PREPARED FOR THE U.S. DEPARTMENT OF ENERGY, UNDER CONTRACT DE-AC02-76CH03073 PRINCETON PLASMA PHYSICS LABORATORY PRINCETON UNIVERSITY, PRINCETON, NEW JERSEY PPPL-3871 PPPL-3871 UC-70 Marginal Stability Boundaries for Infinite-n Ballooning Modes in a Quasi-axisymmetric Stellarator by S.R. Hudson and C.C. Hegna September 2003