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

Journal Article · Fri Nov 04 00:00:00 EDT 2016 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4966691· OSTI ID:1340278

Myers, C. E.  ^[1]; Yamada, M.  ^[2]; Ji, H.  ^[3]; Yoo, J.  ^[2]; Jara-Almonte, J. ^[1]; Fox, W.  ^[2]

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1. Princeton Univ., Princeton, NJ (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
3. Princeton Univ., Princeton, NJ (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Harbin Institute of Technology, Heilongjiang (China)

Here, 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 eruption. 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 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.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE
• Contributing Organization: Harbin Inst Technol, Lab Space Environm & Phys Sci, Harbin 150001, Heilongjiang, Peoples R China This research is supported by Department of Energy (DoE) Contract No. DE-AC02-09CH11466 and by the National Science Foundation/DoE Center for Magnetic Self-Organization (CMSO).
• Grant/Contract Number: AC02-09CH11466
• OSTI ID: 1340278
• Alternate ID(s): OSTI ID: 1330974
• Report Number(s): 5312; TRN: US1701285
• Journal Information: Physics of Plasmas, Vol. 23, Issue 11; Related Information: The digital data for this paper can be found at http://arks.princeton.edu/ark:/88435/dsp014x51hm50z.; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

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70 PLASMA PHYSICS AND FUSION TECHNOLOGY