  When quark-gluon plasma emerges in the wake of a heavy-ion collision,
magnetic field created by the valence charges has already permitted the entire
interaction region. Evolution of this "initial" field in plasma is governed by
Maxwell equations in electrically conducting medium. As the plasma expands
external valence charges induce magnetic field that also contributes to the
total magnetic field in plasma. We solve the initial value problem describing
these processes and argue that the initial magnetic field often dominates over
the one induced by the valence charges. In particular, it grows approximately
proportional to the collision energy, unlike the induced component, which is
energy-independent. As a result, magnetic field has a significant
phenomenological influence on quark-gluon plasma at the LHC energies over its
entire lifetime.
