Historical research guide · 0578 · 2017
Magnetic Helicity, Spheromaks, Solar Corona Loops, and Astrophysical Jets
Paul M. Bellan
In one minute
Paul Bellan’s 2017 monograph follows magnetic helicity—the linking and twisting of magnetic field lines—through laboratory and astrophysical plasmas. In magnetically dominated plasmas, magnetic energy can fall while helicity remains nearly conserved. That constraint sends a tangled configuration toward a lower-energy Taylor state. The book uses the same relaxation argument for spheromaks, coronal loops, interplanetary magnetic clouds and astrophysical jets. It then turns to the driven processes: collimated jets, kink instabilities, Rayleigh–Taylor breakup, reconnection, whistler waves and particle orbits that exceed the magnetohydrodynamic approximation. The scale comparison connects measured laboratory systems to astrophysical structures, but it is a physics account, not proof that a visible shape alone has the same origin at every scale.
Connection
Helicity gives a testable bridge between plasma shapes: compare field topology, energy loss and boundary conditions before treating a laboratory object and a cosmic object as comparable. It turns a visual similarity into a magnetohydrodynamic question with measurements attached.
From the source
Magnetic 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
Across the configurations treated in the book, complex plasma dynamics can relax to a simple Taylor state, and this relaxation connects 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
Relaxation 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
How 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
Parts 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
The 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
The way in
https://doi.org/10.1142/q0151How to cite it
Paul M. Bellan (2017) Magnetic Helicity, Spheromaks, Solar Corona Loops, and Astrophysical Jets doi:10.1142/q0151