Irradiation uniformity at the Laser MegaJoule facility in the context of the shock ignition scheme

The role of the coronal electron plasma temperature for shock-ignition conditions is analysed with respect to the dominant parametric processes: stimulated Brillouin scattering, stimulated Raman scattering, two-plasmon decay (TPD), Langmuir decay instability (LDI) and cavitation. TPD instability and cavitation are sensitive to the electron temperature. At the same time the reflectivity and high-energy electron production are strongly affected. For low plasma temperatures the LDI plays a dominant role in the TPD saturation. An understanding of laser-plasma interaction in the context of shock ignition is an important issue due to the localization of energy deposition by collective effects and hot electron production. This in turn can have consequences for the compression phase and the resulting gain factor of the implosion phase.

Section: Introductionmentioning

confidence: 99%

“…This affects the gain considerably as far as ignition is concerned [11] . More detailed investigations are required concerning the coupling of kinetic simulation results from LPI and radiation hydrodynamic simulations for the compression and ignition phase.…”

Section: Introductionmentioning

confidence: 99%

Temperature dependence of parametric instabilities in the context of the shock-ignition approach to inertial confinement fusion

Weber

Riconda

2015

“…In this case the higher intensity is situated between It is worth noticing that these optimum intensities are located off-centre. This could be regarded as the application of the polar direct-drive [15] (PDD) technique where a centred laser intensity profile moves towards the equator to compensate the over-irradiation of the polar zones [16] . In addition, it has been shown [17,18] that for the configurations C and D elliptical intensity profiles provide a more uniform irradiation than circular ones.…”

Section: Optimal Profile For Some Lmj Configurationsmentioning

confidence: 99%

Optimal laser intensity profiles for a uniform target illumination in direct-drive inertial confinement fusion

Temporal

Canaud

Garbett

et al. 2014

Self Cite

A numerical method providing the optimal laser intensity profiles for a direct-drive inertial confinement fusion scheme has been developed. The method provides an alternative approach to phase-space optimization studies, which can prove computationally expensive. The method applies to a generic irradiation configuration characterized by an arbitrary number N B of laser beams provided that they irradiate the whole target surface, and thus goes beyond previous analyses limited to symmetric configurations. The calculated laser intensity profiles optimize the illumination of a spherical target. This paper focuses on description of the method, which uses two steps: first, the target irradiation is calculated for initial trial laser intensities, and then in a second step the optimal laser intensities are obtained by correcting the trial intensities using the calculated illumination. A limited number of example applications to direct drive on the Laser MegaJoule (LMJ) are described.

“…Due to the intrinsic difficulty of resolving the different time scales involved in SBS and SRS, many studies prefer to focus either on SRS evolution and saturation [12][13][14][15][16][17][18] , or SBS evolution and saturation by itself [19][20][21][22][23][24] . The analysis of parametric instabilities in this paper is mostly of relevance to large-scale, homogeneous plasmas as in intense speckle in indirect-drive conditions [25] , or in the low-density part in shock-ignition conditions [26][27][28][29] .…”

Section: Introductionmentioning

confidence: 99%

Raman–Brillouin interplay for inertial confinement fusion relevant laser–plasma interaction

Riconda

Weber

2016

The co-existence of the Raman and Brillouin backscattering instability is an important issue for inertial confinement fusion. The present paper presents extensive one-dimensional (1D) particle-in-cell (PIC) simulations for a wide range of parameters extending and complementing previous findings. PIC simulations show that the scenario of reflectivity evolution and saturation is very sensitive to the temperatures, intensities, size of plasma and boundary conditions employed. The Langmuir decay instability is observed for rather small k epw λ D but has no influence on the saturation of Brillouin backscattering, although there is a clear correlation of Langmuir decay instability modes and ion-fractional decay for certain parameter ranges. Raman backscattering appears at any intensity and temperature but is only a transient phenomenon. In several configurations forward as well as backward Raman scattering is observed. For the intensities considered, I λ 2 o above 10 15 W µm 2 /cm 2 , Raman is always of bursty nature. A particular setup allows the simulation of multi-speckle aspects in which case it is found that Raman is self-limiting due to strong modifications of the distribution function. Kinetic effects are of prime importance for Raman backscattering at high temperatures. No unique scenario for the saturation of Raman scattering or Raman-Brillouin competition does exist. The main effect in the considered parameter range is pump depletion because of large Brillouin backscattering. However, in the low k epw λ D regime the presence of ion-acoustic waves due to the Langmuir decay instability from the Raman created electron plasma waves can seed the ion-fractional decay and affect the Brillouin saturation.