Experimental X-ray Spectra Research Articles

Soft X-ray emission from a CO2 laser-heated Z-pinch plasma

We report results of soft X-ray measurements in which a high-power (1010–1011 W/cm2) CO2 laser was used to heat a near critical density (<1019 cm−3) helium Z-pinch plasma. Frequency-integrated X-ray data show that the unheated Z-pinch plasma is Maxwellian with a temperature of about 30 eV. During laser heating, the X-ray emissions were enhanced over the unheated emissions. Analysis of the experimental X-ray spectra indicate that the low-energy portion of the X-ray emission spectrum (up to 600 eV) is enhanced over the baseline 30 eV Maxwellian emissions. This result is consistent with an inverse bremsstrahlung-modified distribution which results when the plasma heating rate is more rapid than the collisional thermalization rate. These results suggest that it may be possible to enhance the soft X-ray yield of a plasma lithographic source with laser heating.

Dielectronic satellite spectrum of heliumlike argon: A contribution to the physics of highly charged ions and plasma impurity transport.

Wavelengths and atomic parameters for the satellite spectrum of the 1s/sup 2/-1s2p parent lines of Ar/sup 16 +/ have been calculated using a multiconfiguration intermediate-coupling scheme with a statistical Thomas-Fermi potential. These data, together with radial charge-state distributions given by an impurity transport code, are used to calculate theoretical spectra. The comparison with experimental x-ray spectra from the TFR tokamak plasma shows good agreement between calculated and observed wavelengths. The fitting of relative line intensities in the synthetic spectra to observed values improves the understanding of plasma impurity transport.

δelectrons and continuous x rays in heavy-ion—atom collisions

Doubly differential cross sections have been measured for the production of 10-70-keV $\ensuremath{\delta}$ electrons and \ensuremath{\sim}10-50-keV continuum x rays generated in collisions between 65-MeV nickel ions and nickel foil targets. The data on $\ensuremath{\delta}$ electrons have been used to calculate corresponding yields of secondary-electron bremsstrahlung (SEB) including retardation effects. Magnitude, energy, and angular dependence of resulting SEB yields are discussed in detail. It is concluded that SEB contributions do not dominate experimental continuous x-ray spectra.

Fast-electron production in laser-heated plasmas

The continuum X-ray emission from laser-heated targets gives a measure of the energy deposited in superthermal electrons and an estimate of the spectrum and the average electron energy. The validity of the analysis is, however, limited by possible non-collisional energy-loss processes in the pellet corona. If this effect is ignored, fits to experimental X-ray spectra from glass microspheres at 1.06-µm laser wavelength can be readily obtained showing 15%–48% of the absorbed energy in fast electrons.

On the X-ray and UV photoelectron spectra of the difluorobenzenes

Ab initio calculations with a double zeta contracted gaussian basis are used to discuss the ionization potentials of o-, m- and p-difluorobenzene, and the correlation with benzene. Interpretations of the experimental X-ray and UV photoelectron spectra are given.

Energy Deposition in Laser-Heated Plasmas

The number and energy distribution of suprathermal electrons produced in a laser-heated plasma can be quantitatively obtained directly from the experimental x-ray spectrum with only the assumption that the fast electrons lose energy by bremsstrahlung and electron-electron collisions. The result is independent of the spatial and temporal distribution of electron density and temperature.

Study of the x-ray production mechanism of a dense plasma focus

The x-ray emission from a 375-kJ plasma focus is reported as measured on a time-resolved basis with Ross filters and silicon diode detectors. Thick-target electron beam spectra are calculated with a Monte Carlo electron beam transport program and fit to the experimental time-integrated x-ray spectra. A good fit is obtained with a 2-MA E−2 power law electron beam, with cutoff energies at 8 and 200 keV, incident normal to a thick tungsten target. The source of the beam is judged to be electrons which are accelerated under the influence of strong electric fields. A 20-nsec Q-switched ruby laser pulse injected tungsten ions via laser ablation prior to the initial dense pinch, and the x-ray emission below 4 keV was enhanced and that above 10 keV was reduced. The enhanced low-energy x-ray emission is in agreement with calculated radiation for collisional M-shell excitation of highly stripped tungsten in a 1.5-keV thermal plasma. A 900- μsec ruby laser pulse injected sufficient tungsten ions to degrade greatly the initial dense plasma pinch and reduce the beam target x-ray emission. The time-resolved x-ray emission from this configuration appeared as a smooth Gaussian function in time with FWHM∼200 nsec.

IR absorption spectrum of thiohydantoin

The IR absorption spectrum of thiohydantoin is found in the range 400–3500 cam−1, and the normal-mode frequencies are calculated on the basis of a model. The IR spectrum is interpreted on the basis of the theoretical results, the experimental x-ray spectrum, and the microwave dielectric constants.