Thesis Defense

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Stellarator Beta Limits with Extended MHD Modeling Using NIMROD
Date: Wednesday, April 14th
Time: 1:00 pm
Speaker: Torrin Bechtel, Physics PhD Graduate Student
Abstract: The nonlinear, extended MHD code NIMROD is employed to simulate self-consistent stellarator behavior at high beta. Finite anisotropic thermal conduction allows for sustained pressure gradients within stochastic regions. The configuration under investigation is an l=2, M=10 torsatron with vacuum rotational transform near unity. Finite-beta plasmas are generated from vacuum fields using a volumetric heating source and temperature dependent resistivity. With realistic parameters the configuration is unstable to interchange, which acts to limit the achievable beta. Simulations performed in a single field period domain do not exhibit a complete crash from the instability, but otherwise closely match theorized linear and nonlinear interchange behavior. In more dissipative regimes where instability is suppressed, steady-state solutions are obtained. A conventional equilibrium beta limit is observed due to pressure induced stochastic magnetic field formation. The parametric dependence of the equilibrium limit is examined in detail. Equilibrium results are compared with several reduced models for effective collisional transport across stochastic magnetic fields and with the HINT code. Collisionality independent models also are investigated for more realistic parallel thermal conduction rates. Join Zoom Meeting Meeting ID: 913 2120 9265 Passcode: 298219
Host: Chris Hegna, Faculty Advisor
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