bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma fluctuation diagnostics via maximum entropy spectral estimation
Authors: Levinson S. J. , Kim S. B. , Koh T. , Powers E. J.
Published: July 2002

The objective of this paper is to present a systematic comparison of the conventional fast Fourier transform and maximum entropy method (MEM) of spectral estimation of turbulent plasma fluctuation data. On the basis of this comparison, it appears that the MEM is the preferred approach for the spectral analysis of short time duration fluctuation records.
Coded imaging of thermonuclear neutrons (invited)
Authors: Nugent K. A.
Published: July 2002

Imaging of thermonuclear neutrons from inertial confinement fusion pellets is reviewed. The most promising technique, penumbral imaging, is discussed in detail and the design criteria are outlined. Simulations are presented. More advanced aspects are also briefly discussed, such as nonlinear image reconstruction algorithms and more complex apertures.
Multichord interferometer for edge density profiles in Alcator C-Mod (abstract)
Authors: Sevillano E. , Irby J. H. , Lipschultz B. , Marmar E. S. , Post R. S.
Published: July 2002

The preliminary design of a multichord imaging interferometer system used to measure the density profiles in the scrape-off layer of the Alcator C-Mod tokamak is presented. The system is envisioned to be a two-color vibration compensated double-pass interferometer based on a CO2 laser with λ=10.6 μm; the second color will either use He–Ne emission at 632.8 nm or 3.39 μm, depending on how serious the vibrations are expected to be. A toroidal view of the plasma near the vertical midplane is considered. We present systematic studies of the requirements on fringe resolution and edge density range, from which reasonably accurate profiles can be inferred. Requirements on the spatial resolution, number of detectors, and the possibility of obtaining 2-D images of the edge will be addressed. Longer wavelength alternatives using a FIR laser will also be studied; in this case the main concern is beam refraction caused by the density gradients in the edge region of interest. This work was supported by U. S. DOE Contract No. DE-AC02-78ET51013.
Charge exchange recombination spectroscopy on the JFT-2M tokamak
Authors: Ogawa Hiroaki , Miura Yukitoshi , Kasai Satoshi
Published: July 2002

Charge exchange recombination spectroscopy (CXRS) was used to measure the ion temperature, the toroidal rotation velocity, and the time evolution of fully stripped carbon ions during neutral beam heating in JFT-2M. The ion temperature measured by the CXRS was in good agreement with that measured by the neutral particle analyzer. Fully stripped carbon ions were found to accumulate in the center of the plasma during the H-mode phase. These results are similar to those found for metallic impurity ions such as iron and titanium and suggest that accumulation of impurity ions during the H-mode phase is caused by the improved particle confinement.
Laser-aided measurements of plasma transport (invited) (abstract)
Authors: McWilliams R. , Sheehan D.
Published: July 2002

Laser induced fluorescence (LIF) diagnostic techniques1–3 allow investigation of diverse plasma phenomena. LIF techniques will be discussed in the context of a series of experiments carried out at UCI including: (1) phase space reconstructions of ion response to electron and ion beam generated modes,4,5 ion acceleration and anomalous transport in the near wake of plasma-obstacle systems, (2) optical tomographic techniques2 applied to ion acceleration in velocity space,6 and (3) optical tagging techniques used to quantitatively assess classical and turbulent models of cross-field particle diffusion.7 This work was supported by NSF Grants ♯PHY-8606081 and ♯ATM-8411189.
Laser induced fluorescence measurements in the Pisces plasma (abstract)
Authors: Rettig C. L. , Peebles W. A. , Luhmann N. C. , Gohil P.
Published: July 2002

By resonantly exciting neutrals in a cool plasma, the local neutral density and possibly ion temperature can be measured. If the neutrals are pumped by a laser with an intensity sufficient to saturate the transition, then observation of the fluorescence at the same wavelength will show an enhancement in the spontaneous emission during the laser pulse. The pump radiation changes the excited level population distribution in such a way that theoretical modeling can extract the ground-state population from the measured enhancement. Here, a 350-kW flash-lamp pumped dye laser is being used at 656 and 481 nm to pump the Balmer alpha and beta lines of hydrogen in the continuous Pisces plasma which simulates the edge using a tokamak. The fluorescence is observed with a photomultiplier tube through a narrow-band interference filter. Great care has been taken to reduce stray light to a negligible level. Data will be presented taken from plasmas with densities between 1011 and 1013 cm−3 and electron temperatures between 5 and 25 eV. In addition, by spectrally resolving the fluorescence, local ion temperatures can be inferred from Doppler broadening. However, actual temperatures measured are close to the resolution limit of the spectrometer. Future work could include these temperature measurements in the edge region of a tokamak. This work was supported by the U.S. DOE Contract No. DE-F03-86-ER-53225.
Plasma cathode oxygen-ion source
Authors: Shibuya Takehisa
Published: July 2002

A plasma cathode ion source has been developed to attain a long lifetime in oxygen-ion production. In this ion source, a plasma of a nonreactive gas serves as a cathode in place of a thermionic tungsten hot cathode used in the conventional Kaufman ion source. An anode ring with an annular slit mounted on the top of the ion source contributes to raising spatial uniformity in the ion current density. At 15 cm from the top of the ion source, a current density of 680 μA/cm2 was obtained with a value of 0.85 for the uniformity (defined as the ratio of the lowest density to the highest) in an area of 15 cm diameter. Mass spectrometry results show that considerable amounts of O+ and O2+ ions, especially of O+ ions, as well as Ar+ ions, are contained in ion beams produced by this source. In an oxygen-ion production test, the ion source could continuously be operated for 61 h. It was confirmed that the ion energy distribution in the beam can be well controlled by the anode ring voltage. In an experiment of oxygen-ion-assisted deposition performed with this ion source, a film having a stoichiometric composition very close to SiO2 was successfully produced from a starting material of SiO.
High-voltage deflection plate driver for the scanning-beam switch
Authors: Humphries Stanley
Published: July 2002

The scanning-beam switch is a novel device to generate intense rf radiation for applications to electron accelerators. Operation is based on the transverse deflection of a high-current sheet electron beam by an oscillating electric field. Amplifier experiments require a high-voltage ac driver for beam deflection. This article describes a driver that combines a commercial high-power pulsed triode with a resonant step-up transformer. In initial tests, the device generated ac voltages up to ±12 kV at 50, 150, and 250 MHz.
A wide-range superconductor thermal sensor for low-temperature measurement
Authors: Lakshmi M. V. S. , Ramkumar K. , Satyam M.
Published: July 2002

This paper aims at describing a low-temperature thermal sensor based on superconductor films which can be designed to have required variation of resistance with temperature through an appropriate geometry. Further, it has been shown that the temperature range can be varied to some extent by controlling the bias current.
A secondary wobbling mechanism for a balloon-borne infrared telescope
Authors: Matsuhara Hideo , Hiromoto Norihisa , Shibai Hiroshi , Nakagawa Takao , Okuda Haruyuki , Maihara Toshinori
Published: July 2002

A wobbling mechanism for a secondary mirror has been developed for a balloon-borne infrared telescope. Friction of the wobbling mechanism is negligibly small, and hence the wobbling mechanism is very reliable for the use in a severe environment at balloon altitudes. Motion is controlled by servo electronics, whose transfer function includes the second-order differential term of the error signal in order to improve the waveform. Good performance of the drive mechanism has been confirmed in two balloon flights in 1988 at an altitude of 31 km.
Scanning photoelectron spectromicroscope based on coherent vacuum ultraviolet radiation
Authors: Munakata Toshiaki , Ishikawa Etsuko , Kinoshita Ikuo , Kasuya Takahiro
Published: July 2002

Design and performance of a newly developed scanning photoelectron microscope based on focused coherent vacuum ultraviolet (VUV) light are described. The VUV light at 118 nm wavelength (10.48 eV photon energy) was generated by the frequency upconversion of a pulsed YAG laser light. The microscope is characterized by its high spatial resolution of a few microns, which is consistent with its high-energy resolution of better than 200 meV. The spatial resolution was provided by focusing the VUV light nearly to its diffraction limit, while the photoelectron energy was resolved by a high efficiency time-of-flight (TOF) energy analyzer. The point-to-point data acquisition, as well as the sample scanning, were controlled by a computer system, and the spectral data were accumulated at every two-dimensional mesh point of the specimen. From the photoemission profile across a processed Ag/Si stripe, the spatial resolution was nominally 6 μm. The energy resolving capability of the present microscope was demonstrated by the observation of crystalline facets formed on a polished copper disk.
High-pressure NMR probes for the in situ investigation of gas/liquid reactions
Authors: Woelk K. , Bargon J.
Published: July 2002

Three different types of nuclear magnetic resonance (NMR) probes have been developed for investigating multiple phase (gas/liquid) reactions in situ at ambient and high pressure. Versions requiring only minimal modifications of existing NMR probes, low volume probes, and high precision flow systems have been optimized for specific boundary conditions. Pressures ranging from 1 to 20 bar have been successfully applied. The arrangements are especially attractive for the in situ investigations of homogeneous hydrogenation reactions displaying nuclear spin polarization.
Use of time domain reflectometer measurements on a scale model to predict the effects of a 90° bend in a large coaxial pulse forming line
Authors: Sethian J. D. , Corcoran P. A.
Published: July 2002

We have devised a simple experimental technique for determining the effects of a 90° bend in a coaxial pulse forming line. A time domain reflectometer (TDR) is used to inject a fast rising signal (<25 ps) into a scale model of the proposed line. These measurements could easily establish the effects of the bend and agreed well with the predictions of a 3-D code. While this TDR technique was applied to a coaxial system, it can be valid for many types of pulsed components and networks. In some cases it may be simpler to use than a complicated 3-D code.
Bending tool for stainless-steel tubes using cryogenic technique
Authors: Jacob S. , Kasthurirengan S. , Karunanithi R. , Raguraman R.
Published: July 2002

The design of a special bending tool which is used in the formation of 90° bends for the tube-in-tube helium flow passages of a remote delivery tube is described. The concentric thin walled stainless-steel tube assembly is filled with water and cryofrozen before they are clamped into the bending tool. The tubes are bent by pressing the tube using the bending lever over the guiding wheel. The split bush and split cone clamping arrangement ensures that there is no movement of the tubes during the bending operation. This procedure has yielded kink-free bends with good circularity.
High performance automatic alignment and power stabilization system for a multikilowatt CO2 laser
Authors: Akitt Dale R. , Seguin H. J. J. , Sellathamby Christopher V. , Reshef H.
Published: July 2002

A beam profile sensor for use in an automatic alignment and power stabilization system for a multikilowatt CO2 laser is described. An inexpensive pyroelectric array is used in conjunction with a diamond machined rotating wand, to provide on-line samples of the laser beam. Interface circuits utilize the multiple outputs derived from the detector array for precise monitoring and control of the laser’s output radiation. Data from a 5-kW CO2 laser are presented to characterize the response of this new beam profile sensor to major perturbations in the optical cavity and lasing gas chemistry. The device has demonstrated exceptional performance in the maintenance of both mode quality and optical power level.
Source for excited states of alkali atoms and clusters using diffusion through a thin graphite foil
Authors: Holmlid Leif , Pettersson Jan B. C. , Åman Carina , Lönn Benny , Möller Kenneth
Published: July 2002

A molecular beam source used for the production of excited and ionized clusters of Cs and other materials is described. This source is closed, with the emitting graphite foil as an integral part of the source enclosure. The foil is kept at 1100–1500 K by radiation heating. From the foil, excited clusters (Cs)*n with broad distributions of n, and excited Rydberg atoms Cs* are emitted. These highly excited states can be field ionized at field strengths of less than 400 V/cm. At a Cs reservoir temperature of 400 K, total field ionized flux densities up to 1015 ions cm−2 s−1 (3×10−4 A cm−2) are found.
Erratum: ‘‘Plasma cathode oxygen-ion source’’ [Rev. Sci. Instrum. 62, 2890 (1991)]
Authors: Shibuya Takehisa
Published: July 2002

An inadvertent mistake was made in designating the gas inlets of the ion source shown in Fig. 1. In this figure, ‘‘Inlet for nonreactive discharge gas (Ar)’’ and ‘‘Inlet for working gas (O2)’’ should be exchanged with each other. The corrected version is shown here.
A fiber-optic system for three-phase current sensing using a hybrid sensing technique
Authors: McGarrity C. , Ning Y. N. , Santos J. L. , Jackson D. A.
Published: July 2002

We describe and demonstrate a new hybrid current sensor system which uses a novel time division multiplexed fiber network for the measurement of three-phase currents at high potential. The sensor arrangement combines a conventional current transformer with a fiber-optic interferometer such that the signal is transmitted optically to ground. Sensitivities of ∼0.5 A/√Hz are obtained in each phase at the line frequency of 50 Hz. The sensitivity and dynamic range of each sensor can be tailored for a specific level of current or according to an individual application.
Improved furnace temperature control for the PARC vibrating sample magnetometer
Authors: Sellers C. H. , Lee J. E. , Hyde T. A.
Published: July 2002

Temperature control of furnaces to be used with the PARC vibrating sample magnetometer can be greatly improved if a separate temperature controller is utilized. A control circuit that allows easy temperature programming and ramping is described, as well as sample holder modifications which permit accurate measurement of the sample temperature.
Spectral properties of a tapered gap hard x-ray undulator
Authors: Lai B. , Viccaro P. J. , Dejus R. J. , Gluskin E. , Yun W. B. , McNulty I.
Published: July 2002

A tapered undulator, in which the entrance and exit magnetic gaps are different, will show an increase in the energy width of the harmonics compared to the nontapered case. This increase can occur without substantial broadening in the collimation of the undulator radiation. We present the spectral properties measured for a tapered 3.3-cm period prototype undulator of the Advanced Photon Source at the Cornell High Energy Synchrotron Source. The width of the on-axis first harmonic at 6.9 keV increased from 0.32 to 0.66 keV for a gap tapering of 12%. Minimal angular broadening in the first harmonic x rays was detected and measurements of off-axis radiation were also performed. The results are found to be in good agreement with model calculations.
A moving-mirror Michelson interferometer for probing transient plasma plumes
Authors: Cheung Nai-Ho , Ng Lun-Chiu , Chen Shu-Chi
Published: July 2002

A modified Michelson interferometer was used to probe the electron density in plasma plumes produced by pulsed XeCl laser ablation of Al2O3. With one of the mirrors of the interferometer translating steadily, the phase angle of the sinusoidal interference signal was tracked and the XeCl laser was fired whenever the detected phase angle matched a predefined value. The transient interference waveform produced by the plasma plume was then synchronously captured. This moving-mirror interferometer features minimal vibration isolation, fast response time (∼10 ns), powerful noise rejection, and a detection limit of a thousandth of a fringe shift, or ∼1015 electrons per cm3 for mm size plumes.
Frequency stabilization of a Rayleigh–Brillouin spectrometer
Authors: Cormier Charles A. , Neuman Murray N.
Published: July 2002

A Rayleigh–Brillouin spectrometer that achieves high frequency stability for long integration times by using the exciting laser line as a frequency reference is described. It is economically built around an ordinary confocal Fabry–Pérot étalon that is not equipped with any means for active stabilization of the étalon gap. Weak signals (photon count rates ∼10 Hz) are tolerated without impairing the frequency stability. The relative frequency resolution (one part in 2×107) is limited as much by the finesse of the étalon mirrors as by the stabilization technique.
Piezoelectric sorption sensor for mercury vapors in air using a quartz resonator
Authors: Spassov L. , Yankov D. Y. , Mogilevski A. N. , Mayorov A. D.
Published: July 2002

A quartz resonator with a built-in microheater used as a piezoelectric sorption sensor for mercury vapors in the air is presented. With the construction presented here a maximum sensitivity of 3×10−6 g/m3 can be reached. The built-in microheater heats the crystal up to 150 °C and regenerates the sensor without dismounting it from the equipment. The sensor can be used in devices for environmental pollution control and in cases in which precise determination of low mercury vapor concentrations in air is necessary.
A simple timer-relay-based system for reciprocating rotation of crucible/seed in crystal growing systems
Authors: Rao S. M. , Chen K. M. , Wu M. K.
Published: July 2002

A simple but versatile reciprocating rotation mechanism is described which can be used to rotate crucible and/or crystal in a crystal growing system. It employs commercially available timer relays allowing accurate periods of motion and delay in the rotation.
A 492 GHz quasioptical SIS receiver for submillimeter astronomy
Authors: Engargiola G. , Zmuidzinas J. , Lo K. Y.
Published: July 2002

A 492 GHz quasioptical superconductor-insulator-superconductor (SIS) heterodyne receiver for submillimeter astronomy has been constructed with a double-sideband noise temperature of 170±25 K, where the system response is an average over a 600 MHz i.f. bandwidth centered at 1.5 GHz. The excellent sensitivity is achieved through use of a planar twin-slot antenna feeding a pair of Nb–Al2O3–Nb junctions linked by an inductance. A main beam of f/15 has been measured. The performance of this receiver is comparable to that of the best 492 GHz waveguide receivers currently in operation.
Bending magnet VUV beamline 2B at the Pohang Light Source
Authors: Rah Seung-Yu , Kang Tai-Hee , Chung Youngmin , Kim Bongsoo , Lee Ki-Bong
Published: July 2002

The SGM beamline (2B1), designed for photoemission spectroscopy, accepts a photon beam 10 mrad horizontally and 2 mrad vertically from a bending magnet source. The operating energy range of the monochromator is 12–1230 eV and the grating chamber has five exchangeable laminar gratings to cover the range. The monochromator employs a fixed entrance slit and a movable exit slit to satisfy the focusing condition during photon energy scan. The NIM beamline (2B2) is designed for 5–30 eV photon energy. The type of monochromator to be installed is 3 m normal incident, with off-Rowland circle mounting. A gas-phase experimental system, equipped with differential pumping stages, will be installed in the NIM beamline.
On the heating of the fiber tip in a near-field scanning optical microscope
Authors: Kavaldjiev D. I. , Toledo-Crow R. , Vaez-Iravani M.
Published: July 2002

Variation of the reflectance of the aluminized tip of a near-field scanning optical microscope is used to measure the temperature rise due the confinement of light in the tip. The measurement technique involves a pump-probe beam approach, and uses a two-step process which eliminates the need to know the dependence of the signal on the scattering cross section of the tip.
New experimental setup devoted to the Auger electron–ion coincidence spectroscopy
Authors: Ferrand-Tanaka Laurence , Simon Marc , Thissen Roland , Lavollée Michel , Morin Paul
Published: July 2002

Taking advantage of the pulsed character of the synchrotron-radiation light, an original experimental setup combining an electron analyzer with a time-of-flight mass spectrometer without angular discrimination, operated with a strong pulsed electrostatic field, has been developed. This allows high counting rates for multiple coincidence measurements Auger electron photoion photoion coincidences. The focus is on the experimental setup; new results obtained with core exited N2O are shown and it is demonstrated how to get more insight into the relaxation dynamics by the selection of the excited state combined with the selection of the final state.
The GaAs Hall element as a pressure transducer
Authors: Selim C. Z.
Published: July 2002

With semiconductor compounds of the group III–V and in particular GaAs, energy band structure investigations have been carried out by several researchers by effecting, in particular, Hall effect measurements under hydrostatic pressure. Their results allow one to conclude that the energy gap increase which occurs with increasing pressure up to a transition point of up to approximately 33 kbar, leads the semiconductor Hall sensitivity to increase correspondingly with applied pressure. Thus, commercial n-type GaAs Hall elements can effectively be used as pressure sensors, and subsequently, if appropriate calibration of the output Hall voltage to corresponding values of pressure is carried out, as pressure transducers.
Vacuum ultraviolet radiometry of xenon positive column discharges
Authors: Doughty D. A. , Fobare D. F.
Published: July 2002

In order to judge the potential fluorescent lamp applications of various low-pressure positive column discharges it is necessary to measure the absolute power emitted in the ultraviolet region of the spectrum. For rare-gas discharges the principle emission occurs in the vacuum ultraviolet so that it is difficult to measure the radiant emittance (power per unit area) of the resonance radiation by standard methods. Two independent techniques are discussed for measuring the radiant emittance of positive column discharges in the vacuum ultraviolet. These techniques are used to study xenon positive column discharges at the resonance wavelength of 147 nm. The first method relies on the measurement of the resonance level density by absorption techniques. The effective decay rate of the resonance level is then determined by the simulation of resonance radiation transport. These two quantities are combined to yield the radiant emittance at 147 nm without implementing vacuum ultraviolet techniques. The second method uses a measurement of the resonance radiation normal to the positive column axis made with a calibrated vacuum ultraviolet detector. The angular distribution of the resonance radiation leaving the tube is determined by the simulation of resonance radiation transport. The detector measurement places the angular distribution of the radiance on an absolute scale, which can then be integrated to yield the radiant emittance. These two techniques are compared for pure xenon discharges at various pressures and currents.
Precision of noninvasive temperature measurement by diffuse reflectance spectroscopy
Authors: Pearsall T. P. , Saban Stevan R. , Booth James , Beard Barrett T. , Johnson S. R.
Published: July 2002

Diffuse reflectance spectroscopy can be used as a noninvasive probe for measurement of temperature in real time. We have measured the precision of this technique to determine the temperature of Si and GaAs substrates during semiconductor processing. Our results show that the standard deviation of the noninvasive optical technique is less than 1.5 °C for GaAs and less than 2.0 °C for Si over the temperature range 25 °C<T<600 °C. This standard deviation compares favorably to that for a type-K thermocouple used in the same measurements: s.d.<1.5 °C. These results support the notion that noninvasive optical temperature measurement can be used in semiconductor processing with a precision approaching that of a thermocouple.
Low-cost modification of a contact atomic force microscope (AFM) into a sound-activated tapping mode AFM for use in air and liquids
Authors: Vinckier Anja , Hennau Frans , Kjoller Kevin , Hellemans Louis
Published: July 2002

Tapping mode capabilities are successfully implemented on a commercial contact mode atomic force microscope. In our setup, standard Si3N4 cantilevers are vibrated by an acoustic wave from a small piezo speaker. The minor changes needed in the measurement electronics are presented. Experiments performed both in air and under liquid, on hard as well as on soft samples, clearly demonstrate improvements in image quality, contrast, and resolution. Especially on soft biological samples, such as microtubules, the common problems of smearing and irreversible sample damage by scanning seem to be alleviated.
Deep defect levels of photorefractive sillenites
Authors: Davies D. Eirug , Larkin John J.
Published: July 2002

The photorefractive effect in materials such as bismuth silicon oxide (BSO) depends on photoionizing deep defect levels inadvertently present rather than controllably introduced. Using thermal stimulated conductivity measurements, a preliminary attempt has been made at associating specific levels with a particular sillenite member and impurity dopants. While many of the features prevail throughout, significant changes occur when Ge is substituted for Si to give BGO and when p- (Al) and n-type (P) impurities are added to dope BSO.
Growth of buried SiO2 layers in Si by thermal oxidation: Thermodynamic model
Authors: Gösele U. , Schroer E. , Huh J.-Y.
Published: July 2002

Buried oxides in silicon-on-insulator (SOI) structures have been reported to grow in thickness by thermally oxidizing the superficial silicon layer. A thermodynamic model is presented which is based on the experimental observation that thermal oxidation leads to an increase of the oxygen interstitial concentration in silicon beyond its normal solubility. This increase is assumed to be proportional to the growth rate of the external thermal oxide. Discrepancies between the only two available sets of data are discussed in terms of different levels of oxidation-induced supersaturations of silicon self-interstitials.
Optical and mechanical design of the Antarctic Submillimeter Telescope and Remote Observatory
Authors: Stark Antony A. , Chamberlin Richard A. , Ingalls James G. , Cheng Jingquan , Wright Gregory
Published: July 2002

Antarctic Submillimeter Telescope and Remote Observatory (AST/RO), a 1.7 m diameter telescope for astronomy and aeronomy studies at wavelengths between 200 and 3000 μm, was installed at the South Pole during the 1994–95 Austral summer. The optical design is Gregorian, offset in both azimuth and elevation, with the exit pupil at the chopping tertiary mirror: this arrangement provides for consistent illumination of the primary mirror even when the beam is thrown one degree or more on the sky. Aberrations are minimized by the choice of secondary mirror offset angle. Alignment is accomplished by mechanical means. There is a Coudé focus in a warm, spacious receiver room and also a Nasmyth focus. Both the elevation and azimuth axes are driven by two pinion gears with opposed torques to eliminate backlash. The encoders are unusually robust but have high friction, necessitating a stiff coupling. The azimuth limit switch scheme permits 1.5 rotations, but the switches will operate under extreme conditions with no single point of failure. The instrument is now operational with four heterodyne receivers and three acousto-optical spectrometers.
Monolithic crystalline fiber optic temperature sensor
Authors: Zhang Zhuhong , Herringer J. H. , Djeu N.
Published: July 2002

A fiber optic temperature sensor of the fluorescence decay type using a novel construction has been demonstrated. In this new design, both the fiber and the sensing element are made of crystals, and the two are fused together to produce a monolithic probe. As the entire probe is crystalline, it can potentially be used to measure extremely high temperatures.
Diagnostic instrumentation for microturbulence in tokamaks
Authors: Bretz N.
Published: July 2002

Particle and energy transport in tokamaks and other toroidal confinement devices is dominated by turbulence generated by flows and gradients. In order to understand and control of this transport, diagnostic instrumentation was developed to study the structure and magnitude of microturbulent processes and to identify the origins of plasma loss. This review will cover the primary instruments that have been developed to measure fluctuating quantities associated with transport: density, δn, temperature, δT, potential, δφ, and magnetic field, δB, and their correlations. The methods discussed are Langmuir probes, heavy ion beam probes, collective and phase scintillation scattering, beam emission and ordinary spectroscopy, reflectometry and enhanced scattering, electron cyclotron emission, and several magnetic methods. The emphasis here will be on techniques applicable to microturbulence whose scale length is greater than the ion cyclotron radius and much less than the minor radius. Limitations and strengths of each method will be described and compared. Techniques will be discussed for estimating fluctuation intensities and wave number spectra or, equivalently, multipoint correlations in radial, poloidal, and toroidal directions. Large scale or magnetohydrodynamic-like plasma oscillations are typically studied with tomographic techniques or external probes and are reviewed elsewhere.
Analysis of homogeneity of elements distributions in the FeAl intermetallic samples performed by mass analyzer of mass-reflectron-type with laser ionization of investigated materials
Authors: Mróz W. , Antonik A. , Norek P. , Prokopiuk A. , Jóźwiak S. , Bojar Z. , Bystrzycki Z. , Kirillov N. S. , Mamyrin B. A. , Schmikk D. V.
Published: July 2002

The contribution presents results of the measurements of the homogeneity of the main elements of the FeAl intermetallic alloys as well as the distributions of the light contamination: H, C, O, in investigated samples. The program used for the data processing gives us the possibility of the layer analysis (inside the target material) of the element distributions. Such layer analysis differentiates between the light elements absorbed on the surface of the investigated sample and the same elements contributed as the components of the alloy. The measurements were performed by means of the ion analyzer of mass-reflectron type (MR) with laser ionization of the investigated materials. This method consists of the separation of ions of different mass-to-charge ratios Mi/Z. This separation is accomplished by the time-of-flight method, equivalent to the various arrival times of ions with different Mi/Z ratios and similar energy. The laser power density was chosen during the measurements in such a way that the majority of produced ions had a charge state Z=1. In this case, the time-of-flight method makes possible the separation of ions with different masses Mi. The high mass resolution (M/ΔM∼1000) of the MR makes it very useful for investigations of the chemical compositions of alloys. It enables a registration of all elements from hydrogen up to uranium with sensitivity of about 1 ppm.
Integrated scatter plate and projection lens for scatter plate interferometer
Authors: Räsänen Jari T. , Peiponen Kai-Erik , Abedin Kazi Monowar , Tenjimbayashi Koji , Eiju Tomoaki , Matsuda Kiyofumi
Published: July 2002

Scatter plate interferometers provide a precise method to test the quality of concave mirrors. In this article we describe a method to integrate a scatter plate and a projection lens into a single binary micro-optical element, which is a crucial part of the scatter plate interferometer. We have designed an integrated element with the aid of a computer and fabricated it using the e-beam lithography method. We present experimental verification and some computer simulation results.
A new toroidal electrostatic analyzer and application to surface analysis
Authors: Nishimura Tomoaki , Ikeda Atsushi , Kido Yoshiaki
Published: July 2002

A new toroidal electrostatic analyzer (ESA) configuration for medium energy ion scattering has been designed and fabricated for structural analysis of surfaces. The present analyzer has a wide interelectrode distance of 16 mm and an energy range of 10% of the pass energy at a constant applied voltage. The analyzer is mounted horizontally on a turntable and accepts ions scattered within a well defined angular range. To get a good energy resolution, we employed a photon-counting image acquisition system (PIAS: Hamamatsu Photonics) with spatial resolution of 40–50 μm, combined with a three-stage microchannel plate. The electric fields of the toroidal ESA including the fringing fields were calculated by a finite element method. Ion trajectories through the analyzer were calculated using a Monte Carlo method. In this way, the optimum conditions of the geometry and size of the entrance and exit slits were determined. Our toroidal analyzer resolved three surface peaks from the Si isotopes (Si28, Si29, and Si30) clearly in the aligned spectra from H-terminated Si(001) and Si(111) and the energy resolution (ΔE/E) was estimated to be about 1×10−3. We describe the notable features of the new setup of the toroidal analyzer and show direct detection of H on Si(001) and Si(111) as a typical application.
A setup combining four-point probe and surface magneto-optical Kerr effect for measurements of magnetotransport and magnetic properties of ultrathin films in ultrahigh vacuum
Authors: Li M. , Wang G.-C.
Published: July 2002

A four-point probe, suitable for in situ surface resistance and magnetoresistance (MR) measurements of ultrathin films, is described. The four-point probe head is mounted and fixed at the center of an electromagnet with the probes perpendicular to the applied magnetic field direction. The ultrathin magnetic film sample can be rotated to face the probe and moved to make contact with the probe using the sample manipulator. The resistance and MR of the magnetic ultrathin film can be measured. At the same sample position, the hysteresis loops can be measured using the surface magneto-optical Kerr effect technique.
Electrochemical cell for in situ x-ray diffraction under ultrapure conditions
Authors: Koop Th. , Schindler W. , Kazimirov A. , Scherb G. , Zegenhagen J. , Schulz Th. , Feidenhans’l R. , Kirschner J.
Published: July 2002

An electrochemical cell has been developed for in situ x-ray diffraction from a working electrode under clean conditions equivalent to ultrahigh vacuum conditions of 5×10−10 mbar. The substrate crystals can be prepared ex situ and transferred into the cell under protection of ultrapure water within a few seconds. The oxygen level in the electrolyte is reduced by continuous N2 flow to less than 0.2% compared to that of a fresh electrolyte. This can be done while rotating the cell by 360° about the surface normal. The electrode potential is accurately measured at the position of the crystal using a Luggin capillary and a standard reference electrode. We demonstrate the performance of our cell by in situ synchrotron x-ray diffraction measurements on ultrathin Co layers electrodeposited on Cu(001) in an aqueous H2SO4/CoSO4 solution.
A combined long-term recording system for single-unit activity and neurotransmitter efflux of a brain slice
Authors: Sheu Y. H. , Young M. S.
Published: July 2002

A combined long-term measurement and recording system for neurotransmission research of brain slices is presented in this study. This system, based on the IBM PC or compatible computer, is capable of simultaneously measuring and recording both single-unit neural electropotential signals and the electrochemical signals of neurotransmitter efflux from the same neuron in a brain slice for long periods of time (time limited largely by hard disk capacity, 100 h or more not being unreasonable with contemporary hardware) using a single carbon microelectrode for both measurements. The combined long-term recording system uses a simple switching circuit to switch periodically the single microelectrode between two data acquisition subsystems, one for electrochemical data and one for electrophysiological data. The simple switching circuit separates the electrophysiological signals and electrochemical signals, overcoming the traditional interference problem caused by the two different measuring techniques. Software designed for the proposed system allows easy reconstruction of the full time course of the compressed measured data and easy, simultaneous display of both types of signals on the same time scale. On-line and recorded displays are available. Test results of a practical implementation of the proposed system verify that the combined long-term recording system meets actual requirements for electrophysiological and neurochemical research.
Transverse mode selection in a longitudinal continuous wave CO2 laser with a nominal power of 125 W
Authors: Al-Hawat Sharif , Al-Sadat Walid
Published: July 2002

A simple method was applied to select a fundamental transverse electro-magnetic mode (TEM)00 and a combination of TEM00+TEM10 modes using changeable cylindrical apertures inside the cavity close to the resonator mirrors. The experiment was carried out on a continuous wave CO2 laser, with an internal resonator 3.6 m long and 2.4 cm in diameter. The experimental results were compared with some calculations, and reasonable agreement was observed.
Effect of laser beam deflection on the accuracy of interferometer measurements
Authors: Lisitsyn I. V. , Kohno S. , Katsuki S. , Akiyama H.
Published: July 2002

The laser interferometry is a frequently used diagnostics for plasma density measurements. The measurements in plasmas with no density gradients allow direct correspondence of the fringe shift and plasma density along the laser line of sight. The change of the interferometer contrast due to scene beam deflection in plasmas with density gradients reduces the fidelity of interferometer measurements due to the change in the contrast of the fringe. The analytic expression for the maximum acceptable deflection angle is derived, analyzed, and compared to the experiment. Ways to improve the accuracy of interferometer measurements are proposed.
Charge-coupled devices as particle tracking detectors
Authors: Damerell C. J. S.
Published: July 2002

Following a few years after the invention of the charge-coupled device (CCD) in 1970, the discovery of charmed particles established the need for very high precision (few μm) detectors for tracking high energy charged particles. This review describes the work which has evolved over the past 20 years from these disconnected events, both as regards the application of increasingly refined CCDs to particle tracking (in particular as vertex detectors for identifying heavy flavor quarks and tau leptons), and also the advances in CCD detector design stimulated by these requirements. The lessons learned in this work should provide guidance for the construction of large arrays of CCDs or active pixel devices in the future in a number of areas of science and technology.
A modification of Ångström’s method that employs photothermal radiometry to measure thermal diffusivity: Application to chemical vapor deposited diamond
Authors: Feldman A. , Balzaretti N. M.
Published: July 2002

A modification of the one dimensional Ångström’s method that employs photothermal radiometry has been used to determine the longitudinal thermal diffusivity of three thin long bars of chemical vapor deposited diamond. Long bar specimens permit us to use a simple one-dimensional treatment that employs a linear least squares fitting procedure on both magnitude and phase data as a function of position, provided that the condition for ignoring end effects is fulfilled. Any differences in diffusivities obtained from magnitude data and from phase data can be attributed to surface heat losses; the values of diffusivity obtained with the two types of data showed no significant difference. The diffusivities obtained agree reasonably well with the mean values calculated from measurements made by several other laboratories on the same specimens. The heat source was the beam of an argon-ion laser focused onto the specimen surface either with a cylindrical lens to form a line focus or with a spherical lens to form a point focus. The differences in diffusivities obtained when a line source was used and when a point source was used were not statistically significant. A theoretical calculation indicates that the measurements on the specimen were made sufficiently far from the heat source for the one-dimensional treatment to be valid whether the line source or the point source were used: either source is expected to give the same result as was observed experimentally. A point source is preferable because the optical configuration of the experiment is simpler and larger signals are obtainable.
Temperature dependence of thermophysical properties of GaAs/AlAs periodic structure
Authors: Yu X. Y. , Chen G. , Verma A. , Smith J. S.
Published: July 2002

This work investigates the temperature dependence of GaAs/AlAs thin-film structures. Based on an ac calorimetric method, the thermal diffusivity of a 700 Å/700 Å GaAs/AlAs periodic structure is measured from 190 to 450 K. Thermal conductivity of the structure is derived from the experiment. The results demonstrate that the thermal conductivity/diffusivity of the structure are lower than its corresponding bulk values. The temperature dependence of its thermophysical properties is weaker than that of typical bulk III–V materials. Interface scattering is believed as the major cause of the observed reduction in thermal conductivity.
Multilaser and high spatially resolved multipoint Thomson scattering system for the JT-60U tokamak
Authors: Yoshida H. , Naito O. , Yamashita O. , Kitamura S. , Sakuma T. , Onose Y. , Nemoto H. , Hamano T. , Hatae T. , Nagashima A. , Matoba T.
Published: July 2002

The design and operation performance of the latest ruby Thomson scattering system for the JT-60U are described, which includes many novel approaches to attain the repetitive measurement of 60 spatial points with high resolution (8 mm), precision, and reliability especially for a high temperature and large size tokamak device. A beam combiner composed of a polarizer and a Faraday rotator for two ruby lasers has provided the transient measurement with the minimum time interval of 2 ms in burst operation and the multitime-slice measurement with the repetition rate of 0.5 Hz in normal operation. A newly developed photodiode array detector with high repetitive ability of 1 ms has been used for the high temperature core plasma measurement. A quantitative alignment of collection fiber object field has been utilized for the reliable ne profile measurement. By using Rayleigh scattering light, an in situ inferring method for a coated viewing window transmission has been found to have an effect on the precise correction of electron temperature Te and density ne underestimate for high Te plasmas. Making the most use of this diagnostic in a series of the recent JT-60U reversed shear experiments, the formation of an internal transport barrier even for electrons has been revealed from the clear existence of a steep gradient in both Te and ne profile shapes.
Neutral atom imaging (invited) (abstract)
Authors: Scime Earl E.
Published: July 2002

The space plasma diagnostic technique of neutral atom imaging has its origins in the charge exchange analyzers developed for magnetic fusion. In both the space and laboratory applications, the objective is to detect and measure the energy spectrum of energetic neutrals escaping from a confined plasma. From an experimental standpoint, the technical challenges are similar: detect neutral atoms in the presence of intense charged particle and radiation backgrounds. With sufficient information about the spatial distribution of the neutrals and the plasma ions, it is possible to determine the ion temperature along the instrument’s line-of-sight from the neutral atom energy spectrum. However, the push towards remote imaging of plasmas in the space community has led to the development of multiple line-of-sight neutral atom detectors. These instruments are essentially neutral atom cameras. While deconvolving the image information into ion temperature or ion density spatial profiles is problematic, neutral atom imagers can provide a unique perspective on the large-scale dynamics and structure of complex plasma systems such as planetary magnetospheres. The current status of space-based neutral atom imaging will be reviewed, including data from current missions and expectations for the IMAGE mission to be launched in early 2000. The IMAGE instrument will utilize a new technique involving submicron period, free-standing, transmission gratings that block ultraviolet light while permitting the passage of neutral atoms. It is possible to apply the techniques of neutral atom imaging to laboratory plasmas and a conceptual design for a three-dimensional, divertor neutral atom imager will be discussed.
Design of a cone-penetrometer-compatible probe and housing: The LLNL Raman probe
Authors: Brown S. , Milanovich F. P. , Kyle K. , Myrick M. L.
Published: July 2002

An integrated infinity-focused fiber optic probe designed for cone penetrometer and hand-held use and constructed at Lawrence Livermore National Laboratories is described and evaluated for performance. Throughput efficiency is calculated, distance dependence, background levels, and sensitivity to heterogeneity in samples is evaluated. Representative spectra are presented that make use of the major performance advantages of this probe, which are (a) background rejection, (b) low sample light fluences, (c) distant viewing, (d) sample penetration, and (e) sample averaging capability.
Monte Carlo simulation of hot electron charge transport in diamond under an internal electric field
Authors: Huang Z.-H. , Chung M. S. , Cutler P. H. , Miskovsky N. M. , Sullivan T. E.
Published: July 2002

Charge transport in diamond is studied using the Monte Carlo method, in which the scattering of electrons by phonons is considered stochastically. It is assumed that electrons are injected into the diamond conduction band with an initial equilibrium energy distribution and they are then accelerated by the internal field subject to phonon scattering. It is found that the electron energy distribution is independent of the field up to ≂0.1 V/μm. For larger fields, ‘‘hot’’ electron transport is predicted, i.e., the distribution shows a tail which depends on the internal field and the thickness of the diamond film. It implies that if electron field emission is from the conduction band in a diamond film, the transport and the energy spectrum of the emitted electrons should exhibit hot electron features.