Generation of laboratory nanoflares from multiple braided plasma loops
Yang Zhang · Seth Pree · Paul M. Bellan
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In one page
Solar flares throw out X-rays and fast particles, and nobody can watch the moment they are made, because the making happens on a scale far below what a solar telescope can resolve. Yang Zhang, Seth Pree and Paul Bellan at Caltech built the event instead. Discharging a capacitor between twin electrodes in a vacuum chamber, they make an arched plasma loop about twenty centimetres long that lives for roughly ten microseconds, and film it at ten million frames a second. The loop is not a simple tube: it is braided, like rope, out of separate current-carrying strands. When the loop stretches, an instability pinches one strand until its radius drops to the scale where the smooth fluid description of plasma stops working. At that instant the team measures a several-kilovolt voltage spike and a burst of X-rays at 7.6 kiloelectronvolts, out of a plasma that is otherwise only a couple of electronvolts hot. That is a nanoflare, made on a bench.
Why it matters hereChapter 9 is about self-organised plasma structures that carry their own magnetic field, and this is the sharpest modern demonstration that such a structure stores energy and then releases it in a sudden, local, high-energy burst when its own instability squeezes it down to kinetic scale. It is also the direct descendant of Bostick’s scaled laboratory astrophysics: the same argument that a plasma object on a bench, built at the right scale, tells you what the same object does on the Sun.
What it claims
01The measurement. Transient, localised X-ray bursts of 7.6 kiloelectronvolts and a several-kilovolt voltage spike are observed in braided magnetic flux ropes of a 2-electronvolt plasma when the braid strand radius is choked down to be at the kinetic scale by either magnetohydrodynamic kink or magnetic Rayleigh-Taylor instabilities. A plasma at a couple of electronvolts is producing photons at thousands of electronvolts, which means a small population of particles has been accelerated hard and locally.Published abstract
Published and peer-reviewed02The mechanism is a coupling across scales. This sequence of observations reveals a cross-scale coupling from magnetohydrodynamic to non-magnetohydrodynamic physics that is likely responsible for generating solar energetic particles and X-ray bursts: the large, smooth, fluid-like behaviour of the loop creates the conditions in which the fluid description fails, and it is that failure that accelerates particles.Published abstract, closing sentences
Published and peer-reviewed03Two different instabilities do the same job. In one shot a kink instability develops at the top of the loop starting at about 2.68 microseconds; in another, a magnetic Rayleigh-Taylor instability develops on the expanding loop starting at about 2.54 microseconds and plays the same role as the kink instability, choking the strand radius down and breaking the strand at a later time. A four-strand braided structure is resolved in the time-series images.Extended Data Figure 2 caption and the Supplementary Video 1 and 2 descriptions
Published and peer-reviewed04The voltage spike is a sudden collapse of conductivity, and the circuit says so. Treating the plasma as an inductance of 50 nanohenries in series with a time-dependent resistance, and letting that resistance rise briefly to a peak of 0.4 ohms, reproduces voltage and current spikes like the measured ones in a circuit simulation. Measured directly across the top and bottom electrodes, the voltage spike is several kilovolts larger again.Extended Data Figure 1 caption, panels a to f, shot number 9258
Published and peer-reviewed05The laboratory object is matched against the Sun rather than merely compared to it: the paper carries a direct comparison between solar observation and experimental observation, and states that all the essential components of this mechanism have been separately observed in the solar corona. What remains to be seen on the Sun is the whole sequence in one place at once, which is a question of resolution — the reason the experiment was built in the first place.Published abstract, final sentence, with Figure 5, Comparison between solar observation and experimental observation
What to watch
The way in
https://doi.org/10.1038/s41550-023-01941-xWHAT THIS PAGE IS WRITTEN FROM. Nature Astronomy volume 7, pages 655 to 661, published 6 April 2023; the authors are at Applied Physics and Materials Science, California Institute of Technology, Pasadena. The article is closed: the publisher’s page states that Springer Nature or its licensor holds exclusive rights under a publishing agreement, there is no Creative Commons statement, and the only licence on the Crossref record is Springer Nature’s text-and-data-mining terms, which is not an open licence. OpenAlex and Unpaywall report no open copy; a search of arXiv by title and by author with the plasma-physics category returns no preprint of this paper; the CaltechAUTHORS repository record for it holds only the two supplementary figures and the two supplementary movies, not the text. The body of the paper was therefore not read, and no text of it is reproduced here. WHAT WAS READ. The full published abstract, the titles of Figures 1 to 5, the Extended Data figure captions and the supplementary-video descriptions, all read on 2026-09-08 from the publisher’s own article page and from the CaltechAUTHORS record, and the apparatus description in Caltech’s own account of the experiment published the same day as the paper. Locators name which of those each claim comes from. FUNDING, as stated on the record: NSF awards 1914599 and 2105492 to P. M. Bellan; the X-ray detector was developed with support from the US Department of Energy ARPA-E, grant DE-AR0001159.
How to cite it
Yang Zhang, Seth Pree, Paul M. Bellan (2023) Generation of laboratory nanoflares from multiple braided plasma loops. doi:10.1038/s41550-023-01941-x
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