Taking into account the time behavior of laser power errors in the Laser MegaJoule robustness study

In the Laser MegaJoule indirect drive experiments, the time-averaged radiation asymmetry on a Deuterium-Tritium (DT) capsule must be minimized to achieve high-yield implosions. A two-dimensional model estimates the time-averaged effect of power imbalance, laser beam pointing and target fabrication errors on the final DT deformation, which is then submitted to an ignition threshold. As these errors will take random values from one LMJ shot to another, the robustness study aims at quantifying the probability of failing to reach ignition. Here, we focus on laser power imbalance. We distinguish two types of error sources in laser performance, according to whether they take long-time (more than the laser pulse duration) or short-time (less than the laser pulse duration) correlated values. Indeed, as the final DT deformation results from the whole laser pulse history, the failure probability depends on the error time-correlation. A 1D-time model of the laser beam power, from the front-end to the target, was developed to quantify the variations of the output power imbalance due to the source contributions. Taking into account this detailed time behavior, instead of modeling all errors as long-time correlated values, leads to cut the global effect of power imbalance on ignition probability by half.