Because germanium and silicon may be used as dopants in the ablator of ignition target, the knowledge of their opacities is crucial. We have calculated the opacity by using two approaches. The first one utilizes a detailed line calculation in which the atomic database is provided by the MCDF code. A lineshape code was then adapted to the calculation of opacity profiles. Because the calculation time is prohibitive when the number of lines is huge, a second approach, combining detailed line calculations and statistical calculations is used. This approach necessitates much smaller calculation than the first one and is then well suited for extensive calculations. The monochromatic opacity and the Rosseland and Planck mean opacities are calculated for various relevant densities and temperatures.
We describe our recent progress in the investigation of the spectral properties of collisional XUV lasers, including both
experimental measurements and numerical calculations. Using a wavefront-division, variable path-difference
interferometer, we have characterized the temporal coherence and the spectral width of an injection-seeded transient
XUV laser emitted at 18.9 nm from a Ni-like Mo plasma. Our results show that the temporal coherence of the beam is
significantly increased by the injection-seeded operation, compared to the standard ASE mode, in agreement with
detailed numerical simulations. Using the PPP code we have calculated the intrinsic linewidth of the same lasing line
over a range of electron density and at temperatures that are relevant to transient collisional pumping. We discuss the
relative contributions of homogeneous and inhomogeneous broadening to the overall profile.
We present new calculations on radiative power losses of carbon and gold. Both ions are involved in inertial
confinement fusion. The first element could also be utilized in the walls of future TOKAMAK reactors such as
ITER (International Thermonuclear Experimental Reactor) while the second is present in holraums and its X-ray
emission contributes to the heating in ICF. Because argon impurities may be used in the fusion core, in order to
diagnose the electron temperature, we have calculated the intensities of the He-β line and the Li-like Ar satellite
lines. In fact, the intensity ratio depends on electron temperature. The effect of the plasma electric field on the
line intensities is discussed. Our approach is based on a detailed line calculation in which the atomic database
is provided by the MCDF code. Then a lineshape code allowing for NLTE ionic populations was adapted to the
calculation of RPL profiles. Because the calculation time is sometimes prohibitive, a second approach, based on
the first moments of the RPL, is investigated. This approach was used for extensive calculations on germanium.
We present a detailed analysis of an experiment carried out recently in which the temporal coherence of the Ni-like silver transient X-laser at 13.9 nm was measured. Two main consequences of this measurement will be discussed and interpreted with numerical calculations. First we show that the high temporal coherence length measured corresponds to an extremely narrow spectral width of the X-ray laser line. Second we show that the high temporal coherence helps to explain the presence of small-scale structures observed in the cross-section of all transient X-ray laser beams.
Longitudinal coherence length in x-ray lasers depends strongly on the shape of the amplified line. We have modeled an experiment performed at the Lawrence Livermore National Laboratory. The experiment was devoted to the study of the temporal (longitudinal) coherence of the transient x-ray laser at 14.7 nm in Ni-like palladium (4d-4p transition). Only electron (collisional) and Doppler broadening play a role in the line profile of the 0-1 4d-4p transition. This allows us to use the Voigt shape in conditions where the amplifier, i.e., the plasma produced by the interaction of a high intensity laser with a slab target, is neither stationary nor homogeneous. Our calculations use a ray trace code which is constructed as a post-processor of the hydro-atomic code EHYBRID. In the saturation regime, there is need to account properly for the interaction between the x-ray laser field and the lasing ions. This is done in the framework of the Maxwell-Bloch formalism. The FWHM of the spontaneous emission profile is ~28 mÅ, while the width of the amplified x-ray line ~4 mÅ. Comparison with experiment is discussed.
Metrology of XUV beams and more specifically X-ray laser (XRL) beam is of crucial importance for development of applications. We have then developed several new optical systems enabling to measure the x-ray laser optical properties. By use of a Michelson interferometer working as a Fourier-Transform spectrometer, the line shapes of different x-ray lasers have been measured with an unprecedented accuracy (δλ/λ~10-6). Achievement of the first XUV wavefront sensor has enable to measure the beam quality of laser-pumped as well as discharge pumped x-ray lasers. Capillary discharge XRL has demonstrated a very good wavefront allowing to achieve intensity as high 3*1014 Wcm-2 by focusing with a f = 5 cm mirror. The measured sensor accuracy is as good as λ/120 at 13 nm. Commercial developments are under way.
Recent high temporal resolution Ni-like x-ray laser experiments have yielded important insights into the output characteristics of picosecond pumped x-ray lasers. However, current experimental observations do not fully explain the plasma dynamics which are critical to the gain generation within the x-ray laser medium. A theoretical study of the Ni-like Silver x-ray laser has therefore been undertaken to compliment our experimental results, in an attempt to further our understanding of the processes at play in yielding the observed x-ray laser output. Preliminary findings are presented within this paper.
Large amplification at 25.5 nm in neon-like iron has been demonstrated in experiments where prepulses are used. We show that the interaction between the x-ray laser beam and the amplifying medium must be taken into account in a reliable modeling of the saturation regime. Two approaches for intensity calculations are presented in this contribution. The first one combines the radiative transfer equation and the population rate equations. This approach is fully consistent, in the sense that beam amplification and population kinetics are treated simultaneously. A formalism based on a paraxial Maxwell-Bloch approach is presented. The Maxwell-Bloch calculations give the variation with length of intensity, local gain...Moreover, in the small-signal regime, it is possible to define an effective gain which is comparable to the measured gain. The second approach is based on a raytrace calculation where the saturation effect has been introduced empirically. The two codes need the electron density and the electron and ion temperatures as inputs. These quantities are given by the hydrocode EHYBRID. The two approaches give similar results.
We investigate the polarization state of x-ray beams in collisionally pumped lasers, and compare our results to experimental data on Ne-like Ge lines. The plasma polarization properties are studied in terms of the orientation and alignment, using irreducible tensors of the density matrix. It is shown that the elastic electron-ion collisions tend to equalize the quantum-states populations of each level, and then lessen or even eliminate the polarization of the medium, that is induced by the x-ray beam.
Line profiles taking into account ion (Stark) broadening, ion dynamic effect, and electron collisions are calculated for the Al10+ lines at 154.7 and 105.7 angstrom, and for the S13+ line at 206.5 angstrom in recombination lasers. The first two lines are formed of three fine structure components, while the third is constituted of nine components, and the resulting gain may be defined accordingly. The electron collisions yield an homogeneous broadening, while the Stark interaction with neighboring ions is responsible for an asymmetry of the whole profile. Consistently with the experimental determination of the gain, we calculate the total intensity involving the population inversions of the set of components which contribute to the lasing radiation, and deduce an effective small-signal gain coefficient. We discuss our results and compare them to experimental gains.