bluuebunny/crossref_metadata_2025 huggingface dataset:
Stationary magnetic pertubation diagnostic on TFTR (abstract)a)
Authors: Takahashi H. , Fredrickson F. , McGuire K. , Morris W.
Published: July 2002

Stationary magnetic perturbations (SMPs) in tokamaks may consist of (1) static magnetic field errors, (2) dynamic magnetic field errors, and (3) stationary MHD modes (or locked mode). The diagnostic aimed to detect the latter two classes of SMPs on the TFTR tokamak has two pairs of sensors, each consisting of a saddle loop for measuring predominantly radial field and auxiliary loops for measuring predominantly toroidal and vertical fields. Members of each pair are placed 180° apart toroidally. Predominantly n=1 SMPs are found in various discharges including ohmic discharges. Abrupt changes in SMP signals precede a ‘‘tail-end’’ disruption, suggesting a causality relationship. Variations in the SMP signals are also coincident with severe performance degradation of super shots and pellet injected discharges. An analysis of individual and paired signals appears to indicate that these SMPs are dynamic field errors as well as stationary MHD modes.
Radial distribution of superthermal electrons measured with ECE (abstract)a)
Authors: Preische S. , Kaye S. M. , Efthimion P. C. , Kaita R.
Published: July 2002

To aid in the study of lower hybrid current drive as a means of current profile control, the radial profile and velocity distribution of the fast current-carrying electrons and their time evolution must be known. As part of the recent effort to understand this fast electron transport, a diagnostic has been installed on PBX-M to measure the electron cyclotron emission from the fast electrons. An oblique horizontal view of upshifted cyclotron emission in the midplane can give radial as well as velocity space information about the fast electrons. Emission in X mode frequencies refracted by the right-hand cutoff is radially localized. The observed emission at a specific frequency comes only from the radial region rturn<r<r(Bmin), where rturn is the turning point of the ray, and r(Bmin) is given by the condition of the resonance frequency n2∥+(nΩ/ω)2−1≥0. Emission measured by this new diagnostic has been found to be radially localized as predicted. It is also expected that localized moments of the distribution function may be obtained from these data. A superheterodyne receiver at 60–90 GHz has been built which views the plasma through a focusing gaussian lens antenna at a 57° angle to the toroidal magnetic field. Viewing dumps made of SiC on both the inside and outside walls ensure single pass emission. Results from this new diagnostic will be presented.
Effects of large aspect ratios and fluctuations on hard x-ray detection in lower hybrid driven divertor tokamaks
Authors: Vahala Linda , Vahala George , Bonoli Paul
Published: July 2002

It is shown that lower hybrid wave scattering from fluctuations plays a critical role in large aspect ratio divertor plasmas even though the edge density fluctuation levels are only at 1%. This is seen in the theoretically calculated electron power-density profiles which can be directly correlated to the standard experimental chordal hard x-ray profiles. It thus seems that fluctuation effects must be included in determining rf current-density profiles.
Optical measurements of core density fluctuations in TEXT-U using a helium metastable beam
Authors: Durst R. D. , Denhartog E. A. , Fonck R. J. , Kim J. S. , Karzhavin Y.
Published: July 2002

A compact, portable, eight-channel, filter spectrometer has been designed for beam emission spectroscopy measurements of long-wavelength density fluctuations on TEXT-U and Phaedrus-T. The system uses radially elongated image volumes which maximize the étendue of the system while still resolving the dominant fluctuations (kr<2 cm−1, kθ<6 cm−1). Because of the vertical injection geometry of the TEXT-U diagnostic neutral beam, there is little Doppler shift of the beam emissions and thus a nonhydrogenic species must be used to distinguish between the beam and edge emissions. A He0 metastable beam has been found to provide good beam penetration with little contamination of the detected beam fluorescence by edge emission. A multistep excitation model is used to quantitatively interpret the fluctuations in the intensity of the He0 triplet (3P0–3D, 587.6 nm) as plasma density fluctuations.
Diagnosis of pusher-fuel mix in spherical implosions using x-ray spectroscopy (invited)
Authors: Keane C. J. , Cook R. C. , Dittrich T. R. , Hammel B. A. , Levedahl W. K. , Landen O. L. , Langer S. , Munro D. H. , Scott H. A.
Published: July 2002

Of primary concern in next generation inertial confinement fusion (ICF) implosion experiments is Rayleigh–Taylor (RT) instability of the pusher-fuel interface occurring upon acceleration and deceleration of the pusher. This results in mixing of hot fuel with cold pusher material. One method of diagnosing mix in this case is to place spectroscopic dopants both in the capsule fuel region and the innermost region of the capsule wall adjacent to the fuel. As the degree of pusher/fuel mix is increased (typically through placement of controlled perturbations on the outer surface of the capsule) the pusher dopant x-ray emission increases relative to that of the fuel dopant. Experiments of this type using indirectly driven implosions have been carried out on Nova. In this paper we describe some of the important physics issues underlying spectral line formation in these targets and discuss how they are manifested in the modeling and interpretation of experimental data. The importance of radiative transfer as well as high density plasma phenomena such as continuum lowering and Stark broadening is demonstrated. We provide an overview of recent Nova hydrodynamic instability experiments and discuss how the level of instability growth implicit in a given capsule design impacts the diagnosis of mix through x-ray spectroscopy.
New diagnostic features in the laser implosion of argon-filled targets
Authors: Yaakobi B. , Epstein R. , Marshall F. J. , Bradley D. K. , Jaanimagi P. A. , Su Q.
Published: July 2002

Argon-filled-target implosions on the OMEGA laser system were analyzed and compared to code predictions. For the case of high-pressure argon the diagnostic signatures used were absorption lines of Ar16+ transitions as well as of lower ionizations (shifted Kα lines). The measurements indicate deviations from predictions, which are attributed to a cooler than predicted core.
Shot-to-shot comparison of the first Li-beam-driven hohlraum experiments
Authors: Derzon M. S. , Rochau G. E. , Chandler G. A. , Moats A. R. , Leeper R. J.
Published: July 2002

Shot-to-shot comparison of the first Li-beam hohlraum experiments on PBFA II provides an opportunity to measure and determine the factor that affect the on-axis reproducibility of the Li-ion beam. Both inner-shell and thermal x-ray emission are used to estimate the relative beam power on target from shot to shot. The M- and L-shell Au x-ray yield measurements were made with an array of 11 filtered p-i-n detectors, and the thermal emission measurements were made with an array of three filtered bolometers. The analysis shows that the beam intensity on target varied by more than a factor of 10 during the shot series. By correlating the results of the beam on target with other diagnostics and events, we have identified some potential causes for these variations.
The time-domain triple-probe method
Authors: Meier M. A. , Hallock G. A. , Tsui H. Y. W. , Bengtson Roger D.
Published: July 2002

A new Langmuir-probe technique based on the triple-probe method is being developed to provide simultaneous measurement of plasma temperature, potential, and density with the temporal and spatial resolution required to accurately characterize plasma turbulence. When the conventional triple-probe method is used in an inhomogeneous plasma, local differences in the plasma measured at each probe introduce significant error in the estimation of turbulence parameters. The time-domain triple-probe method (TDTP) uses high-speed switching of Langmuir-probe potential, rather than spatially separated probes, to gather the triple-probe information thus avoiding these errors. Analysis indicates that plasma response times and recent electronics technology meet the requirements to implement the TDTP method. Data reduction techniques of TDTP data are to include linear and higher-order correlation analysis to estimate fluctuation induced particle and thermal transport, and relationships between temperature, density, and potential fluctuations.
Possible integrated diagnostic set for ion cyclotron heating for the tokamak physics experiment (TPX) (abstract)a)
Authors: Rasmussen D. A. , Thomas C. E. , Swain D. W. , Batchelor D. B. , Caughman J. B. , Colchin R. J. , Goulding R. H. , Hanson G. R. , Hoffman D. J. , Isler R. C. , Jaeger E. F. , Wilgen J. B.
Published: July 2002

Heating and current drive with ICRF is one of the major missions of TPX and is crucial to its success. In contrast to the integrated nature of core diagnostic programs, diagnostics that measure ICRF propagation and edge interactions are often assigned lower priority, have not been included in the base diagnositics set, or were included as upgrades. This can result in an incomplete and unoptimized set of measurements. Thus it is important that an integrated set of diagnostics (engineered along with the antenna design), capable of fully diagnosing the interaction, propagation, and absorption of the ICRF be available for TPX. The parameters of interest include: coupling of the ICRF antenna to the plasma, launched spectrum, wave propagation, edge plasma interactions, electron heating, and current drive, and fast ion power deposition and losses. The diagnostic set should be designed so it can be upgraded for control of loading and spectrum by providing feedback information for adjusting phase, power level, fuel gas injection, and plasma position. The proposed set focuses on wave propagation, launched spectrum, absorption, and measuring and comparing the plasma edge properties in the near vicinity of the antenna with that measured at a large toroidal distance from them; thus many would be installed as toroidally separated indentical sets. In addition to the planned core diagnostic set, the ICRF specific diagnostics proposed for TPX include: edge density reflectometers, RF fluctuation reflectometers, fixed and moveable Langmuir probes, visible and IR cameras with spectroscopic line filters, rf magnetic loop probes, local ion energy analyzer, direct ion loss detectors, charge exchange analyzers, fast response ECE, and edge temperature ECE. The anticipated approach is one in which individual diagnostics could be provided by industry, universities, or laboratories but overall coordination, driven by specific ICRF issues, would be required.
A summary of HIBP fluctuation measurements on ATF (abstract)
Authors: Zielinski J. J. , Aceto S. C. , Schwelberger J. G. , Connor K. A.
Published: July 2002

A 160 kV HIBP system was used to make fluctuation measurements on ATF. Most of the fluctuation data were taken with low density ECH heated plasmas at 0.95 T or less. However, there is a limited amount of data taken at less than optimal conditions during plasmas with neutral beam injection. Details of the diagnostic equipment and analysis methods will be presented along with the results of the fluctuation data analysis. The results will be compared with the available data from other ATF fluctuation diagnostics.
A fast microflow apparatus
Authors: Czerlinski George H. , Isaacson Michael , Ramires Richard , Chen Shu , Kanagal Bharath , Venkatesh Chaitanya , Powers Linda S.
Published: July 2002

A microflow apparatus has been built with a time resolution of 1 ms for mixing volumes of at least 80 μl per syringe. A time resolution of 3 ms is attained for mixing volumes of 10 μl per syringe. Equal volumes are mixed and concentration changes are observed photometrically using fiber optics for coupling light into and out of the observation tube having 1 mm diameter and 10 mm light path length. The reaction of ferrocytochrome c with ferrihexacyanide was used to calibrate the apparatus at 550 nm (10 nm half-width).
Scattering effects in neutron diagnosis of DT tokamak plasmas
Authors: Antozzi P. , Gorini G. , Källne J. , Olsson N. , Ramström E. , Campanella M.
Published: July 2002

The scattered background flux accompanying observation of fusion plasma neutrons is a limiting factor in high accuracy neutron diagnostics such as will be required on ITER. The factors determining the shape and magnitude of the scattered neutron spectrum have been investigated in terms of the possibilities for calculating and measuring the spectrum, and to determine the dependence on the nuclide composition of the plasma vessel and changes in the plasma condition.
X-ray imaging spectroscopy of an electron cyclotron resonance discharge
Authors: Lehnert U. , Zschornack G.
Published: July 2002

A pinhole camera with an x-ray sensitive charge-coupled device array was used to analyze x-rays emitted from an electron cyclotron resonance (ECR) discharge. The camera was operated at a temperature of 140 K, allowing single photon detection at integration times up to several hours. This technique simultaneously allows spectroscopic investigations as well as x-ray imaging. Thus, the geometrical size and x-ray emission profiles from an ECR plasma were measured.
High power negative ion sources for fusion at the Japan Atomic Energy Research Institute (invited)
Authors: Okumura Y. , Fujiwara Y. , Inoue T. , Miyamoto K. , Miyamoto N. , Nagase A. , Ohara Y. , Watanabe K.
Published: July 2002

Technologies producing high power negative ion beams have been highly developed over the years at Japan Atomic Energy Research Institute for use in neutral beam injectors for heating the thermonuclear fusion plasmas. At present, it is possible to produce multiampere H−/D− ion beams quasicontinuously at energies of more than a few hundred keV with a good beam optics of beamlet divergence of a few mrad. Based on these technologies, two research and development projects have been initiated; one is to develop a 22 A/500 keV/10 s D− ion source for the neutral beam injector for JT-60U, and the other is to develop a 1 A/1 MeV/60 s H− ion source to demonstrate high current negative ion acceleration up to the energy of 1 MeV, the energy required for the neutral beam injector for the International Thermonuclear Experimental Reactor.
Anomalous oxygen isotopic charge state distribution in ECRIS: New evidence
Authors: Drentje A. G. , Girard A. , Hitz D. , Melin G.
Published: July 2002

The highly performing Electron Cyclotron Resonance Ion Source CAPRICE in Grenoble was operated with a mixture of three oxygen isotopes. The summed currents per charge state show a distribution almost identical to that of natural oxygen. However, the distributions per isotope are distinctly and systematically different in the sense that the heaviest isotopic distribution is most prominently peaked at high charge states. This anomalous effect reduces or disappears if helium is added to the isotopic mixture. The addition of either natural helium or isotopic 3He has no significantly differing result. Presently no quantitative model is available to satisfactorily explain the measurements.
Romanian ECR ion source project RECRIS
Authors: Dobrescu S. , Schächter L. , Badescu-Singureanu A. I. , Zoran V.
Published: July 2002

A 14.5 GHz ECR ion source is in an advanced stage of construction at the Institute of Atomic Physics of Bucharest, Romania. This ECR multicharge heavy ion source (RECRIS) is designed to be independently used in atomic physics research as well as an injector into the existing rf heavy ion postaccelerator of the Bucharest FN tandem accelerator. The general design and main characteristics of RECRIS are presented as well as the present status and the schedule of this project. A research program and facility was started in order to study physical ways to improve the ECR ion source performances.
A design study for a super-EBIT/EBIS without magnetic fielda)
Authors: Becker R. , Donets E. D. , Kleinod M. , Margolis H. S. , Silver J. D.
Published: July 2002

A super-EBIT may be defined by its ability to ionize even hydrogenlike uranium, requiring an electron energy well above 140 keV. The first super-EBIT has been put into operation at Livermore, operating with electron energies up to 200 keV, the second one is in progress in Tokyo, aiming at 300 keV. A distinctive advantage may be obtained by raising the electron energy from 200–300 to 500 keV, thus reducing the radiative recombination of hydrogenlike heavy ions such as U91+ and increasing their relative abundance by an order of magnitude.
Periodic permanent magnets-focusing super electron-beam ion trap (abstract)
Authors: Ovsyannikov V. P. , Kalagin I. V. , Golenitskiy I. I. , Kultashev O. K.
Published: July 2002

An electron-beam ion trap (EBIT) has been built as an instrument for in situ studies of atomic physics with great success. But the high complexity of the superconducting EBIT limits its use at small laboratories. In this article we consider the Super EBIT with focusing of the electron beam by a periodic permanent magnets (PPM) system. The preliminary analysis shows that a PPM Super EBIT with electron energy 200 keV and electron density about 1000 A/cm2 can be built. We would like to note that this device, first of all, is inexpensive and useful, and there are no gas freeze layer ‘‘memory effects’’ on the inner walls that are important for some applications. The proposal design and some computer simulations of EBIT with a periodic permanent magnet focusing system are presented.
Production of high charge state ions with the Advanced Electron Cyclotron Resonance Ion Source at LBNL
Authors: Xie Zu Qi , Lyneis C. M.
Published: July 2002

Production of high charge state ions with the Advanced Electron Cyclotron Resonance ion source (AECR) at Lawrence Berkeley National Laboratory (LBNL) has been significantly improved by application of various new techniques. Heating the plasma simultaneously with microwaves of two frequencies (10 and 14 GHz) has increased the production of very high charge state heavy ions. The two-frequency technique provides extra electron cyclotron resonance heating zone as compared to the single-frequency heating and improves the heating of the plasma electrons. Aluminum oxide on the plasma chamber surface improves the production of cold electrons at the chamber surfaces and increases the performance of the AECR. Fully stripped argon ions, ≥5 enA, were produced and directly identified by the source charge state analyzing system. High charge state ion beams of bismuth and uranium, such as 209Bi51+ and 238U53+, were produced by the source and accelerated by the 88-in. cyclotron to energies above 6 MeV/nucleon for the first time.
Magnet tests and status of the superconducting electron cyclotron resonance source SERSE
Authors: Ciavola G. , Gammino S. , Cafici M. , Castro M. , Chines F. , Marletta S. , Alessandria F. , Bourg F. , Briand P. , Melin G. , Lagnier R. , Seyfert P. , Gaggero G. , Losasso M. , Penco R.
Published: July 2002

At Laboratorio Nazionale del Sud a superconducting 14.5 GHz electron cyclotron resonance (ECR) source will be used as injector for the K-800 superconducting cyclotron. The original project of its magnetic system has been upgraded by taking into account the results of the high B mode operation of the 6.4 GHz SC-ECRIS at MSU-NSCL and now the mirror field may achieve 2.7 T, which is much higher than the confining field of any other ECR source. The magnet design will allow us to operate in a wide range of magnetic configurations making it easy to tune the source. The status of the project will be outlined and the preliminary results of the tests of the superconducting magnets will be described. A brief description of the tests to be carried out on the source during the first period of operation on the test bench in Grenoble follows.
Gas temperature in a hot filament diamond chemical vapor deposition system
Authors: Menningen K. L. , Childs M. A. , Anderson L. W. , Lawler J. E.
Published: July 2002

The gas temperature in a hot filament activated diamond chemical vapor deposition system is derived from the vacuum ultraviolet absorption spectrum of the H2 molecule. Curves of growth for the optically thick spectra are calculated using a Voigt line shape and published oscillator strengths in order to measure relative populations of H2 in various rotational and vibrational levels of the ground electronic state. The H2 vibrational levels are nearly in equilibrium. The gas temperature field is most strongly influenced by the substrate temperature. Heat conduction from the filament produces a large temperature gradient near the filament. Heat released or absorbed in gas phase hydrocarbon chemical reactions does not significantly affect the temperature field.
In situ Kerr microscopy for ultrahigh vacuum applications
Authors: Giergiel J. , Kirschner J.
Published: July 2002

A simple Kerr microscope designed for in situ investigation of magnetic ultrathin films in ultrahigh vacuum environment is described. The system permits quick visualization of domain patterns with 10 μm lateral resolution. Simultaneous optical magnetometry is also possible. The performance of the system is illustrated with domain images in a few layers thick Fe films on Cu(001) and W(110).
A simple low-current scanning tunneling microscope
Authors: Dhirani A. , Fisher A. J. , Guyot-Sionnest P.
Published: July 2002

A rigid scanning tunneling microscope design with an easily implemented two-dimensional approach is presented. Also described is a simple current–voltage converter optimized for low-current (pA) applications. Capabilities of the microscope include atomic resolution on Au(111) and molecular resolution of poorly conducting self-assembled monolayers.
Single beam laser induced fluorescence technique for plasma transport measurements
Authors: Edrich D. A. , McWilliams R. , Wolf N. S.
Published: July 2002

A technique for measuring ion transport using laser-induced fluorescence has been developed and tested in an argon plasma. It uses only one broadband beam thus being simpler than some previous techniques because no detection beam is required. First, a 5 μs laser pulse centered on 611 nm stimulates a transition from the metastable state in Ar(II) 3d 2G9/2 to 4p 2F7/20. A 4p 2F7/20 to 4s2D5/2transition rapidly results with emission at 461 nm. Upon cessation of the laser pulse, the 461 nm light in the detection volume does not return to its background level immediately because the 3d 2G9/2 level is partially depleted. The time history of the 461 nm signal in returning to steady-state background intensity provides a means of determining ion transport because the recovery signal is due to processes including ion excitation, diffusion, convection, and thermal motion. Measurements of the ion velocity distribution yield the contributions of thermal and convective effects to ion transport. By varying the laser beam diameter and the detection volume the plasma ion spatial diffusion coefficient D, and the time, τp it takes for processes other than transport to bring the 461 nm emission back to the steady-state background level are determined. For example, in one set of plasma conditions D=0.58±0.16 m2/s and τp=59±7 μs were found.
An atmospheric electrical voltmeter follower
Authors: Harrison R. G.
Published: July 2002

Horizontal passive antennas used to sense the potential of the atmosphere above the earth’s surface demand high performance from attached electrometer voltmeter circuits. The floating follower circuit described here allows precision dc measurements of potential difference in the range ±10 V, while maintaining input currents of order 10−15 A. Voltage offsets over most of the dynamic range are less than 50 μV, allowing precise guarding of the input electrode to further minimize input leakage currents. The battery-operated system is well suited to atmospheric electrical measurements using horizontal antennas operating within 10 cm of the earth’s surface, and provides an inexpensive means of precision high impedance voltage measurements.
An out-of-plane detector for surface x-ray diffraction
Authors: Taylor J. S. G. , Norris C. , Vlieg E. , Lohmeier M. , Turner T. S.
Published: July 2002

An out-of-plane detector movement has been built for the detector arm of the surface x-ray diffractometer on the wiggler beam line 9.4 on the synchrotron radiation source at Daresbury Lab. For a relative small cost, it significantly increases the volume of reciprocal space that can be accessed with a corresponding improvement in the accuracy of the determination of the interatomic spacings.
Simple techniques for the generation of high peak power pulses with nanosecond and subnanosecond rise times
Authors: Focia R. J. , Schamiloglu E. , Fleddermann C. B.
Published: July 2002

A simple method of generating high peak power pulses with nanosecond rise times is described. This method is based on the use of a drift step recovery diode (DSRD) in an inductive-capacitive storage circuit. A method for sharpening the rise time of the pulses generated using the DSRD to the subnanosecond range is also described. Experimental results show that pulses can be generated with amplitudes of 1.7 kV (into 50 Ω), rise times in the hundreds of picoseconds, and repetition rates of 10 kHz.
Scanning heterodyne optical interferometers
Authors: Riza Nabeel A.
Published: July 2002

Compact, high performance, scanning heterodyne optical interferometers are introduced for interferometric phase-based measurement applications. The novel, in-line, almost common-path optical interferometer design offers robustness to externally induced phase noise via mechanical vibrations, thermal effects, and other environmental effects. Novel instrument designs are introduced for both transmissive and reflective interferometry. These instruments use acousto-optic devices or Bragg cells to implement rapid (e.g., <50 μs/scan spot) optical scanning of the test medium. Although the read optical beam scans a given test region, the double Bragg diffraction optical design of the instrument makes the final interfering output beams stationary on the two high speed photodetectors used for radio frequency signal generation via heterodyne detection. One photodetector acts as the fixed phase reference, while the other fixed photodetector picks up the test medium phase information as the optical beam scans the test region. The transmissive design instrument is built in the laboratory using flint glass Bragg cells. A typical 120 MHz heterodyne detected signal output had a carrier-to-noise ratio of 108.9 dBc/Hz measured at a +160 kHz offset using a spectrum analyzer resolution bandwidth of 30 kHz. The corresponding single-sideband phase noise was estimated at −101.57 dBc/Hz at 160 kHz offset. The measured instrument radio frequency dynamic range was ∼60 dB or an equivalent of 30 dB optical dynamic range, with a 1/1000 of a fringe cycle phase measurement accuracy. Test medium optical phase mapping was successfully tested with the instrument using a large area, 6 μm thick, birefringent-mode nematic liquid crystal cell. Our instrument allows the use of high continuous wave or peak power, broad spectral linewidth, coherent light sources. The instrument can have a high 50% optical power efficiency. High speed two-dimensional optical scanning of a test medium is possible with our instrument by using a fixed one-dimensional output high speed detector array, or via the use of high speed nonmechanical electro-optic deflectors.
A detector for circular polarization of soft x rays
Authors: Holldack K. , Kachel T. , Schäfers F. , Packe I.
Published: July 2002

To satisfy the increasing need for research using circularly polarized x rays we present a compact prototype of a polarization detector based on magnetic circular dichroism (MCD) in bulk transmission using a multilayer at grazing incidence as bandpass filter. The detector features reliability, heat load stability, and for Fe-MCD a polarization sensitivity from 700 to 740 eV. The technique can be easily extended to the L edges of other 3d transition elements giving rise to other energy ranges by just tuning the incidence angle and changing the material of the transmission foil. The detector calibration was made using off plane bend magnet radiation at the BESSY I storage ring and it turns out that the polarization degree of an unknown source can be well detected within a 3% error rms. The detector dimensions are less than 10 cm and only modest vacuum conditions are required. Once calibrated in white light, it can be used to determine the degree of circular polarization behind monochromators, insertion devices as well as in polychromatic light with up to 100 Hz repetition rate without any rotation of its components.
Background technique for detecting correlated colloidal motion masked by thermal noise and projection effects
Authors: Schirato Becky S. , Franck Carl
Published: July 2002

This article presents a novel background technique that enables one to distinguish correlated motion of colloidal particles from random thermal effects and projection effects in video microscopy recordings that have been converted into digital lists of apparent particle trajectories. The idea is that one can construct reference data sets lacking any correlated motion from actual observations by randomly translating single particle trajectories. One, therefore, detects genuine correlations with a statistical measure by comparing the results for the original and background data sets. The success of this technique is demonstrated here by numerical simulations.
A sensitive capacitance thermometer at low temperature for use in magnetic fields up to 20 T
Authors: Penning F. C. , Maior M. M. , Wiegers S. A. J. , van Kempen H. , Maan J. C.
Published: July 2002

We have established the magnetic-field independence up to 20 T of a capacitance thermometer based on the incommensurate crystal (Pb0.45Sn0.55)2P2Se6 in the temperature range from 25 mK to 0.5 K. The sensitivity of the thermometer, d ln C/d ln T, is 5×10−3 at low temperatures and is about an order of magnitude larger than for any other previously reported capacitance thermometer. The most sensitive temperature range of the thermometer can be tuned by varying the measuring ac frequency and voltage. The reproducibility of the thermometer upon cycling below 1 K is better than 1 mK.
Optical triangulation: A dual-channel configuration
Authors: Wang Haiming , Malacara Daniel
Published: July 2002

Scattering of light from a rough surface is modeled and the power of the scattered light received by the collecting lens in optical triangulation measurements is calculated. This light power signal is used to improve displacement measurements and to identify the surface slope or inclination of a sample in the optical triangulation method. In this way, the improved optical triangulation method described here is able to measure smooth samples that are difficult to be measured by conventional optical triangulation techniques. The inaccuracy of the sensor is better than 0.5%.
Review of recent developments for electron-beam ion sources (EBIS) (invited)
Authors: Donets Evgeni D.
Published: July 2002

During recent years developments for electron-beam ion sources (EBIS) in the classic mode of operation were continued. Additionally, studies of EBIS in the reflection mode of operation were begun. This mode of operation leads to the formation of a dense electron string, where electron current flows in a radial direction across the magnetic field of a solenoid. This string is used for production of highly charged ions in RefEBIS.
An intense, broadband emission spectrum, thyratron-gated nanosecond light source using a commercially available Xe short-arc lamp
Authors: Itami Shin , Araki Tsutomu
Published: July 2002

We have developed a thyratron-gated, high-intensity nanosecond pulsed lamp using a commercially available Xe short-arc lamp. A dc voltage higher than 10 kV is applied to the electrode gap through a high-value resistor. A spark discharge in the electrode gap is generated by the trigger of the thyratron. Intense light pulses as large as 80 W (peak value) of 14–16 ns duration full width at half-maximum was obtained repetitively from the Xe lamps. This lamp produced broadband emission spectrum (220–600 nm) according to discharge of Xe gas. Because discharge voltage of the pulsed lamp is much higher than that of a conventional dc lamp, a high electron-temperature pulsed plasma is produced, resulting in enhancement of the UV component of the emitted light. The rich UV light from this lamp can be utilized as an excitation light source in time-resolved spectroscopy.
Design considerations and performance of a combined scanning tunneling and scanning electron microscope
Authors: Wiessner A. , Kirschner J. , Schäfer G. , Berghaus Th.
Published: July 2002

We designed and built a combination of a scanning tunneling microscope (STM) and a scanning electron microscope (SEM) which is working under ultrahigh vacuum conditions (base pressure typically 7⋅10−11 mbar). The SEM is ideally used for surveying the sample and to control the STM tip positioning, while the STM extends the resolution range into the atomic scale. The design concept allows moving the STM tip freely over the sample under SEM control and using both imaging techniques simultaneously. The system is equipped with an electron energy analyzer (cylindrical sector analyzer) providing Auger electron spectroscopy, scanning Auger microscopy (SAM) and x-ray photoelectron spectroscopy capabilities. In addition, low energy electron diffraction and reflection high energy electron diffraction facilities are installed. In order to use these very different imaging techniques in situ, several special solutions had to be incorporated in the design of the system; they are described in detail. Some results are presented which demonstrate the performance of the STM/SEM system. Atomic resolution of the STM, a SEM resolution of up to 20 nm, and a SAM resolution of better than 100 nm were achieved.
Fiber optic thermometry based on Cr-fluorescence in olivine crystals
Authors: Fernicola V. C. , Zhang Z. Y. , Grattan K. T. V.
Published: July 2002

An investigation has been carried out into the use of two crystals of the olivine family, forsterite and olivine, CrMg2SiO4 and Cr:(Mg,Fe) SiO4, respectively, in optical fiber fluorescence thermometry. The results show that the Cr3+-based emission in the near-infrared is dominant under pumping with light from a red diode laser, and a useful sensor performance in the 200° region around room temperature is seen using probes constructed from these materials.
Extra-cavity perturbation method for the measurement of dielectric resonator materials
Authors: Ni Erhu , Ni Yuqing
Published: July 2002

An extra-cavity perturbation method is presented to determine the complex permittivity, εr′(1−j tan δ), of a high dielectric constant materials from measurements of frequency (or length) shift and change in the Q factor of the cavity when a sample is inserted into an evanescent guide outside the TE01n cylindrical cavity resonator. Fundamental principles and the optimum sensitivity and accuracy of the measurements are discussed. Experimental results for εr′, tan δ, and τε (temperature coefficient of εr′) on ceramics (Ba1−xSrx)Ti4O9 and BaO–PbO–Nd2O3–TiO2 are given. The results obtained using the present method and a traditional dielectric resonator method agree within |Δεr′/εr′|⩽5.5%.
Low thermal power electron beam annealing of scanning tunneling microscope tips
Authors: Scholz R. , Agne M. , Breitenstein O. , Jenniches H.
Published: July 2002

An add-on unit was developed that allows the cleaning of scanning tunneling microscope tips by electron beam annealing even if they cannot be disconnected from the piezo scanner in situ. The whole scanner tip combination, which is attached to a linear motion stage, is subjected to a pulsed annealing treatment. The heat impact is focused on the outermost tip by sticking the tip through a hole in a grounded Mo screening plate with the cathode mounted on the opposite side. Tungsten tips attached to the scanner of the Omicron ultrahigh vacuum Multiscan Lab were annealed to achieve atomic resolution of ultrahigh vacuum cleaved GaAs (110) faces. A highly doped superlattice package grown on semi-insulating GaAs was also able to be investigated on the cleaved (110) face due to the ability of exact tip positioning with a scanning electron microscope.
Aberrations due to localized potential defects (patch fields) on apertures
Authors: Read F. H. , Baranova L. A. , Bowring N. J. , Lambourne J. , Whitwell T. C.
Published: July 2002

The aberrations coefficients are derived for electrostatic systems that are axially symmetric except for the presence of a localized potential defect (i.e., a patch field). The near-axis aberrations caused by such a defect near the edge of an aperture are then investigated. When a beam fills the aperture the resulting aberrations cannot be characterized in terms of coefficients, and so a new characterization of the aberrations is defined. Numerical evaluations are carried out for representative types of potential defect. Relationships are presented that enable the increase in spot size of a focused beam to be deduced from the measured or estimated mean deflection of the spot.
Construction of a top-loading adiabatic calorimeter and enthalpy relaxation of glassy (1,3-propanediol)0.5(1,2-propanediamine)0.5
Authors: Tsukushi Itaru , Yamamuro Osamu , Sadanami Keishi , Nishizawa Makoto , Matsuo Takasuke , Takeda Kiyoshi
Published: July 2002

We have developed a top-loading type adiabatic calorimeter which works in the temperature range 13–375 K. This calorimeter drastically reduces the time required for the sample setup (to ∼10 min) and enables us to set up samples at liquid nitrogen temperature (77 K). The heat capacity of an empty cell was measured in a test experiment. The imprecision of the heat capacity measurement was ±0.2% at 13–30 K, ±0.1% at 30–50 K, and ±0.02% at above 50 K. These are as good as the performance of any of the traditional adiabatic calorimeters. The heat capacity of (1,3-propanediol)0.5(1,2-propanediamine)0.5 was measured in the temperature range 20–290 K and the enthalpy relaxation in its glassy state was also measured near Tg(=178 K). Because of the top-loading feature, fast-quenched samples prepared at 77 K outside the cryostat could be set up without ever undergoing a temperature above 100 K.
Development of an adiabatic calorimeter for simultaneous measurement of enthalpy and volume under high pressure
Authors: Takahara Shuichi , Yamamuro Osamu , Ishikawa Mariko , Matsuo Takasuke , Suga Hiroshi
Published: July 2002

A novel adiabatic calorimeter was constructed for simultaneous measurement of enthalpy and volume under high pressure. The calorimeter works under constant pressure up to 100 MPa and in the temperature range 80–380 K. The sample is pressurized hydrostatically by using a liquid pressure transmitting medium. The sample volume is measured with a new type of dilatometer using bellows installed in the cell. The dilatometer has two resolution modes (high and low) with different scanning range. As the calibration and test experiments, the heat capacities and volumes of toluene and water were measured at 0.1 and 50.1 MPa in the temperature range between 275 and 380 K. In the low resolution mode, the accuracies of heat capacity and volume were ±0.2% and 20 ppm of total, respectively. The test of the volume measurement in the high resolution mode showed that the resolution was ±0.1 ppm of total sample volume, which is ∼ ten times better than that of the previous best dilatometer. To demonstrate the performance of the present apparatus, the enthalpy and volume changes due to the structural relaxation of glassy polystyrene were measured simultaneously.
Resonators for accurate dielectric measurements in conducting liquids
Authors: Hamelin Jean , Mehl James B. , Moldover Michael R.
Published: July 2002

The compact, rugged, re-entrant radio-frequency resonator [A. R. H. Goodwin, J. B. Mehl, and M. R. Moldover, Rev Sci. Instrum. 67, 4294 (1996)] was modified for accurate measurements of the zero-frequency dielectric constant (relative electric permittivity) εr of moderately conducting liquids such as impure water. The modified resonator has two modes with frequencies near 216/εr MHz and 566/εr MHz. The results for εr at both frequencies were consistent within 0.0002εr, verifying that the low-frequency limit had been attained with water samples with conductivities in the range 100–2500 μS/m. The results for water and for the insulating liquid cyclohexane were within 0.0005εr of literature values. The present analysis is based on a simplified equivalent circuit that accounts for the loading of the resonator by the external instrumentation. This circuit can easily be generalized for a resonator with three or more modes. The present resonator has a thick gold plating on its interior surfaces. With the plating, the quality factors Q of the resonances varied in a predictable way with frequency and temperature. Predictable Qs were essential for obtaining accurate values of εr.
Optical resonator matching for JAERI free electron laser
Authors: Nishimori N. , Minehara E. J. , Sugimoto M. , Sawamura M. , Nagai R. , Kikuzawa N.
Published: July 2002

An optical resonator length of free electron lasers must be exactly matched with the frequency of the repeated electron beam from the accelerator driver so the incident electron beam can overlap with stored light pulses in the resonator. We made the exact resonator length matching by injecting ultrashort laser light pulses in the resonator as external clock signals. The external laser was a mode-locked Ti:Sapphire laser with 80 fs pulse width and synchronized with the accelerator clock signals. With the simultaneous use of a streak camera and a photo diode, we succeeded in making the quick matching within an accuracy of 1 μm or less in a direct and exact manner.
Manufacture of a compact Ku-band electron cyclotron resonance ion source with two resonance zones and variable frequency
Authors: Tojyo E. , Oyaizu M. , Imanishi A. , Jeong S. C. , Kawakami H. , Niki K. , Shirakabe Y. , Hattori T. , Ohshiro Y.
Published: July 2002

A compact ECR ion source working at a Ku band has been manufactured for the production of both low and multiple charged ions. This source can be formed for both the ordinal ECR zone and second Bernstein resonance zone with a half Becr field. The B minimum field configuration is realized by the use of permanent magnets and its axial mirror field can be adjusted within ±0.03 T by a small auxiliary solenoid. Microwave power can be injected from both axial and radial ports. Effective power of 200–250 W can be supplied to the source with a continuously variable frequency in the range of 12.0–14.5 GHz and with a variable pulse mode. The outer dimension of the source is φ180×230 and its total weight is just 30 kg. The design, manufacture and results of the preliminary test are reported.
Damage introduction in InGaP by electron cyclotron resonance Ar plasmas
Authors: Lee J. W. , Pearton S. J. , Abernathy C. R. , Hobson W. S. , Ren F.
Published: July 2002

Changes in sheet resistance of n- and p-type InGaP exposed to electron cyclotron resonance Ar plasmas have been used to measure the introduction of ion-induced damage. p-type material is much more resistant to change in its conductivity than n-type InGaP, indicating that electron traps are the predominant entity produced by the ion bombardment. For short (∼1 min) plasma exposures the ion current is more important than ion energy in producing resistance changes. Annealing of damage in both conductivity types occurs with an activation energy of ∼3.4±0.5 eV.
Microwave plasma source for the negative hydrogen ion production
Authors: Mozjetchkov M. , Takanashi T. , Oka Y. , Tsumori K. , Osakabe M. , Kaneko O. , Takeiri Y. , Kuroda T.
Published: July 2002

Microwave plasma source for the negative hydrogen ion production was constructed and tested. The plasma source consists of two chambers: a plasma production chamber and a plasma confinement chamber. The production chamber is placed into the strong axial magnetic field and the microwaves (2.45 GHz, up to 5 kW) are introduced through the quartz window along the magnetic field lines. It is found that the suppression of the fast electron loss to the window holder is important to improve the efficiency of hydrogen plasma production. The plasma density increases with the magnetic field strength in the plasma production chamber. For the microwave power of 4 kW the uniform plasma of 3×1012 cm−3 for argon and 3×1011 cm−3 for hydrogen is obtained in the area of 20×20 cm. Electron temperature in the plasma grid region is around 2 eV. The optimum gas pressure is around 6 mTorr.
Electron cyclotron resonance ion source developments at Louvain-la-Neuve
Authors: Barué C. , Biri S. , Cherkani-Hassani S. , Gaelens M. , Loiselet M. , Ryckewaert G.
Published: July 2002

A new 6 GHz electron cyclotron resonance (ECR) ion source has been developed and installed at Louvain-la-Neuve. It replaces the previous ECR ion source OCTOPUS and routinely produces highly charged ion beams from gaseous elements with a better intensity and stability. The magnetic configuration of the ion source and results obtained for the production of gaseous (O,Ar,Xe) and metallic (Ni) ions are presented. The possibility to use the sputtering method to ionize radioactive elements has been tested on F18(T1/2=110 min). Ionization efficiency measurements for F1+18 are reported.
High brightness He3 ion source and plasma target for nuclear astrophysical applications
Authors: Itahashi Takahisa , Takahisa Keiji , Kudomi Nobuyuki , Iki Tetsufumi , Yoshida Sei , Toki Hiroshi , Ejiri Hiroyasu , Ohsumi Hideaki , Komori Masataka
Published: July 2002

The design of a compact low-energy, high-current accelerator for the study of fusion reactions in the field of nuclear astrophysics is reported. The accelerator can produce an intense beam of several ion species, including proton, deuteron, and helium isotopes, of more than 1 mA. In order to provide extremely fine, cross-sectional measurements for fusion reactions at 40 to 50 keV, analyses of ion beam production, extraction and transport to a windowless gas target are made using the GIOS and FUGUN computer codes. The use of multielectrodes for the ion extraction and the application of these electrodes to the NANOGUN ion source is expected to improve the beam quality and to raise the luminosity for the beam-to-gas-target interaction. To study the electron screening effects, an experimental apparatus is proposed and constructed.
Plasma potential profile in a 2.45 GHz electron cyclotron resonance multicharged ion source
Authors: Kato Yushi , Ishii Shigeyuki
Published: July 2002

Plasma potentials are measured in a 2.45 GHz electron cyclotron resonance (ECR) multicharged ion source. Both axial and radial potential profiles are determined for an argon plasma by using a Langmuir probe at various pressures. Multicharged ions up to Ar12+ are observed in the extracted beam. The plasma potentials are positive with respect to the plasma chamber wall and are on the order of several tens of volts. The values in profile measurements of the plasma potential are consistent with the spatial averaged values obtained by ion beam measurement. Along the mirror axis the plasma potential, the electron temperature, and density increase as the ECR zone is approached, and are roughly flat or hollow near the ECR zone. The radial profiles are loosely peaked or flat at the position off the ECR zone, and asymmetrical or hollow near the ECR zone. Due to some serious problems for the probe measurement, the plasma potential is deduced by several methods and the density is estimated from ion saturation currents.