Constant field modes in lattice SU(3) gauge theory at large T

We compute the expectation value of the Wilson line in finite-T SU(3) gauge theory on lattices of the size 2x83, 4x123, 4x83 and 6x103 and for values of β=6/g2 up to 50. We propose two forms for the contribution of constant field modes to the perturbative expansion of and identify in the data for β> or approx.16 a dominant term 0.18(Nt/Ns)3 and a subdominant term 0.03(Nt/Ns)3/2/√β. The former corresponds to a gluon Debye mass of about 2gT. Physically, we measure screening by observing how the effects of the walls of a finite box on a test quark vary when V changes. (orig.)