Photoionization experiments in dense argon gas

At densities above 50 Amagats, light of frequency 2.818 x 10⁴cm^-1 ionizes efficiently argon gas containing less than 1 part per million of impurities. For a given density we find for the number of free charges produced a square law dependence on light intensity. At constant light intensity the number of free charges produced varies approximately like the sixth power of density in the range 200–500 Amagats.     

Analysis of direct-drive capsule compression experiments on the Iskra-5 laser facility

We have analyzed and numerically simulated our experiments on the compression of DT-gas-filled glass capsules under irradiation by a small number of beams on the Iskra-5 facility (12 beams) at the second harmonic of an iodine laser (λ = 0.66 μm) for a laser pulse energy of 2 kJ and duration of 0.5 ns in the case of asymmetric irradiation and compression. Our simulations include the construction of a target illumination map and a histogram of the target surface illumination distribution; 1D capsule compression simulations based on the DIANA code corresponding to various target surface regions; and 2D compression simulations based on the NUTCY code corresponding to the illumination conditions. We have succeeded in reproducing the shape of the compressed region at the time of maximum compression and the reduction in neutron yield (compared to the 1D simulations) to the experimentally observed values. For the Iskra-5 conditions, we have considered targets that can provide a more symmetric compression and a higher neutron yield.     

Generation of terahertz radiation upon the optical breakdown of a gas

Terahertz radiation of plasma oscillations excited upon the optical (axicon) breakdown of a gas in the presence of external fields of other frequency ranges has been analyzed. It has been shown that the spectra and intensity of oscillations and radiation generated by them depend strongly on the character of the spatiotemporal evolution of the formed plasma. The intensity is maximal upon the rapid formation of the plasma with a sharp boundary and decreases to very low values for objects with a smooth density profile. New schemes and regimes of break-down have been proposed, which make possible, according to preliminary estimates, an emitted energy of about 10 mJ with moderate intensities of ionizing laser radiation.     

Indirect (x-ray) irradiation of encapsulated microtargets in the Iskra-5 facility

Experiments on the indirect (x-ray) irradiation of high-aspect-ratio capsules (with a diameter-to-thickness ratio ≈900) filled with DT gas are performed on the Iskra-5 laser facility. It is shown that all the characteristics measured (neutron yield, ion temperature, shell implosion time, etc.) are faithfully reproduced in calculations based on the one-dimensional SNDA (spectral nonequilibrium diffusion of absorption) program for nonequilibrium radiation gas dynamics. The calculations provide an explanation for the experimentally detected generation of a smaller number of neutrons in an experiment with a higher measured value for the ion temperature of DT gas. Zh. éksp. Teor. Fiz. 114, 1993–2003 (December 1998)     

Transverse scattering of radiation upon focusing of pump laser beam to line in experiments on X-ray laser

The force matrix of the SO₂ molecule is calculated without using a priori assumptions on the nature of the force field. The calculations are performed using a comparatively new 3N-matrix method based on the experimental frequencies of characteristic normal vibrations of ³²S¹⁶O₂, ³²S¹⁸O₂, and ³⁴S¹⁶O₂ molecules. It is shown that the direction of the chemical bond between chemically bound S and O atoms does not coincide with the direction of the straight line that connects the nuclei of these atoms. The angle between these directions (deviation angle) is determined. In the approximation of harmonic vibrations, the deviation angle is Δ = 1.092°. The effect of the anharmonicity of vibrations on the deviation angle is evaluated.     

Investigation of the effect of large-scale shell asymmetry on Iskra-5 target operation

Experiments designed to investigate the effect of a controlled large-scale asymmetry of a shell containing deuterium-tritium fuel on the shell compression and neutron production under indirect (x-ray) action are performed on the Iskra-5 laser fusion device. The uniformity of the x radiation near the target is not worse than 3%, and the shell asymmetry is varied from 30 to 100%. The observed decrease of the experimental neutron yield as compared with experiments using symmetric targets is in satisfactory agreement with two-dimensional calculations. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 161–165 (10 February 1998)     

Simulation of the transition radiation detection conditions in the ATLAS TRT detector filled with argon and krypton gas mixtures

Performance of the Transition Radiation Tracker (TRT) at the ATLAS experiment with argon and krypton gas mixtures was simulated. The efficiency of transition radiation registration, which is necessary for electron identification, was estimated along with the electron identification capabilities under such conditions.     

Filamentation control in the temperature gradient argon gas

A novel technique of controlling the evolution of the filamentation was experimentally demonstrated in an argon gas-filled tube. The entrance of the filament was heated by a furnace and the other end was cooled with air, which resulted in the temperature gradient distribution along the tube. The experimental results show that multiple filaments are merged into a single filament and then no filament by only increasing the temperature at the entrance of the filament. Also, the filament can appear and disappear after increasing the local temperature and input pulse energy in turn. This technique offers another degree of freedom to control the filamentation and opens a new way for multi-mJ level monocycle pulse generation through filamentation in the noble gas.     

Gas-Dynamic Research Technique of Indirectly Irradiated Targets in Porous Materials at Iskra-5 Fasility

In this paper, studies of gas-dynamic flows in samples of various materials loaded with an X-ray flux in “Illuminator”-type targets on Iskra-5 laser facility of the ILFI VNIIEF are presented. The obtained results on the velocity of shock waves in the sample under the study are compared with model calculations to match the gas-dynamic parameters to their calculated estimates.     

Measurement of the argon continuum radiation in the near vacuum ultraviolet

Absolute argon continuum emission coefficients have been measured from 330 nm down to 110 nm in the near v.u.v. The radiation originates from a stationary 1 atm arc plasma with temperatures between 16900 and 21500 K. At these high temperatures, single ionization is almost complete and the plasma contains also a number of doubly ionized particles. These cause very intense recombination edges around 120 nm, which have been included in a recent theory. The agreement with these calculations is very good throughout the spectrum for lower plasma temperatures. Measurements at higher temperatures confirm only the results for the Ar(II) edges around 120 nm. At higher wavelengths the experimental values lie above the theoretical ones and do not show the predicted structure. This discrepancy may be partly due to omissions in the calculations and partly to line wing problems in the experiment.     

Absolute line strengths of phosphine gas near 5 μm

Absolute line strengths and line positions for over 200 vibration-rotation transitions of PH₃ gas were measured at 295 K, using a tunable-diode laser spectrometer. The spectral range covered was from 2153.697 to 2210.566 cm^?1. Line strength measurements were reproducible to better than 5% on average, and the uncertainty in line positions was less than 0.002 cm^?1. Certain of the PH₃ lines were pressure-broadened with H₂ gas, and the pressure-broadening coefficients were determined.     

Generation of cyclotron harmonic waves in the ionosphericmodification experiments

In the present paper, the parametric decay instability of the pump X-mode into electron Bernstein wave (EBW) near second harmonics of electron cyclotron frequency and IBW at different harmonics (ωci; n=2,3,4) is examined. Expressions are derived for homogenous threshold, growth rate and convective threshold for this instability. Applications and relevances of the present investigation to ionospheric modification experiment in the F-layer of the ionosphere as well as during intense electron cyclotron resonance heating in the upcoming MTX tokamak have been given     

Atomic line radiation in the infrared

The present paper considers atomic infrared line emission from states of high angular momentum, which should be significally populated in a high-temperature, equilibrium (LTE) gas. Such states are shown to give rise to a “universal” series of strong lines, the first member of which is at ～4μ, and corresponds to the puzzling 4 μ-feature by Taylor and Caledonia.Several of the higher members of the predicated series are found in cesium spectra taken in our laboratory.     

The spatial distribution of argon clusters in gas jet

The spatial distribution of argon clusters in gas jet is tested using the Rayleigh scattering method. A pulsed laser is used to acquire the whole evolution of the cluster inside one event. The measured results at a fixed axial position show that the argon clusters grow in less than one millisecond after the nozzle is opened and the cluster size keeps constant during the whole open period of 20 ms. Further results show that the scattering signal along the radial direction is almost Gaussian-distributed and the full width half maximum (FWHM) increases almost linearly when the distance from nozzle increases. The scattering signal along the axial direction is Landau-distributed and the area near the nozzle is most effective for laser cluster interaction.     

Simulation of high frequency positron behaviour in argon gas

Positron annihilation and average energy in argon have been investigated in the presence of external high frequency electric and steady magnetic fields. The effect of temperature has also been studied. Two models of positron atom interaction have been employed and compared with experimental results wherever possible.     

Generation of infrared radiation by stimulated Raman scattering in para-hydrogen crystal at 5 K

We report the preliminary results of our experiments with stimulated Raman scattering in para-hydrogen crystal aimed at developing a continuously tunable laboratory laser source of mid-infrared radiation. With laser pulses at 532 nm, a conversion efficiency for the first Stokes beam of as much as 20% in the forward direction was observed through a single-pass, 5-cm-long crystal. Generation of mid-infrared pulses at 4.5 microm was achieved by use of the output of a near-infrared pulsed laser (1.6 microm, 3 ns), and an absorption spectrum of gaseous CD4 molecules was successfully recorded. These results suggest use of the solid para-hydrogen Raman shifter as a promising light source for mid-infrared spectroscopy.