bluuebunny/crossref_metadata_2025 huggingface dataset:
Grazing-incidence mirror streak camera diagnostic for emission measurements of imploding z pinches on the Sandia Z-machine
Authors: Wenger D. F. , Sinars D. B. , Keller K. L. , Aragon R. A. , Ruggles L. E. , Simpson W. W. , Primm P. H. , Porter J. L.
Published: October 2004

A soft x-ray (0.1–1 keV) streak camera using a grazing-incidence mirror has been developed for the Sandia Z facility, a 20 MA, 100 ns rise-time accelerator that can generate >200 TW,2 MJ, x-ray pulses. The streak camera is used to measure with one dimension of spatial resolution the continuous time history of sub-kilo-electron-volts emission from z-pinch and radiation flow experiments. Radiation >1 keV is eliminated by the use of a grazing-incidence mirror and transmission filters. The diagnostic has a magnification of 1.22, a 20 mm field-of-view and a spatial resolution of ∼350 μm. The recording length of the instrument is variable in duration up to a maximum of 33 ns, making it well suited for the typical 100 ns Z pinch implosion times. The spatial resolution can readily be changed to be along either the axial or the radial direction.
Improved pinhole-apertured point-projection backlighter geometry
Authors: Blue B. E. , Hansen J. F. , Robey H. F.
Published: October 2004

Pinhole-apertured point-projection x-ray radiography is an important diagnostic technique for obtaining high resolution, high contrast, and large field-of-view images used to diagnose the hydrodynamic evolution of high energy density experiments. In this technique, a pinhole aperture is placed between a laser irradiated foil (x-ray source) and an imaging detector. Future high energy density experiments that utilize more opaque materials will require backlighters with improved contrast as compared to what is currently used. In this article, we present an improved backlighter geometry that utilizes a tilted pinhole for debris mitigation and a front-side illuminated backlighter foil for improved photon statistics.
Preparation and characterization of pixelated phosphor screens for high-resolution linear imaging in the vacuum ultraviolet and x-ray ranges
Authors: Rodríguez-Barquero L. , Zurro B. , Martin P. , McCarthy K. J. , Baciero A.
Published: October 2004

Indirect digital imaging sensors employ tailored phosphors screens to convert incident x-ray or vacuum-ultraviolet (VUV) photons to visible light quanta A convenient method to prepare pixelated phosphor screens that can be easily tailored in thickness, type, and spatial resolution is presented. The characterization and evaluation of these screens in the laboratory is addressed and their application to high-resolution VUV and x-ray cameras is discussed.
Performance of the Thomson scattering diagnostic on Helical Symmetry Experiment
Authors: Zhai K. , Anderson F. S. B. , Willis K. , Likin K. , Anderson D. T.
Published: October 2004

We report the design and the performance of the ten-point Thomson scattering system installed on Helical Symmetry Experiment (HSX). Based upon the design of the GA Thomson scattering system, the HSX Thomson scattering system covers the complete plasma cross section, providing a ten-point plasma parameter profile measurement during a single plasma shot. The system consists of a commercial 1 J–10 ns yttrium–aluminum–garnet laser, ten polychromators from GA, the specially designed collection optics, a CAMAC data acquisition unit, and a controlling computer. The high throughput collection optics enables measurement even at a plasma density of 0.5×1012 cm−3. The system configuration, spectral response calibration, Raman calibration of the system, and operational results are presented.
Shielding a streak camera from hard x rays
Authors: Schneider M. B. , Sorce C. , Loughman K. , Emig J. , Bruns C. , Back C. , Bell P. M. , Compton S. , Hargrove D. , Holder J. P. , Landen O. L. , Perry T. S. , Shepherd R. , Young B. K.
Published: October 2004

The targets used in the hot halfraum campaign at OMEGA create many hot electrons, which result in a large flux of hard x rays. The hard x rays produce a high background in the streak camera. The background was significantly reduced by wrapping the streak camera with a high-Z material; in this case, 1/8 in. of Pb. The large hard x-ray flux also adds noise to images from framing cameras which use charge-coupled devices.
Preliminary performance measurements for a streak camera with a large-format direct-coupled charge-coupled device readout
Authors: Lerche R. A. , McDonald J. W. , Griffith R. L. , Dios G. Vergel de , Andrews D. S. , Huey A. W. , Bell P. M. , Landen O. L. , Jaanimagi P. A. , Boni R.
Published: October 2004

The University of Rochester’s Laboratory for Laser Energetics (Rochester, New York) is leading an effort to develop a modern, fully automated streak camera. Characterization of a prototype camera shows spatial resolution better than 20 lp/mm, temporal resolution of 12 ps, line-spread function of 40 μm (full width at half maximum) contrast transfer ratio of 60% at 10 lp/mm, system gain of 101 charge-coupled device electrons per photoelectron, and a dynamic range of 500 for a 2 ns window.
Implementation of a high energy 4ω probe beam on the Omega laser
Authors: Mackinnon A. J. , Shiromizu S. , Antonini G. , Auerbach J. , Haney K. , Froula D. H. , Moody J. , Gregori G. , Constantin C. , Sorce C. , Divol L. , Griffith R. L. , Glenzer S. , Satariano J. , Whitman P. K. , Locke S. N. , Miller E. L. , Huff R. , Thorp K. , Armstrong W. , Bahr R. , Seka W. , Pien G. , Mathers J. , Morse S. , Loucks S. , Stagnitto S.
Published: October 2004

A high-energy, ultraviolet Thomson scattering probe beam has been implemented on the Omega laser facility at the University of Rochester. The new probe operates at a wavelength of 264 nm, with a maximum energy of 260 J in a pulse length of 1 ns. The probe is focused with an F/6.7 lens to a minimum focal spot of 40 μm within a pointing tolerance of <50 μm. Data obtained from this probe beam have provided new diagnostic information on plasmas relevant for inertial confinement fusion and atomic physics studies.
Development of intense point x-ray sources for backlighting high energy density experiments (invited)
Authors: Workman J. , Fincke J. R. , Keiter P. , Kyrala G. A. , Pierce T. , Sublett S. , Knauer J. P. , Robey H. , Blue B. , Glendinning S. G. , Landen O. L.
Published: October 2004

High-energy-density (HED) experiments are often diagnosed using x-ray backlighting. Recently, experiments have been designed and fielded that require x-ray backlighting having large fields of view and high x-ray energies. These types of experiments will be even more prevalent on the National Ignition Facility laser. Point backlighting offers the potential to obtain higher-energy x rays using less laser energy while giving a large, uniform field of view (millimeters). We present recent results from Los Alamos National Lab, Lawrence Livermore National Lab, and the University of Rochester’s Laboratory for laser energetics obtained on the OMEGA laser at the University of Rochester on the development of such bright sources. We include discussion of the challenges and successes to date.
Multi-imaging x-ray streak camera for ultrahigh-speed two-dimensional x-ray imaging of imploded core plasmas (invited)
Authors: Shiraga H. , Fujioka S. , Jaanimagi P. A. , Stoeckl C. , Stephens R. B. , Nagatomo H. , Tanaka K. A. , Kodama R. , Azechi H.
Published: October 2004

Ultrahigh-speed two-dimensional x-ray imaging by using an image sampling technique on an x-ray streak camera has been developed and applied to observe the imploded core plasmas of inertial confinement fusion targets. Various one-dimensional and two-dimensional sampling techniques of two-dimensional images were compared, and the multi-imaging x-ray streak camera (MIXS), was found to be one of the most successful schemes. MIXS was used in an implosion experiment of a shell target with a cone for fast ignition at the OMEGA laser facility. Nonuniform structure in imploded core plasma dynamics was clearly observed with temporal and spatial resolutions of 10 ps and 10−20 μm, respectively.
Compact optical technique for streak camera calibration
Authors: Bell Perry , Griffith Roger , Hagans Karla , Lerche Richard , Allen Curt , Davies Terence , Janson Frans , Justin Ronald , Marshall Bruce , Sweningsen Oliver
Published: October 2004

To produce accurate data from optical streak cameras requires accurate temporal calibration sources. We have reproduced an older technology for generating optical timing marks that had been lost due to component availability. Many improvements have been made which allow the modern units to service a much larger need. Optical calibrators are now available that produce optical pulse trains of 780 nm wavelength light at frequencies ranging from 0.1 to 10 GHz, with individual pulse widths of approximately 25 ps full width half maximum. Future plans include the development of single units that produce multiple frequencies to cover a wide temporal range, and that are fully controllable via an RS232 interface.
Two-dimensional spectrally resolved position-sensitive proportional counter for plasma imaging
Authors: Thorn D. , Beiersdorfer P.
Published: October 2004

We describe a 160×100 mm two-dimensional position-sensitive proportional counter for use in high-temperature plasma spectroscopy. The detector employs a novel design based on a printed circuit board for the cathode plane and a single-wire switchback design for the anode plane. The spacial resolution for one dimension is 200 μm and for the other dimension is 2–5 mm. The integral nonlinearity is 0.08% for the first and 1% for the second dimension. We demonstrate the utility of the new detector with a spacially resolved measurement of the Lyman-α transitions in hydrogenic Ar17+.
X-ray imaging of an X-pinch plasma with a bubble compound refractive lens
Authors: Gary C. K. , Pikuz S. A. , Mitchell M. D. , Chandler K. M. , Shelkovenko T. A. , Hammer D. A. , Dudchik Yu. I.
Published: October 2004

We present diagnostic images taken of an X-pinch plasma x-ray source driven by the XP pulser (100 ns, 500 kA) at Cornell University using an x-ray bubble compound refractive lens. The lens consists of a 200 μm inside diameter glass capillary that contains about 100 biconcave microlenses formed by a string of bubbles in epoxy. A precise system for lens alignment with of 3–5 arcmin accuracy is described. X-ray images of four-wire X pinches were obtained with a spatial resolution of approximately 2 μm.
Concepts of x-ray diagnostics for WENDELSTEIN 7-X
Authors: Weller A. , Mohr S. , Junghans C.
Published: October 2004

The use of superconducting coils in W7-X will allow to run very long pulses (up to 30 min). Therefore enhanced demands have to be met for plasma diagnostics with respect to hardware components exposed to steady state heat fluxes, but also to the data acquisition and analysis. A multicamera x-ray tomography system inside the vacuum vessel—because of lack of suitable ports—with about 400 viewing chords distributed along the poloidal direction is proposed for magneto hydrodynamics investigations. The system will consist of about 20 compact cameras containing linear photodiode arrays, beryllium-transmission foils, and preamplifiers. A particular technical issue is the control of detector/amplifier offset and gains in steady state plasmas. Another multipurpose x-ray camera system with interchangeable filters will be installed using a particular port combination. In addition x-ray pulse height analysis will be used to deduce spectroscopic information and to provide the central electron temperature.
Close-in nosecone configuration and blast damage in point backlight x-ray radiography
Authors: Fincke J. R. , Workman J. B. , Kryala G. A. , Walsh P. J. , Evans S. C. , Tafoya D. , Landers D. J.
Published: October 2004

Radiography of driven targets using point projection backlighting often requires extensive baffling to mitigate background x rays and physical damage due to target debris. One solution to this problem is a camera configuration that places the nosecone very close to the target such that extraneous light is excluded; however debris and blast damage becomes an issue. A successful close-in (<5 mm from target center) nosecone configuration fielded at the OMEGA laser on a halfraum driven by 6 kJ is described. The design excludes stray light and survives the radiation flux and blast damage due to debris and late-time target expansion. Estimates of blast loading are compared to experimental observations of damage.
X-ray tomography systems for observations of the effects of radially sheared electric fields on fluctuations in plasmas
Authors: Kohagura J. , Cho T. , Numakura T. , Hirata M. , Yokoyama N. , Fukai T. , Tomii Y. , Tokioka S. , Miyake Y. , Kiminami S , Shimizu K. , Miyoshi S. , Yoshida M. , Kondoh T.
Published: October 2004

Experimental verification of the effects of radially sheared electric-field (or potential) formation in plasmas is one of the most critical issues to understand the physics basis for plasma confinement improvements. In the GAMMA 10 tandem mirror, recent experimental results show shear formation effects on the suppression of not only coherent drift waves but turbulence-like fluctuations without any coherent phasing relation during the ion-confining potential formation period. Contours of the central-cell soft x-ray brightness show spatially and temporally fluctuated structures during a weak sheared period by the use of the 50 channel microchannel plate system. A new x-ray tomography system is developed for analyzing temporally and spatially resolved plasma behavior in the presence or absence of these shear formation effects in GAMMA 10. The system consists of two 48-channel silicon semiconductor detector arrays with different viewing angles. X-ray energy responses of the new detector arrays along with response uniformity of detector channels have been characterized using synchrotron radiation at the Photon Factory.
Image plates as x-ray detectors in plasma physics experiments
Authors: Gales S. G. , Bentley C. D.
Published: October 2004

The performance of image plates based on the photostimulable phosphor BaF(Br,l):Eu2+ has been investigated and compared with x-ray film. Evaluation of detective quantum efficiency (DQE), sensitivity, dynamic range, and linearity was carried out for several types of commercially available image plate, using the Excalibur soft x-ray calibration facility at AWE. Image plate response was found to be linear over a dynamic range of 5 orders of magnitude. One type of image plate was found to have a number of advantages for soft x-ray detection, with a measured sensitivity 1 order of magnitude greater than that of Kodak Industrex CX and DEF-5 x-ray film. The DQE of this plate was found to be superior to that of film at low [less than 103 photons/(50 μm)2] and high fluxes [greater than 104 photons/(50 μm)2]. The spatial resolution of image plates, scanned with several models of commercial image plate readers, has been evaluated using a USAF resolution test target. The highest spatial resolution measured is 35 μm. Though this is significantly lower than the resolution possible with film, it is sufficient for many applications. Image plates were fielded in a refractive x-ray lens imaging diagnostic on the 1 TW Helen laser and these results are discussed.
Design of a multilayer mirror monochromatic x-ray imager for the Z accelerator
Authors: Jones B. , Deeney C. , Pirela A. , Meyer C. , Petmecky D. , Gard P. , Clark R. , Davis J.
Published: October 2004

A time-resolved pinhole camera is being developed for monochromatic soft x-ray imaging of z-pinch plasmas on the Z accelerator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] at Sandia National Laboratories. Pinhole images will reflect from a planar multilayer mirror onto a microchannel plate detector. A W/Si or Cr/C multilayer reflects a narrow energy range (full width at half maximum <10 eV) centered at 277 eV with peak reflectivity up to 20%. This choice of energy will allow final implosion imaging of any wire-array z-pinch fielded on Z, as well as bench testing using a carbon Kα source. Aluminized parylene filters will eliminate optical and second harmonic reflection, and the 34° multilayer grazing angle will allow detector shielding from high energy x rays produced by the Z accelerator. The system will also include a standard in-line pinhole camera, which can be filtered to obtain simultaneous higher-photon-energy images. Future instruments could use multiple mirrors to image at several energies, or operate at a low grazing angle to image 1–10 keV K-shell emission.
Framed, 16-image, Kirkpatrick–Baez microscope for laser–plasma x-ray emission
Authors: Marshall F. J. , Oertel J. A. , Walsh P. J.
Published: October 2004

A framed, 16-image, Kirkpatrick–Baez (KB)-type x-ray microscope has been designed for use in imaging laser–plasma x-ray emission. The reflecting elements are 16 pairs of concave mirrors arranged to reflect and focus x rays emanating from a laser-produced plasma. The resolution of the elements is 3 μm at best focus and is better than 5 μm within a 400-μm-diam region. A framing camera will be used in combination with the KB optic to produce 16 gated x-ray images in the energy range from 1.5 to 7 keV over a typical interval of 1.5 ns. This system is designed for use on the University of Rochester’s OMEGA laser facility [T. R. Boehly et al., Opt Commun. 133, 495 (1997)].
Imaging detectors for 20–100 keV x-ray backlighters in high-energy-density experimental science petawatt experiments
Authors: Wickersham J. E. , Park H.-S. , Bell P. M. , Koch J. A. , Landen O. L. , Moody J. D.
Published: October 2004

We are developing a petawatt laser for use as a high-energy backlighter source in the 20–100 keV range on the National Ignition Facility (NIF). High-energy x-ray backlighters will be essential for radiographing high-energy-density experimental science (HEDES) targets, especially to probe implosions and high areal density planar samples. For these high energy backlighter imaging experiments, we are developing two types of detectors: a columnar grown CsI scintillator coupled to a 2 K×2 K charge-coupled device camera, and a CdTe crystal with special application specific integrated circuit readout electronics in a 508×512 format array. We characterized these sensors using Cd109 and Am241 radioactive isotopes. In addition, we employed them to measure the Sm Kα source size generated by the short pulse laser, JanUSP, at Lawrence Livermore National Laboratory. The CsI camera performed well, allowing a measurement of the Sm Kα source size. Calibration of this camera has shown that it has low noise and good resolution. The new CdTe camera performed well, however the noise level was too high for single photon counting. Some modifications to the camera will also be necessary in order to meet the needs of future hard x-ray experiments. Both cameras showed considerable promise as diagnostic tools for future high-energy x-ray backlighters for NIF HEDES experiments. This article will present the results of our characterizations of these detectors, and initial results from the JanUSP experiments.
Static characterization of aerogel targets for high energy density physics using x-ray radiography
Authors: Keiter Paul A. , Kyrala George A.
Published: October 2004

Knowledge of the density of aerogel foams used in high energy density physics experiments is crucial for simulating and understanding the results of experiments. An average density for the foams is gravimetrically determined, but provides no information on the uniformity of the density. X-ray radiography is used to determine the density uniformity of the foams and the average density of the foams. A comparison between a monochromatic and polychromatic method of determining the density from the x-ray radiography is performed and compared to the gravimetric results.
Characterization of the series 1000 camera system
Authors: Kimbrough J. R. , Moody J. D. , Bell P. M. , Landen O. L.
Published: October 2004

The National Ignition Facility requires a compact network addressable scientific grade charge coupled device (CCD) camera for use in diagnostics ranging from streak cameras to gated x-ray imaging cameras. Due to the limited space inside the diagnostic, an analog and digital input/output option in the camera controller permits control of both the camera and the diagnostic by a single Ethernet link. The system consists of a Spectral Instruments Series 1000 camera, a PC104+ controller, and power supply. The 4k by 4k CCD camera has a dynamic range of 70 dB with less than 14 electron read noise at a 1 MHz readout rate. The PC104+ controller includes 16 analog inputs, four analog outputs, and 16 digital input/output lines for interfacing to diagnostic instrumentation. A description of the system and performance characterization is reported.
Analysis of images from videocameras in the Frascati Tokamak Upgrade tokamak
Authors: De Angelis R. , Migliori S. , Borioni S. , Bracco G. , Pierattini S. , Perozziello A.
Published: October 2004

The plasma edge interaction in FTU tokamak is monitored by wide angle videocameras. Data are acquired as movies or single frames at a rate of 50 frames/s. The images show interesting features of the plasma such as the presence of Marfes or runaways and give useful information on the status of large parts of the vacuum vessel and toroidal limiter. Due to the large number of data available visual inspection of the movies is often insufficient to correlate the images to the experimental findings. This article illustrates a number of applications developed in order to correlate the images with plasma signals and to search the image database for specific features relevant to the discharge.
Measurement of low frequency plasma fluctuations with a visible light detector in GAMMA 10
Authors: Higaki H. , Ichimura M. , Horinouchi K. , Nakagome K. , Kakimoto S. , Yamaguchi Y. , Ide K. , Inoue D. , Nagai H. , Yoshikawa M. , Nakashima Y. , Cho T.
Published: October 2004

Low frequency fluctuations of a plasma in the central cell of the GAMMA10 tandem mirror have been observed with electrostatic probes (ESPs) installed at the peripheral region of the plasma. Typical plasma parameters for a hot ion mode operation are ne∼2×1012 cm−3, Ti∼4 keV, Te∼100 eV, B=4 kG, and rp=18 cm. Although the ESP is an effective tool to measure local plasma parameters and fluctuations, it can be damaged with the higher electron temperature. Here, a new visible light detector was introduced, which could measure the plasma fluctuations without contacting the plasma. The obtained results were compared with those of ESPs. It is found that the visible light detector is applicable when the electron temperature becomes much higher in the future experiment.
Absolute calibration of vacuum ultraviolet spectrograph system for plasma diagnostics
Authors: Yoshikawa M. , Kubota Y. , Kobayashi T. , Saito M. , Numada N. , Nakashima Y. , Cho T. , Koguchi H. , Yagi Y. , Yamaguchi N.
Published: October 2004

A space- and time-resolving vacuum ultraviolet (VUV) spectrograph system has been applied to diagnose impurity ions behavior in plasmas produced in the tandem mirror GAMMA 10 and the reversed field pinch TPE-RX. We have carried out ray tracing calculations for obtaining the characteristics of the VUV spectrograph and calibration experiments to measure the absolute sensitivities of the VUV spectrograph system for the wavelength range from 100 to 1100 Å. By changing the incident angle, 50.6°–51.4°, to the spectrograph whose nominal incident angle is 51°, we can change the observing spectral range of the VUV spectrograph. In this article, we show the ray tracing calculation results and absolute sensitivities when the angle of incidence into the VUV spectrograph is changed, and the results of VUV spectroscopic measurement in both GAMMA 10 and TPE-RX plasmas.
Diagnostic system of Hα emission on neutral beam injection experiments in the GAMMA10 central cell
Authors: Higashizono Y. , Nakashima Y. , Ohki T. , Kubota Y. , Yoshikawa M. , Islam M. K. , Watanabe K. , Ogita T. , Kobayashi T. , Murakami R. , Yamada M. , Cho T. , Shoji M. , Kobayashi S.
Published: October 2004

We newly designed and installed a Hα line-emission detector in order to examine neutral particle transport around the beam line of NBI in the central cell of the GAMMA10 tandem mirror. The Hα detector consists of a Hα interference filter, a lens, an optical fiber, and a photomultiplier. The detector is absolutely calibrated using a standard lamp. The Hα detector is located at the angle of 24° to the beam line, which enabled us to directly view the Hα emission due to neutral beam injection (NBI). In standard hot-ion mode plasmas, we measured the Hα line emission in the case of NBI. The Hα line emission during NBI strongly increased by 550% on the beam line compared with that before NBI. Moreover, it was found that hydrogen recycling played an important role in the neutral transport around the beam line. This diagnostic system is confirmed to be considerably helpful for examining the detailed behavior of the neutral particles related to NBI for the first time.
Novel Doppler laser radar for diagnostics in fusion reactors
Authors: Menon Madhavan , Slotwinski Anthony
Published: October 2004

We describe the development of a novel Doppler laser radar (DOLAR) for remote measurement of flow velocity (0–10 m/s) and film thickness of liquid metal walls, currently being studied for their superior heat handling and self-healing characteristics. Small fluctuations in flow velocity(∼mm/s) and flow thickness (∼50 μm) that may arise during plasma discharges can also be measured. The DOLAR is also designed for non intrusive mapping of features of plasma-facing solid surfaces with very high precision (∼50 μm). It can also measure the motion of structural components of a fusion reactor during plasma discharges and during plasma disruptions. The device utilizes frequency modulation laser radar principles for precision range measurements. Compensation of Doppler frequency shift is used to measure flow velocity. The DOLAR probe head is designed with acousto-optic and piezoelectric devices for operation in the harsh fusion environment.
High definition imaging in the Mega Amp Spherical Torus spherical tokamak from soft x rays to infrared (invited)
Authors: Carolan P. G. , Patel A. , Conway N. J. , Akers R. J. , Bunting C. A. , Counsell G. F. , Dowling J. , Dunstan M. R. , Kirk A. , Lott F. , Price M. N. , Tournianski M. R. , Walsh M. J. ,   The MAST Team
Published: October 2004

The Mega Amp Spherical Torus (MAST) diagnostic needs are strongly influenced by physics goals that often require diagnostic integration and cross-mapping, especially in fine-scale investigations, such as transport barriers. Conversely, the unrivalled viewing access to the edge, scrape-off layer (SOL) and divertor regions, provided by the MAST open geometry, impacts on the physics program priorities. A supporting suite diagnostics, such as the high definition Thomson scattering systems, provide considerable added value in detailed data interpretation (e.g., bremsstrahlung emissivity in terms of Zeff). Thus, to exploit these advantages, an extensive set of high-resolution imaging diagnostics have been installed, encompassing soft x-rays, visible bremsstrahlung, charge exchange recognisation radiation, Dα from NBI, and edge plasma neutrals, and infrared (IR) from the divertor and wall regions. Plasma light collection optics provide near parallel illumination of narrow bandpass interference filters to give monochromatic images. One adaptation provides multiwavelength images; another accommodates smooth variation of wavelength across an image (e.g., for a range of Doppler shifts beam fast neutrals). Diagnostic synergy is enhanced by combining such diagnostics to common viewing optics which allow exact-mapping. Soft x-ray tangential imaging has been achieved by using a two dimensional charge coupled device detector in a pinhole camera. Finally, a fast IR camera monitors the power deposition on the first wall and divertor plates, important in quantifying power losses (e.g., ELMs, disruptions), and complemented by visible viewing of the SOL, and linear Dα cameras.
Measurement technique of electric field using ultraviolet/visible spectroscopy in cylindrical plasmas
Authors: Kobayashi T. , Yoshikawa M. , Kubota Y. , Saito M. , Numada M. , Ishii K. , Cho T.
Published: October 2004

The rotation of impurity ion has been measured using ultraviolet (UV) visible spectroscopy in the cylindrical fusion plasma GAMMA 10 to investigate diamagnetic drift and E×B drift. The electric field is estimated with the plasma rotation and E×B drift analysis. Since the detected signal is the line integrated emission, the parametric Abel inversion technique has been developed. In the method, a density profile of impurity ion was assumed. Recently, we can obtain the density profile using collisional–radiative model (CRM) calculation. Then the electric field is obtained independently of that assumption. We present the measurement technique of the electric field using UV/visible spectroscopy and CRM calculation. The experimental result in GAMMA 10 is that consistent with the result of the neutral beam probe measurement.
Multiplexing thermography for International Thermonuclear Experimental Reactor divertor targets
Authors: Itami K. , Sugie T. , Vayakis G. , Walker C.
Published: October 2004

The concept of multiplexing thermography is applied to the design of the divertor thermography system for International Thermonuclear Experimental Reactor (ITER). The combination of the front mirror with multiellipticity and a Czerney–Turner spectrometer with a 0.2 mm pitched multichannel detector enables a spatial resolution of 3 mm and a time resolution of 20 μs above a target temperature of 300 °C to be achieved. This should be sufficient to measure ELM heat fluxes to the targets in ITER. To satisfy the measurement requirement, it is very important to keep an accurate alignment around the optical axis against movement of the vessel during the plasma discharges. Several key engineering problems, such as the survivability of components against mirror coating by redeposited divertor material, remain to be solved. Potential solutions have been identified.
Multichannel and multicolour infrared thermography in Tore Supra
Authors: Reichle R. , Pocheau C. , Balorin C. , Delchambre E. , Desgrange C. , Guilhem D. , Henry S. , Messina P. , Roche H.
Published: October 2004

An imaging spectrometer using a sapphire prism as dispersing element has been conceived at Tore Supra for the spectral range of 1–4 μm. It measures simultaneously at various wavelengths the temperature on distributed high heat-flux elements under plasma impact with 36 optical fibers, four of which are ZrF4 fibers. It employs an InSb focal plane array detector (256*320 pixels) behind a silicon filter and a ZnS window yielding a dynamic range of 200–1500 °C with 20 ms temporal resolution. The fiber transmission and the spatial variation of gain and background of the camera are calibrated using a light source with integrating sphere. With a blackbody source one determines the nonlinearity of the average gain and controls its stability during operation. The spectral dispersion of about 24 nm/pixel is determined with interference filters and controlled with a spectral lamp. The measurements at various wavelengths allow to determine the temperature distribution in the field of view.
Characteristics of high energy Kα and Bremsstrahlung sources generated by short pulse petawatt lasers
Authors: Park H.-S. , Izumi N. , Key M. H. , Koch J. A. , Landen O. L. , Patel P. K. , Phillips T. W. , Zhang B. B.
Published: October 2004

We have measured the characteristics of high energy Kα sources created with the Vulcan Petawatt laser at RAL and the JanUSP laser at Lawrence Livermore National Laboratory. High energy x-ray backlighters will be essential for radiographing high energy-density experimental science targets for NIF projects especially to probe implosions and high areal density planar samples. Hard Kα x-ray photons are created through relativistic electron plasma interactions in the target material after irradiated by short pulse high intensity lasers. For our Vulcan experiment, we employed a CsI scintillator charge coupled device (CCD) camera for imaging and a CCD camera for single photon counting. We have directly measured the 22 keV Ag Kα source size using the RAL petawatt laser and performed knife-edge measurements of a 40 keV Sm Kα source using the JanUSP laser. The measured source sizes are both ∼60 μm full width half maximum. We have also measured the Ag Kα conversion efficiencies. At laser intensities of 1×1018 W/cm2 range, the conversion efficiency at 22 keV is ∼1×10−4.
Design and development of the large helical device TV Thomson scattering
Authors: Yamada I. , Narihara K. , Funaba H. , Hayashi H. ,   LHD experimental group
Published: October 2004

We have developed a television (TV) Thomson scattering and installed it on the large helical device (LHD). The LHD TV Thomson scattering consists of a yttrium–aluminum–garnet (YAG) laser, beam transport system, scattered light collection optics, spectrometer, intensified charge coupled device camera, and data acquisition system. The spatial and temporal resolutions are about 7 mm and a few seconds, respectively. The temporal resolution of the LHD TV Thomson scattering is not good, but will be enough for long-time, steady-state discharge experiments in LHD. In the initial experiments, we measured electron temperature profiles of LHD plasmas at five spatial points. It has been found that the electron temperatures measured by the LHD TV Thomson scattering reasonably agree with those obtained by the LHD YAG Thomson scattering. We will report the details of the LHD TV Thomson scattering system with some experimental data.
Soft x-ray tomography system for the toroidal pinch experiment-RX reversed-field pinch
Authors: Koguchi H. , Shimada T. , Asai T. , Yagi Y. , Hirano Y. , Sakakita H.
Published: October 2004

A soft x-ray (SXR) measurement system for tomography analysis on a reversed-field pinch machine. torodial pinch experiment, RX [TPE-RX, R/a=1.72/0.45 m, Ip<1 MA (designed)], is presented. The soft x-ray imaging system consists of two surface barrier detector (SBD) arrays that are vertical and horizontal. Thirteen SBDs are installed on the vertical ports and used for the measurement along vertical lines of sight. Eleven SBDs are installed on the horizontal port and used for the measurement along a fan-shaped line of sight. These detectors have 15-μm-thick Be foil with sensitivity in the soft x-ray range. This system is installed in order to study the structure of the SXR emission from the plasma core and to know the relation between global performance and magnetohydrodynamics dynamics. This system has been used under several operating conditions in addition to those of standard operation. The first results of these experiments are reported.
Progress on the development of a single line of sight x-ray framing camera
Authors: Bradley D. K. , Holder J. P. , Damian C. M. , Piston K. W. , Bell P. M. , Dymoke-Bradshaw A. K. L. , Hares J. D.
Published: October 2004

High-speed microstrip microchannel plate (MCP) x-ray framing cameras are a well established diagnostic for laser plasma experiments. Each frame acquired with these devices requires a separate image, and with most reasonable x-ray optics, a separate line of sight, causing potential parallax problems. Gated image tubes have a single line of sight capability, but the conventional designs have not been effectively extended to the short gating times of the microstrip-line MCP camera. A hybrid camera combining image tube and microstrip-line MCP technology has been under development at Lawrence Livermore National Lab in collaboration with University of Rochester Lab for Laser energetics, and KENTECH Instruments. The key feature of this single line of sight hybrid image tube is a deflection assembly that continuously divides the electrons from a single photocathode x-ray image into a set of four electron images. Temporal gating of these images is carried out using a microstrip-line microchannel plate framing camera module positioned at the image plane of the electron tube. Characterization measurements performed using both x rays from a Manson source and from laser generated plasmas, will be presented. Some implementation improvements will be discussed.
Study of a CW, two-dimensional Thomson scattering diagnostic system
Authors: Hsieh C. L. , Bray B. D. , Liu C.
Published: October 2004

We describe an approach to Thomson scattering diagnostic that relies upon a high power CW laser cavity and a rf signal detection technique, instead of the more usual pulsed high energy laser. The system has three major elements: an ultra long (∼150 m) laser resonance cavity that includes the plasma region; an array of CW diode lasers of high power and high modulation frequency that pumps and maintains the average cavity energy (∼10 mJ); and a lock-in detection system of narrow frequency bandwidth (∼2 kHz). The resonance cavity consists of a pumping chamber for power input from diode lasers, and many relay chambers (∼30) distributed across the plasma cross section for Thomson measurement. The cavity has a low energy loss (∼2% round trip) and zero output power. It is estimated that signal-to-noise of the system is ∼100 times better than the present pulsed system on DIII-D Tokamak due to the increase in usable laser energy and the improved background signal rejection.
Transmission grating streaked spectrometer for the diagnosis of soft x-ray emission from ultrahigh intensity laser heated targets
Authors: Eagleton R. T. , James S. F.
Published: October 2004

A free-standing gold transmission grating with a period of 5000 Å has been coupled to a soft x-ray sensitive streak camera with a limiting temporal resolution of 10 ps. The streak camera is equipped with a caesium iodide transmission photocathode and observations have been made in the 10–100 Å regime. For a small source (200 μm diameter) the spectral resolution is predicted to be around 2.5 Å. This has been confirmed by examination of the Lyman-α line in hydrogen-like laser heated boron. A recorded linewidth of 2.44 Å is demonstrated. The instrument has been used to diagnose the soft x-ray emission from a plastic (CH) foil target heated by an ultra-intense (2×1020 W cm−2) laser pulse.
Characterization of National Ignitition Facility cryogenic beryllium capsules using x-ray phase contrast imaging
Authors: Montgomery D. S. , Nobile A. , Walsh P. J.
Published: October 2004

Beryllium capsules filled with cryogenic deuterium and tritium fuel layers may provide many advantages for obtaining ignition at the National Ignition Facility. However, characterizing the uniformity and thickness of the frozen fuel layer in such a target is challenging since traditional x-ray radiography techniques, which rely on absorption for image contrast, cannot provide sufficient contrast to image the fuel layer in these low-Z materials. We propose using x-ray phase contrast imaging, which relies on gradients in the refractive index and wave interference, to characterize fuel layer uniformity. We present numerical modeling results of x-ray phase contrast imaging demonstrating the feasibility of this method for target characterization, discuss the necessary x-ray source characteristics, and present concepts for using this technique in the context of dynamic high density plasma experiments.
X-ray detection by direct modulation of an optical probe beam—Radsensor: Progress on development for imaging applications
Authors: Lowry Mark E. , Bennett Corey V. , Vernon Stephen P. , Stewart Richard , Welty Rebecca J. , Heebner John , Landen Otto L. , Bell Perry M.
Published: October 2004

We present a progress report on our new x-ray detection technique based on optical measurement of the effects of x-ray absorption and electron hole pair creation in a direct band-gap semiconductor. The electron–hole pairs create a frequency dependent shift in optical refractive index and absorption. This is sensed by simultaneously directing an optical probe beam through the same volume of semiconducting medium that has experienced an x-ray induced modulation in the electron–hole population. If the wavelength of the optical probe beam is close to the semiconductor band-edge, the optical probe will be modulated significantly in phase and amplitude. We have analyzed the physics of the imaging radsensor, developed modeling tools for device design, and are cautiously optimistic that we will achieve single x-ray photon sensitivity, and picosecond response. These predictions will be tested with Cu Kα xrays at the LLNL USP facility this spring and summer, with a cavity-based radsensor detector suitable for use in x-ray imagers.
Current profile reconstruction using electron temperature imaging diagnostics
Authors: Tritz K. , Stutman D. , Delgado-Aparicio L. F. , Finkenthal M. , Pacella D. , Kaita R. , Stratton B. , Sabbagh S.
Published: October 2004

Flux surface shape information can be used to constrain the current profile for reconstruction of the plasma equilibrium. One method of inferring flux surface shape relies on plasma x-ray emission; however, deviations from the flux surfaces due to impurity and density asymmetries complicate the interpretation. Electron isotherm surfaces should correspond well to the plasma flux surfaces, and equilibrium constraint modeling using this isotherm information constrains the current profile. The KFIT code is used to assess the profile uncertainty and to optimize the number, location and SNR required for the Te detectors. As Te imaging detectors we consider tangentially viewing, vertically spaced, linear gas electron multiplier arrays operated in pulse height analysis (PHA) mode and multifoil soft x-ray arrays. Isoflux coordinate sets provided by Te measurements offer a strong constraint on the equilibrium reconstruction in both a stacked horizontal array configuration and a crossed horizontal and vertical beam system, with q0 determined to within ±4%. The required SNR can be provided with either PHA or multicolor diagnostic techniques, though the multicolor system requires ∼×4 better statistics for comparable final errors.
High-speed optical diagnostic that uses interference filters to measure Doppler shifts
Authors: Paul S. F. , Cates C. J. , Mauel M. E. , Maurer D. A. , Navratil G. A. , Paul R. M. , Pedersen T. S. , Shilov M. A.
Published: October 2004

A high-speed, noninvasive velocity diagnostic has been developed for measuring plasma rotation. The Doppler shift is determined by employing two detectors that view line emission from the identical volume of plasma. Each detector views through an interference filter having a passband that varies linearly with wavelength. One detector views the plasma through a filter whose passband has a negative slope and the second detector views through one with a positive slope. Because each channel views the same volume of plasma, the ratio of the amplitudes is not sensitive to variations in plasma emission. With suitable knowledge of the filter characteristics and the relative gain, the Doppler shift is readily obtained in real time from the ratio of two channels without needing a low throughput spectrometer. The systematic errors—arising from temperature drifts, stability, and frequency response of the detectors and amplifiers, interference filter linearity, and ability to thoroughly homogenize the light from the fiber bundle—can be characterized well enough to obtain velocity data with ±1 km/s with a time resolution of 0.3 ms.
Heuristic reconstructions of neutron penumbral images
Authors: Nozaki Shinya , Chen Yen-Wei
Published: October 2004

Penumbral imaging is a technique of coded aperture imaging proposed for imaging of highly penetrating radiations. To date, the penumbral imaging technique has been successfully applied to neutron imaging in laser fusion experiments. Since the reconstruction of penumbral images is based on linear deconvolution methods, such as inverse filter and Wiener filer, the point spread function of apertures should be space invariant; it is also sensitive to the noise contained in penumbral images. In this article, we propose a new heuristic reconstruction method for neutron penumbral imaging, which can be used for a space-variant imaging system and is also very tolerant to the noise.
Development of background reduced Fresnel phase zone plate
Authors: Tamari Yohei , Azechi Hiroshi
Published: October 2004

In study of hot and dense plasma, a high spatial resolution (a few microns) x-ray imaging is very important to observe these plasmas. The Fresnel phase zone plate (FPZP) consists of alternately material and transparent circular annuli placed concentrically, which image x rays using diffraction x rays from all annuli. FPZP have imaged 4.7–4.77 keV x rays with 2.2 μm spatial resolution. However FPZP has a problem that background level is comparable to signal level. In subtraction of background, the error of 10% is caused. For the accurate background subtraction, we designed new FPZP, which consist of three β layers of a transparent zone and two material zones. The new design FPZP parameters (thickness of material zones, each zone width) have been optimized, and in that optimum design signal-to-background ratio is 4 times better than conventional two layers FPZP.
Energy resolved fast two-dimensional x-ray imaging for MFE plasmas (invited)
Authors: Pacella D. , Bellazzini R. , Brez A. , Finkenthal M.
Published: October 2004

A new approach to time resolved two-dimensional x-ray imaging is presented. It is based on a micropattern gas detector with gas electron multiplier as amplifying stage and pixel readout. It allows x-ray photon counting at high detection efficiency, high signal to noise ratio, extremely high time resolution (framing rate up to 100 kHz), and with an innovative capability: the energy resolution. The detector has a limited number of pixels (up to tens of thousands), but each pixel behaves like a low-resolution spectrometer, allowing quasimonochromatic images or spectral scans. This new approach is proposed as an alternative to the traditional static, spectral integrated, noiser, high definition (millions of pixels) x-ray imaging as performed, for example, with charge coupled device based devices. All these innovative features have been tested on the National Spherical Torus Experiment (Princeton, USA) but the authors are firmly convinced that it will be applied to many other fields of research.
High resolution soft x-ray tomography in the Madison Symmetric Torus
Authors: Franz P. , Bonomo F. , Gadani G. , Marrelli L. , Martin P. , Piovesan P. , Spizzo G. , Chapman B. E. , Reyfman M.
Published: October 2004

We present in this article the description of the upgraded soft x-ray tomographic diagnostic which has been installed in the Madison symmetric torus (MST) reversed field pinch. The previous diagnostic has been extended with two manipulators, for a total of three moveable probes and a fixed one. The line integrated emissivity (brightness) will be measured with arrays of photodiodes and the total number of channels has been increased from 24 to 74. The electronic layout has also been upgraded, and a type of custom made current-to-voltage amplifier has been developed. The diagnostic will be used to continue and extend the magnetohydrodynamics analysis of the MST plasma. The imaging of rotating coherent structures (one or, as recently showed, two) which appear during quasisingle helicity or pulsed poloidal current drive experiments will be performed in more detail. The photocameras can be easily extracted, modified, and inserted again, allowing applications and utilizations of the diagnostic.