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L-shell electron-impact ionization (EII) cross sections for highly charged tungsten ions were measured at incident electron energies of 29.10 and 38.92 keV using the Shanghai-EBIT. Resolved x-rays from radiative recombination (RR) processes were recorded with a high-purity Ge detector in a static electron energy scanning mode. Absolute EII cross sections were obtained by normalizing to the theoretical RR cross sections. The experimental results were compared with the calculated results using the relativistic distorted-wave method implemented in the flexible atomic code and the relativistic Lotz semi-empirical equation. The measurements showed general agreement with the calculated results by two theoretical methods for Li- to N-like W ions. The experimental uncertainties are not sufficiently small to discern the two theoretical results. Furthermore, the influence of Breit interaction on the EII cross sections of open L-shell tungsten ions was studied, and the effect is small but non-negligible. The measured EII cross sections of open L-shell tungsten ions would contribute to fusion plasma studies. [ABSTRACT FROM AUTHOR]

Great efforts have been made to create a bright K-shell source using the thin metal cylindrical cavities in the past few decades. Several metal materials such as titanium (Ti), iron, and so on have been tested for high x-ray conversion efficiency mainly at the OMEGA and NIF laser facilities. Recently, x-ray sources in Ti K-shell transition energy range were investigated at the Shenguang-III prototype laser facility with ∼5 kJ laser energy. The experiments were aimed to reproduce the previous ones at OMEGA, but with an extraordinarily small volume of cylindrical cavity and detailed characterizations of the x-ray source. The cavities were 800 μm inner diameter, 800 μm length, and 30 μm thick plastic tubes supporting 1 μm thick Ti. Seven laser beams were focused to 200 μm diameter. The combination of the small cavity volume and the focused laser spots is intended to improve the electron temperature with limited laser energy since the electron temperature is a key issue for high x-ray conversion efficiency. Thomson scattering was adopted to experimentally probe the electron temperatures at special time and space zones as well as the average temperature obtained from the Ti K-shell spectrum. The evolutions of the electron temperature and density are predicted by the radiation hydrodynamic simulation. A top view and two photon energy bands of x-ray source images provide a way to directly observe the plasma movement toward the cavity axis and distinguish the different emission mechanisms between the Ti K-shell and lower energy x rays. Six Higher-energy x-ray detectors located at different angles were used to record the Ti K-shell x-ray emission and demonstrate its isotropic feature. The characteristics of the x-ray radiate intensity including the time evolution, the angular distribution, and the total yields for both the photon energy regions above and below 4 keV are compared between the cavity and planar targets. Obviously, different behaviors were found between the two photon energy regions and the two types of targets. The x-ray conversion efficiency of the Ti cylinder was determined to be ∼ 4 % and ∼ 21 % in 4 π sr in the Ti K-shell (4–7 keV) and <4 keV range, respectively. The Ti K-shell conversion efficiency obtained in the present experiments is between the ones driven by 13.5 and 4.5 kJ laser energy at OMEGA. [ABSTRACT FROM AUTHOR]

We present ab initio calculations of cross sections for projectile and target excitation occurring in the course of He+ + He collisions using a three-active-electron semiclassical nonperturbative approach. Intermediate impact energies ranging from 1 keV to 225 keV/u are considered. The results of our calculations agree well with available measurements for both projectile and target excitation in the respective overlapping energy regions. A comparison of our results with those of other theoretical calculations further demonstrates the importance of a nonperturbative approach that includes a sufficient number of channels. Furthermore, it is found that the cross sections for target excitation into singlet states show a valley centered at about 25 keV/u, resulting from competition with electron transfer to singlet projectile states. By contrast, the cross sections for target excitation into triplet states do not exhibit any such structures. [ABSTRACT FROM AUTHOR]

A hohlraum used to create uniform and strongly coupled warm dense matter and its radiation flux study on the SG-III prototype laser facility are described. Time evolution of the radiation temperature from laser entrance hole (LEH) and the incident radiation temperature at the target surface are obtained using flat response X-ray diode detectors. Then, a calculation of the radiation flux evolution for this hohlraum is carried out using a view-factor method, and the calculated results agree well with the experimental data within the error bar. Using the incident radiation at the target surface as a source, the validity to create uniform and strongly coupled warm dense matter by this hohlraum is verified. [ABSTRACT FROM AUTHOR]

We present non-collective spectrally resolved X-ray scattering measurements from isochorically heated graphite samples. The elastic and inelastic scattering spectra for the titanium He-α x-ray line at 4.75 keV yield characterization of the temperature and ionization state of the samples. It is found that the plasma theories employing a screened Coulomb potential fail to describe the ion structure of warm dense carbon plasmas and only the models accounting for the effects of the electronic configuration show good agreement with the experimental result. This agreement further suggests that the short-lived chemical bonds play an important role in determining the ion structure of warm dense graphite systems with a temperature of several electron volts. [ABSTRACT FROM AUTHOR]

A 1D space resolving x-ray spectrum diagnostic system has been developed to study the radiation opacity of hot plasma on SG-II laser facility. The diagnostic system consists of a 2400 lines/mm flat-field holographic grating and a gated microchannel plate coupled with an optical CCD and covers the wavelength range of 5-50 Å. The holographic grating was compared with a ruled one by measuring the emission spectra from a laser-produced molybdenum plasma. The results indicate that the holographic grating possesses better sensitivity than the ruled grating having nearly similar spectral resolution. The spectrograph has been used in radiative opacity measurement of Fe plasma. Simultaneous measurements of the backlight source and the transmission spectrum in appointed time range in one shot have been accomplished successfully with the holographic grating spectrometer. The 2p-3d transition absorption of Fe plasma near 15.5Å in has been observed clearly. [ABSTRACT FROM AUTHOR]

The K-shell x-ray spectra from the aluminum plasmas generated by the interaction of the 120 TW, 30 fs laser with aluminum targets have been measured by defocusing the laser beam. Laser energy-normalized intensity of the He-a line increases with the laser intensity approximately as a power law [variant_greek_epsilon]∝ILγ with the much smaller exponent of γ=0.062 compared to γ=0.2∼0.5 in the previous experiments, which is caused by the stronger radial thermal diffusivity in the target for the smaller laser spot. Laser-to-He-a line conversion efficiency of up to 1.9×10-3 and as high as about 3×1013 photons/2π Sr aluminum He-a line x-ray source have been achieved for a single shot due to the preplasma effect and relatively large laser spot and energy for the single shot. The x-ray spectra as a function of the laser intensity are also analyzed to get the electron temperature and density. [ABSTRACT FROM AUTHOR]

The opacity of a molybdenum plasma in local thermodynamic equilibrium with open M-shell configurations was measured in the energy range from 200 eV to 800 eV, corresponding to the Δn = 1 M to N shell and Δn = 2 M to O shell transitions. The sample was heated by thermal x-ray radiation generated with a gold cavity. The electron temperature was diagnosed with the absorption spectrum of doped aluminum, giving a value of Te = (67 ± 4) eV. The density was 9.7 mg/cm3, which was deduced from the known initial area density and the plasma thickness by radiographic measurements of the expansion of the heated foil sample. The spectrally resolved transmission data were compared to a detailed-configuration-accounting model calculation and about 20% to 100% discrepancies were found. [ABSTRACT FROM AUTHOR]

An eight-channel x-ray flat crystal spectrometer was developed for high energy density physics research at the Shenguang-III (SG-III) laser facility. The spectrometer uses trihydroxymethylaminomethane crystals (2 d = 8.78 Å) to record Ti K-shell emission in the photon energy range of 4.65-5.05 keV. The spectrometer couples to an x-ray framing camera to achieve time-resolution. This has four microstrips, and each strip records two snapshots of the emission image. Based on the intersection positioning system with a dual-charge coupled device, the alignment system is easily operated and efficient. The instrument was tested and used for Au hohlraum plasma diagnosis experiments on SG-III. The He- α line and its Li-like satellites and the Ly- α line of a Ti tracer were detected, from which the spectral resolution of the instrument was analyzed. The spectral resolution E /Δ E at the Ti He- α line ranges from about 500 to 880 and mainly limited by the x-ray source size.

We present an experimental determination of the response of a gated flat-field spectrometer at the Shenguang-II laser facility. X-rays were emitted from a target that was heated by laser beams and then were divided into different intensities with a step aluminum filter and collected by a spectrometer. The transmission of the filter was calibrated using the Beijing Synchrotron Radiation Facility. The response characteristics of the spectrometer were determined by comparing the counts recorded by the spectrometer with the relative intensities of the x-rays transmitted through the step aluminum filter. The response characteristics were used to correct the transmission from two shots of an opacity experiment using the same samples. The transmissions from the two shots are consistent with corrections, but discrepant without corrections.