Stochastic homogenization of the laser intensity to improve the irradiation uniformity of capsules directly driven by thousands laser beams

Abstract

Abstract. Illumination uniformity of a spherical capsule directly driven by láser beams has been assessed numerically. Láser facilities characterized by ND = 12, 20, 24, 32, 48 and 60 directions of irradiation with associated a single láser beam or a bundle of NB láser beams have been considered. The láser beam intensity profile is assumed super-Gaussian and the calculations take into account beam imperfections as power imbalance and pointing errors. The optimum láser intensity profile, which minimizes the root-meansquare deviation of the capsule illumination, depends on the valúes of the beam imperfections. Assuming that the NB beams are statistically independents is found that they provide a stochastic homogenization of the láser intensity associated to the whole bundle, reducing the errors associated to the whole bundle by the factor 1/N B , which in turn improves the illumination uniformity of the capsule. Moreover, it is found that the uniformity of the irradiation is almost the same for all facilities and only depends on the total number of láser beams Not = ND X NB •

Illumination uniformity of capsules directly driven by a facility with thousands of laser beams

“…This is a natural way in order to reduce the imperfections associated to the whole bundle. It is found that the illumination uniformity scales as 1/N 1 / 2 tot and is given [16,17] by (N tot ) = [ where N D is the number of irradiation directions.…”

“…It is shown that the optimal focal spot shape depends on the beam imperfections [13] and that taking beam imperfection into account the illumination uniformity is degraded by about one order of magnitude [11]. Finally, it is shown that the use of bundles [14,15] of N B beamlets (laser beam unit) associated to each irradiation direction introduces a stochastic homogenization of the laser intensity which benefits the irradiation uniformity [16,17]. …”

“…In this phase the expansion of the plasma corona does not affect the laser reflection and the uniformity of the energy deposition could be analyzed assuming a direct illumination of the capsule [11]. The laser beams assembled in a facility are affected by unavoidable imperfections as power imbalance and pointing error [11][12][13][14][15][16][17][18]. In this paper we analyze the illumination uniformity provided by five irradiation configurations characterized by N D = 12, 20, 32, 48 and 60 irradiation directions [12].…”

Effect of the laser intensity profile on the shock non-uniformity in a directly driven spherical target

“…2002; Temporal et al. 2011 a , 2013, 2014 a ; Temporal & Canaud 2011 b ; Tian et al. 2015), but the validity of its solutions has only been partially tested in two-dimensional (Temporal et al.…”

Comparison between illumination model and hydrodynamic simulation for a direct drive laser irradiated target

“…The model can also include statistical analyses that take into account beam uncertainties such as power-imbalance, pointing error and target positioning. Several studies have been performed to analyze the capsule illumination uniformity for different facilities (Murakami, et al, 1993(Murakami, et al, , 1995(Murakami, et al, , 2010Canaud et al, 2002;Temporal et al, 2009Temporal et al, , 2010aTemporal et al, , 2010bTemporal et al, , 2011aTemporal et al, , 2011bTemporal et al, , 2014aTemporal et al, , 2014b. In these studies it has been assumed that the quality of the illumination (usually measured by a rootmean-square deviation of the incident intensity on a 2/8 spherical surface) is representative of the non-uniformity induced in the first shock wave, also called imprint phase.…”