  Given a reductive group G, Kostant and Kumar defined a nil Hecke algebra that
may be viewed as a degenerate version of the double affine nil Hecke algebra
introduced by Cherednik. In this paper, we construct an isomorphism of the
spherical subalgebra of the nil Hecke algebra with a Whittaker type quantum
Hamiltonian reduction of the algebra of differential operators on G. This
result has an interpretation in terms of the geometric Satake and the Langlands
dual group. Specifically, the isomorphism provides a bridge between very
differently looking descriptions of equivariant Borel-Moore homology of the
affine flag variety (due to Kostant and Kumar) and of the affine Grassmannian
(due to Bezrukavnikov and Finkelberg), respectively.
  It follows from our result that the category of Whittaker D-modules on G
considered by Drinfeld is equivalent to the category of holonomic modules over
the nil Hecke algebra, and it is also equivalent to a certain subcategory of
the category of Weyl group equivariant holonomic D-modules on the maximal
torus.
