57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015;
Savannah, Georgia
Session DI2: Reconnection from Lab to Space
3:00 PM–5:00 PM,
Monday, November 16, 2015
Room: Chatham Ballroom C
Chair: Paul Cassak, West Virginia University
Abstract ID: BAPS.2015.DPP.DI2.2
Abstract: DI2.00002 : Dynamics of a reconnection-driven runaway ion tail in a reversed field pinch plasma
3:30 PM–4:00 PM
Preview Abstract
Abstract
Author:
Jay Anderson
(University of Wisconsin)
Non-collisional heating and energization of ions is a powerful process in
reversed-field pinch (RFP) plasmas and in many astrophysical settings.
Tearing activity in the RFP (including linearly and nonlinearly driven modes
which span the plasma column) saturates through dynamo-like feedback on
the current density profile, rapidly releasing magnetic energy and inducing
a strong impulsive, parallel-to-B electric field as poloidal magnetic flux is
converted to toroidal flux. The global reconnection leads to strong ion heating
with a known anisotropy in temperature ($T_\perp > T_{||}$), suggestive of a
perpendicular bulk heating mechanism.
In the subset of strongest reconnection events, multiple mechanisms combine to
create a most interesting ion distribution. Runaway of the reduced-friction
naturally-heated ions generates an asymmetric ion tail with $E_{||} >> E_\perp$. The tail is
reinforced by a confinement asymmetry where runaway ions approach the limit of
classical cross-field transport despite magnetic stochasticity from the broad spectrum
of tearing modes. Confinement is lower in other regions of the
$v_\perp/v_{||}$ plane and reduces to Rechester-Rosenbluth-like transport experienced
by thermal particles.
Experiments with neutral beam injection elegantly confirm the ion runaway process
and fast ion confinement characteristics in MST. Neutral particle analyzers measure
an unrestricted parallel acceleration of the fast test particle distribution during the
reconnection event. The energy gain is larger for higher initial ion energy (reduced
drag), and deceleration is observed with reversed electric field (counter-current
injection) according to runaway dynamics and confirmed with Fokker-Planck modeling.
Full orbit test particle tracing in the 3D time evolving electric and magnetic fields (from visco-resistive
MHD simulations) corroborates the understanding of fast ion confinement.
Work supported by by US DoE and NSF.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2015.DPP.DI2.2