Recent enhancements in the performance of the Orion high-resolution x-ray spectrometers.

During the past few years, the Orion high-resolution x-ray spectrometers have been successful tools for measuring x-ray spectra from plasmas generated in the Orion laser facility. Duplicate spectrometers also operate successfully at the Livermore EBIT-I and SuperEBIT electron beam ion traps for measuring x-ray polarization. We have recently implemented very high-quality, optically bonded, spherically bent quartz crystals to remove the structure in the x-ray image that had been observed in earlier measurements. The structure had been caused by focusing defects and limited the accuracy of our measurements. We present before and after images that show a drastic improvement. We, furthermore, have implemented a spherically bent potassium acid phthalate (KAP) crystal on one of our spectrometers. The KAP crystal was prepared in a similar fashion, and we present measurements of the N Ly-ß and Ne Lyß lines taken in first- and second-order reflections at 600 and 1200 eV, respectively. These measurements confirm that KAP crystals can be produced at a quality suitable for extending the spectral coverage to wavelengths longer than those accessible by different quartz crystals, especially those that cover the astrophysically important lines of iron.

A new double crystal calibration system for absolute x-ray emission measurements down to ∼1 keV energies.

Over the past few years, work has been conducted at AWE to accurately characterize x-ray diffraction crystals to allow for absolute measurements of x-ray emission for our Orion opacity campaigns. Diffraction crystals are used in spectrometers on Orion to record the dispersed spectral features emitted by the laser produced plasma to obtain a measurement of the plasma conditions. Previously, based on a Manson x-ray source, our calibration system struggled to attain a high signal at the low energies required in calibration for the use of aluminum as a tracer for higher atomic number experiments. Here, we present data from the newly commissioned CTX400 x-ray source, a twin anode water cooled system, showing it to be a bright source even for ∼1 keV energies. Rocking curve measurements for three of the most commonly used crystals, namely, pentaerythritol, cesium acid phthalate, and germanium, are presented for both convex and flat forms.

High resolution, high signal-to-noise crystal spectrometer for measurements of line shifts in high-density plasmas.

The Orion high-resolution x-ray (OHREX) spectrometer has been a successful tool for measuring the shapes of density-broadened spectral lines produced in short-pulse heated plasmas at the Orion laser facility. We have recently outfitted the instrument with a charge-couple device (CCD) camera, which greatly increased the accuracy with which we can perform line-shift measurements. Because OHREX is located on the outside of the Orion target chamber, no provisions for the shielding of electromagnetic pulses are required. With the CCD, we obtained a higher signal-to-noise ratio than we previously obtained with an image-plate detector. This allowed us to observe structure in the image produced by the diffraction from the two OHREX crystals, which was highly reproducible from shot to shot. This structure will ultimately limit the accuracy of our spectroscopic measurements.

Lineshape spectroscopy with a very high resolution, very high signal-to-noise crystal spectrometer.

We have developed a high-resolution x-ray spectrometer for measuring the shapes of spectral lines produced from laser-irradiated targets on the Orion laser facility. The instrument utilizes a spherically bent crystal geometry to spatially focus and spectrally analyze photons from foil or microdot targets. The high photon collection efficiency resulting from its imaging properties allows the instrument to be mounted outside the Orion chamber, where it is far less sensitive to particles, hard x-rays, or electromagnetic pulses than instruments housed close to the target chamber center in ten-inch manipulators. Moreover, Bragg angles above 50° are possible, which provide greatly improved spectral resolution compared to radially viewing, near grazing-incidence crystal spectrometers. These properties make the new instrument an ideal lineshape diagnostic for determining plasma temperature and density. We describe its calibration on the Livermore electron beam ion trap facility and present spectral data of the K-shell emission from highly charged sulfur produced by long-pulse as well as short-pulse beams on the Orion laser in the United Kingdom.

Observations of the effect of ionization-potential depression in hot dense plasma.

The newly commissioned Orion laser system has been used to study dense plasmas created by a combination of short pulse laser heating and compression by laser driven shocks. Thus the plasma density was systematically varied between 1 and 10 g/cc by using aluminum samples buried in plastic foils or diamond sheets. The aluminum was heated to electron temperatures between 500 and 700 eV allowing the plasma conditions to be diagnosed by K-shell emission spectroscopy. The K-shell spectra show the effect of the ionization potential depression as a function of density. The data are compared to simulated spectra which account for the change in the ionization potential by the commonly used Stewart and Pyatt prescription and an alternative due to Ecker and Kröll suggested by recent x-ray free-electron laser experiments. The experimental data are in closer agreement with simulations using the model of Stewart and Pyatt.

Brain mitochondrial responses to postischemic reperfusion: a role for calcium and hydrogen peroxide?

During early recirculation following global brain ischemia, mitochondria are exposed to markedly elevated Ca(2+) concentrations and a short-lived production of reactive oxygen species, including hydrogen peroxide (H(2)O(2)). A brief increase in mitochondrial Ca(2+) and a subsequent increase in mitochondrial glutathione content have been observed. In the present study, we have confirmed the increase in mitochondrial glutathione in a rat model of global forebrain ischemia. This change was not inhibited by treatment of the rats with FK506, contrasting with our previous finding that cyclosporin A partially blocked the increase. These results suggest that induction of the mitochondrial permeability transition may be necessary for the increase in glutathione content in these organelles. To further investigate possible mitochondrial responses during early postischemic reperfusion, mitochondria isolated from normal brain were exposed to Ca(2+) and H(2)O(2), under conditions similar to those in intact cells. Respiratory activity was substantially modified when the mitochondria were exposed to Ca(2+) and H(2)O(2) together. Two distinct and largely noninteracting mechanisms apparently accounted for the responses to these agents. The effects of Ca(2+), but not H(2)O(2), were inhibited by cyclosporin A, again implicating the permeability transition in some of the mitochondrial changes.

Impairment of brain mitochondrial function by hydrogen peroxide.

Hydrogen peroxide, at concentrations comparable to those observed under some pathological conditions, produced a concentration-dependent inhibition of state 3 (ADP-stimulated) and uncoupled mitochondrial respiratory activity. The ADP:O ratio was also substantially reduced. In contrast, the organic peroxide, t-butylhydroperoxide at the same concentrations produced no significant changes in respiratory activity. Intramitochondrial glutathione was oxidised to a similar extent in the presence of hydrogen peroxide or t-butylhydroperoxide. Thus, changes in this endogenous antioxidant apparently did not underlie the different responses to these peroxides. The effects of hydrogen peroxide were not altered by deferoxamine indicating that the extramitochondrial generation of hydroxyl radicals was not likely to be involved. However, modifications arising from the generation of hydroxyl radicals within the mitochondria remain a likely contributor to the observed deleterious effects on respiratory function. The inhibitory effects of hydrogen peroxide were greatest when pyruvate plus malate were present as respiratory substrates. Lesser inhibition was seen with glutamate plus malate and no significant inhibitory effects were detected in the presence of succinate. The findings suggest that mitochondrial components involved in pyruvate oxidation were particularly sensitive to the hydrogen peroxide treatment. However, no significant change was seen in activity of either the pyruvate dehydrogenase complex or NADH-ubiquinone oxidoreductase (complex I) when measured directly following treatment of the mitochondria with hydrogen peroxide.

Dietary fish oil prevents the development of renal damage in salt-loaded stroke-prone spontaneously hypertensive rats.

1. Stroke-prone spontaneously hypertensive rats (SHRSP) fed a high salt diet rapidly develop proteinuria, a marker of renal damage. We have recently shown that supplementing the diet of these rats with pure omega-3 fatty acids can inhibit the development of proteinuria. The aim of the present study was to examine the underlying renal pathology and to see whether a similar benefit could be obtained with fish oil or canola oil. 2. Diets containing sodium (2% by weight) and 5% fish oil, canola oil, olive oil or safflower oil (the latter two serving as controls) were fed to groups of eight young SHRSP and the development of hypertension and proteinuria was monitored. After 9 weeks, rats were killed and their kidneys were taken for histological examination and fatty acid analysis. Urinary protein was characterized electrophoretically. 3. Patterns of protein excretion were consistent with the appearance of pathological changes in both glomeruli and tubules. Fish oil inhibited the elevation of blood pressure, prevented the development of proteinuria and minimized histological lesions. However, in rats fed canola oil, hypertension and renal damage were equally severe as in rats fed olive or safflower oil. 4. The prevention of hypertensive renal damage by dietary fish oil may be attributable to the increased incorporation of long-chain omega-3 fatty acids in the kidney.