Yang Jia-Min

Beneficial effect of CH foam coating on x-ray emission from laser-irradiated high-Z material

Laser-irradiated Au layer with CH foam coating is investigated numerically. It is found that when coated with under-critical density CH foam more thermal radiation is produced, while less radiation is produced when coated with over-critical density CH foam. The under-critical density CH foam coating, which is heated supersonically and volumetrically by lasers, hampers the expansion of high-Z plasma and helps increase the density and temperature of Auplasma in the radiation zone. It is a practical and simple way to increase the laser x-ray conversion efficiency of hohlraum by coated with low-Z foam of under-critical density. This idea is tested with an experiment in an analogous geometry. The line emission from laser-irradiated Ti layer coated with CH foam was measured, and the increment of x-ray when coated with under-critical density CH foam was found.

Recover soft x-ray spectrum using virtual flat response channels with filtered x-ray diode array.

A method for the recovery of soft x-ray spectra in indirect-drive inertial confinement fusion experiments is presented. Virtual detection channels with bandpass responses are obtained using linear combinations of the channel response functions of a filtered x-ray diode array and a weighted correction is introduced to improve the recovery. These virtual channels can be used to calculate radiation fluxes in some specific photon energy bands and hence to recover the spectrum of the whole photon energy range from 80 eV to 4.5 keV. Examples are listed which demonstrate the capability of this method to unfold various spectra such as Planck spectra with different radiation temperatures and to obtain x-ray flux of certain narrow energy interval.

Measurement of the KLL Dielectronic Recombination Resonances in He-like to C-like Kr Ions

The KLL dielectronic recombination processes of highly charged He-like to C-like Kr ions have been studied experimentally. The measurement was performed on the newly developed Shanghai electron beam ion trap (Shanghai-EBIT) facility. Characteristic x-rays from both dielectronic recombination and radiative recombination are detected as the electron beam energy is scanned through the resonances. The KLL resonant strengths obtained are 5.41 × 10−19, 4.33 × 10−19, 3.59 × 10−19, 2.05 × 10−19 and 0.98 × 10−19 cm2 eV for He-like to C-like Kr ions, respectively.

Intercombination transitions of the carbon-like isoelectronic sequence

Energy levels, wavelengths, transition rates, oscillator strengths, and lifetimes between the 2s22p2 3P1, 2s22p2 3P2, and 2s2p3 5S2 levels of ions in the carbon-like (C-like) isoelectronic sequence (nuclear charges Z = 7–92) are calculated in the valence and core-valence limits using the multiconfiguration Dirac—Fock method. The Breit interaction, quantum electrodynamics (QED), and finite nuclear mass effects are taken into account in subsequent relativistic configuration-interaction calculations. The calculated energies and transition rates are compared with the critically evaluated experimental values and other recent calculated results. Our calculated data are in good agreement with these data.

Rosseland Mean Opacity of a High-Z Mixture Plasma

An eight-beam 0.351-µm laser with pulse duration of about 1.0ns and energy of 260 J per beam was injected into a cylindrical cavity to generate intense x-ray radiation on the Shengguang II high power laser facility. A mixture foil of gold and gadolinium and a gold foil were attached on portion of a diagnostic hole in the mid-plane of the cavity and ablated by the intense x-ray radiation. The propagating time of the radiation heat wave in the mixture and the pure gold foil were measured with soft-x-ray spectrometer and by adopting space- and time-resolved measurement technology, respectively. The results show that the mixture of gold and gadolinium has higher Rosseland mean opacity than the gold sample in our experiment.

Quantitative Measurement of the Proportions of High-Order Harmonics for the 4B7B Soft-X-Ray Source at Beijing Synchrotron Radiation Facility

A transmission grating coupled with an X-ray charge coupled device (CCD) is used to quantitatively measure the proportion of high-order harmonics of the soft-X-ray source of beam line 4B7B. The results show that the monochromatic X-ray has third-order and second-order harmonics. The proportion of second-order harmonic of 4B7B is less than 9.0% and the third-order harmonic is below 0.7% when no suppressing method is applied. When suppression methods are used, the proportion of second-order harmonic is less than 1.7% and the third-order harmonic is ignorable.

Diagnosing the plasma nonuniformity in an iron opacity experiment by spatially resolved Al 1s-2p absorption spectroscopy

Generating a well-characterized hot-dense sample is of great importance to high quality opacity measurements. In this paper, we report on an experimental investigation of the plasma nonuniformity in a radiatively heated iron opacity sample by spatially resolved Al 1s-2p absorption spectroscopy. The iron sample was tamped by plastic at both sides and was heated by thermal x-ray radiation generated in a gold Hohlraum, and an Al layer attached to it was used as a tracer for temperature diagnosis. Spatially resolved 1s-2p transition absorption spectra of the Al tracer were measured by the technique of point-projection-spectroscopy, and temperatures in the sample were obtained by comparing the measured spectra with detailed-term-accounting model calculations, with the density of the sample deduced using a combination of side-on radiography and radiative hydrodynamic simulation. The results showed the existence of axial temperature nonuniformity in the sample, and these temperature variations have been used to ...

Concentric-ring structures in an atmospheric pressure helium dielectric barrier discharge ⁄

This paper performs a numerical simulation of concentric-ring discharge structures within the scope of a twodimensional difiusion{drift model at atmospheric pressure between two parallel circular electrodes covered with thin dielectric layers. With a relative high frequency the discharge structures present difierent appearances of ring structures within difierent radii in time due to the evolvement of the fllaments. The spontaneous electron density distributions help understanding the formation and development of self-organized discharge structures. During a cycle the electron avalanches are triggered by the electric fleld strengthened by the feeding voltage and the residual charged particles on the barrier surface deposited in the previous discharges. The accumulation of charges is shown to play a dominant role in the generation and annihilation of the discharge structures. Besides, the rings split and unify to bring and annihilate rings which form a new discharge structure.

K-Shell Spectra from CH-Tamped Aluminum Layers Irradiated with Intense Femtosecond Laser Pulses

X-ray spectra of H-like and He-like aluminum ions from aluminum buried in CH layers irradiated with 30 fs, 200 TW laser are measured. The electron temperature and density are derived from line ratios of the He-α resonance line to its satellite lines. Typical temperatures of 490–646eV and electron densities up to 7 × 1020 cm−3 are obtained. The results show that the electron density increases and temperature decreases with the increasing CH thickness.

Time-Resolved Measurement of Radiatively Heated Iron 2p−3d Transmission Spectra

An experimental measurement of radiatively heated iron plasma transmission spectra was performed on Shenguang II laser facility. In the measurement, the self-emission spectrum, the backlighting spectrum, and the absorption spectrum were imaged with a flat filed grating and recorded on a gated micro channel plate detector to obtain the time-resolved transmission spectra in the range 10–20 A (approximately 0.6–1.3keV). Experimental results are compared with the calculation results of an unsolved transition array (UTA) code. The time-dependent relative shift in the positions of the 2p−3d transmission array is interpreted in terms of the plasma temperature variations.