Abstract Details
| status: | file name: | submitted: | by: |
|---|---|---|---|
| new | sherwood23_2.pdf | 2023-05-15 11:50:06 | Alexandre Sainterme |
Abstracts
Author: Alexandre P Sainterme
Requested Type: Poster
Submitted: 2023-03-30 17:57:12
Co-authors: C.R. Sovinec
Contact Info:
University of Wisconsin - Madison
318 Norris Ct. Apt. 5
Madison, WI 53703
USA
Abstract Text:
A reduced fluid model for runaway electrons (RE) introduces a separate beam-like fluid electron species traveling parallel to magnetic field lines into a resistive MHD description of background plasma [Bandaru, et al., PRE 99, 063317(2019)].
The RE beam provides a source of resistance-free current density whose direction depends on the time-evolving magnetic field. Analysis of the linearized set of equations for small perturbations about an MHD equilibrium supported by RE current in a cylinder reveals an instability driven by gradients in the RE current density profile. This analysis is akin to prior work addressing the effect of RE density of the tearing and resistive kink modes [Liu, et al., PoP 27, 092507(2020)]. However, the instability described here is largely unaffected by bulk plasma response, and persists in the limit that the perturbed MHD velocity is zero. RE density sources and drift velocity effects are neglected in this analysis. The dominant poloidal and axial mode numbers are (m,n) = (1,1), and the instability grows faster than the tearing and resistive kink modes at large values of resistivity. In the low resistivity limit, the tearing and kink modes in the presence of REs are dominant. The radial structure of the beam eigenmode is localized near the origin but away from any rational surface. A simplified analytic model is presented to complement numerical results from initial-value NIMROD calculations and an eigenvalue solution. Scaling of the growth rate of the instability with the resistivity of the bulk plasma and the parallel speed of the runaway beam is presented. It is posited that this instability is a manifestation of the ‘hose’ instability of a beam-plasma system [Rosenbluth, Phys. Fluids 3, 932(1960)]. The implications for nonlinear simulations of post-disruption tokamak plasmas using this model are discussed.
Work supported by the US DOE through grant DE-SC00180001
Comments: