bluuebunny/crossref_metadata_2025 huggingface dataset:
An all solid-state magnetic pulse compressor with amorphous metals for pumping a repetition-rated KrF excimer laser
Authors: Tanaka Hiroshi , Obara Minoru
Published: July 2002

We have developed an all solid-state exciter consisting of a magnetic pulse compressor with a transfer energy of 10 J/pulse approximately for KrF discharge lasers. The magnetic pulse compressor was operated with an energy transfer efficiency of 65% at a repetition rate frequency of 40 pps. A KrF excimer laser excited by the all solid-state exciter was operated with an average laser power of 2.7 W. Four types of amorphous metals as a magnetic core material were experimentally compared in terms of their magnetic induction and magnetic loss so as to be used in the all solid-state exciter.
Effect of spatial and velocity distributions on the generation of ion cyclotron emission from fusion products
Authors: Dooling J. C. , Sperling J. L. , Moses K. G.
Published: July 2002

Cyclotron motion of fusion products (FPs) or other superthermal ions has been shown theoretically to generate ion cyclotron emission (ICE) which is strongly dependent upon the ratio of ion velocity to the background Alfvén velocity [C. Chu and J. L. Sperling, J. Plasma Phys. 40, 40 (1988)]. This initial work described ICE assuming a uniform plasma embedded in a constant magnetic field; in addition, a delta function velocity distribution was used for the superthermal ions. These assumptions lead to ICE spectra which exist as a series of delta functions at harmonics of the fundamental cyclotron frequency of the superthermal species. It is shown here that source distributions with finite spatial extent such as a higher order parabolic model ((S(R)=S0{1−[(R−R0) /a]2}N,N=6–10)), in conjunction with the magnetic field profile ((B(R)=B0R0 /R)), lead to a significant broadening of the ICE spectra; this is the case even for a delta function velocity distribution. The spectra are further modified when realistic superthermal distributions are employed in the model. In the latter case, a Green’s function approach is employed to calculate the spectra. Results of the ICE calculations are presented for FP protons.
Calculated collective Thomson scattered spectra from tokamak plasma with non-Maxwellian ions
Authors: Rhee D. Y. , Machuzak J. S. , Woskov P. P. , Cohn D. R. , Myer R. C.
Published: July 2002

Theoretical scattered spectra from energetic ions in tokamak plasmas (TFTR and Alcator C-Mod) are calculated. A new numerical code that calculates the collective Thomson scattered spectrum with a completely arbitrary distribution function was developed to model scattered spectra in ICRF heated and DT burning plasmas. Calculated spectra for nonthermal minority He3 ions in ICRF heated plasmas along with results from Maxwellian distributions are shown.
Nuclear diagnostic techniques at Nova (abstract)
Authors: Cable Michael D.
Published: July 2002

Nuclear diagnostic techniques play an ever increasing role in the characterization of final fuel conditions for ICF implosions as target sizes increase. With today’s high neutron yields, many neutron-based measurements can be used to determine final core conditions such as fuel density and temperature, fuel and pusher areal densities, hot spot size and shape, and implosion characteristics such as neutron emission time and burn history. Experiments can be designed to emit neutrons or other nuclear reaction products from which measurements allow the study of processes such as charged particle slowing in plasmas or fuel-pusher mixing. An overview of work in progress at the Lawrence Livermore National Laboratory Nova Laser Fusion Facility will be presented, with particular emphasis on techniques involving the measurement of secondary and tertiary neutron energy spectra. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.
ITER operation and diagnostics (invited)
Authors: Mukhovatov for ITER Team V. S.
Published: July 2002

ITER plasma and device parameters as well as ITER research program and operational plan are described. A set of plasma diagnostics for a feedback control of plasma parameters and for experimental studies in ITER is discussed.
Simulation of ion beam diagnostics on extraction geometry ion diodes (abstract)
Authors: Haill T. A. , Mehlhorn T. A. , Bieg K. W. , Cuneo M. E.
Published: July 2002

Lithium ion beams are a prime driver candidate for light-ion inertial confinement fusion. LEVIS/LIBORS lithium ion sources are being developed for the HELIA extraction ion diode. Beam diagnostics to measure beam intensity, energy, composition, and purity are also being developed. Difficulties in diagnosing the beam are encountered because the diagnostics cannot interfere with the plasma forming and ionizing lasers of the LEVIS/LIBORS source. Efforts to model the transport of lithium ions in the self- and applied-magnetic fields of the HELIA ion diode as well as the calculation of beam diagnostics using the PICDIAG computer code are described. The results directly affect the choice and design of diagnostics to be fielded. Results of the simulations are presented and comparisons with available experimental data are emphasized. This work was supported by the U.S. Department of Energy under contract No. DE-AC04-76DP00789.
Ion impact ionization effects in a 1-D radiation/hydrodynamics code (abstract)
Authors: Dukart R. J. , Mehlhorn T. A.
Published: July 2002

Targets irradiated by ion beams on PBFA II emit characteristic inner shell and thermal line radiation. The inner shell Kα spectra show clearly resolved satellite features which are consistent with thermal ionization of the outer shell electrons (J. E. Bailey et al., submitted to Laser and Particle Beams). This satellite spectra can be used as a diagnostic for particle beam-target interactions, and as a temperature diagnostic [E. Nardi and Z. Zinamon, J. Appl. Phys. 52, 7075 (1981)]. Interpretation of such spectra requires a complete hydrodynamic calculation. Thermal K-shell radiation can also be used as a temperature and density diagnostic if ion impact ionization and excitation are properly accounted for. To accomplish this simulation we have developed a collisional-radiative-equilibrium (CRE) model which includes the effects of ion impact ionization and are modifying a 1-D radiation/hydrodynamics code to include the CRE ionization balance model. Details of the models, the significance of non-LTE effects and ion impact ionization, and simulations of the experiments will be presented. This work was supported by the U.S. Department of Energy under contract No. DE-AC04-76DP00789.
Design of a neutron penumbral-aperture microscope with 10 μm resolution
Authors: Ress D. , Lerche R. A. , Ellis R. J. , Lane S. M.
Published: July 2002

We are currently designing a 10 μm resolution neutron penumbral-aperture microscope to diagnose high-convergence targets at the Nova laser facility. To achieve such high resolution, the new microscope will require developments in three areas. First, we have designed thick penumbral apertures with extremely sharp cutoffs over a useful (≊100 μm) field of view; fabrication of such apertures appears feasible using gold electroplating techniques. Second, the limited field of view and required close proximity of the aperture to the target (2 cm) necessitates a durable mounting and alignment system with ±25 μm accuracy. Finally, a neutron detector containing 160 000 scintillator elements is required. We plan to utilize clad-scintillator elements in this array, bonded together with a high-Z paint to eliminate recoil-proton crosstalk. Two schemes are under consideration for readout of this large array.
Iron concentration measurements on TFTR using charge exchange excited lines of helium-like iron in the 200–700 Å region
Authors: Stratton B. C. , Fonck R. J. , Johnson D. W. , Park H. , Ramsey A. T. , Synakowski E. J. , Timberlake J.
Published: July 2002

Charge exchange excited lines of Fe23+ in the EUV region have been observed on the TFTR tokamak. These lines are emitted by Δn=1 transitions between levels with n=6–10 following charge exchange recombination of He-like iron ions (Fe24+) with deuterium atoms injected by neutral beams. Iron concentrations are obtained by modeling the line brightnesses using a beam attenuation code and iron charge exchange cross sections. The results are in good agreement with iron concentrations obtained from impurity transport code modeling of the brightnesses of EUV electron impact excited lines, demonstrating that charge exchange excited lines may be reliably used to measure local metallic impurity concentrations.
Application of the results of carbon pellet modeling to the problem of plasma penetration
Authors: Vahala L. L. , El Cashlan A. G. , Gerdin G. A. , Parks P. B.
Published: July 2002

The assumptions of the evaporation model for low-Z pellets interacting with magnetic fusion plasmas developed by Parks are tested. These assumptions are that the vapor density profile in the region adjacent to the pellet surface falls off with radial distance as r−α, where 5<α<6, and that the ionization time for the transition between charge states τzi is much less than a flow time for the vapor in this same region τf (i.e., for r<∼3 sonic radii). The first assumption is tested by solving a two-parameter eigenvalue problem for the evaporation cloud in the region interior to the sonic radius; the results are found to be consistent with the low-Z evaporation model. The second assumption, that τzi ≪ τf, is tested at the sonic radius using the results from atomic physics and the low-Z evaporation model. It is found that indeed τzi ≪ τf for plasmas with parameters close to thermonuclear conditions (e.g., CIT), but not for those of smaller Tokamaks such as TEXT. The results of pellet penetration calculations for the conditions of the carbon-pellet injection experiments into TEXT and low-density TFTR plasmas are presented that show better agreement with experiment if the shielding fraction is calculated at each step of the pellet-penetration calculation, the effect of ionization is ignored, and if the effect of possible uncertainties in the background plasma parameters is included.
Visible charge exchange spectroscopy at JET (abstract)
Authors: von Hellermann M. G. , Mandl W. , Summers H. P. , Weisen H. , Boileau A. , Morgan P. D. , Morsi H. , Koenig R. , Stamp M. F. , Wolf R.
Published: July 2002

Recent developments and results of the JET CXRS diagnostic are reported. The measurements of radial profiles of ion temperatures and densities are based on CXR spectra of fully stripped ions of either carbon or beryllium. Considerable effort has been expended in ensuring consistency between radial profiles of low Z impurity densities and those from other diagnostics. The contributions of the main light impurities are used to reconstruct radial profiles of Zeffwhich can be compared with Abel-inverted signals from visible bremsstrahlung or soft x-ray emission. Active Balmer-Alpha spectroscopy (ABAS) is being introduced as a diagnostic tool providing data on local magnetic fields, neutral beam densities, and dilution factors. The effects of collision-energy-dependent CXR cross sections on observed CXR spectra are calculated. Corrections for the values of deduced ion temperatures, toroidal velocities, and impurity densities are discussed for the case of plasmas with high ion temperatures and high toroidal rotation velocities. Some recent results of the JET 1989 operation illustrating the CXRS diagnostic potential are given.
Motional Stark effect polarimetry for a current profile diagnostic in DIII-D (abstract)
Authors: Wróblewski D. , Burrell K. H. , Lao L. L. , Politzer P. , West W. P.
Published: July 2002

Motional Stark effect produces large net linear polarization of Hα emission from neutral beams in tokamaks. Measurement of the polarization direction permits determination of the local magnetic field pitch angle. Design of a single point, spatially scannable, high-sensitivity polarimeter installed on DIII-D is described. Excellent signal-to-noise ratio with good temporal and spatial resolution was obtained in preliminary measurements of magnetic field pitch angle.
Fast reciprocating probe system used to study edge turbulence on TEXT
Authors: Rhodes T. L. , Ritz Ch. P. , Bengtson Roger D. , Carter K. R.
Published: July 2002

We have combined several techniques in a new and unique way that allows us to measure edge profiles (ne, Te, and φp), their gradients, fluctuations (ñe and φ̃f), and fluctuation-induced heat and particle transport on a single discharge of the TEXT tokamak. To do this we utilize a fast reciprocating probe drive, a four pin Langmuir probe array, and suitable data analysis techniques. With this method, many of the quantities of interest to turbulence studies can be obtained on one discharge. Scaling studies of fluctuations versus free-energy drives (gradients) are easily carried out and data from such a scan are presented. This method also allows a study of changes to the profiles, fluctuations, and transport caused by perturbations to the plasma (ECH, pellets, etc.) during a single discharge.
A toroidal projection CO2 laser imaging system for PBX-M
Authors: Nazikian R. , Grek B.
Published: July 2002

A new interferometric technique designed for PBX-M exploits the uniformity of density fluctuations along field lines to render a two-dimensional image of large scale density fluctuations in the edge region of the plasma. The method is capable of producing local measurements of density fluctuations in the low wave number range where standard scattering techniques lack spatial resolution.
Magnetic pitch angle measurements on TEXT using laser-enhanced attenuation of a Li beam
Authors: West W. P. , McChesney J. , Thomas M. K. , Yang X. Z.
Published: July 2002

The polarization of the π component of the Zeeman split Li2P–2S transition allows a direct spectroscopic measurement of the local magnetic pitch angle. Li atoms are injected radially into TEXT as a 95 keV beam and the intensity of the transmitted beam is detected. A polarization-modulated, cavity-dumped dye laser, tuned into resonance with the π line, is injected collinearly with the beam. Laser excitation of the beam results in an enhanced beam attenuation. Time-resolved detection of the transmitted Li beam allows determination of the local magnetic pitch angle. Details of the system and results of recent measurements will be discussed.
Development of a new q-diagnostic for TEXT
Authors: Valanju P. M. , Bengtson Roger D. , Ouroua A.
Published: July 2002

The vertically injected diagnostic neutral beam on TEXT provides a ripple trapped population of fast monoenergetic ions with a large v⊥ and small v∥. The neutrals formed in a second charge exchange collision of these fast ions leave the tokamak in a plane perpendicular to the local magnetic field. The direction of the B field can be accurately determined by locating this plane using a toroidal array of detectors looking for neutrals at the beam energy. This technique should allow full q-profile measurement for all plasma conditions with a time resolution less than 1 ms, and angular resolution better than 0.1°. We describe a series of experiments to establish the proof of principle and present details of the design of a 40-channel detector array for application on TEXT-Upgrade.
Application of modern optical fiber technology to the study of plasmas of closed divertors and pump limiters in reactor-relevant conditions
Authors: Klepper C. C. , Simpkins J. E. , Hills D. L. , Mioduszewski P. K. , Moyer R. A. , Gray D. , Dippel K. H. , Pospieszczyk A.
Published: July 2002

Modern optical fibers, through control of the purity of the materials and the tolerances of the core and clad diameters, provide very good light transmission in the visible and near-ultraviolet regions of the spectrum. This makes it possible to use them in place of traditional optical systems without large losses in light intensity at the detectors. In addition, the same control of the quality of the fiber materials, coupled with novel jacket materials, makes it possible to use the fibers inside vacuum chambers and at elevated temperatures. A fiber-optic bundle recently installed in the TEXTOR tokamak is an example of the use of modern fiber technology. The bundle was made of 80 100-μm fibers held together with a polyimide organic material that has good outgassing specifications up to 400 °C. This fiber bundle has been used for recent measurements of the recycling in the throat region of one of the blades of the Advanced Limiter Test-II (ALT-II) belt pump limiter. Another system presently under design and testing employs individual fibers that are gold plated. These fibers are fed through holes in a vacuum blank flange and silver soldered to the flange. This system is designed to transmit the light from the strike point inside the closed divertor of the DIII-D tokamak out to a spectrometer. There, the spectral profile of the Hα line is analyzed to determine the energy distribution of the recycling particles.
Recent progress in space- and time-resolved x-ray spectroscopy of laser-produced plasmas (abstract)
Authors: Young B. K. F.
Published: July 2002

New diagnostic techniques have provided measurement of relatively gradient-free x-ray spectra from high-powered laser-produced plasmas. Simultaneously space- and time-resolved x-ray spectra were measured from a variety of microdot plasmas using an array of multiframe, imaging, electronically gated x-ray crystal spectrometers with 100 ps time resolution. A multiframed, multicolored gated x-ray pinhole camera provided measurement of the plasma uniformity. A four-frame holographic interferometer was used to measure the electron density profile. Conventional x-ray streaked crystal spectrographs, spatially resolved x-ray (film) spectrometer, and pinhole cameras supplemented these new diagnostics. The instruments allow detailed studies of both the population kinetics of highly charged ions in dense plasmas and the hydrodynamics of laser-produced plasmas for the first time. The new diagnostics are described including data from ongoing experiments. Work was performed in part under the auspices of the U.S. Dept. of Energy by LLNL under Contract No. W-7405-Eng-48.
A new and simple time-of-flight mass filter for cw ion sources
Authors: Cowen K. A. , Coe J. V.
Published: July 2002

A mechanically and electronically simple device for recording time-of-flight mass spectra with continuous (cw) ion sources is demonstrated. The principle of operation involves modulation of a cw ion beam by manipulation of beam energy as opposed to deflection across an aperture. The technique works by tagging pulses of ions within a cw ion beam with higher beam energy and separating them from the cw ion beam by virtue of their higher beam energy. Configurations as a mass filter or to record time-of-flight spectra in real time are reported. The technique might find use for mass analysis at the end of an existing cw ion beam or to produce a high-frequency, high-intensity, mass selected, pulsed ion beam at a short distance from a cw ion source.
Mathematical analysis of a four-point conductivity probe for cylindrical samples
Authors: Marshall S. L. , Redey L.
Published: July 2002

The mathematical analysis of a device for measurement of the conductivity of cylindrical samples is given. This analysis involves calculation of the geometrical factor by evaluating Fourier series of circular and cylindrical harmonics. The results derived are applicable to a wide range of cylindrical samples shapes, including the limiting cases of thin disks and infinitely long rods. Full consideration is given to the finite size of current-bearing electrodes and deviations from two-dimensional current distribution that arise when the electrode width is less than the length of the cylinder. The range of sample geometries in which these deviations are significant is determined.
A remote pressure sensing technique by using the photothermal bending effect
Authors: Hane K. , Inahara Y. , Goto T.
Published: July 2002

Photothermal technique for sensing pressure in a cell is reported. The pressure is monitored from the frequency change of the vibration of the cell itself. The vibration is generated by the photothermal bending effect caused by the chopped laser irradiation, and it is sensed by the deflection of the probe laser beam. The proposed technique is noncontact, and thus it will be useful for remote pressure measurements in hostile environments.
High-flux beam source of fast He*(21S) atoms in the 0.2–5 eV energy range
Authors: Ferkel H. , Feltgen R. , Pikorz D.
Published: July 2002

A very intense source of metastable helium atoms has been obtained using two helium discharges in series: a high-pressure arc, which can only produce He*(23S) beams, sustains a low-pressure arc where the He*(21S) atoms are generated. This double arc source yields total metastable helium fluxes of several 1015 s−1 sr−1. The singlet component reaches about 30%, and the kinetic energy ranges from 0.2 to 5 eV corresponding to velocities from 3000 to 16000 m/s. The velocity distribution can be varied by the pressure and the current in the arcs.
A low-cost filterbank spectrometer for submm observations in radio astronomy
Authors: Tauber Jan A. , Erickson Neal R.
Published: July 2002

We describe the design and construction of a filterbank of novel design which uses sections of coaxial transmission line as filter elements. This filterbank is a lower cost alternative to standard (solid-state) filterbank designs, and is appropriate in situations where large total bandwidths are required, as is the case for submillimeter observations of extragalactic objects.
Sample holder allowing precise orientation, azimuthal rotation, and high temperature flashes in ultrahigh vacuum
Authors: Venus D.
Published: July 2002

A sample holder that converts a linear coaxial motion to a precise azimuthal rotation, while still allowing precise orientation of the sample normal and very high temperature flashes (>2500 K) is described. This is accomplished using large (1 (1)/(2) in.) diameter gears and ball bearings. One gear is bored out to provide space both for a sample mounting platform capable of precise orientation of the sample normal, and for a sample heating assembly. The sample cools to close to room temperature in ten minutes, after which the original sample orientation is regained, to within 0.2°.
Transport and magnetic properties of in situ grown thin-film La–Y–Ca–Mn–O
Authors: Sun J. Z. , Krusin-Elbaum L. , Parkin S. S. P. , Xiao Gang
Published: July 2002

We report a large magnetoresistance in in situ grown La0.60Y0.07Ca0.33MnOx thin films made at a low substrate temperature of 600 °C without postdeposition annealing. The zero-field resistivity peaks around 120 K. The resistivity peak is reduced by two orders of magnitude by a 6 T field. Comparison of transport and magnetization data reveals a correlation of conductivity versus magnetization below the ferromagnetic transition temperature, which may suggest a double-exchange-based conduction mechanism. Above the ferromagnetic transition at low fields, a quadratic dependence of conductivity on magnetization is found, consistent with a spin-scattering-limited conductivity.
Gundestrup: A Langmuir/Mach probe array for measuring flows in the scrape-off layer of TdeV
Authors: MacLatchy Cyrus S. , Boucher Claude , Poirier Deborah A. , Gunn James
Published: July 2002

Gundestrup is a Langmuir/Mach probe array which measures the flow velocity in the scrape-off layer of Tokamak de Varennes (TdeV). It is based on the concept of a Mach probe where presheaths extending upstream and downstream from the probe, parallel to the magnetic field, attract charge to a circular array of collecting pins. The polar distribution of ion saturation currents to the circular array is used to compute the components of flow velocity in the plasma. With Gundestrup, there is an assumed flow perpendicular to the magnetic field as well as parallel to it. Equations representing the collection of charge by individual pins on the probe are presented and sample flow patterns from the scrape-off layer are shown.
In situ calibration of neutron detectors on TEXTOR
Authors: Hoenen F. , Euringer H. , Bosch H. S. , Alevra A. V. , Klein H. , Delvigne T.
Published: July 2002

Neutron yield measurements are performed at the Jülich Tokamak experiment TEXTOR with different detectors located around the Tokamak and on center axis above the shielding roof. Due to the large structure of the machine and the extended diagnostic equipment, both virgin and scattered neutrons are detected. To prepare a Bonner sphere of appropriate response, the shape of the degraded neutron spectrum was determined with a spherical ionization chamber in situ. These investigations have been enlarged under quasi-real conditions at the accelerator facility of the Physikalisch-Technische Bundesanstalt in Braunschweig with a set of Bonner spheres used as a spectrometer. For the calibration the plasma neutron source is simulated by two point sources, 238Pu/B and 252Cf. The sources are moved around the TEXTOR vessel along the position of the magnetic axis.
Error analysis for charge exchange recombination spectrometer measurements of ion temperature
Authors: Bell R. E. , Johnson D. W. , Stratton B. C. , Synakowski E. J.
Published: July 2002

A two-dimensional intensified photodiode array is used to measure charge exchange recombination emission in the TFTR. The noise of this detector has been characterized to provide a better estimation of the error bars associated with ion temperature measurements. Contributions to the measured signal include a dc level offset, an integrated dark signal, and the actual photon signal. In addition to photon noise, there is a significant readout noise. The analysis was complicated by a nonlinear response of the readout circuitry. The detector output is linearized and the pixel-to-pixel gain variation is removed with a white field correction. The noise has been modeled over a range of integration times of the detector and gains of the intensifier, allowing an estimation of the uncertainty in the measurement at each pixel, and therefore its appropriate weight in the fitting function.
Receiver calibration of the JET fast ion and alpha particle diagnostic
Authors: Machuzak J. S. , Woskov P. P. , Bindslev H. , Comiskey M. , Fessey J. , Hoekzema J. A. , Hughes T. P. , Orsitto F.
Published: July 2002

A collective Thomson scattering diagnostic is being implemented at JET to diagnose the velocity distribution and density of alpha particles and energetic ions. This diagnostic consists of a number of major subsystems including: a high-power 140-GHz gyrotron, a 32-channel 12-GHz bandwidth heterodyne receiver, efficient corrugated waveguide systems, variable polarizers, and in vacuum beam steering mirrors. Proper calibration of these subsystems for signal level losses, positioning, and polarization is imperative for the successful operation of the diagnostic and to facilitate the interpretation of the scattered data. A low-power Gunn oscillator was used to verify the polarization rotation induced by the seven miter bends in the receiver transmission line. The full bandwidth receiver front end losses, including the sapphire tokamak vacuum window, were initially calibrated by using the hot tokamak vessel wall as a blackbody source at approximately 310 °C. Background ECE measurements will be presented.
The evanescent neutron wave diffractometer: On the way to surface sensitive neutron scattering
Authors: Dosch H. , Al Usta K. , Lied A. , Drexel W. , Peisl J.
Published: July 2002

A novel experimental technique to observe the Bragg scattering of evanescent neutron waves is presented. The so-called EVA diffractometer, installed at the high-flux reactor of the Institut Laue-Langevin, allows the identification of neutron scattering from single crystal surfaces. We discuss the experimental setup, intensity, and resolution considerations and some first Bragg scattering signals from evanescent neutron waves excited at CaF2, InP, and MnF2 single crystal surfaces. The experimental results are discussed within the framework of the so-called distorted wave Born approximation and within a dynamical scattering theory. The limitations of both theoretical approaches to describe the Bragg scattering of evanescent neutron waves are indicated.
Novel fast spectroscopic rotating-polarizer ellipsometer
Authors: Straaijer A. , Verbruggen M. H. W. , de Nijs J. M. M. , Brongersma H. H.
Published: July 2002

A fast spectroscopic rotating-polarizer ellipsometer has been developed. The machine is equipped with a cascade arc as a light source, a 1024 element linear photodiode array for parallel data processing, and a fast data acquisition interface that allows for hardware averaging of the data prior to transmission to the controlling computer. The ellipsometer has been mounted on an ultrahigh vacuum chamber. As an example the sublimation of an As cap layer from ErAs/GaAs(100) was studied in situ. Fourier spectra in the range from 1.5 to 4.0 eV with an accuracy and precision better than 2×10−2 and 3×10−4, respectively, are obtained within 1.7 s. The spectral response of the photodiode array is presently the factor limiting the energy range.
Construction of a convenient multiple-purpose spectrophotometer system for measurements of the emission (and/or its excitation) and absorption spectra at a temperature ranging from 10 up to 313 K
Authors: Nagamura T. , Ibuki K. , Nakayama T. , Hamanoue K.
Published: July 2002

In order to enhance research in the field of low-temperature photophysics or photochemistry, a convenient multiple-purpose spectrophotometer system was constructed. This system enabled us to measure the emission (and/or its excitation) and absorption (even under steady-state photolysis) spectra of liquid and solid samples at a temperature ranging from 10 up to 313 K. The spectral resolutions (or the peak separations) were estimated to be ∼0.10–0.31 and ∼1.0–7.3 nm for an emission and its excitation spectra, respectively, recorded at a slit width between 0.05 and 0.5 mm. For an absorption spectrum recorded at a slit width of 0.5 mm, the resolution was still better than that recorded by a commercial spectrophotometer with a bandwidth of 0.2 nm. By recording a number of emission spectra (normalized by the excitation-light intensities at various excitation wavelengths), a contour mapping for the simultaneous intensity representation of the emission and its excitation spectra was also possible.
An inexpensive handmade grated integrator
Authors: Yamasaki Katsuyoshi , Tanaka Aki , Kimura Tomoko , Kajimoto Okitsugu
Published: July 2002

An inexpensive gated integrator is made entirely of parts available in an ordinary electronics shop. It works well to average the repetitive signals in observing the spectra of laser-induced fluorescence, multiphoton ionization, and so on. The minimum gate delay of 200 ns and the minimum gate width of 25 ns have been achieved with a rapid analog switch integrated circuit.
Infrared multiwavelength laser system for establishing a surgical delivery path through water
Authors: Pratisto H. , Ith M. , Frenz M. , Weber H. P.
Published: July 2002

A multiwavelength laser system designed for precise and efficient tissue ablation under water was realized by simultaneously coupling radiation of a holmium:YAG laser, emitting at a wavelength of 2.12 μm and an erbium: YSGG laser at 2.79 μm into the same zirconium fluoride (ZrF4) fiber. The beam paths of the two lasers were collinearly combined taking advantage of the dispersion of an Infrasil prism. Fast video flash photographs and laser induced pressure transients simultaneously recorded with a PVDF pressure transducer were used to study the dynamics of bubble formation at the submerged fiber tip. The bubble size and the bubble lifetime were determined as a function of the wavelength and the delay time between the two different laser pulses. The results indicate that the combination of 2 and 3 μm radiation takes specific advantage of both wavelengths and strongly enhances the ablation efficiency of tissue under water.
Shear flow in a two-dimensional Couette cell: A technique for measuring the viscosity of free-standing liquid films
Authors: Martin B. , Wu X-l.
Published: July 2002

A two-dimensional shear viscometer has been constructed and tested using free-standing liquid soap films. The viscometer, which is an analog of a three-dimensional Couette cell, consists of an inner rotating disk and an outer stationary ring. The viscosity of the liquid films can be reliably obtained by measuring either the transient response of the disk upon a stepwise increment of the applied stress on the disk, or by measuring the strain-stress relation in the steady state. The design can be easily modified to accommodate other types of flow which are useful for investigating hydrodynamic and rheological behavior in a variety of thin films, such as liquid crystal and polymer films.
A laser device for perforating materials
Authors: Domankevitz Yacov , Kwok Hoi S. , Copley John A.
Published: July 2002

A Nd:YAG laser device for perforating materials was developed. The device generates a modified temporal pulse structure of both free-running and Q-switched laser irradiation. This modified structure enhances drilling efficiency by a factor of 2 compared to free-running irradiation and is achieved by mechanical blow-off of preheated material. Such a device is well suited for compact portable field applications.
A low coherence ‘‘white light’’ interferometric sensor for eye length measurement
Authors: Wang D. N. , Chen S. , Grattan K. T. V. , Palmer A. W.
Published: July 2002

This article discusses the use of low coherence interferometric techniques, employing the so-called ‘‘white light interferometer,’’ for axial eye length measurement. This system utilizes two Michelson interferometers, each of which locates one of the surfaces of the eye, the cornea and the retina, respectively, and thus a simultaneous determination of the two surface positions of the eye gives the value of eye length. The experimental results carried out on a simulated eye are presented, showing that the proposed system is simple, easy to align, suitable for measuring different kinds of eyes, tolerant to transverse eye movement, and worth further exploration.
An ellipsoidal mirror time-of-flight photoelectron energy analyzer
Authors: Hansch P. , Norby J. R. , Evans S. H. , Van Woerkom L. D.
Published: July 2002

A novel time-of-flight photoelectron energy analyzer that uses an electrostatic field to reflect and focus electrons has been designed and built. By means of high quality ellipsoidal grids, photoelectrons can be collected at high efficiency and focused onto a detector. The problems of space charge and extended electron sources are addressed in the context of the ellipsoidal mirror analyzer. This versatile spectrometer analyzes single and multiphoton ionization processes and operates over a wide energy range. The experimental data demonstrate the high collection efficiency. We have obtained good spectra at target densities of less than 10−7 Torr. For six-photon ionization of xenon a gain of 36 has been achieved.
Double-bracelet resonator Helmholtz probe for NMR experiments
Authors: Serfaty Stephane , Darrasse Luc , Kan Siew
Published: July 2002

A Helmholtz probe made from two parallel-plate bracelet resonators for nuclear magnetic resonance imaging experiments possesses a number of advantages such as high unloaded quality factor, absence of tuning capacitors, low cost, accessibility, easy to design, patient comfort, etc. Energy transfer to and from the probe is assured by a one-turn loop magnetically coupled to the coils, disposing the pair of current feed lines needed for conventional Helmholtz coils. Design procedure and a practical example are given, showing good agreement between calculated and experimental results.
Improved optical diagnostics for the NOVA laser
Authors: Fernández Juan C. , Berggren Ralph R. , Bradley Keith S. , Hsing Warren W. , Gómez Camilo C. , Cobble James A. , Wilke Mark D.
Published: July 2002

This paper describes three diagnostics detecting optical scatter from NOVA laser targets. Detecting such scatter can help to understand instabilities in laser plasmas and to characterize such plasmas, particularly hohlraum plasmas. These diagnostics are the full aperture backscatter station (FABS), presently being built; the oblique scatter array (OSA), just starting operation; and the axial imager, also just starting operation. FABS will allow imaging at high resolution of Brillouin and Raman backscatter. The OSA provides a quantitative measurement of Brillouin and Raman scatter in many directions. The axial imager allows high-resolution imaging of Brillouin, two-plasmon decay and Raman scatter emitted toward the direction of the symmetry axis of the NOVA laser beams.
Fast and precise thermoregulation system in physiological brain slice experiment
Authors: Sheu Y. H. , Young M. S.
Published: July 2002

We have developed a fast and precise thermoregulation system incorporated within a physiological experiment on a brain slice. The thermoregulation system is used to control the temperature of a recording chamber in which the brain slice is placed. It consists of a single-chip microcomputer, a set command module, a display module, and an FLC module. A fuzzy control algorithm was developed and a fuzzy logic controller then designed for achieving fast, smooth thermostatic performance and providing precise temperature control with accuracy to 0.1 °C, from room temperature through 42 °C (experimental temperature range). The fuzzy logic controller is implemented by microcomputer software and related peripheral hardware circuits. Six operating modes of thermoregulation are offered with the system and this can be further extended according to experimental needs. The test results of this study demonstrate that the fuzzy control method is easily implemented by a microcomputer and also verifies that this method provides a simple way to achieve fast and precise high-performance control of a nonlinear thermoregulation system in a physiological brain slice experiment.
A soft x-ray octadecyl hydrogen maleate crystal spectrograph
Authors: Fan P. Z. , Fill E. E. , Tietang Guan
Published: July 2002

A crystal spectrograph is described which can be used to investigate laser-produced plasmas in the region of soft x rays at wavelengths of up to 60 Å. The spectrograph uses an octadecyl hydrogen maleate crystal with a 2d of 63.5 Å, combined with a very thin carbon filter (3000 Å thick). As examples of its application, soft x-ray spectra in the range of 43–51 Å from laser plasmas of Si and Cu are presented. A spectral resolution of λ/Δλ=1100 is deduced from the spectra.
Hollow-anode plasma source for molecular beam epitaxy of gallium nitride
Authors: Anders A. , Newman N. , Rubin M. , Dickinson M. , Jones E. , Phatak P. , Gassmann A.
Published: July 2002

GaN films have been grown by molecular beam epitaxy (MBE) using a hollow-anode nitrogen plasma source. The source was developed to minimize defect formation as a result of contamination and ion damage. The hollow-anode discharge is a special form of glow discharge with very small anode area. A positive anode voltage drop of 30–40 V and an increased anode sheath thickness leads to ignition of a relatively dense plasma in front of the anode hole. Driven by the pressure gradient, the ‘‘anode’’ plasma forms a bright plasma jet streaming with supersonic velocity towards the substrate. Films of GaN have been grown on (0001) SiC and (0001) Al2O3 at 600–800 °C. The films were investigated by photoluminescence, cathodoluminescence, x-ray diffraction, Rutherford backscattering, and particle-induced x-ray emission. The film with the highest structural quality had a rocking curve width of 5 arcmin, the lowest reported value for MBE growth to date.
Quantitative spectroscopy of x-ray lines and continua in Tokamaks
Authors: Peacock N. J. , Barnsley R. , Lawson K. D. , Melnick I. M. , O’Mullane M. G. , Singleton M. A. , Patel A.
Published: July 2002

Crystal and synthetic multilayer diffractors, deployed either as flat Bragg reflectors, or curved, as in the Johann configuration, are used to study the spectrum of COMPASS-D and other tokamaks in the wavelength region of 1–100 Å. In this article, we concentrate on the measurement of absolute photon fluxes and the derivation of volume emissivities of the lines and continua in the x-ray region. The sensitivities of these instruments to absolute photon flux have been constructed ab initio from the individual component efficiencies, including published values of the diffractor reflectivities, which have been checked or supplemented by measurements using a double-axis goniometer or from line branching ratios. For those tokamak plasmas, where the elemental abundances and effective ion charge are documented, the x-ray continuum intensity itself has been used as a calibration source to derive absolute instrument sensitivity, in reasonable agreement with the ab initio method. In the COMPASS-D Tokamak, changes in the effective ion charge state, Zeff, have been derived for different operating conditions, from the absolute intensity of the continuum at ∼4 Å. From the radiances of the line emission, changes in the absolute level of impurities following “boronization” of the vacuum vessel have also been documented.
A low-temperature scanning confocal and near-field optical microscope
Authors: Göhde W. , Tittel J. , Basché Th. , Bräuchle C. , Fischer U. C. , Fuchs H.
Published: July 2002

A scanning near-field optical microscope equipped with an Al-coated glass fiber tip for operation in a He cryostat is described. The instrument is designed for fluorescence detection of nanoscopic particles (single dye molecules and nanocrystallites), and allows optical imaging and spectroscopy of surfaces or thin objects with subwavelength spatial resolution at low temperatures. A shear-force control loop keeps the probing fiber tip aperture at a constant distance, i.e., a few nanometers away from the sample. The shear-force method results in a vertical stability of better than 2 nm. For light collection and confocal imaging, a transmission objective with a high numerical aperture is operated inside the cryostat. For rapid sample inspection, and in cases where no high lateral resolution or topographic imaging is necessary, the instrument can also be used without a tip as a low-temperature conventional or confocal microscope, due to the large scan range of an improved scanner. Details and characteristics of the experimental setup as well as first results are presented. First shear-force images of test patterns taken at low temperatures down to T=22 K, as well as near-field optical fluorescence images of low concentrated sulforhodamine molecules dispersed in a thin polymer film at T=75 K and room temperature, are shown. With this instrument, confocal images of CdS nanocrystallites were taken at 20 K.
Universal metal ion source
Authors: Churkin I. N. , Volosov V. I. , Steshov A. G.
Published: July 2002

The metal ion source based on the magnetic trap with crossed fields (radial electrical and axial magnetic) is considered. This source formes plasma flow with magnetized heavy (metal) ions flowing along the longitudinal magnetic field. The self-supporting heavy ion discharge is existed in the source. The working substance is a cathode material which can be any conducting material. The operating principles and the features of the source are discussed. The plasma flows consisted of various metal ions (Cu, Ni, Ti) were experimentally obtained. The main parameters and the dependences of the titanium ion source are presented in detail. The typical parameters of this plasma flow are following: longitudinal velocity of 2–3×105 cm/s, ion transversal energy of 20–80 eV, average plasma density of 1012 cm−3; electron temperature of 40–60 eV; total ion current of plasma flow reach up to 3.6 A in pulse mode (discharge duration of 4–10 ms) of the source. The application of the source for plasma separation process is discussed.
Construction and characterization of a short pulse slit-jet source based upon the current loop-actuated design
Authors: Müller Thomas , Vaccaro Patrick H.
Published: July 2002

A pulsed slit-jet expansion source capable of generating moderate velocity-collimated pathlengths (∼1 cm) of rovibronically cooled target molecules for spectroscopic interrogation is described and characterized. Based upon the modification of a commercially available current loop-actuated design, this apparatus produces conductance-limited pulses of ⩽50 μs duration at repetition rates of up to 20 pps. The short temporal length of the emerging gas pulse greatly alleviates the demands imposed upon vacuum pumping systems and enables the use of higher stagnation pressures in the expansion process.
Improvements to the floating double probe for time-resolved measurements in pulsed rf plasmas
Authors: Smith Brian A. , Overzet Lawrence J.
Published: July 2002

A double probe is particularly well suited as a pulsed radio-frequency discharge diagnostic because it imposes minimal perturbation on the plasma, can follow the variations in the plasma potential easily, and requires no fixed potential reference from the plasma reactor walls. As pulsed discharges gain more attention in the semiconductor processing industry the double probe may be a more widely applicable diagnostic than the single probe, especially in plasma reactors which have insulating or semi-insulating walls. In order to use a double probe to make fast time-resolved measurements of electron temperature and ion density in a pulsed discharge, care must be taken to eliminate stray capacitance in the measurement circuitry. This difficulty was overcome by using optically isolated circuitry to achieve an ultimate time resolution of better than 500 ns. There must also be a reliable method for cleaning the probe. This was achieved by adding a third, reference electrode to serve as a needed ground reference. The probe was tested in an inductively coupled discharge reactor with a pulsed argon plasma.
A multipurpose scanning near-field optical microscope: Reflectivity and photocurrent on semiconductor and biological samples
Authors: Cricenti A. , Generosi R. , Barchesi C. , Luce M. , Rinaldi M.
Published: July 2002

A multipurpose scanning near field optical microscope (SNOM) operating at ambient pressure is described with the aim of characterizing the inner parts of biological molecules and any semiconductor or metal microstructure. Therefore, in addition to the requirements of reliability and mechanical stability we have carefully considered analyzing a sample with all available geometries for input/output of photons, in order to get as much information as possible. The SNOM unit consists of two separable cylindrical supports; the lower one contains the sample holder mounted on top of a piezoelectric scanner which is contained in a motor controlled x-y-z stage. A piezo-modulated stretched optical fiber with a few tens of nanometer pinhole and a shear-force apparatus mounted inside the top cylinder allow for topography measurements. The reflectivity of the sample can be measured by applying different methods: the sample can be illuminated on top by an external source, as well as by the optical fiber used for the detection of the reflectivity signal. An aperture in the lower cylinder allows for illumination of the sample on the back: in this case the fiber collects the evanescent wave induced at the top of the sample. Another aperture in the lower cylinder allows measurement of the reflected light which includes a contribution due to the interaction with the fiber. Also photocurrent experiments can be easily performed by illuminating the sample with the fiber and detecting the transmitted signal using a current–voltage converter mounted inside the top cylinder. A video-camera that can reach 170 enlargements is mounted on the top cylinder for positioning the fiber on particular regions of the sample. Reflectivity and photocurrent measurements have been performed on uncoated neurons, CsI compound, Au/GaAs, and PtSi/Si systems, reaching a resolution well below the diffraction limit.