  The quad-curl problem arises in magnetohydrodynamics, inverse electromagnetic
scattering and transform eigenvalue problems. In this paper we investigate a
hybridizable discontinuous Galerkin method to solve the quad-curl problem based
on a mixed formulation. The divergence-free condition is enforced by
introducing a Lagrange multiplier into the system. The analysis is performed
for the model problem with low regularity, which is posed on a Lipschitz
polyhedron domain.
