WHY BETA(P) AND L(I) CANNOT BE SEPARATELY MEASURED IN A NEAR-CIRCULARTOKAMAK

An analytical calculation is presented demonstrating why a separate de termination of poloidal beta, beta(p), and plasma internal inductance, l(i), in near circular tokamak plasmas is not possible from experimen tal magnetic data. A second-order expansion in terms of the inverse as pect ratio, epsilon, of the Grad-Shafranov equation provides expressio ns for the measured fields with explicit dependence on beta(p). This d ependence, however, is very weak and is shown to be insufficient for d etermining beta(p) when any reasonable magnetic measurement error esti mates are taken into account.