bluuebunny/crossref_metadata_2025 huggingface dataset:
Perspectives of millimeter-wave collective Thomson scattering of confined alphas in ignited plasmas
Authors: Tartari U. , Nowak S. , Ramponi G.
Published: July 2002

Collective Thomson scattering on alpha density fluctuations in ignited plasma regimes is investigated with reference to a promising candidate source as the mm-wave gyrotron and a representative ITER-like plasma regime. It is shown that a number of intrinsic limitations characterize each of the equatorial scattering geometries selected as more promising, namely a backscattering geometry at f0=80 GHz and two similar quasiorthogonal geometries at f0=180 GHz. A lack of spatial resolution typical of the former geometry has to be contrasted with a significant limitation in plasma access typical of the remaining geometries. Other relevant differences concern the requirements in terms of gyrotron power, acceptable stray radiation levels, etc. Special emphasis is given in the work to a discussion of ECE noise, on which the feasibility itself of the alpha collective scattering diagnostics at mm-waves largely depends in the plasma regimes considered.
Density gradient columns: Dynamic modeling for linear profiles
Authors: Brown J. Michael , Kadlubowski Bryan M. , Forney Larry J. , Sommerfeld Jude T.
Published: July 2002

Rigorous mathematical modeling of the process dynamics associated with the construction and filling of density gradient columns is presented in this article. These models incorporate the hydrostatic driving forces for fluid flow, friction losses associated with this flow, and the unsteady-state behavior of the liquid levels in the filling vessels and in the column itself. Four different filling arrangements are considered, corresponding to the density order of the two fluids in the filling vessels and two methods for introducing the fluid of varying density into the column. Time requirements for filling of the column and the resulting calibration curve for liquid density versus height in the gradient column are both obtained as a result of this modeling procedure. Further, extremely important operating guidelines for the final achievement of a linear density gradient in the column, which is normally the desired objective in most laboratory applications, are derived and presented. Conversely, the causes leading to nonlinear gradients are elucidated and quantified.
Nanosecond time-resolved circular dichroism measurements using an upconverted Ti:sapphire laser
Authors: Wen You-Xian , Chen Eefei , Lewis James W. , Kliger David S.
Published: July 2002

Several years ago a time-resolved circular dichroism technique for the far ultraviolet spectral region with submicrosecond (10−7 s) time resolution was developed using a xenon flash lamp probe source for measurements of circular dichroism (CD) signals. Recent improvements in Ti:sapphire lasers, providing the ability to frequency-convert the fundamental outputs to produce second, third, and fourth harmonic pulses, allow single wavelength measurements of CD with nanosecond (10−9 s) time resolution over a broad spectral region (205–910 nm). This provides a powerful technique to study fast biophysical phenomena such as protein folding processes. In this article, the methodology and preliminary application of this new technique are presented.
The response of longitudinal and transverse pickup coils to a misaligned magnetic dipole
Authors: Miller Lance L.
Published: July 2002

The responses of magnetic pickup coils to various orientations and positions of a point dipole are considered. General solutions which describe the response functions are derived and analyses of the results are presented. The apparent magnetic moment, as determined from these functions, contain significant errors when the dipole is misaligned radially or directionally. The errors fall into three categories: radial off-centering of a correctly oriented dipole, angular misalignment of a centered dipole, and angular misalignment of a radially off-centered dipole. One simple experimental test with a commercial magnetometer showed a 34% error in the apparent moment due to radial off-centering. Practical error correction and minimization involve sample centering and rotational orientation about ẑ for transverse measurements, and include an additional adjustable parameter in the fitting function. Modest attention to these factors will reduce errors from ≊100% difference to ≤1%. The general nature of the calculations indicate that such effects exist for any type of inductive magnetometer.
Subharmonic mixer arrays for millimeter-wave plasma diagnostic applications (abstract)
Authors: Hsia R. P. , Geck W. R. , Domier C. W. , Luhmann, Jr. N. C.
Published: July 2002

A novel approach to low cost millimeter- and submillimeter-wave subharmonically pumped mixer arrays is under investigation which combines the high performance of waveguide mounted mixers with the ruggedness of planar arrays. Each mixer consists of local oscillator (LO) and input signal waveguides and a suspended stripline circuit containing both filters and an antiparallel pair of GaAs beam-lead diodes. In array form, the probe couplers built into each mixer allow the LO waveguides to be connected in an end-to-end fashion to form a single waveguide path for optimum use of LO power. Prototype mixers under fabrication are designed for (i) 280 GHz operation using a 140 GHz LO source, and (ii) 100–140 GHZ operation using a 50–70 GHz LO source. Plasma diagnostic application areas include Fourier infrared interferometry/polarimetry and electron cyclotron emission imaging.
DIII-D divertor reflectometer system
Authors: Rhodes T. L. , Doyle E. J. , Nguyen X. V. , Kim K. W. , Peebles W. A. , Doane J. L.
Published: July 2002

Divertor density profiles, asymmetries, turbulence, and MARFE diagnosis are extremely important and affect the divertor design process for ITER and other future devices. In addition, a functioning divertor density profile system will be essential for the operation of these machines. It is thus critical to prototype and demonstrate diagnostics capable of operating in a divertor environment. To meet these needs a divertor reflectometer system has been designed and installed on DIII-D. The design stresses flexibility, modularity, and simplicity. It consists of a circular, smoothwall, overmoded waveguide followed by a TE11⇒HE11 mode converter (the HE11 mode is a low loss Gaussian mode with a very symmetric radiation pattern, optimal for this use) thus allowing use of an arbitrary polarization (fpe,fLH,fRH). The design provides for testing of a variety of antennas/probing directions including: upward to probe the X-point region, including MARFEs, sideways to probe outboard/inboard divertor legs, and oppositely directed to probe both divertor legs simultaneously. System design, operational considerations, and experimental data are presented.
Calibration and test of the tangential phase contrast imaging diagnostic on CDX-U (abstract)
Authors: Lo E. , Nazikian R. , Stutman D. , Choe W. , Kaita R.
Published: July 2002

The novel CO2 laser based tangential imaging diagnostic has been completely calibrated and the system has been tested on CDX-U plasmas. It has been shown that localized, two-dimensional images of the plasma electron density fluctuations in the tokamak core can be obtained from a tangential imaging beam.1 A variation of the Zernike phase mirror is used. Test measurements made on soundwaves verify that the system will image phase variations placed at the object plane. An absolute sensitivity of ≈1×107 cm−3/Hz has been determined. A series of plasma measurements made on CDX-U are described. Results show that the plasma fluctuations are 2–3 orders of magnitude above the noise floor of the diagnostic. It is also verified that a high-pass cutoff wave number (from ≈1–8 cm−1) for the fluctuations can be selected by translating the phase mirror. The density fluctuation k spectrum is measured and found to peak at ≈1–3 cm−1.
Recent results from tokamak divertor plasma measurements (invited) (abstract)
Authors: Allen S. L.
Published: July 2002

New diagnostics have been developed to address key divertor physics questions, including: target plate heat flux reduction by radiation, basic edge transport issues, and plasma wall interactions (PWIs) such as erosion. A system of diagnostics measures the target plate heat flux (imaging ir thermography) and particle flux (probes, pressure and Penning gauges, and visible emission arrays). Recently, Te, ne, and Pe (electron pressure) have been measured in two-dimensions (2D) with divertor Thomson Scattering. During radiative divertor operation Te is less than 2 eV, indicating that new atomic processes are important. Langmuir probes measure higher Te in some cases. In addition, the measured Pe near the separatrix at the target plate is lower than the midplane pressure, implying radial momentum transport. Bolometer arrays, inverted with reconstruction algorithms, provide the two-dimensional core and divertor radiation profiles. Spectroscopic measurements identify the radiating species and provide information on impurity transport; both absolute chordal measurements and tomographic reconstructions of images are used. Either intrinsic carbon or an inert species (e.g., injected Ne) are usually observed, and absolute particle inventories are obtained. Computer codes are both benchmarked with the experimental data and provide important consistency checks. Several techniques are used to measure fundamental plasma transport and fluctuations, including probes and reflectometry. PWI issues are studied with in situ coupons and insertable samples (DiMES). Representative divertor results from DIII-D with references to results on other tokamaks will be presented.
Full aperture backscatter station imager diagnostics system for far-field imaging of laser plasma instabilities on Nova
Authors: Wilke Mark D. , Fernández Juan C. , Berggren Ralph R. , Horton Richard F. , Montgomery David S. , Faulkner James A. , Looney Larry D. , Jimerson John R.
Published: July 2002

In ICF, the understanding of laser plasma scattering processes is essential for laser target coupling and for controlling the symmetry of indirect drive implosions. The existing Nova full aperture backscatter station has been useful in understanding laser plasma instabilities occurring in hohlraums by measuring the quantity, spectral distribution, and near-field spatial distributions of Brillouin and more recently Raman backscatter. Equally important is an understanding of the far-field spatial intensity distribution which could help in understanding filamentation, threshold and saturation processes. This article describes a broadband, color-corrected far-field imager and associated diagnostics capable of imaging the source of scattered light to better than 25 μm resolution. Brillouin and Raman backscatter can be imaged through the Nova beam-7 focusing lens or the imager can be used like a microscope to image side scatter from other beams.
Signal processing and general purpose data acquisition system for on-line tomographic measurements
Authors: Murari A. , Martin P. , Hemming O. , Manduchi G. , Marrelli L. , Taliercio C. , Hoffmann A.
Published: July 2002

New analog signal conditioning electronics and data acquisition systems have been developed for the soft x-ray and bolometric tomography diagnostic in the reverse field pinch experiment (RFX). For the soft x-ray detectors the analog signal processing includes a fully differential current to voltage conversion, with up to a 200 kHz bandwidth. For the bolometers, a 50 kHz carrier frequency amplifier allows a maximum bandwidth of 10 kHz. In both cases the analog signals are digitized with a 1 MHz sampling rate close to the diagnostic and are transmitted via a transparent asynchronous xmitter/receiver interface (TAXI) link to purpose built Versa Module Europa (VME) modules which perform data acquisition. A software library has been developed for data preprocessing and tomographic reconstruction. It has been written in C language and is self-contained, i.e., no additional mathematical library is required. The package is therefore platform-free: in particular it can perform online analysis in a real-time application, such as continuous display and feedback, and is portable for long duration fusion or other physical experiments. Due to the modular organization of the library, new preprocessing and analysis modules can be easily integrated in the environment. This software is implemented in RFX over three different platforms: open VMS, digital Unix, and VME 68040 CPU.
Software architecture of data acquisition control process during TJ-II operation
Authors: Vega J. , Crémy C. , Sánchez E. , Portas A. , Dormido S.
Published: July 2002

Data from the diagnostics on the TJ-II device will be collected by several independent systems linked to local area networks (LANs). Some of these systems will consist of digitizers based on well-known standards: CAMAC, VME, VXI, etc. Other allowable systems would be personal computers or workstations with direct control over a specific diagnostic. In principal, any equipment capable of being linked in a LAN can be used as a controller for data collection. All systems will be programmed from a central computer. In this computer, an application program will allow the set up of data acquisition in any system. This will be achieved by communicating systems through a network standard protocol: TCP/IP. The central computer will also centralize the database of discharges. For this purpose, immediately after a discharge, data will be sent from the autonomous systems to the main computer. The latter will coordinate data reception, organize discharge information, and compress data. Data will be transferred rapidly so all diagnostic signals will be available to users for immediate analysis. The computer processes outlined here will provide an application program to provide users with an interface for all operations related to data acquisition, fast signal analysis, and remote control of diagnostics. A second functionality will be the management of TJ-II discharge database.
Integration of autonomous systems for remote control of data acquisition and diagnostics in the TJ-II device
Authors: Vega J. , Mollinedo A. , López A. , Pacios L. , Dormido S.
Published: July 2002

The data acquisition system for TJ-II will consist of a central computer, containing the data base of the device, and a set of independent systems (personal computers, embedded ones, workstations, minicomputers, PLCs, and microprocessor systems among others), controlling data collection, and automated diagnostics. Each autonomous system can be used to isolate and manage specific problems in the most efficient manner. These problems are related to data acquisition, hard (μs–ms) real time requirements, soft (ms–s) real time requirements, remote control of diagnostics, etc. In the operation of TJ-II, the programming of systems will be carried out from the central computer. Coordination and synchronization will be performed by linking systems to local area networks. Several Ethernet segments and FDDI rings will be used for these purposes. Programmable logic controller devices (PLCs) used for diagnostic low level control will be linked among them through a fast serial link, the RS485 Profibus standard. One VME crate, running on the OS-9 real time operating system, will be assigned as a gateway, so as to connect the PLCs based systems with an Ethernet segment.
Statistically robust linear and nonlinear wavelet analysis applied to plasma edge turbulence
Authors: van Milligen B. Ph. , Hidalgo C. , Sánchez E. , Pedrosa M. A. , Balbı́n R. , Garcı́a-Cortés I. , Tynan G. R.
Published: July 2002

The analysis of turbulence requires adequate analysis tools. In particular, two general properties of turbulence make the application of standard analysis tools (spectral analysis) difficult: (1) intermittency, which causes the characteristics of turbulence to change on a relatively short time scale, implies that analysis tools must not integrate over time scales longer than the intermittent time scale; (2) nonlinearity, a basic property of all numerical models of chaos and turbulence, requires specially adapted tools for its proper detection. In the present work, we develop a statistically stable formalism for the application of wavelet analysis techniques to the analysis of turbulence. We apply these techniques to the analysis of Langmuir probe data in the plasma edge region of the TJ-IU Torsatron. We draw some tentative conclusions about radial correlation lengths. Further, we analyze the L/H transition at the Continous Current Tokamak and reconstruct a radial profile of bicoherence in the plasma edge in the H-mode.
Extreme ultraviolet probing of laser imprint in a thin foil using an x-ray laser backlighter
Authors: Kalantar D. H. , Da Silva L. B. , Glendinning S. G. , Remington B. A. , Weber F. , Weber S. V. , Key M. H. , Kim N. S. , Neely D. , Wolfrum E. , Zhang J. , Wark J. S. , Demir A. , Lin J. , Smith R. , Tallents G. J. , Lewis C. L. S. , MacPhee A. , Warwick J. , Knauer J. P.
Published: July 2002

For direct drive inertial confinement fusion, a capsule is imploded by directly illuminating the surface with laser light. Beam smoothing and uniformity of illumination affect the seeding of instabilities at the ablation front. We have developed a technique for studying the imprint of a laser beam on a thin foil using an x-ray laser as an extreme ultraviolet (XUV) backlighter. We use multilayer XUV optics to relay the x-ray laser onto the directly driven foil, and then to image the foil modulation onto a charged coupled device camera. This technique allows us to measure small fractional variations in the foil thickness. We have measured the modulation due to imprint from a low intensity 0.35 μm drive beam incident on a 3 μm Si foil using an yttrium x-ray laser on Nova. We present results from a similar technique to measure the imprinted modulation due to a low intensity 0.53 μm drive beam incident on a 2 μm Al foil using a germanium x-ray laser at the Vulcan facility.
Modeling of three-dimensional camera imaging in a tokamak torus
Authors: Edmonds P. H. , Medley S. S.
Published: July 2002

A procedure is described for precision modeling of the views for imaging diagnostics monitoring tokamak internal components, particularly high heat flux divertor components. Such modeling is required to enable predictions of resolution and viewing angle for the available viewing locations. Since oblique views are typically expected for tokamak divertors, fully three-dimensional (3D) perspective imaging is required. A suite of matched 3D CAD, graphics and animation applications are used to provide a fast and flexible technique for reproducing these views. An analytic calculation of the resolution and viewing incidence angle is developed to validate the results of the modeling procedures. The tokamak physics experiment (TPX) diagnostics1 for infrared viewing are used as an example to demonstrate the implementation of the tools. As is generally the case in tokamak experiments, the available diagnostic locations for TPX are severely constrained by access limitations and the resulting images can be marginal in both resolution and viewing incidence angle. The procedures described here provide a complete design tool for in-vessel viewing, both for camera location and for identification of viewed surfaces. Additionally, these same tools can be used for the interpretation of the actual images obtained by the diagnostic cameras.
An inversion technique to obtain full poloidal velocity profiles in a tokamak plasma (abstract)
Authors: Bell Ronald E.
Published: July 2002

An inversion technique has been developed to calculate local poloidal rotation velocities of impurity ions from line-integrated measurements of an extended emission source in a tokamak plasma. This technique can recover radial spatial resolution that is lost due to the curvature of the field lines. With charge exchange emission from neutral beams, it can be used to obtain poloidal velocity profiles across the entire minor radius of the plasma without requiring restricted neutral beam height to localize the emission. The technique consists of two Abel-like matrix inversions to obtain the emissivity and the velocity-weighted emissivity from which the velocity is obtained. Use of the neutral beams breaks the assumed symmetry, but knowledge of the beam deposition and geometry allow analogous matrices to be generated. The inversion technique is demonstrated with a simulation of a poloidal rotation diagnostic for the TFTR tokamak with tangential neutral beams with a height of 80 cm. Two opposing vertical views are required to handle effects of the charge exchange cross section which can cause apparent velocities greatly in excess of expected poloidal velocities. The simulated errors due to the inversion process are about 1.5 km/s near the plasma center.
Polychromators in the ultraviolet/infrared (350–750 nm) spectral range for high-resolution, high sensitivity plasma spectroscopy (abstract)
Authors: Orsitto F. , Brusadin A. , Giovannozzi E.
Published: July 2002

The necessity of measuring different impurity lines at the same time with a good spectral resolution and high sensitivity has led to the construction of two filter polychromators working in the range of 350/750 nm and detecting lines emitted by metals (Ni,Fe,Mo,Cr) as well as light impurities (O,He,C), respectively. The Hα line at 656.3 nm is detected by both devices, since it could be very important to compare the results of the measurements with data given by other diagnostics operating in the same spectral range.
Spectroscopic method to directly measure electric field distribution in tokamak plasma edge
Authors: Takiyama K. , Katsuta T. , Watanabe M. , Li S. , Oda T. , Ogawa T. , Mizuno K.
Published: July 2002

A supersonic helium beam source operated in pulse mode was constructed for direct measurement of electric field distribution in the tokamak plasma edge region with the aid of laser-induced fluorescence (LIF) technique. In this technique only the polarization has to be observed of a LIF resulting from a laser-excited forbidden transition due to the Stark effect and the electric quadrupole to determine the electric field strength. No calibration is needed of the absolute intensity of LIF and tunable laser used. The helium atom beam density was obtained (about 1020 He atoms cm−2 s−1) at a distance of 7 cm from the pulsed nozzle. A model-type experiment to make clear the influence of a magnetic field on the LIF is reported. Design study was also made to install the supersonic beam and spectroscopic measurement system on a medium size tokamak.
Characteristics of a multilayer mirror polarimeter for measurements at extreme ultraviolet wavelengths
Authors: Bailey M. , Bruch R. , Shevelko A. , Vasilyev A.
Published: July 2002

We have developed and tested a multilayer mirror (MLM) polarimeter optimized for λ=304 Å using electron impact on helium. Specifically we present the first experimental results of the polarization of the extreme ultraviolet Lyman-α emission from He+ [He II (2p)2P°→(1s)2S] as a function of the electron impact energy for impact energies ranging from 150 to 980 eV. A major challenge to performing this measurement is the suppression of the dominant He I (1snp)1P°→(1s2)1S radiation originating from the excitation of helium. Excellent spectral selectivity has been achieved with a VYNS copolymer filter whose transmission ratio of He II to He I emission has been measured to be greater than 1200:1. Additionally, we have measured the instrumental polarization using two identical MLMs in a crossed polarizer configuration.
Line emission tomography for CDX-U using filtered diodes
Authors: Stutman D. , Menard J. , Hwang Y. S. , Choe W. , Ono M. , Finkenthal M. , Soukhanovskii V. , May M. J. , Regan S. P. , Moos H. W.
Published: July 2002

Electron density and temperature in the CDX-U low aspect ratio tokamak are too low to allow observation of fast magnetohydrodynamic activity using soft x-ray continuum emission. However, spectroscopic measurements show that extreme ultraviolet (XUV) line emission of intrinsic impurities is bright enough to observe such activity. In addition, a fast monitoring system for local temperature changes in the plasma core is required for planned auxiliary heating experiments. We present a spectrally resolved tomographic system for fast imaging of O VI 2s–np, 2p–nd (n⩾3), C V 1s2–1s2p and C VI 1s–2p XUV transitions. Using this emission, we can study both core and edge MHD activity, while the C VI to C V intensity ratio can indicate local changes in electron temperature. To achieve maximal throughput together with the needed spectral resolution, we use arrays of surface barrier diodes filtered with bandpass elemental filters. Using M edge filters (Zr, Pd, and Ag), we achieve both good discrimination between the above charge states and large transmission at the wavelengths of interest. Preliminary results obtained from CDX-U are presented.
A high-resolution transmission-type x-ray spectrometer designed for observation of the Kα transitions of highly charged high-Z ions
Authors: Widmann K. , Beiersdorfer P. , Brown G. V. , Crespo López Urrutia J. R. , Decaux V. , Savin D. W.
Published: July 2002

High-resolution reflection-type crystal spectrometers have been used for x-ray energies up to 13 keV, e.g., the K-shell radiation of heliumlike Kr. In order to extend crystal spectrometer measurements to higher energy x rays from higher-Z elements, we employ the crystal in transmission. The geometry we use is known as DuMond geometry. Using such a transmission-type crystal x-ray spectrometer, we have measured the K-shell radiation of various highly charged high-Z ions. In particular, we present a measurement of the 1s2p 1P1→1s2 1S0 transition in heliumlike xenon, Xe52+. For this transition, we measure a linewidth of 34 eV, which demonstrates that the resolving power we achieved with the new spectrometer is on the order of 1000.
Implementation of a SELFOC lens for the light collection element for single molecule spectroscopy at cryogenic temperatures
Authors: Vacha Martin , Liu Yi , Itho Junji , Komuro Masanori , Tani Toshiro , Nakatsuka Hiroki
Published: July 2002

We introduce the use of a SELFOC gradient index lens as a micro-optical element for collection and focusing of luminescence of single molecules in solid matrices. We demonstrate its performance by measuring single molecule spectra of terrylene in n-alkanes and compare its signal-to-noise ratio and collection efficiency with that of a microscope objective.
High-accuracy time- and space-resolved Stark shift measurements (invited)
Authors: Bailey J. E. , Adams R. , Carlson A. L. , Ching C. H. , Filuk A. B. , Lake P.
Published: July 2002

Stark-shift measurements using emission spectroscopy are a powerful tool for advancing understanding in many plasma physics experiments. We use simultaneous two-dimensional space- and time-resolved spectra to study the electric field evolution in the 20 TW Particle Beam Fusion Accelerator II ion diode acceleration gap. Fiber optic arrays transport light from the gap to remote streaked spectrographs operated in a multiplexed mode that enables recording time-resolved spectra from eight spatial locations on a single instrument. Design optimization and characterization measurements of the multiplexed spectrograph properties include the astigmatism, resolution, dispersion, and sensitivity. A semiautomated line-fitting procedure determines the Stark shift and the related uncertainties. Fields up to 10 MV/cm are measured with an accuracy ±2%–4%. Detailed tests of the procedure confirm that the uncertainty in the wavelength-shift error bars is less than ±20%. Development of an active spectroscopy probe technique that uses laser-induced fluorescence from an injected atomic beam to obtain three-dimensional space- and time-resolved measurements of the electric and magnetic fields is in progress.
Avalanche photodiodes operating parameter optimization for the Frascati Tokamak Upgrade Thomson scattering system (abstract)
Authors: Orsitto F. , Brusadin A. , Giovannozzi E.
Published: July 2002

Measured figures (linearity, avalanche gain, frequency response, and noise) of the avalanche photodiodes (APD) detectors used on the FTU Thomson scattering system (FTU-TS) are reported. This investigation on the APD figures is motivated by the necessity of knowing their values over a wide range of input signals, and also of checking the validity of McIntyre model of APD noise, since using this model the experimental signal-to-noise ratio is calculated. From the noise analysis, a method of optimization of the detection system sensitivity is derived, leading to the optimization of the signal-to-noise ratio over the entire FTU-TS system.
Quantitative spectroscopy of x-ray lines and continua in tokamaks (abstract)
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, have been used to study the spectrum of COMPASS-D and other tokamaks in the wavelength region 1–100 Å. In particular, line emission from CIXVI and other He-like ions of the third atomic period elements have been shown to be a rich source of diagnostic information on ion transport and impurity ion accumulation, ion and electron temperatures, and plasma fluid velocities. 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 are constructed from the individual component efficiencies, including published values of the diffractor reflectivities. Where diffractors have been used for which there is no published information, the reflectivity is measured using a double-axis goniometer or from line branching ratios. 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 in COMPASS-D. From the irradiances of the line emission, changes in the absolute level of impurities following “boronization” of the vacuum vessel have been documented.
SPARTUVIX II: An improved x-ray ultraviolet spectrograph with temporal and spatial capabilities for indirect drive inertial confinement fusion experiments (abstract)
Authors: Bourgade J. L. , Guilly E. , Bruneau J. , Gary S. , Gontier D. , Renaudin P. , Reverdin C. , Thiell G. , Eidmann K. , Winhart G.
Published: July 2002

An improved version of the initial x-ray ultraviolet spectrograph SPARTUVIX1 has been developed to record the time evolution of spatially resolved spectra in the soft x-ray range (from 30 to 300 Å). This diagnostic can be applied to the new class of laser produced plasma experiments now performed in order to better understand the physical evolution of x-ray indirect drive plasmas. Instead of a one-dimensional streak camera used for the first version, a new widely used 2-D soft x-ray time gated imager allows us to follow the time evolution of the spatially resolved soft x-ray spectra. This instrument was designed for plastic foam soft x-ray opacity measurements. The soft x-rays, emitted by an auxiliary radiography laser plasma source, are transmitted through the foam and dispersed into two parts (+1 and −1 order of the transmission grating). Each dispersed spectrum is placed on two different gated striplines of the soft x-ray imager and thus recorded at two different times (exposure time 300 ps, adjustable interframe 600 ps). The spatial resolution is obtained with a slit added in front of the spectrograph, that images the plasma onto the detector with a magnification ratio of 15 and a spatial resolution of 50 μm. A detailed description of this instrument and the main results obtained for two different plastic foam opacity measurements (undoped and doped with chlorine) will be presented. This work is supported by European Community Contract No. CEE/CHGF-CT-92-0016.
Design and performance study of a scanning magnetron sputtering target
Authors: Panwar N. S. , Deenamma Vargheese K. , Mohan Rao G.
Published: July 2002

A scanning magnetron sputtering system has been developed and its performance studies are carried out in terms of target utilization, substrate temperature, and film uniformity. The magnetic field on the target surface is scanned by electromechanical movement of magnet array along the length using a step motor. The target utilization efficiency is almost 100%. The substrate temperature rise was minimum (around 50 °C) even when the deposition rate is about 6500 Å/min. It was found that at a target-substrate distance of 6.5 cm, and a sputtering pressure of 0.025 mbar, thickness uniformity of +3% has been achieved over an area of 120 mm ×80 mm.
Suppression of accelerated electrons in a high-current large negative ion source
Authors: Takeiri Y. , Oka Y. , Osakabe M. , Tsumori K. , Kaneko O. , Takanashi T. , Asano E. , Kawamoto T. , Akiyama R. , Kuroda T.
Published: July 2002

Accelerated electrons, which would lead to high thermal load of grids, have been suppressed in a high-current large hydrogen negative ion source. An extraction grid, with apertures shaped as the secondary electrons generated on the grid aperture surface would be shielded against the acceleration electric field, works well to prevent the secondary electrons from leaking to the acceleration gap, compared with a straight aperture extraction grid. Although the strong magnetic field at the extraction grid also lowers the electron leakage downstream, the aperture shaping of the extraction grid is more effective for the suppression of the accelerated electrons. The acceleration efficiency, defined by the ratio of the negative-ion current to the acceleration drain current, is improved to around 85%. There remains the accelerated electrons generated in the negative ion neutralization by collision with the residual neutral molecules during the acceleration. The direct interception of the accelerated negative ions with the downstream grid is small. The reduction of the operational gas pressure is quite important to achieve further improvement of the acceleration efficiency.
An oxygen-compatible radiant substrate heater for thin film growth at substrate temperatures up to 1050 °C
Authors: Clark J. C. , Maria J. P. , Hubbard K. J. , Schlom D. G.
Published: July 2002

The design and performance of a radiative substrate heater that operates under vacuum in a highly oxidizing environment is described. Using this heater, substrate temperatures exceeding 1050 °C are readily achieved. These are the highest temperatures reported for a pulsed laser deposition (PLD) heater that operates in an oxidizing ambient. This heater was designed for the growth of oxide thin films by PLD, but the design concept is suitable for other vacuum deposition methods requiring high substrate temperatures to be achieved in an oxidizing environment. In addition to the high substrate temperatures achievable, the design described enables easy switching between on-axis PLD and off-axis PLD (allowing both sides of the wafer to be coated in the same growth) and allows the target-to-substrate distance to be easily adjusted from outside the chamber.
An improved lamellae drop-off technique for sharp tip preparation in scanning tunneling microscopy
Authors: Klein M. , Schwitzgebel G.
Published: July 2002

A superior lamellae etching drop-off technique is described for the preparation of W tips without the use of CCl4. Sharp tips with an apex of 25 nm or less can be produced routinely. In the case of Pt/Ir wire, the chemical inertness of the material means that it has to be reduced in diameter before being etched to yield a tip. In order to accomplish this, a capillary diameter reduction technique has also been developed for use in combination with the lamellae etching drop-off technique. The apparatus does not require the use of micromanipulators or micromovers. The shapes of tips with apexes as small as 25 nm can be investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This low cost method of producing sharp tips scanning tunneling microscopy is very effective and it would probably be feasible to develop an automatic tip preparation with a little more technical effort. Since it is possible to produce well shaped W tips almost every time after acquiring a little skill, it is not usually necessary to check their shape by TEM or SEM before use. In contrast, the success rate with Pt/Ir tips is only up to 70%, so that it is advisable to check their shapes by TEM.
Paper II: Simulation of flow conditions in low-pressure flow reactors (Knudsen cells) using a Monte Carlo technique
Authors: Fenter Frederick F. , Caloz François , Rossi Michel J.
Published: July 2002

A Monte Carlo program has been developed to simulate the gas dynamics inside flow reactors (Knudsen cells) specially adapted to study heterogeneous reactions. Because the reactors are operated under molecular flow conditions, the Monte Carlo technique can be applied to calculate trajectories of individual molecules considering only gas-wall collisions. Ensembles of trajectories are then used to generate synthetic kinetic data as a function of specific reactor geometries (surface-to-volume ratio, injector position, reactive-surface diameter, etc.) and analyzed to yield rate constants. The calculated rate constants thus obtained are useful in assessing the systematic error associated with a rate-constant determination and in the designing of future geometries of Knudsen cells.
Design study and experimental performance of a multistage electron collector
Authors: Roy Prabir Kumar , Moon Ahsa , Ohkubo Koichi , Nakao Naoya , Mima Kunioki , Nakai Sadao , Fujita Masayuki , Imasaki Kazuo , Yamanaka Chiyoe , Sano Eisaku , Tsunawaki Yoshiaki
Published: July 2002

A multistage electron collector has been designed for an electron-beam energy recovery system. The electrodes of the collector are cylindrical and partially conical or spiky near the axis in order to maintain a continuous field effect on the beam. The field effect of these electrodes is so efficient that a magnetic field is not necessary between the deceleration and collection gap to confine the beam on the axis. The energy recovery efficiency, 99.8%, of the collector was calculated by using a computer code with about 10 mA beam current and −75 keV. To test the performance of the collector, it has been assembled with a laser-heated electron gun and electrically connected to its power supply. The potentials of each electrode have been provided through a voltage divider of several hundred megaohms. Experimentally, the efficiency obtained was 73%–98% with a beam current of 0.67 mA.
A nondisturbing electric-field sensor using piezoelectric and converse piezoelectric resonances
Authors: Lee Yongkwan , Kim Ilryong , Lee Soonchil
Published: July 2002

An electric-field sensor was developed using both piezoelectric and converse piezoelectric resonances. Composed of no metallic parts, this probe minimizes field disturbance. The most distinguishing feature of this probe is that a signal is transmitted neither electrically nor optically, but mechanically. To demonstrate the field sensing capability of this probe, we measured both the capacitive and inductive fields inside empty and plasma-filled solenoidal coils. The result shows that the capacitive field is dominant in an empty solenoid, although it is almost completely shielded by inductively excited plasma.
New extruder-based deuterium feed system for centrifuge pellet injection
Authors: Combs S. K. , Foust C. R.
Published: July 2002

The pellet injection systems for the next-generation fusion devices (such as the International Thermonuclear Experimental Reactor) and future fusion reactors will have to provide deuterium-tritium fueling for much longer pulse lengths (up to ≈1000 s) than present applications (typically limited to less than several seconds). Thus, a prototype pellet feed system for centrifuge pellet injection has been developed and used in long-pulse (>100 s) tests at the Oak Ridge National Laboratory (ORNL). The new apparatus has two key components: (1) a cryogenic deuterium extruder and (2) an electromagnetic pellet punch mechanism. For maximum testing flexibility, the prototype is equipped with several other active components that allow remote adjustments, including precise positioning of the punch and the capability to index through eight different pellet lengths. The new feed system was designed to mate with an existing centrifuge accelerator facility at ORNL, and experiments in the facility were carried out to document the performance and reliability of the new feed system. With 2.3-mm-diam deuterium pellets and a catenary-shaped accelerator (≈1.2 m diam), the prototype feed system was found to be capable of placing up to ≈90% of the punched pellets in the proper time/space window for pickup and acceleration by the high-speed rotating (≈50 Hz) arbor. For these operating parameters, the pellet nominal speed was ≈430 m/s, and maximum pellet feed rates of 10 pellets/s and greater were tested. In this article the equipment is briefly described, and the experimental test results are summarized. Also, issues affecting overall pellet delivery efficiency are discussed.
Maximum entropy digital signal processing for acoustic Doppler imaging
Authors: Wright F.
Published: July 2002

A maximum-entropy algorithm is developed for real time estimation of the power spectrum mean frequency of a Doppler shifted probe. This technique is compared with a covariance argument approximation and performance is given in terms of noise immunity, measurement bias, and accuracy. Estimator evaluation is made from numerical results with a computer simulated signal having a Gaussian spectral density. The maximum-entropy and covariance argument algorithms are implemented on a digital signal processing microprocessor (Analog Devices ADSP2181) for comparison. The maximum entropy technique demonstrates substantial improvement over covariance processing with respect to noise immunity and exhibits no bias in the presence of band limited noise. The maximum-entropy algorithm can be implemented, without any post-processing required, using the ADSP2181 on typical acoustic Doppler signals in the frequency range between 150 and 1200 kHz by frequency down conversion to a fundamental Nyquist interval of 4 kHz.
Floating electrometer for scanning tunneling microscope applications in the femtoampere range
Authors: Heer R. , Eder C. , Smoliner J. , Gornik E.
Published: July 2002

In this work, a floating, high precision current–voltage converter, applicable to scanning tunneling microscopy (STM) and ballistic electron emission microscopy (BEEM) measurements, is described. The electrometer circuit presented shows a bias independent output offset, adds low noise, and has low thermal drift. The amplifier is useful for any floating applications where an ultrasmall current has to be measured with high resolution (±20 fA). The circuit is fast enough for typical sampling rates required for BEEM or STM image measurements and can also be used for fA measurements related to ground.
Measurement of 0.1 cm2 surface areas by xenon adsorption at liquid oxygen temperature using an adsorption apparatus with a temperature-compensated, differential tensimeter of symmetrical design
Authors: Suzuki Isao , Oosawa Kaoru
Published: July 2002

Areas of solid surfaces as small as 0.1 cm2 were determined by xenon adsorption at liquid oxygen temperature using an adsorption apparatus with a temperature-compensated, differential tensimeter of symmetrical design. The thermal transpiration effect was considered to determine the adsorption pressures and the amount adsorbed. The Brunauer–Emmett–Teller monolayer volume of xenon for 4, 8, or 12 1 mm steel ball bearings was proportional to the number of balls used. The coefficient of proportionality agreed with the results on 9880 ball bearings. The surface area of four ball bearings is 0.12 cm2, which suggests that it is feasible to measure surface areas as small as 0.1 cm2.
Novel needle microbalance for adsorption studies
Authors: Bruschi L. , Borghesani A. F. , Delfitto G. , Mistura G.
Published: July 2002

Microbalances are quite often used in the investigation of adsorption phenomena. In this article we describe a novel “needle” microbalance characterized by a magnetic restoring torque particularly fit to study the growth of thick films on solid surfaces. In particular, it does not present any particular problem in the study of thick solid films which generally affect the stiffness of the restoring springs, present in nearly all mechanical devices, in a difficult to predict way. Another important feature of this microbalance is that its use is not limited to one specific adsorbing solid surface.
A modified stopped-flow apparatus for time-resolved protein phosphorescence
Authors: Strambini Giovanni B. , Puntoni Alessandro , Gonnelli Margherita
Published: July 2002

A type of commercial apparatus was modified and integrated in order to implement the detection of time-resolved protein phosphorescence in the stopped-flow technique. Laser excitation, photomultiplier protection from the intense fluorescence pulse, fluorescence integration, and data acquisition are all synchronized by a trigger module that takes over standard computer control of the stopped-flow apparatus. A detailed protocol is given for effective deoxygenation of the sample and flow lines and for avoiding contamination of the solutions by quenching impurities. The performance of the apparatus was tested by comparing the phosphorescence decay kinetics of the protein horse liver alcohol dehydrogenase in the stopped-flow apparatus and in a standard phosphorimeter. The time resolution of phosphorescence detection in the stopped-flow apparatus is 10 ms and the sensitivity in terms of chromophores concentration is about 0.1 μM.
Demonstration of low temperature radiative cooler for future space missions
Authors: Cushman G. Mark , Mather J. C. , Fixsen D. J.
Published: July 2002

Low temperature radiative coolers permit more sensitive, lower temperature detectors for science instruments in space, and can extend the length of missions at low cost and mass. A miniature radiative cooler was designed, constructed, and tested and achieved a stabilized temperature of 34 K with no load and an outer shell temperature of 91 K. This is an improvement upon previous lower limits of radiative coolers of 50 K. Thermal modeling and experiment agree within 2 K.
Microphone detection of laser ablation
Authors: Chae Heebyung , Park Seung Min
Published: July 2002

The microphone technique has been applied to the study of laser ablation of a silicon target. The momentum flux of silicon atoms generated by laser ablation at 266 nm was detected both at high vacuum and at background gas conditions. The response of the microphone to an atomic pulse of a few μs was in agreement with theoretical expectations. The magnitude of the microphone signal increased linearly with laser fluence. A pulsed valve was adopted to also compare the response of the microphone at longer pulse durations.