bluuebunny/crossref_metadata_2025 huggingface dataset:
Fourier-space image processing for spherical experiments on OMEGA (invited)
Authors: Smalyuk V. A. , Boehly T. R. , Iwan L. S. , Kessler T. J. , Knauer J. P. , Marshall F. J. , Meyerhofer D. D. , Stoeckl C. , Yaakobi B. , Bradley D. K.
Published: February 2004

Studies of compressed shell integrity of spherical targets on the 60-beam 30 kJ UV OMEGA laser system involve spatially and temporally resolved measurements of core emission at different x-ray energies. Hot-core emission backlights a titanium-doped shell that is imaged at x-ray energies above and below the titanium K edge. The difference between the two images is related to perturbations in the cold, or absorbing, part of the shell. The core emission has been imaged by a pinhole array on a framing camera and recorded on film. The resolution and noise of all parts of the imaging system have been characterized. Using this information, a Wiener filter that reduces noise, compensates for detector resolution, and facilitates measurement of shell nonuniformities has been formulated.
Density profile of the ablating plasma produced by soft x-ray irradiation
Authors: Nishikino M. , Shiraga H. , Matsuoka M. , Fujioka S. , Shigemori K. , Nakai M. , Azechi H. , Miyanaga N. , Yamanaka T. , Nakai S.
Published: February 2004

Indirect/direct-hybrid irradiation has been proposed for suppressing the initial imprint of laser-irradiation nonuniformities. Indirect soft x-ray preirradiation of the target generates a plasma expansion layer on the target surface. When the drive laser beam comes later, the target has a substantial stand-off distance between the ablation front and the beam absorption region, in which the thermal smoothing effect is expected to take place, and then, the initial imprint of the laser irradiation nonuniformities can be significantly reduced. Stand-off distance is of great importance in the imprint mitigation. We measured the preformed plasma profile by using the x-ray side-on backlighting method. The preformed plasma was backlit by x rays and imaged onto an x-ray streak camera. The scale length of the preformed plasma was found to increase with duration of the soft x-ray irradiation. The expansion velocity was found to be 6×105 cm/s at an x-ray irradiation of 1×1011 W/cm2.
X-ray imaging techniques on
Z
using the Z-Beamlet laser
Authors: Bennett G. R. , Landen O. L. , Adams R. F. , Porter J. L. , Ruggles L. E. , Simpson W. W. , Wakefield C.
Published: February 2004

The Z-Beamlet laser backlighter system at Sandia National Laboratories, which will be operational in 2001, will create a point or area source of high (or moderate) energy x rays behind a Z-accelerator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] -driven target. In the former case with >2 kJ in up to four pulses of <2 ns total duration in a 20 ns interval, and >80% of the 2ω energy in a ∼50-μm-diam focal spot, the resulting >4×1016 W/cm2 irradiances will generate ⩾8.950, 8.999 keV (zinc He-α, etc.) x rays. This high-energy source, as either a single point or four separate spots, will be used directly for four-frame point-projection x-ray imaging, and will attain spatial resolutions and signal-to-noise levels significantly better than presently possible on Z using existing methods. In combination with a ∼1 cm field of view, the technique will be well suited to the large, relatively opaque objects characteristic of Z experiments. This addition is anticipated to have a major impact upon the basic physics of z-pinch implosions, and therefore, possibly the ultimate x-ray powers and hohlraum (vacuum or dynamic) radiation temperatures that may be attainable. Furthermore, in combination with a slightly defocused point source and a medium-energy grazing-incidence microscope, Z-Beamlet may allow various inertial confinement fusion and high-energy-density physics experiments to be studied at even higher spatial resolution and signal-to-noise levels.
Fiberoptic heterodyne magnetic field sensor for long-pulsed fusion devices
Authors: Tsuji-lio S. , Akiyama T. , Sato E. , Nozawa T. , Tsutsui H. , Shimada R. , Takahashi M. , Terai K.
Published: February 2004

A heterodyne polarimeter which measures the Faraday effect has been under development as a magnetic field sensor for long-pulsed fusion devices. The wavelength of laser beam was chosen to be 850 nm since the radiation-induced loss in optical fibers is significant below 800 nm while the Faraday rotation angle decreases with increasing wavelength. By the use of a distributed Bragg reflector laser diode and a Faraday isolator, excellent stability of phase measurement was attained. The phase resolution was raised to up to 0.02° by the digital complex demodulation and digital bandpass filtering of beat signals. Although the Verdet constant of heavily Tb3+-doped paramagnetic glass is larger than that of ZnSe by about a factor of 1.4, ZnSe is superior to the former in terms of negligible temperature dependence. With a 40-mm-long ZnSe sensing rod, resolutions of the magnetic field strength of about 5 and 2 G were found to be possible with time responses of 1 and 10 ms, respectively.
Integration of magnetic and nonmagnetic measurements for current profile reconstruction in RFX
Authors: Bagatin M. , Chitarin G. , Desideri D. , Murari A. , Piovan R. , Zabeo L.
Published: February 2004

A crucial issue in magnetically confined plasmas characterized by relevant internal current redistribution, such as high beta and low field toroidal devices, is the determination of their internal magnetic structure. The article presents a method for the integration of magnetic and nonmagnetic measurements in a model which considers a plasma described by stationary ideal magnetohydrodynamic equilibrium equations, with toroidal and poloidal plasma currents represented by distributed discrete filaments and current sheets. The model also includes the massive conductors representing the vessel, the shell, and the machine windings. The discrete current sets are determined by using as input data the total currents flowing in the plasma, in the windings and in the vessel, as deduced by external integral magnetic measurements. The obtained filamentary current sets are then adjusted by imposing further constraints. One of the constraints is given by the set of local magnetic field measurements provided by external pickup coils. A further and more significant constraint is imposed by far infrared polarimeter, which gives an integral condition for each implemented measurement chord. The method is validated by using experimental data from the reversed field pinch Reversed Field eXperiment, and the results suggest that the current density distribution is rather different from that usually predicted by conventional data inversion algorithms.
Triple Langmuir probe measurements in the Hanbit magnetic mirror device
Authors: Lee S. G. , Bak J. G.
Published: February 2004

A triple Langmuir probe was used in the initial physics operation phase of the Hanbit magnetic mirror device. The experimental data from the triple Langmuir probe were obtained in the edge of the central cell during radio frequency (rf) discharge plasma operation. Up to 200 kW rf heating power was applied at the frequency of 3.75 MHz. The position of the triple Langmuir probe was controlled by 0.1 mm accuracy. Measurements of the edge electron temperature, electron density, and floating potential were made in a radial scan of the plasma.
First results of reverse field experiment vertical time-of-flight
Authors: Costa S. , Murari A. , Lotto L.
Published: February 2004

The charge exchange neutral particle outfluxes and ion temperature are important quantities for the determination of the power balances and the plasma’s energetic content; therefore they constitute a long term issue of reversed field pinch research. In order to improve the experimental knowledge of these plasma quantities, in the reversed field experiment a vertical time-of-flight (TOF) neutral particle analyzer (NPA) has been recently installed. It sees the plasma along a vertical chord, whose impact parameter is about half radius, and it is meant to complement the other two NPAs, which are installed on the equatorial plane. In this article, the new vertical TOF is reported, with particular attention to its more original components. An “in situ” method to calibrate the electron multiplier gain absolutely is described in detail. The first measurements of the ion temperature are reported, showing the reliable operation of the system and the acceptable signal-to-noise ratio obtained up to now. The results are also compared with the measurements of the horizontal NPAs mainly in the experimental regime of high plasma density. Possible improvements of the new diagnostic and its use in combination with a neutral particle beam are also briefly described and discussed.
An application of electrically cooled Si detector to fast neutral measurement on CHS
Authors: Yamamoto T. , Osakabe M. , Isobe M. , Yoshimura Y. , Kumazawa R. , Mutoh T. , Watari T. , Takeiri Y. , Kaneko O. , Takahasi C. , Matsuoka K. ,   CHS Group, Kado S.
Published: February 2004

A new type of fast neutral particle analyzer using Si diode cooled by Peltier module has been designed and developed. It is known that leak current in a solid-state detector is reduced by its use in low temperature. It is shown in this article that Peltier effect provides a very handy way of cooling the detector as long as a temperature around 0 °C is aimed at. The detector was easily cooled down to −1.6 °C and the performance of the detector was studied by the use of x/γ rays from Am241. The leak current was remarkably reduced as the detector is cooled improving energy resolution from 9.2 keV at room temperature to 4.3 keV at −1.6 °C. In addition, the lower detectable energy limit was expanded from 25 keV to 14 keV. A Si detector is also sensitive to visible light and x ray. Therefore, the detector of our “reference design” is furnished with an evaporated 1000-Å-thick aluminum layer to reduce the visible light and with a lead collimator to reduce the x ray. The detector was finally installed on the Compact Helical System device for a test of overall performance and an energy spectrum from a diagnostic neutral beam was successfully measured. This test was conducted without an Al layer and this result suggests a possibility of eliminating it.
Suppression of plasma electrons in the diagnostic ports of the MST
Authors: Demers D. R. , Connor K. A. , Lei J. , Schoch P. M. , Shah U.
Published: February 2004

The recent application of a heavy ion beam probe (HIBP) to the Madison Symmetric Torus (MST) has motivated the development of permanent magnet plasma suppression structures. Unconfined plasma at the MST diagnostic ports is free to flow out the ports and into adjoining diagnostic chambers. The HIBP system incorporates seven pairs of high voltage, electrostatic steering plates. Stray charged particles that exit the MST-HIBP ports are attracted to these biased steering plates, loading down the power supplies, and detrimentally affecting the desired operation of the plates. A second source of loading is electron current generated by UV light emitted from the MST plasma. Structures comprised of steel keepers and nickel plated magnets were designed to conform to the walls of the two HIBP diagnostic ports. The magnetic fields in the keeper aperture are able to suppress most of the plasma that would otherwise flow into the HIBP chambers. The fields external to the keeper structure are sufficiently small to avoid perturbing the confining fields at the plasma edge. Analysis indicates that electron current from UV radiation dominates the remaining loading of the HIBP steering plates.
Development of mesh probe for the calibration of the HIBP diagnostic system in the JFT-2M tokamak
Authors: Kamiya K. , Miura Y. , Tsuzuki K. , Ido T. , Hamada Y. , Nakayama T.
Published: February 2004

A direct calibration technique for the heavy ion beam probe system using the mesh probe is established. The mesh probe makes it possible to calibrate the diagnostic system with the same condition as a real plasma measurement. The location of the sample volume could be determined with the spatial resolution of about 7.5 mm. It shows good agreement with this expected result by the trajectory code with an accuracy of about 1%.
A diagnostic neutral beam system for the MST reversed-field pinch
Authors: Abdrashitov G. F. , Davydenko V. I. , Deichuli P. P. , Den Hartog D. J. , Fiksel G. , Ivanov A. A. , Korepanov S. A. , Murakhtin S. V. , Shulzhenko G. I.
Published: February 2004

A diagnostic neutral beam system has been developed for the Madison symmetric torus (MST) reversed-field pinch. The system is primarily used: (1) for measurement of the majority ion equilibrium and fluctuating velocity and temperature by Rutherford scattering (RS); (2) for measurement of the impurity ion velocity and temperature, both equilibrium and fluctuating, by charge-exchange recombination spectroscopy (CHERS); and (3) for magnetic field measurement via motional Stark effect (MSE). The system consists of two neutral beam injectors, and two neutral particle analyzers. One injector creates a 20 keV, 4 A helium beam for RS. The energy spectra of the helium beam atoms scattered from the plasma ions is measured with two 12-channel, 45° electrostatic energy analyzers equipped with a hydrogen stripping cell. A second injector creates a 30 keV, 4 A hydrogen beam, which is used for the CHERS and MSE diagnostics. In each injector ions are extracted from a plasma created by an arc discharge source and, after acceleration and focusing, neutralized in a gaseous target. A low ion perpendicular temperature at the plasma emission surface, achieved via plasma expansion cooling, results in a low (0.016 rad) intrinsic beam divergence. A hallmark of the beam design is the focusing ion optical system that consists of four multiaperture spherically curved electrodes. The geometric focusing, together with a low intrinsic beam divergence, provides a small beam size—5 cm in diameter-on the MST axis and a high neutral current density (0.4 equivalent A/cm2). A beam injector is compact in size—30 cm in diameter and 70 cm in length—and weighs about 70 kg. In this article we present details of the beam and analyzer designs and first results of their tests on the MST.
X-ray yield scaling studies performed on the OMEGA laser
Authors: Workman J. , Kyrala G. A.
Published: February 2004

We have performed experiments with planar targets on the OMEGA laser facility at the University of Rochester. These experiments investigated the scaling of x-ray yield and conversion efficiency with the laser energy and focusing properties for several different target materials. The experiments were also designed to investigate the feasibility of high-energy backlighters under typical irradiance geometries. The scaling of Fe emission near 6.7 keV was investigated by varying laser irradiance from 1014 to 1016 W/cm2. In addition, the scaling of x-ray yield with emitted x-ray energy was studied at fixed laser irradiance near 1016 W/cm2 for Fe, Zn, and Ge. The time-integrated spectra as well as filtered x-ray film gave relative x-ray yields.
10 and 5 μm pinhole-assisted point-projection backlit imaging for the National Ignition Facility
Authors: Bullock A. B. , Landen O. L. , Bradley D. K.
Published: February 2004

In pinhole-assisted point-projection backlighting, pinholes are placed a small distance (of order 1 mm) away from the backlighter source to produce images with large field of view. Pinholes placed close to high-power backlighter sources can vaporize and, if sufficiently small, close due to x-ray driven ablation, thereby potentially limiting the usefulness of this method. A study of streaked one-dimensional backlit imaging of 25 μm W wires using the OMEGA laser at the University of Rochester is presented. The pinhole closure time scale for 10 μm pinholes placed 0.45 and 1 mm distant from a 0.6 TW Ti backlighter is 1.3 and 2.2 ns, respectively. Similar time scales for 5 μm pinholes is also presented. Successful wire imaging prior to pinhole closure is clearly demonstrated.
Imaging of laser–plasma x-ray emission with charge-injection devices
Authors: Marshall F. J. , Ohki T. , McInnis D. , Ninkov Z. , Carbone J.
Published: February 2004

This work details the method of obtaining time-integrated images of laser–plasma x-ray emission using charge-injection devices (CIDs), as has been demonstrated on the University of Rochester’s 60-beam UV OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. The CID has an architecture similar to a charge-coupled device. The differences make them more resistant to radiation damage and, therefore, more appropriate for some application in laser–plasma x-ray imaging. CID-recorded images have been obtained with x-ray pinhole cameras, x-ray microscopes, x-ray spectrometers, and monochromatic x-ray imaging systems. Simultaneous images obtained on these systems with calibrated x-ray film have enabled determination of the absolute detection efficiency of the CIDs in the energy range from 2 to 8 keV.
Photon-counting CCD detector as a tool of x-ray imaging
Authors: Liang Y. , Ida K. , Kado S. , Minami T. , Okamura S. , Nomura I. , Watanabe K. Y. , Yamada H. ,   CHS Group, and,   LHD Group
Published: February 2004

A new x-ray imaging technique to measure magnetic axis and two-dimensional soft x-ray energy spectra for a long-pulse discharge has been developed by utilizing a soft x-ray photon-counting charge-coupled-device (CCD) camera. This system consists of pinholes, Be filters, and a 1024×1024 frame-transfer back-illumination CCD detector (the imaging area has 1024×512 pixels). By choosing appropriate combinations of pinholes and Be filters, the x-ray flux is adjusted to the level suited for photon-counting mode and imaging mode, respectively. The Shafranov shift is derived from a two-dimensional soft x-ray intensity map measured in the imaging mode in the compact helical system (CHS) and large helical device. Two-dimensional profiles of electron temperature and two-dimensional profiles of high-Z impurity Kα radiation intensity are derived from two-dimensional energy spectra of x rays measured in photon-counting mode for the CHS hot-electron-mode plasma.
Monochromatic x-ray imaging with bent crystals for laser fusion research
Authors: Fujita K. , Nishimura H. , Niki I. , Funakura J. , Uschmann I. , Butzbach R. , Förster E. , Nakai M. , Fukao M. , Sunahara A. , Takabe H. , Yamanaka T.
Published: February 2004

Monochromatic x-ray imaging with toroidally bent crystals has been applied to investigate critical issues in laser fusion research in collaboration with Jena University [for example, I. Uschmann et al., Rev. Sci. Instrum. 66, 734 (1995)]. Described in this article is the study on x-ray diagnostics to provide simultaneously time, space, and spectral resolutions for the laser fusion experiments by the use of toroidally bent crystals. A monochromatic x-ray imager was developed, which consists of two sets of identical five bent crystals and a fast x-ray framing camera. The attained spatial resolution of 6 μm, time resolution of 34 ps, and spectral resolution of 10 eV are high enough to observe temporal evaluation and temperature distribution of the laser fusion hot core. In addition, a new x-ray imager with bent crystal was developed to investigate hydrodynamic instabilities occurring in laser-driven planer targets as one of the most critical issues in laser fusion research. The imager was so designed as to match the experiments using rather thick, massive targets irradiated under the same condition as in the high-gain experiments. Configuration and specifications of the imager are presented.
Optimizing data recording for the NIF core diagnostic x-ray streak camera
Authors: Kalantar D. H. , Bell P. M. , Perry T. S. , Sewall N. , Kimbrough J. , Weber F. , Diamond C. , Piston K.
Published: February 2004

Quantitative measurements of the sensitivity, dynamic range, and image resolution of a Nova secondary ion mass-based x-ray streak camera have been made. Comparisons were made using film versus a 4k×4k optical charge-coupled device for data readout. These tests were performed with and without an optical image intensifier tube, and with a direct electron-sensitive microchannel plate. We present results from these tests and recommendations for the National Ignition Facility core x-ray streak camera.
Development of wide-field, multi-imaging x-ray streak camera technique with increased image-sampling arrays
Authors: Heya M. , Fujioka S. , Shiraga H. , Miyanaga N. , Yamanaka T.
Published: February 2004

In order to enlarge the field of view of a multi-imaging x-ray streak (MIXS) camera technique [H. Shiraga et al., Rev. Sci. Instrum. 66, 722 (1995)], which provides two-dimensionally space-resolved x-ray imaging with a high temporal resolution of ∼10 ps, we have proposed and designed a wide-field MIXS (W-MIXS) by increasing the number of image-sampling arrays. In this method, multiple cathode slits were used on the photocathode of an x-ray streak camera. The field of view of the W-MIXS can be enlarged up to 150–200 μm instead of ∼70 μm for a typical MIXS with a spatial resolution of ∼15 μm. A proof-of-principle experiment with the W-MIXS was carried out at the Gekko-XII laser system. A cross-wire target was irradiated by four beams of the Gekko-XII laser. The data streaked with the W-MIXS system were reconstructed as a series of time-resolved, two-dimensional x-ray images. The W-MIXS system has been established as an improved two-dimensionally space-resolved and sequentially time-resolved technique.
Fast ion losses in the W7-AS stellarator
Authors: Werner A. , Weller A. , Darrow D. S. ,   the W7-AS Team
Published: February 2004

A new probe for the detection of fast escaping ions has been installed and operated at the W7-AS stellarator. Fast ions generated from neutral beam injection or ion cyclotron heating were used to study the fast ion confinement properties of the partially drift-optimized magnetic field structure as well as losses induced by magnetohydrodynamic perturbations. The design of the probe is based on the α-particle detectors of the Tokamak Fusion Test Reactor using scintillator plates and allows the detection of co-and countergoing ions simultaneously in a wide range of gyroradii and pitch angles.
Fast ion loss diagnostic plans for the National Spherical Torus Experiment
Authors: Darrow D. S. , Bell R. , Johnson D. W. , Kugel H. , Wilson J. R. , Cecil F. E. , Maingi R. , Krasilnikov A. , Alekseyev A.
Published: February 2004

The prompt loss of neutral beam ions from the National Spherical Torus Experiment is expected to be between 12% and 42% of the total 5 MW of beam power. There may, in addition, be losses of fast ions arising from high harmonic fast wave (HHFW) heating. Most of the lost ions will strike the HHFW antenna or the neutral beam dump. To measure these losses in the 2000 experimental campaign, thermocouples in the antenna, several infrared camera views, and a Faraday cup lost ion probe will be employed. The probe will measure loss of fast ions with E>1 keV at three radial locations, giving the scrape-off length of the fast ions.
A thin film device as a low energy, high flux charged particle spectrometer
Authors: Cecil F. E. , Roy Brian , Sutton Christian , Wasinger Nicole
Published: February 2004

We are continuing our investigation of the use of stacks of electrically isolated thin metal foils as spectrometers for lost ions from tokamak fusion plasmas. Devices of this type in which the foil thicknesses were a few micrometers were installed on the Joint European Torus during the recent first deuterium–tritium experiment in an effort to observe lost energetic alpha particles. While there was no convincing evidence of lost alpha particles in this experiment, we did observe significant fluxes of low energy (<500 keV) charged particles. In an effort to provide an instrument for the investigation of this phenomenon and of escaping relatively low energy (<100 keV) ions from other fusion plasma devices, we have developed alternative devices with very thin (few hundred nanometers) alternating layers of conductor and insulator. Four such devices have been fabricated and tested for protons with energies between 20 and 160 keV and demonstrated good energy resolution (typically about 10%) for proton bombarding energies between about 40 and 120 keV. One of the devices, consisting of deposited layers of Al, Ti, and SiO2 was operated up to a current density of about 100 m/cm2 at an energy of 100 keV, corresponding to a power volume density of 100 kW/cm3
Improved charge coupled device detectors for the edge charge exchange spectroscopy system on the DIII-D tokamak
Authors: Burrell K. H. , Kaplan D. H. , Gohil P. , Nilson D. G. , Groebner R. J. , Thomas D. M.
Published: February 2004

Charge exchange spectroscopy is one of the key ion diagnostics on the DIII-D tokamak. It allows measurement of impurity densities, toroidal and poloidal rotation speeds, ion temperatures, and the radial electric field. For the 2000 experimental campaign, we have replaced the intensified photodiode array detectors on the edge portion of the system with advanced charge-coupled device (CCD) detectors mounted on faster (f/4.7) Czerny–Turner spectrometers equipped with toroidal mirrors. The combination has improved the photoelectron signal level by about a factor of 20 and the signal to noise by a factor of 2–8, depending on the absolute signal level and readout mode. A major portion of the signal level improvement comes from the improved quantum efficiency of the back-illuminated, thinned CCD detector (70% to 85% quantum efficiency for the CCD versus 10% for the image intensifier) with the remainder coming from the faster spectrometer. The CCD camera also allows shorter minimum integration times: 0.33 ms while archiving to computer memory and 0.15 ms using temporary storage on the CCD chip.
The multichord far infrared polarimeter of the RFX experiment
Authors: O’Gorman M. , Zilli E. , Giudicotti L. , Prunty S. , Milani F. , Murari A. , Boboc A.
Published: February 2004

A multichannel far infrared (FIR) polarimeter has been installed on the reversed field experiment (RFX) to measure the poloidal magnetic field profile, BΘ. The polarimeter uses a FIR laser (λ=118.8 μm) whose beam is transmitted to the machine via a 31 m long, nitrogen filled beam line. Faraday rotation measurements are reported for five of six parallel chords crossing the 1 m diameter RFX plasma on a poloidal cross section. The density profile is known from a CO2 interferometer. Low noise deuterated L-alaine doped triglycene sulphate (DLATGS) detectors are used. An accuracy of about 0.2° is obtained in the measured Faraday rotation angle, which is sufficient to estimate the characteristics of the BΘ profile. Removal of the noise induced by mechanical vibrations allowed acceptable measurements of Faraday rotation angles.
Test of a periodic multipass-intracavity laser system for the TEXTOR multiposition Thomson scattering diagnostics
Authors: Kantor M. Yu. , Barth C. J. , Kouprienko D. V. , van der Meiden H. J.
Published: February 2004

A multipass intracavity laser probing system operating in a burst mode has been tested for the Torus Experiment for Technology Oriented Research Thomson scattering diagnostics. The parameters tested were the probing pulse energy and power as well as pulse repetition frequency. The system is to be applied for the dynamic study of fast plasma phenomena (e.g., transport barrier formation and filaments) requiring both high time and spatial resolutions of the electron temperature measurements.
Continuum-based diagnostics of weakly nonideal laser-produced plasmas
Authors: Kim Yong W. , Lloyd-Knight Conrad D.
Published: February 2004

We have developed a novel diagnostic technique for weakly nonideal laser-produced plasma (LPP) plumes, based entirely on the continuum, and present the result for aluminum plasma. Due to significant self-absorption, the analysis is carried out in close coupling with plasma equilibrium calculations. We first invoke scaling relations linking the time- and position-resolved specific continuum intensity I, integrated over the spectral range of a streak camera, to the local temperature T and pressure p: T=STIα and p=SpIα+β. Inversion of the two-dimensional luminosity profile into the specific continuum intensity profile (three-dimensional) is carried out self-consistently, subject to the 16 independent measurements: target mass loss, energy deposited into the LPP plume and laser beam attenuation at fundamental and its harmonic frequencies, all at four different laser energies. An agreement to within 6.1% of the measurements overall has been achieved with α=0.45±0.03, β=1.0±0.03, ST=0.190±0.003 and Sp=340±5.
Edge temperature and density measurements by helium line intensity ratios in the reversed field experiment RFX with high time resolution
Authors: Carraro L. , Puiatti M. E. , Sattin F. , Scarin P. , Valisa M.
Published: February 2004

In the reversed field experiment the electron temperature and density at the edge are measured from the intensity ratio of selected lines emitted by an atomic helium beam injected into the plasma. Helium is injected through a single microtube 30 mm long and with 150 μm of internal diameter. Four beam splitters allow three interference filters, coupled to linear array cameras or alternatively to photomultipliers, and a charge coupled device camera to observe the same beam volume. The application of photomultipliers as detectors has recently increased the time resolution of the diagnostic. This allows following the time evolution of edge density and temperature during nonstationary processes. Moreover, the enhanced time resolution increases the capability of the diagnostic to measure the edge electron temperature and density fluctuations, which are relevant to the edge electrostatic transport studies.
Near to backscattered light imaging diagnostic on the National Ignition Facility
Authors: Mascio W. A. , Sewall N. R. , Kirkwood R. , Lee F. D. , Hibbard W. J.
Published: February 2004

The National Ignition Facility (NIF) is being built at Lawrence Livermore National Laboratory for the U.S. Department of Energy Stockpile Stewardship Program. It will perform experiments for inertial confinement fusion ignition, high energy density science, and basic science. A target diagnostic is being developed for the NIF that will image nearly all the light scattered near the laser axis, (i.e., just outside the laser focusing lens). The diagnostic is called the near backscatter imager (NBI) and is presently required to measure stimulated Brillouin (SBS) and stimulated Raman (SRS) scattering so that the backscatter fraction will be determined with a goal of 30% uncertainty, and SBS and SRS temporal response with ∼200 ps resolution. The NBI will also provide an option to measure temporally resolved spectrum with 50 ps and ∼1 nm resolution. The diagnostic will obtain SBS and SRS scatter plate images with a retro-viewing optical digital camera placed inside the target chamber. Time integrated optical diodes and fast optical diodes will be placed at several locations on the scatter plate to obtain the power and total energy data, as well as a calibration for the scatter plate image at several points. Fibers will be placed near the diodes to provide the option to make spectral measurement. A calibration system using a low power laser, in situ, to illuminate a series of points on the plate while recording the plate image with an external camera system is also being considered.
First charge exchange recombination spectroscopy and motional Stark effect results from the Madison Symmetric Torus reversed field pinch
Authors: Craig D. , Den Hartog D. J. , Fiksel G. , Davydenko V. I. , Ivanov A. A.
Published: February 2004

We report on the first results of charge exchange recombination spectroscopy (CHERS) and motional Stark effect (MSE) measurements in the Madison Symmetric Torus reversed field pinch. A 30 keV, 4 A neutral H beam is used in combination with visible and ultraviolet spectroscopy to make the measurements. For CHERS, we find that the C VI line at 3433.69 Å yields the largest charge-exchange signal/background ratio and is most clearly resolved from other nearby lines. Equilibrium ion temperature measurements have been made with an existing fast Doppler spectrometer and a higher throughput spectrometer is being designed to do velocity and temperature fluctuation measurements. MSE measurements are made by recording the Doppler shifted Hα spectrum emitted by the beam with a charge coupled device and imaging spectrometer. We have observed separation of the π components of the Stark manifold at magnetic fields of about 0.5 T and are considering options for increasing measurement accuracy.
A motional stark effect instrument to measure q(R) on the C-mod tokamak
Authors: Bretz N. , Simon D. , Parsells R. , Bravenec R. , Rowan W. , Eisner N. , Sampsell M. , Yuh H. , Marmar E. , Terry J.
Published: February 2004

A motional Stark effect (MSE) instrument to measure q(r) using the Torus Experiment for Technology (TEXT) neutral beam on the Alcator C-Mod tokamak has been designed and installed. The neutral beam is on the midplane, aimed radially, and designed to operate in hydrogen at 50 keV. The MSE optics view the outer half of the plasma −0.3<(R−R0)/a<1.05. This geometry results in a spatial resolution of 1 (edge)–3 (center) cm from a beam apertured horizontally to 2 cm. Estimates of the signal levels indicate for Hα that photoelectron statistical errors in the measurement of Bθ/Bφ can be less than 0.2% for ne0<2.0×1014 cm−3 similar to other MSE instruments. The collection optics reside within the vacuum chamber reflecting and imaging the neutral beam through a vacuum window in the neutral beam port. The optics are designed so that beam emission spectroscopy can be carried out simultaneously with MSE measurements. Optical signals are transmitted to remote detectors by fiber optics. Low Verdet glass and dielectric mirrors are used to minimize polarization changes caused by the ambient fields. Polarization is measured by conventional techniques using photoelastic modulators, optical filters, and photomultipliers.
Design of the motional Stark effect diagnostic in FTU
Authors: De Angelis R. , Sarkissian A. , Segre S. E. , Tartoni N. , Zanza V.
Published: February 2004

This article reports on the design of the motional Stark effect diagnostic (MSE) for the Frascati Tokamak Upgrade tokamak (Rmaj=93 cm, rmin=33 cm, BT<8 T). The attenuation and emissivity of a diagnostic hydrogen beam have been estimated for typical discharges to assess the feasibility of the diagnostic. Due to the geometrical constraints the beam direction and the polarimeter lines of sight lie on a vertical plane on the same horizontal port. This layout has the advantage of a more convenient projection of the polarization vector on the line of sight, which increases the sensitivity of the measure. The relay optics has been designed so as to minimize Faraday rotation effects which would perturb the measurements. Two polarimeters based on different modulating techniques are compared and discussed. The first one makes use of photoelastic modulators. The second employs a fast rotating retarder plate.
Spectra polarimetry of the motional Stark effect at TEXTOR-94
Authors: Jaspers R. , Elzendoorn B. S. Q. , Donné A. J. H. , Soetens T.
Published: February 2004

The Balmer-α light emitted by neutral particles injected into tokamaks is polarized with respect to the Lorentz electric field experienced by these atoms: El=ν×B, known as the motional Stark effect (MSE). On TEXTOR-94 a new MSE system is under development which exploits the full spectral information, along with its polarization. The advantages of exploiting the full spectral information are obvious: beam velocity, observation volume, absolute value of B, the plasma radial electric field and the beam density can in principle all be extracted from the measurement, whereas the polarization can be detected as several lines simultaneously. The TEXTOR-94 MSE system consists of 30 radial channel, of which the full Balmer-α spectrum is measured at two orthogonal angles. This is accomplished by inserting a Glan–Laser prism in the optical path. All the optics is located inside the vessel to improve the radial resolution and minimize changes in polarization due to optical elements. Fibers transfer the light by a vacuum feedthrough towards a spectrometer. It is shown that the measured spectra can be adequately fitted. The accuracy for determining the safety factor q is estimated to be 10%–15% and for the radial electric field to be 30 kV/m.
Prospects for edge current density determination using LIBEAM on DIII-D
Authors: Thomas D. M. , Bozek A. S. , Robinson J. I. , Burrell K. H. , Carlstrom T. N. , Osborne T. H. , Snider R. T. , Finkenthal D. K. , Jayakumar R. , Makowski M. A. , Nilson D. G. , Rice B. W.
Published: February 2004

The specific size and structure of the edge current profile has important effects on the magnetohydrodynamic stability and ultimate performance of many advanced tokamak (AT) operating modes. This is true for both bootstrap and externally driven currents that may be used to tailor the edge shear. Absent a direct local measurement of j(r), the best alternative is a determination of the poloidal field. Measurements of the precision (0.1°–0.01° in magnetic pitch angle and 1–10 ms) necessary to address issues of stability and control and provide constraints for EFIT are difficult to do in the region of interest (ρ=0.9–1.1). Using Zeeman polarization spectroscopy of the 2S–2P lithium resonance line emission from the DIII-D LIBEAM [D. M. Thomas, Rev. Sci. Instrum. 66, 806 (1995); D. M. Thomas, A. W. Hyatt, and M. P. Thomas, Rev. Sci. Instrum. 61, 340 (1990)] measurements of the various field components may be made to the necessary precision in exactly the region of interest to these studies. Because of the negligible Stark mixing of the relevant atomic levels, this method of determining j(r) is insensitive to the large local electric fields typically found in enhanced confinement (H mode) edges, and thus avoids an ambiguity common to motional Stark effect measurements of B. Key issues for utilizing this technique include good beam quality, an optimum viewing geometry, and a suitable optical prefilter to isolate the polarized emission line. A prospective diagnostic system for the DIII-D AT program will be described.
Measurement of electron transport in the Madison Symmetric Torus reversed-field pinch (invited)
Authors: Lanier N. E. , Craig D. , Anderson J. K. , Biewer T. M. , Chapman B. E. , Den Hartog D. J. , Forest C. B. , Prager S. C. , Brower D. L. , Jiang Y.
Published: February 2004

A recent study investigating the role of electron density fluctuations in particle transport has been conducted on the Madison Symmetric Torus reversed-field pinch. Four diagnostics enabled this experiment: a high-speed multichord far-infrared laser interferometer, a multichord Hα array, a 64-position magnetic coil array, and a Doppler spectrometer that measured impurity ion flow fluctuations. Correlation analysis is used to elucidate the relationship among density, magnetic, and impurity ion flow fluctuations. We observe that the electron density fluctuations are highly coherent with the magnetic fluctuations resulting from core-resonant resistive tearing modes. Moreover, the fluctuation-induced particle transport, obtained from the correlation between electron density and flow fluctuations, indicates that the core-resonant tearing modes do not drive significant particle transport in the plasma edge. We will address these four primary diagnostics, details of the analysis techniques, and principal results from this study.
ECE imaging of electron temperature and electron temperature fluctuations (invited)
Authors: Deng B. H. , Domier C. W. , Luhmann N. C. , Brower D. L. , Cima G. , Donné A. J. H. , Oyevaar T. , van de Pol M. J.
Published: February 2004

Electron cyclotron emission imaging (ECE imaging or ECEI) is a novel plasma diagnostic technique for the study of electron temperature profiles and fluctuations in magnetic fusion plasma devices. Instead of a single receiver located in the tokamak midplane as in conventional ECE radiometers, ECEI systems utilize large diameter imaging optics coupled with planar millimeter-wave imaging arrays to form multichannel ECE diagnostics with excellent spatial resolution. Combined with specially designed imaging optics, the use of these compact, low cost arrays has resulted in the excellent spatial resolution of the ECEI systems, the unique capability of two-dimensional measurements, and flexibility in the measurement of plasma fluctuations. Technical details and principles of this emerging diagnostic technique are described in this article. Illustrative experimental results are presented, together with a discussion of the further development of the diagnostic.
X-mode heterodyne reflectometer for edge density profile measurements on Tore Supra
Authors: Clairet F. , Sabot R. , Bottereau Ch. , Chareau J. M. , Paume M. , Heuraux S. , Colin M. , Hacquin S. , Leclert G.
Published: February 2004

A new broadband reflectometer operating in the frequency range 50–75 GHz in extraordinary mode polarization has been developed and tested on Tore Supra to measure edge density profiles. Using solid state source and active frequency multipliers, it performs routine measurements in 20 μs. Modulation of the source frequency is the clue to heterodyne detection in order to ensure a high dynamic sensitivity without any phase locking system. The reflectometer can achieve a repetition rate of 5 μs between sweeps, so the dynamic behavior of fast plasma events can be followed. The profile is reconstructed fully automatically from raw data and initialization is given by detection of the first cutoff. The profiles are part of the public database of Tore Supra. High reliability of the measurements for various plasma conditions makes this diagnostic an ideal tool to study the plasma–surface interaction physics and rf antenna coupling processes.
Mass data acquisition systems in JT-60 data processing system
Authors: Oshima T. , Matsuda T. , Tsugita T. , Sakata S. , Sato M. , Koiwa M.
Published: February 2004

In the data processing system for the JT-60 tokamak, a unique mass data acquisition system with fast sampling, a transient mass data storage system (TMDS), has been used since 1988. It is composed of a minicomputer and 61 channels of 4/6 MB memory modules with a sampling rate up to 200 kHz and about 300 MB of data are transferred to a main computer by using a special LAN developed by Fujitsu Ltd. TMDS can handle a large amount of data, but cannot be enlarged in its capability, such as CPU power or the number of channels. To solve the problems of TMDS, a new fast VME data acquisition system (FDS), has been developed. It can acquire 6 MB of data per channel with a sampling rate of 200 kHz or 1 MHz and consists of a workstation with VMEbus memory modules. Up to now there are three FDSs with 24 channels. The minicomputer of TMDS has been replaced with a new system based on the technology of FDS. To cope with mass data transfer to a data server, they are connected with a gigabit ethernet switch.
In situcalibration of neutral beam port-through power and estimation of neutral beam deposition on LHD
Authors: Osakabe M. , Takeiri Y. , Tsumori K. , Murakami S. , Kaneko O. , Ikeda K. , Oka Y. , Asano E. , Kawamoto T. , Akiyama R. , Kawahata K. , Komori A. , Inoue N. , Yonezu Y. , Ohyabu N. , Motojima O. ,   LHD Experimental group
Published: February 2004

The neutral beam (NB) shine-through profile is routinely monitored on the Large Helical Device (LHD) both to calibrate the port-through power of the NB and to evaluate the NB-deposition power to LHD plasmas. The profile is measured with a calorimeter (CM) array on an armor plate of the NB counter wall inside the LHD vacuum vessel. An infrared camera is also used to check the beam profile where CMs are not located, and measures a temperature increase of the armor plate due to the NB heat load. The measured beam profile is compared to the calculated NB profile at the armor plate. The measurement indicates that the beam is not uniform at the exit of the ion source and that the steering angle of the beam in the horizontal direction is not the same as the designed value. It is found that the monitoring of the NB shine-through profile is important to estimate the NB port-through power and the NB deposition power, especially when the neutral beam injector (NBI) is based on a large negative-hydrogen ion source.
Simultaneous observations of temporally and spatially resolved two-dimensional profiles of ion-confining potentials and ion fluxes using novel ion-energy spectrometer arrays
Authors: Yoshida M. , Cho T. , Hirata M. , Kohagura J. , Nishizawa Y. , Sasuga T. , Nagashima S. , Yatsu K. , Miyoshi S.
Published: February 2004

Newly designed spectrometer arrays for ion-energy-spectrum observations are proposed and constructed in both end regions of the GAMMA 10 tandem mirror so as to obtain two dimensionally resolved radial profiles of end-loss-ion fluxes IELA, ion temperatures, and ion-confining potentials φc by the use of a single plasma discharge alone. Each spectrometer unit in the array has a specific structure with obliquely placed multiple grids with respect to the direction of the ambient plasma-confining magnetic fields. This structure is proposed to obtain precise ion-energy spectra without the disturbance of simultaneously incident energetic electrons into the array, since widely distributed “multigridded Faraday cup” signals have significant electron disturbances on ion spectra even if over a few tens of kV are applied to the electron-repeller grid. In tandem-mirror experiments, plasma-confining potentials produced by electron cyclotron heatings play one of the most critical roles in the improvement of simple-mirror confinement. Thus, diagnostics of these confining potentials using clear ion spectra are of essential importance. From these motivations, the spatial distribution details and relations of φc and IELA are investigated by the use of the novel ion spectrometers. Axisymmetric profiles of φc are found to have a good correlation with axisymmetric plugging distributions in IELA. These are consistently interpreted in terms of the Pastukhov theory of the relation of φc with IELA. Information on such specific spectrometer arrays would contribute to researchers in a wide variety of plasma devices, who employ analyzers for flux, temperature, and potential diagnostics under energetic plasma circumstances.
Measured response of bubble neutron detectors and prospects for alpha knock-on diagnostics
Authors: Fisher R. K. , Parks P. B. , Liptac J. , Belian A. , Morse E. C. , Ingram D. C. , Brient C. E. , Medley S. S. , Roquemore A. L. , Loughlin M. L.
Published: February 2004

Measurement of the neutron energy spectrum above ∼16 MeV will yield information on the spatial and energy distributions of confined fast alphas in deuterium–tritium (DT) tokamaks (Fisher, Nucl. Fusion; Gorini Rev. Sci. Instrum.). The energetic neutrons result from fusion reactions involving the energetic ions created by alpha-fuel ion knock-on collisions. Standard two-gas bubble neutron detectors, designed to only detect neutrons with energies above a selectable threshold determined by the gas mixture, were used in preliminary attempts to measure the knock-on neutrons from DT plasmas in the Tokamak Fusion Test Reactor and Joint European Torus (JET). Subsequent measurements at accelerator neutron sources showed an unexpected below-threshold detector response that prevented observations of the alpha-induced neutron tails. Spontaneous bubble nucleation measurements show that the majority of this below-threshold response is due to slight variations in the gas mixture, and is not present in single-gas detectors. Single-gas detectors will be tested at the University of California Berkeley to determine the neutron energy threshold as a function of detector operating temperature and to confirm their suitability for alpha knock-on tail measurements. An array of single-gas detectors operating at different temperatures should allow measurements of the alpha knock-on neutron tail during planned DT experiments on JET.