bluuebunny/crossref_metadata_2025 huggingface dataset:
Automatic measurement of resistance of high-temperature superconductors
Authors: Ouseph P. J. , Bruning D. , O’Bryan M. Ray , Ouseph John P. , Carter Stewart
Published: July 2002

We describe an automatic system using a Keithley scanning thermometer controlled by a personal computer. The system is capable of measuring the resistance and temperature of six high-temperature superconducting samples simultaneously. Transition temperatures may be measured with a precision of 0.1 K, with an absolute-zero offset of less than 0.1 K. Sample-to-sample variation in the temperature is less than 0.1 K. Maximum difference in temperature from one end to the other end of a sample is 0.2 K, but the difference is only about 0.1 K in 70% of the temperature range of the experiment.
Spiral optical-frequency shifter for lower-velocity measurement of the laser Doppler velocimeter
Authors: Fukuoka Yutaka , Okada Eiji , Minamitani Haruyuki
Published: July 2002

A spiral optical-frequency shifter for the laser Doppler velocimeter (LDV) is described, which offers lower shifted frequencies of 50 Hz–50 kHz manually. These lower shifted frequencies cannot be easily obtained from conventional optical-frequency shifters (Bragg cell, rotating diffracting grating, etc.). However, these lower shifted frequencies are useful for LDV measurement of lower-velocity flow such as blood flow in microvessels. A spiral optical element consisting of acrylic resin (refractive index, n=1.61) is inserted into one of the dual incident beams of a differential LDV, in which an optical frequency shift is brought about by rotation of the spiral element. The shifted frequency is changed by rotational frequency mechanically. The performance of the shifter is discussed; the experimental results are in good agreement with the theoretical values of shifted frequencies (error <1%).
On-board data analysis techniques for space plasma particle instruments
Authors: Curtis D. W. , Carlson C. W. , Lin R. P. , Paschmann G. , Rème H. , Cros A.
Published: July 2002

This article describes the on-board data analysis techniques used on two recent space plasma particle instruments to compute meaningful parameters of three-dimensional plasma distributions in real time. These parameters may be transmitted with much higher time resolution than the full distribution within the limited telemetry. In addition, they greatly reduce the ground processing requirements.
Measurements of heat capacities, temperatures, and absorptivities of single particles in an electrodynamic balance
Authors: Monazam E. R. , Maloney D. J. , Lawson L. O.
Published: July 2002

A rapid measurement technique to determine heat capacities, temperatures, and absorptivities of single submillimeter size (50–200 μm diam) particles in an electrodynamic balance (EDB) is described. Accurate estimates of heat capacities and absorptivities are made for single carbon particles at temperatures ranging from 800 to 1200 K with measurement times of less than 0.5 s. Measurements are made by isolating and holding charged particles at the null position in an EDB. Particles are heated using the output from a well-characterized CO2 laser which is modulated to provide heating pulses of 3-ms duration at a repetition rate of 100 Hz. The resulting periodic temperature oscillations are monitored continuously using a single wavelength high-speed optical pyrometer. Heat capacities and absorptivities are determined based on comparisons of the recorded heating and cooling profiles with theoretical predictions obtained from numerical solution of the Fourier equation. Experimentally determined heat capacities for carbon spheres are in excellent agreement (±10%) in terms of their absolute value and temperature dependence when compared with published heat capacity correlations for chars and graphite. Absorptivity estimates are also in excellent agreement with published values for carbons.
Measurement of rapid i
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o response to an agonist of ion channel forming cell surface receptors
Authors: Marque Jeffrey
Published: July 2002

We describe an instrument that is used for spatially homogeneous, submillisecond application of low-molecular-weight substrates (hundreds of daltons) in the neighborhood of a single biological cell and the measurement of the subsequent response of the cell to the substrate. Substrate application is accomplished by ultraviolet photolysis of caged substrate. Cell response is measured, in our particular case, as current flux into the cell in response to membrane conductance changes caused by substrate binding to cell surface receptors. We present data that show fast channel-opening kinetics of nicotinic acetylcholine receptors on the surface of a BC3H1 cell, a transformed cell line from mouse brain, and we discuss the measurements of ultraviolet-induced cell damage and radiation fluence at the cell surface. The technique described is also useful for nonbiological studies requiring known fluences applied to microscopic samples.
Capacitive probes for rf process plasmas
Authors: Savas S. E. , Donohoe K. G.
Published: July 2002

Easily built capacitive probes designed for rf potential measurements in low-density reactive process plasmas are shown. The probes use no auxiliary circuitry and are made from easily available materials. They permit accurate measurements of rf fundamental and harmonic amplitudes in the plasma, in sheaths, and on insulating or conducting surfaces in vacuum or plasma environments. Measured values of plasma, sheath, and electrode surface rf potential amplitudes are shown for ∼1010 cm−3 density, unmagnetized and magnetically enhanced 13.56-MHz capacitive discharges in oxygen and nitrogen. Overall probe accuracy is estimated to be about 10% in these plasmas with the spatial resolution as fine as 0.5 mm.
Automatic mutual inductance bridge for accurate ac susceptibility measurements from 1.2 to 300 K
Authors: Deutz A. F. , Hulstman R. , Kranenburg F. J.
Published: July 2002

We describe a completely computer-driven sensitive ac susceptometer for experiments at frequencies between 10 Hz and 5 kHz in the temperature range from 1.2 to 300 K and in magnetic fields from 0 to 6 T. The susceptibility is measured by moving the sample between the secondary coils, which form part of a mutual inductance bridge controlled by a personal computer. The temperature is regulated by a newly developed clamped PI algorithm. The calibration procedure is described as well as the experimental control program. Absolute values of the susceptibility are measured with an accuracy of 2% with a lower limit set by the noise of 10−12 m3 (or about 10−7 emu). Typical experimental results are presented.
Construction of a shuttered time-of-flight mass spectrometer for selective ion detection
Authors: Rinnen Klaus-Dieter , Kliner Dahv A. V. , Blake Richard S. , Zare Richard N.
Published: July 2002

By placing a pulsed, high-voltage steering plate between the ion source and detector in a time-of-flight mass spectrometer, the signal-to-noise ratio of the mass of interest is improved by more than an order of magnitude. This improvement arises from (1) suppression of ions of other masses formed at the same time as the ion of interest and (2) suppression of ions formed at different times and different locations whose arrival time at the detector is nearly coincident with the mass of interest. The advantages of this simple device are demonstrated in the detection of molecular hydrogen in the presence of other species.
Neutron multiple scattering and absorption factors
Authors: Johnson Elijah , Robinson Larry
Published: July 2002

Absorption and multiple scattering factors for neutrons are determined using the Monte Carlo integration method. This procedure gives results that are as accurate as that from other methods. It is also simpler and apparently converges more rapidly than other methods.
A combustion/deposition entrained reactor for high-temperature/pressure studies of coal and coal minerals
Authors: Anderson Rodney J. , Logan Ronald G. , Meyer Charles T. , Dennis Richard A.
Published: July 2002

The combustion of coal and coal-derived fuels in heat engines poses significant technical challenges in terms of establishing high combustion rates and efficiencies, controlling emissions, and minimizing the impact of fuel contaminants on engine components. An entrained reactor has been designed and constructed to study coal particle combustion, the tendency of coal ash to form deposits on heat engine components, and the effects of fuel additives on residual ash composition. The reactor is designed for high temperature/pressure conditions similar to those of a coal-fired gas turbine. Optical access ports and advanced instrumentation allow the in situ measurement of gas and particle temperatures, and vapor phase alkali concentrations. The reactor has been used to study the deposition potential of several coals as a function of process conditions, and to determine the effects of selected additives on the deposition rate.
Impurity ion production in alkali ion sources
Authors: Hogan M. J. , Ong P. P.
Published: July 2002

It has long been known that new alkali ion sources utilizing thermionic emission from alkali aluminosilicates can achieve high percentages of the desired ion by a sufficiently long ‘‘burn-in.’’ Observations are reported here of instances where increased impurity ion emission can reoccur and lead to possible measurement errors in experimental systems lacking mass spectrometers. The ratio of impurity K+ ions to Na+ ions from a burned-in Na2O⋅Al2O3⋅2SiO2 source was measured to be 0.55.
CAMAC-PC analyzer for neutron slowing-down-time spectrometry
Authors: Baczyński Janusz
Published: July 2002

A personal computer controlled CAMAC analyzer for time resolved spectroscopy and the design of a specially interfaced CAMAC module for routing data are described. The system is intended for spectroscopic data acquisition of slowing-down-time or time-of-flight neutron spectrometers. Its maximum throughput rate is 140 kHz and can be increased up to 250 kHz.
uv-laser photofragmentation instrument: Multiphoton ionization and dissociation of small molecules
Authors: Turner B. P. , Hill W. T. , Yang S. , Zhu J. , Pinkas A. , Bao L.
Published: July 2002

An excimer laser-based photofragmentation instrument capable of quantitatively probing ionization and dissociation dynamics in small molecular systems is described. This instrument combines single and multiphoton excitation techniques, with fluorescence and time-of-flight ion detection techniques to excite specific excited states of parent molecules and to determine the partitioning of energy among neutral and ionic photofragments. The results of a series of prototype photofragmentation experiments on CO will be used to demonstrate how the experimenter obtains a clearer picture of the fragmentation mechanism when both the ionic and neutral photofragments are interrogated quantitatively rather than when only one type of fragment is studied. Specifically, the authors address the discrepancy in the interpretations of previous fluorescence work on the CO system. It will be shown further that the spectra of the photofragments generated after decomposition of CO by 193-nm radiation can be used to calibrate the laser bandwidth (0.75 cm−1) and the absolute frequency (to within 2 cm−1) when an ArF* excimer laser is employed.
Interference method for monitoring the refractive index and the thickness of transparent films during deposition
Authors: Alius H. , Schmidt R.
Published: July 2002

An interferometric method is described for simultaneous measurement of the refractive index and the thickness of transparent isotropic films during the deposition process. Two laser beams are focused impinging at two different angles onto the film. The intensity of the beams reflected from the growing film shows minima and maxima, which are counted and evaluated to determine the refractive index n and the thickness d of the film in the range of some 100 nm up to several micrometers using 633-nm laser light. n and d can be determined within an accuracy better than 1%, if the thickness is larger than three times the vacuum wavelength of the laser. The measurements are well in accordance with calculations of the intensity modulation. The method can easily be extended to multilayer systems.
A pulsed halogen atom source for kinetic measurements in a Knudsen cell reactor
Authors: Müller-Markgraf Wolfgang , Rossi Michel J.
Published: July 2002

A simple solenoid-valve pulsed halogen atom source for the measurement of heterogeneous reaction kinetics in a very low pressure reactor (VLPR) is described. The source leads to injection of 300 μs–300 ms pulses of halogen atoms into a Knudsen cell, where their number density can be monitored in real time by means of resonance enhanced multiphoton ionization (REMPI). The operation of the source does not interfere with the detection technique. The performance of the source has also been verified using effusive molecular beam mass spectrometric analysis of the effluents of the Knudsen cell. The source is expected to find application in a variety of studies related to fundamental questions regarding etching and deposition reactions, as well as in fundamental chemical kinetic studies involving atoms and stable free radicals.
Fast-imaging method of plasma density spatial distribution by a microwave heterodyne interferometer
Authors: Okazaki K. , Yamada Y. , Nishida Y.
Published: July 2002

By using a microwave heterodyne interferometer assisted by microwave scattering techniques, computer tomographic images of spatial distributions of plasma density can be obtained. Two 9.5 GHz Gunn diodes, whose frequencies are offset by 35 MHz, are used in a heterodyne branch. In front of the detection horn antenna, multiple diodes are lined up, which scatter the microwave power with modulation frequency of 5 kHz, and the whole spatial information in one direction can be obtained by a pair of launcher-detector systems assisted by these diodes. This system is a simple and low-cost means to get images compared with popularly known multichannel interferometer techniques; still, precise, spatial resolution in the images has been observed.
Studies of an expansion-type tandem rf bucket source
Authors: Oka Y. , Shoji T. , Kuroda T. , Kaneko O. , Ando A.
Published: July 2002

A new rf source producing a large and uniform plasma with magnetic field-free geometry for neutral beam has been developed. The source consists of a small-diameter multiple-rf plasma generator and a bucket chamber as a plasma expansion section. The plasma density scaling, the spatial profile, and the ion beam extraction have been studied by using the single rf plasma generator. It was found that under the optimized conditions the plasma density and the profile in the expanded plasma were essentially ruled by qualities of the bucket chamber itself. The present rf source is promising for the application of large-volume positive-ion source or plasma processing.
Performance of a modified Calutron-Bernas ion source
Authors: Pratap R. , Lal K. B. , Salvi V. P.
Published: July 2002

The Calutron-Bernas ion source has been modified for high-dose ion implantation (>1016 ions/cm2). The modified ion source has stable arc, uniformly bright illumination, and dense plasma. It consists of a hairpin-shaped tungsten (W) filament as a hot cathode at one end, and a disk-type graphite anode at the other end about 8 cm away; both the electrodes are fitted in an arc discharge chamber made of graphite only. The anode potential of 150–200 V and filament current of about 60 A initiates a stable bright arc. A magnetic field (0.1–0.5 kG) along the cathode-anode axis enhances the electron ionizing efficiency, helps in collimating the electrons, and contributes also in the plasma confinement near the aperture. The operational life of W filament (1.2 mm diam) in an ambient of oxygen or nitrogen at pressure 10−3–10−4 Torr varies from 25 to 35 h. Further, a needle valve or an in-built minioven is used, respectively, when the feed material is a gas/liquid or a solid charge. The gas/vapors is/are admitted at a proper location into the arc chamber so as to be conducive for the generation of high-density plasma. One rectangular face of the arc chamber (graphite box) is provided with an aperture (8 cm×0.2 cm) for lateral extraction of ions. For most elements, the extracted ion beam that is subsequently accelerated through a mass analyzing 60° magnetic sector is quite intense at the target; the nitrogen ion-beam current has been achieved up to 60 μA/cm2. Consequently, high-dose implantation (≳1017 ions/cm2) of singly charged 30-keV ions has been carried out for surface modification of materials.
The University of Washington polarized ion source
Authors: Gossett C. A. , Balsley D. R. , Harper G. C. , Bitz C. M. , Eisenberg J. K. , Rogers J. A.
Published: July 2002

A colliding-beam polarized ion source has been in operation for nuclear physics experiments at the University of Washington tandem-linac facility since late 1987. Thermal beams of polarized atomic hydrogen or deuterium are ionized by charge exchange in collisions with a collinear, fast, neutral cesium beam. Negative ions are extracted, and the polarization symmetry axis is precessed to any desired direction in a crossed-field spin precessor. The design of the cesium-beam system differs from previous sources in that magnetic deflection and focusing are used, and beams of several milliamperes at energies of 40 keV are produced. The source is controlled by a microprocessor-based system which is connected via fiber-optic links to the main linac-control and data-acquisition computers. To date, currents of 1 μA and polarizations in excess of 90% have been produced.
Plasma parameters of a radio frequency discharge
Authors: Anderson C. A. , Hopkins M. B. , Graham W. G.
Published: July 2002

A low-frequency (100 kHz) radio frequency discharge has been characterized by making time-resolved measurements of the basic plasma parameters, including the electron energy-distribution function. Measurements obtained when operating with H2, D2, and Ar are compared. Surprisingly low electron temperatures (∼0.2 eV) have been found in H2 and D2 discharges.
High-current solid-feed ion source
Authors: Taylor T. , Wills J. S. C. , Douglas E. C. , Tran Ngoc T.
Published: July 2002

A duoPIGatron augmented by magnetic cusp confinement has been equipped with a large-volume external oven. The oven has operated at temperatures as high as 1100 °C. Beams of lithium, phosphorus, calcium, and bismuth have been extracted with a multiple-aperture triode column at voltages of up to 40 kV. Mass normalized current densities of as much as 250 mA cm−2 of singly charged ions have been obtained.
Experimental results from a diagnostic beamline for the PBX-M experiment
Authors: Coupland J. R. , Gray I. L. S. , Hancock O. J. , Martel K. P. , Mepham J. W. , Preest A. A. , Kugel H. W. , Kaita R.
Published: July 2002

The experimental performance of a high-brightness neutral-beam system is described which has been designed and manufactured by Culham Laboratory under contract to the Princeton Plasma Physics Laboratory. The neutral beam serves as a diagnostic on the PBX-M experiment and is used to perform studies of high-beta, bean-shaped, neutral-beam-heated plasmas, and plasma-current profile shaping using ion Bernstein wave and lower hybrid rf systems. A maximum extracted current of ∼2.7 A of positive hydrogen ions at 80 keV has been obtained from a multiaperture extraction system. The full-energy H0-equivalent neutral-current density measured 370 cm from the extraction plane was ∼6 mA cm−2.
Production of atomic nitrogen ion beams
Authors: Walther S. R. , Leung K. N. , Kunkel W. B.
Published: July 2002

A small multicusp ion source has been used to generate beams of nitrogen ions. To achieve a high percentage of N+ ions, the source was equipped with a magnetic filter and operated with a high N2 gas density. A nearly pure atomic nitrogen ion (N+) beam (98.5% N+, 1.5% N2+), suitable for implantation purposes, was produced. The operating characteristics of this source, including species mix, are presented.
Broad beam ion source for ion implantation
Authors: Yucai Feng , Feng Tian
Published: July 2002

A broadbeam ion source for ion implantation has been developed. The features of this source include high current density, large beam spot area, and good beam current density uniformity. It can be equipped with a single or multiaperture ion extraction system and can be operated over energy and current ranges of 3–120 keV and 1–60 mA, respectively. Ion beam current densities ranging from 10–500 μA/cm2 and beam spot diameter ranging from 8 to 25 cm are measured at a target location 60 cm downstream from the source. The drift in beam current is less than ±3% with simple unregulated power supply. Many gases, such as nitrogen, argon, hydrogen, oxygen, and other gaseous compounds, can be implanted with this source. A dual-beam dynamic recoil ion mixing system equipped with this kind of source has been built. By using this machine a good mixture between a deposited Mo film and Fe in the Cr4Mo4V steel substrate has been made at near room temperature. Implantation at high dose rates as high as 300 μA/cm2 has been shown to induce deeper penetration than that realized using lower dose rates at the same beam energy.
The effect of space charge on beams extracted from the room temperature electron cyclotron resonance ion source (abstract)
Authors: Xie Z. Q. , Antaya T. A.
Published: July 2002

We have obtained excellent agreement between BEAM-3D calculations and beam profile and emittance measurements of the total extracted beam from the room temperature electron cyclotron resonance (RTECR), when a low degree of beam neutralization is assumed in the calculations, as will be presented in this paper. The beam envelope has approximately a quadratic dependence on drift distance, and space-charge effects dominate the early beam formation and beamline optics matching process.
Electron cyclotron resonance ion source frequency scaling and radial confinement in a quadrupole magnetic field
Authors: Pu Y. K. , Halverson W. , Petty C. , Smatlak D. , Torti R.
Published: July 2002

Experiments have been conducted on Constance B to study transport properties in electron cyclotron resonance (ECR) heated plasmas of high-charge-state neon ions. Measurements were made of confinement parallel and perpendicular to the magnetic field at heating frequencies of 10.5 and 14 GHz, and corresponding ECR magnetic field strengths. Although radial ion losses scaled approximately as B−2, the total particle confinement time was independent of magnetic field. Thus, higher current densities of multicharged neon ions were extracted at higher ECR heating frequency and magnetic field.
Ecris development at GANIL
Authors: Sortais P. , Attal P. , Bisch M. , Bourgarel M. P. , Lehérissier P. , Pacquet J. Y.
Published: July 2002

The realization of the ’’O.A.E.’’ project at GANIL (Fermi et al., 11th Conference on Cyclotrons and Their Applications, Tokyo, Oct. 1986) (modification of the stripping ratio between the two cyclotrons from 3.5 to 2.5) requires the use of an ECRIS producing an optimized current for ions such as Ar7+, Kr13+, Xe17+, Ta22+ Pb23+, and U24+. We describe the new ECR3 (Caprice source) built at GANIL and we show the last results with gaseous and metallic ions. With the O.A.I. project we plan to increase the beam current and the efficiency of the axial injection line by putting the source on a 100-kV insulated platform. ECR4 is a source with a maximum field corresponding to twice the resonance field for 14.5 GHz. The electrical power is 40 kW. The hexapole made of FeNdB has a field of 1.1 T on poles and weight of 22 kg. The UHF injection is coaxial.
Microwave plasma source for remote low energy ion stream
Authors: Popov Oleg A. , Hale William , Westner August O.
Published: July 2002

A plasma source capable of delivering a narrow (2 to 3-in. diameter), low ion energy (10–30 eV), plasma stream has been designed and tested. Microwave plasmas were excited in a 3-in.-diam chamber by cw electromagnetic waves (2.45 GHz, 200–1000 W) in the presence of static axial magnetic fields of 875–930 G. Plasma was delivered to the sample via a 12-in.-long, 2-in.-diam-metal tube. Ion current densities of several hundred μA/cm2 at gas pressures 1–3×10−4 Torr (N2, Xe) were achieved at distances of 15–16 in. from the source output.
Single stage ECR ion source for the mass separation of xenon radioisotopes
Authors: Hofer M. , Reist H. W.
Published: July 2002

The main features of ECR ion sources (high efficiency, almost unlimited lifetime, stable running conditions, low ion energy spread) make them, when optimized for a high yield at charge state 1+, ideally suited for on-line mass separation. For this reason a single stage 6.4 GHz test source was built for the Paul Scherrer Institute medical radioisotope production facility. Source geometry and operation conditions were optimized for the mass separation of xenon isotopes. Different support gases were tested and an ionization efficiency of 60% for Xe+ was achieved with H2 as support gas. The best results were found at a source pressure of 5×10−4 mbar and at a microwave power level of about 100 W. At an axial magnetic field of about 3 kG the mirror ratio showed no strong effect on the general performance of the source. Our tests showed the advantages of the ECR source type for the mass separation of gaseous isotopes in terms of efficiency and reliability.
Two asymmetric double-probe configurations that measure I-V characteristics in an unstable plasma
Authors: Shun’ko E. V.
Published: July 2002

Two asymmetric double-probe configurations are presented. In each pair, one probe (antiprobe) has a surface area much larger than the other one (e probe). This asymmetry enables one to obtain the entire electron branch of the I-V characteristic and its second derivative. The e probe is axisymmetrically surrounded by the antiprobe and this geometrical arrangement leads to the removal of the influence of plasma potential fluctuations on the measurements. One of the configurations, owing to the supplement of another probe (ion probe or i probe), enables one to remove fluctuations of plasma density and thus to obtain the complete parameters of a turbulent plasma.
A cell for x-ray absorption studies of the emersed electrochemical interphase
Authors: Hansen Galen J. , O’Grady William E.
Published: July 2002

A cell has been constructed which allows the electrochemical interphase on electrode surfaces to be studied ex situ using glancing angle x-ray and gas phase electron yield detection. The various components of the cell are described. The electrode and interphase are emersed using the thin strip emersion technique, and the x-ray beam is totally reflected from the vertical electrode surface above the horizontal electrolyte thin strip. Examples of Au L3 edge and XAFS spectra of an anodically oxidized gold electrode at θ=4 mrad show the technique to be very surface sensitive.
A method of measuring the resistivity of copper from 298 to 77 K
Authors: Ross Keith A. , Kim Hyung-Taek
Published: July 2002

The resistivity of a 0.254-mm-(10-mil-) thick rectangular parallelepiped copper foil was measured from 298 to 77 K by a simple four-point probe technique where probe wires are lead/tin soldered to the foil. Resistivity data indicates that the resistivity correction factor is approximately 2.8 for probes that are approximately 0.3 cm in diameter and spaced approximately 0.9 cm center to center.
A probe for real-time images of particle beams and their analyses in a merged-beams apparatus
Authors: Forand J. L. , Timmer C. , Wahlin E. , DePaola B. D. , Dunn G. H. , Swenson D. R. , Rinn K.
Published: July 2002

We have developed a real-time charged particle beam probe which can be used both as a beam diagnostic (beam tuning) and to quantitatively determine the three-dimensional density distribution of a beam. The probe consists of a microchannel plate, an aluminized phosphor screen deposited on a fiber-optic faceplate, a flexible fiber-optic bundle, and a charge injection device (CID) in tandem. Digital or analog video output of the CID is fed into a computer or oscilloscope, respectively, for analysis or observation. The probe can be moved continuously along the beams’ paths to obtain ‘‘pictures’’ of the beam at any desired interval thus giving three- dimensional form factors. Either beam singly or both beams simultaneously may be observed on the monitor facilitating the task of beam adjustment for optimum overlap. The digital output is used for quantitative computation of the beam overlaps. The device is linear with beam intensity, but the performance degrades with time due to beam damage of the microchannel plate.
High resolution time-of-flight mass spectrometers. Part III. Reflector design
Authors: Bergmann T. , Martin T. P. , Schaber H.
Published: July 2002

The reflector has a central influence on the properties of a time-of-flight mass spectrometer. The mass resolution can be greatly improved using a reflector with homogeneous fields. A reflector with homogeneous fields can also have focusing properties and thus enhance sensitivity of the instrument. In this case it is important to be aware of design limitations. We present a mathematical method of determining these limitations and also give a guideline for mechanical design.
Edge effect correction for small planar Langmuir probes
Authors: Johnson J. D. , Holmes A. J. T.
Published: July 2002

One problem inherent in the use of small planar Langmuir probes to analyze low-density plasma is expansion of the space-charge sheath with increased probe potential due to the departure from planarity caused by a nonnegligible sheath edge. Experimental evidence showing the existence of significant edge effects in the ion saturation region of the characteristic obtained from such probes is presented. The extra ion current ΔI+ collected as a result is shown to depend on the (negative) probe potential V according to the empirical relation ΔI+∝V0.75. A theoretical justification for this is obtained. Finally, the effectiveness of the technique in eliminating the edge effect for this type of probe is demonstrated by the equivalence of ion and electron densities measured in a helium discharge.
A fast gauge for energy flux density measurement
Authors: Garcia Jorge , de Schor Beatriz Baña
Published: July 2002

Herein the design and characterization of a fast energy flux density gauge are described. The gauge is based on a thermoelectrical pair with the junction made of a thin layer of silver. High absorptivity is attained by an electrolytic deposit of platinum black on the silver coat. Dynamic calibration gives a response time below 100 μs. Computer methods to obtain the energy flux density from temperature-time history were evaluated: constant thermophysical properties of the thermoelectrical pair can be assumed in the ignition studies for which the gauge has been developed. The results of the tests performed with igniters of pelleted boron/potassium nitrate and black powder, used in solid propellant ignition, are shown. The gauge developed can be applied to fast processes which require small response time. The gauge does not need previous calibration, it is resistant to vibrations and accelerations, and at the same time it is small in size, economical, and easy to build. Changing the substrate or the thermoelectrical pair, the applications and ranges of temperature can be extended.
Electron beam ion sources and their development at JINR (invited)
Authors: Donets E. D.
Published: July 2002

The principles of action and main types of electron beam ion sources (EBIS) developed in various laboratories are considered. The reasons limiting an ability of EBIS to ionize are discussed. Primary consideration is given to the program of EBIS development at the Joint Institute for Nuclear Research at Dubna. The method of ion-by-ion cooling and preliminary results of its study for increasing the highly charged ion yield and for increasing the charge state of ions are described. The ion-at-surface spectroscopy is shown as a useful diagnostic method of EBIS. Possible prospects for development of EBIS and for its application are pointed out.
Nanosecond-length electron pulses from a laser-excited photocathode
Authors: Young A. T. , D’Etat B. , Stutzin G. C. , Leung K. N. , Kunkel W. B.
Published: July 2002

A photocathode made from polycrystalline lanthanum hexaboride (LaB6) has produced nanosecond-length electron pulses when excited by an excimer laser at 308 nm. Peak currents in excess of 1 A have been observed, with quantum yields of 4×10−5 being measured. A method for extracting the electrons from an emission-limited cathode, plasma extraction, has been demonstrated. This technique uses a low-power continuous discharge to provide the electric field needed to extract the photoelectrons. This technique may be useful in producing high-repetition-rate short-pulse ion sources.
Effect of the electrode thickness on the extraction system of an ion source
Authors: Ortiz Tar , Ondarza Ricardo , Camps Enrique
Published: July 2002

The electrode thickness influence on the extraction system of an ion source is shown, by using a modified Popov’s model. This modified model includes the effect of the electrode thickness as well as the effect of the extraction electrode opening. In other words, all the geometrical parameters of the extraction system are included and a good agreement with experimental data is observed. Taking into account these effects it is possible to discuss the adjustment of the distance between the plasma boundary (virtual cathode) and the extraction electrode.
Beam instabilities stabilization as a result of strong nonlinear interaction between waves
Authors: Soloshenko I. A. , Taranov V. B. , Tsyolko V. V. , Shamrai K. P. , Shulzhenko P. M.
Published: July 2002

It is shown that the nonlinear interaction between unstable low-frequency ion waves and high-frequency electron waves growing in an ion beam plasma can result in stabilization of one of the modes if the level of the other is sufficiently high. A theoretical model of the phenomenon has been developed, and its predictions are in reasonable agreement with experimental results. The suppression mechanism is considered, and appears to be essentially nonlinear. The effect of this mutual suppression of ion beam instabilities may be important for improved ion beam transport.
Solid state cesium ion guns for surface studies (abstract)
Authors: Souzis A. E. , Carr W. E. , Kim S. I. , Seidl M.
Published: July 2002

Three cesium ion guns covering the energy range of 5–5000 V are described. These guns use a novel source of cesium ions that combine the advantages of porous metal ionizers with those of aluminosilicate emitters. Cesium ions are chemically stored in a solid electrolyte pellet and are thermionically emitted from a porous thin film of tungsten at the surface. Cesium supply to the emitting surface is controlled by applying a bias across the pellet. A total charge of 10.0 C can be extracted, corresponding to greater than 2000 h of lifetime with an extraction current of 1.0 μA. This source is compact, stable, and easy to use, and produces a beam with >99.5% purity. It requires none of the differential pumping or associated hardware necessary in designs using cesium vapor and porous tungsten ionizers. It has been used in ultrahigh-vacuum (UHV) experiments at pressures of <10−10 Torr with no significant gas load. Three different types of extraction optics are used depending on the energy range desired. For low-energy deposition, a simple space-charge-limited planar diode with a perveance of 1×10−7 A/V3/2 is used. Current densities of 10.0 μA/cm2 at the exit aperture for energies ≤20 V are typical. This type of source provides an alternative to vapor deposition with the advantage of precise flux calibration by integration of the ion current. For energies from 50 to 500 V and typical beam radii of 0.5 to 0.2 mm, a high perveance Pierce-type ion gun is used. This gun was designed with a perveance of 1×10−9 A/V3/2 and produces a beam with an effective temperature of 0.35 eV. For the energy range of 0.5 to 5 keV, the Pierce gun is used in conjunction with two Einzel lenses, enabling a large range of imaging ratios to be obtained. Beam radii of 60 to 300 μm are typical for beam currents of 50 nA to 1.0 μA. Results are presented and discussed for UHV studies of ion implantation, electronic surface changes induced by adsorbates, and negative secondary-ion mass spectrometry.
High-current metal-ion source for ion implantation
Authors: Huixing Zhang , Xiaoji Zhang , Fengsheng Zhou , Shenji Zhang , Zhuen Han
Published: July 2002

High-current metal-ion beams, as needed for material modification of metal surfaces, can be produced using the MEVVA ion source. In this article a brief description of the ion source is given, and its operational characteristics and preliminary results are presented. A range of metal ions such as Cu, Ti, Al, Fe, Mo, and W, etc., have been extracted from the source. The ion-beam current is 0.5–1 A (total current in all charge states) and is a function of the cathode material, arc current, and extractor voltage. The beam pulse width is 300–550 μs, the repetition rate several pulses per second, the extraction voltage about 30 kV, and the arc current 150–350 A. The extraction system has a set of three multiaperture extractor grids, including three different sizes: 37 holes 2 mm in diameter, and 207 and 495 holes 1 mm in diameter. The operating pressure is in the 2×10−6-Torr range, obtained with a diffusion pump.
Broad-beam multi-ampere metal ion source
Authors: Brown Ian G. , Galvin James E. , MacGill Robert A. , Paoloni Frank J.
Published: July 2002

An embodiment of the MEVVA (metal vapor vacuum arc) high current metal ion source has been developed in which the beam is formed from a 10-cm-diam set of extractor grids and which produces a peak beam current of up to several amperes. The source, MEVVA V, operates in a pulsed mode with a pulsewidth, at present, of 0.25 ms and a repetition rate of up to several tens of pulses per second (power supply limited). The multi-cathode feature that was developed for the prior source version, MEVVA IV, has been incorporated here also; one can switch among any of 18 separate cathodes and thus metallic beam species. Maximum beam extraction voltage is over 90 kV, and since the ion charge states are typically from Q=1 to 5, depending on the metal employed, the ion energy in the extracted beam can thus be up to several hundred keV. This source is a new addition to the MEVVA family of metal ion sources, and we are at present investigating the operational regimes and the limits to the source performance. In this article we describe the source, and present some preliminary results.
Operational characteristics of a metal vapor vacuum arc ion source
Authors: Shiraishi Hiroshi , Brown Ian G.
Published: July 2002

The MEVVA ion source can produce high current pulsed beams of metallic ions using a metal vapor vacuum arc discharge as the plasma medium from which the ions are extracted. In this study, the operational characteristics of the MEVVA IV ion sources are summarized. Results are presented of measurements of the ion beam current as a function of arc current over a range of extraction voltage. Ti, Ta, and Pb were examined as the cathode materials. The arc current ranged from 50 to 250 A and the extraction voltage from 10 to 80 kV. The ion beam current was measured at two different distances from the ion source using Faraday cups, so as to investigate the beam divergence. Additionally, the cathode erosion rates were measured. Optimum operating conditions of the MEVVA ion source were determined.
Laser diagnostics on magnetically insulated pulsed ion sources
Authors: Horioka K. , Tazima N. , Kasuya K.
Published: July 2002

Laser-based diagnostic methods are developed for the investigation of the behavior of a flashover-type magnetically insulated, pulsed-ion source. The effects of neutral particles on the diode characteristics are examined with laser resonant interferometry. For the quantitative estimation of the particle density, a laser resonance scattering method is also applied. These techniques could allow direct determination of the particle distribution in the diode gap.
Influence of a biased beam dump on H− beam neutralization measurements with a four-grid energy analyzer
Authors: Sherman Joseph , Pitcher Eric , Allison Paul
Published: July 2002

A four-grid energy analyzer diagnostic has been developed for the study of H− beam space-charge compensation, and first measurements have been reported previously. Biased beam-dump measurements were undertaken to clarify the origin of electron currents measured in the FGA because they far exceeded predictions based on H−-beam ionization and stripping processes. This experiment partially explains the anomalously large radial electron current. The FGA observations for negative beam-dump bias suggest electron ionization of the background gas is an additional mechanism for producing positive ions.
An autoneutralizing neutral molecular beam gun
Authors: Delmore J. E. , Appelhans A. D. , Dahl D. A.
Published: July 2002

A high-energy (up to 28 keV) neutral molecular beam gun has been developed and put into routine use that takes advantage of the autoneutralization properties of the sulfur hexafluoride anion for the production of high-energy sulfur hexafluoride neutral molecules. The anions are produced in an electron-capture source, accelerated, and focused in a lens assembly designed to minimize residence time, allowed to drift at their terminal velocity for a suitable distance during which up to 30% auto-eject an electron, and all remaining charged particles are electrostatically skimmed, resulting in a focused neutral beam. Rasterable neutral beams focused to a 5-mm spot size up to 3 m from the source have been produced with beam currents up to 40 pA equivalent. Spot sizes of 1 mm can be produced with intensity levels of a few picoamperes equivalent.
The plasma-chemical reactions of several materials in a rf ion source
Authors: Bin Bai Gui
Published: July 2002

The plasma-chemical reactions of several materials are described in this paper. Materials such as quartz and platinum are used for containers of chemical reactions in various fields. Because of their stability chemical reactions do not occur easily, but such reactions can occur within the plasma of a rf ion source, and ion beams of such materials have been extracted from the ion source. This is because of the energetic plasma constituents and the bombardment of material surfaces by these high-energy particles. Various high-temperature chemical reactions can take place in the low-temperature (cool) plasma environment.
Calibration of a Si(Li) detector system with different radiation entrance windows
Authors: Eggert F. , Maneck M. , Scholze F. , Krumrey M. , Tegeler E.
Published: July 2002

The spectral quantum detection efficiency of a Si(Li) detector was determined using the electron storage ring BESSY as a standard source of calculable spectral photon flux. The calibrations were performed for the same detector system with a Be window, an ultrathin silicon-based window and without window for photon energies above 300 eV. For comparison the transmission of the windows was measured in monochromatic radiation from 350–2000 eV with high spectral resolution.
A cryogenic double-resonant parabridge motion transducer for resonant-mass gravitational wave detectors
Authors: Aguiar O. D. , Johnson W. W. , Hamilton W. O.
Published: July 2002

We designed, constructed, and tested at 4.2 K (using two different low phase noise electrical pump generators) a cryogenic double-resonant parabridge motion transducer made out of niobium, whose electrical output was amplified by a two-stage metal-semiconductor field-effect transistor cryogenic amplifier. Most of the experimental results agreed well with the theoretical models. We were able to adjust the two electrical bridge resonant frequencies at the pump frequency, allowing us to obtain an electromechanical coupling as high as 0.054, and we successfully measured the mechanical Brownian motion of this transducer. In one case, we observed a dip in the electrical noise spectrum near the mechanical resonant frequency due to destructive interference between this noise and its ‘‘reflection’’ from the mechanical resonator. At the bottom of this dip, in a bandwidth of 0.7 Hz, we measured an equivalent displacement noise of 4 × 10−16 m/√Hz with a systematic error of less than 10%.
Lag compensation of optical fibers or thermocouples to achieve waveform fidelity in dynamic gas pyrometry
Authors: Warshawsky I.
Published: July 2002

Fidelity of waveform reproduction requires constant amplitude ratio and constant time lag of a temperature sensor’s indication, at all frequencies of interest. However, heat-transfer type sensors usually cannot satisfy these requirements. Equations for the actual indication of a thermocouple and an optical-fiber pyrometer are given explicitly, in terms of sensor and flowing-gas properties. A practical, realistic design of each type of sensor behaves like a first-order system with amplitude-ratio attenuation inversely proportional to frequency when the frequency exceeds the corner frequency. Only at much higher frequencies does the amplitude-ratio attenuation for the optical fiber sensor become inversely proportional to the square root of the frequency. Design options for improving the frequency response are discussed. On-line electrical lag compensation, using a linear amplifier and a passive compensation network, can extend the corner frequency of the thermocouple 100 fold or more; a similar passive network can be used for the optical-fiber sensor. Design details for these networks are presented.
An electrostatic time-of-flight analyzer for simultaneous energy and mass determination of neutral particles
Authors: de Zeeuw W. A. , van der Ven H. W , de Wit J. M. M. , Donné A. J. H.
Published: July 2002

A neutral particle energy analyzer has been developed to measure both the energy and the mass of the incoming particles with only one array of detectors. Energy analysis is performed by means of deflection in an electrostatic field. The mass of the particle is determined by measuring the flight time from a stripping foil to a channel electron multiplier in the focal plane of the analyzer. The application of a stripping foil instead of a gas cell increases the stripping efficiency and simplifies the vacuum system. Monte Carlo simulation studies and first calibration experiments show that the analyzer can be used even at energies down to 1 keV, as long as the stripping foil does not exceed a thickness of 2.0 μg/cm2. These simulations take into account the angular and energy straggling processes that take place in the foil. A triple-coincidence technique can be applied to decrease the sensitivity of the analyzer to neutron and gamma background radiation considerably, as will be shown by calculations.
Optimization of thinning rates in an argon ion beam thinner
Authors: McCredie Geoffrey M. , Phillips Matthew R. , Moon Anthony R.
Published: July 2002

A simple and inexpensive ‘‘feedback’’ circuit has been devised that regulates the gas flow in an argon ion gun system and thus optimizes the specimen thinning rate. The circuit is easily adapted to suit a broad range of similar applications.