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Oct 2004

Volume 75, Issue 10, pp. 3091-4349

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back to top X-RAY IMAGING

Development of intense point x-ray sources for backlighting high energy density experiments (invited)

J. Workman, J. R. Fincke, P. Keiter, G. A. Kyrala, T. Pierce, S. Sublett, J. P. Knauer, H. Robey, B. Blue, S. G. Glendinning, and O. L. Landen

Rev. Sci. Instrum. 75, 3915 (2004); http://dx.doi.org/10.1063/1.1789248 (6 pages) | Cited 16 times

Online Publication Date: 12 October 2004

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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.
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52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.La X-ray and γ-ray measurements

Multi-imaging x-ray streak camera for ultrahigh-speed two-dimensional x-ray imaging of imploded core plasmas (invited)

H. Shiraga, S. Fujioka, P. A. Jaanimagi, C. Stoeckl, R. B. Stephens, H. Nagatomo, K. A. Tanaka, R. Kodama, and H. Azechi

Rev. Sci. Instrum. 75, 3921 (2004); http://dx.doi.org/10.1063/1.1789249 (5 pages) | Cited 5 times

Online Publication Date: 12 October 2004

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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.
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52.70.La X-ray and γ-ray measurements
07.68.+m Photography, photographic instruments; xerography
07.85.-m X- and γ-ray instruments
07.05.Pj Image processing
52.58.-c Other confinement methods
52.58.Qv Electrostatic and high-frequency confinement
28.52.Cx Fueling, heating and ignition

Energy resolved fast two-dimensional x-ray imaging for MFE plasmas (invited)

D. Pacella, R. Bellazzini, A. Brez, and M. Finkenthal

Rev. Sci. Instrum. 75, 3926 (2004); http://dx.doi.org/10.1063/1.1791750 (4 pages) | Cited 2 times

Online Publication Date: 12 October 2004

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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.
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52.70.La X-ray and γ-ray measurements
52.55.Jd Magnetic mirrors, gas dynamic traps
07.85.Nc X-ray and γ-ray spectrometers
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.Dq Photometers, radiometers, and colorimeters

Compact optical technique for streak camera calibration

Perry Bell, Roger Griffith, Karla Hagans, Richard Lerche, Curt Allen, Terence Davies, Frans Janson, Ronald Justin, Bruce Marshall, and Oliver Sweningsen

Rev. Sci. Instrum. 75, 3930 (2004); http://dx.doi.org/10.1063/1.1789250 (4 pages) | Cited 1 time

Online Publication Date: 12 October 2004

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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.
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07.68.+m Photography, photographic instruments; xerography
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
84.30.Ng Oscillators, pulse generators, and function generators
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Two-dimensional spectrally resolved position-sensitive proportional counter for plasma imaging

D. Thorn and P. Beiersdorfer

Rev. Sci. Instrum. 75, 3937 (2004); http://dx.doi.org/10.1063/1.1789251 (4 pages) | Cited 1 time

Online Publication Date: 12 October 2004

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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+.
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29.40.Cs Gas-filled counters: ionization chambers, proportional, and avalanche counters
52.70.La X-ray and γ-ray measurements

Extreme ultraviolet imaging of wire array z-pinch experiments

S. N. Bland, D. J. Ampleford, S. C. Bott, S. V. Lebedev, J. B. A. Palmer, S. A. Pikuz, and T. A. Shelkovenko

Rev. Sci. Instrum. 75, 3941 (2004); http://dx.doi.org/10.1063/1.1787926 (3 pages) | Cited 14 times

Online Publication Date: 12 October 2004

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A multi-frame extreme ultraviolet imaging system based on four pinhole cameras, each backed by a gated microchannel plate (MCP) detector, was used to analyze plasma formation and dynamics in wire array z-pinch experiments on the MAGPIE generator (1 MA, 240 ns) at Imperial College (London). The use of pinhole size, object, and image distances, and MCP sensitivity to determine the spatial and spectral response of the diagnostic is discussed. A high magnification, high resolution version of the diagnostic has produced important information on wire initiation and plasma ablation in various materials. A low magnification version has allowed direct study of the snowplough sheath during array implosion, and of plasma instabilities during stagnation.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.59.Qy Wire array Z-pinches
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
85.60.Gz Photodetectors (including infrared and CCD detectors)
52.50.Lp Plasma production and heating by shock waves and compression
85.60.Ha Photomultipliers; phototubes and photocathodes
52.25.-b Plasma properties
42.79.Pw Imaging detectors and sensors

Use of X-pinches of diagnose behavior of low density CH foams on axis of wire array Z-pinches

S. C. Bott, J. B. A. Palmer, D. J. Ampleford, S. N. Bland, J. P. Chittenden, and S. V. Lebedev

Rev. Sci. Instrum. 75, 3944 (2004); http://dx.doi.org/10.1063/1.1787927 (3 pages) | Cited 4 times

Online Publication Date: 12 October 2004

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X-pinch radiography was used to analyze the interaction between streams of coronal plasma and on-axis foam targets in wire array z-pinch experiments on the MAGPIE generator (1 MA,240 ns). The implosion of the x-pinch, used in place of a current return conductor to the load, provided a short (<2 s) small ( ∼ 5 μm) intense burst of soft x-rays, ideal for point projection backlighting. Timimg of the x-pinch was adjusted via the mass of its wires, allowing us to study the evolution of the foam during the experiment. Choice of the x-pinch materials, filters, and recording film determined the probing radiation, and hence the plasma/foam densities were resolved. Quantitative results will be discussed.
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52.70.La X-ray and γ-ray measurements
52.59.Qy Wire array Z-pinches
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.-b Plasma properties
52.80.Qj Explosions; exploding wires
52.30.-q Plasma dynamics and flow

Correcting for gain effects in an x-ray framing camera in a cylindrical implosion experiment

C. J. Horsfield, K. W. Parker, S. D. Rothman, J. Fincke, and N. E. Lanier

Rev. Sci. Instrum. 75, 3947 (2004); http://dx.doi.org/10.1063/1.1787928 (3 pages)

Online Publication Date: 12 October 2004

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A program to investigate the mixing of a marker layer in a convergent cylindrical geometry has been carried out on the Omega laser facility. The principal diagnostic for these experiments was the Los Alamos National Laboratory (Los Alamos, NM) QXI framing camera. The results obtained displayed an unphysical pattern, partly attributed to nonlinear gain effects. We propose a method to compensate for these effects, which relies only on shot data and so can be used retrospectively on previously obtained data. Modifications carried out on the camera to minimize the effect are described and the results are compared with compensated data from previous runs. We also present results which evaluate the state of gain effects in the camera during each experimental shot day.
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52.70.La X-ray and γ-ray measurements
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Pw Imaging detectors and sensors

X-ray imaging of an X-pinch plasma with a bubble compound refractive lens

C. K. Gary, S. A. Pikuz, M. D. Mitchell, K. M. Chandler, T. A. Shelkovenko, D. A. Hammer, and Yu. I. Dudchik

Rev. Sci. Instrum. 75, 3950 (2004); http://dx.doi.org/10.1063/1.1789252 (3 pages) | Cited 2 times

Online Publication Date: 12 October 2004

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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.
Show PACS
52.70.La X-ray and γ-ray measurements
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.59.Px Hard X-ray sources
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
41.50.+h X-ray beams and x-ray optics

Three-dimensional plasma structure reconstruction from mutually orthogonal streaks of nonaxisymmetric laser-produced plasma plumes

Yong W. Kim and Hedok Lee

Rev. Sci. Instrum. 75, 3953 (2004); http://dx.doi.org/10.1063/1.1781378 (3 pages) | Cited 2 times

Online Publication Date: 12 October 2004

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A method is developed for structure reconstruction of an arbitrary plasma from two luminosity streaks and a front-view snapshot as a weighting function (WF). Two scaling relations link the pressure and temperature to the local specific emission intensity. A trial plasma structure is proposed in terms of specific intensity, and the luminosity streaks are calculated according to the Saha equilibrium. Plasma absorption is included. Error signals between the calculated and measured luminosity are allocated according to the WF to find corrections to local specific intensities. Minimization of the errors completes the reconstruction at a given time, which in turn updates the WF for the next time step. Summing over the full plasma over time facilitates calculation of the total plasma mass, energy and beam attenuation through the plasma. When agreement with their measured counterparts is maximized, the scaling relations are calibrated.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.-b Plasma properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Optical and x-ray streak camera gain measurements

S. Ghosh, R. Boni, and P. A. Jaanimagi

Rev. Sci. Instrum. 75, 3956 (2004); http://dx.doi.org/10.1063/1.1787929 (3 pages)

Online Publication Date: 12 October 2004

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Measurements of streak camera gain as the number of CCD (charge-coupled-device) electrons recorded per single-electron events hitting the streak tube phosphor are presented. The CCD is fiber optically coupled to the streak tube output; there is no image intensifier in the system. The gain is measured from the signal-to-noise ratio (SNR) of the recorded photoelectrons. This technique allows us to verify that the photoelectron SNR follows Poisson statistics and to establish the linear dynamic range. Superpixel histograms of sparse streak records are also used to generate the pulse-height distribution (PHD) for recording single-electron events and corroborate the gain measurement. The noise factor and the number distribution of secondary electrons emitted per absorbed x ray from Au, KBr, and CsI photocathodes are derived from the PHD’s recorded with an x-ray streak camera.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.68.+m Photography, photographic instruments; xerography

Initial operation of the national spherical torus experiment fast tangential soft x-ray camera

B. C. Stratton, R. Feder, S. von Goeler, G. F. Renda, V. J. Mastrocola, and J. L. Lowrance

Rev. Sci. Instrum. 75, 3959 (2004); http://dx.doi.org/10.1063/1.1787930 (3 pages) | Cited 8 times

Online Publication Date: 12 October 2004

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Fast, two-dimensional, soft x-ray imaging is a powerful technique for the study of magnetohydrodynamic instabilities in tokamak plasmas. We have constructed an ultra-fast frame rate soft x-ray camera for the national spherical torus experiment (NSTX). It is based on a recently developed 64×64 pixel charge-coupled device (CCD) camera capable of capturing 300 frames at up to 500 000 frames per second. A pinhole aperture images the plasma soft x-ray emission (0.2–10 keV) onto a P47 scintillator deposited on a fiber-optic faceplate; the scintillator visible light output is detected and amplified by a demagnifying image intensifier and lens-coupled to the CCD chip. A selection of beryllium foils provides discrimination of low-energy emission. The system is installed on NSTX with a wide-angle tangential view of the plasma. Initial plasma data and an assessment of the system performance are presented.
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52.70.La X-ray and γ-ray measurements
52.55.Fa Tokamaks, spherical tokamaks
42.79.Pw Imaging detectors and sensors
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
42.79.Ls Scanners, image intensifiers, and image converters
42.79.Bh Lenses, prisms and mirrors

Concepts of x-ray diagnostics for WENDELSTEIN 7-X

A. Weller, S. Mohr, and C. Junghans

Rev. Sci. Instrum. 75, 3962 (2004); http://dx.doi.org/10.1063/1.1789253 (4 pages) | Cited 1 time

Online Publication Date: 12 October 2004

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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.
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52.70.La X-ray and γ-ray measurements
52.55.Jd Magnetic mirrors, gas dynamic traps
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.-b Plasma properties

Close-in nosecone configuration and blast damage in point backlight x-ray radiography

J. R. Fincke, J. B. Workman, G. A. Kryala, P. J. Walsh, S. C. Evans, D. Tafoya, and D. J. Landers

Rev. Sci. Instrum. 75, 3966 (2004); http://dx.doi.org/10.1063/1.1789254 (3 pages) | Cited 4 times

Online Publication Date: 12 October 2004

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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.
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52.70.La X-ray and γ-ray measurements
07.85.-m X- and γ-ray instruments
07.68.+m Photography, photographic instruments; xerography

Transmission grating streaked spectrometer for the diagnosis of soft x-ray emission from ultrahigh intensity laser heated targets

R. T. Eagleton and S. F. James

Rev. Sci. Instrum. 75, 3969 (2004); http://dx.doi.org/10.1063/1.1790053 (5 pages) | Cited 11 times

Online Publication Date: 12 October 2004

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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.
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52.70.La X-ray and γ-ray measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Preliminary design of the soft x-ray array tomographic diagnostic system for Korea Superconducting Tokamak Advanced Research (KSTAR) plasmas

Junghee Kim and Wonho Choe

Rev. Sci. Instrum. 75, 3974 (2004); http://dx.doi.org/10.1063/1.1787931 (3 pages) | Cited 3 times

Online Publication Date: 12 October 2004

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Analyses of x-ray (SXR) emission from tokamak plasmas provide valuable information about magnetohydrodynamics activities and transport phenomena. In this study, design and optimization of the SXR detector arrays were performed for the KSTAR (Korea superconducting tokamak advanced research) device. Geometrical arrangement of the array system was made by coverage mapping and tomographic reconstruction tests. The space-time tomography algorithm was developed for KSTAR-like plasmas using the fast maximum entropy method combined with singular value decomposition. Spatial setup of the components in each detector array was determined and optimized by geometrical calculation. A curved beryllium window and a developed cooling system will be mounted on the detector arrays. Due to the existence of the complex structures between outer vessel and passive stabilizers, each array is designed to be miniaturized. Hardware-optimization of the array system was cross-checked with the tomographic test results.
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52.70.La X-ray and γ-ray measurements
52.55.Fa Tokamaks, spherical tokamaks
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
42.30.Wb Image reconstruction; tomography
07.85.Nc X-ray and γ-ray spectrometers

Independent component analysis based filtering for penumbral imaging

Yen-Wei Chen, Xian-Hua Han, and Shinya Nozaki

Rev. Sci. Instrum. 75, 3977 (2004); http://dx.doi.org/10.1063/1.1787932 (3 pages) | Cited 2 times

Online Publication Date: 12 October 2004

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We propose a filtering based on independent component analysis (ICA) for Poisson noise reduction. In the proposed filtering, the image is first transformed to ICA domain and then the noise components are removed by a soft thresholding (shrinkage). The proposed filter, which is used as a preprocessing of the reconstruction, has been successfully applied to penumbral imaging. Both simulation results and experimental results show that the reconstructed image is dramatically improved in comparison to that without the noise-removing filters.
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07.85.Nc X-ray and γ-ray spectrometers
07.05.Pj Image processing
42.30.Wb Image reconstruction; tomography

Heuristic reconstructions of neutron penumbral images

Shinya Nozaki and Yen-Wei Chen

Rev. Sci. Instrum. 75, 3980 (2004); http://dx.doi.org/10.1063/1.1791334 (3 pages) | Cited 3 times

Online Publication Date: 12 October 2004

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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.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
28.52.Lf Components and instrumentation
52.57.-z Laser inertial confinement

Grazing-incidence mirror streak camera diagnostic for emission measurements of imploding z pinches on the Sandia Z-machine

D. F. Wenger, D. B. Sinars, K. L. Keller, R. A. Aragon, L. E. Ruggles, W. W. Simpson, P. H. Primm, and J. L. Porter

Rev. Sci. Instrum. 75, 3983 (2004); http://dx.doi.org/10.1063/1.1787933 (3 pages) | Cited 6 times

Online Publication Date: 12 October 2004

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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.
Show PACS
52.70.La X-ray and γ-ray measurements
52.58.Lq Z-pinches, plasma focus, and other pinch devices
42.79.Bh Lenses, prisms and mirrors
41.50.+h X-ray beams and x-ray optics
07.85.Nc X-ray and γ-ray spectrometers

Characterization of National Ignitition Facility cryogenic beryllium capsules using x-ray phase contrast imaging

D. S. Montgomery, A. Nobile, and P. J. Walsh

Rev. Sci. Instrum. 75, 3986 (2004); http://dx.doi.org/10.1063/1.1790054 (3 pages) | Cited 21 times

Online Publication Date: 12 October 2004

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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.
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07.85.Tt X-ray microscopes
41.50.+h X-ray beams and x-ray optics
42.25.Fx Diffraction and scattering
52.70.La X-ray and γ-ray measurements

Improved pinhole-apertured point-projection backlighter geometry

B. E. Blue, J. F. Hansen, and H. F. Robey

Rev. Sci. Instrum. 75, 3989 (2004); http://dx.doi.org/10.1063/1.1787936 (3 pages) | Cited 3 times

Online Publication Date: 12 October 2004

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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.
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52.70.La X-ray and γ-ray measurements
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.59.Px Hard X-ray sources

X-ray tomography systems for observations of the effects of radially sheared electric fields on fluctuations in plasmas

J. Kohagura, T. Cho, T. Numakura, M. Hirata, N. Yokoyama, T. Fukai, Y. Tomii, S. Tokioka, Y. Miyake, S Kiminami, K. Shimizu, S. Miyoshi, M. Yoshida, and T. Kondoh

Rev. Sci. Instrum. 75, 3992 (2004); http://dx.doi.org/10.1063/1.1789255 (3 pages) | Cited 1 time

Online Publication Date: 12 October 2004

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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.
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52.25.Gj Fluctuation and chaos phenomena
52.58.-c Other confinement methods
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.70.La X-ray and γ-ray measurements
52.35.Kt Drift waves
52.35.Ra Plasma turbulence
52.50.-b Plasma production and heating

X-ray detection by direct modulation of an optical probe beam—Radsensor: Progress on development for imaging applications

Mark E. Lowry, Corey V. Bennett, Stephen P. Vernon, Richard Stewart, Rebecca J. Welty, John Heebner, Otto L. Landen, and Perry M. Bell

Rev. Sci. Instrum. 75, 3995 (2004); http://dx.doi.org/10.1063/1.1790055 (3 pages) | Cited 5 times

Online Publication Date: 12 October 2004

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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.
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42.79.Pw Imaging detectors and sensors
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
29.40.-n Radiation detectors
07.85.-m X- and γ-ray instruments
42.65.-k Nonlinear optics

Preparation and characterization of pixelated phosphor screens for high-resolution linear imaging in the vacuum ultraviolet and x-ray ranges

L. Rodríguez-Barquero, B. Zurro, P. Martin, K. J. McCarthy, and A. Baciero

Rev. Sci. Instrum. 75, 3998 (2004); http://dx.doi.org/10.1063/1.1787937 (3 pages)

Online Publication Date: 12 October 2004

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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.
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07.07.Hj Display and recording equipment, oscilloscopes, TV cameras, etc.
42.79.Pw Imaging detectors and sensors

Image plates as x-ray detectors in plasma physics experiments

S. G. Gales and C. D. Bentley

Rev. Sci. Instrum. 75, 4001 (2004); http://dx.doi.org/10.1063/1.1789256 (3 pages) | Cited 20 times

Online Publication Date: 12 October 2004

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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.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.70.La X-ray and γ-ray measurements
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