On conservation of helicity and energy of reflecting electron magnetohydrodynamic vortices

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.