  We propose magnetic SU(N) pure gauge theory as an effective field theory
describing the long distance nonperturbative magnetic response of the
deconfined phase of Yang-Mills theory. The magnetic non-Abelian Lagrangian,
unlike that of electrodynamics where there is exact electromagnetic duality, is
not known explicitly, but here we regard the magnetic SU(N) Yang-Mills
Lagrangian as the leading term in the long distance effective gauge theory of
the plasma phase. In this treatment, which is applicable for a range of
temperatures in the interval T_c < T < 3 T_c accessible in heavy ion
experiments, formation of the magnetic energy profile around a spatial Wilson
loop in the deconfined phase parallels the formation of an electric flux tube
in the confined phase. We use the effective theory to calculate spatial Wilson
loops and the magnetic charge density induced in the plasma by the
corresponding color electric current loops. These calculations suggest that the
deconfined phase of Yang-Mills theory has the properties of a closely-packed
fluid of magnetically charged composite objects.
