Talk 1. Meta Variance Reduction Schemes for Estimation of Alpha Particle Confinement
Abstract: Numerical estimation of energetic particle confinement using Monte Carlo methods remains a computationally demanding task in stellarator optimization loops, due to the large number of simulated trajectories required at each iteration. We introduce meta estimators to accelerate the estimation of confinement statistics, by simultaneously leveraging multiple constituent variance reduction techniques including multifidelity Monte Carlo, importance sampling, and information reuse. Each constituent technique takes advantage of a different facet of the estimation problem, leading to quasi-multiplicative speedup when combined. We test our meta estimators, using data-driven surrogates and biasing densities, on a coil optimization seeking to reproduce a quasi-axisymmetric configuration (Landreman and Paul, 2022). We observe that each meta estimator outperforms its constituent variance reduction techniques, with the highest performing meta estimator yielding two orders of magnitude speedup compared to standard Monte Carlo estimation at an equivalent computational cost.
Talk 2. Geometry Induced Activation of Zonal Flows in Stellarator Plasmas
Abstract: One of the prominent physical processes in confined plasmas is spontaneous formation of mesoscopic coherent structures, e.g., zonal flows, geodesic acoustic oscillations, and radially elongated streamers, which are nonlinearly excited in microscopic turbulence. Then, how can we “activate” or “enhance" such nonlinear structures? The diversity of 3D magnetic geometries in stellarators motivates us to explore the capabilities of enhancing the zonal-flow formation. This talk presents a recent activity on the geometry-induced activation of the zonal flows in a context of stellarator optimizations with a nonlinear proxy model.
Talk time in other timezones: AEDT 11:00 AM Fri 20 Jan, JST 09:00 AM Fri 20 Jan, CEST 01:00 AM Fri 20 Jan, GMT 12:00 AM Fri 20 Jan, UTC 0:00 Fri 20 Jan, EST 7:00 PM Thu 19 Jan, CST 6:00 PM Thu 19 Jan, MST 5:00 PM Thu 19 Jan