  The zero trace of the known energy-momentum tensors (EMT) of the
electromagnetic field (EMF) leads to contradictions in the virial theorem for a
system of charged particles and incorrect conclusions on the equilibrium state
of the plasma. From the EMF and induction tensors, in the form of their matrix
product, a EMT with a non-zero trace is obtained. Its trace is a quadratic
invariant of the EMF. The consequences of the new EMT for electromagnetic
forces, the virial theorem and the conditions of the equilibrium state of a
system of charged particles and long-lived plasma phenomena are shown.
