Equilibrium q-profile determination and stability analysis from magnetic field pitch angle measurements using motional Stark effect polarimetry

Abstract

The motional Stark effect polarimetry technique has been used to measure the magnetic pitch angle in a variety of PBX-M plasma conditions. For high aspect ratio, circular plasmas, the q profile can be obtained directly from the γp profile using the cylindrical expression q(r)=(rBT/RBp). In strongly shaped PBX-M plasmas, the magnetic pitch angle data are used as an internal constraint on the plasma equilibrium calculated by solving the Grad–Shafranov equation, subject to external flux measurements. Thus, an accurate determination of q(r) depends upon detailed knowledge of the plasma equilibrium. Discussion of uncertainties in the equilibrium determination and their effect on q(r) will be presented. The equilibrium solutions using the pitch angle data are required for MHD stability calculations, which are being used to investigate the relationship between internal kink modes and plasma shape.