bluuebunny/crossref_metadata_2025 huggingface dataset:
W7-X magnetic diagnostics: Rogowski coil performance for very long pulses
Authors: Werner Andreas , Endler Michael , Geiger Joachim , Koenig Ralf
Published: November 2008

Stellerators can be operated without the need of significant plasma current for generation of poloidal magnetic field components. Wendelstein 7-X (W7-X) is optimized for stiff magnetic configurations by minimizing pressure driven currents, such as bootstrap and Pfirsch–Schlüter currents. In Addition to the largely reduced plasma currents, the HELIAS-type device is a low magnetic shear configuration required for magnetic boundary islands. However, the diverting magnetic field structure is already influenced by small net plasma currents. In particular, the W7-AS divertor results revealed a significant sensitivity of the X-point location with respect to favorable edge plasma states. Thus, a precise X-point control for W7-X is envisaged and, although expected net plasma currents range in the order of 10–100kA only, stabilization by adaptive controllers is foreseen to an accuracy of about 1kA. This stabilization should be reliable even after 2000s of plasma operation. A precondition for achieving this is a reliable current detection. For this purpose, W7-X will be equipped with Rogowski of which the first has now been assembled onto one of the plasma vessel sectors. The integral performance and sensitivity inhomogeneities have been tested by employing the digital integrator of W7-X [A. Werner, Rev. Sci. Instrum. 77, 10E307 (2006)] and a cable energized with 200A, representing the plasma current.
Different methods of reconstructing spectra from filtered x-ray diode measurements
Authors: Seifter Achim , Kyrala George A.
Published: November 2008

Filtered x-ray diodes, sensitive in different spectral regions, are used to measure the emission spectrum of laser-driven hohlraums at the Omega laser facility in Rochester, NY. Here we present two new methods to reconstruct the emission spectra from the response of the x-ray diodes and compare them to the method currently used to extract a spectrum and a temperature in the hohlraum. We also use simulated spectra to characterize the different methods with respect to uncertainty, emission temperature, and the ability to reconstruct the input spectrum as closely as possible.
Accuracy of EFIT equilibrium reconstruction with internal diagnostic information at JET
Authors: Brix M. , Hawkes N. C. , Boboc A. , Drozdov V. , Sharapov S. E. ,   JET-EFDA Contributors
Published: November 2008

In tokamak experiments, equilibrium reconstruction codes are used to calculate the location of the last closed flux surface, to map diagnostic information, and to derive important properties like current density and safety factor. At JET, the equilibrium code EFIT is automatically executed after each discharge. For speed and robustness, intershot EFIT is based on magnetic probe measurements only. As a consequence, the intershot profiles of the safety factor can be wrong for a variety of plasma scenarios. Internal diagnostic information, the pitch angle as measured with the motional stark effect, Faraday rotation angles, as well as pressure profile information can increase the accuracy of the EFIT equilibrium. In this paper, the accuracy of the internal diagnostics at JET and their impact on the EFIT results are discussed in detail. The influence of control parameters like the form of the test functions for ff′ and p′ on the equilibrium is investigated. The qmin from this analysis agrees with information from magnetohydrodynamics analysis (e.g., Alfvén cascades and sawtooth analysis) to within 10%–15%.
A simple apparatus for quick qualitative analysis of CR39 nuclear track detectors
Authors: Gautier D. C. , Kline J. L. , Flippo K. A. , Gaillard S. A. , Letzring S. A. , Hegelich B. M.
Published: November 2008

Quantifying the ion pits in Columbia Resin 39 (CR39) nuclear track detector from Thomson parabolas is a time consuming and tedious process using conventional microscope based techniques. A simple inventive apparatus for fast screening and qualitative analysis of CR39 detectors has been developed, enabling efficient selection of data for a more detailed analysis. The system consists simply of a green He–Ne laser and a high-resolution digital single-lens reflex camera. The laser illuminates the edge of the CR39 at grazing incidence and couples into the plastic, acting as a light pipe. Subsequently, the laser illuminates all ion tracks on the surface. A high-resolution digital camera is used to photograph the scattered light from the ion tracks, enabling one to quickly determine charge states and energies measured by the Thomson parabola.
The ITER bolometer diagnostic: Status and plans
Authors: Meister H. , Giannone L. , Horton L. D. , Raupp G. , Zeidner W. , Grunda G. , Kalvin S. , Fischer U. , Serikov A. , Stickel S. , Reichle R.
Published: November 2008

A consortium consisting of four EURATOM Associations has been set up to develop the project plan for the full development of the ITER bolometer diagnostic and to continue urgent R&D activities. An overview of the current status is given, including detector development, line-of-sight optimization, performance analysis as well as the design of the diagnostic components and their integration in ITER. This is complemented by the presentation of plans for future activities required to successfully implement the bolometer diagnostic, ranging from the detector development over diagnostic design and prototype testing to RH tools for calibration.
Investigating the possibility of a monitoring fast ion diagnostic for ITER
Authors: De Angelis R. , von Hellermann M. G. , Orsitto F. P. , Tugarinov S.
Published: November 2008

In burning plasma fusion devices, fast ion transport plays a central role in the performances of the machines. Moreover the losses of energetic particles might cause severe damages on plasma facing components. Therefore real time measurements of fast ion transport would provide valuable information for safe and reliable plasma operations. In this paper, we examine the feasibility of a monitoring system based on active charge exchange recombination spectroscopy making use of the 0.5MeV∕amu ITER heating neutral beams for detecting fast He+24 (alphas) particles in ITER plasmas. There are two time scales relevant to fast ion dynamics: the first is the slowing down time of the distribution function which is of the order of 1s, and the second is the time scale of burstlike transport events such as collective Alfvén mode excitations, which—for typical ITER plasma parameters—can be as low as 0.2–1ms. To detect such fast events a broadband high-throughput spectrometer is needed, while for the reconstruction of the alpha velocity distribution function a higher resolution spectrometer and longer integration time are necessary. To monitor a spatial redistribution of fast particles due to the propagation of the instability, it is proposed to use a limited number of spatial channels, looking at the charge exchange HeII spectra induced by the heating beams, whose energy matches the slowing down energies of fast particles. The proposal is to share the motional stark effect periscope on equatorial port 3 [A. Malaquias et al., Rev. Sci. Instrum. 75, 3393 (2004)] adding additional fibers and suitable instruments. A signal to noise ratio of 5 could be achieved with a spatial resolution of a∕15 and a time resolution of 5ms, in a broad spectral band of 100Å, corresponding to the spectral broadening of the line emitted by alpha particles with energies ΔE⩽1.5MeV. Fast H and D ion populations created by heating neutral beam or ion cyclotron resonance heating are expected to produce significantly lower charge exchange signal levels and can only be monitored on substantially longer time scales as it is expected because of the strong energy difference with respect to the heating neutral beam and the consequently low charge exchange cross sections.
One-dimensional and multichannels multi-imaging x-ray streak camera for imploded core plasma of shell-cone target
Authors: Zhong Jiayong , Shiraga Hiroyuki , Azechi Hiroshi
Published: November 2008

Recently one-dimensional and multichannels multi-imaging x-ray streak camera (1D+McMIXS) has been proposed as an ultrafast diagnostic tool for imploded core plasma of shell-cone target. This diagnostic system can provide much more information of core plasma dynamics, such as the shell trajectory before the maximum compression, two dimensional (2D) x-ray images, and 2D map of electron temperature. The 1D+McMIXS was used in an implosion experiment of a shell target with a cone for fast ignition at Gekko XII laser facility. The interaction between the core plasma and the tip of the cone was observed and revealed some detailed structures. A series of time-resolved 2D x-ray images were reconstructed and a nominal temperature evolution was also mapped.
Two dimensional radiated power diagnostics on Alcator C-Mod
Authors: Reinke M. L. , Hutchinson I. H.
Published: November 2008

The radiated power diagnostics for the Alcator C-Mod tokamak have been upgraded to measure two dimensional structure of the photon emissivity profile in order to investigate poloidal asymmetries in the core radiation. Commonly utilized unbiased absolute extreme ultraviolet (AXUV) diode arrays view the plasma along five different horizontal planes. The layout of the diagnostic set is shown and the results from calibrations and recent experiments are discussed. Data showing a significant, 30%–40%, inboard/outboard emissivity asymmetry during ELM-free H-mode are presented. The ability to use AXUV diode arrays to measure absolute radiated power is explored by comparing diode and resistive bolometer-based emissivity profiles for highly radiative L-mode plasmas seeded with argon. Emissivity profiles match in the core but disagree radially outward resulting in an underprediction of Prad of nearly 50% by the diodes compared to Prad determined using resistive bolometers.
Review of atomic data needs for active charge-exchange spectroscopy on ITER
Authors: Marchuk O. , Bertschinger G. , Biel W. , Delabie E. , von Hellermann M. G. , Jaspers R. , Reiter D.
Published: November 2008

The quantitative exploitation of active beam spectra is largely based on an advanced atomic modeling. Under the ITER operating conditions the penetration depth of a diagnostic beam into the plasma core crucially affects the intensities of spectral lines and hence the uncertainties of derived plasma parameters. A critical review of atomic data and an assessment of its error margins are, therefore, urgently needed. The aim of the present work is to verify the existing beam-stopping and beam-emission data for hydrogen beam in fusion plasmas. The agreement between the ADAS database and the present calculations is found to be within 5% for the beam-stopping data in a H-plasma. The calculation of beam attenuation in the presence of He-ash (4%) and Be ions (2%) demonstrates the agreement between the present data and the ADAS database within 10%. Finally, the maximum deviation of 15% is found only for beam-emission data at the electron density of 1×1012–2×1012cm−3, which is significantly below the ITER density of 1014cm−3.
Feature extraction for improved disruption prediction analysis at JET
Authors: Rattá G. A. , Vega J. , Murari A. , Johnson M. ,   JET-EFDA Contributors
Published: November 2008

Disruptions are major instabilities and remain one of the main problems in tokomaks. Using Joint European Torus database, a disruption predictor is developed by computational methods including supervised learning techniques. The main objectives of the work are to develop accurate automatic classifiers, to test their performances, and to determine how much in advance of the disruption they can operate with acceptable reliability.
Design of a streaked radiography instrument for ICF ablator tuning measurements
Authors: Olson R. E. , Hicks D. G. , Spears B. K. , Celliers P. M. , Holder J. P. , Landen O. L. , Geissel M. , Kellogg J. W. , Bennett G. R. , Edens A. D. , Atherton B. W. , Leeper R. J.
Published: November 2008

A streaked radiography diagnostic has been proposed as a technique to determine the ablator mass remaining in an inertial confinement fusion ignition capsule at peak velocity. This instrument, the “HXRI-5,” has been designed to fit within a National Ignition Facility Diagnostic Instrument Manipulator. The HXRI-5 will be built at Sandia National Laboratories (SNL), and initial testing will be done at the SNL Z-Beamlet Facility. In this paper, we will describe the National Ignition Campaign requirements for this diagnostic, the instrument design, and the planned test experiments.
Monochromatic x-ray sampling streak imager for fast-ignitor plasma observation
Authors: Tanabe Minoru , Fujiwara Takashi , Fujioka Shinsuke , Nishimura Hiroaki , Shiraga Hiroyuki , Azechi Hiroshi , Mima Kunioki
Published: November 2008

Ultrafast two-dimensional (2D) x-ray imaging is required to investigate the dynamics of fast-heated core plasma in inertial confinement fusion research. A novel x-ray imager, consisting of two toroidally bent Bragg crystals and an ultrafast 2D x-ray imaging camera, has been demonstrated. Sequential and 2D monochromatic x-ray images of laser-imploded core plasma were obtained with a temporal resolution of 20ps, a spatial resolution of 31μm, and a spectral resolution of over 200, simultaneously.
A pulse-burst laser system for a high-repetition-rate Thomson scattering diagnostic
Authors: Den Hartog D. J. , Jiang N. , Lempert W. R.
Published: November 2008

A “pulse-burst” laser system is being constructed for addition to the Thomson scattering diagnostic on the Madison Symmetric Torus (MST) reversed-field pinch. This laser is designed to produce a burst of up to 200 approximately 1J Q-switched pulses at repetition frequencies 5–250kHz. This laser system will operate at 1064nm and is a master oscillator, power amplifier. The master oscillator is a compact diode-pumped Nd:YVO4 laser, intermediate amplifier stages are flashlamp-pumped Nd:YAG, and final stages will be flashlamp-pumped Nd:glass (silicate). Variable pulse width drive (0.3–20ms) of the flashlamps is accomplished by insulated-gate bipolar transistor switching of large electrolytic capacitor banks. The burst train of laser pulses will enable the study of electron temperature (Te) and electron density (ne) dynamics in a single MST shot, and with ensembling, will enable correlation of Te and ne fluctuations with other fluctuating quantities.
Grazing-incidence spectrometer on the SSPX spheromak
Authors: Clementson J. , Beiersdorfer P. , Magee E. W.
Published: November 2008

The silver flat field spectrometer (SFFS) is a high-resolution grazing-incidence diagnostic for magnetically confined plasmas. It covers the wavelength range of 25–450Å with a resolution of Δλ=0.3Å full width at half maximum. The SFFS employs a spherical 1200lines∕mm grating for flat-field focusing. The imaging is done using a backilluminated Photometrics charge-coupled device camera allowing a bandwidth of around 200Å per spectrum. The spectrometer has been used for atomic spectroscopy on electron beam ion traps and for plasma spectroscopy on magnetic confinement devices. Here we describe the design of the SFFS and the spectrometer setup at the sustained spheromak physics experiment in Livermore.
Dichroic filters to protect milliwatt far-infrared detectors from megawatt ECRH radiation
Authors: Bertschinger G. , Endres C. P. , Lewen F. , Oosterbeek J. W.
Published: November 2008

Dichroic filters have been used to shield effectively the far infrared (FIR) detectors at the interferometer/polarimeter on TEXTOR. The filters consist of metal foils with regular holes, the hole diameter, the mutual spacing and the thickness of the foils are chosen to transmit radiation at the design frequency with transmission >90%. The attenuation at the low frequency end of the bandpass filter is about 30dB per octave, the high frequency transmission is between 20% and 40%. The filters have been used to block the stray radiation from the megawatt microwave heating beam to the detectors of the FIR interferometer, operating with power on the detector in the milliwatt range. If required, the low frequency attenuation can be still enhanced, without compromising the transmission in the passband. The FIR interferometer used for plasma density and position control is no longer disturbed by electromagnetic waves used for plasma heating.
Magnetic fluctuation profile measurement using optics of motional Stark effect diagnostics in JT-60U
Authors: Suzuki T. , Isayama A. , Matsunaga G. , Oyama N. , Fujita T. , Oikawa T.
Published: November 2008

Motional Stark effect (MSE) diagnostics in JT-60U works as polarimeter to measure the pitch angle of magnetic field as well as beam-emission-spectroscopy (BES) monochromator simultaneously at 30 spatial channels. Fluctuation in the BES signal using MSE optics (MSE/BES) contains fluctuations in not only the density but also the pitch angle (or the magnetic field). Correlation analysis of the magnetic fluctuation between two spatial channels is applied to high-beta plasma with a magnetohydrodynamic activity at frequency of about 0.9 kHz. It has been found that the magnetic fluctuation measured by the MSE/BES is spatially localized near the magnetic flux surface having safety factor and that the phase of the fluctuation is inverted at about the surface, suggesting magnetic island structure by tearing mode. The phase of the magnetic fluctuation measured by the MSE/BES at outside of the q=2 surface is consistent with that by the pickup coil placed outside the plasma.
X-ray diagnostics of imploding plasmas from planar wire arrays composed of Cu and few tracer Al wires on the 1MA pulsed power generator at UNR
Authors: Safronova A. S. , Kantsyrev V. L. , Esaulov A. A. , Ouart N. D. , Yilmaz M. F. , Williamson K. M. , Shlyaptseva V. , Shrestha I. , Osborne G. C. , Coverdale C. A. , Jones B. , Deeney C.
Published: November 2008

Tracer aluminum alloyed wires (Al5056) are used to provide additional information for x-ray diagnostics of implosions of Cu planar wire arrays (PWAs). Specifically, the analysis of combined PWA experiments using the extensive set of x-ray diagnostics is presented. In these experiments, which were conducted at the 1MA pulsed power generator at University of Nevada, Reno, the Z-pinch load consisted of several (eight) Cu alloyed (main material) and one to two Al alloyed (tracer) wires mounted in a single plane row or double parallel plane rows, single planar wire array (SPWA) or double planar wire array (DPWA), respectively. The analysis of x-ray spatially resolved spectra from the main material indicates the increase in the electron temperature Te near the cathode. In general, the axial gradients in Te are more pronounced for SPWA than for DPWA due to the more “columnlike” plasma formation for SPWA compared to “hot-spot-like” plasma formation for DPWA. In addition, x-ray spectra from tracer wires are studied, and estimated plasma parameters are compared with those from the main material. It is observed that the x-ray K-shell Al spectra manifest more opacity features for the case of SPWA with about 18% of Al mass (to the total load mass) compared to the case of DPWA with about 11% of Al mass. The analysis of time-gated spectra shows that the relative intensity of the most intense K-shell Al line, small before the x-ray burst, increases with time and peaks close to the maximum of the sub-keV signal.
Soft x-ray measurements using photoconductive type-IIa and single-crystal chemical vapor deposited diamond detectors
Authors: Moore A. S. , Bentley C. D. , Foster J. M. , Goedhart G. , Graham P. , Taylor M. J. , Hellewell E.
Published: November 2008

Photoconductive detectors (PCDs) are routinely used alongside vacuum x-ray diodes (XRDs) to provide an alternative x-ray flux measurement at laser facilities such as HELEN at AWE Aldermaston, UK, and Omega at the Laboratory for Laser Energetics. To evaluate diamond PCDs as an alternative to XRD arrays, calibration measurements made at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory are used to accurately calculate the x-ray flux from a laser-heated target. This is compared to a flux measurement using the Dante XRD diagnostic. Estimates indicate that the photoinduced conductivity from measurements made at Omega are too large, and calculations using the radiometric calibrations made at the NSLS agree with this hypothesis. High-purity, single-crystal, chemical vapor deposited (CVD) diamond samples are compared to natural type-IIa PCDs and show promising high resistivity effects, the corollary of which preliminary results show is a slower response time.
Magnetic field fluctuation measurement with a heavy ion beam probe in the Large Helical Device
Authors: Shimizu A. , Ido T. , Nishiura M. , Nakano H. , Ohshima S.
Published: November 2008

The measurements of magnetic field fluctuation with a heavy ion beam probe (HIBP) in the Large Helical Device (LHD) are considered in this article. Measured value reflects not only the fluctuation at the observation point (sample volume) but also the fluctuation on the beam path. These effects (called as the path integral effects) are considered and calculated for variations of fluctuations in LHD. The distortion of the measured profile by the path integral effect is not significant at the peak of the fluctuation amplitude. In contrast, in the region far from the peak, phony signals due to path integral effects are observed. Finally, the resolution of magnetic field fluctuation measurements with our HIBP system is estimated. Estimated results show that the magnitude of 4.1×10−5 T can be measured with our system.
Performance test of the integrator system for magnetic diagnostics in KSTAR
Authors: Ka E. M. , Lee S. G. , Bak J. G. , Son D.
Published: November 2008

Ten modules of the integrator system of the initial magnetic diagnostics for the first plasma operation have been simultaneously tested in the Korea superconducting tokamak advanced research device by measuring the magnetic flux density from various magnetic diagnostics sensors when a small current was applied to the superconducting poloidal field coils. The measured drifts from the integrators show between 1×10−6 and 1×10−5 Wb/s. The results from the field tests before the first plasma generation are described.
Systematic and routine analysis of radial correlation reflectometry data in JET
Authors: Figueiredo António C. A. , Fonseca António , Meneses Luís ,   JET-EFDA Contributors
Published: November 2008

This paper discusses a tool specially developed for the analysis of radial correlation reflectometry data in JET. The tool, which calculates the correlation length and coherent reflection from the raw data, has been designed for offline analysis and to assist diagnostic operators. After being verified in controlled tests using theoretical signals, the tool is validated by means of a study of ITB plasmas in JET.
Fast ion charge exchange spectroscopy measurement using a radially injected neutral beam on the large helical device
Authors: Osakabe Masaki , Murakami Sadayoshi , Yoshinuma Mikirou , Ida Katsumi , Whiteford Allan , Goto Motoshi , Kato Daiji , Kato Takako , Nagaoka Kenichi , Tokuzawa Tokihiko , Takeiri Yasuhiko , Kaneko Osamu
Published: November 2008

An experimental technique to investigate fast ion confinement based on charge exchange spectroscopy of Hα-light was applied to evaluate the confinement property of perpendicular fast ions in large helical device (LHD). Sensitivities of the Hα spectra to the pitch angles of injected neutral beams (NBs) and these to the angle between the sight line of the measurement and NB injection path are examined. The energy dependence of the charge exchange cross section significantly affects the observed spectra since the driving NB is injected perpendicular to the magnetic field lines in the geometry of LHD. The measured spectra are compared to the spectra of GNET simulation results and the simulated spectra agreed well with the experimental measurement when we take into account the contribution of halo neutrals. Although it is difficult to obtain the fast ion distribution functions directly, this technique provides useful experimental data in benchmarking simulation codes.
Absolute calibration of microfission chamber in JT-60U
Authors: Hayashi Takao , Nishitani Takeo , Sukegawa Atsuhiko M. , Ishikawa Masao , Shinohara Kouji
Published: November 2008

We have conducted calibrations of a microfission chamber, which was installed between the vacuum vessel and the toroidal field coils, by both a Cf-252 neutron source and real deuterium plasmas in JT-60U. The detector employs both pulse counting and Campbell (mean square voltage) modes in the electronics to cover a wide dynamic range of the neutron source strength. The pulse counting and Campbell modes were calibrated by Cf-252 and deuterium plasmas, respectively. Point efficiencies, counts per neutron from a point at a single angle, were measured for 27 locations of the neutron point source in toroidal scan. The efficiencies were influenced by the various components such as the vacuum vessel, port, and graphite tiles. The point efficiencies can be integrated and averaged with angle to provide toroidal line efficiencies. The line efficiencies of the microfission chamber and the nearest neutron monitor of the U-235 fission chamber were 5.38×10−9 and 1.77×10−8, respectively. Then the calibration for the Campbell mode was also performed by using a real deuterium plasma. The detection efficiency in the Campbell mode was about three-tenths of that of the nearest neutron monitor, which is consistent with the calibration result obtained by using a Cf-252 neutron source for pulse counting mode.
Multicentimeter long high density magnetic plasmas for optical guiding
Authors: Pollock B. B. , Froula D. H. , Tynan G. R. , Divol L. , Price D. , Costa R. , Yepiz F. , Fulkerson S. , Mangini F. , Glenzer S. H.
Published: November 2008

We present a platform for producing long plasma channels suitable for guiding lasers over several centimeters by applying magnetic fields to limit the radial heat flux from a preforming laser beam. The resulting density gradient will be used as an optical plasma waveguide. The plasma conditions have been chosen to be consistent with the requirements for laser wakefield acceleration where multi-GeV electrons are predicted. A detailed description of the system used to produce the high (5 T) magnetic fields and initial results that show a 5 cm long plasma column are discussed.
Monte Carlo simulations of high-speed, time-gated microchannel-plate-based x-ray detectors: Saturation effects in dc and pulsed modes and detector dynamic range
Authors: Kruschwitz Craig A. , Wu Ming , Moy Ken , Rochau Greg
Published: November 2008

We present here results of continued efforts to understand the performance of microchannel plate (MCP)-based, high-speed, gated, x-ray detectors. This work involves the continued improvement of a Monte Carlo simulation code to describe MCP performance coupled with experimental efforts to better characterize such detectors. Our goal is a quantitative description of MCP saturation behavior in both static and pulsed modes. A new model of charge buildup on the walls of the MCP channels is briefly described. The simulation results are compared to experimental data obtained with a short-pulse, high-intensity ultraviolet laser, and good agreement is found. These results indicate that a weak saturation can change the exponent of gain with voltage and that a strong saturation leads to a gain plateau. These results also demonstrate that the dynamic range of a MCP in pulsed mode has a value of between 102 and 103.
Design of microfission chamber for ITER operations
Authors: Ishikawa Masao , Kondoh Takashi , Nishitani Takeo , Kusama Yoshinori
Published: November 2008

Microfission chambers (MFCs) are one of the most important diagnostics for measuring neutron source strength in ITER. Using MFCs for high-power operations (fusion power of 100kW–1GW) and for low-power operations (<100kW) in combination is one way to fulfill the target measurement requirements of ITER. The MFCs for high-power operations will be installed behind blanket modules in both the upper and lower outboard regions of the vacuum vessel so as to be insensitive to changes in the position of the plasma. For low-power operations, one possible location of MFCs is inside the equatorial (EQ) port. The effect of streaming neutrons and of changes in the position of the plasma on the responses of MFCs is estimated based on a neutron Monte Carlo calculation using the MCNP Version 5 code. Results suggest that the effect of streaming neutrons should be taken into account if the MFCs for high-power operations are installed closer than 20cm to the gap between blanket modules. It has also been found for MFCs of low-power operations that the averaged output of the MFCs installed at the top and bottom of the EQ port is sensitive to horizontal plasma shifts but not to vertical shifts. This finding suggests that corrections based on the position of the plasma center will be needed for the absolute measurement of neutron source strength.
Simulation of the motional Stark effect diagnostic gas-filled torus calibration
Authors: Yuh Howard Y. , Levinton F. M. , Scott S. D. , Ko J.
Published: November 2008

Many motional Stark effect diagnostics around the world make use of a calibration procedure in which the observed neutral beam is injected into a gas-filled torus with known vacuum fields. The instrument is calibrated by reconciling measured angles with vacuum magnetic reconstructions through a range of pitch angles. This in situ gas-filled torus calibration most closely approximates the working conditions of the diagnostic and includes effects such as beam and viewing geometries, beam voltages, Faraday and stress induced birefringence (in most cases) of the transmissive optics, as well as the polarimeter response. However, secondary neutrals, produced after ionization then reneutralization of a beam neutral, have been found to contaminate measured angles by emitting Balmer alpha with similar Doppler shifts and Stark polarizations as beam neutrals, but with different polarization angles. Simulation results that show spectral and angle behavior versus calibration parameters such as fill gas pressure will be presented. Data from NSTX and C-Mod will be compared to simulations results.
Development of a multichannel dispersion interferometer at TEXTOR
Authors: Lizunov A. , Bagryansky P. , Khilchenko A. , Kovalenko Yu. V. , Solomakhin A. , Biel W. , Lambertz H. T. , Krasikov Yu. , Mitri M. , Schweer B. , Dreier H.
Published: November 2008

The design and main characteristics of 14-channel dispersion interferometer for plasma profile measurement and control in TEXTOR tokamak are presented. The diagnostic is engineered on the basis of modular concept, the 10.6 μm CO2 laser source and all optical and mechanical elements of each module are arranged in a compact housing. A set of mirrors and retroreflectors inside the TEXTOR vacuum vessel provides full coverage of the torus cross section with 12 vertical and two diagonal lines of sight, no rigid frame for vibration isolation is required. Results of testing of the single-channel prototype diagnostic and the pilot module of the multichannel dispersion interferometer are presented.
Using Cramer–Rao theory as spectrometer design tool aimed at quantitative complex-spectrum analysis
Authors: Klinkhamer J. F. F. , van der Valk N. C. J. , von Hellermann M. G. , Jaspers R.
Published: November 2008

In this paper the use of the Cramer–Rao lower bound (CRLB) to aid in the design of diagnostic systems dealing with complex spectra is discussed. Specifically it is discussed how a priori knowledge, used to improve the estimation, can be included in the CRLB analysis. This provides improved predictions for the spectrometer characteristics that will lead to an optimal system.
Robust measurement of group delay in the presence of density fluctuations by means of ultrafast swept reflectometry
Authors: Cavazzana Roberto , Moresco Maurizio
Published: November 2008

It is well known that reflectometric measurements can be seriously disturbed by density fluctuations. In this paper the basic mechanisms that critically affect the measurements are outlined with the help of a simplified two-dimensional model which simultaneously mimics the dynamic of the plasma turbulence and the frequency sweep. It turns out that an adequate modulation rate can easily overcome the adverse effect of wave scattering produced by short wavelength fluctuations even when measurements taken at a single frequency would fail. Nevertheless the Doppler effect caused by long wavelength fluctuations can produce a substantial shift in the group delay, which accounts for nonmonotonous density profile reconstructions. In turn this effect can be corrected using a very fast ascending and descending frequency modulation, similarly to what is done in FM radars. The technical feasibility of such a system is demonstrated using the Ka band reflectometer of RFX, where a triangular modulation of 2.5 MHz, with a bidirectional modulation rate up to 4 GHz/200 ns, has been obtained.
TRIDENT high-energy-density facility experimental capabilities and diagnostics
Authors: Batha S. H. , Aragonez R. , Archuleta F. L. , Archuleta T. N. , Benage J. F. , Cobble J. A. , Cowan J. S. , Fatherley V. E. , Flippo K. A. , Gautier D. C. , Gonzales R. P. , Greenfield S. R. , Hegelich B. M. , Hurry T. R. , Johnson R. P. , Kline J. L. , Letzring S. A. , Loomis E. N. , Lopez F. E. , Luo S. N. , Montgomery D. S. , Oertel J. A. , Paisley D. L. , Reid S. M. , Sanchez P. G. , Seifter A. , Shimada T. , Workman J. B.
Published: November 2008

The newly upgraded TRIDENT high-energy-density (HED) facility provides high-energy short-pulse laser-matter interactions with powers in excess of 200TW and energies greater than 120J. In addition, TRIDENT retains two long-pulse (nanoseconds to microseconds) beams that are available for simultaneous use in either the same experiment or a separate one. The facility’s flexibility is enhanced by the presence of two separate target chambers with a third undergoing commissioning. This capability allows the experimental configuration to be optimized by choosing the chamber with the most advantageous geometry and features. The TRIDENT facility also provides a wide range of standard instruments including optical, x-ray, and particle diagnostics. In addition, one chamber has a 10in. manipulator allowing OMEGA and National Ignition Facility (NIF) diagnostics to be prototyped and calibrated.
Diagnostic components in harsh radiation environments: Possible overlap in R&D requirements of inertial confinement and magnetic fusion systems
Authors: Bourgade J. L. , Costley A. E. , Reichle R. , Hodgson E. R. , Hsing W. , Glebov V. , Decreton M. , Leeper R. , Leray J. L. , Dentan M. , Hutter T. , Moroño A. , Eder D. , Shmayda W. , Brichard B. , Baggio J. , Bertalot L , Vayakis G. , Moran M. , Sangster T. C. , Vermeeren L. , Stoeckl C. , Girard S. , Pien G.
Published: November 2008

The next generation of large scale fusion devices—ITER/LMJ/NIF—will require diagnostic components to operate in environments far more severe than those encountered in present facilities. This harsh environment is the result of high fluxes of neutrons, gamma rays, energetic ions, electromagnetic radiation, and in some cases, debris and shrapnel, at levels several orders of magnitude higher than those experienced in today’s devices. The similarities and dissimilarities between environmental effects on diagnostic components for the inertial confinement and magnetic confinement fusion fields have been assessed. Areas in which considerable overlap have been identified are optical transmission materials and optical fibers in particular, neutron detection systems and electronics needs. Although both fields extensively use cables in the hostile environment, there is little overlap because the environments and requirements are very different.
First density profile measurements using frequency modulation of the continuous wave reflectometry on JET
Authors: Meneses L. , Cupido L. , Sirinelli A. , Manso M. E. ,   JET-EFDS Contributors
Published: November 2008

We present the main design options and implementation of an X-mode reflectometer developed and successfully installed at JET using an innovative approach. It aims to prove the viability of measuring density profiles with high spatial and temporal resolution using broadband reflectometry operating in long and complex transmission lines. It probes the plasma with magnetic fields between 2.4 and 3.0 T using the V band [~(0–1.4)×1019 m−3]. The first experimental results show the high sensitivity of the diagnostic when measuring changes in the plasma density profile occurring ITER relevant regimes, such as ELMy H-modes. The successful demonstration of this concept motivated the upgrade of the JET frequency modulation of the continuous wave (FMCW) reflectometry diagnostic, to probe both the edge and core. This new system is essential to prove the viability of using the FMCW reflectometry technique to probe the plasma in next step devices, such as ITER, since they share the same waveguide complexity.
Prompt radiochemistry at the National Ignition Facility (invited)
Authors: Grim G. P. , Bradley P. A. , Bredeweg T. A. , Keksis A. L. , Fowler M. M. , Hayes A. C. , Jungman G. , Obst A. W. , Rundberg R. S. , Vieira D. J. , Wilhelmy J. B. , Bernstein L. A. , Cerjan C. J. , Fortner R. J. , Moody K. J. , Schneider D. H. , Shaughnessy D. A. , Stoeffl W. , Stoyer M. A.
Published: November 2008

Understanding mix in inertial confinement fusion (ICF) experiments at the National Ignition Facility requires the diagnosis of charged-particle reactions within an imploded target. Radiochemical diagnostics of these reactions are currently under study by scientists at Los Alamos and Lawrence Livermore National Laboratories. Measurement of these reactions requires assay of activated debris and tracer gases from the target. Presented below is an overview of the prompt radiochemistry diagnostic development efforts, including a discussion of the reactions of interest as well as the progress being made to collect and count activated material.
The observation of nonlinear ion cyclotron wave excitation during high-harmonic fast wave heating in the large helical device
Authors: Kasahara H. , Seki T. , Kumazawa R. , Saito K. , Mutoh T. , Kubo S. , Shimozuma T. , Igami H. , Yoshimura Y. , Takahashi H. , Yamada I. , Tokuzawa T. , Ohdachi S. , Morita S. , Nomura G. , Shimpo F. , Komori A. , Motojima O. , Oosako T. , Takase Y. , Zhao Y. , Kwak J.
Published: November 2008

A wave detector, a newly designed magnetic probe, is installed in the large helical device (LHD). This wave detector is a 100-turn loop coil with electrostatic shield. Comparing a one-loop coil to this detector, this detector has roughly constant power coupling in the lower frequency range of 40MHz, and it can easily detect magnetic wave in the frequency of a few megahertz. During high-harmonic fast wave heating, lower frequency waves (<10MHz) were observed in the LHD for the first time, and for the power density threshold of lower frequency wave excitation (7.5MHz) the power density of excited pumped wave (38.47MHz) was approximately −46dBm∕Hz. These lower frequencies are kept constant for electron density and high energy particle distribution, and these lower frequency waves seem to be ion cyclotron waves caused by nonlinear wave-particle interaction, for example, parametric decay instability.
Development of a reconstruction procedure for the halo current distribution
Authors: Alessi Edoardo , Cavinato M. , Chitarin G.
Published: November 2008

In magnetic-confinement toroidal machines, only a limited number of first wall modules can be equipped with current sensors, giving partial information about the distribution of the “halo” current (HC) injected into the vessel when the plasma hits the wall during disruptions. The knowledge of the complete distribution of the HC is necessary for evaluating the J×B loads exerted on the vessel structure. Since the pattern of contact areas of plasma with the wall during disruptions is spatially discontinuous, the HCs injected in the first wall (FW) cannot be efficiently fitted using harmonic functions. A procedure has been developed and implemented for estimating all the currents injected in vessel on the basis of a limited number of current sensors on the FW modules. The results obtained in the case of a numerical machine model with simplified geometry indicate that the procedure can be successfully applied to machines with more complex HC distribution, such as ITER.
Diagnostics for fast ignition science (invited)
Authors: MacPhee A. G. , Akli K. U. , Beg F. N. , Chen C. D. , Chen H. , Clarke R. , Hey D. S. , Freeman R. R. , Kemp A. J. , Key M. H. , King J. A. , Le Pape S. , Link A. , Ma T. Y. , Nakamura H. , Offermann D. T. , Ovchinnikov V. M. , Patel P. K. , Phillips T. W. , Stephens R. B. , Town R. , Tsui Y. Y. , Wei M. S. , Van Woerkom L. D. , Mackinnon A. J.
Published: November 2008

The ignition concept for electron fast ignition inertial confinement fusion requires sufficient energy be transferred from an ∼20 ps laser pulse to the compressed fuel via approximately MeV electrons. We have assembled a suite of diagnostics to characterize such transfer, simultaneously fielding absolutely calibrated extreme ultraviolet multilayer imagers at 68 and 256 eV; spherically bent crystal imagers at 4.5 and 8 keV; multi-keV crystal spectrometers; MeV x-ray bremmstrahlung, electron and proton spectrometers (along the same line of sight), and a picosecond optical probe interferometer. These diagnostics allow careful measurement of energy transport and deposition during and following the laser-plasma interactions at extremely high intensities in both planar and conical targets. Together with accurate on-shot laser focal spot and prepulse characterization, these measurements are yielding new insights into energy coupling and are providing critical data for validating numerical particle-in-cell (PIC) and hybrid PIC simulation codes in an area crucial for fast ignition and other applications. Novel aspects of these diagnostics and how they are combined to extract quantitative data on ultrahigh intensity laser-plasma interactions are discussed.
Design of collective Thomson scattering system using 77 GHz gyrotron for bulk and tail ion diagnostics in the large helical device
Authors: Nishiura M. , Tanaka K. , Kubo S. , Saito T. , Tatematsu Y. , Notake T. , Kawahata K. , Shimozuma T. , Mutoh T.
Published: November 2008

Collective Thomson scattering (CTS) system is expected to be a strong diagnostic tool for measuring thermal and fast ion distribution function at a local point inside plasmas. The electron cyclotron resonance heating system using a gyrotron at the frequency range of 77 GHz has been installed at the large helical device (LHD). The feasibility of CTS system using the 77 GHz gyrotron is assessed in terms of scattering spectrum and a background noise of the electron cyclotron emission, which affect the signal to noise ratio, with the realistic plasma parameters and incident port locations of LHD. Based on the calculated scattering spectra for bulk and tail fast ion diagnostics, the scattering radiation receiver system with gyrotron frequency feedback circuit is proposed to avoid the frequency chirping.
Conversion efficiency of high-Z backlighter materials
Authors: Keiter Paul A. , Comely Andrew , Morton John , Tierney Heidi , Workman Jonathan , Taylor Mark
Published: November 2008

High-Z backlighter materials are commonly used as x-ray sources for diagnosing laser-driven experiments. In order to properly plan for experiments and analyze the data, it is important to understand both the number and distribution of photons emitted by the x-ray source when it is irradiated by a laser. The conversion efficiency of L-shell and M-shell emitters is not as well understood as K-shell emitters. The conversion efficiency of the former is typically presented in terms of the entire L- or M-shell spectral region. However, for some applications, one may only want to use a subset of this spectral region. Laser conversion efficiency for L-shell and M-shell emitters suitable for high-energy (>3 keV) absorption spectroscopy is presented at multiple laser intensities. The measured conversion efficiency of the materials ranges from 0.2% to 0.6%.
Wide-view charge exchange recombination spectroscopy diagnostic for Alcator C-Mod
Authors: Rowan W. L. , Bespamyatnov I. O. , Granetz R. S.
Published: November 2008

This diagnostic measures temperature, density, and rotation for the fully stripped boron ion between the pedestal top and the plasma core with resolution consistent with the profile gradients. The diagnostic neutral beam used for the measurements generates a 50 keV, 6 A hydrogen beam. The optical systems provide views in both poloidal and toroidal directions. The imaging spectrometer is optimized to simultaneously accept 45 views as input with minimum cross-talk. In situ calibration techniques are applied for spatial location, spectral intensity, and wavelength. In the analysis, measured spectra are fitted to a model constructed from a detailed description of the emission physics. Methods for removal of interfering spectra are included. Applications include impurity and thermal transport.
A comparison of planar, laser-induced fluorescence, and high-sensitivity interferometry techniques for gas-puff nozzle density measurements
Authors: Jackson S. L. , Weber B. V. , Mosher D. , Phipps D. G. , Stephanakis S. J. , Commisso R. J. , Qi N. , Failor B. H. , Coleman P. L.
Published: November 2008

The distribution of argon gas injected by a 12-cm-diameter triple-shell nozzle was characterized using both planar, laser-induced fluorescence (PLIF) and high-sensitivity interferometry. PLIF is used to measure the density distribution at a given time by detecting fluorescence from an acetone tracer added to the gas. Interferometry involves making time-dependent, line-integrated gas density measurements at a series of chordal locations that are then Abel inverted to obtain the gas density distribution. Measurements were made on nominally identical nozzles later used for gas-puff Z-pinch experiments on the Saturn pulsed-power generator. Significant differences in the mass distributions obtained by the two techniques are presented and discussed, along with the strengths and weaknesses of each method.
Singular value decomposition filtering for enhanced signal extraction from two-dimensional beam emission spectroscopy measurements
Authors: Shafer M. W. , McKee G. R. , Schlossberg D. J.
Published: November 2008

The signal-to-noise ratio (SNR) of extracted turbulence features from beam emission spectroscopy (BES) data is significantly enhanced via application of singular value decomposition (SVD) methods. BES measures two-dimensional localized density fluctuations in DIII-D. The SNR of core turbulence characteristics is typically limited by noise arising from electronic noise, photon noise, and fluctuations in the observed neutral beam. SVD filtering has led to a significant enhancement in the SNR, reducing errors in time-resolved measurements of core turbulence characteristics, including correlation lengths, decorrelation rates, and group velocities. The SVD filtration technique is applied to BES data by combining multiple physically adjacent sampling locations to extract spatially correlated signals while partially removing unwanted incoherent noise. Using approximately half of the singular value weighted modes to reconstruct turbulence signals is found to improve SNR by up to a factor of 4, while maintaining the spatial structure of the turbulence. Unique aspects of application of SVD to broadband turbulence data are discussed.