J(sub longitudinalPS)(sup 2)/J(sub transverseDIA)(sup 2) estimate of geodesic curvature for tokamak discharges and its application to DIIID

摘要

In a magnetic configuration endowed with flux surfaces, if the lines of force have zero geodesic curvature (omnigeneous configuration), the magnetic drifts v(sub m) of all the charged particles are aligned with flux surfaces ((v(sub m)) ((nabla)(sub (psi)))=0). Consequently, a minimization of the geodesic curvature of the lines of force produces a minimization of the neoclassical transport, and could as well reduce any other transport induced by the drifts across the magnetic surfaces. Also the neoclassical Pfirsch-Schluter current density J(sub longitudinalPS) is due to the geodesic curvature of the lines of force. A simple criterion for estimating how far a magnetic configuration is from omnigeneity is obtained by evaluating the flux surface average of the squared ratio between the Pfirsch-Schluter current density and the diamagnetic current density J(sub longitudinalPS)(sup 2)/J(sub transverseDIA)(sup 2). In the case of a tokamak a good estimate of the geodesic curvature is obtained as the ratio between , averaged over the magnetic surfaces, and the square of the safety factor q(sup 2). The absence or presence of a correlation between the measured transport properties and /q(sup 2) criterion, which can be accurately estimated with the use of an equilibrium reconstruction code, can give relevant indications upon the nature of the transport processes. In the case of DIIID the global estimate for the squared geodesic curvature Kg=left braceJ(sub longitudinalPS)(sup 2)/J(sub transverseDIA)(sup 2)(r brace)(sub vol)/left braceq(sup 2)(r brace)(sub vol) of the discharges has been correlated with the global confinement.