Classification of Orbits in Poincaré Maps using Machine Learning
This work provides plasma physicists with a less tedious and more reliable tool for analyzing magnetic field topology in tokamak simulations, though it is incremental as it applies existing ML methods to a specific domain problem.
The paper tackled the problem of classifying orbits in Poincaré maps from tokamak simulations using machine learning, achieving a more objective and accurate automated approach compared to visual classification. It overcame challenges in creating a high-quality training set and extracting discriminating features from orbit coordinates.
Poincaré plots, also called Poincaré maps, are used by plasma physicists to understand the behavior of magnetically confined plasma in numerical simulations of a tokamak. These plots are created by the intersection of field lines with a two-dimensional poloidal plane that is perpendicular to the axis of the torus representing the tokamak. A plot is composed of multiple orbits, each created by a different field line as it goes around the torus. Each orbit can have one of four distinct shapes, or classes, that indicate changes in the topology of the magnetic fields confining the plasma. Given the (x,y) coordinates of the points that form an orbit, the analysis task is to assign a class to the orbit, a task that appears ideally suited for a machine learning approach. In this paper, we describe how we overcame two major challenges in solving this problem - creating a high-quality training set, with few mislabeled orbits, and converting the coordinates of the points into features that are discriminating, despite the variation within the orbits of a class and the apparent similarities between orbits of different classes. Our automated approach is not only more objective and accurate than visual classification, but is also less tedious, making it easier for plasma physicists to analyze the topology of magnetic fields from numerical simulations of the tokamak.