Abstract Details
Abstracts
Author: Sanket A. Patil
Requested Type: Consider for Invited
Submitted: 2025-02-21 21:00:02
Co-authors: Carl R. Sovinec
Contact Info:
University of Wisconsin-Madison
1500 Engineering Dr
Madison, WI 53706
United States
Abstract Text:
Assessing the macroscopic properties of stellarator designs with high fidelity extended MHD codes is an essential step in determining experimental feasibility. To this end, the NIMSTELL code has been developed to solve the extended MHD equations in stellarator geometries. NIMSTELL uses spectral elements in the poloidal plane and toroidal Fourier series for spatial representation. In the linear algebraic solves that constitute the time-advance, Fourier harmonics of the time-dependent fields are coupled due to toroidal asymmetry. Recent developments in the preconditioner account for coupling between families of non-consecutive harmonics, improving the efficiency of multi-field-period calculations. Additionally, the specific block structure of matrices is exploited to reduce the memory used in linear algebra routines significantly. The equation for generalized Ohm's law is implemented with the option to use either the vector potential in Hcurl elements or the magnetic field in H1 elements. While both yield the same numerical results, the latter is found to be numerically more stable at low resistivities. The code is benchmarked against CASTOR3D for linear tearing modes in two different stellarators. The first case is based on a previous benchmark of JOREK against CASTOR3D for the (2, 1) tearing mode in W7-A [1]. The largest difference in growth rates is 1.5% between NIMSTELL and CASTOR3D. The second case is generated by adding an artificial current profile to a quasi-axisymmetric equilibrium [2], so that it admits the (2, 1) tearing mode. Here, the largest difference in NIMSTELL and CASTOR3D growth rates is 1.0%. Initial calculations of tearing mode saturation in the W7-A and QA cases enabled by the recent development of nonlinear capabilities will also be presented.
[1] N. Nikulsin, et al., Phys. Plasmas 29, 063901 (2022).
[2] M. Landreman and E. Paul, Phys. Rev. Lett. 128, 035001 (2022).
*Work supported by US DOE grants DE-SC0024548 and DE-FG02-99ER54546
Characterization: 4.0
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