Predicting hot electrons for inertial confinement fusion
Shihui Cao, PhD Qualifying Exam, Advised by Chuang Ren
Tuesday, April 27, 2021
The understanding of laser plasma instabilities (LPIs) is important for successful inertial confinement fusion (ICF) designs. In the shorter-scale-length experiments at the OMEGA laser system, LPI is dominated by Two-plasmon decay (TPD). TPD is a three-wave parametric decay instability in which an electromagnetic wave decays into two electron plasma waves (EPWs). It's undesirable because of its ability to generate energetic electrons via staged acceleration and cause anomalous absorption. Stimulated Raman Scattering (SRS) is a three-wave decay instability in which an incident light wave decays into a scattered light wave and an EPW. Ignition-scale direct-drive targets have a corona plasma of long density scale length, which lowers the threshold of TPD and SRS. Experiments on National Ignition Facility (NIF) shows the prevalence of SRS over TPD due to high coronal electron temperature.
Superthermal electrons generated from SRS and TPD can raise the shell entropy to reduce implosion efficiency and is a major concern for direct-drive ICF. It's challenging to predict nanosecond-scale hot electron fraction in experiments via picosecond-scale PIC simulations due to the lack of reliable and comprehensive scaling laws that cover laser smoothing, LPIs in the low-density region and 3D LPI coupling. In this talk, we will show an attempt to obtain reliable scaling laws of hot electron generation. This includes the discussion of (1) 2D/3D saturation and hot electron generation mechanisms, (2) reliable scaling laws of hot electron generation and (3) implement of the obtained scaling laws to hard x-ray signal prediction.
Meeting ID: 804 037 1784