bluuebunny/crossref_metadata_2025 huggingface dataset:
Features of the microstrip proportional counter technology (invited)
Authors: Budtz-Jo/rgensen Carl
Published: July 2002

The microstrip proportional counter (MSPC) is a new approach in gas-filled detector technology. In contrast with the classical multiwire proportional counter (MWPC) detectors, the electrodes of the MSPC are deposited by photolithographic techniques onto a rigid substrate. The technique offers many important advantages: An optimal energy resolution; The possibility of matching the electrode structure to the expected spatial resolution, i.e., smaller electrode distances than are possible for MWPCs; A much faster signal development than for the MWPC because of the small distance (few 100 μm) between the anode and cathode strips which allows the positive ion cloud created in the avalanche to be collected rapidly with reduced space charge effects and increased counting-rate capability; A rigid electrode structure which is not deformed under the action of an electric field; A relatively simple fabrication technique which allows the rapid replacement of damaged electrode structures. The applications of the MSPC within the fields of x-ray astronomy, neutron diffraction, high energy physics, and synchrotron radiation will be discussed.
H− and D− temperature in volume sources
Authors: Leroy R. , Bacal M. , Berlemont P. , Courteille C. , Stern R. A.
Published: July 2002

A new technique using laser induced photodetachment has been developed for measuring the negative ion temperature in H− and D− sources. Using this technique, we have investigated the dependence of the negative ion temperature on source parameters such as pressure, discharge current, and electron temperature. Simultaneous measurements of negative ion density, temperature, and extracted current lead to the conclusion that the extracted negative ion current is, at most, equal to the thermal flux.
Sagitally focusing scanning monochromator produces 0.4-mm focus (abstract)
Authors: Rosenbaum G. , Sullivan M. , Fischetti R. , Rock L.
Published: July 2002

A sagitally focusing stage has been constructed for the double-crystal scanning monochromator on beam line X9-A at the NSLS which can be exchanged with the normally used flat crystal stage. The bending device located at 12.0 m from the source is designed to accept a beam up to 200-mm wide. The monochromator with bending stage can be scanned over Bragg angles from 10° to 71° corresponding to photon energies from 11.4 to 2.1 keV with Si-111 crystals. In conjunction with the vertically focusing mirror a point focus of 0.38 mm×0.18 mm [horizontal×vertical, full width at half maximum (FWHM) each] has been achieved at a focal length of 3.8 m (center of a four-circle diffractometer). Focused at the back of the experimental hutch (focal length=5.4 m) the focal size was 0.55 mm×0.30 mm. The measured horizontal width of the focus equals the calculated size of the demagnified source and is independent of the horizontal convergence used. The horizontal focus produced by the crystal is very clean: the full width at 1% of maximum is 1.5 mm and at 0.01% it is about 4 mm. The flux into the focus is 5×1011 photons/s at a photon energy of 7.4 keV and beam current of 200 mA.

The average flux density in the center of the focus (FWHM area) is 5×1011 photons/s/mm2. The preliminary crystal presently used has been made from a thin Si plate of 0.4-mm thickness, 80-mm width, and 75-mm length (in the direction of the beam). Steel ribs of 0.6-mm thickness have been glued at 3-mm pitch to the back of the crystal in order to stiffen the plate and reduce anticlastic bending.1 Plates have been glued to this crystal plate to extend the width to size the bending stage. The crystal was cut in 111 orientation with a 4° angle between the lattice planes and the crystal surface. The asymmetric cut was used to increase the angle of incidence and thus decrease the effect of the remaining anticlastic bending. The bending stage has a bending couple at both ends of the crystal in order to produce the desired curvature of the crystal. The bending couples can be adjusted to produce a conical shape as needed for the particular choice of focal length.2 Small piezotranslators push on the bending couples to remove small amounts of twist in the crystal introduced by alignment errors of the bending couples. All of the adjustment drives are outside of the monochromator tank and transmitted to the bending stage via linear feedthroughs and cables. A full description of this device and the crystal with glued ribs will be submitted shortly to this journal. This work was supported by Grant RR-01633, National Institutes of Health, Division of Research Resources.
Variable-metric diffraction crystals for x-ray optics (abstract)a)
Authors: Smither Robert K. , Fernandez Patricia B.
Published: July 2002

A variable-metric (V-M) crystal is one in which the spacing between the crystalline planes changes with position in the crystal. This variation can be either parallel to the crystalline planes or perpendicular to the crystalline planes of interest and can be produced by either introducing a thermal gradient in the crystal or by growing a crystal made of two or more elements and changing the relative percentages of the two elements as the crystal is grown. A series of experiments was performed in the laboratory to demonstrate the principle of the variable-metric crystal and its potential use in synchrotron beam lines. One of the most useful applications of the V-M crystal is to increase the number of photons per unit bandwidth in a diffracted beam without losing any of the overall intensity. In a normal synchrotron beam line that uses a two-crystal monochromator, the band width of the diffracted photon beam is determined by the vertical opening angle of the beam which is typically 0.10–0.30 mrad or 20–60 arcsec. When the V-M crystal approach is applied, the band width of the beam can be made as narrow as the rocking curve of the diffracting crystal which is typically 0.005–0.050 mrad or 1–10 arcsec. Thus a very large increase of photons per unit bandwidth (or per unit energy) can be achieved through the use of V-M crystals. When the V-M principle is used with bent crystals, new kinds of x-ray optical elements can be generated that can focus and defocus x-ray beams much like simple lenses where the focal length of the lens can be changed to match its application. Thus both large magnifications and large demagnifications can be achieved as well as parallel beams with narrow bandwidths.
Iodine as a tuning standard for laser ablation–inductively coupled plasma-mass spectrometry
Authors: Hollocher Kurt
Published: July 2002

For inductively coupled plasma-mass spectrometry analysis of aqueous solutions the plasma and ion optics are optimized (tuned) using elements added to the solution for that purpose, or suitable elements in the dissolved sample. Laser ablation sampling produces transient signals that are difficult to use for tuning. For laser ablation sampling iodine can be used to produce a stable peak at mass 127 for tuning purposes. Iodine is easily introduced into the argon carrier gas stream by room-temperature evaporation of a 1-mm-size grain. The iodine grain should be supported in a glass tube to avoid reaction with plastic or metal. Iodine apparently does not form significant quantities of polyatomic ions such as ArI+ in the plasma, and so does not interfere with the analysis of isotopes having masses ≳127.
A simple profilometer for film thickness measurement
Authors: Wood J. W. , Redin R. D.
Published: July 2002

A simple profilometer based upon a commercial strain gauge force transducer is described. It has been used on polymer film coated substrates to determine film thicknesses on the order of 10.0 μm. Measured film thicknesses agree with gravimetrically determined values to within ±0.3 μm.
Full-bridge capacitive extensometer
Authors: Peters Randall D.
Published: July 2002

Capacitive transducers have proven to be very effective sensors of small displacements, because of inherent stability and noninvasive high resolution. The most versatile ones have been those of a differential type, in which two elements are altered in opposite directions in response to change of the system parameter being monitored. Oftentimes, this differential pair has been incorporated into a bridge circuit, which is a useful means for employing synchronous detection to improve signal to noise ratios. Unlike previous differential capacitive dilatometers which used only two active capacitors, the present sensor is a full-bridge type, which is well suited to measuring low-level thermal expansions. This analog sensor is capable of 0.1 μm resolution anywhere within a range of several centimeters, with a linearity of 0.1%. Its user friendly output can be put on a strip chart recorder or directed to a computer for sophisticated data analysis.
A new high-frequency rheometer based on the torsional waveguide technique
Authors: Gaglione R. , Attané P. , Soucemarianadin A.
Published: July 2002

A new high-frequency rheometer for measuring mechanical properties of fluids with viscosities as low as 0.5 mPa s is described. The operation is based on the torsional waveguide technique. The torsional motion is generated by a bismuth and germanium oxide Bi12GeO20 piezoelectric crystal. A specific numerical processing is developed for rapid computation of acoustic attenuation and phase retardation. Dynamic viscosity of several Newtonian liquids is determined at 98 kHz. The accuracy of acoustic measurements is better than 1%, and the resolution in terms of the Maxwell relaxation time is 2×10−8 s. The apparatus is used successfully for measuring the viscoelastic moduli G′ and G″ of polystyrene-isobutylmethylketone solutions.
Ultrahigh vacuum cold finger for surface reaction studies
Authors: Frankel D. J. , Fruhberger B. , Jackson R. H. , Dwyer D. J.
Published: July 2002

The design of a cold finger and sample holder for use with a long-strong XYZ manipulator in a multitechnique ultrahigh vacuum chamber is presented. The cold finger design, based on the concept of a cryogenic transfer line, minimizes unwanted cryosorption on the surface of the cold finger. The simple, durable design allows samples to be cooled to below 90 K, rapidly heated to above 1000 K, and quickly returned to low temperatures. The rapid heating and cooling rates coupled with low outgassing make the design ideal for thermal desorption spectroscopy studies.
Simple noncontact temperature sensor for diagnostic use in electron beam evaporators
Authors: Bhatia M. S. , Chatterjee U. K. , Sharma G. L.
Published: July 2002

A simple experimental setup for noncontact temperature monitoring of the vapor emitting surface in an electron beam evaporator is described. The setup consists of optics that focuses optical radiation emanating from the heated surface onto a sensor (photodiode). The photodiode transduces the optical input to a proportionate electrical signal that is indicative of the temperature. Suitability of this method at providing space and time resolved temperature distribution on the heated surface is discussed. Besides diagnostic work, the setup is used to determine transient thermal response of the heated surface.
Detector response in time-of-flight mass spectrometry at high pulse repetition frequencies
Authors: Gulcicek Erol E. , Boyle James G.
Published: July 2002

Relative signal response differences are shown between the continuous and the discrete dynode-type detectors for time-of-flight mass spectrometry at increasing pulse repetition rates.
A new powder diffraction method for linear detectors
Authors: Beno M. A. , Knapp G. S.
Published: July 2002

In this article we describe a new type of powder diffractometer that gives a significant improvement in count rate over existing methods. The key to the new technique is the use of a flat, diffracted beam monochromator in combination with a position sensitive detector. The incident x rays fall on a flat plate or capillary sample and multiple diffraction lines are reflected by the monochromator out of the equatorial plane onto a position sensitive detector. Since the monochromator is tuned for the incident beam energy, background from fluorescence or other scattering is eliminated and data can be recorded over a range of several degrees thereby providing a large improvement in counting efficiency over conventional diffractometers. This new method is also compared to a previous article which employed a focusing analyzer crystal and position sensitive detector.
Small dc motor for producing motion in a cryogenic environment, and a method for monitoring its orientation
Authors: Walker I. R.
Published: July 2002

In the field of condensed matter physics, it is frequently necessary to produce motion at low temperatures. While this can often be done using a mechanical linkage which connects the cryogenic and ambient environments, space constraints sometimes render such a solution impractical. The following paper describes a miniature dc electric motor which can be used to produce motion under these conditions, and also presents a novel scheme for monitoring its position. The motor is a skew-wound ironless device with a coaxial gearhead, and is capable of operating at a temperature of 4 K, in a vacuum, and in a magnetic field of several hundred gauss. The position monitoring arrangement requires no modifications to the motor or the addition of extra hardware, such as rotary encoders or potentiometers. Based on the angular dependence of the rotor inductance, it has been found to work with a number of different motors of the skew-wound ironless type, both at room temperature and at 4°. Provisions have been made to allow the motor and position monitor to be operated by computer control. The author anticipates that they will find applications in other areas where motion is needed and space is at a premium.
Simple micrometer driven coarse motion stage with lateral kinematic mount for scanning probe microscopy
Authors: Teuschler T. , Ley L.
Published: July 2002

We have designed a simple micrometer driven coarse motion stage for scanning probe microscopy. It was tested with a tube scanner based scanning tunneling microscope (STM) of the Lægsgaard/Besenbacher type. A lateral kinematic mount is used for sample positioning. The reproducibility of sample positioning is in principle only limited by the quality of the micrometers. Our design involves exchangeable sample mounts which may be adapted to the users’ requirements. The stage does not cause deterioration in the resonance behavior of the STM and preserves the capability to obtain atomic resolution on graphite.
Instantaneous measurement of hydrogen isotope retention in collector probes in the scrape-off layer of a tokamak by pulsed laser desorption
Authors: Guo H. Y. , Terreault B.
Published: July 2002

The pulsed laser desorption technique is employed for the first time for the instantaneous analysis of hydrogen isotope fluxes in the scrape-off layer (SOL) of a tokamak. The laser desorption system developed for the TdeV tokamak is described. It has been used recently for the investigation of hydrogen isotope behavior in the SOL of TdeV during an isotope exchange experiment. A silicon probe is utilized for the collection of deuterium and hydrogen fluxes in both ion and electron drift directions. After exposure to a tokamak discharge, the hydrogen isotopes retained in the probe are analyzed in situ between two tokamak discharges by means of laser desorption. The measurements of the isotopic ratio D/(H+D) from hydrogen and deuterium retention in the Si collector probes show good agreement with neutral particle analysis, optical spectroscopy, mass spectrometry, and nuclear microanalysis. At the beginning of the experiment, the isotopic ratio decreases radially from the separatrix due to hydrogen recycling from the wall. As the changeover proceeds, the radial profile of the isotopic ratio becomes flat, showing evidence of the replacement of H with D in the wall. Hydrogen isotope retention is larger on the ion side than on the electron side. Measurements done during a plasma density scan show that the radial profile of retention changed with density due to the variation of the incident fluxes.
Higher acceleration technique of microprojectiles in a magnetoplasmadynamic accelerator
Authors: Tamura Hideki , Sawaoka Akira B.
Published: July 2002

For the simulation of hypervelocity impact of micrometeoroids and microdebris on a spacecraft, an improved acceleration technique is proposed in a magnetoplasmadynamic accelerator. The compression of the plasma flow was enhanced due to modification of the magnetic-compressor-coil geometry in the accelerator. Such enhancement was found to be effective for the improvement of the flight parameters of microprojectiles. Due to the modification of the coil geometry, the velocity of glass beads of 500–600 μm diam was increased from about 3 to 6 km/s which is included in the hypervelocity impact regime of projectiles in space. In addition, the main direction of the projectile flight was improved to become more parallel to the central axis of the accelerator.
A 2 MeV, 100 mA electron accelerator for a small laboratory environment
Authors: Clayton C. E. , Marsh K. A.
Published: July 2002

A small, high performance electron linear accelerator is described. It is a modified version of a commercially available portable x-ray source. The 9.3 GHz rf linac and beamline deliver a 3 ns train of approximately 15 ps pulses with a peak current, limited by beam loading of the rf structure, of more than 100 mA and a beam energy of around 2 MeV with a 5% full width at half maximum energy spread. The beam emittance is 6π mm mrad and the final spot size is 250 μm diam for f/10 focusing.
Cesium liquid metal ion source for secondary ion mass spectrometry
Authors: Umemura Kaoru , Shichi Hiroyasu , Nomura Setsuo
Published: July 2002

A Cs liquid metal ion source (LMIS) and focused ion beam system for microarea secondary ion mass spectrometry (SIMS) have been developed. Because of the chemical activity, low surface tension, and high vapor pressure of Cs, few successful Cs LMISs have heretofore been reported, as opposed to the many successful applications of Ga in LMIS. A new Cs-LMIS design had to be developed to supply Cs to the emitter/reservoir under UHV to prevent oxidation, to prevent liquid Cs from dripping off the emitter substrate, and to minimize the surface area exposed so as to minimize thermal evaporation. The last consideration is very important since the evaporation rate of Cs is many orders of magnitude higher than, e.g., Ga at the melting point. A focused Cs beam was obtained with a newly designed SIMS system, which is about 0.1 μm beam size and a beam current density on the specimen of 0.8 A/cm2. An operating time of more than 600 h has been achieved at a total emission current of 1 μA without resupplying the source material at room temperature.
Determination of the second derivative of a Langmuir probe characteristic by current continuity
Authors: Zhong Guangwu , Zhang Jiquan
Published: July 2002

A simple technique has been proposed and tested in a dc plasma machine to determine the second derivative of a Langmuir probe characteristic. The principle of current continuity was used to arrange the current sampling network of a group of three probes so that the second-order difference was achieved without any active arithmetic circuits. In this way, the second derivative signal of the probe characteristic is obtained automatically and accurately. The error remaining in this technique can be monitored easily and then minimized to a tolerable extent.
Dead-time and afterpulsing correction in multiphoton timing with nonideal detectors
Authors: Höbel M. , Ricka J.
Published: July 2002

The influence of detector nonidealities on multiphoton timing experiments is investigated. Deviations from ideal detector behavior include dead-time, afterpulsing, and a smeared detector response. A statistical model of dead-time effects combined with cumulative afterpulsing is developed which allows the correction of distorted experimental data. The theory is verified with both Monte Carlo simulations and experimentally, whereby particular emphasis is put on fiberoptic optical time-domain reflectometry measurements. Though the theory is applicable to any kind of detector we discuss the various effects for two examples of commercially available single photon avalanche diode modules. One of the two detectors is the passive quenched EG&G SPCM-100 while the other module contains an active quenching circuit and is manufactured at the Czech Technical University at Prague.
Simple apparatus for producing single liquid drops
Authors: Panda Dhiren , Robertson David
Published: July 2002

A simple experimental apparatus has been used to produce individual mercury and sodium amalgam drops in the size range of 0.3–2.5 mm diam. A high resistance to the flow of liquid was provided by a capillary tube. The cross section consisted of a 0.20 mm o.d. tungsten wire placed in a 0.25 mm capillary bore. By this method, flow rates of 1 μl/s and lower were obtained, which enabled the formation of drops as small as 1 mm diam in a time interval of 20 s. The drops were formed at a plastic tip, and on reaching the desired size, were stripped off by a stream of argon. An optical sensor was used to detect the growing drop and to switch on the argon stream at the desired time. The growth of the drops at the tip was observed using an image analysis system which showed good agreement between the observed and calculated drop sizes at various instants. The consistency in size from drop to drop, for any particular setting of the apparatus, was evaluated by analyzing magnified pictures of the drops as well as by measuring their weights. The variation in the drop size was found to be within ±2% of the mean value.
Artificial spectral broadening of lasers with random telegraph noise
Authors: Hamilton M. W. , Sinclair G. N.
Published: July 2002

Three methods are given for imposing random telegraph phase or frequency noise on a stabilized cw laser thus giving explicit control of the coherence of the laser field. In the case of phase noise, the resulting laser spectrum consists of a carrier part with nearly Lorentzian shaped noise sidebands which have full-width at half maximum up to 14 MHz. Complete suppression of the carrier is possible if the phase is made to jump by π radians. Frequency telegraph noise results in a laser power spectrum that can be single or double peaked, depending on the relative sizes of the average dwell time and the frequency jump. The laser field has been produced for studies of noise in nonlinear spectroscopic interactions. Measurements of the resulting laser spectra are presented. As an example of the application of such a noisy laser, some results from studies of the dependence of two photon absorption on higher-order optical coherences are given.
In situ force calibration of high force constant atomic force microscope cantilevers
Authors: Scholl D. , Everson M. P. , Jaklevic R. C.
Published: July 2002

A miniature capacitive force sensor which fits in the sample position of an atomic force microscope (AFM) has been used to calibrate the force applied by the scanning tip during nanohardness measurements. The sensor is simple, physically robust, and easily fabricated from readily available materials. It can be operated with commonly available electronic instrumentation. The device described here is optimized for tip-sample forces between 10−4 and 10−2 N, a range useful for micrometer-scale mechanical modification of surfaces. With minor design changes, sensors of this general type should be capable of much greater sensitivity. The sensor is calibrated outside the AFM by the application of free weights. Calculated estimates of AFM cantilever force constants are difficult for all but the simplest geometries and may rely on uncertain values for certain critical dimensions and material properties. These estimates can thereby be replaced by a simple and direct measurement.
An inexpensive sidereal drive unit for 1-m class astronomical telescopes
Authors: Manian K. S. B. , Pathan F. M. , Anandarao B. G.
Published: July 2002

We describe here the details of the concept, the construction, and the performance of an accurate and inexpensive sidereal tracking drive unit (SDU) for the 1-m or larger class of astronomical telescopes. The SDU is tunable and has a very highly stable and undistorted sinusoidal wave shape. The SDU consists mainly of a variable drift-free drive rate generator and a distortion-free, low-cost power amplifier. Tracking accuracies of less than a couple of arcseconds in sky are achieved in 60 min of observation time. The unit can also be used in negative feed back mode to correct any errors in the tracking system. The accuracies in frequency stability obtainable with the SDU and the feasibility of operation in negative feedback mode for correcting tracking errors are not possible in the commercially available battery back-up uninterrupted power supply (UPS) units. The total cost of the SDU currently works out to be approximately $200 (US) and requires about one man-month for building and testing.
Repetitive flash x-ray generator having a high-durability diode driven by a two-cable-type line pulser
Authors: Shikoda A. , Sato E. , Sagae M. , Oizumi T. , Tamakawa Y. , Yanagisawa T.
Published: July 2002

The fundamental studies of a repetitive soft flash x-ray generator having a high-durability diode for high-speed radiography in biomedical and technological fields are described. This generator consisted of the following essential components: a constant negative high-voltage power supply, a line-type high-voltage pulser with two 10 m coaxial-cable condensers, each with a capacity of 1.0 nF, a thyratron pulser as a trigger device, an oil-diffusion pump, and a flash x-ray tube. The x-ray tube was of a diode type which was evacuated by an oil-diffusion pump with a pressure of approximately 6.7×10−3 Pa and was composed of a planar tungsten anode, a planar ferrite cathode, and a polymethylmethacrylate tube body. The space between the anode and cathode electrodes (AC space) could be regulated from the outside of the tube. The two cable condensers were charged from −40 to −60 kV by a power supply, and the output voltage was about −1.5 times the charged voltage. Both the first peak voltage and current increased according to increases in the charged voltage, and the maximum values of the voltage and current were about 90 kV and 0.72 kA, respectively. The pulse widths had values of less than 100 ns, and the maximum x-ray intensity was approximately 1.1 μC/kg at 0.5 m per pulse. The repetition rate was less than 54 Hz, and the maximum focal spot size was about 2.0×2.5 mm.
An all-carbon cathode for dc plasma chemical vapor deposition of diamond films
Authors: Bögli U. , Bächli A. , Blatter A.
Published: July 2002

The fabrication and behavior of an all-carbon cathode for the growth of diamond films by dc discharge plasma chemical vapor deposition is presented. A graphite rod with a diameter of 2.5 mm was passivated in a methane dc plasma. During this process, the graphite was coated with pyrolytic carbon. Simultaneously, a thorn shaped protuberance (hereafter referred to simply as the thorn) of the same material grew from the end face of the rod towards the anode. The pyrolytic carbon prevented excessive sputtering of the cathode during diamond film synthesis in the hydrogen–methane plasma and the thorn presented a pointlike electron emitter providing a stable discharge. Using such cathodes, polycrystalline diamond films with well faceted crystallites have been grown at rates of approximately 5 μm/h. Nucleation and growth of individual, well faceted diamond crystallites even occurred on the cathode. When producing diamond films at methane concentrations above 1 vol %, a tubular form grows on the end of the cathode thorn.
Low-energy ion beam space-charge neutralization
Authors: Dudin S. V. , Zykov A. V. , Farenik V. I.
Published: July 2002

In technology intense (propagation without space-charge neutralization is impossible) ion beams of low energy (<1 keV) are often used. In this energy range neutralization as a result of ambient gas ionization immediately by ions is not effective. Different channels of electron appearing have been investigated by authors experimentally and theoretically with different modes of neutralization. Detail probe measurements of electron temperature and energy distribution, electron and ion densities, plasma potential have been carried out. On the basis of the experimental results a self-consistent theoretical model has been developed. The electron temperature and plasma potential are calculated from self-consistent energy and particle balance equations. The energy distribution of plasma electrons is found using the Fokker–Planck equation. All theoretical results are given in comparison with experimental data.
Oil impurities harm to arc discharge in multiampere DuoPIGatron ion source (abstract)
Authors: Peng Zhu Dong , Wang Shao Hu , Zhang Xiao Dong
Published: July 2002

The major purpose of this paper is to describe that organic impurities cause harm to the arc discharge in the multiampere DuoPIGatron ion source and attempt to analyze the mechanism. Though we knew before that the existence of oil in the source is always harmful, for financial reasons, we had to use the available oil pump to pump gas. But we did not think that the oil pollution in the discharge chamber of the source could cause arc discharge failure so seriously that the source cannot operate normally. After encountering and solving the problem, we have recognized the severe action of oil pollution, and seen the damage mechanism. The up-stream oil vapor from big pumps entered the chamber of the plasma generator. Should the parts of plasma chamber, especially, the target cathode be polluted by oil vapor, it resulted in destroying the reflected discharge in the chamber so that the stable condition of plasma, that is Iig≫Iil could not be maintained. Here Iig and Iil represent generated and lost ion current, respectively. The arc discharge died. After protecting the target cathode from oil pollution by various ways, our 15-cm duoPIGatron can keep high performance operation for more than one year without recleaning. During this period, the arc current was larger than 300 A and the saturated ion current was above 234 mA/cm2.
High sensitivity Trouton–Noble experiment
Authors: Hayden Howard C.
Published: July 2002

The 1903 Trouton–Noble (TN) experiment, which sought a torque on a charged capacitor, is often regarded as the electrostatic equivalent of the Michelson–Morley experiment, inasmuch as it was supposed to have detected ether drift, and it yielded a null result. The present experiment was designed to be the electrostatic equivalent of the Michelson–Gale experiment, which was performed to detect the rotational velocity of the earth and which yielded a nonnull result. The present experiment is 105 times as sensitive as the original TN experiment, but yields a null result nonetheless. Although the TN experiment is often regarded as crucial, a footnote in the original paper reveals the conjectural nature of the theory.
The progress of ion sources in China (invited)
Authors: Hua-sheng Zhang , Chia-erh Chen , Weijiang Zhao
Published: July 2002

The progress of ion source research in China, including the main achievements, present status, suggestions, and problems are reviewed.
Microwave ion source with linear antennae (abstract)a)
Authors: Wada Motoi , Hamabe Makoto , Tsuji Kousei , Tsuda Hiroshi , Miyamoto Naoki , Ohtani Yoshiaki
Published: July 2002

A microwave ion source equipped with two linear antennae set parallel to the wall of the source chamber has been designed and built. A homogeneous plasma of Ar was produced in an aluminum chamber of 22 cm long, 9 cm wide, and 6 cm deep. Beam forming grids produced a rectangular beam of 17 cm by 3 cm. The current density of the extracted Ar+ beam was 0.16 mA/cm2 at the center of the extraction area when the input power to the magnetrons was 360 W. The energy distribution function of the extracted ions was measured with an electrostatic analyzer. The measured energy distribution showed a presence of high energy ions in the extracted beam.
A compact ECR ion source for bio-organic mutation (abstract)
Authors: Chundong Hu , Zengliang Yu , Xiuluan Yao , Jianjun He , Xiaodong Zhang
Published: July 2002

An ECR ion source was excited by microwaves (2.45 GHz). The discharge chamber diameter of the ECR ion source into which microwaves were introduced by a waveguide and a vacuum window, is smaller than the cut off for TE or TM modes. The magnetic structure is built with an NdFeB permanent magnet where the magnetization M is perpendicular to the source axis. This cusp structure enables us to produce an N+ ion current of 1.1 mA (ion current density of 16 mA/cm2) at an extraction voltage of 8 kV with an aperture of 3 mm diameter by a two grid system; ion beam diameter is 0.2 mm by focusing. This ion source is used for bio-organic mutation.
Design and investigation of a microwave plasma cathode
Authors: Rao Yusheng , Zhang Yong , Wu Jiannan , Qi Lei
Published: July 2002

The physical consideration, design, and characteristics of a compact microwave plasma cathode are expounded in this paper. The impedance matching is calculated to improve the microwave transmission efficiency. The influence of the magnetic field on the discharge property and the extracted electron beam current is investigated. The off-resonance discharge mode (a non-ECR discharge mode) is put forward, in which the magnetic field is bigger than 875 G in the discharge chamber. The dependence of the extracted electron beam current on the extraction voltage, the input microwave power, and the operation pressure is described. The 2.45-GHz microwave power is transmitted to the cathode via a coaxial line. The permanent magnets made from NdFeB are used to excite the magnetic field and the magnetic induction of 800–2600 G can be produced. This cathode can obtain the electron beam current of up to 500 mA at the input microwave power of 30–60 W, with N2 used as the support gas.
Spark source of some metals and carbon
Authors: Vasiliev A. A. , Kondratiev L. N. , Rogal A. D.
Published: July 2002

Experimental results of comparative tests of a spark ion source (closed geometry) with a MEVVA ion source (open geometry) are presented in this paper. Carbon (graphite) and some pure metals (such as Al, Cu, Ta) have been used as the working substances. It was discovered that the vapor ionization degree in the spark depended on the discharge gap shape that changed in time and became self-sustaining during the tests. It is supposed that this dependence had been determined both by the considerably increased value of power density released in the discharge, accompanied by the intense working substance transfer, and by a voltage drop growth in the spark ion source which led to deeper ionization of the vapors by fast electrons. Prolonged tests of the closed shape ion source (22 000 pulses, f=0.3 Hz) have been carried out. Spectra have been obtained for different times from the beginning of the test. Results are discussed.
Ion sources for induction linac driven heavy ion fusion (abstract)a)
Authors: Rutkowski H. L. , Eylon S. , Chupp W. W.
Published: July 2002

The use of ion sources in induction linacs for heavy ion fusion is fundamentally different from their use in the rf linac-storage rings approach. Induction linacs require very high current, short pulse extraction usually with large apertures which are dictated by the injector design. One is faced with the problem of extracting beams in a pulsed fashion while maintaining high beam quality during the pulse (low emittance). Four types of sources have been studied for this application. The vacuum arc and the rf cusp field source are the plasma-types and the porous plug and hot alumino–silicate surface source are the thermal types. The hot alumino–silicate potassium source has proved to be the best candidate for the next generation of scaled experiments. The porous plug for potassium is somewhat more difficult to use. The vacuum arc suffers from noise and lifetime problems and the rf cusp field source is difficult to use with very short pulses. Operational experience with all of these types of sources is presented.
H− beam characteristics from a cesiated rf-driven multicusp source
Authors: Gammel G. , Debiak T. W. , Melnychuk S. , Sredniawski J.
Published: July 2002

A special dual function collar and getter strip holder subassembly was placed around the aperture of an rf-driven multicusp source. With the source at 35 kV, and the rf pulsing at 24 kW for 1 ms at 1 Hz, the cesium in the getter strips was dispensed gradually over a half hour. No high-voltage reconditioning time was needed. After the cesium was dispensed, the strips were used to maintain the collar temperature at ≊150 °C, which optimized the H− current enhancement and electron current reduction. An electrostatic analyzer was used to measure beam emittance and divergence with and without gas neutralization (using argon or xenon). The neutralizing gas reduced the beam divergence by as much as a factor of 2, but had little effect on emittance. Effects on H− and electron currents of pulse length (300 μs vs 1 ms) and bias voltage on the first grid were studied. The source pressure was lower by almost a factor of 2 for the shorter pulse, and the H− yield was higher. The highest H− currents were obtained for short pulse, negative bias. The effects on electron current were not as pronounced.
Design studies for an advanced ECR ion source (abstract)a)
Authors: Alton G. D. , Smithe D. N.
Published: July 2002

Magnet design codes, plasma dispersion solvers, and particle-in-cell (PIC) simulation codes have been used to arrive at the first step in the design of an advanced ion source based on ECR technology. The advanced concept design uses a minimum-B magnetic mirror geometry, which consists of a multicusp magnetic field, to assist in confining the plasma radially, a flat central field for tuning to the ECR resonant condition, and specially tailored mirror fields in the end zones to confine the plasma in the axial direction. The magnetic field is designed to achieve an axially symmetric plasma volume with constant mode-B, which extends over the length of the central field region. The design permits separation of the ‘‘tune’’ and confinement magnetic fields, thus enabling the use of low-frequency, low-cost microwave power sources; the location and increased physical size of the ECR zone over those in conventional sources is commensurate with the generation of higher beam intensities, higher charge states and a higher degree of ionization. A summary of the results of these studies is presented in this report.
Measuring microwave shielding effectiveness in liquid nitrogen
Authors: Namboodri S. L. , Davis W. A. , Kander R. G.
Published: July 2002

A technique to distinguish between materials that can and cannot shield microwaves in liquid nitrogen was developed. The samples are placed in a modified X-band waveguide, which operates by the same ‘‘insertion loss’’ principle as a coaxial device used to measure shielding effectiveness from 300 to 1000 MHz. Verification of the waveguide fixture was accomplished by measuring the shielding effectiveness of a good conductor, coppper; a nonconductor, Teflon; and two intermediate conductors, steel and a carbon-filled elastomer. After verification, the waveguide fixture was used at liquid nitrogen temperatures to compare the shielding effectiveness of YBa2Cu3O7−x, a high temperature superconductor, with copper, a known shielding material.
An autocollimator based optical system for precise angular alignment control over large exploring areas
Authors: Martinelli P. , Musazzi S. , Perini U.
Published: July 2002

An autocollimator based optical system has been developed which allows the relative angular positions of separate reflecting targets to be measured with high accuracy over a relatively large area. Misalignments suffered by the autocollimator head during translation between different measuring points are accounted for by utilizing a large plane reference mirror. Accuracies better than ±2 arcsec have been obtained over a 0.5 m diameter circular exploring area.
Hermetic sealing of a coaxial cable by a double tourniquet
Authors: Ponsonby J. E. B.
Published: July 2002

A method for sealing a semirigid solid dielectric radio frequency quality coaxial cable against ultrahigh vacuum is described. It was developed for the output cable of a hydrogen maser frequency standard that operates at the single spot frequency of 1420.4 MHz. The cable is squeezed in two places a quarter of a wavelength apart so that the two impedance mismatches introduced cancel to the first order at the spot working frequency. The length of solid dielectric trapped between the two ‘‘tourniquets’’ forms an excellent and enduring vacuum seal.
Fast averaging data acquisition unit for pulse spectrometers
Authors: Pieper M. W. , Caspary E.-G. , Kötzler J. , Nehrke K.
Published: July 2002

A combined pulse generator and digitizer based on a RISC processor has been designed and tested by 59Co NMR. The pulse generator provides a 16-bit TTL-level output with 100 ns resolution and is programmable in the high-level language FORTH. The digitizer supports two channels, each with a 10 bit, 40 MSPS analog-digital converter and online averaging in a 24×1024 bit memory, which is directly accessible by the RISC processor.
Large area thermal target board: A new design
Authors: Watkins Wendell R. , Bean Brent L. , Munding Peter D.
Published: July 2002

A large area (1.8 m by 1.8 m), uniform temperature, thermal target was used for characterization of phenomena that impact target contrast. The target board is equipped with several bar patterns. It has a unique design that uses a tilted oven surface making it lightweight with near perfect transition between the hot and cold portions of the bar patterns. The oven surface maintains a ±1 °C uniformity when heated to 10–20 °C above ambient temperature.
Development of a simple electrolytic jet thinning apparatus for the preparation of thin metal foils for transmission electron microscopy
Authors: Chini T. K. , Bhattacharyya S. R. , Basu D.
Published: July 2002

A very simple and inexpensive electrolytic jet thinning apparatus for rapid thinning of metal foils for transmission electron microscopy has been described. Regarding the specimen holder assembly, either a polytetrafluoroethylene (PTFE) holder or a platinum tipped locking tweezer-type holder, can be attached electrically and mechanically to a micromanipulator to be used in the same jet thinning apparatus. This gives a unique feature to our unit, in which the specimen remains above the electrolyte during the polishing process. Also the constructional simplicity of the unit provides easy drainage of the electrolyte for lengthy polishing and a simple way of stopping the thinning process. Transmission electron micrographs of bombarded and unbombarded specimens electrothinned in the unit are presented herein.
A differential retarding potential method for improving ion-beam kinetic energy resolution
Authors: Li X. , Huang Y.-L. , Flesch G. D. , Ng C. Y.
Published: July 2002

We present a differential retarding potential (DRP) method for improving the kinetic energy resolution of a reactant ion beam for scattering experiments. This method allows ion-molecule reaction absolute total cross-section measurements to be performed down to thermal energies using the simple electrostatic aperture ion lenses of a tandem quadrupole mass spectrometric ion-molecule reaction apparatus, even though the reactant ions are formed originally with a broad kinetic energy distribution. To illustrate the principle of the DRP method, examples are given for its application to reactant ion beams prepared in an electron impact ion source and in an ion-molecule reaction ion source.
Production of centimeter-scale, high-density plasmas with a linear gas jet
Authors: Coverdale C. A. , Darrow C. B. , Jones R. , Sawyer W. , Crane J. , Ditmire T. , Perry M. D. , Filbert P. C.
Published: July 2002

A novel linear gas jet has been developed and used to produce centimeter-scale, 1019 cm−3 electron density plasmas. Long regions of high density are important to many types of experiments, including x-ray laser and laser-plasma interaction studies. This new type of gas jet has been characterized by stimulated Raman backscatter emission from the plasma.
Highly accurate electrical resistance measurement apparatus for high temperature
Authors: Osono H. , Kino T.
Published: July 2002

In order to investigate the details of an atomic configuration in metals and alloys, a precise electrical resistance measurement apparatus at high temperatures was constructed. Accuracy of temperature control is found to be 0.01 °C at around 300 °C, and the accuracy of the electrical resistivity measurement is 0.01 nΩ cm for an aluminum sample which has an electrical resistivity of 6×103 nΩ cm at around 300 °C. Using the apparatus, thermal generation of a vacancy at 320 °C in a highly perfect aluminum crystal was detected.
Novel photoacoustic Stark cell
Authors: Thöny A. , Sigrist M. W.
Published: July 2002

In order to further enhance the detection selectivity of a mobile CO2-laser photoacoustic (PA) system for air monitoring we have developed a novel type of Stark cell and an appropriate power supply that provides variable dc and ac high voltages. The special design of the electrode profile enables the operation of the cell with electric field strengths of up to 16.7 kV/cm at atmospheric pressure without any appearance of arcing. The Stark PA cell is of special interest for the detection of compounds exhibiting a permanent electric dipole moment such as ammonia. We present results on the absorption of ammonia, ethene, and nonabsorbing synthetic air derived from PA measurements with variable dc and/or ac electric field applied. Good agreement with theoretical predictions is obtained.
Sample load-lock and manipulation system with heating capacity
Authors: Alonso E. V. , Jiménez-Rodríguez J. J. , Pérez-Martín A. M. C.
Published: July 2002

An apparatus consisting basically of a fast entry load-lock system with sample manipulation and heating capacity is described. Special attention is paid to the differential pumping details and the sample heating. This low-cost system is within the possibilities of tradesmen and workshops.
Design and performance of a high-temperature, high-speed scanning tunneling microscope
Authors: Kuipers L. , Loos R. W. M. , Neerings H. , ter Horst J. , Ruwiel G. J. , de Jongh A. P. , Frenken J. W. M.
Published: July 2002

This article describes the design and performance of a new scanning tunneling microscope (STM) which operates at elevated temperatures and high scanning speeds. To minimize the thermal displacements within the STM, a symmetric configuration was chosen with a large temperature gradient between the sample and the piezoelectric scanner. The thermal behavior of the STM was optimized further by means of a finite element analysis. The high scan rates (105 data points/s) are accomplished with fast analogue electronics and a combination of a workstation and three transputers. The STM has imaged surfaces with atomic resolution between room temperature and 750 K, with low residual drifts only two hours after a major temperature change. The sample surface remains within the vertical range of the piezo actuator over a temperature interval of 159 K.