ICF hohlraum comparison on the LMJ facility

We present here the ICF hohlraum experimental campaign which was carried out in 2024 on the LMJ laser facility. Since the first ICF shot, the LMJ facility has been improving its capabilities, increasing the number of beams and the delivered laser energy. Accompanying this LMJ mounting phase, all these experiments aimed to gain a better understanding of the implosion and hohlraum physics and to identify the best design options for high performances at LMJ.

The main concern of the recent campaigns has been to identify the acceptable hohlraum shapes on the specific LMJ facility. Two different cylinder aspect ratio and two different rugby shapes were tested in 2024. The cylinders exhibited the lowest backscatter levels, lower than 3 % of the laser energy. But achieving a symmetric implosion requires cone fraction, thus to reduce the inner laser power on LMJ where the number of inner beams and the number of outer beams are the same. Less cone fraction is required in a rugby hohlraum but, on the other hand, higher levels of Brillouin scattering were measured, nearly 10 % of the laser energy. 2D and 3D calculations are shown which try to match the measured hot spot shapes.

Finally, we present our future designs for the next years, as more energy and beams will be available. We show how trade-offs must be made between the irradiation symmetry on the capsule and the deleterious effects of laser plasma interaction which could become a main concern with the laser energy increase.