The former fire chief of Babbitt, Minn., who is awaiting sentencing for setting a series of fires in the Superior National Forest, has been diagnosed as a pyromaniac, according to a prosecutor quoted in a document filed Tuesday in federal court in Minneapolis. Ryan G. Scharber, 30, who resigned as chief of the St. Louis County community’s volunteer fire department in December 2012, should be given a five-year sentence, based on federal sentencing guidelines, Assistant U.S. Attorney Andrew Dunne argued in the memorandum. Scharber’s attorney is seeking a downward departure from that sentence.