Let G be a connected reductive algebraic group over an algebraically closed field k,gamma is an element of g( k(( epsilon ))) a semisimple regular element, we introduce a fundamental domain F gamma for the affine Springer fibers X gamma. We show that the purity conjecture of X gamma is equivalent to that of F gamma via the Arthur-Kottwitz reduction. We then concentrate on the unramified affine Springer fibers for the group GL(d). It turns out that their fundamental domains behave nicely with respect to the root valuation of gamma. We formulate a rationality conjecture about a generating series of their Poincare polynomials, and study them in detail for the group GL(3). In particular, we pave them in affine spaces and we prove the rationality conjecture.