[en] A plasma model of the relaxation of a medium within the tracks of heavy ions in condensed matter is proposed that is based on solving time-dependent radiative collisional kinetic equations with the initial condition corresponding to a medium's state described by the classical model of multiple ionization of the target atoms by the field of fast multicharged ions. It is shown that the plasma model allows one to describe X-ray spectra recorded in the interaction of ion beams with condensed targets. An X-ray spectral method for plasma diagnostics is proposed that is based on the plasma model. The results obtained can also be used to study the initial stage of the formation of defects in solid bodies under the action of individual fast heavy ions

[en] A plasma model of the relaxation of a medium within the tracks of heavy ions in condensed matter is proposed that is based on solving time-dependent radiative collisional kinetic equations with the initial condition corresponding to a medium’s state described by the classical model of multiple ionization of the target atoms by the field of fast multicharged ions. It is shown that the plasma model allows one to describe X-ray spectra recorded in the interaction of ion beams with condensed targets. An X-ray spectral method for plasma diagnostics is proposed that is based on the plasma model. The results obtained can also be used to study the initial stage of the formation of defects in solid bodies under the action of individual fast heavy ions.

[en] We address an issue of measuring the parameters of an envolving laser-produced plasma commonly observable in high-energy density physics experiments. Available diagnostic equipment does not provide enough temporal, and often spatial, resolution to distinguish the signal coming from the region and timeframe of outmost interest, where deposited energy density reaches its maximum. In this paper, we propose and describe an approach that makes it possible to estimate the plasma parameters existing at the time of the main laser pulse arrival, as well as on later stages of plasma expansion. It is based on the analysis of X-ray spectral line profiles in multicharged ion spectra registered in simple time and spatially integrated mode. As an example, specific calculations were made for Ly_β line of Al XIII and He_β line of Al XII and can be used to diagnose aluminum plasmas with an electron temperature of 400–1000 eV, assuming that expanding plasma was homogeneous at every moment.

[en] The possibility is discussed of using optical laser radiation with an intensity of >10²⁰ W cm⁻² to create an ultraintense X-ray source capable of producing polychromatic radiation with a power flux of 10¹⁹ W cm⁻² or higher. X-ray radiation of so high an intensity permits not only transforming a condensed matter of the target into a plasma state but also obtaining an exotic plasma state with a high density of hollow ions. Currently not yet in wide use and available in only a few laboratories in the world, lasers with a radiation intensity of about 10²⁰ W cm⁻² are more compact and less expensive than free-electron X-ray lasers or lasers used for the indirect heating of fusion targets. The source under discussion can produce by far higher X-ray intensities than plasma X-ray lasers of a similar scale. (from the current literature)

[en] A plasma model of relaxation of a medium in heavy-ion tracks in condensed matter has been proposed. The model is based on the solution of time-dependent equations of radiative-collisional kinetics. The state of the medium, which is described in the framework of the classical model of multiple ionization of target atoms by a field of fast multiply charged ions, is used as the initial condition. The relaxation in the plasma is investigated using molecular dynamics simulation. An analysis of the results of the calculations performed has made it possible to determine the range of material parameters at which the plasma model actually changes over to the atomic model and to establish the conditions where the atomic model is a very rough approximation. It is demonstrated that the plasma model adequately describes the X-ray spectra recorded upon interaction of ion beams with condensed targets. An X-ray spectral method based on the plasma model is proposed for diagnosing the plasma in fast-ion tracks. The results obtained can be useful in examining the initial stage of defect formation in solids under irradiation with single fast heavy ions

[en] A plasma model of relaxation of a medium in heavy ion tracks in condensed matter is proposed. The model is based on three assumptions: the Maxwell distribution of plasma electrons, localization of plasma inside the track nanochannel and constant values of the plasma electron density and temperature during the x-ray irradiation. It is demonstrated that the plasma relaxation model adequately describes the x-ray spectra observed upon interaction of a fast ion with condensed target. Assumptions of plasma relaxation model are validated by the molecular dynamics modeling and simulation.

[en] Mica crystals are widely applied in x-ray spectroscopy diagnostics since their ability to effectively reflect the radiation in different orders covering a wide range of photon energy, including sub-keV range hardly accessible with other crystals. Particularly, spherically bent mica crystals are commonly used in high energy density plasma imaging spectrometry diagnostics. However, the detailed reflectivity properties of bent mica crystals are not known well. Here we propose and verify the way to calibrate mica crystal spectral reflectivity in the experiment with relativistic laser plasma. The approach is based on the comparison of dense laser plasma x-ray spectra measured by focusing spectrometers with spatial resolution equipped, with examined mica and pre-calibrated alpha-quartz bent crystals. As a result, the normalized reflectivity of spherically bent mica crystal operated in 2^nd order of reflection was experimentally evaluated for the first time versus wavelength in the range of 6.7-8.7 Å. The obtained spectral calibration curve for bent mica crystal demonstrates remarkable difference to that one calculated for flat mica crystal and given in Henke tables and has to be applied further for a correct interpretation of the measured x-ray spectra. (paper)

[en] Spherically bent crystals are widely used in focusing monochromators, spectrometers and other x-ray optical systems. In particular, they are used in focusing spectrometers with spatial resolution, applied in high energy density diagnostics and warm dense matter studies. In this case, plasma parameters are obtained via measurements of relative intensities of characteristic spectral emission lines for multiply charged ions, which are affected by an instrumental function. Here we develop and use the ray-tracing computer simulations to study reflectivity properties of spherically bent crystals in a particular experimental conditions and to provide the method to adjust and validate the measured spectral line intensities on quantitative basis. (paper)

[en] A new technique for X-ray spectromicroscopy of fast heavy ion radiation during the ion interaction with stopping media is presented using focusing spectrometers with spatial resolution. Spherically bent crystals of quartz and mica with small curvature radii, R=150 mm, and large apertures were used as dispersive elements in experiments on fast Ni ions with energies of 5.9 and 11.2 MeV/u which are being stopped in different media: Ar gas, SiO₂-aerogels and solid quartz. Spectrally high (λ/Δλ=1000-3000) and spatially high (up to 10-100 μm) resolved Kα-satellite spectra of Ni projectiles as well as of the ionized stopping media were observed

[en] We diagnose the self-channeled propagation of intense femtosecond pulses over an extended distance in a N₂O cluster gas target using high resolution kilovolt x-ray pinhole images of the channel and spatially resolved x-ray spectra. The x-ray images are consistent with femtosecond optical scattering, shadowgraphy, and interferometry images. We observe extended plasma channels (∼9 mm) limited either by the cluster jet length or by absorption, for injected laser intensities in the range of 10¹⁶-10¹⁷ W/cm². Spectral line shapes for the OVII 1s²-1s3p and OVIII 1s-2p transitions (at 1.8627 and 1.8969 nm, respectively) show significant broadening to the blue side and with truncated emission on the red side. We attribute this effect to Doppler blueshifted emission from fast ions from exploding clusters moving toward the spectrometer; redshifted emission from the opposite side of the cluster is absorbed