|approved||poster.pdf||2018-04-24 23:59:52||Cihan Akcay|
Author: Cihan Akcay
Requested Type: Poster
Submitted: 2018-02-28 13:07:13
Co-authors: J. M. Finn, A. J. Cole
Tibbar Plasma Technologies
274 DP Rd
Los Alamos, NM 87544
Analysis shows that, for tearing regimes with real frequencies, the Maxwell torque locks the plasma to the tearing mode phase velocity. Real frequencies for tearing modes are due to diamagnetic effects or the Glasser effect in the resistive-inertial (RI) tearing regime, and it has recently been shown that similar propagation frequencies occur in the viscoresistive (VR) regime. In Ref.  it was suggested that an effect like that of Ref.  might occur for the nonlinear behavior of RI and VR tearing modes: namely, for large island width the sound wave might flatten the pressure gradient, causing the propagation to decrease to zero. A case was made in Ref.  that this decrease in propagation frequency might reduce the effect of locking to the phase velocity and therefore allow locking to zero velocity.
We have performed simulations with NIMROD to investigate this possibility, using cylindrical geometry and a hollow equilibrium pressure profile. For an initial tearing unstable equilibrium with zero pressure we have increased the pressure, causing stabilization due to the outer region as well as favorable curvature in the layer. As pressure is increased, real frequencies are indeed observed and the mode is stabilized. In the presence of a small error field and plasma rotation, the maximum reconnected flux is observed to be at the phase velocity of the tearing mode, and this response is most peaked when the stable tearing mode is close to marginal stability. For increasing error field a locking bifurcation is observed, with locking to a rotation just above the tearing mode phase velocity. Simulations with larger error fields, or with modes closer to marginal stability, will be shown.
1. J. Finn, A. Cole, D. Brennan, PoP Letters 22, 120701 (2015).
2. A. Glasser, J. Greene, J. Johnson, Phys. Fluids 18, 875 (1975).
3. J. Finn, A. Cole, D. Brennan, arXiv:1708.04700 (2017).
4. B. Scott, A. Hassam, J. Drake, Phys Fluids, 28, 275 (1985).