bluuebunny/crossref_metadata_2025 huggingface dataset:
Neutron-induced background in charge-coupled device detectors
Authors: Jaanimagi P. A. , Boni R. , Keck R. L.
Published: February 2004

The inertial confinement fusion (ICF) community must become more cognizant of the neutron-induced background levels in charge-coupled device (CCD) detectors that are replacing film as the recording medium in many ICF diagnostics. This background degrades the signal-to-noise ratio (SNR) of the recorded signals and for the highest-yield shots comprises a substantial fraction of the pixel’s full well capacity. CCD detectors located anywhere in the OMEGA Target Bay are precluded from recording high precision signals (SNR>30) for deuterium–tritium neutron yields greater than 1013. CCDs make excellent calibrated neutron detectors. The average CCD background level is proportional to the neutron yield, and we have measured a linear response over four decades. The spectrum of deposited energy per pixel is heavily weighted to low energies, <50 keV, with a few isolated saturated pixels. Most of the background recorded by the CCDs is due to secondary radiation produced by interactions of the primary neutrons with all the materials in the Target Bay as well as the shield walls and the floor. Since the noise source comes from all directions it is very difficult to shield. The fallback position of using film instead of CCD cameras for high-neutron-yield target shots is flawed, as we have observed substantially increased fog levels on our x-ray recording film as a function of the neutron yield.
Technical feasibility study on a fusion power monitor based on activation of water flow
Authors: Kaneko Junichi , Uno Yoshitomo , Nishitani Takeo , Maekawa Fujio , Tanaka Teruya , Shibata Yoshinari , Ikeda Yujiro , Takeuchi Hiroshi
Published: February 2004

As a part of development of nuclear instrumentation for the international thermonuclear experimental reactor (ITER), technical feasibility of a fusion power monitor based on activation of water flow was studied. The fusion power monitor determines D–T neutron yield, i.e., fusion power, by measuring 6.1 and 7.1 MeV γ rays accompanied by disintegration of N16 nuclei that are produced by the O16(n,p) 16N reactions with 14 MeV neutrons in water. The fusion power monitor consists of a water pipe loop laid from the first wall to the outside of the bioshield and a γ-ray detector, e.g., a BGO scintillator. Fusion power can be measured in an absolute value by this monitor similar to a neutron activation method with a pneumatic tube system; in addition, this monitor has a feature that continuously measures the fusion power with time resolution faster than 1 s. This monitor also has other excellent features in terms of long-term stability, sensitivity only for D–T neutrons and being maintenance free. In order to confirm the technical feasibility of the fusion power monitor based on activation of water flow, experiments for dependence of N16 γ-ray yield on the velocity of water flow and for time response were carried out. It was found that the time response was described in a turbulent flow model, and time resolution of 50 ms that fully satisfied the time resolution of 100 ms required from plasma diagnostics was achieved. Furthermore, detection sensitivity of the fusion power monitor when it is applied to the ITER was estimated based on the experimental results; it was determined that the monitor had sufficiently high sensitivity.
Neutron emission study of DT plasmas heated with tritium neutral beams
Authors: Henriksson Hans , Ballabio L. , Conroy S. , Ericsson G. , Gorini G. , Hjalmarsson A. , Källne J. , Tardocchi M.
Published: February 2004

The neutron emission energy spectrum from deuterium–tritium fusion reactions has been measured in experiments carried out at the Joint European Torus for plasmas heated with high power neutral beam (NB) injection of tritium beams at Eb≈150 keV using a magnetic proton recoil neutron spectrometer. High quality data were obtained in which up to three spectral components due to different ion reactions could be distinguished with the help of dedicated model calculations of the fusion neutron emission based on Monte Carlo simulations. The analysis model involved neutrons from reactions of NB ions on passing and trapped orbits interacting with thermal bulk ions. Moreover, a narrow Gaussian component, due to neutrons from thermal d+t→α+n reactions, could be resolved in some cases. Results are presented and the plasma information obtained is discussed as an illustration of the capabilities of neutron emission spectroscopy diagnostics.
Neutron time-of-flight spectrometer for high rate diagnosis of deuterium plasmas
Authors: Hjalmarsson A. , Conroy S. , Ericsson G. , Henriksson H. , Källne J. , Thun J. , Gorini G.
Published: February 2004

The new concept for the design of a neutron time of flight spectrometer operating at high rates of events has been studied based on instrumental modeling and neutron transport calculations. The aim is to find an optimized design for an instrument that can measure the 2.5 MeV neutron emission from deuterium plasmas and attain diagnostics capabilities comparable to those as has been demonstrated possible with the 14 MeV magnetic proton recoil spectrometer for deuterium–tritium plasmas at Joint European Torus. Preliminary results are presented and used to project the potential for realizing an advanced neutron emission spectrometry diagnosis of plasmas.
Visualization of plasma turbulence with laser-induced fluorescence (invited)
Authors: Levinton Fred M. , Trintchouk Fedor
Published: February 2004

Turbulence is a key factor limiting the performance of fusion devices. Plasma edge turbulence determines the boundary values of the plasma density and temperature, which in turn determine the internal gradients and controls global plasma transport. In recent years, significant progress has been made in modeling turbulence behavior in plasmas and its effect on transport. Progress has also been made in diagnostics for turbulence measurement; however, there is still a large gap in our understanding of it. An approach to improve this situation is to experimentally visualize the turbulence, that is, a high resolution 2-D image of the plasma density. Visualization of turbulence can improve the connection to theory and help validate theoretical models. One method that has been successfully developed to visualize turbulence in gases and fluids is planar laser-induced fluorescence. We have recently applied this technique to visualize turbulence and structures in a plasma. This was accomplished using an Alexandrite laser that is tunable between 700 and 800 nm, and from 350 to 400 nm with second harmonic generation. The fluorescence light from an argon ion transition has been imaged onto an intensified charged coupled device camera that is gated in synchronization with the laser. Images from the plasma show a rotating structure at 30 kHz in addition to small scale turbulence.
Edge turbulence measurements in NSTX by gas puff imaging
Authors: Maqueda R. J. , Wurden G. A. , Zweben S. , Roquemore L. , Kugel H. , Johnson D. , Kaye S. , Sabbagh S. , Maingi R.
Published: February 2004

Turbulent filaments in visible light emission corresponding mainly to density fluctuations at the edge have been observed in large aspect ratio tokamaks: TFTR, ASDEX, Alcator C-Mod, and DIII-D. This article reports on similar turbulent structures observed in the National Spherical Torus Experiment (NSTX) using a fast-framing, intensified, digital visible camera. These filaments were previously detected mainly in high recycling regions, such as at limiters or antennas, where the line emission from neutral atoms was modulated by the fluctuations in local plasma density. However, by introducing controlled edge gas puffs, i.e., gas puff imaging, we have increased the brightness and contrast in the fluctuation images and allowed the turbulent structure to be measured independently of the recycling. A set discrete fiber-optically coupled sight-lines also measured the frequency spectra of these light fluctuations with a 200 kHz bandwidth. Initial results in NSTX show that the turbulent filaments are well aligned with the magnetic field which can be up to 45° from the horizontal at the outer midplane of NSTX. The dominant wavelength perpendicular to the magnetic field is ∼7–11 cm, corresponding to a k⊥ ρs of ∼0.3 at an assumed Te=25 eV, and the frequency spectra has a typical broad shape characteristic of edge turbulence extending to about 100 kHz. By imaging a He gas puff along a magnetic field line the characteristic radial scalelength appears to be in the 3–5 cm range.
Neutron emission spectroscopy at JET—Results from the magnetic proton recoil spectrometer (invited)
Authors: Ericsson Göran , Ballabio L. , Conroy S. , Frenje J. , Henriksson H. , Hjalmarsson A. , Källne J. , Tardocchi M.
Published: February 2004

The principles and operation at Joint European Torus (JET) of the first magnetic proton recoil (MPR) spectrometer for measurement of fusion neutron spectra are described. Some technical aspects of the instrument are discussed, including energy calibration and monitoring system. Data from the recent experimental campaign with tritium at JET are presented as examples of the MPR’s diagnostic abilities. It is shown that the spectrometer is a flexible and versatile instrument, capable of delivering high-quality data on a number of plasma parameters. In particular, the observation of the so-called α knock-on effect in neutron emission spectroscopy is discussed.
2D turbulence imaging in DIII-D via beam emission spectroscopy
Authors: Fenzi C. , Fonck R. J. , Jakubowski M. , Mc Kee G. R.
Published: February 2004

Two-dimensional measurements of density fluctuations have been performed in DIII-D using the beam emission spectroscopy diagnostic. The 32 spatial channels are arranged to image a 5×6 cm2 (radial×poloidal) region in the plasma cross section, at a nominal 1 cm spatial resolution and separation. The typical decorrelation time, poloidal and radial correlation lengths, as well as a time-averaged flow field plot are obtained from spatial and temporal correlation analyses. A biorthogonal decomposition algorithm is applied to expand the data set into a set of modes that are orthogonal in time and in space, thus providing a simultaneous analysis of the space and time dependencies of fluctuation data.
New diagnostics for physics studies on TEXTOR-94 (invited)
Authors: Donné A. J. H. , Jaspers R. , Barth C. J. , Bindslev H. , Elzendoorn, B. S. Q. , van Gorkom J. C. , van der Meiden H. J. , Oyevaar T. , van de Pol, M. J. , Udintsev V. S. , Widdershoven H. L. M. , Biel W. , Finken K. H. , Krämer-Flecken A. , Kreter A. , Oosterbeek H. , Schweer B. , Unterberg B. , Deng B. H. , Domier C. W. , Luhmann N. C. , Mazzucato E. , Munsat T. , Park H. , Porte L. , Woskov P. , Shmaenok L.
Published: February 2004

Recently the Dutch, Belgian, and North-Rhine Westphalian Fusion Institutes have consolidated their fusion research on the medium-sized tokamak TEXTOR-94 in the so-called Trilateral Euregio Cluster. To aid the new physics program of TEC, a large number of advanced core diagnostics has recently been implemented. In this article we will discuss the reasoning that has led to the choices of the various diagnostics. Furthermore, we will briefly describe the new diagnostics systems.
High resolution multiposition Thomson scattering for the TEXTOR tokamak
Authors: Barth C. J. , v. d. Meiden H. J. , Oyevaar T. , Cardozo N. J. Lopes
Published: February 2004

In this article, the recently installed high resolution multiposition Thomson scattering (TS) system of the TEXTOR tokamak is presented. Light from a pulsed ruby laser is scattered by the free electrons of the plasma and transmitted by fiber optics to a polychromator for spectral analysis. The Doppler broadened spectrum of the scattered light is analyzed with a Littrow spectrometer, detected with an image intensifier, and recorded with two intensified charge coupled device cameras. Values of the electron temperature (Te) in the range of 50 eV up to 4 keV can be measured at 450 spatial elements of 2 mm along a chord of 900 mm, with a resolution of 8 mm. The observational error on Te was found to be <3% at an electron density (ne) of 3.5×1019 m−3 using a laser energy of ∼8 J. These features make—to our knowledge—the multiposition TS system of TEXTOR to be the one with the highest spatial and spectral resolution in the world. In this article the first results of this powerful diagnostic will be presented.
Implementation of collective Thomson scattering on the TEXTOR tokamak for energetic ion measurements
Authors: Porte L. , Bindslev H. , Hoekzema F. , Machuzak J. , Woskov P. , Van Eester D.
Published: February 2004

Knowledge of the energy spectrum of fast ions in magnetically confined fusion plasmas is important and fundamental for achieving fusion energy production. Collective Thomson scattering (CTS) of high-power electromagnetic radiation is one of the most promising diagnostic methods for measuring the energy spectrum of confined fast ions. A CTS diagnostic has been implemented on the TEXTOR tokamak for the study of fast ions. It uses a 400 kW, 110 GHz gyrotron source as the probe and a high-resolution heterodyne radiometer as the receiver. Details of the system are given in this article. First results from the diagnostic show that scattered radiation has been detected.
Diagnostics on Z (invited)
Authors: Nash T. J. , Derzon M. S. , Chandler G. A. , Fehl D. L. , Leeper R. J. , Porter J. L. , Spielman R. B. , Ruiz C. , Cooper G. , McGurn J. , Hurst M. , Jobe D. , Torres J. , Seaman J. , Struve K. , Lazier S. , Gilliland T. , Ruggles L. A. , Simpson W. A. , Adams R. , Seaman J. A. , Wenger D. , Nielsen D. , Riley P. , French R. , Stygar B. , Wagoner T. , Sanford T. W. L. , Mock R. , Asay J. , Hall C. , Knudson M. , Armijo J. , McKenney J. , Hawn R. , Schroen-Carey D. , Hebron D. , Cutler T. , Dropinski S. , Deeney C. , LePell P. D. , Coverdale C. A. , Douglas M. , Cuneo M. , Hanson D. , Bailey J. E. , Lake P. , Carlson A. , Wakefield C. , Mills J. , Slopek J. , Dinwoodie T. , Idzorek G.
Published: February 2004

The 100 ns, 20 MA pinch-driver Z is surrounded by an extensive set of diagnostics. There are nine radial lines of sight set at 12° above horizontal and each of these may be equipped with up to five diagnostic ports. Instruments routinely fielded viewing the pinch from the side with these ports include x-ray diode arrays, photoconducting detector arrays, bolometers, transmission grating spectrometers, time-resolved x-ray pinhole cameras, x-ray crystal spectrometers, calorimeters, silicon photodiodes, and neutron detectors. A diagnostic package fielded on axis for viewing internal pinch radiation consists of nine lines of sight. This package accommodates virtually the same diagnostics as the radial ports. Other diagnostics not fielded on the axial or radial ports include current B-dot monitors, filtered x-ray scintillators coupled by fiber optics to streak cameras, streaked visible spectroscopy, velocity interferometric system for any reflector, bremsstrahlung cameras, and active shock breakout measurement of hohlraum temperature. The data acquisition system is capable of recording up to 500 channels and the data from each shot is available on the Internet. A major new diagnostic presently under construction is the BEAMLET backlighter. We will briefly describe each of these diagnostics and present some of the highest-quality data from them.
Low-cost, robust, filtered spectrometer for absolute intensity measurements in the soft x-ray region
Authors: Lanier N. E. , Gerhardt S. P. , Den Hartog D. J.
Published: February 2004

We have developed a low-cost, robust, multifoil-filtered spectrometer to provide absolute measurements of low-Z impurity concentrations in the Madison Symmetric Torus reversed-field pinch. The spectrometer utilizes an array of six thin-film coated soft x-ray diodes. Each multilayered coating is specifically tailored to isolate the K-shell emission lines of H- and He-like oxygen, carbon, and aluminum. With calibrations obtained via a synchrotron source, absolute measurements of photon flux have been made. We address the technical aspects of this diagnostic and present impurity data from both standard and high-confinement plasma discharges.
Hard x-ray detectors for OMEGA and NIF
Authors: Stoeckl C. , Glebov V. Yu. , Meyerhofer D. D. , Seka W. , Yaakobi B. , Town R. P. J. , Zuegel J. D.
Published: February 2004

Laser–plasma instabilities that produce an unacceptably high level of hot electrons are potentially dangerous for both direct-drive and indirect-drive inertial confinement laser fusion. The hot electrons preheat the fuel and prevent compression of the capsule to the requisite conditions for ignition. Fast electron generation and preheat can be inferred from the hard x-ray radiation generated by the interaction of the hot electrons with the target. On the University of Rochester’s OMEGA laser system, time-resolved hard x-ray detectors have been operating in an energy range from 10 to 500 keV. In this article we will present initial results for the yield and spectrum of the hard x-ray radiation. The concept used on OMEGA can be easily extended to infer the amount of laser energy coupled to suprathermal electrons and to the target for both direct- and indirect-drive implosions on the upcoming National Ignition Facility, as well as to measure the conversion efficiency in high-x-ray-yield experiments.
Diagnostic arrangement on S-300 facility
Authors: Bakshaev Yu. L. , Blinov P. I. , Chernenko A. S. , Dan’ko S. A. , Kalinin Yu. G. , Korolev V. D. , Tumanov V. I. , Shashkov A. Yu. , Chesnokov A. V. , Ivanov M. I.
Published: February 2004

A set of experiments on neutron and x-ray generation was performed on the S-300 facility for the last few months. The S-300 facility is a pulse generator with electric current achieving 3.5 MA, voltage 400–500 kV, and rise time ∼100 ns. (Chernenko et al., Proc. of the 11th International Conference of Power Particle Beams, Prague, 1966, p. 154). It is designed as van eight-module machine transmitting electromagnetic power to the low-inductive load through the vacuum line with self-magnetic isolation. Diagnostic techniques and methods on S-300 used are described in this article. Ten-channel polychromator is used for the soft x-ray and vacuum ultraviolet bands (50–500 eV) measurements with spectral resolution of 5%–20% and time resolution less than 2.5 ns. Radiated power measurements in the region of 0.1–10 keV are performed by vacuum x-ray diodes and semiconductor detectors equipped with different filters. Curved crystal x-ray spectrography is intended for plasma density, electron, and ion temperature evaluation. Visible and x-ray radiation image converter tubes and a streak camera reproduce plasma dynamics. Laser shadow and schlieren probing are used to investigate rare periphery plasma motion. Time-of-flight and activation technique is designed for total neutron yield determination.
Time resolved neutron emission spectroscopy of DT plasmas with ion cyclotron resonance heating
Authors: Tardocchi M. , Ballabio L. , Conroy S. , Ericsson G. , Gorini G. , Henriksson H. , Hjalmarsson A. , Källne J.
Published: February 2004

The energy spectrum of the DT neutron emission was measured in experiments carried out at JET for plasmas of deuterium–tritium heated with different ion cyclotron resonance heating (ICRH) schemes. The spectrum was measured with the magnetic proton recoil spectrometer. The data were analyzed in up to three spectral components, which were ascribed to the underlying reactions involving thermal, epithermal, and high-energy ions. The results include time resolved information for individual discharges. High-energy components in the fuel ion population were found in most cases and analyzed in terms of a tail temperature. Changes in the (minority) deuterium concentration in the range of 12–20% were found to affect significant the ICRH power absorption and its perturbation of the minority velocity distribution.
A sensitive neutron spectrometer for the National Ignition Facility
Authors: Watt R. G. , Chrien R. E. , Klare K. A. , Murphy T. J. , Wilson D. C. , Haan S.
Published: February 2004

We are developing a sensitive neutron spectrometer for the National Ignition Facility laser at Livermore. The spectrometer will consist of a 1020 channel single-neutron-interaction time-of-flight detector array fielded 23 m from the neutron-producing target. It will use an existing detector array together with upgraded electronics for improved time resolution. Measurements of neutron yield, ion and electron temperatures, and density-radius product are all possible under certain conditions using one-, two-, or three-step reaction processes. The locations of the most important potential sources of scattered neutron backgrounds are determined as the first step in designing collimation to reduce these backgrounds.
A neutron spectrometer for precise measurements of DT neutrons from 10 to 18 MeV at OMEGA and the National Ignition Facility
Authors: Frenje J. A. , Green K. M. , Hicks D. G. , Li C. K. , Séguin F. H. , Petrasso R. D. , Sangster T. C. , Phillips T. W. , Glebov V. Yu. , Meyerhofer D. D. , Roberts S. , Soures J. M. , Stoeckl C. , Fletcher K. , Padalino S. , Leeper R. J.
Published: February 2004

A model independent method to determine fuel 〈ρR〉 is to measure the energy spectrum and yield of elastically scattered primary neutrons in deuterium–tritium (DT) plasmas. As is the case for complementary methods to measure fuel 〈ρR〉 (in particular from knock-on deuterons and tritons [S. Skupsky and S. Kacenjar, J. Appl. Phys. 52, 2608 (1981); C. K. Li et al. (unpublished)]), minimizing the background is critical for successful implementation. To achieve this objective, a novel spectrometer for measurements of neutrons in the energy range 10–18 MeV is proposed. From scattered neutrons (10–13 MeV), the DT fuel 〈ρR〉 will be measured; from primary neutrons (∼14 MeV), the ion temperature and neutron yield will be determined; and from secondary neutrons, in the energy range 12–18 MeV, the fuel 〈ρR〉 in deuterium plasmas will be inferred at the National Ignition Facility. The instrument is based on a magnetic spectrometer with a neutron-to-deuteron (nd) conversion foil for production of deuteron recoils at nearly forward scattered angles. In its initial phase of implementation, CR-39 track detectors will be used in the focal plane to detect the recoil deuterons with extremely high spatial resolution. Besides simplicity, CR-39 track detectors will facilitate a highly accurate energy calibration. However, in a later implementation of the spectrometer design, the recoils will also be detected by an array of fast scintillation counters functioning in current mode. In either detection scheme, the detection efficiency is about 10−9 for measuring 14 MeV neutrons with an energy resolution of about 3%. Due to its large dynamic range, its relatively high efficiency, and a compliant design that allows for significant background rejection, this spectrometer can be effectively used, with very high resolution, at both OMEGA and the National Ignition Facility.
Synergy of multiviewing spectroscopic diagnostics on COMPASS-D (invited)
Authors: Carolan P. G. , Conway N. J. , Field A. R. , Jones P. B. , Meyer H. F.
Published: February 2004

In the COMPASS-D tokamak three multiviewing diagnostic systems are combined by using the same collection optics. HeI line ratios from a helium thermal jet provide detailed edge Te(r) and ne(r) profiles. The spectrometer also provides the Dα profile. A Doppler spectrometer system provides Ti and Vθ profiles using HeII emission. The Te and ne profiles are used in extracting neutral densities from the Dα emissivities, and the radial electric field from the Doppler measurements. The behavior of Te(r), ne(r), 2nD(r), Er, and Vθ and their gradients can now be compared in detail to investigate the H-mode transition physics.
High resolution visible continuum imaging diagnostic on the Alcator C-Mod tokamak
Authors: Marmar E. S. , Boivin R. L. , Granetz R. S. , Hughes J. W. , Lipschultz B. , McCool S. , Mossessian D. , Pitcher C. S. , Rice J. E. , Terry J. L.
Published: February 2004

A high spatial resolution CCD based one-dimensional imaging system to measure visible continuum emissivity profiles from Alcator C-Mod tokamak plasmas is described. The instrument has chordal resolution that is better than 1 mm for the edge region of the plasma, where very sharp (1 to 10 mm) gradient lengths in plasma parameters are observed after the formation of the H-mode transport barrier. Each image has up to 2048 pixels, and total spatial coverage goes from 2 cm inside of the magnetic axis to ∼4 cm outside of the last closed flux surface in the ∼22 cm horizontal minor radius plasmas. Time resolution can be varied from 0.21 ms to 4 ms; good signal to noise is achieved with 1 ms integration under typical plasma conditions. The emission over most of the plasma volume is dominated by free–free bremsstrahlung, and can be used to infer local values of the average ion charge (Zeff). Toroidally localized puffing of deuterium, nitrogen, and helium reveals that a significant contribution to the signal in the scrape-off layer at the extreme edge of the plasma can come from diatomic molecular band pseudocontinuum emission.
CO
2
laser imaging interferometer on LHD
Authors: Tanaka K. , Vyacheslavov L. N. , Kawahata K. , Tokuzawa T. , Okajima S.
Published: February 2004

A CO2 laser (λ=10.6 μm) imaging interferometer is designed for electron density profile and electron density fluctuation measurements on large helical device (LHD). The purposes of this diagnostic are reliable electron density monitor in high density operation (especially in pellet injection discharge), precise measurement of electron density profiles and observations of density fluctuations. By using a CO2 laser, refraction effect becomes negligible, and the interferometer promises to be free from fringe jumps at high density. We plan to get 5 mm spatial resolution, (56 ch for each of two 280 mm slab beams, 50 ch for one 250 mm and 16 ch for 80 mm crossed beam), 3×10−3 rad phase resolution and 200 kHz frequency response for the above purpose. And fluctuation will be studied within the wave number range of 7×10−3⩽k⩽0.6 mm−1.
Point-projection x-ray radiography using an X pinch as the radiation source
Authors: Shelkovenko T. A. , Sinars D. B. , Pikuz S. A. , Chandler K. M. , Hammer D. A.
Published: February 2004

Using an X pinch as a source of radiation for point-projection radiography, it is possible to project a high-resolution (1–10 μm) shadow image of dense plasma or test objects onto x-ray-sensitive film. The emission characteristics of X pinches composed of a wide variety of materials have been studied using several diagnostics. The pulse duration and shape of the x-ray bursts were measured in the 1.5–6 keV band using fast diamond PCDs and an x-ray streak camera with sweep speeds as fast as 10 ns for the full sweep (3.5 cm). To investigate the line and continuum radiation emitted by the X pinches, a convex spectrograph using a mica or KAP crystal, and a spectrograph based on a spherically bent mica crystal were used. Summarizing the data, including radiography results, wires known to have slower expansion rates and high boiling temperatures (NiCr, Ti, Nb, Mo, Pd, Ta, W, and Pt) appeared to yield the smallest x-ray source sizes, i.e., gave the best spatial resolution in radiographs and provided subnanosecond time resolution. All of these materials yield intense continuum radiation with energy up to 6 keV, and the highest resolution images are achieved using only the continuum radiation from the X pinch.
Multilayer mirror and foil filter AXUV diode arrays on CDX-U spherical torus
Authors: Soukhanovskii V. A. , Stutman D. , Iovea M. , Finkenthal M. , Moos H. W. , Munsat T. , Jones B. , Hoffman D. , Kaita R. , Majeski R.
Published: February 2004

Recent upgrades to CDX-U spherical torus diagnostics include two 10-channel AXUV diode arrays. The multilayer mirror (MLM) array measures the λ150 O VI brightness profile in the poloidal plane using the Mo/B4C synthetic multilayer structures as dispersive elements. The foil filter array has a tangential view and is equipped with interchangeable clear aperture, beryllium and titanium filters. This allows measurements of radiated power, O VI or C V radial distributions, respectively. The O VI and C V emissivity and the radiated power profiles are highly peaked. A Neoclassical impurity accumulation mechanism is considered as an explanation. For radiated power measurements in the Te⩽100 eV plasmas, photon energy dependent corrections must be used in order to account for nonlinear AXUV sensitivity in the range Ephot⩽20 eV. The arrays are also used for characterization of resistive MHD phenomena, such as the low m modes, saw-tooth oscillations and internal reconnection events. Based on the successful operation of the diagnostics, a new ultra soft x-ray multilayer mirror diode AXUV diode array monitoring the 34 Å emissivity distribution of C VI will be built and installed on the National Spherical Torus Experiment.
Microwave reflectometry for turbulence studies on ASDEX upgrade (abstract)
Authors: Ribeiro T. T. , Serra F. , Manso M. E. , Vergamota S. , Cupido L. , Silva A. , Conway G. D. , Ryter F. , Suttrop, and the W. ,   ASDEX Upgrade Team
Published: February 2004

The reflectometry system installed in the tokamak ASDEX Upgrade has 11 channels primarily aimed at profile measurements and two dedicated channels operating at fixed frequency to study density fluctuations. The channels used for profile measurements can also be operated at fixed frequency. In this article we describe the potential of the system to study important characteristics of the plasma turbulence, from combined fixed frequency and profile measurements (to localize the reflecting layers). The numerical tools used to treat fixed frequency data are briefly described. Using a set of similar discharges and the ability of the microwave reflectometry system to probe simultaneously different layers with several channels, we obtain the time evolution of the integrated power spectra of the different signals versus the minor radius of the plasma. In plasma with H-mode edge and internal transport barrier we could identify a zone at the plasma core and another at the edge with reduced fluctuation levels, coinciding with the increase of central electron temperature and the L–H transition, respectively. Before each barrier is established, the turbulence is observed to decrease at the lower frequency range and is enhanced at the higher frequencies. In modulation electron cyclotron resonance heating experiments similar modifications in turbulence spectra are observed and may be correlated with the modulation period.
Fast wave density and species mix diagnostic (abstract)
Authors: Watson G. W. , Heidbrink W. W. , Ikezi H. , Pinsker R. I.
Published: February 2004

Since fast Alfvén waves propagate across a plasma at the Alfvén speed, the plasma mass density can be determined through interferometry. In previous measurements on the DIII-D tokamak,1 fast waves (∼100 MHz, ∼5 W) were launched from an antenna at the outer midplane, but detection of the signal was hampered by poor sensitivity of the receiving antenna, which was mounted behind protective graphite tiles on the inner wall. We modified several graphite tiles to act as more sensitive receiving antennas. At lower frequencies (∼25 MHz), fast waves can reflect from the ion–ion hybrid cutoff layer. The position of this layer is sensitive to the ratio of hydrogen to deuterium in the plasma. Receiving antennas on the outer wall will measure the hydrogen concentration through reflectometry. Launching other frequencies may yield impurity density ratios as well. These techniques may be useful for measuring relative densities if D, T, and α particles in burning plasmas.
A study on the modification of density and plasma potential in presence of electron temperature fluctuations (abstract)
Authors: Riccardi C. , Longoni G. , Chiodini G. , Fontanesi M.
Published: February 2004

Electron temperature fluctuations have been investigated in the plasma of “Thorello,” a small toroidal device (minor radius a=8 cm and major radius R=40 cm) which produces a magnetized plasma in steady-state condition without rotational transform (n≅1011 cm−3; Te≅2 eV; B=1000 G).1 In our experiment two techniques are applied to estimate T̃e: triple Langmuir probe technique and fast-sweep Langmuir probe method, in both cases, varying the density of the neutral source (in our plasma, H2). The so-called triple probe is the conventional method used to investigate T̃e, while fast-sweep Langmuir probe is a new diagnostic technique recently developed on Thorello.2 Our measurements have been performed in the frequency range between 0 and 500 kHz. The turbulent plasma exhibits a spectrum quite broad in frequency: power spectra of floating potential and density show the characteristic frequencies are in the range 0–100 kHz, while power spectra of electron temperature can extend up to 150–200 kHz. In the plasma core relative levels of electron temperature fluctuations are about 20%, but in the edge region these relative levels raise up to 50%. In situations where electron temperature fluctuations are not negligible, the measurement of T̃e is essential for obtaining a correct interpretation of density and potential fluctuations. In our case the level of electron temperature fluctuations is not negligible in the edge region and it was possible to separate ĨSi and ñ according to the hypothesis ĨSi/ISi=ñ/n+12T̃e/Te and to the theory of thermal drift wave turbulence. Then we can particularly compare the mean values of Te, the level of temperature fluctuations measured in the same plasma, the power spectrum, and the correlation between temperature, density, and potential fluctuations applying the digital correlation technique.3
4 K charge coupled device: A universal approach to diagnostic readout for the National Ignition Facility (abstract)
Authors: Sewall Noel , Nielsen Darron , Moody James , Vitalich Michel
Published: February 2004

This article describes an approach for data acquisition and retrieval to be used on several key diagnostics for experimental support on the National Ignition Facility. The major feature is a direct replacement for film with a large format, scientific grade charge coupled device (CCD) imager requiring minimum space in the diagnostic environment. Additionally, the system provides rapid data acquisition without film developing or digitizing time, equivalent or better resolution than film (9 μm pixel spacing), and compatibility with our existing diagnostic front ends. The CCD camera has been shown to provide very good linearity and signal to noise. Features of this camera include a modular design approach from the clocking state machine through the digitizer/data buffer including diagnostic controller software. Changing the imaging device will require only a change in the clock state machine and the pointers in the internal data buffer storage. Also the camera will provide digital output for transmission on a fiber optic line to provide better noise immunity and resistance to electromagnetic pulse. Results of the 4 K×4 K imaging front end used on laser experiments at the LLE Omega facility will be presented.
Diagnostic requirements for high power auxiliary heating on NSTX (abstract)
Authors: Roquemore A. L. , Johnson D. , Kaita R.
Published: February 2004

National Spherical Torus Experiment (NSTX) has recently completed its first phase of operation. The primary objective for the baseline diagnostic1 set during this phase has been to aid in plasma control and machine operation, which successfully led to attainment of 1 MA of plasma current and some encouraging initial results with coaxial helicity injection (CHI). This first set of diagnostics relied on techniques previously established on tokamaks and related plasma devices. In the next phase of operation, strong auxiliary heating will become available in the form of rf heating through high harmonic fast waves (HHFWs) and neutral beam injection (NBI) for a combined total power of 11 MW. With intense auxiliary heating, accurate and reliable measurements of the plasma parameters for both machine operation and characterization of the plasma performance over a wide range of conditions will require an extended set of diagnostics. Profile diagnostics will be particularly important in this phase, and in some cases this capability can be achieved by upgrading existing diagnostics. However, many new diagnostic approaches must be implemented which take into account the constraints of a spherical torus device. An overview of the full complement of diagnostics planned for NSTX will be presented, and issues related to implementing each diagnostic will be discussed.
Soft x-ray imaging for spheromak-like plasmas (abstract)
Authors: Bellan P. M. , Hansen J. F. , Zweben S. , Stutman D.
Published: February 2004

A pinhole soft x-ray imaging camera is being developed for use on the Caltech solar prominence simulation experiment and also the Caltech spheromak experiment. The camera is based upon a commercial gated intensifier which produces an image on a phosphor screen. Moderate signal level, excellent time resolution, and reasonable imaging have been obtained, but there has not been any determination of the x-ray energy spectrum. An estimation of the spectrum is now underway using filtered AXUV diodes and it is expected that knowledge of the x-ray energy will enable further optimization of the camera.
X-ray imaging diagnostics for the inertial confinement fusion experiments (abstract)
Authors: Aglitsky Y. , Lehecka T. , Obenschain S. , Pawley C. , Brown C. M. , Seely J. , Koch J. A.
Published: February 2004

We report on our continued development of the advanced x-ray plasma diagnostics based on spherically curved crystals. The diagnostics include x-ray spectroscopy with one-dimensional (1D) spatial resolution, 2D monochromatic self-imaging, and backlighting, and can be extended to the x-ray collimating and 2D absorption and emission spectroscopy. The system is currently used, but not limited to diagnostics of the targets ablatively accelerated by the NRL Nike KrF laser. A spherically curved quartz crystal (2d=6.687 03 Å, R=200 mm) has been used to produce monochromatic backlit images with the He-like Si resonance line (1865 eV) as the source of radiation. The spatial resolution of the x-ray optical system is 1.7 μm in selected places and 2–3 μm over a larger area. Another quartz crystal (2d=8.5099 Å, R=200 mm) with the H-like Mg resonance line (1473 eV) has been used for backit imaging with higher contrast. Sherically curved mica (2d=9.969 Å in the second order or reflection, R=200 mm) has been used for backlighting of the low density foam cryotargets with the backlighter energy of 1.26 keV. Time resolution is obtained with the help of a four-strip x-ray framing camera. Time resolved, 20×magnified, backlit monochromatic images of CH planar targets driven by the Nike facility have been obtained with spatial resolution of 2.5 μm in selected places and 5 μm over the focal spot of the Nike laser. A second crystal with a separate backlighter has been added to the imaging system. This makes it possible to use all four strips of the framing camera. As a result we have four monochromatic snapshots of developing instabilities. We are currently exploring the enhancement of this technique to the higher and lower x-ray energies. A progress in high energy (4.5 keV) backlighting that has been made in cooperation with the LLNL will be reported.
Tangential soft x-ray camera for Large Helical Device
Authors: Ohdachi S. , Toi K. , Fuchs G. , von Goeler S.
Published: February 2004

A tangentially viewing soft x-ray camera system is to be installed on the Large Helical Device (LHD). This camera system is aimed at exploring both detailed structures of the magnetic surfaces of the LHD plasma and helical islands induced either due to magnetic field errors or MHD instabilities. The frequency range this system is capable of exploring is 0<v<2 kHz; this range can be extended, if the space resolution or the viewing area were reduced.
New type of digital phase linearizer for real-time interferometric measurement
Authors: Tokuzawa T. , Kawahata K. , Tanaka K. , Ito Y. , Ejiri A. , Simizu T.
Published: February 2004

A new type of digital phase linearizer has been developed for real-time electron density measurement using a multichannel far-infrared (FIR) interferometer. The phase linearizer can measure phase shifts up to 640 fringes. The size of internal memory is 16 bits-2 Mwords and the sampling frequency of the waveform data is up to 1 MHz. The internal clock for the counter is selectable to 100 or 200 MHz and the frequencies of the input signals, i.e., the reference signal and the probe one, are around 1 MHz. In the performance test the resolution of the phase components is achieved at 1/100 fringes, which corresponds to the line integrated density of 9.0×1016 m−2. For real-time measurements the phase linearizer has digital-to-analog converter (DAC) output. The resolution of DAC output is 12 bits and the amplitude is ± 5 V. The density feedback system on the large helical device has been utilized.
Multilayer mirror based soft x-ray spectrometer as a high temperature plasma diagnostic
Authors: Duorah S. , Ejiri A. , Lee S. , Iguchi H. , Fujisawa A. , Kojima M. , Matsuoka K. , Ishiyama E. , Hanada K. , Shiraiwa S. , Toyama H. , Takase Y.
Published: February 2004

A fully calibrated multilayer mirror (MLM) based soft x-ray spectrometer has been developed and installed on the Compact Helical System (CHS). This MLM based spectrometer is a new approach to devising a soft x-ray spectrometer with medium time and energy resolutions. The spectrometer mainly consists of a MLM as the dispersive element and a 20-channel (p-i-n) pin diode array for the detection of the soft x-rays. Both the MLM and the pin diodes have been calibrated at the KEK (High Energy Accelerator Research Organization) Photon Factory for an energy range of 300–1200 eV. The reflectivity of the mirror was found to increase from 3% (photon energy of 335 eV) to 25% (photon energy of 1050 eV). The pin diodes were found to have almost 100% efficiency for creating electron-hole pairs in the calibrated energy range. The spectrometer was installed on the CHS with the aim of fast electron temperature measurement and study of fast magneto-hydrodynamic (MHD) events occurring in plasmas. The experiments show that in the energy range of measurement, the electron “temperature” determined from the slope of the soft x-ray spectrum is much lower than that measured by the Thomson scattering diagnostic. Analysis showed that the soft x-ray spectrum is highly contaminated by impurity emission. Therefore it may be possible to measure electron temperature with this diagnostic if we choose another energy range where we can measure the continuous spectrum. The present time resolution of the system is of the order ∼0.1 ms, which made it possible to study the behavior of the plasma during fast MHD events. Modulations in the soft x-ray intensity were observed during MHD events in CHS plasmas. Analysis of these shows that these may be due to modulations in the temperature or the impurity concentration.
First result from x-ray pulse height analyzer with radial scanning system for LHD
Authors: Muto Sadatsugu , Morita Shigeru ,   LHD Experimental Group
Published: February 2004

Radial profiles of x-ray spectrum have been successfully obtained using an assembly of x-ray pulse height analyzer in large helical device. The observed profile is obtained from plasma heated by ICRF and neutral beam injection (NBI). As a detector, Si(Li) semiconductor is used with a histogramming memory and analog-to-digital converter (ADC) basically working at high counting rate up to 500 kcps. In routine operation a count rate of 62 kcps has been normally obtained with energy resolution better than 400 eV at iron Kα line. The assembly is equipped with four detectors and a radial scanning system which modulates sight lines of the detectors in major radius direction. The profiles of electron temperature and the intensity of metallic impurities have been obtained with a spatial resolution of a few centimeters. Measured electron temperature is in good agreement with that from Thomson scattering. The system is applicable to steady-state discharge. The design philosophy of the assembly and recent results on the performance tests are also presented.
Hohlraum temperature inference via measurement of aluminum shock velocity and time- and spatially resolved x-ray re-emission
Authors: Olson R. E. , Sanford T. W. L. , Chandler G. A. , Leeper R. J. , Mock R. C. , McGurn J. S. , Lazier S. E. , Armijo J. C. , Dropinski S. , Ruggles L. E. , Simpson W. W. , Torres J. A. , Wakefield C.
Published: February 2004

The radiation field in a hohlraum (4 mm diameter×4 mm length) with a ∼10 TW x-ray input has been simultaneously measured by two independent techniques. An active shock breakout measurement of radiation-driven shock velocity in aluminum indicates a peak radiation field with incident flux equivalent to a Planckian distribution with a temperature of 147±3 eV. In the same experiment, a time- and spatially resolved measurement of x-ray re-emission from the gold hohlraum wall indicates re-emission flux equivalent to a Planckian brightness temperature of 145±5 eV.
Measurement of the efficiency of gold transmission gratings in the 100 to 5000 eV photon energy range
Authors: Ruggles L. E. , Cuneo M. E. , Porter J. L. , Wenger D. F. , Simpson W. W.
Published: February 2004

Three x-ray spectrometers, each with a transmission grating dispersion element, are routinely used at the Z soft x-ray facility to measure the spectrum and temporal history of the absolute soft x-ray power emitted from z-pinch and hohlraum radiation sources. Our goal is to make these measurements within an accuracy of ±10%. We periodically characterize the efficiency of the gratings used in the spectrometers by using an electron-impact soft x-ray source, a monochromator, grazing-incidence mirrors, thin filters, and an x-ray charge-coupled device (CCD) detector. We measure the transmission efficiency of the gratings at many photon energies for several grating orders. For each grating, we calculate efficiency as a function of photon energy using published optical constants of gold and multiple-slit Fraunhofer diffraction theory and fit the calculation to the measurements using the physical parameters of the grating as variables. This article describes the measurement apparatus and calibration techniques, discusses the grating efficiency calculation and fitting procedure, and presents recent results.
Plasma diagnostics for x-ray driven foils at Z
Authors: Heeter R. F. , Bailey J. E. , Cuneo M. E. , Emig J. , Foord M. E. , Springer P. T. , Thoe R. S.
Published: February 2004

We report the development of techniques to diagnose plasmas produced by x-ray photoionization of thin foils placed near the Z-pinch on the Sandia Z Machine. The development of 100+ TW x-ray sources enables access to novel plasma regimes, such as the photoionization equilibrium. To diagnose these plasmas one must simultaneously characterize both the foil and the driving pinch. The desired photoionized plasma equilibrium is only reached transiently for a 2-ns window, placing stringent requirements on diagnostic synchronization. We have adapted existing Sandia diagnostics and fielded an additional gated three-crystal Johann spectrometer with dual lines of sight to meet these requirements. We present sample data from experiments using 1-cm, 180-eV tungsten pinches to photoionize foils made of 200 Å Fe and 300 Å NaF co-mixed and sandwiched between 1000 Å layers of Lexan (C16H14O3), and discuss the application of this work to benchmarking astrophysical models.