bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison between fast-sweep Langmuir probe and triple probe for fluctuations measurements
Authors: Riccardi C. , Longoni G. , Chiodini G. , Fontanesi M.
Published: February 2004

Two techniques are applied and the results compared both in the plasma core and in the edge region of “Thorello,” to estimate electron temperature fluctuations. The first method is a fast-sweep Langmuir probe: it is a new apparatus based on a dual channel circuit that compensates for stray capacitance and permits sweep speeds up to 400 kHz, so that we can investigate the electrostatic turbulence with good temporal resolution. The second technique is the conventional triple probe: this method allows us to measure density, temperature, and floating potential as a function of time. The fast-sweep Langmuir probe provides a more reliable electron temperature fluctuations and these measurements are essential for a correct interpretation of density and potential fluctuations.
Filamentary current detection in stellarator plasmas
Authors: Medina F. , Pedrosa M. A. , Ochando M. A. , Rodrı́guez L. , Hidalgo C. , Fraguas A. L. , Carreras B. A. ,   the TJ-II Team
Published: February 2004

In this work we present the experimental setup, combining edge, and x-ray diagnostics, used to localize the currents generated by fast electrons confined near the plasma periphery in TJ-II plasmas. The method is similar to that used for the experimental determination of the magnetic field mapping in stellarators, just intercepting the trajectories of test electrons. The fact that stellarators can keep magnetic structures “frozen” in vacuum during the field plateau enables the detection of local currents near the plasma periphery in the TJ-II stellarator.
Diagnostic first mirrors for burning plasma experiments (invited)
Authors: Voitsenya V. , Costley A. E. , Bandourko V. , Bardamid A. , Bondarenko V. , Hirooka Y. , Kasai S. , Klassen N. , Konovalov V. , Nagatsu M. , Nakamura K. , Orlinskij D. , Orsitto F. , Poperenko L. , Solodovchenko S. , Stan’ A. , Sugie T. , Taniguchi M. , Vinnichenko M. , Vukolov K. , Zvonkov S.
Published: February 2004

The current state of investigations of the problem of providing first mirrors (FMs) for diagnostic systems in a reactor-grade fusion device is summarized. Results obtained in simulation experiments that have been conducted during recent years in several laboratories are presented. Attention is concentrated on two processes that can have an opposite effect but both can lead to degradation of mirror optical properties, namely: sputtering by charge exchange atoms which leads to erosion, and deposition which leads to surface contamination. It is shown in the analysis that when sputtering dominates, mirrors of monocrystalline refractory metals (Mo, W) can have a sufficiently long lifetime even for FMs that have to be located close to the first wall. Similarly, films of low sputtering yield metals on high thermal conductivity substrates (e.g., Rh on Cu) can be used for FMs in locations where the charge exchange flux is reduced to about a tenth of that at the first wall. However, deposition poses a serious threat to the lifetime of FMs but more modeling and experimental investigations are necessary before quantitative conclusions can be reached. Some mitigation methods are possible and these are briefly discussed.
Target area and diagnostic interface issues on the National Ignition Facility (invited)
Authors: Bell Perry , Lee Dean , Wootton Alan , Mascio Bill , Kimbrough Joe , Sewall Noel , Hibbard Wilthea , Dohoney Pat , Landon Mark , Christianson George , Celeste John , Chael Jerry
Published: February 2004

The National Ignition Facility (NIF) is under construction at Lawrence Livermore National Laboratory for the DOE Stockpile Stewardship Program. It will be used for experiments for inertial confinement fusion ignition, high energy density science, and basic science. Many interface issues confront the experimentalist who wishes to design, fabricate, and install diagnostics, and to help this process, a set of standards and guideline documents is being prepared. Compliance with these will be part of a formal diagnostic design review process. In this article we provide a short description of each, with reference to more complete documentation. The complete documentation will also be available through the NIF Diagnostics web page. Target area interface issues are grouped into three categories. First are the layout and utility interface issues which include the safety analysis report, target area facility layout; target chamber port locations; diagnostic interferences and envelopes; utilities and cable tray distribution; and timing and fiducial systems. Second are the environment interface issues which include radiation electromagnetic interference/electromagnetic pulse effects and mitigation; electrical grounding, shielding, and isolation; and cleanliness and vacuum guidelines. Third are the operational interface issues which include manipulator based target diagnostics, diagnostic alignment, shot life cycle and setup, diagnostic controllers; integrated computer control system; shot data archival; classified operations; and remote operations.
Multiparameter data acquisition system for spectroscopy
Authors: Beiersdorfer P. , Brown G. V. , Hildebrandt L. , Wong K. L. , Ali R.
Published: February 2004

A powerful and versatile, simple to use multiparameter data acquisition system has been implemented for use in spectroscopy. In its standard configuration, the system can acquire signal from 16 time-to-digital converter channels, 16 analog-to-digital converter channels, and 12 scaler inputs. The system was put to use on the electron beam ion trap experiment to record the output from four position-sensitive proportional counters in two soft x-ray spectrometers together with the signal from an x-ray pulse height analyzer. Also recorded are the electron beam energy and the pulse height distribution of the proportional counters. All data are recorded as a function of time. Because the relevant parameters are recorded simultaneously, software gates instead of hardware gates are used to select the data of interest. This has led to a substantial cost saving over earlier data acquisition systems. Data are stored in binary or in ascii format for system-independent processing. The operation of the system is demonstrated in a measurement of the M-shell soft x-ray spectrum of gold. We used the system to record the 3–4 and 3–5 transitions of gold (Au44+–Au51+) excited with a simulated Maxwellian with electron temperature of 2.5 keV.
Calibration and initial operation of the HIBP on the MST
Authors: Lei J. , Shah U. , Demers D. R. , Connor K. A. , Schoch P. M.
Published: February 2004

For the first time, a heavy ion beam probe (HIBP) has been installed on a reversed field pinch, i.e., Madison symmetric torus (MST), to measure the plasma potential profile, potential, and electron density fluctuations, etc. The application of a HIBP on MST has presented new challenges for this diagnostic. The primary sources of difficulty are small access ports, high plasma, and, ultraviolet (UV) flux and a confining magnetic field produced largely by plasma currents. The requirement to keep ports small so as to avoid magnetic field perturbations led to the development of the cross-over sweep system. The effectiveness and calibration of this sweep system will be reported. In addition, this diagnostic is now operating with greater plasma/UV loading effects than most previous Rensselaer HIBPs. The plasma flux is reduced by using a magnetic suppression structure. The UV flux appears to be the dominant cause of the remaining loading, which is substantial. The magnetic field being largely produced by the plasma makes determination of measurement locations exclusively from trajectory calculations difficult. Initial operation results have shown that the magnetic field model we are using to calculate our ion trajectories has an inaccuracy of about 10%, and thus subsequent development of improved confining field models is important. Secondary signals have been detected, and the levels are smaller than that from the UV induced noises. Methods to increase the signal levels are discussed. A very rough estimation of the potential at a typical MST core location is 0.8–2 kV. Fluctuations in the frequency range 100–20 kHz have also been observed.
Modified biased split detectors for the HIBP electrostatic energy analyzer
Authors: Nedzelskiy I. S. , Dreval N. B. , Khrebtov S. M. , Komarov A. D. , Kozachok A. S. , Krupnik L. I.
Published: February 2004

In electrostatic energy analyzers of heavy ion beam probes the required accuracy of plasma potential measurements is provided by differential detection of the ion beam on the split detector. Secondary electrons created on the detector surface by the analyzed ions and ultraviolet plasma radiation can strongly disturb the measurements. In this article we consider the influence on analyzer operation of secondary electrons emitted from the detector, describe the relation for corresponding errors in the plasma potential measurements, and present two modified biased split detectors which avoid these errors.
Omegatron mass spectrometer for analysis of ion concentrations in hydrogenic plasmas
Authors: Hollmann E. M. , Antar G. , Doerner R. P. , Luckhardt S. C.
Published: February 2004

We describe an omegatron-type mass spectrometer used for measurement of the molecular and atomic ion concentrations as well as the ion species temperatures in hydrogenic plasmas. The experiments were performed in the PISCES-A linear plasma experiment with electron densities n≈1011–1012 cm−3, ion temperatures Ti≈2–8 eV, electron temperatures Te≈3–30 eV, and magnetic fields B=0.8–1.9 kG. The resulting mass spectra show clear evidence of atomic hydrogen H+, as well as of the molecular ions H2+ and H3+, with H+ and H3+ usually being dominant. It is found that large electron repeller voltages (≈−200 V) are important for preventing electrons from entering the diagnostic region and ionizing the residual gas. The relative peak heights for the different ions are found to vary as a function of ion repeller voltage, probably due to differences in ion temperature.
Multichannel electron cyclotron emission radiometry in TJ-II stellarator
Authors: de la Luna E. , Sánchez J. , Tribaldos V. , Estrada T.
Published: February 2004

Electron cyclotron emission measurements are routinely performed in TJ-II stellarator by means of a multichannel heterodyne radiometer. The radiometer is absolutely calibrated and measures the temperature profile with high temporal resolution. The description of the radiometer, the calibration procedure, and some data taken during the occurrence of fast phenomena in the plasma (edge localized mode-like events and central temperature crashes) are presented in the article.
Electron cyclotron resonance heating in spherical plasmas: O–X–EBW mode conversion in MAST
Authors: Preinhaelter J. , Irzak M. A. , Vahala L. , Vahala G.
Published: February 2004

Using a full wave solution, the O–X–EBW mode conversion is examined for density and magnetic profiles in MAST. The effects of magnetic shear and the sharp density pedestal for H-mode operation are considered with an eye to understanding both electron cyclotron emission (ECE) and electron cyclotron resonance heating (ECRH).
X-ray backlighting for the National Ignition Facility (invited)
Authors: Landen O. L. , Farley D. R. , Glendinning S. G. , Logory L. M. , Bell P. M. , Koch J. A. , Lee F. D. , Bradley D. K. , Kalantar D. H. , Back C. A. , Turner R. E.
Published: February 2004

X-ray backlighting is a powerful tool for diagnosing a large variety of high-density phenomena. Traditional area backlighting techniques used at Nova and Omega cannot be extended efficiently to National Ignition Facility scale. New, more efficient backlighting sources and techniques are required and have begun to show promising results. These include a backlit-pinhole point-projection technique, pinhole and slit arrays, distributed polychromatic sources, and picket-fence backlighters. In parallel, there have been developments in improving the data signal-to-noise and, hence, quality by switching from film to charge-coupled-device-based recording media and by removing the fixed-pattern noise of microchannel-plate-based cameras.
Radiographic image analysis of cylindrical implosion experiments (invited)
Authors: Scott J. M. , Beck J. B. , Batha S. H. , Barnes C. W. , Tubbs D. L.
Published: February 2004

Radiography is a heavily used tool for diagnosing laser-based hydrodynamic experiments. A successful experiment relies on the gathering of data over a time window where the relevant physics occurs and on an accurate analysis of those data. Comparison of this experimental data to theory is often best done by generating simulated images from hydrodynamic calculations, including all necessary and important experimental details. Care must be taken to treat both the experimental and theoretical images identically in the analysis. Frequently, image filtering and enhancement routines are used to obtain interface location and perturbation information from the radiographic image. Previous techniques were found to be too sensitive to global image details. New procedures have been developed which utilize local operators that provide better edge or interface identification without bias. These procedures are benchmarked and validated using static radiographic targets of known configuration that mock up experimental situations of interest. The experiment and the image analysis development are described, including discussion of key contributions to the uncertainty of the results.
Advanced x-ray and extreme ultraviolet diagnostics and first applications to x-pinch plasma experiments at the Nevada Terawatt Facility
Authors: Kantsyrev V. , Bauer B. , Shlyaptseva A. , Fedin D. , Hansen S. , Presura R. , Batie S. , Brinsmead W. , Faretto H. , Le Galloudec B. , Oxner A. , Chamberlain D. , Ouart N. , Jones A. , LeBeau H. , Gharaibeh M.
Published: February 2004

A wide variety of x-ray and extreme ultraviolet (EUV) diagnostics are being developed to study z-pinch plasmas at the Nevada Terawatt Facility at the University of Nevada, Reno. Time-resolved x-ray/EUV imaging and spectroscopy, x-ray polarization spectroscopy, and backlighting will be employed to measure profiles of plasma temperature, density, flow, and charge state, and to investigate electron distribution functions and magnetic fields. The instruments are state-of-the-art applications of glass capillary converters (GCC), multilayer mirrors (MLM), and crystals. New devices include: a novel GCC-based two-dimensional imaging spectrometer, a six-channel crystal/MLM spectrometer (“polychromator”) with a transmission grating spectrometer, and two sets of x-ray/EUV polarimeters/spectrometers. An x-pinch backlighter is under development. X-ray polarimeter/spectrometer, a survey spectrometer, a multichannel time-gated x-ray pinhole camera, and filtered fast x-ray diodes have observed the structure of Ti and Fe x pinches driven by a 0.9 MA current. X-ray yield and pulse duration depend sensitively on the wire load.
X-ray backlighting of wire array Z-pinch implosions using X pinch
Authors: Lebedev S. V. , Beg F. N. , Bland S. N. , Chittenden J. P. , Dangor A. E. , Haines M. G. , Zakaullah M. , Pikuz S. A. , Shelkovenko T. A. , Hammer D. A.
Published: February 2004

The dynamics of wire arrays have been studied using a point-projection X-pinch x-ray backlighter installed in one of the return posts of the MAGPIE generator. Variations of diameter (15–50 μm aluminum) and number of wires (two or four) in the X-pinch enabled backlit images in the range of 140–200 ns after the current start. A temporal and spatial resolution of <1 ns and 5 μm is achieved. The radiographic images of aluminum wire array show that the wire cores are present at the original position until 80% of the implosion time and the size of the wire cores is 0.25 mm for aluminum and 0.1 mm for tungsten. A very fine structure of the order of 10 μm has been observed in titanium wire arrays.
One-dimensional x-ray imaging using a spherically bent mica crystal at 4.75 keV
Authors: Workman J. , Evans S. , Kyrala G. A.
Published: February 2004

One-dimensional x-ray imaging of static gold bars using a spherically bent mica crystal is presented for the first time at an x-ray energy of 4.75 keV. X rays are produced using 1-ns-square pulses on the TRIDENT laser facility driving the He-like resonance transition in solid titanium disks. Time-integrated images of square profile parallel gold bars are recorded on direct exposure film with a magnification of ∼10. Rising edge measurements of the bars demonstrate resolutions of about 6–7 μm over a 400 μm field of view.
Relative x-ray backlighter intensity comparison of Ti and Ti/Sc combination foils driven in double-sided and single-sided laser configuration
Authors: Bullock A. B. , Landen O. L. , Bradley D. K.
Published: February 2004

Use of multiple backlighter foils and/or double-sided laser interaction geometry with backlit imaging can result in improved backlighter efficiency. An experimental comparison of backlighter intensity for Ti foils and Ti/Sc combination foils in both the one-sided and double-sided laser-interaction configuration is presented. Spectrally integrated framing camera images show intensity contributions of front and rear backlighter surfaces for both foil types. Analysis of time-resolved x-ray spectra collected from foil targets show the relative contribution of Ti and Sc 2–1 He-like resonance lines to the total backlighter intensity.
The ten-channel pulsed radar reflectometer at the TEXTOR-94 tokamak
Authors: van Gorkom J. C. , van de Pol M. J. , Donné A. J. H.
Published: February 2004

A new ten-channel pulsed radar reflectometer has been taken into operation at the Torus Experiment for Technology Oriented Research-94. The system will be used simultaneously as a density profile and as a density fluctuation diagnostic. Ten density layers from 0.4×1019 to 4×1019 m−3 can be probed simultaneously at 2 MHz. The design of the diagnostic has undergone some changes, to improve reliability of the system. Examples of time delay measurements are shown. These examples illustrate the fluctuation capabilities of the diagnostic at high time resolution, as well as the response of the different channels to density profile changes.
Electron cyclotron emission imaging diagnostic on TEXTOR
Authors: Deng B. H. , Domier C. W. , Luhmann N. C. , Donné A. J. H. , van de Pol M. J.
Published: February 2004

A 16-channel electron cyclotron emission imaging diagnostic system, developed by UC Davis in collaboration with the FOM-Instituut voor Plasmafysica Rijnhuizen, has been installed on the Torus Experiment for Technology Oriented Research tokamak. The system is designed to collect multichannel electron temperature profile and fluctuation data along a vertical chord of constant magnetic field, by collecting second harmonic X-mode emission. Technical details of the system are presented together with preliminary experimental data.
Heterodyne wave number measurement using a double B-dot probe
Authors: Eom G. S. , Kwon G. C. , Bae I. D. , Cho G. , Choe W.
Published: February 2004

An in situ method of wave number measurement inside a helicon plasma has been developed using a double B-dot probe with a heterodyne detection scheme. Each probe in the double B-dot probe measures the wave magnetic field. The signals from the two separately located probes inside the plasma are mixed with a local oscillator signal transforming the signals into transistor–transistor logic signals with intermediate frequency. The phase difference is obtained by a phase comparator yielding wave number information of a plasma wave.
Small, high frequency probe for internal magnetic field measurements in high temperature plasmas
Authors: Slough J. T. , Miller K. E.
Published: February 2004

In previous experiments on high temperature (>50 eV), high density (>1020 m−3) plasmas such as the field-reversed configuration (FRC), it has not been possible to obtain direct information of the internal field structure in a nondestructive way. The probe surface would vaporize due to high electron thermal transport as well as ablate due to high energy ion bombardment. To minimize these processes, the smallest possible probes made from materials with the longest thermal time to melting were constructed and tested. In order to measure fast magnetic field changes (∼several MHz), as well as not influence the FRC internal electric fields, the probe wall material was constructed from a nonconducting material. Of several insulating materials tested, beryllia was the only material that was found to be suitable. The probe wall consisted of a 0.3-m-long 2-mm-diam beryllia tube bored out to 1.5 mm. Inside the small bore, a “chain” probe of 24 loops was constructed out of 50-μm-diam magnet wire. The two axis probe measured axial and azimuthal FRC magnetic fields as small as a few gauss with centimeter resolution and a frequency response of 1 MHz or better. With the probe inserted, no changes in FRC confinement or behavior were observed over the entire 1 ms lifetime of the discharge.
Diagnostic of electron temperature fluctuations in a turbulent plasma
Authors: Fredriksen Å. , Riccardi C. , Longoni G.
Published: February 2004

Measurements of fluctuations have been performed in the steady-state magnetoplasma BLAAMANN characterized by a turbulent regime. In such a plasma electron temperature fluctuations can be of the same order of the floating potential ones, when the plasma is produced at high neutral pressure P>5×10−4 mbar. Measurements of electron temperature fluctuations are performed through triple probe diagnostic.
Accessing TJ-II data with remote procedure call
Authors: Sánchez E. , Vega J. , Crémy C. , Portas A. B.
Published: February 2004

A new software, based on the de facto standard Open Network Computing Remote Procedure Call (ONC RPC) has been developed for TJ-II database access. This software solution replaces a previous development based on Berkeley sockets in which the client implementation had the drawback that was platform dependent. From the user point of view, the access to the TJ-II database can be done from codes running in the central server or from any other computer in the network in exactly the same way. From the development point of view, the ONC RPC tools allow to generate source code for the clients in an easy and flexible manner, thus reducing the work needed to maintain/upgrade the library for different platforms. The access to the database is managed by a concurrent server program, running on the central server, which implements each access routine as a service on the network. This allows controlling the accesses to the database. A client library has been developed to provide connection with the data server. This library implements a client routine per service, that interchanges parameters between client and server programs using External Data Representation. The client library has been installed in different UNIX and UNIX-like platforms, including ALPHA AXP/Digital UNIX, Sparc/SOLARIUS, INTEL/LINUX and CRAY/UNICOS and in Windows (NT/95/98) platforms. The support for Windows platforms allows autonomous PC-based acquisition systems to integrate experimental data into the data base. A basic in-house developed identification system is used to control client connections. An access policy has been defined in order to assign different permissions to different clients.
Design of the National Ignition Facility diagnostic instrument manipulator
Authors: Hibbard W. J. , Landon M. D. , Vergino M. D. , Lee F. D. , Chael J. A.
Published: February 2004

The diagnostic instrument manipulator (DIM) provides a diagnostic platform to insert and retract a variety of instruments into and out of the National Ignition Facility target chamber. The DIM is a two-stage telescoping system, designed to fit on any of the DIM designated diagnostic ports on the target chamber, and will provide precision radial positioning, pointing, and alignment-to-target capability. The DIM provides a standard set of utilities, and cables to support the operation of instruments that require insertion into the target chamber. The DIM provides for positioning of diagnostic packages, and enables exchange of manipulator diagnostics between fusion laboratories. Principal design requirements for the DIM are presented. A half-length prototype of the DIM was designed and fabricated by Atomic Weapons Establishment in England and is being tested at Lawrence Livermore National Laboratory. The results of this testing are presented.
Optical characterization of plasma facing mirrors for a Thomson scattering system of a burning plasma experiment
Authors: Orsitto F. P. , Del Bugaro D. , DiFino M. , Maiolo A. , Montecchi M. , Nichelatti E. , Gowers C. , Nielsen P.
Published: February 2004

The general requirements for a plasma facing mirror (PFM) of a Thomson scattering system (TS) for a burning plasma experiment are (i) high and approximately constant reflectivity in the wavelength spectral range 400–800 nm; (ii) low sputtering yield and low erosion; (iii) high power damage threshold; (iv) good thermo-mechanical properties to preserve quality imaging. Rhodium-coated mirrors are chosen because they meet these requirements. Rhodium coated mirror were realized with substrates of copper and vanadium. The detailed optical characterization of these mirrors is presented: i.e., surface planarity measurements as well as roughness and reflectivity figures are presented. These data can be used for the choice of the PFM of a TS system for international thermonuclear experimental reactor.
Fluctuation studies using combined Mach/triple probe
Authors: Solomon W. M. , Shats M. G.
Published: February 2004

A probe consisting of two poloidally separated triple probes and a Mach probe (TMT probe) has been designed and installed on the H-1 heliac to study fluctuations. Mach probes are shown to be sensitive to the fluctuations in the electron density, electron and ion temperatures, and ion drift velocity. If the ion Larmor radius is much larger than the characteristic probe dimension, then the Mach probe is insensitive to the magnetic field. When the Mach probe is oriented such that the two tips are separated radially, it becomes sensitive to the radial velocity of the ions. A model has been devised to allow the above mentioned time-resolved plasma parameters to be reconstructed from the data obtained using the TMT probe. One of the important results of these studies is that ion temperature fluctuations cannot be neglected.
A synchrotron radiation diagnostic to observe relativistic runaway electrons in a tokamak plasma
Authors: Jaspers R. , Lopes Cardozo N. J. , Donné A. J. H. , Widdershoven H. L. M. , Finken K. H.
Published: February 2004

In present day tokamaks runaway electrons can be confined long enough to gain energies in the order of several tens of megaelectron volts. At these energies synchrotron radiation is emitted in the infrared wavelength range which can easily be detected by thermographic cameras. The spectral features of this synchrotron radiation are reviewed. On TEXTOR-94 a diagnostic exploiting this synchrotron radiation has been developed and is presented here. It is shown how to deduce the runaway parameters like runaway energy, pitch angle, runaway current and beam radius from the measurements. Based on the experience at TEXTOR-94 the feasibility of a similar synchrotron diagnostic on the International Thermonuclear Experimental Reactor is discussed. The maximum emission is expected in the wavelength range from 1–5 μm. A beam of 10 MeV runaway electrons with a current of about 15 kA will already be detectable.
Plasma diagnostics for the sustained spheromak physics experiment
Authors: McLean H. S. , Ahmed A. , Buchenauer D. , Den Hartog D. , Domier C. W. , Hill D. N. , Holcomb C. , Hooper E. B. , Morse E. C. , Nagata M. , Roh Y. , Stallard B. , Wood R. D. , Woodruff S. , Wurden G. , Wang Z. ,   SSPX Team
Published: February 2004

In this article we present an overview of the plasma diagnostics operating or planned for the sustained spheromak physics experiment device now operating at Lawrence Livermore National Laboratory. A set of 46 wall-mounted magnetic probes provide the essential data necessary for magnetic reconstruction of the Taylor relaxed state. Rogowski coils measure currents induced in the flux conserver. A CO2 laser interferometer is used to measure electron line density. Spectroscopic measurements include an absolutely-calibrated spectrometer recording extended domain spectrometer for obtaining time-integrated visible ultraviolet spectra and two time-resolved vacuum monochrometers for studying the time evolution of two separate emission lines. Another time-integrated spectrometer records spectra in the visible range. Filtered silicon photodiode bolometers provide total power measurements, and a 16 channel photodiode spatial array gives radial emission profiles. Two-dimensional imaging of the plasma and helicity injector is provided by gated television cameras and associated image-processing software. An array of fiber-coupled photodetectors with H alpha filters view across the midplane and in the injector region to measure neutral hydrogen concentrations. Several novel diagnostics are being fielded including a transient internal probe (TIP) and an ultrashort-pulse reflectometer (USPR) microwave reflectometer. The TIP probe fires a very high velocity optical bullet through the plasma and will provide fairly nonpertabative internal magnetic field and current measurements to compare with an equilibrium code model fitted to wall-mounted probes. The USPR is being designed to study edge density and turbulent fluctuations. A multipoint Thomson scattering system is currently being installed to give radial temperature and density profiles.
Charge exchange neutral particle analysis with natural diamond detectors on LHD heliotron
Authors: Isobe M. , Sasao M. , Iiduka S. , Krasilnikov A. V. , Murakami S. , Mutoh T. , Osakabe M. , Sudo S. , Kawahata K. , Ohyabu N. , Motojima O. ,   LHD experiment group
Published: February 2004

Semiconductor detectors based on natural diamonds have been installed on the Large Helical Device (LHD) heliotron to measure the energy distribution of charge exchange fast neutral particles from different viewing angles. Advantages of a natural diamond detector (NDD) are (1) very compact size, (2) relatively easy handling, and (3) high energy resolution. Although NDDs are sensitive to visible light, vacuum ultraviolet, and soft x rays, unfavorable pulses produced by such radiation were greatly reduced by choosing an appropriate stainless steel shield in this experiment. In LHD, the time-resolved energy distribution of counter-going beam ions and ion cyclotron range of frequency-produced energetic ions have been successfully obtained by means of an NDD. The performance of NDDs as a neutral particle analyzer and its good suitability to LHD plasmas were demonstrated throughout this work.
Fluorescence concerns in high energy x-ray yield scaling and imaging studies
Authors: Kyrala George A. , Workman Jonathan B.
Published: February 2004

X rays at high photon energies are needed to backlight and image large objects of high opacity on large lasers, such as the National Ignition Facility, or large pulsed power facilities, such as ATLAS. Attenuators and filters are usually used to bring the signals to scale and to filter the x rays from un-needed low energy components. As the x-ray energy increases, the secondary effect of the interactions of the x rays with the filter or attenuator material must be addressed. This is especially true when one considers using the very high energy x rays from the hot electrons generated during the interaction of intense lasers with high Z materials. We will show how these concerns can be quantified and reduced in at least one case; an experiment on the OMEGA laser facility, designed to investigate the scaling of absolute x-ray yield and conversion efficiency with laser energy and power. This investigation is part of the study to determine the feasibility of high-energy backlighters using Ge emission near 10.3 keV. We will also show how these results apply to imaging at larger x-ray energies.
Development and characterization of a single-line-of-sight framing camera
Authors: Bradley D. K. , Bell P. M. , Dymoke-Bradshaw A. K. L. , Hares J. D. , Bahr R. E. , Smalyuk V. A. , Hargrove D. R. , Piston K.
Published: February 2004

We present initial characterization data from a new single-line-of-sight (SLOS) x-ray framing camera. The instrument uses an image-dissecting structure inside an electron optic tube to produce up to four simultaneous dc images from a single image incident on the cathode and a microchannel plate-based device to provide the temporal gating of those images. A series of gated images have been obtained using a short-pulse UV laser source, and the spatial resolution of those images is compared to those obtained using a more traditional-microchannel plate based system.
Design of the National Ignition Facility static x-ray imager
Authors: Landon M. D. , Koch J. A. , Alvarez S. S. , Bell P. M. , Lee F. D. , Moody J. D.
Published: February 2004

Two static x-ray imagers (SXI) will be used to monitor beam pointing on all target shots in the National Ignition Facility. These pinhole-based instruments will provide time integrated two-dimensional images of target x-ray emissions in the energy range between 2 and 3 keV. These instruments are not DIM based and will view along dedicated lines of sight from near the top and bottom ports of the target chamber. Beams that miss or clip the hohlraum laser-entrance holes will produce x-ray emission on the ends of the hohlraum, indicating improper beam pointing and/or target positioning. The SXIs will also be used to quantify beam focusing and pointing by producing x-ray images of dedicated test targets irradiated by focused beams at precalculated positions. A proposed design is presented, along with supporting data from NOVA target experiments.
Angular sensitivity of gated microchannel plate framing cameras
Authors: Landen O. L. , Lobban A. , Tutt T. , Bell P. M. , Costa R. , Hargrove D. R. , Ze F.
Published: February 2004

Gated, microchannel-plate-based (MCP) framing cameras have been deployed worldwide for 0.2–9 keV x-ray imaging and spectroscopy of transient plasma phenomena. For a variety of spectroscopic and imaging applications, the angular sensitivity of MCPs must be known for correctly interpreting the data. We present systematic measurements of angular sensitivity at discrete relevant photon energies and arbitrary MCP gain. The results can been accurately predicted by using a simple two-dimensional approximation to the three-dimensional MCP geometry and by averaging over all possible photon ray paths.
Soft x-ray detector array for the study of magnetohydrodynamics instabilities in the compact helical system heliotron/torsatron
Authors: Takagi S. , Toi K. ,   CHS Group
Published: February 2004

A 20 channel PIN-photodiode array is installed on the compact helical system (CHS) heliotron/torsatron to measure the radial profiles of soft x-ray (SXR) emission and fluctuations. In neutral beam injection (NBI) heated plasma on CHS, sawtooth oscillations are often observed in the SXR signals. The sawtooth has a characteristic feature of the off-axis sawtooth crash that takes place first near the 1/q=1/2 rational surface located at the normalized minor radius ρ≈0.4−0.6, where q is the safety factor. In most of cases high frequency precursor and low frequency postcursor oscillations having m/n=2/1 mode structure (m, n: the poloidal and toroidal mode numbers) appear before and after the crash. The total plasma beta derived from the measurement of SXR emission-peak position is slightly but clearly decreased by the sawtooth crash. This reduction suggests rapid transport of energetic beam ions from the core region toward the plasma edge region.
Ultrasoft x-ray telescopes for fluctuation imaging in fusion plasmas
Authors: Stutman D. , Finkenthal M. , Iovea M. , Soukhanovskii V. , May M. J. , Moos H. W.
Published: February 2004

We present the design for a novel spectroscopic instrument for two-dimensional imaging of low-amplitude, fast fluctuations from magnetically confined fusion devices. The instrument is similar in principle to an ultrasoft x-ray (USXR) telescope recently developed for astrophysics application and uses a large (10–20-cm-diam), spherical multilayer mirror to select and concentrate a bright USXR impurity line (e.g., C VI Lyα at 33.7 Å, or C VI Hα at 182 Å), onto a low-noise fast, two-dimensional detector. A first version of the telescope will use a fast phosphor to convert the USXR image into visible light, which is then guided using fiber optics to a fast/gated charge-coupled-device camera outside the vacuum. Detailed signal-to-noise analysis indicates that, due to the high energy and brightness of the USXR line emission and large reflectivity of the present mirrors, such an instrument would allow imaging of subpercent amplitude fluctuations with ⩽10 μs time resolution and sub-cm spatial resolution. At the same time, ray-tracing calculations show that a quite large plasma region (up to a few tens of cm extent) can be imaged. Another version of the telescope would use a two-dimensional array of extreme ultraviolet diodes at the focal plane, in which case fluctuations up to ≈0.1% could be imaged.
National Ignition Facility core x-ray streak camera
Authors: Kimbrough J. R. , Bell P. M. , Christianson G. B. , Lee F. D. , Kalantar D. H. , Perry T. S. , Sewall N. R. , Wootton A. J.
Published: February 2004

The National Ignition Facility (NIF) core x-ray streak camera will be used for laser performance verification experiments as well as a wide range of physics experiments in the areas of high-energy-density science, inertial confinement fusion, and basic science. The x-ray streak camera system is being designed to record time-dependent x-ray emission from NIF targets using an interchangeable family of snouts for measurements such as one-dimensional (1D) spatial imaging or spectroscopy. the NIF core x-ray streak camera will consist of an x-ray-sensitive photocathode that detects x rays with 1D spatial resolution coupled to an electron streak tube to detect a continuous time history of the x rays incident on the photocathode over selected time periods. A charge-coupled-device (CCD) readout will record the signal from the streak tube. The streak tube, CCD, and associated electronics will reside in an electromagnetic interference, and electromagnetic pulse protected, hermetically sealed, temperature-controlled box whose internal pressure is approximately 1 atm. The streak tube itself will penetrate through the wall of the box into the target chamber vacuum. We are working with a goal of a spatial resolution of 15 lp/mm with 50% contrast transfer function at the photocathode and adjustment sweep intervals of 1–50 ns. The camera spectral sensitivity extends from soft x rays to 20 keV x rays, with varying quantum efficiency based on photocathode selection. The system will have remote control, monitoring, and Ethernet communications through an embedded controller. The core streak camera will be compatible with the instrument manipulators at the OMEGA (University of Rochester) and NIF facilities.
Nuclear diagnostics for petawatt experiments (invited)
Authors: Stoyer M. A. , Sangster T. C. , Henry E. A. , Cable M. D. , Cowan T. E. , Hatchett S. P. , Key M.H. , Moran M. J. , Pennington D. M. , Perry M. D. , Phillips T. W. , Singh M. S. , Snavely R. A. , Tabak M. , Wilks S. C.
Published: February 2004

With the operation of successively more intense and powerful lasers, such as the NOVA petawatt laser with I∼3×1020 W/cm2, several novel (to laser physics) nuclear diagnostics were used to determine the nature of the laser/matter interaction at the target surface. A broad beam of hot electrons, whose centroid varied from shot to shot, width was remarkably constant, and intensity was about 40% of the incident laser energy was observed. New nuclear phenomenon included photonuclear reactions [e.g., (γ,xn)], photofission of U238 and intense beams of ions. Photonuclear reactions were observed and quantified in Cu, Ni, and Au samples, and produced activation products as neutron deficient as Au191 [a (γ,6n) reaction!], requiring gamma rays exceeding 50 MeV in energy. The spectral features of the gamma-ray source have been investigated by comparing activation ratios in Ni and Au samples, and angular distributions of higher energy photons have been measured with activation of spatially distributed Au samples. Extraordinarily intense beams of charged particles (primarily protons) were observed normal to the rear surface of the target and quantified using the charged particle reaction Ti48(p,n)48V, radiochromic film and CR39 plastic track detectors. Approximately 3×1013 protons, with energies up to 55 MeV were observed in some experiments. Collimation of this beam increases with increasing proton energy. Correlations of activation with laser performance will be discussed.
Nuclear diagnostics for the National Ignition Facility (invited)
Authors: Murphy Thomas J. , Barnes Cris W. , Berggren R. R. , Bradley P. , Caldwell S. E. , Chrien R. E. , Faulkner J. R. , Gobby P. L. , Hoffman N. , Jimerson J. L. , Klare K. A. , Lee C. L. , Mack J. M. , Morgan G. L. , Oertel J. A. , Swenson F. J. , Walsh P. J. , Walton R. B. , Watt R. G. , Wilke M. D. , Wilson D. C. , Young C. S. , Haan S. W. , Lerche R. A. , Moran M. J. , Phillips T. W. , Sangster T. C. , Leeper R. J. , Ruiz C. L. , Cooper G. W. , Disdier L. , Rouyer A. , Fedotoff A. , Glebov V. Yu. , Meyerhofer D. D. , Soures J. M. , Stöckl C. , Frenje J. A. , Hicks D. G. , Li C. K. , Petrasso R. D. , Seguin F. H. , Fletcher K. , Padalino S. , Fisher R. K.
Published: February 2004

The National Ignition Facility (NIF), currently under construction at the Lawrence Livermore National Laboratory, will provide unprecedented opportunities for the use of nuclear diagnostics in inertial confinement fusion experiments. The completed facility will provide 2 MJ of laser energy for driving targets, compared to the approximately 40 kJ that was available on Nova and the approximately 30 kJ available on Omega. Ignited NIF targets are anticipated to produce up to 1019 DT neutrons. In addition to a basic set of nuclear diagnostics based on previous experience, these higher NIF yields are expected to allow innovative nuclear diagnostic techniques to be utilized, such as neutron imaging, recoil proton techniques, and gamma-ray-based reaction history measurements.
High-yield neutron activation system for the National Ignition Facility
Authors: Barnes Cris W. , Murphy Thomas J. , Oertel John A.
Published: February 2004

The most accurate absolutely calibrated measurement of the total yield of neutrons from experiments on the National Ignition Facility will be from activation of threshold nuclear reactions. The high-yield neutron activation system is being designed to provide high-accuracy (similar to the ±7% achieved on other fusion experiments) linear measurements over a 9-order-of-magnitude dynamic range from the facility limit of ∼1019 neutrons/shot down to a minimum of ∼3×1010 neutrons/shot. The system design requirements are presented, and a conceptual design to meet those requirements described.
Design of a bolometer for Hanbit magnetic mirror device
Authors: Yoo Suk-Jae , Choi Seong-ho , Kwon Myeun , Lee Soonil , Oh Soo-ghee
Published: February 2004

We designed and constructed a metal-resistor bolometer to measure the total radiation of the plasma in the Hanbit device, a magnetic mirror machine at the Korea Basic Science Institute. The target parameters for the plasma, the duration of which was 100–500 ms, at the central cell were the ion energy of 1 keV, the electron temperature of 200 eV, and the electron density of 5×1012 cm−3. A preliminary test showed that the cooling time constant and the absolute sensitivity of the homemade bolometer were 12 ms and 0.031 V/mW, respectively; the sensitivity was calibrated using an Ar ion laser. A test run of the homemade bolometer in the Hanbit device produced a signal of ∼25 mW/cm2, which was equivalent to the total power loss of about 40 kW, for the input rf power of 200 kW.
High resolution measurements of neutral density and ionization rate in the Alcator C-Mod tokamak
Authors: Boivin R. L. , Hughes J. W. , LaBombard B. , Mossessian D. , Terry J. L.
Published: February 2004

Two new high resolution detectors have been installed on the Alcator C-Mod tokamak to measure the neutral density and ionization rate at the edge of the main chamber plasma. Using a silicon detector sensitive to UV light, and a very narrow filter with transmission peaking at 1216 Å, the Lyman alpha radiation emanating from neutral deuterium (and hydrogen) is measured. The detectors consist of 20 channel arrays which view the plasma tangentially 12.5 cm below the outer midplane, and 10 cm above the inner midplane. The imaging is performed using a 1 mm×3 mm slit, which gives a nominal radial resolution of 2 and 3 mm, respectively. The local emissivity is obtained via a standard Abel inversion technique. Employing well-known branching ratios, and using measured local electron density and temperature, the neutral density and ionization rate are inferred with similar radial resolution. Details of the setup and sensitivity of the results to plasma conditions are discussed.
Density and Hα diagnostics and results for the sustained spheromak physics experiment
Authors: Wang Zhehui , Wurden G. A. , Barnes Cris W. , Buchenauer C. J. , McLean H. S. , Hill D. N. , Hooper E. B. , Wood R. D. , Woodruff S.
Published: February 2004

A newly installed density diagnostic using CO2 laser interferometry and an Hα diagnostic using interference filters and photomultiplier tubes for the recently constructed sustained spheromak physics experiment (SSPX) are described. First diagnostic results of the Hα diagnostic were useful to understand the breakdown physics in the new SSPX experiments. Low-noise density data validates techniques to reduce vibration and electronic pickup. The data-processing electronics of the new interferometer can yield unambiguous density data that is equivalent to 16 fringe shifts. Density data is also critical to understand the particle source, and the J/ne parameter for SSPX.
Multichannel interferometer system for the helically symmetric experiment
Authors: Brower D. L. , Deng C. , Ding W. X. , Anderson D. T. , Mason W.
Published: February 2004

A multichannel millimeter-wave interferometer system has been designed, fabricated and installed on the helically symmetric experiment (HSX), located at the University of Wisconsin, Madison. The interferometer system will view the plasma cross section along nine adjacent chords with 1.5 cm spacing. With this arrangement, coverage will span from the low-field side plasma scrape-off layer to well past the magnetic axis. For the plasma densities anticipated on HSX, a solid-state source operating at 288 GHz will be utilized. At this frequency refraction will be manageable, being less than the channel spacing. The source will be bias-tuned and modulated with a sawtooth wave form at 750 kHz in order to generate the intermediate frequency necessary for the heterodyne detection scheme. The signals will be measured using Schottky-diode corner-cube mixers. The interferometer will have sensitivity nedl≈8×1011 cm−2, being able to measure density changes <1%. Initially, the phase will be evaluated using analog electronics with bandwidth <10 kHz providing real-time line-integrated output. A digital phase comparator scheme will also be implemented whereby the measured wave forms are directly digitized and the phase evaluated using a software-based algorithm. This will increase the time response up to the modulation frequency of 750 kHz. Improved time response will permit measurement of high-frequency density fluctuations along with “fast changes in” the equilibrium profile.