  In the CGC framework the initial stages of a heavy ion collision at high
energy are described as "glasma" field configurations. The initial condition
for these evolving fields depends, in the CGC effective theory, on a
probability distribution for color charges. The energy dependence of this
distribution can be calculated from the JIMWLK renormalization group equation.
We discuss recent work on a practical implementation of the running coupling
constant in the Langevin method of solving the JIMWLK equation.
