Title: Plasmoid Instability in Evolving Current Sheets and Onset of Fast Reconnection

Abstract

The scaling of the plasmoid instability maximum linear growth rate with respect to the Lundquist number S in a Sweet–Parker current sheet, $${\gamma }_{\max }\sim {S}^{1/4}$$, indicates that at high S, the current sheet will break apart before it approaches the Sweet–Parker width. Therefore, a proper description for the onset of the plasmoid instability must incorporate the evolving process of the current sheet. We carry out a series of two-dimensional simulations and develop diagnostics to separate fluctuations from an evolving background. It is found that the fluctuation amplitude starts to grow only when the linear growth rate is sufficiently high $$({\gamma }_{\max }{\tau }_{A}\gt O(1))$$ to overcome advection loss and the stretching effect due to the outflow. The linear growth rate continues to rise until the sizes of plasmoids become comparable to the inner layer width of the tearing mode. At this point, the current sheet is disrupted and the instability enters the early nonlinear regime. The growth rate suddenly decreases, but the reconnection rate starts to rise rapidly, indicating that current sheet disruption triggers the onset of fast reconnection. We identify important timescales of the instability development, as well as scalings for the linear growth rate, current sheet width, and dominant wavenumber at disruption. These scalings depend not only on the Lundquist number, but also on the noise amplitude. A phenomenological model that reproduces scalings from simulation results is proposed. The model incorporates the effect of reconnection outflow, which is crucial for yielding a critical Lundquist number S _c below which disruption does not occur. As a result, the critical Lundquist number S _c is not a constant value, but has a weak dependence on the noise amplitude.

Authors:

Huang, Yi -Min  ^[1];

• Search DOE PAGES for author "Huang, Yi -Min"
• Search DOE PAGES for ORCID "0000-0002-4237-2211"

Comisso, Luca  ^[1];

• Search DOE PAGES for author "Comisso, Luca"
• Search DOE PAGES for ORCID "0000-0001-8822-8031"

Bhattacharjee, A. ^[1]

---

+ Show Author Affiliations

1. Princeton Univ., Princeton, NJ (United States)

Publication Date:

Fri Nov 03 00:00:00 EDT 2017

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Princeton Univ., NJ (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1511010

Grant/Contract Number:  

SC0016470

Resource Type:

Accepted Manuscript

Journal Name:

The Astrophysical Journal (Online)

Additional Journal Information:

Journal Name: The Astrophysical Journal (Online); Journal Volume: 849; Journal Issue: 2; Journal ID: ISSN 1538-4357

Publisher:

Institute of Physics (IOP)

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; magnetic reconnection; magnetohydrodynamics (MHD); Sun: coronal mass ejections (CMEs); plasmas; Sun: magnetic fields; Sun: transition region