Magnetic Helicity, Spheromaks, Solar Corona Loops, and Astrophysical Jets
Paul M. Bellan
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In one page
Magnetically dominated plasmas — the ones where the magnetic field, not the gas pressure, runs the show — do something remarkable. However violently they start out, they end in the same simple shape. Paul Bellan of Caltech spends this book explaining why, and it turns on one quantity: magnetic helicity, which counts how thoroughly the field lines are looped and linked through each other. Helicity is very nearly conserved while energy is not, so a tangled plasma can shed energy and keep its linkage, and what it settles into is the lowest-energy state still open to it. Bellan then shows the same argument covering a spheromak in a laboratory vessel, a loop in the solar corona, a magnetic cloud drifting through interplanetary space and a jet thousands of light years long. The second half asks how the plasma gets there, not just why: self-collimated jets, kink instabilities, magnetic reconnection, and behaviour that leaves magnetohydrodynamics behind entirely.
Why it matters hereChapter 9 is about plasma that organises itself into a stable object and holds, and this is the textbook of that subject — the argument, the experiments and the mathematics behind the claim that a messy plasma relaxes to one predictable state. It is also where the site’s laboratory plasmoids and its astrophysical jets turn out to be the same physics at different scales.
What it claims
01Magnetic helicity — the topological measure of how thoroughly magnetic field lines link one another — is the organising quantity for magnetically dominated plasmas, and a helicity-based model predicts the ultimate state towards which such plasmas evolve.Chapter 3, Magnetic Helicity, pages 55 to 94
Settled physics02No matter how messy or complicated the dynamics, a great range of plasma configurations always self-organise to a unique, simple final state — the Taylor state — and this relaxation is what unifies spheromaks, solar corona loops, interplanetary magnetic clouds and astrophysical jets.Chapter 4, Relaxation of an Isolated Configuration to the Taylor State, pages 95 to 113; Chapter 6, The MHD Energy Principle, Helicity, and Taylor States, pages 123 to 142
Settled physics03Relaxation is not confined to isolated configurations: a continuously driven plasma relaxes too, and the driven case is where helicity flow and dynamo action live.Chapter 5, Relaxation in Driven Configurations, pages 115 to 122; Chapter 12, Helicity Flow and Dynamos, pages 237 to 266
Published and peer-reviewed04How relaxation happens is a sequence of complex non-equilibrium dynamics rather than a smooth settling: fast self-collimated plasma jets, then kink instabilities, Rayleigh–Taylor breakup and hard X-ray emission, then magnetic reconnection.Chapter 17, Initial dynamics leading to relaxation: MHD jets, pages 355 to 375; Chapter 18, Dynamics associated with relaxation, pages 377 to 396
Published and peer-reviewed05Parts of that sequence lie outside magnetohydrodynamics altogether — whistler waves are what make magnetic reconnection fast, and charged particles can follow extreme orbits in helical magnetic fields.Chapter 19, Beyond MHD: Whistler Waves and Fast Magnetic Reconnection, pages 397 to 436; Chapter 22, Beyond MHD: Extreme particle orbits in helical magnetic fields, pages 511 to 521
Published and peer-reviewed06The same physics is presented as valid over twenty orders of magnitude in both time and space, carried from spheromak experiments and their diagnostics through to astrophysical jets, accretion, angular momentum removal and space dynamos.Publisher’s synopsis; Chapter 15, Basic Diagnostics for Spheromaks, pages 309 to 329; Chapter 24, Astrophysical Jets, Accretion, Angular Momentum Removal, and Space Dynamos, pages 531 to 560
Published and peer-reviewed
The way in
https://doi.org/10.1142/q0151A 630-page monograph by Paul M. Bellan of Caltech, registered by the publisher on 7 November 2017 and dated April 2018 on the author’s own group page, under the publisher’s copyright with no Creative Commons statement. The book itself could not be read for this sheet: the summary and claims are written from the publisher’s synopsis, quoted in the bibliographic record, and from the book’s own chapter titles and page ranges as registered chapter by chapter with Crossref, which is where every locator below comes from. Bellan’s related work on kink instabilities, spheromak formation and laboratory jets is free to read on arXiv and was consulted for the physics.
How to cite it
Paul M. Bellan (2017) Magnetic Helicity, Spheromaks, Solar Corona Loops, and Astrophysical Jets. doi:10.1142/q0151
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