bluuebunny/crossref_metadata_2025 huggingface dataset:
Conceptual designs of fast-ion loss detectors for the TJ-II stellarator
Authors: Burgos C. , Zurro B. , Guasp J. , Ochando M. A. , McCarthy K. J. , Medina F. , Baciero A. , Liniers M. , Fuentes C.
Published: March 2003

We present conceptual designs for two compact, flexible fast-ion loss detectors for quantifying the direct loss term, which is predicted by theoretical calculations to be the most relevant one, from TJ-II plasmas heated by Neutral Beam Injectors. In both conceptual designs, we attempt to encompass the need for a very sensitive system with no imaging capabilities and that for a less sensitive system with some imaging capacity. Finally, we model fast-ion losses from this device in order to identify the optimal locations for such detectors, while also taking experimental constrains into account, and we estimate the ion currents in these detectors as well as the resultant output signal levels.
Development and initial operation of the pellet charge exchange diagnostic on LHD heliotron
Authors: Goncharov P. R. , Saida T. , Tamura N. , Ozaki T. , Sasao M. , Isobe M. , Sudo S. , Khlopenkov K. V. ,   LHD Experimental Groups I/II, Krasilnikov A. V. , Sergeev V. Yu.
Published: March 2003

An active corpuscular diagnostic with an artificially created localized target for the charge-exchange process has been developed and tested on a large helical device. The diagnostic is a combination of an impurity pellet injector and a natural diamond detector-based energy analyzer. High-energy particles neutralized at the pellet ablation cloud are detected while the pellet travels across the plasma column. Time-resolved atomic energy spectra translate into local measurements along the pellet trajectory. Thus, local parameters are obtained in the toroidally non-axis-symmetrical configuration. Physical basis, data interpretation, and the technical description of the diagnostic are given. The requirements to the analyzer geometry, electronics, and data acquisition needed to provide the desired spatial resolution are described. The initial experimental results are presented along with the other diagnostic data. The scope of experiments, possible comparisons with multichord passive charge-exchange measurements and future work on the diagnostic are also discussed.
Spatially resolved measurements of energetic neutral particle distributions in the Large Helical Device
Authors: Lyon J. F. , Goncharov P. R. , Murakami S. , Ozaki T. , Greenwood D. E. , Spong D. A. , Sudo S. ,   LHD Groups I/II
Published: March 2003

A silicon-detector-based neutral particle analyzer array was used to study fast ion distributions in the Large Helical Device for different plasma heating conditions. GNET code simulations of the measurements are needed for accurate interpretation of the data.
Charge exchange fast neutral measurement with natural diamond detectors in neon plasma on LHD
Authors: Saida T. , Sasao M. , Isobe M. , Krasilnikov A. V. ,   LHD Experimental Group
Published: March 2003

Charge exchange (CX) fast neutral spectra produced by ion cyclotron resonance frequency hydrogen minority heating in neon and helium majority plasmas sustained by neutral beam injection were measured with perpendicular Natural Diamond Detectors during the fifth campaign in 2002 on large helical devices (LHDs). It was observed that there were differences between fast neutral spectra shapes in neon plasma and those in helium of the same discharge condition with similar plasma parameters. Dominant CX processes in neon and helium plasmas were studied for ionization components from outside of the last closed flux surface. High-energy proton spectra were obtained by taking account of each charge state distribution and responsible charge exchange cross sections. The high-energy proton tail formations in both plasmas were similar for the same heating regime. The relaxation time tendencies of the effective temperatures of a high-energy proton have also shown no differences, indicating that the acceleration and confinement of energetic ions in LHDs are similar in neon and helium plasmas.
Diagnosis and study of Alfvén eigenmodes stability in JET (invited)
Authors: Testa D. , Fasoli A. , Solano E. ,   JET-EFDA Contributors
Published: March 2003

Experiments are conducted on JET to assess the potential for plasma diagnostic spectroscopy and mode stability control of Alfvén eigenmodes (AEs), excited by external antennas and by energetic particles. Information on the time evolution of the nonmonotonic current profile in advanced scenarios can be obtained from the frequency and mode number of AEs driven by energetic particles. The appearance of a rational surface associated with a minimum value in the safety factor profile can be inferred with a time resolution of 10–20 ms. An indication on the presence of a region with negative current in the plasma core can be obtained from the simultaneous appearance of AEs with positive and negative helicity. By synchronously detecting the antenna-driven perturbations, the damping rate of low-n AEs can be measured in real-time every 10–50 ms. The dependence of the AE damping rate on the edge plasma shape may lead to the development of feedback control schemes for the modes.
Carbon activation diagnostic for tertiary neutron measurements
Authors: Glebov V. Yu. , Stoeckl C. , Sangster T. C. , Meyerhofer D. D. , Radha P. B. , Padalino S. , Baumgart L. , Colburn R. , Fuschino J.
Published: March 2003

The yield of tertiary neutrons with energies greater than 20 MeV has been proposed to determine the high ρR of inertial confinement fusion targets. The activation of carbon is a valuable measurement technique because of its high reaction threshold, the availability of high-purity samples, and relatively low cost. The C12(n,2n)11C reaction has a Q value of 18.7 MeV, well above the 14.1 MeV primary DT neutron energy. The isotope C11 decays with a half-life of 20.3 min and emits a positron, resulting in the production of two back-to-back, 511 keV gamma rays upon annihilation. The positron decay of C11 is nearly identical to the copper decay used in the activation measurements of 14.1 MeV primary DT yields; therefore, the present copper activation gamma-detection system can be used to detect the tertiary-produced carbon activation. Because the tertiary neutron yield is more than six orders of magnitude lower than primary neutron yield, the carbon activation diagnostic requires ultrapure carbon samples, free from any positron-emitting contamination. In recent years we have developed carbon purification, packaging, and handling procedures that minimize the contamination signal to a level low enough to use carbon activation for tertiary neutron measurements in direct-drive implosion experiments with DT cryogenic targets on OMEGA. Experimental results of contamination measurements in carbon samples performed on high-neutron-yield shots on OMEGA in 2001–2002 will be presented. A concept for implementing a carbon activation system on the National Ignition Facility (NIF) will be discussed.
Gamma-diagnostics of alpha-particles in He4 and D–T plasmas
Authors: Kiptily V. G. , Popovichev S. , Sharapov S. E. , Bertalot L. , Cecil F. E. , Conroy S. , Mantsinen M. J.
Published: March 2003

This article reports on γ-ray diagnosis of ICRF-accelerated He4 ions and fusion α particles used in the JET tokamak. This diagnostic based on the analysis of γ rays emitted in nuclear reaction Be9(α,nγ)12C. The results of the first observation of the 4.44-MeV γ-radiation due to the reaction Be9(α,nγ)12C in JET deuterium–tritium experiment (DTE1) are presented. Gamma-ray spectra have been recorded with collimated spectrometer, and the γ-ray emission radial profiles measured with the JET neutron/gamma profile monitor. Doppler broadening effects which could be used for the ICRF-accelerated He-ion4 diagnosis with high energy resolution γ-ray detectors are discussed. Capabilities of the γ-ray measurements in next step D–T devices are discussed.
High-quality video streaming system for plasma diagnostics using super SINET
Authors: Emoto M. , Watanabe K. , Masuzaki S. , Ohno N. , Okada H.
Published: March 2003

Smooth cooperative research requires effective remote participation. Toward this end, the National Institute for Fusion Science (NIFS) has enhanced its network among domestic institutes. The new network, called the Super Science information network (SINET), connects national universities and governmental organizations and has a 10 G bps backbone. NIFS connected Kyoto University and Nagoya University to this network at a speed of 1 G bps each way in 2002, and plans to connect other universities. In addition, a real-time video streaming system is being developed for remote participation in this network. Due to bandwidth limitations of the network, lossy motion image formats, such as Real Video or MPEG, are widely used for video streaming service. For example, the minimum transfer ratio to send a VGA-sized video image at the rate of 30 fps is 27 MB/s, or 220 M bps, which exceeds ordinal network capacities. However, lossy images cannot be used for physical analysis, because the original information is lost. NIFS can connect universities at a speed of 1 G bps by Super SINET, and this speed is fast enough to send lossless motion images. The new system uses this network, and thereby can provide high-quality durable lossless images for scientific analyses.
Design of the TJ-II remote participation system
Authors: Vega J. , Sánchez E. , López A. , Portas A. , Ochando M. , Mollinedo A. , Sánchez A. , Ruiz M. , López S. , Barrera E.
Published: March 2003

The TJ-II remote participation design has focused initially on providing remote access to elements that depend exclusively on characteristics of the TJ-II environment: data acquisition, data access, and diagnostics control systems. Aspects related to advanced display tools, audio information from the control room or videoconference sessions can be addressed, at least in a first step, by using standard solutions. Remote access will be accomplished through http servers and web browsers as they are standard elements available on all platforms. Access security rests on a validation scheme in which users are identified through a username and password, these data being transferred in a secure way by using a secure socket layer (SSL). After username and password validation, the security system assigns a session ticket to the user, in which the user profile (access authorization list) is encoded. User profiles determine several access levels to the system. Such levels delimit the authorizations for accessing different services according to the allowed degree of interaction of remote users with the TJ-II environment. The ticket will be sent in every user query, in order to test user permission for the requested action. Services can be classified into five groups: Measurement channel setup, read/write access to the TJ-II databases (raw data, analyzed data, elaborated data, and relational databases), diagnostic control system monitoring/programming, advanced data acquisition system configuration and, finally, reading/writing information on TJ-II operation logbook. The TJ-II remote participation system is strongly coupled with the local data acquisition system.
Results of the remote participation on TJ-II neutral particle analyzer
Authors: Castejón F. , Balbı́n R. , López A. , Vega J. , Sánchez E. , Portas A. , Jiménez J. A. ,   TJ-II Team, Fontdecaba J. M. , Dies J. , Izquierdo J. , Petrov S.
Published: March 2003

Neutral Particle Analyzer diagnostic has been operated remotely from Universitat Politecnica de Catalunya in Barcelona, separated by more than 600 km from Laboratorion Nacional de Fusion in Madrid. Remote participation tools are used to control the diagnostic, to visualize the experimental TJ-II data, and to participate in scientific meetings on TJ-II experiments and models. The results of such participation are shown in this work, namely the charge-exchange neutral spectra, the ion temperature profiles in TJ-II, and the results of transport analysis. Neutral spectra have two slopes, one of them attributed to the core neutrals and the other one to the neutrals coming from the edge. The ion temperature is obtained in a series of reproducible discharges, at every point from regression analysis of those spectra. The ion temperature profile happens to be pretty flat. Ion heat transport analysis is performed with Proctr and PRETOR-STELLARATOR codes and the results are compared.
A low cost, real-time DSP-based diagnostic for the control of operation of a fusion experiment
Authors: Carvalho B. B. , Fernandes H. , Varandas C. A. F.
Published: March 2003

This article describes a low cost, digital signal processor (DSP)-based system for real-time control of the tokamak Instituto Superior Tecnico tokamak (ISTTOK) operation, aimed at enlarging the plasma duration of ac discharges. This system is based on (i) a new set of 12, 1 MHz pick-up coils measuring the poloidal field, (ii) an on-site developed analog active integrator and signal conditioning module, (iii) a commercial DSP board and a modified digitizer module, and (iv) specially developed real-time software running on the DSP and a feedback control routine (e.g., PID). The system has been implemented on the ISTTOK, providing for the extraction of plasma equilibrium parameters in a time interval that fulfill the real-time constraints.
A low cost, fully integrated, event-driven, real-time control and data acquisition system for fusion experiments
Authors: Batista A. J. N. , Combo A. , Sousa J. , Varandas C. A. F.
Published: March 2003

A new, real-time, distributed, control and data acquisition system architecture for long duration fusion experiments was developed based on the new optical communications technologies and the “System on a Chip” methodology. The architecture integrates data routing, data storage, real-time data processing and control and data acquisition nodes, interconnected by a switched-packed, gigabit, point-to-point, communications network. The routing nodes provide connections to the autonomous storage and processing nodes through standard network links. The control and data acquisition nodes are connected to the routing nodes by specifically designed optical links which provide both data transport and timing/synchronism support. The acquired data are time stamped and can be dynamically processed for local control or sent to the external storage, the real-time processing or the control nodes. The standard processor and the reconfigurable field programmable gate array included in each node allow the programming of the data reduction, adaptive signal processing, and control algorithms from a high level system description language. All nodes will be controlled through an instrumentation-specific implementation of the Extensible Markup Language. A control and data acquisition node with 32 independent and galvanically isolated analog channels of 16 bits resolution is under development. All input signals are continuously and simultaneously sampled at a rate of 2 MSPS, time stamped, optionally digitally filtered, and stored in a large circular memory buffer. Three other node configuration sets will also be implemented: 16 channels, 20 MSPS, 16 bit; 8 channels, 100 MSPS, 12 bit; 2 channels, 1 GSPS, 8 bit.
Wavelet analysis application for remote control room operation
Authors: Semenov Oleg I. , Semenov Igor B.
Published: March 2003

Compression algorithm for data transfer from tokamak installation to remote control room was developed on the basis of wavelet analyses. The algorithm is useful in the case of low speed Internet channel (∼20 kbytes/s) for real time express analysis of row noisy data between shots (i.e., ∼5–10 times compression of the initial row data array (∼50–100 Mbytes), transmission, restoration, and analysis in time interval ∼15 min). The developed algorithm is based on some amount of data losses so that the amplitude and phase difference between the initial and restored data were less then 5% to signal amplitude. The algorithm was tested for Mirnov signal transmission in the case of disruption instability. It was shown that the error of restoration does not depend on form of the signal, i.e., applied method has good characteristics both in the case of the spikes and smooth functions. Experiments show that the coefficient of compression 5–15 could be achieved if the errors are in 0.5%–5%.
An event-driven reconfigurable real-time processing system for the next generation fusion experiments
Authors: Combo A. , Batista A. J. N. , Sousa J. , Varandas C. A. F.
Published: March 2003

This article presents a new event-driven processing platform which uses a mixture of digital signal processors and field programmable gate arrays to provide data reduction and real-time processing and control capabilities for long discharge fusion experiments. The architecture and physical implementation aims to provide more processing power, a mathematical algorithm description interface, and an easy integration with existing acquisition systems as well as the seamless integration with an event-driven data acquisition and control system for current and upcoming fusion experiments. A complete framework from the algorithm description to the physical implementation of the new platform in a heterogeneous processing system will be described.
ICF ignition capsule neutron, gamma ray, and high energy x-ray images
Authors: Bradley P. A. , Wilson D. C. , Swenson F. J. , Morgan G. L.
Published: March 2003

Post-processed total neutron, RIF neutron, gamma-ray, and x-ray images from 2D LASNEX calculations of burning ignition capsules are presented. The capsules have yields ranging from tens of kilojoules (failures) to over 16 MJ (ignition), and their implosion symmetry ranges from prolate (flattest at the hohlraum equator) to oblate (flattest towards the laser entrance hole). The simulated total neutron images emphasize regions of high DT density and temperature; the reaction-in-flight neutrons emphasize regions of high DT density; the gamma rays emphasize regions of high shell density; and the high energy x rays (>10 keV) emphasize regions of high temperature.
Neutron imaging of ICF target plasmas (invited)
Authors: Disdier L. , Rouyer A. , Fedotoff A. , Bourgade J.-L. , Marshall F. J. , Glebov V. Yu. , Stoeckl C.
Published: March 2003

Using a penumbral technique with a biconical aperture we have obtained neutron images with a spatial resolution of 20 μm. Implosions of DT filled CH microballons of ∼932 μm diameter at the Omega laser produced asymmetric images with full width at half maximum of 40 and 80 μm for 18.9 μm thick CH shells. Image sizes and shapes are in good agreement with the 4–7 keV x-ray images of the same capsule. The improved resolution compared to our previous measurements arises from a longer line-of-sight (13 vs 8 m) and a new neutron detector obtained by filling an array of glass capillaries with a high optical index scintillator.
Observation of d–t fusion gamma rays (invited)
Authors: Caldwell S. E. , Berggren R. R. , Davis B. A. , Evans S. C. , Faulkner J. R. , Garcia J. A. , Griffith R. L. , Lash D. K. , Lerche R. A. , Mack J. M. , Morgan G. L. , Moy K. J. , Ortel J. A. , Sturges R. E. , Young C. S.
Published: March 2003

Deuterium–tritium (DT) reaction rates of imploding capsules have historically been measured using neutron detectors. Temporal resolution is limited by the size of the detector and distance from the source to detector. The reaction rates can also be measured using the 16.7 MeV gamma ray, which is produced by the same DT reaction, but statistically far less often than the 14.1 MeV neutron. Cherenkov detectors detect gamma rays by converting the gamma rays to electrons, which in turn produce Cherenkov light and record this visible light using a fast optical detector. These detectors can be scaled to large volumes in order to increase detection efficiency with little degradation in time resolution, and placed well away from the source since gamma rays do not suffer velocity dispersion between the source and detector. Gas-based Cherenkov detectors can also discriminate against lower-energy photons produced in and around the target. A prototype gas Cherenkov detector has been built and tested for detector response at the Idaho State University electron linear accelerator (LINAC). Later tests at the University of Rochester’s OMEGA laser facility proved the feasibility of this diagnostic by successfully recording the 16.7 MeV gamma ray. A second version has now been built to demonstrate the temporal resolution.
Trajectory simulations for an NSTX HIBP
Authors: Zhang X. , Schoch P. M. , Connor K. A.
Published: March 2003

The ion trajectories for a heavy ion beam probe (HIBP) diagnostic for the National Spherical Torus experiment NSTX are simulated. The National Spherical Torus experiment (NSTX) equilibria modeled include both low β and high β (β=23%) discharges. The simulation used a sodium ion beam with energies varying from 350 to 550 keV. Sodium is used to minimize attenuation in the large NSTX plasma. The energy range and beam deflection limits are consistent with existing equipment. The locations of the effective ion source and detector points were varied with the goal of maximizing the plasma coverage for both low β and high β discharges while minimizing the port space required. The effective source and detector locations are determined by the location of electrostatic steering plates. The optimal design may require crossover sweep systems such as those used on the Madison Symmetric Torus (MST) HIBP. The distance of the accelerator (source) and energy analyzer (detector) from NSTX can be increased with some reduction in plasma coverage. Puncture plots of the beam trajectory at port locations are presented along with plots of plasma coverage. There are clear trade-offs between the plasma coverage and the required port size. A single cord could be scanned with port diameters of only a few inches, but this would require scanning the ion energy and that implies using multiple shots. Single shot scans are practical with ports sizes of 8–12 in. The stringent requirements on sample volumes for zonal flow measurements can be met.
Zonal flow measurements using a heavy ion beam probe
Authors: Schoch P. M. , Connor K. A. , Demers D. R. , Zhang X.
Published: March 2003

Zonal flows are of keen interest in efforts to understand transport in magnetically confined plasma. Of the well-developed diagnostics, the heavy ion beam probe, HIBP, is most suited to measure the radial electric field, Er, associated with the flows in present medium to large devices. This paper discusses why the HIBP is capable of measuring Er and how to design a HIBP to optimize zonal flow measurements. The TEXT HIBP is used as an example of a typical system. The NSTX spherical torus is used in a design study for future work with emphasis on zonal flow measurements. The key diagnostic considerations are (1) sample volume size, (2) sample volume orientation, and (3) the ability to rapidly scan the sample volume in the radial direction. The measurement of principal interest here is Er but there is additional information in a nonlinear analysis of the fluctuations.
Laser-based methods for ultrasensitive trace-isotope analyses
Authors: Lu Z.-T. , Wendt K. D. A.
Published: March 2003

An overview of experimental approaches to sensitive and selective trace analysis of long-lived radioactive isotopes is given, emphasizing methods based upon laser spectroscopy techniques. Two such laser-based methods, resonance ionization mass spectrometry and atom trap trace analysis, have recently demonstrated high sensitivities and selectivities which are comparable to those of more mature methods such as accelerator mass spectrometry and low level counting. The analysis of long-lived radioactive isotopes has been used for a variety of applications in a broad range of scientific and technological fields and is steadily gaining importance. The development of these new laser-based methods can enhance our analysis capability and further expand the area of applications.
An iodine stabilized laser source at two wavelengths for accurate dimensional measurements
Authors: Jaatinen Esa
Published: March 2003

A tunable laser system is described that provides wavelength references at both 633 and 640 nm by locking to hyperfine components of molecular iodine using a simple external cell technique. The frequency uncertainty at each wavelength is less than 1 MHz and no calibration of the frequencies is required as they are both referenced to iodine transitions. Switching between references requires a simple adjustment of laser wavelength that produces no change in beam alignment. At either wavelength the laser provides more than 3 mW of unused light that is not modulated, making it useful for dimension measuring interferometry. The measurement of the diameter of silicon spheres to 2×10−8 is given as an example.
A microscope for imaging, spectroscopy, and lithography at the nanometer scale: Combination of a two-photon laser scanning microscope and an atomic force microscope
Authors: Schrey F. F. , Chaban E. E. , Matthews M. J. , Hsu J. W. P.
Published: March 2003

We designed and built a unique instrument that combines a two-photon laser scanning microscope (LSM) with an inverted atomic force microscope (AFM). Local photoluminescence (PL) spectroscopy and three-dimensional lithography are demonstrated using the two-photon LSM. High spatial resolution topographic images from the AFM can be recorded simultaneously with the PL images of the same region, allowing us to correlate PL variation and surface features of the sample. The wavelength of the short-pulse laser excitation can be varied continuously from 700 to 800 nm while the detection setup is optimized for signals between 350 and 650 nm. We demonstrate the performance of this instrument by examining the spatial variation of PL signals in GaN samples and by fabricating photonic crystal structures in polymer films.
Growth characteristics and potential applications in optical sensors of composite Cr4+:yttrium–aluminum–garnet (YAG)–Nd3+:YAG crystal fiber
Authors: Shen Yonghang , Chen Shuying , Zhao Weizhong , Chen Jun , Ye Linhua , Gu Jueguan , Grattan Kenneth T. V.
Published: March 2003

Composite Cr4+:yttrium–aluminum–garnet (YAG)–Nd3+:YAG crystal fiber was grown by means of the laser heated pedestal growth method. By using a high quality Nd3+:YAG as the seed and a sintered powder rod as the source rod, it was shown that Cr4+:YAG can be readily grown on a Nd3+:YAG end surface. The crystal fiber thus produced was processed and preliminary results showed that the crystal fiber demonstrated laser performance as a compact passively Q-switched laser device. A Q-switched laser output showing a 9 ns pulse duration, a 19 mW average output and a 10 kHz repetition rate was achieved. The use of the fiber in high temperature optical sensor application is discussed.
Self-consistent photoacoustic techniques for thermal diffusivity measurements of self-curable resins
Authors: Balderas-López J. A.
Published: March 2003

Two self-consistent photoacoustic methodologies, for measuring thermal diffusivity of self-curable resins, are presented. These methodologies make use of the analytical solution for the one-dimensional heat diffusion problem for a three-layer system, assuming the surface absorption model. The analytical procedure relies on the normalization of the theoretical photoacoustic signal from the three layers with the corresponding signal from the uppermost two layers, involving linear fits on the normalized amplitude (in semilog scale) and phase, as functions of the modulation frequency root square. The normalization procedure eliminates the frequency-dependent instrumental electronic contribution (transfer function) and some thermophysically nonrelevant proportionality factors in the theoretical equations, thus making the analysis feasible. The thermal diffusivity of two different self-curable resins was measured and good agreement was obtained between results from both the amplitude and phase, showing consistency between these two photoacoustic methodologies.
Combined molecular beam epitaxy and diffractometer system for in situ x-ray studies of crystal growth
Authors: Jenichen Bernd , Braun Wolfgang , Kaganer Vladimir M. , Shtukenberg Alexander G. , Däweritz Lutz , Schulz Carl-Günther , Ploog Klaus H. , Erko Alexei
Published: March 2003

A combination of a molecular beam epitaxy (MBE) machine and a six circle diffractometer has been constructed at a dedicated wiggler beamline at the storage ring BESSY II for in situ investigations of III–V compound crystal growth. The growth conditions in our system reach a high MBE standard with a noncooled base pressure of 2×10−10 mbar. A fast entry load lock is available for sample exchange. Large-area Be windows in the ultrahigh vacuum chamber allow us to measure reflections at entrance and exit angles up to 45°, i.e., large perpendicular momentum transfers are possible. In situ reflection high energy electron diffraction and x-ray fluorescence measurements can be performed simultaneously with x-ray scattering. A GaAs(001) surface prepared and examined in our system reveals terrace widths of 450 nm and β(2×4) reconstruction domain sizes of 210 nm. The possibility of time-resolved x-ray diffraction studies is demonstrated by observation of intensity oscillations during layer-by-layer homoepitaxial growth on the GaAs(001)β(2×4) surface. The resolution functions of our experiment are determined.
Compensated current injection circuit, theory and applications
Authors: Fontana Giorgio
Published: March 2003

This article presents a detailed description, analysis and example of the practical application of a wide frequency band voltage-to-current converter. The converter is characterized by a combination of positive and negative feedback loops. This feature allows compensation for parasitic impedance connected in parallel with the useful load, which in turn keeps an excitation current flowing through the useful load independent of its impedance. The simplicity of the circuit and its good electrical properties are additional advantages of the scheme.
X-ray emission line profile modeling of hot stars
Authors: Kramer Roban H. , Tonnesen Stephanie K. , Cohen David H. , Owocki Stanley P. , ud-Doula Asif , MacFarlane Joseph J.
Published: March 2003

The launch of high-spectral-resolution x-ray telescopes (Chandra, XMM) has provided a host of new spectral line diagnostics for the astrophysics community. In this paper we discuss Doppler-broadened emission line profiles from highly supersonic outflows of massive stars. These outflows, or winds, are driven by radiation pressure and carry a tremendous amount of kinetic energy, which can be converted to x rays by shock-heating even a small fraction of the wind plasma. The unshocked, cold wind is a source of continuum opacity to the x rays generated in the shock-heated portion of the wind. Thus the emergent line profiles are affected by transport through a two-component, moving, optically thick medium. While complicated, the interactions among these physical effects can provide quantitative information about the spatial distribution and velocity of the x-ray-emitting and absorbing plasma in stellar winds. We present quantitative models of both a spherically symmetric wind and a wind with hot plasma confined in an equatorial disk by a dipole magnetic field.
High-resolution soft x-ray spectrometer for the NSTX tokamak
Authors: Beiersdorfer P. , Bitter M. , May M. J. , Roquemore L.
Published: March 2003

A high-resolution spectrometer for measuring the soft x-ray emission (7–24 Å) has been implemented on the National Spherical Tokamak Experiment (NSTX). The instrument will be used to study the K-shell spectra of O, Ne, and Mg as well as the L-shell spectra of Fe and Ni and to calibrate spectral diagnostics of fusion and astrophysical plasmas. The spectrometer employs a spherically bent crystal for dispersion and two microchannel-plate intensified 1D charged-coupled devices for recording the x rays. The temporal resolution is 25 ms per spectrum.
Results from the National Spherical Torus Experiment x-ray crystal spectrometer
Authors: Bitter M. , Hill K. , Roquemore L. , Beiersdorfer P. , Thorn D. , Gu Ming Feng
Published: March 2003

A high-resolution x-ray crystal spectrometer has recently been installed at the National Spherical Torus Experiment to record the satellite spectra of helium-like argon, Ar XVII, in the wavelength range from 3.94 to 4.00 A for measurements of ion and electron temperatures, and measurements of the ionization equilibrium of argon, which is of interest for studies of ion transport. The instrument presently consists of a spherically bent quartz crystal and a conventional one-dimensional position-sensitive multiwire proportional counter, but it will soon be upgraded to a new type of x-ray imaging crystal spectrometer by the installation of a large size (10 cm×30 cm) two-dimensional position-sensitive detector that will allow us to obtain temporally and spatially resolved spectra from a 80 cm high cross-section of the plasma. In its present configuration, the spectrometer has been optimized for high throughput so that it is possible to record spectra with small statistical errors with a time resolution of 10 ms by adding only small, nonperturbing amounts of argon to the plasma. The spectrometer is most valuable for measurements of the ion temperature in the absence of a neutral beam in ohmically heated and rf heated discharges, when charge exchange recombination spectroscopy does not function. Electron temperature measurements from the satellite-to-resonance line ratios have been important for a quantitative comparison with (and verification of) the Thomson scattering data. The article will describe the instrumental details of the present and future spectrometer configurations and present recent experimental results.
Imaging x-ray crystal spectrometers for KSTAR
Authors: Lee S. G. , Bak J. G. , Bitter M. , Moon M. K. , Nam U. W. , Jin K. C. , Kong K. N. , Seon K. I.
Published: March 2003

Two x-ray imaging crystal spectrometers are presently designed for the KSTAR tokamak. The instruments will provide temporally and spatially resolved spectra of heliumlike argon (or krypton) from a large cross section of the plasma. The spectral data will be used for profile measurements—both within and perpendicular to the horizontal midplane of KSTAR—of the ion and electron temperatures, the rotation velocity, and the ionization equilibrium. Each spectrometer will consist of a spherically bent quartz crystal and large area two-dimensional position-sensitive multiwire proportional counter. The article presents the design for the KSTAR x-ray imaging crystal spectrometers, and the fabrication and initial test results from the large area two-dimensional multiwire proportional counter.
Measurement of fast electron distribution using a flexible, high time resolution hard x-ray spectrometer
Authors: O’Connell R. , Den Hartog D. J. , Forest C. B. , Harvey R. W.
Published: March 2003

A 16 spatial channel hard x-ray (HXR) diagnostic using solid state CdZnTe detectors (active area 10 mm×10 mm×2 mm, 50 mm×20 mm×20 mm packaged) has recently been installed on the Madison Symmetric Torus (MST) reversed field pinch to measure the XR flux from ∼10 to 300 keV. Rather than using conventional pulse height analysis, the shaped output pulses from the detector are digitized using 12-bit, 10 MHz ADCs. The resulting waveforms are then fitting with multiple Gaussians; this allows a fraction of normally discarded pile-up events to be recovered. The technique is cost effective and allows for (a) excellent energy resolution—limited by the detector resolution rather than electronics; (b) dynamic time binning—rather than counting over predefined time bins, x-ray events are recorded as discretely timed events; (c) better noise rejection/pile up detection—achieved by fitting using the full information of the time history and known pulse shape from the amplifier; and (d) simple hardware implementation. The measured HXR energy flux is coupled to the Fokker–Planck code CQL3D to derive the electron distribution function for the fast electrons and infer the diffusion coefficient. The diagnostic has been used to measure diffusion coefficient on MST during improved confinement plasmas and measurements of radial diffusion of electron Bernstein wave (EBW) heated fast electrons are planned.
Real-time signal analysis on the TCV PHA diagnostic
Authors: Madeira T. I. , Rodrigues A. P. , Varandas C. A. F. , Amorim P. , Duval B. P.
Published: March 2003

A pulse height analysis (PHA) x-ray system has been successfully implemented on the tokamak TCV, aiming at a low cost monitor system of the plasma electron temperature and impurity content. To meet the need for high throughput and fast acquisition, mandatory in tokamaks with relatively short pulse duration and high-energy fluxes, the original germanium detector is being replaced by a Silicon Drifted Detector and the traditional dedicated analog electronics for a Digital X-Ray Signal CAMAC compatible unit. A separate DSP system will provide higher quality spectra with an increased time resolution. An in-site developed DSP-based VME intelligent module, specially designed for real-time plasma control, is being programmed for fast data acquisition and simultaneous real-time data processing. The current goal is to obtain spectra with sufficient statistics every 10 ms, fit the data in real-time, evaluate the quality of the measurement and adjust remotely controllable x-ray PHA filters and apertures and finally provide the PHA data to the TCV control system. The final goal is to provide real-time data analysis with a temperature and impurity content monitor that can be used for machine feedback. Trials with the SDD and the DSP unit have shown that this is achievable.
Design and noise model for CCD-based, time-resolved PHA measurements
Authors: Schooff R. , Diem S. , Fonck R. , Reinke M. , Tritz K.
Published: March 2003

A CCD pulse height analysis system is considered for the measurement of electron temperature on the Pegasus Toroidal Experiment. The first-generation CCD/PHA system will have one spatial point and obtain seven time points with a time resolution of 2.4 ms. Time resolution is achieved by shifting the exposed rows of the CCD behind a masked off portion of the chip during the plasma discharge. Criteria for valid photon detection are developed to account for pulse pileup effects and maximize count rate. Error analysis and Monte Carlo calculations indicate that the CCD/PHA system should achieve typical uncertainties to <5% of the deduced temperature.
Photometric calibration of an EUV flat field spectrometer at the advanced light source
Authors: May M. , Lepson J. , Beiersdorfer P. , Thorn D. , Chen H. , Hey D. , Smith A.
Published: March 2003

The photometric calibration of an extreme ultraviolet flat field spectrometer has been done at the Advanced Light Source at Lawrence Berkeley National Laboratory. This spectrometer is used to record spectrum for atomic physics research from highly charged ions in plasmas created in the Livermore electron beam ion traps EBIT-I and SuperEBIT. Two calibrations were done each with a different gold-coated grating, a 1200 l/mm and a 2400 l/mm, that covered 75–300 Å and 15–160 Å, respectively. The detector for this calibration was a back thinned charge coupled device. The relative calibration was determined for several different incident angles for both gratings. Within the scatter of the data, the calibration was roughly insensitive to the incidence angle for the range of angles investigated.
Turbulence imaging and applications using beam emission spectroscopy on DIII-D (invited)
Authors: McKee G. R. , Fenzi C. , Fonck R. J. , Jakubowski M.
Published: March 2003

Two-dimensional measurements of density fluctuations are obtained in the radial and poloidal plane of the DIII-D tokamak with the Beam Emission Spectroscopy (BES) diagnostic system. The goals are to visualize the spatial structure and time evolution of turbulent eddies, as well as to obtain the 2D statistical properties of turbulence. The measurements are obtained with an array of localized BES spatial channels configured to image a midplane region of the plasma. 32 channels have been deployed, each with a spatial resolution of about 1 cm in the radial and poloidal directions, thus providing measurements of turbulence in the wave number range 0<k⊥⩽3 cm−1. A 5 (radial)×6 (poloidal) channel grid provides time-resolved images near the outer midplane at the sampling frequency of 1 MHz, thus providing a modest spatial resolution, high throughput, high time resolution turbulence imaging system. The images and resulting movies have broad application to a wide variety of fundamental turbulence studies: imaging of the highly complex, nonlinear turbulent eddy interactions, measurement of the 2D correlation function, and S(kr,kθ) wave number spectra, and direct measurement of the equilibrium and time-dependent turbulence flow field. The time-dependent, two-dimensional turbulence velocity flow-field is obtained with time-delay-estimation techniques.
Gas puff imaging of edge turbulence (invited)
Authors: Maqueda R. J. , Wurden G. A. , Stotler D. P. , Zweben S. J. , LaBombard B. , Terry J. L. , Lowrance J. L. , Mastrocola V. J. , Renda G. F. , D’Ippolito D. A. , Myra J. R. , Nishino N.
Published: March 2003

The gas puff imaging (GPI) diagnostic can be used to study the turbulence present at the edge of magnetically confined plasmas. In this diagnostic the instantaneous two-dimensional (2D) radial vs poloidal structure of the turbulence is measured using fast-gated cameras and discrete fast chords. By imaging a controlled neutral gas puff, of typically helium or deuterium, the brightness and contrast of the turbulent emission fluctuations are increased and the structure can be measured independently of natural gas recycling. In addition, recent advances in ultrafast framing cameras allow the turbulence to be followed in time. The gas puff itself does not perturb the edge turbulence and the neutral gas does not introduce fluctuations in the emission that could possibly arise from a nonsmooth (turbulent) neutral gas puff. Results from neutral transport and atomic physics simulations using the DEGAS 2 code are discussed showing that the observed line emission is sensitive to modulations in both the electron density and the electron temperature. The GPI diagnostic implementation in the National Spherical Torus Experiment (NSTX) and Alcator C-Mod tokamak is presented together with example results from these two experiments.
High-speed, electronically shuttered solid-state imager technology (invited)
Authors: Reich R. K. , Rathman D. D. , O’Mara D. M. , Young D. J. , Loomis A. H. , Kohler E. J. , Osgood R. M. , Murphy R. A. , Rose M. , Berger R. , Watson S. A. , Ulibarri M. D. , Perry T. , Kosicki B. B.
Published: March 2003

Electronically shuttered solid-state imagers are being developed for high-speed imaging applications. A 5 cm×5 cm, 512×512-element, multiframe charge-coupled device (CCD) imager has been fabricated for the Los Alamos National Laboratory DARHT facility that collects four sequential image frames at megahertz rates. To operate at fast frame rates with high sensitivity, the imager uses an electronic shutter technology designed for back-illuminated CCDs. The design concept and test results are described for the burst-frame-rate imager. Also discussed is an evolving solid-state imager technology that has interesting characteristics for creating large-format x-ray detectors with short integration times (100 ps to 1 ns). Proposed device architectures use CMOS technology for high speed sampling (tens of picoseconds transistor switching times). Techniques for parallel clock distribution, that triggers the sampling of x-ray photoelectrons, will be described that exploit features of CMOS technology.
Acceleration characteristics of spherical and nonspherical pellets by the LHD impurity pellet injector
Authors: Nozato Hideaki , Morita Shigeru , Goto Motoshi , Ejiri Akira , Takase Yuichi
Published: March 2003

An impurity pellet injector with three differential pumping systems has been developed to study the particle/impurity transport in combination with bremsstrahlung profile measurement in the Large Helical Device (LHD) plasma. For this purpose three different shaped pellets are tested; sphere, hemisphere, and cylinder. The characteristics of the pellets accelerated by pressurized helium gas were studied as a function of shape and mass of the pellets and He gas pressure. The velocity of the pellets was measured at two different positions using a He–Ne laser, two optical fibers, two lenses, and a slit with two narrow apertures. The delay time until the pellet begins to accelerate, and the effect of opening time of the vacuum valves for differential pumping on the amount of He gas leakage were also investigated. The difference in the velocities among the three different shaped pellets is discussed with the simple analytical model.
Space-resolved VUV spectroscopy using the 3 m normal incidence spectrometer with back-illuminated CCD detector in the LHD
Authors: Morita Shigeru , Goto Motoshi
Published: March 2003

Space-resolved VUV (300–3100 Å) spectroscopy using the 3 m normal incidence spectrometer has been developed for the study of edge plasmas in the Large Helical Device (LHD). The radial (vertical) profile is obtained with a space-resolved slit placed horizontally between the entrance slit and the grating of the spectrometer. Using a cylindrical mirror placed in the front of the entrance slit, which magnifies the vertical image five times, a full vertical distribution of the LHD plasma is projected on the back-illuminated CCD detector. The two-dimensional distribution can be measured by scanning a toroidal slit placed vertically between the spectrometer and LHD during a single discharge. Recently, first results were successfully obtained. Some examples of the vertical profile and temporal behaviors of the ion temperature are presented with a description of the instrumentation. Unfortunately, the poloidal rotation could not be measured, because the data from the CCD operated in room temperature included a lot of thermal noise. After repairing the cooling system, the S/N ratio can be much improved. The simultaneous measurement of the vertical profiles of VUV line emissions, ion temperature, and poloidal rotation will become possible.
Focusing x-ray spectrograph with crossed dispersion
Authors: Song B. M. , Pikuz S. A. , Shelkovenko T. A. , Chandler K. M. , Mitchell M. D. , Hammer D. A.
Published: March 2003

We present a focusing spectrograph configuration, the Focusing Spectrograph with Crossed Dispersion (FSCD), that enables us to solve the problem in a crystal spectrograph of reflected radiation in many orders. In the FSCD, the x-ray radiation from a small source is dispersed by a transmission grating placed in front of the Bragg reflector (mica crystal). This configuration retains the advantages of a spherically bent mica crystal spectrograph while enabling the analysis of the radiation in a number of spectral bands simultaneously and independently. Results using a 150 mm radius spherically bent mica crystal combined with 0.5 μm period gold transmission gratings in X pinch experiments are presented.