Wei Minxi

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.

Demonstration of X-ray Thomson Scattering on Shenguang-II Laser Facility

X-ray Thomson scattering technique for diagnosing dense plasma was demonstrated on Shenguang-II laser facility. Laser plasma x-ray source of titanium He-α lines (~4.75 keV), generated by laser beam (1.5 kJ/527 nm/2 ns) heated titanium thin foil, was used as x-ray probe beam. The x-ray probe was then scattered by cold CH foam column of 1 g/cm3 density. The scattered radiation at 90° was diffracted by polyethylene terephthalate (PET) crystal and recorded on x-ray charge-coupled device. Well-defined scattering spectra were obtained with good signal to noise ratio.

K-Shell Spectra from CH Foam Tamped Ti Layers Irradiated with Nanosecond Laser Pulses

Hot dense titanium plasma was produced by irradiating a CH foam coated titanium layer with nanosecond laser pulses. The time-integrated emission spectra of He-like titanium were measured by using an absolutely calibrated flat crystal spectrometer. The synthetic spectra obtained by the steady collisional-radiative (CR) equilibrium model associated with the hydrodynamic simulations were compared with the experimental spectra. The results show that the electron density increases up to 5 × 1021 cm−3 with CH foam of density 40 mg/cc. This work indicates that an overlay of CH foam on a solid target is beneficial to create an optimum condition for K-shell emissions from a high density plasma region.

Space-Resolved Diagnosis for Electron Temperature of Laser-Produced Aluminum Plasma

The K-shell emission spectra of laser-produced aluminum plasma are measured by a space-resolved spectrometer consisting of a flat crystal spectrometer with a 20 μm wide space-resolved slit. By using the approximation of the steady collisional-radiative equilibrium model, the interstage line intensity ratios of Ly-α resonance line to He-α resonance line are given as a function of electron temperature. The spectra profiles are decomposed to resonance line and the overlapped high-order satellites manifold. Thus reliable electron temperature is deduced from the interstage line intensity ratios of the decomposed resonance lines. The results of spaced-resolved temperature are compared with the hydrodynamic simulations. The diagnostics of electron temperature for laser-produced plasma is developed.

Flat Crystal x-ray Spectrometer for Quantitative Spectral Measurement in the 2–5 keV Region

A technique of flat crystal x-ray spectrometer for quantitative spectral measurement is described. For the flat crystal spectrograph geometry, the quantitative reduction of relating the CCD counts back to the photon flux from the x-ray source is established. The absolute calibrations of the integral diffraction coefficients of the crystal and the CCD sensitivity make it possible to measure absolute photons flux within the energy range of 2000–5000 eV. The uncertainty analysis of the calibrations is carried out to obtain the energy resolved uncertainties of crystal and CCD. Thus, the experimental spectra with spectral resolved intensity uncertainties are available. Then, a performing experiment of laser-produced Ti plasma is carried out and the absolute x-ray spectra with intensity uncertainty less than 8.5% are obtained. The technique is promising for absolute spectral measurement of high temperature plasmas in a kilo-electron-volt region.

Electron Temperature Measurement of Radiation-Heated CH Foam on Shenguang II Laser Facility

A spectroscopic diagnostic method, to measure electron temperature of radiation-heated CH foam on Shenguang II laser facility, is described. A tracer layer of aluminum was embedded in the middle of the CH foam and a point-projection method used in the opacity experiment was induced to measure the transmission spectrum of the embedded A1 foil. The electron temperature, of about 80 eV, was deduced through a comparison of the experimental absorption spectrum with the calculated one with a detailed level accounting opacity code. The results of hydrodynamic simulation show that its reasonable to determine the CH foam temperature by measuring the embedded Al absorption spectrum. Thus, the electron temperature of radiation-heated CH foam was obtained.