X-ray Crystal Spectrometer Research Articles

Time-dependent electron temperature diagnostics for high-power, aluminum z-pinch plasmas

Time-resolved x-ray pinhole photographs and time-integrated radially resolved x-ray crystal-spectrometer measurements of azimuthally symmetric aluminum-wire implosions suggest that the densest phase of the pinch is composed of a hot plasma core surrounded by a cooler plasma halo. The slope of the free-bound x-ray continuum, provides a time-resolved, model-independent diagnostic of the core electron temperature. A simultaneous measurement of the time-resolved K-shell line spectra provides the electron temperature of the spatially averaged plasma. Together, the two diagnostics support a one-dimensional radiation–hydrodynamic model prediction of a plasma whose thermalization on axis produces steep radial gradients in temperature, from temperatures in excess of 1 kV in the core to below 1 kV in the surrounding plasma halo.

High-resolution von Hamos crystal X-ray spectrometer

A high-resolution von Hamos Bragg crystal X-ray spectrometer is described. The instrument was designed for the study of X-ray emission from low- Z elements and L X-ray spectra of medium to high Z targets induced by photon and particle impact. The construction details and operational characteristics of the spectrometer are presented along with the data illustrating the utility of this facility in different areas of research in atomic physics.

Time- and space-resolved observation of population inversion in a He-like Al plasma pumped by fundamental and second-harmonic pulses of a Nd:glass laser

Time- and space-resolved spectra of laser-produced aluminum plasma are observed with a framing crystal x-ray spectrometer. A massive slab Al target is irradiated by the fundamental or second-harmonic laser pulse from a Nd:glass system at a peak intensity of 8.5 ± 0.9 × 1014 W/cm2. Population inversion are observed between the 4 and 3 levels of He-like Al for fundamental pumps and also between the 3 and 2 levels for the second harmonics. The origin of the 3– 2 inversion can be attributed to the higher initial electron density of the plasma produced by the second-harmonic pump. A discussion of reabsorption effects of the resonance line is given.

High resolution PIXE instrumentation survey. Part III

High resolution PIXE facilities (X-ray crystal spectrometers working on ion beams of accelerators) and their applications in chemical analysis and in basic research are surveyed.

Development of a prototype superconducting X-ray spectrometer using a Ta crystal as an absorber

Superconducting tunnel junctions can be used as high resolution X-ray and γ-ray spectrometers. Until recently, most results were from detectors that consisted of niobium and aluminium thin films deposited on insulating substrates. Typically Nb films with thicknesses of several hundred nanometers are used as absorbers. These thin-film devices inherently suffer from poor quantum efficiency. To increase this efficiency a foil or a single crystal can be used as the supercounducting absorber. We are working on using ultra-pure, high- Z , superconducting crystals as the X-ray and γ-ray absorbers. We are developing a prototype detector with a 10 μm-thick Ta crystal as an absorber, which will have a quantum efficiency of greater than 99% at 6 keV. In this paper we present several of the design and fabrication issues involved in assembling the prototype superconducting crystal X-ray spectrometer.

Time and space resolved observation of population inversion in helium like aluminum plasma

Time and/or space-resolved spectra of laser produced aluminium (Al) plasma are observed using a framing crystal x-ray spectrometer. A massive slab Al target is irradiated by the second harmonic laser pulse from a Nd:Glass laser system. The pump energy is ∼15J, and the peak intensity is 8.5 (±0.9)× 10 14 W/cm 2. Population inversions are observed between the 3-2 and 4-3 principle levels of He-like All plasma farther than 150 μm from the target surface. Opacity and escape factors are estimated from the mismatch of electron densities deduced from two different line pair ratios.

Plasma diagnostics using Kα satellite emission spectroscopy in light ion beam fusion experiments

Kα satellite spectroscopy can be a valuable technique for diagnosing conditions in high energy density plasmas. Kα emission lines are produced in intense light ion beam plasma interaction experiments as 2p electrons fill partially open Is shells created by the ion beam. In this paper, we present results from collisional-radiative equilibrium (CRE) calculations which show how Kα emission spectroscopy can be used to determine target plasma conditions in intense lithium beam experiments on Particle Beam Fusion Accelerator-II (PBFAII) at Sandia National Laboratories. In these experiments, 8–10 MeV lithium beams with intensities of 1–2 TW/cm2 irradiate planar multilayer targets containing a thin Al tracer. Kα emission spectra are measured using an X-ray crystal spectrometer with a resolution of λ/∆λ = 1200. The spectra are analyzed using a CRE model in which multilevel (NL ∼ 103) statistical equilibrium equations are solved self-consistently with the radiation field and beam properties to determine atomic level populations. Atomic level-dependent fluorescence yields and ion-impact ionization cross sections are used in computing the emission spectra. We present results showing the sensitivity of the Kα emission spectrum to temperature and density of the Al tracer. We also discuss the dependence of measured spectra on the X-ray crystal spectral resolution, and how additional diagnostic information could be obtained using multiple tracers of similar atomic number.

Spectroscopic measurement of impurity transport coefficients and penetration efficiencies in Alcator C-Mod plasmas

Impurity transport coefficients and the penetration efficiencies of intrinsic and injected impurities through the separatrix of diverted Alcator C-Mod discharges have been measured using x-ray and vacuum ultraviolet (VUV) spectroscopic diagnostics. The dominant low Z intrinsic impurity in C-Mod is carbon which is found to be present in concentrations of less than 0.5%. Molybdenum, from the plasma facing components, is the dominant high Z impurity and is typically found in concentrations of about 0.02%. Trace amounts of medium and high Z nonrecycling impurities can be injected at the midplane using the laser blow-off technique and calibrated amounts of recycling, gaseous impurities can be introduced through fast valves either at the midplane or at various locations in the divertor chamber. A five chord crystal x-ray spectrometer array with high spectral resolution is used to provide spatial profiles of high charge state impurities. An absolutely calibrated, grazing incidence VUV spectrograph with high time resolution and a broad spectral range allows for the simultaneous measurement of many impurity lines. Various filtered soft x-ray diode arrays allow for spatial reconstructions of plasma emissivity. The observed brightnesses and emissivities from a number of impurity lines are used together with the mist transport code and a collisional-radiative atomic physics model to determine charge state density profiles and impurity transport coefficients. Comparisons of the deduced impurity content with the measured Zeff and total radiated power of the plasma are made.

High resolution PIXE instrumentation survey, part I

High-resolution PIXE facilities (X-ray crystal spectrometers working on ion beams of accelerators) and their applications are surveyed. Some examples of research possibilities at these facilities are given.

Analysis of a proton driven, exploding pusher target on PBFA II (abstract)

During the past year we have conducted a series of PBFA II target experiments. The design of the experiments was threefold: to characterize the response of targets to ion beams, develop our experimental diagnostic capability, and benchmark our theoretical ability to design and predict the response of the experimental diagnostics to ion-beam-heated, ICF targets. We present here an analysis of spherical exploding pusher experiments. The targets were 6-mm-diam, 100-μm-thick, Cl-doped CH spheres, filled with 1.2 atm of deuterium doped with 7 Torr of H2S. The diagnostics included XRDs, x-ray pinhole, framing, and streak cameras, and a spatially resolved, x-ray crystal spectrometer. Our analysis includes comparisons between experimental results and theoretical predictions of diagnostics responses and sulfur line emission from the compressed target using one- and two-dimensional radiation/hydrodynamic code runs. This work supported by the U. S. Department of Energy under Contract No. DE-AC04-76-DP00789.

General purpose high-resolution x-ray crystal spectrometer (abstract)

This spectrometer was designed to give access to a wide range of Bragg angles and crystal focal lengths while using the Rowland circle radius as a free parameter. Stability is achieved using a rigid beam or ‘‘Rowland chord,’’ which provides a reference axis for all the critical alignments, the chord length being variable between about 0.2 and 5 m. Crystals of size up to 100×30×0.5 mm can be accommodated in a novel four-pillar jig, (λ/δλ) is typically 104 in the wavelength range from 0.1 to 1.3 nm, depending on the crystal. Various detectors have been used, including photographic film, multiwire gas proportional counters and large area CCD detectors, the latter having a 2-D spatial resolution of 22.5 μm (1152×1242 pixels, 26×28 mm2), a quantum efficiency greater than 20% between 0.7 and 12 keV and an energy resolution of about 150 eV. By sacrificing energy resolution, a one-dimensional mode with on-chip binning allows ∼ms time resolution of spectra from high flux sources such as tokamaks and synchrotrons. Results presented include photographic spectra from tokamak, beam foil and laser produced sources, and CCD spectra from tokamak and standard electron-beam excitation laboratory sources.

High resolution PIXE using different orders of reflection

A Soller-type X-ray crystal spectrometer on an ion beam of the ATOMKI 5 MV Van de Graaff generator was used to perform high resolution PIXE measurements. The measurement of the dolomitization grade of natural limestones served as a case study for several methods on how to optimize such an analysis.

HIGH RESOLUTION SOFT X-RAY SPECTROMETER FOR CHEMICAL STATE ANALYSIS BY PIXE

A soft X-ray crystal spectrometer designed for chemical state analysis by PIXE is described. A windowless, microchannel plate (MCP) electron multiplier combined with a photodiode array was used as a position-sensitive detector for X-rays diffracted by a plane crystal. The spectrometer was tested for Al Kα and Fe L X-ray spectra induced by 15 MeV N2+ ion impact. An energy resolution (FWHM) of 1.5 eV for the 1487 eV Al Kα1, 2 line was obtained for metallic Al, and satellite structures of Al Kα arising from multiply ionized states were well resolved. Fe L X-ray spectra were measured for Fe2O3 and metallic Fe. Chemical effects were clearly recognized in the Fe Lα/Lβ intensity ratio and in the intensity distributions of their multiple vacancy satellites.

Compact convex crystal x-ray spectrometer

The construction of a compact and low cost convex crystal x-ray spectrometer is described. A mica sheet of about 100 μm thick is bent over a cylindrical surface to form the convex crystal. The spectrometer is expected to be able to cover the wavelength range between 1 and 19 Å. This spectrometer can serve as a convenient means for obtaining a preliminary scanning of the probable x-ray emission spectrum of plasma as a prelude to more careful and accurate spectral measurements.

Observations from the Hinotori mission

The satellite Hinotori was launched in 1981 by the Institute of Space and Astronautical Science of Japan. Two major experiments on board the Hinotori satellite were a hard X-ray imaging telescope with modulation collimators, and a high dispersion soft X-ray crystal spectrometer utilizing the Bragg diffraction of X-rays on quartz crystals. These two instruments have revealed for the first time that solar flares show varying characteristics depending on the environment of flaring regions, and that flares produce plasmas as hot as 3-4 x 10 7 K.

Angular distribution of Ti K X-rays and Sn L X-rays induced by 6 MeV nucleon N-ion impact

The angular distribution of Ti K X-rays and Sn L X-rays and their satellites due to 6 MeV/nucleon N-ion impact have been measured using an Si(Li) detector and an X-ray crystal spectrometer. The X-rays are observed to be isotropic.

The Mg/Ca ratio determination by high resolution PIXE

Small amounts of Mg in the presence of much Ca can be measured with a PIXE system, using a plane crystal X-ray spectrometer. The dolomitization grade of limestones can be measured with this method. Some possibilities for improving the method are given.

An experiment to measure the mass density of a plasma armature

A diagnostic technique for determining the mass density, and possibly the plasma composition, of the plasma armature in the MIDI-3 accelerator free-running arc is described. The armature primarily consists of components of polyethylene and copper, and can reach velocities in excess of 8 km/s. The approach in this proof-of-principle experiment utilizes a flash X-ray source (with X-rays energies from 3 keV to 20 keV), an elliptical X-ray crystal spectrometer, and an appropriate detector array and data acquisition system. >

Recent progress in space- and time-resolved x-ray spectroscopy of laser-produced plasmas (abstract)

New diagnostic techniques have provided measurement of relatively gradient-free x-ray spectra from high-powered laser-produced plasmas. Simultaneously space- and time-resolved x-ray spectra were measured from a variety of microdot plasmas using an array of multiframe, imaging, electronically gated x-ray crystal spectrometers with 100 ps time resolution. A multiframed, multicolored gated x-ray pinhole camera provided measurement of the plasma uniformity. A four-frame holographic interferometer was used to measure the electron density profile. Conventional x-ray streaked crystal spectrographs, spatially resolved x-ray (film) spectrometer, and pinhole cameras supplemented these new diagnostics. The instruments allow detailed studies of both the population kinetics of highly charged ions in dense plasmas and the hydrodynamics of laser-produced plasmas for the first time. The new diagnostics are described including data from ongoing experiments. Work was performed in part under the auspices of the U.S. Dept. of Energy by LLNL under Contract No. W-7405-Eng-48.

Proof-of-principle experiment for a hot electron pumped XUV amplifier

An X-ray laser scheme was recently proposed based on the pumping of neon-like 3s-3p transitions using inner-shell ionization of sodium-like ions by suprathermal electrons. Since this laser operates in principle with no population in the neon-like charge-state power requirements can be reduced from the standard collisionally driven amplifier, and the problem of line-trapping can be ameliorated. Model calculations using a quasi-steady state collisional-radiative model indicated that measurable gains could be obtained in practical experiments. We propose a proof-of-principle experiment to demonstrate the pumping of neon-like excited states by hot electrons. A ~ 1 ns long, 0.53 µ laser beam, will be focussed on a solid dot target of dilute (5%) bromine, to create a cool, dense plasma. The pulse and target will be optimized to produce as much sodium-like population as possible in the corona. This low-fluence green pulse does not produce suprathermals. A second, ~ 100 ps, 1.06 µm pulse of 1015 W/cm2 will be "piggybacked" on the first, to create hot electrons. The timing of the red beam will be optimized with respect to the sodium-like fraction of the cool plasma. The hot electrons create a transient population of neon-like ions, coincident with the red beam, that are detected by their characteristic n=3-n=2 resonant X-ray emission. If, as expected while the red beam is present, the neon-like excited states are produced by inner-shell ionization (as opposed to collisional excitation), n = 3-2 line ratios will carry a distinctive signature indicating a statistical feeding mechanism. The same signature will imply the existence of a population inversion. Proposed detection systems include space and time resolving crystal X-ray spectrometers for measuring the neon-like lines, and an array of filtered X-ray diodes to measure suprathermal electron temperature and number.