major radius of observation and the radial electric field are determined. Because the MSE diagnostic on TEXTOR-94 employs the full spectral information, in addition to the complete polarization, the measurements are independent from other experimental data. In this article we present the first preliminary results of the MSE diagnostic on TEXTOR-94.
In-vessel tritium measurements using beta decay in the Tokamak Fusion Test Reactor
Authors: Zweben S. J. , Gentile C. , Mueller D. , Nagy A. , Pearson G. , Skinner C. H. , Walsh J.
Published: July 2002

Tritium on the inside walls of the Tokamak Fusion Test Reactor was detected by configuring the vacuum vessel as an ionization chamber and measuring the secondary electron current from the tritium beta decay. The vessel was typically filled with ≈5 Torr of dry nitrogen and the secondary electron current was collected by an internal electrode biased to about +15 V with respect to the vessel wall. The measured variations of the collected current with gas pressure, bias voltage, and applied magnetic fields are described, as well as an in situ calibration made by injecting a known amount of tritium gas. Improved versions of this diagnostic may be useful to track the in-vessel content of surface tritium in future fusion devices.
Neutron profile measurements for trace tritium experiments
Authors: Loughlin M. J. , Watkins N. , Adams J. M. , Basse N. , Hawkes N. P. , Jarvis O. N. , Matthews G. , Marcus F. B. , O’Mullane M. , Sadler G. , Strachan J. D. , van Belle P. , Zastrow K-D.
Published: July 2002

The JET neutron profile monitor was used to study the transport of tritium into a magnetically confined deuterium plasma. Trace amounts of tritium were introduced through a gas valve beyond the plasma edge into a variety of plasma confinement regimes. The d(t,n)α fusion cross section is two orders of magnitude greater than the d(d,n)3He cross section and so a puff of tritium which has a negligible effect on the plasma nevertheless produces a large d–t neutron signal. The profile monitor consists of two cameras each made up of a fan-shaped array of collimated lines of sight. It was used to measure the d–d and d–t neutron profiles simultaneously. This article describes the detection system, its operation and assesses the difficulties due to scattered neutrons. The profiles can be used to determine tritium density and transport coefficients.
Design and operation of a low cost, reliable millimeter-wave interferometer
Authors: Porte L. , Rettig C. L. , Peebles W. A. , Ngyuen X.
Published: July 2002

Knowledge of basic plasma parameters, such as line integrated density and turbulence spectra, is essential for physics understanding and plasma control. Integration of plasma diagnostic systems into a single port combined with diagnostic cost reduction is an important advance that can impact measurement availability on all fusion devices. This article presents preliminary data from a unique, low cost and reliable millimeter-wave interferometer that has been integrated to operate simultaneously with a collective Thomson scattering system. The interferometer uses only one commercially available frequency chirped source and only one detector. The DIII-D system design will be described together with preliminary design of a tangentially viewing system for the Pegasus spherical torus experiment.
Neutron yield measurements by use of activation techniques on TEXTOR-94
Authors: Wolle B. , Gadelmeier F. , Beikert G. , Hübner K. , Bätzner R.
Published: July 2002

The time integrated neutron yield on TEXTOR is measured with an activation system which pneumatically sends the samples near to and from the plasma edge. After irradiation the samples are counted by an absolutely calibrated high purity germanium (HPGe) detector. The uncertainty in the calibration of the HPGe detector is less than 2%. By using threshold reactions for indium and silicon samples it is possible to distinguish between the 2.5 and 14 MeV neutron emission. MCNP code simulations have been performed in order to determine the neutron fluence and energy distribution at the irradiation position. This allows calculation of an activation coefficient which relates the activation of the sample to the total yield from the TEXTOR plasma. For the 2.5 MeV neutron emission the corresponding error is less than 15%. Details on the measuring procedure as well as on the calibration method of the HPGe detector are provided. Results of calibration monitoring of the neutron source strength measurements and the triton burnup measurements are presented.
Dual CO2 laser polarimeter for Faraday rotation measurement in tokamak plasmas
Authors: Kawano Yasunori , Chiba Shin-ichi , Shirai Hiroshi , Inoue Akira , Nagashima Akira
Published: July 2002

The first operational results of the dual CO2 laser polarimeter to measure the Faraday rotation in large tokamaks is described. The polarimeter consists of two same type polarimeters except those wavelengths of 10.6 and 9.27 μm. By simultaneous measurement of two wavelengths, the Faraday rotation component at vacuum windows is expected to be eliminated from the measured polarization angle. Each polarimeter utilizes photoelastic modulators for reliable polarization detection. Such a polarimeter scheme is easily compatible with the dual CO2 laser interferometer, hence, the new system is called as the dual CO2 laser polarimeter/interferometer. The Faraday rotation by the JT-60U plasma is successfully measured even at a fast disruption. The Faraday rotation angle from the 9.27 μm polarimeter shows good agreement with the calculation. It is found that the calibration of the 10.6 μm polarimeter should be improved for full two-color operation. The accuracy of the polarization angle is 0.1° for the data sampling rate of 250 Hz, which is sufficient for large devices like ITER.
Wavelet analysis of plasma fluctuations in microwave reflectometry
Authors: Bruskin L. G. , Mase A. , Tokuzawa T. , Kubota S. , Oyama N. , Itakura A. , Tamano T.
Published: July 2002

A time–frequency analysis of plasma turbulence is performed for the GAMMA10 tandem mirror plasma. The method is based on the decomposition of the reflectometer signal into a set of wavelets. Excellent resolution in the time–frequency domain, inherent to wavelet analysis, allowed us to observe fast changes in the instantaneous spectra of fluctuations, which would be averaged out if treated using conventional Fourier analysis. In order to estimate the propagation velocity of turbulent fluctuations, a wavelet cross-correlation function was calculated. Comparison of wavelet spectra, corresponding to different reflectometer channels, demonstrates the existence of short-time flashes of fluctuation intensity, as well as elongation of low-frequency disturbances along the magnetic field lines and their rotation in the E×B direction. Plasma fluctuations in the Alfvén range of frequencies sometimes propagate from the center towards the magnetic plugs with velocities close to 1000 km/s. In general, the wavelet spectra of plasma turbulence in the Alfvén range of frequencies, viewed by means of the microwave reflectometer, appear to be much more irregular than the corresponding spectra of magnetic field fluctuations obtained using magnetic probes.
Absolute, soft x-ray calorimetry on the Z facility at Sandia National Laboratories (invited)
Authors: Fehl D. L. , Muron D. J. , Leeper R. J. , Chandler G. A. , Deeney C. , Stygar W. A. , Spielman R. B.
Published: July 2002

Simple and reliable x-ray fluence measurements, in addition to time-resolved diagnostics, are needed to understand the physics of hot Z-pinch plasmas. A commercially available laser calorimeter has been modified for measuring soft x-ray fluence from the Z facility at Sandia National Laboratories. The x-ray absorber of this calorimeter is an aluminum disk, attached to a two-dimensional thermopile and surrounded by an isoperibol shroud. The time integral and the maximum of the thermopile voltage signal are both proportional to the x-ray energy deposited. Data are collected for 90 s, and the instrument has, thus far, been used in the 1–25 mJ range. A wider dynamic measuring range for x-ray fluence (energy/area) can be achieved by varying the area of the defining aperture. The calorimeter is calibrated by an electrical substitution method. Calibrations are performed before and after each x-ray experiment on the Z facility. The calibration of the time integral of the thermopile voltage versus energy deposited (or the peak of thermopile voltage versus energy deposited) is linear with zero intercept at the 95% confidence level. The irreproducibility of the calibration is <2%, and the imprecision in the measurement of the incident x-ray energy (inferred from signal noise and the calibration) is estimated to be ∼0.9 mJ (95% confidence level). The systematic uncertainty (inaccuracy), due to correctable baseline shifts, is estimated at ±10%. Comparisons have been made of the calorimeter to time-resolved x-ray diagnostics, e.g., bolometers and x-ray diode arrays, by integrating the flux measured by such instruments over time.
Calibration of the distance between electrodes of mechanically controlled break junctions using field emission resonance
Authors: Kolesnychenko O. Yu. , Shklyarevskii O. I. , van Kempen H.
Published: July 2002

This article presents an accurate method for calibration of the relative displacement Δz of mechanically controllable break junction electrodes and determination of the metal work function φ using oscillating behavior of tunnel conductance (known also as a Gundlach oscillation) in a field emission region. The precision of the proposed method is at least one order of magnitude better than the most reasonable estimations that have previously been possible. In combination with tunnel current-distance dependence I(z) measurements, the absolute vacuum gap can be evaluated with an accuracy ±0.25 Å.
A circuit for measuring the gap voltage of a scanning tunneling microscope on a nanosecond time scale
Authors: Ochmann M. , Münzer H.-J. , Boneberg J. , Leiderer P.
Published: July 2002

We demonstrate a new circuit design for fast measurements of the voltage drop across the gap of a scanning tunneling microscope (STM) based on the simultaneous operation of two different amplifiers. The first is a fast instrumentation amplifier, sensing directly the voltage drop across the tunneling barrier, the second is a medium speed current amplifier with an overall gain of 108 V/A, suitable for normal STM operation. We obtained a time resolution of 10 ns measuring the plasma ignition under a STM tip during illumination with an intense 10 ns laser pulse. Possible applications include the study of STM point contacts.
Soft, entirely photoplastic probes for scanning force microscopy
Authors: Genolet G. , Brugger J. , Despont M. , Drechsler U. , Vettiger P. , de Rooij N. F. , Anselmetti D.
Published: July 2002

A new probe made entirely of plastic material has been developed for scanning probe microscopy. Using a polymer for the cantilever facilitates the realization of mechanical properties that are difficult to achieve with classical silicon technology. The new cantilever and tip presented here are made of an epoxy-based photoplastic. The fabrication process is a simple batch process in which the integrated tip and the lever are defined in one photolithography step. The simplicity of the fabrication step, the use of a polymer as material, and the ability to reuse the silicon mold lead to a soft low-cost probe for scanning force microscopy. Imaging soft condensed matter with photoplastic levers, which uses laser beam deflection sensing, exhibits a resolution that compares well with that of commercially available silicon cantilevers.
New fiber-optic attenuator calibration technique using linear intensity modulation characteristics of a laser diode
Authors: Singh Ranjit , Kawakami Tomoteru
Published: July 2002

A new fiber-optic attenuator calibration technique has been developed using linear intensity modulation characteristics of a laser diode. It does not require detector linearity to be known. The uncertainty of attenuation calibration for a typical 10 dB attenuator is 0.020 dB at two standard deviation levels. The resolution of the system is 0.001 dB and the dynamic range is 25 dB in a single step.
Group-phase refractive index method for improving the accuracy in two-color interferometric length measurements
Authors: Zeng Lijiang , Matsumoto Hirokazu , Seta Katuo
Published: July 2002

A group-phase refractive index method was developed for improving the accuracy of a conventional two-color method used in an interferometer for length measurements. This method uses two closer wavelengths to reduce the errors caused by air turbulence and the chromatic aberration. We describe the new method and demonstrate preliminarily its effectiveness by measuring the group refractive index of air using a vacuum cell. We then compared the results with those calculated using the Edlén equation. The mean difference between the measured and calculated values was 2.15×10−6 with a standard deviation of 2.0×10−6 for the vacuum cell with a length of 184.5 mm.
Optical properties of mirrors for focusing of non-normal incidence atom beams
Authors: Wilson R. J. , Holst B. , Allison W.
Published: July 2002

Calculations of focal properties and third-order aberration coefficients are presented for atom mirrors based on elastically deformed single-crystal surfaces. Biaxial loading of the mirrors is achieved by a combination of a uniform applied pressure and rectangular boundary conditions. The results are calculated for readily available single-crystal wafers of Si(111) with a thickness of 50 μm and a usable free standing diameter of 18 mm. Focusing of beams at non-normal incidence requires the principal radii of curvature, in planes normal to the mirror plane, to be different. The ratio of these principal radii of curvature is shown to be insensitive to the applied pressure and can be varied by a factor greater than 10 by changing the boundary conditions from square (1:1) to rectangular (1:2).
Hollow-cathode plasma electron gun for beam generation at forepump gas pressure
Authors: Burdovitsin Viktor , Oks Efim
Published: July 2002

The characteristics, performance, and design feature of a filamentless plasma-cathode electron gun for beam generation in the forepump gas pressure range are presented. The plasma cathode is based on a hollow-cathode direct current (dc) discharge. Using the method of “grid stabilization” it was possible to generate an e beam at a background gas pressure as high as about 10−1 Torr. This pressure can be easily obtained by using mechanical pump only. The operation of the gun with a magnetic field up to 0.1 T was investigated. The presence of a magnetic field (B field) is often required, for instance in plasma chemistry and surface treatment processes. The effect of the B field both on discharge and emission parameters of the gun are observed. The results obtained can be explained based on the concept of electron confinement and motion across the B field. With the accelerating voltage up to 8 kV, the gun is able to generate an electron beam of about 0.7 A dc.
High sensitivity 2 T vibrating sample magnetometer
Authors: Dufeu D. , Lethuillier P.
Published: July 2002

A new version of the vibrating sample magnetometer with a 2 T vertical axis superconducting magnet has been developed. The vertical vibration is made by a small superconducting magnet fed with an alternating current exerting a force on a magnet fixed on the sample rod. The latter, which is very light (10–20 g), is centered by two CuBe springs so as to eliminate random frictions. The sensitivity is 2.10−7 emu. Any temperature between 1.5 and 300 K can be regulated within 0.01 K. The remanent field is about 10−5 T.
Gas dynamics of ethylene oxide during sterilization
Authors: Zhu Z. , Matthews I. P. , Wang C.
Published: July 2002

This article reports a case study of the dynamics of ethylene oxide gas during sterilization using a microwave spectrometer. A diffusion equation is used to describe the processes of gas penetration, gas sorption, and chemical reactions. The three processes, although mathematically related, may be solved separately under simplified assumptions. This permits the prediction of gas penetration and sorption as well as the effect of chemical reactions upon the gas concentration for loads of differing dimensions and densities.
A method for measuring low capacitance for tomography
Authors: Shao FuQun , Mong QinGuo
Published: July 2002

The applications of electrical capacitance tomography (ECT) to image multiphase flows in pipelines, fluidization process, interfaces in separation vessels, and combustion phenomena in internal combustion engines have been studied for some years. In these applications, none of the equipment imaged has an inner diameter exceeding 1 m. When ECT techniques for large industrial equipment like blast furnaces are explored, the existing methods for measuring low capacitance have some limitations. This article proposes a method for measuring low capacitance which is suitable to construct ECT systems for imaging large industrial equipment. The method is based on single high-voltage excitation and magnetic C/V converting principle which can resist interference by stray capacitance. Experiment results indicated that the method has good performance in regard to resolution, linearity, and stability. Though the method was designed for imaging large equipment, it can also be applicable to other fields where low capacitance measurements are required.