  Glasma in high energy heavy ion collisions is longitudinal classical color
electric and magnetic fields. The color electric field has been shown to
produces quark and anti-quark pairs by the Schwinger mechanism and to oscillate
with time in non-expanding glasma, that is, plasma oscillation. On the other
hand, in the expanding glasma we show that the field decreases with the plasma
oscillation. We can explicitly obtain the solutions representing such temporal
behaviors in the system with $\tau$ and $\eta$ coordinates. We show these
results by using massless QED as a simplified model of QCD.
