A. P. Shevelko

Compact focusing von Hamos spectrometer for quantitative x-ray spectroscopy

A compact focusing crystal spectrometer based on the von Hamos scheme is described. Cylindrically curved mica and graphite crystals with a radius of curvature of R=20 mm are used in the spectrometer. A front illuminated charge-coupled device (CCD) linear array detector makes this spectrometer useful for real-time spectroscopy of laser-produced plasma x-ray sources within the wavelength range of λ=1.8–10 A. Calibration of crystals and the CCD linear array makes it possible to measure absolute photon fluxes. X-ray spectra in an absolute intensity scale were obtained from Mg, Ti, and Fe laser-produced plasmas, with a spectral resolution λ/δλ=800–2000 for the mica and λ/δλ=200–300 for graphite crystal spectrometers. The spectrometer has high efficiency in a wide spectral range, it is compact (40 mm diam, 150 mm length), easy to align, and flexible. The spectrometer is promising for absolute spectral measurements of x-ray radiation of low-intensity sources (femtosecond laser-produced plasmas, micropinches, ele...

EUV spectroscopy of plasmas created in the final anode-cathode gap of the Z-Machine high-current pulsed generator (SNL)

The effect of short-circuit across the final anode-cathode gap of powerful pulsed current generators could hamper efficient power delivery to the Z-pinch plasma. To study this effect, a novel EUV diagnostics of plasmas created in the final section of the transmission line (the anode-cathode gap near the main load) of the Z-Machine high-current generator (Sandia National Laboratories, United States) was developed. The work included developing spectroscopic instruments, theoretical and experimental studies of EUV spectra of iron ions in well-diagnosed laser-produced plasmas, and a comparison of these spectra with those of plasmas created in the final anode-cathode gap of the transmission line. The EUV spectra of highly charged Fe ions in the spectral range λ ∼ 20–800 Å were investigated. In experiments performed at Sandia National Laboratories, spectra of FeXIII-FeXVII ions were observed. A comparison of the measured and calculated spectra shows that the electron plasma temperature in the anode-cathode gap is Te ∼ 200 eV.

Radiative heating of thin Al foils by intense extreme ultraviolet radiation

The effect of induced transparency of thin Al foils radiatively heated by intense extreme ultraviolet (EVU) radiation has been observed. The radiation of the plasma of Z-pinches appearing under the compression of tungsten liners at the Angara-5-1 facility has been used as the radiation that heats the Al foil (peak illumination on the foil ~0.55 TW/cm2) and is transmitted through it. The photoabsorption has been studied in the formed aluminum plasma at temperatures of ~10–30 eV in the density range of ~1–20 mg/cm3 in the wavelength range of ~5–24 nm. Absorption lines of Al4+...7+ ions have been identified in the experimental spectrum. In addition, radiative gas-dynamic simulations of the foil heating and expansion have been performed taking into account radiation transfer processes.

Characteristics of a multilayer mirror polarimeter for measurements at extreme ultraviolet wavelengths

We have developed and tested a multilayer mirror (MLM) polarimeter optimized for λ=304 A using electron impact on helium. Specifically we present the first experimental results of the polarization of the extreme ultraviolet Lyman-α emission from He+ [Heu2009II (2p)2P°→(1s)2S] as a function of the electron impact energy for impact energies ranging from 150 to 980 eV. A major challenge to performing this measurement is the suppression of the dominant Heu2009I (1snp)1P°→(1s2)1S radiation originating from the excitation of helium. Excellent spectral selectivity has been achieved with a VYNS copolymer filter whose transmission ratio of Heu2009II to Heu2009I emission has been measured to be greater than 1200:1. Additionally, we have measured the instrumental polarization using two identical MLMs in a crossed polarizer configuration.

Method for formation of quasi-monochromatic divergent X-ray fluxes from laser-produced plasmas

Conditions and applicability limits of a new method for formation of quasi-monochromatic, with a large solid angle of divergence, linear X-ray fluxes from laser-produced plasmas are considered. The method is based on a special combination of laser target elements and -absorption filters, when the spectra of [H]- and [He]-like ions are excited in laser-produced plasma and -absorption filters select only the resonance lines of these ions from the linear spectrum. Experimental and theoretical studies have shown that, in the fluxes formed, the degree of monochromatisation may reach at the radiation contrast ratio of 5 – 10 and angular divergence of .

Research of non-cylindrical wire arrays on Angara-5-1 facility

To verify the codes which describe implosion of wire conical wire arrays with a mass of 200–400µg and large and small radii of cone 12–20mm and 5–10mm, correspondingly, were used. In spite of the fact that these liners produce a less powerful pulse of X-radiation than cylindrical ones, they have some features especially important to verify codes. For a cone angle of > 20° the X-pulse has three peaks. Comparison of their relative magnitude and duration obtained by experiment and in calculations allows us to more reliably verify some assumptions introduced into the code than would be the case of cylindrical liners. At the Angara-5-1 facility due to the electrostatic stretching of the cylindrical wire array occurred by an additional electrode the quasi-spherical arrays of 30-6- tungsten wires 6µm thick are formed with a radius of 8–12mm and a mass of 200–400µg. The implosion of Z pinches formed with such liners was effected by 3–4 MA current with a rise front of 100ns at the Angara-5-1 facility. It was shown that the central part of such a liner forms a hotter area compared with its edges and a hotter one than in the case of cylindrical liners.

A fully characterized multilayer mirror (MLM) polarimeter in the EUV range for application in atomic and surface collision experiments

A new multilayer mirror (MLM) polarimeter has been designed, constructed and optimized to analyze polarization in the extreme ultraviolet (EUV) wavelength range. In particular, a MLM polarimeter with a resolving power of about 6 at 304 A (Lyman α of He+) has been developed and fully characterized for detailed polarization studies at wavelengths of 256 A (HeII (3p→1s) and 304 A (HeII (2p→1s). The MLM has also been used as a single flat surface mirror polarimeter for the analysis of longer wavelength, from 517 to 584 A for HeI(1snp)1P0→(1s2)1S transitions.