April 4-6

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Author: Urvashi Gupta
Requested Type: Poster
Submitted: 2022-03-03 09:22:05

Co-authors: C. R. Sovinec

Contact Info:
University of Wisconsin-Madison
1500 Engineering Drive
Madison, Wisconsin   53706
United States

Abstract Text:
Early analytic studies of resistive tearing with an adiabatic energy equation in diffuse cylindrical pinches proved that bad curvature implies instability, even with negative Δ’(Coppi et al., NF 6, 101, 1966). This means that pressure can drive tearing in reversed-field pinches (RFPs), where curvature is largely poloidal. When thermal conduction effects are taken into account, a marginal stability criterion for the tearing mode can be derived (Bruno et al., PoP 10, 2330, 2003). Nonlinearly, the role of pressure in the relaxation dynamics and global thermal transport of RFPs is not well understood. In this work, finite-beta visco-resistive MHD computations are being applied to self-consistently model an RFP. A shear-less self-consistent cylindrical pinch equilibrium with balanced perpendicular thermal conduction and Ohmic heating is nonlinearly evolved, resulting in a tearing-dominant RFP state. The final state has a sheared safety factor profile and a flattened pressure profile in the core. Linear resistive MHD analysis of the dominant tearing modes from the final non-linear state shows that these RFP equilibria are marginally stable. The linear eigenfunctions are then used to compare the pressure drive to the parallel-current drive based on relevant terms from the linear energy integral. It is observed that irrespective of the linear growth or decay of the modes, a pressure drive always exists, indicating that pressure does contribute to tearing in RFP dynamics. Magnetic stochasticity from core resonant tearing modes results in net outward energy transport. Parallel thermal conductive heat flux from fluctuations is larger than convective transport in the core. However, second-order correlations in the conductive heat flux alone do not result in net outward transport over all radii. Third-order correlations are larger in magnitude and cancel most of the inward heat flux due to quadratic correlations near the edge.

Supported by U.S. DOE grant DE-FG02-85ER53212