bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoacoustic enhancement of photoacoustic spectroscopy: Theory and measurements of the signal to noise ratioa)
Authors: Arnott W. Patrick , Moosmüller Hans , Abbott Robert E. , Ossofsky Michael D.
Published: July 2002

Recent developments in thermoacoustics have shown that the quality factor, Q, of an acoustic resonator can be controlled by establishing a temperature gradient across properly positioned thermoacoustic elements. Quite separate from thermoacoustics, acoustic resonators are used in photoacoustic spectroscopy, where a laser beam, modulated at the acoustic resonance frequency, is partially absorbed, thereby producing sound. The photoacoustic signal is typically measured with a microphone, and is proportional to the laser power, to the absorption coefficient, and to the resonator Q, among other factors. The acoustic signal to noise ratio is proportional to Q1/2. Thermoacoustics can be used to enhance the signal to noise ratio of photoacoustic spectrometers by increasing Q. Measurements and theory are reported for the signal to noise ratio of a photoacoustic cell, with thermoacoustic enhancement, as a function of both resonator Q and the bandwidth of the lock-in amplifier. Regimes where thermoacoustic enhancement is useful are identified.
Debris elimination in a droplet-target laser-plasma soft x-ray source
Authors: Rymell L. , Hertz H. M.
Published: July 2002

A tabletop high-brightness line-emitting laser-plasma soft x-ray source utilizing single microscopic droplets as target is shown to produce several orders of magnitude less debris than conventional-target sources. Quantitative measurements of debris deposition rates and x-ray flux at different directions around the droplet plasma are presented. With ethanol droplets and a 10 Hz, 70 mJ/pulse laser, typically ∼1×1012 photons/(sr⋅pulse⋅line) are emitted from the C V and C VI lines in the water window. The debris deposition is further reduced with a small, localized gas jet shield, which is transparent to the x-rays. The deposition rate through the gas shield has been determined to be ∼0.2 pg/(sr⋅pulse). Thus, this droplet-target laser-plasma x-ray source is four orders-of-magnitude cleaner than a low-debris plastic tape target laser plasma of similar brightness, making it useful for x-ray microscopy and lithography.
Cross calibration of neutron detectors for deuterium-tritium operation in TFTR
Authors: Johnson L. C. , Barnes Cris W. , Duong H. H. , Heidbrink W. W. , Jassby D. L. , Loughlin M. J. , Roquemore A. L. , Ruskov E. , Strachan J. D.
Published: July 2002

During the initial deuterium-tritium experiments on TFTR, neutron emission was measured with 235U and 238U fission chambers, silicon surface barrier diodes, spatially collimated 4He proportional counters and ZnS scintillators, and a variety of elemental activation foils. The activation foils, 4He counters, and silicon diodes can discriminate between 14 and 2.5 MeV neutrons. The other detectors respond to both DD and DT neutrons but are more sensitive to the latter. The proportional counters, scintillators, and some of the fission chambers were calibrated absolutely, using a 14 MeV neutron generator positioned at numerous locations inside the TFTR vacuum vessel. Although the directly calibrated systems were saturated during the highest-power deuterium-tritium operation, they allowed cross calibration of less sensitive fission chambers and silicon diodes. The estimated absolute accuracy of the uncertainty-weighted mean of these cross calibrations, combined with an independent calibration derived from activation foil determinations of total neutron yield, is ±7%.
Low temperature linear magnetic field sensor based on magnetoresistance of the perovskite oxide La–Sr–Co–O
Authors: Mahendiran R. , Raychaudhuri A. K. , Chainani A. , Sarma D. D.
Published: July 2002

A linear magnetic field sensor for low temperature (T≤60 K) use based on magnetoresistance of the perovskite oxide material La0.7Sr0.3CoO3 is reported. The magnetoresistance is negative and is linear in field up to at least 7 T. It is temperature independent for T≤60 K and has a small anisotropy (20%) with respect to the direction of the measuring field.
A low temperature scanning tunneling microscope for use in high magnetic fields
Authors: Dubois J. G. A. , Gerritsen J. W. , Hermsen J. G. H. , van Kempen H.
Published: July 2002

We describe the design and performance of a low temperature (1.3–4.2 K) scanning tunneling microscope (STM) setup that can be used in magnetic fields up to 9.5 T. Due to the compact, rigid, and concentric design, the STM is very insensitive to external vibrations. The influence of external magnetic fields on the performance of the STM has been minimized by making a version completely out of titanium (instead of stainless steel). The STM routinely shows atomic resolution on various samples over the whole magnetic field range. We demonstrate the spectroscopic capability by local spectroscopy of the Abrikosov flux lattice on NbSe2.
Vibration-induced noise in a fiber lead of an optical current measurement system
Authors: Zhang W. , Ning Y. N. , Chu B. C. B. , Grattan K. T. V. , Palmer A. W.
Published: July 2002

A comparative experimental study on the effect of the vibration of an optical fiber lead in an optical current measurement system has been made with the use of a polarimeter. The experimental results obtained have shown that both the depolarization effect and the decoherence effect of a multimode fiber can be used to suppress the vibration-induced noise in a fiber lead in such an optical current measurement system. With the use of a low-coherence source and a long multimode fiber of 2200 m, an improvement of more than 40 dB of the output signal-to-noise ratio has been demonstrated.
A Stern–Gerlach polarized ion source for the Munich tandem accelerator
Authors: Hertenberger R. , Abiary K. El , Schiemenz P. , Graw G.
Published: July 2002

A Stern–Gerlach polarized ion source for intense polarized H and D beams is under construction at the Munich tandem accelerator laboratory. The goal is to achieve negative beams of about 2 μA on target with excellent brightness. This development goes in parallel with our collaboration at the HERMES ABS and compatibility between both systems is strived for. Intensity tests of electron polarized H beams just started. A flux of 4×1016H/s was observed so far in preliminary tests.
Pulsed optically pumped polarized H− ion source development
Authors: Zelenski A. N. , Davydenko V. I. , Dimov G. I. , Levy C. D. P. , van Oers W. T. H. , Schmor P. W. , Wight G. W. , Dutto G. , Sakae T.
Published: July 2002

Results are presented of a pulsed optically pumped polarized H− ion source development for high energy accelerators. An atomic hydrogen beam intensity of 2×1018 atoms/s within the polarizer acceptance was obtained with an atomic H injector at BINP. A pulsed polarized H− ion current of about 10–20 mA should be obtainable using this injector. Limitations on beam characteristics due to space charge were studied. A polarization scheme to avoid space charge limitations is considered, in which charge exchange and spin exchange are combined.
Preliminary results of a broad beam radio frequency ion source with electron plasma interaction
Authors: Abdelaziz M. E. , Zakhary S. G. , Ghanem A. A. , Abdelghaffar A. M.
Published: July 2002

A new design of a broad beam rf ion source is made to deliver currents of 100 μA–30 mA with extraction voltages of 200 V–2 kV. Its plasma intensifying system is made with both the addition of electrons from an immersed filament in the discharge and an axial magnetic field of 70–300 G. Uniform beam density distribution is made with a planner graphite cathode which has a number of holes of varying diameters arranged to produce perveance matching with the normal Gaussian distribution of the beam density. Variations of the output currents are studied with variations of extraction voltage, magnetic field intensity, discharge pressure, and electron injection into the plasma. The influence of electron injection into the plasma is found to have a great effect on increasing the extracted current to about four times its value without electron injection. The increase of extraction voltage is limited to the use of electron injection at Vex≳2 kV due to the presence of breakdown inside the discharge tube.
Investigations on AuSi liquid alloy ion sources (abstract)
Authors: Mühle R. , Germann D. , Nebiker P.
Published: July 2002

We have done extensive investigations on AuSi liquid alloy ion sources of different alloy compositions. The influence of source temperature and tip radius on current–voltage characteristics, emission current stability, and angular distribution has been investigated. The results are compared with those of other investigated liquid alloy ion sources. The mass spectra were measured as a function of source current, source temperature, and source operating time. The sources were tested in the ETH/PSI 30 kV focused ion beam system in Zurich.
Beam emittance measurements on multicusp ion sources
Authors: Sarstedt M. , Lee Y. , Leung K. N. , Perkins L. T. , Pickard D. S. , Weber M. , Williams M. D.
Published: July 2002

Multicusp ion sources are used for various applications. Presently, the implementation of this type of ion source is planned for the development of an ion beam lithography machine, which will be used for the projection of sub-0.2 μm patterns onto a wafer substrate. Since, for this application, a very good beam quality and a small ion energy spread are required, emittance measurements have been performed on a multicusp ion source for various source conditions. It is shown that the installation of proper capacitors between the extraction electrodes is necessary to avoid rf pickup, which otherwise leads to a distortion of the beam emittance. The influence of the magnetic filter field on the beam emittance has been investigated, and the beam emittance of a dc filament-discharge plasma has also been compared to that of a rf-generated plasma.
Thomson parabola ion spectrograph with the microchannel plate image converter in investigations of high-Z laser plasma ion sources
Authors: Mróz W. , Parys P. , Wol/owski J. , Woryna E. , Straka P. , Králiková B. , Krása J. , Láska L. , Mašek K. , Rohlena K. , Mocek T. , Pfeifer M. , Skála J. , Haseroth H. , Collier J. , Sharkov B. Yu. , Shumshurov A. V. , Golubev A. V. , Farny J.
Published: July 2002

The results of experimental investigations on ion production from tantalum targets, made with the application of the Thomson parabola ion spectrograph (TP) to an image converter equipped with a microchannel plate of the size of 70×90 mm2, are presented. In the experiments, the iodine photodissociation laser system PERUN (λ=1.315 μm, EL≤50 J, τ∼350–650 ps. I≤1015 W/cm2) was used for ion generation. The TP can give useful information about physical processes, ion species, their energies, and charge states from a single laser shot. The results obtained are compared with the results of measurements made with an electrostatic ion energy analyzer and charge collectors and they are used to estimate the Ta ion yield with an average charge state of 40+. The obtained values are N∼2.6×1011 sr−1.
New design method for the extraction electrodes of high-brightness space charge dominated ion beams
Authors: Lemaître S. , Reckenfelderbäumer R. , Paetz gen. Schieck H.
Published: July 2002

A nonideal potential distribution inside an ion gun gives rise to emittance growth of the beam. The aberrations caused by the lens system (extractor) and the space charge of the beam can be reduced to a minimum by appropriately modifying the shape of the anode. For an intense Cs+ beam this was reached in a computer experiment and realized with the aid of numerically controlled machines. Experimentally the brightness of the beam could be shown to exceed the value at the conventional design by a factor of about 3.
Improvement of highly charged ion production in the ECR source of heavy ions
Authors: Shirkov G. D.
Published: July 2002

Some physical limitations of the highly charged ion production in the ECR source are analyzed in this report. A few possible ways to improve the output of highly charged ions from the ECR source for heavy ions are proposed. A new library of computer codes for the numerical simulation of heavy ion production in the ECR ion source is used to examine these ways to improve the ECR source operation according to the CERN program of heavy ion acceleration.
An 18-cm-diam intense beam current broad beam ion source for surface modifications (abstract)
Authors: Feng Y. C. , Li X. G.
Published: July 2002

A large diameter intense beam current broad beam ion source used for surface modifications is described. It consists of a discharge chamber and a three-grid extraction system. The discharge chamber has two anodes (front and rear) and a specially designed cusped magnetic field is used for forming a large field free region in the chamber so that a very uniform and intense ion beam has been extracted from this source. Beam currents of more than 900 mA for hydrogen and 750 mA for argon at 2.5 kV extraction voltage have been obtained. The highest beam current density is over 2.5 mA/cm2, measured at a location 25 cm downstream of the source. The density uniformity changes from +5% to +15% over a 15-cm-diam circle. The feature and the performance of this source will be described in this paper.
High-energy and high-current hydrogen negative-ion beam production with an external-filter-type large negative-ion source
Authors: Takeiri Y. , Kaneko O. , Oka Y. , Tsumori K. , Asano E. , Akiyama R. , Kawamoto T. , Kuroda T. , Ando A.
Published: July 2002

A large hydrogen negative-ion source with an external magnetic filter has been developed for a neutral beam injection (NBI) system in the Large Helical Device (LHD), and a high-energy and high-current H− ion beam has been produced. The ion source is operated at a high arc efficiency of 0.1 A/kW at an operational gas pressure of less than 3.5 mTorr, and produces 47 keV–16.2 A of a H− ion beam from a grid area of 25 cm×50 cm. With two-stage acceleration, 13.6 A of a H− ion beam has been successfully accelerated to 125 keV. Multibeamlet focusing by the aperture displacement technique has been achieved 11.2 m downstream with a gross divergence angle of 9 mrad. The alternate beamlet deflection by the magnetic field at the extraction grid, which results in beam broadening in the deflection direction, was well compensated also by the aperture displacement technique. These results satisfy the specification of the negative-ion-based LHD–NBI system.
Directed cesium deposition into a large volume negative-ion source
Authors: Belchenko Yu. , Jacquot C. , Pamela J. , Riz D.
Published: July 2002

A compact, safe system for directed cesium deposition into large volume sources is described. It consists of a small oven mounted on a feedthrough, which permits one to rotate and move the oven across the discharge chamber length or to remove it from the vacuum box to reload the oven. Special industrial pellets containing the cesium compound (30% of cesium chromate +70% titanium) were used for a pure cesium release. The pellets are insensitive to pollution by air and can provide the cesium release during several cycles of heating and cooling in long-term experiments. There was no ‘‘poisoning’’ impurities degassing (oxygen, water) during the standard oven operation. The Cs system was reliably operated for cesium deposition in multiampere negative-ion source experiments.
Numerical simulation research of a high-current ion source extraction system for nuclear fusion
Authors: Wang H. S. , Jian G. D. , Jiang S. F.
Published: July 2002

We have studied beam optical characteristics of a high-current ion source extraction system for nuclear fusion research by means of numerical simulation. The effect of ion source plasma parameters (plasma density, electron, and ion temperature) on initial emission conditions is taken into account, and the effect of stray electrons from the source plasma and the effect of ion space charge nonlinear force in the beam on the beam optical characteristic are also taken into account in an improved calculation program. For a 55 keV high-current ion extraction system, the calculation results show: the matched ion current density of hydrogen and deuterium is 0.22 and 0.155 A cm−2, respectively, when the ion temperature is increased, the beam optical characteristic is degraded, and the effect of first-electrode geometry on the beam optics is the most sensitive. Attention should be paid to the design and manufacture of the electrode. Those results are essentially in agreement with experimental measurements.
Numerical simulation of cesium effects on plasma parameter dependence of H− production in a tandem ion source (abstract)
Authors: Fukumasa Osamu , Niitani Eiji
Published: July 2002

Effects of cesium vapor injection on H− production in a tandem negative ion source are studied numerically as a function of plasma parameters. Model calculation is done by solving a set of particle balance equations in steady-state hydrogen discharge plasmas. By including H− surface production processes caused by both H atoms and positive hydrogen ions, enhancement of H− production and pressure dependence of H− production observed experimentally are well reproduced in the model. Besides these, electron temperature dependence of H− production is also discussed.
Modeling the electron heating in a compact electron cyclotron resonance ion source
Authors: Grotjohn T. A.
Published: July 2002

An electromagnetic particle-in-cell (PIC) model and a guiding-center particle model are developed and used to model a compact electron cyclotron resonance (ECR) plasma source. The finite-difference time-domain technique is used to model the microwave fields which excite the plasma at 2.45 GHz. The PIC technique is used to model the dynamics of the electrons in the plasma. The electromagnetic fields and the plasma dynamics are solved in a self-consistent manner. The ECR heated electrons are confined to magnetic field lines and subsequently make multiple passes through ECR regions experiencing both increases and decreases in energy. The distribution function of these energy changes is determined from the electromagnetic PIC model and used in a guiding-center particle model. The longer time scale collisional phenomenon in the plasma is modeled using this guiding-center particle model. A compact ECR plasma source used for the generation of ions for materials processing is simulated. This source has a plasma size of 3.6 cm in diameter and 3 cm in height.
Review of resonant laser ionization sources for on-line mass separators for radioactive ion beams (invited) (abstract)
Authors: Mishin V. I.
Published: July 2002

The basic operation principles of laser ion sources (LIS) based on resonance ionization of atoms in a hot cavity are discussed. Since the atom of each element has its own specific energy level structure the ionization process has an exceptionally high elemental selectivity if the laser radiation frequencies coincide with the atomic transition frequencies. The efficiency of a single laser pulse ionization may reach tens of percent. If a sample containing studied isotopes is placed in a closed hot cavity and light beams of high repetition rate lasers are introduced into the cavity via a small hole which is also used for extraction of the photoions, the overall efficiency of such an ion source may also reach tens of percent. The elemental selectivity of the LIS will be determined by the efficiency of the surface ionization of undesirable isotopes and the efficiency of laser ionization of the studied isotope. The LIS is naturally coupled with the mass separator because the diameter of the cavity hole is small (1–3 mm). Rydberg levels of Fr were studied using LIS in off-line experiments at the Institute of Spectroscopy/Troitzk. The production rate of a Fr isotope source was around 1000 atom/s. The LIS has been applied to produce radioactive ion beams at IRIS/St.-Petersburg, ISOLDE/CERN, and GSI/Darmstadt on-line facilities. At GSI neutron-deficient Sn (102,103,104) isotopes have been studied using the LIS. The on-line measured overall efficiency of the LIS was equal to 8.5%. At ISOLDE neutron-rich Ag (121–127) isotopes produced by the LIS have been studied by a neutron long counter and beta detector. The efficiency of the LIS measured in off-line experiments with stable isotopes is as great as 11%. The LIS of Yb, Sm, Sn, Li, and Ni have also been developed at ISOLDE. At the IRIS the LIS was used to obtain radioactive beams of Yb and Ho.
Characteristics of a nozzle–beam-type microwave radical source
Authors: Yoshida Yoshikazu
Published: July 2002

The characteristics and application of an antenna–nozzle-type microwave radical source are described. This source generates microwave plasma in a space between a nozzle and a skimmer to excite a processing gas. The source has a nozzle of 0.6 mm aperture at the tip of the microwave radiation antenna, followed by a 1.2 mm skimmer, and gases pass through the skimmer so that a molecular beam contains radicals. The total atomic oxygen flux is 1.2×1016 atoms/s at a power of 50 W and an O2 flow rate of 0.5 sccm. Thus, a high-density radical source with a compact structure and low power consumption is realized. Moreover, p-type doping of ZnSe films was achieved by employing this source with N2 plasma, which was installed in a molecular-beam epitaxy system. A net acceptor concentration of 5.1×1017 cm−3 was obtained by C–V measurements with a lower microwave power of 30 W and a lower gas flow of 0.02 sccm. This source is promising for film growth in ultrahigh vacuum processing.
An automated magnetometer using the Tchebycheff method of numerical integration
Authors: Ray Anindita , Chakravarti A. , Ranganathan R.
Published: July 2002

We present the details of an automated flux-type magnetometer that uses numerical integration of the voltage induced in the sensing coils when the sample is moved. The Tchebycheff quadrature method of numerical integration has been used to achieve high accuracy in the integrated output. In relevance to this, we also present design and construction of an electronic circuit (integration limit setting circuit) together with the software for data acquisition using a Z-80 microprocessor. We discuss the advantages and disadvantages of this particular method with reference to others. We also discuss the calibration of this magnetometer.
Microbial diffraction gratings as optical detectors for heavy metal pollutants
Authors: Noever David , Matsos Helen , Brittain Andrew , Obenhuber Don , Cronise Raymond , Armstrong Shannon
Published: July 2002

As a significant industrial pollutant, cadmium is implicated as the cause of itai-itai disease. For biological detection of cadmium toxicity, an assay device has been developed using the motile response of the protozoa species, Tetrahymena pyriformis. This mobile protozoa measures 50 μm in diameter, swims at 10 body lengths per second, and aggregates into macroscopically visible patterns at high organism concentrations. The assay demonstrates a Cd+2 sensitivity better than 1 μM and a toxicity threshold to 5 μM, thus encouraging the study of these microbial cultures as viable pollution detectors. Using two-dimensional diffraction patterns within a Tetrahymena culture, the scattered light intensity varies with different organism densities (population counts). The resulting density profile correlates strongly with the toxic effects at very low dosages for cadmium (<5 ppm) and then for poison protection directly (with nickel and copper antagonists competing with cadmium absorption). In particular, copper dosages as low as 0.1–0.5 mM Cu have shown protective antagonism against cadmium, have enhanced density variability for cultures containing 1 mM Cd+2, and therefore have demonstrated the sensitivity of the optical detection system. In this way, such microbial diffraction patterns give a responsive optical measure of biological culture changes and toxicity determination in aqueous samples of heavy metals and industrial pollutants.
A microlens to improve the optical signal from a diamond anvil cell
Authors: Scheerboom M. I. M. , Schouten J. A.
Published: July 2002

A plano-convex microlens has been designed and tested in order to intensify the optical signal from a sample in a diamond anvil cell. The gain appears to be more than a factor of 3 and can be improved if the size of the image is reduced before entering the entrance slit of the spectral equipment.
An alternative fiber-optic backreflectance method for measurement of distances using a continuous wave laser
Authors: Ilev I. , Kumagai H. , Toyoda K. , Uttamchandani D. , Culshaw B.
Published: July 2002

We present a new and simple fiber-optic backreflectance method for precise short distance measurement using a single-mode fiber and cw laser. The method is based on the intensity sensing of focused backreflectance laser emission, and the spatial location of three specific points: the focal point of the focusing optical element and two object points. The optical fiber is used in a multifunctional regime where it serves simultaneously as a point light source, an object for projecting, and a point receiver that is highly sensitive to spatial displacements of the focused backreflectance emission. The experimental and analytical investigations conducted demonstrate the usefulness of the method for distance measurement with submicron (about 370 nm) and millimeter accuracies in the near and far distance region, respectively, for a mirror target 1 m away.
A point-focusing small angle x-ray scattering camera using a doubly curved monochromator of a W/Si multilayer
Authors: Sasanuma Yuji , Law Robert V. , Kobayashi Yuji
Published: July 2002

A point-focusing small angle x-ray scattering (SAXS) camera using a doubly curved monochromator of a W/Si multilayer has been designed, constructed, and tested. The two radii of curvature of the monochromator are 20 400 and 7.6 mm. The reflectivity of its first-order Bragg reflection for CuKα radiation was calculated to be 0.82, being comparable to that (0.81) of its total reflection. By only 10 s x-ray exposure, scattering from a high-density polyethylene film was detected on an imaging plate (IP). A rotating-anode x-ray generator operated at 40 kV and 30 mA was used. Diffraction from rat-tail collagen has shown that the optical arrangement gives the Bragg spacing up to, at least, 30 nm for CuKα radiation. Combined with IPs, the camera may permit us to carry out time-resolved SAXS measurements for phase behaviors of liquid crystals, lipids, polymer alloys, etc., on conventional x-ray generators available in laboratories.
Medium and high energy x-ray instrument for sample characterization
Authors: Petrillo C. , Rocchi C. , Sacchetti F.
Published: July 2002

A medium to high energy x-ray diffractometer, based on commercial components, is described. The performances of such an instrument in investigating relatively thick crystalline samples are exploited. Results of test measurements, among which is the characterization of a single crystal of Ge as thick as 1 cm, are reported.
Improved control and data-acquisition electronics for high-resolution electron energy loss spectroscopy
Authors: Xie Jun , Wang Youqi , Mitchell William J. , Felino Anthony , Schick Matthias , Weinberg W. Henry
Published: July 2002

A new version of low-noise, high-stability control, data-acquisition electronics has been designed and constructed for high-resolution electron energy loss spectroscopy to meet the requirements imposed by new digital signal processing techniques. The improved electronics feature fast, low-noise, high-stability, programable voltage sources with 16 bit precision for the electron optics and a custom-built 16 bit 100 MHz pulse counter. These electronics, controlled by an IBM-compatible PC through a user-friendly, graphical software interface, allow easy computerized tuning and spectral recording.
The Texas Thermal Interface: A real-time computer interface for an Inframetrics infrared camera
Authors: Storek D. J. , Gentle K. W.
Published: July 2002

The Texas Thermal Interface (TTI) offers an advantageous alternative to the conventional video path for computer analysis of infrared images from Inframetrics cameras. The TTI provides real-time computer data acquisition of 48 consecutive fields (version described here) with 8-bit pixels. The alternative requires time-consuming individual frame grabs from video tape with frequent loss of resolution in the D/A/D conversion. Within seconds after the event, the TTI temperature files may be viewed and processed to infer heat fluxes or other quantities as needed. The system cost is far less than commercial units which offer less capability. The system was developed for and is being used to measure heat fluxes to the plasma-facing components in a tokamak.
Flux pinning enhancement in melt processed YBa2Cu3O7−δ through rare-earth ion (Nd, La) substitutions
Authors: Varanasi Chakrapani , McGinn Paul J. , Blackstead Howard A. , Pulling David B.
Published: July 2002

Stoichiometric YBa2Cu3O7−δ (Y123) samples doped with excess Nd2O3 and La2O3 additions were melt processed in air. Because decomposition and reformation of 123 occurs during melt processing, lighter rare-earth ion substitution in 123 takes place. As the lighter rare-earth ion sizes (Nd, La) are comparable to that of Ba2+, in addition to Y ion site substitution, partial substitution into the Ba2+ sites is also anticipated. The Tc and magnetic properties of lighter rare-earth oxide doped samples were analyzed and compared with undoped Y123 to investigate the flux pinning enhancement due to these substitutions. The lighter rare-earth oxide doped, melt processed 123 shows significant improvement in magnetization compared to undoped samples, which is likely due to point defects created by partial substitutions of the lighter rare-earth ions.
Surface plasma source to generate high-brightness H− beams for ion projection lithography (abstract)a)
Authors: Dudnikov V. G. , Derevyankin G. E. , Kovalevsky D. V. , Savkin V. Ya. , Sokolovsky E. A. , Guharay S. K.
Published: July 2002

A surface plasma source with Penning-type electrodes is developed to generate H− beams for ion projection lithography applications. The source presently runs in pulsed mode with a pulse width of about 1 ms and repetition rate of 10 Hz. The discharge and the extracted H− beam are maintained in stable, noiseless condition; gas pressure plays a critical role here. The maximum H− beam current density at the emission surface is about 1.7 A/cm2. Preliminary measurements suggest that the normalized brightness of the core beam is ∼1.7×1013 A/(m rad)2 and its perpendicular temperature is about 0.2 eV.
Theoretical investigation of electron temperature variation across magnetic filter in a negative ion source
Authors: Shirai Mikito , Ogasawara Masatada , Koishimine Takehiko , Hatayama Akiyoshi
Published: July 2002

Electron temperature variation over the magnetic filter region and the extraction region is investigated theoretically. We assume qx/{(5/2)TΓx}=β between heat flux qx and electron flux Γx, where β is a ratio of the heat flux to the enthalpy flux and T is the electron temperature. Terms of diamagnetic drift in the expressions of the flux and heat flux are important in obtaining temperature T(x) that agrees with Haas et al.’s experimental results. Electron loss along the magnetic field is important in determining the exponential dependence of the electron number density and temperature on y. Flux inversion is attributed to the negative flux due to the electric field.
A solenoidal and monocusp ion source (SAMIS) (abstract)
Authors: Burns E. J. T. , Brainard J. P. , Draper C. H. , Ney R. H. , Leung K. N. , Perkins L. T. , Williams M. D. , Wilde S. B.
Published: July 2002

We have developed a new magnetic monocusp ion source for single aperture applications such as neutron generators. Coupling solenoidal magnetic fields on both sides of a monocusp magnetic field has generated over 70% atomic deuterium ions at pressures as low as 0.4 Pa (3 mTorr). This article describes the performance and characteristics of the solenoidal and monocusp ion source.
Ion sources for accelerator mass spectrometry (invited) (abstract)a)
Authors: Kutschera Walter
Published: July 2002

In accelerator mass spectrometry (AMS), extremely low concentrations of trace isotopes are measured from sample materials in the milligram range. This requires ion sources with high overall efficiency and great versatility. Since almost all AMS work is performed with tandem accelerators, negative ion sources are required and the Cs-beam sputter source became the workhorse of AMS. A variety of sophisticated multiple-sample sputter sources, for both solid and gaseous sample materials, are now available for AMS. More recently, electron cyclotron resonance sources in conjunction with heavy-ion accelerators such as linacs and cyclotrons have been explored for AMS of long-lived noble gas radionuclides (which do not form negative ions). This paper will attempt to review the particular features of ion sources relevant for AMS, with emphasis on recent developments and future possibilities.
Ion energy spread and current measurements of the rf-driven multicusp ion source
Authors: Lee Y. , Gough R. A. , Kunkel W. B. , Leung K. N. , Perkins L. T. , Pickard D. S. , Sun L. , Vujic J. , Williams M. D. , Wutte D.
Published: July 2002

Axial energy spread and useful beam current of positive ion beams have been carried out using a radio frequency (rf)-driven multicusp ion source. Operating the source with a 13.56 MHz induction discharge, the axial energy spread is found to be approximately 3.2 eV. The extractable beam current of the rf-driven source is found to be comparable to that of filament-discharge sources. With a 0.6 mm diameter extraction aperture, a positive hydrogen ion beam current density of 80  mA/cm2 can be obtained at a rf input power of 2.5 kW. The expected source lifetime is much longer than that of filament discharges.
Compensation techniques for high-temperature superconducting quantum interference device gradiometers operating in unshielded environment
Authors: Borgmann J. , David P. , Krause H. J. , Otto R. , Braginski A. I.
Published: July 2002

We have tested two methods of compensating environmental disturbances applicable to high-temperature superconducting quantum interference device (SQUID) systems operating in magnetically unshielded environments. For testing, we used first- and second-order axial electronic gradiometer setups with rf SQUID magnetometers operating at 77 K and base lines between 7 and 8 cm. The magnetometers were single-layer washer rf SQUIDs with bulk or thin-film magnetic flux concentrators in flip-chip geometry. The tested methods resulted in disturbance compensation levels comparable to those attained using electronically formed gradiometers. The white noise of the compensated magnetometers resulted in 13.5 fT/cm √Hz for first-order and 22 fT/cm2 √Hz for second-order compensation down to a few Hz. Common mode rejection was balanced to better than 10 000 for homogeneous fields and better than 200 for gradient fields with second-order compensation.
Assessment of thermomechanical stresses and stability of ion-source grids with peripheral cooling
Authors: Beklemishev A. , Davydenko V. , Ivanov A. , Podyminogin A.
Published: July 2002

Application of peripheral cooling for ion-optics grids of diagnostic neutral beam injector is considered. The injector is designed to operate with up to 10 s pulse duration and 1 pulse/5 min repetition rate. The grid deformations under thermoloads during the beam-on phase were determined by using an appropriate semianalytical model. Distribution of thermo-mechanical stresses over grids and thermostability limit as a function of the grid’s characteristics and heat loads were determined as well. The simulation results are compared with those obtained in the experiment with the grid prototype.
High repetition inboard launch of hydrogen pellets
Authors: Lang P. T. , Cierpka P.
Published: July 2002

The centrifuge hydrogen pellet injection system at ASDEX Upgrade was extended for inboard launching. Successful and efficient inboard pellet refueling was realized up to pellet velocities of about 400 m/s. In order to achieve maximum available pellet particle rates of the system still at the low centrifuge revolution needed in this velocity range, the injector has been modified. Thus, operational conditions have been developed yielding the potential to inject pellets at rather low speed but high repetition rate. Since pellets injected from the inboard are obviously not hampered by the low velocity but show better performance than fast pellets injected from the outside, this scheme seems to allow for an efficient and flexible particle refueling of hot plasmas. The system is now capable of launching pellet series at rates up to 60 Hz at a speed of 240 m/s. With the biggest available pellet size, this enables a pellet particle flux of 2.6×1022/s.
Spectral brightness and other improvements to the tunable ArF excimer laser
Authors: Balla R. Jeffrey , Hart R. C.
Published: July 2002

We present two oscillator designs and a new amplification design which improves many characteristics of the dual-discharge tube tunable ArF excimer laser. We demonstrate bandwidths from 0.17–11.0 cm−1 (5–330 GHz) can be selected by appropriate choice of oscillator slit width and diffraction-grating dispersion. Amplification is achieved using three consecutive passes through the discharge tubes. This amplifier design decreases divergence (9×diffraction limit) and increases output energy (33%), locking efficiency (20%), range of tunability (40%), and spectral brightness (two orders-of-magnitude) when compared to the standard unstable-resonator amplifier.
A reliable calibration method based on ion current measurement for an electron beam transition metal deposition source
Authors: Bullock E. T. , Coyle S. T. , Hembree G. G. , Scheinfein M. R.
Published: July 2002

A calibration scheme based on ion-current measurement has been implemented for an electron-beam transition metal deposition source. Repeatable and practical means of positioning the source (tip), measuring the ion current, and determining the flux rate are given. Intrinsic variations in the structural parameters of the source and thermal effects which can modify the observed deposition rate were examined and compensated for. A stable regime where ion-beam current is directly proportional (±5%) to the growth rate has been determined.
Ion flux measurements with the improved collector probe system at the TEXTOR-94 tokamak
Authors: Larsson D. , Rubel M.
Published: July 2002

A collector probe system at the TEXTOR-94 tokamak has been upgraded becoming a versatile tool in studies of erosion and deposition processes under plasma discharges. The reconstruction dealt with the distinct modification of the computer aided probe steering system and the collector probe head. The new operation system, based on a LabView environment, allows unlimited number of preprogrammed linear and angular probe movements and is applied for either integrated or time-resolved measurements of ion fluxes in the scrape-off plasma. Particular advantage is related to the possibility of such measurements during a selected part of a tokamak discharge, for instance the flat top, neutral beam injection phase, neon injection for plasma cooling, etc. The upgraded system and the results from some of the experiments, where the new possibilities have been beneficial, are presented in the article.
Plasma measurements with triple and single probes in an asymmetrical parallel plate rf plasma reactor
Authors: Kubo Takashi , Kawata Hiroaki , Murata Kenji
Published: July 2002

In an asymmetrical parallel plate reactor measurements of Ar radio-frequency (rf) plasmas are done with both single and triple probes. All measurements are carried out with the same probe construction and the probe systems are realized by changing probe circuit connections. Ar plasmas are generated with a frequency of 13.56 MHz at a pressure of 50 mTorr and a power of 20 W. In order to remove the alternative component the compensation circuits are connected to the probe system. It is found that there is a fairly good agreement between two probe characteristics obtained with the single and the triple probes. Influences of a time variation of the plasma potential on the results are reduced, but cannot be completely removed. The reason why the measurement results obtained with the single and the triple probes suffer from the same effect of the alternative component is explained using the equivalent circuits of the probe systems.
Computer-controlled apparatus for Young’s modulus measurements as a function of temperature
Authors: Bayard J. , Philippe T. , Grenet J.
Published: July 2002

This article deals with the realization of a low cost thermoanalyzer. The measurement cell is a TMS2 assembly (Perkin-Elmer) and the whole setup is governed by a compatible PC fitted with a PCL812 card (Digilab). We describe how to control the sample temperature and how to measure its elastic modulus. We explain how to calibrate the temperature and the load applied on the sample and how to measure the probe displacement. In addition we present some results obtained on amorphous poly(ethylenetereptalate).
Development of a local internal magnetic field measurement via dual mode (O-X) correlation reflectometry
Authors: Gilmore M. , Peebles W. A. , Nguyen X. V.
Published: July 2002

A new method to measure the local magnetic field strength internal to a plasma is described using cross correlation of ordinary (O) and extraordinary (X) mode reflectometer signals originating from the naturally occurring turbulence present in all plasmas. This method relies on determination of the peak cross correlation between O- and X-mode signals, which are then assumed to originate from the same spatial location. Since the density at cutoff is known from the incident O-mode frequency, the magnetic field may be determined from the X-mode frequency. This method is expected to be widely applicable to many magnetic confinement devices, including those with magnetic fields ⩽0.2–0.3 T, where application of other diagnostics may be difficult.
Polarization in millimeter-wavelength collective Thomson scattering on FTU tokamak
Authors: Tartari U. , Grosso G. , Nowak S.
Published: July 2002

We investigate performance degradation caused in mm-wave collective Thomson scattering on the high-field tokamak FTU by the joint effects of refraction and polarization. It is shown that optimized performances can be recovered, in different parts of the FTU density range, by selecting the most suitable of the four modal combinations potentially contributing to the scattered signal. This can be achieved by matching the limiting polarization of the selected mode at both the transmitting and the receiving side. A full polarization-control capability is required at this purpose.
Characterization and preliminary results of the collective Thomson scattering system on FTU tokamak
Authors: Orsitto F. , Brusadin A. , Brodsky Yu. , Filchenkov S. , Grosso G. , Giovannozzi E. , Lubyako L. , Perminov A. , Suvorov E. , Tartari U. , Volpe F.
Published: July 2002

A collective Thomson scattering (CTS) experiment is now installed on FTU aimed to measure the plasma ion temperature and test the theory of CTS. A high power 140 GHz gyrotron beam is focalized into the plasma center by means of a circular corrugated transmission line and an in-vessel optical system to a radius of 0.025 m. The scattered radiation is collected at 90° scattering angle by a symmetric in-vessel optical system and a low-power quasioptical transmission line which collects the scattered radiation on a superheterodyne receiver. Both in-vessel optical systems are placed in a vertical port. The receiver is based on 32 channels, 1.2 GHz global bandwidth, with a measured noise temperature Trec=1 eV and minimum integration time of 1 ms. The antenna decoupling measurement resulted about 60 dB, while the attenuation introduced by the collecting system is evaluated in 5 dB. The angle of the scattering wavevector and the magnetic field directions is 25°. The experiment is run at a magnetic field B=7.4–7.7 T, i.e., the gyrotron frequency is well below the first electron cyclotron emission (ECE) harmonic, so the ECE plasma background temperature is low and it is measured TECE=70–50 eV, respectively. The detected polarization is the ordinary mode. In this experiment the calculated signal is of the order of the ECE noise level. Indeed in a series of dedicated FTU runs, CTS signals with signal-to-noise consistent with calculation (made using standard formulas) were found. Some features of the detected scattered spectra are reported, as well as plasma radiation measurements in various plasma conditions including lower hybrid rf heating.
Hard x-ray production from high intensity laser solid interactions (invited)
Authors: Perry M. D. , Sefcik J. A. , Cowan T. , Hatchett S. , Hunt A. , Moran M. , Pennington D. , Snavely R. , Wilks S. C.
Published: July 2002

Intense laser (>1021 W/cm2) driven hard x-ray sources offer a new alternative to conventional electron accelerator bremsstrahlung sources. These laser driven sources offer considerable simplicity in design and cost advantage for multiple axis views and have the potential for much higher spatial and temporal resolution than is achievable with accelerator sources. We have begun a series of experiments using the Petawatt laser system at LLNL to determine the potential of these sources for radiography applications. Absolutely calibrated spectra extending to 20 MeV and high resolution radiographs through a ρr⩾150 g/cm2 have been obtained. The physics of these sources and the scaling relationships and laser technology required to provide the dose levels necessary for radiography applications will be discussed. Diagnostics of the laser produced electrons and photons will be addressed.
Calibration of the Joint European Torus energetic ion and alpha particle collective Thomson scattering diagnostic receiver
Authors: Egedal Jan , Machuzak John S. , Fessey John S. , Bindslev Henrik , Hoekzema A. J. , Hughes Thomas P. , Davies Poul , Gatcombe Christopher , Woskov Paul P.
Published: July 2002

The receiver of the Joint European Torus (JET) energetic ion and alpha particle collective Thomson scattering diagnostic is calibrated assuming blackbody emission from the torus vacuum vessel (VV) and using electron cyclotron emission (ECE). The 32 receiver channels are absolutely calibrated with a mechanical chopper in the quasioptical arm of the receiver, alternating the receiver view between the torus vacuum at 320 °C and room temperature. This calibration is noisy due to the small difference between torus and room temperatures. A more accurate relative calibration is achieved with the ECE during plasma shots. The intensity of the ECE is found to be a smooth function of frequency, which enables the combination of the ECE calibration with the VV calibration. The accuracy of the absolute VV calibration is hereby improved to nearly the same standard as the relative ECE calibration. ECE signals measured by the calibrated receiver agree well with standard JET ECE diagnostics. Based on mathematical considerations presented here, noise is injected into the receiver final intermediate frequency stage during VV calibrations to provide more bit transitions for accurate analog-to-digital (AD) conversion of the low level calibration signals. This yields a resolution which is better than 1% of an (AD) step.