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Events on Monday, October 16th, 2023

Plasma Physics (Physics/ECE/NE 922) Seminar
Fluid Modeling of Runaway Electron Beams
Time: 12:00 pm - 1:15 pm
Place: 1610 Engineering
Speaker: Alex Sainterme, UW-Madison
Abstract: A now-common approach for modeling runaway electron (RE) effects on
macroscopic tokamak plasma dynamics introduces a simple fluid
description of a separate beam-like electron species traveling parallel to
magnetic field lines in a resistive MHD 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 timeevolving
magnetic field. Sources of runaway electron density are
included to approximate the acceleration of electrons to high energies in
the presence of strong parallel electric fields. This fluid RE model has
been implemented in the non-ideal MHD code NIMROD. Some initial
calculations are shown to benchmark the implementation of the RE
source model. The model has also been used to study linear stability of a
particular MHD equilibrium supported entirely by RE current. It is
found that in addition to modifying the growth of the tearing mode, the
RE beam is itself unstable to a form of ’resistive hose’ instability
[Rosenbluth, Phys. Fluids 3, 932(1960)]. Scaling of the growth rate with
the resistivity of the bulk plasma shows that for Lundquist number less
than 104, the resistive hose is the fastest growing linear
instability in the system. This is relevant for RE beams generated in
tokamak disruptions where the background plasma is cold and resistive.
Preliminary nonlinear simulations of the hose mode are presented.

Alex Sainterme is a fifth year PhD student in the Nuclear Engineering
and Engineering Physics department working under Professor Carl Sovinec.
Alex’s research focuses focuses on simulation and modeling of runaway
electron dynamics and disruptions in tokamaks.
Host: Prof. Steffi Diem
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