Energetics of multiple-ion species hohlraum plasmas

Neumayer, P.; Berger, R. L.; Callahan, D.; Divol, L.; Froula, D. H.; London, R. A.; MacGowan, B. J.; Meezan, N. B.; Michel, P. A.; Ross, J. S.; Sorce, C.; Widmann, K.; Suter, L. J.; Glenzer, S. H.
May 2008
Physics of Plasmas;May2008, Vol. 15 Issue 5, p056307
Academic Journal
A study of the laser-plasma interaction processes has been performed in multiple-ion species hohlraum plasmas at conditions similar to those expected in indirect drive inertial confinement fusion targets. Gas-filled hohlraums with electron densities of 5.5×1020 and 9×1020 cm-3 are heated by 14.3 kJ of laser energy (wavelength 351 nm) to electron temperatures of 3 keV and backscattered laser light is measured. Landau damping of the ion acoustic waves is increased by adding hydrogen to a CO2 or CF4 gas. Stimulated Brillouin backscattering of a 351 nm probe beam is found to decrease monotonically with increasing Landau damping, accompanied by a comparable increase in the transmission. More efficient energy coupling into the hohlraum by suppression of backscatter from the heater beams results in an increased hohlraum radiation temperature, showing that multiple-ion species plasmas improve the overall hohlraum energetics. The reduction in backscatter is reproduced by linear gain calculations as well as detailed full-scale three-dimensional laser-plasma interaction simulations, demonstrating that Landau damping is the controlling damping mechanism in inertial confinement fusion relevant high-electron temperature plasmas. These findings have led to the inclusion of multiple-ion species plasmas in the hohlraum point design for upcoming ignition campaigns at the National Ignition Facility.


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