Abstract Details
Abstracts
Author: Allen H Boozer
Requested Type: Consider for Invited
Submitted: 2025-02-20 19:27:34
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Columbia University
500 W. 120th Street
New York, New York 10027
USA
Abstract Text:
In both tokamaks and stellarators, the transition from the lines of a given magnetic field lying in surfaces: (a) in time defines properties of disruptions and (b) in space defines properties of divertors. Two methods of analysis [1] allow more information to be extracted, using a far shorter integration of a magnetic field line from an arbitrary starting point, than traditional methods based on Poincaré plots: (a) When a line either lies on or lingers near a surface, a Fourier decomposition of its trajectory using a Gaussian window function determines the shape of that surface and any normal magnetic field that causes flux leakage across that surface. (b) The ratio of infinitesimal separations of the line from all other lines in its neighborhood versus the distance along the line is determined by the simultaneous integration of three ordinary differential equations with two sets of initial conditions. When the natural logarithm of the largest of these separations is greater than ten, the line is sufficiently chaotic to allow rapid surface destruction by resistivity. In the presence of plasma gradients, the electric potential required for quasi-neutrality leads to Bohm-like cross-field diffusion [2]. The flux leakage across a surface defines a magnetic flux tube that enters the surface but leaves after a number of toroidal transits. Such flux tubes that make many toroidal transits have a central role in defining the strike locations of non-resonant stellarator divertors [3], which could be designed for tokamaks as well. References: [1] Efficient analysis of magnetic field line behavior in toroidal plasmas, A. H. Boozer, < https://arxiv.org/pdf/2502.00981>. [2] Electric field effects during disruptions, A. H. Boozer, Phys Plasmas 31, 102506 (2024). [3] Resilient stellarator divertor characteristics in the Helically Symmetric eXperiment, K. A. Garcia et al, Plasma Phys. Control. Fusion 67 035011 (2025). Supported by U.S. DoE grant DE-FG02-95ER54333.
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