Abstract Details
Abstracts
Author: Sanket Patil
Requested Type: Poster
Submitted: 2026-03-20 14:45:51
Co-authors: C. R. Sovinec
Contact Info:
University of Wisconsin-Madison
1500 Engineering Dr
Madison, WI 53706
United States
Abstract Text:
A common strategy in stellarator optimization is to target low shear, possibly by bounding the rotational transform (iota) between two low-order rational numbers, which avoids magnetic islands. The resulting iota profile admits low global shear and may admit a zero-shear region when the profile is non-monotonic. The magnetic field line bending is minimal in such cases, making it easier for pressure-driven modes to grow. An example of this behavior is observed with linear and nonlinear NIMSTELL [1] computations of a quasi-helically symmetric configuration [2]. Here, the extremum of the non-monotonic iota profile is close to unity, resulting in (m, n)-dominant global ideal interchange modes with m = n. The stabilizing effect of imperfect resonance is shown by offsetting the iota profile away from unity. Additionally, a preferential destabilization of higher-(m, n) modes is observed with increasing beta. Nonlinear computations demonstrate that the instability leads to a significant loss of core pressure within a thousand Alfven times. To develop physical insight and a stability metric for optimization algorithms, an analytical model is derived analogous to the WKB model for ballooning modes [3]. The model captures many of the qualitative features of the low-shear interchange modes and approximates the growth rate reasonably.
References:
[1] C. R. Sovinec, S. A. Patil, J. V. Cauilan, UW-CPTC 25-1 (www.cptc.wisc.edu/reports)
[2] M. Landreman, et al., Phys. Plasmas 29, 082501 (2022)
[3] R.L. Dewar, et al., Nucl. Fusion 21, 493 (1981)
Characterization: 4.0
Comments: