bluuebunny/crossref_metadata_2025 huggingface dataset:
A pulsed supersonic expansion with a source temperature below 100 K
Authors: Bucher J. P. , Douglass D. C. , Xia P. , Bloomfield L. A.
Published: July 2002

We have produced a pulsed supersonic expansion of helium with an effective pre-expansion temperature below 100 K. This low initial gas temperature is achieved by cooling a pulsed gas valve and gas channel with liquid nitrogen. The resulting supersonic helium beam has a translational velocity that is approximately 55% that of the room-temperature source and an internal temperature of 270 mK. The increased Mach number for a cold supersonic expansion agrees with theoretical predictions and reflects the increased cross section of helium at low collision energies.
Measurements of volume flow through microporous membranes by an automated fluximeter
Authors: Forte J. , Victoria L. , Ibañez J. A.
Published: July 2002

This article presents a solution for the problem of determining small fluxes such as that of a liquid flowing through a solid microporous membrane. This measurement is automatized by a programmable controller governing the action of a fluximeter. The device permits the determination of small flows (0–5 mℓ ) with an error over the range ±0.025–±0.001 mℓ/min. We study a functional dependence between the volume flux (Jv), and therefore the hydraulic permeability (Lp), and time. This dependence is adjusted to a function of type y=1/(A+Bx). The device can also be applied to small pulsating flows such as that generated by a peristaltic pump.
A high spatial resolution optical pyrometer
Authors: Nason D. O. , Yen C. T. , Feigelson R. S. , Tiller W. A.
Published: July 2002

An optical pyrometer has been developed which resolves 20 μm at a working distance of 24 in. and measures relative temperature differences of ±2 °C over the range 1000–2000 °C. The instrument is particularly suitable for measuring temperature or emissivity distributions in very small heated objects.
Apparatus for studying premixed laminar flames using mass spectrometry and fiber-optic spectrometry
Authors: Olsson Jim O. , Andersson Lars L. , Lenner Magnus , Simonson Margaret
Published: July 2002

An integrated flat-flame/ microprobe sampling quadrupole mass spectrometer system, complemented by optical spectrometry based on optical fibers, is presented. The short microprobe sampling line (total 25 cm) is directly connected to an open ion source closely flanked by two nude cryopumps (900 ℓ/s) yielding a background pressure of 10−9 Torr and a sampling pressure of about 10−5 Torr. Due to this improved microprobe system, mass spectrometry can be used for analysis of stable species (including fuel, O2, H2O, CO2, CO, and Ar) with less disturbance of the sample than with a conventional microprobe with a back pressure of about 1 Torr. Optical spectrometry is used for the study of emission from important radical species (such as C2, CH, and OH). The system is proposed as a complement to more conventional flat-flame/MBMS systems in which the sampling cone can effect the experimental system. Details are provided concerning the configuration of the whole system ranging from gas delivery to data evaluation. Test data are presented for a 16% methanol/68% oxygen/16% argon flame studied at a pressure of 40 Torr, to elucidate the special features of this system.
Measurements of polarization effects: A pseudorandom polarization switching time-of-flight spectrometer
Authors: Düren R. , Lackschewitz U. , Milos̆ević S.
Published: July 2002

A new method is presented to measure the polarization dependence of double-differential cross sections for the scattering of laser-excited atoms. This allows us to study these polarization effects separated for different scattering processes, which contribute to the total differential cross section at one laboratory angle. A first application demonstrates that the new technique allows us to study the polarization dependence of the reactive and the nonreactive cross sections for collisions of Na(32P3/2) with HF molecules even though, in this example, the polarization dependence of the total differential cross section is only 0.5%.
Apparatus for dynamic and static measurements of mechanical properties of solids and of flux-lattice in type-II superconductors at low frequency (10−5–10 Hz) and temperature (4.7–500 K)
Authors: D’Anna G. , Benoit W.
Published: July 2002

A forced torsional pendulum which permits us to examine anelastic mechanical properties of solids as well as for flux-lattice in type-II superconductors, has been built to explore the low frequency and low temperature range. It works on the principle of dynamic frequency response function measurement and appears to be a powerful instrument for studying structural defect motions as well as flux line dynamics. As an additional quantity, the magnetization or the plastic strain can be statically measured by the same apparatus.
A pendulum feedback system to measure the lateral force on a magnet placed above a high-T
c superconductor
Authors: Johansen T. H. , Bratsberg H. , Yang Z. , Helgesen G. , Skjeltorp A. T.
Published: July 2002

Based on a simple mechanical pendulum design, we developed a sensor for measurement of the horizontal force on a permanent magnet placed at any distance above a high-Tc superconductor. In this fully computerized system, which employs closed-loop feedback control, the lateral interaction with its restoring and hysteretic nature can be studied under conditions of constant vertical separation. Results are presented for the case of a small Nd-Fe-B magnet at a distance of 1 mm above a large planar disk of a YBa2Cu3Ox superconductor.
The inert gases Ar, Xe, and He as cryogenic pressure media
Authors: Burnett J. H. , Cheong H. M. , Paul W.
Published: July 2002

We have investigated the inert gases Ar, Xe, and He for suitability as pressure media in a diamond anvil cell at liquid-helium temperature, from 0 to 30 kbar, and compared these with a 4:1 methanol/ethanol mixture. Xe gives severe nonhydrostaticity and is of no value as a low-temperature medium. Ar gives much less nonhydrostaticity, but little improvement over the 4:1 methanol/ethanol mixture. He gives no observable nonhydrostaticity even when the pressure is changed at low temperature. A technique for loading with He is presented.
A miniature electron-beam evaporator for an ultrahigh-vacuum atom-probe field-ion microscope
Authors: Lin X. W. , Hu J. G. , Seidman D. N. , Morikawa H.
Published: July 2002

A miniature electron-beam evaporator (MEBE) has been fabricated and adapted to our ultrahigh-vacuum atom-probe field-ion microscope (APFIM). The MEBE allows for in situ vapor deposition−under ultrahigh-vacuum conditions ( < 4 × 10−10 Torr)−of a wide range of elements, on the surface of an atomically clean FIM specimen; the surface is prepared via the field-evaporation process. The deposition rate of an evaporant from the MEBE is calibrated to give an accurate value of this quantity. Examples of the deposition−at ≊0.3 nm min−1− of silicon or titanium on tungsten FIM specimens are presented. And in the case of a Ti/W couple it is demonstrated that an interface between a tungsten substrate and a titanium overlayer is chemically sharp on an atomic scale; the titanium was vapor deposited at a substrate temperature of 77 K. Also a 20-kV electron-beam gun was adapted to our APFIM. This gun is useful for in situ electron-beam heating of bilayer couples, or the introduction of point defects in metal oxide or semiconductor overlayers via electronic mechanisms.
Development of high-power millimeter and submillimeter wavelength collective Thomson scattering diagnostics for energetic ion measurements in tokamaks
Authors: Machuzak J. S. , Rhee D. Y. , Woskov P. P. , Cohn D. R. , Myer R. C. , Bretz N. , Efthimion P.
Published: July 2002

High-power, large-angle (≳10°), collective Thomson scattering diagnostics can provide localized density and velocity distribution data of confined alpha particles, ICRH simulated alpha particles, and ions related to ICRH and neutral beam energy deposition. Millimeter-wave gyrotron systems are under development for TFTR and JET. Scattering with a submillimeter gyrotron is being investigated for Alcator C-Mod. Major design issues include plasma accessibility, scattering angle, orientation to magnetic field, spectra of non-Maxwellian velocity distributions, signal-to-noise ratio, refraction, electron cyclotron emission, and beam and viewing dumps.
Plasma diagnostics for the DIII-D divertor upgrade
Authors: Hill D. N. , Futch A. , Buchenauer D. , Doerner R. , Lehmer R. , Schmitz L. , Klepper C. C. , Menon M. , Leikind B. , Lippmann S. , Mahdavi M. A. , Schaffer M. , Smith J. , Salmonson J. , Watkins J.
Published: July 2002

The DIII-D tokamak is being upgraded to allow for divertor biasing, baffling, and pumping experiments. This paper gives an overview of the new diagnostics added to DIII-D as part of this advanced divertor program. They include tile current monitors, fast reciprocating Langmuir probes, a fixed probe array in the divertor, fast neutral pressure gauges, and Hα measurements with TV cameras and fiber optics coupled to a high-resolution spectrometer.
Space-charge effects in a velocity analyzer of variable geometry
Authors: Donoso Guillermo , Martín Pablo
Published: July 2002

A velocity analyzer of adjustable interelectrode distance has been used to study the space-charge effects on the characteristic curve. The effects become apparent for distances larger than about 10λD. The theoretical analysis considering the trapped ions in the vicinity of the entrance grid leads to a better correlation with the experiments than that omitting them.
A small electron cyclotron resonant plasma-based neutral-flux ionizer
Authors: Cain B. L. , Ruzic D. N.
Published: July 2002

The design and operation of a neutral-hydrogen flux detection system is described. The central feature of the detector is an inductively driven electron cyclotron resonance heated (ECRH) discharge, which functions as the neutral-flux ionizer. The prominent features of the ionizer are its small (5×3×3 cm3) size and excitation of the ECRH mode using a 200-W, 30-MHz rf driver and static magnetic field level near 30 G. The ability of the system to ionize 910-eV neutral-hydrogen fluxes with subsequent detection in a high resolution energy analyzer is shown. The detection efficiency of the ionizer was found to be ≊6×10−4, based on scattering and charge exchange cross sections measured using a methane charge exchange cell. The ionizer has potential applications in angle-resolved reflected neutral-flux measurements and in beam-plasma interaction analysis.
Visible spectroscopy measurements in the PBFA II ion diode (invited)
Authors: Bailey J. , Carlson A. L. , Morrison R. L. , Maron Y.
Published: July 2002

We describe a new visible spectroscopy diagnostic system for measuring plasma properties in the PBFA II applied-B ion diode. The system transports light from the ion diode to a remote screen room where it is recorded by a spectrograph coupled to a streak camera. We developed extensive calibration techniques for measuring the collection efficiency into the fiber link, the effects of the background bremsstrahlung radiation on the fibers, the fiber transmission as a function of wavelength, and the absolute streaked-spectrograph sensitivity as a function of wavelength. We have recorded time-dependent spectral line profiles and intensities from the PBFA II plasma opening switch, the beam-transport gas cell, and the anode plasma. The Stark shift of the LiI 2s-2p transition observed on LiF-anode shots shows that the time-resolved electric field peaks at 7–8 MV/cm, the highest field ever measured using the Stark effect. The potential of these measurements to expand our knowledge of ion-diode physics is being explored.
Stark-effect measurement of high free-electron laser electric fields in MTX by laser-aided particle-probe spectroscopy
Authors: Oda T. , Odajima K. , Mizuno K. , Ohasa K. , Shiho M. , Takiyama K. , Foote J. H. , Nilson D. G.
Published: July 2002

We are constructing a diagnostic system to measure the electric field (≳100 kV/cm) of a free-electron laser (FEL) beam when injected into the plasma of the Microwave Tokamak Experiment (MTX). The apparatus allows a crossed-beam measurement, with 2 cm spatial resolution in the plasma, involving the FEL beam (with 140 GHz, ≊1 GW ECH pulses), a neutral helium beam, and a dye laser beam. After the laser beam pumps metastable helium atoms to higher excited states, their decay light is detected by an efficient optical system. Because of the Stark effect arising from the FEL electric field (E), a forbidden transition can be strongly induced. The intensity of emitted light resulting from the forbidden transition is proportional to E2. Because photon counting rates are estimated to be low, extra effort is made to minimize background and noise levels. It is possible that the lower E of an MTX gyrotron-produced ECH beam with its longer duration pulses can also be measured using this method. Other applications of the apparatus described here may include measurements of ion temperature (using charge-exchange recombination), edge-density fluctuations, and core impurity concentrations.
Energy analyzer for the ATF heavy ion beam probe
Authors: Aceto S. C. , Connor K. A. , McLaren P. E. , Zielinski J. J. , Schatz J. G. , Henkel G. H.
Published: July 2002

The energy analyzer for the ATF heavy ion beam probe has been built and tested. Because the analyzer will be required to operate in fields as high as 550 G on ATF and since calibration of the analyzer in the absence of a field will not be possible once it is installed, a special emphasis has been made to characterize its performance on a test stand. In order to ensure accurate knowledge of the analyzer geometric parameters, it was assembled with the aid of a coordinate axis measuring machine. The results of these tests are presented and a comparison to ideal analyzer performance is made.
A study on an induced voltage-type laser light-pressure energy meter
Authors: Yuan Yipeng
Published: July 2002

This paper describes some further improvements on a new type of pulse laser energy meter with an airtight method to make its structure more simplified. A study has been made on its measurement performance for laser beam power. This energy meter, fitted with an optical shutter, can be used for the measurement of lower-middle range laser power as well as high laser power.
A low-cost multiple Hall probe current transducer
Authors: Scoville J. T. , Petersen P. I.
Published: July 2002

An inexpensive but highly stable and accurate transducer has been developed for the measurement of large currents associated with the operation of the DIII-D tokamak at General Atomics. The inherent problems with integrator circuits required by Rogowski loops and the excessive cost of ‘‘secondary compensation current’’ devices have led to this development. The transducer requires several inexpensive Hall effect devices and a simple, stable, and linear interface circuit. Analysis of the initial performance characteristics is very encouraging and has led to several useful applications of the transducer to date, with plans for the installation of additional devices in the future. The low cost and reasonable accuracy of the transducer make it an attractive alternative to commercially available devices.
Simple, high precision linear-motor-driven XYΘ positioner (Walker)
Authors: Dudnikov V. G. , Kovalevsky D. V. , Shabalin A. L.
Published: July 2002

A very simple construction of a linear-motor-driven XYΘ positioner has been developed. The velocities can be controlled up to 4 mm/s. Positioning accuracy of better than 0.05 μm can easily be obtained.
Device for radiometric or high temperature radiance measurement in a vacuum
Authors: Neuhaus Dietmar
Published: July 2002

A new radiometer concept is presented that allows pyrometric temperature measurements on evaporating bodies, in particular liquid metal samples, in vacuum. The new device is characterized by a transmission grating that deflects radiation onto the radiation detector of the pyrometer, so no sample vapor will degrade the measurement device.
Spectroscopic plasma tomography with multiple photocollector arrays
Authors: Sugimoto Satoshi , Goto Seiich
Published: July 2002

A spectroscopic plasma tomography measurement system has been developed and operated on a field-reversed configuration (FRC) plasma machine with the use of five photocollector arrays. Each photocollector array that is located azimuthally around the plasma column consists of ten optical fibers and a pinhole. Two-dimensional (2D) and time-resolved visible emission profiles can be reconstructed numerically from the fifty-channel projection data. The use of five multichannel visible monochromators makes it possible to obtain a result that has explicit physical meanings. A computer simulation has been performed to demonstrate the potential to reconstruct the 2D profile without the assumptions about plasma rotation or symmetry. The first experimental result for visible bremsstrahlung emission profiles of the FRC plasma is presented.
A method to measure poloidal field coil irregularities in toroidal plasma devices
Authors: La Haye R. J. , Scoville J. T.
Published: July 2002

A ring of accurately placed and matched printed circuit coils is placed at the center of the DIII-D tokamak vacuum vessel, aligned magnetically with the toroidal field and used to measure the nonaxisymmetric magnetic field of each of the 18 poloidal field coils. [Toroidal and poloidal variations can be of mode n and m, respectively, with helical variations of form cos(nφ−mθ).] From the error fields, it is computed that the most irregular poloidal field coil is one of the outer vertical field coils having a shift of 1.9 ±0.2 cm (compared to a diameter of 482 cm), and having an ellipticity 1.0027. All the 18 poloidal field coils together make a resonant, helical, radial error field for m=2, n=1 of about 1.4 × 10−4 of the toroidal field.
A low temperature NMR probe for use in a dilution refrigerator
Authors: Kuhns P. L. , Lee S.-H. , Coretsopoulos C. , Hammel P. C. , Gonen O. , Waugh J. S.
Published: July 2002

We report an NMR probe that we use in ultra low temperature experiments in a top-loading dilution refrigerator. The probe is thermally anchored to the 1.2 K pumped 4He pot and is thermally isolated from the sample located inside a Kel-F cup containing liquid 3He. The probe is adapted from a standard double resonance probe, using air trimmer capacitors, a λ/4 cable, a homemade saddle coil, and metal film resistors. The double resonance design breaks the probe’s tuning ranges into two bands. The high frequency band tunes from 100 to 150 MHz covering all the nuclei with large gyromagnetic ratios, 3H, 19F, 1H, 3He. The low frequency band tunes for 17 to 54 MHz covering all nuclei with gyromagnetic ratios between 133Cs and 119Sn. The air trimmer capacitors have an open structure that allows efficient pumping and the metal film resistors are used to reduce the Q of the probe. This probe has been successfully used for a wide range of nuclei including 1H, 19F, 3He, 119Sn, 117Sn, 115Sn, 11B, 13C, 29Si, 27Al, and 2H.
Time domain dielectric spectroscopy with nonuniform signal sampling
Authors: Ermolina I. V. , Polygalov E. A. , Romanychev G. D. , Zuev Yu. F. , Feldman Yu. D.
Published: July 2002

The hardware and software designs for fast measurement of dielectric properties of different substances over a wide range of characteristic times (10−5–10−10 s) by means of time domain dielectric spectroscopy (TDS) are presented. The characteristic feature of the described installation is the nonuniform time sampling of measured signals, which enables one to cover a wide range of characteristic times with a single measurement. Comparative results for an aqueous solution of lysozyme obtained on the traditional apparatus and on the described one are presented.
Development of a quadrupole mass spectrometer using the second stable zone in Mathieu’s stability diagram
Authors: Hiroki Seiji , Abe Tetsuya , Murakami Yoshio
Published: July 2002

A quadrupole mass spectrometer (QMS) utilizing the second stable zone in Mathieu’s stability diagram was developed. The system performance was experimentally compared with the conventional QMS using the first stable zone. The peak shapes obtained were sharper and the tail components arising from adjacent peaks were less than those of the conventional QMS, although the analyzable range was limited to lower mass and the attenuation in sensitivity was about 1/50. This improved QMS is usable in detecting very small peaks adjoining large ones.
Measuring hysteresis loops of ferroelectric polymers using the constant charging current corona triode
Authors: Alves Neri , Giacometti José A. , Oliveira Osvaldo N.
Published: July 2002

A novel method is proposed for measuring the hysteresis loops of ferroelectric polymers. The samples need to have only one electrode and are poled by corona discharge in a constant current corona triode. It is shown how the sample surface potential and the charging current are related to the remanent polarization and coercive field, so that the hysteresis loops can be obtained. An illustrative example is given for samples of β-PVDF for which the hysteresis cycles were remarkably close to those obtained with the traditional Sawyer–Tower circuit. Values of 80 MV/m and 70 mC/m2 were estimated for the coercive field and remanent polarization, respectively.
A high-speed nuclear-magnetic-resonance data-acquisition system with a personal computer for a polarized target in high-energy physics
Authors: Sakanaka Shogo , Dohmae Kazuhiko , Hayashi Naoki , Horikawa Naoaki , Iwata Takahiro , Kishi Atsushi , Matsuda Tatsuro , Nakanishi Tsutomu , Okumi Shoji , Wakai Atsushi , Mori Kunikazu
Published: July 2002

A high-speed nuclear-magnetic-resonance (NMR) data-acquisition system, incorporating a personal computer, has been developed to determine the polarization of the polarized target for high-energy physics experiments. A dedicated analog-to-digital converter (ADC) board is used for automatic ADC sampling synchronizing with an internal clock. Within about 1.5 s, 128 NMR signals are obtained and the averaged signal is derived.
A rotating input polarizer for a double polarization modulation far infrared spectrometer
Authors: Fiske T. G. , Da Costa V. M. , Coleman L. B.
Published: July 2002

We report modifications for a recently described double polarization modulation far infrared spectrometer. By changing the input polarizer switching dynamics, we further reduce spectral noise caused by instability of the plasma in the mercury arc source.
Automatic rough approximation system for a scanning tunneling microscope
Authors: Chornik B. , Aravena R. , Grahmann C. , Venegas R. , Gaete L.
Published: July 2002

An automatic initial approximation system for a scanning tunneling microscope is presented. The device includes a dc motor that is fed by pulses, so that it performs as a stepping motor. A full description of the circuit is given. It is much simpler than the circuit for a true stepping motor, and it is designed to stop motion as soon as a tunneling current appears, thereby avoiding a tip crash.
A mechanical thickness scale for opaque parts
Authors: Ables E. , Bionta R. M. , Miller K. A. , Olsen H. E. , Skulina K. M.
Published: July 2002

A method for measuring the thickness of opaque parts to within 4 μm by inserting a small scale into the part or along side has been developed. A combination digital and analog scale is used to determine the length of the scale when viewed from the edge. This scale should be useful for applications where only one surface is exposed during machining or polishing, and where the side is also inaccessible.
Repetitive two-stage light gas gun for high-speed pellet injection
Authors: Combs S. K. , Foust C. R. , Fehling D. T. , Gouge M. J. , Milora S. L.
Published: July 2002

A repetitive two-stage light gas gun for high-speed pellet injection has been developed at Oak Ridge National Laboratory. In general, applications of the two-stage light gas gun have been limited to only single shots, with a finite time (at least minutes) needed for recovery and preparation for the next shot. The new device overcomes problems associated with repetitive operation, including rapidly evacuating the propellant gases, reloading the gun breech with a new projectile, returning the piston to its initial position, and refilling the first- and second-stage gas volumes to the appropriate pressure levels. In addition, some components are subjected to and must survive severe operating conditions, which include rapid cycling to high pressures and temperatures (up to thousands of bars and thousands of kelvins) and significant mechanical shocks. Small plastic projectiles (4 mm nominal size) and helium gas have been used in the prototype device, which was equipped with a 1-m-long pump tube and a 1-m-long gun barrel, to demonstrate repetitive operation (up to 1 Hz) at relatively high pellet velocities (up to 3000 m/s). The highest experimental velocity is twice that available from conventional repeating single-stage pneumatic injectors that accelerate frozen pellets of hydrogen isotopes and are now used to fuel magnetically confined plasmas for controlled thermonuclear fusion research. Also, the pellet test repetition rate of 1 Hz is relevant for fueling applications on future large fusion research devices. The equipment is described, and experimental results are presented and compared with calculated results from gas dynamics models.
An inexpensive rotamak device
Authors: Cottrell G. , Jones I. R. , Lee S. , Xu S.
Published: July 2002

The components of a typical rotamak device are described and the constructional details of an inexpensive version are given. The operating range of this particular version is described and, as an example, a detailed set of measurements made for one set of initial conditions are presented. Typically, steady toroidal currents of ∼100 A are generated and maintained for the full 40 ms of operation by a ∼1-MHz rotating magnetic field of a few Gauss in amplitude. Plasmas having electron temperatures lying between 5–10 eV and number densities in the 1017-m−3 range are routinely and very reproducibly produced.
Formation of fast ‘‘notched’’ current waveforms through a high inductance
Authors: Spanjers G. , Nelson B. A. , Ribe F. L.
Published: July 2002

A fast ‘‘notch’’ current has been produced on the (4 μH) hardcore central conductor [C. M. Greenfield, M. E. Koepke, and F. L. Ribe, Phys. Fluids B 2, 133 (1990)] of the high beta Q machine, a 2.6 m theta pinch [S. O. Knox, H. Meuth, E. Sevillano, and F. L. Ribe, 3rd IEEE International Pulsed Power Conf., 1981, IEEE Publ. 81 CH1662/6, paper 3.1]. With the notch circuitry, the current can be slowly (τ1/4 = 14 μs) brought to a crowbarred dc value (20 kA) and then quickly (τ1/4 = 1.3 μs) ‘‘notched’’ to a different value (typically either 0 kA or twice the dc value) and then quickly returned to the dc value. The use of a new inductively loaded spark gap switch eliminates extraneous ringing in the final crowbarred current waveform. As described here, by driving the hardcore circuit with two isolated capacitor banks, and a voltage stepup transformer, the notch current is created using spark gaps and ignitrons for switching, resulting in an inexpensive and technically simple circuit.
Spin-polarized electron gun for electron spectroscopies
Authors: Ciccacci F. , Vescovo E. , Chiaia G. , De Rossi S. , Tosca M.
Published: July 2002

A spin-polarized electron gun for electron spectroscopies is described in detail. The gun consists of an electron source based on a negative electron affinity GaAs photocathode coupled to an appropriate transport electron optics. The gun has been designed with the aid of ray-tracing analysis and then accurately tested. It produces a transversely polarized (P0∼27%) electron beam at variable energy with a small spot size and angular spread (less than 2 mm and 5°, respectively). Such performances are attained up to sample currents as high as 10 μA for the whole beam energy range (8–50 eV). As an application we present data on spin-dependent absorbed current spectroscopy from bcc Fe films epitaxially grown on Ag(100).
Pulsed ECR ion source using the afterglow mode (invited)
Authors: Sortais P.
Published: July 2002

We make a review of the very first observations of a sharp current peak of multicharged ions observed at the turnoff of the rf power in ECR ion sources called the afterglow pulsed current. An elementary model is presented in order to explain the charge dependence of this phenomenon. Preliminary transmission measurement shows that this kind of current seems useful for accelerator applications.
Numerical modeling of a compact ECR ion source
Authors: Grotjohn T. A.
Published: July 2002

A compact ECR ion/plasma source is numerically modeled using a Monte Carlo particle method coupled with a solution of the Maxwell equations. The source modeled is a small, coaxial cavity source that utilizes rare earth permanent magnets to create electron cyclotron resonance (ECR) zones in the cavity. The model includes the calculation of the static magnetic field produced by the permanent magnets, the microwave fields at 2.45 GHz, the electron spatial and energy distributions, and the ion spatial and energy distributions. The numerical model is a 2d3v model that assumes an axial symmetry. The electric fields and time-varying magnetic fields are solved using a time-domain finite-difference solution of the Maxwell equations. The electron and ion behaviors are modeled by using the Monte Carlo particle technique, where each particle moves subject to the Lorentz force equation and to the appropriate elastic and inelastic collision processes. The solution obtained is a self-consistent solution where the Maxwell equations are solved iteratively with the particle technique until a steady state condition is reached. Sample simulation results are presented including a spatial electron heating distribution.
Center for advanced microstructures and devices (CAMD)
Authors: Craft B. C. , Feldman M. , Morikawa E. , Poliakoff E. D. , Saile V. , Scott J. D. , Stockbauer R. L.
Published: July 2002

The new synchrotron-radiation facility, Center for Advanced Microstructures and Devices, at Louisiana State University is described with regard to the status of installation of the storage ring, implementation of the various programs, and construction of the first beamlines.
A combined scanning electron microscope and scanning tunneling microscope for studying nanostructures
Authors: Rosolen G. C. , Welland M. E.
Published: July 2002

An instrument which incorporates an electrostatic scanning electron microscope and a scanning tunneling microscope in an ultrahigh vacuum environment has been developed to study nanostructures. To facilitate positioning the nanostructures for examination with the instrument a high precision orthogonal motion sample stage has been designed. The instrument has been applied to locate and study both nanometer size trenches and wires. These structures have been fabricated using electron beam lithography and a polymethlymethacrylate lift-off process.
Atomic force microscope with integrated optical microscope for biological applications
Authors: Putman Constant A. J. , van der Werf Kees O. , de Grooth Bart G. , van Hulst Niek F. , Segerink Frans B. , Greve Jan
Published: July 2002

Since atomic force microscopy (AFM) is capable of imaging nonconducting surfaces, the technique holds great promises for high-resolution imaging of biological specimens. A disadvantage of most AFMs is the fact that the relatively large sample surface has to be scanned multiple times to pinpoint a specific biological object of interest. Here an AFM is presented which has an incorporated inverted optical microscope. The optical image from the optical microscope is not obscured by the cantilever. Using a XY stage to move the sample, an object is selected with the optical microscope and an AFM image of the selected object can be obtained. AFM images of chromosomes and K562 cells show the potential of the microscope. The microscope further enables a direct comparison between optically observed features and topological information obtained from AFM images.
Narrow bandpass layered synthetic microstructure-based pinhole camera to image a tokamak plasma in H-like carbon emission at 34 Å
Authors: Regan S. P. , Huang L. K. , Finkenthal M. , Moos H. W.
Published: July 2002

The layered synthetic microstructure (LSM) technology has made two-dimensional soft x-ray imaging of a tokamak plasma in a single impurity spectral line emission feasible. The curved LSM is used both as an optical filter, with a bandpass in the range of interest on the order of 1.5 Å, and as a focusing optic. A detailed design of a narrow bandpass curved LSM-based pinhole camera, which will image the the region from the scrape-off layer 26 cm into the plasma in the DIII-D tokamak plasma in C vi Lyman α emission at 34 Å, will be presented.
MLM-based monochromator for molybdenum impurity monitoring on the Alcator C-MOD tokamak in the 30–130 Å range
Authors: May M. J. , Zwicker A. P. , Moos H. W. , Finkenthal M. , Terry J. L.
Published: July 2002

Molybdenum, from the vessel wall armor tiles and divertor plates, is expected to be the dominant high-Z impurity in the Alcator C-MOD tokamak plasma. To monitor the molybdenum emission in the extreme ultraviolet (XUV), a monochromator utilizing multilayer mirrors (MLMs) as dispersive elements will be installed on the C-MOD tokamak with a 10° above the mid-plane view across the plasma’s center. Much of the strong Mo emission under the C-MOD experimental conditions will be emitted between 30–50 Å and 65–90 Å by M-shell ions (n=3–3 and n=3–4 transitions), at 116 Å from MoXXXI and at 127 Å from MoXXXII. The monochromator will have three MLMs and either three-channel electron multipliers or three XUV silicon photodiodes mounted on a single θ-2θ goniometer. Each MLM and detector unit will simultaneously monitor a separate molybdenum emission range with a 1–10-ms temporal resolution. The resolution of the MLMs range from 1 to 5 Å depending on the wavelength, and each MLM will be optimized for one of the above spectral regions. This low-resolution monitoring of many charge states will enable radiative power loss estimates and can be used in impurity transport analysis. The design of the monochromator and the expected Mo emission will be presented and discussed.
K- and L-shell x-ray spectroscopy of indirectly driven implosions (invited)
Authors: Hammel B. A. , Keane C. J. , Kania D. R. , Kilkenny J. D. , Lee R. W. , Pasha R. , Turner R. E. , Delamater N. D.
Published: July 2002

Time-resolved x-ray spectroscopy is used to study the implosion of indirectly driven inertial confinement fusion capsules on the Nova laser. Through the use of high-Z dopants (Ar and Xe) in the fuel, measurements of the peak temperature, from emission line ratios, and density, from line broadening, are obtained. These measurements indicate peak electron temperatures of ∼1–1.6 keV and electron (and deuteron) densities in the range of 1.0–2.0×1024 cm−3, depending on the type of laser drive used. The higher densities are achieved on targets that are driven with a shaped laser drive that allows a more isentropic compression of the fuel. Emission from high-Z pusher dopants have also been studied. These dopants can provide information on pusher conditions and can be used to study mix at the pusher fuel interface.
The DIII-D lithium beam edge diagnostic system (abstract)
Authors: Thomas D. M. , Lee R. L. , Patterson R. M. , Brooks N. H. , Robinson J. , McChesney J. M.
Published: July 2002

We are installing a diagnostic system based on a neutral lithium beam to investigate plasma behavior in the edge region of DIII-D discharges [D. M. Thomas et al., Rev. Sci. Instrum. 61, 3040 (1990]. The system will provide neutral equivalent current densities of several mA/cm2 at beam energies from 5 to 30 keV, sufficient to penetrate several centimeters past the last closed flux surface in most of the DIII-D operating regime. Fluorescence of the beam atoms is induced by collisions with plasma particles and is a sensitive measure of the edge density behavior. The emitted 670.8-nm fluorescence is collected and coupled via fiber optics to a multichannel high-speed data acquisition system based on silicon diode detectors. Because of the favorable atomic properties of lithium (i.e., high electron impact excitation cross section, resonance wavelength well separated from Hα) we should be able to study density fluctuations in this region from an analysis of the associated fluctuations in the beam fluorescence. A description of the installed diagnostic, test stand measurements of intrinsic beam fluctuations and any initial operating experience on DIII-D will be presented. This work supported by U. S. Department of Energy Grant No. DE-FG03-90ER5408 and Contract DE-AC03-89ER51114, which support does not constitute an endorsement by DOE of views expressed in this publication.
LaNSA: A large neutron scintillator array for neutron spectroscopy at Nova
Authors: Nelson M. B. , Cable M. D.
Published: July 2002

A very sensitive neutron time-of-flight spectrometer is now in use at Nova. LaNSA consists of 960 channels of a neutron sensitive liquid scintillator (10×10×10 cm) coupled to a photomultiplier tube followed by a discriminator, TDC, and ADC to allow the measurement of neutron arrival time as well as pulse size. LaNSA is capable of measuring yields as low as 2.3×105 DT neutrons (100 detected hits) with resolution of 2.3 ns (170 keV for 14-MeV neutrons with 20-m flight path). Shielding and collimation provide background levels low enough to allow measurement of secondary and tertiary reaction neutrons. Details of design, testing, calibration, and experimental results will be presented.
Geometry compensation for improving speed and efficiency of scintillator-based neutron time-of-flight detectors
Authors: Lerche R. A. , Murphy T. J.
Published: July 2002

Scintillator-based neutron detectors record time-of-flight (TOF) information used for estimating inertial-confinement-fusion plasma temperatures. Nova TOF detectors, which have 1.3 ns resolution and contain 30 cm3 of scintillator, lack the combination of temporal resolution and sensitivity necessary to measure 1 keV temperatures for deuterium plasmas emitting fewer than 1.5×109 neutrons. Significant time dispersion is caused by neutron detection-point uncertainty in thick scintillators. We describe a geometrical compensation technique by which this dispersion can be substantially reduced while retaining large scintillator volume. We estimate that scintillator/streak camera detectors can achieve 100 ps resolution for 2.45 MeV neutrons, and that scintillator/photomultiplier systems can achieve 150–300 ps resolution.
ICF target diagnostics on PBFA II (invited)
Authors: Chandler G. A. , Aubert J. , Bailey J. , Carlson A. , Derzon D. , Derzon M. , Dukart R. , Humphreys R. , Hunter J. , Johnson D. J. , Matzen M. K. , Moats A. , Olson R. , Pantuso J. , Rockett P. , Ruiz C. , Sawyer P. , Torres J. , Hussey T.
Published: July 2002

Particle Beam Fusion Accelerator II is a light-ion fusion accelerator that is presently capable of irradiating a 6-mm-diam sphere with ∼50 kJ of 5.5-MeV protons in ∼15 ns. An array of particle and x-ray diagnostics fielded on proton Inertial Confinement Fusion target experiments quantifies the incident particle beam and the subsequent target response. An overview of the ion and target diagnostic setup and capabilities will be given in the context of recent proton beam experiments aimed at studying soft x-ray emission from foam-filled targets and the hydrodynamic response of exploding-pusher targets. Ion beam diagnostics indicate ∼100 kJ of proton beam energy incident within a 1.2-cm radius of the center of the diode with an azimuthal uniformity which varied between 6% and 29%. Foam-filled target temperatures of 35 eV and closure velocities of 4 cm/μs were measured.
Effect of fluctuations on lower hybrid power deposition and hard x-ray detection
Authors: Vahala George , Vahala Linda , Bonoli Paul T.
Published: July 2002

The hard x-ray intensity radial profiles from lower hybrid current drive experiments are interpreted as being correlated with fluctuations in the bulk plasma. This view seems to be dictated by comparing the hard x-ray data for various n∥ with the Monte Carlo solutions of the lower hybrid wave energy deposition on plasma electrons. Information on internal magnetic fluctuations may, under certain conditions, be unfolded from a n∥ scan of the hard x-ray profiles.
Characteristics of an 8-cm-diam electron cyclotron resonance source for plasma processing
Authors: Popov Oleg A. , Westner August O. , Drybanski Antoni Z.
Published: July 2002

Performance and characteristics of a microwave source designed for the generation of overdense (Ne≥Ncr=7.4×1010 cm−3) uniform plasmas are presented. Microwave power ( f=2.45 GHz, P=20–1000 W) was introduced into the cylindrical nonresonant (for any TE and TM microwave modes) cavity (D=8.25 cm, L=22 cm) via a matched dielectric window. Two magnetic coils produced the axial static magnetic field of B≥Bce=875 G. Two plasma stream modes were observed: (i) narrow mode with a maximum plasma density on the axis, and with the magnetic field near the introduction window of B≤960 G; and (ii) wide mode with lower but uniform plasma density across the stream, and with magnetic fields near the window of 1000–1200 G. Ion current density of 7–8 mA/cm2 was typical for the narrow mode, and 4–5 mA/cm2 for the uniform mode. Ion current density relationship with gas pressure and microwave power is discussed.
Validation of spatial profile measurements of neutron emission in TFTR plasmas (invited)
Authors: Johnson L. C.
Published: July 2002

The TFTR multichannel neutron collimator provides spatially localized information on nuclear reaction rates in fusion plasmas. Absolutely calibrated NE 451 ZnS scintillators detect chord-integrated neutron emission along ten vertical sightlines, which are defined by a massive shielding structure in the facility basement. If such observations are to be of value, virgin neutrons along each sightline must be distinguishable from a background of gamma rays and scattered neutrons, and the measurements must be sufficiently precise, over a wide range of plasma conditions, to allow meaningful comparison with results of transport analysis computer codes. As a useful check, the volume-integrated neutron emission must agree with independent measurements of the global neutron source strength. Although NE 451 detectors are insensitive to gamma rays and to neutrons with energy less than ∼2 MeV, the scintillation pulse height distribution depends on both the incident neutron energy spectrum and the physical parameters of the individual detector. In order to establish the validity of our measurements, we have carried out a detailed characterization of our detectors, including computer modeling of scintillation pulse height spectra and of temporal pulse pileup effects in the counting circuitry. Satisfactory operation of the system has been demonstrated for all deuterium plasmas encountered in TFTR. The detector modeling, together with further laboratory measurements, will enable us to prepare for deuterium–tritium experiments.
A source of cold molecular ions for Coulomb explosion imaging
Authors: Graber T. , Zajfman D. , Kanter E. P. , Naaman R. , Vager Z. , Zabransky B. J.
Published: July 2002

A specialized ion source for use in the high voltage terminal of an electrostatic accelerator has been developed to produce vibrationally cold beams of molecular ions. A pulsed valve is used to produce a supersonic expansion of the source gas which is ionized by electron impact near the beginning of the free expansion. Because of the harsh electromagnetic environment in the terminal, special care has been taken to protect the electronic components related to the ion source. The effect of vibrational cooling in the supersonic expansion is demonstrated using Coulomb explosion techniques with a He2+ beam.
Low-noise high-response prebreakdown current measurement system
Authors: Yamada Hiroshi , Fujiwara Tamiya , Kimura Shingo
Published: July 2002

The electrical prebreakdown currents in liquid and solid dielectrics under a highly nonuniform electric field condition have been measured successfully using an electro-optical current measuring system in conjunction with a 760-ns rectangular high-voltage pulse generator. The breakdown time lag was precisely measured from the current. The discharge propagation velocity was estimated from the linear relation to formative time lag and gap spacing to be 18 km/s in liquid nitrogen at +40-kV point voltage.
Production and metrology of 5 μm x-ray apertures for 100 keV diffraction studies in the diamond anvil cell
Authors: Ruoff Arthur L. , Luo Huan , Vanderborgh Craig , Xia Hui , Brister Keith , Arnold Volker
Published: July 2002

Microminiaturization of the diamond anvil tip is necessary in order to obtain multimegabar pressures. Because of this and the steep pressure gradients present tiny x-ray beams are required. This paper describes the production and metrology of 5 μm x-ray apertures for x-ray diffraction studies to 100 keV in the diamond anvil cell. It is expected that this design will serve as the basis for 2 μm apertures.
Theoretical study of cylindrical energy analyzers for MeV range heavy-ion beam probes
Authors: Fujisawa A. , Hamada Y.
Published: July 2002

A cylindrical energy analyzer with drift spaces is shown to have a second-order focusing for beam incident angle when the deflection angle is properly chosen. The analyzer has a possibility to be applied to MeV range heavy-ion beam probes, and will also be available for accurate particle energy measurements in many other fields.
CLULU: An experimental setup for luminescence measurements on van der Waals clusters with synchrotron radiation
Authors: Karnbach R. , Joppien M. , Stapelfeldt J. , Wörmer J. , Möller T.
Published: July 2002

We describe a new experimental setup for photoluminescence spectroscopy on van der Waals clusters. It consists of a molecular beam apparatus with a cluster beam installed behind a high intensity vacuum ultraviolet synchrotron radiation beamline. Special emphasis was given to the design of a very intense cluster source which can also be used for the preparation of quantum clusters (He,H2). For the determination of the cluster size a time-of-flight mass spectrometer can be attached to the setup. In addition, an atomic cross jet is installed in the experimental chamber which can be used for mass separation or for doping of the clusters. The luminescence light can be recorded with several different detectors or spectrally analyzed with a secondary monochromator which is equipped with a position sensitive detector. The pulsed nature of synchrotron radiation provides the basis for time-resolved measurements in the regime 100 ps–3 μs.
A bipolar amplifier for controlling piezo translator
Authors: Barchesi Claudio , Generosi Renato , Cricenti Antonio
Published: July 2002

A bipolar amplifier, optimized to control a piezo translator of a scanning tunneling microscope, is described. The apparatus is completely designed using discrete components and it offers a very simple solution to controlling movement of any piezo translator.