Linearity-independent method for a safety factor profile

Imazawa, Ryota; Kawano, Yasunori; Itami, Kiyoshi; Kusama, Yoshinori

This paper proposes a new method to calculate a safety factor, , profile from gridded data of a poloidal flux, , efficiently and accurately. Difficulties of calculating are derived from a difficulty of specifying a contour line of and a singularity at a magnetic axis. In order to solve the first difficulty, the proposed method interpolates knots, which are located on a target , by utilizing a normalized arc length and constraints expressed by a magnetic field. Regarding the second difficulty, the proposed method identifies by extrapolating profile around a magnetic axis with a constraint of at the magnetic axis. Accuracy assessments of the proposed method are carried out by utilizing Solov'ev type equilibrium. The results show the validity and high performance of the proposed method.