  The collinear color electric and magnetic fields have been discussed to be
produced immediately after high energy heavy ion collisions. We discuss
anomalous gluon production under the background gauge fields. The gluons are
Nielsen-Olesen unstable modes. The production rate of the modes by Schwinger
mechanism has recently been found to be anomalously larger than the rate of
quarks or other stable gluons. Analyzing classical evolutions of the modes with
initial conditions given by vacuum fluctuations, we find that their production
makes the color electric field decay very rapidly. The life time of the field
is approximately given by the inverse of saturation momentum in the collisions.
We also show that the mode with zero momentum form a Bose condensate and its
gluon number density grows up to be of the order of $1/\alpha_g$. After the
saturation of the gluon number density, the condensate melts into quark gluon
plasma owing to nonlinear interactions in QCD.
