Electromagnetic field energy containment

An electromagnetic virial relation in cylindrical geometry is derived which shows that limits on field energy containment imposed by the tensile strength of containment structures can be circumvented. The result is illustrated by two possible machines for which there is a much weakened theoretical virial constraint on the containment of field energy and which should be practically realisable with low dissipation. Not only do these machines represent potentially very useful high energy storage devices given development of appropriate technology, but also, one of them provides helpful insights into the dipolar rotating electric field model of ball lightning with confinement of electromagnetic field energy by atmospheric pressure.