%0 Journal Article %1 breslau.2003 %A Breslau, J. A. %A Jardin, S. C. %A Park, W. %D 2003 %I AIP %J Physics of Plasmas %K JET current_hole current_reversal r-mhd reconnection tokamak %N 5 %P 1665-1669 %R 10.1063/1.1556299 %T Simulation studies of the role of reconnection in the ``current hole'' experiments in the Joint European Torus %U http://link.aip.org/link/?PHP/10/1665/1 %V 10 %X Injection of lower hybrid current drive into the current ramp-up phase of Joint European Torus (JET) discharges has been observed to produce an annular current distribution with a core region of essentially zero current density Hawkes et al., Phys. Rev. Lett. 87, 115001 (2001). Similar ``current holes'' have been observed in Japan Atomic Energy Research Institute Tokamak 60 Upgrade discharges with off-axis current drive supplied by bootstrap current T. Fujita et al., Phys. Rev. Lett. 87, 245001 (2001). In both cases, the central current does not go negative, although current diffusion calculations indicate that there is sufficient noninductive current drive for this to occur. This is explained by the multilevel 3D code (M3D) nonlinear 2D and 3D resistive magnetohydrodynamic (MHD) simulations in toroidal geometry, which predict that these discharges undergo $n = 0$ reconnection events-``axisymmetric sawteeth''-that redistribute the current to hold its core density near zero. Unlike conventional sawteeth, these events retain the symmetry of the equilibrium, and thus are best viewed as a transient loss of equilibrium caused when an $= 0$ rational surface enters the plasma. If the current density profile has a central minimum, this surface will enter on axis; otherwise it will enter off-axis. In the first case, the reconnection is limited to a small region around the axis and clamps the core current at zero. In the second case, more typical of the JET experiments, the core current takes on a finite negative value before the $= 0$ surface appears, resulting in discrete periodic axisymmetric sawtooth events with a finite minor radius. Interpretation of the simulation results is given in terms of analytic equilibrium theory, and the relation to conventional sawteeth and to a recent reduced-MHD analysis of this phenomenon in cylindrical geometry Huysmans et al., Phys. Rev. Lett. 87, 245002 (2001) is discussed.

@article{breslau.2003, abstract = {Injection of lower hybrid current drive into the current ramp-up phase of Joint European Torus (JET) discharges has been observed to produce an annular current distribution with a core region of essentially zero current density [Hawkes et al., Phys. Rev. Lett. 87, 115001 (2001)]. Similar ``current holes'' have been observed in Japan Atomic Energy Research Institute Tokamak 60 Upgrade discharges with off-axis current drive supplied by bootstrap current [T. Fujita et al., Phys. Rev. Lett. 87, 245001 (2001)]. In both cases, the central current does not go negative, although current diffusion calculations indicate that there is sufficient noninductive current drive for this to occur. This is explained by the multilevel 3D code (M3D) nonlinear 2D and 3D resistive magnetohydrodynamic (MHD) simulations in toroidal geometry, which predict that these discharges undergo $n = 0$ reconnection events-``axisymmetric sawteeth''-that redistribute the current to hold its core density near zero. Unlike conventional sawteeth, these events retain the symmetry of the equilibrium, and thus are best viewed as a transient loss of equilibrium caused when an $\iota = 0$ rational surface enters the plasma. If the current density profile has a central minimum, this surface will enter on axis; otherwise it will enter off-axis. In the first case, the reconnection is limited to a small region around the axis and clamps the core current at zero. In the second case, more typical of the JET experiments, the core current takes on a finite negative value before the $\iota = 0$ surface appears, resulting in discrete periodic axisymmetric sawtooth events with a finite minor radius. Interpretation of the simulation results is given in terms of analytic equilibrium theory, and the relation to conventional sawteeth and to a recent reduced-MHD analysis of this phenomenon in cylindrical geometry [Huysmans et al., Phys. Rev. Lett. 87, 245002 (2001)] is discussed.}, added-at = {2009-07-31T16:30:31.000+0200}, author = {Breslau, J. A. and Jardin, S. C. and Park, W.}, biburl = {https://www.bibsonomy.org/bibtex/200fa5b9c071712841f4ee1e258c9b600/prodrigues}, description = {Resistive MHD modelling of JET discharges with shear reversal (3D effects).}, doi = {10.1063/1.1556299}, interhash = {67938d8153a0e4fb16717c843102a049}, intrahash = {00fa5b9c071712841f4ee1e258c9b600}, journal = {Physics of Plasmas}, keywords = {JET current_hole current_reversal r-mhd reconnection tokamak}, month = May, number = 5, numpages = {5}, pages = {1665-1669}, publisher = {AIP}, timestamp = {2009-07-31T16:30:31.000+0200}, title = {Simulation studies of the role of reconnection in the ``current hole'' experiments in the Joint European Torus}, url = {http://link.aip.org/link/?PHP/10/1665/1}, volume = 10, year = 2003 }