April 15-17

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newtbernard_sherwood_2019.pdf2019-04-26 14:14:36Tess Bernard

Abstracts

Author: Tess N. Bernard
Requested Type: Pre-Selected Invited
Submitted: 2019-02-21 08:44:06

Co-authors: E.L. Shi, K. Gentle, A. Hakim, G.W. Hammett, T. Stoltzfus-Dueck, E.I. Taylor

Contact Info:
Univ of Texas, Austin
2515 Speedway, C1600
Austin, Texas   78712
United States

Abstract Text:
Simple magnetized torus (SMT) experiments, such as the Texas Helimak, use vertical and toroidal field coils to create open, helical magnetic-field-line configurations with curvature and shear. With dimensionless parameters and magnetic geometry similar to the SOL, these devices can be used to compare analytic and numerical models of SOL turbulence to experimental data. Prior to this work, only fluid simulations had been performed of the Helimak. Building on work by Shi et. al.[1-3] using the computational plasma physics framework Gkeyll, we present the first continuum gyrokinetic simulations of plasma turbulence in the Texas Helimak[4]. The device has features similar to the scrape-off layer region of tokamaks, such as bad-curvature-driven instabilities and sheath boundary conditions on the end plates, which are included in our model. A bias voltage can be applied across conducting plates to drive ExB flow and study the effect of velocity shear on turbulence suppression. We performed simulations of grounded and limiter-biased scenarios. Comparisons between simulations and measurements from the experiment show good qualitative similarities, including equilibrium profiles and fluctuation amplitudes that approach experimental values, but also some important quantitative differences. We discuss how including additional physical and geometric effects in our model, such as real ion-to-electron mass ratio and vertical ExB flow could improve agreement with experiment. Both experimental and simulation results exhibit turbulence statistics that are characteristic of blob transport, and, overall, results demonstrate good progress towards modeling turbulence on helical, open-field lines in tokamak SOL-like conditions with gyrokinetic equations.

[1] E. Shi, et. al. J. Plasma Phys (2017).
[2] E. Shi, Ph.D. thesis, Princeton University (2017).
[3] E. Shi, et. al. Phys. Plasmas (2019).
[4] T. Bernard, et. al. Phys. Plasmas, in review. arXiv:1812.05703

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