Magnetic Helicity: What Is It and What Is It Good For?

Comments Plasma Phys. Controlled Fusion 9, 111 (1985)https://ui.adsabs.harvard.edu/abs/1985CoPPC...9..111F1985Journal ArticlePlasma, Accelerator, and Nuclear Physics

A general gauge invariant definition of helicity in a closed volume is presented and compared with other, more restricted definitions. Examples are shown for four geometries of interest to the fusion program. Speculations on the significance of helicity to low frequency current drive schemes are presented.