Abstract
AbstractThe use of the Laser MegaJoule facility within the shock ignition scheme has been considered. In the first part of the study, one-dimensional hydrodynamic calculations were performed for an inertial confinement fusion capsule in the context of the shock ignition scheme providing the energy gain and an estimation of the increase of the peak power due to the reduction of the photon penetration expected during the high-intensity spike pulse. In the second part, we considered a Laser MegaJoule configuration consisting of 176 laser beams that have been grouped providing two different irradiation schemes. In this configuration the maximum available energy and power are 1.3 MJ and 440 TW. Optimization of the laser–capsule parameters that minimize the irradiation non-uniformity during the first few ns of the foot pulse has been performed. The calculations take into account the specific elliptical laser intensity profile provided at the Laser MegaJoule and the expected beam uncertainties. A significant improvement of the illumination uniformity provided by the polar direct drive technique has been demonstrated. Three-dimensional hydrodynamic calculations have been performed in order to analyse the magnitude of the azimuthal component of the irradiation that is neglected in two-dimensional hydrodynamic simulations.
Highlights
One of the main goals of inertial confinement fusion (ICF)[1,2,3] concerns the ignition of the thermonuclear fusion reactions in a mixture of deuterium–tritium (DT) nuclear fuel
The Laser MegaJoule facility has been considered in the context of the shock ignition scheme
A set of mono-dimensional numerical simulations has been performed to enlighten some aspect of the shock ignition scheme
Summary
A crucial issue concerns the uniformity of the capsule irradiation. A successful capsule implosion requires a very uniform irradiation and capsule target; otherwise, the imploding shell suffers the growth of dangerous hydrodynamic instabilities (Richtmyer–Meshkov[6, 7] and Rayleigh–Taylor (RT)[8, 9]) and shell deformations that could even destroy the hot-spot. The SI pulse must be carefully tuned in time to synchronize the strong shock wave with the compression shock rebounded from the centre after stagnation This new scheme promises higher gain[18,19,20,21] in comparison to central ignition, and the separation between the compression and the ignition phase allows for less stringent conditions in terms of irradiation uniformity[22, 23]. Caution is necessary due to the uncertainties related to laser– plasma instabilities such as stimulated Raman scattering (SRS)[26], stimulated Brillouin scattering (SBS)[27], and the two-plasmon decay (TPD)[28] expected at the high laser intensities I λ2 > 1015 W cm−2 μm2[29] provided during the shock ignition pulse These dangerous instabilities act to reduce the energy deposition efficiency and generate highenergetic (≈10–40 keV) electrons[30,31,32].
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