bluuebunny/crossref_metadata_2025 huggingface dataset:
Multichannel Doppler transmission grating spectrometer at the Alcator C-Mod tokamak
Authors: Graf A. , May M. , Beiersdorfer P.
Published: November 2008

Upgrades to an existing transmission grating spectrometer for visible light used for Doppler velocity and temperature measurements at the Alcator C-Mod tokamak are given. These include a new Princeton Instruments Photonmax 512B charge-coupled device and a four channel fiber optic input. These together allow improvements to the signal level, time resolution, and the number of spatial channels. The fiber optic input allows four simultaneous spatial channels each of which offers a larger percentage of input light flux when compared to the standard fiber slit combination. The “on chip” amplification combined with versatile pixel binning further increases the signal to noise ratio allowing a continuous acquisition of spectra every 8ms. The error bars for extracted velocity and temperature values are potentially smaller owing to the smaller pixel size and increased light flux which allow a more detailed line shape and simplifies line fitting. Examples of time and space resolved spectra are shown and further improvements are discussed.
Detection of zonal flow spectra in DIII-D by a dual-channel Doppler backscattering system
Authors: Schmitz L. , Wang G. , Hillesheim J. C. , Rhodes T. L. , Peebles W. A. , White A. E. , Zeng L. , Carter T. A. , Solomon W.
Published: November 2008

Doppler backscattering (DBS) has been successfully used to measure the E×B flow velocity and local intermediate wavenumber density fluctuation levels in the DIII-D tokamak. Depending on the launch angle and the frequency of the probing beam, the signal backscattered from the plasma cut-off layer is sensitive to density fluctuations at a specific perpendicular wavenumber (1⩽k⊥ρs⩽4). Due to the localization and high time resolution for poloidal flow measurements, DBS is well suited to detect stationary and time-dependent shear flows [zonal flows (ZFs)]. We present a novel scheme to measure ZF spectra using a dual-channel DBS system capable of simultaneously probing two minor radii separated by a distance of 0.2cm<Δr<3cm. Frequency spectra of geodesic acoustic modes and low frequency ZFs (f⩽10kHz) have been obtained for 0.6<r∕a<0.95.
Fast visible imaging of turbulent plasma in TORPEX
Authors: Iraji D. , Diallo A. , Fasoli A. , Furno I. , Shibaev S.
Published: November 2008

Fast framing cameras constitute an important recent diagnostic development aimed at monitoring light emission from magnetically confined plasmas, and are now commonly used to study turbulence in plasmas. In the TORPEX toroidal device [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)], low frequency electrostatic fluctuations associated with drift-interchange waves are routinely measured by means of extensive sets of Langmuir probes. A Photron Ultima APX-RS fast framing camera has recently been acquired to complement Langmuir probe measurements, which allows comparing statistical and spectral properties of visible light and electrostatic fluctuations. A direct imaging system has been developed, which allows viewing the light, emitted from microwave-produced plasmas tangentially and perpendicularly to the toroidal direction. The comparison of the probability density function, power spectral density, and autoconditional average of the camera data to those obtained using a multiple head electrostatic probe covering the plasma cross section shows reasonable agreement in the case of perpendicular view and in the plasma region where interchange modes dominate.
Reconstruction of edge density profiles on Large Helical Device using ultrashort-pulse reflectometry
Authors: Yokota Yuya , Mase Atsushi , Kogi Yuichiro , Tokuzawa Tokihiko , Kawahata Kazuo , Nagayama Yoshio , Hojo Hitoshi
Published: November 2008

Reflectometry has been expected to be one of the key diagnostics to measure density profiles. We have applied an ultrashort-pulse reflectometry (USPR) system to Large Helical Device in the National Institute for Fusion Science. Wide frequency band system is required to obtain wide density profile since an incident wave is reflected at the density layer corresponding to its cutoff frequency. The reflectometry utilizes an impulse with less than 30ps pulse width as a source. Since the bandwidth of an impulse has an inverse relation to the pulse width, we can cover the frequency range of micro- to millimeter waves (18–40GHz) with a single source. The density profiles can be reconstructed by collecting time-of-flight (TOF) signals for each frequency component of an impulse reflected from the corresponding cutoff layer. We utilize the signal record analysis (SRA) method to reconstruct the density profiles from the TOF signal. The effectiveness of the SRA method for the profile reconstruction is confirmed by a simulation study of the USPR using a finite-difference time domain method.
Magnetic diagnostics for the lithium tokamak experiment
Authors: Berzak L. , Kaita R. , Kozub T. , Majeski R. , Zakharov L.
Published: November 2008

The lithium tokamak experiment (LTX) is a spherical tokamak with R0=0.4m, a=0.26m, BTF∼3.4kG, IP∼400kA, and pulse length ∼0.25s. The focus of LTX is to investigate the novel low-recycling lithium wall operating regime for magnetically confined plasmas. This regime is reached by placing an in-vessel shell conformal to the plasma last closed flux surface. The shell is heated and then coated with liquid lithium. An extensive array of magnetic diagnostics is available to characterize the experiment, including 80 Mirnov coils (single and double axis, internal and external to the shell), 34 flux loops, 3 Rogowskii coils, and a diamagnetic loop. Diagnostics are specifically located to account for the presence of a secondary conducting surface and engineered to withstand both high temperatures and incidental contact with liquid lithium. The diagnostic set is therefore fabricated from robust materials with heat and lithium resistance and is designed for electrical isolation from the shell and to provide the data required for highly constrained equilibrium reconstructions.
Analysis of anisotropic suprathermal ion distributions using multidirectional measurements of escaping neutral atom fluxes
Authors: Goncharov P. R. , Ozaki T. , Veshchev E. A. , Sudo S.
Published: November 2008

A feasible approach in obtaining experimental data on the angular dependence of the ion distribution function in a fusion plasma is to perform angle-resolved measurements of kinetic energy spectra of escaping neutral atoms. A general calculation scheme has been developed and realized as a FORTRAN code that has a predictive force to simulate the experimentally measurable anisotropic distributions and random samples of escaping neutral atom kinetic energies for any given angle-dependent ion distribution law, electron density, and temperature profiles, plasma composition, magnetic surface structure, and experiment geometry on any toroidal plasma device with magnetic confinement. As a particular application of the method to a specific experiment, measured signals for all 20 channels of the angle-resolved multisightline neutral particle analyzer on Large Helical Device have been numerically simulated for certain predefined model fast ion distribution functions.
An experimental system for spectral line ratio measurements in the TJ-II stellarator
Authors: Zurro B. , Baciero A. , Fontdecaba J. M. , Peláez R. , Jiménez-Rey D.
Published: November 2008

The chord-integrated emissions of spectral lines have been monitored in the TJ-II stellarator by using a spectral system with time and space scanning capabilities and relative calibration over the entire UV-visible spectral range. This system has been used to study the line ratio of lines of different ionization stages of carbon (C5+ 5290Å and C4+ 2271Å) for plasma diagnostic purposes. The local emissivity of these ions has been reconstructed, for quasistationary profiles, by means of the inversion Fisher method described previously. The experimental line ratio is being empirically studied and in parallel a simple spectroscopic model has been developed to account for that ratio. We are investigating whether the role played by charge exchange processes with neutrals and the existence of non-Maxwellian electrons, intrinsic to Electron Cyclotron Resonance Heating (ECRH) heating, leave any distinguishable mark on this diagnostic method.
Using x-rays to test chemical vapor deposited diamond detectors for areal density measurement at the National Ignition Facility
Authors: Dauffy L. S. , Koch J. A. , Tommasini R. , Izumi N.
Published: November 2008

At the National Ignition Facility (NIF), 192 laser beams will compress a target containing a mixture of deuterium and tritium that will release fusion neutrons, photons, and other radiation. Diagnostics are being designed to measure this emitted radiation to infer crucial parameters of an ignition shot. Chemical vapor deposited (CVD) diamond is one of the ignition diagnostics that will be used as a neutron time-of-flight detector for measuring primary (14.1MeV) neutron yield, ion temperature, and plasma areal density. This last quantity is the subject of this study and is inferred from the number of downscattered neutrons arriving late in time, divided by the number of primary neutrons. We determine in this study the accuracy with which this detector can measure areal density when the limiting factor is detector and electronics saturation. We used laser-produced x-rays to reproduce NIF signals in terms of charge carrier density, time between pulses, and amplitude contrast and found that the effect of the large pulse on the small pulse is at most 8.4%, which is less than the NIF accuracy requirement of ±10%.
A compact flexible pellet injector for the TJ-II stellarator
Authors: McCarthy K. J. , Combs S. K. , Baylor L. R. , Caughman J. B. O. , Fehling D. T. , Foust C. R. , McGill J. M. , Carmona J. M. , Rasmussen D. A.
Published: November 2008

A compact pellet injector is being built for the TJ-II stellarator. It is an upgraded version of the “pellet injector in a suitcase” developed at Oak Ridge National Laboratory and installed on the Madison Symmetric Torus where it continues to be used in many plasma experiments. The design aim is to provide maximum flexibility at minimal cost, while allowing for future upgrades. It is a four-barrel system equipped with a cryogenic refrigerator for in situ hydrogen pellet formation, a combined mechanical punch/propellant valve system, pellet diagnostics, and an injection line, destined for use as an active diagnostic and for fueling. In order to fulfill both objectives it will be sufficiently flexible to permit pellets, with diameters from 0.4to1mm, to be fabricated and accelerated to velocities from 150to∼1000ms−1.
Real-time plasma control based on the ISTTOK tomography diagnostic
Authors: Carvalho P. J. , Carvalho B. B. , Neto A. , Coelho R. , Fernandes H. , Sousa J. , Varandas C. , Chávez-Alarcón E. , Herrera-Velázquez J. J. E.
Published: November 2008

The presently available processing power in generic processing units (GPUs) combined with state-of-the-art programmable logic devices benefits the implementation of complex, real-time driven, data processing algorithms for plasma diagnostics. A tomographic reconstruction diagnostic has been developed for the ISTTOK tokamak, based on three linear pinhole cameras each with ten lines of sight. The plasma emissivity in a poloidal cross section is computed locally on a submillisecond time scale, using a Fourier–Bessel algorithm, allowing the use of the output signals for active plasma position control. The data acquisition and reconstruction (DAR) system is based on ATCA technology and consists of one acquisition board with integrated field programmable gate array (FPGA) capabilities and a dual-core Pentium module running real-time application interface (RTAI) Linux. In this paper, the DAR real-time firmware/software implementation is presented, based on (i) front-end digital processing in the FPGA; (ii) a device driver specially developed for the board which enables streaming data acquisition to the host GPU; and (iii) a fast reconstruction algorithm running in Linux RTAI. This system behaves as a module of the central ISTTOK control and data acquisition system (FIRESIGNAL). Preliminary results of the above experimental setup are presented and a performance benchmarking against the magnetic coil diagnostic is shown.
Modeling the effect of reflection from metallic walls on spectroscopic measurements
Authors: Zastrow K.-D. , Keatings S. R. , Marot L. , O’Mullane M. G. , de Temmerman G. ,   JET-EFDA Contributors
Published: November 2008

A modification of JET is presently being prepared to bring operational experience with ITER-like first wall (Be) and divertor (W) materials, geometry and plasma parameters. Reflectivity measurements of JET sample tiles have been performed and the data are used within a simplified model of the JET and ITER vessels to predict additional contributions to quantitative spectroscopic measurements. The most general method to characterize reflectivity is the bidirectional reflection distribution function (BRDF). For extended sources however, such as bremsstrahlung and edge emission of fuel and intrinsic impurities, the results obtained in the modeling are almost as accurate if the total reflectivity with ideal Lambertian angular dependence is used. This is in contrast to the experience in other communities, such as optical design, lighting design, or rendering who deal mostly with pointlike light sources. This result is so far based on a very limited set of measurements and will be reassessed when more detailed BRDF measurements of JET tiles have been made. If it is true it offers the possibility of in situ monitoring of the reflectivity of selected parts of the wall during exposure to plasma operation, while remeasurement of the BRDF is performed during interventions. For a closed vessel structure such as ITER, it is important to consider multiple reflections. This makes it more important to represent the whole of the vessel reasonably accurately in the model, which on the other hand is easier to achieve than for the more complex internal structure of JET. In both cases the dominant contribution is from the first reflection, and a detailed model of the areas intersected by lines of sight of diagnostic interest is required.
Real-time digital heterodyne interferometer for high resolution plasma density measurements at ISTTOK
Authors: Marques T. G. , Gouveia A. , Pereira T. , Fortunato J. , Carvalho B. B. , Sousa J. , Silva C. , Fernandes H.
Published: November 2008

With the implementation of alternating discharges (ac) at the ISTTOK tokamak, the typical duration of the discharges increased from 35to250ms. This time increase created the need for a real-time electron density measurement in order to control the plasma fueling. The diagnostic chosen for the real-time calculation was the microwave interferometer. The ISTTOK microwave interferometer is a heterodyne system with quadrature detection and a probing frequency of 100GHz (λ0=3mm). In this paper, a low-cost approach for real-time diagnostic using a digital signal programable intelligent computer embedded system is presented, which allows the measurement of the phase with a 1% fringe accuracy in less than 6μs. The system increases its accuracy by digitally correcting the offsets of the input signals and making use of a judicious lookup table optimized to improve the nonlinear behavior of the transfer curve. The electron density is determined at a rate of 82kHz (limited by the analog to digital converter), and the data are transmitted for each millisecond although this last parameter could be much lower (around 12μs—each value calculated is transmitted). In the future, this same system is expected to control plasma actuators, such as the piezoelectric valve of the hydrogen injection system responsible for the plasma fueling.
Bayesian experimental design of a multichannel interferometer for Wendelstein 7-X
Authors: Dreier H. , Dinklage A. , Fischer R. , Hirsch M. , Kornejew P.
Published: November 2008

Bayesian experimental design (BED) is a framework for the optimization of diagnostics basing on probability theory. In this work it is applied to the design of a multichannel interferometer at the Wendelstein 7-X stellarator experiment. BED offers the possibility to compare diverse designs quantitatively, which will be shown for beam-line designs resulting from different plasma configurations. The applicability of this method is discussed with respect to its computational effort.
Spectrally filtered fast imaging of internal magnetohydrodynamic activity in the DIII-D tokamak
Authors: Yu J. H. , Van Zeeland M. A.
Published: November 2008

The detailed poloidal structure of internal magnetohydrodynamic (MHD) modes is imaged using broadband visible bremsstrahlung emission from the core of the DIII-D tokamak. Spectral analysis of individual pixel time series recorded by a fast framing camera (up to 26000frames∕s at 256×256 spatial resolution) is used to reconstruct two-dimensional images of mode amplitude. Application of this spectrally filtered fast imaging (SFFI) technique reveals spatially extended coherent structures that correspond to a (m,n)=(1,1) kink mode and a (2,1) neoclassical tearing mode rotating in the laboratory frame. The SFFI technique produces images with significantly less noise than images produced with the commonly used background subtraction method. Extension of SFFI to other core MHD events and coherent fluctuations in general is straightforward and could lead to further understanding of core MHD activity in fusion devices.
Filterscopes: Spectral line monitors for long-pulse plasma devices
Authors: Brooks N. H. , Colchin R. J. , Fehling D. T. , Hillis D. L. , Mu Y. , Unterberg E.
Published: November 2008

A photomultiplier (PMT)-based diagnostic system for monitoring spectral lines along multiple viewchords, named the “Filterscope” [R. J. Colchin et al., Rev. Sci. Instrum. 74, 2068 (2003)], is currently in use at the DIII-D, NSTX, and CDX-U fusion plasma devices in the US, and has been installed at the KSTAR device in Korea. This diagnostic has recently been upgraded for application to long-pulse devices, such as KSTAR, EAST in China, and the future ITER in France. A new data acquisition system, employing the PXI instrumentation platform with an embedded Windows microprocessor controller, can simultaneously record up to 72 channels at 100kHz sampling rates for plasma periods lasting up to 20min. Based on the average signal level during an adjustable time interval (100ms in the present DIII-D implementation), the controller digitally adjusts PMT dynode voltage throughout the course of a discharge, thereby maintaining the output signals at a level where they are neither saturated nor dominated by digitizer noise. The new system’s ability to accommodate large variations in source strength, discharge to discharge and within a single discharge, has proved particularly valuable during DIII-D operations, since changes between top, bottom, and double-null divertor magnetic configurations lead to large temporal variations in signal brightness.
Measurements of high-current electron beams from X pinches and wire array Z pinches
Authors: Shelkovenko T. A. , Pikuz S. A. , Blesener I. C. , McBride R. D. , Bell K. S. , Hammer D. A. , Agafonov A. V. , Romanova V. M. , Mingaleev A. R.
Published: November 2008

Some issues concerning high-current electron beam transport from the X pinch cross point to the diagnostic system and measurements of the beam current by Faraday cups are discussed. Results of computer simulation of electron beam propagation from the pinch to the Faraday cup give limits for the measured current for beams having different energy spreads. The beam is partially neutralized as it propagates from the X pinch to a diagnostic system, but within a Faraday cup diagnostic, space charge effects can be very important. Experimental results show evidence of such effects.
Performance of the EBIT calorimeter spectrometer
Authors: Porter Frederick Scott , Gygax John , Kelley Richard L. , Kilbourne Caroline A. , King Jonathan M. , Beiersdorfer Peter , Brown Gregory V. , Thorn Daniel B. , Kahn Steven M.
Published: November 2008

The EBIT calorimeter spectrometer (ECS) is a new high-resolution, broadband x-ray spectrometer that has recently been installed at the Electron Beam Ion Trap Facility (EBIT) at the Lawrence Livermore National Laboratory. The ECS is an entirely new production class spectrometer that replaces the XRS/EBIT spectrometer that has been operating at EBIT since 2000. The ECS utilizes a 32-pixel x-ray calorimeter array from the XRS instrument on the Suzaku x-ray observatory. Eighteen of the pixels are optimized for the 0.1–10keV band and yield 4.5eV full width at half maximum energy resolution and 95% quantum efficiency at 6keV. In addition, the ECS includes 14 detector pixels that are optimized for the high-energy band with a bandpass from 0.5 to over 100keV with 34eV resolution and 32% quantum efficiency at 60keV. The ECS detector array is operated at 50mK using a five stage cryogenic system that is entirely automated. The instrument takes data continuously for over 65h with a 2.5h recycle time. The ECS is a nondispersive, broadband, highly efficient spectrometer that is one of the prime instruments at the EBIT facility. The instrument is used for studies of absolute cross sections, charge exchange recombination, and x-ray emission from nonequilibrium plasmas, among other measurements in our laboratory astrophysics program.
Extreme ultraviolet spectroscopy diagnostics of low-temperature plasmas based on a sliced multilayer grating and glass capillary optics
Authors: Kantsyrev V. L. , Safronova A. S. , Williamson K. M. , Wilcox P. , Ouart N. D. , Yilmaz M. F. , Struve K. W. , Voronov D. L. , Feshchenko R. M. , Artyukov I. A. , Vinogradov A. V.
Published: November 2008

New extreme ultraviolet (EUV) spectroscopic diagnostics of relatively low-temperature plasmas based on the application of an EUV spectrometer and fast EUV diodes combined with glass capillary optics is described. An advanced high resolution dispersive element sliced multilayer grating was used in the compact EUV spectrometer. For monitoring of the time history of radiation, filtered fast EUV diodes were used in the same spectral region (>13nm) as the EUV spectrometer. The radiation from the plasma was captured by using a single inexpensive glass capillary that was transported onto the spectrometer entrance slit and EUV diode. The use of glass capillary optics allowed placement of the spectrometer and diodes behind the thick radiation shield outside the direction of a possible hard x-ray radiation beam and debris from the plasma source. The results of the testing and application of this diagnostic for a compact laser plasma source are presented. Examples of modeling with parameters of plasmas are discussed.
Progress of the ITER equatorial vis/IR wide angle viewing system optical design
Authors: Davi M. , Corre Y. , Guilhem D. , Jullien F. , Reichle R. , Salasca S. , Travère J. M. , de la Cal E. , Manzanares A. , de Pablos J. L. , Migozzi J. B.
Published: November 2008

The equatorial vis/IR wide angle viewing system is present in four ITER diagnostic equatorial ports. This instrument will cover a large field of view with high spatial and temporal resolutions, to provide real time temperature measurements of plasma facing components, spectral data in the visible range, information on runaway electrons, and pellet tracking. This diagnostic needs to be reliable, precise, and long lasting. Its design is driven by both the tokamak severe environment and the high performances required for machine protection. The preliminary design phase is ongoing. Paramount issues are being tackled, relative to wide spectral band optical design, material choice, and optomechanical difficulties due to the limited space available for this instrument in the ports, since many other diagnostics and services are also present. Recent progress of the diagnostic optical design and status of associated R&D are presented.
Study of radial potential fluctuations by using a gold neutral beam probe system
Authors: Mizuguchi M. , Yoshikawa M. , Miyata Y. , Goshu S. , Nakada M. , Oono Y. , Nakashima Y. , Imai T.
Published: November 2008

A study of fluctuation is one of the main issues in fusion plasma researches. The potential and its fluctuation are measured by a gold neutral beam probe (GNBP) in the tandem mirror GAMMA10. Since there is no stable isotope (Au197∼100%), there are little measurement errors. GNBP system can measure the potential with about ±30V of error. The time and spatial resolutions are estimated to be about 3μs and 5mm, respectively. During the formation of axial confining potentials, the radial profiles of the potential and its fluctuation were successfully measured in GAMMA10. GNBP is a useful tool for the study of radial potential fluctuation directly in plasmas.
Near-infrared spectroscopy for burning plasma diagnostic applications
Authors: Soukhanovskii V. A.
Published: November 2008

Ultraviolet and visible (UV-VIS, 200–750nm) atomic spectroscopy of neutral and ionized fuel species (H, D, T, and Li) and impurities (e.g., He, Be, C, and W) is a key element of plasma control and diagnosis on International Thermonuclear Experimental Reactor and future magnetically confined burning plasma experiments (BPXs). Spectroscopic diagnostic implementation and performance issues that arise in the BPX harsh nuclear environment in the UV-VIS range, e.g., degradation of first mirror reflectivity under charge-exchange atom bombardment (erosion) and impurity deposition, permanent and dynamic loss of window, and optical fiber transmission under intense neutron and γ-ray fluxes, are either absent or not as severe in the near-infrared (NIR, 750–2000nm) range. An initial survey of NIR diagnostic applications has been undertaken on the National Spherical Torus Experiment. It is demonstrated that NIR spectroscopy can be used for machine protection and plasma control applications, as well as contribute to plasma performance evaluation and physics studies. Emission intensity estimates demonstrate that NIR measurements are possible in the BPX plasma operating parameter range. Complications in the NIR range due to the parasitic background emissions are expected to occur at very high plasma densities, low impurity densities, and at high plasma-facing component temperatures.
A Bremsstrahlung spectrometer using k-edge and differential filters with image plate dosimeters
Authors: Chen C. D. , King J. A. , Key M. H. , Akli K. U. , Beg F. N. , Chen H. , Freeman R. R. , Link A. , Mackinnon A. J. , MacPhee A. G. , Patel P. K. , Porkolab M. , Stephens R. B. , Van Woerkom L. D.
Published: November 2008

A Bremsstrahlung spectrometer using k-edge and differential filtering has been used with image plate dosimeters to measure the x-ray fluence from short-pulse laser/target interactions. An electron spectrometer in front of the Bremsstrahlung spectrometer deflects electrons from the x-ray line of sight and simultaneously measures the electron spectrum. The response functions were modeled with the Monte Carlo code INTEGRATED TIGER SERIES 3.0 and the dosimeters calibrated with radioactive sources. An electron distribution with a slope temperature of 1.3MeV is inferred from the Bremsstrahlung spectra.
Analysis of time-resolved argon line spectra from OMEGA direct-drive implosions
Authors: Florido R. , Nagayama T. , Mancini R. C. , Tommasini R. , Delettrez J. A. , Regan S. P. , Smalyuk V. A. , Rodríguez R. , Gil J. M.
Published: November 2008

We discuss the observation and data analysis of argon K-shell line spectra from argon-doped deuterium-filled OMEGA direct-drive implosion cores based on data recorded with two streaked crystal spectrometers. The targets were 870μm in diameter, 27μm wall thickness plastic shells filled with 20atm of deuterium gas, and a tracer amount of argon for diagnostic purposes. The argon K-shell line spectrum is primarily emitted at the collapse of the implosion and its analysis provides a spectroscopic diagnostic of the core implosion conditions. The observed spectra includes the Heα, Lyα, Heβ, Heγ, Lyβ, and Lyγ line emissions and their associated He- and Li-like satellites thus covering a broad photon energy range from 3100to4200eV with a spectral resolution power of approximately 500. The data analysis relies on detailed atomic and spectral models that take into account nonequilibrium collisional-radiative atomic kinetics, Stark-broadened line shapes, and radiation transport calculations.
Characterization of detection efficiency as function of energy for soft x-ray detectors
Authors: Pacella D. , Mazon D. , Romano A. , Malard P. , Pizzicaroli G.
Published: November 2008

A new technique has been especially developed for determining the detection efficiency of the silicon surface barrier diodes used for tomography reconstructions at Tore Supra, as function of the energy of the x-ray photons, in the range of 4–25keV. The response of these diodes has been studied for different bias voltages (0–120V), with a portable x-ray electronic tube and a cooled Si-p-i-n diode, working in photon counting mode, for the absolute calibration.
Comparison of genetic-algorithm and emissivity-ratio analyses of image data from OMEGA implosion cores
Authors: Nagayama T. , Mancini R. C. , Florido R. , Tommasini R. , Koch J. A. , Delettrez J. A. , Regan S. P. , Smalyuk V. A. , Welser-Sherrill L. A. , Golovkin I. E.
Published: November 2008

Detailed analysis of x-ray narrow-band images from argon-doped deuterium-filled inertial confinement fusion implosion experiments yields information about the temperature spatial structure in the core at the collapse of the implosion. We discuss the analysis of direct-drive implosion experiments at OMEGA, in which multiple narrow-band images were recorded with a multimonochromatic x-ray imaging instrument. The temperature spatial structure is investigated by using the sensitivity of the Lyβ/Heβ line emissivity ratio to the temperature. Three analysis methods that consider the argon Heβ and Lyβ image data are discussed and the results compared. The methods are based on a ratio of image intensities, ratio of Abel-inverted emissivities, and a search and reconstruction technique driven by a Pareto genetic algorithm.
The diagnostic system of the neutral beam injectors for ITER heating and current drive
Authors: Serianni Gianluigi , Pomaro Nicola , Pasqualotto Roberto , Spolaore Monica , Valisa Marco
Published: November 2008

The neutral beam injectors for ITER are designed to deliver hydrogen or deuterium atoms accelerated at 1 MV for a total power of 34 MW. Design of the neutral beam and of the ion source test facilities is presently ongoing. Among the various activities, also the definition and assessment of necessary diagnostics are being carried out. Within this framework, requirements and constraints of the diagnostic system will be discussed in the present paper with the aim of providing data relevant for protection, operation, characterization, and improvement of the performances of the test facilities. The definition of the most suitable locations for the diagnostics and of their preliminary integration into the mechanical design will be proposed. Proposals for the extraction of signals from the high voltage components will also be presented.
Flat field anomalies in an x-ray charge coupled device camera measured using a Manson x-ray source
Authors: Haugh M. J. , Schneider M. B.
Published: November 2008

The static x-ray imager (SXI) is a diagnostic used at the National Ignition Facility (NIF) to measure the position of the x rays produced by lasers hitting a gold foil target. The intensity distribution taken by the SXI camera during a NIF shot is used to determine how accurately NIF can aim laser beams. This is critical to proper NIF operation. Imagers are located at the top and the bottom of the NIF target chamber. The charge coupled device (CCD) chip is an x-ray sensitive silicon sensor, with a large format array (2k×2k), 24 μm square pixels, and 15 μm thick. A multianode Manson x-ray source, operating up to 10 kV and 10 W, was used to characterize and calibrate the imagers. The output beam is heavily filtered to narrow the spectral beam width, giving a typical resolution E/ΔE≈10. The x-ray beam intensity was measured using an x-ray photodiode that has an accuracy better than 1% up to the Si K edge and better than 5% at higher energies. The x-ray beam provides full CCD illumination and is flat, within ±1% maximum to minimum. The spectral efficiency was measured at ten energy bands ranging from 930 to 8470 eV. We observed an energy dependent pixel sensitivity variation that showed continuous change over a large portion of the CCD. The maximum sensitivity variation occurred at 8470 eV. The geometric pattern did not change at lower energies, but the maximum contrast decreased and was not observable below 4 keV. We were also able to observe debris, damage, and surface defects on the CCD chip. The Manson source is a powerful tool for characterizing the imaging errors of an x-ray CCD imager. These errors are quite different from those found in a visible CCD imager.
Streaked x-ray backlighting with twin-slit imager for study of density profile and trajectory of low-density foam target filled with deuterium liquid
Authors: Shiraga H. , Mahigashi N. , Yamada T. , Fujioka S. , Sakaiya T. , Shigemori K. , Nakai M. , Azechi H. , Sunahara A.
Published: November 2008

Low-density plastic foam filled with liquid deuterium is one of the candidates for inertial fusion target. Density profile and trajectory of 527 nm laser-irradiated planer foam-deuterium target in the acceleration phase were observed with streaked side-on x-ray backlighting. An x-ray imager employing twin slits coupled to an x-ray streak camera was used to simultaneously observe three images of the target: self-emission from the target, x-ray backlighter profile, and the backlit target. The experimentally obtained density profile and trajectory were in good agreement with predictions by one-dimensional hydrodynamic simulation code ILESTA-1D.
Measurements of the internal magnetic field on DIII-D using intensity and spacing of the motional Stark multiplet
Authors: Pablant N. A. , Burrell K. H. , Groebner R. J. , Kaplan D. H. , Holcomb C. T.
Published: November 2008

We describe a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of Stark split Dα emission from the neutral beams. This system, named B-Stark, has been recently installed on the DIII-D tokamak. To find the magnetic pitch angle, we use the ratio of the intensities of the π3 and σ1 lines. These lines originate from the same upper level and so are not dependent on the level populations. In future devices, such as ITER, this technique may have advantages over diagnostics based on MSE polarimetry. We have done an optimization of the viewing direction for the available ports on DIII-D to choose the installation location. With this placement, we have a near optimal viewing angle of 59.6° from the vertical direction. All hardware has been installed for one chord, and we have been routinely taking data since January 2007. We fit the spectra using a simple Stark model in which the upper level populations of the Dα transition are treated as free variables. The magnitude and direction of the magnetic field obtained using this diagnostic technique compare well with measurements from MSE polarimetry and EFIT.
Diagnostic of charge balance in high-temperature tungsten plasmas using LLNL EBIT
Authors: Osborne G. C. , Safronova A. S. , Kantsyrev V. L. , Safronova U. I. , Yilmaz M. F. , Williamson K. M. , Shrestha I. , Beiersdorfer P.
Published: November 2008

Diagnostic of high-temperature M-shell W plasmas is challenging because of contribution of numerous ionization stages in a relatively narrow x-ray spectral region. A method using LLNL EBIT data generated at different electron beam energies has been established for the identification of prominent spectral features and for the determination of charge balance in x-ray M-shell W spectra between 3.5 and 8.5Å. It extends previous work [A. S. Safronova et al., Can. J. Phys. 86, 267 (2008)] which used only Ni-like lines to include the neighboring ionization stages. This diagnostic procedure was tested with results from Z-pinch plasmas produced on the 1MA pulse power generator Zebra at UNR. These results are of particular importance for fusion research.
Measurement of heating laser injection time to imploded core plasma by using x-ray framing camera
Authors: Koga Mayuko , Fujiwara Takashi , Sakaiya Tatsuhiro , Lee Myongdok , Shigemori Keisuke , Shiraga Hiroyuki , Azechi Hiroshi
Published: November 2008

A simultaneous measurement of imploded core plasma and injection time of heating laser is conducted by using an x-ray framing camera (XFC). The experiments are performed using Gekko XII laser system for implosion of the deuterated polystyrene (CD) plastic shell target and Peta Watt (PW) laser system for heating. The time of PW laser injection is observed as the bright zone in the XFC image. The measured x-ray intensity profiles fit the Gaussian profiles well. The calculations of microchannel plate by using dynode model explain these broadened temporal profiles qualitatively. The peak position of fitted x-ray intensity profile is almost in agreement with the time when the high energy x ray is observed by x-ray streak camera. Moreover, the peak position is delayed corresponding to the delayed setting of PW laser injection time. From these results, it is concluded that we can estimate the heating laser injection time with resolution of the order of 10ps by using XFC.
V
-band frequency hopping microwave reflectometer in LHD
Authors: Tokuzawa T. , Ejiri A. , Kawahata K. , Tanaka K. , Ito Y.
Published: November 2008

In order to measure the internal structure of fluctuation, the broadband frequency tunable system, which has the ability of fast and stable hopping operation, is applied in the Large Helical Device. One of the important issues of density fluctuation measurements using this reflectometer is the study of energetic particle driven magnetohydrodynamics instability. During one plasma discharge, the launching frequency changes from one frequency to another frequency, which this operation is called as frequency hopping, and the cutoff position can be scanned in the wide area. As a hopping source, a synthesizer is used because it has a quite stable and low phase noise. The frequency component of the source output is multiplied to V-band (50–75 GHz) region for plasma measurements in extraordinary mode polarization. Also this system has a heterodyne detection with single side band frequency modulation for sensitive phase and amplitude measurement. We can obtain the radial profile of Alfvén eigenmodelike oscillation in a neutral beam injected plasma.
Multicolor, time-gated, soft x-ray pinhole imaging of wire array and gas puff Z pinches on the Z and Saturn pulsed power generators
Authors: Jones B. , Coverdale C. A. , Nielsen D. S. , Jones M. C. , Deeney C. , Serrano J. D. , Nielsen-Weber L. B. , Meyer C. J. , Apruzese J. P. , Clark R. W. , Coleman P. L.
Published: November 2008

A multicolor, time-gated, soft x-ray pinhole imaging instrument is fielded as part of the core diagnostic set on the 25 MA Z machine [M. E. Savage et al., in Proceedings of the Pulsed Power Plasma Sciences Conference (IEEE, New York, 2007), p. 979] for studying intense wire array and gas puff Z-pinch soft x-ray sources. Pinhole images are reflected from a planar multilayer mirror, passing 277 eV photons with <10 eV bandwidth. An adjacent pinhole camera uses filtration alone to view 1–10 keV photons simultaneously. Overlaying these data provides composite images that contain both spectral as well as spatial information, allowing for the study of radiation production in dense Z-pinch plasmas. Cu wire arrays at 20 MA on Z show the implosion of a colder cloud of material onto a hot dense core where K-shell photons are excited. A 528 eV imaging configuration has been developed on the 8 MA Saturn generator [R. B. Spielman et al., and A. I. P. Conf, Proc. 195, 3 (1989)] for imaging a bright Li-like Ar L-shell line. Ar gas puff Z pinches show an intense K-shell emission from a zippering stagnation front with L-shell emission dominating as the plasma cools.
Tests and calibration of NIF neutron time of flight detectors
Authors: Ali Z. A. , Glebov V. Yu. , Cruz M. , Duffy T. , Stoeckl C. , Roberts S. , Sangster T. C. , Tommasini R. , Throop A. , Moran M. , Dauffy L. , Horsefield C.
Published: November 2008

The National Ignition Facility (NIF) neutron time of flight (NTOF) diagnostic will measure neutron yield and ion temperature in all NIF campaigns in DD, DT, and THD* implosions. The NIF NTOF diagnostic is designed to measure neutron yield from 1×109 to 2×1019. The NTOF consists of several detectors of varying sensitivity located on the NIF at about 5 and 20m from the target. Production, testing, and calibration of the NIF NTOF detectors have begun at the Laboratory for Laser Energetics (LLE). Operational tests of the NTOF detectors were performed on several facilities including the OMEGA laser at LLE and the Titan laser at Lawrence Livermore National Laboratory. Neutron calibrations were carried out on the OMEGA laser. Results of the NTOF detector tests and calibration will be presented.
Imaging interferometers for analysis of Thomson scattered spectra
Authors: Howard J. , Hatae T.
Published: November 2008

Polarization interferometers have some potential efficiency advantages for imaging Thomson scattering spectral analysis. In this article we present a number of designs for high-efficiency imaging polarization interferometers for Thomson scattering spectral analysis. The use of high-efficiency crystal polarizing beamsplitters (both displacement and angle) results in low-loss complementary passbands (no edge losses), simple imaging systems, and wide field of view. The efficiency and relative merits of both multiple-filter and dispersive-type configurations are being assessed before installation on the JT-60U ruby-laser Thomson scattering system. Light is transferred from the viewing port via a linear array of optical fiber bundles which will be imaged through the interferometer onto the photocathode of an intensified charge coupled device camera. Because of the broadband nature of the Thomson light, the optical delays required to Fourier analyze the spectrum are quite small. This leads to compact multicolor or dispersive systems based on combinations of Wollaston and Savart splitters and traditional waveplates.
Dust measurements in tokamaks (invited)
Authors: Rudakov D. L. , Yu J. H. , Boedo J. A. , Hollmann E. M. , Krasheninnikov S. I. , Moyer R. A. , Muller S. H. , Pigarov A. Yu. , Rosenberg M. , Smirnov R. D. , West W. P. , Boivin R. L. , Bray B. D. , Brooks N. H. , Hyatt A. W. , Wong C. P. C. , Roquemore A. L. , Skinner C. H. , Solomon W. M. , Ratynskaia S. , Fenstermacher M. E. , Groth M. , Lasnier C. J. , McLean A. G. , Stangeby P. C.
Published: November 2008

Dust production and accumulation present potential safety and operational issues for the ITER. Dust diagnostics can be divided into two groups: diagnostics of dust on surfaces and diagnostics of dust in plasma. Diagnostics from both groups are employed in contemporary tokamaks; new diagnostics suitable for ITER are also being developed and tested. Dust accumulation in ITER is likely to occur in hidden areas, e.g., between tiles and under divertor baffles. A novel electrostatic dust detector for monitoring dust in these regions has been developed and tested at PPPL. In the DIII-D tokamak dust diagnostics include Mie scattering from Nd:YAG lasers, visible imaging, and spectroscopy. Laser scattering is able to resolve particles between 0.16 and 1.6 μm in diameter; using these data the total dust content in the edge plasmas and trends in the dust production rates within this size range have been established. Individual dust particles are observed by visible imaging using fast framing cameras, detecting dust particles of a few microns in diameter and larger. Dust velocities and trajectories can be determined in two-dimension with a single camera or three-dimension using multiple cameras, but determination of particle size is challenging. In order to calibrate diagnostics and benchmark dust dynamics modeling, precharacterized carbon dust has been injected into the lower divertor of DIII-D. Injected dust is seen by cameras, and spectroscopic diagnostics observe an increase in carbon line (CI, CII, C2 dimer) and thermal continuum emissions from the injected dust. The latter observation can be used in the design of novel dust survey diagnostics.
Measurement of electrostatic potential fluctuation using heavy ion beam probe in large helical device
Authors: Ido Takeshi , Shimizu Akihiro , Nishiura Masaki , Nakano Haruhisa , Ohshima Shinsuke , Kato Shinji , Hamada Yasuji , Yoshimura Yasuo , Kubo Shin , Shimozuma Takashi , Igami Hiroe , Takahashi Hiromi , Toi Kazuo , Watanabe Fumitake
Published: November 2008

Heavy ion beam probe (HIBP) for large helical device (LHD) has been improved to measure the potential fluctuation in high-temperature plasmas. The spatial resolution is improved to about 10 mm by controlling the focus of a probe beam. The HIBP is applied to measure the potential fluctuation in plasmas where the rotational transform is controlled by electron cyclotron current drive. The fluctuations whose frequencies change with the time constant of a few hundreds of milliseconds and that with a constant frequency are observed. The characteristics of the latter fluctuation are similar to those of the geodesic acoustic mode oscillation. The spatial profiles of the fluctuations are also obtained.
Development of terahertz laser diagnostics for electron density measurements
Authors: Kawahata K. , Akiyama T. , Tanaka K. , Nakayama K. , Okajima S.
Published: November 2008

A two color laser interferometer using terahertz laser sources is under development for high performance operation on the large helical device and for future burning plasma experiments such as ITER. Through investigation of terahertz laser sources, we have achieved high power simultaneous oscillations at 57.2 and 47.6 μm of a CH3OD laser pumped by a cw 9R(8) CO2 laser line. The laser wavelength around 50 μm is the optimum value for future fusion devices from the consideration of the beam refraction effect and signal-to-noise ratio for an expected phase shift due to plasma. In this article, recent progress of the terahertz laser diagnostics, especially in mechanical vibration compensation by using a two color laser operation and terahertz laser beam transmission through a dielectric waveguide, will be presented.
A spatially resolved ion temperature diagnostic for the National Ignition Facility
Authors: Grim G. P. , Finch J. P. , King N. S. P. , Morgan G. L. , Oertel J. A. , Wilde C. H. , Wilke M. D. , Wilson D. C. , Johnson D. E.
Published: November 2008

The concepts and initial development efforts for a spatially resolved ion temperature diagnostic are described. The diagnostic is intended for Inertial Confinement Fusion experiments at the National Ignition Facility and is an integration of neutron aperture imaging and ion temperature techniques. The neutron imaging technique is extended by recording tomographic projections of the radiation-to-light converter on a streak camera. The streak record is used to calculate images at multiple times during the arrival of the thermally broadened 14.1MeV neutron flux. The resulting set of images is used to determine the spatially resolved ion temperature.