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Measurements of parametric instabilities at laser intensities relevant to strong shock generation

  Articoli su Riviste JCR/ISI  (anno 2018)

Autori:  Cristoforetti G., Antonelli L., Atzeni S., Baffigi F., Barbato F., Batani D., Boutoux G., Colaitis A., Dostal J., Dudzak R., Juha L., Koester P., Marocchino A., Mancelli D., Nicolai Ph., Renner O., Santos J.J., Schiavi A., Skoric M.M., Smid M., Straka P., Gizzi LA

Affiliazione Autori:  1Intense Laser Irradiation Laboratory, INO-CNR, 56124 Pisa, Italy 2Dipartimento SBAI, Universita di Roma “La Sapienza,” 00185 Roma, Italy 3Empa Swiss Federal Laboratories for Materials Science and Technology, 8600 D€ubendorf, Switzerland 4Universite Bordeaux, CNRS, CEA, CELIA, UMR 5107, F-33405 Talence, France 5Institute of Plasma Physics, Czech Academy of Sciences, 182 00 Prague 8, Czech Republic 6Institute of Physics, Czech Academy of Sciences, 182 21 Prague 8, Czech Republic 7Laboratori Nazionali di Frascati, 00044 Frascati, Rome, Italy 8Donostia International Physics Center (DIPC), 20018 Donostia/San Sebastian, Basque Country, Spain 9National Institutes of Natural Sciences, 105-0001 Tokyo, Japan

Riassunto:  Parametric instabilities at laser intensities in the range (2–6)  1015 W/cm2 (438 nm, 250 ps, 100–300 J) have been investigated in planar geometry at the Prague Asterix Laser System facility via calorimetry and spectroscopy. The density scalelength of the plasma was varied by using an auxiliary pulse to form a preplasma before the arrival of the main laser beam and by changing the delay between the two pulses. Experimental data show that Stimulated Brillouin Scattering (SBS) is more effective than Stimulated Raman Scattering (SRS) in degrading laser-plasma coupling, therefore reducing the energy available for the generation of the shock wave. The level of the SBS backscatter and laser reflection is found to be in the range between 3% and 15% of the incident laser energy, while Backward SRS (BRS) reflectivity ranges between 0.02% and 0.2%, depending on the delay between the pulses. Half-integer harmonic emission is observed and provides a signature of Two Plasmon Decay (TPD) occurring around the quarter of the critical density. Data analysis suggests that SRS is driven in beam speckles with high local intensity and occurs in bursts, particularly at higher laser intensities, due to the presence of kinetic mechanisms saturating the SRS growth in the speckles. Time-resolved measurements also show that BRS occurs in the trailing part of the laser pulse, when the plasma has a longer density scalelength. Our measurements also indicate that hot electrons are predominantly produced by SRS rather than TPD.

Rivista/Giornale:  PHYSICS OF PLASMAS
Volume n.:  25      Pagine da: 012702  a: 012702
Parole chiave: Shock Ignition - laser-plasma

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