  A finite-size scaling technique is applied to the SU(2) gauge theory (without
matter fields) to compute a non-perturbatively defined running coupling
alpha(q) for a range of momenta q given in units of the string tension K. We
find that already at rather low q, the evolution of alpha(q) is well described
by the 2-loop approximation to the Callan-Symanzik beta-function. At the
highest momentum reached, q=20 sqrt(K), we obtain alpha_MSbar(q)=0.187 +/-
0.005 +/- 0.009 for the running coupling in the MSbar scheme of dimensional
regularization.
