bluuebunny/crossref_metadata_2025 huggingface dataset:
Conceptual design of the charge exchange recombination spectroscopy diagnostic for ITER
Authors: Tugarinov S. , Krasilnikov A. , Dokouka V. , Khayrutdinov R. , Beigman I. , Tolstikhina I. , Vainshtein L. , von Hellermann M. , Malaquias A.
Published: March 2003

Active charge exchange recombination spectroscopy (CXRS) is used in most of the present fusion experiments as a proven tool for local measurements of the main ions in the plasma [R. Isler, Plasma Phys. Controlled Fusion 36, 171 (1994)]. A comprehensive diagnostic coverage of intrinsic and injected impurities is essential for any self-consistent plasma simulation and prediction of plasma performance. In particular, for the assessment of local helium ash densities [M. von Hellermann et al., Plasma Phys. Controlled Fusion 35, 799 (1993)], CXRS will play a key role for future fusion devices such as ITER. However, it should be emphasized that any helium ash analysis is only viable in a fully diagnosed plasma, that is, all other ions need to be measured as well. Two fundamental limitations are considered in the following assessment. First is the detectability of a weak CX signal against a strong background of plasma continuum radiation. A second, equally important requirement is the accuracy with which local neutral beam densities can be established in order to derive absolute ion densities from the extracted active CX signals. The second problem can be approached either by experimental data from beam emission spectroscopy (M. von Hellerman et al., Conference on Advanced Diagnostics for Magnetic and Inertial Fusion Varenna, Sept. 2001), or calculated by beam attenuation codes using electron and both bulk and impurity ion density profiles. This report includes a description of the CXRS measurement concept, the experimental and optical scheme of measurements for ITER (S. Tugarinov et al., Conference on Advanced Diagnostics for Magnetic and Inertial Fusion, Varenna, Sept. 2001), and the main conclusions and recommendation that we have made from the results of a signal-to-noise (SN) value calculations. The main conclusions are the following: CXRS at ITER appears to be a viable diagnostic tool and the projected diagnostic neutral beam will provide adequate SN ratios for spectral analysis. A comprehensive approach to helium ash measurement, making use of a simultaneous measurement of the main low-Z impurities, will considerably increase the overall data consistency and will also significantly reduce the statistical error of each single impurity density determination. Three periscopes located in upper port for the intrinsic impurity measurements will also provide ion temperature, plasma rotation, and deuteron density profiles.
JET experimental program and related diagnostics developments
Authors: Orsitto Francesco P. , Sanchez Joaquin ,   Contributors to EFDA-Jet Workprogramme
Published: March 2003

New diagnostic measurements have driven important steps forward in the JET experimental program in areas related to H-mode, advanced tokamak physics, and divertor erosion-redeposition phenomena. As a consequence, a program of diagnostics developments has been started. The first part of the article describes recent diagnostic measurements, with special emphasis on the motional stark effect observation of the currentless core, the poloidal velocity measurements by charge exchange recombination spectroscopy, the edge profile measurements with light detecting and ranging Thomson scattering and Li-beam emission, the real-time control of the q profile, and the first results from the quartz microbalance on divertor carbon deposition. The second part describes the program of diagnostics developments on JET that is being prepared for commissioning in 2004. Special emphasis will be devoted to the new high-resolution Thomson scattering, the Li-beam polarimetry system (still under assessment), ITER-relevant activity, like the mirror test program (as a support activity for the ITER diagnostics), and the effort on fusion products diagnostics: neutron spectroscopy and lost alpha collectors.
Development of a charge exchange recombination spectroscopy method for determination of ion temperature from Hα line broadening in the Hanbit mirror device
Authors: Yoo S. J. , Yang H. L. , Na H. K.
Published: March 2003

Ion temperatures can be determined from Hα line broadening measured by charge exchange recombination spectroscopy on Hanbit, a mirror device. Since the Hα line emission from hydrogen atoms in plasma edges is much larger than that of the charge exchange recombination emission of ions, the line shape of the latter is submerged into the former when measured by an array detector such as a CCD detector. Thus, a notching filter in front of a detector is needed to block out the central region of the emission line. An optical fiber array detector, which works as a notching filter as well as an array detector, has been developed, since the transmission characteristics of commercial notching filter are not suitable for the line-broadening measurements. The design concept of the optical fiber array detector is described, and the feasibility to determine ion temperatures from the Hα line broadening measurements is estimated.
Polarization spectroscopic imaging of charge separation in neutral gas-confined laser-produced plasmas
Authors: Kim Y. W. , Lee H.-D.
Published: March 2003

Weakly nonideal plasmas can be produced by a high power-density laser incident on a metallic target. We have shown that plasma nonideality of the laser-produced plasma (LPP) plume may be further increased when its free expansion is suppressed by immersing the target in a dense neutral gas. As the gas density is further increased, the LPP plume develops interfacial instability, which turns out to be of Rayleigh–Taylor nature. We have developed a diagnostic method to help visualize development of local electric fields due to charge separation in the regions of significant density and temperature gradients. A bandpassed view of the LPP plume is split into two mutually exclusively polarized images, which are then captured simultaneously by a single, gated, intensified CCD detector. Representative results are presented of the two-dimensional distribution of the degree of polarization for a LPP plume of aluminum confined by low-density argon.
Stovepipe optical setup at the Livermore electron beam ion trap
Authors: Träbert E. , Beiersdorfer P.
Published: March 2003

A fast light-collection system with optical filters for spectral selection has been set up at the Livermore electron-beam ion trap for monitoring highly charged ions by the time dependence of electric–dipole forbidden transitions in the visible spectrum. When switching between the electron and magnetic trapping mode, the system yields measurements of atomic lifetimes in the many-millisecond range. Moreover, the response is sensitive to the neutral particle density inside the trap volume, where no vacuum gauge reaches. Hence, measurements of transitions with well-established atomic lifetimes can be exploited for determining the neutral background particle density in the trap.
4.5- and 8-keV emission and absorption x-ray imaging using spherically bent quartz 203 and 211 crystals (invited)
Authors: Koch J. A. , Aglitskiy Y. , Brown C. , Cowan T. , Freeman R. , Hatchett S. , Holland G. , Key M. , MacKinnon A. , Seely J. , Snavely R. , Stephens R.
Published: March 2003

We have used spherically-bent quartz 203 and 211 crystals to image 4.5- and 8-keV sources in both emission and absorption geometries. These imaging systems are straightforward to align, provide high throughput, and can provide high spatial resolution over large fields of view. We discuss the imaging geometry and alignment strategies, and we present experimental results we have obtained from a 1-ns-duration, multikilojoule laser facility and from sub-ps-duration, ultrahigh-intensity laser facilities. Our successful applications suggest that high-quality, spherically-bent quartz crystals may be used to image at many different x-ray energies due to the numerous diffraction planes available from quartz. This range of usable x-ray energies increases the number of applications that might benefit from high-resolution, high-brightness, monochromatic x-ray imaging using bent crystals.
High-speed tangentially viewing soft x-ray camera to study magnetohydrodynamic fluctuations in toroidally confined plasmas (invited)
Authors: Ohdachi S. , Toi K. ,   LHD Experimental Group, Fuchs G. , von Goeler S. , Yamamoto S.
Published: March 2003

A high-speed tangentially viewing soft x-ray camera system has been developed and installed on the large helical device (LHD) using a video camera with a maximum framing rate of 13.5 kHz. Low-frequency activities, for example, structures with toroidal/poloidal mode number n/m=1/2, are directly detected with this system.
Simultaneous measurements of temporally and spatially resolved ion and electron temperatures using a semiconductor detector array in a single plasma discharge
Authors: Numakura T. , Cho T. , Minami R. , Kohagura J. , Hirata M. , Nakashima Y. , Yatsu K. , Miyoshi S.
Published: March 2003

A method is proposed for obtaining radial profiles of both plasma ion (Ti) and electron temperatures (Te) simultaneously using a semiconductor detector. This method for semiconductor Ti diagnostics is proposed on the basis of an alternative “positive” use of a semiconductor “dead layer” as an energy-analysis filter. Filtering dependence of charge-exchange (cx) neutral particles from plasmas on the thickness on the order of a nanometer-thick SiO2 layer is used for analyzing Ti in the range from hundreds to thousands of electron volts. Even under the circumstances of simultaneous incidence of such particles and x rays along the same lines of sight of a semiconductor detector array, it is found that the different dependence on their penetration lengths and deposition depths in semiconductor materials makes it possible to distinguish cx neutral particles for Ti diagnostics from x rays for Te diagnostics. Experimental verification of this concept of the simultaneous Ti and Te diagnostics is carried out in the GAMMA 10 tandem mirror by the use of a matrix-type semiconductor detector. The detector is characterized in terms of compact formation of six rows with different thicknesses of thin dead layers (SiO2) on its surface. Each row has seven channels (columns) for measuring radiation profiles in the radial direction of plasmas so as to make tomographic reconstructions for attaining the actual emissivity profiles in the plasmas. These various SiO2 layers are proposed to be applied as “unbreakable ultrathin radiation-absorption filters” having various thicknesses to distinguish x rays from neutral particles simultaneously.
Further development of a single line of sight x-ray framing camera
Authors: Holder J. P. , Piston K. W. , Bradley D. K. , Bell P. M. , Dymoke-Bradshaw A. K. L. , Hares J. D.
Published: March 2003

High-speed 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 MCP camera. A hybrid camera combining image tube and microstrip MCP technology has been under development at Lawrence Livermore National Laboratory in collaboration with the University of Rochester, Laboratory for Laser Energetics, and KENTECH Instruments. Characterization measurements using laser generated plasma x rays are presented. Simulations as a guide to improving this hybrid camera are also presented.
X-ray imaging diagnostics for laser-driven hydrodynamic instability experiments
Authors: Shiraga Hiroyuki , Azechi Hiroshi , Nakai Mitsuo , Shigemori Keisuke , Nishikino Masaharu , Sakaiya Tatsuhiro , Fujioka Shinsuke , Tamari Yohei , Yamanaka Tatsuhiko
Published: March 2003

Rayleigh–Taylor (RT) instability is one of the most important physical issues in the inertial confinement fusion research. The reduction of its growth rate due to laser-driven ablation, which is described by the modified Takabe formula, is of great importance for a precise understanding of the target physics. We have developed various diagnostic techniques for the measurement of the parameters appearing in the Takabe formula, such as the growth rate, the acceleration, the mass ablation rate, and the density structure including ablation density and density scalelength. Face-on and side-on x-ray backlighting were coupled with moire interferometry imaging, penumbral imaging, and Fresnel zoneplate imaging. All the physical parameters related to RT instability were measured experimentally, and compared with simulation results.
Side-on measurement of hydrodynamics of laser-driven plasmas with high space- and time-resolution x-ray imaging technique
Authors: Fujioka Shinsuke , Shiraga Hiroyuki , Nishikino Masaharu , Tamari Yohei , Shigemori Keisuke , Nakai Mitsuo , Azechi Hiroshi , Tanaka Kazuo A. , Yamanaka Tatsuhiko
Published: March 2003

We developed and improved high space- and time-resolution x-ray imaging techniques (3–6 μm, 100–200 ps). These techniques were coupled with side-on x-ray backlighting for observing hydrodynamics of directly laser-driven polystyrene plasmas. As a high sensitive x-ray image detector, Imaging Plate was introduced to penumbral imaging technique [S. Fujioka et al., Rev. Sci. Instrum. 73, 2588 (2002)]. Noise in penumbral images was reduced by this improvement, and high quality density profiles of plasmas were obtained. A large-magnification slit camera, whose slit width and magnification were 4 μm and 82.8, was coupled with an x-ray streak camera (XSC). Due to the advantage of the large-magnification, high spatial resolution of 5.8 μm was found even with an XSC, the photocathode of which usually has low spatial resolution. These techniques are useful in understanding of hydrodynamic instability in inertial confinement fusion.
Monochromatic x-ray backlighting of wire-array z-pinch plasmas using spherically bent quartz crystals
Authors: Sinars D. B. , Cuneo M. E. , Bennett G. R. , Wenger D. F. , Ruggles L. E. , Vargas M. F. , Porter J. L. , Adams R. G. , Johnson D. W. , Keller K. L. , Rambo P. K. , Rovang D. C. , Seamen H. , Simpson W. W. , Smith I. C. , Speas S. C.
Published: March 2003

X-ray backlighting systems are being developed to diagnose z-pinch, inertial confinement fusion capsule, and complex hydrodynamics experiments on the 20 MA Sandia Z machine. The x-ray backlighter source is a laser-produced plasma created using the Z-Beamlet laser, a 2 TW, 2 kJ Nd:glass laser recently constructed at Sandia. As an alternative to point-projection radiography, we are investigating a different geometry [S. A. Pikuz et al., Rev. Sci. Instrum. 68, 740 (1997)] that uses spherically bent crystal mirrors to simultaneously obtain high spatial resolution and a narrow spectral bandwidth. Backlighting systems using the Si Heα line (1.865 keV) and the Mn Heα line (6.15 keV) are discussed. These systems are capable of spatial resolutions in the 5–10 μm range, a field of view as large as 5 mm by 20 mm, and a spectral bandwidth comparable to the width of the emission line used for backlighting.
Measurements of 4–10 keV x-ray production with the Z-Beamlet laser
Authors: Ruggles L. E. , Porter J. L. , Rambo P. K. , Simpson W. W. , Vargas M. F. , Bennett G. R. , Smith I. C.
Published: March 2003

In order to characterize the current backlighting capability of Sandia’s Z-Beamlet laser (ZBL) over a range of high photon energies, we measured the x-ray conversion efficiency of the focused 527 nm ZBL beam into 4–10 keV x rays from He-like emission of the elements Sc through Ge (excluding Ga). The measurements approximated ZBL’s nominal backlighting geometry and laser performance at Sandia’s Z soft x-ray facility by irradiating planar foil targets several microns thick rotated 30° to the laser beam axis with a 600 ps pulse at 1 TW. The focal spot diameter was about 150 μm. This study includes measurements of the K-shell x-ray spectrum, x-ray power, and x-ray spot size with an array of filtered high-bandwidth silicon diodes, a convex LiF crystal spectrometer, step wedge filtered x-ray film, and a filtered x-ray pinhole camera. We found agreement with previous work for comparable laser parameters and recorded decreasing conversion efficiency versus atomic number and He-like photon energy.
Two-dimensional imaging of radiation temperature in dynamic Hohlraums on Z
Authors: Nash T. J. , Chandler G. A. , Leeper R. J. , McGurn J. , Jobe D. , Torres J. , Seamen J. , Lazier S. , Gilliland T. , Nielsen D. , Stygar B. , Deeney C. , Smelser R. , Moore T. , Pyle J. , LePell P. D. , Coverdale C. A. , Bailey J. E.
Published: March 2003

We present a technique for experimentally measuring two-dimensional radiation temperatures in dynamic Hohlraums on Z. In principle the technique can be applied to any radiation source. Total radiated power from the source is measured by normalizing the area under an x-ray diode signal to energy yield measured by a bolometer. The radiated power as a function of time, which is just the normalized x-ray diode signal, can then be used to normalize gated microchannel plate x-ray pinhole camera images. The procedure is most accurate when the gated x-ray pinhole camera has the same filter as the x-ray diode and when the filter is transmissive near the peak of the Planckian radiation temperature being measured. We present results for two-dimensional radiation temperatures as a function of time for dynamic Hohlraum experiments on Z. In these experiments a z pinch consisting of nested tungsten wire arrays driven by the 20 MA, 100 ns Z accelerator implodes onto cylindrical foam located on axis. X-ray diodes and bolometers located along the axis measure the power radiated along the pinch axis. Pinhole-imaged time-resolved microchannel plate framing cameras located on axis measure the spatial distribution of this radiation. Results from the analysis of many shots taken on Z show that a symmetrical strongly radiating shock wave is launched in the foam. The shock wave stagnates to less than 1 mm diameter with radiation temperatures exceeding 300 eV. Applications for this source include driving inertial confinement fusion capsules within the dynamic Hohlraum and weapons physics experiments that use the dynamic Hohlraum as a radiation source.
Dynamic range measurements on streak image tubes with internal and external microchannel plate image amplification
Authors: Eagleton R. T. , James S. F.
Published: March 2003

Electron–optic streak chronoscopy is an important diagnostic technique for the diagnosis of laser driven hydrodynamic and radiative phenomenon. To minimize the undesirable effects of excessive space charge in streak image tubes an image amplification stage is often used. Microchannel plate (MCP) electron amplifiers are frequently employed for this purpose. These devices may be utilized in two ways: either to amplify light from the streak image tube phosphor screen by externally coupling a proximity-focus MCP wafer intensifier tube, or by insertion inside the streak tube body to amplify the streaked electrons directly. To investigate how the operating regime of the MCP influences the dynamic range of the streak camera system, dynamic range measurements have been made on two identical streak image tubes (English Electric Valve Co. type P8307) one incorporating an internal MCP, the other, externally coupled image amplification. Dynamic range measurements have been made for 30 ps full width half maximum (FWHM) and 100 ps (FWHM) laser pulses and comparison made to a previous study of this type of image tube. For internal MCP and externally coupled intensifier camera systems of equal radiant gain the dynamic range for the pulse widths studied was found to be comparable.
Investigation into the aging effect of experiment use on x-ray diode photocathodes, and the calibration of p-i-n silicon diodes
Authors: Bentley C. D. , Slark G. , Gales S. G.
Published: March 2003

Vacuum x-ray diode photocathodes are commonly employed in temperature diagnostic instruments on the Helen laser at AWE Aldermaston, UK. The photocathodes are used in a Dante filtered x-ray diode spectrometer and in conjunction with a compound x-ray filter to yield a quasi-flat response detector the flat response diode. Investigations carried out in 1999 indicated that the response of these photocathodes diminished over time. Following these investigations [C. D. Bentley and A. C. Simmons, Rev. Sci. Instrum. 72, 1202 (2001)] a number of refurbished photocathodes were produced and the effect of their use in the above instruments investigated. Initial characterization was carried out using the hot cathode Excalibur soft x-ray calibration facility at AWE and at the National Synchrotron Light Source (NSLS) at Brookhaven. Diode sensitivity was remeasured 14 months later again at Brookhaven and at AWE. These results are compared with the earlier study and some degradation in sensitivity is noted. Possible reasons for this change are discussed. Additionally in the latest study the sensitivity of a number of silicon p-i-n diodes was measured at the NSLS and at AWE. The different detector characteristics demand different approaches and these are discussed. Sensitivity results are presented and compared.
Hard x-ray imaging using free-standing spherically bent crystals
Authors: Faenov A. Ya. , Pikuz T. A. , Avrutin V. , Izyumskaya N. , Shabelnikov L. , Shulakov E. , Kyrala G. A.
Published: March 2003

We report the attempt to prepare free-standing spherically bent Si crystals with radii of curvature as small as 30 cm and large uniform working areas up to several cm2. We also report on the use of these crystals in the Laue geometry to record two-dimensional high spatial resolution x-ray images in the hard x-ray region (λ∼0.5 Å). We discuss how these bent crystals were made, and show how these spherically bent crystals were used in the Laue geometry to obtain hard x-ray images of test objects at the silver K-alpha wavelength at two different magnifications. The mean spatial resolution of this x-ray imaging scheme, determined from the recorded image traces, was found to be better than 10 μm over a field of view of 1.5×1.5 mm. Contributions of possible focusing mechanisms (dynamical and polychromatic) are discussed. Additional theoretical understanding of how such a scheme is working is needed.
Bent Bragg–Fresnel lenses for x-ray imaging diagnostics
Authors: Aglitskiy Y. , Obenschain S. , Yunkin V.
Published: March 2003

Bent Bragg–Fresnel lenses were tested under conditions relevant to the NRL Nike Laser monochromatic backlighting experiments. This hybrid two-dimensional (2D) x-ray imaging diagnostics incorporates high resolution and 1D focusing of the linear Fresnel structure as well as monochromatic and 1D focusing nature of cylindrically bent Bragg crystals. Lenses made of silicon (111) and quartz (101_1 and 101_0) with focal length of 125 mm were tested on our x-ray test bench. First images of backlit targets were obtained. Experimental issues, possible applications and future developments including extension of these diagnostics to the harder x rays (>10 keV), are discussed.
Tomographic resolution of uniformly redundant arrays coded aperture
Authors: Chen Yen-Wei , Kishimoto Keisaku
Published: March 2003

Uniformly redundant arrays (URA) is one coded aperture imaging technique. Since the URA camera can view the object with a large solid angle, it can provide some tomographic resolution for a three-dimensional object. The performance of a URA camera for three-dimensional imaging has been investigated in detail by computer simulations. The tomographic (depth) resolution of the camera has also been estimated quantitatively as a full width at half maximum of a depth point spread function, which is obtained by reconstructing a point source at different depths. We also show that the tomographic resolution can be improved by the use of small pinholes for URA aperture and fine sampling for decoding.
Heuristic reconstruction of three-dimensional laser-imploded targets from x-ray pinhole images
Authors: Chen Yen-Wei , Kohatsu Tetsuya , Nozaki Shinya , Kodama Ryosuke
Published: March 2003

Implosion symmetry has long been an important issue in inertial confinement fusion (ICF) research. In order to evaluate the implosion symmetry of ICF, a computer tomography (CT) technique developed for medical diagnostics is traditionally employed. This attempt was made to reconstruct the three-dimensional (3D) compressed core from several x-ray pinhole images. Unfortunately the reconstructed result is often constrained by the number of available pinhole images and is affected by the noise in them. In this article, we propose a heuristic method for 3D image reconstruction from a limited number of pinhole images and in the presence of noise. We represent the 3D compressed core as a summation of 3D Gaussian functions. The 3D image can be reconstructed by estimating the width and height of each Gaussian function. One heuristic method, simulated annealing, is used. The technique has been successfully applied to real laser–plasma experiments for the reconstruction of 3D compressed core utilizing only three x-ray pinhole images.
Blind reconstruction of x-ray penumbral images based on a heuristic method
Authors: Nozaki Shinya , Chen Yen-Wei , Nakao Zensho , Kodama Ryosuke , Shiraga Hiroyuki
Published: March 2003

We apply a heuristic method to blind reconstruction of noisy penumbral images. Penumbral imaging is a powerful technique for imaging with penetrating radiation such as neutrons and hard x ray with a high spatial resolution. Limitations of the conventional reconstruction method are that it will introduce a significant distortion if the penumbral image is distorted by the noise, and that the point spread function (PSF) must be exactly known beforehand. The proposed method can estimate both the source image and the diameter of the PSF from only the penumbral image. The efficacy of the method is demonstrated by computer simulation and real laser plasma experiments.
Application of a refractive bubbles-in-capillary x-ray lens to X pinch experiments
Authors: Pikuz S. A. , Asadchikov V. E. , Chandler K. M. , Hammer D. A. , Dudchik Yu. I. , Kolchevsky N. N. , Komarov F. F. , Mitchell M. D. , Popov A. V. , Shelkovenko T. A. , Senin R. A. , Suloev I. A. , Vinogradov A. V.
Published: March 2003

A new type of x-ray refractive lens, the refractive bubbles-in-capillary lens (RBC lens), for plasma diagnostics is presented. The lens consists of a glass capillary filled with a large number of biconcave microlenses. The fabrication technique for the lens is described. It is shown that the microlenses have a spherical shape and can focus x-ray radiation with photon energies E>4 keV. Ray-tracing and analytical calculations of lens properties have been performed and have predicted high efficiency and good spatial resolution for RBC lenses. Real lenses were tested using Cr Kα x-ray radiation (λ=2.29 Å), and spatial resolution of about 10 μm was obtained. In plasma experiments, x-ray radiation from a Ti X pinch (λ=2.62 Å) was focused by a lens with 35 bubbles in a 100 μm diam capillary (focal length of about 8 cm) to a spot with diameter less than 6 μm. The shape of the hot plasma could be seen. Possibilities for RBC lens applications to plasma measurements are discussed.
High-throughput, high-resolution Kirkpatrick–Baez microscope for advanced streaked imaging of ICF experiments on OMEGA
Authors: Gotchev O. V. , Jaanimagi P. A. , Knauer J. P. , Marshall F. J. , Meyerhofer D. D. , Bassett N. L. , Oliver J. B.
Published: March 2003

A Kirkpatrick-Baez (KB) x-ray microscope with a streak camera at the image plane is being developed for OMEGA to increase the sensitivity and spatial resolution in planar direct-drive hydrodynamic stability experiments. A four-mirror, iridium-coated, KB optic has been designed to couple to the high-current PJX streak tube. This design, using a bilayer Ir/Cr coating and a relatively high grazing angle of 2.1°, provides up to three-orders-of-magnitude-higher throughput than a pinhole array coupled to an x-ray framing camera. The angle of reflection has been calculated to maximize the solid angle and the coating reflectivity. The spectral window, peaked at 1.56 keV with a FWHM of about 400 eV, eliminates the contrast impairment caused by the high-energy x-ray emission of the backlighter. Calculations show that the device is capable of registering 2-μm spatial features over a field of view of 120 μm. A series of sputtering and e-beam evaporation deposition tests have been performed on superpolished (<0.1 nm rms) test plates to determine the density and smoothness of the film. Detailed ray tracing has been used to fully characterize and optimize the optical parameters of the system, including diffraction response. Its resolving capabilities and throughput have been confirmed by several test experiments.
Optimizing area-backlighter performance in a difficult geometry
Authors: Kyrala George A. , Klare Ken , Workman Jonathan
Published: March 2003

It is relatively easy to predict backlighter performance when few beams intercept a simple flat target and backlight an optically thin object. However, when faced with a thick target, noncooperating geometry, and multiple objects in the path of the laser beams, it becomes a challenge to find the optimum arrangement to satisfy all these conditions. On Omega, we came up with a unique solution, using more than one coaxial foil to optimize, not only the pointing and focusing, but also the uniformity and flux of x rays on the target using as many of the laser beams as possible. We will describe the method used, the geometry used, and compare the prediction and the measurement.
Time and spatially resolved measurements of x-ray burnthrough and re-emission in Au and Au:Dy:Nd foils
Authors: Olson R. E. , Leeper R. J. , Dropinski S. C. , Mix L. P. , Rochau G. A. , Glenzer S. H. , Jones O. S. , Suter L. J. , Kaae J. L. , Shearer C. H. , Smith J. N.
Published: March 2003

In experiments at the Omega laser facility, x-ray framing and streak cameras were used to explore a technique for simultaneously measuring the relative x-ray burnthrough and re-emission properties of pure Au and high-Z mixture “cocktail” foils exposed to a Hohlraum radiation field. For the Au:Dy:Nd cocktail used in these preliminary experiments, the burnthrough measurements indicated a cocktail opacity ∼1.5 times that of pure Au. The x-ray re-emission fluxes from the cocktail and Au appeared to be equivalent. In the future, we propose to use this experimental arrangement to compare the relative x-ray burnthrough and re-emission properties of other potential wall materials proposed for use in National Ignition Facility Hohlraums.
Fast x-ray imaging of the National Spherical Tokamak Experiment plasma with a micropattern gas detector based on gas electron multiplier amplifier
Authors: Pacella D. , Pizzicaroli G. , Leigheb M. , Bellazzini R. , Brez A. , Finkenthal M. , Stutman D. , Blagojevic B. , Vero R. , Kaita R. , Roquemore A. L. , Johnson D.
Published: March 2003

An innovative fast system for x-ray imaging has been developed at ENEA-Frascati, Italy, in collaboration with INFN-Pisa, Italy. It is based on a pinhole camera coupled to a micropattern gas detector (MPGD) having a gas electron multiplier (GEM) as amplifying stage. This detector (2.5 cm×2.5 cm active area) is equipped with a two dimensional readout printed circuit board with 144 pixels (12×12). It is able to get x-ray images of the plasma at very high framing rate (up to 100 kHz) in a selectable x-ray energy range, with different magnifications or views of the plasma. The system has been tested successfully on the Frascati Tokamak Upgrade (FTU) during Summer 2001, with a one-dimensional perpendicular view of the plasma. In collaboration with ENEA, the Johns Hopkins University (JHU) and Princeton Plasma Physics (PPPL), this system has been setup and calibrated in the x-ray energy range 3–8 keV and it has been installed, with a tangential view, on the NSTX experiment at PPPL. Time resolved, two-dimensional x-ray images of the NSTX plasma core will be presented, with different magnifications and different orientations of the optical axis of the x-ray pinhole camera. Fast acquisitions, performed up to 50 kHz of framing rate, allow the study of the plasma evolution and the 2D shaping during MHD activity.
Compact soft x-ray multichord camera: Design and initial operation
Authors: Franz P. , Gadani G. , Pasqualotto R. , Marrelli L. , Martin P. , Spizzo G. , Brunsell P. , Chapman B. E. , Paganucci F. , Rossetti P. , Xiao C.
Published: March 2003

A compact and low cost diagnostic for spatially resolved measurements of soft x-ray or total radiation emission has been designed and realized to be flexibly applied to different plasma physics experiments. Its reduced size (outer diameter=35 mm) makes it suited to a variety of devices. The line integrated emissivity (brightness) has been measured along up to 20 lines of sight, using an array of miniaturized silicon photodiodes. Preliminary prototypes of the diagnostic have been installed in the Madison Symmetric Torus reversed field pinch (RFP) device at University of Wisconsin and in the EXTRAP T2 RFP device at the Royal Institute of Technology in Stockholm. Application of the diagnostic to a gas-fed (argon, helium) magnetoplasma dynamic thruster (MPDT) with an external magnetic field will also be discussed.
Soft-x-ray emission, plasma equilibrium, and fluctuation studies on Madison Symmetric Torus
Authors: Xiao C. , Franz P. , Chapman B. E. , Craig D. , Ding W. X. , Gadani G. , Marrelli L. , Martin P. , Pasqualotto R. , Spizzo G. , Sarff J. S. , Terry S. D.
Published: March 2003

A miniature multichord soft-x-ray detection system has been installed on the Madison Symmetric Torus (MST) reversed-field pinch to study the plasma equilibrium and fluctuation properties of standard- and improved-confinement discharges. Because of the relatively flat MST density and temperature profiles, the spatial resolution is relatively poor along the line of sight. However, the system can resolve line-integrated-emissivity fluctuations which are strongly correlated with the rotating m=1 global magnetic fluctuations as well as heat pulse propagation with edge-resonant m=0 bursts during improved-confinement discharges. Abel inversion based on Park’s inversion techniques indicates peaking of the equilibrium emissivity profile following sawtooth events during standard discharges and profile flattening after m=0 bursts during improved-confinement discharges.
Tangential soft x-ray imaging for shape and current profile measurements
Authors: Tritz K. , Fonck R. , Reinke M. , Winz G.
Published: March 2003

Flux surface shape information is imaged with an x-ray pinhole camera and used as a constraint for reconstruction of the plasma current and q profiles of plasmas in the low-aspect ratio PEGASUS Toroidal Experiment. The camera system is comprised of a 30 cm Gd2O2S:Pr scintillator plate whose x-ray incident side is lens coupled to a microchannel plate (MCP) image intensifier. A slow-scan charge coupled device (CCD) camera is then lens coupled to the MCP for a time resolution of ∼1 ms. This system will provide photon noise <1% with a 1 ms integration time for intensities typical of Pegasus plasmas. Installation of a 0.2 μm nickel x-ray filter provides necessary contrast between the hot interior and cooler plasma edge region. The scintillator system is compared to direct x-ray illumination of a CCD sensor. Direct illumination uses a custom chip mask and frame transfer for exposure control and sampling at multiple time points. Increased sensitivity of direct illumination imaging system will raise the signal to noise ratio allowing for shorter integration times.
Analysis of Ti K-shell emission produced from solid targets using nanosecond pulses on the TRIDENT laser facility
Authors: Workman J. , Lanier N. E. , Kyrala G. A.
Published: March 2003

Measurements of Ti He-like x-ray emission (4.75 keV) from solid targets irradiated with nanosecond pulses on the TRIDENT laser facility are examined. Relative x-ray emission and conversion efficiency was measured as a function of laser irradiance conditions using a crystal spectrometer and step-filtered charge coupled device and x-ray film. Data on the x-ray emission with and without random phase plates is presented. Difficulties and caveats in the diagnostic techniques are also presented. Analysis of step-filtered data suggests a high-energy x-ray tail.
Feasibility of fluorescence-based imaging of high-energy-density hydrodynamics experiments
Authors: Lanier N. E. , Barnes Cris W. , Perea R. , Steckle W.
Published: March 2003

Experiments conducted on the LANL Trident two-beam facility show the viability of fluorescence-based imaging as a diagnostic in high-energy-density (HED) hydrodynamics experiments. Passive fluorescence experiments using titanium-pumped scandium-oxide, or iron-pumped manganese-oxide, show that fluorescence emission can be produced at sufficient intensities to be useful. Dynamic experiments, designed to demonstrate particle tracking in time for particle imaging velocimetry (PIV), were marginally successful in that only very large particulates could be definitively observed. However, our results indicate that experiments conducted on facilities offering a greater energy would be less susceptible to the limitations confronted in this study and thus, significantly enhance the prospect of PIV as an effective diagnostic tool in HED experiments.
Backlighter predictive capability
Authors: Batha Steven H. , Barnes Cris W. , Christensen Cindy R.
Published: March 2003

Correctly predicting the intensity and spatial extent of an area backlighter is important in optimizing the design and analysis of a laser-based experiment. In this work, the spatial extent of an area backlighter is calculated using a view factor code to obtain the laser illumination pattern and then converting to x rays using the measured x-ray conversion efficiency. The view factor model can also be compared to a simple illumination calculation. The models were validated with experiments where five 1-ns-square OMEGA [Boehly et al., Opt. Commun. 133, 495 (1997)] laser beams containing a total of 1.85 kJ were directed onto Fe or Ti foils. The predicted emission size was compared to time-gated two-dimensional images of the Fe emission region or to time-integrated images from both Fe and Ti. The models correctly predict the spatial extent of the emitting region for the first hundred picoseconds. The emission region grows logarithmically with time during the laser pulse; eventually reaching a diameter that is 1.6 times the initial laser spot size. Folding the x-ray conversion efficiency into the calculated intensities allows prediction of backlighter brightness and structure that is useful in optimizing the experimental design.
X-mode pulsed radar reflectometer for density fluctuation measurements on LHD
Authors: Tokuzawa T. , Kawahata K. , Tanaka K. , Nagayama Y. ,   LHD Experimental Group, Kaneba T. , Ejiri A.
Published: March 2003

A four channel pulsed radar reflectometer system has been installed on the Large Helical Device (LHD). The complicated magnetic structure in LHD causes mode conversion and/or polarization rotation of the microwaves. Pulsed radar reflectometry is a suitable reflectometric technique, because it measures the delay time of the reflected wave, not the phase, and X-mode and O-mode polarized waves can be distinguished. By using X-mode operation of the pulsed radar reflectometer so that each pulse width is about 2 ns, and the repetition rate is up to 200 kHz, the critical density where the microwave is reflected is about 1×1016 m−3. Also it is found that the static natural island affects the X-mode reflectometric measurements.
Measurement of the plasma radial electric field by the motional Stark effect diagnostic on JET plasmas
Authors: Reyes Cortes S. , Hawkes N. C. , Lotte P. , Fenzi C. , Stratton B. C. , Hobirk J. , De Angelis R. , Orsitto F. , Varandas C. A. F. ,   Contributors to the EFDA-JET work program
Published: March 2003

The radial electric field gradient or the E×B flow shear has been pointed out as the underlying mechanism for turbulence suppression, responsible for an internal transport barrier formation in advanced tokamak scenarios. A comprehensive study on these subjects requires a direct measurement of the plasma radial electric field Er. The poloidal component of the magnetic field is assessed by the motional Stark effect (MSE) polarimeter, which is currently a standard diagnostic in fusion devices, allowing a local and nonperturbative measurement of the magnetic pitch angle. A precise measure to the state of polarization of the Stark components gives the information on the direction of the magnetic field. Due to the particular orientation of the Lorentz component, that is nearly perpendicular to Er, the MSE diagnostic is very sensitive to the plasma intrinsic radial electric field. This article describes a technique to measure Er involving the change of the polarization angle of the MSE emission, by using two beam injectors at different energies, firing sequentially. Experimental results for the low Er case, i.e., with very little plasma rotation, showing the ability of the MSE to perform this measurement, will be presented. This is the first time that evidence of a direct measurement of the plasma Er is reported from the Joint European Torus.
Combined visible and infrared Thomson scattering on the MAST experiment
Authors: Walsh M. J. , Arends E. R. , Carolan P. G. , Dunstan M. R. , Forrest M. J. , Nielsen S. K. , O’Gorman R.
Published: March 2003

A dual laser Thomson scattering system is implemented in the Mega Amp Spherical Tokamak (MAST). The complementary features of each approach are exploited. One system is ideally suited to measuring detailed profile behavior across the plasma while the other is ideally suited though not exclusively to studying fast changing events and general characterization of the plasma. Both systems are designed to be flexible and allow future expansion to suit the needs of a changing physics program.
Spatial resolved high-energy particle diagnostic system using time-of-flight neutral particle analyzer in large helical device
Authors: Ozaki Tetsuo , Murakami Sadayoshi , Goncharov Pavel , Watanabe Tsuguhiro , Sudo Shigeru , Narihara Kazumichi , Tanaka Kenji , Kubo Shin , Simozuma Takashi , Idei Hiroshi , Oka Yoshihide , Osakabe Masaki , Takeiri Yasuhiko , Tsumori Katsuyoshi , Ida Katsumi , Shoji Mamoru , Nakanishi Hideya , Sasao Mamiko , Kaneko Osamu , Kawahata Kazuo , Nakamura Yukio , Ohyabu Nobuyoshi , Motojima Osamu ,   G1/G2 Experimental Group
Published: March 2003

The time-of-flight-type neutral particle analyzer has an ability of horizontal scanning from 40 to 100° of the pitch angle. The information from the spatially resolved energy spectrum gives not only the ion temperature but also the information of the particle confinement and the electric field in plasmas. We have been studying the energy distributions at various magnetic configurations in the neutral beam injection (NBI) plasma. The spatially resolved energy spectra can be observed during long discharges of the NBI plasma by continuous scanning of the neutral particle analyzer. The shape of spectra is almost similar from 44° to 53°. However, the spectra from 55° are strongly varied. They reflect the injection pitch angle of the beam. The pitch angle scanning experiment during the long discharge of NBI plasma has also been made under the reversal of the magnetic field direction. NBI2 becomes counter injected with the reversal. We can easily observe the difference between co- and counter injections of NBI. During the electron cyclotron heating in the low-density plasma for the formation of the internal thermal barrier, large neutral particle increase or decease can be observed. The degree of the increase/decrease depends on the energy and the density. The reason for the variation of the particle flux is that the orbit of the trapped particle changes due to the electric field formed by the strong electron cyclotron heating.
Double-sphere model in the enclosed cavity perturbation technique
Authors: Inoue Ryotaro , Kitano Haruhisa , Maeda Atsutaka
Published: March 2003

Electrical conductivity can be conveniently measured by the enclosed microwave cavity perturbation technique. We have investigated the double-sphere model, in which the exact solutions of the full Maxwell’s equations can be calculated analytically. Focusing on the complex frequency shift Δω̂/ω0 as a function of the filling factor for conducting or the insulating sample, we argue that Waldron’s perturbation formula, which has been considered fundamental in the cavity perturbation technique, cannot be applied beyond the depolarization regime, even when |Δω̂/ω0|≪1. Based on the exact solutions for a spherical sample, we obtain approximating formulas that are sufficiently accurate for both the filling factor appearing in the actual measurements and the wide range of conductivity values. We found that the effects of the induced fields just outside the sample must be taken into consideration.
Growth of fullerene-like carbon nitride thin solid films by reactive magnetron sputtering; role of low-energy ion irradiation in determining microstructure and mechanical properties
Authors: Neidhardt J. , Czigány Zs. , Brunell I. F. , Hultman L.
Published: March 2003

Fullerene-like (FL) carbon nitride (CNx) films were deposited on Si (100) substrates by dc reactive, unbalanced, magnetron sputtering in a N2/Ar mixture from a high-purity pyrolythic graphite cathode in a dual-magnetron system with coupled magnetic fields. The N2 fraction in the discharge gas (0%–100%) and substrate bias (−25 V; −40 V) was varied, while the total pressure (0.4 Pa) and substrate temperature (450 °C) was kept constant. The coupled configuration of the magnetrons resulted in a reduced ion flux density, leading to a much lower average energy per incorporated particle, due to a less focused plasma as compared to a single magnetron. This enabled the evolution of a pronounced FL microstructure. The nitrogen concentration in the films saturated rapidly at 14–18 at. %, as determined by elastic recoil analysis, with a minor dependence on the discharge conditions. No correlations were detected between the photoelectron N1s core level spectra and the different microstructures, as observed by high-resolution electron microscopy. A variety of distinct FL structures were obtained, ranging from structures with elongated and aligned nitrogen-containing graphitic sheets to disordered structures, however, not exclusively linked to the total N concentration in the films. The microstructure evolution has rather to be seen as in equilibrium between the two competing processes of adsorption and desorption of nitrogen-containing species at the substrate. This balance is shifted by the energy and number of arriving species as well as by the substrate temperature. The most exceptional structure, for lower N2 fractions, consists of well-aligned, multi-layered circular features (nano-onions) with an inner diameter of approximately 0.7 nm and successive shells at a distance of ∼0.35 nm up to a diameter of 5 nm. It is shown that the intrinsic stress formation is closely linked with the evolution and accommodation of the heavily bent fullerene-like sheets. The FL CNx structures define the mechanical response of the films as revealed by nano-indentation. The material is highly elastic and fracture tough, and has reasonable hardness and elastic modulus values. On a nano-structured level, it is inferred the CNx stores deformation energy elastically by compression of the interplanar lattice spacing and buckling of the sheets, while crosslinks between sheets prevent gliding. Increasing the bias voltage from −25 to −40 V multiplies hardness and modulus values, while keeping their high ratio of up to 0.2, due to a higher degree of cross-linking.