(TH/P3-9) Computation of Toroidal-Current Reversal Equilibria for the JT60-U Tokamak

Abstract.  A toroidal-current reversal Grad-Shafranov (GS) equilibrium is computed, using poloidal-magnetic-field and plasma-pressure profiles retrieved from experimental JT60-U data [T. Fujita et al., Phys. Rev. Lett. 87, 245001 (2001)], which is representative of a typical current-hole discharge. Since first observed, stable plasma configurations for which the measured poloidal field is nearly zero throughout a significant region around the magnetic axis (the so-called current-hole) raised a number of questions about possible GS solutions displaying toroidal-current reversal. Indeed, the development in such magnetic configurations of a poloidal-field reversal layer, for which the enclosed toroidal current does vanish, poses several problems to conventional GS equilibrium solvers and precludes their use in toroidal-current reversal scenarios. However, recent developments enabled GS codes to cope with the poloidal-field reversal layer and to handle a large variety of internal plasma profiles [P. Rodrigues, J.P.S. Bizarro, Phys. Rev. Lett. 95, 015001 (2005)], allowing in this way a suitable modeling of experimental data. In current-hole regimes, the poloidal-field profiles obtained from motional-stark-effect (MSE) measurements display significant relative errors inside the core region, with the error bar spanning from small positive values into small negative ones. Therefore, such uncertainty does not exclude (at least by itself) toroidal-current reversal equilibria, some of which are herein computed using poloidal-field and plasma-pressure profiles that best fit available experimental data for current-hole discharges in the JT60-U tokamak. Computing GS equilibria in these scenarios may aid to understand the physics behind the reported resilience of tokamak magnetic configurations with a current-hole [T. Fujita et al., Phys. Rev. Lett. 95, 075001 (2005)].

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