摘要:

This is a progress report on development of a new x‐ray imaging system, called a Fourier transform microscope, intended for use with x‐ray emitting targets in laser fusion experiments. It is being built by Naval Research Laboratory and Lawrence Livermore National Laboratory. The system works at energies from 3 to 7 keV. We describe the development of the design, which utilizes fine etched grids to extract Fourier amplitudes for the source brightness distribution at selected spatial frequencies. The finest grids in the prototype system will have rib dimensions of 2 &mgr;m. The prototype system is expected to achieve position resolution of 4 &mgr;m in 3–7 keV. Simulations of the expected imaging performance are presented.

ISSN:0034-6748    

DOI:10.1063/1.1143501

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The use of photodiode arrays (PDAs), as the detectors in laser‐plasma x‐ray diagnostics, is explored in this paper. Traditionally, in laser‐fusion and laser‐plasma research, film has been used in x‐ray diagnostics to record the integrated x‐ray flux. The advantages of film are its low cost and relative simplicity of use. Photodiode arrays, although more complex, offer the advantages of near instantaneous results, high sensitivity, stability of response, and in principle are easy to calibrate. A Hughes PDA has been used to image laser‐plasma x rays by incorporating it into a pinhole camera. The readout electronics were developed at the Space Science Laboratory and experiments were performed on the University of Rochester’s OMEGA target chamber.

ISSN:0034-6748    

DOI:10.1063/1.1143449

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Two diagnostics for the study of hard x‐ray emission produced by plasmas during inertial confinement fusion experiments, are described: (i) a hard x‐ray spectrometer to measure the high‐energy tail of the spectrum, with eight spectral bands in the 50–400‐keV range, by fluorescence and simple filter techniques; (ii) a time‐integrated pinhole imaging device using a microchannel plate converter tube and a 7.5‐&mgr;m‐thick tantalum photocathode adjusted for a mean spectral sensitivity around 200 keV. Adjustment and test of these diagnostics have been performed with a pulsed hard x‐ray generator using a plasma focus device. Absolute calibration of the spectrometer detectors (scintillator Photomultiplier) was obtained on an x‐ray tube with fluorescent emission lines (10–100 keV) and with a cobalt radioactive source at 1.23 MeV.

ISSN:0034-6748    

DOI:10.1063/1.1143450

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An effective technique for measuring the local electron temperature and density of a laser‐produced plasma involves analysis of the emission and/or absorption spectrum from an impurity dopant. However, when an intense high‐energy radiation field is present the ionization balance, level population, and resulting spectrum produced by the impurity may be significantly perturbed. We are currently using several computer models to study the effects of such a radiation field for experimental conditions that could be obtained using the Nova laser facility, and are concentrating on the behavior of line intensity ratios that are typically used for density and temperature diagnosis. The goal of this work is to determine the feasibility of spectroscopic diagnosis when an intense high‐energy radiation field is present.

ISSN:0034-6748    

DOI:10.1063/1.1143451

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have measured the 8–11‐keV emission spectra from plasmas produced by impinging 0.53‐&mgr;m, 100‐ and 200‐ps FWHM Gaussian laser pulses on targets of different materials. The experimental spectra from W and Zn are identified by comparison with local thermodynamic equilibrium plasma emission calculations.

ISSN:0034-6748    

DOI:10.1063/1.1143452

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Over the past five years we have performed an extensive series of experiments on hydrodynamic (Rayleigh–Taylor) instabilities. Typically such experiments involve the time‐resolved radiography of an accelerated foil (planar geometry) with the line‐of‐sight of the radiograph along the direction of motion. In comparing experimental data to simulations, the simplest approach is to extract the modulation in exposure level of such a radiograph versus time and compare the inferred growth rate (assumed to be exponential) with the growth rate in column density (&Dgr;&rgr;z) from a simulation. We have found that this gives unsatisfactory results. We will discuss the techniques for experimental analysis and post processing of simulations which we use for a more direct comparison of the data with the simulation, including the extraction of Fourier components versus time from the data, the effect of backlighter spectra, emission from sources other than the backlighter, and the nonlinear effects of instrument response.

ISSN:0034-6748    

DOI:10.1063/1.1143453

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A spatial coherence diagnostic for measuring the spatial coherence of laboratory x‐ray lasers has been developed. The x‐ray laser beam illuminates a uniformly redundant array of slits, producing a partially coherent diffraction pattern which can be analyzed to yield the complex coherence factor for the x‐ray laser beam from a single x‐ray laser pulse. Measurements using x‐ray lasers at LLNL will be presented and discussed in detail. Results from experiments conducted in collaboration with the Rutherford x‐ray laser consortium to improve the spatial coherence of x‐ray lasers will also be discussed. A definition of a highly spatially coherent x‐ray laser based on simple physical arguments will be given. This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W‐7405‐ENG‐48.

ISSN:0034-6748    

DOI:10.1063/1.1143454

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

To study the x‐ray laser beam deflection and divergence due to the refraction within the plasma, a specific diagnostic called CADIX has been developed at the Centre d’Etudes de Limeil‐Valenton (CEL‐V). When the beam refraction analysis is required a multilayer mirror is inserted on the x‐ray laser output beam. It selects the lasing wavelengths and reflects them to an off‐axis streak camera which records x rays as a function of time and angle. A detailed description of the instrument is presented including multilayer mirror calibration at the LURE (Laboratoire pour L’Utilisation du Rayonnement Synchrotron, Orsay, France). An experimental measurement on neon‐like silver amplification is presented and analyzed with the response of the mirror. An important refraction effect is observed.

ISSN:0034-6748    

DOI:10.1063/1.1143455

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The characterization of subpicosecond laser produced plasmas is currently being investigated by the Livermore ultrashort pulse laser group. A 800‐nm, 150‐fs, 35‐mJ laser is focused to a 7‐&mgr;m spot on solid aluminum targets, producing XUV (<1 keV),Kshell (1.5–30 keV), and hard (≥3.0 keV) x‐ray emission. TheK‐shell emission is studied using a Von Hamos crystal spectrograph with a KAP crystal curved to an 80‐mm radius, resulting in a calculated resolution ofE/&Dgr;E≊400. The dispersed x rays are detected with a microchannel plate intensified reticon detector which relays the images out of the chamber and displayed on a computer monitor. The hard x rays are monitored with an array of filter x‐ray diodes, covering energies from 3 to 75 keV. The XUV emission is monitored with a variably spaced line grating, flat field spectrometer, and a grazing incidence spectragraph. The diagnostics will be presented along with current data from experiments. This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W‐7405‐ENG‐48.

ISSN:0034-6748    

DOI:10.1063/1.1143456

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An x‐ray streak camera is used to diagnose a laser‐produced Al plasma with time resolution of ∼10 ps. A streak record of filtered emission and a time‐integrated transmission grating spectrum reveal that the plasma radiation is dominated by emission from He‐ and H‐like resonance lines.

ISSN:0034-6748    

DOI:10.1063/1.1143457

出版商:AIP    

年代:1992

数据来源: AIP