Comparative studies of Laser induced plasma in TEOS and MTMS based aerogels and solid quartz
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Comparative studies of Laser induced plasma in TEOS and MTMS based aerogels and solid quartz 1
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A. Venkateswara Rao* , Channprit Kaur, A. A. Pisal , S. Chaurasia , M. N. Deo and S. M. 2 Sharma 1 Air Glass Laboratory, Department of Physics, Shivaji University, Kolhapur – 416004, Maharashtra, India. 2 High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai – 400085, Maharashtra, India. Abstract: The interaction of laser radiation with low density aerogels is of crucial importance in areas such as the creation of coherent radiation sources in the X-ray range, simulation of astrophysical as well as nuclear fusion phenomena in laboratory and fundamental studies of the properties of soft condensed matter under dynamic pressure in the Mbar range. In the present paper, the experimental results on the X-ray emission of laser induced plasma in TEOS based, MTMS based aerogels and solid quartz targets, are reported. The aerogels were produced by the sol-gel processing of tetraethoxysilane (TEOS) and methyltrimethoxysilane (MTMS) followed by supercritical drying. Silica alcogels were produced using 0.001 M oxalic acid (C 2H4O4), 0.5 M ammonium hydroxide (NH4OH) catalysts. Different densities of aerogels varying from 0.02 3 to 0.06 g/cm have been obtained using different molar ratios of TEOS, MTMS, ethanol and 14 2 catalysts. The laser, with intensity up to 2 x 10 W/m , interaction with TEOS and MTMS based aerogels have been conducted using 30J/500 ps Nd : glass laser system. The resulting soft (0.8 – 1.56 Kev) and hard (>4 Kev) X-ray emissions have been measured using semiconductor photodiodes. It has been observed that the soft X-ray yield increases by a factor of two for the silica aerogel targets compared to the X-ray emission from the solid quartz target, whereas the hard X-ray yield reduces. The enhanced soft X-ray yield in silica aerogel targets is attributed to the large volume heating. INTRODUCTION The use of low-density porous media of various types of targets illuminated by highpower laser pulses is a very promising approach to study the Physics of interaction between a laser beam and matter, and can lead to the successful resolution of a number of important scientific and technical applications. The interaction of laser beam with low-density silica aerogels is considered as very important and suitable in advanced inertial confinement fusion (ICF) target design. In the direct drive scheme, it is possible to significantly alter the spatial density distribution of the plasma corona that forms at the illuminated surface of a spherical thermonuclear target by depositing, on the surface, a layer of aerogel foam with a suitably chosen thickness and initial density made from elements with low atomic numbers [1–3]. This will lead to efficient smoothening, i.e. uniform energy deposition, to the targets in the direct drive ICF. In the indirect drive scheme, implosion efficiency of the fuel pellet directly depends on the laser to X-ray conversion efficiency of the hohlraum walls
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