On Conservation of Helicity and Energy of Reflecting Electron Magnetohydrodynamic Vortices

The reflection of a magnetic vortex from a conducting boundary is studied experimentally in an electron magnetohydrodynamic plasma. The reflection conserves energy but not helicity, which reverses sign. Field line slippage occurs in a thin boundary layer, creating a divergence in the ac helicity flow vector yet negligible dissipation. The change in self-helicity is accounted for by the volume term $-2\mathrm{}\int \tilde{\mathbf{E}}̇\tilde{\mathbf{B}}\mathrm{dV}$ which, for Hall electric fields, does not produce dissipation.