bluuebunny/crossref_metadata_2025 huggingface dataset:
Validating TRANSP simulations using neutron emission spectroscopy with dual sight lines
Authors: Hellesen C. , Sundén E. A. , Conroy S. , Ericsson G. , Giacomelli L. , Hjalmarsson A. , Johnsson M. G. , Källne J. , Ronchi E. , Weiszflog M. , Ballabio L. , Gorini G. , Tardocchi M. , Voitsekhovitch I. ,   JET-EFDA Contributors
Published: November 2008

A method to generate modeled neutron spectra from bulk and fast ion distributions simulated by TRANSP has been developed. In this paper, modeled data generated from fuel ion distrubutions modeled with TRANSP is compared to measured data from two neutron spectrometers with different lines of sight; TOFOR with a radial one and the MPRu with a tangential one. The information obtained from the analysis of the measured neutron spectra such as the relative intensity of the emission from different ion populations places additional constraints on the simulation and can be used to adjust the parameters of the simulation.
X-ray diagnostic calibration with the tabletop laser facility EQUINOX
Authors: Reverdin Charles , Paurisse M. , Caillaud T. , Combis P. , Duval A. , Gontier D. , Husson D. , Rubbelynck C. , Zuber C.
Published: November 2008

The broadband x-ray emission of a target irradiated by a laser can be used to check the calibration of detectors. At CEA-DIF we have a tabletop picosecond laser facility called EQUINOX with 0.3J at 800nm. The laser is focused inside a target chamber onto a solid target and produces bright radiation in the 100–2000eV spectral range. The x-ray source is routinely monitored with a pinhole camera for source dimension measurement and with x-ray diodes for flux measurement. In addition an x-ray transmission grating spectrometer, a crystal spectrometer, and a single count charge coupled device camera measure the x-ray spectrum between 100eV and 15keV. The absolute calibration of those sets of spectrometers allows us to fully characterize x-ray emission spectra. Typical duration is less than 100ps. The spectrum can be tuned by changing target material, pulse length, and x-ray filters. An application to checking the calibration of x-ray diodes used in the broad band spectrometer DMX with single shots will be presented.
Rapid, absolute calibration of x-ray filters employed by laser-produced plasma diagnostics
Authors: Brown G. V. , Beiersdorfer P. , Emig J. , Frankel M. , Gu M. F. , Heeter R. F. , Magee E. , Thorn D. B. , Widmann K. , Kelley R. L. , Kilbourne C. A. , Porter F. S.
Published: November 2008

The Electron Beam Ion Trap (EBIT) facility at the Lawrence Livermore National Laboratory is being used to absolutely calibrate the transmission efficiency of x-ray filters employed by diodes and spectrometers used to diagnose laser-produced plasmas. EBIT emits strong, discrete monoenergetic lines at appropriately chosen x-ray energies. X rays are detected using the high resolution EBIT Calorimeter Spectrometer (ECS), developed for LLNL at the NASA/Goddard Space Flight Center. X-ray filter transmission efficiency is determined by dividing the x-ray counts detected when the filter is in the line of sight by those detected when out of the line of sight. Verification of filter thickness can be completed in only a few hours, and absolute efficiencies can be calibrated in a single day over a broad range from about 0.1to15keV. The EBIT calibration lab has been used to field diagnostics (e.g., the OZSPEC instrument) with fully calibrated x-ray filters at the OMEGA laser. Extensions to use the capability for calibrating filter transmission for the DANTE instrument on the National Ignition Facility are discussed.
Electron heated target temperature measurements in petawatt laser experiments based on extreme ultraviolet imaging and spectroscopy
Authors: Ma T. , Beg F. N. , MacPhee A. G. , Chung H.-K. , Key M. H. , Mackinnon A. J. , Patel P. K. , Hatchett S. , Akli K. U. , Stephens R. B. , Chen C. D. , Freeman R. R. , Link A. , Offermann D. T. , Ovchinnikov V. , Van Woerkom L. D.
Published: November 2008

Three independent methods (extreme ultraviolet spectroscopy, imaging at 68 and 256eV) have been used to measure planar target rear surface plasma temperature due to heating by hot electrons. The hot electrons are produced by ultraintense laser-plasma interactions using the 150J, 0.5ps Titan laser. Soft x-ray spectroscopy in the 50–400eV region and imaging at the 68 and 256eV photon energies give a planar deuterated carbon target rear surface pre-expansion temperature in the 125–150eV range, with the rear plasma plume averaging a temperature approximately 74eV.
Demonstration of x-ray Thomson scattering using picosecond K-α x-ray sources in the characterization of dense heated matter
Authors: Kritcher A. L. , Neumayer P. , Lee H. J. , Döppner T. , Falcone R. W. , Glenzer S. H. , Morse E. C.
Published: November 2008

We present K-α x-ray Thomson scattering from shock compressed matter for use as a diagnostic in determining the temperature, density, and ionization state with picosecond resolution. The development of this source as a diagnostic as well as stringent requirements for successful K-α x-ray Thomson scattering are addressed. Here, the first elastic and inelastic scattering measurements on a medium size laser facility have been observed. We present scattering data from solid density carbon plasmas with >1×105 photons in the elastic peak that validate the capability of single shot characterization of warm dense matter and the ability to use this scattering source at future free electron lasers and for fusion experiments at the National Ignition Facility (NIF), LLNL.
Effects of filament geometry on the arc efficiency of a high-intensity He+ ion source
Authors: Kobuchi T. , Kisaki M. , Shinto K. , Okamoto A. , Kitajima S. , Sasao M. , Tsumori K. , Kaneko O. , Sakakita H. , Kiyama S. , Hirano Y. , Wada M.
Published: November 2008

A strongly focusing high-intensity He+ ion source equipped with three concave electrodes has been designed and constructed as the beam source for a high-energy He0 neutral beam probe system to diagnose fusion-produced alpha particles in thermonuclear fusion plasmas. The reduction of heat load onto the concave extraction electrodes is particularly important for a long pulse operation, as the heat load deforms the electrodes and thus the beam focal length. The effects on the arc efficiency (beam current/arc power) of the ion source due to the discharge filament structure (straight-type and L-shape-type filaments), size (filament diameters of 2 and 1.5mm), number, and the locations have been studied. Choice of the appropriate filament structure improved the arc efficiency by 17%.
Subterahertz gyrotron developments for collective Thomson scattering in LHD
Authors: Notake T. , Saito T. , Tatematsu Y. , Kubo S. , Shimozuma T. , Tanaka K. , Nishiura M. , Fujii A. , Agusu La , Ogawa I. , Idehara T.
Published: November 2008

Collective Thomson scattering (CTS) is expected to provide the spatially resolved velocity distribution functions of not only thermal and tail ions but also alpha particles resulting from fusion reactions. CTS using gyrotrons with frequency higher than the conventional ones used for plasma heating would have advantages to alleviate refraction, cutoff effects, and background electron cyclotron emission noise. Therefore, a high-power pulse gyrotron operating at approximately 400 GHz is being developed for CTS in Large Helical Device (LHD). A single-mode oscillation with a frequency greater than 400 GHz, applying the second-harmonic resonance, was successfully demonstrated in the first stage. At the same time, concrete feasibility study based on ray tracing, scattering spectra, and electron cyclotron emission calculations has been conducted.
Calibration and characterization of single photon counting cameras for short-pulse laser experiments
Authors: Maddox B. R. , Park H. S. , Remington B. A. , McKernan M.
Published: November 2008

The x-ray photon counting efficiency of various charged-coupled device (CCD) based cameras was studied as a function of photon energy and exposure. A pair of Spectral Instruments model 800 CCD cameras fitted with 16 μm thick back-illuminated CCDs were calibrated at low x-ray energy using two well established histogram methods. In addition, two new thick substrate CCDs were evaluated for use at high energy. One was a commercially available Princeton Instruments PI-LCX1300 deep depletion CCD camera, while the other used a custom designed 650 μm thick partially depleted CCD fitted to a Spectral Instruments model 800 camera body. It is shown that at high x-ray energy, a pixel-summing algorithm is necessary to reconstruct the x-ray spectra in the thicker substrate CCDs. This paper will describe the different algorithms used to extract spectra and the absolute detection efficiencies using these algorithms. These detectors and algorithms will be very useful in detecting high-energy x-ray photons from high-intensity short-pulse laser interactions.
High order reflectivity of highly oriented pyrolytic graphite crystals for x-ray energies up to 22 keV
Authors: Döppner T. , Neumayer P. , Girard F. , Kugland N. L. , Landen O. L. , Niemann C. , Glenzer S. H.
Published: November 2008

We used Kr Kα (12.6 keV), Zr Kα (15.7 keV), and Ag Kα (22.2 keV) x-rays, produced by petawatt-class laser pulses, to measure the integrated crystal reflectivity Rint of flat highly oriented pyrolytic graphite (HOPG) up to the fifth order. The maximum Rint was observed in first order (3.7 mrad at 12.6 keV), decreasing by a factor of 3–5 for every successive order, and dropping by a factor of 2–2.5 at 22.2 keV. The current study indicates that HOPG crystals are suitable for measuring scattering signals from high energy x-ray sources (E≥20 keV). These energies are required to penetrate through the high density plasma conditions encountered in inertial confinement fusion capsule implosions on the National Ignition Facility.
Development of multichannel intermediate frequency system for electron cyclotron emission radiometer on KSTAR Tokamak
Authors: Kogi Yuichiro , Sakoda Takuya , Mase Atsushi , Ito Naoki , Yokota Yuya , Yamaguchi Soichiro , Nagayama Yoshio , Jeong Seung H. , Kwon Myeun , Kawahata Kazuo
Published: November 2008

Plasma experiments on KSTAR are scheduled to start up this year (2008). We have developed an electron cyclotron emission (ECE) radiometer to measure the radial electron temperature profiles in KSTAR experiments. The radiometer system consists, briefly, of two downconversion stages, amplifiers, bandpass filter banks, and video detectors. These components are made commercially or developed in house. The system detects ECE power in the frequency range from 110 to 196 GHz, the detected signal being resolved by means of 48 frequency windows. Before installation of this system on KSTAR, we installed a part of this system on large helical device (LHD) to study the system under similar plasma conditions. In this experiment, the signal amplitude, considered to be proportional to the electron temperature, is measured. The time-dependent traces of the electron temperature measured by this radiometer are in good agreement with those provided by the LHD Michelson spectrometer. The system noise level which limits the minimum measurable temperature (converted to the electron temperature) is about 30 eV.
Scrape-off layer reflectometer for Alcator C-Mod
Authors: Hanson G. R. , Wilgen J. B. , Lau C. , Lin Y. , Wallace G. M. , Wukitch S. J.
Published: November 2008

A two-frequency x-mode reflectometer operating from 100 to 146 GHz is deployed on Alcator C-Mod to measure the density profile and fluctuations in the scrape-off layer (SOL) immediately in front of the new J-port ICRF antenna and the new C-port lower hybrid launcher. The reflectometer covers densities from 1016 to 1020 m−3 at 5–5.4 T. To provide the greatest flexibility and capability to deal with density fluctuations approaching 100% peak-to-peak in the SOL, both full-phase and differential-phase measurement capabilities with sweep speeds of ∼10 μs to >1 ms are implemented. The differential-phase measurement uses a difference frequency of 500 MHz, corresponding to cutoff layer separations ranging from about 0.1 to 1 mm. The reflectometer has six sets of launchers: three on the ICRF antenna and three on the lower hybrid launcher. Both the ICRF antenna and the lower hybrid launcher incorporate reflectometer antennas at their top, bottom, and midplane locations.
The next generation of electron cyclotron emission imaging diagnostics (invited)
Authors: Zhang P. , Domier C. W. , Liang T. , Kong X. , Tobias B. , Shen Z. , Luhmann N. C. , Park H. , Classen I. G. J. , van de Pol M. J. , Donné A. J. H. , Jaspers R.
Published: November 2008

A 128 channel two-dimensional electron cyclotron emission imaging system collects time-resolved 16×8 images of Te profiles and fluctuations on the TEXTOR tokamak. Electron cyclotron emission imaging (ECEI) is undergoing significant changes which promise to revolutionize and extend its capabilities far beyond what has been achieved to date. These include the development of a minilens array configuration with increased sensitivity antennas, a new local oscillator pumping scheme, enhanced electron cyclotron resonance heating shielding, and a highly flexible optical design with vertical zoom capability. Horizontal zoom and spot size (rf bandwidth) capabilities are also being developed with new ECEI electronics. An interface module is under development to remotely control all key features of the new ECEI instrument, many of which can be changed during a plasma discharge for maximum flexibility.
Fast soft x-ray images of magnetohydrodynamic phenomena in NSTX
Authors: Bush C. E. , Stratton B. C. , Robinson J. , Zakharov L. E. , Fredrickson E. D. , Stutman D. , Tritz K.
Published: November 2008

A variety of magnetohydrodynamic (MHD) phenomena have been observed on NSTX. Many of these affect fast particle losses, which are of major concern for future burning plasma experiments. Usual diagnostics for studying these phenomena are arrays of Mirnov coils for magnetic oscillations and p-i-n diode arrays for soft x-ray emission from the plasma core. Data reported here are from a unique fast soft x-ray imaging camera (FSXIC) with a wide-angle (pinhole) tangential view of the entire plasma minor cross section. The camera provides a 64×64 pixel image, on a charge coupled device chip, of light resulting from conversion of soft x rays incident on a phosphor to the visible. We have acquired plasma images at frame rates of 1–500 kHz (300 frames/shot) and have observed a variety of MHD phenomena: disruptions, sawteeth, fishbones, tearing modes, and edge localized modes (ELMs). New data including modes with frequency >90 kHz are also presented. Data analysis and modeling techniques used to interpret the FSXIC data are described and compared, and FSXIC results are compared to Mirnov and p-i-n diode array results.
Implementation of local area network extension for instrumentation standard trigger capabilities in advanced data acquisition platforms
Authors: López J. M. , Ruiz M. , Barrera E. , de Arcas G. , Vega J.
Published: November 2008

Synchronization mechanisms are an essential part of the real-time distributed data acquisition systems (DASs) used in fusion experiments. Traditionally, they have been based on the use of digital signals. The approach known as local area network extension for instrumentation (LXI) provides a set of very powerful synchronization and trigger mechanisms. The Intelligent Test Measurement System (ITMS) is a new platform designed to implement distributed data acquisition and fast data processing for fusion experiments. It is based on COMPATPCI technology and its extension to instrumentation (PXI). Hardware and software elements have been developed to include LXI trigger and synchronization mechanisms in this platform in order to obtain a class A LXI instrument. This paper describes the implementation of such a system, involving the following components: commercial hardware running a Linux operating system; a real-time extension to an operating system and network (RTAI and RTNET), which implements a software precision time protocol (PTP) using IEEE1588; an ad hoc PXI module to support hardware implementation of PTP-IEEE 1588; and the multipoint, low-voltage differential signaling hardware LXI trigger bus.
High resolution soft x-ray spectroscopy of low Z K-shell emission from laser-produced plasmas
Authors: Dunn J. , Magee E. W. , Shepherd R. , Chen H. , Hansen S. B. , Moon S. J. , Brown G. V. , Gu M.-F. , Beiersdorfer P. , Purvis M. A.
Published: November 2008

A large radius, R=44.3m, high resolution grating spectrometer (HRGS) with 2400lines∕mm variable line spacing has been designed for laser-produced plasma experiments conducted at the Lawrence Livermore National Laboratory Jupiter Laser Facility. The instrument has been run with a low-noise, charge-coupled device detector to record high signal-to-noise spectra in the 10–50Å wavelength range. The instrument can be run with a 10–20μm wide slit to achieve the best spectral resolving power, approaching 1000 and similar to crystal spectrometers at 12–20Å, or in slitless operation with a small symmetrical emission source. We describe preliminary spectra emitted from various H-like and He-like low Z ion plasmas heated by 100–500ps (full width at half maximum), 527nm wavelength laser pulses. This instrument can be developed as a useful spectroscopy platform relevant to laboratory-based astrophysics as well as high energy density plasma studies.
Spatially resolved high resolution x-ray spectroscopy for magnetically confined fusion plasmas (invited)
Authors: Ince-Cushman A. , Rice J. E. , Bitter M. , Reinke M. L. , Hill K. W. , Gu M. F. , Eikenberry E. , Broennimann Ch. , Scott S. , Podpaly Y. , Lee S. G. , Marmar E. S.
Published: November 2008

The use of high resolution x-ray crystal spectrometers to diagnose fusion plasmas has been limited by the poor spatial localization associated with chord integrated measurements. Taking advantage of a new x-ray imaging spectrometer concept [M. Bitter et al., Rev. Sci. Instrum. 75, 3660 (2004)], and improvements in x-ray detector technology [Ch. Broennimann et al., J. Synchrotron Radiat. 13, 120 (2006)], a spatially resolving high resolution x-ray spectrometer has been built and installed on the Alcator C-Mod tokamak. This instrument utilizes a spherically bent quartz crystal and a set of two dimensional x-ray detectors arranged in the Johann configuration [H. H. Johann, Z. Phys. 69, 185 (1931)] to image the entire plasma cross section with a spatial resolution of about 1cm. The spectrometer was designed to measure line emission from H-like and He-like argon in the wavelength range 3.7 and 4.0Å with a resolving power of approximately 10 000 at frame rates up to 200Hz. Using spectral tomographic techniques [I. Condrea, Phys. Plasmas 11, 2427 (2004)] the line integrated spectra can be inverted to infer profiles of impurity emissivity, velocity, and temperature. From these quantities it is then possible to calculate impurity density and electron temperature profiles. An overview of the instrument, analysis techniques, and example profiles are presented.
Application of reflectometry power flow for magnetic field pitch angle measurements in tokamak plasmas (invited)
Authors: Gourdain P.-A. , Peebles W. A.
Published: November 2008

Reflectometry has successfully demonstrated measurements of many important parameters in high temperature tokamak fusion plasmas. However, implementing such capabilities in a high-field, large plasma, such as ITER, will be a significant challenge. In ITER, the ratio of plasma size (meters) to the required reflectometry source wavelength (millimeters) is significantly larger than in existing fusion experiments. This suggests that the flow of the launched reflectometer millimeter-wave power can be realistically analyzed using three-dimensional ray tracing techniques. The analytical and numerical studies presented will highlight the fact that the group velocity (or power flow) of the launched microwaves is dependent on the direction of wave propagation relative to the internal magnetic field. It is shown that this dependence strongly modifies power flow near the cutoff layer in a manner that embeds the local magnetic field direction in the “footprint” of the power returned toward the launch antenna. It will be shown that this can potentially be utilized to locally determine the magnetic field pitch angle at the cutoff location. The resultant beam drift and distortion due to magnetic field and relativistic effects also have significant consequences on the design of reflectometry systems for large, high-field fusion experiments. These effects are discussed in the context of the upcoming ITER burning plasma experiment.
Enhancement of the JET edge LIDAR Thomson scattering diagnostic with ultrafast detectors
Authors: Kempenaars M. , Flanagan J. C. , Giudicotti L. , Walsh M. J. , Beurskens M. , Balboa I. ,   JET-EFDA Contributors
Published: November 2008

The edge light detection and ranging (LIDAR) Thomson scattering diagnostic at the Joint European Torus fusion experiment uses a 3 J ruby laser to measure the electron density and temperature profile at the plasma edge. The original system used a 1 GHz digitizer and detectors with response times of ≈650 ps and effective quantum efficiencies <7%. This system has recently been enhanced with the installation of a new 8 GHz digitizer and four new ultrafast GaAsP microchannel plate photomultiplier tube detectors with response times of <300 ps and effective quantum efficiencies in the range of ∼13%−20% (averaged over λ=500–700 nm). This upgrade has enabled the spatial resolution to be reduced to ∼6.3 cm along the laser line of sight for a laser pulse of 300 ps full width at half maximum, which is close to the requirements for the ITER core LIDAR. Performance analysis shows that the new system will have an effective spatial resolution of up to 1 cm in the magnetic midplane via magnetic flux surface mapping.
A spatially resolving x-ray crystal spectrometer for measurement of ion-temperature and rotation-velocity profiles on the Alcator C-Mod tokamak
Authors: Hill K. W. , Bitter M. L. , Scott S. D. , Ince-Cushman A. , Reinke M. , Rice J. E. , Beiersdorfer P. , Gu M.-F. , Lee S. G. , Broennimann Ch. , Eikenberry E. F.
Published: November 2008

A new spatially resolving x-ray crystal spectrometer capable of measuring continuous spatial profiles of high resolution spectra (λ/dλ>6000) of He-like and H-like Ar Kα lines with good spatial (∼1 cm) and temporal (∼10 ms) resolutions has been installed on the Alcator C-Mod tokamak. Two spherically bent crystals image the spectra onto four two-dimensional Pilatus II pixel detectors. Tomographic inversion enables inference of local line emissivity, ion temperature (Ti), and toroidal plasma rotation velocity (vϕ) from the line Doppler widths and shifts. The data analysis techniques, Ti and vϕ profiles, analysis of fusion-neutron background, and predictions of performance on other tokamaks, including ITER, will be presented.
ITER LIDAR performance analysis
Authors: Beurskens M. N. A. , Giudicotti L. , Kempenaars M. , Scannell R. , Walsh M. J.
Published: November 2008

The core LIDAR Thomson scattering for ITER is specified for core profile measurements with a spatial resolution of 7 cm (a/30) for the range of 500 eV<Te<40 keV and ne>3×1019 m−3 at an accuracy of <10% for Te. These specifications are verified using a full profile Monte Carlo simulation code. In the simulations it is assumed that the input transmission is 50% and the collection transmission is 10% for λ=300–1200 nm and F/#=6–17. A crucial design decision lies on the choice of laser and detector combination. It is evaluated that the system can meet its spatial and accuracy specifications for higher temperatures of Te>5 keV with a combination of a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (λ0=1064 nm, Δλ<1 nm, 5 J, and ΔtFWHM=250 ps, 5–10 Hz) and S20, GaAs, and GaAsP microchannel plate photomultipliers (ΔtFWHM<300 ps, effective quantum efficiency, EQE=3%–4%, and D=18 mm). In order to reach the required Te of 500 eV with Nd:YAG first harmonic, this choice requires a development of fast near infrared detectors.
Application of a digital pileup resolving method to high count rate neutron measurements
Authors: Belli Francesco , Esposito Basilio , Marocco Daniele , Riva Marco , Zimbal Andreas
Published: November 2008

The possibility of working in high count rate conditions is an important issue for neutron measurements applied to fusion experiments in order to extend the measurement dynamic range and time resolution. One of the main issues of high count rate operation is the overlapping of closely spaced events (pileup) that produces a distortion in their amplitude and therefore in the pulse height spectra. The usual way to deal with such pileup events using standard analog electronics is to reject them in the energy analysis process. Thanks to digital acquisition techniques, the waveforms of pileup events can be recorded and elaborated in order to reconstruct the contributing original single events. This work presents the results of the application of a pileup resolving method for the reconstruction and analysis of overlapping events to pulses acquired digitally from a NE213 liquid scintillator detector. The measurements have been carried out at the PTB accelerator facility with 14MeV neutrons at total count rates over 400kHz.
Reproducible, rugged, and inexpensive photocathode x-ray diode
Authors: Idzorek G. C. , Tierney T. E. , Lockard T. E. , Moy K. J. , Keister J. W.
Published: November 2008

The photoemissive cathode type of x-ray diode (XRD) is popular for measuring time and spectrally resolved output of pulsed power experiments. Vitreous carbon XRDs currently used on the Sandia National Laboratories Z-machine were designed in the early 1980s and use materials and processes no longer available. Additionally cathodes used in the high x-ray flux and dirty vacuum environment of a machine such as Z suffer from response changes requiring recalibration. In searching for a suitable replacement cathode, we discovered very high purity vitreous-carbon planchets are commercially available for use as biological substrates in scanning electron microscope (SEM) work. After simplifying the photocathode mounting to use commercially available components, we constructed a set of 20 XRDs using SEM planchets that were then calibrated at the National Synchrotron Light Source at Brookhaven National Laboratory. We present comparisons of the reproducibility and absolute calibrations between the current vitreous-carbon XRDs and our new design.
Design study of polychromators for ITER edge Thomson scattering diagnostics
Authors: Kajita Shin , Hatae Takaki , Kusama Yoshinori
Published: November 2008

In this study, we investigate designs for polychromators of the ITER edge Thomson scattering system by means of numerical calculations. For this purpose, we discuss the optimum transmission wavelength ranges of the optical filters and the optimum number of filters. Five different filter arrangements, including those with an optical notch filter to eliminate Dα emission, are compared with each other. The measurement accuracy when using a polychromator is evaluated for midplane port configuration. It is found that the optimum filter number keeping in mind the cost performance cost is 5 or 6. Moreover, the use of an optical notch filter increases the measurement accuracy by approximately 5%.
Spatial resolution study and power calibration of the high-k scattering system on NSTX
Authors: Lee W. , Park H. K. , Cho M. H. , Namkung W. , Smith D. R. , Domier C. W. , Luhmann N. C.
Published: November 2008

NSTX high-k scattering system has been extensively utilized in studying the microturbulence and coherent waves. An absolute calibration of the scattering system was performed employing a new millimeter-wave source and calibrated attenuators. One of the key parameters essential for the calibration of the multichannel scattering system is the interaction length. This interaction length is significantly different from the conventional one due to the curvature and magnetic shear effect.
Diagnosing ignition with DT reaction history
Authors: Wilson D. C. , Bradley P. A. , Cerjan C. J. , Salmonson J. D. , Spears B. K. , Hatchet S. P. , Herrmann H. W. , Glebov V. Yu.
Published: November 2008

A full range DT reaction history of an ignition capsule, from 109to1020neutrons∕ns, offers the opportunity to diagnose fuel conditions hundreds of picoseconds before and during burn. The burn history begins with a sharp rise when the first shock reaches the center of the capsule. The level of this jump reflects the combined shock strength and the adiabat of DT fuel. Changes to the four laser pulses driving the capsule implosion which are large enough to degrade the yield make measurable changes to the reaction history. Low mode asymmetries grow during convergence but change the reaction history during the final ∼100ps. High mode asymmetry or turbulence mixing affects only the reaction history within ∼50ps of peak burn rate. A capsule with a tritium fuel layer containing a small amount of deuterium (∼1%) creates a reaction history similar to the ignition capsule, but without the final ignition burn. A combination of gas Cerenkov detectors and the neutron temporal diagnostic could be capable of diagnosing the full history of ignition and tritium rich capsules.
Triple probe signal detection electronics for systems lacking a well defined ground
Authors: Compeau R. , Gilmore M. , Watts C.
Published: November 2008

Triple probes have been used to measure plasma parameters of low temperature and edge plasmas, yielding simultaneous measurements of electron temperature, ion density, and floating potential. Unlike standard Langmuir and double probe techniques, there is no requirement to sweep the probe potential relative to the plasma, thus allowing fast time resolution. However, in some plasma systems “ground” is not well defined with respect to a known ground, may vary strongly in time, or may be at an inconveniently high voltage. The resulting high plasma (or floating) potential requires common mode rejection before the signals can be digitized. A signal detection circuit constructed from inexpensive operational amplifiers and that makes use of a novel floating bias generation configuration is described.
Performance of Au transmission photocathode on a microchannel plate detector
Authors: Lowenstern M. E. , Harding E. C. , Huntington C. M. , Visco A. J. , Rathore G. , Drake R. P.
Published: November 2008

X-ray framing cameras, employing microchannel plates (MCPs) for detection and signal amplification, play a key role in research in high-energy-density physics. These instruments convert radiographic x-rays into electrons produced by plasma during such experiments into electrons that are amplified in the channels and then detected by a phosphor material. The separation of detection from signal amplification offers potential improvements in sensitivity and noise properties. We have implemented a suspended Au transmission photocathode (160 Å thick) on a MCP and are evaluating it using a 1.5 keV Al Kα x-ray source. We find an approximately twofold increase in the ratio of detected events to incident photons when the photocathode-to-MCP voltage difference is sufficiently large. Our calculations indicate that this increase is probably caused by a combination of signal produced by the photocathode and an increase in the efficiency of detection of x-rays that reach the MCP surface through modification of the local electric field.
High repetition rate neutron flux array using digital-signal processing and scintillators for study of high performance plasma at JT-60U
Authors: Shinohara K. , Okuji T. , Ishikawa M. , Baba M. , Itoga T.
Published: November 2008

Aiming at increasing the count rate capability of the radial neutron collimator system in JT-60U, a digital-signal processing system has been extended to seven channels for data acquisition of stilbene crystal detector using analog-to-digital converters equipped with a fast flash memory. In this method, the detected pulses were postprocessed concerning pulse shape and pulse height. Using this system, the radial neutron collimator system can provide the information on the temporal evolution of emission rate of d-T neutrons and gamma rays as well as d-D neutrons. On the course of the development, the fast and stable handling of the large data around 7 GB is undertaken for a discharge.
Temporal dispersion of a spectrometer
Authors: Visco A. , Drake R. P. , Froula D. H. , Glenzer S. H. , Pollock B. B.
Published: November 2008

The temporal dispersion of an optical spectrometer has been characterized for a variety of conditions related to optical diagnostics to be fielded at the National Ignition Facility (e.g., full-aperture backscatter station, Thomson scattering). Significant time smear is introduced into these systems by the path length difference through the spectrometer. The temporal resolution is shown to depend only on the order of the grating, wavelength, and the number of grooves illuminated. To enhance the temporal resolution, the spectral gratings can be masked limiting the number of grooves illuminated. Experiments have been conducted to verify these calculations. The size and shape of masks are investigated and correlated with the exact shape of the temporal instrument function, which is required when interpreting temporally resolved data. The experiments used a 300 fs laser pulse and a picosecond optical streak camera to determine the temporal dispersion. This was done for multiple spectral orders, gratings, and optical masks.
Classifier based on support vector machine for JET plasma configurations
Authors: Dormido-Canto S. , Farias G. , Vega J. , Dormido R. , Sánchez J. , Duro N. , Vargas H. , Murari A. ,   JET-EFDA Contributors
Published: November 2008

The last flux surface can be used to identify the plasma configuration of discharges. For automated recognition of JET configurations, a learning system based on support vector machines has been developed. Each configuration is described by 12 geometrical parameters. A multiclass system has been developed by means of the one-versus-the-rest approach. Results with eight simultaneous classes (plasma configurations) show a success rate close to 100%.
Calibration of a high spatial resolution laser two-color heterodyne interferometer for density profile measurements in the TJ-II stellarator
Authors: Acedo Pablo , Pedreira P. , Criado A. R. , Lamela Horacio , Sánchez Miguel , Sánchez Joaquín
Published: November 2008

A high spatial resolution two-color (CO2, λ=10.6μm, He–Ne, λ=633nm) interferometer for density profile measurements in the TJ-II stellarator is under development and installation, based in the currently operational single channel two-color heterodyne interferometer. To achieve the objectives of 32 channels, with 4–5mm lateral separation between plasma chords, careful design and calibration of the interferometric waveforms for both the measurement and vibration compensation wavelengths are undertaken. The first step has been to set up in our laboratories an expanded-beam heterodyne/homodyne interferometer to evaluate the quality of both interferometric wavefronts, a reported source of poor vibration compensation and thus low resolution in the density profile measurements. This novel interferometric setup has allowed us to calibrate the spatial resolution in the profile measurements resulting in ∼2mm lateral resolution in the reconstruction of the interferometric wavefront.
Full orbit calculation for lost alpha particle measurement on ITER
Authors: Funaki D. , Isobe M. , Nishiura M. , Sato Y. , Okamoto A. , Kobuchi T. , Kitajima S. , Sasao M.
Published: November 2008

An orbit following calculation code with full gyromotion under the ITER magnetic field configuration has been developed to investigate escaping alpha particle orbits in ITER and to determine the geometrical arrangement for alpha particle detection. The code contained the full geometrical information of the first wall panels. It was carefully investigated whether an alpha particle escaping from the plasma through the last closed flux surface does not touch or intersect the first wall boundary before reaching the detection point. Candidates of blanket module modification have been studied to achieve effective measurement geometry for escaping alpha particle detection. The calculations showed that direct orbit loss and banana diffusion can be detected with a probe head recessed from the first wall surface.
Use of d-H3e proton spectroscopy as a diagnostic of shell ρr in capsule implosion experiments with ∼0.2 NIF scale high temperature Hohlraums at Omega
Authors: Delamater N. D. , Wilson D. C. , Kyrala G. A. , Seifter A. , Hoffman N. M. , Dodd E. , Singleton R. , Glebov V. , Stoeckl C. , Li C. K. , Petrasso R. , Frenje J.
Published: November 2008

We present the calculations and preliminary results from experiments on the Omega laser facility using d-H3e filled plastic capsule implosions in gold Hohlraums. These experiments aim to develop a technique to measure shell ρr and capsule unablated mass with proton spectroscopy and will be applied to future National Ignition Facility (NIF) experiments with ignition scale capsules. The Omega Hohlraums are 1900 μm length×1200 μm diameter and have a 70% laser entrance hole. This is approximately a 0.2 NIF scale ignition Hohlraum and reaches temperatures of 265–275 eV similar to those during the peak of the NIF drive. These capsules can be used as a diagnostic of shell ρr, since the d-H3e gas fill produces 14.7 MeV protons in the implosion, which escape through the shell and produce a proton spectrum that depends on the integrated ρr of the remaining shell mass. The neutron yield, proton yield, and spectra change with capsule shell thickness as the unablated mass or remaining capsule ρr changes. Proton stopping models are used to infer shell unablated mass and shell ρr from the proton spectra measured with different filter thicknesses. The experiment is well modeled with respect to Hohlraum energetics, neutron yields, and x-ray imploded core image size, but there are discrepancies between the observed and simulated proton spectra.
Cherenkov radiation conversion and collection considerations for a gamma bang time/reaction history diagnostic for the NIF
Authors: Herrmann Hans W. , Mack Joseph M. , Young Carlton S. , Malone Robert M. , Stoeffl Wolfgang , Horsfield Colin J.
Published: November 2008

Bang time and reaction history measurements are fundamental components of diagnosing inertial confinement fusion (ICF) implosions and will be essential contributors to diagnosing attempts at ignition on the National Ignition Facility (NIF). Fusion gammas provide a direct measure of fusion interaction rate without being compromised by Doppler spreading. Gamma-based gas Cherenkov detectors that convert fusion gamma rays to optical Cherenkov photons for collection by fast recording systems have been developed and fielded at Omega. These systems have established their usefulness in illuminating ICF physics in several experimental campaigns. Bang time precision better than 25 ps has been demonstrated, well below the 50 ps accuracy requirement defined by the NIF system design requirements. A comprehensive, validated numerical study of candidate systems is providing essential information needed to make a down selection based on optimization of sensitivity, bandwidth, dynamic range, cost, and NIF logistics. This paper presents basic design considerations arising from the two-step conversion process from γ rays to relativistic electrons to UV/visible Cherenkov radiation.
Validation of the ITER CXRS design by tests on TEXTOR
Authors: Jaspers R. J. E. , von Hellermann M. G. , Delabie E. , Biel W. , Marchuk O. , Yao L.
Published: November 2008

The charge exchange recombination spectroscopy system (CXRS) for ITER is designed to measure the core helium concentration, and in addition, profiles of ion temperature and rotation. This highly demanding task, due to the huge background radiation (bremsstrahlung) and the high attenuation of the dedicated diagnostic neutral beam, requires high throughput spectrometers with high resolution. On TEXTOR, a CXRS system has been developed with the aim to test the physics implications of these specifications. (i) A relevant spectrometer has been tested. (ii) A method to determine the helium concentrations from the CXRS intensity, using the beam emission has been evaluated. A 20% discrepancy in beam emission was revealed. (iii) The determination of the magnetic pitch angle by the ratio of Balmer lines showed qualitatively the right behavior, although the accuracy was limited by the polarization sensitivity of the first mirror. (iv) The simulation code developed for the prediction of the CXRS spectra was quantitatively confronted with experimental data.
Optical design study of an infrared visible viewing system for Wendelstein 7-X divertor observation and control
Authors: Cantarini J. , Hildebrandt D. , König R. , Klinkhamer F. , Moddemeijer K. , Vliegenthart W. , Wolf R.
Published: November 2008

For the Wendelstein 7-X stellarator, which will allow quasicontinuous operation (τ≤30 min) with 10 MW of electron cyclotron radiation heating power, a conceptual design study for an IR/visible viewing system (IVVS) has been elaborated. Ten such systems, as part of the machine protection system, will be required for real time monitoring of all ten discrete, water cooled divertor modules with high spatial (<10 mm) resolution, in order to prevent local overheating of the target tiles, which could easily lead to their destruction. On the physics side, the systems will be used for divertor symmetry investigations by studying the power load distribution on all targets modules and by observing the island divertor plasmas in the light of Hα, C II, and C III using the visible imaging section of the systems. The optics of the system can be divided into three parts: a mirror based optical head, creating an intermediate image, a Cassegrain telescope system, and individual lens based imaging optics adapted to the various detectors for IR (3–5 μm and 8–14 μm) and visible observations, with their optical light paths being separated by in-vacuum dichroic beam splitters.
A novel backscatter focus diagnostic for the TRIDENT 200 TW laser
Authors: Gautier D. C. , Flippo K. A. , Letzring S. A. , Shimada J. Workman T. , Johnson R. P. , Hurry T. R. , Gaillard S. A. , Hegelich B. M.
Published: November 2008

Here we present the first direct focal spot images and analysis of an ultrahigh intensity short-pulse laser focus (>5×1019 W/cm2) on target. Such a focal spot characterization is typically done previous to the shot with a low-power alignment beam using equivalent plane imaging techniques. The resulting intensity of the shot is then inferred from these results. We report on the development of a backscatter focus diagnostic, which enables imaging of the on-target full-power focal spot.
Diagnostics for the biased electrode experiment on NSTX
Authors: Roquemore A. L. , Zweben S. J. , Kaita R. , Marsalsa R. J. , Bush C. E. , Maqueda R. J.
Published: November 2008

A linear array of four small biased electrodes was installed in NSTX in an attempt to control the width of the scrape-off layer by creating a strong local poloidal electric field. The set of electrodes was separated poloidally by a 1 cm gap between electrodes and were located slightly below the midplane of NSTX, 1 cm behind the rf antenna, and oriented so that each electrode is facing approximately normal to the magnetic field. Each electrode can be independently biased to ±100 V. Present power supplies limit the current on two electrodes to 30 A and the other two to 10 A each. The effect of local biasing was measured with a set of Langmuir probes placed between the electrodes and another set extending radially outward from the electrodes, and also by the gas puff imaging diagnostic located 1 m away along the magnetic field lines intersecting the electrodes. Two fast cameras were also aimed directly at the electrode array. The hardware and controls of the biasing experiment will be presented and the initial effects on local plasma parameters will be discussed.
Nonperturbative measurement of the local magnetic field using pulsed polarimetry for fusion reactor conditions (invited)
Authors: Smith Roger J.
Published: November 2008

A novel diagnostic technique for the remote and nonperturbative sensing of the local magnetic field in reactor relevant plasmas is presented. Pulsed polarimetry [Patent No. 12/150,169 (pending)] combines optical scattering with the Faraday effect. The polarimetric light detection and ranging (LIDAR)-like diagnostic has the potential to be a local Bpol diagnostic on ITER and can achieve spatial resolutions of millimeters on high energy density (HED) plasmas using existing lasers. The pulsed polarimetry method is based on nonlocal measurements and subtle effects are introduced that are not present in either cw polarimetry or Thomson scattering LIDAR. Important features include the capability of simultaneously measuring local Te, ne, and B∥ along the line of sight, a resiliency to refractive effects, a short measurement duration providing near instantaneous data in time, and location for real-time feedback and control of magnetohydrodynamic (MHD) instabilities and the realization of a widely applicable internal magnetic field diagnostic for the magnetic fusion energy program. The technique improves for higher neB∥ product and higher ne and is well suited for diagnosing the transient plasmas in the HED program. Larger devices such as ITER and DEMO are also better suited to the technique, allowing longer pulse lengths and thereby relaxing key technology constraints making pulsed polarimetry a valuable asset for next step devices. The pulsed polarimetry technique is clarified by way of illustration on the ITER tokamak and plasmas within the magnetized target fusion program within present technological means.
Spectral resolution measurement of an x-ray imaging crystal spectrometer for KSTAR
Authors: Lee S. G. , Bak J. G. , Nam U. W. , Moon M. K. , Cheon J. K. , Bitter M. , Hill K.
Published: November 2008

A spectral resolution measurement of the x-ray imaging crystal spectrometer for the Korea Superconducting Tokamak Advanced Research machine utilizing a segmented position-sensitive detector and time-to-digital converter based delay-line readout electronics was performed by using an x-ray tube in a laboratory. The measured spectral resolution is about 12 600, which means the actual energy resolution is 0.32 eV for the x-ray tube’s bremsstrahlung peak energy of 4 keV. The results from the spectral resolution measurement are described.
Collective backscattering of gyrotron radiation by small-scale plasma density fluctuations in large helical device
Authors: Kharchev Nikolay , Tanaka Kenji , Kubo Shin , Igami Hiroe , Batanov German , Petrov Alexandr , Sarksyan Karen , Skvortsova Nina , Azuma Yoshifumi , Tsuji-Iio Shunji
Published: November 2008

A version of the collective backscattering diagnostic using gyrotron radiation for small-scale turbulence is described. The diagnostic is used to measure small-scale (ks≈34 cm−1) plasma density fluctuations in large helical device experiments on the electron cyclotron heating of plasma with the use of 200 kW 82.7 GHz heating gyrotron. A good signal to noise ratio during plasma production phase was obtained, while contamination of stray light increased during plasma build-up phase. The effect of the stray radiation was investigated. The available quasioptical system of the heating system was utilized for this purpose.