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Generation of laboratory nanoflares from multiple braided plasma loops

Nature Astronomy volume 7, pages 655–661 (2023)Cite this article

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Abstract

Solar flares are intense bursts of electromagnetic radiation accompanied by energetic particles and hard X-rays. They occur when magnetic flux loops erupt in the solar atmosphere. Solar observations detect energetic particles and hard X-rays but cannot reveal the generating mechanism because the particle acceleration happens at a scale smaller than the observation resolution. Thus, details of the cross-scale physics that explain the generation of energetic particles and hard X-rays remain a mystery. Here, we present observations from a laboratory experiment that simulates solar coronal loop physics. Transient, localized 7.6-keV X-ray bursts and a several-kilovolt voltage spike are observed in braided magnetic flux ropes of a 2-eV plasma when the braid strand radius is choked down to be at the kinetic scale by either magnetohydrodynamic (MHD) kink or magnetic Rayleigh–Taylor instabilities. This sequence of observations reveals a cross-scale coupling from MHD to non-MHD physics that is likely responsible for generating solar energetic particles and X-ray bursts. All the essential components of this mechanism have been separately observed in the solar corona.

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Fig. 1: Experimental setup.
Fig. 2: Time series images of experimental plasma loop evolution and X-ray and voltage measurements.
Fig. 3: X-ray energy measurements.
Fig. 4: Two experimental nanoflare events.
Fig. 5: Comparison between solar observation and experimental observation.

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Data availability

The experimental data reported here were generated by the Caltech Solar Loop Experiment and have been uploaded to https://data.caltech.edu/records/rcrh7-7ps89.

Code availability

Information about LTspice circuit simulation software is available at https://www.analogue.com/en/design-centre/design-tools-and-calculators/ltspice-simulator.html.

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Acknowledgements

This material is based upon work supported by the NSF (Awards 1914599 and 2105492 to P.M.B.). The X-ray detector used in this work was developed with support from the USDOE ARPA-E (Grant DE-AR0001159 to P.M.B.).

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Authors and Affiliations

  1. Applied Physics and Materials Science, California Institute of Technology, Pasadena, CA, USA

    Yang Zhang, Seth Pree & Paul M. Bellan

Authors
  1. Yang Zhang
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Contributions

Y.Z. designed the braided loop experiment from the suggestions and guidance of P.M.B. S.P. built the X-ray camera from the suggestions and guidance of P.M.B. Y.Z. and S.P. performed the experiment. The interpretation of the results was done jointly by all authors. Y.Z. drafted the manuscript. All authors revised the manuscript together.

Corresponding author

Correspondence to Yang Zhang.

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The authors declare no competing interests.

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Nature Astronomy thanks Markus Aschwanden and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Solar loop experiment circuit simulation.

(a) Experiment circuit diagram. The plasma part of the circuit is represented as an inductor and a time-dependent resistor. The plasma inductance is assumed to be 50 nH, which is obtained by simplifying the plasma loop as a half circle loop of wire with 5 cm loop major radius and 1 cm minor (wire) radius. The voltage and current spikes are both peak functions, so the corresponding resistance change is presumed to be also a peak function. We use Gaussian function \({R}_{plasma}={R}_{0}\exp (-a{(t-{t}_{0})}^{2})\) to represent the transient change of the plasma resistance where R0 is the peak resistance value, and t0 is the resistance peak time, and a is related to the full width at half maximum (FWHM). They are chosen according to the relative voltage spike amplitude, voltage peak time and the voltage spike FWHM. In the simulation, R0 = 0.4Ω, t0 = 3.65 μs and a = 5 μs −2 are used. The corresponding plasma resistance is plotted in (b). (c, d) Voltage and current measurement from experiment Shot # 9258. As shown in (a), the voltage measured in (c) is the voltage across the plasma part and an extra inductor. We also measured the voltage across the plasma part by connecting two voltage probes directly to the top electrode and bottom electrode and then subtracting the two voltages. The voltage trace across the plasma is similar but has a several kV larger voltage spike compared with (c). (e, f) Voltage and current curves from the simulation. Voltage and current spikes similar to the experimentally observed spikes are reproduced by the transient resistance increase.

Extended Data Fig. 2 Magnetic Rayleigh Taylor instability observation.

A four-strand braided structure is shown in time series images of hydrogen plasma loop evolution. With the expansion of the plasma loop, a magnetic Rayleigh Taylor instability occurs on the loop and plays the same role as a kink instability to choke the strand radius down and break the strand at later time. The full evolution video can be found in Supplementary Movie 2.

Supplementary information

Supplementary Video 1

This video shows an example of braided plasma loop evolution where a kink instability develops on the top of the loop starting at around 2.68 μs.

Supplementary Video 2

This video shows an example of braided plasma loop evolution where a magnetic Rayleigh–Taylor instability develops on the loop starting at around 2.54 μs.

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Zhang, Y., Pree, S. & Bellan, P.M. Generation of laboratory nanoflares from multiple braided plasma loops. Nat Astron 7, 655–661 (2023). https://doi.org/10.1038/s41550-023-01941-x

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