Quasi-isodynamic stellarator

A quasi-isodynamic (QI) stellarator is a type of stellarator (a magnetic confinement fusion reactor) that satisfies the property of omnigeneity, avoids the potentially hazardous toroidal bootstrap current, and has minimal neoclassical transport in the collisionless regime. ^[1]

Wendelstein 7-X, the largest stellarator in the world, was designed to be roughly quasi-isodynamic (QI).

In contrast to quasi-symmetric fields, ^[2] exactly QI fields on flux surfaces cannot be expressed analytically. ^[3] However, it has been shown that nearly-exact QI can be extremely well approximated through mathematical optimization, ^[4] and that the resulting fields enjoy the aforementioned properties.

In a QI field, level curves of the magnetic field strength ${\displaystyle B}$ on a flux surface close poloidally (the short way around the torus), and not toroidally (the long way around), causing the stellarator to resemble a series of linked magnetic mirrors.

References

1. Helander, Per; Nührenberg, Jurgen (February 2009). "Bootstrap current and neoclassical transport in quasi-isodynamic stellarators" . Plasma Physics and Controlled Fusion. 51 (5): 055004. Bibcode:2009PPCF...51e5004H. doi:10.1088/0741-3335/51/5/055004. hdl: 11858/00-001M-0000-0026-F470-B . S2CID   250779652.
2. Boozer, Allen H. (1983). "Transport and isomorphic equilibria" . Physics of Fluids. 26 (2): 496–499. Bibcode:1983PhFl...26..496B. doi:10.1063/1.864166.
3. Cary, John R.; Shasharina, Svetlana G. (September 1997). "Omnigenity and quasihelicity in helical plasma confinement systems" . Physics of Plasmas. 4 (9): 3323–3333. Bibcode:1997PhPl....4.3323C. doi:10.1063/1.872473. ISSN   1070-664X.
4. Goodman, Alan; et al. (September 2023). "Constructing precisely quasi-isodynamic magnetic fields". Journal of Plasma Physics. 89 (5): 905890504. arXiv: 2211.09829 . Bibcode:2023JPlPh..89e9004G. doi: 10.1017/S002237782300065X . S2CID   253708037.