  We extensively study the growing behavior of the energy and the pressure
components depending on the space-time rapidity in the framework of the Glasma,
which describes the early-time dynamics in the ultra-relativistic heavy-ion
collisions. We simulate the Glasma solving the classical equations of motion in
the SU(2) Yang-Mills theory and systematically investigate the dependence of
the Glasma instability on the model parameters. We have checked that the
transverse and longitudinal grid sizes in our simulation are large enough to
handle cutoff effects under control. By comparing the numerical results from
several initial conditions with different magnitudes of instability seed and
also those with different wave-numbers for rapidity fluctuations, we clearly
see that unstable modes dominantly grow up in the linear regime and we also
confirm non-linear effects in the time evolution. To extract more detailed
information on the evolving Glasma, we decompose the energy into the components
in terms of rapidity wave-numbers. We observe an energy flow from low
wave-number modes into higher wave-number modes due to non-linearity in the
equations of motion. We find that the energy spectrum approaches an asymptotic
scaling that is consistent with Kolmogorov's power-law form even in the
expanding system of the Glasma.
