Jerome Powell heads for his first interest rate increase as Federal Reserve chairman this week with an unanswered question looming above others: could his optimism about the U.S. economy lead to more hikes than markets have prepared for? Powell's public comments and Reuters conversations with his Fed colleagues since January, when he was confirmed as chairman, suggest such fears are overblown: Powell, the consensus-builder, may make some tweaks to reflect changing economic conditions but is as committed to gradual, moderate rate increases as his predecessor Janet Yellen who adopted that approach.