THE MODE STRUCTURE OF HIGH-N RESISTIVE BALLOONING MODES

The higher-order corrections (in an n-1/2 expansion) to resistive ballooning theory are analyzed in order to gain information about the radial structure of the DELTA'-driven modes. This higher-order theory also predicts that the ballooning phase angle theta(0) (which is undetermined in the leading-order theory) must be chosen so as to maximize the value of DELTA'. The importance of applying this maximization is illustrated by an analytical calculation of DELTA' as a function of theta(0) for the s-alpha model in the limit of small alpha. It is demonstrated that for this case, one should choose theta(0) = 90-degrees and that the resulting value of DELTA' can be very different from that obtained by setting theta(0) = 0, as is frequently imposed.