Invitation to higher local fields, Part I, section 13: Abelian   extensions of absolutely unramified complete discrete valuation fields
  This is an introduction to the author theory of cyclic p-extensions of an absolutely unramified complete discrete valuation field K with arbitrary residue field of characteristic p. In this theory a homomorphism is constructed from the p-part of the group of characters of K to Witt vectors over its residue field. 
Masato Kurihara