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Title: Laboratory study of low-beta forces in arched, line-tied magnetic flux ropes

Abstract

The loss-of-equilibrium is a solar eruption mechanism whereby a sudden breakdown of the magnetohydrodynamic force balance in the Sun's corona ejects a massive burst of particles and energy into the heliosphere. Predicting a loss-of-equilibrium, which has more recently been formulated as the torus instability, relies on a detailed understanding of the various forces that hold the pre-eruption magnetic flux rope in equilibrium. Traditionally, idealized analytical force expressions are used to derive simplified eruption criteria that can be compared to solar observations and modeling. What is missing, however, is a validation that these idealized analytical force expressions can be applied to the line-tied, low-aspect-ratio conditions of the corona. In this paper, we address this shortcoming by using a laboratory experiment to study the forces that act on long-lived, arched, line-tied magnetic flux ropes. Three key force terms are evaluated over a wide range of experimental conditions: (1) the upward hoop force; (2) the downward strapping force; and (3) the downward toroidal field tension force. First, the laboratory force measurements show that, on average, the three aforementioned force terms cancel to produce a balanced line-tied equilibrium. This finding validates the laboratory force measurement techniques developed here, which were recently used to identifymore » a dynamic toroidal field tension force that can prevent flux rope eruptions [Myers et al., Nature 528, 526 (2015)]. The verification of magnetic force balance also confirms the low-beta assumption that the plasma thermal pressure is negligible in these experiments. Next, the measured force terms are directly compared to their corresponding analytical expressions. While the measured and analytical forces are found to be well correlated, the low-aspect-ratio, line-tied conditions in the experiment are found to both reduce the measured hoop force and increase the measured tension force with respect to analytical expectations. These two co-directed effects combine to generate laboratory flux rope equilibria at lower altitudes than are predicted analytically. Such considerations are expected to modify the loss-of-equilibrium eruption criteria for analogous flux ropes in the solar corona.« less

Authors:
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  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
DOE Contract Number:  
AC02-09CH11466
Product Type:
Dataset
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Laboratory Astrophysics Solar Eruptions Magnetohydrodynamic Equilibrium
Keywords:
Laboratory Astrophysics Solar Eruptions Magnetohydrodynamic Equilibrium
OSTI Identifier:
1367081
DOI:
10.11578/1367081

Citation Formats

Myers, Clayton, Yamada, Masaaki, Ji, Hantao, Yoo, Jongsoo, and Jara-Almonte, Jonathan. Laboratory study of low-beta forces in arched, line-tied magnetic flux ropes. United States: N. p., 2016. Web. doi:10.11578/1367081.
Myers, Clayton, Yamada, Masaaki, Ji, Hantao, Yoo, Jongsoo, & Jara-Almonte, Jonathan. Laboratory study of low-beta forces in arched, line-tied magnetic flux ropes. United States. doi:10.11578/1367081.
Myers, Clayton, Yamada, Masaaki, Ji, Hantao, Yoo, Jongsoo, and Jara-Almonte, Jonathan. 2016. "Laboratory study of low-beta forces in arched, line-tied magnetic flux ropes". United States. doi:10.11578/1367081. https://www.osti.gov/servlets/purl/1367081. Pub date:Tue Nov 01 00:00:00 EDT 2016
@article{osti_1367081,
title = {Laboratory study of low-beta forces in arched, line-tied magnetic flux ropes},
author = {Myers, Clayton and Yamada, Masaaki and Ji, Hantao and Yoo, Jongsoo and Jara-Almonte, Jonathan},
abstractNote = {The loss-of-equilibrium is a solar eruption mechanism whereby a sudden breakdown of the magnetohydrodynamic force balance in the Sun's corona ejects a massive burst of particles and energy into the heliosphere. Predicting a loss-of-equilibrium, which has more recently been formulated as the torus instability, relies on a detailed understanding of the various forces that hold the pre-eruption magnetic flux rope in equilibrium. Traditionally, idealized analytical force expressions are used to derive simplified eruption criteria that can be compared to solar observations and modeling. What is missing, however, is a validation that these idealized analytical force expressions can be applied to the line-tied, low-aspect-ratio conditions of the corona. In this paper, we address this shortcoming by using a laboratory experiment to study the forces that act on long-lived, arched, line-tied magnetic flux ropes. Three key force terms are evaluated over a wide range of experimental conditions: (1) the upward hoop force; (2) the downward strapping force; and (3) the downward toroidal field tension force. First, the laboratory force measurements show that, on average, the three aforementioned force terms cancel to produce a balanced line-tied equilibrium. This finding validates the laboratory force measurement techniques developed here, which were recently used to identify a dynamic toroidal field tension force that can prevent flux rope eruptions [Myers et al., Nature 528, 526 (2015)]. The verification of magnetic force balance also confirms the low-beta assumption that the plasma thermal pressure is negligible in these experiments. Next, the measured force terms are directly compared to their corresponding analytical expressions. While the measured and analytical forces are found to be well correlated, the low-aspect-ratio, line-tied conditions in the experiment are found to both reduce the measured hoop force and increase the measured tension force with respect to analytical expectations. These two co-directed effects combine to generate laboratory flux rope equilibria at lower altitudes than are predicted analytically. Such considerations are expected to modify the loss-of-equilibrium eruption criteria for analogous flux ropes in the solar corona.},
doi = {10.11578/1367081},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2016},
month = {11}
}

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Works referenced in this record:

Laboratory study of low-β forces in arched, line-tied magnetic flux ropes
journal, November 2016

  • Myers, C. E.; Yamada, M.; Ji, H.
  • Physics of Plasmas, Vol. 23, Issue 11
  • DOI: 10.1063/1.4966691

    Works referencing / citing this record:

    Laboratory study of low-β forces in arched, line-tied magnetic flux ropes
    journal, November 2016

    • Myers, C. E.; Yamada, M.; Ji, H.
    • Physics of Plasmas, Vol. 23, Issue 11
    • DOI: 10.1063/1.4966691