Relative field-line helicity in bounded domains

@article{Yeates2018RelativeFH,
  title={Relative field-line helicity in bounded domains},
  author={Anthony R. Yeates and Marcus Page},
  journal={Journal of Plasma Physics},
  year={2018},
  volume={84}
}
Models for astrophysical plasmas often have magnetic field lines that leave the boundary rather than closing within the computational domain. Thus, the relative magnetic helicity is frequently used in place of the usual magnetic helicity, so as to restore gauge invariance. We show how to decompose the relative helicity into a relative field-line helicity that is an ideal-magnetohydrodynamic invariant for each individual magnetic field line, and vanishes along any field line where the original… 

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