bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of charge coupled device vs film readouts for gated micro-channel plate cameras
Authors: Turner R. E. , Landen O. L. , Bradley D. K. , Alvarez S. S. , Bell P. M. , Costa R. , Moody J. D. , Lee D.
Published: February 2004

We have used a large format (4000×4000) high resolution (9 μm pixels) charge coupled device (CCD) to record images from the rear of a gated micro-channel plate (MCP) intensifier, and compared the results with conventional film recording. Measurements of linearity, dynamic range, dark noise, and distortion all show that the CCD is a superior replacement for film. Furthermore, its excellent registration allows for easy flat fielding, using data from a uniformly exposed MCP. As we increase the signal level to where the signal to noise is not dominated by photon counting statistics, we find that this flat fielding procedure produces a significant improvement in signal to noise. The small spatial scale of this noise has led to its identification as high spatial frequency variations in the MCP phosphor.
Three-dimensional fluctuation imaging diagnostic for TEXTOR (abstract)
Authors: Domier C. W. , Deng B. H. , Donn A. J. H. , Hsu P. L. , Luhmann N. C. , Mazzucato E. , Park H. K. , van de Pol M. J. , Wang J.
Published: February 2004

After more than 4 decades of fusion research, plasma transport in tokamaks remains an outstanding issue. The standard hypothesis, that the observed anomalous transport is caused by small scale turbulence, is consistent with experimental observations, but it is neither based on a self-consistent theory of plasma turbulence nor on an exhaustive set of turbulence measurements. One of the major obstacles to the development of a satisfactory anomalous transport theory is the inability of standard fluctuation diagnostics to provide the full spectrum of turbulent fluctuations. The result is a nearly complete reliance on numerical simulations. Unfortunately, in spite of the enormous capabilities of today’s computers, this is extremely unsatisfactory since any theory or simulation of plasma turbulence can only be driven by direct experimental observations. The first step in achieving such data was the highly successful UC Davis Electron Cyclotron Emission (ECE) Imaging system, which was first developed for use on the TEXT-U tokamak and later modified for use on the Rijnhuizen Tokamak Project tokamak.1 Here, correlation techniques are applied to spatially resolved second harmonic ECE signals to provide detailed information about the microturbulence associated with Te fluctuations. The present work extends this work by developing a similar technique for spatially resolved ne fluctuations via microwave imaging reflectometry. The result is a diagnostic capable of the simultaneous measurement of both Te and ne fluctuations (both turbulent and coherent) and profiles on toroidal devices such as tokamaks and stellarators. A 16 channel ECE imaging system has recently been installed on the Torus Experiment for Technology Oriented Research (TEXTOR) tokamak. A prototype millimeter wave imaging reflectometry system will be installed on TEXTOR in July 2000, which will operate in V band (50–75 GHz) and reflect from the X-mode cutoff. Data collected with this system will be utilized in the design of the full three- dimensional (3D) imaging system, which is scheduled for installation on TEXTOR in April 2001. System details and laboratory characterization results of the prototype reflectometric imaging system will be presented, along with a preliminary design for the full 3D system.
Diagnostic suite used for magnetohydrodynamics equilibrium reconstruction on the PEGASUS toroidal experiment (abstract)
Authors: Sontag A. C. , Garstka G. D. , Fonck R. J. , Schooff R. J. , Thorson T. A. , Tritz K. L.
Published: February 2004

Magnetic equilibrium reconstruction on the PEGASUS toroidal experiment is a crucial tool to determine macroscopic plasma parameters, such as geometry, li, βt, and qψ. These parameters are tightly coupled to the plasma shape due to the very high toroidicity in PEGASUS where A≈1.1–1.3. A systematic scan of model plasma parameters in a magnetic equilibrium code has been employed to determine an acceptable array of magnetic diagnostics for accurately characterizing the plasma equilibrium. The magnetic diagnostics used include a poloidal array of magnetic pickup coils and flux loops along with a Rogowski loop for the toroidal plasma current. A 270 GHz μ wave interferometer for line averaged density in conjunction with spectroscopic temperature estimates provide a central pressure constraint. Visible images of the plasma provide constraints on the plasma size and location. A one-dimensional SXR camera is being developed to provide a measurement of the magnetic axis location. A time evolving current filament model and wall flux loops are used to determine the induced currents flowing in the continuous, resistive vacuum vessel wall. The ability of the equilibrium reconstruction code to reproduce model equilibria using this diagnostic set provides a quantitative measure of the accuracy of these equilibrium reconstructions. A Monte Carlo analysis with Gaussian noise added to the model data tests the robustness of this technique. A comparison of the model equilibria with the reconstructions obtained using noisy data is shown.
Observations of radial wild cables in tokamak plasmas (abstract)
Authors: Kukushkin A. B. , Rantsev-Kartinov V. A.
Published: February 2004

The results of processing the plasma images with the help of the method of multilevel dynamical contrasting (MDC)1 are presented. The images are taken in visible light, with space resolution ∼100 μm and time resolution ∼10 μs, in various tokamaks (TM-2, T-4, T-6, and T-10). The presence of rigid-body filamentary structures is found. They are similar to those structures formerly found in a Z-pinch, whose long life was proven2 in tracing their dynamics. The reliability of results is supported by the rich statistics and considerable similarity of the structures in various facilities and regimes, as well as by the insensitivity of observed structuring to a specific way of imaging (strick camera, fast photography, etc.). Sometimes the structuring may be seen without MDC processing (in such cases, the MDC allows fine resolution of structuring). The most typical structure is a straight cylindrical block varying in length from few centimeters up to a diameter of plasma column. The diameter of such a block varies, respectively, from a few millimeters to several centimeters. The most attention is paid to radially directed filaments which, together with toroidal and poloidal filaments, form a network. Detailed analysis of individual cylindrical blocks of several centimeters in diameter revealed them to be a coaxial tubular structure with an inner rod (which may be of tubular form as well) of a few millimeters diameter. The similarity of the above structures to coaxial cables may appear to not be occasional: according to the hypothesis3 the elementary coaxial block of diameter not exceeding few millimeters, is a “wild cable” in which the propagating high-frequency (HF) electromagnetic wave produces a vacuum channel around the hypothetical microsolid skeleton2 and thus protects the skeleton from the ambient high-temperature plasma. An analysis of measurements of HF electric fields, both inside and outside the plasma column in tokamak T-10, reveals their reasonable agreement with predictions based on the hypothesis.3
Observations of radial wild cables in z-pinch plasma (abstract)
Authors: Kukushkin A. B. , Rantsev-Kartinov V. A.
Published: February 2004

The results of processing the z-pinch plasma images with the help of the method of multilevel dynamical contrasting (MDC)1(a),1(b) are presented. This method was earlier used for: (i) analyzing the filaments (and their networks) in a gaseous z-pinch1(a),1(c) and (ii) characterization of long-living filaments2 of the lifetime comparable with the entire duration of discharge. The original images were taken in visible light, with space resolution ∼100 μm and time resolution ∼2–60 ns. The long-life structures are found, which are assembled from straight cylindrical blocks varying in length from a few millimeters to a few centimeters. Such blocks are of various orientation in space, and often they form a common frame. The most important phenomenon is the presence of radial (with respect to z-pinch axis) filaments directed from the periphery to the core, up to the z-pinch axis. An analysis of the fine structure of the above cylindrical blocks of few millimeter diameter reveals them to be a coaxial structure with the diameter of an inner rod (which may be of tubular form) approximately smaller by an order of magnitude. A comparison is made with similar structures recently observed in tokamak plasmas.3(a) The reliability of the above results is supported by the rich statistics and considerable similarity of the structuring in various regimes, and insensitivity to specific way of imaging. Sometimes the structuring may be seen without MDC processing (in such cases, the MDC allow fine resolution of structuring). The experimental results are analyzed from the viewpoint of the hypothesis3 about “wild cables” in plasmas of high-current electric discharges. The correlation is found between the measured values of the high-frequency electric fields in z-pinch plasma and the values of the Miller force needed to sustain vacuum channels in the plasma which are the essential elements of the wild cable
Calibration facilities at Bechtel Nevada–Livermore operations (abstract)
Authors: Perry T. S. , Hargrove D. , Diamond C. , Piston K. , Sammons T. , Bell P. M.
Published: February 2004

Since moving to a new location in March of 1999, Bechtel Nevada–Livermore Operations has established a modern laboratory for the characterization of optical and x-ray diagnostics for high temperature plasmas. Some of the facilities include a short pulse laser facility, a streak tube production facility, a microchannel plate characterization laboratory, an optical streak camera calibration laboratory, and a charge coupled device calibration laboratory. Descriptions of the facilities will be presented as well as examples of data taken at the laboratory. Future upgrades to the facility will be discussed.
A direct electron bombarded charge coupled device for dynamic plasma imaging applications (abstract)
Authors: Weber F. , Celliers P. , Bell P. , Diamond C.
Published: February 2004

A variety of plasma physics experiments require the recording of continuous time history of x-ray emission. Many laboratories have developed x-ray streak camera technology in order to time resolve x-ray spectra or images produced by laser-driven plasma experiments. These cameras record x rays by converting photons to electrons, which in turn are focused and swept across an electron sensitive area detector as a function of time. X-ray photons impinging on a transmission type photocathode generate photoelectrons which are accelerated to energies between 10 and 20 keV and focused onto a phosphor screen. The light from the phosphor image may be intensified using a microchannel plate, and is usually optically coupled directly onto film or an optical charge coupled device. We have designed and built an x-ray sensitive streak camera readout where we replaced the microchannel plate based intensifier and film package with a modified charge coupled device area detector to directly absorb accelerated photoelectrons emitted from the cathode. This system has been integrated into the streak tube arrangement. We will present a set of system performance data, which have been obtained from both bench top experiments on a dc source and dynamic measurements at the Nova laser facility. X-ray images at various exposure times show better spatial resolution, improved signal to noise ratio, and higher dynamic range. Other advantages include instantaneous data readout, which enables fast postprocessing, and no increase in overall cost for an engineered system.
Advanced plasma diagnostics for investigation of physical processes in laser-irradiated foam targets (abstract)
Authors: Bugrov A. E. , Burdonsky I. N. , Gavrilov V. V. , Goltsov A. Yu. , Kondrashov V. N. , Kovalsky N. G. , Pergament M. I. , Petryakov V. M. , Sorokin A. A. , Yankovskii G. M. , Zhuzhukalo E. V.
Published: February 2004

Recently the low-density foam-like materials have been found to be very attractive for various applications in high energy-density physics. Irradiation of these materials by powerful laser pulses is a promising approach for plasma formation with parameters being of interest for inertial confinement fusion, x-ray lasers, modeling of astrophysical phenomena, etc. This article is devoted to development and application of diagnostic methods in experiments on irradiation of planar low-density (0.5–10 mg/cm3) porous targets with powerful laser pulses (1013–1014 W/cm2). To obtain reliable information on high-temperature dense plasma formation, plasma dynamics, and energy transfer in the target interior, we used a number of optical and x-ray diagnostics providing high spatial (∼10 μm) and temporal (∼10 ps) resolution. High-speed x-ray imaging, multiframe optical shadowgraphy, and interferometry, as well as scattered laser light spectroscopy at the fundamental frequency and its harmonics were used in each experiment. Only being used simultaneously these diagnostic methods provide the possibility of understanding the complicated physical processes inside laser irradiated foam-like materials. The possibilities of the diagnostic complex are illustrated by examples of obtained results and corresponding data analysis.
Operation of the ultrasoft x-ray system on NSTX (abstract)
Authors: Stutman D. , Iovea M. , Finkenthal M. , Kaita R. , Johnson D. , Roquemore L. , Roney P. ,   The NSTX Team
Published: February 2004

The ultrasoft x-ray imaging system on National Spherical Torus Experiment (NSTX) became operational and provided the first data in the filtered diode slow bow tie configuration. Using different band pass filters on each of three arrays allows an approximate spectroscopic estimate of the plasma impurity content, as well as of the electron temperature. Magnetohydrodynamics (MHD) activity from different plasma regions is also observed. The soft x-ray emission profiles are well behaved until an Internal Reconnection Event occurs. Examples of NSTX MHD phenomena seen in the ultrasoft x-ray emission under different operational regimes will be presented. From a technical point of view, we point out that the industrial PC based data acquisition system was not adversely affected by stray magnetic fields due to its close proximity to the NSTX device. Also, the surface barrier diodes withstood baking to 100 °C relatively well.
Neutron flux monitoring system for ITER-FEAT (abstract)
Authors: Kaschuck Yu. , Krasilnikov A. , Alekseyev A. , Amosov V. , Frunze V.
Published: February 2004

The concept of the neutron flux measurements for International Thermonuclear Experimental Reactor ITER-FEAT is discussed. In spite of the fact that ITER-FEAT has reduced fusion power with respect to ITER-FDR, the requirements for neutron flux monitors are similar—wide dynamic range (seven orders), good temporal resolution (1 ms), and high accuracy (10%). It is clear that fission chambers are the most suitable detectors for this application. However high neutron intensity of the fusion plasma and hard requirements lead to a more sophisticated detection system than the ordinary fission chamber. Another problem is an absolute calibration of the detectors. We propose a neutron flux monitoring system, which consist of microfission chambers placed inside the ITER vacuum chamber, three wide range fission chambers placed outside the vacuum chamber, natural diamond detector based compact neutron monitors placed inside the channels of the neutron cameras, and a compact neutron generator for calibration. Microfission chambers could be installed in the standard plugs with other detectors (vacuum x-ray diode, magnetic probe). 235U could be used as well as threshold fission materials (238U, 237Np, 232Th). In the last case the fission chamber will be covered by a boron shield to reduce the changes in the sensitivity. Wide range fission chambers will operate in both pulse count mode and Campbell mode. High linearity is provided by count mode. Temporal resolution of 1 ms is provided by the count mode at low neutron flux and by the Campbell mode at high flux. The nonlinearity of the fission chamber during the switch from count mode to Campbell mode will be corrected by another fission chamber with low sensitivity operating in count mode. Compact neutron flux monitors placed inside neutron cameras will consist of up to ten natural diamond neutron counters with sensitivity to DT neutrons doubled by properly installed poliethilen radiators. Such monitors provide DT neutron flux profile measurements with dynamic range (three orders), temporal resolution (1 ms), and accuracy (10%). The full system could be calibrated by compact moveable neutron generator with neutron yield 1011 neutron/s, which operate in continuous mode. All elements of the system are commercially available, except for the neutron generator and diamond detector based monitors. The neutron generator and multidiamond detector based DT neutron monitors are now under development. An existing prototype of the neutron generator operates with a yield of one order less. Performance and major characteristics of the proposed systems of neutron flux monitoring will be discussed from the point of view of their application for neutron flux measurements and control of deuterium and deuterium–tritium phases of the ITER-FEAT operation.
Calibration of the MEDUSA neutron spectrometer (abstract)
Authors: Sangster T. C. , Glebov V. Yu. , Lerche R. A. , Phillips T. W. , Stoeckl C. , Padalino S. J. , Olliver H. , Thompson S.
Published: February 2004

The MEDUSA array is a multielement, scintillator-based neutron time-of-flight spectrometer designed primarily to measure primary and secondary neutron production from indirect drive DD and DT capsule implosions at the Omega Laser in Rochester, NY. The array consists of 824 identical scintillator-photomultiplier tube detectors coupled to analog signal discriminators and high resolution, multihit time-to-digital converters, and is located 19.4 m from the center of the Omega target chamber. It is possible to accurately measure the neutron energy spectrum by simply measuring an adequate sample of neutron flight times to the array (the burn time width is negligible). However it is essential to understand the response of the array detectors to the fusion neutrons before an energy spectrum can be deduced from the data. This array response function is generally given in terms of a calibration constant that relates the expected number of detector hits in the array to the number of source neutrons. The calibration constant is a function of the individual detector gains, the thresholds of the discriminators, and the amount of neutron attenuating material between the array and the target. After gain matching the detectors, a calibration constant can be generated by comparing the array response against a known yield of neutrons (this requires dozens of implosions) or from a first principles measurement of the individual detector efficiencies. In this article, we report on the results of both calibrations of the MEDUSA array. In particular, we will focus on the issues and errors associated with the very different measurements required and discuss a new technique being considered for rapid in situ future calibrations.
Diagnostic use of secondary proton spectra for D2-filled inertial confinement  fusion  targets  (abstract)
Authors: Séguin F. H. , Li C. K. , Hicks D. G. , Frenje J. A. , Petrasso R. D. , Soures J. M. , Glebov V. Yu. , Stoeckl C. , Radha P. B. , Meyerhofer D. D. , Roberts S. , Sorce C. , Sangster T. C. , Cable M. D. , Padalino S. , Fletcher K.
Published: February 2004

The use of measured spectra of secondary fusion protons for studying physical characteristics of D2-filled inertial confinement fusion capsules is described theoretically and demonstrated with data from implosions in the OMEGA 60-beam laser facility. Spectra were acquired with a magnet-based charged-particle spectrometer and with a range-filter-based spectrometer utilizing filters and CR39 nuclear track detectors. Measurement of mean proton energy makes possible the study of a capsule’s total areal density (ρR), since that is what affects the energy loss suffered by protons as they pass through fuel and shell while leaving the capsule. Details of specific shots will be presented. It is also shown that similar techniques should prove useful for diagnosis of future experiments with cryogenic D2-filled capsules.
Measuring fusion yields, areal densities, and ion temperatures of imploded capsules at OMEGA (abstract)
Authors: Li C. K. , Hicks D. G. , Séguin F. H. , Frenje J. , Petrasso R. D. , Soures J. M. , Radha P. B. , Glebov V. Yu. , Stoeckl C. , Knauer J. P. , Marshall F. J. , Meyerhofer D. D. , Skupsky S. , Roberts S. , Sorce C. , Sangster T. C. , Phillips T. W. , Cable M. D.
Published: February 2004

With charged-particle spectroscopy implemented on OMEGA, we have been able to routinely measure the particle spectra (both nuclear lines and continua) from a variety of capsule implosions. Important parameters such as fusion yields, fuel and shell areal densities, and ion temperatures can be readily deduced. We will report on details of this work with emphasis on the implosion physics.
Fast ion loss measurement by infrared television in reduced ripple experiment with ferritic inserts on JFT-2M (abstract)
Authors: Kawashima H. , Tsuzuki K. , Tani T. , Sato M. , Kimura H. ,   JFT-2M Group
Published: February 2004

In the medium size tokamak, JFT-2M, the ferritic steel boards (FBs) were inserted to reduce the toroidal field ripple which causes the fast ion losses. To evaluate the effect of FB insertion, two-dimensional (2D) infrared television (IRTV) system with high resolutions in time and space was developed, which is quite suitable to measure the first wall temperature increment caused by the ripple ion losses in a medium size tokamak. We adopt an IR thermal imager (Mitsubishi IR-M300) that provides a field time of 1/60 s. The detectable temperature range is 0–500 °C with resolution of 0.2 °C. The PtSi (26×20 μm) detector being sensitive to 3–5 μm IR radiation is composed of a 256×256 array. The optical system to view the first wall consists of an IR lens (f:25 mm, F:2.0), a reflecting mirror, and a sapphire vacuum window, in which distance from the camera position to the target wall is shortened to ∼3.5 m. Thus, we obtained a high spatial resolution of ∼3 mm. By using this system, the local hot spot due to the ripple trapped losses of fast ions was observed during neutral beam injection (36 kV, 500 kW) heating. The peak temperature increment ΔTs reached to ∼75 °C before FB insertion. After FB insertion, the ΔTs were reduced clearly. In the most optimized case, the temperature increment became negligibly small. These IRTV data make clear the effectiveness of FBs for reduction of fast ion losses.
Development of fast response calorimeter for neutral beam shine-through measurement on CHS
Authors: Osakabe M. , Takeiri Y. , Takanashi T. , Tsumori K. , Okamura S. , Matsuoka K. , Akiyama R. , Asano E. , Kaneko O. , Kawamoto Y. , Oka T. ,   CHS-Group
Published: February 2004

A fast response calorimeter has been developed for the neutral-beam (NB) shine-through measurement. This calorimeter has the following advantages. (1) Temporal variation of the heat load onto the calorimeter can be measured. (2) Measurement under the relatively high heat flux environment is possible. (3) The calorimetric measurement under continuous and steady-state heat load environment is also possible. The verification of the measurement principle was done using an NB-injection system on the compact helical system (CHS) at the National Institute for Fusion Science (NIFS). The measured NB power densities are compared to the power densities being evaluated by the CHS-NB profile database. It was experimentally confirmed that the time constant of the measurement is about 7 ms.
Edge plasma turbulence analysis by collective light scattering in the Tore Supra tokamak
Authors: Hennequin P. , Honoré C. , Truc A. , Quéméneur A. , Gervais F. , Zou X. L. , Fenzi C. , Garbet X. , Sabot R. , Thouvenin D.
Published: February 2004

Collective light scattering measurement is a powerful tool for investigating fluctuations and their relation with anomalous transport since it allows a direct, discriminating analysis of the turbulent scales. This high scale resolution has a counterpart in a poor spatial resolution, but some localization can be recovered allowing us to discriminate edge from core turbulence behavior and to determine turbulence profiles. More information about localization can be obtained using temporal dynamics of the scattered signal when the fluctuation velocity in the poloidal plane is sheared. Making use of the consequently separated Doppler shifts, different technics are used to extract localized information from frequency spectra and from the signal phase derivative. Capabilities of the diagnostic are illustrated by recent results obtained on Tore Supra in different regimes.
Simulating the radiation environment in
Z
experiments using a 3D view factor code with 1D radiation-hydrodynamics emission modeling
Authors: MacFarlane J. J. , Bailey J. E. , Mehlhorn T. A. , Chandler G. A. , Nash T. J. , Deeney C. , Douglas M. R.
Published: February 2004

We present an approach for simulating the multidimensional radiation environment in Z-pinch hohlraums at the Sandia Z facility. In this approach we use a three-dimensional (3D) view factor code to compute the incident flux distribution onto all surface elements of the view factor grid. At each surface element, the frequency-dependent re-emission is computed by performing a one-dimensional (1D) radiation-hydrodynamics simulation for the element. The pinch radiation source is treated as a uniformly emitting cylinder, with a size and emission flux given by the experimentally measured time-dependent radius and radiation power. Here, we describe our modeling procedure, and present results from simulations of Z experiments in which a plastic-tamped aluminum foil was located in an open slot in the Z-pinch hohlraum (i.e., the return current structure). We also discuss the sensitivity of the Al plasma conditions to the incident spectrum onto the sample and the re-emission characteristics of the hohlraum walls.
Axially resolved z-pinch density, electron temperature, and K-shell emitting mass estimates from charge-coupled device based diagnostics
Authors: Failor B. H. , Coleman P. A. , Levine J. S. , Song Y. , Sze H. M. , Chong Y. K. , Apruzese J. P.
Published: February 2004

Timely estimates of z-pinch plasma conditions can aid in the optimization of plasma radiation source K-shell emission. For example, a shell-on-shell argon gas puff has many parameters, such as the axial gas density profile, inner to outer shell mass ratio, total mass, and pinch load length, which can be varied on a shot by shot basis. At the Double-EAGLE facility at Maxwell Physics International, digital cameras have been implemented to routinely record pinhole images, x-ray spectra, and axially resolved streak images. A computer algorithm has been implemented to take as input the data (pinch diameter, Ar Lyα to Heα line ratio, and K-shell power) and output the plasma parameters (density, electron temperature, and K-shell-emitting mass) as a function of z-pinch axial location. We describe the algorithm and present results for three different z-pinch loads.
X-ray line polarization spectroscopy of He-like Si satellite line spectra
Authors: Hakel Peter , Mancini Roberto C. , Gauthier Jean-Claude , Mı́nguez Emilio , Dubau Jacques , Cornille Marguerite
Published: February 2004

Laser-produced plasmas driven by high-intensity, femtosecond-duration pulsed lasers have been recognized as sources of short-duration x-ray line emissions. Electron kinetics simulations of such transient and nonequilibrium plasmas predict non-Maxwellian electron distributions and even the presence of electron beams. X-ray line polarization spectroscopy is a diagnostic that can be used to study the directionality of the electron distribution function and thus test electron kinetics simulation results. To this end, we use a time-dependent, collisional-radiative atomic kinetics model of magnetic sublevels to understand the underlying processes and mechanisms leading to the formation of polarized x-ray line emission in Si plasmas driven by high-intensity, ultrashort duration pulsed lasers. We focus on the polarization properties of the He-like Si satellites of the Lyα line. In the cases under consideration, the relevant line emissions last less than 1 ps during which the plasma undergoes a rapid development. We identify suitable polarization markers, which are sensitive to the anisotropy of the electron distribution function and can be used for diagnostic applications.
Ionization balance in EBIT and tokamak plasmas
Authors: Peacock N. J. , Barnsley R. , O’Mullane M. G. , Tarbutt M. R. , Crosby D. , Silver J. D. , Rainnie J. A.
Published: February 2004

The equilibrium state in tokamak core plasmas has been studied using the relative intensities of resonance x-ray lines, for example Lyα (H-like), “w” (He-like), and “q” (Li-like) from test ions such as Ar+15, Ar+16, and Ar+17. A full spatial analysis involves comparison of the line intensities with ion diffusion calculations, including relevant atomic rates. A zero-dimensional model using a global ion loss rate approximation has also been demonstrated by comparison with the data collected from a Johann configuration spectrometer with a charged coupled device (CCD) detector. Since the lines are nearly monoenergetic, their intensities are independent of the instrument sensitivity and are directly proportional to the ion abundances. This method has recently been applied to Ar in the Oxford electron beam ion trap (EBIT) with a beam energy in the range 3–10 keV. Taking into account the cross sections for monoenergetic electron collisions and polarization effects, model calculations agree with the observed line ratios at 4.1 keV beam energy. This work will be expanded to provide nomograms of ionization state versus line intensity ratios as a function of EBIT beam energy.
The large format x-ray imager
Authors: Oertel J. A. , Archuleta T. N. , Schrank L. S.
Published: February 2004

We introduce a new Large Format X-ray Imaging Camera (LFC) for the Los Alamos National Laboratory (LANL) Inertial Confinement Fusion/Radiation Physics (ICF/RP) program. This instrument is intended as a prototype for use at the National Ignition Facility (NIF), but is capable of operating at LANL’s Trident and the University of Rochester’s OMEGA laser systems. The LFC is based upon similar x-ray camera architecture and is currently in the final design stages. It is constructed around a mosaic of 3 large (35×105 mm2) microchannel plate (MCP) detectors, primarily to give a larger field of view, but also for greater temporal coverage and higher magnification while maintaining spatial resolution. The camera is designed to have 30 data channels, six 13-mm-wide microstrips, continuous temporal coverage of 4.2 ns, adjustable electrical gate width, and variable gain on each microstrip and magnifications up to 20×. In the process of designing the LFC we scrutinized every element of the gated x-ray imaging process and designed optimization experiments for many of these elements. From the results of two of these experiments, improvements were made in impedance matching to MCPs and, in another, optimization of phosphor on faceplates.
A multi-channel spectroscopic system for measuring impurity ion temperatures and poloidal rotation velocities in TJ-II
Authors: Baciero A. , Zurro B. , McCarthy K. J. , Burgos C. , Tribaldos V.
Published: February 2004

In this article, we report on the hardware and software of an eight-channel, high-resolution, spectroscopic diagnostic system that has been built for the TJ-II flexible heliac. This system is currently being used on TJ-II to measure impurity ion temperature and poloidal rotation using passive emission spectroscopy. The principal features of the diagnostic include independent focusing of its channels, high sensitivity for performing Doppler measurements in low-density ECR-heated plasmas, as well as a flexible and fast in-house-developed software program for performing integrated data reduction and analysis.
Simulations of beam-emission spectroscopy on Alcator C-Mod (abstract)
Authors: Sampsell M. B. , Bravenec R. V. , Rowan W. L. , Eisner E. C. , Patterson D. M. , Bretz N. L. , Boivin R. L. , Hubbard A. E. , Irby J. H. , Marmar E. S. , Terry J. L.
Published: February 2004

An eight-channel beam-emission-spectroscopy (BES)1 system has been installed on the Alcator C-Mod tokamak, intended for use with a diagnostic neutral hydrogen beam (DNB). Capable of localized measurements from the plasma edge to the plasma core, the BES diagnostic collects light from the first Balmer transition (Hα) resultant from beam/plasma collisions. The Hα line splits into several components whose central wavelengths depend on the viewing geometry, the magnetic field, and the beam energy. This is due to the Doppler shifts from viewing the beam off perpendicular, the different velocities of the three mass components of the beam (H, H2, H3), and the large motional Stark effect. Optimal signal-to-noise requires collecting these components while attenuating all other emission: primarily bremsstrahlung and Dα radiation (from plasma D0/e− collisions). Tunable bandpass filters are thus required. A BES simulation code has been developed that calculates the brightnesses (bremsstrahlung, Dα, Hα) versus wavelength using plasma profile data from the C-Mod MDSplus database,2 a computation of the beam penetration, the viewing and DNB geometries, and bandpass filter characteristics. The model was first used to estimate signal levels and choose the optimal BES bandpass filters; its ultimate purpose is to determine the shot-to-shot tuning requirements of the filters for different discharge conditions. Comparisons of measured and predicted background bremsstrahlung and Dα brightnesses are presented, as are first measurements and calculations of the beam emission. The code is written in the IDL programming language3 utilizing the “widget” graphical user interface. Designed for geometrical and spectral flexibility, it can be modified to simulate other beam diagnostics such as motional-Stark-effect plasma current measurements and charge-exchange recombination spectroscopy, as well as passive diagnostics measuring chord-averaged spectral emission.
Time resolved displacement interferometry for the characterization of preheat and free surface motion (abstract)
Authors: Evans A. M. , Rothman S. D. , Graham P.
Published: February 2004

We report results from two separate experiments fielded on the AWE Helen laser facility both diagnosed by interferometry. In the first experiment, measurements were made on preheat in flat targets indirectly driven by 1.8 and 2.2 mm (length and diameter) hohlraums heated by two 0.53 μm, 3 ns duration shaped laser pulses, each of 400 J. The rear surface of the target acts as one mirror of a Michelson interferometer, and the fringe pattern produced is temporally resolved using an optical streak camera. Motion of the fringes prior to the arrival of the shock at the rear surface enables expansion due to preheating to be measured. In the second experiment spallation measurements were made on pure Al. Cylindrical targets (800 μm diameter×500 μm long) were directly driven with one beam of 0.53 μm. 200 ps duration laser pulses of 3–15 J. A time resolved Michelson interferometer recorded the motion of the free surface. Pull back, elastic precursor, and spallation signatures were observed and strain rates of 3×106 s−1 and spall strengths of 33 kbar were measured.
Advances in the CO2 laser collective Thomson scattering fast ion/alpha particle diagnostic (abstract)
Authors: Richards R. K. , Hutchinson D. P.
Published: February 2004

A collective Thomson scattering diagnostic is being developed for the measurement of confined fast ions in hot, dense plasmas. This includes such measurements as the ion tail in JT-60U and the alphas produced in a burning reactor or the upgraded Joint European Torus device. The diagnostic also has the capability of measuring the isotopic ratio of the core ions such as the D/T ratio (required in optimizing a burning plasma experiment). The advances under development for this diagnostic include improvements in the high power source laser, increased bandwidth and reduced noise in the receiver, and the development of an intermediate frequency electronic filter bank. Such improvements are designed to permit the temporal measurement of the fast ions and improve the accuracy in determining their velocity distribution. Modeling of the expected scattered signals produced by these improvements and the diagnostics capability to measure the velocity distribution and isotopic ratio are presented.
X-ray Ross filter method for impurity transport studies on DIII-D (abstract)
Authors: Bogatu I. N. , Kim J. S. , Egdell D. H. , Snider R. T. , Brooks N. H. , Wade M. R. , West W. P.
Published: February 2004

The injection of Ar into the region of the DIII-D divertor is a promising technique for energy dissipation (through radiation and collisions) and consequently for reduction of the heat load on the plates. An important problem related to this technique, is the inherent poisoning of the core plasma by migrating Ar. The Ar core contamination seems also to improve the thermal transport in an advanced operating mode of the tokamak. It is therefore of great importance to measure the evolution of the impurity concentration profile within the core plasma. This goal could be achieved by using the Ross filter method in conjunction with the existing x-ray diagnostics on DIII-D. A basic Ross filter system consists of two identical detectors placed behind two different x-ray absorbing foils looking at the same plasma volume. The foils are made of different elements or compounds with adjacent or nearly adjacent atomic numbers. Their accurate thickness causes the x-ray transmission curves of the two foils to be effectively identical over the entire energy range except within the narrow region between their absorption edges. Since the transmission characteristics of the foils above and below their absorption edges are the same, any difference in the two detected signals is proportional to the total x-ray power of the emission spectrum between these two edge energies. An x-ray Ross filter with its energy pass band centered on the Ar XVII Kα line at 3.14 keV has been designed. This allows for the discrimination of the Ar Kα line only, regardless of Ar ionization state, against any background radiation with energies outside the energy pass band. The Ross filter was installed in front of two of the fan shaped poloidal x-ray arrays on DIII-D. The first measurements showed very good discrimination against Ne, another injected impurity. Emissivity profile evolution of the Kα lines and Ar enhanced continuum within the energy pass band of the Ross filter can be determined from the x-ray brightness signals by inverting techniques and by using the Te, ne, and Ar16+ profiles as measured by other diagnostics. The transport code MIST1 can be used to calculate both the emissivity profiles of the Kα of all the ions and their concentration profiles when the measured Te, and ne are used as input. The Ar16+ profiles as measured by charge exchange spectroscopy can be used as a constraint for the MIST code to accurately calculate the Ar18+ profile and thus unfold all the Ar ions Kα emissivity profiles. From these one can determine the Ar concentration profile evolution and the particle diffusion coefficient. In conclusion, using the Ross filter method with the existing x-ray imaging systems results in a powerful and cost-effective diagnostic for impurity transport studies.
Thin-window high-efficiency position sensitive proportional counter for the vacuum flat crystal spectrometers on the Lawrence Livermore National Laboratory electron beam ion trap (abstract)
Authors: Brown G. V. , Beiersdorfer P. , Goddard R. , Wargelin B. , Utter S. B.
Published: February 2004

We have mounted 1 μm thick aluminized polyimide windows onto the position sensitive proportional counters employed by the wide-band flat crystal spectrometers at the Lawrence Livermore National Laboratory electron beam ion trap experiment. The aluminized polyimide, supported by thin wires across the short axis of the window, is used to isolate the detection chamber of the proportional counters, which operate at a pressure of 760 Torr, from the vacuum chamber of the spectrometer. The windows are modified versions of those developed for the proportional counters which were used during ground calibration of the Chandra X-ray Observatory. The transmission properties of these windows are, therefore, well known. The increased transmission efficiency of the polyimide windows relative to the 4 μm thick polypropylene window material previously employed by our proportional counters has extended the useful range of the spectrometer from roughly 20 to 30 Å at energies below the carbon edge, as well as increasing detection efficiency at wavelengths beyond the carbon edge. Using an octadecyl hydrogen maleate crystal with 2d=63.5 Å, we demonstrate the increased wavelength coverage by measuring the resonance, intercombination, and forbidden lines in helium-like N VII in two different density regimes. The thin polyimide windows have also increased the efficiency of the spectrometers entire wavelength range. To demonstrate the increased efficiency we compare the Fe XVII spectrum in the 15–17 Å band measured with the 1 μm aluminized polyimide windows to the 4 μm aluminized polypropylene windows. The comparison shows an average increase in efficiency of ∼40%. The polyimide windows have a significantly lower leak rate than the polypropylene windows making it possible to achieve approximately an order of magnitude lower pressure in the spectrometer vacuum chamber which reduces the gas load on the trap region.
Measurements of shock heating using Al absorption spectroscopy in planar targets (abstract)
Authors: Boehly T. R. , Yaakobi B. , Knauer J. P. , Meyerhofer D. D. , Town R. , Hoarty D. , Bahr R. , Millecchia M.
Published: February 2004

In direct-drive laser fusion, the tradeoff between stability and overall efficiency requires precise control of the implosion isentrope. Most target designs use the temporal shape of the drive pulse to create shocks that slightly preheat the capsule shell and establish the isentrope for the rest of the implosion. Also, the use of foam overcoatings has been proposed as a means to reduce laser imprinting. These foams can alter the structure and intensity of the initial shock. To ensure that our hydrocodes adequately model these effects it is important that shock heating of targets be measured and understood. We report on measurements of shock heating in planar targets irradiated with the OMEGA laser system. Planar 20-μm-thick CH targets were irradiated with six ultraviolet (UV) beams at intensities of ∼2×1014  W/cm2 with temporally square and ramped pulses. Some targets also have low-density foam (30 mg/cc) on the irradiated surface. A thin (0.5 μm) Al layer, imbedded in the target, is probed with x rays from a Sm backlighter. The 1s-2p absorption lines in the Al are observed with a streaked x-ray spectrometer. The absorption lines from the F-like to Ne-like ion populations provide a measure of the temperature of the target as a function of time. We present data on measurements that show the relative shock heating by square and ramp pulses. We also present results of atomic physics calculations1 of the absorption spectra that are used to infer the target temperature and show results from hydrodynamic simulations of the experiments.
Pulsed radar reflectometry on the LHD
Authors: Tokuzawa T. , Kawahata K. , Pavlichenko R. O. , Tanaka K. , Ejiri A.
Published: February 2004

Pulsed radar reflectometry is a suitable reflectometric technique with which to study the effect of strong magnetic shear for the polarization of microwaves in the Large Helical Device. Because pulsed radar reflectometry measures the delay time of the reflected wave, not the phase, X-mode and O-mode polarized waves can be distinguished. At a preliminary stage of X-mode operation it is found that the position of the ergodic edge layer is steady in spite of the increased density in the core region when a neutral beam is injected. If the electron density does not reach the critical cutoff density, the pulsed radar system could be used as a delayometer. The measured delayometer signal is almost in agreement with the numerical calculation under the assumption that polarization of the wave propagated into the plasma is decided at the edge region.
Optical coherence techniques for plasma spectroscopy (invited)
Authors: Howard J. , Michael C. , Glass F. , Cheetham A. D.
Published: February 2004

A new electro-optically modulated optical solid-state (MOSS) spectrometer has been constructed for high temporal resolution measurement of the coherence of line radiation from plasmas. The instrument is an electro-optically modulated fixed delay polarization interferometer, or Fourier transform spectrometer. It has high light throughput compared with conventional grating based instruments of comparable resolving power while being compact and robust against alignment errors. By employing electro-optical path-length modulation techniques, the spectral information is transferred to the temporal frequency domain and can be obtained using a single photodetector. A wide field-of-view MOSS camera has been developed for imaging applications, while multiple-delay variants of the basic single fixed delay instrument have also been successfully tested. We discuss applications including passive Doppler spectroscopy, charge exchange recombination spectroscopy, and Zeeman and motional Stark effects. For Doppler tomographic applications, we show that such time-domain instruments have certain fundamental advantages, not least of which is a simple relationship between fringe visibility and the line integral of the intensity weighted velocity distribution function.
The MOSS camera on H-1NF
Authors: Michael C. A. , Howard J. , Blackwell B. D.
Published: February 2004

We have configured the modulated optical solid-state spectrometer, a recently developed high-resolution instrument for plasma Doppler spectroscopy, as an imaging spectroscopic camera. The camera features a wide field of view (∼10°), large aperture (40 mm), and high spectral resolution ν/Δν greater than 10 000. The camera installation on the H-1NF Heliac is described, together with the steps in the design process, including field widening. Calibration and characterization of the instrument function is discussed and the instrument performance is illustrated with some sample results of spatially resolved ion temperature measurements in H-1NF.
Reconstruction of time-resolved continuum intensity profile of nonaxisymmetric laser-produced plasma
Authors: Kim Yong W. , Oh Jaechul
Published: February 2004

A single laser pulse is used to produce weakly nonideal plasma from a metallic aluminum target immersed in a dense neutral gas. The attendant increase in plasma density due to neutral gas confinement precipitates interfacial instability when the gas density exceeds a threshold value. This is accompanied by large fluctuations in the total attenuation of the laser beam by the laser-produced plasma plume. We have developed a new diagnostic method utilizing two mutually orthogonal side-view streak photographs of plasma continuum luminosity at a fixed distance from the target surface. The lack of axial symmetry is overcome by using a front-view luminosity image of the plasma at time zero as a two-dimensional weighting factor. The resulting profile at one time is used as the weighting factor for the next time segment. The time-resolved reconstructed plasma profiles clearly exhibit the near-threshold behavior of Rayleigh–Taylor type instability.