Rl. Stenzel et al., On conservation of helicity and energy of reflecting electron magnetohydrodynamic vortices, PHYS REV L, 82(20), 1999, pp. 4006-4009
The reflection of a magnetic vortex from a conducting boundary is studied e
xperimentally in an electron magnetohydrodynamic plasma. The reflection con
serves energy but not helicity, which reverses sign. Field line slippage oc
curs in a thin boundary layer, creating a divergence in the ac helicity flo
w vector yet negligible dissipation. The change in self-helicity is account
ed for by the volume term -2 integral (E) over tilde . (B) over tilde dV wh
ich, for Hall electric fields, does not produce dissipation.